CN220356828U - Device for measuring fatigue crack growth rate of metal sheet - Google Patents
Device for measuring fatigue crack growth rate of metal sheet Download PDFInfo
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- CN220356828U CN220356828U CN202321182428.3U CN202321182428U CN220356828U CN 220356828 U CN220356828 U CN 220356828U CN 202321182428 U CN202321182428 U CN 202321182428U CN 220356828 U CN220356828 U CN 220356828U
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- 229910052751 metal Inorganic materials 0.000 title claims abstract description 44
- 239000002184 metal Substances 0.000 title claims abstract description 44
- 238000012360 testing method Methods 0.000 claims abstract description 52
- 239000000853 adhesive Substances 0.000 claims description 11
- 230000001070 adhesive effect Effects 0.000 claims description 11
- 238000000034 method Methods 0.000 abstract description 28
- 238000005259 measurement Methods 0.000 abstract description 12
- 239000007769 metal material Substances 0.000 abstract description 9
- 238000006073 displacement reaction Methods 0.000 description 20
- 239000004033 plastic Substances 0.000 description 8
- 238000010586 diagram Methods 0.000 description 6
- 238000013461 design Methods 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 238000009417 prefabrication Methods 0.000 description 4
- 238000004364 calculation method Methods 0.000 description 2
- 238000005520 cutting process Methods 0.000 description 2
- 238000005553 drilling Methods 0.000 description 2
- 238000009434 installation Methods 0.000 description 2
- 229910000838 Al alloy Inorganic materials 0.000 description 1
- 230000001133 acceleration Effects 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000011549 displacement method Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 229920006332 epoxy adhesive Polymers 0.000 description 1
- 239000003822 epoxy resin Substances 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000009661 fatigue test Methods 0.000 description 1
- 230000000977 initiatory effect Effects 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 229920000647 polyepoxide Polymers 0.000 description 1
- 238000004313 potentiometry Methods 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000004080 punching Methods 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 239000010455 vermiculite Substances 0.000 description 1
- 238000011179 visual inspection Methods 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
- Y02E30/30—Nuclear fission reactors
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- Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
Abstract
The utility model discloses a device for measuring the fatigue crack growth rate of a metal sheet, which belongs to the field of metal material fatigue and damage tolerance test, and comprises the following components: the metal sheet fatigue crack propagation test piece is characterized in that one end of the metal sheet fatigue crack propagation test piece is a clamping end, the other end of the metal sheet fatigue crack propagation test piece is a loading end, and a pre-fabricated crack is arranged on the surface of the test piece; the first COD gauge clamping knife edge and the second COD gauge clamping knife edge are fixedly arranged on the surface of the test piece and positioned at two sides of the prefabricated crack, and a knife edge protruding part is arranged on each of the first COD gauge clamping knife edge and the second COD gauge clamping knife edge; the COD gauge comprises a first chuck and a second chuck, wherein a chuck clamping groove is formed in each of the first chuck and the second chuck, and the knife edge protruding part is clamped in the chuck clamping groove. The utility model provides a device and a method for measuring the fatigue crack growth rate of a thin-wall metal wallboard, which solve the problem of poor measurement precision caused by installing a COD gauge in bolt connection.
Description
Technical Field
The utility model belongs to the field of metal material fatigue and damage tolerance test, and particularly relates to a device for measuring the fatigue crack growth rate of a metal sheet.
Background
At present, a large amount of metal materials exist in the body structure of the advanced civil aircraft, and under the action of fatigue load, cracks in the metal structure are initiated and expanded, so that the structure is finally invalid. In fatigue experiments, it is necessary to measure the relationship between the opening displacement amount of a crack and the load in order to calculate the fracture energy, fracture parameters, etc. of a material.
The crack monitoring method for fatigue fracture test of metal material includes visual inspection method, potentiometric method and crack opening displacement method (COD method). The COD method is also called as a flexibility method and is a common method for testing the opening displacement of fatigue cracks. The crack opening displacement extensometer (COD gauge) is an accurate length change value measuring instrument, is used for testing the displacement change quantity of the crack mouth position of a sample in a test, is widely applied to a material fracture mechanical test, and the accuracy of performance indexes of the crack opening displacement extensometer directly influences the measurement and result judgment of the fracture toughness of the tested metal material.
For the thin-wall metal fatigue crack propagation test piece, the COD gauge clamping knife edge is installed by punching, as shown in figure 1. In practice, however, the measuring range L of this installation is 0 As shown in fig. 1, the measured fatigue crack opening displacement amount includes the deformation amount of the thin-wall metal material between the two connecting bolts, and cannot reflect the actual fatigue crack opening displacement.
