Method and testing device for biaxial tensile test of fabric

Abstract

The present application relates to a method for biaxial tensile testing of a fabric, characterized in that it comprises the steps of: stretching a first sample of a fabric at a prescribed stretching speed in each of a first axial direction and a second axial direction orthogonal to each other until the first sample breaks, and determining the breaking strength; in the first axial direction and the second axial direction which are orthogonal to each other, the second sample of the fabric is subjected to reciprocating stretching at the specified stretching speed with the stretching force lower than the breaking strength, and test data are recorded in the reciprocating stretching process of the second sample of the fabric, the reciprocating stretching includes stretching which is alternately performed simultaneously in a first axial direction and a second axial direction and relaxation following the stretching. The invention further relates to a testing device for the biaxial tensile test of the fabric.

Description

Technical Field

[0001] The present application relates to a method for biaxial tensile testing of fabrics and a testing device for biaxial tensile testing of fabrics. Background Art

[0002] In actual use, fabrics are generally not subjected to a single form of destructive force, but to the combined effects of complex stresses. Compared with uniaxial tensile tests, biaxial tensile tests can more accurately reflect the material properties under complex load conditions and better reflect the ease with which fabrics are damaged by stretching during use. Due to the limitations of instruments and test methods, there is currently a lack of research on biaxial tensile test methods for fabrics, especially biaxial high-speed tensile test methods, as well as related test equipment.

[0003] In practice, for example, in the field of vehicle safety, when developing airbags for vehicles, in order to meet the modeling specifications and simulation requirements for airbag CAE (Computer Aided Engineering), it is necessary to provide CAE with test data of fabrics used for airbags under different working conditions. In particular, this involves test data of fabrics under dynamic working conditions, so as to simulate and analyze the airbag deployment process of airbags. However, since the current research on test methods for bidirectional high-speed stretching of fabrics and related test equipment is relatively limited, how to obtain test parameters that are closer to the actual application conditions of fabrics has become an urgent problem to be solved. Summary of the invention

[0004] The object of the present application is to provide a method for biaxial tensile testing of fabrics and a testing device for biaxial tensile testing of fabrics, which can overcome at least one defect in the prior art and thereby can reflect the material properties of the fabric under complex load conditions.

[0005] The object is achieved by a method for biaxial tensile testing of textile fabrics and a testing device for biaxial tensile testing of textile fabrics.

[0006] A first aspect of the present application relates to a method for biaxial tensile testing of fabrics, characterized in that the method comprises the following steps:

[0007] - stretching a first sample of the fabric along a first axial direction and a second axial direction orthogonal to each other at a specified stretching speed, respectively, until the first sample breaks, and determining the breaking strength;

[0008] - reciprocatingly stretching the second sample of the fabric along a first axial direction and a second axial direction orthogonal to each other at a tensile force lower than the breaking strength and at a specified stretching speed, and recording test data during the reciprocating stretching of the second sample of the fabric, wherein the reciprocating stretching includes stretching alternately performed in the first axial direction and the second axial direction simultaneously and relaxation immediately after the stretching.

[0009] According to an implementation mode of the present application, the method is implemented using the same first sample and second sample. Here, the "same" first sample and second sample can be understood as the same in terms of material, size, shape, etc.

[0010] According to one embodiment of the present application, the test data includes at least one of force, displacement, stress, and strain.

[0011] According to an embodiment of the present application, one of the first axial direction and the second axial direction corresponds to a warp direction of the fabric, and the other of the first axial direction and the second axial direction corresponds to a weft direction of the fabric.

[0012] According to one embodiment of the present application, before stretching the first sample of the fabric:

[0013] - providing a first sample of said fabric;

[0014] - Clamping the first sample with a first clamp, a second clamp, a third clamp and a fourth clamp, wherein the first clamp and the third clamp are opposite to each other in the first axial direction, and the second clamp and the fourth clamp are opposite to each other in the second axial direction.

[0015] According to one embodiment of the present application, the first sample is stretched in a plane where the first sample is located along a first axial direction and a second axial direction orthogonal to each other at a specified stretching speed until the first sample breaks in any direction, and the breaking strength in the first axial direction and the breaking strength in the second axial direction are determined respectively. Here, the breaking can occur, for example, in the first axial direction and / or the second axial direction. It is possible that the first sample breaks in the middle area between the first clamp, the second clamp, the third clamp and the fourth clamp; it is also possible that the first sample breaks near the jaws of the first clamp and / or the second clamp and / or the third clamp and / or the fourth clamp, that is, the so-called "jaw fracture" occurs. Advantageously, in the present application, only the case where the first sample breaks in the middle area between the first clamp, the second clamp, the third clamp and the fourth clamp is considered, and the case where the jaw fracture occurs is preferably discarded.

[0016] According to one embodiment of the present application, before reciprocatingly stretching the second sample of fabric:

[0017] - providing a second sample of said fabric;

[0018] - clamping the second sample with a first clamp, a second clamp, a third clamp and a fourth clamp, wherein the first clamp and the third clamp are opposite to each other in the first axial direction, and the second clamp and the fourth clamp are opposite to each other in the second axial direction.

[0019] According to one embodiment of the present application, when the second sample of the fabric is reciprocatedly stretched, the following loading step and unloading step are repeatedly and alternately performed:

[0020] - in the loading step, stretching the second sample at the specified stretching speed along the first axial direction and the second axial direction orthogonal to each other in the plane where the second sample is located until the tensile force applied to the second sample reaches a first predetermined percentage of the breaking strength;

[0021] - In the unloading step, the second specimen is relaxed along a first axial direction and a second axial direction orthogonal to each other at the prescribed tensile speed until the tensile force applied to the second specimen is unloaded to a second predetermined percentage of the breaking strength.

[0022] According to an embodiment of the present application, the first predetermined percentage is 80%±5%, and / or the second predetermined percentage is 10%±5%.

[0023] According to one embodiment of the present application, the loading step and the unloading step are repeatedly and alternately performed two, three or more times.

[0024] According to an embodiment of the present application, the jaws of the first clamper and the third clamper are perpendicular to the first axial direction, and the jaws of the second clamper and the fourth clamper are perpendicular to the second axial direction.

[0025] According to one embodiment of the present application, the warp centerline of the first sample or the second sample passes through the centerline of the first clamp and the third clamp, and the weft centerline of the first sample or the second sample passes through the centerline of the second clamp and the fourth clamp.

[0026] According to one embodiment of the present application, when stretching a first or second sample of a fabric, the first or second sample of the fabric is stretched synchronously along a first direction, a second direction, a third direction and a fourth direction respectively by means of a first clamp, a second clamp, a third clamp and a fourth clamp, wherein the first direction and the third direction are opposite to each other along a first axial direction, and the second direction and the fourth direction are opposite to each other along a second axial direction.

[0027] According to one embodiment of the present application, when determining the breaking strength:

[0028] - respectively determine the maximum value of the tensile force in the first direction, the second direction, the third direction and the fourth direction as the unilateral breaking strength in the direction;

[0029] - calculating the average value of the single-sided breaking strength in the first direction and in the third direction as the breaking strength in the first axial direction, and calculating the average value of the single-sided breaking strength in the second direction and in the fourth direction as the breaking strength in the second axial direction.

