Method for testing fracture toughness of dissimilar materials, double cantilever beam specimen and manufacturing method

Abstract

The application relates to the technical field of material performance testing, and particularly relates to a heterogeneous material fracture toughness testing method, a double cantilever beam sample and a manufacturing method. The heterogeneous material fracture toughness testing method comprises the following steps: a double cantilever beam sample is provided, the double cantilever beam sample comprises a base layer, a first substrate and a separation layer, the first substrate is provided with the base layer on both sides in a first direction, the separation layer is arranged between the first substrate and any base layer, a separation area and a to-be-tested area are formed between the first substrate and the base layer adjacent to the separation layer in a second direction, and the separation area has a prefabricated crack; a sample testing step is performed, the double cantilever beam sample is installed on a testing device, the double cantilever beam sample is loaded by the testing device to make the to-be-tested area delaminate, and target data is acquired; and a result calculation step is performed, and a type I interlaminar fracture toughness value is acquired according to the target data. The heterogeneous material fracture toughness testing method provided by the application can improve testing accuracy.

Description

Technical Field

[0001] The present application relates to the technical field of material performance testing, and in particular to a fracture toughness testing method for heterogeneous materials, a double cantilever beam specimen, and a manufacturing method thereof. Background Art

[0002] Delamination between material layers can be divided into three basic types based on the crack plane and load direction: opening type (Type I), sliding type (Type II), and tearing type (Type III). Double cantilever beam specimens, as a mechanical testing structure, are widely used to test the fracture toughness of interlaminar materials.

[0003] Since the fracture behavior of the dual cantilever beam specimen depends on the material properties of the substrate, in related technologies, substrates made of two different materials are usually used to make dual cantilever beam specimens based on the principle of equal bending stiffness to test the mode I interlaminar fracture toughness of dissimilar materials.

[0004] However, the double cantilever beam specimen still has mode II deformation during the test, which affects the test results and reduces the accuracy of the mode I interlaminar fracture toughness test of heterogeneous materials. Summary of the Invention

[0005] The present application provides a fracture toughness testing method for heterogeneous materials, a dual cantilever beam specimen and a manufacturing method thereof, to solve the problem of low accuracy in the current type I interlaminar fracture toughness testing of heterogeneous materials.

[0006] In order to achieve the above objectives, the technical solutions of this application are as follows:

[0007] In a first aspect, the present application provides a method for testing the fracture toughness of heterogeneous materials, comprising the following steps: providing a double cantilever beam specimen, the double cantilever beam specimen comprising a base layer, a first substrate and an isolation layer, the first substrate being provided with base layers on both sides in a first direction, an isolation layer being provided between the first substrate and any base layer, the base layer and the first substrate being fixedly connected, an isolation region and a region to be tested being formed between the first substrate and the base layer adjacent to the isolation layer in a second direction, the isolation region having a prefabricated crack; a specimen testing step, installing the double cantilever beam specimen on a testing device, gradually loading the double cantilever beam specimen through the testing device to cause stratification in the region to be tested, and obtaining target data; a result calculation step, obtaining the mode I interlaminar fracture toughness value of the double cantilever beam specimen based on the target data.

[0008] In a possible implementation, in the fracture toughness testing method for heterogeneous materials provided in the present application, in the step of providing a double cantilever beam specimen, in the second direction, the elastic modulus of the base layer is greater than the elastic modulus of the first substrate.

[0009] In one possible implementation, the fracture toughness testing method for heterogeneous materials provided in the present application, the target data includes multiple load values ​​applied by the testing device to the double cantilever beam specimen and displacement values ​​corresponding to each load value, wherein the displacement value is the opening displacement value of the double cantilever beam specimen in the loading direction.

[0010] In one possible implementation, the fracture toughness testing method for heterogeneous materials provided in the present application further includes a dual cantilever beam sample insulation step before the sample testing step, including: placing the dual cantilever beam sample in a constant temperature environment, and determining the insulation temperature of the dual cantilever beam sample based on the actual use environment temperature of the base layer and the first substrate; maintaining the dual cantilever beam sample at a constant temperature for a predetermined period of time based on the insulation temperature; and separately monitoring the temperature of the base layer and the first substrate of the dual cantilever beam sample to ensure that the temperature difference between the base layer and the first substrate is within a preset temperature difference range.

[0011] In a possible implementation, the fracture toughness testing method for heterogeneous materials provided in the present application further includes, before the sample testing step: measuring the size of the double cantilever beam sample and marking the double cantilever beam sample with scales.

[0012] In one possible implementation, the present application provides a method for testing the fracture toughness of heterogeneous materials, wherein the base layer includes a second substrate, the two second substrates are respectively located on opposite sides of the first substrate in a first direction, and the isolation layer is arranged between the first substrate and any second substrate.

[0013] In one possible implementation, in the fracture toughness testing method for heterogeneous materials provided in the present application, the elastic modulus of the first substrate is E1, the elastic modulus of the second substrate is E2, wherein E2 ≥ 1.4×E1; and / or, along the first direction, the thickness of the first substrate is h1, the thickness of the second substrate is h2, wherein h2 ≥ 2.3×h1.