Therefore, it is desirable to provide a solution that can react to the true fatigue crack opening displacement.
Disclosure of Invention
In order to achieve the above purpose and to improve the measurement precision of the fatigue crack growth rate of the thin-wall structure, the utility model provides a device for measuring the fatigue crack growth rate of a thin-wall metal wallboard, which solves the problem of poor measurement precision caused by installing a COD gauge in a bolt connection way.
According to the technical scheme of the utility model, a device for measuring the fatigue crack growth rate of a metal sheet is provided, and comprises the following components:
a sheet metal fatigue crack propagation test piece having two ends, and having a pre-crack on a surface thereof;
the first COD gauge clamping knife edge and the second COD gauge clamping knife edge are fixedly arranged on the surface of the test piece and are positioned on two sides of the prefabricated crack;
the COD gauge comprises a first chuck and a second chuck, wherein a chuck clamping groove is formed in each of the first chuck and the second chuck.
Further, a knife edge protruding part is arranged on each of the first COD gauge clamping knife edge and the second COD gauge clamping knife edge, and the knife edge protruding parts are clamped in the clamping head clamping grooves.
Further, the knife edge protruding part is positioned at the inner vertex angle of the first COD gauge clamping knife edge and the second COD gauge clamping knife edge facing the prefabricated crack.
Further, the inner top angles of the first COD gauge clamping knife edge and the second COD gauge clamping knife edge, which face the prefabricated cracks, are respectively provided with an inward-sinking groove.
Further, the invagination groove is a right-angle invagination groove.
Further, the right angle side of the right angle invagination groove and the included angle bulge of the upper surfaces of the first COD gauge clamping knife edge and the second COD gauge clamping knife edge form the knife edge protruding part.
Further, the right-angle invagination groove is an inclined groove, so that the angle of the included angle protrusion is 45 degrees or 60 degrees. Here, the included angle between the clamping groove of the clamping head and the side edges of the first clamping head and the second clamping head is 110 degrees, and the included angle between the clamping groove of the clamping head and the bottom edges of the first clamping head and the second clamping head is 70 degrees.
Further, the clamping grooves of the clamping heads are positioned on the outer sides of the bottoms of the first clamping heads and the second clamping heads of the COD gauge.
Further, adhesive fixing points are arranged between the first COD gauge clamping knife edge and the surface of the test piece and between the second COD gauge clamping knife edge and the surface of the test piece.
Further, the adhesive is a metal-to-metal adhesive, such as an epoxy adhesive.
Further, one end of the metal sheet fatigue crack growth test piece is a clamping end, and the other end is a loading end.
The utility model has the beneficial effects that:
(1) The left and right chucks of the COD gauge are respectively clamped at the clamping knife edge; meanwhile, the COD gauge clamping knife edge is provided with a groove which is matched with the COD gauge chuck, the groove is a right-angle groove, so that the COD gauge can be clamped more firmly, and meanwhile, the free rotation between the COD gauge and the knife edge contact point is ensured, so that reliable test data are obtained.
(2) The COD gauge clamping knife edge is bonded to the surface of the metal sheet fatigue crack propagation test piece in an adhesive connection mode, is different from the traditional COD gauge knife edge bolt connection scheme, can effectively measure the change of the displacement between the two clamping knife edges in the test process, effectively reduces the influence of the deformation of the sheet metal structure body on the test result, and obtains more accurate crack opening displacement. Meanwhile, the utility model can avoid the change of boundary conditions caused by drilling holes on the surface of the metal sheet, and has influence on the fatigue crack expansion performance of the metal sheet structure.
Drawings
FIG. 1 is a schematic diagram of a COD gauge installation mode in the prior art;
FIG. 2 is a schematic diagram of an apparatus for measuring crack growth rate of a sheet according to an embodiment of the present utility model;
FIG. 3 is a schematic illustration of an extension test piece according to an embodiment of the present utility model;
FIG. 4 is a schematic diagram of a COD gauge according to an embodiment of the utility model;
FIG. 5 is a schematic diagram of a left blade of a COD gauge clamp according to an embodiment of the utility model;
FIG. 6 is a schematic diagram of a COD gauge clamping knife edge groove according to an embodiment of the utility model;
FIG. 7 is a schematic view of an assembly of a fatigue test piece and a clamp according to an embodiment of the present utility model;
FIG. 8 is a schematic illustration of determining effective crack length by a cut line method according to an embodiment of the present utility model;
FIG. 9 is a schematic diagram of determining physical crack length by compliance in accordance with an embodiment of the present utility model.
