Analysis of microdamage evolution histories in composites

Evolution of microdamage in advanced composites was experimentally studied in this paper. A new method of acoustic emission (AE) analysis of histories of different damage mechanisms was formulated based on a combination of transient AE classification and multiparameter filtering. The capabilities of the method were illustrated on examples of damage evolution in several graphite/epoxy composites. Three characteristic AE waveforms with different frequency spectra were identified based on the transient analysis. Regions occupied by these waveforms in the amplitude-rise time parametric space were identified for the [0]₈ and [90]₁₆ unidirectional composites. Multiparameter filtering was applied to extract evolution histories for the characteristic waveforms. The results were compared with actual damage in the specimens and the three characteristic AE waveforms were associated with matrix cracks, fiber breaks, and `macrodamage', such as delaminations or longitudinal splitting in unidirectional plies. The multiparameter filters based on the analysis of the unidirectional composites were used to extract the damage evolution histories for the cross-ply [0/90]_3S and angle-ply [±45]_4S composites. The results compared favourably with the observed damage in these materials. An inverse analysis of the quality of the multiparameter filtering for the laminated composites indicated that the filters developed for unidirectional composites can be applied to the analysis of laminated composites with reasonable reliability. The new method of acoustic emission analysis of damage micromechanisms is expected to be especially advantageous for fatigue damage evolution studies in composites and structures.