[0014] In one possible implementation, the present application provides a method for testing the fracture toughness of heterogeneous materials, wherein the base layer includes a second substrate and a reinforcing plate. Along a first direction, the second substrate is arranged close to the first substrate relative to the reinforcing plate, and the isolation layer is arranged between the first substrate and any second substrate.

[0015] In one possible implementation, in the fracture toughness testing method for heterogeneous materials provided in the present application, the elastic modulus of the first substrate is E1, the elastic modulus of the reinforcement plate is E3, wherein E3 ≥ 1.4×E1; and / or, along the first direction, the thickness of the first substrate is h1, the thickness of the reinforcement plate is h3, wherein h3 ≥ 2.3×h1.

[0016] In a possible implementation, in the fracture toughness testing method for heterogeneous materials provided in the present application, along the first direction, the thickness of the first substrate is h1, and the thickness of the isolation layer is h4, where h4≤0.1×h1.

[0017] In a second aspect, the present application provides a dual cantilever beam specimen, comprising: a base layer; a first substrate, wherein the base layer is provided on both sides of the first substrate in a first direction; and an isolation layer is provided between the first substrate and any base layer; wherein, along the second direction, the extension length of the isolation layer is less than the extension length of the first substrate, and along the first direction, the isolation layer and the first substrate are stacked so that an isolation area and a test area are formed between the first substrate and the base layer adjacent to the isolation layer in the second direction, and the first direction and the second direction are intersecting.

[0018] On the third aspect, the present application provides a method for manufacturing a double cantilever beam specimen, which is applied to the above-mentioned double cantilever beam specimen, including: laying one of the two base layers in a specimen manufacturing mold; laying the first substrate and the isolation layer in the specimen manufacturing mold according to a predetermined laying order; laying the other of the two base layers in the specimen manufacturing mold, and the two base layers are symmetrically arranged along a first direction; connecting the base layer and the first substrate; wherein, along the second direction, the isolation layer extends from one end of the first substrate toward the other end of the first substrate by a predetermined length to form an isolation area between the base layer adjacent to the isolation layer and the first substrate.

[0019] The present application provides a fracture toughness testing method for heterogeneous materials, a double cantilever beam specimen and a manufacturing method. The fracture toughness testing method for heterogeneous materials includes the step of providing a double cantilever beam specimen. The double cantilever beam specimen includes a base layer, a first substrate and an isolation layer. The first substrate is provided with a base layer on both sides of the first direction. An isolation layer is provided between the first substrate and any base layer. The isolation layer is used to form an isolation area between the first substrate and the base layer adjacent to the isolation layer. The isolation area is a prefabricated crack. The area without the isolation layer between the first substrate and the base layer adjacent to the isolation layer forms the area to be tested. In this way, the isolation area formed by the isolation layer is used as the starting point for stratification expansion to guide the stratification phenomenon between the first substrate and the base layer adjacent to the isolation layer from the junction of the isolation area and the area to be tested, and expand into the area to be tested along the second direction and toward the area to be tested. Therefore, by providing a base layer on both sides of the first substrate in the first direction, the geometric structure symmetry, material consistency and bending stiffness balance of the double cantilever beam specimen on both sides in the first direction can be improved, thereby reducing the probability of type II deformation and improving the accuracy of type I interlaminar fracture toughness testing of heterogeneous materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0021] Figure 1 A schematic diagram of a process for testing the fracture toughness of heterogeneous materials provided in an embodiment of the present application;

[0022] Figure 2 A schematic flow chart of the heat preservation step of a double cantilever beam specimen provided in an embodiment of the present application;

[0023] Figure 3 Schematic diagram of the structure of the double cantilever beam sample provided in the embodiment of this application Figure 1 ;

[0024] Figure 4 Schematic diagram of the structure of the double cantilever beam sample provided in the embodiment of this application Figure 2 ;

[0025] Figure 5 Schematic diagram of the structure of the double cantilever beam sample provided in the embodiment of this application Figure 3 ;

[0026] Figure 6 A schematic diagram comparing test results of a double cantilever beam specimen provided in an embodiment of the present application and a double cantilever beam specimen provided in the related art;

[0027] Figure 7 A schematic flow chart of a method for fabricating a double cantilever beam specimen according to an embodiment of the present application.

[0028] Description of reference numerals:

[0029] 10-Double cantilever beam specimen;

[0030] 100 - base layer; 100a - first base layer; 100b - second base layer; 110 - second substrate; 120 - reinforcement plate;

[0031] 200-first substrate;

[0032] 300-isolation layer;

[0033] X-first direction; Y-second direction.

[0034] The above drawings illustrate specific embodiments of the present application, which will be described in more detail below. These drawings and the textual description are not intended to limit the scope of the present application in any way, but rather to illustrate the concepts of the present application to those skilled in the art by reference to specific embodiments. DETAILED DESCRIPTION

[0035] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions in the embodiments of this application will be described in more detail below in conjunction with the drawings in the preferred embodiments of this application. Obviously, the described embodiments are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0036] It should be noted that in the description of the embodiments of the present application, terms such as "upper", "lower", "inside", and "outside" indicating orientation or positional relationships are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of description. They do not indicate or imply that the device or component must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the embodiments of the present application.

