A method for detecting the tensile property of a vortex spun yarn

Abstract

The application discloses the technical field of yarn performance detection, and discloses a vortex spinning yarn tensile property detection method, which comprises the following steps: intercepting a main detection sample, pre-tensioning the main detection sample, and collecting an initial stress value; stretching the main detection sample, generating a stress change curve, collecting continuous stress data of a relaxation process when the sample is detected to be stretched to a preset strain, continuing to stretch to sample fracture, and recording the breaking strength; identifying a stress stable section, extracting stress characteristic parameters, and obtaining the breaking strength through coupling correction; calculating stress relaxation characteristic parameters based on the continuous stress data; preparing parallel detection samples, repeating the stretching process for each parallel detection sample, calculating the strength uniformity index through the numerical group of the parallel detection samples; and correlating and integrating through a detection evaluation system to form a comprehensive detection report. The application effectively offsets the detection error caused by non-stress factors, so that the corrected breaking strength obtained by calculation is closer to the real mechanical properties of the yarn.

Description

Technical Field

[0001] This manual relates to the field of yarn performance testing technology, and in particular to a method for testing the tensile properties of eddy current spun yarn. Background Technology

[0002] Jet-jet vortex spinning technology, with its ultra-high spinning efficiency, has become one of the mainstream processes in cotton spinning and blending. The vortex-spun yarns produced by this technology, due to their "core-cladding" binary structure, have advantages such as low spacing and hairiness, and uniform yarn evenness, making them widely used in downstream fields such as knitting and weaving. With the implementation of new industry standards, tensile performance indicators such as single yarn breaking strength and coefficient of variation of breaking strength have become the core basis for quality grading of vortex-spun yarns. The accuracy of tensile testing directly determines the market access and application reliability of yarn products, and is a key link in ensuring the stability of the quality of the industrial chain.

[0003] However, the core-cladding structure of vortex-spun yarns gives them stress relaxation characteristics that are significantly different from those of traditional ring-spun yarns: the core layer, consisting of approximately 30% untwisted or weakly twisted fibers, has weak bonding, and the outer spirally wrapped fibers offer limited constraint. During low-strain-rate stretching, relative slippage easily occurs between fibers, causing the yarn stress to continuously decrease over time, forming a distinct stress plateau. This characteristic differs significantly from the "uniform twist, tightly bonded fibers" structure of ring-spun yarns. Furthermore, current mainstream tensile testing technologies, which employ constant-speed stretching and static strength reading modes, cannot effectively distinguish between yarn breaking strength and the apparent strength weakened by relaxation.

[0004] The lack of adaptability of existing testing technologies has led to a series of quality control problems: the strength measurement deviation of pure cotton eddy yarn can reach 15%-20%, far exceeding the ±5% error range allowed by the standard; stress relaxation causes the CV value of the strength test to increase to 8%-12%, which is 2-3 times that of ring-spun yarn, and cannot provide reliable data support for the optimization of spinning process (such as nozzle air pressure adjustment and draft ratio matching). Summary of the Invention

[0005] This specification provides one or more embodiments of a method for testing the tensile properties of eddy current spun yarn, the method comprising:

[0006] S1. Cut a preset length of eddy-spun yarn as the main test sample, pre-stretch the main test sample to eliminate initial defects, and collect the initial stress value at the end of the pre-stretching load holding.

[0007] S2. The main test sample is stretched at a preset rate, and stress data and time data of the stretching process are collected simultaneously and stress change curve is generated. When the sample is detected to be stretched to a preset strain, the strain is kept constant to perform stress relaxation detection, and continuous stress data of the relaxation process is collected. Then the sample is stretched until it breaks and the fracture strength at the fracture moment is recorded.

[0008] S3. Based on the stress change curve, identify the stress stability segment, extract the average stress of the stability segment as the stress characteristic parameter, and perform coupling correction with the initial stress value and the apparent fracture strength. Calculate the fracture strength using the following formula:

[0009] ;

[0010] Where F is the corrected fracture strength; F' is the apparent fracture strength; σ is the initial stress value; σ is the mean stress value;

[0011] Based on the continuous stress data, calculate the stress relaxation characteristic parameters;

[0012] S4. Prepare parallel test samples. Repeat steps S1-S3 for each parallel test sample to obtain the fracture strength of each parallel sample and form a numerical group. After outlier judgment and elimination of the numerical group, obtain valid data. Calculate the coefficient of variation and extreme value difference based on the valid data, and then calculate the strength uniformity index based on the coefficient of variation and extreme value difference.

[0013] S5. The fracture strength, stress relaxation characteristic parameters and strength uniformity index are correlated and integrated into a detection and evaluation system composed of preset weights and qualified thresholds to form a comprehensive detection report containing original data and judgment results and output it.

[0014] In some embodiments, identifying the stress stability segment based on the stress change curve includes:

[0015] The stress variation curve is preprocessed to remove abnormal stress values ​​and corrected using linear interpolation;

[0016] Set stress fluctuation coefficient and stability duration threshold as judgment indicators; slide through the preprocessed curve with a preset step size, and mark the interval that continuously meets the fluctuation coefficient requirement and the duration target as candidate stable segments;

[0017] Calculate the boundary stress gradient of each candidate stable segment, and determine the candidate stable segment whose absolute value of the boundary stress gradient is less than a preset threshold as a stress stable segment.

[0018] In some embodiments, calculating the boundary stress gradient of each candidate stable segment includes:

[0019] Locate the starting and ending boundaries of the candidate stable segment, and extract four continuous stress data points before and after the starting boundary and four continuous stress data points before and after the ending boundary to form two sets of boundary data.

