JP2002122526A - Sacrifice test piece and fatigue loss prediction and stress information acquisition method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a sacrifice test piece which is simple with a higher sensitivity and moreover, allows the expectations of various advantages such as broader applicable range. SOLUTION: In the sacrifice test piece artificially torn across the width at the central part in the longitudinal direction of the body thereof, the plate surface of the body is cut off along the direction of the extensions of the artificial tearing to form a very thin part. In the process, the plate surface of the body is worked to make a circular arc-shaped groove or to make a V groove thereby forming the very thin part. The thickness of the very thin part is selected to be about 0.1 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for measuring and monitoring the stress state and cumulative fatigue damage of steel structures such as ships, bridges, offshore structures, steel towers, construction machines, cranes and the like, and more particularly to a sensor technology. .

[0002]

2. Description of the Related Art Conventionally, in order to measure or monitor the cumulative fatigue damage of a structure, a method of attaching a strain gauge to the structure and measuring a temporal change of stress is generally evaluated. Met. However, although such an evaluation method is easy and inexpensive to attach a strain gauge, the measurement requires a power supply of AC100V class and a dynamic strain measuring device and a recording device driven by the AC power source, and the measurement must be performed for a long time. There is a drawback that is not suitable for typical measurement. For this reason, a so-called sacrificial test piece has been developed as an alternative method (for example, see Japanese Patent Application Laid-Open No. 9-3042).
40).

[0003] Japanese Patent Application Laid-Open No. 9-304240 discloses a method of attaching a sacrificial test piece to a structure and observing the amount of propagation of an artificial crack provided on the test piece to obtain information on stress acting on the structure and accumulated fatigue damage. The degree is estimated. in this case,
Artificial cracks must be designed to propagate at the appropriate rate under the appropriate applied stress levels, and generally create stress concentrations at the tip of the artificial crack to encourage crack propagation. It is devised. Although the above publication discloses the concept of such a sacrificial test piece, the stress level acting on the structure greatly differs depending on the type of the structure, the use environment, and the site of interest. In order to propagate a crack, it is necessary to increase the stress acting on the artificial crack by utilizing the structural stress concentration effect.

From such a viewpoint, Japanese Patent No. 302016 is disclosed.
In the invention of No. 2, the sensitivity at which the artificial crack propagates is increased by bonding a resin-made laminated plate provided with slits in accordance with the artificial crack portion. Although a sacrificial test piece with high sensitivity has been obtained by this measure, it cannot be said that sufficient sensitivity has yet been reached. Also, regarding the manufacturing method, it is necessary to manually attach a resin plate to the main body of the sacrificial test piece, and there is a problem that the manufacturing is troublesome.

The document [1] listed at the end of this paragraph number has a concept similar to that of the sacrificial test piece. However, the gauge length is increased in order to improve the sensitivity and acts on the gauge. In addition to the disadvantage that the measurement accuracy is deteriorated due to the averaging of strain or stress, there is a disadvantage that when a compressive stress is applied, the test specimen buckles and the measurement cannot be performed correctly. Therefore, as a countermeasure for the latter drawback, means has been considered to prevent buckling by applying an initial tensile stress using thermal strain at the time of attaching the test piece, but this work is extremely time-consuming and requires There were problems such as difficulty in providing a constant tensile force. Document [1]
Mitsuru Abe et al., "System for Monitoring the Live Load of Structures", 2nd Symposium on Structural Diagnosis, August 1999.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and further improves the sensitivity of each conventional sacrificial test piece and simplifies the manufacturing process. And to increase the number of measures to be attached to a structure. Conventionally, the method of attaching to a structure is based on the premise that only the sacrificial test piece is adhered to the structure. In the present invention, in addition to adhesion, any one of three types of attaching means, bolt connection and welding, is used. We added a device that can be selected.

