CN106017345A - Graded material coupling strain field in-situ measuring system and method based on speckle technique - Google Patents

Abstract

The invention discloses a gradient material coupled strain field in-situ measurement system and method based on speckle technology. Applying the digital speckle correlation method based on electron microscopy system imaging to the in-situ observation of the micro-scale coupling strain field of gradient materials, it overcomes the temporal and spatial distribution of coupling effects caused by the micro-scale mobility coupling interface of gradient materials Inhomogeneity makes it impossible to effectively characterize the coupling process using traditional macro and mesomechanics experimental methods. High-quality micro-nano-scale speckles are prepared by electro-etching, which overcomes the small size of heterogeneous particle speckles prepared by traditional methods, poor uniformity, low gray intensity gradient, complicated operation, high economic cost, and may not be suitable. Electron field imaging, weak bonding is easy to fall off, and strong bonding will restrain the deformation of the sample surface and distort or even cover the shortcomings of small gradient coupling strain components.

Description

In-situ measurement system and method of gradient material coupling strain field based on speckle technology

technical field

The invention relates to the field of in-situ measurement of coupling strain fields, in particular to a system and method for in-situ measurement of gradient material coupling strain fields based on speckle technology.

Background technique

From large-scale civil engineering to microelectronic devices, structural materials are required to have high strength and high toughness. However, for conventional homogeneous materials, strength and plasticity are mutually exclusive. For example, coarse-grained metal materials have good plasticity but low strength, while nano-metal materials have high strength, but low plastic deformation ability is extremely easy to sudden and destructive damage. Through the study of natural gradient materials such as shells and bones, researchers have found that multi-scale gradient structural materials composed of a variety of mechanically incompatible units can have high strength and high plasticity at the same time. In order to optimize and guide the structural design of gradient materials, we are required to have a clear understanding of their load-bearing and deformation mechanisms. During the deformation process, due to the inconsistency of elastic and plastic deformation, plastic stability and unstable rheological state between mechanically uncoordinated unit layers, gradient materials exhibit interlayer interaction constraints, multi-scale and multi-field coupling, stress-strain gradient distribution, Interfacial coupling effects such as the preferential development of the long-range internal stress field. The mechanical constitutive performance of the unit layer in the gradient material is completely different from the results of its separate test, which makes it difficult for classical numerical simulation methods such as finite elements to simulate the above coupling process, so the exploration of the coupling mechanism strongly depends on experimental observations. However, whether it is a continuous gradient structure in which the interface continuously migrates and transforms with the load state, or a layered gradient structure with a clear and stable interface, the influence range of a single interface is limited to within a few microns on both sides of the interface, which requires The experimental observation method and system should achieve micro-nano spatial resolution; the gradient stress and strain coupling across the interface is still a very small component compared to the macro-uniform component, and it is extremely easy to be covered by the noise of the macro-uniform component, which requires high Observation systems and methods with high precision and low noise; in addition, the coupling strength between unit layers varies nonlinearly with the load state, loading path, and coupling accumulation degree, which requires experimental methods and systems to realize in-situ observation of multiple load paths. Traditional methods such as overall performance testing of samples such as tension or compression, local performance testing of micro-nano indentation, macro-micro-optical observation or electrical strain characterization have been unable to effectively characterize the coupled deformation process of gradient materials.

Contents of the invention

To solve the above technical problems, the present invention provides an in-situ measurement system and method for gradient material coupled strain field based on speckle technology.

