Studies on interlaminar fracture of composites for aerospace structures

Abstract

The interlaminar fracture toughness is a measure of the ability of material to resist delamination The experimental determination of the resistance to delamination is very important in aerospace applications newlineDifferent kind of specimens and experimental methods are employed to newlinemeasure the interlaminar fracture toughness of composite materials The aim newlineof the present research is to gain a better understanding of interlaminar newlinefacture of polymer matrix composites in different modes and to develop newlinemathematical model to predict the critical strain energy release rates newlineEmphasis has been placed on the root rotation at the crack tip newlinewhich was believed to be a critical factor which affects the delamination newlinefracture toughness and critical load. A combined experimental and newlinetheoretical study has been conducted to determine the role of root rotation on newlinecritical load The goal of predicting the dependence of root rotation on critical newlinestrain energy release rate under mode I is achieved The first part of the newlinepresent study examines interlaminar fracture toughness of Double Cantilever newlineBeam (DCB) specimens based on a modified Timoshenko beam model newlineconsidering the root rotation Load displacement and crack length are prone to measurement errors A weighted residual approach is proposed in this thesis to minimize newlinethe scatter in measurements The critical fracture energy has been evaluated newlinebased on the proposed approach and hence the influence of error in newlinemeasurements has been minimized The critical fracture energy evaluated newlinebased on the weighted residual approach gives a unique value for the newlineparticular specimen newline newline