[0030] According to one embodiment of the present application, in the loading step, the second sample of the fabric is stretched synchronously along the first direction, the second direction, the third direction and the fourth direction until the force in one of the first direction, the second direction, the third direction and the fourth direction reaches a first predetermined percentage of the breaking strength corresponding to the direction.

[0031] According to one embodiment of the present application, in the unloading step, the second sample of the fabric is unloaded synchronously along the first direction, the second direction, the third direction and the fourth direction until the forces in the first direction, the second direction, the third direction and the fourth direction all reach a second predetermined percentage of the breaking strength corresponding to the direction.

[0032] According to one embodiment of the present application, when the first specimen or the second specimen is clamped by the clamp, a pre-tensioning force is provided by the clamp.

[0033] According to one embodiment of the present application, the pre-tensioning force is 5N to 10N.

[0034] According to one embodiment of the present application, the method includes marking strain measurement points on the surface of the second sample, and determining the strain and strain rate of the sample by a DIC measurement system when the second sample of the fabric is reciprocally stretched.

[0035] According to one embodiment of the present application, during the reciprocating stretching of the second sample of the fabric, the following are recorded:

[0036] a force applied to the second specimen along the first direction, the second direction, the third direction and the fourth direction, and / or

[0037] displacement of the first clamp, the second clamp, the third clamp and the fourth clamp in the first direction, the second direction, the third direction and the fourth direction respectively, and / or

[0038] Speeds of the first gripper, the second gripper, the third gripper, and the fourth gripper in the first direction, the second direction, the third direction, and the fourth direction, respectively.

[0039] According to one embodiment of the present application, the method includes:

[0040] Calculate the average value of the force applied to the second specimen along the first direction and along the third direction at a certain moment as the average force in the first axial direction at that moment, and calculate the average value of the force applied to the second specimen along the second direction and along the fourth direction at a certain moment as the average force in the second axial direction at that moment; and / or

[0041] calculating the sum of the displacement of the first clamp in the first direction and the displacement of the third clamp in the third direction as the total displacement in the first axial direction, and calculating the sum of the displacement of the second clamp in the second direction and the displacement of the fourth clamp in the fourth direction as the total displacement in the second axial direction; and / or

[0042] The sum of the speed of the first clamp in the first direction and the speed of the third clamp in the third direction is calculated as the total stretching speed in the first axial direction, and the sum of the speed of the second clamp in the second direction and the speed of the fourth clamp in the fourth direction is calculated as the total stretching speed in the second axial direction.

[0043] According to one embodiment of the present application, the method includes: calculating the engineering stress in the first axial direction and the engineering stress in the second axial direction respectively based on the average force in the first axial direction, the average force in the second axial direction and the original cross-sectional area of ​​the second specimen.

[0044] According to one embodiment of the present application, the first sample and / or the second sample of the fabric is a cross-shaped sample.

[0045] According to one embodiment of the present application, the gauge length of the cross-shaped specimen is 100 mm ± 1 mm, or the effective area size of the cross-shaped specimen is 100 ± 1 mm × 100 ± 1 mm; and / or

[0046] The clamping area size of the cross-shaped specimen is 80±1 mm×50±1 mm; and / or

[0047] Adjacent clamping areas of the cross-shaped specimen have chamfers with a radius of 10 mm±1 mm.

[0048] According to an embodiment of the present application, two orthogonal directions of the cross-shaped sample are respectively parallel to the warp direction and the weft direction of the fabric.

[0049] According to one embodiment of the present application, the prescribed stretching speed in the first axial direction and in the second axial direction is respectively ≥900 mm / s, preferably ≥1000 mm / s, particularly preferably in the range of 1000 to 1200 mm / s.

[0050] According to one embodiment of the present application, the prescribed stretching speed is ≥450 mm / s, preferably ≥500 mm / s, and particularly preferably in the range of 500 to 600 mm / s along the first direction, the second direction, the third direction, and the fourth direction, respectively.

[0051] In some embodiments, the speed accuracy is within ±10%, and / or the speed fluctuation is within ±10%.

[0052] According to one embodiment of the present application, the prescribed stretching speed is achieved within a displacement of 1 mm.

[0053] According to one embodiment of the present application, the fabric is a fabric for an airbag of a motor vehicle.

[0054] A second aspect of the present application relates to a test device for a biaxial tensile test of a fabric, characterized in that the test device comprises four tensile units, each of which comprises a clamp for clamping a sample of the fabric, a motor module for driving the clamp, and a linear guide module for linearly guiding the clamp.

[0055] The first stretching unit and the third stretching unit of the four stretching units are opposite to each other in a first axial direction, and the second stretching unit and the fourth stretching unit of the four stretching units are opposite to each other in a second axial direction, and the first axial direction and the second axial direction are orthogonal to each other,

[0056] The individual stretching units are designed in such a way that their grippers can be moved in the respective axial direction at a speed of at least 450 mm / s, preferably at least 500 mm / s.

[0057] According to one embodiment of the application, each stretching unit is designed such that its gripper can be accelerated from rest to a speed of at least 450 mm / s, preferably at least 500 mm / s within a displacement of 1 mm.

[0058] According to one embodiment of the present application, each stretching unit comprises a force sensor, which is configured to detect a force exerted by the corresponding stretching unit on the textile sample.

[0059] According to one embodiment of the present application, the motor module is constructed as a linear motor module, and the linear guide module includes a slider fixedly connected to the connecting rod of the linear motor module and a slide rail cooperating with the slider, and the connecting rod of the linear motor module is connected to the clamp.

[0060] According to one embodiment of the present application, each linear guide module includes two slider-slide rail assemblies, and the two slider-slide rail assemblies are respectively arranged on both sides of the connecting rod of the linear motor module, and the connecting rod of the linear motor module is connected to the sliders of the two slider-slide rail assemblies via a connecting piece.

[0061] According to one embodiment of the present application, the connecting rod of the linear motor module is connected to the clamp via the connecting member.

[0062] According to an embodiment of the present application, the force sensor is arranged on the connecting member.

[0063] According to one embodiment of the present application, the stretching unit includes a grating ruler for recording the displacement of the clamp.

[0064] According to one embodiment of the present application, the test device includes a controller, which is connected to the grating scale, force sensor and driver signal of the motor module, and the controller is configured to issue control commands to the driver based on measurement signals from the grating scale and force sensor.

[0065] According to one embodiment of the present application, the linear motor module can achieve a maximum acceleration of 30g and / or an acceleration slope of at least 30g / ms and / or a peak thrust greater than or equal to 10KN and / or a control force resolution less than or equal to 10N.

[0066] According to one embodiment of the present application, the test device includes a fixed frame, the fixed frame includes four support structures arranged in a cross shape, the four support structures are respectively equipped with a stretching unit, and the stretching unit is installed on the support structure.

[0067] According to an embodiment of the present application, the fixing frame has a reinforcement portion between two adjacent supporting structures.

[0068] According to one embodiment of the present application, the test device is configured to implement the method for biaxial tensile testing of fabrics according to the first aspect of the present application. Advantageously, the same test device or a plurality of the same test devices are configured to implement the method for biaxial tensile testing of fabrics according to the first aspect of the present application.