The present invention realizes through following technical scheme:

The in-situ measurement method of gradient material coupling strain field based on speckle technology includes the following steps:

Step 1. Prepare micro-nano scale speckles on the surface of the gradient material sample;

Step 2. Under the electron microscope, obtain the speckle field I ₀ of the gradient material sample in the coupling region of the mechanical gradient surface in the unloaded state;

Step 3. Load the gradient material sample to a predetermined load state P ₁ , and obtain the speckle field I ₁ of the coupled deformation area of the mechanical gradient surface under this load state;

Step 4. Repeat step 3 to load the gradient material sample into the predetermined loading state P _i , where i is a natural number greater than 1; and obtain the speckle field I _i of the same area under the corresponding loading state until the predetermined loading path is completed;

Step 5. Perform preprocessing on the speckle field I, and then perform correlation calculations on the digital speckle field I _j and I ₀ to obtain the coupling strain field ε _j in the loaded state of P _j relative to the unloaded state, where j is greater than 0 A natural number; the digital speckle field I _j and I _n are correlated to obtain the coupling strain field ε _jn from the P _n load state to the P _j load state, where n is a natural number greater than 0 and less than j;

Step 6. According to ε _j and ε _jn , the distribution law of the coupling strain field of the gradient material across the interface and its evolution process with the load state are obtained.

The full name of speckle technology is digital speckle correlation technology, which is a high-precision, non-contact deformation measurement method, and its theory is not limited by the measurement size. The present invention combines the technology with the in-situ observation experiment platform based on the high-spatial-resolution electron microscopic imaging system to meet the requirements for in-situ observation of the micro-scale coupling strain field of the gradient material, and then from the evolution of the strain with the load state and the interactive coupling The perspective reveals the coupling deformation mechanism of gradient structure materials. The experimental characterization of the coupled deformation process of gradient materials requires in-situ experimental systems and methods with very high spatial and precision resolution, which is a major problem in the academic community. The invention applies "digital speckle correlation technology" to its research for the first time and effectively characterizes the strain coupling and evolution process in the deformation process of gradient materials, and realizes in-situ observation with high precision, low noise and multiple load paths.

In step 1, micro-nanoscale speckles are fabricated by electroetching.

The method for preparing micro-nano scale speckles by the electro-etching method comprises the following steps:

Step 1-1, polishing the gradient material sample;

Step 1-2, connect the gradient material sample to the anode of the DC constant voltage power supply, switch on the DC constant voltage power supply, adjust the electroetching voltage and time according to the required speckle size, and perform electroetching;

Step 1-3, take out the gradient material sample and quickly wash the residual electroetching solution on the surface with deionized water, clean the gradient material sample and dry it.

Although digital speckle correlation technology has been widely used in macro-scale strain measurement, there are still a series of problems in the application of this technology for the in-situ measurement of micro-nano-scale coupled strain fields with large gradients: (a ) The preparation of micro-nano-sized uniform speckles requires the speckle size to reach tens or even several nanometers, while the traditional micro-nano speckle preparation methods such as nano-spraying and chemical vapor deposition have problems of large size, poor uniformity, complicated operation, and economical (b) The speckle prepared by the traditional heterogeneous particle coverage method has a constraining effect on the sample surface, which is easy to distort or even cover the tiny interlayer coupling strain component, so the prepared speckle The speckle field should have no surface confinement effect and can truly reflect the intrinsic deformation of the material; (c) the speckle field should have the characteristics of low noise and high gray intensity gradient, so as to avoid the small coupling gradient strain component being overwhelmed by the noise of the uniform strain component. Interference or coverage; (d) Obtaining speckle images with micro-nano spatial resolution generally requires complex electronic imaging equipment, such as scanning electron microscopes, which also requires that the speckle of the sample should be conductive and suitable for electronic field imaging; ( e) In-situ continuous measurement requires electronic imaging equipment to be equipped with an in-situ loading device with a high enough displacement load resolution. Correspondingly, the packaging of the loading table and the connection with the external control cabinet in a high vacuum and electronic field environment in a limited space are also necessary. is a difficult problem. The present invention uses the electroetching method for the first time to prepare micro-nano-scale speckles on the surface of metal materials, and effectively solves the problem of low-cost, high-quality, high-precision, and suitable for high-resolution electron field imaging micro-nano-scale speckle preparation. The electroetching method uses a finely polished sample as an anode, and forms a closed circuit with a DC power supply, a cathode, and an electroetching solution. Under the action of low-voltage DC, the surface of the sample simultaneously undergoes bump dissolution and lattice defect pitting corrosion reactions. , and quickly form a fine, uniform, and low-roughness concave-convex topography. In an electronic field environment with high spatial resolution and high contrast, the above concave-convex topography is imaged as a speckle topography with a relatively high gray intensity gradient.

