Definition
The bending resistance tester of finished shoes is a special testing equipment that simulates the repeated bending conditions of footwear during wearing. It uses a mechanical structure to drive the shoe or sole specimen to bend back and forth at a specific angle and frequency to evaluate the fatigue resistance, crack resistance and overall structural integrity of the upper, sole and bonding part under dynamic stress. The instrument is widely used in footwear manufacturing, quality inspection institutions, and R&D departments, providing key data support for product quality control and material improvement.
Principle
The testing machine is based on a crank connecting rod or cam drive mechanism, which converts the rotational motion of the motor into the reciprocating bending motion of the fixture. Specimens are usually fixed to a last or a specific clamp that simulates the shape of the foot and is repeatedly bent at a set angle (e.g., 45° to 90° for forefoot bending) and frequency (e.g., 100 to 300 times per minute). The built-in counter of the equipment records the number of bends and automatically stops the machine when the specimen has cracks, glue opening, and other failure phenomena. The motion process can be roughly described as a function of angular displacement and time: θ(t)=θ_max·sin(2πft), where θ is the instantaneous bending angle, θ_max is the maximum bending angle, f is the bending frequency, and t is the time.
Measurement method
Before testing, samples should be prepared according to target market standards (such as ISO 17707, SATRA TM3, GB/T 3903.1, etc.), usually made shoes or intercepted sole parts. Mount the specimen on the clamp and adjust the bending axis so that it aligns with the natural bend of the forefoot. Set the bending angle, frequency and termination conditions (e.g. preset number of times or complete breakage). After starting, the device automatically runs and records the number of bends. During the test, the machine can be stopped regularly to observe the crack propagation on the surface of the specimen, or the crack length change can be recorded with the help of a video extensometer. Finally, the number of bends when cracks of the specified length appear, or the degree of damage of the specimen after reaching the preset number of times is used as the evaluation index.
Influencing factors
Test results are influenced by multiple factors. In terms of material properties, the elastic modulus, fatigue strength, and flexibility of the upper material determine the initial crack resistance of the sole polymer. Structural design factors include the depth of the sole pattern, the thickness of the bend and the uniformity of the sole bonding process (e.g., gluing or molding). In the test parameters, the increase of the bending angle or the increase of frequency usually accelerates the accumulation of fatigue. Environmental conditions such as temperature will affect the glass transition behavior of polymer materials, and low temperatures may make the materials brittle. In addition, insufficient fixture alignment accuracy can lead to deviations in stress distribution, which in turn affects the consistency of results.
Applications
The equipment is mainly used in quality verification and R&D analysis in footwear and related industries. In manufacturing enterprises, it is used to sample durability tests on batch finished products to ensure that the product meets the design life requirements. Quality inspection agencies carry out conformity assessments according to regional standards to provide technical basis for market access. R&D optimizes product fatigue resistance by comparing test data from different formulations, structures, or process specimens. In addition, in the field of sports science, biomechanical data can be combined to simulate bending conditions in specific sports modes to assist the development of functional shoes.
Selection considerations
When selecting a model, the compatibility of test standards, the range of equipment parameters and the extended functions should be comprehensively considered. The core parameters include the maximum bending angle range, frequency adjustment accuracy, number of test specimens and counting capacity at the same time. The clamping system needs to be adapted to different shoe sizes and styles, and provides an adjustable bending axis mechanism. The equipment should have overload protection and abnormal shutdown functions to ensure safe operation. The data recording method should support the export of the bend number and crack length curve to facilitate quantitative analysis. For research use, models with integrated environmental chambers are available to simulate temperature effects; The production line quality inspection scenario can focus on operational stability and test throughput. In addition, the supplier's technical support capabilities and standard update services should also be included in the evaluation.