Abstract

The reliability of notched composite laminates is determined to find its worthiness for the intended application and it is affected by various factors, such as, application of fatigue loading, notch location, notch shape and size, etc. In the present work, an attempt has been made to study the effects of fatigue loading and notch location on the reliability of notched composite laminates. The reliability values of notched laminates are calculated by using the following parameters: the stress developed in the laminate due to external loading and the strength of the corresponding un-notched laminates. Since composite laminates exhibit stochastic variations in material properties, Stochastic Finite Element Analysis (SFEA) is used to calculate the stresses developed in the laminate. The ultimate strengths of the un-notched laminates are found out experimentally. Tests are conducted on specimens made of NCT301 graphite/epoxy material to determine the material properties that are required for the SFEA. The material properties are modeled using Markov model based on the test data by two dimensional stochastic processes. Tests are also conducted on center-notched laminates subjected to fatigue loading conditions, Edge-notched laminates and un-notched laminates to determine their ultimate strength values. In practical applications, it is difficult to achieve a perfect circular profile during the drilling operation of notched composite laminates and there is a possibility that the drilled hole is offset from the desired location. These imperfections affect the reliability of the notched laminate. In the present work the perturbation in the circular profile of the hole is modeled using a hypotrochoid variation and the location of the hole center is modeled using a Gaussian random variable. The ultimate strength values of center-notched laminates subjected to fatigue loading conditions, Edge-notched laminates and un-notched laminates, obtained from experiments are used to determine the sets of characteristic length values for both the point stress criterion and average stress criterion. The distributions of the strength and characteristic length of laminates are determined. Stochastic simulations are performed on the laminates by subjecting them to tensile load. Probabilistic moments of the point stress and average stress parameters are found out for controlled hole and un-controlled hole laminates. The reliability values are calculated for the center-notched laminates subjected to fatigue loading conditions and Edge-notched laminates using point stress criterion and average stress criterion by combining the SFEA and experimental results.