Strength Analysis of a Composite Laminate by First Order Reliability and Branch & Bound Methods

Composite materials are used frequently in industrial structures such as airplane and space vehicles. Strength and probability of failure is an important challenge for designer engineers. In this paper a practical method to determine ultimate strength of a composite laminate is explained, this method based on reliability prediction. Strength of each layers and total strength is calculated using First Order Reliability Method and failures sequence is determined by Branch & bound method. In this study two modes for failure are assumed: fiber fracture and matrix fracture. At first step, stress distribution is calculated by FE software (ANSYS Package) then according to failure mode and first order reliability method, reliability index is determined. At the second step, probability of failures mode in all layers are determined. At the end, the important sequences for the failures are determined using branch and bound method. Comparison of this method result with Monte Carlo simulation shows accuracy of this method to predict failure mode and probability of composite laminate failure.