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Polymers
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Additive Manufacturing of Fibre Reinforced Polymer Composites
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Additive Manufacturing of Fibre Reinforced Polymer Composites

A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Composites and Nanocomposites".

Deadline for manuscript submissions: closed (15 November 2024) | Viewed by 20358

Special Issue Editors

Dr. Chengxing Yang

E-Mail Website
Guest Editor
School of Traffic & Transportation Engineering, Central South University, Changsha 410075, China
Interests: additive manufacturing; fibre-reinforced polymer composites; composite structure; mechanical property
Prof. Dr. Kui Wang

E-Mail Website
Guest Editor
School of Traffic & Transportation Engineering, Key Laboratory of Traffic Safety on Track, Central South University, Changsha 410075, China
Interests: 3D printing; fibre-reinforced polymer composites; formulation; thermo environment
Special Issues, Collections and Topics in MDPI journals
Dr. Jianxun Zhang

E-Mail Website
Guest Editor
State Key Laboratory for Strength and Vibration of Mechanical Structures, School of Aerospace Engineering, Xi’an Jiaotong University, Xi’an 710049, China
Interests: lightweight design; composite material; cellular material; failure; impact mechanism
Special Issues, Collections and Topics in MDPI journals
Dr. Andrea Codolini

E-Mail Website
Guest Editor
Engineering and Physical Science Research Council, CIMComp, University of Cambridge, Cambridge, UK
Interests: mineral-filled polymers; material modelling; composites technology; artificial intelligence

Special Issue Information

Dear Colleagues,

Additive manufacturing has been adopted in many applications (e.g., aerospace, automotive, railway, consumer, and biomedical) due to its revolution in fabricating complex products with customised features. Additive manufacturing of fibre-reinforced polymer composites has attracted increasing attention because of its excellence in improving and diversifying material properties by introducing reinforcements. This Special Issue focuses on recent advances in additive manufacturing of fibre-reinforced polymer composites. Example topics may include different additive manufacturing processes, formulations of different materials, strengths and drawbacks of additive manufacturing methods, and multi-physical characterisation of fibre-reinforced polymer composites. Original research papers, short reports, and reviews are welcome to be published on this Special Issue. It will be an opportunity to take a look at the latest trends and future technologies in the research field of advanced fibre-reinforced polymer composites.

Dr. Chengxing Yang
Prof. Dr. Kui Wang
Dr. Jianxun Zhang
Dr. Andrea Codolini
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • additive manufacturing
  • 3D printing
  • continuous fibre
  • short fibre
  • polymer
  • composite material
  • formulation
  • mechanical properties
  • characterisation

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Published Papers (13 papers)

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Research

16 pages, 17447 KiB  
Article
Research on Interlayer Toughening and Damage Detection of Laser-Induced Graphene and Short Kevlar Fibers Aramid Fiber/Epoxy Resin Composites
by Baolai Wang, Weidong Tian, Chao Wang and Qi Wang
Polymers 2024, 16(23), 3380; https://doi.org/10.3390/polym16233380 - 30 Nov 2024
Viewed by 489
Abstract
The poor interlaminar fracture toughness is a critical limiting factor for the structural applications of aramid fiber/epoxy resin composites. This study investigates the effects of laser-induced graphene (LIG) and short Kevlar fibers on the interfacial toughness and damage detection of aramid composite materials. [...] Read more.
The poor interlaminar fracture toughness is a critical limiting factor for the structural applications of aramid fiber/epoxy resin composites. This study investigates the effects of laser-induced graphene (LIG) and short Kevlar fibers on the interfacial toughness and damage detection of aramid composite materials. Mode II tests and tensile tests were conducted to evaluate mechanical properties and damage detection using the piezoresistive characteristics of LIG. The results indicate that LIG combined with short Kevlar fibers significantly enhances the interfacial toughness of the composites, achieving a 381.60% increase in initial Mode II fracture toughness. Although LIG reduced the tensile strength by 14.02%, the addition of short Kevlar fibers mitigated this effect, preserving the overall mechanical performance. Scanning electron microscopy (SEM) analysis revealed enhanced toughening mechanisms, including increased surface roughness, altered crack propagation paths, and fiber bridging. Additionally, LIG enabled real-time damage monitoring, showing a significant increase in resistance upon delamination or crack propagation and a marked increase in resistance upon the tensile fracture. This research indicates that the synergistic effects of LIG and short Kevlar fibers not only enhance the interlaminar toughness of aramid composites but also provide a novel strategy for effective damage detection in fiber-reinforced materials. Full article
(This article belongs to the Special Issue Additive Manufacturing of Fibre Reinforced Polymer Composites)
►▼ Show Figures

Figure 1

Figure 1
<p>Preparation process of short Kevlar fiber film.</p> Full article ">Figure 2
<p>Generation of graphene on the surface of aramid fibers.</p> Full article ">Figure 3
<p>Schematic diagram of Mode II specimens.</p> Full article ">Figure 4
<p>(<b>a</b>) Schematic diagram of the tensile specimens (front view); (<b>b</b>) Schematic diagram of tensile specimens (side view).</p> Full article ">Figure 5
<p>(<b>a</b>) Raman spectrum of aramid fibers LIG-coated; (<b>b</b>) Raman spectrum of untreated aramid fibers.</p> Full article ">Figure 6
<p>(<b>a</b>) Average load displacement curves for the four types of specimens; (<b>b</b>) Fracture toughness at the onset of delamination.</p> Full article ">Figure 7
<p>(<b>a</b>–<b>c</b>) SEM micrographs of the fracture surfaces of untreated specimens.</p> Full article ">Figure 8
<p>(<b>a</b>–<b>c</b>) SEM micrographs of the fracture surfaces of only short Kevlar fiber specimens.</p> Full article ">Figure 9
<p>(<b>a</b>–<b>c</b>) SEM micrographs of the fracture surfaces of only LIG-coated specimens.</p> Full article ">Figure 10
<p>(<b>a</b>–<b>c</b>) SEM micrographs of the fracture surfaces of combined specimens.</p> Full article ">Figure 11
<p>(<b>a</b>) Stress/resistance–strain curves of aramid fiber laminate with only LIG-coated; (<b>b</b>) Stress/resistance–strain curves of aramid fiber laminates containing LIG-coated and short Kevlar fibers.</p> Full article ">Figure 12
<p>(<b>a</b>) Average load displacement curves of the four types of specimens; (<b>b</b>) Tensile strength and tensile modulus of the four types of specimens.</p> Full article ">Figure 13
<p>(<b>a</b>) Stress/resistance–strain curves of the aramid fiber laminate with only LIG-coated; (<b>b</b>) Stress/resistance–strain curves of the aramid fiber laminate containing LIG-coated and short Kevlar fibers.</p> Full article ">
24 pages, 10885 KiB  
Article
Study on Acoustic Emission Characteristics and Damage Mechanism of Wind Turbine Blade Main Spar with Different Defects
by Yanan Zhang, Shaojie Xue, Chuanyong Chen, Tianchang Ma and Bo Zhou
Polymers 2024, 16(23), 3261; https://doi.org/10.3390/polym16233261 - 23 Nov 2024
Viewed by 673
Abstract
This paper aimed to understand the AE signal characteristics and damage mechanism of wind turbine blade main spar materials with different defects during the damage evolution process. According to the typical delamination and wrinkle defects in wind turbine blades, the GFRP composite with [...] Read more.
This paper aimed to understand the AE signal characteristics and damage mechanism of wind turbine blade main spar materials with different defects during the damage evolution process. According to the typical delamination and wrinkle defects in wind turbine blades, the GFRP composite with defects is artificially prefabricated. Through acoustic emission experiments, the mechanical properties and acoustic emission characteristic trends of wind turbine blade main spar composites with different defects under tensile loading conditions were analyzed, and the damage evolution mechanism of different defects was explained according to the microscopic results. The results show that the existence of artificial defects will not only affect the mechanical properties of composite materials but also affect the damage evolution process of the materials. The size and location of delamination defects and the different aspect ratio of the wrinkle defects have a certain influence on the damage mechanism of the material. K-means cluster analysis of AE parameters identified the damage models of GFRP composites. The types of damage modes of delamination defects and wrinkle defects are the same, and the range of characteristic frequency is roughly the same. This study has important reference significance for structural damage monitoring and damage evolution research of wind turbine blade composites. Full article
(This article belongs to the Special Issue Additive Manufacturing of Fibre Reinforced Polymer Composites)
►▼ Show Figures

