What Is a Bending Test?
Bending test is a tester to check the durability of products, such as robot cables and optical fiber cables that are likely to deteriorate as the number of bending cycles increases, by daring to bend them repeatedly.
For long, thin products, such as cables and wires, the weight of the cable itself may cause the wire to bend, and bending may be applied during the wiring process. If the durability against bending is weak, there is a risk of wire breakage, so a bending test is necessary.
There are two types of bending tests: a three-point test with two fulcrums and one action point, and a four-point test with two fulcrums and two action points. The three-point test is mainly used because the process of cable bending in wiring is the same situation as in the three-point test.
However, in examining the durability of a cable, it is important to choose the test method that best suits the purpose, since the 3-point test and the 4-point test are sometimes used interchangeably.
Uses of Bending Test
Bending test is used to examine the durability of cables by bending power supply cables and wiring devices. The purpose of bending test is to check the durability of cables when they are bent in various directions and to determine whether the cables have the desired durability.
Cables bend in different directions depending on the product. Therefore, test methods differ depending on the bending direction and torsion, and the test content is customized for each product. For example, a 3-point or 4-point test is used for bending test. A torsion test may also be used to examine the durability of external force due to torsion.
Usually used for electric wires and cables, but also often used to check for cracks and tears in rubber products that stretch and shrink rapidly, thin optical films, and so on.
Principle of Bending Test
Bending test consists of forcing a cable-like object to bend using a jig. Usually, the cable is bent by placing it between jigs called mandrels with radii. The test with the jig is the same as the principle of the 3-point test for bending tests.
By using jigs with different R values, it is possible to set the desired angle of bending. The objective is to check the durability by repeating the bending operation. In the bending test, the test sample is bent along the curved surface of the R of the jig, so the selection of the jig is also important for evaluating the correct durability.
The twist test and U-bend test are used in conjunction with the bending test to evaluate the durability of cable-like materials. As in the bending test, the durability of the cable is checked by forcibly twisting and folding the test sample. The items required for these tests vary depending on the uses of the test sample and the processing process.
Other Information About Bending Test
Other Test Methods
Bending test requires a twist test or a U-fold test in addition to the bending test. There are also testing machines that use the same principle as the 3-point test for bending tests.
The phenomena to be evaluated vary with each testing method. For example, the torsion test evaluates torsion phenomena, while the U-fold test evaluates bending phenomena.
1. Twisting Test
The twist test is a test to examine the durability of a cable when it is twisted. The cable is set in the durability tester and supported at both ends by a jig, then bending is applied to the cable.
2. U-Fold Test
The U-bend test is a test in which a jig is attached to the top of a bent cable and an external force is applied. Some testing machines can test many cables at once by arranging them in parallel.
3. 3-Point Test
The three-point test is a test in which an external force is applied to the center of the specimen, supporting both ends of the material. It is called a 3-point test because the external force is applied to three points: two at both ends and one at the center.
The purpose of the three-point test is to determine whether a material is suitable for bending since the external force is applied similarly to the bending process of the material. The bending test, which is used to examine the durability of a cable, consists of supporting both ends of the testing machine with a jig and applying an external force to the center.