[0020] Calculate the absolute value of the stress difference between two adjacent points within each data set, and then calculate the maximum absolute value of the difference between the two data sets, denoted as . and ,in The absolute value of the maximum difference between the initial boundary data sets. The absolute value of the maximum difference between the terminating boundary data sets;

[0021] A corresponding qualified threshold is set according to a preset range of yarn breaking strength. The preset range and the corresponding threshold are pre-calibrated based on the mechanical characteristics of the yarn material and the detection accuracy requirements.

[0022] like and If all values ​​are less than or equal to their corresponding qualified threshold, then the boundary stress gradient of the candidate segment is determined to meet the requirements, and the current candidate segment is the stress-stable segment.

[0023] In some embodiments, the average stress value of the extracted stable segment is used as a stress characteristic parameter, and coupled with the initial stress value after pre-stretching and the fracture strength at the fracture moment for correction, the fracture strength is calculated as follows:

[0024] Extract stress characteristic parameters from the stress stability segment, the stress characteristic parameters including the average stress of the stress stability segment. ;

[0025] The fracture strength is corrected by using a coupling correction formula:

[0026] ;

[0027] in, This is the corrected fracture strength; The tensile strength at the moment of fracture is represented by k, where k is the elasticity correction factor corresponding to the yarn material. This represents the initial stress value.

[0028] In some embodiments, the continuous stress data includes the instantaneous stress at the relaxation initiation moment. The stress values ​​at each time point during the relaxation and load holding process, and the residual stress at the end of the load holding process. The stress relaxation characteristic parameters include relaxation rate, first relaxation time, and relaxation modulus; based on the continuous stress data, the stress relaxation characteristic parameters are calculated as follows:

[0029] The relaxation rate is calculated using the formula... Calculated;

[0030] Determine the first relaxation time, perform an exponential fit on the stress decay data to obtain the stress decay curve over time, and solve for the stress drop to the value in the curve. The corresponding time is the first relaxation time. If the load is not reached within the preset maintenance period... If the first relaxation time is greater than the preset load holding time, then the first relaxation time is greater than the preset load holding time.

[0031] Calculate the relaxation modulus E: based on the preset strain during stress relaxation testing. According to the formula calculate.

[0032] In some embodiments, the calculation of the strength uniformity index includes:

[0033] ;

[0034] Where: CV is the coefficient of variation, ∆F is the extreme value difference, μ is the mean of the effective data; α and β are the preset weighting coefficients and The preset weighting coefficient is pre-calibrated based on the key points of yarn quality control; U∈[0,1], its qualified threshold Pre-set based on downstream application requirements.

[0035] The beneficial effects of this invention are as follows:

[0036] Traditional testing methods often neglect the influence of initial stress after pre-stretching and stress stability during stretching on breaking strength, leading to significant deviations between test results and actual performance. This method eliminates initial yarn defects through pre-stretching, collects the initial stress value at the end of the load-bearing period, and accurately identifies the stress stability segment based on the stress change curve. The mean stress is extracted as a feature parameter, and a coupled correction model is constructed, incorporating initial stress, mean stress, and the representative breaking strength. This correction method fully considers the stress fluctuation characteristics of the yarn's initial state and during stretching, effectively offsetting detection errors caused by non-stress factors, making the calculated corrected breaking strength closer to the yarn's true mechanical properties. Attached Figure Description

[0037] This specification will be further described by way of exemplary embodiments, which will be described in detail with reference to the accompanying drawings. These embodiments are not limiting; in these embodiments, the same reference numerals denote the same structures, wherein:

[0038] Figure 1 This is an exemplary flowchart of a method for testing the tensile properties of eddy-spun yarn according to some embodiments of this specification. Detailed Implementation

[0039] To more clearly illustrate the technical solutions of the embodiments in this specification, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some examples or embodiments of this specification. For those skilled in the art, these drawings can be applied to other similar scenarios without creative effort. Unless obvious from the context or otherwise specified, the same reference numerals in the drawings represent the same structures or operations.

[0040] It should be understood that the terms "system," "unit," and / or "module" used herein are a method of distinguishing different components, elements, parts, sections, or assemblies at different levels. However, if other terms can achieve the same purpose, they may be replaced by other expressions.

[0041] Unless the context clearly indicates an exception, words such as "a," "an," "a kind," and / or "the" do not specifically refer to the singular and may also include the plural. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0042] Flowcharts are used in this specification to illustrate the operations performed by the system according to embodiments of this specification. It should be understood that the preceding or following operations are not necessarily performed in exact order. Instead, the steps can be processed in reverse order or simultaneously. Furthermore, other operations can be added to these processes, or one or more steps can be removed from them.

[0043] Example 1: Figure 1 This is an exemplary flowchart illustrating the tensile properties testing of eddy current spun yarns according to some embodiments of this specification. Figure 1 As shown, the method includes:

[0044] S1. Cut a preset length of eddy-spun yarn as the main test sample, pre-stretch the main test sample to eliminate initial defects, and collect the initial stress value at the end of the pre-stretching load holding.

[0045] The main test sample refers to a representative sample taken from the vortex-spun yarn package to be tested, used to complete the entire process of testing. Its test data provides a benchmark for subsequent parallel sample verification and comprehensive evaluation.

[0046] The preset length is the effective sample length pre-set based on the linear density of the eddy-spun yarn and the characteristics of the tensile testing machine clamps. It must meet the dual requirements of stable clamping without slippage and realistic mechanical response, which is different from the natural length of the yarn package.

