Tearing of rubber

Abstract

There have been several studies on the tearing of rubber materials since the seminal paper on rupture of rubber was published by Rivlin and Thomas (1953).The behaviour is typically characterised using a fracture mechanics approach whereby the rubber has a geometrically independent relationship between crack growth rate during tearing versus strain energy release rate. This approach works well under conditions of steady tearing as the crack growth rate is easy to measure. However, this approach is much harder to interpret under the condition where the rubber exhibits discontinuous crack growth behaviour such as knotty tearing or stick slip tearing. Unfortunately, these are common tearing conditions observed in practice for filled rubbers as well as for some unfilled rubbers, especially those such as natural rubber that are capable of strain-induced crystallisation. Under these conditions it is not clear what the actual crack growth rate is as the value typically given results from the average of a very rapid tearing rate and a zero velocity tearing rate. The aim of this work is to develop a new approach to characterise the unsteady tearing behaviour of rubber in terms of the relationship between the rate of increase in the strain energy at the crack tip just immediately prior to the onset of the tearing which is quantified directly as the time derivative of the strain energy release rate · T , and the critical strain energy release rate T* required to propagate the crack. The approach adopted in this study is then evaluated using a range of different crystallising and non-crystallising rubbers as well as crystallising rubbers that have been modified to alter their crystallisation over a range of different test temperatures. Additionally, a new elastic-viscous transition diagram in association with the rate of change in the strain energy release rate at the tip of the crack is presented.