Figure 1

Figure 1
<p>Profile structure of wind turbine blade.</p> Full article ">Figure 2
<p>Typical manufacturing process defects of wind turbine blade main spar structure: (<b>a</b>) wrinkle defects; (<b>b</b>) delamination defects; (<b>c</b>) air bubble defects; (<b>d</b>) lack glue defects; (<b>e</b>) pore defects; (<b>f</b>) inclusion defects [<a href="#B16-polymers-16-03261" class="html-bibr">16</a>].</p> Full article ">Figure 3
<p>Diagram of resin introduction layer structure.</p> Full article ">Figure 4
<p>GFRP composite manufacturing process.</p> Full article ">Figure 5
<p>Size diagram of delamination defect specimens (units: mm).</p> Full article ">Figure 6
<p>Size diagram of wrinkle defect specimens (units: mm).</p> Full article ">Figure 7
<p>Morphological features of defects: (<b>a</b>) artificial wrinkle defects; (<b>b</b>) natural wrinkle defects; (<b>c</b>) artificial delamination defects; (<b>d</b>) natural delamination defects.</p> Full article ">Figure 8
<p>Acoustic emission testing system.</p> Full article ">Figure 9
<p>Definition of acoustic emission parameters.</p> Full article ">Figure 10
<p>Sound velocity calibration for acoustic emission lead break test.</p> Full article ">Figure 11
<p>The schematic of pencil lead break test.</p> Full article ">Figure 12
<p>Correlation tree diagram of acoustic emission signal parameters.</p> Full article ">Figure 13
<p>Evaluation of the number of clusters: specimens A1, A2, A3, and A4.</p> Full article ">Figure 14
<p>Time domain and frequency domain signals of different damage modes.</p> Full article ">Figure 15
<p>Frequency and load changes with time for different specimens.</p> Full article ">Figure 16
<p>Acoustic emission signal spectrum characteristics of specimen A1 at different damage stages.</p> Full article ">Figure 17
<p>Displacement curve of specimens in tensile test.</p> Full article ">Figure 18
<p>AE accumulation energy and accumulation count distribution over time: specimens A1, A2, A3, and A4.</p> Full article ">Figure 19
<p>Tensile force and acoustic emission impact history of delamination defect specimens: specimens A1, A2, A3, and A4.</p> Full article ">Figure 20
<p>Relationship between load and energy of wrinkle defect.</p> Full article ">Figure 21
<p>Time history of AE amplitude and accumulated hits of wrinkle defect.</p> Full article ">Figure 22
<p>Micrograph of delamination defect specimens after fracture.</p> Full article ">Figure 23
<p>Micrograph of wrinkle defect specimens after fracture.</p> Full article ">
14 pages, 5049 KiB  
Article
Compression Behavior of 3D Printed Composite Isogrid Structures
by Marina Andreozzi, Carlo Bruni, Archimede Forcellese, Serena Gentili and Alessio Vita
Polymers 2024, 16(19), 2747; https://doi.org/10.3390/polym16192747 - 28 Sep 2024
Viewed by 1007
Abstract
Composite materials, particularly carbon fiber-reinforced polymers (CFRPs), have become a cornerstone in industries requiring high-performance materials due to their exceptional mechanical properties, such as high strength-to-weight ratios, and their inherent lightweight nature. These attributes make CFRPs highly desirable in aerospace, automotive, and other [...] Read more.
Composite materials, particularly carbon fiber-reinforced polymers (CFRPs), have become a cornerstone in industries requiring high-performance materials due to their exceptional mechanical properties, such as high strength-to-weight ratios, and their inherent lightweight nature. These attributes make CFRPs highly desirable in aerospace, automotive, and other advanced engineering applications. However, the compressive behavior of CFRP structures remains a challenge, primarily due to the material sensitivity to structural instability, leading to matrix cracking and premature failure under compressive loads. Isogrid structures, characterized by their unique geometric patterns, have shown promise in enhancing the compressive behavior of CFRP panels by providing additional support that mitigates these issues. Traditionally, these structures are manufactured using automated techniques like automated fiber placement (AFP) and automated tape laying (ATL), which, despite their efficacy, are often cost-prohibitive for small-scale or custom applications. Recent advancements in 3D-printing technology, particularly those involving continuous fiber reinforcement, present a cost-effective and flexible alternative for producing complex CFRP structures. This study investigates the compressive behavior of 3D-printed isogrid structures, fabricated using continuous carbon fiber reinforcement via an Anisoprint Composer A3 printer equipped with towpreg coextrusion technology. A total of eight isogrid panels with varying infill percentages were produced and subjected to buckling tests to assess their performance. The experimental results indicate a direct correlation between infill density and buckling resistance, with higher infill densities leading to increased buckling loads. Additionally, the failure modes were observed to shift from local to global buckling as the infill density increased, suggesting a more uniform distribution of compressive stresses. Post-test analyses using optical microscopy and scanning electron microscopy (SEM) revealed the presence of voids within the 3D-printed structures, which were found to negatively impact the mechanical performance of the isogrid panels. The findings of this study demonstrate that 3D-printed isogrid CFRP structures can achieve significant buckling resistance, making them a viable option for high-performance applications. However, the presence of voids remains a critical issue, highlighting the need for process optimizations in 3D-printing techniques to enhance the overall performance and reliability of these structures. Full article
(This article belongs to the Special Issue Additive Manufacturing of Fibre Reinforced Polymer Composites)
►▼ Show Figures

Figure 1

Figure 1
<p>Scheme of the printing process of the Anisoprint A3 machine.</p> Full article ">Figure 2
<p>Example of the 30% isogrid.</p> Full article ">Figure 3
<p>Infill densities of the isogrid structures.</p> Full article ">Figure 4
<p>Buckling test of the 30% isogrid.</p> Full article ">Figure 5
<p>Typical compressive force–displacement curve.</p> Full article ">Figure 6
<p>Tomography analysis of the 40% isogrid structure.</p> Full article ">Figure 7
<p>Average load–displacement curves.</p> Full article ">Figure 8
<p>Buckling load (<b>a</b>) and specific buckling load (<b>b</b>) as a function of % infill, reported on a logarithmic scale: emphasis on the change in slope between lower 30% infills and higher.</p> Full article ">Figure 9
<p>The tested 30% infill isogrid structure.</p> Full article ">Figure 10
<p>The tested 60% infill isogrid structure.</p> Full article ">Figure 11
<p>(<b>a</b>) Infill 30%, 16×, local buckling; (<b>b</b>) infill 60%, 12.5× global buckling.</p> Full article ">Figure 12
<p>(<b>a</b>) The 500× and (<b>b</b>) 1000× SEM magnification of the 3D-printed composite.</p> Full article ">
25 pages, 16876 KiB  
Article
Optimization of 3D Printing Parameters of High Viscosity PEEK/30GF Composites
by Dmitry Yu. Stepanov, Yuri V. Dontsov, Sergey V. Panin, Dmitry G. Buslovich, Vladislav O. Alexenko, Svetlana A. Bochkareva, Andrey V. Batranin and Pavel V. Kosmachev
Polymers 2024, 16(18), 2601; https://doi.org/10.3390/polym16182601 - 14 Sep 2024
Viewed by 1418
Abstract
The aim of this study was to optimize a set of technological parameters (travel speed, extruder temperature, and extrusion rate) for 3D printing with a PEEK-based composite reinforced with 30 wt.% glass fibers (GFs). For this purpose, both Taguchi and finite element methods [...] Read more.
The aim of this study was to optimize a set of technological parameters (travel speed, extruder temperature, and extrusion rate) for 3D printing with a PEEK-based composite reinforced with 30 wt.% glass fibers (GFs). For this purpose, both Taguchi and finite element methods (FEM) were utilized. The artificial neural networks (ANNs) were implemented for computer simulation of full-scale experiments. Computed tomography of the additively manufactured (AM) samples showed that the optimal 3D printing parameters were the extruder temperature of 460 °C, the travel speed of 20 mm/min, and the extrusion rate of 4 rpm (the microextruder screw rotation speed). These values correlated well with those obtained by computer simulation using the ANNs. In such cases, the homogeneous micro- and macro-structures were formed with minimal sample distortions and porosity levels within 10 vol.% of both structures. The most likely reason for porosity was the expansion of the molten polymer when it had been squeezed out from the microextruder nozzle. It was concluded that the mechanical properties of such samples can be improved both by changing the 3D printing strategy to ensure the preferential orientation of GFs along the building direction and by reducing porosity via post-printing treatment or ultrasonic compaction. Full article
(This article belongs to the Special Issue Additive Manufacturing of Fibre Reinforced Polymer Composites)
►▼ Show Figures