[0069] Other features of the present application are derived from the drawings and the specific embodiments. All the features and feature combinations mentioned above in the specification and the features and feature combinations mentioned below in the specific embodiments and / or shown separately in the drawings can be used not only in the corresponding given combination, but also in other combinations, or can be used alone. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] After reading the following detailed description in conjunction with the accompanying drawings, various aspects of the present application will be better understood, in which:

[0071] Figures 1 to 4 The steps of a method for biaxial tensile testing of a fabric according to some embodiments of the present application are shown;

[0072] Figure 5 Schematically illustrating biaxial stretching of a sample of fabric;

[0073] Figure 6 Schematically illustrates a test specimen suitable for use in a method for biaxial tensile testing of a fabric according to some embodiments of the present application;

[0074] Figure 7 Schematically illustrating an acceleration motion curve in a method for biaxial tensile testing of a fabric according to some embodiments of the present application;

[0075] Figure 8 Schematically illustrating stretching and unloading motion curves in a method for biaxial tensile testing of a fabric according to some embodiments of the present application;

[0076] Fig. 9 Schematically showing a test device for biaxial tensile test of fabric according to some embodiments of the present application;

[0077] Fig.10 Schematically shows Fig. 9 A portion of a test apparatus wherein the fabric sample has not yet been stretched;

[0078] Fig.11 Schematically shows Fig. 9 A portion of a test apparatus in which a sample of fabric has been stretched;

[0079] Fig.12 A control block diagram of a testing device for biaxial tensile testing of fabric according to some embodiments of the present application is schematically shown. DETAILED DESCRIPTION

[0080] The present application will be described below with reference to the accompanying drawings, wherein the accompanying drawings illustrate several embodiments of the present application. However, it should be understood that the present application can be presented in a variety of different ways and is not limited to the embodiments described below; in fact, the embodiments described below are intended to make the disclosure of the present application more complete and fully explain the scope of protection of the present application to those skilled in the art. It should also be understood that the embodiments disclosed herein can be combined in various ways to provide more additional embodiments.

[0081] It should be understood that the same reference numerals represent the same elements throughout the drawings. In the drawings, the dimensions of certain features may be distorted for clarity.

[0082] It should be understood that the terms used in the specification are only used to describe specific embodiments and are not intended to limit the present application. All terms (including technical terms and scientific terms) used in the specification have the meanings commonly understood by those skilled in the art unless otherwise defined. For the sake of simplicity and / or clarity, well-known functions or structures may not be described in detail.

[0083] The present application is not limited to the embodiments shown, but includes or extends to all technical equivalents that may fall within the effective scope of the appended claims. The position descriptions selected in the specification, such as top, bottom, left, right, etc., refer to the direct description and the drawings shown and can be transferred to the new position according to the meaning when the position changes.

[0084] Although some aspects are described in association with a device, it should be understood that these aspects are also descriptions of the corresponding methods, so that a unit of the device or a device of the system can also be understood as a corresponding method step or a feature of the method step. Similarly, aspects described in association with a method step or as a method step are also descriptions of corresponding units or details or features of the corresponding device.

[0085] Figures 1 to 4 The steps of a method for biaxial tensile testing of a fabric according to some embodiments of the present application are shown.

[0086] The fabric used as the test object may be, for example, a fabric for a vehicle airbag. The fabric may be used to manufacture an airbag of the airbag, which is inflated and deployed, for example, when a vehicle crashes, to protect passengers in the vehicle. Since the inflation and deployment process of the airbag is very rapid, the fabric used for the airbag is subjected to the combined effects of complex stresses during this process, and the material properties of the fabric used for the airbag are very important for the functional reliability and safety of the airbag, it is beneficial to study the material properties of the airbag fabric, especially the material properties under high-speed dynamic conditions, by performing a biaxial tensile test for the fabric according to the present application.

[0087] The fabric used for airbags can generally have the characteristics of high strength, heat resistance, low air permeability, lightness, thinness and softness. Among them, the high strength enables the fabric to withstand huge impact force in an instant to prevent the airbag from rupturing during the inflation process. Generally, high-strength synthetic fiber materials such as nylon (PA66) and polyester (PET) can be used as fabrics for airbags. Heat resistance means that high temperatures may be generated when the airbag is deployed, so the fabric used for the airbag needs to have good heat resistance to ensure that its strength and performance can be maintained in a high temperature environment. In order to ensure that the airbag can be inflated quickly and maintain pressure, the fabric used for the airbag needs to have low air permeability. In addition, the light, thin and soft fabric makes the airbag easy to fold, with a small volume after folding and good assembly performance, reducing the outward impact force of the bag during inflation to avoid harm to passengers. In some cases, the gram weight of the fabric used for the airbag can be less than 260g / m 2 , and / or the thickness of the fabric for the airbag may be less than 0.40 mm.

[0088] The fabric used for airbags can be made by special weaving methods to give the fabric sufficient strength and stability. Common weaving methods include plain weave, twill and satin. In addition, in order to improve the heat resistance, wear resistance and sealing of the fabric, the fabric can be coated. The coating material can be silicone, polyurethane, etc.

[0089] Naturally, the method according to the present application is not limited to fabrics for airbags, and can be applied to any fabric as required.

[0090] like Figure 1 As shown, the method 100 for biaxial tensile testing of fabric according to the present application may include the following steps:

[0091] Step S1: determining the breaking strength of a fabric sample when the fabric sample is stretched at a specified stretching speed along a first axial direction and a second axial direction orthogonal to each other;

[0092] Step S2: within the breaking strength, reciprocatingly stretch the fabric sample along a first axial direction and a second axial direction orthogonal to each other at a specified stretching speed, and record test data during the process of reciprocatingly stretching the fabric sample.

[0093] In the context of the present application, "biaxial stretching" is understood to mean that the specimen is simultaneously acted on along a first axial direction X and a second axial direction Y orthogonal to each other so that the specimen is stretched and elongated (see Figure 5). For example, when the airbag is deployed and performs buffering and restraining functions, the fabric of the airbag will be subjected to complex multi-directional forces. Compared with the uniaxial tensile test, the biaxial tensile test can better reflect the stress of the fabric in this process. Therefore, the biaxial tensile test is particularly suitable for studying fabrics used in airbags.

[0094] In some embodiments, one of the first axial direction X and the second axial direction Y may correspond to a warp direction of the fabric, and the other of the first axial direction X and the second axial direction Y may correspond to a weft direction of the fabric.

[0095] In some embodiments, Figure 5 As shown, the fabric sample 1 can be stretched along the first direction R1, the second direction R2, the third direction R3 and the fourth direction R4 respectively. The first direction R1 and the third direction R3 can be opposite to each other along the first axial direction X, and the second direction R2 and the fourth direction R4 can be opposite to each other along the second axial direction Y. Here, the stretching along the first direction R1 and the stretching along the third direction R3 can jointly form the stretching in the first axial direction X, and the stretching along the second direction R2 and the stretching along the fourth direction R4 can jointly form the stretching in the second axial direction Y. Advantageously, the stretching along the first direction R1, the second direction R2, the third direction R3 and the fourth direction R4 can be performed simultaneously.

