Fabric bendability testing method and device based on performance inversion correction

Abstract

The invention discloses a fabric bendability testing method and device based on performance inversion correction, and the method comprises the steps: cutting different tested fabrics into a plurality of sample strips, fixing one end of each sample strip at the edge of a sample carrying platform, and suspending the other end of each sample strip; the bending rigidities of the corresponding tested fabric in different directions are measured by collecting the extension lengths and the drooping heights of different sample strips, so that the bendability test of different fabrics can be completed in the same time period. Meanwhile, in the process of obtaining the bending rigidity, the bending rigidity is correspondingly updated by continuously adjusting the deflection of the free end, and the deflection of the free end is fed back according to the updated bending rigidity until an iteration termination condition is met; and the finally updated bending rigidity is used as the final bending rigidity of the measured fabric, so that the accuracy of measuring the bending rigidity of the measured fabric is improved.

Description

Technical Field

[0001] This invention belongs to the field of textile and apparel performance testing technology, specifically relating to a fabric bending test method and apparatus based on performance inversion correction. Background Technology

[0002] The bending properties of a fabric largely determine the aesthetics and comfort of clothing. Soft fabrics produce lightweight, flowing garments that are more comfortable to wear, while stiff fabrics create a rigid, shapely garment that is less comfortable. Therefore, accurately evaluating fabric bending properties is crucial for understanding material characteristics, achieving processing goals, and meeting usage requirements. Testing techniques and evaluation methods for fabric bending properties have attracted considerable attention, with various methods such as the inclined plane method, fabric style meter method, and pressure knife method already available, providing important support for improving fabric quality, performance, and processing.

[0003] Although various testing methods exist, including traditional methods such as the inclined plane method, the FAST2 bending tester, and the KES fabric style tester, as well as other methods such as the bow method, the cross method, the CHES-FY test method, the finite element simulation method, and the image method, each has its own limitations. Some methods can only measure the bending of one sample at a time, while others can obtain bending results in multiple directions in a single test, greatly improving testing efficiency. However, these methods also have some limitations. First, the shapes of the cut samples are too complex. Some are in the shape of a star, while others are in the shape of a sandwich containing five samples in each of the three directions of warp, weft, and oblique. Cutting the required fabric samples takes a lot of time, and the complex shape is prone to producing burrs, which increases the error. Second, according to GB / T 18318.1—2009 "Determination of bending properties of textiles - Part 1: Inclined plane method", the five samples of the fabric in the same direction should be sampled at different positions to reduce the error. However, in the above methods, the samples in the same direction are all cut together, and the sampling interval of the samples in the same direction is small, resulting in a high random error rate. This cannot meet the accuracy requirements of batch quality inspection, and the results mainly rely on experimental verification, lacking mechanical modeling of "geometric shape-mechanical stiffness". Summary of the Invention

[0004] The purpose of this invention is to provide a method and apparatus for testing the bending properties of fabrics based on performance inversion correction.

[0005] In a first aspect, the present invention provides a fabric bending property testing method based on performance inversion correction, the method comprising:

[0006] Cut multiple test fabrics into multiple sample strips along different directions; fix one end of all sample strips to the edge of the sample stage, and suspend the other end in the air; collect the extension length and droop height of different sample strips;

[0007] The initial bending stiffness is obtained based on the droop height and the extension length; the bending stiffness is then used in the current iteration process. Obtain the corresponding dimensionless bending angle And based on the dimensionless bending angle Update the free end deflection and obtain the free end deflection during the current iteration. If the free end deflection If the deviation from the sag height is calculated based on the free end deflection... For bending stiffness Make adjustments and repeat the above process; otherwise, use the bending stiffness in the current iteration process. As the final bending stiffness.

[0008] Preferably, the method for updating the free end deflection is as follows:

[0009]

[0010] in, The extension length.

[0011] As a preferred method, the dimensionless bending angle is as follows:

[0012]

[0013] in, Weight per unit length; The extension length.

[0014] Preferably, the free end deflection The criterion for determining deviation from the sag height is: free end deflection. The absolute value of the difference between the droop height and the sag height is greater than the preset threshold.

[0015] Preferably, the multiple sample strips are extended to the same length.

[0016] Preferably, the protrusion length is the horizontal distance from the midpoint of the outer edge of the sample strip to the edge of the sample stage; the drooping height is the vertical distance from the midpoint of the outer edge of the sample strip to the edge of the sample stage.

[0017] Secondly, the present invention provides a fabric bending test device based on performance inversion correction, which is used to perform the above-mentioned fabric bending test method; the fabric bending test device includes a sample stage, a data acquisition module and a processor; the sample stage is used to place different sample strips; the data acquisition module is used to acquire the extension length and sag height of the sample strips; the processor is used to acquire the corresponding bending stiffness based on the data acquired by the data acquisition module.