[0047] The initial stress value refers to the stress value collected when the yarn reaches the pre-stretch state and is kept under a constant load (i.e., under a sustained load) during the pre-stretching process, and the stress data stabilizes. It reflects the baseline mechanical state of the yarn after pre-treatment.

[0048] Specifically, firstly, select three or more vortex-spun yarn packages to be tested (if it is a single package, select the beginning, middle and end of the package), with each position as a sampling unit, excluding yarn segments with surface contamination, broken ends or abnormal tension; secondly, use a yarn length measuring instrument (accuracy ±0.1mm) to cut the yarn. Before cutting, the yarn should be laid flat on the measuring platform with constant tension (tension value is 5%~8% of the yarn's breaking strength to avoid stretching deformation), and the cutting point should be marked according to the preset length (e.g., 250mm, 500mm, 500mm is preferred when the linear density is ≤10tex); finally, use sharp yarn-specific scissors to cut perpendicular to the yarn axis, the cut should be flat and free of fiber fuzz, and the cut sample should be placed in a constant temperature and humidity environment (temperature 20±2℃, relative humidity 65%±3%) for equilibration for 24 hours to eliminate the influence of ambient temperature and humidity on the yarn's mechanical properties.

[0049] The pre-stretching operation is performed using an electronic universal tensile testing machine. The core of this operation is standardized pre-treatment achieved through precise parameter control. The process consists of three parts: First, sample clamping: the two ends of the balanced main test sample are fixed to the upper and lower clamps of the testing machine, ensuring that the yarn axis coincides with the center line of the clamps. The clamping force is set to "no yarn slippage and no clamping damage" (usually adjusted according to linear density; for every 1 tex increase, the clamping force increases by 0.5~1N), avoiding uneven stress distribution caused by clamping deviations. Second, pre-stretching parameters are executed: the pre-stretching rate is set to 50~100 mm / min. (Too slow a rate results in low efficiency, while too fast a rate easily generates impact stress). The pre-stretching force is 10%~15% of the expected breaking strength of the yarn of this specification (the range is determined through preliminary tests). When the test machine force value reaches the preset pre-stretching force, the holding program is started, and the holding time is set to 30~60s to ensure that the internal fibers of the yarn are fully adjusted to a stable state. Third, the initial stress value is collected. Within 5s before the end of the holding period, 5 stress data points are continuously collected through the test machine data acquisition system, and their average value is calculated as the initial stress value after pre-stretching. After the collection is completed, the sample is kept in the clamped state to prepare for subsequent tensile testing.

[0050] It should be noted that if yarn slippage or breakage occurs during the pre-stretching process, the sample must be re-cut and pre-treated. The pre-stretching operation of the same main test sample must not be repeated. The initial stress value acquisition must be synchronized with the recording of ambient temperature and humidity and testing machine parameters to ensure data traceability.

[0051] S2. The main test sample is stretched at a preset rate, and stress data and time data of the stretching process are collected simultaneously and stress change curve is generated. When the sample is detected to be stretched to a preset strain, the strain is kept constant to perform stress relaxation detection, and continuous stress data of the relaxation process is collected. Then the sample is stretched until it breaks and the fracture strength at the fracture moment is recorded.

[0052] The preset rate refers to the moving rate of the testing machine fixture during the stretching process. It needs to be set in conjunction with the yarn linear density and testing standards to ensure that the stress data is stable and free from impact interference, which is different from the low rate in the pre-stretching stage.

[0053] The preset strain is a pre-calibrated stress relaxation trigger condition. The value must be lower than the yarn yield strain (usually 5%-10%) to avoid permanent deformation of the yarn affecting subsequent fracture performance testing.

[0054] The tensile strength refers to the maximum force value collected by the force sensor of the testing machine at the moment of yarn breakage. It directly reflects the yarn's breaking capacity and is the basic data for subsequent coupling correction.

[0055] S3. Based on the stress change curve, identify the stress stability segment (the segment with stress fluctuation amplitude ≤ ±5%), extract the average stress of the stability segment as the stress characteristic parameter, and perform coupling correction with the initial stress value and the apparent fracture strength. Calculate the fracture strength using the following formula:

[0056] ;

[0057] Where F is the corrected fracture strength; F' is the apparent fracture strength; σ is the initial stress value; σ is the mean stress value;

[0058] Based on the continuous stress data, calculate the stress relaxation characteristic parameters;

[0059] The stress stability segment refers to a continuous curve segment in the stress variation curve where the stress value fluctuates around a certain mean value with a fluctuation range of less than or equal to ±5%. This segment reflects the relatively balanced stress state of the fiber during the stretching process of eddy spinning yarn, providing a stable data basis for subsequent parameter extraction.

[0060] Stress relaxation characteristic parameters are quantitative indicators calculated based on continuous stress data during the stress relaxation stage. They are used to characterize the ability of yarn to reduce stress over time under constant strain and are core parameters for evaluating the long-term stability of yarn.

[0061] In some embodiments, identifying stress stability segments based on the stress change curve includes:

[0062] The stress variation curve is preprocessed to remove abnormal stress values ​​and corrected using linear interpolation;

[0063] Set stress fluctuation coefficient and stability duration threshold as judgment indicators; slide through the preprocessed curve with a preset step size, and mark the interval that continuously meets the fluctuation coefficient requirement and the duration target as candidate stable segments;

[0064] Calculate the boundary stress gradient of each candidate stable segment, and determine the candidate stable segment whose absolute value of the boundary stress gradient is less than a preset threshold as a stress stable segment.

