The mechanical properties of the webbing directly determine the probability of occupant survival in collision accidents, and qualified seat belts can reduce the casualty rate of traffic accidents by more than 50%. As the core mechanical index of webbing, tensile performance is divided into two types of tests: static and dynamic, which simulates the smooth force of the vehicle and the instantaneous impact scenario of collision, which is the key means to verify the compliance of the webbing, and strictly follows domestic and foreign standards such as GB 14166 and FMVSS 209.
1. Static tensile test
The static tensile test focuses on the mechanical response of the webbing under constant load, simulates low-speed stress scenarios such as sudden braking and slow collision, and detects the ultimate bearing capacity and deformation characteristics at the core.
Test preparation
The specimens need to be pretreated in an environment of 20°C±5°C and 65%±5% relative humidity for 24 hours, and two new non-damaging webbing ribbons are selected as parallel samples for each group to ensure stable performance.
Testing process
The computerized tensile testing machine is used to fix both ends of the specimen in the wedge-shaped anti-skid fixture, set a constant loading rate of 100mm/min, and control the free length between the fixtures at 200mm±40mm, and collect force value and displacement data in real time.
Core standards
Three key parameters were recorded, including the width of the webbing at 9800N and the elongation at 11100N, as well as the tensile strength at break. The tensile strength of the belt ≥ 26700N, the elongation is ≤15%, the tensile strength of the shoulder belt is ≥17700N, the elongation is ≤30%, and the deviation of the parallel sample needs to be controlled.
2. Dynamic tensile test
The dynamic tensile test focuses on simulating the instantaneous impact load during high-speed collision, restoring the mechanical behavior of the webbing under millisecond strong stress, and evaluating the energy absorption capacity and dynamic failure characteristics of the webbing.
Test for differences
Different from static testing, an impact tensile testing machine is required, and the loading rate can reach 10-100m/s, which is more suitable for actual collision scenarios. The connection part with the buckle and adjustment device should be retained to avoid performance deviation caused by cutting.
Testing process
The instantaneous force, displacement and deformation rate are captured by high-speed sensors, and the three major indicators of peak impact force, energy absorption value and fracture time are mainly analyzed.
Core requirements
Qualified webbing needs to achieve "soft restraint" through moderate deformation to avoid secondary injuries caused by excessive peak force; The breaking time is not shorter than the collision buffer time, and the fracture part is not located at the connection between the webbing and the metal parts, and the performance stability in extreme environments needs to be verified.
3. Test core summary and development trend
1. Test correlation: Static testing is the premise of dynamic testing to verify the basic bearing capacity. Dynamic testing is the final verification of safety performance, restoring actual working conditions, and the two complement each other.
2. Key control points: It is necessary to strictly control the preparation of specimens, environmental conditions, and equipment calibration to avoid test errors caused by factors such as fixture slippage and loading deviation.
3. Development direction: With the upgrading of safety standards and the application of new fiber materials, tensile testing is developing towards high precision and intelligence, providing technical support for the optimization of webbing design.
