Subsurface fatigue crack growth in Glare fibre metal laminates
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Abstract
The investigation of the present thesis is concerned with the fatigue crack growth behaviour of part through the thickness cracks in Glare™ fibre metal laminate (FML) subjected to combined tension and bending. An experimental program was executed which required the development of a novel fatigue specimen, the Milled Open Hole Tension Bending (MOHTB) specimen. This was developed in order to have an easily configured specimen with desired combined tension and bending stress states, and to ensure the stability of the stress levels during fatigue loading. Fatigue data was captured for all plies of the laminates. Tests were conducted on Glare 2A and Glare 3 specimens. A hybrid analytical/numerical fatigue crack growth prediction model for surface and subsurface cracks in Glare 2A was developed. Finite element modelling was required to gather fibre bridging stress distributions for the plies of the laminates. Analysis led to a stress intensity factor formulation for the crack restraining effects of the fibre bridging. This stress intensity factor, and one to account for far field loading and the specimen geometry, were superimposed into a Paris law crack growth model and was solved numerically. With this crack growth model, crack propagation curves were generated correlating to experimental conditions observed in the laboratory. The hybrid crack growth model was evaluated against the experimental data for the Glare 2A and Glare 3 specimens. The results of the comparison showed good agreement between the prediction and the experimental data.