When polishing the gradient material sample, the steps of coarse sandpaper polishing, fine sandpaper polishing and electrolytic polishing are sequentially included.

In step 1-2, the time adjustment range of electroetching is from 3s to 15s.

Described step 2 specifically comprises the following steps:

Step 2-1, adjusting the mechanical gradient surface of the gradient material sample into the field of view and zooming in on the imaging factor to focus on the coupling deformation area;

Step 2-2. Adjust the electronic field to increase the gray intensity gradient of the electronic speckle field, refocus and take a speckle image.

When the imaging multiple is enlarged in step 2-1, the size of a single speckle diameter is not less than 3 pixels and not greater than 8 pixels.

In step 2-2, the specific method of adjusting the electron field includes increasing the electron beam acceleration voltage, increasing the brightness and contrast of the electron field.

The coupling deformation region is the elastic and plastic deformation coupling interface on the mechanical gradient gradient surface of the gradient material, the migration region of the plastic stable rheological and unstable rheological coupling interface, or the area near the interface on the mechanical gradient surface of the layered material.

The preprocessing of the speckle field I includes filter noise reduction processing, gray intensity gradient calculation, and statistical speckle average diameter.

Based on the above method, the inventors developed the following system.

Gradient material coupling strain field in-situ measurement system based on speckle technology, including:

A sample preprocessing module that processes the gradient material sample to form micro-nano scale speckles on its surface;

The sample loading module placed on the in-situ loading platform of the electron microscope sample chamber to realize the unidirectional tension and compression of the gradient material sample at different loading rates and control the cyclic loading and unloading process;

The speckle field shooting module for shooting the speckle field of the coupled deformation area on the surface of the gradient material sample;

Calculation and analysis module that performs correlation calculation and analysis on the speckle field according to the shooting results.

Preferably, the sample pretreatment module includes sandpaper, electrolytic polishing liquid, and electroetching device.

Preferably, the sample loading module includes a base, a front clamp fixed to the base, and a rear clamp slidably connected to the base, the front clamp and the rear clamp are provided with sample suspension grooves Yes, it also includes a loading screw for adjusting the relative displacement of the front clamp and the rear clamp and a displacement load reading device for marking the relative displacement of the front clamp and the rear clamp, and the bottom of the base is provided with a loading table fixing device . The sample hanging grooves are respectively set on the front clamping block and the rear clamping block to form a pair of sample hanging grooves. The pair of sample hanging grooves respectively fix the tensile samples from both ends. The relative distance between them is used to realize the loading and unloading of the tensile sample; the clamping of the compression sample does not need the pair of sample suspension grooves, and the compression sample is directly adjusted to the observation surface and clamped on the front clamp block and the rear clamp. Between the clamping blocks, adjust the loading screw to adjust the relative distance between the front clamping block and the rear clamping block to realize the compression of the compression sample. The loading device is fixed on the imaging system stage through the loading device fixing structure at the bottom of the base. The device adopting the above structure is compact, exquisite, light in weight and small in size, and can adapt to the limited sample chamber space of the imaging system; the relative distance between the front clamping block and the rear clamping block is adjusted by the loading screw, that is, the relative distance is adjusted by thread transmission. and in actual application, the whole device can be directly applied to the high-vacuum electron field environment of electronic imaging equipment after ultrasonic cleaning with acetone solution, and the structure does not have the problems of water, oil stains and magnetic field packaging of the device itself.