[0007]

According to the present invention, there is provided a sacrificial test piece having an artificial crack in a width direction provided at a central portion in a longitudinal direction of a main body. Is a sacrificial test piece in which an ultrathin portion is formed by cutting off the sample. Further, in the above, a sacrificial test piece in which an extremely thin portion is formed by applying a circular arc groove processing to the plate surface of the main body. Further, in the above, a sacrificial test piece in which the plate surface of the main body is subjected to V-groove processing to form an extremely thin portion is formed.
In the above, the thickness of the ultra-thin portion is set to approximately 0.1 mm.
Of the sacrificial test piece selected in (1). Further, the present invention provides a sacrificial test piece having a width direction artificial crack provided at a central portion in a length direction of a main body made of a metal plate, and cutting the groove in a groove shape along the direction of propagation of the artificial crack. This is a sacrificial test piece having a thin portion and a hollow portion penetrating the plate thickness on the outside in the width direction of the extremely thin portion. Further, the present invention provides a sacrificial test piece having a width direction artificial crack provided at a central portion in a length direction of a main body made of a metal plate, and cutting the groove in a groove shape along the direction of propagation of the artificial crack. A sacrificial test piece was formed in which a thin portion was formed, a hollow portion penetrating the plate thickness was provided outside the width direction of the ultra-thin portion, and openings were formed at both ends in the length direction of the main body. Things. Also, the present invention provides a method for predicting fatigue damage of a structure by attaching the sacrificial test piece according to any one of claims 1 to 6 to a structure and detecting the growth of an artificial crack in the sacrificial test piece. Is adopted. Further, the present invention adopts a method of acquiring stress information acting on a structure by detecting the growth of an artificial crack by the method of claim 7.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 1A and 1B are explanatory views showing a basic configuration of the present invention. FIG. 1A is a plan view, FIG. 1B is a cross-sectional view of FIG. 1A, FIG. 1C is a partially enlarged view of FIG. FIGS. 4A and 4B are explanatory views showing the configuration of the first and second embodiments, wherein FIG. 4A is a perspective view, FIG. 4B is an enlarged plan view, and FIGS.
(B) is a sectional view of an extremely thin portion. In FIG. 1, reference numeral 1 denotes a sacrificial test piece, and 2 denotes a main body of the sacrificial test piece 1. The main body 2 is formed in an oval shape as shown in the figure, and the material is basically the same as the structure to be predicted if the material has basically stable fatigue crack propagation characteristics and small variations. There is no. For example, iron, copper, titanium, aluminum and alloys thereof, stainless steel and the like can be considered. However, there may be additional requirements such as heat resistance, weather resistance, corrosion resistance, and no problem of electrolytic corrosion with the structure body so as to conform to the use environment conditions.

Reference numeral 3 denotes an artificial crack provided on the main body 2 (reference numeral 3).
, 4 and 4 are cavities and 5, 5 are openings. In the first embodiment, the artificial crack 3 is formed in a substantially “Φ shape” including a small hole 31 at the center and fine line-shaped cracks 32 extending on both sides thereof. Also, the cavities 4 and 4
For example, it is configured as a "sign" of a bus stop. Then, as shown in FIG. 1, an artificial crack 3 in the width direction is directly formed in the central portion of the main body 2 of the thin oval thin metal plate in the longitudinal direction by precision machining technology such as machining, electric discharge machining, and electrolytic polishing. It is formed. Further, through similar processing, a pair of cavities 4 and 4 are provided symmetrically with a gap around the small circular hole 31, and openings 5 and 5 are provided at both ends in the length direction.
Is pierced. The “marked” cavities 4 and 4 symmetrically provided in the width direction with the small circular holes 31 being axially symmetrical have a function of effectively increasing the stress concentration of the artificial crack 3 at the center. Become.

In the main body 2 having such a basic structure,
In the present invention, as shown in FIGS.
The ultra-thin portion 6 (6 is a generic name) for further reducing the thickness in the vicinity of the artificial crack 3 is applied using the above-mentioned precision processing technique so that the acting stress of the artificial crack 3 is increased. Two types of A and B are employed in the processing area of the ultra-thin portion 6. The type A is a divided region from the vicinity of the tip of the cracks 32, 32 to the "marked" legs in the cavities 4, 4 on both sides, as clearly indicated by the hatched portions in FIG. is there. In the B type, as shown in FIG. 3 (shown in FIG. 3B), a single region connecting the cavities 4 and 4 sandwiching the artificial crack 3 is an extremely thin portion 6.

The cross-sectional shape of the ultra-thin portion 6 includes
Here, two shapes of a first ultra-thin portion 61 and a second ultra-thin portion 62 are further adopted. The first ultra-thin portion 61 is shown in FIG.
As shown in the enlarged view of (a), the front and back surfaces of the plate surface of the main body 1 are formed by cutting into square grooves along the direction in which the cracks 32 and 32 progress. Also, the second ultra-thin portion 62 includes (b) in FIG.
As shown in the figure, arc grooves are formed on both surfaces.

