Long-term fracture of partially crystalline polymer materials in a plane stress state and nonstationary cyclic loading

Abstract

It was shown in [i, 2] that the force equation of damage of the hereditary type can be used to describe the long-term fracture of partially crystalline polymer materials and composites in a multiaxial stress state and nonstationary loading. The damage equations derived in these studies were used for the case of the so-called static fatigue which is associated with holding the element of the material with time under the stress of a specific level. However, as indicated by the experimental data in [i], the partially crystalline polymer materials and, evidently, various composites show not only static but also cyclic fatigue in the cyclic loading conditions. Cyclic fatigue is associated with periodic changes of the stresses and not with holding under stress with time. It is well known that the ductile crystalline materials, primarily structural metals and alloys, are susceptible to cyclic fatigue~