[0096] In the scope of the present application, "stretching speed" can be understood as the speed at which the sample 1 is stretched and elongated in the first axial direction X and the second axial direction Y, respectively ("bilateral stretching speed"). The stretching speed can be set according to the test requirements, for example, the stretching speed can be selected according to the size of the fabric sample and the actual application conditions or target application conditions of the fabric. For example, for a fabric used for an airbag, the airbag filling time of the airbag can be about 40ms, and the maximum strain rate during the inflation of the airbag can be about 10 / s. On this basis, for example, for a sample with an effective length or effective area of ​​100mm×100mm, the prescribed stretching speed can be 1000mm / s in the first axial direction X and in the second axial direction Y, respectively. On this basis, for the stretching performed simultaneously along the first direction R1, the second direction R2, the third direction R3 and the fourth direction R4, the stretching speed ("unilateral stretching speed") in the first direction R1, the second direction R2, the third direction R3 and the fourth direction R4 can be 500mm / s, respectively.

[0097] In the method 100 proposed in the present application, the breaking strength F of the fabric sample 1 at a specified tensile speed can be determined in step S1. max . Breaking strength F maxIt can be the maximum force recorded when the sample 1 is broken during the tensile test under specified conditions. max It can reflect the tensile limit of sample 1.

[0098] It can be understood that since the fabric sample 1 has been stretched to break in step S1, the broken sample in step 1 is not suitable for use in step S2. Instead, a new sample 1 should be used in step S2. The sample 1 used in step S1 can be called a first sample. And the sample 1 used in step S2 can be called a second sample.

[0099] In step S2, the determined breaking strength F max The fabric sample 1 (second sample) is reciprocally stretched within 1000 seconds and the test data is recorded in the process. The test data may include at least one of force, displacement, stress and strain. The breaking strength F determined in step S1 max It can be used as a reference for the load level applied to the fabric sample 1 during reciprocating stretching. During reciprocating stretching, the peak force applied to the fabric sample 1 should be less than the breaking strength F max “Reciprocating stretching” can be understood as first stretching the fabric sample 1 to a certain extent, and then relaxing or unloading the sample 1. The stretching and unloading process can be repeated multiple times.

[0100] By reciprocatingly stretching the fabric sample 1 at a specified stretching speed, it is possible to simulate the situation where the fabric is subjected to repeated stress. Therefore, the recorded test data can well reflect the dynamic performance of the fabric. For fabrics used for airbags, force oscillations may occur, for example, when the airbag is inflated and deployed, and when the airbag is performing a cushioning effect, which can be reflected by reciprocatingly stretching the fabric sample. On the other hand, by comparing the results of multiple reciprocating tests, the fatigue performance and durability of the material can also be reflected. The small difference in the results of multiple reciprocating tests shows that the airbag material has better durability and can maintain good performance after multiple uses or long-term storage, which means that the airbag can function reliably throughout its service life, reducing safety hazards caused by material aging or performance degradation.

[0101] For fabrics used in airbags, the obtained test data can be used, for example, for modeling and simulation of airbag CAE, and provide a data basis for simulation results that are closer to actual working conditions.

[0102] In some embodiments, the method 100 may be implemented with the aid of a test apparatus. An exemplary embodiment of the test apparatus 2 will be described in detail below. Figures 9 to 12The test device 2 may include a clamp for clamping a sample of fabric. The sample 1 may be held by the clamp and acted on to achieve stretching and unloading of the sample 1.

[0103] In some embodiments, the method according to the present application can be implemented with the aid of the same test device. In this case, the broken first sample can be removed, for example, after step S1 and before step S2, and replaced with a new second sample. In other embodiments, step S1 and step S2 can be performed separately in two (preferably identical) test devices. In this case, the first sample can be set in one test device (for implementing step S1) and the second sample can be set in another test device (for implementing step S2).

[0104] Generally speaking, the test device should be able to apply load to the specimen at a specified rate simultaneously along a first axial direction X and a second axial direction Y that are orthogonal to each other. Therefore, the first axial direction X and the second axial direction Y can also be understood as two orthogonal machine axes of the test device. The clamp of the test device should be able to hold the specimen without allowing the specimen to slip, and should be designed to minimize damage to the specimen. The clamping surface of the clamp should be flat and smooth. When a flat clamp cannot prevent the specimen from slipping, a grooved clamp with texture can be used. Other auxiliary materials (including paper, leather, plastic and rubber) can be attached to the flat or textured clamp surface to improve the specimen clamping force.

[0105] In some embodiments, Figure 2 As shown, step S1, i.e., "determining the breaking strength of a fabric sample when it is stretched at a prescribed stretching speed along a first axial direction and a second axial direction orthogonal to each other" may include:

[0106] Step S11: providing a sample of the fabric (a first sample);

[0107] Step S12: clamping the sample with a clamp;

[0108] Step S13: stretching the sample at a specified stretching speed along a first axial direction X and a second axial direction Y orthogonal to each other in the plane where the sample is located until the sample breaks in any direction, and determining the breaking strength in the first axial direction and the breaking strength in the second axial direction respectively.

[0109] Specifically, in some embodiments, step S11 “providing a fabric sample” may include preparing a fabric sample 1 .

[0110] Figure 6An example of a specimen 1 suitable for use in a method for biaxial tensile testing of a fabric according to some embodiments of the present application is schematically shown. The specimen 1 may be a cross-shaped specimen 10. The cross-shaped specimen 10 may have an effective area 11 located in the middle and four clamping areas 12 extending from the effective area 11 in four directions. The clamping areas 12 may be used to be clamped or gripped by corresponding clamps. The two orthogonal directions of the cross-shaped specimen 10 may be parallel to the warp and weft directions of the fabric, respectively.

[0111] Figure 6 The cross-shaped test piece 10 shown may have a total length of 200 mm, where the total length may be understood as the length of two mutually opposite clamping regions 12 ( Figure 6 The upper clamping area 12 and the lower clamping area 12, or Figure 6 The distance between the free edges 121 of the clamping area 12 on the left and the clamping area 12 on the right, which are parallel to each other. Advantageously, the width of the free edge 121 of the clamping area 12 can be 80 mm, and the length of the clamping area 12 extending from the effective area 11 can be 50 mm. When clamping the specimen, the jaws of the clamp can at least substantially cover the width of the clamping area 12, so that the clamp can act on the cross-shaped specimen 10 over the entire width of the clamping area 12. Therefore, the width of the clamping area 12 can also be called the clamping width.

[0112] In addition, when gripping the specimen, the jaws of the gripper can be substantially aligned with the Figure 6 In particular, the effective clamping point of the clamp can be substantially located on the jaw line 122. The jaw line 122 can be located at the transition between the effective area 11 and the corresponding clamping area 12. When the effective clamping point of the clamp is aligned with the jaw line 122, the effective area 11 of the cross-shaped specimen 10 can be defined by the jaw line 122, and the distance between two mutually opposite jaw lines 122 can also be referred to as the gauge length. Figure 6 The cross-shaped specimen 11 shown has an effective area 11 with a size of 100 mm x 100 mm. When the cross-shaped specimen 10 is stretched by means of a clamp, substantially only the effective area 11 is stretched and deformed.

[0113] Advantageously, a chamfer, for example a chamfer with a radius of 10 mm, may be provided between two adjacent clamping areas 12 of the cross-shaped test specimen 10 in order to reduce the influence of stress concentration.

[0114] Within the scope of the present application, a tolerance of the above parameters within ±2 mm, preferably ±1 mm is acceptable.