[0037] In addition, it should be noted that the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or suggesting relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of this application, "multiple" means two or more, unless otherwise clearly and specifically defined.

[0038] In this application, unless otherwise expressly specified or limited, terms such as "installed," "connected," and "fixed" should be interpreted broadly. For example, they may refer to fixed connections, detachable connections, or integration; mechanical connections, electrical connections, or communication; direct connections or indirect connections through an intermediate medium; and internal connections between two components or interactions between two components. Those skilled in the art will understand the specific meanings of these terms in this application based on specific circumstances.

[0039] Because the fracture behavior of dual cantilever beam specimens depends on the material properties of the substrate, related art testing of Mode I interlaminar fracture toughness of dissimilar materials typically involves using substrates made of two different materials to create dual cantilever beam specimens based on the principle of equal bending stiffness. This involves using substrates made of different materials and thicknesses but with the same bending stiffness to test the Mode I interlaminar fracture toughness of dissimilar materials. However, due to the different materials and thicknesses, these dual cantilever beam specimens exhibit Mode II deformation during testing, which affects the test results and reduces the accuracy of the Mode I interlaminar fracture toughness test.

[0040] In view of this, the present application provides a fracture toughness testing method for heterogeneous materials, a double cantilever beam specimen and a manufacturing method. The fracture toughness testing method for heterogeneous materials includes the step of providing a double cantilever beam specimen. The double cantilever beam specimen includes a base layer, a first substrate and an isolation layer. The first substrate is provided with a base layer on both sides of the first direction. An isolation layer is provided between the first substrate and any base layer. The isolation layer is used to form an isolation area between the first substrate and the base layer adjacent to the isolation layer. The isolation area is a prefabricated crack. The area without the isolation layer between the first substrate and the base layer adjacent to the isolation layer forms the area to be tested. In this way, the isolation area formed by the isolation layer is used as the starting point for stratification expansion to guide the stratification phenomenon between the first substrate and the base layer adjacent to the isolation layer from the junction of the isolation area and the area to be tested, and expand into the area to be tested along the second direction and toward the area to be tested. Therefore, by providing a base layer on both sides of the first substrate in the first direction, the geometric structure symmetry, material consistency and bending stiffness balance of the double cantilever beam specimen on both sides in the first direction can be improved, thereby reducing the probability of type II deformation and improving the accuracy of type I interlaminar fracture toughness testing of heterogeneous materials.

[0041] The present application will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0042] This application provides a method for testing the fracture toughness of heterogeneous materials. Figure 1 , including the following steps:

[0043] S1: Provide the double cantilever beam specimen 10 steps, see Figure 3 and Figure 5 The double cantilever beam specimen 10 includes a base layer 100, a first substrate 200 and an isolation layer 300. The base layer 100 is provided on both sides of the first substrate 200 in the first direction X. The isolation layer 300 is provided between the first substrate 200 and any base layer 100. The base layer 100 and the first substrate 200 are fixedly connected. An isolation area and a test area are formed between the first substrate 200 and the base layer 100 adjacent to the isolation layer 300 in the second direction Y, and the isolation area has a prefabricated crack.

[0044] The first direction X may be understood as the thickness direction of the double cantilever beam sample 10 , and the second direction Y may be understood as the length direction of the double cantilever beam sample 10 .

[0045] It should be noted that in order to measure the Mode I interlaminar fracture toughness of dissimilar materials, a double cantilever beam specimen 10 is first provided. The double cantilever beam specimen 10 may include two substrate layers 100, which may include steel, unidirectional carbon fiber laminate, or the like. One of the two substrate layers 100 may be a first substrate layer 100a, and the other may be a second substrate layer 100b. The first substrate layer 100a and the second substrate layer 100b may be made of the same material. The first substrate 200 may include fiberglass fabric, carbon-glass blend fabric, or the like. The first substrate 200 and the substrate layer 100 may be made of different materials. The bending stiffness of the substrate layer 100 may be set to be greater than that of the first substrate 200. This helps improve the symmetry of the bending stiffness of the double cantilever beam specimen 10.

[0046] In a specific implementation, the first base layer 100a, the first substrate 200, and the second base layer 100b can be stacked in sequence along the first direction X. Figure 3 and Figure 4 The isolation layer 300 can be disposed between the first base layer 100a and the first substrate 200, or between the first substrate 200 and the second base layer 100b. The isolation layer 300 disposed between the first base layer 100a and the first substrate 200 is used as an example for description. The isolation layer 300 partially isolates the first base layer 100a from the first substrate 200 to form an isolation region. The region between the first base layer 100a and the first substrate 200 where the isolation layer 300 is not disposed can be fixedly connected to form a region to be tested. The isolation region and the region to be tested are arranged along the second direction Y. The second base layer 100b and the first substrate 200 can also be fixedly connected. The function of the isolation layer 300 is to form a prefabricated crack (i.e., an isolation area) between the first base layer 100a and the first substrate 200, so that during the test process, delamination between the first base layer 100a and the first substrate 200 (which can also be understood as a crack between the first base layer 100a and the first substrate 200) initiates at the junction of the prefabricated crack and the area to be tested, and expands toward the area to be tested.