Detailed Description
Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, the same numbers in different drawings refer to the same or similar elements, unless otherwise indicated. The implementations described in the following exemplary examples are not representative of all implementations consistent with the present disclosure. Rather, they are merely examples of apparatus and methods consistent with some aspects of the present disclosure as detailed in the accompanying claims.
The terms first, second and the like in the description and in the claims, are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments of the disclosure described herein may be capable of being practiced otherwise than as specifically illustrated and described.
Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
A plurality, including two or more.
And/or, it should be understood that for the term "and/or" used in this disclosure, it is merely one association relationship describing associated objects, meaning that there may be three relationships. For example, a and/or B may represent: a exists alone, A and B exist together, and B exists alone.
Aiming at the problem of fatigue crack damage expansion of the thin-wall metal plate, the utility model provides an improved device for measuring the crack expansion rate of the thin plate, thereby effectively improving the test accuracy of the fatigue crack expansion rate. In the technical scheme of the utility model, an improved device for measuring the crack growth rate of the sheet based on the compliance method mainly comprises the following parts: 1. clamping ends of the metal sheet fatigue crack propagation test pieces; 2. a loading end of the metal sheet fatigue crack propagation test piece; 3. a sheet metal fatigue crack propagation test piece; COD gauge; 5, a left chuck of the COD gauge; 6, a right chuck of the COD gauge; 7, clamping a left knife edge by a COD gauge; 8, clamping a right knife edge by a COD gauge; 9. and (5) prefabricating cracks. The improved means for measuring the crack growth rate of the sheet is shown in FIG. 2. The sheet metal fatigue crack growth test piece 3 is shown in fig. 3. The COD gauge 4 is shown in FIG. 4. The left blade 5 of the COD gauge is shown in figure 5, a groove 10 is arranged on the left blade, and the right blade 6 of the COD gauge is similar to the left blade. Different from the design scheme of the bevel cutting of the clamping knife edge of the traditional COD gauge, as shown in figure 1, the clamping knife edge of the COD gauge is provided with the groove, the right-angle edge of the groove and the included angle bulge on the upper surface of the knife edge form the knife edge protruding part, and the knife edge protruding part is clamped in the clamping groove of the clamping head arranged on the clamping head, so that a better clamping effect of the COD gauge can be obtained.
The left and right chucks 5 and 6 of the COD gauge are respectively clamped at the clamping knife edges 7 and 8; meanwhile, a groove 10 is designed on the COD gauge clamping knife edge and is matched with the COD gauge clamping head, the groove is a right-angle groove, the related angle is shown in figure 6, the right-angle edge of the groove and the included angle bulge on the upper surface of the knife edge form a knife edge protruding part, and the knife edge protruding part is clamped in a clamping head clamping groove arranged on the clamping head, so that the purpose of better clamping the COD is achieved.
Meanwhile, unlike the traditional COD gauge blade bolt connection scheme, the COD gauge clamping blade is adhered to the surface of the thin-wall metal fatigue crack propagation test piece in an adhesive connection mode, so that the displacement change between the two clamping blades in the test process can be effectively measured, and the measuring range L is shown in figure 6. Measuring range L of traditional COD gauge knife edge bolt connection scheme 0 As shown in fig. 1.
When the displacement of crack surface opening of the crack tip is measured by adopting two different modes of the scheme and the traditional measurement scheme, the measurement range L of the scheme is closer to the actual fatigue crack opening, and the measurement range L of the traditional COD gauge clamping knife edge bolting scheme 0 The method not only comprises the actual fatigue crack opening amount, but also comprises the deformation amount of the sheet metal material body between the two connecting bolts. Therefore, by the knife edge design scheme and the adhesive connection scheme, the measurement precision of the fatigue crack propagation rate of the thin-wall structure can be effectively improved, and the problem of poor measurement precision of the fatigue crack opening displacement caused by installing the COD gauge by bolt connection is solved. Meanwhile, the utility model can avoid the change of boundary conditions caused by drilling holes on the surface of the metal sheet, and has influence on the fatigue crack propagation performance of the metal thin-wall fatigue crack propagation test piece.