Figure 1

Figure 1
<p>The S/N ratios for different levels of the technological parameters: (<b>a</b>) tensile strength; (<b>b</b>) elastic modulus; (<b>c</b>) elongation at break.</p> Full article ">Figure 2
<p>The SEM micrographs of the PEEK/30GF composites additively manufactured using the modes presented in <a href="#polymers-16-02601-t002" class="html-table">Table 2</a>.</p> Full article ">Figure 3
<p>The 3D printing modes of the laboratory experiments in the space of the (input) parameters.</p> Full article ">Figure 4
<p>The dependences of the mechanical properties of the samples of the PEEK/30 GF composite on the 3D printing parameters (<b>a</b>), as well as both dependences and histograms (<b>b</b>) after verification.</p> Full article ">Figure 4 Cont.
<p>The dependences of the mechanical properties of the samples of the PEEK/30 GF composite on the 3D printing parameters (<b>a</b>), as well as both dependences and histograms (<b>b</b>) after verification.</p> Full article ">Figure 5
<p>The parameters’ space and the result of checking the 3D-printing modes for compliance with the minimum acceptable property values.</p> Full article ">Figure 6
<p>The 3D printing modes and a priori knowledge, as well as the SOP area, drawn using the RBFNN model: (<b>a</b>) spread = 0.3, goal = 0.001, the training sample size of 66 vectors; (<b>b</b>) spread = 0.3, goal = 0.01, the training sample size of 66 experimental + 54 a priori vectors.</p> Full article ">Figure 7
<p>The experimental modes and a priori knowledge, as well as the SOP area, drawn using the FFNN model: (<b>a</b>) 4 hidden layer neurons, the sample size of 66 experimental + 132 synthesized vectors; (<b>b</b>) 6 hidden layer neurons, the sample size of 66 experimental + 54 prior + 240 synthesized vectors.</p> Full article ">Figure 8
<p>Results of models’ verification within priory knowledge planes as a function of the size of experimental and prior vectors of the properties.</p> Full article ">Figure 9
<p>Schematic locations of pores with the diameters of 20 µm (<b>a</b>), 100 µm (<b>b</b>), and from 20 to 100 µm (<b>c</b>) in the computational domains at the porosity of 30%.</p> Full article ">Figure 10
<p>The elastic modulus versus porosity dependences for pores with different diameters <span class="html-italic">d</span>.</p> Full article ">Figure 11
<p>The stress distribution surfaces over the representative volume in the presence of pores with the diameters of 20 µm (<b>a</b>), 100 µm (<b>b</b>), and from 20 to 100 µm (<b>c</b>) at a porosity of 30%.</p> Full article ">Figure 12
<p>The three-dimensional micro-CT views of the samples, from both supporting table (<b>a</b>–<b>c</b>) and 3D-printing head (<b>d</b>–<b>f</b>) sides; mode 12 (<b>a</b>,<b>d</b>); mode 14 (<b>b</b>,<b>e</b>); mode 10 (<b>c</b>,<b>f</b>).</p> Full article ">Figure 13
<p>The orthogonal projections of the samples near the fracture surfaces at the image (slice) sizes of 7.5–8.0 mm (<b>a</b>–<b>c</b>), 7.5–4.5 mm (<b>d</b>–<b>f</b>), and 8.0–4.5 mm (<b>g</b>–<b>i</b>). Red denotes Z- axis section; Blue denotes X-axis section; Green denotes Y-axis section.</p> Full article ">Figure 14
<p>The comparative results of assessing the cross-sectional areas of the samples depending on the position of the height section (along the Z axis): mode 12 (sample No.19); mode 14 (sample No.28); mode 10 (sample No.30).</p> Full article ">Figure 15
<p>Visualizations of a full tomogram (<b>a</b>) and a cut-out VOI (<b>b</b>).</p> Full article ">Figure 16
<p>Visualizations of the areas (sections) selected for each of the modes to calculate the porosity levels for the images with sizes of 4.5–7.5 mm (<b>a</b>–<b>c</b>).</p> Full article ">Figure 17
<p>The orthogonal projections of an individual PEEK granule. Red denotes Z- axis section; Blue denotes X-axis section; Green denotes Y-axis section.</p> Full article ">
19 pages, 2735 KiB  
Article
Low-Velocity Impact of Clamped Rectangular Sandwich Tubes with Fiber Metal Laminated Tubes
by Yao Wang, Jianxun Zhang, Hui Guo and Hui Yuan
Polymers 2024, 16(13), 1833; https://doi.org/10.3390/polym16131833 - 27 Jun 2024
Viewed by 698
Abstract
Fiber metal laminated sandwich tubes are made up of alternating fiber-reinforced composite and metal layers. Fiber metal laminated tubes have the advantages of the high strength and high stiffness of fiber and the toughness of metal, so they have become an excellent load-bearing [...] Read more.
Fiber metal laminated sandwich tubes are made up of alternating fiber-reinforced composite and metal layers. Fiber metal laminated tubes have the advantages of the high strength and high stiffness of fiber and the toughness of metal, so they have become an excellent load-bearing and energy-absorbing, lightweight structure. Due to the complexity of the fiber layup, it is difficult to establish an analytical model of the relevant structural properties. In this work, introducing the number and volume fraction of fiber layup, based on the modified rigid–plastic model, an analytical model is established for low-velocity impacts on sandwich tubes with fiber metal laminated tubes, which provided a theoretical basis for the design of fiber–metal composite tubes. In addition, a numerical simulation was conducted for low-velocity impacts on clamped rectangular sandwich tubes with fiber metal laminated (FML) tubes and a foam core. By comparing the results obtained from the theoretical analysis and numerical calculations, it is shown that the analytical results can reasonably agree with the numerical results. The influences of the metal volume fraction (MVF), the strength ratio factor of the FML metal layer to the FML composite layer, and the relative strength of the foam on the dynamic response of the rectangular sandwich tubes with FML tubes and a metal foam core (MFC) are discussed. It is shown that by increasing the fiber content and fiber strength of the FML tubes and the foam strength, the load-carrying and energy-absorbing capacity of the rectangular sandwich tubes can be effectively improved, especially by changing the fiber properties. In addition, present analytical solutions can be applied to make predictions about the dynamic response of the rectangular sandwich tubes with FML tubes and MFC during impacts with low-velocity and reasonably heavy-mass. Full article
(This article belongs to the Special Issue Additive Manufacturing of Fibre Reinforced Polymer Composites)
►▼ Show Figures