Ultra-thin portions 61, 6 formed by such ultra-thin processing
By configuring 2, it becomes possible to prevent the direction of a crack c (not shown) that propagates back to back from the cracks 32, 32 from becoming abnormal due to lateral displacement or the like. As a result, crack 3
The growth of the crack c formed from the tip of the body 2 or 32 is guided by the ultrathin portion 6 and is extended in the direction along the width direction of the main body 2. Further, stress concentration other than the artificial crack 3 is also alleviated, so that the propagation of the crack c is reliably generated from the tip of the cracks 32 in the artificial crack 3.
On the other hand, in the first embodiment, a pair of holes 5 and 5 for bolt connection are provided at two locations on both sides in the longitudinal direction of the main body 2 so that the sacrificial test piece 1 can be used for attaching to the structure. It is configured.

5A and 5B show a modification of the first and second embodiments. FIG. 5A is a plan view showing a basic configuration of the modification, and FIG. FIG. 3C is a cross-sectional view showing another shape of the ultra-thin portion. Modified body 1
1 is formed in an oval shape similarly to FIG. 1, and an artificial crack 3 in a width direction is formed at a central portion in a length direction. Further, in the width direction and the length direction of the artificial crack 3, each pair of hollow portions 4, 4
And the openings 5, 5 are provided symmetrically. However, in this modification, the fine line-shaped cracks 32 and 3
An artificial crack 3 consisting solely of 2 is separately communicated with each of the circular cavities 4 and 4 and faces the center line in the width direction at an interval.

Then, as shown in FIG. 2B, an extremely thin portion 6 having a constant width is formed including both ends of the cracks 32 and 32 facing each other. In this case, of course, the groove processing of the ultra-thin portion 6 is carried out by the above-mentioned "square groove type" or "arc groove type" shown in FIGS. 4 (a) and 4 (b). As shown in ()), both sides are cut in a loose V-shape along the cracks 32, 32 to form a "V-groove-shaped" third ultrathin portion 63. Also in the sacrificial test piece 1 configured as described above, the third ultrathin portion 63 allows the ultrathin portion 61 and the ultrathin portion 62 to be formed.
The propagation of the crack c is guided to the ultra-thin portion 63 just as in the case of (1). For this reason, the propagation of crack c is
There is no change in that the same effect as above can be obtained, for example, it is surely generated from the tip of No. 2.

Embodiment 2 FIG. 6 shows a state in which the sacrificial test piece 1 is attached to the structure using the openings 5 and 5. 6A to 6C, reference numeral 7 denotes an adhesive, and reference numeral 8 denotes a fluororesin film. Numerals 9 and 10 are bolts and nuts, 11 is a washer, 12 is a welded portion, and 13 is a structure whose fatigue damage is to be predicted. In FIG. 6 (a), a sacrifice test piece 1 is bonded to a structure 13 by interposing a fluororesin film 8 in the vicinity of the artificial crack 3 and using openings 5, 5 provided at both ends in the longitudinal direction. Bonded with agent 7. Opening 5,
The adhesive 7 solidified in a rivet shape in 5 performs a wedge function, and both ends of the sacrificial test piece 1 are surface-bonded to predetermined positions of the structure 13 so as not to come out.

In FIG. 6B, the sacrifice test piece 1 is separated from the surface of the structure 13 by two bolts 9, 9 inserted through the openings 5, 5, via two washers 11, 11, respectively. Attached. In (c), the threaded nuts 10 and 10 are previously welded to the structure 13 at the welding portion 12 by spot welding or percussion welding. Thereafter, the sacrificial test piece 1 is directly fixed to the structure 13 with the bolts 9, 9 via the washers 11, 11. In addition, the sacrificial test piece 1 was previously bolted 9 or screwed nut 10
And the like, and the integrated threaded nuts 10, 10 may be welded to the structure 13.

According to the configurations shown in FIGS. 6B and 6C in which the openings 9 are provided and the bolts 9 are inserted therethrough, the bolts 9 can be loosened when necessary and the sacrificial test piece 1 can be replaced. It has features that can be. Thus, according to the configurations of Embodiments 1 and 2 of the present invention, three types of bonding of (a) and fixing with bolts by (b) and (c) are performed according to the situation of the attaching position of the structure 13. It is possible to affix the sacrificial test piece 1 on the structure 13 by selecting any optimal means of fixing.

