Leisure table and chair pipe bending degree analysis method

Abstract

This invention discloses a method for analyzing the bending degree of tubing used in leisure tables and chairs, comprising: acquiring the original curvature signal of the bending segment from a continuous curvature scanning probe on a tubing bending testing platform, and simultaneously acquiring wall thickness distribution data of the bending segment from an ultrasonic thickness gauge probe at the arc apex; identifying the boundary between the positioning bending segment and the straight segment where the bending transition characteristic changes stably from non-zero to zero in the measured bending morphology, and extracting the steepness of the bending-straight boundary in the boundary between the positioning bending segment and the straight segment; locating the arc apex position of the bending segment in the measured bending morphology, extracting the target wall thickness at the arc apex position from the wall thickness distribution data, and using this as the target residual wall thickness at the arc apex; obtaining the overall arc length constraint set by the tubing bending process, calculating the total arc length of the actual bending segment using the measured bending morphology, and determining the difference between the overall arc length constraint and the total arc length as the arc length surplus.

Description

Technical Field

[0001] This invention relates to the field of information technology, and in particular to a method for analyzing the bending degree of tubing used in leisure tables and chairs. Background Technology

[0002] In the leisure furniture industry, the backrests and armrests of tables and chairs formed by bending metal tubing are core components of the product's structural strength. Their bending quality directly determines the safety and durability under long-term sitting pressure. As people's demands for comfort and lifespan of leisure chairs continue to increase, ensuring the stability of the bent tubing sections under repeated sitting pressure loads has become a crucial issue that manufacturers must address. Currently, many manufacturers, when controlling tubing bending, primarily focus on the symmetry of the overall arc and the smoothness of the appearance, often attempting to reduce stress concentration by increasing the radius of the mold corners or extending the transition area.

[0003] A prior art table and chair bending device, publication number CN210231103U, discloses a technology that can bend tubes of different outer diameters and adjust the length of the bending position. However, this technology suffers from a problem: it fails to accurately analyze the degree of bending during the bending process, leading to wall thinning in the middle of the bent section, shifting the location of fatigue failure, and failing to achieve balanced fatigue risk management throughout the entire process. When the total arc length of the bent section is strictly limited by the seat design dimensions, simply extending the transition zone compresses the length of the effective load-bearing arc segment in the middle, forcing an increase in the curvature in the middle of the bent section. This results in greater stretching of the tube wall at the apex of the arc during forming, causing significant thinning. This wall thinning is not uniformly distributed but concentrated near the highest point of the arc, forming a locally weakest area.

[0004] More importantly, the gentler the curvature change in the transition zone, the lower the local stress peak at the interface, but the simultaneous increase in curvature and thinning of the wall thickness at the central apex exacerbate the problem, creating a direct inverse relationship between the two. As a result, even if the risk of fatigue cracking at the interface decreases, the apex region, due to its excessively thin wall thickness, shows visible permanent deformation or even fine cracks after only a few cycles. This shift in fatigue failure location makes it difficult for manufacturers to determine which part is the truly weak point determining the overall bending life, and traditional testing methods struggle to simultaneously consider the combined effects of the smoothness of the transition zone and the degree of wall thinning in the middle.

[0005] Therefore, under the constraint of limited total arc length of pipe bending, accurately identifying the shift of fatigue weak points caused by changes in the length of the transition zone, and finding the decisive contradiction between the smoothness of the transition zone and the thinning of the wall thickness in the middle section that leads to the shortest service life, has become a key issue in achieving balanced control of fatigue risk throughout the bending section. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for analyzing the bending degree of tubing used in leisure tables and chairs. This method solves the problem in existing technologies of how to accurately identify the location shift of fatigue weak points caused by changes in the length of the transition zone under the constraint of limited total arc length of the tubing bending, and how to find the decisive contradiction point that leads to the shortest service life between the smoothness of the transition zone and the thinning of the wall thickness in the middle.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for analyzing the bending degree of tubing used in leisure tables and chairs includes:

[0009] The original curvature signal of the bent section is acquired from the continuous curvature scanning probe of the pipe bending test bench, and the wall thickness distribution data of the bent section is acquired from the ultrasonic thickness measuring probe at the top of the arc.

[0010] The original curvature signal is processed using a sliding window filtering algorithm to obtain a filtered curvature signal. The measured bending shape is determined based on the numerical distribution of the filtered curvature signal along the tube axis.

[0011] On the measured bending morphology, the boundary range between the positioning bending segment and the straight segment where the bending transition feature changes stably from non-zero to zero is identified, and the steepness of the bending-straight boundary in the boundary range is extracted.

[0012] Locate the apex of the curved segment on the measured bending shape, and extract the wall thickness value corresponding to the apex position from the wall thickness distribution data as the target residual wall thickness at the apex.

[0013] Obtain the overall arc length constraint set in the pipe bending process, calculate the total arc length of the actual bending segment based on the measured bending shape, and determine the difference between the overall arc length constraint and the total arc length as the arc length surplus.

[0014] Using the target residual wall thickness at the apex of the arc, the arc length surplus, and the steepness of the bend-straight junction as evaluation inputs, the fuzzy comprehensive evaluation method is used to assess the fatigue risk level of the wall thickness reduction region at the apex of the arc, and the steepness of the bend-straight junction is compared with the steepness threshold to assess the stress concentration fatigue risk level of the junction region.

[0015] Based on the fatigue risk level of the thinned wall region at the apex and the stress concentration fatigue risk level of the boundary region, a pipe bending quality classification code is generated. The pipe bending quality classification code represents the thinned wall region at the apex, the stress concentration boundary, and the overall risk balance.

[0016] Preferably, the step of acquiring the original curvature signal of the bent section from the continuous curvature scanning probe of the pipe bending testing table, and simultaneously acquiring the wall thickness distribution data of the bent section from the ultrasonic thickness gauge probe at the apex of the arc, includes:

[0017] A continuous curvature scanning probe collects curvature values ​​point by point on the outer arc surface along the tube axis. The position identifier of each measuring point in the tube axis coordinate system is determined according to the displacement of the scanning probe and the sampling frequency. The position identifier is the x-coordinate value along the tube axis. The position identifier and the corresponding curvature value are arranged in the acquisition order to form the original curvature signal.

