Controlling Failure of Polymer Skin/Foam Bilaminate Sheets 2007-01-1216
Controlling the failure of polymer skin/foam bilaminate sheets is often accomplished by creating a line-shape weakening. For applications such as certain types of passenger-side seamless airbag systems, the failure must occur only along the weakened line with no fragmentation and the line's location must not be visible before airbag deployment. When the weakening is created by mechanically scoring the polymer skin on its back surface, where it is bonded to the foam, the weakness of the bilaminate is determined by the depth of the score groove. The deeper the groove, the weaker the bilaminate and the easier it is to control the failure. But also, the deeper the groove, the more likely the groove will read-through to the front surface, allowing its location to be visible. Several quasi-shear and tensile tests were conducted. Fragmentation was found to be likely when the skin and foam delaminated and failed separately, rather than failing together, but delamination could be avoided if the local strain at the groove reached the ultimate strain of the skin prior to the general strain in the bilaminate reaching the ultimate strain of the foam. Techniques found to minimize the groove depth, to avoid read-through, and still achieving fragmentation-free failure, were to increase skin thickness, reduce skin strain hardening, and increase foam ultimate elongation.