Accelerated testing for the durability of composite materials and structures

Abstract

Accelerated testing methodologies for metals have been studied for some time, but not enough studies have been performed on composite materials. One of the most popular tools used to predict the fatigue life of metals is the S-N curve, which is based on the assumption that fatigue life depends on cycles, but not on time. Accelerating the test is an easy task using the S-N curves, as the cyclic loads can be applied at much higher frequencies than the actual loading. Developing a testing procedure to establish the lifetimes of materials in extreme service environments is becoming a high priority. Existing accelerated testing methodologies for metals cannot be simply applied to composite materials, because these methodologies are not intended for visco-elastic materials such as polymeric composite materials, which exhibit strong time and temperature dependencies. The accelerated testing methodology is based on the time-temperature superposition principle for polymeric materials. This principle was originally developed for nondestructive material properties, but recent studies have shown that it can also be applied to failure properties of composite materials.