[0115] Back to Figure 2In step S12, the sample 1 can be clamped by the first clamp, the second clamp, the third clamp and the fourth clamp respectively, for example Figure 6 The cross-shaped specimen 10 is shown. Figure 5 , the first clamp and the third clamp can be opposite to each other in the first axial direction X, and the second clamp and the fourth clamp can be opposite to each other in the second axial direction Y. The stretching in the first direction R1 can be caused by means of the first clamp, the stretching in the second direction R2 can be caused by means of the second clamp, the stretching in the third direction R3 can be caused by means of the third clamp, and the stretching in the fourth direction R4 can be caused by means of the fourth clamp. It is advantageous for uniformly stretching the sample 1 of the fabric that when clamping the sample 1 of the fabric, the jaws of the first clamp and the third clamp can be perpendicular to the first axial direction X, and the jaws of the second clamp and the fourth clamp can be perpendicular to the second axial direction Y. In addition, the warp centerline of the sample 1 can pass through the centerline of the first clamp and the third clamp, and the weft centerline of the sample 1 can pass through the centerline of the second clamp and the fourth clamp, thereby ensuring a reasonable force flow.

[0116] Advantageously, the sample 1 can be prepared and clamped in such a way that the warp and weft directions of the fabric, the two orthogonal directions of the sample 1 and the first axial direction X and the second axial direction Y of the stretching movement correspond one to one with each other.

[0117] In some embodiments, a pre-tension may be provided by the holder when the holder clamps the sample 1 , and the pre-tension may be 5N to 10N.

[0118] Subsequently, the breaking strength in the first axial direction X and the breaking strength in the second axial direction Y may be determined in step S13. The breaking strength may be determined, for example, by the tensile forces of the four clamps when the sample 1 breaks. Specifically, in some embodiments, the sample 1 of the fabric may be stretched synchronously at a prescribed stretching speed along the first direction R1, the second direction R2, the third direction R3, and the fourth direction R4, respectively, and when the fabric breaks in any of the four directions R1 to R4, the maximum value of the force occurring in the first direction R1, the second direction R2, the third direction R3, and the fourth direction R4 is taken as the unilateral breaking strength F in the direction. max1 To F max4 In other embodiments, the average value of the forces occurring in the first direction R1, the second direction R2, the third direction R3 and the fourth direction R4 for a period of time before the fabric breaks in any of the four directions R1 to R4, for example, 1-3 ms before the fabric breaks can be used as the single-sided breaking strength F in the direction. max1 To F max4 .

[0119] On this basis, the breaking strength F in the first axial direction X max1,3 It can be determined as the unilateral breaking strength F in the first direction R1 max1 And the single-sided breaking strength F in the third direction R3 max3 The average value of: The breaking strength F in the second axial direction Y max2,4 It can be determined as the unilateral breaking strength F in the second direction R2 max2 and the unilateral breaking strength F in the fourth direction R4 max4 The average value of:

[0120] It can be understood that since the fabric sample 1 (the first sample) has been stretched to break in step S13, in some embodiments, Figure 3 As shown, step S2, i.e., "stretching the fabric sample back and forth within the breaking strength along the first axial direction and the second axial direction orthogonal to each other at a specified stretching speed" may include: step S21: (re)providing a fabric sample 1 (a second sample); and step S22: clamping the new sample 1 with a clamp. Here, the new sample 1 provided in step S21 should be the same as the sample 1 provided in step S11, so the specific details of step S21 and step S22 can refer to the content already described in detail for steps S11 and S12 above, and therefore will not be repeated.

[0121] Subsequently, the sample 1 may be reciprocally stretched in step S23. Specifically, Figure 4 As shown, step S23 may include:

[0122] Loading step S231: stretching the sample 1 along the first axial direction X and the second axial direction Y at the prescribed tensile speed, for example, greater than or equal to 900 mm / s, preferably greater than or equal to 1000 mm / s, and particularly preferably at a bilateral tensile speed in the range of 1000 to 1200 mm / s until a first predetermined percentage of the determined breaking strength, for example, 70% to 95%, such as 80%; and

[0123] Unloading step S232: Unload the sample 1 along the first axial direction X and the second axial direction Y at the prescribed tensile speed, for example, greater than or equal to 900 mm / s, preferably greater than or equal to 1000 mm / s, and particularly preferably at a bilateral tensile speed in the range of 1000 to 1200 mm / s until a second predetermined percentage of the determined breaking strength, for example 5% to 20%, such as 10%.

[0124] Steps S231 and S232 may be repeated multiple times to simulate the dynamic working condition of the fabric.

[0125] In this case, the breaking strength F in the first axial direction X determined above can be used. max1,3 As the boundary conditions of the reciprocating tensile motion along the first direction R1 and the third direction R3, the breaking strength F in the second axial direction Y determined above can be used. max2,4 As the boundary condition of the reciprocating stretching motion along the second direction R2 and the fourth direction R4. In some embodiments, it can be provided in step S231 that the fabric sample 1 is stretched synchronously along the first direction R1, the second direction R2, the third direction R3 and the fourth direction R4 until the force in one of the first direction R1, the second direction R2, the third direction R3 and the fourth direction R4 reaches a first predetermined percentage of the breaking strength associated with the direction. Accordingly, the breaking strength F in the first axial direction X is max1,3 It can be configured in the first direction R1 and the third direction R3, and the breaking strength F in the second axial direction Y max2,4 It can be arranged in the second direction R2 and the fourth direction R4.

[0126] “Synchronously stretching the fabric sample 1” can be understood as that the stretching motions along the first direction R1, the second direction R2, the third direction R3 and the fourth direction R4 are performed synchronously, so that the force in one of the four directions (for example, the first direction R1) reaches the breaking strength corresponding to the direction (for example, the breaking strength F in the first axial direction X). max1,3 ), although the forces in the other three directions (e.g., the second direction R2, the third direction R3, and the fourth direction R4) have not yet reached the predetermined percentage of the rupture strengths assigned thereto, the tensile motions in these four directions still synchronously reach a state of speed being 0. To this end, for example, in step S1, not only the rupture strength of the sample 1 but also the stiffness curve of the sample 1 can be determined. The tensile motion in each direction can be controlled according to the stiffness curve.

[0127] Different from the process of stretching the sample 1 in step S231, in some embodiments, it can be provided in step 232 that the sample 1 of the fabric is unloaded synchronously along the first direction R1, the second direction R2, the third direction R3 and the fourth direction R4 until the forces in the first direction R1, the second direction R2, the third direction R3 and the fourth direction R4 simultaneously reach the second predetermined percentage of the breaking strength corresponding to the direction. In other words, the unloading movement along the first direction R1, the second direction R2, the third direction R3 and the fourth direction R4 is performed in such a way that the movement in each direction synchronously reaches a stationary state while reaching the second predetermined percentage of the breaking strength corresponding to the direction. After this, a predetermined time period, such as 50-1000ms, can be paused, and then the next stretching process according to step S231 is performed.

[0128] For example, it is particularly suitable for fabrics for airbags that the prescribed stretching speed is a bilateral stretching speed of 1000 mm / s, which can correspond to a unilateral stretching speed of 500 mm / s. It is advantageously provided that the prescribed stretching speed is reached within a displacement of 1 mm. The first predetermined percentage is 80%±5%, and the second predetermined percentage is 10%±5%. In addition, the above steps S231 and S232 can be repeated three times. This can well reflect the dynamic working conditions of the fabric of the airbag when in use.