[0018] The arc-top ultrasonic thickness gauge probe is positioned along the pipe axis coordinate system in the arc-top region of the curved section, and the wall thickness values ​​of each measuring point are measured sequentially. The wall thickness values ​​of each measuring point are arranged according to their positions in the pipe axis coordinate system to form the wall thickness distribution data of the curved section.

[0019] Preferably, the step of processing the original curvature signal using a sliding window filtering algorithm to obtain a filtered curvature signal, and determining the measured bending morphology based on the numerical distribution of the filtered curvature signal along the tube axis, includes:

[0020] The sliding window slides sequentially along the tube axis, and the average value of the original curvature signal is calculated within each window position. The tube axis coordinates of the window center point are used as the output position, and the average calculation result is assigned to this position to obtain the filtered curvature signal.

[0021] Using the value of the filtered curvature signal as the vertical axis and the tube axis coordinate as the horizontal axis, the measurement points are connected in sequence to form a continuous curve, and this continuous curve is determined as the measured bending shape.

[0022] For each measurement point on the measured bending shape, the ratio of the curvature difference between the measurement point and its adjacent measurement points to the tube axis coordinate spacing is calculated to obtain the local curvature gradient;

[0023] Based on the comparison between the local curvature gradient of each measurement point and the abruptness threshold, it is determined whether each measurement point has abrupt bending transition characteristics or gentle bending transition characteristics.

[0024] Preferably, the step of identifying the boundary between the positioning curved segment and the straight segment where the curved transition feature stably changes from non-zero to zero on the measured curved shape, and extracting the steepness of the curved-straight boundary within the boundary, includes:

[0025] Traverse the bending transition features of each measurement point on the measured bending shape along the pipe axis, identify the region where the bending transition features continuously change from a rapid type to a gentle type, select the starting measurement point and the ending measurement point where the absolute value of the local curvature gradient continuously decreases from a high value and approaches zero, and determine the pipe axis coordinate interval between the starting measurement point and the ending measurement point as the boundary range.

[0026] Within the boundary range, the absolute value of the local curvature gradient at the starting measurement point is obtained as the boundary inlet gradient, and the absolute value of the local curvature gradient at the ending measurement point is obtained as the boundary outlet gradient. The difference between the boundary inlet gradient and the boundary outlet gradient is divided by the tube axis length corresponding to the boundary range to obtain the gradient decay rate.

[0027] Based on the comparison between the gradient decay rate and the steepness threshold, the steepness of the straight-bend boundary in the boundary range is determined to be either steep or gentle.

[0028] Preferably, the step of locating the apex of the curved segment on the measured bending shape and extracting the wall thickness value corresponding to the apex position from the wall thickness distribution data as the target residual wall thickness at the apex includes:

[0029] The filtered curvature values ​​of each measurement point on the measured bending shape are traversed along the tube axis, the location of the measurement point where the filtered curvature value reaches the maximum value is identified, and the tube axis coordinates corresponding to the maximum value are determined as the arc apex position of the bending segment.

[0030] Based on the pipe axis coordinates at the arc apex position, the corresponding wall thickness value is found from the wall thickness distribution data, and the found wall thickness value is used as the target residual wall thickness at the arc apex.

[0031] Preferably, the step of obtaining the overall arc length constraint set in the pipe bending process, calculating the total arc length of the actual bending segment based on the measured bending shape, and determining the difference between the overall arc length constraint and the total arc length as the arc length surplus includes:

[0032] The overall arc length constraint is obtained from the preset parameters of the pipe bending process;

[0033] Based on the distribution of tube axis coordinates of each measuring point on the measured bending shape, the tube axis coordinate spacing between adjacent measuring points is accumulated segment by segment, and the accumulated result of all coordinate spacings is determined as the total arc length of the actual bending segment.

[0034] Subtracting the total arc length from the overall arc length constraint yields the arc length surplus.

[0035] Preferably, the step of using the residual wall thickness at the arc apex, the arc length surplus, and the steepness of the bend-straight junction as evaluation inputs, employing a fuzzy comprehensive evaluation method to assess the fatigue risk level of the arc apex wall thickness reduction region, and comparing the steepness of the bend-straight junction with a steepness threshold to assess the stress concentration fatigue risk level of the junction region includes:

[0036] The residual wall thickness of the target at the top of the arc, the arc length surplus, and the steepness of the intersection of the curve and the straight line are used as evaluation input factors. For each input factor, three membership intervals of low risk, medium risk, and high risk are divided. The membership value of each input factor to each risk level is determined according to the value of each input factor.

[0037] The safety threshold of the residual wall thickness of the target at the arc apex is adjusted according to the value of the arc length surplus to obtain the adjusted wall thickness safety threshold.

[0038] The residual wall thickness at the arc apex is compared with the adjusted wall thickness safety threshold. The membership degree of the residual wall thickness at the arc apex to each risk level is combined to determine the risk level with the largest membership degree as the fatigue risk level of the arc apex wall thickness reduction area.

[0039] The steepness of the bend-straight boundary is compared with the steepness threshold, and the membership degree value of the bend-straight boundary steepness to each risk level is combined to determine the risk level with the largest membership degree value as the stress concentration fatigue risk level of the boundary area.

[0040] Preferably, the step of generating a pipe bending quality classification code based on the fatigue risk level of the thinned wall region at the apex and the stress concentration fatigue risk level of the interface region, wherein the pipe bending quality classification code characterizes the thinned wall region at the apex, the stress concentration interface, and the overall risk balance, includes:

[0041] Obtain the fatigue risk level of the arc top wall thickness reduction region and the fatigue risk level of the interface stress concentration, compare the two fatigue risk levels, and determine the high-low relationship between the two fatigue risk levels.

[0042] Based on the high-low relationship, the weak type identification is determined. When the fatigue risk level of the arc apex wall thickness reduction area is higher than the fatigue risk level of the boundary stress concentration, the weak type identification is arc apex thinning type weak. When the fatigue risk level of the boundary stress concentration is higher than the fatigue risk level of the arc apex wall thickness reduction area, the weak type identification is boundary stress concentration type weak. When the two fatigue risk levels are the same, the weak type identification is full-process risk balance.

