A method for detecting the tensile properties of protective clothing

Abstract

The application discloses a kind of tensile property detection methods for protective clothing, it is related to fabric seam performance detection technical field.In the image under reference tension, respectively set up proximal reference section and distal reference section on both sides of seam, to establish common displacement reference;Gradually load and synchronously collect tension and image, linear extrapolate the axial displacement of each reference section to the same seam reference position, verify the consistency of proximal and distal extrapolated displacement on each side, obtain seam additional elongation;Unload to reference tension, after the strain of each reference section and seam additional elongation are stable, determine residual additional elongation, and adjust the next level loading increment accordingly.The method controls the loading process through spatial consistency determination and unloading recovery stability determination, reduces the interference of material non-uniform deformation and recovery process on seam tensile property detection.

Description

Technical Field

[0001] This invention relates to the field of protective clothing material performance testing technology, and in particular to a method for testing the tensile properties of protective clothing. Background Technology

[0002] The seams of protective clothing connect adjacent garment pieces, and these seams bear tensile loads under wearing activities and external pulling. When performing tensile tests on samples containing seams, the total elongation of the sample includes not only the elongation of the unsewn material but also the stitching adjustment, yarn slippage, and local deformation in the seam area. When the orientation, thickness, or constraint state of the materials on both sides of the seam differs, the deformation of the materials on both sides may also differ.

[0003] Existing tensile testing methods can acquire loads using tensile sensors and characterize specimen elongation through beam displacement or gauge length changes in images. For example, Chinese patent application CN113670811A discloses a tensile force and waterproofness testing device for protective clothing production; image measurement technology can also obtain local displacements by tracking marks on the specimen surface, providing a measurement method for deformation analysis of seam areas.

[0004] In joint local deformation detection, directly using the change in the distance between measuring points on both sides of the joint as the joint elongation will simultaneously account for the material deformation between the measuring points and the joint. When using a material reference segment for subtraction, if the reference segment has already undergone non-uniform deformation, extrapolation based on a single reference segment will also introduce bias; if only the extrapolation difference between the two sides is compared, the extrapolation biases on different sides may even cancel each other out. After unloading, material recovery and joint area recovery may occur at different time scales. Using the temporary stability of joint elongation as a condition for value selection can easily lead to residual elongation results while the material is still recovering, affecting the selection of subsequent loading.

[0005] Therefore, it is necessary to establish a correlation between the applicable state of local displacement extrapolation and the timing of value taking after unloading, so that the progressive tensile test can adjust the loading based on the joint deformation results that meet the requirements of the reference section under the same displacement reference. Summary of the Invention

[0006] This invention provides a method for testing the tensile properties of protective clothing. The residual additional elongation used for loading adjustment is determined by judging the spatial consistency of reference sections on both sides of the seam and by judging the stability of the strain of the reference sections and the additional elongation of the seam after unloading.

[0007] This invention adopts the following technical solution: a method for testing the tensile properties of protective clothing, comprising: clamping a sample containing a seam, setting a proximal reference segment and a distal reference segment on both sides of the seam respectively, and establishing a common displacement reference for each level using an image under a reference tensile force; loading the sample level by level and simultaneously acquiring the tensile force and images, extrapolating the axial displacement and axial displacement gradient of each reference segment to the same seam reference position to obtain the proximal extrapolation displacement and the distal extrapolation displacement; comparing the proximal extrapolation displacement and the distal extrapolation displacement side by side, and obtaining the additional seam elongation from the difference between the proximal extrapolation displacements on both sides when the consistency condition is met on all sides; otherwise, unloading and terminating the level loading; unloading to the reference tensile force at each level, and determining the residual additional elongation after the strain of each reference segment and the additional seam elongation meet the stability condition; adjusting the loading increment of the next level according to the residual additional elongation, and outputting the correspondence between the tensile force, the additional seam elongation, and the residual additional elongation.

[0008] Optionally, in the aforementioned displacement reference and reference segment setting scheme, the setting method of the proximal reference segment and the distal reference segment includes: along the tensile direction perpendicular to the joint, a first marking section, a second marking section, and a third marking section are sequentially set in the unstitched material area on each side of the joint; the distances of the first marking section, the second marking section, and the third marking section from the joint increase sequentially, the proximal reference segment is formed between the first marking section and the second marking section, and the distal reference segment is formed between the second marking section and the third marking section; the center position of the joint in the displacement reference is used as the joint reference position, and the material point identity of each marking section remains unchanged during the progressive loading and unloading process.

[0009] Optionally, in the aforementioned marking section setting scheme, the determination of the axial displacement gradient, the proximal extrapolation displacement, and the distal extrapolation displacement includes: determining the section displacement by the axial displacement of multiple material points on the same marking section in the image; for the proximal reference section and the distal reference section, dividing the difference in section displacement at both ends of the reference section by the initial axial coordinate difference of the corresponding marking section to obtain the axial displacement gradient, and using the axial displacement gradient as the strain of the reference section; and performing linear extrapolation based on the axial displacement gradient, the section displacement at one end of the reference section, and the directed distance along the initial tensile axis from that end to the joint reference position to obtain the corresponding proximal extrapolation displacement or the distal extrapolation displacement.

[0010] Optionally, in the aforementioned extrapolation displacement determination scheme, the determination method of the consistency condition includes: determining the extrapolation tolerance of the proximal extrapolation displacement and the distal extrapolation displacement on each side based on the cross-sectional displacement calibration tolerance, the reference segment length, and the distance from the reference segment to the joint reference position; the consistency condition is: the absolute value of the difference between the proximal extrapolation displacement and the distal extrapolation displacement on the same side is not greater than the sum of the two extrapolation tolerances on that side and the preset spatial tolerance; when any side does not meet the consistency condition, the increase of tension is stopped and the load is unloaded to the reference tension, and the corresponding loading level is marked as the reference segment inconsistency state.

[0011] Optionally, in the aforementioned consistency condition determination scheme, the determination method of the stability condition and the residual additional elongation includes: after unloading to the reference tensile force, calculating the range of strain of each reference segment and the range of additional elongation of the joint within a continuous sampling window; when the tensile force remains within the allowable deviation of the reference tensile force within the continuous sampling window, the consistency condition is continuously met on each side, the range of strain of each reference segment is not greater than the strain stability threshold, and the range of additional elongation of the joint is not greater than the elongation stability threshold, the stability condition is determined to be met; the average value of the additional elongation of the joint within the continuous sampling window where the stability condition is first met is taken as the residual additional elongation of the current loading stage.