[0129] Here, it is advantageous to use the force applied to the sample 1 as a reference to control the reciprocating stretching process of the fabric. Compared with the reference displacement control method, this can obtain better test repeatability and more accurate test data, especially for fabrics used for airbags. This is because the fabric used for airbags generally has a higher strength, and its breaking strength may reach more than 2500N / 5cm, while its thickness is relatively thin (generally less than 0.4mm). In the process of tensile testing such fabrics, it is inevitable that the sample will slip in the fixture. The reference displacement control method may be affected by different fixtures or personnel operating techniques, while the reference force control method according to the present application can advantageously avoid the influence of sample slippage, thereby having better repeatability and accuracy.

[0130] The test data recorded in the method according to the present application may involve various parameters reflecting the dynamic tensile properties of the sample. Advantageously, the test data may include force (e.g. applied to the sample by the clamp), displacement (e.g. of the clamp), speed (e.g. of the clamp), strain of the sample, etc. Specifically, the force may be measured, for example, by means of a force sensor of the test device, the displacement may be measured by means of a grating ruler of the test device, and the strain of the sample may be measured by means of a DIC measurement system. In some embodiments, strain measurement points 123 may be identified on the surface of the sample 1, particularly in the effective area 11 in the middle (see, for example Figure 6 ) in order to measure the strain of the specimen and determine the strain rate of the specimen with the help of the DIC measurement system. Figure 6 1 and 2 , relatively regularly distributed strain measurement points 123 are depicted. It should be understood that the identified strain measurement points 123 may be randomly distributed.

[0131] In some embodiments, the recorded test data may be processed and calculated to derive further output parameters.

[0132] Specifically, refer to Figure 5, the recorded force data may be the forces F1 to F4 applied to the specimen 1 by the corresponding grippers along the first direction R1, the second direction R2, the third direction R3, and the fourth direction R4, respectively. The average values ​​of the forces F1 and F3 applied to the specimen 1 along the first direction R1 and along the third direction R3 may be calculated as the average force in the first axial direction X: And the average values ​​of the forces F2 and F4 applied to the specimen 1 along the second direction R2 and along the fourth direction R4 can be calculated as the average force in the second axial direction Y: It is understood that the average force calculated here is not the average value of the force over a period of time, but the average value of the force in two directions opposite to each other at a certain moment. In the present application, this average value can be referred to as the average force in the corresponding axial direction (formed by the two directions opposite to each other).

[0133] Alternatively or additionally, the recorded displacement data may be the displacements X1 to X4 of the first, second, third and fourth grippers in the first, second, third and fourth directions R1, R2, R3 and R4, respectively. The sum of the displacement X1 of the first gripper in the first direction R1 and the displacement X1 of the third gripper in the third direction R3 may be calculated as the total displacement in the first axial direction X: X 1,3 =X1+X3, and the sum of the displacement X2 of the second clamper in the second direction R2 and the displacement X4 of the fourth clamper in the fourth direction R4 can be calculated as the total displacement in the second axial direction Y: X 2,4 =X2+X4.

[0134] Alternatively or additionally, the recorded speed data may be the speeds of the first clamp, the second clamp, the third clamp and the fourth clamp in the first direction R1, the second direction R2, the third direction R3 and the fourth direction R4, respectively. The sum of the speed of the first clamp in the first direction R1 and the speed of the third clamp in the third direction R3 may be calculated as the total stretching speed in the first axial direction X, and the sum of the speed of the second clamp in the second direction R2 and the speed of the fourth clamp in the fourth direction R4 may be calculated as the total stretching speed in the second axial direction Y.

[0135] Furthermore, in some embodiments, the engineering stress in the first axial direction X can be calculated based on the average force and the original cross-sectional area of ​​the specimen: And the engineering stress in the second axial direction Y: Wherein, L0 is the width of the sample perpendicular to the corresponding axial direction in the initial state, and d is the thickness of the sample in the initial state. The initial state can be understood as the state after the sample is clamped by the clamp but before it is stretched at the specified speed.

[0136] For example, for a test of a fabric for an airbag, the above measured and / or calculated test data may be exported to an airbag CAE, for example, so as to simulate and analyze the airbag of the airbag in the CAE.

[0137] It is understood that in some embodiments, in addition to the breaking strength, other test data, such as the various test data mentioned above in conjunction with step S2, may also be recorded and / or determined in addition in step S1. These test data may also be exported to the airbag CAE, for example, so as to simulate and analyze the airbag of the airbag in the CAE.

[0138] Combine the following Figures 9 to 12 An exemplary embodiment of a test apparatus 2 for biaxial tensile testing of fabrics according to the present application is described. Such a test apparatus 2 can be used to implement the method 100 for biaxial tensile testing of fabrics described above.

[0139] like Fig. 9 As shown, the test device 2 includes four stretching units 20, each of which includes a clamp 21 for clamping a sample of the fabric 1, a motor module 22 and a linear guide module 23 provided with the clamp 21. The clamp 21 can move along a straight line under the drive of the motor module 22 and under the guidance of the linear guide module 23, thereby stretching the clamped fabric 1. For the test device 2, there can be two mutually orthogonal virtual machine axes, which correspond to the first axial direction X and the second axial direction Y respectively. The first axial direction X and the second axial direction Y are located in the same plane. Therefore, the test device 2 can also be called a biaxial tester.

[0140] like Fig. 9 As shown in FIG. 1 , the first stretching unit 201 and the third stretching unit 203 of the four stretching units 20 are opposite to each other in the first axial direction X, and the second stretching unit 202 and the fourth stretching unit 204 of the four stretching units are opposite to each other in the second axial direction Y. The following can be achieved by means of the four stretching units 20: Figure 5 The test apparatus 2 is particularly suitable for performing high-speed dynamic biaxial tensile tests on fabrics for airbags. Advantageously, each stretching unit 20 can be configured so that the clamp 21 of the stretching unit 20 can be accelerated from rest to a speed of 500 mm / s within a displacement of 1 mm. In other words, when the clamp 21 of the stretching unit 20 is accelerated to a speed of 500 mm / s, the displacement it passes through is less than 1 mm.

[0141] The motor module 22 can be constructed as a linear motor module. An actuator with a linear motor as the core can advantageously achieve the requirements for acceleration level, dynamic control of power and displacement stroke. However, an actuator using a rotary motor may be relatively difficult to meet such high-speed and high-dynamic requirements due to the existence of a transmission mechanism. Fig.10 As shown, the connecting rod 221 of each linear motor module can be connected to the corresponding clamp 21 via the connecting member 24. Thus, the motor module 22 can drive the corresponding clamp 21 to move via the connecting rod and the connecting member 24. A force sensor 25 can be provided on the connecting member 24, and the force sensor 25 is configured to detect the force applied to the sample 1 by the corresponding stretching unit 20. In addition, a grating ruler (not shown) can be provided within the linear motor module. The corresponding displacement can be measured with the help of the grating ruler.