For the two types A and B described above,
The procedure for estimating the rupture life Nf and calculating the cumulative fatigue damage is as follows:
This is shown in the flowchart of FIG. In step S2 of the flow chart 7, based on the measured values of the lengths c to N of the row c,
The fracture (life) Nf is estimated using the reference curve of FIG. 8 obtained in advance by an experiment. Further, although detailed description is omitted, the cumulative fatigue damage is calculated in step S7 through steps S3 to S6.

In FIG. 9, a dotted line A and a solid line B represent a conventional type in which there is no ultrathin portion 6 or the like and only an artificial crack is provided (reference [2] ...
With respect to the fatigue test results (see the end), the test results of the A type and the B type of the sacrificial test piece 1 according to the present invention are plotted with ○ and ●. In the present invention, by increasing the stress concentration at the tip of the crack 32 of the artificial crack 3, the sacrificial test piece 1 with much higher sensitivity than before can be obtained. From this figure, it can be seen that even at a very low action level (20 MPa), crack c is generated very early, leading to fracture. Reference [2] Yukio Fujimoto et al. "Development of Highly Sensitive Sacrificial Specimen for Long-Term Stress Monitoring of Structures" Proceedings of the Society of Shipbuilding Engineers of Japan, No.18
No. 7, June 2000.

[0020]

Examples By way of example, FIGS. 10A and 10B show examples in which specific numerical values are entered in the sacrificial test piece 1 of the first embodiment.
It was shown to. FIG. 10A is a drawing showing a basic configuration of the main body 2 of the sacrificial test piece 1, and FIG. 10B is a design drawing around the ultra-thin portion 6 of the main part of the present invention. The surface in the ultra-thin portion 6 is:
Precision processing was added by electrolytic polishing or the like. The groove width w of the square groove or the arc groove according to the specification of the embodiment is about 2 mm, and the preferable value of the plate thickness t of the ultra-thin portion 6 (see FIGS. 4 and 5C) is A and B types. Both are approximately 0.1mm to 0.3mm
It is. A desirable range of the radius of the radius processing is 0.1.
It is about 5 mmR to 3 mmR. Body 2 has a thickness of 0.5
mm artificial copper plate was used, and the artificial crack 3 was processed by wire cutting.

In the above-described embodiment of the present invention, an artificial row 3 extending in the width direction is formed at the center in the longitudinal direction of the oval-shaped main body 2 having a long lateral direction. The main body 2 does not necessarily have to have different vertical and horizontal lengths. In other words, the main body 2 has a width direction crossing at right angles to the length direction. In addition, in the basic configuration diagram of the main body and the design drawings of the embodiment, “marked” cavities and circular openings are shown, but these shapes as well as the first to third poles are used. The thin portion is not limited to the shape and dimensions of the embodiment as long as the thickness of the plate surface is made relatively thin to induce crack propagation. Further, although the ultra-thin portion is formed by cutting the front and rear surfaces of the plate surface, it may be formed by processing only one of the front side and the back side depending on the density of the surface of the material.

Furthermore, although the rupture life Nf and the cumulative fatigue damage were determined by the flow chart of FIG. 7, other estimation methods and calculation methods may be used. For example, the following two methods that are simpler than the flow of FIG. 7 can be considered. One of them is c ~
This is a method using an N / Nf curve (FIG. 8). It has been experimentally confirmed that this curve is almost the same whether the load is random or constant. Therefore, the degree of fatigue damage can be calculated by the procedure shown in FIG.
Furthermore, there is a method (FIG. 12) using an SN diagram in which the crack length is used as a parameter. In this method, the same as in FIG. 11 is performed using an SN diagram using the crack length of the fatigue sensor as a parameter.

When the calculation of the cumulative fatigue damage and the prediction of the fatigue life are performed by the method shown in FIG. 7, the probability density function f of the acting stress is obtained.
(S) can be determined, and stress information acting on the structure can be accurately obtained. By using this stress information, for example, a probability amount such as a maximum expected value of the stress acting within the design life range can be obtained.
Not only fatigue strength but also various strength evaluations of a structure, for example, evaluation of buckling strength, yield strength, final strength, and the like, and further can be used for structure design. In the case of simple evaluation using the methods shown in FIGS. 11 and 12, the equivalent stress range △ σeq serves as stress information, so that the life of the structure can be evaluated and the fatigue design of the structure can be used.