[0012] Optionally, in the aforementioned stability condition determination scheme, the effectiveness control of the continuous sampling window includes: using the initial axial coordinates and material point correspondence when establishing the displacement reference in each loading stage; when image loss, material point mismatch, or tension exceeding the allowable deviation occurs within the continuous sampling window, the continuous sampling window is re-accumulated; when a continuous sampling window that meets the stability condition is not obtained within the preset longest recovery time, the progressive loading is terminated and the unstable state is output.

[0013] Optionally, in the aforementioned stability condition determination scheme, the method of adjusting the next level loading increment based on the residual additional elongation includes: setting a first residual threshold, a second residual threshold, a first loading increment, and a second loading increment, wherein the first residual threshold is less than the second residual threshold, and the second loading increment is less than the first loading increment; when the residual additional elongation is less than the first residual threshold, the first loading increment is selected; when the residual additional elongation is not less than the first residual threshold and is less than the second residual threshold, the second loading increment is selected; when the residual additional elongation is not less than the second residual threshold, the addition of loading levels is stopped; when the progressive loading has not terminated and the peak tensile force of the current loading level is lower than the preset tensile force upper limit, the smaller value among the sum of the peak tensile force of the current loading level and the selected loading increment and the preset tensile force upper limit is used as the target tensile force for the next level; when the peak tensile force of the current loading level reaches the preset tensile force upper limit, the addition of loading levels is stopped.

[0014] Optionally, the aforementioned loading increment adjustment scheme further includes determining the residual detection load range or critical resolution state based on measurement tolerance: using the second residual threshold as the residual detection threshold, and determining the measurement tolerance of the residual additional elongation based on the measurement tolerance of the proximal extrapolation displacement on both sides; before determining the target tensile force of the next stage, the following determination is performed: when the residual additional elongation of the current loading stage minus the corresponding measurement tolerance is not less than the residual detection threshold, and the residual additional elongation of the previous effective loading stage plus the corresponding measurement tolerance is less than the residual detection threshold, the range formed by the peak tensile force of the previous effective loading stage and the current loading stage is output as the residual detection load range under this loading process; when the residual additional elongation minus the corresponding measurement tolerance is less than the residual detection threshold, and the residual additional elongation plus the corresponding measurement tolerance is not less than the residual detection threshold, the loading stage is stopped and the critical resolution state is output.

[0015] Optionally, the aforementioned scheme for determining axial displacement gradient and extrapolated displacement further includes synchronous acquisition of image and tensile force and recognition of clamping slippage: image and tensile force are acquired using a common trigger signal, and the tensile force sampling value is time-aligned according to the midpoint of image exposure; simultaneously, the clamp mark at the clamping end and two sample marks adjacent to the clamping jaws are tracked, the axial displacement of the two sample marks is linearly extrapolated to the initial position of the clamping jaws, and compared with the axial displacement of the clamp mark to identify clamping slippage; when clamping slippage exceeding the preset slippage tolerance occurs, the sample is unloaded, the current loading process is terminated, and the clamping slippage status is output.

[0016] Optionally, in the aforementioned loading increment adjustment scheme, the loading adjustment method of multiple measuring bands includes: setting multiple mutually separated measuring bands along the length direction of the joint, with each measuring band having a proximal reference segment and a distal reference segment located on both sides of the joint; determining the additional elongation of the joint and the residual additional elongation of each measuring band respectively, and adjusting the next level loading increment with the maximum value of the residual additional elongation of each measuring band when all measuring bands meet the consistency condition and the stability condition within the same continuous sampling window; stopping the increase of tension and outputting the inconsistency state of the reference segment of the measuring band when any measuring band does not meet the consistency condition.

[0017] Compared with the prior art, the present invention uses a proximal reference segment and a distal reference segment on each side of the joint to push outwards to the same joint reference position. First, it determines whether the outward pushing results are consistent on each side, and then calculates the difference in proximal outward pushing displacement on both sides. When the difference in proximal and distal outward pushing displacement on the same side exceeds the range specified by the consistency criterion, even if the differences on both sides cancel each other out after subtraction, the inconsistency state of the reference segment on that side can still be identified through side-by-side determination, thus linking the calculation of the additional elongation of the joint with the current deformation state of the reference segment.

[0018] This invention maintains the same displacement reference in each loading stage and simultaneously examines the stability of strain and additional elongation at the joint in each reference segment after unloading to the reference tensile force. The residual additional elongation is determined by a window that satisfies the common stability condition, thus excluding value windows where the additional elongation at the joint has met the stability condition, but the strain change in the reference segment still exceeds the stability threshold. The residual additional elongation is further used to select subsequent loading increments, enabling a continuous detection process for determining measurement validity, restoring values, and controlling loading.

[0019] This invention can also combine measurement tolerance output with residual detection load range under a given loading process, and terminate the current loading process when clamping slippage, recovery instability or inconsistency of reference segment, retain the corresponding state and the obtained valid records, so as to facilitate the distinction between sample deformation results and changes in measurement conditions. Attached Figure Description

[0020] Figure 1 This is a schematic flowchart of the tensile performance testing method for protective clothing according to the present invention.

[0021] Figure 2 This is a schematic diagram showing the arrangement of the specimen, the marked cross section, and the near-end reference section and the far-end reference section of the present invention. Detailed Implementation

[0022] The invention will be further explained below in conjunction with the testing process and sample arrangement. The testing object of this method is a strip-shaped sample containing seams in protective clothing, with the tensile direction intersecting the length direction of the seam to be tested. The following example, with the tensile direction perpendicular to a straight seam, illustrates the process of obtaining the additional elongation and residual additional elongation of the seam under progressive loading and unloading conditions. The test results correspond to the sample at the specified sampling location, tensile direction, loading process, and recovery conditions.

[0023] like Figure 1 As shown, the testing process sequentially includes establishing a displacement reference, loading and image acquisition, consistency determination of side-by-side extrapolation, unloading and recovery determination, and selection of the next loading stage. The testing equipment includes a tensile testing machine with tensile force control capabilities, a tensile sensor, an image acquisition component, and a controller. The tensile testing machine clamps the specimen at both ends, and the tensile sensor is connected in series in the force path; the image acquisition component covers the joint, each reference segment, and the area adjacent to the clamps; the controller receives images and tensile force, and sends the target tensile force, loading rate, and unloading command to the testing machine.