[0018] Preferably, the fabric bending test device also includes a background paper; the background paper is placed at the bottom of the sample stage; the background paper and the sample stage are both provided with scales; the data acquisition module includes a camera; the camera is used to collect the extension length and droop height of different sample strips in conjunction with the background paper and the scales on the sample stage.

[0019] Thirdly, the present invention provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the memory stores the computer program; and the processor executes the above-described fabric bending test method.

[0020] Fourthly, the present invention provides a readable storage medium storing a computer program; when the computer program is executed by a processor, it is used to implement the above-described fabric bending test method.

[0021] The beneficial effects of this invention are:

[0022] 1. This invention obtains the bending properties of fabrics based on the drooping height and extension length of the sample strip fixed on the sample stage. Its evaluation index is simple to extract, and the sample strip is easy to cut. The extension length and spacing of different sample strips can be adjusted arbitrarily as needed, and any sample can be combined to compare bending properties, making the differences in fabric bending properties clear at a glance, thus adapting to the special testing needs of industrial textiles (such as filter cloth and medical protective cloth).

[0023] 2. This invention obtains the bending stiffness of the tested fabric by inverting and correcting the free end deflection. Compared with traditional fabric bending test methods that rely solely on experimental verification, this invention constructs an integrated inversion model of "visual image-mechanical parameters". The error in testing the bending stiffness of different tested fabrics is small, thus enabling the output and comparison of the stiffness of different tested fabrics in a single test. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the fabric bending test device of the present invention.

[0025] Figure 2 This is a schematic diagram of the method for fixing the fabric under test in this invention.

[0026] Figure 3 This is a top view of the fabric being tested being fixed in multiple directions on the sample platform in this invention.

[0027] Figure 4 This is a schematic diagram of the longitudinal parameters of the sample strip in this invention.

[0028] Figure 5 This is a schematic diagram of the mechanical model and parameters of the cantilever beam in this invention.

[0029] Figure 6This is a schematic diagram of the fabric bending stiffness inversion process in this invention.

[0030] Figure 7 This is a schematic diagram illustrating the relationship between the extension length and the bending length in this invention.

[0031] Figure 8 This is a schematic diagram illustrating the relationship between the droop height and the bending length in this invention.

[0032] Figure 9 This is a schematic diagram illustrating the relationship between the projected area and the bending length in this invention.

[0033] Figure 10 This is a schematic diagram illustrating the relationship between the bending coefficient and the bending length in this invention.

[0034] Figure 11 This is a schematic diagram of the bending morphology of different experimental strips in this invention.

[0035] Figure 12 The diagram shows the bending shape of the 24# fabric in different directions in this invention; (a) is a schematic diagram of the bending shape in the 0° direction; (b) is a schematic diagram of the bending shape in the 90° direction; (c) is a schematic diagram of the bending shape in the 45° direction; and (d) is a schematic diagram of the bending shape in the 135° direction.

[0036] Figure 13 The diagram shows the bending shape of fabric #2 at different angles under the same ejection length in this invention; wherein, (a) is a diagram showing the bending shape at an angle of 0° to 75°; and (b) is a diagram showing the bending shape at an angle of 90° to 165°.

[0037] Figure 14 The diagram shows the bending shape of fabric #2 at the same angle with different extension lengths; where (a) is a bending shape diagram with an extension length of 2cm; and (b) is a bending shape diagram with an extension length of 3cm. Detailed Implementation

[0038] The present invention will be further described below with reference to the accompanying drawings.

[0039] Example 1

[0040] like Figure 1 and Figure 2As shown, a fabric bending property testing device based on performance inversion correction includes a sample stage, background paper, a data acquisition module, and a processor. The sample stage is a regular hexahedron with four crossbeams on its top surface for fixing the fabric under test. The four crossbeams are positioned at the edges of the top surface of the sample stage in different directions. Multiple sample strips cut from the fabric under test are evenly positioned on the four crossbeams with one end attached by paperclips, and the other end is suspended. The sample strips on the same crossbeam are arranged at equal intervals and fixed by pressure plates with the same shape as the top surface of the sample stage. The top surface and four sides of the sample stage are marked with graduations; the graduations on the top surface are used to limit the fixed position of the fabric under test, and the graduations on the sides are used to ensure that the effective length of the fabric protruding from the test is uniform. The graduations on the sides gradually increase from top to bottom, with the 0 graduation aligned with the top surface. The background paper is placed directly below the sample stage and has graduations along the crossbeams, with the 0 graduation aligned with the four edges of the bottom surface of the sample stage. The data acquisition module includes a camera; the camera measures the area of ​​the fabric being tested fixed on the crossbeam, and, in conjunction with the background paper and the scale on the sample stage, acquires the extension length and sag height of different sample strips. The data acquisition module obtains the extension length and sag height of different sample strips. The processor uses the data acquired by the data acquisition module to obtain the corresponding bending stiffness, thus completing the bending test of the fabric being tested.

