Customer
Our client is the world leader for aeronautics’ equipment and systems in planes. The company also has an important part in aeronautics safety.
Tested product
Strap
Tear-off straps are safety elements that allow for long-distance shock absorption. The damping is controlled by tearing (separation of 2 straps sewn together) which is carried out gradually, at a controlled force. It is the tearing force that absorbs the energy of the shock. These straps are used, for example, to protect people on harnesses for work at height, or to hold down vehicle stop nets.
Objective
To test and characterise tearing straps by measuring the tearing force at low and high speeds, over long lengths.
Problematic issues
These tests require a high tensile force (up to 1800daN), over long lengths (up to 10m) with highly variable test speeds (from 1 to 100m/s), which implies very high tensile powers.
The system must also be capable of performing high energy tests, even at low speeds.
Solution and result
Our engineers designed a machine that can tear straps from 0.4 to 10m in length at speeds between 1 and 100m/s, with force measurement and high frequency displacement measurement up to 1MHz.
Test principle:
The strap is hooked, fixed side, to a high frequency force transducer. The other side of the strap is attached to a bar.
The machine is equipped with several winding drums of different diameters. These drums, which have a very high inertia, are gradually brought up to the test speed. Once the speed is reached, a high-speed system is used to hook the strap bar onto the drum. The rotation of the drum pulls on the strap with very high energy (up to 1000kJ) and allows the strap to be wound up as it tears between the fixed point and the drum.
The use of different drum diameters allows a wide range of test speeds to be achieved, while maintaining high energy. For very low speeds, the machine is additionally equipped with a inertia multiplier that provides additional kinetic energy storage.
Thanks to the high starting energy, the loss of speed during the test is minimal.
The test stand ensures user safety with numerous impact resistant covers and doors and redundant safety systems, coupled with a dedicated safety PLC.
In addition, the machine's fixed point is equipped with an automatic release system if the maximum force is exceeded. This principle is used to protect the machine in case of installation of a non-conforming strap whose tearing force is beyond the machine limits.
The PC control is simplified by a specific software, specific to this test bench. The control can be done remotely, the visualization of the parameters and acquisition results is presented simply with curves and tables. It saves the test conditions and parameters as well as the results.
The software is also equipped with a system for optimising the test conditions (choice of drum and test mode according to the user's needs for force, speed and length).