[0047] The isolation layer 300 may include a polytetrafluoroethylene film.

[0048] Take the two materials to be tested as an example, namely co-cured steel and glass fiber fabric, see Figure 6 According to the measurement, the strain energy release rate of the double cantilever beam specimen 10 provided by the present application at the crack tip is 0.1 J / m 2 , which is less than the mode II strain energy release rate of 7.8 J / m at the crack tip of the double cantilever beam specimen 10 in the related art. 2 Due to the influence of the mode II shear load, the mode I fracture toughness value of the double cantilever beam specimen in the related art is 164.9 J / m 2The mode I fracture toughness value of the double cantilever beam specimen provided in this application is 182.3 J / m 2 .

[0049] Therefore, by providing the base layer 100 on both sides of the first substrate 200 in the first direction X, the geometric structure symmetry, material consistency and bending stiffness balance of the double cantilever beam specimen 10 on both sides in the first direction X can be improved, thereby reducing the probability of type II deformation, and further improving the accuracy of type I interlaminar fracture toughness testing of heterogeneous materials.

[0050] S2: Sample testing step, installing the double cantilever beam sample 10 on a testing device, gradually loading the double cantilever beam sample 10 through the testing device to cause delamination in the area to be tested, and acquiring target data.

[0051] The target data includes multiple load values ​​applied by the test device to the double cantilever beam specimen 10 and displacement values ​​corresponding to each load value. The displacement values ​​are the opening displacement values ​​of the double cantilever beam specimen 10 in the loading direction.

[0052] In a specific implementation, the dual cantilever beam specimen 10 is first mounted on a testing device. Along the second direction Y, the dual cantilever beam specimen 10 may have a first end and a second end disposed opposite each other. The first end may be fixedly mounted on a fixed end of the testing device. The isolation region may be positioned closer to the first end relative to the region to be tested.

[0053] Illustratively, the testing apparatus may include a tensile testing machine.

[0054] It should be noted that the first end of the dual cantilever beam specimen 10 is further connected to loading blocks or piano-style hinges on both sides along the first direction X. The loading blocks or piano-style hinges are also connected to the testing device on the side facing away from the dual cantilever beam specimen 10 to load the dual cantilever beam specimen 10. The testing device may also be provided with a latch embedded in the loading block or a fixture for clamping the piano-style hinge to enable the first end of the dual cantilever beam specimen 10 to rotate relative to the test piece.

[0055] Specifically, the loading process of the testing apparatus can be performed in accordance with test specifications (e.g., ASTM D5528). For example, the testing apparatus can load the dual-cantilever beam specimen 10 at a loading rate of 2 mm / min. A data acquisition system connected to the testing apparatus can collect target data at a frequency of 5 Hz, specifically, the load value and the displacement value corresponding to the load value.

[0056] S3: result calculation step, obtaining the mode I interlaminar fracture toughness value of the double cantilever beam specimen 10 according to the target data.

[0057] It should be noted that after obtaining the data such as the width, thickness, delamination length, load value, and displacement value of the double cantilever beam specimen 10, the calculation formula of the type I interlaminar fracture toughness value can be used: G Ic =Pδ / (2b•a) The mode I interlaminar fracture toughness value of the double cantilever beam specimen 10 is calculated.

[0058] The delamination length of the double cantilever beam specimen 10 is a, the width of the double cantilever beam specimen 10 is b, the applied load value is P, and the displacement value of the loading point is δ.

[0059] In addition, in order to ensure the accuracy and reliability of the test results, the number of the dual cantilever beam specimens 10 can be set to at least five, so that the specimen testing step and the result calculation step are performed on each dual cantilever beam specimen 10 .

[0060] In some embodiments, in the step of providing the dual cantilever beam specimen 10 , in the second direction Y, the elastic modulus of the base layer 100 is greater than the elastic modulus of the first substrate 200 .

[0061] It is understood that the base layer 100 and the first substrate 200 are made of different materials. To improve the balance of the bending stiffness of the dual cantilever beam specimen 10 in the first direction X and reduce the difficulty of acquiring target data, the base layer 100 can include the material with the larger elastic modulus along the second direction Y of the two tested materials, and the first substrate 200 can include the material with the smaller elastic modulus along the second direction Y of the two tested materials. For example, when testing the fracture toughness between steel and fiberglass fabric, the base layer 100 can be made of steel and the first substrate 200 can be made of fiberglass fabric. This facilitates observation of the delamination length of the dual cantilever beam specimen 10 during loading, facilitating the collection of load and displacement values. In other words, if the base layer 100 is made of the material with the smaller elastic modulus along the second direction Y of the two tested materials, and the first substrate 200 is made of the material with the larger elastic modulus along the second direction Y of the two tested materials, the delamination of the dual cantilever beam specimen 10 will expand relatively rapidly during loading, hindering the collection of target data and thus affecting the accuracy of the test results.