[0041] In this embodiment, the camera resolution is 24 megapixels and the shooting distance is fixed at 50cm.

[0042] In this embodiment, the width of the sample strip is 2.5 cm and the effective length is 6 cm.

[0043] Example 2

[0044] A fabric bending property testing method based on performance inversion correction, using the fabric bending property testing device in Example 1; the fabric bending property testing method includes the following steps:

[0045] Step 1: Cut and fix the fabric to be tested.

[0046] like Figure 3As shown, multiple test fabrics are cut into multiple sample strips, with each test fabric corresponding to one or more sample strips. All sample strips are left to stand in a standard atmospheric environment for 24 hours. Before testing, the camera is calibrated and all shooting parameters are fixed. All sample strips are evenly arranged on the crossbeam of the sample stage using paperclips, with strips on the same crossbeam arranged at equal intervals. The position of the sample strips is adjusted to ensure that the extension length of all strips is consistent, and any excess length is hidden at the end of the crossbeam. All sample strips are then fixed to the top surface of the sample stage using pressure plates. After fixing the sample strips, they bend and droop under their own weight. The more flexible the sample strip, the greater its longitudinal droop and the smaller its transverse projected area. After the sample strip shape stabilizes for 30 seconds, a top-view image of the bent shape of the sample strip is taken using a camera.

[0047] In this embodiment, the extension length of all sample strips is 3cm to 4cm.

[0048] Step 2: Data Collection

[0049] Four parameters were collected for different sample strips, including extension length, sag height, projected area, and curvature coefficient. The collection methods are as follows:

[0050] 1) Extension length L (cm)

[0051] The extension length is the horizontal distance from the midpoint of the outer edge of the sample strip to the edge of the sample stage. The extension length can be read directly from the scale on the background paper. The larger the extension length, the stiffer and less prone to bending the fabric. In addition, to avoid errors caused by reading the extension length of multiple sample strips one by one, the extension length of each sample strip can also be read from the top view taken by the camera, ensuring that the extension length of all samples is read at the same time.

[0052] 2) Height H (cm)

[0053] like Figure 4 As shown, the sag height is the vertical distance from the midpoint of the outer edge of the sample strip to the edge of the sample stage. The sag height can be read directly from the scale on the side of the sample stage. The greater the sag height, the softer the fabric.

[0054] 3) Projected area A (cm²) 2 )

[0055] The projected area is the area formed by the bending and sagging of the sample strip. It is similar to the extended length; for fabrics that are not easily bent, the larger the projected area, the better. The method for extracting the projected area is as follows: A reference object (1cm x 1cm on each side) is placed on the pressure plate. The sample strip and the reference object are photographed using a camera, and the images are imported into image processing software such as AutoCAD or Photoshop to obtain the virtual projected area (in pixels) of the sample strip. 2) and the virtual area (pixels) of the reference object 2 Based on the actual area of ​​the reference object (1cm). 2 The actual projected area (cm²) of the sample strip is calculated by proportional conversion. 2 ).

[0056] 4) Bending coefficient I

[0057] The bending factor is the ratio of the extended length to the sag height. The bending factor is directly proportional to the stiffness of the fabric; that is, the larger the bending factor, the stiffer the fabric.

[0058] Of the four indicators above, except for the projected area A, the rest can be obtained directly from the scale on the fabric bending test device, or through simple calculations. All indicators are performed by the same operator, using the same device, and under the same environmental conditions to ensure repeatability.

[0059] In some embodiments, all four parameters of the test strip are acquired through images captured by a camera, ensuring that the four parameters of all test strips are collected at the same time.

[0060] Step 3: Obtain the bending stiffness of the fabric being tested.

[0061] Step 3-1. Obtain the initial bending stiffness (initial value based on small deformation theory).

[0062] like Figure 5 and Figure 6 As shown, based on the elastic solution of the cantilever beam under uniform self-weight, the relationship between the free end deflection δ and the initial bending stiffness is constructed as follows:

[0063]

[0064]

[0065] Where q is the self-weight per unit length (uniformly distributed load, unit: N / cm); The extended length; ρ is the initial bending stiffness, in N·cm; ρ is the density of the specimen strip, in g / cm³. 2 b is the width of the sample strip, 2.5 cm; Let the acceleration be gravitational force, and take it as 980 cm / s². 2 .

[0066] Using the droop height H as the free end deflection δ, the equation is... Substitute into equation (1) to obtain the initial bending stiffness. It is represented as:

[0067]

[0068] Equation (3) establishes new indices (ρ, b, L, δ) and bending stiffness. The quantitative correlation provides a theoretical formula for inverting mechanical properties through geometric parameters.

