Predicting interlaminar damage behaviour of fibre-metal laminates containing adhesive joints under bending loads

This study includes experimental and numerical investigations on fibre-metal laminate structures containing adhesive joints under static bending loads. Experimental tests were carried out on Glare® 4B specimens manufactured in-house and containing doubler joint features. Numerical analyses were performed using Abaqus software including damage in the glass fibre reinforced polymer layers, ductile damage in the resin pockets (FM94 epoxy) and plasticity in the metal layers. A new cohesive zone model coupling friction and interfacial shear under through-thickness compressive stress has been developed to simulate delamination initiation and growth at the metal/fibre interfaces with the adhesive joint under flexural loading. This model is implemented through a user-defined VUMAT subroutine in the Abaqus/Explicit software and includes two main approaches, firstly, combining friction and interfacial shear stresses created in the interlaminar layers of the fibre-metal laminate as a result of through-thickness stresses and secondly, considering elastic-plastic damage behaviour using a new cohesive zone model based on the trapezoidal law (which provides more accurate results for the simulation of toughened epoxy matrices than the commonly used bilinear cohesive zone model). Numerical results have been validated against experimental data from 4-point bending tests and a good correlation observed with respect to both crack initiation and evolution. Delamination and shear failure were noted to be the predominant failure modes under bending stresses as expected. This is due to the higher mode-II stresses introduced during bending which cause different damage evolution behaviour to that seen for axial stresses. Finite element results revealed that both friction and shear strength parameters generated from through-thickness compression stresses have a significant effect in predicting damage in fibre-metal laminate structures under this type of loading.

A Numerical Approach to Estimate First Ply Failure of Fibre Metal Laminate

Fibre Metal Laminates (FMLs) are laminates consisting of metal layers and fibre reinforced composite layers. These laminates are designed to improve some specific properties of constituent metals and composites layers. Estimation of First Ply Failure (FPF) Loads of these FMLs is a part in the broad characterization of these materials. A numerical method is developed for the estimation of FPF when these laminates are used as simply supported plates subjected to uniformly distributed load. Various failure criterions are used to identify these loads. The proposed method has been validated with the results of exact (Navier) solution available in the literature. FPFs are estimated for different groups of FMLs based on Aluminum, Titanium and Magnesium layers. The results are presented in the form of non-dimensional FPF and deformation values for various aspect ratios.