[0062] In some embodiments, prior to the sample testing step, see Figure 2 , further comprising S4: a step of heat preservation of the double cantilever beam specimen 10, comprising:

[0063] S41 : placing the dual cantilever beam sample 10 in a constant temperature environment, and determining the insulation temperature of the dual cantilever beam sample 10 according to the actual use environment temperature of the base layer 100 and the first substrate 200 .

[0064] It should be noted that the dual cantilever beam sample 10 is insulated at the actual ambient temperature of use according to the materials involved in the base layer 100 and the first substrate 200. That is, the insulation temperature can be set to be consistent with the actual ambient temperature of use, which can ensure that the dual cantilever beam sample 10 can reach a stable temperature state before the sample testing step, thereby reducing the impact of temperature on the test results.

[0065] In addition, by simulating the actual ambient temperature of use to heat the double cantilever beam specimen 10, the test results of the mode I interlaminar fracture toughness value can be made closer to the actual application situation, thereby improving the accuracy and reliability of the test results.

[0066] S42: Maintaining the double cantilever beam sample 10 at a constant temperature for a predetermined period of time according to the insulation temperature.

[0067] The double cantilever beam sample 10 can be placed in a heat preservation structure that can accurately control the temperature, and the temperature of the heat preservation structure can be set according to the heat preservation temperature to ensure that the double cantilever beam sample 10 is in a constant temperature condition during the heat preservation process.

[0068] The predetermined time period may be determined based on specific test requirements and the material properties of the dual cantilever beam specimen 10 to ensure that the temperature inside the dual cantilever beam specimen 10 is uniformly distributed and reaches a thermally stable state.

[0069] Optionally, the predetermined duration can be set between 2 hours and 10 hours.

[0070] S43: performing temperature detection on the base layer 100 and the first substrate 200 of the dual cantilever beam sample 10 respectively to ensure that the temperature difference between the base layer 100 and the first substrate 200 is within a preset temperature difference range.

[0071] It is understandable that temperature sensors may be used to detect the temperatures of the base layer 100 and the first substrate 200 respectively, thereby avoiding experimental errors caused by a large temperature difference between the base layer 100 and the first substrate 200 .

[0072] Optionally, the preset temperature difference range can be set below 2°C.

[0073] For example, when the materials involved in the base layer 100 and the first substrate 200 of the double cantilever beam specimen 10 are used in the field of wind turbine blade technology, and the actual operating environment temperature of the wind turbine blade can be between -40°C and 60°C, then the type I interlaminar fracture toughness value of the double cantilever beam specimen 10 can be tested under the two end value conditions of -40°C and 60°C. In other words, the insulation temperature of the double cantilever beam specimen 10 can be set to -40°C for insulation and testing, and then the insulation temperature can be set to 60°C for insulation and testing. Thus, by simulating the actual use environment temperature to insulate and test the double cantilever beam specimen 10, the test results of the type I interlaminar fracture toughness value can be made closer to the actual application situation, thereby improving the accuracy and reliability of the test results. Among them, the predetermined time can be set between 2 hours and 5 hours.

[0074] In some embodiments, before the sample testing step, the method further includes: measuring the dimensions of the dual cantilever beam sample 10 and marking the dual cantilever beam sample 10 .

[0075] It should be noted that a measuring instrument can be used to measure the dimensions of the dual cantilever beam specimen 10 to ensure the accuracy of the test results. Optionally, the measuring instrument can include a micrometer, a vernier caliper, etc. to ensure the accuracy of the obtained data. The measured dimensions can include the length, width, and thickness of the dual cantilever beam specimen 10.

[0076] In addition, it is necessary to mark the double cantilever beam specimen 10. The purpose of the mark is to accurately measure the delamination length during the test.

[0077] See also Figure 3 and Figure 4 In some embodiments, the base layer 100 includes a second substrate 110 , the two second substrates 110 are respectively located on opposite sides of the first substrate 200 in the first direction X, and the isolation layer 300 is disposed between the first substrate 200 and any second substrate 110 .

[0078] It can be understood that the first substrate 200 is made of one of the two materials to be tested, and the second substrate 110 is made of the other of the two materials to be tested. The two second substrates 110 are respectively located on opposite sides of the first substrate 200 in the first direction X. As a result, the geometric structure symmetry, material consistency and bending stiffness balance of the dual cantilever beam specimen 10 on both sides in the first direction X can be improved, thereby reducing the probability of type II deformation and improving the accuracy of type I interlaminar fracture toughness testing of dissimilar materials.

[0079] In some embodiments, the elastic modulus of the first substrate 200 is E1, and the elastic modulus of the second substrate 110 is E2, where E2 ≥ 1.4×E1.

[0080] It can be understood that E2 ≥ 1.4 × E1, which makes the second substrate 110 more resistant to deformation than the first substrate 200. Or, under the same deformation conditions, the second substrate 110 requires a greater external force to produce the same deformation as the first substrate 200. This configuration can improve the geometric structure symmetry and bending stiffness balance of the dual cantilever beam specimen 10.