[0024] The image acquisition component can employ two stereo-calibrated global shutter cameras. Spatial coordinates of surface material points are reconstructed through synchronized exposure, and the coordinate changes are then projected onto the initial stretching axis. The cameras are fixed to a support stably connected to the loading frame, and diffuse illumination is used to reduce glare. In cases where tolerances for planar deformation and out-of-plane displacement are met, a single camera calibrated on a planar scale can also be used. The stereo-calibrated working distance, field of view, and depth of field cover the predetermined loading range; if field of view shifts outward, occlusion occurs, or out-of-plane movement exceeds the calibration range, effective measurement for that stage is stopped and the load is unloaded.

[0025] like Figure 2 As shown, a specimen with a seam is clamped, and near-end and far-end reference segments are set on both sides of the seam, respectively. A common displacement reference for each stage is established using the image under the reference tension. The reference tension is used to straighten the specimen and keep the image markers traceable. Its value is selected within a low load range where the initial relaxation is eliminated and the reference segments remain intact. The load is first slowly applied to the reference tension, and the initial image is recorded after the tension and the material point position in the image stabilize within the set window. Subsequent unloading at each stage returns to the reference tension.

[0026] The seam area of ​​the specimen retains the original stitching and joint structure, while the clamping area is separated from the seam area. A specimen arrangement with a width of 50 mm, a total length of 200 mm, and a free clamping distance of 100 mm can be used, with the seam located in the middle of the free clamping distance. The clamping surface covers the entire width of the specimen, the seam is kept laterally extended, and the tensile axis passes through the centerline of the specimen. For different protective clothing materials, the reference section position is selected according to the actual seam width and free clamping distance, ensuring that all reference sections are located within the unstitched material area.

[0027] Along the stretching direction perpendicular to the joint, a first marking section, a second marking section, and a third marking section are sequentially provided in the unstitched material area on each side of the joint.

[0028] The distances from the seam to the first, second, and third marked sections increase sequentially. A proximal reference segment is formed between the first and second marked sections, and a distal reference segment is formed between the second and third marked sections. Adjacent marked sections are represented by identifiable material points spaced apart. Each section can have five material points within a measurement zone. These material points are determined by fiber texture or low-coverage speckle patterns attached to the material surface. The marks move with the material and do not cross the seam. The closest distance from the section to the seam is greater than half the width of the seam area and the width of its initial visible influence zone.

[0029] The center position of the joint within the displacement reference is used as the joint reference position, and the material point identity of each marked section remains unchanged during progressive loading and unloading. Initial material point numbers are used to maintain inter-frame correlation. Adjacent images can be used to improve tracking speed, but the current displacement is always restored to the same material point in the initial image; the initial coordinates of the joint reference position are retained during the restoration process.

[0030] Establish axial coordinates along the initial tension direction, setting the coordinates of the joint reference position to 0, with the positive axial direction pointing from the left clamp to the right clamp. Let 's' represent the joint side, where 's' can be L or R, representing the left or right side respectively; The markings indicate the section numbers from near to far on one side. Choose 1, 2, or 3; use This represents the axial coordinate of the cross-section in the initial image, in mm. The coordinates of the left cross-section are negative, and the coordinates of the right cross-section are positive. For ease of explanation, the coordinates of the three left cross-sections can be taken as -10 mm, -25 mm, and -40 mm, respectively, and the coordinates of the right cross-sections as 10 mm, 25 mm, and 40 mm, respectively.

[0031] The cross-sectional displacement is determined by the axial displacement of multiple material points on the same marked cross-section in the image. The cross-sectional displacement is obtained by averaging the axial displacements of matched material points on the same cross-section, and the initial axial coordinates are taken as the average of the initial coordinates of these material points. After the benchmark is established, the set of material points for each cross-section is fixed; if any point is mismatched, the frame is marked as invalid. The initial position of the material points is within a narrow cross-sectional band in the axial direction, and the influence of the cross-sectional bandwidth on the displacement averaging is included in the calibration tolerance.

[0032] Image scale and lens distortion are confirmed using a calibration plate, and the calculation of axial displacement from the image is verified using a rigid translation target with known displacement. The equivalent displacement caused by reference image error, current frame tracking error, exposure and tension alignment error, and the influence of axial coordinate error within the working range are all included in the cross-sectional displacement calibration tolerance. A maximum allowable range for reference segment strain and out-of-plane displacement is set; data exceeding this range is marked as exceeding the measurement range and the current loading process is terminated.

[0033] After establishing the baseline, the tensile force and images are acquired synchronously while loading is performed at each stage. The axial displacement and axial displacement gradient of each reference segment are extrapolated to the same joint baseline position to obtain the proximal and distal extrapolated displacements. The target tensile force at each stage is greater than the baseline tensile force. The controller increases the tensile force according to the set loading rate, maintains a preset peak dwell time near the target tensile force, and then unloads. Images, tensile force, and timestamps are continuously recorded during loading, peak dwell, and unloading. The total amount of all reference segments at that moment is calculated using the same frame image.

[0034] The system acquires images and tension using a common trigger signal, and aligns the tension sample values ​​with the midpoint of the image exposure. When the midpoint of the image exposure lies between two adjacent tension sampling times, linear interpolation of these two tension sample values ​​is used to obtain the tension at that moment in the image. Time correspondence is established through calibration using a common trigger pulse and a fixed trigger delay; if any adjacent tension sample value is missing near the exposure, or if the sampling interval exceeds a preset synchronization limit, the corresponding image frame is marked as invalid.

[0035] For example, the image sampling frequency can be set to 100 frames / s, the tensile force sampling frequency to 1000 times / s, and the exposure time to no more than 1 ms; the absolute values ​​of the loading and unloading rates can be set to 5 N / s, and the peak dwell time to 1 s. These parameters are fixed before testing and associated with the sample record. The upper limit of the tensile force is set based on the sensor range, clamping capacity, and the allowable detection range of the sample. Hardware limits and overload protection operate independently of image processing. In the event of sudden loss of load, exceeding the safe tensile force, or the travel limit, a safety stop is executed, and the effective load before termination is recorded; the next loading stage is not continued.

[0036] For the near-end reference segment and the far-end reference segment, the axial displacement gradient is obtained by dividing the difference in cross-sectional displacement at both ends of the reference segment by the initial axial coordinate difference of the corresponding marked cross-section, and the axial displacement gradient is used as the strain of the reference segment.

