A NEW MECHANISM FOR INCREASING TEAR STRENGTH AND CUT-GROWTH RESISTANCE OF ELASTOMERS

A new mechanism is presented for increasing the tear strength of noncr ystallizing elastomers over a broad temperature range. It is shown tha t the incorporation, into elastomers, of a plastic filler with the pro per yield strength can substantially increase tear strength by decreas ing the excess stress that develops at the tip of a sharp cut in an el astomer strip under tension. To be effective at low aspect (length/dia meter) ratio, the yield strength of the plastic must be of the same or der of magnitude as the tensile strength of the elastomer to which it is added. The analysis is strictly valid only for very small deformati ons, where crack-tip blunting can be ignored, and for an applied stres s sufficiently low that the plastic-yielding zone is very small relati ve to the crack length. It provides a useful model, at least, for the development of a new mechanism for increasing the tear strength of flu oroelastomers at sufficiently high temperatures, which is of significa nt practical importance. Examples of the use of a new fluoroplastic mi cropowder to provide over a fourfold increase in tear strength of seve ral fluoroelastomers at high temperatures are given.