Figure 1

Figure 1
<p>Sketch of a rectangular sandwich tube with FML tubes and MFC under heavy-impact with low-velocity at midspan. (<b>a</b>) Rectangular sandwich tube and (<b>b</b>) the cross-section of the rectangular sandwich tube. The red arrow indicates a partial enlarged view of the FML tube.</p> Full article ">Figure 2
<p>Global bending deformation model of the left plastic neutral surface of the rectangular sandwich tube with MFC under low-velocity impact at mid-span.</p> Full article ">Figure 3
<p>Results of the mesh sensitivity examination of the relationship between impact force and deflection for the rectangular sandwich tube with FML tubes and MFC under low-velocity impact with <span class="html-italic">G*</span> = 1000 and <span class="html-italic">V<sub>I</sub></span> = 2.5 m/s.</p> Full article ">Figure 4
<p>Numerical results of the impact response for the rectangular sandwich tube with FML tubes and MFC under low-velocity impact with <span class="html-italic">G*</span> = 1000, <span class="html-italic">V<sub>I</sub></span> = 2.5 m/s. (<b>a</b>) The relationship between the impact force of the impactor and time, and (<b>b</b>) the relationship between the velocity of the impactor and time.</p> Full article ">Figure 5
<p>Numerical results of the equivalent plastic strain distribution of rectangular sandwich tubes with FML tubes and MFC impacted by a heavy mass of <span class="html-italic">G*</span> = 1000 and an initial low-velocity of <span class="html-italic">V<sub>I</sub></span> = 2.5 m/s. (<b>a</b>) The outer tube of the rectangular sandwich tube, (<b>b</b>) the MFC of the rectangular sandwich tube, and (<b>c</b>) the inner tube of the rectangular sandwich tube. It should be noted that “5e-01” means “5 × 10<sup>−1</sup>” in the color bars.</p> Full article ">Figure 5 Cont.
<p>Numerical results of the equivalent plastic strain distribution of rectangular sandwich tubes with FML tubes and MFC impacted by a heavy mass of <span class="html-italic">G*</span> = 1000 and an initial low-velocity of <span class="html-italic">V<sub>I</sub></span> = 2.5 m/s. (<b>a</b>) The outer tube of the rectangular sandwich tube, (<b>b</b>) the MFC of the rectangular sandwich tube, and (<b>c</b>) the inner tube of the rectangular sandwich tube. It should be noted that “5e-01” means “5 × 10<sup>−1</sup>” in the color bars.</p> Full article ">Figure 6
<p>Analytical predictions and numerical results of the relationship between the dimensionless impact force and deflection for the rectangular sandwich tubes with FML tubes and MFC under low-velocity impact with a heavy mass impactor. (<b>a</b>) <span class="html-italic">G*</span> = 1000, <span class="html-italic">V<sub>I</sub></span> = 2.5 m/s and (<b>b</b>) <span class="html-italic">G*</span> = 2500, <span class="html-italic">V<sub>I</sub></span> = 1 m/s.</p> Full article ">Figure 7
<p>Comparisons of analytical and numerical results of the dimensionless maximum deflection for the middle span of the outer surface of the rectangular sandwich tubes with FML tubes and MFC versus the initial impact energy of the impactor with (<b>a</b>) a given constant mass ratio <span class="html-italic">G*</span> = 1000 and (<b>b</b>) a given constant initial velocity <span class="html-italic">V<sub>I</sub></span> = 2.5 m/s.</p> Full article ">Figure 8
<p>The influence of the MVF <span class="html-italic">f</span> on the dynamic response of rectangular sandwich tubes with FML tubes and MFC under low-velocity impact. (<b>a</b>) The curves of <math display="inline"><semantics> <mrow> <msubsup> <mi>W</mi> <mn>0</mn> <mo>*</mo> </msubsup> </mrow> </semantics></math> versus <math display="inline"><semantics> <mrow> <msubsup> <mi>P</mi> <mi mathvariant="normal">r</mi> <mo>*</mo> </msubsup> </mrow> </semantics></math> and (<b>b</b>) the curves of <math display="inline"><semantics> <mrow> <msubsup> <mi>U</mi> <mi>K</mi> <mo>*</mo> </msubsup> </mrow> </semantics></math> versus <math display="inline"><semantics> <mrow> <msubsup> <mi>W</mi> <mrow> <mn>0</mn> <mi>m</mi> </mrow> <mo>*</mo> </msubsup> </mrow> </semantics></math>.</p> Full article ">Figure 9
<p>The influence of the strength ratio <span class="html-italic">q</span> on the dynamic response of rectangular sandwich tubes with FML tubes and MFC under low-velocity impact. (<b>a</b>) The curves of <math display="inline"><semantics> <mrow> <msubsup> <mi>W</mi> <mn>0</mn> <mo>*</mo> </msubsup> </mrow> </semantics></math> versus <math display="inline"><semantics> <mrow> <msubsup> <mi>P</mi> <mi mathvariant="normal">r</mi> <mo>*</mo> </msubsup> </mrow> </semantics></math> and (<b>b</b>) the curves of <math display="inline"><semantics> <mrow> <msubsup> <mi>U</mi> <mi>K</mi> <mo>*</mo> </msubsup> </mrow> </semantics></math> versus <math display="inline"><semantics> <mrow> <msubsup> <mi>W</mi> <mrow> <mn>0</mn> <mi>m</mi> </mrow> <mo>*</mo> </msubsup> </mrow> </semantics></math>.</p> Full article ">Figure 10
<p>The influence of the foam strength <math display="inline"><semantics> <mrow> <msub> <mrow> <mover accent="true"> <mi>σ</mi> <mo stretchy="true">¯</mo> </mover> </mrow> <mi mathvariant="normal">c</mi> </msub> </mrow> </semantics></math> on the dynamic response of rectangular sandwich tubes with FML tubes and MFC under low-velocity impact. (<b>a</b>) The curves of <math display="inline"><semantics> <mrow> <msubsup> <mi>W</mi> <mn>0</mn> <mo>*</mo> </msubsup> </mrow> </semantics></math> versus <math display="inline"><semantics> <mrow> <msubsup> <mi>P</mi> <mi mathvariant="normal">r</mi> <mo>*</mo> </msubsup> </mrow> </semantics></math> and (<b>b</b>) the curves of <math display="inline"><semantics> <mrow> <msubsup> <mi>U</mi> <mi>K</mi> <mo>*</mo> </msubsup> </mrow> </semantics></math> versus <math display="inline"><semantics> <mrow> <msubsup> <mi>W</mi> <mrow> <mn>0</mn> <mi>m</mi> </mrow> <mo>*</mo> </msubsup> </mrow> </semantics></math>.</p> Full article ">
13 pages, 5774 KiB  
Article
The Development of Biocomposite Filaments for 3D Printing by Utilizing a Polylactic Acid (PLA) Polymer Matrix Reinforced with Cocoa Husk Cellulose Fibers
by Victor Hugo Martins de Almeida, Raildo Mota de Jesus, Gregório Mateus Santana, Sabir Khan, Erickson Fabiano Moura Sousa Silva, Iago Silva da Cruz, Ian de Souza Santos and Paulo Neilson Marques dos Anjos
Polymers 2024, 16(13), 1757; https://doi.org/10.3390/polym16131757 - 21 Jun 2024
Cited by 2 | Viewed by 1588
Abstract
Vegetable fibers are increasingly used in biocomposites, but there is a need for further development in utilizing by-products like cocoa husks. Three-dimensional printing, through Fused Filament Fabrication (FFF), is advancing rapidly and may be of great interest for applying biocomposite materials. This study [...] Read more.
Vegetable fibers are increasingly used in biocomposites, but there is a need for further development in utilizing by-products like cocoa husks. Three-dimensional printing, through Fused Filament Fabrication (FFF), is advancing rapidly and may be of great interest for applying biocomposite materials. This study focuses on developing innovative and fully biodegradable filaments for the FFF process. PLA filaments were prepared using cellulose fibers derived from cocoa husks (5% mass ratio). One set of filaments incorporated fibers from untreated husks (UCFFs), while another set utilized fibers from chemically treated husks (TCFFs). The fabricated materials were analyzed using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR) techniques, and they were also tested for tensile strength. ANOVA reveals that both UCFFs and TCFFs significantly predict tensile strength, with the UCFFs demonstrating an impressive R2 value of 0.9981. The optimal tensile strength for the filament test specimens was 16.05 MPa for TCFF8 and 13.58 MPa for UCFF8, utilizing the same printing parameters: 70% infill and a layer thickness of 0.10 mm. Additionally, there was an 18% improvement in the tensile strength of the printed specimens using the filaments filled with chemically treated cocoa husk fibers compared to the filaments with untreated fibers. Full article
(This article belongs to the Special Issue Additive Manufacturing of Fibre Reinforced Polymer Composites)
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Figure 1