Preferably, the calculation and analysis module includes an image input and output module, a speckle field preprocessing module, a speckle field correlation calculation module, a strain data matrix singular point elimination module, a strain data matrix cloud map visualization module, and a strain field local area data extraction module. module, data text output module.

Compared with the prior art, the present invention has at least the following advantages and beneficial effects:

1. The present invention applies the digital speckle correlation method based on the electron microscope system image acquisition to the in-situ measurement of the micro-scale coupling strain field of the gradient material, which overcomes the continuous migration of the coupling interface of the gradient material, the small span of the affected area of a single interface, and the The whole field is not uniform, the coupling strain component is easily distorted or covered by noise, and the coupling strength changes continuously with the load state and coupling accumulation degree, so it is impossible to effectively characterize the coupling process using traditional methods such as stretching, indentation, and macroscopic digital speckle correlation. The problem has achieved the observation conditions of high spatial resolution at the micro-nano scale, high precision and low noise, full-field consideration of local, and in-situ continuous observation.

2. The present invention uses the electro-etching method to prepare micro-nano-scale speckles, which overcomes the small size of speckles prepared by traditional nano-spraying and vapor deposition methods, poor uniformity, complicated operation, high economic cost, low gray intensity gradient, It may not be suitable for electron field imaging, the weak bond will easily fall off, and the strong bond will restrain the deformation of the sample surface and distort or even cover the small gradient coupling strain components.

Description of drawings

The drawings described here are used to provide a further understanding of the embodiments of the present invention, constitute a part of the application, and do not limit the embodiments of the present invention. In the attached picture:

FIG. 1 is a micro-nano speckle pattern prepared by electroetching on the surface of the gradient material in Example 4 of the present invention and photographed by a scanning electron microscope.

FIG. 2 is a pixel distribution diagram of a single correlation search window at A in FIG. 1 .

Fig. 3 is a micro-scale coupled strain field diagram of a gradient material observed in Example 4 of the present invention under a certain load state relative to the stretching direction of the initial state, where X represents the interface; Y represents the stretching direction.

Fig. 4 is a micro-scale coupled strain field diagram perpendicular to the stretching direction of a gradient material observed in Example 4 of the present invention under a certain load state relative to the initial state.

Fig. 5 is a microscale relative coupling strain field diagram perpendicular to the stretching direction of two loading states of the gradient material observed in Example 5 of the present invention.

Fig. 6 is a strain distribution diagram along the white dotted line in Fig. 5 in Example 5 of the present invention.

detailed description

In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the examples and accompanying drawings. As a limitation of the present invention.

Example 1

An in-situ measurement method for gradient material coupling strain field based on speckle technology, comprising the following steps,

Step 1. Prepare micro-nano scale speckles on the surface of the gradient material sample;

Step 2. Under the electron microscope, obtain the speckle field I ₀ of the gradient material sample in the coupling region of the mechanical gradient surface in the unloaded state;

Step 3. Load the gradient material sample to a predetermined load state P ₁ , and obtain the speckle field I ₁ of the coupling deformation region under this load state;

Step 4. Repeat step 3 to load the gradient material sample into the predetermined loading state P _i , where i is a natural number greater than 1; and obtain the speckle field I _i of the same area under the corresponding loading state until the predetermined loading path is completed;

Step 5. Perform preprocessing on the speckle field I, and then perform correlation calculations on the digital speckle field I _j and I ₀ to obtain the coupling strain field ε _j in the loaded state of P _j relative to the unloaded state, where j is greater than 0 A natural number; the digital speckle field I _j and I _n are correlated to obtain the coupling strain field ε _jn from the P _n load state to the P _j load state, where n is a natural number greater than 0 and less than j;

Step 6. According to ε _j and ε _jn , the distribution law of the coupling strain field of the gradient material across the interface and its evolution process with the load state are obtained.

In the next embodiment, a detailed implementation example of preparing micro-nano-scale speckles by electro-etching method will be given.