[0043] The pipe bending quality classification code is obtained by concatenating the weak type identifier with the higher of the two fatigue risk levels.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] This invention discloses a method for analyzing the bending degree of tubing used in leisure tables and chairs. Addressing the fatigue risks caused by wall thickness reduction at the apex of the bend, stress concentration at the bend-to-straight junction, and arc length deviation during tubing bending, a comprehensive analysis and evaluation scheme is proposed. This invention acquires curvature signals and wall thickness data of the bending segment using continuous curvature scanning and ultrasonic thickness measurement technology. A sliding window filtering algorithm is employed to reconstruct the measured bending morphology, accurately identifying the bend transition characteristics and the bend-to-straight junction range, extracting the junction steepness, and combining the target residual wall thickness at the apex and the arc length surplus. A fuzzy comprehensive evaluation method is used to dynamically adjust the safety threshold, assessing the fatigue risk level of apex thinning and junction stress concentration, and finally generating a quality classification code to guide sorting and control. The core innovation of this invention lies in achieving accurate assessment and risk classification of tubing bending quality through multi-dimensional data fusion and dynamic threshold adjustment, effectively improving the scientific nature and reliability of product quality control and reducing the risk of fatigue failure. Attached Figure Description

[0046] Fig. 1 This is a flowchart of a method for analyzing the bending degree of tubing used in leisure tables and chairs according to the present invention.

[0047] Fig. 2 This is a schematic diagram of a method for analyzing the bending degree of tubing used in leisure tables and chairs according to the present invention.

[0048] Fig. 3 This is another schematic diagram of a method for analyzing the bending degree of tubing used in leisure tables and chairs according to the present invention. Detailed Implementation

[0049] The present invention will now be described in detail through specific embodiments:

[0050] like Figs. 1-3 This embodiment of the method for analyzing the bending degree of leisure table and chair tubing may specifically include:

[0051] Step S101: Acquire the original curvature signal of the bent section from the continuous curvature scanning probe of the pipe bending test table, and at the same time acquire the wall thickness distribution data of the bent section from the ultrasonic thickness measuring probe at the top of the arc.

[0052] A continuous curvature scanning probe on the pipe bending testing platform moves along the pipe axis and collects curvature values ​​point by point on the outer arc surface of the bending section. Based on the displacement of the scanning probe and the sampling frequency, the position identifier of each measuring point in the pipe axis coordinate system is determined. The origin of the pipe axis coordinate system is set at the starting point of the bending section. The displacement is measured by an encoder, and the position identifier is the x-coordinate value along the pipe axis, calculated as x=s×(n / f), where s is the moving speed of the scanning probe, n is the sampling point number, and f is the sampling frequency. The position identifier and the corresponding curvature value are arranged in the acquisition order to form the original curvature signal. The arc-top ultrasonic thickness probe is positioned in the arc-top region of the curved section according to the pipe axis coordinate system. The thickness value of the pipe wall is obtained by the time difference between ultrasonic wave transmission and echo reception. The thickness calculation formula is d=(v×Δt) / 2, where v is the propagation speed of ultrasonic waves in the pipe and Δt is the time difference between transmission and echo. Measurements are taken sequentially at preset intervals along both sides of the arc-top. The wall thickness values ​​of each measurement point are arranged according to their positions in the pipe axis coordinate system to form the wall thickness distribution data of the curved section.

[0053] In one embodiment, the pipe bending detection platform is equipped with a guide rail mechanism that slides along the pipe axis. A continuous curvature scanning probe is mounted on the guide rail mechanism, and a contact curvature sensor is provided at the front end of the probe. The sensor senses the local curvature change of the outer arc surface of the pipe through a three-point contact method.

[0054] Specifically, the three-point contact method uses three equally spaced contact points to simultaneously adhere to the pipe surface. Based on the radial displacement δ of the middle contact point relative to the two side contacts, the radius of curvature R of the contact position is calculated using the formula R=L² / (8δ), where L is the distance between the two side contacts. Then, the curvature value κ of the contact position is obtained according to the curvature κ=1 / R=8δ / L². The calculation steps are as follows: after measuring δ, first substitute it into the formula to calculate the radius of curvature R, and then take the reciprocal to obtain the curvature value κ. The curvature value and the corresponding pipe axis coordinate position are recorded once every time the probe moves one sampling interval.

[0055] For example, the arc-top ultrasonic thickness gauge probe works on the principle of pulse-echo thickness measurement. The probe emits ultrasonic pulses that penetrate the pipe wall and are reflected on the inner wall surface. The thickness of the pipe wall is calculated based on the time interval between the emission time and the echo reception time and the propagation speed of the ultrasonic wave in the pipe material.

[0056] In one possible implementation, the measuring points in the arc apex region are arranged at preset intervals along the pipe axis coordinate system, and the wall thickness value of each measuring point corresponds to its pipe axis coordinate position, thus forming complete wall thickness distribution data. This data, together with the original curvature signal from the pipe bending measurement, is calibrated based on the same pipe axis coordinate system.

[0057] Step S102: The original curvature signal is processed using a sliding window filtering algorithm to restore the measured bending shape of the bending segment. Based on the abruptness of the local bending transition along the pipe axis of the measured bending shape, the bending transition characteristics of each measurement point are identified.

[0058] A sliding window filtering algorithm is used to process the original curvature signal. A window slides sequentially along the tube axis, and the average value of the original curvature signal is calculated within each window position. The tube axis coordinates of the window's center point are used as the output position, and the average result is assigned to that position. This process is repeated point-by-point to smooth all curvature signals, resulting in a filtered curvature signal. Based on the numerical distribution of the filtered curvature signal along the tube axis, the filtered curvature value of each measurement point is used as the ordinate, and the tube axis coordinates are used as the abscissa. These measurement points are connected sequentially to form a continuous curve, which is then defined as the measured bending shape. For each measurement point on the measured bending shape, the curvature value difference between that point and its adjacent measurement points is obtained. This difference is divided by the tube axis coordinate spacing between adjacent measurement points to obtain the local curvature gradient at that measurement point. This local curvature gradient characterizes the abruptness of the bending transition at that location. Based on the local curvature gradient of each measurement point, if the absolute value of the local curvature gradient exceeds a preset abruptness threshold, the measurement point is determined to have abrupt curved transition characteristics; if the absolute value of the local curvature gradient is lower than the abruptness threshold, the measurement point is determined to have gentle curved transition characteristics.

[0059] In one embodiment, the window width of the sliding window filtering algorithm is set according to the sampling density of the pipe bending section, and the window moves point by point along the pipe axis from the beginning end to the end end of the bending section.