[0065] Specifically, the collected stress change curves are first processed through data purification, the core purpose of which is to eliminate accidental interference during the detection process (such as instantaneous equipment fluctuations or brief yarn slippage). The Grubbs test (significance level α=0.05) is used to identify outliers in the stress data of the curves. When a stress value exceeds the range of "mean ± 3 standard deviations", it is identified as an outlier and removed. For the data gaps that appear after removing outliers, linear interpolation is used for correction—using two adjacent valid data points before and after the gap as a benchmark, a linear function is constructed to calculate the stress correction value at the gap location, ensuring that the pre-processed curve is continuous and smooth, and avoiding data breakpoints affecting subsequent identification accuracy.

[0066] To ensure the stability of the identification, a dual judgment index is set: the first is the stress fluctuation coefficient, which, considering the structural characteristics of eddy current spinning yarn, is typically set to a fluctuation amplitude of ≤±5% (i.e., fluctuation coefficient ≤5%, calculated based on the average stress value of a certain interval); the second is the stability duration threshold, which needs to cover at least 3 data sampling periods. Combining the sampling frequency of ≥10Hz mentioned earlier, a duration threshold of ≥0.3s is set to avoid misjudging instantaneous stress stability as a stable segment. Subsequently, the preprocessed curve is traversed by a preset step size (0.2s; too short a step size is inefficient, and too long a step size may miss local stable segments). Within each sliding window, the average stress value and fluctuation coefficient are calculated. Intervals where multiple consecutive windows meet the condition of "fluctuation coefficient ≤5%" and a total duration of ≥0.3s are marked as candidate stable segments.

[0067] In some embodiments, calculating the boundary stress gradient of each candidate stable segment includes:

[0068] Locate the starting and ending boundaries of the candidate stable segment, and extract four continuous stress data points before and after the starting boundary and four continuous stress data points before and after the ending boundary to form two sets of boundary data.

[0069] Calculate the absolute value of the stress difference between two adjacent points within each data set, and then calculate the maximum absolute value of the difference between the two data sets, denoted as . and ,in The absolute value of the maximum difference between the initial boundary data sets. The absolute value of the maximum difference between the terminating boundary data sets;

[0070] A corresponding qualified threshold is set according to a preset range of yarn breaking strength. The preset range and the corresponding threshold are pre-calibrated based on the mechanical characteristics of the yarn material and the detection accuracy requirements.

[0071] like and If all values ​​are less than or equal to their corresponding qualified threshold, then the boundary stress gradient of the candidate segment is determined to meet the requirements, and the current candidate segment is the stress-stable segment.

[0072] Boundary stress gradient refers to the rate of stress change before and after the start and end of a candidate stable segment. It is quantified by the stress values ​​of adjacent data points, reflecting the stress transition characteristics at the junction of stable and unstable segments, and is a key indicator for distinguishing between true stable segments and pseudo-stable segments.

[0073] In the preprocessed stress variation curve, the starting boundary (the position corresponding to the first data point of the stable segment) and the ending boundary (the position corresponding to the last data point of the stable segment) of the candidate stable segment are accurately located. Data is extracted around the two boundaries respectively: four continuous stress data points before and after the starting boundary (a total of eight points, covering the data of the four unstable segments before the boundary and the data of the four stable segments after the boundary), and four continuous stress data points before and after the ending boundary (a total of eight points, covering the data of the four stable segments before the boundary and the data of the four unstable segments after the boundary), forming the starting boundary data group and the ending boundary data group.

[0074] The two sets of boundary data are processed separately. The stress difference between two adjacent data points within each set is calculated, and the absolute value of the difference is taken. The maximum value is selected from all absolute values ​​of the differences in the initial boundary data set and denoted as ∆S1; the maximum value is selected from all absolute values ​​of the differences in the final boundary data set and denoted as ∆S2. The original difference data must be retained during the calculation process. If a sudden change in the difference occurs (e.g., a single difference exceeds three times the average of adjacent differences), the data must be verified to ensure it is a valid detection value, and equipment interference factors must be eliminated.

[0075] First, establish the correspondence between the preset range of yarn breaking strength and the acceptable threshold. This correspondence needs to be calibrated based on the yarn material. For example, for cotton eddy-spun yarn, the threshold corresponds to 0.8 cN for the breaking strength range of 50-100 cN and 1.2 cN for the breaking strength range of 100-150 cN. For polyester eddy-spun yarn, due to its stronger elasticity, the threshold can be increased by 20%-30% within the same strength range. Specific values ​​are determined through at least three sets of parallel pre-tests. After matching the breaking strength range and acceptable threshold of the candidate stable segment yarn, if... Less than or equal to Corresponding threshold and Less than or equal to If the boundary stress transition of a candidate stable segment is smooth and meets the requirements, the candidate segment is the final stress stable segment. If any difference exceeds the threshold, the curve needs to be traversed again to select a new candidate stable segment.

[0076] To eliminate pseudo-stable segments (such as the brief stable interval before a sudden change in the curve slope) by checking the boundary stress gradient: Locate the starting and ending boundaries of each candidate stable segment, extract three consecutive effective stress data points before and after each boundary, calculate the stress difference between adjacent data points, and thus obtain the stress gradient at the boundary (unit: cN / (tex·s)); Preset a gradient threshold (set in conjunction with the yarn stretching rate, usually 0.3~0.5cN / (tex·s)). If the absolute value of the stress gradient at the starting and ending boundaries of a candidate stable segment is less than the threshold, it indicates that the stress transition before and after the segment is smooth and there is no sudden change interference, and it is determined to be the final stress stable segment.