Example 2

In this embodiment, on the basis of the above-mentioned embodiments, the fabrication method of micro-nano-scale speckle is refined. The whole process includes steps 1-6.

Prepare the electropolishing solution and electroetching solution of the species gradient material in advance;

Step 1-1, polishing the mechanical gradient surface of the gradient material sample with coarse sandpaper and fine sandpaper in sequence, and then electropolishing;

Step 1-2, connect the gradient material sample to the anode of the DC constant voltage power supply, switch on the power supply, select the appropriate electroetching voltage and time parameters for electroetching, and adjust the voltage and time parameters according to "The higher the electroetching voltage Larger, the shorter the time, the finer the speckle size; the smaller the electro-etching voltage, the longer the time, the larger the speckle size" principle, the optimal selection range of electro-etching time parameters is 3s-15s;

Step 1-3, take out the gradient material sample, quickly rinse the residual electroetching solution on the surface with deionized water, then ultrasonically clean the sample with alcohol and dry it with a hair dryer.

This method is based on the digital speckle method of electron microscope imaging, so the gradient material sample is clamped on the in-situ loading stage based on the electron microscope, and step 2 is carried out:

Step 2-1, adjust the coupling deformation area of the mechanical gradient surface into the field of view through the scanning electron microscope control cabinet, select an appropriate magnification and focus on this area;

Step 2-2, increasing the gray intensity gradient of the speckle field by adjusting the acceleration voltage of the electron field and increasing the contrast and brightness of the electron field, and photographing the speckle field I ₀ of the region under no load.

The coupling deformation region is the elastic and plastic deformation coupling interface on the mechanical gradient gradient surface of the gradient material, the migration region of the plastic stable rheological and unstable rheological coupling interface, or the area near the interface on the mechanical gradient surface of the layered material.

The selection of magnification is based on the spatial resolution and speckle size of the required speckle field. While ensuring the resolution, the span of the diameter d of a single speckle should be controlled within the range of not less than 3 pixels and not more than 8 pixels.

Step 3: Load the gradient material sample to a predetermined load state P ₁ through the in-situ loading platform, and take pictures to obtain the speckle field I ₁ under this load state.

Step 4: Repeat step 3 to load the gradient material sample into the predetermined loading state P _i , where i is a natural number greater than 1; and capture the speckle field I _i under the corresponding loading state until the predetermined loading path is completed, where the predetermined The loading path refers to the unidirectional tension, compression or controlled cyclic loading and unloading process through the in-situ loading table to achieve preset different strain rates.

All the speckle fields captured in steps 2-2 to step 4 correspond to the same coupling deformation region.

Step 5. Preprocess the speckle field I by filter noise reduction, gray intensity gradient calculation, and statistical speckle average diameter d ₀ , and then perform correlation calculations on the digital speckle field I _j and I ₀ to obtain the relative load state of P _j The coupling strain field ε _j in the no-load state, that is, the initial state, where j is a natural number greater than 0; the digital speckle field I _j and I _n are correlated to obtain the coupling strain from the P _n load state to the P _j load state Field ε _jn , where n is a natural number greater than 0 and less than j, where the search window side length L used for correlation calculation of the digital speckle field I _j and I _n has a size span of 6d ₀ to 10d ₀ , and the search step The length l is about 0.2d ₀ .

Step 6. Carry out singular point exclusion, cloud map visualization processing, extract local area coupling strain, and export strain cloud map and strain field data text for ε _j and ε _jn in sequence. The inductive analysis of ε _j and ε _jn can extract cross-interface coupling strain The distribution law of the field and the change law of the coupling strain at some specific locations with the overall load.

Example 3

Gradient material coupling strain field in-situ measurement system based on speckle technology, including:

A sample preprocessing module that processes the gradient material sample to form micro-nano scale speckles on its surface;

The sample loading module placed on the in-situ loading platform of the electron microscope sample chamber to realize the unidirectional tension and compression of the gradient material sample at different loading rates and control the cyclic loading and unloading process;

The speckle field shooting module for shooting the speckle field of the coupled deformation area on the surface of the gradient material sample;

Calculation and analysis module that performs correlation calculation and analysis on the speckle field according to the shooting results.

