What are the main steps in cable tension testing?

2023-11-30 09:56:44

The cable tension test mainly covers the measurement of linear density, lay length, braid length, elongation and breaking strength. The main ones are the measurement of elongation and breaking strength. Elongation refers to the length increment when the tension of the cable increases from the initial value (pre-tensioned) to 50% of the rated minimum breaking strength of the cable.

Breaking strength refers to the large load required when a cable is gradually stressed until it breaks. When the cable reaches a large load, it will face the serious consequences of cable breakage. Therefore, the user of the cable should be clear about the type, length, size, safe load and breaking strength of the cable used.

Main steps of cable tension test

1. Without significant tension (no more than 20% of the pre-tensioned force), place the sample cable straight on a flat surface, measure its length, and make two "w" marks as shown in the picture above (the two marks are the same as the test cable). The midpoint of the sample cable is symmetrical, and the distance between the two points is 500mm).

2. According to the type of tensile testing machine, fix the buttonholes at both ends of the sample cable and make two "r" marks as shown in the picture above (as a sample interval, the distance between the two points is 2m). When the break occurs in this interval Internal time is considered normal. The distance from each mark "r" to the closed end is 200mm-250mm.

3. According to the type of cable, apply the specified pre-tension to the sample cable and measure the distance between the two "w" (the pre-tension is based on the national standards). The distance is represented by L2 and the unit is mm.

4. Elongation measurement: Gradually increase the tension through uniform stretching of the tensile testing machine. When the tension reaches 50% of the minimum breaking strength of the rope, measure the distance between the two "w". The distance is represented by L3, and the unit is mm. .

Elongation (E) measurement formula: E=[(L3-L2)/L2]*100%

5. Breaking strength measurement: According to different materials and different sizes of cables, the breaking strength is temporarily set to "N".

① Pre-stretch once at 10%*N load, ② Pre-stretch at 20%*N load 3 times, ③ Pre-stretch 2 times at 30%*N load. There are two situations in which the rope can be broken:

① If it breaks from r to r, the breaking strength is the value displayed on the tensile testing machine at this time, which is represented by Fc;

② If it breaks from r to the closed end of the cable, the breaking strength is Fc/0.9.

Tips: The buttonhole should be kept level with the cable. During the breaking strength test, the rope should break from "r" to "r". If it breaks at other parts, the buttonhole is not spliced correctly.