The process of measuring the crack growth rate of a sheet using the improved device according to the present utility model is briefly described as follows:
when the COD method is used for measuring the fracture toughness of the metal material, the clamping mode of the metal thin-wall fatigue crack extension test piece is shown in figure 7, and an electrohydraulic servo fatigue tester can be used for the test. Meanwhile, prefabricating cracks on the metal thin-wall fatigue crack propagation test piece, wherein the length of the prefabricating cracks is larger than or equal to 1.3mm, and the crack prefabricating can be finished by adopting a constant-load (or constant K) method; if the crack prefabrication process is to be completed through multi-stage loading, the final load of crack prefabrication cannot be reduced by more than 30% of the initial load.
For aluminum alloy materials, the recommended value of the crack prefabrication stress intensity factor is delta K=10-12 MPa.m 0.5 ，K max <16.5MPa·m 0.5 。
The crack initiation stress strength factor recommended by ASTM E561 is: k (K) max /E＝0.00013m 0.5 The final stress intensity factor value satisfies K max /E＝0.0001m 0.5 Wherein E represents the elastic modulus.
Then, installing COD gauge clamping edges at two sides of the prefabricated crack, wherein in the concrete structure, left and right chucks (5) and (6) of the COD gauge are respectively clamped at the clamping edges (7) and (8); meanwhile, a groove (10) is designed on the COD gauge clamping knife edge and is matched with the COD gauge chuck. The COD gauge clamping knife edge structures (7) and (8) are bonded to two sides of the surface pre-crack (9) of the thin-wall metal fatigue crack propagation test piece (3) in an adhesive connection mode, and the bonding surface is a bottom surface far away from the groove (10) side, so that the COD gauge (4) is clamped.
The test process adopts displacement loading, and the displacement loading speed is controlled to ensure that the acceleration of the stress intensity factor K value is between 0.55 and 2.75 MPa.m 0.5 Between them. And after the test is started, applying a certain displacement to the test piece according to the requirement of the displacement loading rate, and recording the length of the crack and the load at the moment after the crack growth is stabilized. The crack length measurement may be performed using direct measurement and compliance.
The direct measurement method can observe the crack length of the surface of the test piece, and the effective crack length needs to consider the influence of a plastic region, as shown in the formula (1):
a e ＝a p +r y …………………………………………(1)
wherein:
a e -effective crack length;
a p -observing crack length;
r y ——crack tip plastic zone size.
The size of the plastic area of the crack tip can be calculated by the formulas (2) to (3)
Wherein:
p-applied load;
-corresponding to the observed crack length a p Is a stress intensity factor of (2);
σ YS -yield strength of the material.
The KR value corresponding to each effective crack length (shown in formula (1)) was calculated using formula (3).
The compliance method adopts a compliance equation to determine the length of cracks through Deltav/DeltaP, and the effective modulus E eff Determined by an initial load-displacement curve (corresponding to crack length a at the completion of prefabrication 0 ) The calculation method is shown in the formula (4).
Wherein:
E eff -effective modulus;
b-sample thickness;
w-sample width;
Deltav/DeltaP—test piece compliance;
y-half of the distance between crack measurement points;
a-the load-displacement curve with increasing load corresponds to the effective crack length a e The method comprises the steps of carrying out a first treatment on the surface of the Load-bit with unloadingWhen the curve is shifted, the curve corresponds to the observed crack length a p ；
v-poisson ratio.
When the effective crack length is calculated by the line cutting method, at least 20 different points (v i ，P i ) As shown in fig. 8.
Using equation (5), the slope of the cut line is calculated:
calculating effective crack length a by using the slope of the secant given by formula (5), the effective modulus calculated by formula (4) and the test piece size e . The effective crack length and the load corresponding to each point obtained by calculation in the process are adopted to calculate K under different effective crack lengths according to the formula (3) R 。
Will K R Substituting the value of (2) to calculate the plastic region size r' y From this, the physical crack length is found:
at the point of adding a' p Substituting into (2) to obtain the plastic region size r y The size of the real plastic region is r y ～r′ y By taking different values in the interval, the real plastic region size r is obtained y Further, the physical crack length a is obtained according to the formula (1) p 。
Calculating effective crack length using unload compliance, determining slope (Deltav/DeltaP) of unload curve at each test point unload As shown in fig. 9.
By (Deltav/DeltaP) unload ，E eff The test piece size, the physical crack length a is calculated according to the formula (4) p And calculating the plastic region size, effective crack length and K according to the formulas (1) to (3) R 。
Continuing to load at the same displacement rate, repeating the above process until testThe piece breaks. After the test is finished, observing the fracture of the test piece, and measuring the initial crack length a 0 ，a 0 The average value of the crack lengths of the test piece at 1/4B, 1/2B and 3/4B along the thickness direction is taken. To ensure test result K R The reliability of the curve is usually required to be no less than 5 data points, preferably 10-15 data points are needed to increase the reliability, and more data points are needed for materials with better toughness.