[0037] To convert the material deformation of each reference segment into a spatial change in axial displacement, the strain of the reference segment is calculated using the following formula:

[0038] ,

[0039] In the formula, For seams Side Each reference segment at time The axial displacement gradient, i.e. the axial engineering strain of the reference segment used in this method, is a dimensionless quantity. The reference segment number is 1, which indicates the near-end reference segment formed by the first and second marked sections, and 2, which indicates the far-end reference segment formed by the second and third marked sections. This represents the sampling time corresponding to the midpoint of the image exposure, measured in seconds. and The cross-sections at both ends of the reference segment are marked at time [time]. Axial displacement relative to the displacement reference, in mm; and These are the initial axial coordinates of the two cross-sections, in mm. Using the lateral definitions of left-side L and right-side R, and The section number of the corresponding endpoint is also specified. The sign of the retained coordinate difference is calculated, with the coordinate difference from near to far on the left side section being negative; the reference section length is the absolute value of the corresponding coordinate difference, and it is checked in advance that it is greater than the minimum allowable spacing.

[0040] Based on the axial displacement gradient, the cross-sectional displacement of one end of the reference segment, and the directed distance along the initial tension axis from that end to the joint reference position, linear extrapolation is performed to obtain the corresponding proximal extrapolation displacement or the distal extrapolation displacement.

[0041] To deduct the axial deformation of the material corresponding to the linear extension of the reference segment, the linear displacement relationship of each reference segment is extended to the position where the initial coordinate is 0. The extrapolated displacement is determined according to the following formula:

[0042] ,

[0043] In the formula, For seams Side Each reference segment at time The axial displacement obtained by extrapolating to the joint reference position, in mm; When the value is 1, it represents the proximal extrapolation displacement; when the value is 2, it represents the distal extrapolation displacement. Choose L or R. The sampling time. This represents the axial displacement of the reference segment at the end section closest to the joint, in mm. This represents the dimensionless axial displacement gradient of the reference segment. Let be the initial axial coordinate of the endpoint section, in mm. The initial coordinate of the joint reference position is 0, therefore the directed distance from this endpoint to the joint reference position is the negative of the initial coordinate of the endpoint; multiplying the displacement gradient by this directed distance and adding it to the endpoint displacement gives the above formula.

[0044] Both the proximal and distal extrapolated displacements represent the intercepts of the corresponding reference segment's displacement line at the same initial coordinates. For materials with the same axial displacement gradient on the same side, the two extrapolation results are identical; however, when local strain gradient changes occur, the extrapolation results for the two reference segments may diverge. The axial engineering strain of the reference segment is used for axial projection characterization in this test, and the allowable rotation and out-of-plane displacement ranges are determined by image calibration.

[0045] Based on the cross-sectional displacement calibration tolerance, the reference segment length, and the distance from the reference segment to the joint reference position, the extrapolation tolerances for the near-end and far-end extrapolation displacements on each side are determined. The calibration tolerances of the cross-sectional displacements at both ends of the reference segment can be used as error propagation inputs. For a given initial coordinate, the extrapolation displacement is equivalent to the weighted sum of the displacements at both ends: the weight closer to the joint endpoint is the ratio of the initial coordinate of the other endpoint to the difference between the initial coordinates of both ends; the weight farther from the joint endpoint is the ratio of the negative of the initial coordinate of the closer endpoint to the initial coordinate difference. The extrapolation tolerance of the reference segment is obtained by multiplying the absolute values ​​of the two weights by the corresponding cross-sectional displacement calibration tolerance and then summing them.

[0046] When the displacement calibration tolerances at both endpoints are the same, the extrapolation tolerance is the common tolerance multiplied by the ratio of the sum of the absolute values ​​of the initial coordinates of the two endpoints to the length of the reference segment. The effect of the initial coordinate error on the extrapolation is converted into displacement based on the maximum allowable strain and included in the endpoint calibration tolerance. When the coordinate error is large, the maximum deviation of the extrapolated displacement can also be calculated within the calibration interval of each coordinate and displacement as the extrapolation tolerance. Therefore, when the extrapolation distance is large or the reference segment is short, a correspondingly increased tolerance is adopted, and this tolerance is included in the subsequent residual detection judgment.

[0047] The consistency condition is as follows: the absolute value of the difference between the proximal extrapolation displacement and the distal extrapolation displacement on the same side is not greater than the sum of the two extrapolation tolerances on that side and the preset spatial tolerance. The preset spatial tolerance is an additional allowable deviation used when comparing the proximal extrapolation displacement and the distal extrapolation displacement on the same side. Before detection, this tolerance is set according to the minimum unresolved joint additional elongation and the reference segment spacing, and is kept consistent in the same group of samples. The joint additional elongation measurement tolerance determined according to the cross-sectional displacement calibration tolerance and the reference segment arrangement is less than the residual detection threshold to be used; when the device's measurement capability does not meet the resolution requirement, the imaging magnification or the reference segment spacing is adjusted and the initial benchmark is re-established.

[0048] The proximal extrapolation displacement is compared with the distal extrapolation displacement on each side. If the consistency condition is met on both sides, the additional seam elongation is obtained from the difference between the proximal extrapolation displacements on both sides; otherwise, the loading is unloaded and the progressive loading process is terminated. Independent consistency judgment results are formed on both sides. If the condition is not met on either side, no valid additional seam elongation is generated at that moment. This judgment is performed frame by frame during loading, peak dwell, and unloading. The same spatial tolerance is used during unloading recovery.

[0049] If either side fails to meet the consistency condition, the increase in tension is stopped and the load is unloaded to the reference tension, marking the corresponding loading level as a reference segment inconsistency state. This state is saved along with the specimen number, loading level number, time of occurrence, and inconsistency side; the already obtained valid loading level records remain unchanged, and the current loading level does not enter the next level selection driven by residual additional elongation. When rearranging the reference segment, a new specimen is used or a new and numbered testing process is started.

[0050] At the sampling time when the consistency condition is met on both the left and right sides, the additional elongation of the joint is determined according to the following formula:

[0051] ,

[0052] In the formula, For a moment Additional seam elongation, in mm; and These represent the displacements of the right and left proximal reference segments to the joint reference position at the same time, respectively, in mm; subscripts R and L indicate the side, and subscript 1 indicates the proximal reference segment. This represents the sampling time of the synchronized image. The additional seam elongation characterizes the additional axial deformation relative to the linear deformation extension state of the reference segments on both sides, including the deformation generated by the seam region and its adjacent local structures within this measurement scale. This quantity retains its sign and is used to construct the curve corresponding to the synchronized tensile force and the residual value after unloading.

