Reliability of notched composite laminates using a combined experimental investigation and stochastic finite element analysis methodology

摘要

The design of notched composite laminates is based on the averaged stress over certain characteristic distance from the notch edge and the strength of the corresponding un-notched laminate. In practice, the notch geometry is not perfect due to machining conditions and the mechanical properties of composite laminates. The imperfections in notch geometry have a stochastic distribution. On the other hand, tests on laminate coupons show that the un-notched strength also has a stochastic distribution. Accordingly, the characteristic length used in design has a stochastic distribution. Therefore, in order to achieve a design with a required reliability and safety, (ⅰ) the stress analysis of the notched laminate has to be conducted based on a stochastic approach, (ⅱ) the strength distribution and its probabilistic parameters have to be determined through a number of tests, and (ⅲ) the reliability analysis has to be conducted. The present work considers these objectives. A stochastic finite element analysis of notched symmetric cross-ply [0/90]_(4s) and angle-ply [0_2/+-45]_(2s) composite laminates is conducted. The hole shape is modeled using a hypotrochoid variation and further, the location of the hole centre is modeled as a Gaussian random variable. The resulting stress distribution and the averaged stress are determined and they are modeled using both Gaussian and Lognormal random variables. The distributions of the strength and the characteristic length of the laminates with symmetric cross-ply [0/90]_(4s) configuration are determined through testing 25 samples of notched and 25 samples of un-notched laminates. In a similar manner, tests on angle-ply laminate [0_2/+-45]_(2s) are conducted. The reliability indices for the two laminate configurations are calculated by combining the stochastic finite element analysis and the test results.