[0142] In order to achieve high-speed dynamic stretching of sample 1, in particular, to achieve a stretching speed of 500 mm / s and to accelerate to 500 mm / s within 1 mm (or within 4 ms), Figure 7 A possible acceleration process curve is shown. In this exemplary acceleration process, the acceleration can rise evenly to about 240 m / s within 0.8 ms. 2 The peak acceleration is reached and maintained until about 1.4ms. From 1.4ms onwards, the acceleration can gradually decrease from the peak acceleration. At about 3.2ms, the acceleration can drop to 0 and the acceleration process ends. Figure 7 It can be seen that at the moment of 3.2ms, the speed has reached 500mm / s, and the displacement at this time has not yet reached 1mm.

[0143] On this basis, the appropriate linear motor can be selected according to the following parameters:

[0144] Maximum acceleration: 30g;

[0145] Acceleration slope: 30g / ms;

[0146] Peak thrust ≥10KN;

[0147] Control force resolution ≤10N.

[0148] Figure 8A feasible stretching and unloading motion curve is shown by way of example. Here, during the stretching process, it can first be accelerated to about 500 mm / s and a uniform motion can be performed, and then a deceleration motion can be performed until the speed drops to 0 at time point T1. At time point T1, the clamp reaches the maximum displacement and the maximum force applied to the fabric appears here, which can be, for example, about 80% of the determined breaking strength. Due to the presence of acceleration, the unloading process can be directly entered after time point T1. Here, from time point T1, the speed can increase in the unloading direction opposite to the stretching direction, and decelerate again after a uniform motion until the speed reaches zero at time point T2. At time point T2, the force applied to the fabric can be, for example, about 10% of the determined breaking strength. Since the speed and acceleration at time point T2 are both 0, the clamp reaches a stationary state at time point T2. The clamp can, for example, start the next stretching motion again after maintaining a predetermined period of time in a stationary state.

[0149] Continue to refer to Fig.10 , each linear guide module 23 may include two slider-slide rail assemblies 231, and the two slider-slide rail assemblies 231 are respectively arranged on both sides of the corresponding connecting rod 221. The slide rail 232 in the slider-slide rail assembly 231 can be arranged in parallel with the corresponding connecting rod 221, and the slider 233 that cooperates with the slide rail can be fixedly connected to the corresponding connecting rod 221 via the connecting piece 24. The linear motion of the connecting rod 221 and the corresponding clamp 21 can be guided by means of these two slider-slide rail assemblies 231. Advantageously, the sliding pairs of the two slider-slide rail assemblies 231 are basically located in the same plane as the connecting rod 221 of the linear motor. As can be seen from the figure, the jaws 211 of each clamp 21 can be aligned with the motion direction defined by the corresponding linear guide module 23 (or the corresponding first axial direction X or the second axial direction Y, see Fig. 9 ) is essentially vertical.

[0150] In addition, if Fig.11As shown, the test device 2 may include a fixed frame 26. The fixed frame 26 may include four support structures 261, each of which may be respectively equipped with a stretching unit 20. The four support structures 261 may therefore be arranged in a cross shape. Each support structure 261 may include two first support plates 262 parallel to each other and a second support plate 263 connecting the two first support plates. The two first support plates 262 and the second support plate 263 may together form a substantially U-shaped shape. The slider-rail assembly 231 of the stretching unit 20 may be mounted on the first support plate 262. The motor module 22 may be held on the second support plate 263 via a thermal insulation pad 27. In addition, a reinforcement portion 264 may be constructed between two adjacent support structures 261, in particular between adjacent first support plates 262 of two adjacent support structures 261 that are 90° to each other.

[0151] Fig.12 The control block diagram of the test device 2 for biaxial tensile test of fabric according to some embodiments of the present application is schematically shown. The test device 2 may include a controller 28. The controller 28 may be connected to the computer 3 by signal to receive programs and target parameters, etc. The motor 222 of the motor module 22 may drive the various operating parts to move. Among them, the motor 222, especially the mover 223 of the linear motor 222, may be provided with a grating ruler 224, and the signal of the grating ruler 224 located on the mover 223 may be read by means of a laser reader to measure the displacement of the mover 223 (or the clamp 21 connected to the mover 223). The displacement signal from the grating ruler may be fed back to the controller 28. In addition, the force signal from the force sensor 25 may also be fed back to the controller 28. The controller 28 may be configured to send a control command to the driver 225 of the motor 222 to control the operation of the motor 222 according to the target parameters and the fed-back displacement signal and force signal. Thereby, a high-speed and high-dynamic stretching process is achieved.

[0152] The above describes exemplary embodiments according to the present application with reference to the accompanying drawings. However, it should be understood by those skilled in the art that various changes and modifications can be made to the exemplary embodiments of the present application without departing from the spirit and scope of the present application. All changes and modifications are included in the scope of protection of the present application as defined by the claims. The present application is defined by the appended claims, and the equivalents of these claims are also included.

Claims

1. A method (100) for biaxial tensile testing of fabrics, characterized in that: The method comprises the following steps: - stretching a first sample of the fabric along a first axial direction (X) and a second axial direction (Y) orthogonal to each other at a specified stretching speed until the first sample breaks, and determining the breaking strength; - reciprocatingly stretching the second sample of the fabric along a first axial direction and a second axial direction orthogonal to each other at a tensile force lower than the breaking strength and a specified stretching speed, and recording test data during the reciprocating stretching of the second sample of the fabric, wherein the reciprocating stretching includes stretching alternately performed in the first axial direction and the second axial direction simultaneously and relaxation immediately after the stretching; Preferably: the method is implemented using the same first sample and second sample; and / or the test data includes at least one of force, displacement, stress, and strain; and / or one of the first axial direction and the second axial direction corresponds to the warp direction of the fabric, and the other of the first axial direction and the second axial direction corresponds to the weft direction of the fabric.

2. The method according to claim 1, characterized in that Before stretching the first specimen of fabric: - providing a first sample of said fabric; - clamping the first sample with a first clamp, a second clamp, a third clamp and a fourth clamp, wherein the first clamp and the third clamp are opposite to each other in the first axial direction, and the second clamp and the fourth clamp are opposite to each other in the second axial direction; and / or Stretching the first specimen at a specified tensile speed along a first axial direction and a second axial direction orthogonal to each other in the plane where the first specimen is located until the first specimen breaks in any direction, and determining the breaking strength in the first axial direction and the breaking strength in the second axial direction respectively; and / or Before reciprocating stretching of the second sample of fabric: - providing a second sample of said fabric; - clamping the second sample with a first clamp, a second clamp, a third clamp and a fourth clamp, wherein the first clamp and the third clamp are opposite to each other in the first axial direction, and the second clamp and the fourth clamp are opposite to each other in the second axial direction; and / or When the second sample of the fabric is reciprocatedly stretched, the following loading and unloading steps are repeatedly and alternately performed: - in the loading step, stretching the second sample at the specified stretching speed along the first axial direction and the second axial direction orthogonal to each other in the plane where the second sample is located until the tensile force applied to the second sample reaches a first predetermined percentage of the breaking strength; - in the unloading step, relaxing the second specimen along the first axial direction and the second axial direction orthogonal to each other at the specified tensile speed until the tensile force applied to the second specimen is unloaded to a second predetermined percentage of the breaking strength; Preferably: the first predetermined percentage is 80%±5%, and / or the second predetermined percentage is 10%±5%; and / or the loading step and the unloading step are repeatedly and alternately implemented twice, three times or more times.