[0053] For example, under the aforementioned cross-sectional coordinate arrangement, suppose that at a certain loading moment, the displacements of the three cross-sections on the left are -1.50 mm, -3.00 mm, and -4.50 mm, respectively, and those on the right are 1.70 mm, 3.50 mm, and 5.30 mm, respectively. Calculations show that the strain of the reference sections at the near and far ends on the left is 0.10 mm, and the two extrapolated displacements are both -0.50 mm; the strain of the corresponding reference sections on the right is 0.12 mm, and the two extrapolated displacements are both 0.50 mm; the additional elongation at the joint is 1.00 mm. The displacement difference between the first marked cross-sections on both sides is 3.20 mm, of which 2.20 mm is calculated from the distance of the displacement gradient of the reference section along the marked cross-section to the reference position.

[0054] The role of side-by-side comparison is further explained using spatial consistency determination. Keeping the aforementioned proximal section displacement unchanged, the displacement of the third marked section on the left is set to -4.59 mm, and the displacement of the third marked section on the right is set to 5.21 mm. Then, the extrapolated displacement of the left distal end is -0.35 mm, and the extrapolated displacement of the right distal end is 0.65 mm. At this point, the difference between the extrapolated displacements of the proximal ends on both sides and the difference between the extrapolated displacements of the distal ends on both sides are 1.00 mm, while the absolute value of the difference between the extrapolated displacements of the proximal and distal ends on both the left and right sides is 0.15 mm. If the upper limit of the tolerance used for consistency comparison on each side is 0.03 mm, then both sides are judged to be inconsistent with the reference segment, triggering unloading and terminating the step-by-step loading.

[0055] For example, if the calibration tolerance for end-section displacement, including the influence of coordinate errors, is set to 0.003 mm, then in arrangements with initial absolute coordinate values ​​of 10 mm, 25 mm, and 40 mm, the near-end extrapolation tolerance is 0.007 mm, and the far-end extrapolation tolerance is 0.013 mm. Taking a preset spatial tolerance of 0.010 mm, the sum of the two extrapolation tolerances on the same side and the preset spatial tolerance is 0.030 mm. The sum of the left and right near-end extrapolation tolerances is 0.014 mm, which can be used as a conservative measurement tolerance for the additional elongation of the joint and its average window value. The average window value uses this measurement tolerance to account for the common calibration errors at each sampling time.

[0056] After unloading to the reference tensile force at each stage, the residual additional elongation is determined after the strain of each reference segment and the additional elongation of the joint meet the stability conditions. The recovery timing begins when the tensile force first enters the allowable deviation range of the reference tensile force after unloading. Additionally, the return time is accumulated from the time the unloading command is issued: the difference between the peak tensile force of this stage and the reference tensile force is divided by the absolute value of the preset unloading rate, and then added to the allowable stabilization time determined based on the control loop response, to obtain the return timeout limit; if the reference tensile force is not entered within the allowable deviation range after reaching this limit, the loading control deviation status is output and the detection is terminated. The material points of each reference segment correspond to the initial reference, and the detection controller continuously calculates the strain of the four reference segments (left proximal end, left distal end, right proximal end, and right distal end) and the additional elongation of the joint.

[0057] After unloading to the reference tensile force, the range of strain for each reference segment and the range of additional elongation at the joint are calculated within a continuous sampling window. The range is the difference between the maximum and minimum values ​​of the quantity within the same continuous window. The range of strain for each reference segment is calculated separately, maintaining the side and reference segment number; the range of additional elongation at the joint is calculated independently. After acquiring a new image, the nearest consecutive image frame is selected backward according to the preset window duration, and the reference segments and additional elongation at the joint use a common start and end time. The frame timestamps are monotonically increasing, and the interval between adjacent frames is within the allowable range of the calibrated sampling interval; duplicate, out-of-order, or timestamps exceeding this range are treated as invalid samples.

[0058] The stability condition is determined to be met when the tensile force remains within the allowable deviation of the reference tensile force within the continuous sampling window, the consistency condition is continuously met on each side, the range of strain in each reference segment is not greater than the strain stability threshold, and the range of additional elongation at the joint is not greater than the elongation stability threshold. The allowable deviation of the reference tensile force is set based on the tensile force measurement tolerance and control accuracy; the strain stability threshold is set based on the reference segment length, displacement repeatability, and the amount of recovery variation to be excluded; the elongation stability threshold is set based on the short-term repeatability of the additional elongation at the joint and the required recovery resolution level. Continuous images of a constant displacement target can be used to determine the lower limit of measurement fluctuations for the reference segment strain and the additional elongation at the joint, respectively. The two stability thresholds are respectively higher than the corresponding lower limit of fluctuation; the elongation stability threshold is also less than the residual threshold interval used for load grading.

[0059] In a set of detection parameters, the reference tensile force can be set to 5 N, the allowable deviation to 0.2 N, the window duration to 2 s, the strain stability threshold to 0.0008, the elongation stability threshold to 0.008 mm, and the maximum recovery time to 120 s. At a sampling rate of 100 frames / s, the 2-s window, including start and end times, has 201 frames; both window coverage duration and image continuity are determined by timestamps. Stability determination uses a threshold determined by the short-term repeatability of the measurement system, while residual detection uses a measurement tolerance including calibration error.

[0060] The average value of the additional seam elongation within the continuous sampling window that first satisfies the stability condition is taken as the residual additional elongation of the current loading level.

[0061] To obtain the recovery value corresponding to the current load level, the arithmetic mean of the additional elongation of the effective seams in the first qualified window is calculated:

[0062] ,

[0063] In the formula, For the first Residual additional elongation of each loading stage, in mm; The load level number is incremented starting from the first peak load. The total number of valid sampling points within the continuous sampling window that first satisfies the stability condition is a positive integer. The sampling points within this window are numbered sequentially by time, ranging from 1 to... ; For the first The first load level in this window Each sampling time is measured in seconds (s). The additional elongation of the joint at this sampling moment is obtained from the difference in outward displacement of the proximal ends on both sides, in mm. The summation is applied to all sampling points of the qualified window. This residual additional elongation is the remaining axial additional deformation under the same reference tensile force and specified stability conditions; the recovery time and the start and end times of the window are saved during output.

[0064] In each loading stage, the initial axial coordinates and material point correspondences used when establishing the displacement reference are retained. At the beginning of each stage, the initial coordinates and initial image are preserved, and the current material point displacement is accumulated to the same reference. The residual additional elongation of the next stage includes the accumulated residual deformation formed by the previous loading process, and the same zero point is used in each loading stage.

[0065] When image loss, material point mismatch, or tension exceeding the allowable deviation occurs within the continuous sampling window, the continuous sampling window is re-accumulated. Window recounting starts from the first frame recovered from continuous valid sampling, and the longest recovery time is still accumulated from the start point of the current level's recovery time. Spatial consistency failure is a termination condition; simple frame loss, recoverable tracking interruption, or short-term tension deviation are window recounting conditions. If frame loss or material point mismatch occurs during loading or peak dwell phase, force application is immediately stopped and unloaded, and the current level is marked as invalid acquisition.