[0060] Specifically, when the window moves to a certain position, all the original curvature values ​​within the window's coverage area participate in the averaging calculation. The calculation result is assigned to the tube axis coordinate position corresponding to the window's center point, forming the filtered curvature value at that position. The averaging calculation is repeated every time the window moves by one sampling interval until the window's center point has traversed all the measurement points on the curved section. This completes the smoothing of the original curvature signal and eliminates random noise interference introduced during the acquisition process.

[0061] For example, in the scenario of curvature detection of a curved tube for a lounge chair back, the original curvature signal often contains high-frequency fluctuations caused by probe vibration or minor unevenness on the tube surface. The sliding window filtering algorithm smooths these high-frequency fluctuations by locally averaging the curvature readings of adjacent measurement points, thus preserving the main trend of the overall curvature change of the curved section. Based on the filtered curvature signal, the measured bending shape is constructed using a coordinate mapping method.

[0062] In one possible implementation, a two-dimensional coordinate space is established with the tube axis coordinates as the horizontal axis and the filtered curvature value as the vertical axis. The tube axis coordinates and the corresponding filtered curvature value of each measurement point are marked as coordinate points in this space. Adjacent coordinate points are connected sequentially according to the tube axis coordinates to form a continuous curve that reflects the distribution of curvature along the tube axis of the bending section, i.e., the measured bending morphology.

[0063] It should be noted that the shape characteristics of the measured bending profile curve directly correspond to the actual effect of pipe bending. A flat curve indicates a relatively uniform curvature change in that section of pipe, while a steep curve indicates a more drastic curvature change. Furthermore, the local curvature gradient is obtained based on the numerical relationship between adjacent measurement points on the measured bending profile curve.

[0064] Specifically, for any target measurement point on the measured bending profile, the filtered curvature value of that target measurement point and the filtered curvature value of the next measurement point adjacent to it along the tube axis are obtained, and the difference between the two is calculated as the curvature change. Simultaneously, the tube axis coordinate distance between the target measurement point and the adjacent measurement point is obtained as the position change. The curvature change is divided by the position change, and the quotient is the local curvature gradient at that target measurement point. The magnitude of the local curvature gradient reflects the degree of change in the bending profile along the tube axis at that location; a larger absolute value indicates a more abrupt bending transition at that location, while a smaller absolute value indicates a smoother bending transition.

[0065] In one embodiment, for the detection of the curved section of the handrail bend, the boundary area between the curved section and the straight section usually exhibits a large absolute value of the local curvature gradient, while the arc apex area in the middle of the curved section usually has a smaller absolute value of the local curvature gradient due to the relatively stable curvature.

[0066] Preferably, the determination of the bending transition characteristics is achieved by comparing the absolute value of the local curvature gradient at each measurement point with a preset abruptness threshold. The abruptness threshold is determined comprehensively based on the pipe material, pipe diameter, and bending process requirements, and is used to distinguish the critical state between abrupt and gradual transitions.

[0067] Understandably, when the absolute value of the local curvature gradient at a measurement point exceeds the abruptness threshold, it indicates that the curvature at that location has undergone a relatively drastic change along the pipe axis, and the measurement point is determined to have abrupt bending transition characteristics. Conversely, when the absolute value of the local curvature gradient is below the abruptness threshold, it indicates that the curvature change at that location is relatively gradual, and the measurement point is determined to have gentle bending transition characteristics. By performing the above determination on all measurement points of the curved section one by one, the bending transition characteristic identifier of each measurement point is obtained, thereby achieving complete identification of the abruptness of the bending transition at each location along the pipe axis of the curved section.

[0068] Step S103: On the measured bending morphology, identify the boundary range between the positioning bending segment and the straight segment where the bending transition feature changes stably from non-zero to zero, and extract the steepness of the bending-straight boundary range between the positioning bending segment and the straight segment.

[0069] The bending transition characteristics at each measurement point along the pipe axis are traversed to identify regions where the bending transition characteristics continuously transition from abrupt to gradual. Within these regions, the starting and ending measurement points where the absolute value of the local curvature gradient continuously decreases from a high value and approaches zero are selected. The pipe axis coordinate interval between the starting and ending measurement points is defined as the boundary between the bending and straight segments. Within this boundary, the absolute value of the local curvature gradient at the starting measurement point is obtained as the boundary inlet gradient, and the absolute value of the local curvature gradient at the ending measurement point is obtained as the boundary outlet gradient. The difference between the boundary inlet gradient and the boundary outlet gradient is divided by the pipe axis length corresponding to the boundary range to obtain the gradient decay rate, which is measured in cubic meters. The steepness of the bend-straight junction is determined based on the gradient decay rate. If the gradient decay rate exceeds a preset steepness threshold, the steepness of the bend-straight junction in that range is determined to be steep. If the gradient decay rate is lower than the steepness threshold, the steepness of the bend-straight junction in that range is determined to be gentle. The determination result is then output for subsequent pipeline structure optimization analysis.

[0070] In one embodiment, the boundary between the curved segment and the straight segment is identified based on the variation of the curved transition feature along the pipe axis.

[0071] Specifically, in the measured bending morphology, the bending transition characteristics of each measurement point are traversed from the middle of the bending segment to both ends. When the bending transition characteristics of several consecutive measurement points are detected to change from a gentle type to a rapid type and then back to a gentle type, the boundary position of the transition area is marked. The measurement point where the absolute value of the local curvature gradient begins to rise continuously is determined as the starting measurement point, and the measurement point where the absolute value of the local curvature gradient approaches zero and remains stable is determined as the ending measurement point.

[0072] For example, in the detection scenario of a curved tube in the backrest of a lounge chair, the arc apex region in the middle of the curved section typically exhibits a gentle curved transition characteristic, while the region near the straight section shows a gradual transition from abrupt to a gentle curve. Furthermore, the boundary inlet and outlet gradients are obtained at the boundary measurement points within the determined boundary range. The absolute value of the local curvature gradient at the starting measurement point reflects the degree of curvature change during the transition from the curved section to the boundary region, while the absolute value of the local curvature gradient at the ending measurement point reflects the residual curvature change when the boundary region completes its transition to the straight section.

[0073] In one possible implementation, the gradient decay rate characterizes how quickly the curvature gradient decreases within the boundary region. A larger value indicates that the curvature change in the boundary region is completed rapidly within a shorter tube axis length, and the boundary region exhibits a steep transition shape; a smaller value indicates that the curvature change in the boundary region is completed slowly within a longer tube axis length, and the boundary region exhibits a gentle transition shape.