3. The method according to claim 1 or 2, characterized in that: The jaws of the first and third clamps are perpendicular to the first axial direction, and the jaws of the second and fourth clamps are perpendicular to the second axial direction; and / or The warp centerline of the first sample or the second sample passes through the centerline of the first clamp and the third clamp, and the weft centerline of the first sample or the second sample passes through the centerline of the second clamp and the fourth clamp; and / or When stretching the first or second sample of the fabric, the first or second sample of the fabric is stretched synchronously along a first direction (R1), a second direction (R2), a third direction (R3) and a fourth direction (R4) respectively by means of a first clamp, a second clamp, a third clamp and a fourth clamp, wherein the first direction and the third direction are opposite to each other along a first axial direction, and the second direction and the fourth direction are opposite to each other along a second axial direction, preferably: When determining the breaking strength: - respectively determine the maximum value of the tensile force in the first direction, the second direction, the third direction and the fourth direction as the unilateral breaking strength in the direction; - calculating the average value of the unilateral breaking strength in the first direction and in the third direction as the breaking strength in the first axial direction, and calculating the average value of the unilateral breaking strength in the second direction and in the fourth direction as the breaking strength in the second axial direction; and / or In the loading step, the second sample of the fabric is stretched synchronously along the first direction, the second direction, the third direction and the fourth direction until the force in one of the first direction, the second direction, the third direction and the fourth direction reaches a first predetermined percentage of the breaking strength associated with the direction; and / or In the unloading step, the second sample of the fabric is unloaded synchronously along the first direction, the second direction, the third direction and the fourth direction until the forces in the first direction, the second direction, the third direction and the fourth direction all reach a second predetermined percentage of the breaking strength corresponding to the direction.

4. The method according to any one of claims 1 to 3, characterized in that When the first sample or the second sample is clamped by the clamp, a pre-tension is provided by the clamp, preferably, the pre-tension is 5N to 10N; and / or The method includes marking strain measurement points on the surface of a second sample, and determining the strain and strain rate of the sample by a DIC measurement system when the second sample of the fabric is reciprocally stretched; and / or During the reciprocating stretching of the second sample of fabric, record: a force applied to the second specimen along the first direction, the second direction, the third direction and the fourth direction, and / or displacement of the first clamp, the second clamp, the third clamp and the fourth clamp in the first direction, the second direction, the third direction and the fourth direction respectively, and / or speeds of the first gripper, the second gripper, the third gripper, and the fourth gripper in the first direction, the second direction, the third direction, and the fourth direction, respectively; Preferably, the method comprises: Calculate the average value of the force applied to the second specimen along the first direction and along the third direction at a certain moment as the average force in the first axial direction at that moment, and calculate the average value of the force applied to the second specimen along the second direction and along the fourth direction at a certain moment as the average force in the second axial direction at that moment; and / or calculating the sum of the displacement of the first clamp in the first direction and the displacement of the third clamp in the third direction as the total displacement in the first axial direction, and calculating the sum of the displacement of the second clamp in the second direction and the displacement of the fourth clamp in the fourth direction as the total displacement in the second axial direction; and / or calculating the sum of the speed of the first gripper in the first direction and the speed of the third gripper in the third direction as the total stretching speed in the first axial direction, and calculating the sum of the speed of the second gripper in the second direction and the speed of the fourth gripper in the fourth direction as the total stretching speed in the second axial direction; Preferably, the method comprises: calculating the engineering stress in the first axial direction and the engineering stress in the second axial direction respectively according to the average force in the first axial direction, the average force in the second axial direction and the original cross-sectional area of ​​the second specimen.

5. The method according to any one of claims 1 to 4, characterized in that The first sample and / or the second sample of the fabric is a cross-shaped sample; and / or The gauge length of the cross-shaped specimen is 100 mm ± 1 mm; and / or The clamping area size of the cross-shaped specimen is 80±1 mm×50±1 mm; and / or There is a chamfer with a radius of 10 mm ± 1 mm between adjacent clamping areas of the cross-shaped specimen; and / or The two orthogonal directions of the cross-shaped specimen are respectively parallel to the warp direction and the weft direction of the fabric.

6. The method according to any one of claims 1 to 5, characterized in that The prescribed stretching speed is ≥900 mm / s in the first axial direction and in the second axial direction, respectively, preferably ≥1000 mm / s, particularly preferably in the range of 1000 to 1200 mm / s; preferably: the prescribed stretching speed is ≥450 mm / s, preferably ≥500 mm / s, particularly preferably in the range of 500 to 600 mm / s along the first direction, the second direction, the third direction and the fourth direction, respectively; and / or the prescribed stretching speed is reached within a displacement of 1 mm; and / or The fabric is a fabric for an airbag of a motor vehicle.

7. A test device (2) for biaxial tensile testing of fabrics, characterized in that: The test device comprises four stretching units (20), each of which comprises a clamp (21) for clamping a fabric sample, a motor module (22) for driving the clamp and a linear guide module (23) for linearly guiding the clamp. The first stretching unit and the third stretching unit of the four stretching units are opposite to each other in a first axial direction, and the second stretching unit and the fourth stretching unit of the four stretching units are opposite to each other in a second axial direction, and the first axial direction and the second axial direction are orthogonal to each other, Each stretching unit is configured so that the gripper of the stretching unit can move in the corresponding axial direction at a speed of at least 450 mm / s, preferably at least 500 mm / s; Preferably: Each stretching unit is configured such that its gripper can be accelerated from rest to a speed of at least 450 mm / s, preferably at least 500 mm / s within a displacement of 1 mm; and / or Each stretching unit comprises a force sensor (25) configured to detect a force applied by the corresponding stretching unit to the fabric sample; and / or The motor module is constructed as a linear motor module, and the linear guide module comprises a slider (233) fixedly connected to a connecting rod of the linear motor module and a slide rail (232) matched with the slider, and the connecting rod (221) of the linear motor module is connected to a clamp.

8. The test device according to claim 7, characterized in that: Each linear guide module comprises two slider-slideway assemblies (231), the two slider-slideway assemblies are respectively arranged on both sides of the connecting rod of the linear motor module, the connecting rod of the linear motor module is connected to the sliders of the two slider-slideway assemblies via a connecting member (24), preferably: The connecting rod of the linear motor module is connected to the clamp via the connecting piece; and / or The force sensor is arranged on the connecting member.

9. The test device according to claim 7 or 8, characterized in that: The stretching unit comprises a grating ruler (224) for recording the displacement of the gripper. Preferably, the test device comprises a controller (28) connected to the grating ruler, the force sensor and the driver (225) of the motor module by signals. The controller is configured to issue a control command to the driver according to the measurement signals from the grating ruler and the force sensor; and / or The linear motor module can achieve a maximum acceleration of 30g and / or an acceleration slope of at least 30g / ms and / or has a peak thrust greater than or equal to 10KN and / or has a control force resolution less than or equal to 10N; and / or The test device comprises a fixed frame (26), wherein the fixed frame comprises four support structures (261) arranged in a cross shape, each support structure is respectively equipped with a stretching unit, and the stretching unit is installed on the support structure. Preferably, the fixed frame has a reinforcement part (264) between two adjacent support structures.

10. The test device according to any one of claims 7 to 9, characterized in that The same test device or a plurality of similar test devices are jointly designed to carry out the method for biaxial tensile testing of textile fabrics according to any one of claims 1 to 6 .

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