[0066] If a continuous sampling window satisfying the stability condition is not obtained within the preset longest recovery time, the progressive loading is terminated and the unstable state is output. The unstable state retains the peak tensile force and effective time period curve of this stage, but does not generate residual additional elongation for the next stage of control. When the longest recovery time is reached, if a qualified window that has completely ended no later than that time already exists, the earliest window is used; otherwise, the unstable state is output.

[0067] For example, when the displacements of the three sections on the left after unloading are -0.12 mm, -0.21 mm, and -0.30 mm, and those on the right are 0.14 mm, 0.26 mm, and 0.38 mm, the strains of the two reference sections on the left are both 0.006 mm, and the extrapolated displacements are both -0.06 mm; the strains of the two reference sections on the right are both 0.008 mm, and the extrapolated displacements are both 0.06 mm; the additional elongation at the joint is 0.12 mm. If all quantities within the continuous window satisfy the aforementioned stability conditions, then the average value of this window can be used to form the residual additional elongation.

[0068] If, within a certain window, the strains of the two reference segments on the left both change from 0.006 to 0.005, and the strains of the two reference segments on the right both change from 0.008 to 0.007, while the extrapolated displacements on both sides remain at -0.06 mm and 0.06 mm respectively, then although the additional elongation of the joint remains at 0.12 mm, the range of strains in each reference segment is still 0.001, which is greater than the strain stability threshold of 0.0008. Therefore, this window does not meet the stability condition. Subsequent windows only generate residual values ​​after the strains of each reference segment and the additional elongation of the joint have simultaneously stabilized.

[0069] After obtaining the effective residual value, the next loading increment is adjusted based on the residual additional elongation, outputting the correspondence between the tensile force, the joint additional elongation, and the residual additional elongation. The output record is associated with the sample number and loading level number, and each level includes the target tensile force, actual peak tensile force, loading rate, joint additional elongation curve, residual additional elongation, and measurement status. The controller selects the next target tensile force based on the most recently completed loading level record that simultaneously satisfies spatial consistency and stability recovery conditions.

[0070] A first residual threshold, a second residual threshold, a first loading increment, and a second loading increment are set, wherein the first residual threshold is less than the second residual threshold, and the second loading increment is less than the first loading increment. Both residual thresholds are length quantities, and both loading increments are tensile forces greater than 0. The first residual threshold is used to enter the fine loading zone, and the second residual threshold is used to stop increasing the loading level. The residual thresholds are determined based on the target additional elongation dimension of the joint to be detected, and the loading increments are determined based on the required peak tensile force resolution interval. The required force resolution interval should be greater than the combined tolerance of the tensile sensor and the control loop.

[0071] When the residual additional elongation is less than the first residual threshold, the first loading increment is selected; when the residual additional elongation is not less than the first residual threshold and is less than the second residual threshold, the second loading increment is selected; when the residual additional elongation is not less than the second residual threshold, the loading level is stopped. For example, the first residual threshold can be set to 0.10 mm, the second residual threshold to 0.20 mm, the first loading increment to 10 N, and the second loading increment to 5 N. When the residual additional elongation is less than 0, its original record is maintained, and it is processed as a branch less than the first residual threshold; the threshold comparison uses signed measurements.

[0072] When the progressive loading process has not terminated and the peak tensile force of the current loading stage is lower than the preset tensile force limit, the smaller of the peak tensile force of the current loading stage, the sum of the selected loading increment, and the preset tensile force limit is used as the target tensile force for the next stage. When the peak tensile force of the current loading stage reaches the preset tensile force limit, the addition of loading stages stops. The initial peak target tensile force is pre-selected between the reference tensile force and the preset tensile force limit, and subsequent stages are started after the previous loading stage completes the recovery determination. The actual peak tensile force is taken as the maximum value in the effective synchronous tensile force record of the current loading stage. When the deviation between the actual peak and the target tensile force exceeds the preset control allowable range, the loading stage is marked as a loading control deviation state and progressive loading stops, while the actual load record is retained. Reaching the limit includes situations where the limit is reached or slightly exceeded due to control tolerance; a hardware overload threshold separately limits dangerous overshoot.

[0073] The second residual threshold is used as the residual detection threshold, and the measurement tolerance of the residual additional elongation is determined based on the measurement tolerance of the proximal extrapolation displacement on both sides. The measurement tolerance of the proximal extrapolation displacement on both sides is obtained through the aforementioned endpoint tolerance propagation, and the sum of the two is taken as the measurement tolerance of the current residual additional elongation. For cases where the content difference within the window is different, the maximum value of the sum of the tolerances at each time point in the window is used. Tolerance coverage judgment is performed first, and then it is decided whether to directly classify according to the residual value or output the interval.

[0074] Before determining the target tensile force for the next stage, the following judgment is performed: if the residual additional elongation of the current loading stage minus the corresponding measurement tolerance is not less than the residual detection threshold, and the residual additional elongation of the previous effective loading stage plus the corresponding measurement tolerance is less than the residual detection threshold, then the interval formed by the peak tensile force of the previous effective loading stage and the current loading stage is output as the residual detection load interval for this loading process. This interval starts with the lower peak tensile force and closes with the upper peak tensile force, while simultaneously storing the measurement tolerances of the actual peak tensile forces of both stages. The load interval represents the detection range from below the residual detection threshold to reaching the threshold during the executed loading and recovery processes. The two endpoints of the residual detection load interval correspond to adjacent effective loading stages in the same uninterrupted loading process.

[0075] When the residual additional elongation minus the corresponding measurement tolerance is less than the residual detection threshold, and the residual elongation plus the corresponding measurement tolerance is not less than the residual detection threshold, the loading stage is stopped and the critical resolution state is output. When the tolerance range is generally lower than the residual detection threshold, the loading increment is selected according to the first residual threshold; when the tolerance range is generally at or above the residual detection threshold, the loading stage is stopped, and the residual detection load range is output when the previous effective loading stage meets the upper bound condition. If the detection condition is met in the first loading stage, the detection state of the first stage and its peak tensile force are taken as the detection result.

