Viscoelastic Strip

Associate Professor, Graduate Aeronautical laboratories, California Institute of Technology, Pasadena, Calif. The tip velocity of a crack propagating through a vi scoelastic material depends on geometry, apptied toad and its history , and material properties. A consideration of the work done by the unloading tractions at the crack tip shows that, f or a large crack propagating throitgh an infini tely long strip under constant lateral strain, the rate of propagation can be calrnlated from a knowledge of the i ntri nsic fracture energy (a material constant), the material creep compliance, and an additional size parameter. This parameter vanishes from the analysis if the material is elastic, and the familiar instability criterion is obtained in this case. Comparison with experimental data i s provided and the consequences of step loadings are examined.