[0069] Step 3-2. Obtain the dimensionless bending angle

[0070] Based on the mechanical equilibrium equations of a cantilever beam under large deformation, the curvature equation of a cantilever beam subjected to a uniformly distributed self-weight q is constructed as follows:

[0071]

[0072] Where θ is the rotation angle of any section of the beam axis, in rad; s is the arc length of the beam axis after deformation, in cm; EI is the bending moment at section s, in cN·cm; EI is the bending stiffness, i.e., B.

[0073] For a section at a distance x from the fixed end, the bending moment Represented as:

[0074]

[0075] Introducing dimensionless coordinates It is represented as:

[0076]

[0077] dimensionless coordinates Substituting into equation (5), we get:

[0078]

[0079] When δ / L > 0.3, the error of the small deformation theory increases significantly. The specimen δ / L = 1.6–17 (far exceeding the small deformation limit) leads to deviations between theoretical and measured values. An elliptic integral is introduced for large deformation correction (referencing the large deformation theory of elastic beams). Under the large deformation correction, the relationship between the arc length element ds of the beam and the horizontal coordinate element dx and the vertical coordinate element dy is:

[0080]

[0081] The geometric relationship between the rotation angle θ and the displacement y in the deflection direction is constructed as follows:

[0082]

[0083] Substituting the above relationships (Equations (6) to (9)) into the curvature equation (Equation (4)) and rearranging, we get:

[0084]

[0085] Integrating over the free end (ξ=1, θ=θ0), considering the boundary conditions at the fixed end (ξ=0, θ=0), the integral result is:

[0086]

[0087] Calculate the integral over both sides separately, and obtain the integral results for both sides as follows:

[0088]

[0089]

[0090] Let ψ = 2θ0 (defined as a dimensionless bending angle), and use the trigonometric identities:

[0091] (14)

[0092] When θ0 is small:

[0093]

[0094] Simplifying, we obtain the formula for the dimensionless bending angle:

[0095]

[0096] The bending stiffness in the current iteration process Substituting into the formula for dimensionless bending angle, we can obtain the corresponding dimensionless bending angle. The dimensionless bending angle ψ is a core parameter describing the coupling relationship between the degree of bending and stiffness of a fabric under large deformation scenarios in cantilever beams. It is a dimensionless expression of the ratio of bending moment to stiffness. As a cantilever beam, the bending of the fabric under its own weight is essentially the result of the interaction between the bending moment generated by the uniformly distributed load and the fabric's own stiffness in resisting bending. A larger dimensionless bending angle ψ indicates a stronger bending effect from the load or weaker fabric stiffness, corresponding to a more pronounced fabric bending shape (more pronounced sag, shorter extension).

[0097] Step 3-3. Free End Deflection Update

[0098] Based on the dimensionless bending angle in the current iteration process Obtain the corresponding free end deflection Its expression is:

[0099]

[0100] Steps 3-4. If the sag height and the free end deflection... The absolute value of the difference is greater than 5%, i.e., |δ1-δ kIf |>5%, then according to the relationship that "B is inversely proportional to δ", the bending stiffness in the current iteration process is... Adjustments are made to obtain the bending stiffness in the next iteration. And repeat steps 3-2 and 3-3; otherwise, use the bending stiffness in the current iteration process. As the final bending stiffness.

[0101] In this embodiment, regarding bending stiffness The adjustment method is to adjust the bending stiffness. Adjust by 20%.

[0102] In some embodiments, the final bending stiffness is compared with the bending stiffness measured by the conventional method. If the absolute value of the difference between the final bending stiffness and the measured bending stiffness is greater than 5%, i.e. |B1-B|>5%, then the data is re-acquired to obtain and correct the bending stiffness.

[0103] Step 4: Method Evaluation

[0104] Step 4-1. Selecting a sample

[0105] Twenty-four typical woven fabrics with different structures, fiber compositions and bending properties were selected as research objects, and their detailed specifications are shown in Table 1.

[0106] Table 1 Fabric Specifications

[0107]

[0108]

[0109] Step 4-2. Inclined plane method for testing fabric bending properties

[0110] Referring to GB / T 18318.1—2009 "Determination of bending properties of textiles—Part 1: Inclined plane method", five sample strips were cut from the fabric in Table 1 along both the warp (0°) and weft (90°) directions. The bending length and bending stiffness were tested using a YG(B)022D fully automatic fabric stiffness tester, with ten test values ​​in each direction. The fabric bending test results are shown in Table 2. The four new indicators of this invention, as well as the bending length and bending stiffness in the inclined plane method, are all averages of the test results of five samples in each of the warp and weft directions, i.e., the average of ten test results. Furthermore, all indicators of this invention are obtained when the sample extension length is 4 cm.

[0111] Table 2 Results of Fabric Bending Test

[0112]

[0113] Step 4-3. Obtain the correlation between various indicators

[0114] To investigate whether the test results of this invention and the inclined plane method have a good correlation, the indicators in Table 2, namely the extension length, projected area, droop height and bending coefficient at 0° (longitude) and 90° (latitude), were correlated with the bending length and bending stiffness measured by the inclined plane method. The Pearson correlation coefficients are shown in Table 3.