Figure 1
<p>Processing steps for cocoa husk fibers.</p> Full article ">Figure 2
<p>Extrusion steps for PLA with untreated cocoa husk fiber filament (UCFFs) and PLA with chemically treated cocoa husk fiber filaments (TCFFs).</p> Full article ">Figure 3
<p>Type I test specimen for tensile strength testing according to ASTM D638-14.</p> Full article ">Figure 4
<p>SEM images of (<b>a</b>) the cellulose fibers from untreated cocoa husk (UCFs); and (<b>b</b>) of the cellulose fibers from the chemically treated cocoa husk (TCFs).</p> Full article ">Figure 5
<p>SEM images of fractured specimens after tensile testing: (<b>a</b>) pure PLA specimen; (<b>b</b>) PLA specimen with untreated cocoa husk cellulose fibers (UCFFs); (<b>c</b>) PLA specimen with chemically treated cocoa husk cellulose fibers (TCFFs).</p> Full article ">Figure 6
<p>TGA (<b>a</b>) and DTG (<b>b</b>) graphs of cellulose fibers from untreated cocoa husks (UCF) and cellulose fibers from chemically treated cocoa husks (TCF).</p> Full article ">Figure 7
<p>FTIR spectra of untreated cocoa husk fiber (UCF) and chemically treated cocoa fiber (TCF).</p> Full article ">Figure 8
<p>Surface response plot for tensile strength: σt (MPa) × layer height (mm)/infill (%) for (<b>a</b>) UCFF filament specimens and (<b>b</b>) TCFF filament specimens.</p> Full article ">
18 pages, 14551 KiB  
Article
Design and Optimization of 3D-Printed Variable Cross-Section I-Beams Reinforced with Continuous and Short Fibers
by Xin Zhang, Peijie Sun, Yu Zhang, Fei Wang, Yun Tu, Yunsheng Ma and Chun Zhang
Polymers 2024, 16(5), 684; https://doi.org/10.3390/polym16050684 - 2 Mar 2024
Cited by 3 | Viewed by 1708
Abstract
By integrating fiber-reinforced composites (FRCs) with Three-dimensional (3D) printing, the flexibility of lightweight structures was promoted while eliminating the mold’s limitations. The design of the I-beam configuration was performed according to the equal-strength philosophy. Then, a multi-objective optimization analysis was conducted based on [...] Read more.
By integrating fiber-reinforced composites (FRCs) with Three-dimensional (3D) printing, the flexibility of lightweight structures was promoted while eliminating the mold’s limitations. The design of the I-beam configuration was performed according to the equal-strength philosophy. Then, a multi-objective optimization analysis was conducted based on the NSGA-II algorithm. 3D printing was utilized to fabricate I-beams in three kinds of configurations and seven distinct materials. The flexural properties of the primitive (P-type), the designed (D-type), and the optimized (O-type) configurations were verified via three-point bending testing at a speed of 2 mm/min. Further, by combining different reinforcements, including continuous carbon fibers (CCFs), short carbon fibers (SCFs), and short glass fibers (SGFs) and distinct matrices, including polyamides (PAs), and polylactides (PLAs), the 3D-printed I-beams were studied experimentally. The results indicate that designed and optimized I-beams exhibit a 14.46% and 30.05% increase in the stiffness-to-mass ratio and a 7.83% and 40.59% increment in the load-to-mass ratio, respectively. The CCFs and SCFs result in an outstanding accretion in the flexural properties of 3D-printed I-beams, while the accretion is 2926% and 1070% in the stiffness-to-mass ratio and 656.7% and 344.4% in the load-to-mass ratio, respectively. For the matrix, PAs are a superior choice compared to PLAs for enhancing the positive impact of reinforcements. Full article
(This article belongs to the Special Issue Additive Manufacturing of Fibre Reinforced Polymer Composites)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Schematic diagrams of the 3D-printing process and structural configurations: (<b>a</b>) a scheme of the Mark Two desktop 3D printer, (<b>b</b>) a scheme of the HB250 desktop 3D printer, (<b>c</b>) the three configurations of 3D-printed I-beams, and (<b>d</b>) the geometry parameters of the 3D-printed I-beams.</p> Full article ">Figure 2
<p>A (<b>a</b>) schematic diagram and (<b>b</b>) snapshot of the three-point bending testing.</p> Full article ">Figure 3
<p>The finite element mode for three-point bending loading conditions.</p> Full article ">Figure 4
<p>Optimizable parameters of the 3D-printed I-beams.</p> Full article ">Figure 5
<p>A flow chart of NSGA-II multi-objective optimization algorithm.</p> Full article ">Figure 6
<p>The collection of Pareto optimum solutions.</p> Full article ">Figure 7
<p>The geometry of variable cross-sections.</p> Full article ">Figure 8
<p>The flexural properties of the primitive, designed, and optimized configurations: (<b>a</b>) the force-to-displacement curve, (<b>b</b>) the mass, (<b>c</b>) the stiffness-to-mass ratio, and (<b>d</b>) the load-to-mass ratio.</p> Full article ">Figure 9
<p>A comparison of the failed specimens of (<b>a</b>) the primitive, (<b>b</b>) designed, and (<b>c</b>) optimized configurations of SCFs-reinforced PAs in (<b>i</b>) top, (<b>ii</b>) side, (<b>iii</b>) down, and (<b>iv</b>) zoom views.</p> Full article ">Figure 10
<p>The flexural properties of CCFs-, SCFs-, and SGFs-reinforced PAs and PAs in the configuration of the O-type I-beam: (<b>a</b>) the force-to-displacement curve, (<b>b</b>) the stiffness-to-mass ratio, and (<b>c</b>) the load-to-mass ratio.</p> Full article ">Figure 11
<p>A comparison of the failed specimens of (<b>a</b>) CCFs-, (<b>b</b>) SGFs-, and (<b>c</b>) non-reinforced PAs in the configuration of the O-type I-beam in (<b>i</b>) top, (<b>ii</b>) side, (<b>iii</b>) down, and (<b>iv</b>) zoom views.</p> Full article ">Figure 12
<p>The flexural properties of SCFs- and SGFs-reinforced PLAs, and PLAs in the configuration of the O-type I-beam: (<b>a</b>) the force-to-displacement curve, (<b>b</b>) the mass, (<b>c</b>) the stiffness-to-mass ratio, and (<b>d</b>) the load-to-mass ratio.</p> Full article ">Figure 13
<p>A comparison of the failed specimens of (<b>a</b>) SCFs-, (<b>b</b>) SGFs-, and (<b>c</b>) non-reinforced PLAs in the configuration of the O-type I-beam in (<b>i</b>) top, (<b>ii</b>) side, (<b>iii</b>) down, and (<b>iv</b>) zoom views.</p> Full article ">Figure 14
<p>Ashby-type material selection maps: (<b>a</b>) stiffness-to-mass ratio and (<b>b</b>) load-to-mass ratio.</p> Full article ">
20 pages, 10693 KiB  
Article
PLA-Based Composite Panels Prepared via Multi-Material Fused Filament Fabrication and Associated Investigation of Process Parameters on Flexural Properties of the Fabricated Composite
by Zhaogui Wang, Lihan Wang, Feng Tang and Chengyang Shen
Polymers 2024, 16(1), 109; https://doi.org/10.3390/polym16010109 - 29 Dec 2023
Cited by 1 | Viewed by 1497
Abstract
This study prepares composite panels with three Polylactic acid (PLA)-based materials via the multi-material fused filament fabrication method. The influences of four processing parameters on the mechanical properties of 3D-printed samples are investigated employing the Taguchi method. These parameters include the relative volume [...] Read more.
This study prepares composite panels with three Polylactic acid (PLA)-based materials via the multi-material fused filament fabrication method. The influences of four processing parameters on the mechanical properties of 3D-printed samples are investigated employing the Taguchi method. These parameters include the relative volume ratio, material printing order, filling pattern, and filling density. A “larger is better” signal-to-noise analysis is performed to identify the optimal combination of printing parameters that yield maximum bending strength and bending modulus of elasticity. The results reveal that the optimal combination of printing parameters that maximizes the bending strength involves a volume ratio of 1:1:2, a material sequence of PLA/foam-agent-modified eco-friendly PLA (ePLA-LW)/glass fiber-reinforced eco-friendly PLA (ePLA-GF), a Gyroid filling pattern, and a filling density of 80%, and the optimal combination of printing parameters for maximum bending modulus involves a volume ratio of 1:2:1 with a material sequence of PLA/ePLA-LW/ePLA-GF, a Grid filling pattern, and 80% filling density. The Taguchi prediction method is utilized to determine an optimal combination of processing parameters for achieving optimal flexural performances, and predicted outcomes are validated through related experiments. The experimental values of strength and modulus are 43.91 MPa and 1.23 GPa, respectively, both very close to the predicted values of 46.87 MPa and 1.2 GPa for strength and modulus. The Taguchi experiments indicate that the material sequence is the most crucial factor influencing the flexural strength of the composite panels. The experiment result demonstrates that the flexural strength and modulus of the first material sequence are 67.72 MPa and 1.53 GPa, while the flexural strength and modulus of the third material sequence are reduced to 27.09 MPa and 0.72 GPa, respectively, only 42% and 47% of the first material sequence. The above findings provide an important reference for improving the performance of multi-material 3D-printed products. Full article
(This article belongs to the Special Issue Additive Manufacturing of Fibre Reinforced Polymer Composites)
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Figure 1
<p>Three materials: DSC Curves.</p> Full article ">Figure 2