[0081] Specifically, E2 can be set to 1.5×E1, 1.7×E1, etc., which helps reduce the difficulty of acquiring target data. In other words, if E2 is set to 1.1×E1 or 0.7×E1, the elastic modulus of the second substrate 110 is similar to or smaller than the elastic modulus of the first substrate 200. As a result, during the loading process, the delamination expansion trend of the dual cantilever beam specimen 10 is relatively rapid, which is not conducive to the acquisition of target data and thus affects the accuracy of the test results.

[0082] In some other embodiments, along the first direction X, the thickness of the first substrate 200 is h1, and the thickness of the second substrate 110 is h2, where h2 ≥ 2.3×h1.

[0083] It should be noted that h2 ≥ 2.3 × h1 helps improve the geometric symmetry of the dual cantilever beam specimen 10. In other words, if h2 is set to 1.2 × h1 or 1.4 × h2, the thickness of the second substrate 110 is similar to that of the first substrate 200, which will reduce the symmetry of the dual cantilever beam specimen 10 and affect the accuracy of the test results.

[0084] See also Figure 5 In some embodiments, the base layer 100 includes a second substrate 110 and a reinforcing plate 120 . Along the first direction X, the second substrate 110 is arranged close to the first substrate 200 relative to the reinforcing plate 120 , and the isolation layer 300 is arranged between the first substrate 200 and any second substrate 110 .

[0085] It should be noted that the first substrate 200 can be made of one of the two materials to be tested, and the second substrate 110 can be made of the other of the two materials to be tested. When the elastic moduli of the two materials to be tested are similar and relatively small, that is, when the elastic moduli of the first substrate 200 and the second substrate 110 are similar and relatively small, a reinforcing plate 120 can be added to provide support for the first substrate 200 and the second substrate 110, thereby improving the geometric structure symmetry, material consistency, and bending stiffness balance of the dual cantilever beam specimen 10 on both sides in the first direction X, while avoiding the rapid delamination expansion trend of the dual cantilever beam specimen 10. This can reduce the difficulty of obtaining target data and improve the reliability and accuracy of the test results.

[0086] In some embodiments, the elastic modulus of the first substrate 200 is E1, and the elastic modulus of the reinforcing plate 120 is E3, where E3 ≥ 1.4×E1.

[0087] As a result, the reinforcing plate 120 has a higher ability to resist deformation than the first substrate 200. In other words, under the same external force, the reinforcing plate 120 tends to deform less than the first substrate 200. This configuration can improve the geometric symmetry and bending stiffness of the dual cantilever beam specimen 10.

[0088] For example, E3 can be set to 1.6×E1, 1.9×E1, etc., which helps improve the bending stiffness of the dual cantilever beam specimen 10 on both sides in the first direction X and reduces the difficulty of collecting target data. In other words, if E3 is set to 1.2×E1 or 0.8×E1, the elastic modulus of the reinforcing plate 120 is similar to or lower than the elastic modulus of the first substrate 200. As a result, during loading, the dual cantilever beam specimen 10 will delaminate and expand relatively quickly, which is not conducive to collecting target data.

[0089] In some other embodiments, along the first direction X, the thickness of the first substrate 200 is h1, and the thickness of the reinforcing plate 120 is h3, where h3 ≥ 2.3×h1.

[0090] This configuration helps improve the geometric symmetry of the dual cantilever beam sample 10. That is, if h2 is set to 1.2×h1 or 1.4×h2, the thickness of the second substrate 110 is relatively close to that of the first substrate 200, which will reduce the symmetry of the dual cantilever beam sample 10.

[0091] In some embodiments, along the first direction X, the thickness of the first substrate 200 is h1, and the thickness of the isolation layer 300 is h4, where h4≤0.1×h1.

[0092] In order to simulate the delamination cracks generated between the two materials to be tested in actual applications and reduce the impact on the first substrate 200 and the second substrate 110 to ensure the accuracy of the test results, the thickness h4 of the isolation layer 300 can be set to be less than or equal to 0.1×h1.

[0093] Based on the above embodiment, the present invention provides a double cantilever beam specimen 10. Figures 3 to 5, comprising a base layer 100, a first substrate 200, and an isolation layer 300. The base layer 100 is provided on both sides of the first substrate 200 in the first direction X. The isolation layer 300 is provided between the first substrate 200 and any base layer 100. The extension length of the isolation layer 300 along the second direction Y is less than the extension length of the first substrate 200, and the isolation layer 300 and the first substrate 200 are stacked along the first direction X, so that an isolation area and a test area are formed between the first substrate 200 and the base layer 100 adjacent to the isolation layer 300 in the second direction Y. The first direction X and the second direction Y are intersecting.

[0094] By providing two base layers 100 in plate-like structures and symmetrically arranging them along the first direction X, the uniformity and symmetry of the double cantilever beam specimen 10 when subjected to force are ensured, which is beneficial to improving the accuracy and reliability of the test.