[0115] Table 3. Correlation between indicators of the two methods

[0116]

[0117] Note: ** indicates a significant correlation at the 0.01 level (two-tailed); * indicates a significant correlation at the 0.05 level (two-tailed).

[0118] Table 3 shows that all four indicators are significantly correlated with bending length C and bending stiffness B in both the warp and weft directions. Furthermore, the correlation with bending length (all greater than 0.8) is greater than that with bending stiffness. This is because the bending stiffness in the inclined plane method considers the fabric's mass per unit area based on the bending length, while the four indicators are derived from the fabric's bending morphology and do not involve the fabric's mass per unit area. Table 3 also shows that the correlation between indicators in a certain direction and the inclined plane method indicators in that direction is greater than in other directions. For example, the correlation coefficient between the 0° extension length and the 0° bending length is greater than the correlation coefficient with 90°. This is because the bending behavior of fabrics exhibits significant anisotropy; the bending performance of the same fabric in the warp and weft directions may differ significantly.

[0119] Table 3 shows that, except for four data points without an asterisk (*), all others are significantly correlated at the 0.01 or 0.05 level. This can be explained by the fact that fabrics with stiff warp may also be stiff in the weft, with exceptions such as those using different fibers in the warp and weft, i.e., interwoven fabrics. Furthermore, it can be observed that the correlation coefficients between the extension length L and the bending length C and bending stiffness B are greater than those between the projected area A and the bending length C in the inclined plane method. This is because the bending length C in the inclined plane method uses length as a metric, and the bending stiffness B is also calculated based on the bending length C and considering the mass per unit area.

[0120] Step 4-4. Relationship between the inclined plane method and the indicators measured in this invention

[0121] Since the correlation between the various indicators and the bending length C in this invention is greater than that with the bending stiffness B, the relationship between the present invention and the indicators measured by the inclined plane method is further explored using the bending length C as an example. The method is as follows:

[0122] Step 4-4-1. As Figure 7 As shown, the extension length and bending length have a linear relationship, specifically: Y = 6.5502X1 + 11.855, R 2=0.8148. Where Y represents the bending length (mm) in the inclined plane method; X1 represents the extension length (cm) in this invention. The bending length C and the extension length L are positively correlated; that is, the greater the extension length of the fabric, the greater the bending length. Therefore, regardless of whether the inclined plane method or this invention is used, the stiffer the fabric, the less prone it is to bending deformation, and thus the larger the obtained index value.

[0123] Step 4-4-2. Figure 8 As shown, the relationship between the sag height and the bending length is a quadratic polynomial, specifically: Y = -5.285X2 2 +35.079 X2-27.433, R 2 =0.7953. Where, Y represents the bending length (mm) in the inclined plane method; X2 represents the sag height (cm) in this invention. The larger the sag height H, the smaller the bending length tends to be; that is, the softer the fabric, the greater the sag height and the smaller the bending length.

[0124] Step 4-4-3. (As shown) Figure 9 As shown, there is a positive linear correlation between the projected area and the bending length. Since the width of the sample strips is 2.5 cm, the projected area is also highly correlated with the extension length. However, obtaining the projected area is not as simple as obtaining the extension length, requiring image processing and formula conversion, while the extension length can be directly read from the testing device. Figure 7 R in 2 Greater than Figure 9 Therefore, using the extension length is more accurate.

[0125] Step 4-4-4. As Figure 10 As shown, the bending coefficient and bending length have a quadratic polynomial relationship, R 2 The bending coefficient is the largest among the four relationships, and the bending length also tends to increase with the increase of the bending coefficient. That is, the stiffer the fabric, the larger the bending coefficient and the bending length.

[0126] In summary, the four bending indices of this invention have a good correlation with the bending length of the inclined plane method. Considering both the degree of correlation and the convenience of extracting the indices, the best choice is the extension length, because it can be directly read from the top view taken by the camera using the scale on the testing device. This is convenient, avoids errors caused by camera distortion, and ensures the consistency of reading time for all samples.

[0127] Steps 4-5. Visualization of test results

[0128] like Figure 11 As shown, 23 different fabric bending shapes were captured using a camera. From Figure 11As can be seen, stiff fabrics are less prone to bending and deformation, resulting in larger projected areas. For example, the first sample from top to bottom on the left shows very little bending, leading to a large projected area. In contrast, soft fabrics produce smaller projected areas. Figure 11 The first fabric piece from left to right at the bottom has a very small projected area, almost coinciding with the edge of the pressure plate, indicating it is the most flexible. The image also shows that some fabrics exhibit twisting deformation after bending and drooping, such as the last sample from top to bottom on the right, which projects into a near-triangular shape. In summary, using this invention, the bending behavior of all samples can be clearly observed from the top-down view captured by the camera, thus visualizing the fabric's bending behavior. This is the greatest advantage of this method compared to other methods.

