A testing method for the fracture toughness of soft materials based on a trouser-leg tearing experiment

Abstract

The present invention discloses a test method for the fracture toughness of soft materials based on the trouser-leg tearing experiment, and the present invention belongs to the technical field of material property testing. Aiming at the problem that it is difficult to comprehensively characterize the fracture toughness of soft materials at the present stage, the test method of the present invention introduces the concept of free size on the basis of the traditional trouser-leg tearing experiment, controls the characteristic size of the crack tip field damage zone by adjusting the free size of the specimen, and further controls the contribution degree of the non-intrinsic dissipation of the soft material to the fracture toughness. Finally, the variation relationship between the apparent fracture toughness of the soft material and the free size of the specimen is obtained, which has a clear physical meaning. This method not only has a simple principle and is easy to operate, but also can comprehensively and multi-angularly characterize the fracture performance of soft materials, making up for the deficiencies of the traditional test methods for the fracture toughness of soft materials, and has potential application value.

Description

Technical Field

[0001] The present invention relates to the technical field of material property testing, and particularly relates to a method for testing the fracture toughness of soft materials based on a trouser-leg tearing experiment. Background Art

[0002] The wide application of soft materials poses higher requirements for their mechanical properties. To ensure that soft materials do not fail during application, it is necessary to study their ability to resist crack propagation. In soft materials, fracture toughness is usually used to describe the ability of a material to resist crack propagation. Fracture toughness is defined as the energy dissipated per unit area of crack propagation, and the higher its value, the stronger the material's ability to resist crack propagation. Widely used methods for testing the fracture toughness of soft materials include pure shear experiments, peeling experiments, single-edge crack experiments, trouser-leg tearing experiments, etc. However, these experimental tests often only obtain a single fracture toughness value and are difficult to comprehensively characterize the fracture behavior of soft materials. In particular, for soft materials that exhibit significant damage during deformation, such as double-network hydrogels, their fracture toughness values are often related to the specimen size, which poses difficulties for the characterization of fracture toughness. Summary of the Invention

[0003] To overcome the deficiencies of existing testing techniques, the present invention provides a method for testing the fracture toughness of soft materials based on a trouser-leg tearing experiment. On the basis of the traditional trouser-leg tearing experiment, this testing method introduces the concept of free size, controls the characteristic size of the crack tip field damage zone by adjusting the free size of the specimen, and then controls the contribution degree of non-intrinsic dissipation of the soft material to the fracture toughness. Finally, the variation relationship between the apparent fracture toughness of the soft material and the free size of the specimen is obtained. This method can comprehensively characterize the fracture characteristics of soft materials, and obtain the intrinsic fracture toughness of the soft material, the contribution of non-intrinsic dissipation to the fracture toughness, and the characteristic size of the fracture damage zone.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A method for testing the fracture toughness of soft materials based on a trouser-leg tearing experiment, and the specific steps of this method are as follows:

[0006] Step 1: Fabricate a soft material specimen with a prefabricated crack. The length, width, and thickness of the soft material specimen are l, w, and t respectively;

[0007] Step 2: Paste two backings with high tensile stiffness (3000N - 5000N) and low bending stiffness (1.5×10 -5 N·m 2 -2.5×10 -5 N·m 2 ) on the surface of the soft material specimen. The distance between the two backings is the size of the free size, denoted by the symbol b;

[0008] Step 3: Change the size of the free dimension b and conduct a tearing experiment on a tensile machine to obtain the force-displacement curves of the soft material specimens under different free dimensions.

[0009] Step 4: Process the force-displacement curves to obtain the values of the apparent fracture toughness of the soft material specimens under different free dimensions.

[0010] Step 5: Fit the experimental results of the apparent fracture toughness varying with the free dimension to obtain the relationship curve between the two.

[0011] Step 6: Analyze the relationship curve between the apparent fracture toughness and the free dimension to obtain the intrinsic fracture toughness of this soft material, the contribution of non-intrinsic dissipation to the fracture toughness, and the characteristic size of the fracture damage zone.