[0076] For example, suppose the actual peak tensile force of the current effective loading stage is 70 N, the residual additional elongation is 0.12 mm, the residual detection threshold is 0.20 mm, and the measurement tolerance is 0.014 mm. Its upper tolerance limit is 0.134 mm, which is still lower than the residual detection threshold. Since 0.12 mm is between the first and second residual thresholds, a loading increment of 5 N is selected. With a preset tensile force upper limit of 100 N, the target tensile force for the next stage is 75 N. If the actual peak force of the next stage is 75 N, and its effective residual additional elongation is 0.24 mm, then subtracting 0.014 mm from this value gives 0.226 mm. This allows us to output the residual detection load range greater than 70 N and not greater than 75 N during this loading process.

[0077] If the effective residual additional elongation at a certain stage is 0.19 mm, and the measurement tolerance remains 0.014 mm, then its tolerance range is 0.176 mm to 0.204 mm, covering the residual detection threshold of 0.20 mm. The critical resolution state is then output, and further loading stages are stopped. The detection results retain this tolerance range and peak tensile force, thus distinguishing the termination state when resolution is insufficient from the state where the detection threshold has been clearly reached.

[0078] Simultaneously, the clamp mark at the clamping end and two sample marks adjacent to the clamping jaws are tracked. The axial displacement of the two sample marks is linearly extrapolated to the initial position of the clamping jaws and compared with the axial displacement of the clamp mark to identify clamping slippage. The two sample marks are located in the free material region outside the same clamping jaw and have different initial axial coordinates. The clamp mark is fixed to the corresponding clamping body. The initial coordinates of the two sample marks and the initial coordinates of the clamping jaws are incorporated into the same axial coordinate system, and the extrapolated displacement of the sample at the initial position of the clamping jaws is obtained by extrapolating according to the reference segment. The absolute value of the difference between the extrapolated displacement and the corresponding clamp displacement is calculated for the left and right clamping jaws respectively, and compared with a preset slippage tolerance.

[0079] Two sample marks adjacent to the clamp can be set at positions 2 mm and 5 mm from the clamp, respectively, with their local material segments separated from the far-end reference segment. The preset slip tolerance includes mark displacement error, clamp position calibration error, and the error generated by extrapolation of the short material segment within the allowable strain range. The lower limit of the tolerance is determined by calibrating the known rigid displacement under the complete clamping state, and then the detection limit is set according to the allowable relative clamping displacement. When visible damage, mark mismatch, or local non-uniform deformation exceeding the calibration occurs near the clamp, the measurement of the clamping area is recorded as invalid and the detection is terminated.

[0080] When clamping slippage exceeding the preset slippage tolerance occurs, the sample is unloaded, the current loading process is terminated, and the clamping slippage status is output. This slippage determination compares the change in the position of the sample marker extrapolated to the clamp with the change in the clamp itself, distinguishing between the normal elongation of the free material near the clamp and the relative movement of the clamp within a given measurement tolerance. The clamping slippage status has priority for stopping loading; once it occurs, the previous valid level record is retained, and the current level residual value is not used as a basis for subsequent loading.

[0081] Multiple separate measuring bands are arranged along the length of the joint. Each measuring band contains a proximal reference segment and a distal reference segment located on both sides of the joint. For joints with deformation differences along the length direction, three measuring bands can be set within the sample width. The centers of each band are located, for example, at -15 mm, 0 mm, and 15 mm positions along the width direction. Each band can be 6 mm wide and is separated from each other, avoiding the cutting edge. Local axial coordinates are established for each band with the initial center at the corresponding position of the joint. The positive axial directions are the same, and the material point, initial coordinates, and tracking number are stored separately for each band.

[0082] The additional seam elongation and residual additional elongation of each measurement zone are determined separately. When all measurement zones meet the consistency and stability conditions within the same continuous sampling window, the maximum value of the residual additional elongation of each measurement zone is used to adjust the next level of loading increment. All measurement zones use the same image frame and the same start and end times of the recovery window. Each zone first independently passes the side-by-side consistency judgment, and then jointly passes the stability condition judgment. The additional seam elongation of each zone is calculated based on the proximal extrapolation displacement. The average value of each zone's residual additional elongation is obtained within the same initial common qualification window, and then the maximum value is selected. When performing residual detection in conjunction with measurement tolerance, the residual value of each zone plus the maximum value of its respective tolerance is used as the upper bound, and the residual value of each zone minus the maximum value of its respective tolerance is used as the lower bound. Based on this, it is determined whether the common loading process has reached the residual detection threshold.

[0083] If any measurement band fails to meet the consistency condition, the increase in tension is stopped and the inconsistency status of the reference segment of that measurement band is output. For recovery processes that are not terminated and only involve short-term sampling invalidation, all measurement bands are recalculated within a continuous window. If no common qualified window is found after the longest recovery time, an unstable recovery state is output, and the measurement band that did not meet the condition is indicated. The residual values ​​used for load control for each measurement band are all taken from the same recovery period.

[0084] The system assumes valid data acquisition, effective clamping, and a safe tensile force. If the reference segment is inconsistent, the system terminates. If the reference segment is consistent but the recovery window is not yet qualified, the system continues acquiring data while maintaining the baseline tensile force. Once the recovery window is qualified for the first time, the residual additional elongation is determined, and then the next loading stage is selected or the termination result is output. Termination results include reaching residual detection conditions, critical resolution, reaching the upper limit of tensile force, unstable recovery, inconsistent reference segment, clamping slippage, and invalid data acquisition. Each result is associated with the corresponding load record.

[0085] For specimens with different warp and weft directions, joint structures, or sampling locations, initial benchmarks were established and their orientation and structure were recorded. When comparing specimens in the same group, the same benchmark tension, reference segment arrangement, window conditions, and loading parameters were used. The load-joint additional elongation relationship, load-residual additional elongation relationship, and termination state of the effective loading level were reported to characterize the tensile deformation and recovery characteristics of the joint under the test conditions.

Claims

1. A method for testing the tensile properties of protective clothing, characterized in that, include: The specimen with the joint is clamped, and a near-end reference segment and a far-end reference segment are set on both sides of the joint respectively. The displacement reference for each level is established based on the image under the reference tensile force. Gradually load and synchronously acquire tensile force and images. Extrapolate the axial displacement and axial displacement gradient of each reference segment to the same joint reference position to obtain the proximal extrapolation displacement and the distal extrapolation displacement. The proximal extrapolation displacement and the distal extrapolation displacement are compared side by side. When the consistency condition is met on each side, the additional elongation of the joint is obtained from the difference between the proximal extrapolation displacements on both sides. Otherwise, the loading is unloaded and the step-by-step loading is terminated. After each stage of unloading to the reference tensile force, the residual additional elongation is determined after the strain of each reference segment and the additional elongation of the joint meet the stability conditions. The next level of loading increment is adjusted based on the residual additional elongation, and the correspondence between the output tensile force and the additional elongation of the joint and the residual additional elongation is determined.