[0129] twenty four # The bending morphology of the fabric in the 0°, 90°, 45° and 135° directions is as follows: Figure 12 As shown. To more clearly illustrate the differences in shape, the image was taken at close range from four different directions, rather than as a single, unedited shot. From Figure 12 As can be seen, the warp (0°) sample strip is the stiffest, followed by 135°, 45° is relatively soft, and the weft (90°) is the softest. In addition, the differences between the five samples in the same direction are also obvious. For example, the second sample at 0° is the softest, the first sample at 90° is the stiffest, the third sample at 45° is the stiffest, and the first sample at 135° is the stiffest.

[0130] 2 # The bending morphology of the fabric samples at different angles (expansion length 4cm) is as follows: Figure 13 As shown. Because the woven fabric is symmetrical, only the range of 0° to 180° is considered. Since 0° and 180° are in the same direction, the diagram lists the bending forms from 0° to 165° at 15° intervals. Figure 13 (a) shows samples from 0° to 75° from left to right. Figure 13 (b) shows samples from left to right ranging from 90° to 165°. Figure 13 As can be seen from (a) in the figure, from 0° to 75°, the softness of the sample first increases and then decreases with the increase of angle. The 0° sample has the highest stiffness, the 30° and 45° samples are the softest, while the 75° sample has obvious torsion. Figure 13 As shown in (b), the 90° specimen is the stiffest, the 120° specimen is the softest, and the stiffness of the 165° specimen is slightly lower than that of the 120° specimen. In summary, the method of this invention can clearly reveal the differences in the bending properties of specimens at different angles.

[0131] 2 # The bending morphology of the fabric samples at different ejection lengths, from 0° to 75°, is as follows: Figure 14 .contrast Figure 14From (a) and 14(b), it can be seen that when the extension length is 3cm, the overall extension length of each sample is significantly less than 2cm. Combined with... Figure 14 (a) When the extension length is 4 cm, the extension length of each sample further decreases. Although there are differences in the curvature of the fabric samples at different angles when the extension length is 2 cm, the difference is not significant. As the extension length reaches 3 cm, the difference between the samples gradually becomes more obvious, and at 4 cm, the difference is very obvious. When the extension length continues to increase to 5 cm, the difference in curvature between the samples becomes less obvious again. This is because after reaching a certain extension length, the weight of the samples increases, and all samples cannot resist the effect of gravity and begin to bend and sag. Therefore, it can be seen that when using the method in this paper in practice, the extension length must be set reasonably; too large or too small a length will not reflect the difference.

[0132] In summary, this invention has significant visualization advantages, and can be used to compare the differences in the curvature of different fabrics, to evaluate the curvature of the same fabric at different angles, and to distinguish the curvature of fabrics at different push-out lengths.

[0133] Steps 4-6. Comparison of theoretical and measured values ​​of bending stiffness

[0134] The calculated bending stiffness of the 24 fabric pieces before correction is shown in Table 4, where the error is... The calculation formula is:

[0135]

[0136] in, This is the final bending stiffness; The bending stiffness (traditional bending stiffness) obtained by the inclined plane method.

[0137] Table 4 Comparison of errors before and after correction

[0138]

[0139] The bending stiffness in Table 4 represents the bending stiffness of different fabrics in the 0° direction. As can be seen from Table 4, the calculation error of the stiffness for the 24 fabrics after correction is significantly reduced, as analyzed below:

[0140] (1) The theoretical value of small deformation deviates greatly from the measured value (-87.6% to 180.0%). This is because the measured δ / L of the fabric being tested far exceeds the small deformation limit of 0.15, and the linear model cannot adapt to the geometric nonlinear deformation.

[0141] (2) After the large deformation correction, the error between the theoretical value and the measured value was significantly reduced, with most of them falling within ±5%, which verified the necessity of geometric nonlinear correction.

[0142] Steps 4-7. Combining theoretical formulas and experimental data, quantitatively analyze the physical meaning of the four indicators in this invention from the perspective of mechanical essence, thereby providing a theoretical basis for indicator selection.

[0143] (1) Extension length L: Geometric amplifier of stiffness and surface density

[0144] The expression for the extension length obtained by transforming equation (3) is:

[0145]

[0146] From equation (18), it can be seen that L and 1 / 4 Proportional to ρ 1 / 4 Inversely proportional, it's a "geometric amplifier" resulting from the combined effect of bending stiffness and areal density—for the same δ, stiffer fabrics (high B) or lightweight fabrics (low ρ) have a larger L. As shown in Table 2, 4 # Fabric B = 32.5 cN.cm, ρ = 142 g / m², L = 1.91 cm, is 19 # The fabric has a stiffness B of 12.8 cN·cm, a density of 198 g / m², and a length L of 0.29 cm, which is 6.6 times the stiffness of the fabric. This clearly reflects the sensitivity of L to differences in stiffness. Furthermore, L can be directly read using the scale of the testing device, eliminating the need for additional areal density measurement. This ease of operation is significantly superior to other indicators.