[0012] The length of the prefabricated crack in Step 1 has no influence on the load value during the stable crack propagation.

[0013] In Step 2, the range of the free dimension b should be limited to 0 ≤ b ≤ 0.5w; when b > 0.5w, the specimen is prone to torsion during the tearing process, resulting in unstable crack propagation and unable to obtain the corresponding apparent fracture toughness.

[0014] In Step 4, the apparent fracture toughness is obtained from the force-displacement curve; the apparent fracture toughness is defined as the sum of the intrinsic fracture toughness Γ0 and the contribution Γ of non-intrinsic dissipation to the fracture toughness; the calculation formula for the apparent fracture toughness is: d The sum; the calculation formula for the apparent fracture toughness is:

[0015]

[0016] In the formula, Γ is the apparent fracture toughness, F c is the average value of the force during the stable crack propagation, defined as the statistical average of the load at 30% to 80% of the total displacement. When the free dimension b is 0, F c needs to be corrected as follows:

[0017] F c = F total - F backing (2)

[0018] In the formula, F total is the directly measured average value of the force during the stable crack propagation, and F backing is the average value of the force during the stable crack propagation obtained by conducting a tearing experiment on the backing alone.

[0019] In Step 5, the following formula is used to fit the experimental results of the apparent fracture toughness and the free dimension:

[0020]

[0021] In the formula, a1, a2, and a3 are all fitting parameters and have corresponding physical meanings; a3 is the plateau value Γ of the apparent fracture toughness. p , a1 is the contribution Γ of non-intrinsic dissipation to the fracture toughness when the apparent fracture toughness reaches Γ p . d , a2 is the convergence rate when the apparent fracture toughness reaches Γ p .

[0022] In step 6, according to the fitting results of step 5, the intrinsic fracture toughness Γ0, the contribution Γ of non-intrinsic dissipation to the fracture toughness d , and the characteristic size l of the fracture damage zone d are obtained; where Γ0 is the value of a3 - a1, Γ d is the value of a1, and the characteristic size l d is the value of the free size b corresponding to when the apparent fracture toughness is 0.99Γ p , and its calculation method is as follows:

[0023]

[0024]

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] The present invention improves on the basis of traditional trouser leg tearing. By changing the distance between the two backings, i.e., the free size, the size of the dissipation zone at the crack tip of the soft material can be directly regulated, and the values of the apparent fracture toughness at different free sizes can be obtained. By fitting the experimental results of the apparent fracture toughness and the free size, the apparent fracture toughness can be decomposed into the intrinsic fracture toughness Γ0 and the contribution Γ of non-intrinsic dissipation to the fracture toughness d , and at the same time, the characteristic size l of the fracture damage zone d is obtained. The present invention solves the problem that the existing soft material fracture toughness test methods cannot directly measure the values of the intrinsic fracture toughness Γ0, the contribution Γ of non-intrinsic dissipation to the fracture toughness d , and the characteristic size l of the damage zone d . The principle of this test method is simple, easy to operate, and can comprehensively characterize the fracture properties of soft materials, making up for the deficiencies of traditional soft material fracture toughness test methods and being suitable for popularization and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is the flowchart of the method of the present invention.

[0028] Figure 2 is the schematic diagram of the soft material specimen with a prefabricated crack in the present invention.

[0029] Figure 3 This is a schematic diagram of the process of pasting the backing onto the surface of the soft material in the present invention.

[0030] Figure 4 This is a schematic diagram of the trouser-leg tearing specimen with a backing and prefabricated cracks used in the present invention.

[0031] Figure 5 This is a schematic diagram of the trouser-leg tearing experiment process in the present invention.

[0032] Figure 6 This is a force-displacement curve result diagram of the trouser-leg tearing experiment process obtained in Example 1 of the present invention.

[0033] Figure 7 This is an experimental result and fitting curve result diagram of the apparent fracture toughness varying with the free size obtained in Example 1 of the present invention.

