ABSTRACT

The paper presents the calibration of a numerical collapse model of unidirectional fiberglass epoxy panels with an initially embedded delamination. The panels were tested under axial compression, able to induce buckling collapse. The penalty stiffness, the strength and the fracture toughness are the key parameters governing the cohesive interface. Their influence is investigated by a sensitivity analysis, aimed at adjusting the cohesive properties in order to calibrate the FE model based on the results of the experiments. The work serves as the basis for a promising strategy aimed at improving the current numerical models with progressive growing delaminations.

INTRODUCTION

The present work describes the calibration process of the cohesive parameters of a numerical model simulating a unidirectional fiberglass epoxy plate with an embedded delamination. The high thickness of the plate is typical for large wind turbine blades, but it may also apply to naval vessels or large yachts. Delamination is a critical failure mode for composites, in particular when subjected to compressive force, since local and global buckling modes may occur in the sub-laminates giving rise to sudden catastrophic failure. Typically, delaminations may be generated in the manufacturing stage, due to impact load during service, or they may grow from decohesion due to cyclic loads.

Two plates were manufactured by vacuum bag infusion and two by preimpregnated layers consolidated in a vacuum bag. A Teflon® rectangle is embedded to originate an initial delamination, whose size and depth are properly chosen. Initially, the four plates were tested to failure under a compressive force. Later, small specimens were cut out from the intact edges of the plates and prepared for small-scale experiments according to ASTM standard D3846-79, to assess the inter-laminar shear strength of the laminate. Since a previous experimental campaign found important imperfections originating in the manufacturing methods of the pre-preg panels, the calibration focuses on the infusion made plates (Godani et al. 2015).

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