[0147] (2) Sag height δ: a direct representation of bending ease

[0148] The expression for obtaining the droop height by transforming equation (3) is as follows:

[0149] (19)

[0150] As shown in equation (19), δ is inversely proportional to B and directly proportional to ρ and b, directly reflecting the "bending ease" of the fabric under its own weight. That is, the δ of soft fabrics (low B) is greater. As shown in Table 2, 22 # Fabric B = 37.2 cN·cm, δ = 4.06 cm, less than 16 # The fabric has a stiffness of B = 8.2 cN·cm and a sag of δ = 4.95 cm, consistent with the measured pattern that "the lower the stiffness, the more pronounced the sag." However, the accuracy of the δ measurement is limited by the scale division and it needs to be used in conjunction with L to invert the stiffness; when used alone, it provides insufficient information.

[0151] (3) Bending coefficient I: a dimensionless index of relative stiffness

[0152] Define I = L / δ, and substitute it into equation (3) to get:

[0153] (20)

[0154] Equation (20) shows that I is a dimensionless index related to the intrinsic properties (B, ρ, b) of the fabric, directly proportional to B and inversely proportional to ρ and b. As shown in Table 2, 8 # Fabric B = 35.1 cN.cm, ρ = 144 g / m², I = 0.37, is 17 # Fabric B = 11.9 cN.cm, ρ = 254 g / m², I = 1.68 times 0.22, with "8 # The measured results for "the fabric is stiffer" are a perfect match. Furthermore, the wider the tested sample, the smaller I becomes. However, I needs to be calculated using L and δ, which involves more steps than L, and can only be used as an auxiliary evaluation indicator.

[0155] (4) Projected area A

[0156] Since the sample width b is fixed (2.5cm), the projected area A has an approximately linear relationship with L, A≈b×L. Its physical meaning is the same as L, but it needs to be converted through image processing (with a 1cm×1cm reference object to calibrate the pixel area), which is more complicated than L. Therefore, it is recommended as an auxiliary indicator.

[0157] Steps 4-8. Effective Extension Length

[0158] From the perspectives of "deformation response sensitivity" and "force-dominant mechanism", this paper systematically explains the underlying reasons why the fabric bending difference is most significant when the length is 3cm to 4cm.

[0159] 1. If the length is too short (<3cm): the absolute value of deflection is small, and the bending difference is masked by the "scale effect".

[0160] ① The deflection is at the "lower limit of measurement sensitivity".

[0161] For stiff fabrics (such as 4) # For twill cotton (E≈5GPa), when L=2cm, substituting into the formula yields δ≈0.15cm; for soft fabrics (such as 19... # Plain silk (E≈1GPa) has a deflection of δ≈0.75cm under the same L, and the difference in deflection between the two is only 0.6cm. However, the smallest division of the ruler in the experiment is 0.1cm, and the camera has a pixel error of 0.05cm. The difference of 0.6cm is in the "critical error range", which is difficult to distinguish accurately by observation or reading.

[0162] The slippage between yarns was not fully stimulated, and the structural differences could not be reflected.

[0163] The difference in fabric bending is essentially a combination of "yarn bending stiffness + inter-yarn slip resistance". Stiff fabrics have high yarn elastic modulus and high slip resistance, while soft fabrics have the opposite. However, when L < 3cm, the bending moment M generated by the fabric's own weight is M = qL. 2 If the ratio is too small, it is insufficient to overcome the initial static friction between the yarns. There is almost no relative slippage between the yarns, and only a small elastic deformation of the yarns themselves occurs. At this time, the bending deformation of different fabrics all exhibits a "linear elastic response". Structural differences (such as interlacing density and fiber type) cannot be fully exposed through deflection differences, resulting in "the bending shape of stiff and soft fabrics becoming similar".

[0164] II. When the ejection length is too long (>4cm): Gravity dominates deformation, and the "stiffness difference" is masked by "geometric nonlinearity".

[0165] When L>4cm, δ varies with L 4 The bending increases exponentially, at which point the fabric bending enters the "large deformation range" δ / L>0.5, requiring the introduction of Bisshopp elliptic integrals to correct the small deformation model. The "gravity-dominated deformation" mechanism weakens the influence of stiffness differences on deflection, specifically manifested as follows:

[0166] The sensitivity of deflection to stiffness decreases.