[0034] In the figure: 1 PAMPS / PAAm double-network hydrogel, 2 prefabricated crack, 3 backing, 4 glue, 5 backing pasting area. Detailed implementation manners

[0035] The present invention will be further described in detail below with reference to the accompanying drawings, taking the PAMPS / PAAm double-network hydrogel as an example, but not limited to the following embodiments.

[0036] A test method for the fracture toughness of soft materials based on the trouser-leg tearing experiment specifically includes the following steps:

[0037] (1) As shown in Figure 2 , a soft material specimen with a prefabricated crack 2 is made. The length, width, and thickness of the soft material specimen are l, w, and t respectively. The length of the prefabricated crack 2 has no influence on the load value during the stable crack propagation. Here, two different sizes of specimens are used, namely: 50 mm in length, 30 mm in width, and 1.5 mm in thickness (for the specimen with b = 0) and 70 mm in length, 30 mm in width, and 1.5 mm in thickness (for the specimen with b > 0).

[0038] (2) A backing 3 with a relatively high tensile stiffness and a relatively low bending stiffness is pasted onto the surface of the double-network hydrogel 1 with glue 4. The pasting areas 5 are located on both sides of the soft material specimen respectively. The pasting process is as shown in Figure 3 . The distance between the backings, that is, the size of the free size, is denoted by the symbol b. The schematic diagram of the tearing specimen after pasting the backing is as shown in Figure 4 .

[0039] Preferably, the value of the free dimension b is: 0 mm, 0.6 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.4 mm, 1.6 mm, 1.8 mm, 2.0 mm, 3.0 mm, 4.0 mm, 5.0 mm, 6.0 mm, 8.0 mm, 10.0 mm.

[0040] (3) Change the size of the free dimension b and conduct a tearing experiment on a tensile machine. The schematic diagram of the tearing experiment process is as shown in Figure 5 . Among them, the two trouser legs are respectively clamped in the upper and lower chucks of a universal material testing machine and stretched at a constant speed of 200 mm / min until the soft material specimen is completely damaged, and the force-displacement curve of the soft material specimen under the corresponding free dimension is obtained. At least 3 repeated experiments are carried out under each free dimension. Figure 6 The figure shows the force-displacement curve results of the tearing process of the double-network hydrogel when b is 6 mm.

[0041] (4) Process the force-displacement curve to obtain the apparent fracture toughness values of the soft material specimens under different free dimensions. The apparent fracture toughness is defined as the sum of the intrinsic fracture toughness Γ0 and the non-intrinsic dissipation contribution to the fracture toughness Γ d . The calculation formula of the apparent fracture toughness is:

[0042]

[0043] In the formula, Γ is the apparent fracture toughness, F c is the average value of the force during the stable crack propagation, which is taken as the statistical average value of the load at 30% to 80% of the total displacement. In particular, when the free dimension b is 0, the following correction needs to be made to F c :

[0044] F c = F total - F backing (2)

[0045] In the formula, F total is the directly measured average value of the force during the stable crack propagation, and F backing is the average value of the force during the stable crack propagation obtained by conducting a tearing experiment on the backing alone.

[0046] (5) Fit the experimental results of the apparent fracture toughness varying with the free dimension to obtain the relationship curve between the two. The following formula is used to fit the experimental results of the apparent fracture toughness and the free dimension:

[0047]

[0048] By fitting the experimental results, a3 = 3622 J / m 2 is the plateau value Γ of the apparent fracture toughnessp , a1 = 1607 J / m 2 is the contribution Γ of non-intrinsic dissipation to fracture toughness when the apparent fracture toughness reaches Γ p ; a2 = 0.45 is the convergence rate when the apparent fracture toughness reaches Γ d . The experimental results and fitting curves of the apparent fracture toughness of the double-network hydrogel are as p shown. Figure 7 shown.