[0074] It should be noted that the steepness threshold is related to the material properties of the pipe, bending process parameters, and fatigue life requirements of the subsequent application scenarios. The dimension of the steepness threshold is consistent with the gradient decay rate, and its specific value is related to the material properties of the pipe, bending process parameters, and fatigue life requirements of the subsequent application scenarios. When the gradient decay rate exceeds this threshold, the steepness of the bend-straight junction is determined to be steep, indicating that there is a high risk of stress concentration in this junction area under repeated loading; when the gradient decay rate is below this threshold, the steepness of the bend-straight junction is determined to be gentle, indicating that the transition in this junction area is relatively smooth.

[0075] Step S104: Locate the apex of the curved section on the measured bending shape, and extract the target wall thickness at the apex from the wall thickness distribution data as the target residual wall thickness at the apex.

[0076] The filtered curvature values ​​of each measurement point along the pipe axis are traversed on the measured bending morphology. The location of the measurement point where the filtered curvature value reaches its maximum value is identified, and the pipe axis coordinate corresponding to the maximum value is determined as the arc apex position of the bending segment. Based on the pipe axis coordinate of the arc apex position, the wall thickness value corresponding to the pipe axis coordinate is found from the wall thickness distribution data, and the found wall thickness value is taken as the target residual wall thickness at the arc apex.

[0077] In one embodiment, the location of the apex of the arc is determined based on the distribution characteristics of the filtered curvature readings on the measured bending morphology.

[0078] Specifically, the apex of the bend is the location where the pipe bends the most. The filtered curvature reading at this location exhibits a maximum value across the entire bend. By comparing the filtered curvature readings at each measurement point along the pipe axis, the measurement point with the maximum reading is identified, and the pipe axis coordinates of this measurement point are determined as the apex of the bend.

[0079] For example, in detecting the curved section of a lounge chair armrest tube, the apex of the arc is usually located near the geometric center of the curved section, and its filtered curvature value exhibits a maximum value within the curved section. Furthermore, the extraction of the target residual wall thickness at the apex is based on the correspondence between wall thickness distribution data and tube axis coordinates. According to the determined tube axis coordinates of the apex position, a wall thickness measurement value matching these coordinates is searched in the wall thickness distribution data. Since the apex region is subjected to stretching during the bending process, its tube wall thickness will be thinner than the original tube material. The found wall thickness value is taken as the target residual wall thickness at the apex.

[0080] Step S105: Obtain the overall arc length constraint set in the pipe bending process, calculate the total arc length of the actual bending segment using the measured bending shape, and determine the difference between the overall arc length constraint and the total arc length as the arc length surplus.

[0081] The overall arc length constraint is obtained from the preset parameters of the tube bending process. This overall arc length constraint represents the maximum arc length allowed for the bent segment within the seat design size limitations. Based on the tube axis coordinate distribution of each measurement point on the measured bending shape, the tube axis coordinate spacing between adjacent measurement points within the bent segment is obtained. The coordinate spacing between adjacent measurement points is accumulated segment by segment along the tube axis from the starting measurement point to the ending measurement point of the bent segment. The accumulated result of all coordinate spacings is determined as the total arc length of the actual bent segment. The overall arc length constraint is subtracted from the total arc length to obtain the difference between the two, which is determined as the arc length surplus.

[0082] In one embodiment, the overall arc length constraint is obtained based on preset parameters in the pipe bending process file.

[0083] Specifically, the overall arc length constraint is the maximum allowable arc length of the bending segment determined during the seat design phase based on the external dimensions of the backrest or armrest. This value is written into the process parameter file before bending processing, and can be directly read from this file during the bending inspection process.

[0084] For example, in the detection scenario of a curved tube in the backrest of a lounge chair, the overall arc length constraint is usually determined by the design height and tilt angle of the backrest. The actual arc length of the curved section must not exceed this constraint value; otherwise, the overall dimensions of the chair will exceed the design specifications. Furthermore, the calculation of the total projected arc length is based on the distribution of tube axis coordinates at each measurement point on the measured bending shape. The tube axis coordinate distribution refers to the coordinates of each measurement point uniformly collected along the axis of the curved tube using equipment such as a 3D scanner, which is used to describe the actual spatial shape of the curved tube.

[0085] In one possible implementation, the three-dimensional coordinate spacing between adjacent measurement points is obtained sequentially along the tube axis, and the spacing is calculated using the Euclidean distance formula between two points. The calculation shows that the total arc length of the actual curved segment is obtained by accumulating the coordinates from the starting point of the curved segment towards the ending point.

[0086] It should be noted that arc length surplus represents the remaining space of the actual curved segment relative to the arc length constraint set by the process. When the difference between the overall arc length constraint and the actual arc length is positive, it indicates that the arc length of the actual curved segment is less than the maximum allowable value by the process, and there is a certain arc length surplus. When the difference approaches zero, it indicates that the actual curved segment is close to the upper limit of the arc length constraint, and the arc length surplus is small. The size of the arc length surplus directly affects the adjustment space of the transition area of ​​the curved segment. A larger arc length surplus means that the transition area has more room for extension, where the transition area of ​​the curved segment is the part connecting the curved segment and the straight segment.

[0087] Understandably, the arc length surplus reflects the degree of tolerance for bending process to adjust the shape of the bending section under current processing conditions. This value, together with the target residual wall thickness at the arc apex and the steepness of the bend-straight junction, constitutes the input basis for fatigue risk assessment of the bending section.

[0088] Step S106: Using the fuzzy comprehensive evaluation method, the residual wall thickness of the target at the top of the arc, the arc length surplus, and the steepness of the bend-straight junction are used as evaluation inputs. The safety threshold of the residual wall thickness of the target at the top of the arc is dynamically adjusted according to the arc length surplus. The fatigue risk level of the thinned area at the top of the arc is evaluated. The steepness of the bend-straight junction is compared with the steepness threshold to evaluate the stress concentration fatigue risk level of the junction area.