The sample pretreatment module includes sandpaper, electrolytic polishing liquid, and an electroetching device, and the speckle on the surface of the gradient material sample is prepared by using the above device and the method in Example 2.

Specifically, the sample loading module includes a base, a front clamping block fixed on the base, and a rear clamping block slidably connected to the base, and the front clamping block and the rear clamping block are provided with sample suspension grooves Yes, it also includes a loading screw for adjusting the relative displacement of the front clamp and the rear clamp and a displacement load reading device for marking the relative displacement of the front clamp and the rear clamp, and the bottom of the base is provided with a loading table fixing device . Specifically, the fixing device of the loading device can adopt the structure of dovetail groove.

Specifically, the calculation and analysis module includes an image input and output module, a speckle field preprocessing module, a speckle field correlation calculation module, a strain data matrix singular point elimination module, a strain data matrix cloud image visualization module, a strain field local area data extraction module, Data text output module.

The image input and output module is mainly responsible for the input of speckle images and the output of strain field cloud images; the speckle field preprocessing module is mainly responsible for speckle image filtering noise reduction, gray intensity gradient calculation, and speckle average size calculation; speckle field correlation calculation The module is mainly responsible for calculating the correlation of the speckle field to obtain the strain field data matrix; the singular point elimination module of the strain data matrix is mainly responsible for the singular point elimination of the strain field data matrix; the cloud image visualization module of the strain data matrix is mainly responsible for the cloud image visualization and comparative analysis of the strain field data matrix; The data extraction module in the local area of the strain field is mainly responsible for the extraction and analysis of data points in the local area of the strain field; the data text output module is mainly responsible for the text output of the strain field data.

Example 4

This embodiment takes a scanning electron microscope-based measurement process and results of the microscale coupling strain field of layered gradient materials as an example. On the one hand, it is used to illustrate the characteristics of the coupling strain field at the interface of the gradient material and its observation method and system. The required conditions, on the other hand, are used to reflect the practicability and superior performance of the method and system of the present invention. The selected material is a layered gradient material, specifically a structure in which a layer of high-strength and low-plasticity nanocrystalline brass is sandwiched by two layers of low-strength and high-plasticity coarse-grained pure copper. The layered gradient material has sharp, stable elastic/plastic, plastic rheological stable/unstable coupling interfaces, and has obvious interface effects and coupling characteristics during deformation. For the preparation and properties of specific materials, please refer to X.L.Ma, C.X.Huang, et al. Strain hardening and ductility in acoarse-grain/nanostructure laminate material[J], Scripta Materialia, 2015, 103:57-60.

Prepare the electrolytic polishing solution and electroetching solution first. The electrolytic polishing solution for this type of material is the electrolytic polishing solution used in conventional copper-based alloys. The electrolytic solution formula is 120ml of distilled water, 2ml of dilute hydrochloric acid, 5g of ferric chloride and trace additives . Use 600#, 1000#, 1500# sandpaper to polish the mechanical gradient surface of the layered gradient material sample in turn, and use the electrolytic polishing solution prepared in advance to electropolish, then connect the sample to the anode of the DC power supply, and electro-etch at 1.2V for 8s After taking out the sample, the sample was ultrasonically cleaned with deionized water and alcohol in turn and dried. Clamp the sample to the in-situ loading stage based on the scanning electron microscope, adjust the scanning electron microscope to focus on the mechanical gradient surface of the sample, select the magnification as 1200 times, the electron beam acceleration voltage of 20KV, and increase the brightness and contrast of the electron field. The speckle field of the interface transition area in the unloaded state is shown in Figure 1. The size of the speckle field is 2210×1820pixel ² , the pixel resolution is 41.7nm/pixel, the gray intensity gradient of the whole field is 48.5, and the full-field scattered The average spot size d ₀ is 4.6 pixels. The sample was uniaxially stretched and the speckle patterns were taken at the overall strain states of 0.5%, 2%, 6%, 10%, and 15%, respectively. Correlation calculations and analysis are performed on the speckle patterns of different load states and the initial state speckle field. The correlation calculation window size is selected as 30×30pixel ² , and the correlation search step size is 3pixel. Fig. 2 is a pixel distribution diagram of a local single search window in the speckle field. Figure 3 and Figure 4 show the grayscale images of the coupled strain field in the stretching direction and perpendicular to the stretching direction of the interfacial transition region taken under the 10% global strain state, respectively, and the average strains in the whole field are 10.1% and -5.48 %. The position of the interface can be clearly distinguished from the two figures, and there is no abnormal coupling of strain in the tensile direction at the interface. However, as shown in Figure 4, the strain field perpendicular to the tensile direction shows a large number of interface-influenced areas where coupled negative strain accumulates, and the average span of the strain gradient in this area is only 182.4 pixels, about 7.6 μm.

