Matrix Cracking of High-Performance Composite Laminates with Variation of Laminate Stacking Sequence and Testing Temperature

Abstract

Extensive investigation has been done on composite cross-ply laminates; however, in practical use, the laminate layers are in multiple angles. The quasi-laminate is one example of a multi-angle laminate. Matrix fracture mechanisms of quasi-laminates are significant in composites design and application. This paper describes the experimental details in laminate parameter selection, microcracking tests, observation of matrix cracking mechanisms, and documentation of test results. The first material failure mode, matrix crack initiation, and matrix cracking propagation in the width and length of the specimen were determined. Results are presented for high-performance X5250/IM7 cross-ply and quasi-laminates in thin and thick prepregs. Ultrasonic C-scanning and optical microscopy were used as the primary means to detect and track matrix cracking. The specimens have a variety of lay-up sequences and thicknesses. The effects of stacking sequence and ply thickness on the matrix cracking behavior were determined. Based on test results, a finite element modeling approach was performed for quasi-laminates, which includes three-dimensional stress distribution analysis for the free edge and middle plane of the specimen. Both test results and theoretical analyses provide a deeper understanding of the matrix cracking mechanisms that operate at the microstructure level.