[0095] Secondly, the first substrate 200 is sandwiched between the two base layers 100, and by providing an isolation layer 300, effective isolation is achieved between one end of the first substrate 200 in the second direction Y and either base layer 100, thereby forming an isolation region and a test region in the second direction Y between the first substrate 200 and the base layer 100 adjacent to the isolation layer 300. The function of the isolation layer 300 is to form a prefabricated crack (i.e., the isolation region) between the first base layer 100a and the first substrate 200, so that delamination between the first base layer 100a and the first substrate 200 (which can also be understood as a crack between the first base layer 100a and the first substrate 200) during testing initiates at the interface between the prefabricated crack and the test region and propagates toward the test region.

[0096] On the basis of the above embodiment, the present invention provides a method for manufacturing a double cantilever beam specimen, which is applied to the double cantilever beam specimen provided in the above embodiment. Figure 7 ,include:

[0097] S101: Laying one of the two base layers 100 in a sample preparation mold.

[0098] It should be noted that when the base layer 100 is made of a metal material, a surface treatment device can be used to treat the base layer 100 before laying the base layer 100. For example, when the base layer 100 is made of steel, a dry vacuum sandblasting machine can be used to sandblast the base layer 100. In practice, a blasting pressure of 0.5 MPa can be used for 10 seconds to increase the surface roughness of the base layer 100. This setting is intended to improve the adhesion of the base layer 100.

[0099] Furthermore, after sandblasting, the base layer 100 can be placed in a 100°C oven for drying for 30 to 40 minutes to ensure complete drying. After removal from the oven, the base layer 100 is cooled to room temperature and allowed to stand for 12 to 15 hours. The base layer 100 is then placed in the sample preparation mold.

[0100] S102: Laying the first substrate 200 and the isolation layer 300 in a sample production mold according to a predetermined laying order.

[0101] It is understood that one of the two base layers 100 can be the first base layer 100a, and the other can be the second base layer 100b. For the purpose of illustration, the second base layer 100b is first laid on the sample preparation mold. The predetermined laying order can be to lay the first substrate 200 first and then the isolation layer 300, so that the isolation layer 300 is located between the first substrate 200 and the first base layer 100a. Alternatively, the isolation layer 300 can be laid first and then the first substrate 200, so that the isolation layer 300 is located between the first substrate 200 and the second base layer 100b.

[0102] When the first substrate 200 includes glass fiber fabric, the fiber direction of the glass fiber fabric can be set parallel to the width direction or length direction of the double cantilever beam specimen 10 itself, and can be specifically set according to the actual application scenario of the glass fiber fabric.

[0103] It should be noted that when the first substrate 200 includes fiberglass fabric, the fiberglass fabric is typically provided in multiple layers. Prior to laying the first substrate 200 and the isolation layer 300, the multiple layers of fiberglass fabric need to be impregnated and cured. The fiberglass fabric and isolation layer 300 are then cut, leaving a portion of the isolation layer 300. The isolation layer 300 may include a polytetrafluoroethylene film.

[0104] S103 : Laying the other of the two base layers 100 in a sample production mold, and the two base layers 100 are symmetrically arranged along the first direction X.

[0105] S104 : Connecting the base layer 100 and the first substrate 200 .

[0106] After the other of the two base layers 100 is laid in the sample preparation mold to cover the first substrate 200 and the isolation layer 300, a vacuum-assisted infusion molding process can be used to infuse resin into the sample preparation mold to bond and cure the base layer 100 and the first substrate 200 to form the dual cantilever beam sample 10. In other words, by infusing the resin, the two base layers 100 can be bonded and cured to the first substrate 200 except for the area where the isolation layer 300 is laid.

[0107] The resin may include epoxy resin. Specifically, the double cantilever beam sample 10 may be cured at 70° C. for 3 hours.

[0108] Along the second direction Y, the isolation layer 300 extends from one end of the first substrate 200 toward the other end of the first substrate 200 by a predetermined length to form an isolation region between the base layer 100 adjacent to the isolation layer 300 and the first substrate 200 .

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for testing the fracture toughness of heterogeneous materials, characterized in that: The following steps are involved: A step of providing a double cantilever beam specimen (10), wherein the double cantilever beam specimen (10) comprises a base layer (100), a first substrate (200), and an isolation layer (300), wherein the base layer (100) is provided on both sides of the first substrate (200) in a first direction (X), an isolation layer (300) is provided between the first substrate (200) and any of the base layers (100), the base layer (100) and the first substrate (200) are fixedly connected, and an isolation region and a region to be tested are formed between the first substrate (200) and the base layer (100) adjacent to the isolation layer (300) in a second direction (Y), and the isolation region has a prefabricated crack; a sample testing step, installing the double cantilever beam sample (10) on a testing device, gradually loading the double cantilever beam sample (10) through the testing device to cause delamination in the area to be tested, and acquiring target data; A result calculation step, obtaining a mode I interlaminar fracture toughness value of the double cantilever beam specimen (10) according to the target data; The isolation layer (300) partially isolates any of the base layers (100) from the first substrate (200) to form the isolation area, and an area between the base layer (100) and the first substrate (200) adjacent to the isolation layer (300) where the isolation layer (300) is not provided is fixedly connected to form the area to be tested.