[0049] (6) Analyze the relationship curve between the apparent fracture toughness and the free size to obtain the intrinsic fracture toughness Γ0, the contribution Γ of non-intrinsic dissipation to fracture toughness d , and the characteristic size l of the fracture damage zone d . Among them, Γ0 is equal to the value of a3 - a1, which is 2015 J / m 2 , and Γ d is equal to the value of a1, which is 1607 J / m 2 . The characteristic size l d is the value of the free size b corresponding to when the apparent fracture toughness is 0.99Γ p , and its calculation method is as follows:

[0050]

[0051]

[0052] For the double-network hydrogel in this example, its characteristic size l is calculated to be 8.5 mm through calculation. d is 8.5 mm.

Claims

1. A test method for the fracture toughness of soft materials based on a trouser-leg tearing experiment, characterized in that: The specific steps of this method are as follows: Step 1: Fabricate a soft material specimen with a prefabricated crack. The length, width, and thickness of the soft material specimen are l, w, and t respectively; Step 2: Paste two backings with high tensile stiffness of 3000N - 5000N and low bending stiffness of 1.5×10 -5 N·m 2 -2.5×10 -5 N·m 2 onto the surface of the soft material specimen. The distance between the two backings is the size of the free dimension, denoted by the symbol b; Step 3: Change the size of the free dimension b and conduct a tearing experiment on a tensile machine to obtain the force-displacement curve of the soft material specimen under different free dimensions; Step 4: Process the force-displacement curve to obtain the values of the apparent fracture toughness of the soft material specimen under different free dimensions; Step 5: Fit the experimental results of the apparent fracture toughness varying with the free dimension to obtain the relationship curve between the two; Step 6: Analyze the relationship curve between the apparent fracture toughness and the free dimension to obtain the intrinsic fracture toughness of this soft material, the contribution of non-intrinsic dissipation to the fracture toughness, and the characteristic size of the fracture damage zone; In Step 4, the apparent fracture toughness is obtained from the force-displacement curve; the apparent fracture toughness is defined as the sum of the intrinsic fracture toughness Γ0 and the non-intrinsic dissipation contribution Γ to the fracture toughness; the calculation formula for the apparent fracture toughness is as follows: d The sum; the calculation formula for the apparent fracture toughness is: where Γ is the apparent fracture toughness, and F c is the average value of the force during the stable crack propagation, defined as the statistical average of the load at 30% to 80% of the total displacement. When the free dimension b is 0, F c needs to be corrected as follows: F c = F total - F backing (2) where F total is the average value of the force during the stable crack propagation directly measured, and F backing is the average value of the force during the stable crack propagation obtained from the tearing test on the backing alone; In Step 5, the following formula is used to fit the experimental results of the apparent fracture toughness and the free dimension: In the formula, a1, a2, and a3 are all fitting parameters and have corresponding physical meanings; a3 is the plateau value Γ of the apparent fracture toughness p , a1 is the contribution Γ of non-intrinsic dissipation to the fracture toughness when the apparent fracture toughness reaches Γ p ; d , a2 is the convergence rate at which the apparent fracture toughness reaches Γ p ; In step 6, based on the fitting results of step 5, the intrinsic fracture toughness Γ0, the contribution Γ of non-intrinsic dissipation to the fracture toughness, and the characteristic size l of the fracture damage zone are analyzed and obtained. d , and the value of the characteristic size l d ; where Γ0 is the value of a3 - a1, Γ d is the value of a1, and the characteristic size l d is the value of the free size b corresponding to when the apparent fracture toughness is 0.99Γ p , and its calculation method is as follows:

2. The test method for the fracture toughness of soft materials based on a trouser-leg tearing experiment according to claim 1, characterized in that: In Step 1, the length of the prefabricated crack has no influence on the load value during the stable crack propagation; 3. The test method for the fracture toughness of soft materials based on a trouser-leg tearing experiment according to claim 1, characterized in that: In Step 2, the range of the free dimension b should be limited to 0 ≤ b ≤ 0.5w; when b > 0.5w, the specimen is prone to torsion during the tearing process, resulting in unstable crack propagation and unable to obtain the corresponding apparent fracture toughness.

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