Numerical simulation of fatigue failure in carbon fibre reinforced aluminium alloy laminates

Hybrid laminates typically consist of alternate layers of fibre reinforced plastic and aluminium alloy. Developed for fatigue critical aerospace applications i.e. fuselage and lower wing skins, the hybrid laminates are orthotropic materials with lower density and higher strength compared to the alloy monolith. A remote sensing system reliant upon fibre optic technology has been developed to monitor the strain field encountered across composite laminae. This fibre optic system has been applied initially to the problem of characterising delamination zone development about a fatigue crack initiated at a through thickness fastener hole. Delamination measurements obtained using an in-situ ultrasonic C-scanner have been utilised in numerical simulations of the fatigue failure process and the data compared with measured strain profiles

Miniature multiplexed fibre-grating-array sensor for the interrogation of localised strain patterns during crack growth studies upon hybrid laminate panels

As part of a project to optimise hybrid laminates for resistance to fatigue failure, arrays of fibre Bragg gratings are being used to monitor small-scale strain perturbations in composite materials. A remote multiplexed sensing system with 40 remote sensing sites using fibre optic technology, has been developed to monitor the strain field developed across the composite lamina of a hybrid laminate in the vicinity of a fatigue crack. Developed primarily for fatigue-critical aerospace applications, i.e. fuselage and lower wing skins, the hybrid laminates are orthotropic materials having lower density and higher strength than a simple alloy monolith without reinforcement. Fatigue crack growth in hybrid laminates is a complex process that involves a combination of delamination and fibre bridging. The fibre optic system has been applied to the problem of characterising delamination zone development about a fatigue crack, initiated at a through-thickness fastener hole

Damage assessment across hybrid laminates using an array of embedded fibre optic sensors

Hybrid laminates typically consist of alternate layers of fibre-reinforced polymer and aluminium alloy. Developed primarily for fatigue critical aerospace applications, the hybrid laminates are orthotropic materials with lower density and higher strength compared to the aluminium alloy monolith. One of the damage mechanisms of particular interest is that of fatigue crack growth, which for hybrid laminates is a relatively complex process that includes a combination of delamination and fibre bridging. To facilitate the development of a unified model for both crack and damage growth processes, a remote sensing system, reliant upon fibre optic sensor technology, has been utilised to monitor strain within the composite layer. The fibre optic system, with capacity for sub microstrain resolution, combines time domain multiplexing with line switching to monitor continuously an array of Bragg grating sensors. Herein are detailed the findings from a study performed using an array of 40 sensors distributed across a small area of a test piece containing a fatigue crack initiated at a through-thickness fastener hole. Together with details of system operation, sensor measurements of the strain profiles associated with the developing delamination zone are reported

Fatigue damage in carbon fibre reinforced aluminium alloy laminates

This research seeks to develop a unified model for fatigue crack and damage growth processes in a hybrid laminate. The progress of damage in a carbon fibre reinforced aluminium alloy laminate has been monitored, while simultaneously the strain within a defined area in the vicinity of the crack has been measured directly, by means of fibre optic sensors. Some preliminary finite element modelling results are presented. It is shown that the range of the stress intensity factor remains the most significant parameter for characterising fatigue crack growth. A stress intensity factor, modified to account for the changing compliance introduced by fibre-bridging and delamination, was found to be appropriate for these materials