<p>Diagram of Volume Ratio: (<b>a</b>) 2:1:1, (<b>b</b>) 1:2:1, (<b>c</b>) 1:1:2; The schematic diagram refers to the ordering of materials based on a sample volume ratio of 2:1:1. (<b>d</b>) PLA/ePLA-LW/ePLA-GF; (<b>e</b>) PLA/ePLA-GF/ePLA-LW; (<b>f</b>) PLA/ePLA-LW/ePLA-GF/PLA.</p> Full article ">Figure 3
<p>Filling pattern when filling density is 40%: (<b>a</b>) Gyroid, (<b>b</b>) Grid, (<b>c</b>) 45°/135° Lines (Different colors indicate the overlap of 45°/135° straight lines between layers).</p> Full article ">Figure 4
<p>Example of the printed sandwich specimen (volume fraction ratio 1:2:1, material stacking order: PLA/ePLA-LW/ePLA-GF).</p> Full article ">Figure 5
<p>Three-point bending test.</p> Full article ">Figure 6
<p>Main effects plot of the levels of each factor on the bending strength.</p> Full article ">Figure 7
<p>The main effects plot shows the levels of each factor on the bending modulus.</p> Full article ">Figure 8
<p>Taguchi comparison of predicted values and experimental values.</p> Full article ">Figure 9
<p>Crack propagation from a side view (The loading direction for all specimens in the figures is consistent with (<b>a</b>)). Note that numbers 1–9 correspond to the experimental cases appearing in <a href="#polymers-16-00109-t003" class="html-table">Table 3</a>. (<b>a</b>) Number 1; (<b>b</b>) Number 2; (<b>c</b>) Number 3; (<b>d</b>) Number 4; (<b>e</b>) Number 5; (<b>f</b>) Number 6; (<b>g</b>) Number 7; (<b>h</b>) Number 8; (<b>i</b>) Number 9.</p> Full article ">Figure 10
<p>Crack propagation from a bird’s-eye view. Note that numbers 1–9 correspond to the experimental cases appearing in <a href="#polymers-16-00109-t003" class="html-table">Table 3</a>. (<b>a</b>) Number 1; (<b>b</b>) Number 2; (<b>c</b>) Number 3; (<b>d</b>) Number 4; (<b>e</b>) Number 5; (<b>f</b>) Number 6; (<b>g</b>) Number 7; (<b>h</b>) Number 8; (<b>i</b>) Number 9.</p> Full article ">Figure 11
<p>Microscopic imaging of interfaces between different materials: (<b>a</b>) PLA and ePLA-GF; (<b>b</b>) ePLA-LW and ePLA-GF; (<b>c</b>) PLA and ePLA-LW.</p> Full article ">Figure 12
<p>Three-point bending mechanical curve.</p> Full article ">Figure 13
<p>Histogram of average mechanical data for each horizontal bend.</p> Full article ">Figure A1
<p>Strength-to-Weight ratio.</p> Full article ">Figure A2
<p>Modulus-to-Weight ratio.</p> Full article ">
21 pages, 20803 KiB  
Article
Study on the Properties of Multi-Walled Carbon Nanotubes (MWCNTs)/Polypropylene Fiber (PP Fiber) Cement-Based Materials
by Xiangjie Niu, Yuanzhao Chen, Zhenxia Li, Tengteng Guo, Meng Ren and Yanyan Chen
Polymers 2024, 16(1), 41; https://doi.org/10.3390/polym16010041 - 21 Dec 2023
Cited by 2 | Viewed by 1381
Abstract
In order to improve the mechanical properties and durability of cement-based materials, a certain amount of multi-walled carbon nanotubes (MWCNTs) and polypropylene fiber (PP fiber) were incorporated into cement-based materials. The mechanical properties of the multi-walled carbon nanotubes/polypropylene fiber cement-based materials were evaluated [...] Read more.
In order to improve the mechanical properties and durability of cement-based materials, a certain amount of multi-walled carbon nanotubes (MWCNTs) and polypropylene fiber (PP fiber) were incorporated into cement-based materials. The mechanical properties of the multi-walled carbon nanotubes/polypropylene fiber cement-based materials were evaluated using flexural strength tests, compressive strength tests, and splitting tensile tests. The effects of multi-walled carbon nanotubes and polypropylene fiber on the durability of cement-based materials were studied using drying shrinkage tests and freeze–thaw cycle tests. The effects of the multi-walled carbon nanotubes and polypropylene fibers on the microstructure and pore structure of the cement-based materials were compared and analyzed using scanning electron microscopy and mercury intrusion tests. The results showed that the mechanical properties and durability of cement-based materials can be significantly improved when the content of multi-walled carbon nanotubes is 0.1–0.15%. The compressive strength can be increased by 9.5% and the mass loss rate is reduced by 27.9%. Polypropylene fiber has little effect on the compressive strength of the cement-based materials, but it significantly enhances the toughness of the cement-based materials. When its content is 0.2–0.3%, it has the best effect on improving the mechanical properties and durability of the cement-based materials. The flexural strength is increased by 19.1%, and the dry shrinkage rate and water loss rate are reduced by 14.3% and 16.1%, respectively. The three-dimensional network structure formed by the polypropylene fiber in the composite material plays a role in toughening and cracking resistance, but it has a certain negative impact on the pore structure of the composite material. The incorporation of multi-walled carbon nanotubes can improve the bonding performance of the polypropylene fiber and cement matrix, make up for the internal defects caused by the polypropylene fiber, and reduce the number of harmful holes and multiple harmful holes so that the cement-based composite material not only has a significant increase in toughness but also has a denser internal structure. Full article
(This article belongs to the Special Issue Additive Manufacturing of Fibre Reinforced Polymer Composites)
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Figure 1
<p>SEM of PP fibers.</p> Full article ">Figure 2
<p>Preparation process and test flow chart.</p> Full article ">Figure 3
<p>Fluidity test.</p> Full article ">Figure 4
<p>The macroscopic morphology of the specimens. (<b>a</b>) The macroscopic morphology of the specimens after the flexural strength test. (<b>b</b>) The macroscopic morphology of the specimens after the compressive strength test.</p> Full article ">Figure 5
<p>Flexural strength test results.</p> Full article ">Figure 6
<p>Compressive strength test results.</p> Full article ">Figure 7
<p>The macroscopic morphology of the specimens after the split tensile strength test.</p> Full article ">Figure 8
<p>T0–T12 results of the splitting tensile tests.</p> Full article ">Figure 9
<p>Results of the drying shrinkage tests.</p> Full article ">Figure 10
<p>The macroscopic morphology of the specimens after the freeze–thaw cycle test.</p> Full article ">Figure 11
<p>Strength loss rate.</p> Full article ">Figure 12
<p>T0 microtopography.</p> Full article ">Figure 13
<p>T2 microtopography.</p> Full article ">Figure 14
<p>T6 microtopography.</p> Full article ">Figure 15
<p>T10 microtopography.</p> Full article ">Figure 16
<p>Cumulative pore volume.</p> Full article ">
16 pages, 9944 KiB  
Article
Path Planning and Bending Behaviors of 3D Printed Continuous Carbon Fiber Reinforced Polymer Honeycomb Structures
by Kui Wang, Depeng Wang, Yisen Liu, Huijing Gao, Chengxing Yang and Yong Peng
Polymers 2023, 15(23), 4485; https://doi.org/10.3390/polym15234485 - 22 Nov 2023
Cited by 6 | Viewed by 1783
Abstract
Continuous fiber reinforced polymer composites are widely used in load-bearing components and energy absorbers owing to their high specific strength and high specific modulus. The path planning of continuous fiber is closely related to its structural defects and mechanical properties. In this work, [...] Read more.
Continuous fiber reinforced polymer composites are widely used in load-bearing components and energy absorbers owing to their high specific strength and high specific modulus. The path planning of continuous fiber is closely related to its structural defects and mechanical properties. In this work, continuous fiber reinforced polymer honeycomb structures (CFRPHSs) with different printing paths were designed and fabricated via the fused deposition modeling (FDM) technique. The investigation of fiber dislocation at path corners was utilized to analyze the structural defects of nodes caused by printing paths. The lower stiffness nodes filled with pure polymer due to fiber dislocation result in uneven stiffness distribution. The bending performance and deformation modes of CFRPHSs with different printing paths and corresponding pure polymer honeycomb structures were investigated by three-point bending tests. The results showed that the enhancement effect of continuous fibers on the bending performance of honeycomb structures was significantly affected by the printing paths. The CFRPHSs with a staggered trapezoidal path exhibited the highest specific load capacity (68.33 ± 2.25 N/g) and flexural stiffness (627.70 ± 38.78 N/mm). In addition, the fiber distributions and structural defects caused by the printing paths determine the stiffness distribution of the loading region, thereby affecting the stress distribution and failure modes of CFRPHSs. Full article
(This article belongs to the Special Issue Additive Manufacturing of Fibre Reinforced Polymer Composites)
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Figure 1
<p>Schematic presentations of (<b>a</b>) the diamond-filled CFRPHSs with geometrical dimensions and (<b>b</b>) 3D printer using the in situ impregnation FDM technique.</p> Full article ">Figure 2
<p>Printing path planning: (<b>a</b>) printing path strategies at the nodes, and (<b>b</b>–<b>e</b>) four printing paths of the CFRPHSs (the arrows indicate the printing directions, and the colors indicate different printing orders of continuous fibers).</p> Full article ">Figure 3
<p>Schematic diagram of the three-point bending test (the arrow indicates the loading direction).</p> Full article ">Figure 4