[0167] When L > 4 cm, large deformation causes "tension-bending coupling" of the fabric's neutral axis. At this point, δ is no longer solely determined by E, but is also strongly correlated with ψ. When L is sufficiently large (e.g., L = 5 cm, ψ approaches π / 2sinπ ≈ 1), cosπ ≈ 0, and δ ≈ L, meaning the deflection approaches the extension length itself, and its correlation with stiffness E decreases significantly. For example, when L = 5 cm, 4 # Fabric δ≈4.8cm, 19 # The fabric has a stiffness of δ≈4.9cm, which is only 0.1cm different from the other two. The difference in stiffness is completely masked by the "gravity-dominated ultimate deformation".

[0168] The overall instability modes of the fabric converge, and structural specificity disappears.

[0169] When L>4cm, most fabrics, especially those with a areal density>100g / m², will be suitable for this purpose. 2Heavy fabrics, due to their own weight exceeding the "critical bending moment," enter a state of "overall sag instability." At this point, the fabric no longer maintains a "cantilever beam-like linear bend" but instead exhibits an "arc-shaped overall sag," with yarn slippage reaching saturation (regardless of whether the fabric is stiff or soft, the yarns have already slipped sufficiently). This "convergence of instability modes" causes the differences in bending morphology among different fabrics to shift from "stiffness-dominated" to "area density-dominated," and the area density variation coefficient of the 24 fabrics is only 35% (far lower than the stiffness variation coefficient of 82%), ultimately resulting in "insignificant differences in bending."

[0170] III. Introducing the "Optimal Balance Range" for the Correlation between Deflection Sensitivity and Stiffness in Lengths of 3cm to 4cm

[0171] When L=3cm~4cm, the fabric bending is in the "critical range of transition from small deformation to large deformation", which avoids the "scale effect" of too short length and does not enter the "instability range" of too long length, becoming a sensitive range of bending difference.

[0172] In summary, this study established a quantitative correlation between the geometric indices of this invention and the bending stiffness of the fabric by using a cantilever beam model and large deformation correction theory, clarified the basis for index selection and the parameter optimization range, and provided systematic theoretical support for the engineering application of this invention.

[0173] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. All equivalent changes and modifications made within the scope of the claims of this invention are within the technical scope of this invention.

Claims

1. A fabric bending property testing method based on performance inversion correction, characterized in that: The method includes: Cut multiple test fabrics into multiple sample strips along different directions; fix one end of all sample strips to the edge of the sample stage, and suspend the other end in the air; collect the extension length and droop height of different sample strips; The initial bending stiffness is obtained based on the droop height and the extension length; the bending stiffness is then used in the current iteration process. Obtain the corresponding dimensionless bending angle And based on the dimensionless bending angle Update the free end deflection and obtain the free end deflection during the current iteration. If the free end deflection If the deviation from the sag height is calculated based on the free end deflection... For bending stiffness Make adjustments and repeat the above process; otherwise, use the bending stiffness in the current iteration process. As the final bending stiffness.

2. The fabric bending property testing method based on performance inversion correction according to claim 1, characterized in that: The method for updating the free end deflection is as follows: in, The extension length.

3. The fabric bending property testing method based on performance inversion correction according to claim 1, characterized in that: The method for obtaining the dimensionless bending angle is as follows: in, Weight per unit length; The extension length.

4. The fabric bending property testing method based on performance inversion correction according to claim 1, characterized in that: The free end deflection The criterion for determining deviation from the sag height is: free end deflection. The absolute value of the difference between the droop height and the sag height is greater than the preset threshold.

5. The fabric bending test method based on performance inversion correction according to claim 1, characterized in that: The multiple sample strips are extended to the same length.

6. The fabric bending test method based on performance inversion correction according to claim 1, characterized in that: The protrusion length is the horizontal distance from the midpoint of the outer edge of the sample strip to the edge of the sample stage; the drooping height is the vertical distance from the midpoint of the outer edge of the sample strip to the edge of the sample stage.

7. A fabric bending property testing device based on performance inversion correction, characterized in that: The fabric bending test device is used to perform the fabric bending test method based on performance inversion correction as described in claim 1. The fabric bending test device includes a sample stage, a data acquisition module, and a processor. The sample stage is used to place different sample strips. The data acquisition module is used to acquire the extension length and sag height of the sample strips. The processor is used to acquire the corresponding bending stiffness based on the data acquired by the data acquisition module.

8. A fabric bending property testing device based on performance inversion correction according to claim 7, characterized in that: It also includes background paper; the background paper is placed at the bottom of the sample stage; the background paper and the sample stage are both provided with scales; the data acquisition module includes a camera; the camera is used to collect the extension length and droop height of different sample strips in conjunction with the scales on the background paper and the sample stage.

9. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: The memory stores a computer program; the processor executes the fabric bending test method as described in any one of claims 1-6.

10. A readable storage medium storing a computer program; characterized in that: When the computer program is executed by the processor, it is used to implement the fabric bending test method as described in any one of claims 1-6.

Images