2. The fracture toughness testing method of heterogeneous materials according to claim 1, characterized in that: In the step of providing the dual cantilever beam sample (10), in the second direction (Y), the elastic modulus of the base layer (100) is greater than the elastic modulus of the first substrate (200).

3. The fracture toughness testing method of heterogeneous materials according to claim 1, characterized in that: The target data includes a plurality of load values ​​applied by the testing device to the double cantilever beam specimen (10) and a displacement value corresponding to each load value, wherein the displacement value is an opening displacement value of the double cantilever beam specimen (10) in the loading direction.

4. The fracture toughness testing method of heterogeneous materials according to claim 1, characterized in that: Before the sample testing step, a double cantilever beam sample (10) insulation step is also included, including: Placing the double cantilever beam sample (10) in a constant temperature environment, and determining the insulation temperature of the double cantilever beam sample (10) according to the actual use environment temperature of the base layer (100) and the first substrate (200); Maintaining the double cantilever beam specimen (10) at a constant temperature for a predetermined period of time according to the insulation temperature; Temperature monitoring is performed on the base layer (100) and the first substrate (200) of the dual cantilever beam specimen (10) to ensure that the temperature difference between the base layer (100) and the first substrate (200) is within a preset temperature difference range.

5. The fracture toughness testing method of heterogeneous materials according to claim 1, characterized in that: Before the sample testing step, the method further includes: measuring the dimensions of the double cantilever beam sample (10) and marking the double cantilever beam sample (10).

6. The fracture toughness testing method of heterogeneous materials according to claim 1, characterized in that: The base layer (100) comprises a second substrate (110), two second substrates (110) are respectively located on opposite sides of the first substrate (200) in the first direction (X), and the isolation layer (300) is arranged between the first substrate (200) and any one of the second substrates (110).

7. The method for testing the fracture toughness of heterogeneous materials according to claim 6, characterized in that: The elastic modulus of the first substrate (200) is E1, and the elastic modulus of the second substrate (110) is E2, wherein E2 ≥ 1.4 × E1; And / or, along the first direction (X), the thickness of the first substrate (200) is h1, and the thickness of the second substrate (110) is h2, wherein h2≥2.3×h1.

8. The fracture toughness testing method of heterogeneous materials according to claim 1, characterized in that: The base layer (100) comprises a second substrate (110) and a reinforcing plate (120); along the first direction (X), the second substrate (110) is arranged close to the first substrate (200) relative to the reinforcing plate (120); and the isolation layer (300) is arranged between the first substrate (200) and any one of the second substrates (110).

9. The method for testing the fracture toughness of heterogeneous materials according to claim 8, characterized in that: The elastic modulus of the first substrate (200) is E1, and the elastic modulus of the reinforcing plate (120) is E3, wherein E3 ≥ 1.4 × E1; And / or, along the first direction (X), the thickness of the first substrate (200) is h1, and the thickness of the reinforcing plate (120) is h3, wherein h3≥2.3×h1.

10. The method for testing the fracture toughness of dissimilar materials according to any one of claims 1 to 9, characterized in that: Along the first direction (X), the thickness of the first substrate (200) is h1, and the thickness of the isolation layer (300) is h4, wherein h4≤0.1×h1.

11. A double cantilever beam specimen, characterized in that: include: base layer (100); A first substrate (200), wherein the base layer (100) is provided on both sides of the first substrate (200) in a first direction (X); an isolation layer (300) disposed between the first substrate (200) and any one of the base layers (100); The isolation layer (300) has an extension length that is less than an extension length of the first substrate (200) along the second direction (Y), and the isolation layer (300) and the first substrate (200) are stacked along the first direction (X) so that an isolation region and a region to be tested are formed between the first substrate (200) and the base layer (100) adjacent to the isolation layer (300) in the second direction (Y). The first direction (X) and the second direction (Y) are intersected, and the isolation layer (300) partially isolates any base layer (100) from the first substrate (200) to form the isolation region. A region between the base layer (100) adjacent to the isolation layer (300) and the first substrate (200) where the isolation layer (300) is not provided is fixedly connected to form the region to be tested.

12. A method for manufacturing a double cantilever beam specimen, applied to the double cantilever beam specimen according to claim 11, characterized in that: include: Laying one of the two base layers (100) in a sample preparation mold; Laying the first substrate (200) and the isolation layer (300) in the sample production mold according to a predetermined laying order; Laying the other of the two base layers (100) in the sample production mold, and the two base layers (100) are symmetrically arranged along a first direction (X); Connecting the base layer (100) and the first substrate (200); Wherein, along the second direction (Y), the isolation layer (300) extends from one end of the first substrate (200) toward the other end of the first substrate (200) by a predetermined length to partially isolate any of the base layers (100) from the first substrate (200), so as to form the isolation area between the base layer (100) adjacent to the isolation layer (300) and the first substrate (200), and the area between the base layer (100) adjacent to the isolation layer (300) and the first substrate (200) where the isolation layer (300) is not provided is fixedly connected to form the area to be tested.

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