2. The method for testing the tensile properties of protective clothing according to claim 1, characterized in that, The configuration methods for the proximal reference segment and the distal reference segment include: Along the stretching direction perpendicular to the seam, a first marking section, a second marking section, and a third marking section are sequentially provided in the unstitched material area on each side of the seam; The distances from the first marking section, the second marking section, and the third marking section to the joint increase sequentially. The proximal reference section is formed between the first marking section and the second marking section, and the distal reference section is formed between the second marking section and the third marking section. The center position of the joint in the displacement reference is taken as the joint reference position, and the material point identity of each marked section remains unchanged during the progressive loading and unloading process.

3. The method for testing the tensile properties of protective clothing according to claim 2, characterized in that, The determination methods for the axial displacement gradient, the proximal extrapolation displacement, and the distal extrapolation displacement include: The cross-sectional displacement is determined by the axial displacement of multiple material points on the same marked cross section in the image; For the near-end reference segment and the far-end reference segment, the axial displacement gradient is obtained by dividing the cross-sectional displacement difference at both ends of the reference segment by the initial axial coordinate difference of the corresponding marked cross-section, and the axial displacement gradient is used as the strain of the reference segment. Based on the axial displacement gradient, the cross-sectional displacement of one end of the reference segment, and the directed distance along the initial tension axis from that end to the joint reference position, linear extrapolation is performed to obtain the corresponding proximal extrapolation displacement or the distal extrapolation displacement.

4. The method for testing the tensile properties of protective clothing according to claim 3, characterized in that, The methods for determining the consistency conditions include: Based on the cross-sectional displacement calibration tolerance, the reference segment length, and the distance from the reference segment to the joint reference position, determine the extrapolation tolerance of the proximal extrapolation displacement and the distal extrapolation displacement on each side; The consistency condition is: The absolute value of the difference between the proximal extrapolation displacement and the distal extrapolation displacement on the same side is not greater than the sum of the two extrapolation tolerances and the preset spatial tolerance on that side; if either side does not meet the consistency condition, stop increasing the tension and unload to the reference tension, and mark the corresponding loading level as a reference segment inconsistency state.

5. The method for testing the tensile properties of protective clothing according to claim 4, characterized in that, The stability conditions and the method for determining the residual additional elongation include: After unloading to the reference tensile force, the range of strain of each reference segment and the range of additional elongation of the joint are calculated in the continuous sampling window. When the tensile force remains within the allowable deviation of the reference tensile force within the continuous sampling window, the consistency condition is continuously met on each side, the range of strain in each reference segment is not greater than the strain stability threshold, and the range of additional elongation of the joint is not greater than the elongation stability threshold, the stability condition is determined to be met. The average value of the additional seam elongation within the continuous sampling window that first satisfies the stability condition is taken as the residual additional elongation of the current loading level.

6. The method for testing the tensile properties of protective clothing according to claim 5, characterized in that, The validity control of the continuous sampling window includes: The initial axial coordinates and material point correspondences used when establishing the displacement reference are retained in each loading stage; When an image is missing, material point mismatch occurs, or tensile force exceeds the allowable deviation within the continuous sampling window, the continuous sampling window is re-accumulated. If a continuous sampling window that meets the stability condition is not obtained within the preset longest recovery time, the stepwise loading is terminated and the unstable state is output.

7. The method for testing the tensile properties of protective clothing according to claim 5, characterized in that, The methods for adjusting the next level of loading increment based on the residual additional elongation include: Set a first residual threshold, a second residual threshold, a first loading increment, and a second loading increment, wherein the first residual threshold is less than the second residual threshold, and the second loading increment is less than the first loading increment; When the residual additional elongation is less than the first residual threshold, the first loading increment is selected; When the residual additional elongation is not less than the first residual threshold and is less than the second residual threshold, the second loading increment is selected; When the residual additional elongation is not less than the second residual threshold, the loading stage is stopped. If the progressive loading has not terminated and the peak tensile force of the current loading level is lower than the preset tensile force limit, the smaller value among the sum of the peak tensile force of the current loading level, the selected loading increment, and the preset tensile force limit shall be used as the target tensile force for the next level. When the peak tensile force of the current loading stage reaches the preset tensile force limit, the addition of loading stages will stop.

8. The method for testing the tensile properties of protective clothing according to claim 7, characterized in that, This also includes determining the residual detection load range or critical resolution state based on measurement tolerance: The second residual threshold is used as the residual detection threshold, and the measurement tolerance of the residual additional elongation is determined based on the measurement tolerance of the proximal extrapolation displacement on both sides. Before determining the next level of target tension, the following criteria are applied: If the residual additional elongation of the current loading stage minus the corresponding measurement tolerance is not less than the residual detection threshold, and the residual additional elongation of the previous effective loading stage plus the corresponding measurement tolerance is less than the residual detection threshold, the interval formed by the peak tensile force of the previous effective loading stage and the current loading stage is output as the residual detection load interval under this loading process. When the residual additional elongation minus the corresponding measurement tolerance is less than the residual detection threshold, and the residual elongation plus the corresponding measurement tolerance is not less than the residual detection threshold, the loading stage is stopped and the critical resolution state is output.

9. The method for testing the tensile properties of protective clothing according to claim 3, characterized in that, It also includes simultaneous acquisition of images and tension, and recognition of clamping slippage: Images and tensile force are acquired using a common trigger signal, and the tensile force sampling values ​​are time-aligned according to the midpoint of the image exposure. Simultaneously track the clamp mark at the clamping end and two sample marks adjacent to the clamping opening, linearly extrapolate the axial displacement of the two sample marks to the initial position of the clamping opening, and compare it with the axial displacement of the clamp mark to identify clamping slippage; When clamping slippage occurs that exceeds the preset slippage tolerance, the sample is unloaded, the current loading process is terminated, and the clamping slippage status is output.

10. The method for testing the tensile properties of protective clothing according to claim 7, characterized in that, The loading adjustment methods for multiple measurement bands include: Multiple separate measuring bands are provided along the length of the joint, and each measuring band contains a proximal reference segment and a distal reference segment located on both sides of the joint; The additional seam elongation and the residual additional elongation of each measuring band are determined respectively. When all measuring bands meet the consistency condition and the stability condition within the same continuous sampling window, the maximum value of the residual additional elongation of each measuring band is used to adjust the next level of loading increment. If any measuring band fails to meet the consistency condition, stop increasing the tension and output the inconsistency status of the reference segment of that measuring band.

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