Example 5

The difference between this embodiment and the above-mentioned embodiment 4 lies in the difference in the loading path. In this embodiment, the sample is directly loaded to the 10% overall strain load state and the speckle field image I ₁ is taken, and then the sample is unloaded to 0 stress state and capture the speckle field I ₂ . Computing and analyzing I ₂ relative to I ₁ , the strain field perpendicular to the stretching direction is shown in Figure 5. It can be seen that the result does not appear the interface affected zone described in Example 4, but there are obvious strain differences on both sides of the interface. Figure 6 shows the strain distribution along the white dotted line in Figure 5. There is a strain difference of about 0.038% on both sides of the interface marked by the black dotted line in Figure 6, which shows that even during the unloading process, there is still obvious coupling between the mechanical gradient layers. Constraint.

Can find out from above-mentioned two concrete examples:

(1) The electro-etching method can produce high-quality micro-nano-sized speckles with high gray intensity gradient and low noise;

(2) The method and system of the present invention can effectively meet the micro-nanoscale high-resolution, high-precision, low-noise, multiple load paths, and in-situ continuous conditions required for the coupled strain characterization of gradient materials.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the scope of the present invention. Protection scope, within the spirit and principles of the present invention, any modification, equivalent replacement, improvement, etc., shall be included in the protection scope of the present invention.

Claims (11)

1. functionally gradient material (FGM) based on Speckles Technique coupling strain field in-situ measuring method, its feature It is, comprises the following steps:

Step 1, prepare micro-nano-scale speckle at functionally gradient material (FGM) specimen surface；

Step 2, under an electron microscope, obtains functionally gradient material (FGM) sample and exerts oneself in no-load state Learn the speckle field I of gradient face coupling regime₀；

Step 3, functionally gradient material (FGM) sample is loaded into predetermined loading status P₁, and obtain this load The speckle field I in Coupling Deformation region, mechanical gradient face under state₁；

Functionally gradient material (FGM) sample is loaded into predetermined loading status P by step 4, repetition step 3_i, its Middle i is the natural number more than 1；And obtain the speckle of same area under corresponding loading status Field I_i, until completing predetermined load path；

Step 5, speckle field I is done pretreatment, then by digital speckle field I_jAnd I₀Make correlometer Calculation obtains P_jLoading status is relative to coupling strain field ε under no-load state_j, wherein j For the natural number more than 0；By digital speckle field I_jAnd I_nDo correlation computations to obtain from P_n Loading status is to P_jCoupling strain field ε of loading status_j-n, wherein, n is oneself more than 0 So count and less than j；

Step 6, according to ε_jAnd ε_j-nObtain the regularity of distribution in functionally gradient material (FGM) coupling strain field face transboundary And the evolutionary process with loading status.