Aiming at a metal thin-wall fatigue crack propagation test piece, the utility model mainly provides 2 innovations: the COD clamping knife edge structure design and the bonding connection mode of the clamping knife edge structure are designed, wherein the novel structure design has higher preparation maturity of the COD clamping knife edge and aims at a plurality of adhesive products such as metal-metal adhesives (epoxy resin adhesives) on the market of metal materials. Therefore, the technical scheme of the utility model has higher technical implementation feasibility.
From the above description of the embodiments, it will be apparent to those skilled in the art that the above implementation may be implemented by means of software plus necessary general purpose hardware platform, or of course by means of hardware, but in many cases the former is a preferred embodiment. Based on such understanding, the technical solution of the present utility model may be embodied essentially or in a part contributing to the prior art in the form of a software product stored in a storage medium (e.g. ROM/RAM, magnetic disk, optical disk) comprising instructions for causing a terminal (which may be a mobile phone, a computer, a server, an air conditioner, or a network device, etc.) to perform the method according to the embodiments of the present utility model.
The embodiments of the present utility model have been described above with reference to the accompanying drawings, but the present utility model is not limited to the above-described embodiments, which are merely illustrative and not restrictive, and many forms may be made by those having ordinary skill in the art without departing from the spirit of the present utility model and the scope of the claims, which are to be protected by the present utility model.
Claims (10)
1. An apparatus for measuring the fatigue crack growth rate of a sheet metal, the apparatus comprising:
a sheet metal fatigue crack propagation test piece having two ends, and having a pre-crack on a surface thereof;
the first COD gauge clamping knife edge and the second COD gauge clamping knife edge are fixedly arranged on the surface of the test piece and are positioned on two sides of the prefabricated crack;
the COD gauge comprises a first chuck and a second chuck, wherein a chuck clamping groove is formed in each of the first chuck and the second chuck.
2. The device for measuring the fatigue crack growth rate of the metal sheet according to claim 1, wherein a knife edge protruding part is arranged on each of the first COD gauge clamping knife edge and the second COD gauge clamping knife edge, and the knife edge protruding parts are clamped in the clamping grooves of the clamping heads.
3. The apparatus for measuring the fatigue crack growth rate of a metal sheet according to claim 2, wherein the knife edge protrusion is positioned at an inner top angle of the first and second COD gauge holding knife edges toward the pre-crack.
4. The device for measuring the fatigue crack growth rate of the metal sheet according to claim 2, wherein the first COD gauge clamping knife edge and the second COD gauge clamping knife edge are provided with an inward recess at the inner top angle of the first COD gauge clamping knife edge towards the prefabricated crack.
5. The apparatus for measuring the fatigue crack growth rate of a metal sheet according to claim 4, wherein the invagination groove is a right angle invagination groove.
6. The apparatus for measuring a fatigue crack growth rate of a metal sheet according to claim 5, wherein the right-angle side of the right-angle invagination groove and the angle protrusion of the upper surfaces of the first COD gauge clamping knife edge and the second COD gauge clamping knife edge form the knife edge protrusion.
7. The apparatus for measuring a fatigue crack growth rate of a metal sheet according to claim 6, wherein the right-angled invagination groove is an inclined groove such that the angle of the included protrusion is 45 degrees or 60 degrees.
8. The apparatus for measuring the fatigue crack growth rate of a metal sheet according to claim 1, wherein the chuck clamping groove is positioned outside the bottoms of the first chuck and the second chuck of the COD gauge.
9. The apparatus for measuring the fatigue crack growth rate of a metal sheet according to claim 1, wherein adhesive fixing points are provided between the first and second COD gauge clamping edges and the surface of the test piece.
10. The apparatus for measuring the fatigue crack growth rate of a metal sheet according to claim 1, wherein one end of the fatigue crack growth test piece of the metal sheet is a clamping end and the other end is a loading end.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202321182428.3U CN220356828U (en) | 2023-05-16 | 2023-05-16 | Device for measuring fatigue crack growth rate of metal sheet |
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| CN202321182428.3U CN220356828U (en) | 2023-05-16 | 2023-05-16 | Device for measuring fatigue crack growth rate of metal sheet |
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