[0077] In some embodiments, the average stress of the stable segment is extracted as a stress characteristic parameter, and coupled with the initial stress value after pre-stretching and the fracture strength at the fracture moment for correction, the fracture strength is calculated to include:

[0078] Extract stress characteristic parameters from the stress stability segment, the stress characteristic parameters including the average stress of the stress stability segment. ;

[0079] The fracture strength is corrected by using a coupling correction formula:

[0080] ;

[0081] in, This is the corrected fracture strength; To represent breaking strength; k is the elasticity correction coefficient corresponding to the yarn material; This represents the initial stress value.

[0082] Stress characteristic parameters are quantitative indicators extracted from the stress stability segment that characterize the stable stress state of the yarn. In this embodiment, the average stress of the stability segment is used. The core parameter reflects the level of equilibrium of fiber stress during yarn stretching.

[0083] After completing the yarn tensile testing and generating the stress change curve, the effective stress stability segment is determined through data preprocessing (outlier removal and smoothing correction) and stability segment identification. Then, all continuous stress data within this stability segment are extracted, and the average stress is calculated using the arithmetic mean method. (Unit: cN / tex) Before calculation, the data integrity must be verified again to remove outliers caused by equipment interference and ensure accuracy. Representativeness.

[0084] Two core sets of basic data were retrieved: one was the initial stress value collected after the pre-stretching process was completed. (Unit: cN / tex) reflects the baseline stress state of the yarn after pretreatment; secondly, it reflects the tensile strength directly collected by the testing equipment at the moment the yarn breaks. (Unit: cN), this data serves as the original basis for subsequent correction calculations.

[0085] stress characteristic parameters Initial stress value Exhibiting fracture strength And the pre-calibrated yarn material elasticity correction coefficient k, substituted into the coupling correction formula, yields the accurate breaking strength, as follows:

[0086] Coupling correction formula: ;

[0087] F is the corrected breaking strength (unit: cN), which is the core indicator used to evaluate the breaking performance of yarn; the k value needs to be calibrated through pre-tests for specific yarn materials (e.g., the k value of pure cotton eddy yarn is set in combination with the elastic characteristics of cotton fibers, and the k value of polyester eddy yarn is matched with its high elastic recovery characteristics). It is the average of the initial stress and the average stress in the stable section, used to comprehensively characterize the stress benchmark level of the yarn throughout the entire testing process and achieve error compensation.

[0088] In some embodiments, the continuous stress data includes the instantaneous stress at the relaxation initiation moment. The stress values ​​at each time point during the relaxation and load holding process, and the residual stress at the end of the load holding process. The stress relaxation characteristic parameters include relaxation rate, first relaxation time, and relaxation modulus; based on the continuous stress data, the stress relaxation characteristic parameters are calculated as follows:

[0089] The relaxation rate is calculated using the formula... Calculated;

[0090] Determine the first relaxation time, perform an exponential fit on the stress decay data to obtain the stress decay curve over time, and solve for the stress drop to the value in the curve. The corresponding time is the first relaxation time. If the load is not reached within the preset maintenance period... If the first relaxation time is greater than the preset load holding time, then the first relaxation time is greater than the preset load holding time.

[0091] Calculate the relaxation modulus E: based on the preset strain during stress relaxation testing. According to the formula calculate.

[0092] Continuous stress data refers to the complete set of stress information collected during the stress relaxation detection phase of eddy current spinning yarn, specifically including the instantaneous stress at the start of relaxation. The stress values ​​at each time point during the relaxation and load holding process, and the residual stress at the end of the load holding process. These are the fundamental data for calculating stress relaxation characteristic parameters.

[0093] Stress relaxation characteristic parameters are an index system used to quantify the stress attenuation ability of yarn under constant strain. This method includes relaxation rate, first relaxation time and relaxation modulus, which together reflect the morphological stability of yarn during long-term use.

[0094] The first relaxation time refers to the instantaneous stress at which the yarn stress begins to relax. decay to The time required is a key indicator characterizing the yarn stress relaxation rate.

[0095] It should be noted that the above and The same stress unit must be used. Substitute the decimal formula to avoid calculation errors caused by unit confusion.

[0096] S4. Prepare parallel test samples. Repeat steps S1-S3 for each parallel test sample to obtain the fracture strength of each parallel sample and form a numerical group. After outlier judgment and elimination of the numerical group, obtain valid data. Calculate the coefficient of variation and extreme value difference based on the valid data, and then calculate the strength uniformity index based on the coefficient of variation and extreme value difference.

[0097] Parallel test samples refer to vortex-spun yarn samples that are produced in the same batch as the main test sample and have completely identical specifications (linear density, twist, raw material composition, etc.). They are used to verify the reliability of the main test data through repeated testing.

[0098] The coefficient of variation is a relative index reflecting the dispersion of numerical fracture strength data. By combining the mean and standard deviation, the influence of data magnitude on the evaluation of dispersion can be eliminated.

[0099] For example, 6-10 groups of yarns of the same specification are randomly selected from the same yarn batch of the main test sample, and the preset length is cut and constant humidity and temperature equilibration is completed (20±2℃, relative humidity 65%±3%, equilibration for 24h) to ensure that the pretreatment conditions of the parallel samples are completely consistent with those of the main sample, and to avoid errors introduced by environmental or preparation differences.

