Definition
A bending resistance tester is a specialized testing equipment used to evaluate the ability of materials to resist fatigue failure under repeated bending or folding stress. It quantifies the flexural resistance of a material by simulating the reciprocating folding action experienced by actual use, measuring the number of folds before it breaks or degrades its properties. This instrument is widely used to evaluate the durability of flexible materials and is an important tool in quality control and material research and development.
How it works:
The working principle of the Flexural Resistance Tester is based on the application of periodic bending stress to the specimen. The specimen is usually clamped between two grips, one of which allows for reciprocating motion. When the machine is running, the dynamic fixture drives the specimen part to bend repeatedly at a specified angle, so that the specimen is subjected to alternating stress at the fixed part. Each complete reciprocating motion is counted as one fold. The test continues until the specimen breaks or reaches a preset number of folds. The device automatically records the number of folds, which directly reflects the folding life of the material. The core mechanical process can be simplified to the fatigue accumulation of the material under the bending moment, and its stress change follows the basic relationship of bending stress in material mechanics.
Measurement method
The measurement of folding resistance follows a standardized test process. First, bar specimens of specified sizes are prepared according to relevant standards (such as ISO, ASTM, GB/T, etc.). The specimen is mounted flat in the fixture to ensure a secure grip and no initial twisting of the specimen. The test parameters are then set, including the fold angle, reciprocating frequency, applied tension, and termination conditions (such as complete break or a specific number of times). After starting the device, the machine automatically performs the folding action and counts. After the test, record the number of folds when the specimen finally breaks, or observe whether there are cracks, pilling, etc. on the surface of the specimen. Some tests require measurement of strength retention of folded specimens. The results are usually expressed as the average number of folds or the median of the sample group.
Influencing factors
The results of the folding resistance test are affected by a variety of factors and need to be strictly controlled in the test. The properties of the material itself are the decisive factors, including the molecular structure, flexibility, strength, and internal defects of the substrate. Environmental conditions such as temperature and humidity can affect the physical state of the material, and tests are usually performed at standard temperature and humidity. Instrument parameter setting is crucial, and larger folding angles or higher test frequency often lead to accelerated fatigue. The gripping force of the fixture on the specimen should be uniform and moderate, too tight may cause stress concentration, and too loose will cause sliding. The quality of the specimen's preparation, such as whether the edges are smooth and whether there are scratches, can also have a direct impact on the results. Understanding these factors helps in interpreting data comprehensively and improving test consistency.
Applications:
Flexural testing machines are used in a wide range of industries where life assessment of flexible materials is required. In the textile and apparel sector, it is used to test the folding resistance of fabrics, nonwovens, leather and sewing threads. In the packaging industry, it is used to evaluate the durability of paper, cardboard, plastic film, and composite packaging materials during repeated opening, closing, or use. In the printing and coating industry, it is used to check the adhesion and crack resistance of inks or coatings on the surface of printed materials after folding. In the field of electronic materials, it can be used to evaluate the flexural life of flexible circuit substrates. In addition, it is also widely used in the research and quality inspection of rubber products, safety protection products, and daily consumer goods.
Key points of selection
Choosing a suitable bending resistance tester requires comprehensive consideration of testing needs and technical specifications. First, the standards to be followed by the test should be clarified to ensure that the instrument's motion pattern, fixture design, angle range, and counting capacity comply with the standards. Depending on the type and thickness of the material to be tested, confirm the device's fixture compatibility with the maximum tension range. In terms of testing efficiency, it is necessary to pay attention to the maximum reciprocating frequency of the equipment and the number of specimens that can be tested at the same time. The convenience and accuracy of data recording are important, and prefer models that can automatically record and store data, and may have abnormal interruption detection functions. The durability and ease of maintenance of the equipment should also be taken into account, with stable mechanics and easily accessible spare parts conducive to long-term use. Finally, combine laboratory space and budget to meet core testing requirements.