Novel High Performance Fiber-High Speed Test Development 2002-01-0681
The major objective of this paper is to address how the actual force versus extension relationship for a seat belt during a collision is different from the one obtained at typical low rate (static) conditions. We also look at what features of the tensile stress-strain characteristic are important for the optimal performance of a seat belt.
To answer these questions experimentally we use our high rate Instron -1331. We also designed an experimental set up that required special grips and contact sensors for characterizing samples of belt and yarn.
In the theoretical part we demonstrate the selected rates for the tensile testing as relevant to the collisions. We also discuss the importance of the energy absorbing capacity of the belts as the most relevant characteristic of the tensile curves for this application. We then show the effect of visco-elastic factors on energy absorbing properties of fibers during collisions and the role of weaving and dyeing the belt.
We obtained and compared stress-strain curves at the rates in the range 0.1-10 sec-1 (and selectively at 100 sec-1) for three materials in fiber and belt form: the novel high performance SECURUS™ fiber (polyethylene terephthalate - polycaprolactone copolymer), standard PET (polyethylene terephthalate homopolymer) and relaxed PET. We show that SECURUS™ fiber retains at high loading rates the characteristics that had at slow rates maintaining its advantage over the conventional yarns. We show that the amount of energy absorbed by SECURUS™ at the rates experienced by the belt during an accident is about 25% higher than the amount predicted by the static test. We conclude that the dynamic stress-strain curves should be used in mathematical models simulating sled tests or modeling collisions.