[0100] For each group of parallel test samples, the pre-stretching and stretching test procedures were repeated one by one, that is, the same pre-stretching rate (50-100 mm / min), pre-stretching force range (10%-15% of the expected breaking strength), and stretching rate (200-500 mm / min) were used to ensure the uniformity of the test parameters; only the breaking strength at the breaking moment of each group of samples was recorded (no need to repeat the stress relaxation test), and finally all the data were organized into a breaking strength numerical group.

[0101] Data processing and parameter calculation. First, outlier identification and removal: The Grubbs test (significance level α=0.05) is used to test the numerical groups, and the residuals for each group are calculated. When the absolute value of the residual exceeds the range of "mean ± Grubbs critical value × standard deviation", it is identified as an outlier and removed. After removal, at least 5 groups of valid data should be retained; if insufficient, additional parallel samples are added for retesting. Then, core parameters are calculated based on the valid data.

[0102] Coefficient of variation (CV): according to the formula Calculate, where S is the standard deviation of the valid data and μ is the mean of the valid data;

[0103] Extreme value difference (∆F): Calculated as the difference between the maximum and minimum values ​​of valid data.

[0104] In some embodiments, the calculation of the strength uniformity index includes:

[0105] ;

[0106] Where: CV is the coefficient of variation, ∆F is the extreme value difference, μ is the mean of the effective data; α and β are the preset weighting coefficients and The preset weighting coefficient is pre-calibrated based on the key points of yarn quality control; U∈[0,1], its qualified threshold Pre-set based on downstream application requirements.

[0107] S5. The fracture strength, stress relaxation characteristic parameters and strength uniformity index are correlated and integrated into a detection and evaluation system composed of preset weights and qualified thresholds to form a comprehensive detection report containing original data and judgment results and output it.

[0108] The testing and evaluation system is a comprehensive evaluation framework that uses preset weights to reflect the importance of each parameter and qualified thresholds to clarify the performance standards. It is used to systematically determine the mechanical performance level of eddy current spun yarn.

[0109] The preset weights are importance coefficients (the sum of the weights is 1) set for breaking strength, stress relaxation characteristic parameters, and strength uniformity index, respectively. In some embodiments, the preset weights can be pre-calibrated based on the downstream application requirements of the yarn (such as strength priority, stability priority).

[0110] The pass threshold is the critical value set for the performance of each test parameter. It is determined by yarn quality standards, customer requirements and industry specifications, and is the core basis for the judgment result.

[0111] Specifically, the three key parameters obtained from the entire testing process are summarized as follows: first, the accurate fracture strength after coupling correction (including the original data such as the apparent fracture strength and correction coefficient); second, the stress relaxation characteristic parameter set (including relaxation rate R, first relaxation time, etc.). The data includes: 1) relaxation modulus E and corresponding stress decay curve data; and 2) strength uniformity index U (including basic data such as the numerical group of fracture strength of parallel samples, coefficient of variation CV, and extreme value difference ∆F). All parameters are validated to ensure traceability of data sources and error-free calculation processes.

[0112] A testing and evaluation system is constructed and integrated. Parameter weights are set according to the yarn application scenario. For example, for high-strength yarn used in industry, the weights are set as follows: breaking strength 0.5, stress relaxation characteristic parameter 0.3, and uniformity index 0.2; for knitting yarn, the weights are set as follows: uniformity index 0.4, breaking strength 0.4, and stress relaxation characteristic parameter 0.2. Simultaneously, qualified thresholds for each parameter are matched (e.g., breaking strength ≥120cN, relaxation rate ≤30%, uniformity index U≥0.8). The system is integrated by comparing actual parameter values ​​with thresholds, calculating a comprehensive score according to weights, and determining the overall compliance status. A comprehensive score ≥80 points (out of 100) is considered overall qualified.

[0113] The report should include four core components: 1) Basic testing information (sample specifications, batch, testing equipment, environmental conditions, etc.); 2) Summary of raw data (including pre-stretching parameters, stress variation curves, parallel sample data, etc., presented in tables or attachments); 3) Parameter calculation and judgment results (listing the calculation process, actual value, pass threshold, and individual judgment result for each parameter, and indicating the handling of abnormal data); 4) Comprehensive evaluation conclusions (clarifying the overall compliance status, analyzing the advantages and disadvantages of core parameters, and providing quality improvement suggestions).

[0114] For example, consider the tensile testing of pure cotton eddy current spun yarn:

[0115] This embodiment uses pure cotton eddy-spun yarn for knitting as the test object. The yarn specifications are 21 tex (linear density) and 800 twists / meter. The purpose of the test is to obtain its breaking strength, stress relaxation characteristics, and strength uniformity indicators, providing a quality basis for downstream knitted fabric production. The testing equipment is an electronic universal tensile testing machine, and the testing environment is maintained at a temperature of 20℃ and a relative humidity of 65%.

[0116] Sample preparation and pre-stretching:

[0117] From pure cotton vortex-spun yarn packages, a flawless section of yarn from the middle of the package was selected. With a breaking strength of 5% (preliminary tests determined the breaking strength of this yarn specification to be approximately 140 cN, so the tension was set to 7 cN), the yarn was laid flat on a length measuring instrument, and a 500 mm section was cut as the main test sample. One set was prepared. The sample was placed in the testing environment for 24 hours to equilibrate and eliminate the influence of temperature and humidity.

[0118] Meanwhile, eight sampling points were randomly selected from the same batch of rolls, and eight parallel samples were cut according to the master sample preparation process, numbered P1-P8, and equilibrated together with the master sample.

