Time Dependent Static Strength and Reliability for Composites

Abstract

An experimental investigation was conducted to study the fracture properties of laminated composites under uni-axial tension. It was found that the distribution of breaking strength of a composite ma terial under a constant stress rate or variable stress history can be described accurately by the Weibull distribution. The shape param eter of the distribution was shown to remain nearly constant under varying loading conditions, temperatures and strength degradations. A relation between the shape parameter and breaking strength- lifetime curve was established. Using these data, a reliability plan was developed, taking into consideration order statistics, sample size and time dependence. A proof test experiment was performed which showed that, for this particular material at least, proof testing is an effective method of removing weak members from a population. It is concluded that composite materials can be designed to yield structure with a higher degree of reliability per unit weight than its equivalent metallic structure.