Accelerated testing for the durability of composite materials and structures

Developing a testing procedure to establish the lifetimes of materials in extreme service environments is becoming a high priority. With service lifetimes measured in years, it is almost unthinkable to do real time testing under a variety of conditions. Existing accelerated testing methodologies for metals cannot be simply applied to composite materials, since these methodologies are not intended for viscoelastic materials such as polymeric composite materials, which exhibits strong time and temperature dependencies. Our accelerated testing methodology is based on the time-temperature superposition principle for polymeric materials. This principle was originally developed for non-destructive material properties, but recent studies have shown that it can also be applied to failure properties of composite materials. Using this principle as the building block, we have developed a methodology to predict the long-term life of composite materials, such as the static (constant strain rate) strength, creep life, and fatigue life. The details of the methodology and its four required conditions are shown in this paper. The range of applicability of the methodology has been studied for various material systems and test configurations, and was found applicable to most typical polymeric composite materials.