[0119] Core testing process and data acquisition:

[0120] The main sample was fixed at both ends to the upper and lower clamps of the testing machine, with a clamping force of 1.5N (matching a linear density of 21 tex), ensuring that the yarn axis coincided with the center line of the clamps. The pre-tensioning rate was set to 80 mm / min, and the pre-tensioning force to 14 cN (10% of the expected breaking strength). After reaching the preset force value, the load was held for 45 seconds. Five stress data points were continuously collected 5 seconds before the end of the load holding period: 2.32, 2.30, 2.31, 2.33, and 2.32 cN / tex. The average value was calculated to be 2.316 cN / tex, which was recorded as the initial stress value. (Keep two decimal places).

[0121] Constant rate stretching: Set the stretching rate to 300 mm / min, start the stretching program, and synchronously collect stress and time data at a frequency of 15 Hz to generate a stress change curve.

[0122] Stress relaxation test: When the strain reaches 8% (below the yield strain of pure cotton yarn of 12%), the testing machine locks the displacement to maintain a constant strain and starts the relaxation test. Data is collected at 20Hz for the first 10 seconds, then reduced to 5Hz after 10 seconds, and the load holding time is 300 seconds. The instantaneous stress at the start of relaxation is recorded as σ1 = 8.65 cN / tex, and the residual stress after 300 seconds is recorded as σ2 = 6.12 cN / tex.

[0123] Fracture tensile test: After relaxation, the tensile force was restored to 300 mm / min. Fracture was defined as the force value dropping sharply from the peak value of 142.5 cN to 12.8 cN, and the fracture strength was recorded. The strain at fracture was 15.3%.

[0124] The above procedure was repeated for 8 parallel samples, and only the fracture strength data was recorded to obtain the numerical group (unit: cN): 141.8, 143.2, 140.5, 145.1, 138.9, 142.3, 144.6, 151.2.

[0125] Data processing and parameter calculation:

[0126] Stress stability segment identification: Preprocessing of the stress variation curve of the master sample: One abnormal peak (10.2 cN / tex) was removed using the Grubbs test (α=0.05), and corrected by linear interpolation. With a fluctuation coefficient ≤ ±5% and a duration ≥ 0.3 s, the curve was traversed in 0.2 s increments, marking the 3.2-4.8 s interval as a candidate stable segment (lasting 1.6 s). The stress gradient was calculated from three data points before and after this interval; the absolute value was 0.28 cN / (tex·s) < 0.3 cN / (tex·s), confirming this interval as a stable segment. Twenty-four stress data points within this interval were extracted, and the average stress was calculated. .

[0127] Fracture strength coupling correction: Consulting the pure cotton yarn elasticity correction coefficient database, k=0.92. Substituting this into the coupling correction formula:

[0128] .

[0129] Stress relaxation characteristic parameter calculation: relaxation rate: That is, 29.2%;

[0130] First relaxation time: exponential fitting of the relaxation data ( ), to obtain the attenuation curve The calculation shows that t = 291s when the stress drops to 4.325 cN / tex, therefore the first relaxation time is... s;

[0131] Relaxation modulus: Preset strain , .

[0132] Calculation of strength uniformity index:

[0133] Parallel sample data processing: Grubbs' test was used ( After removing outliers (151.2 cN), 7 valid data sets remained: 141.8, 143.2, 140.5, 145.1, 138.9, 142.3, and 144.6. The mean μ was calculated to be 142.34 cN, the standard deviation S to be 1.98 cN, and the coefficient of variation to be... Extreme value difference .

[0134] Uniformity index: For knitting yarns, uniformity is emphasized, with α=0.4 and β=0.6 set. Substituting into the formula:

[0135] .

[0136] Comprehensive test report and judgment:

[0137] Evaluation system settings: Weights of parameters for knitting yarn: breaking strength 0.4, stress relaxation characteristics 0.2, uniformity index 0.4; Pass thresholds: F≥130cN, R≤35%. ≥200s, E≥60cN / tex, U≥0.8.

[0138] Comprehensive assessment and report output:

[0139] Individual criteria: Fracture strength 147.2 cN (meets standards), relaxation rate 29.2% (meets standards). (Meets the standards) (Meets the standards) (Meets the standard). The overall result was deemed satisfactory.

[0140] Output a comprehensive test report, including sample information, raw data (with stress change curves), calculation process, individual and comprehensive judgment results, and a suggestion that "this batch of yarn has excellent uniformity and is suitable for the production of high-end knitted fabrics".

[0141] The basic concepts have been described above. Obviously, for those skilled in the art, the detailed disclosure above is merely illustrative and does not constitute a limitation of this specification. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements, and corrections to this specification. Such modifications, improvements, and corrections are suggested in this specification and therefore remain within the spirit and scope of the exemplary embodiments described herein.

[0142] Furthermore, unless expressly stated in the claims, the order of processing elements and sequences, the use of numbers and letters, or other names described in this specification are not intended to limit the order of the processes and steps in this specification. Although various examples have been discussed in the foregoing disclosure of some embodiments of the invention that are currently considered useful, it should be understood that such details are for illustrative purposes only, and the appended claims are not limited to the disclosed embodiments. Rather, the claims are intended to cover all modifications and equivalent combinations that conform to the substance and scope of the embodiments in this specification. For example, while the system components described above can be implemented using hardware devices, they can also be implemented solely using software solutions, such as installing the described system on existing servers or mobile devices.