[0089] A fuzzy comprehensive evaluation method is adopted, using the residual wall thickness at the arc apex, arc length surplus, and steepness of the bend-straight boundary as evaluation input factors. For each input factor, three membership intervals—low risk, medium risk, and high risk—are defined. The membership degree of each input factor to each risk level is determined based on the position of its actual value within the membership interval. The safety threshold for the residual wall thickness at the arc apex is dynamically adjusted according to the magnitude of the arc length surplus. If the arc length surplus is lower than a preset lower surplus threshold, the safety threshold is lowered to a tightened state; if the arc length surplus is higher than a preset upper surplus threshold, the safety threshold is raised to a relaxed state, resulting in the adjusted wall thickness safety threshold. The residual wall thickness at the arc apex is compared with the adjusted wall thickness safety threshold. Combining the membership degree values ​​of the residual wall thickness at the arc apex to each risk level, the risk level with the highest membership degree value is selected as the fatigue risk level of the arc apex wall thickness thinning region. The steepness of the bend-straight boundary is compared with a preset steepness threshold. Combining the membership degree value of the bend-straight boundary steepness with the risk level of each risk level, the risk level with the largest membership degree value is selected as the stress concentration fatigue risk level of the boundary area.

[0090] In one embodiment, the division of the membership degree interval of the fuzzy comprehensive evaluation method is realized based on the engineering experience data of the fatigue risk in the bending section. The implementation process of the fuzzy comprehensive evaluation method is as follows: Let the evaluation factor set U = {u1, u2, u3} correspond to the arc top target residual wall thickness, arc length surplus, and steepness at the bend-straight junction respectively, and the comment set V = {low risk, medium risk, high risk}. For each evaluation factor ui, a triangular membership function is used to determine its membership degree to each risk level. Taking the arc top target residual wall thickness u1 as an example, set the upper bound a1 of the low-risk interval, the central value b1 of the medium-risk interval, and the lower bound c1 of the high-risk interval. When u1 ≥ a1, the membership degree of low risk μlow = 1; when c1 ≤ u1 < a1, μlow = (u1 - c1) / (a1 - c1); when u1 < c1, μlow = 0. The membership functions of medium risk and high risk are constructed in a similar triangular piecewise linear manner, and the sum of the membership degrees of the same factor to the three risk levels is 1. The membership degree values of each factor form a fuzzy relation matrix R, and a fuzzy synthesis operation B = W º R is carried out in combination with the weight vector W = [w1, w2, w3], where º is the fuzzy synthesis operator, taking the maximum-minimum synthesis method. The risk level corresponding to the largest component in B is the comprehensive evaluation result.

[0091] Specifically, for the evaluation input factor of the arc top target residual wall thickness, the wall thickness numerical range is divided into three membership degree intervals: low-risk interval, medium-risk interval, and high-risk interval. The larger the wall thickness value, the higher the membership degree falling into the low-risk interval; the smaller the wall thickness value, the higher the membership degree falling into the high-risk interval. For the evaluation input factor of the arc length surplus, the larger the arc length surplus value, the more abundant the adjustment space and the higher the membership degree falling into the low-risk interval; the smaller the arc length surplus value, the closer the bending section is to the process limit and the higher the membership degree falling into the high-risk interval. For the evaluation input factor of the steepness at the bend-straight junction, the larger the steepness value, the more rapid the transition in the junction area and the higher the membership degree falling into the high-risk interval.

[0092] Exemplarily, when the actual value of a certain evaluation input factor exactly falls near the boundary of two adjacent membership degree intervals, this input factor has certain membership degree values to the two adjacent risk levels, and the sum of the membership degree values is 1. Further, the dynamic adjustment of the wall thickness safety threshold by the arc length surplus reflects the coupling relationship between the geometric constraints of the bending section and the wall thickness thinning risk. Specifically, the dynamic adjustment of the wall thickness safety threshold is realized by linear interpolation. Let the reference wall thickness safety threshold be T0, the lower limit threshold of the surplus be E min and the upper limit threshold of the surplus be E max , the tightening coefficient be α (α < 1), and the relaxation coefficient be β (β > 1). When the arc length surplus E < E min , the adjusted wall thickness safety threshold T = T0 × α; when E > E max , T = T0 × β; when E min≤E≤E max At that time, T = T0 × [α + (β - α) × (EE)] min ) / (E max -E min This allows for continuous and smooth adjustment of the safety threshold based on the arc length surplus.

[0093] In one possible implementation, when the arc length surplus is small, the transition area of ​​the curved section lacks sufficient extension space, and the deformation in the arc apex area is relatively concentrated. At this time, the requirements for the residual wall thickness of the target at the arc apex should be more stringent. Therefore, the wall thickness safety threshold is lowered to a tightened state, which means that only when the residual wall thickness of the target at the arc apex is higher than the tightened threshold is it judged as low risk.

[0094] It should be noted that when the arc length surplus is large, the transition area of ​​the curved section has sufficient extension space, and the deformation distribution in the arc apex area is relatively uniform. At this time, the requirement for the residual wall thickness at the arc apex is appropriately relaxed, so the wall thickness safety threshold is adjusted to a relaxed state.

[0095] Specifically, the determination of the fatigue risk level of the thinned wall region at the apex of the arc comprehensively considers the relationship between the actual value of the residual wall thickness at the apex and the adjusted wall thickness safety threshold, as well as the membership value of the residual wall thickness at the apex to each risk level. When the residual wall thickness at the apex is lower than the adjusted wall thickness safety threshold and has the largest membership value to the high-risk level, the fatigue risk level of the thinned wall region at the apex is determined to be high-risk; when the residual wall thickness at the apex is higher than the adjusted wall thickness safety threshold and has the largest membership value to the low-risk level, the fatigue risk level of the thinned wall region at the apex is determined to be low-risk.

[0096] In one embodiment, for the detection scenario of the curved tube of the backrest of a lounge chair, the fatigue risk level of the area with reduced wall thickness at the top of the arc directly reflects the possibility of permanent deformation or fatigue cracks occurring in this area under long-term sitting pressure load.

[0097] Preferably, the determination of the stress concentration fatigue risk level in the interface region is based on the comparison between the steepness of the bend-straight junction and the steepness threshold. The steepness of the bend-straight junction uses the gradient decay rate value determined in S103. When the gradient decay rate exceeds the preset steepness threshold and the membership value to the high-risk level is maximized, the stress concentration fatigue risk level in the interface region is determined to be high-risk. This indicates that there is a relatively rapid curvature gradient change in the transition region between the curved and straight sections, which easily leads to stress concentration points under cyclic loading.