<p>Fiber dislocation of the path corners: (<b>a</b>) three path corners in the printing paths: 45°, 90°, and 135°; (<b>b</b>) the printing paths for three path corners; (<b>c</b>) schematic diagram of the evaluation methods; geometric images of three path corners in different <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>L</mi> </mrow> <mrow> <mi mathvariant="normal">s</mi> </mrow> </msub> </mrow> </semantics></math>, (<b>d</b>) <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>L</mi> </mrow> <mrow> <mi mathvariant="normal">s</mi> </mrow> </msub> </mrow> </semantics></math> = 10 mm, (<b>e</b>) <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>L</mi> </mrow> <mrow> <mi mathvariant="normal">s</mi> </mrow> </msub> </mrow> </semantics></math> = 15 mm, and (<b>f</b>) <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>L</mi> </mrow> <mrow> <mi mathvariant="normal">s</mi> </mrow> </msub> </mrow> </semantics></math> = 20 mm.</p> Full article ">Figure 5
<p>The degree of fiber dislocation at the path corners in different <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>L</mi> </mrow> <mrow> <mi mathvariant="normal">s</mi> </mrow> </msub> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>α</mi> </mrow> <mrow> <mn>0</mn> </mrow> </msub> </mrow> </semantics></math>: (<b>a</b>) angle distortion ratio (<math display="inline"><semantics> <mrow> <mi mathvariant="sans-serif">φ</mi> </mrow> </semantics></math>) and (<b>b</b>) height distortion ratio (<math display="inline"><semantics> <mrow> <mi mathvariant="sans-serif">δ</mi> </mrow> </semantics></math>).</p> Full article ">Figure 6
<p>Schematic diagrams of the fiber dislocation at the path corners: (<b>a</b>) the incompletely solidified matrix could not constrain the CCF effectively; (<b>b</b>) the CCF could not maintain a fixed position relative to the printing nozzle port.</p> Full article ">Figure 7
<p>Photographs of the three-point bending test samples at displacements of (<b>a</b>) 0 mm and (<b>b</b>) 20 mm.</p> Full article ">Figure 8
<p>The bending properties of the CFRPHSs with different printing paths and the PPHS; (<b>a</b>) three-point bending test load-displacement curves; (<b>b</b>) specific load capability and flexural stiffness.</p> Full article ">Figure 9
<p>Fiber distribution modes at the nodes in the loading region of the CFRPHSs with different printing paths: (<b>a</b>) the red node beneath the loading roller; (<b>b</b>) the green node close to the lower face sheet (the red circles indicate the region beneath the loading roller, and the green circles indicate the region close to the lower face sheet).</p> Full article ">Figure 10
<p>Deformation states of the PPHSs at displacements of (<b>a</b>) 6 mm and (<b>b</b>) 18 mm.</p> Full article ">Figure 11
<p>Deformation state <math display="inline"><semantics> <mrow> <mi mathvariant="normal">I</mi> </mrow> </semantics></math> of the CFRPHSs with (<b>a</b>) path A, (<b>b</b>) path B, (<b>c</b>) path C, and (<b>d</b>) path D.</p> Full article ">Figure 12
<p>Deformation state <math display="inline"><semantics> <mrow> <mi mathvariant="normal">I</mi> <mi mathvariant="normal">I</mi> </mrow> </semantics></math> of the CFRPHSs with (<b>a</b>) path A, (<b>b</b>) path B, (<b>c</b>) path C, and (<b>d</b>) path D.</p> Full article ">
16 pages, 7112 KiB  
Article
Spatial 3D Printing of Continuous Fiber-Reinforced Composite Multilayer Truss Structures with Controllable Structural Performance
by Daokang Zhang, Xiaoyong Tian, Yanli Zhou, Qingrui Wang, Wanquan Yan, Ali Akmal Zia, Lingling Wu and Dichen Li
Polymers 2023, 15(21), 4333; https://doi.org/10.3390/polym15214333 - 6 Nov 2023
Cited by 5 | Viewed by 2313
Abstract
Continuous fiber-reinforced composite truss structures have broad application prospects in aerospace engineering owing to their high structural bearing efficiency and multifunctional applications. This paper presents the design and fabrication of multilayer truss structures with controlled mechanical properties based on continuous fiber-reinforced thermoplastic composite [...] Read more.
Continuous fiber-reinforced composite truss structures have broad application prospects in aerospace engineering owing to their high structural bearing efficiency and multifunctional applications. This paper presents the design and fabrication of multilayer truss structures with controlled mechanical properties based on continuous fiber-reinforced thermoplastic composite 3D printing. Continuous fiber composite pyramid trusses fabricated by 3D printing have high specific stiffness and strength, with maximum equivalent compression modulus and strength of 401.91 MPa and 30.26 MPa, respectively. Moreover, the relative density of a truss structure can be as low as 1.45%. Additionally, structural units can be extended in any direction to form a multilayer truss structure. Structural performance can be controlled by designing the parameters of each layer. This study offers a novel approach for designing a multifunctional multilayer truss structure, a structure with low-density needs and unique load-bearing effects. Full article
(This article belongs to the Special Issue Additive Manufacturing of Fibre Reinforced Polymer Composites)
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<p>Pyramid composite truss units and their different types of arrays stacked in 0/90°and 45° directions.</p> Full article ">Figure 2
<p>(<b>a</b>) Continuous fiber composite 3D printer physical image, and (<b>b</b>) continuous fiber composite space structure printing schematic.</p> Full article ">Figure 3
<p>Main errors of continuous fiber-composite-printed space truss structure: (<b>a</b>) inclination angle error, (<b>b</b>) lateral error of starting and landing point, and (<b>c</b>) inter-layer error.</p> Full article ">Figure 4
<p>(<b>a</b>) The 2 × 2 pyramidal truss unit structure samples, (<b>b</b>) pyramidal truss structure samples of different scales, (<b>c</b>) pyramidal truss structure samples of different tilt angles, (<b>d</b>,<b>f</b>) compressive curves with different truss inclination angles, and (<b>g</b>,<b>e</b>) compressive curves with different truss scales.</p> Full article ">Figure 5
<p>Samples of multilayer truss structure: (<b>a</b>) vertically stacked three-layer truss sample (uniform structure design and non-uniform structure design per layer), and (<b>b</b>) 45° connected stacked three-layer truss sample (uniform structure design and non-uniform structure design per layer).</p> Full article ">Figure 6
<p>Compression performance curves of different multilayer pyramid structures. (<b>a</b>,<b>b</b>) compression performance curves of vertically stacked three-layer truss sample (uniform structure design and non-uniform structure design per layer), and (<b>c</b>,<b>d</b>) ompression performance curves of 45° connected stacked three-layer truss sample (uniform structure design and non-uniform structure design per layer).</p> Full article ">Figure 7
<p>(<b>a</b>) Actual photo of 2*2 pyramid truss unit compression, (<b>b</b>) force analysis diagram of pyramid truss unit, (<b>c</b>) force analysis of simplified pyramid single truss, and comparison of experimental data and theoretical peak force: (<b>d</b>) different truss length and (<b>e</b>) different inclination.</p> Full article ">Figure 8
<p>(<b>a</b>) Compression failure performance of different structures, (<b>b</b>) compression failure damage form of inclined trusses, and (<b>c</b>) deformation in different stages.</p> Full article ">
29 pages, 9901 KiB  
Article
Simulation-Based Identification of Operating Point Range for a Novel Laser-Sintering Machine for Additive Manufacturing of Continuous Carbon-Fibre-Reinforced Polymer Parts
by Michael Baranowski, Zijin Shao, Alexander Spintzyk, Florian Kößler and Jürgen Fleischer
Polymers 2023, 15(19), 3975; https://doi.org/10.3390/polym15193975 - 3 Oct 2023
Cited by 1 | Viewed by 2036
Abstract
Additive manufacturing using continuous carbon-fibre-reinforced polymer (CCFRP) presents an opportunity to create high-strength parts suitable for aerospace, engineering, and other industries. Continuous fibres reinforce the load-bearing path, enhancing the mechanical properties of these parts. However, the existing additive manufacturing processes for CCFRP parts [...] Read more.
Additive manufacturing using continuous carbon-fibre-reinforced polymer (CCFRP) presents an opportunity to create high-strength parts suitable for aerospace, engineering, and other industries. Continuous fibres reinforce the load-bearing path, enhancing the mechanical properties of these parts. However, the existing additive manufacturing processes for CCFRP parts have numerous disadvantages. Resin- and extrusion-based processes require time-consuming and costly post-processing to remove the support structures, severely restricting the design flexibility. Additionally, the production of small batches demands considerable effort. In contrast, laser sintering has emerged as a promising alternative in industry. It enables the creation of robust parts without needing support structures, offering efficiency and cost-effectiveness in producing single units or small batches. Utilising an innovative laser-sintering machine equipped with automated continuous fibre integration, this study aims to merge the benefits of laser-sintering technology with the advantages of continuous fibres. The paper provides an outline, using a finite element model in COMSOL Multiphysics, for simulating and identifying an optimised operating point range for the automated integration of continuous fibres. The results demonstrate a remarkable reduction in processing time of 233% for the fibre integration and a reduction of 56% for the width and 44% for the depth of the heat-affected zone compared to the initial setup. Full article