[0143] Similarly, it should be noted that, in order to simplify the description disclosed herein and thus aid in the understanding of one or more embodiments of the invention, the foregoing description of embodiments in this specification may sometimes combine multiple features into a single embodiment, drawing, or description thereof. However, this method of disclosure does not imply that the subject matter of this specification requires more features than those mentioned in the claims. In fact, the embodiments contain fewer features than all the features of a single embodiment disclosed above.

[0144] Finally, it should be understood that the embodiments described in this specification are merely illustrative of the principles of the embodiments described herein. Other variations may also fall within the scope of this specification. Therefore, alternative configurations of the embodiments described herein are intended to be illustrative rather than limiting, and should be considered consistent with the teachings of this specification. Accordingly, the embodiments described herein are not limited to those explicitly introduced and described herein.

Claims

1. A method for testing the tensile properties of eddy current spun yarn, characterized in that, The method includes the following steps: S1. Cut a preset length of eddy-spun yarn as the main test sample, pre-stretch the main test sample to eliminate initial defects, and collect the initial stress value at the end of the pre-stretching load holding. S2. The main test sample is stretched at a preset rate, and stress data and time data of the stretching process are collected simultaneously and stress change curve is generated. When the sample is detected to be stretched to a preset strain, the strain is kept constant to perform stress relaxation detection, and continuous stress data of the relaxation process is collected. Then the sample is stretched until it breaks and the fracture strength at the fracture moment is recorded. S3. Based on the stress change curve, identify the stress stability segment, extract the average stress of the stability segment as the stress characteristic parameter, and perform coupling correction with the initial stress value and the apparent fracture strength. Calculate the fracture strength using the following formula: ； Where F is the corrected fracture strength; F' is the apparent fracture strength; σ represents the initial stress value; σ is the mean stress value. Based on the continuous stress data, calculate the stress relaxation characteristic parameters; The continuous stress data includes the instantaneous stress at the relaxation initiation moment. The stress values ​​at each time point during the relaxation and load holding process, and the residual stress at the end of the load holding process. The stress relaxation characteristic parameters include relaxation rate, first relaxation time, and relaxation modulus; based on the continuous stress data, the stress relaxation characteristic parameters are calculated as follows: Calculate the relaxation rate, the relaxation rate Through formula Calculated; Determine the first relaxation time, perform an exponential fit on the stress decay data to obtain the stress decay curve over time, and solve for the stress drop to the value in the curve. The corresponding time is the first relaxation time. If the load is not reached within the preset maintenance period... If the first relaxation time is greater than the preset load holding time, then the first relaxation time is greater than the preset load holding time. Calculate relaxation modulus Preset strain based on stress relaxation detection According to the formula calculate; S4. Prepare parallel test samples. Repeat steps S1-S3 for each parallel test sample to obtain the fracture strength of each parallel sample and form a numerical group. After outlier judgment and elimination of the numerical group, obtain valid data. Calculate the coefficient of variation and extreme value difference based on the valid data, and then calculate the strength uniformity index based on the coefficient of variation and extreme value difference. The calculation of the strength uniformity index includes: ； in, The strength uniformity index is represented by CV, which is the strength variation coefficient. α represents the extreme value difference; μ represents the mean of effective data; α and β are both preset weighting coefficients, which are pre-calibrated based on the key points of yarn quality control. S5. The fracture strength, stress relaxation characteristic parameters and strength uniformity index are correlated and integrated into a detection and evaluation system composed of preset weights and qualified thresholds to form a comprehensive detection report containing original data and judgment results and output it.

2. The method according to claim 1, characterized in that, The identification of stress stability segments based on the stress change curve includes: The stress variation curve is preprocessed to remove abnormal stress values ​​and corrected using linear interpolation; Set stress fluctuation coefficient and stability duration threshold as judgment indicators; slide through the preprocessed curve with a preset step size, and mark the interval that continuously meets the fluctuation coefficient requirement and the duration target as candidate stable segments; Calculate the boundary stress gradient of each candidate stable segment, and determine the candidate stable segment whose absolute value of the boundary stress gradient is less than a preset threshold as a stress stable segment.

3. The method according to claim 2, characterized in that, The calculation of the boundary stress gradient for each candidate stable segment includes: Locate the starting and ending boundaries of the candidate stable segment, and extract four continuous stress data points before and after the starting boundary and four continuous stress data points before and after the ending boundary to form two sets of boundary data. Calculate the absolute value of the stress difference between two adjacent points within each data set, and then calculate the maximum absolute value of the difference between the two data sets, denoted as . and ,in The absolute value of the maximum difference between the initial boundary data sets. The absolute value of the maximum difference between the terminating boundary data sets; A corresponding qualified threshold is set according to a preset range of yarn breaking strength. The preset range and the corresponding threshold are pre-calibrated based on the mechanical characteristics of the yarn material and the detection accuracy requirements. like and If all values ​​are less than or equal to their corresponding qualified threshold, then the boundary stress gradient of the candidate segment is determined to meet the requirements, and the current candidate segment is the stress-stable segment.

4. The method according to claim 1, characterized in that, The average stress value of the extracted stable segment is used as a stress characteristic parameter. This parameter is then coupled and corrected with the initial stress value after pre-stretching and the fracture strength at the fracture moment. The calculated fracture strength includes: Extract stress characteristic parameters from the stress stability segment, the stress characteristic parameters including the average stress of the stress stability segment. ; The fracture strength is corrected by using a coupling correction formula: ； in, This is the corrected fracture strength; To represent breaking strength; k is the elasticity correction coefficient corresponding to the yarn material; This represents the initial stress value.

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