Abstract
The prediction of delamination onset is a challenging task in the design of thick tapered composite laminates, where multiple ply terminations (“drop-offs”) are present. This paper addresses the development of a global-local finite element-based design approach for tapered laminates, whereby layered Timoshenko beam models are employed to predict delamination initiation from individual drop-offs. This modelling strategy provides a fast and conservative method for evaluating the strength of tapered composite laminates. Parametric test cases are presented in order to validate the methodology and understand its limitations. Finally, the application of the tool to a relatively thick tapered composite test specimen comprising multiple ply-drops is demonstrated.
Highlights
The delamination initiation loads, Pinitiation, which correspond to a kink or a significant load drop in the load-displacement curves are obtained from Model (i) and Model (ii) for each of the tapered laminates considered here
It is found that delamination initiates from resin pocket in the thin section in all laminates, except for the case of 4_4_4_7°, i.e. for shallowest tapering angle
A considerable extent of interfacial failure between the resin pocket and the “belt” sub-laminate must occur before a thin section delamination can initiate
Summary
The design of tapered composite laminates is usually based on rules of thumb [3,4,5], which have been deduced both from experimental testing, strength/buckling optimisation and/or elementary fracture mechanics. These design guidelines involve: 1) having a minimum number of plies (thickness) dropped at any given station; 2) keeping the stagger distance between ply terminations to at least three times the dropped thickness; 3) terminating plies in order, starting from the stiffest (0°) and ending with the most compliant (90°); 4) keeping the laminate symmetric and balanced while plies are dropped, in order to avoid membrane/bending and bending/twisting coupling. The design guidelines discussed above do not allow for a strength assessment, even in an approximated fashion
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