[0024]

As described above, according to the present invention having an extremely thin portion, as shown in FIG. 9, the propagation of the crack c is confirmed even at a minute stress level of about ± 20 MPa. And reached practically sufficient sensitivity. In addition, since the sacrificial test piece is manufactured from one metal plate, the manufacturing is simplified, and the variation in manufacturing accuracy is reduced. In addition, since the sacrificial test piece is unitized, it can be widely applied to fields other than steel structures such as the aforementioned ships, bridges and cranes. In addition, the method of joining to a structure can be selected from a plurality of types, so that the application is facilitated.

Thus, according to the present invention, it is possible to provide a sacrificial test piece which is simple and has high sensitivity and can be expected to have various advantages such as a wide application range.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a basic configuration of the present invention.

FIG. 2 is an explanatory diagram showing a configuration of the first embodiment.

FIG. 3 is an explanatory diagram showing a configuration of a second embodiment.

FIG. 4 is a sectional view of an extremely thin portion.

FIG. 5 is an explanatory diagram showing a modification of the basic configuration of the present invention.

FIG. 6 is an explanatory view showing an attached state of a sacrificial test piece.

FIG. 7 is a flowchart showing an operation of the first embodiment.

FIG. 8 is a diagram for explaining the operation of the first embodiment.

FIG. 9 is another diagram for explaining the operation of the embodiment.

FIG. 10 is a drawing showing specifications of an example.

FIG. 11 is an explanatory diagram of a simple calculation method of fatigue damage.

FIG. 12 is an explanatory diagram of another simple method of calculating fatigue damage.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sacrificial test piece 2 Main body 3 Artificial crack 4 Cavity part 5 Opening part 6 Ultrathin part 7 Adhesive 8 Fluororesin film 9 Bolt 10 Nut 11 Washer 12 Welded part 13 Structure 31 Small circular hole 32 Crack 61 First Ultra-thin section 62 Second ultra-thin section 63 Third ultra-thin section c Growing crack t Plate thickness of ultra-thin section w Groove width of ultra-thin section

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Eiji Shintaku, Inventor 317-3 Kagamiyamakita, Higashihiroshima City, Hiroshima Prefecture (72) Hisashi Ito, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo F-term (Reference) 2G050 AA01 BA12 DA03 EB01 EC06 2G061 AB05 BA03 BA15 DA19 EA02 EA03 EA10

Claims (8)

[Claims] 1. A sacrificial test piece provided with an artificial crack in a width direction at a central portion in a longitudinal direction of a main body, wherein an extremely thin portion is formed by cutting a plate surface of the main body along a direction in which the artificial crack propagates. A sacrificial test piece characterized by forming a. 2. A sacrificial test piece according to claim 1, wherein an extremely thin portion is formed by subjecting the plate surface of the main body to arc groove processing. 3. A sacrificial test piece according to claim 1, wherein the plate surface of the main body is subjected to V-groove processing to form an extremely thin portion. 4. A sacrificial test piece according to claim 2, wherein the thickness of the ultra-thin portion is selected to be approximately 0.1 mm. 5. A sacrificial test piece having an artificial crack in a width direction provided at a central portion in a longitudinal direction of a main body made of a metal plate, wherein the sacrificial test piece is cut in a groove shape along the direction of propagation of the artificial crack. A sacrificial test piece, wherein a thin portion is formed, and a hollow portion that penetrates a plate thickness is provided outside a width direction of the extremely thin portion. 6. A sacrificial test piece provided with an artificial crack in a width direction at a central portion in a length direction of a main body made of a metal plate, wherein the sacrificial test piece is cut into a groove along the direction of propagation of the artificial crack. Forming a thin portion, providing a hollow portion penetrating the plate thickness on the outside in the width direction of the ultra-thin portion, and providing openings penetrating the plate thickness at both ends in the length direction of the main body. Sacrificial test specimen 7. A method for predicting fatigue damage of a structure by adhering the sacrificial test piece according to claim 1 to a structure and detecting the growth of an artificial crack in the sacrificial test piece. Method. 8. A method of acquiring stress information acting on a structure by detecting the growth of an artificial crack by the method of claim 7.