Design of a test for investigation of failure mode interaction in composite laminates

The curved composite parts are used in several modern aircraft and the mechanism of the failure requires detailed analysis. To correlate and validate non-linear analyses, experiments must be conducted. Without a preliminary examination of the specimen, it would be impossible to conduct the experiments and reach the data properly. In this study, the failure analysis and Monte Carlo Simulation are performed by applying criteria calibrated on the basis of the material allowables. The material allowables of Hexcel 8552 AS4 Unidirectional prepreg at 190 gsm 35 RC are determined by the tests that have been performed in different places and are collected in public database. A statistical approach is necessary for the failure analysis because the mechanical properties cannot be certainly defined. The data have shown that the inspected properties can be fitted to a normal distribution by normality test. Hashin’s failure criteria are applied to 3 curved composite laminates that have different stacking sequences. The reason for the application of Hashin’s criterions was the convenience to discriminate the failure modes. Finite Element Models by using solid elements are created in Abaqus CAE and the linear computation is done by Abaqus/Standard. To be able to observe and obtain the results of criteria, the data about the positions of a failure, the userdefined output must have been created in Abaqus. This was a inconvenient procedure since it requires several manipulation by hand and time. Moreover, Abaqus has user-subroutine called UVARM and this makes possible to call necessary variables for the equations for element calculation points that are asked. The subroutine is linked to Abaqus/Standard by Fortran file. The whole procedure is automatized by writing MATLAB scripts that are creating the necessary input and Fortran files to Abaqus and linking them together to run it by sending commands for each different sampling. The displacements at the failure initiation with respect to the criteria are calculated. The results have shown that some failure modes can be initiated in different plies. Importantly, they show how the test designed can be used to study different types of failure, including interlaminar cracks, delamination, and interaction between both type of damages.