(This article belongs to the Special Issue Additive Manufacturing of Fibre Reinforced Polymer Composites)
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<p>View of the process chamber of the developed LS machine (<b>a</b>) with a detailed view of the fibre integration unit (<b>b</b>). Schematic representation of the heat fluxes and influencing factors (<b>c</b>).</p> Full article ">Figure 2
<p>Schematic representation of the influence of the HAZ on the roving overlap <math display="inline"><semantics> <mrow> <msub> <mrow> <mrow> <mo> </mo> <mi mathvariant="normal">h</mi> </mrow> </mrow> <mi mathvariant="normal">R</mi> </msub> </mrow> </semantics></math>.</p> Full article ">Figure 3
<p>Three-dimensional view of the additional heat source with fibre nozzle, feeler gauge tape, and guide (<b>a</b>), and geometry implemented in COMSOL for process zone (<b>b</b>).</p> Full article ">Figure 4
<p>Process zone with the occurring mesh zones and initially assumed mesh resolution.</p> Full article ">Figure 5
<p>The initial state of the moving mesh at time t = 0 s (<b>a</b>) and the extruded mesh at a relative fibre nozzle offset of 40 mm (<b>b</b>).</p> Full article ">Figure 6
<p>The volumes (purple) involved in the FE model in which heat conduction occurs (<b>a</b>) and the surfaces (purple) involved in the FE model which are involved in radiation exchange (<b>b</b>).</p> Full article ">Figure 7
<p>Isometric view of the evolution of the HAZ within the part when moving mesh is executed (<b>a</b>), as well as a front view of the HAZ with half width and total depth of the HAZ (<b>b</b>).</p> Full article ">Figure 8
<p>3D view of the arrangement of the specimens in the built volume of the LS machine (<b>a</b>) and a top view (<b>b</b>) with the movement path of the fibre nozzle (red lines).</p> Full article ">Figure 9
<p>The surface of a sample with embedded 1K roving uncut (<b>a</b>) and cut open with a scalpel (<b>b</b>).</p> Full article ">Figure 10
<p>Schematic representation for calculating the roving overlap within a specimen.</p> Full article ">Figure 11
<p>Depth of the HAZ as a function of the number of elements (<b>a</b>) and required calculation time (<b>b</b>) for meshing zone 1.</p> Full article ">Figure 12
<p>Depth of the HAZ as a function of the number of elements (<b>a</b>) and required calculation time (<b>b</b>) for meshing zone 2.</p> Full article ">Figure 13
<p>Depth of the HAZ as a function of the time step ∆t (<b>a</b>) and required calculation time (<b>b</b>) for the moving mesh.</p> Full article ">Figure 14
<p>The results (red dots) of the initial CCD simulated with the FE model and the surface response diagram (<b>a</b>) derived with Minitab. Possible parameter constellations (blue line) for <math display="inline"><semantics> <mrow> <msub> <mrow> <mrow> <mo> </mo> <mi mathvariant="normal">v</mi> </mrow> </mrow> <mi mathvariant="normal">D</mi> </msub> <mo> </mo> </mrow> </semantics></math>and <math display="inline"><semantics> <mrow> <msub> <mi mathvariant="normal">T</mi> <mi mathvariant="normal">D</mi> </msub> </mrow> </semantics></math> for which the condition <math display="inline"><semantics> <mrow> <msub> <mi mathvariant="normal">t</mi> <mrow> <mi>HAZ</mi> </mrow> </msub> <mo>≈</mo> </mrow> </semantics></math> 365 µm applies (<b>b</b>). Selected operating point at <math display="inline"><semantics> <mrow> <msub> <mi mathvariant="normal">T</mi> <mi mathvariant="normal">D</mi> </msub> <mo>=</mo> </mrow> </semantics></math> 345 °C (black dot).</p> Full article ">Figure 15
<p>Surface response diagram for the results determined with the FE model (<b>top</b>) and the experimental results (<b>bottom</b>).</p> Full article ">Figure 16
<p>Surface response diagram of the FE model (bottom) and surface response diagram of the experimentally performed CCD with the influence of roving integration (top) (<b>a</b>). Contour diagram of the upper surface response diagram from (<b>a</b>) with contour lines (<b>b</b>).</p> Full article ">Figure 17
<p>Influence of nozzle feed rate on roving overlap (<b>a</b>) and uncontrolled roving orientation within the specimen (<b>b</b>). The blue dots indicate the roving overlap and the red line in (<b>a</b>) indicates the layer thickness during printing.</p> Full article ">Figure 18
<p>Three-dimensional view of the 3D model in the slicer app with roving paths in red (<b>a</b>) and manufactured suction gripper with integrated spring (<b>b</b>).</p> Full article ">
17 pages, 21553 KiB  
Article
Digital Image Correlation Analysis of Strain Fields in Fibre-Reinforced Polymer–Matrix Composite under ±45° Off-Axis Tensile Testing
by Paweł Bogusz
Polymers 2023, 15(13), 2846; https://doi.org/10.3390/polym15132846 - 28 Jun 2023
Cited by 7 | Viewed by 2142
Abstract
This study presents an experimental investigation of an in-plane shear of a glass lamina composite using a ±45° off-axis tension test. Typically, the shear stress curve, shear modulus, and in-plane shear strength for composite lamina-type materials are identified. Previous research indicated that a [...] Read more.
This study presents an experimental investigation of an in-plane shear of a glass lamina composite using a ±45° off-axis tension test. Typically, the shear stress curve, shear modulus, and in-plane shear strength for composite lamina-type materials are identified. Previous research indicated that a loading rate affects the strength of this composite. This study extends the existing literature by utilising a non-contact optical digital image correlation (DIC) method to measure strain distribution during the test. Two cross-head displacement rates were examined. The obtained strain maps reveal an uneven distribution resembling fabric texture. As the deformation progresses, the differences in the strain pattern increase. Subsequently, a quantitative analysis of the differences between regions with extreme (minimum and maximum) strain values and regions with average values was conducted. Based on these measurements, shear stress–strain curves, indicating variations in their courses, were constructed. These differences may reach several percent and may influence the analysis of numerical simulations. The DIC results were validated using strain gauge measurements, a commonly utilised method in this test. It was demonstrated that the location of the strain gauge installation impacts the results. During the tests, the occurrence of multiple microcracks in the resin was observed, which can contribute to the nonlinearity observed in the shear stress–shear strain curve. Full article
(This article belongs to the Special Issue Additive Manufacturing of Fibre Reinforced Polymer Composites)
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<p>The scheme of a glass/vinyl-ester sample.</p> Full article ">Figure 2
<p>A sample with a T-rosette attached and a stochastic pattern applied.</p> Full article ">Figure 3
<p>Testing setup (<b>a</b>) with DIC measurement cameras (<b>b</b>).</p> Full article ">Figure 4
<p>In-plane shear strength as a function of loading rate.</p> Full article ">Figure 5
<p>Facet maps representing strain distribution in the X direction for a sample tested at a loading rate of 0.02 mm/min: (<b>a</b>) stage 2; (<b>b</b>) stage 30; (<b>c</b>) stage 60; (<b>d</b>) stage 90.</p> Full article ">Figure 6
<p>Facet maps representing strain distribution in the X direction for a sample tested at a loading rate of 20 mm/min: (<b>a</b>) stage 2; (<b>b</b>) stage 26; (<b>c</b>) stage 52; (<b>d</b>) stage 78.</p> Full article ">Figure 7
<p>Facet fields: (<b>a</b>) area of high-value facets, (<b>b</b>) area of average-value facets, and (<b>c</b>) area of low-value facets for a sample investigated with 0.02 mm/min loading rate.</p> Full article ">Figure 8
<p>Facet fields: (<b>a</b>) area of high-value facets, (<b>b</b>) area of average-value facets, and (<b>c</b>) area of low-value facets for a sample investigated with 20 mm/min loading rate.</p> Full article ">Figure 9
<p>Directional strain comparison for different strain measuring methods. The loading rate is equal to 0.02 mm/min.</p> Full article ">Figure 10
<p>Directional strain comparison for different strain measuring methods. The loading rate is equal to 20 mm/min.</p> Full article ">Figure 11
<p>Shear stress–shear strain curve waveforms for different strain measuring methods and various facet areas. The loading rate is equal to 0.02 mm/min. The shear offset yield strength was determined using dashed lines.</p> Full article ">Figure 12
<p>Shear stress–shear strain curve waveforms for different strain measuring methods and various facet areas. The loading rate is equal to 20 mm/min. The shear offset yield strength was determined using dashed lines.</p> Full article ">Figure 13
<p>An example image of a DIC area from one of the samples tested with a loading rate of 20 mm/min reveals the presence of multiple visible cracks in the field, examples of which were indicated with the red ellipses.</p> Full article ">
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