[0098] Understandably, the fatigue risk level of the wall thickness reduction area at the top of the arc and the fatigue risk level of stress concentration in the boundary area describe the fatigue weakness characteristics of the bending section from two dimensions: wall thickness reduction and stress concentration. Together, they constitute the core output of the fatigue risk assessment of the entire bending section, providing a basis for subsequent bending quality classification.

[0099] Step S107: Generate a pipe bending quality classification code based on the fatigue risk level of the thinned area at the top of the arc and the fatigue risk level of the stress concentration at the interface, and distinguish between thinned area at the top of the arc, stress concentration at the interface and balanced risk throughout the process, for use in controlling the sorting and management process.

[0100] The fatigue risk level of the thinned wall region at the apex and the fatigue risk level of the boundary stress concentration are obtained. The two fatigue risk levels are compared to determine whether the fatigue risk level of the thinned wall region at the apex is higher than that of the boundary stress concentration, thus establishing a hierarchical relationship between the two fatigue risk levels. Based on this relationship, a weakness type identifier is determined. If the fatigue risk level of the thinned wall region at the apex is higher than that of the boundary stress concentration, the weakness type identifier is identified as an apex-thinning type weakness; if the boundary stress concentration is higher, it is identified as a boundary stress concentration type weakness; if both fatigue risk levels are the same, the weakness type identifier is identified as a balanced risk throughout the entire process. Based on the weakness type identifier and the corresponding fatigue risk level, the weak type identifier is concatenated with the higher of the two fatigue risk levels. When both fatigue risk levels are the same, either level is used for concatenation to obtain a pipe bending quality classification code. This classification code is used to control the sorting and management process.

[0101] In one embodiment, the comparison between the fatigue risk level of the arc apex wall thickness reduction region and the fatigue risk level of the interface stress concentration is achieved based on the numerical representation of the risk level.

[0102] Specifically, the risk level is mapped to a numerical value: low corresponds to 1, medium corresponds to 2, and high corresponds to 3. Then, the two values ​​are compared. If the value of thinning at the apex of the arc is greater than the value of stress concentration at the boundary, then the former is higher, and vice versa. If they are equal, then they are the same.

[0103] For example, in the testing scenario of a curved tube for a lounge chair back, when the fatigue risk level of the thinned area at the apex of the arc is high while the fatigue risk level of the stress concentration at the boundary is low, the fatigue risk level of the thinned area at the apex is determined to be higher than that of the stress concentration at the boundary. Furthermore, when the fatigue risk level of the thinned area at the apex is higher than that of the stress concentration at the boundary, the weakness type is identified as apex thinning, thus directly reflecting the dominant factor of the fatigue weakness characteristics of the bending section.

[0104] In one possible implementation, the thinning at the apex indicates that the fatigue life of the curved section is mainly constrained by the degree of wall thinning at the apex, and the apex is more prone to permanent deformation or fatigue cracks under long-term sitting load; the stress concentration at the interface indicates that the fatigue life of the curved section is mainly constrained by the stress concentration at the interface between the curved section and the straight section, and the interface is more likely to become the starting point of fatigue failure; the balanced risk throughout indicates that the fatigue risk of the apex and the interface is at a comparable level, and the overall fatigue risk distribution of the curved section is relatively uniform.

[0105] It should be noted that the characters in the pipe bending quality classification code are arranged in the order of weak type identifier first and fatigue risk level second. When two fatigue risk levels are the same, either level is used in the splicing.

[0106] Understandably, the pipe bending quality classification code, as the output of the bending section quality inspection, directly drives the subsequent sorting and control process. Different classification codes correspond to different handling paths, thereby realizing the classification and control of fatigue risk in the bending section.

[0107] If the technical solution of this application involves the acquisition of personal information, the product using this solution has clearly informed the user of the processing rules and obtained the user's consent before processing. If sensitive personal information is involved, the user's individual consent has been obtained and the "express consent" requirement has been met. For example, a clear sign is placed at the collection device to indicate the collection scope, and the user's voluntary entry is considered as consent; or authorization is obtained through pop-up windows, user uploads, etc. The processing rules include the processor, purpose, method, and type of information.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for analyzing the bending degree of tubing used in leisure tables and chairs, characterized in that, include: The original curvature signal of the bent section is acquired from the continuous curvature scanning probe of the pipe bending test bench, and the wall thickness distribution data of the bent section is acquired from the ultrasonic thickness measuring probe at the top of the arc. The original curvature signal is processed using a sliding window filtering algorithm to obtain a filtered curvature signal. The measured bending shape is determined based on the numerical distribution of the filtered curvature signal along the tube axis. On the measured bending morphology, the boundary range between the positioning bending segment and the straight segment where the bending transition feature changes stably from non-zero to zero is identified, and the steepness of the bending-straight boundary in the boundary range is extracted. Locate the apex of the curved segment on the measured bending shape, and extract the wall thickness value corresponding to the apex position from the wall thickness distribution data as the target residual wall thickness at the apex. Obtain the overall arc length constraint set in the pipe bending process, calculate the total arc length of the actual bending segment based on the measured bending shape, and determine the difference between the overall arc length constraint and the total arc length as the arc length surplus. Using the target residual wall thickness at the apex of the arc, the arc length surplus, and the steepness of the bend-straight junction as evaluation inputs, the fuzzy comprehensive evaluation method is used to assess the fatigue risk level of the wall thickness reduction region at the apex of the arc, and the steepness of the bend-straight junction is compared with the steepness threshold to assess the stress concentration fatigue risk level of the junction region. Based on the fatigue risk level of the thinned wall region at the apex and the stress concentration fatigue risk level of the boundary region, a pipe bending quality classification code is generated. The pipe bending quality classification code represents the thinned wall region at the apex, the stress concentration boundary, and the overall risk balance.

2. The method for analyzing the bending degree of leisure table and chair tubing according to claim 1, characterized in that, The process involves acquiring the original curvature signal of the bent section from the continuous curvature scanning probe of the pipe bending testing station, and simultaneously acquiring the wall thickness distribution data of the bent section from the ultrasonic thickness gauge probe at the apex of the arc, including: A continuous curvature scanning probe collects curvature values ​​point by point on the outer arc surface along the tube axis. The position identifier of each measuring point in the tube axis coordinate system is determined according to the displacement of the scanning probe and the sampling frequency. The position identifier is the x-coordinate value along the tube axis. The position identifier and the corresponding curvature value are arranged in the acquisition order to form the original curvature signal. The arc-top ultrasonic thickness gauge probe is positioned along the pipe axis coordinate system in the arc-top region of the curved section, and the wall thickness values ​​of each measuring point are measured sequentially. The wall thickness values ​​of each measuring point are arranged according to their positions in the pipe axis coordinate system to form the wall thickness distribution data of the curved section.