Functionally gradient material (FGM) based on Speckles Technique the most according to claim 1 coupling strain field In-situ measuring method, it is characterised in that: in step 1, micro-nano-scale speckle Electricity consumption lithographic method prepares.

Functionally gradient material (FGM) based on Speckles Technique the most according to claim 2 coupling strain field In-situ measuring method, it is characterised in that described electroetching method prepares micro-nano meter ruler The method of degree speckle comprises the following steps:

Step 1-1, functionally gradient material (FGM) sample is polished；

Step 1-2, functionally gradient material (FGM) sample is connected on DC constant voltage power anode, connects direct current permanent Voltage source, according to required speckle size regulation electroetching voltage and time, carries out electroetching；

Step 1-3, taking-up functionally gradient material (FGM) sample also clean remained on surface electroetching liquid, cleaning ladder Degree material sample is also dried.

Functionally gradient material (FGM) based on Speckles Technique the most according to claim 3 coupling strain field In-situ measuring method, it is characterised in that: in step 1-2, the time of electroetching Range of accommodation is 3s to 15s.

Functionally gradient material (FGM) based on Speckles Technique the most according to claim 1 coupling strain field In-situ measuring method, it is characterised in that described step 2 specifically includes following steps:

Step 2-1, visual field is called in functionally gradient material (FGM) sample mechanical gradient face in and zoom into as times Number focuses on Coupling Deformation region；

Step 2-2, regulation field are to improve the gray-scale intensity gradient of electronic speckle field.

Functionally gradient material (FGM) based on Speckles Technique the most according to claim 5 coupling strain field In-situ measuring method, it is characterised in that: when amplifying imaging magnification in step 2-1 The size of single speckle diameter is not less than 3 pixels and no more than 8 pixels.

Functionally gradient material (FGM) based on Speckles Technique the most according to claim 5 coupling strain field In-situ measuring method, it is characterised in that: in step 2-2, regulation field Concrete grammar includes improving beam voltage, improves the brightness of field and right Degree of ratio.

Functionally gradient material (FGM) based on Speckles Technique the most according to claim 1 coupling strain field In-situ measuring method, it is characterised in that: described Coupling Deformation region is functionally gradient material (FGM) Elasticity on mechanical gradient transitional surface and plastic deformation coupled interface, plasticity stationary flow Become the migration region with unstable rheology coupled interface or stratified material mechanical gradient face On near interface region.

9. functionally gradient material (FGM) based on Speckles Technique coupling strain field in-situ measurement system, its feature It is, including:

Process functionally gradient material (FGM) sample to form the examination of micro-nano-scale speckle on its surface Sample pretreatment module；

It is placed in the add in-place microscope carrier in electron microscope sample storehouse to realize to functionally gradient material (FGM) sample not With loading speed simple tension, compress and control the sample of cyclic loading and unloading process and add Carry module；

The speckle field shooting functionally gradient material (FGM) specimen surface Coupling Deformation region speckle field is clapped Take the photograph module；

The computation analysis module according to shooting results speckle field calculated and analyze.

Functionally gradient material (FGM) based on Speckles Technique the most according to claim 9 coupling strain field In-situ measurement system, it is characterised in that: described sample load-on module include pedestal, The front fixture block being fixed on pedestal and the rear fixture block being slidably connected on pedestal, described before It is provided with sample suspension groove pair on fixture block and rear fixture block, also includes before regulation Fixture block and the loading screw rod of rear fixture block relative displacement and for front fixture block and rear folder Block relative displacement carries out the displacement load reading plotter indicated, and described base bottom sets Put loading bench fixing device.

11. functionally gradient material (FGM) based on Speckles Technique according to claim 9 coupling strain fields In-situ measurement system, it is characterised in that: described computation analysis module includes that image is defeated Enter output module, speckle field pretreatment module, speckle field correlation calculations module, Strain data Singular Value point gets rid of module, strain data matrix cloud atlas visualization mould Block, strain field part area data extraction module, data text output module.