Strength and crack resistance of fibrous composite materials with polymer matrix under long-time static loading

Abstract

The essence of the method of determining the characteristics of crack resistance of composite materials with polymer matrix under long-time static load" 9 consists in the experimental determination of the curves of long-time strength, of the curves of crack growth or crack opening vs time at specified levels of a constant load. On the basis of these curves the functions of growth rate or opening rate of the cracks in dependence on the stress intensity factor and the duration of action of the load are determined. According to the nature of rupture of specimens with a crack under long-time static loading, composite materials can be divided into three types. In type A the crack propagates in the direction of the initial notch, rupture of the specimen occurs by its being split into two parts along the crack. Type B is characterized by the crack propagating perpendicularly to the initial crack up to the grips of the testing machine which may prevent the splitting of the specimens into two parts. In type C length of the crack does not increase during the testing, failure occurs suddenly in consequence of cumulation of damage that is hard to discover.