3. The method for analyzing the bending degree of leisure table and chair tubing according to claim 1, characterized in that, The process of processing the original curvature signal using a sliding window filtering algorithm to obtain a filtered curvature signal, and determining the measured bending morphology based on the numerical distribution of the filtered curvature signal along the tube axis, includes: The sliding window slides sequentially along the tube axis, and the average value of the original curvature signal is calculated within each window position. The tube axis coordinates of the window center point are used as the output position, and the average calculation result is assigned to this position to obtain the filtered curvature signal. Using the value of the filtered curvature signal as the vertical axis and the tube axis coordinate as the horizontal axis, the measurement points are connected in sequence to form a continuous curve, and this continuous curve is determined as the measured bending shape. For each measurement point on the measured bending shape, the ratio of the curvature difference between the measurement point and its adjacent measurement points to the tube axis coordinate spacing is calculated to obtain the local curvature gradient; Based on the comparison between the local curvature gradient and the abruptness threshold at each measurement point, it is determined whether each measurement point has abrupt bending transition characteristics or gentle bending transition characteristics.

4. The method for analyzing the bending degree of leisure table and chair tubing according to claim 1, characterized in that, On the measured bending morphology, the boundary range between the positioning bending segment and the straight segment where the bending transition feature stably changes from non-zero to zero is identified, and the steepness of the bending-straight boundary range is extracted, including: Traverse the bending transition features of each measurement point on the measured bending shape along the pipe axis, identify the region where the bending transition features continuously change from a rapid type to a gentle type, select the starting measurement point and the ending measurement point where the absolute value of the local curvature gradient continuously decreases from a high value and approaches zero, and determine the pipe axis coordinate interval between the starting measurement point and the ending measurement point as the boundary range. Within the boundary range, the absolute value of the local curvature gradient at the starting measurement point is obtained as the boundary inlet gradient, and the absolute value of the local curvature gradient at the ending measurement point is obtained as the boundary outlet gradient. The difference between the boundary inlet gradient and the boundary outlet gradient is divided by the tube axis length corresponding to the boundary range to obtain the gradient decay rate. Based on the comparison between the gradient decay rate and the steepness threshold, the steepness of the straight-bend boundary in the boundary range is determined to be either steep or gentle.

5. The method for analyzing the bending degree of leisure table and chair tubing according to claim 1, characterized in that, The step of locating the apex of the curved segment on the measured bending shape and extracting the wall thickness value corresponding to the apex position from the wall thickness distribution data as the target residual wall thickness at the apex includes: The filtered curvature values ​​of each measurement point on the measured bending shape are traversed along the tube axis, the location of the measurement point where the filtered curvature value reaches the maximum value is identified, and the tube axis coordinates corresponding to the maximum value are determined as the arc apex position of the bending segment. Based on the pipe axis coordinates at the arc apex position, the corresponding wall thickness value is found from the wall thickness distribution data, and the found wall thickness value is used as the target residual wall thickness at the arc apex.

6. The method for analyzing the bending degree of leisure table and chair tubing according to claim 1, characterized in that, The process of obtaining the overall arc length constraint set for the pipe bending process, calculating the total arc length of the actual bending segment based on the measured bending shape, and determining the difference between the overall arc length constraint and the total arc length as the arc length surplus includes: The overall arc length constraint is obtained from the preset parameters of the pipe bending process; Based on the distribution of tube axis coordinates of each measuring point on the measured bending shape, the tube axis coordinate spacing between adjacent measuring points is accumulated segment by segment, and the accumulated result of all coordinate spacings is determined as the total arc length of the actual bending segment. Subtracting the total arc length from the overall arc length constraint yields the arc length surplus.

7. The method for analyzing the bending degree of leisure table and chair tubing according to claim 1, characterized in that, The evaluation process uses the residual wall thickness at the arc apex, the arc length surplus, and the steepness of the bend-straight junction as inputs. A fuzzy comprehensive evaluation method is employed to assess the fatigue risk level of the arc apex wall thickness reduction region. The steepness of the bend-straight junction is compared with a steepness threshold to assess the stress concentration fatigue risk level of the junction region, including: The residual wall thickness of the target at the top of the arc, the arc length surplus, and the steepness of the intersection of the curve and the straight line are used as evaluation input factors. For each input factor, three membership intervals of low risk, medium risk, and high risk are divided. The membership value of each input factor to each risk level is determined according to the value of each input factor. The safety threshold of the residual wall thickness of the target at the arc apex is adjusted according to the value of the arc length surplus to obtain the adjusted wall thickness safety threshold. The residual wall thickness at the arc apex is compared with the adjusted wall thickness safety threshold. The membership degree of the residual wall thickness at the arc apex to each risk level is combined to determine the risk level with the largest membership degree as the fatigue risk level of the arc apex wall thickness reduction area. The steepness of the bend-straight boundary is compared with the steepness threshold, and the membership degree value of the bend-straight boundary steepness to each risk level is combined to determine the risk level with the largest membership degree value as the stress concentration fatigue risk level of the boundary area.

8. The method for analyzing the bending degree of leisure table and chair tubing according to claim 1, characterized in that, The process generates a pipe bending quality classification code based on the fatigue risk level of the thinned wall region at the apex and the stress concentration fatigue risk level of the interface region. This pipe bending quality classification code characterizes apex-thinning weakness, interface stress concentration weakness, and overall risk balance, including: Obtain the fatigue risk level of the arc top wall thickness reduction region and the fatigue risk level of the interface stress concentration, compare the two fatigue risk levels, and determine the high-low relationship between the two fatigue risk levels. Based on the high-low relationship, the weak type identification is determined. When the fatigue risk level of the arc apex wall thickness reduction area is higher than the fatigue risk level of the boundary stress concentration, the weak type identification is arc apex thinning type weak. When the fatigue risk level of the boundary stress concentration is higher than the fatigue risk level of the arc apex wall thickness reduction area, the weak type identification is boundary stress concentration type weak. When the two fatigue risk levels are the same, the weak type identification is full-process risk balance. The pipe bending quality classification code is obtained by concatenating the weak type identifier with the higher of the two fatigue risk levels.

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