Acoustic emission characteristics of micro-failure processes in polymer blends and composites

Acoustic emission (AE)characteristics of micro-failure processes in HDPE/PP blends with and without compatibilizer, single- ®bre composites (glass/epoxy, carbon/epoxy, glass/polycarbonate)and unidirectionally reinforced multi-®bre composites (glass/ polypropylene)were studied. For blends, the number and the elastic fracture energy release of micro-failure processes are theore- tically approximated and correlated with the number of AE signals and the AE energy. A qualitative correlation of the mechanical energy released from ®bre/matrix debonding and ®bre-fracture processes in single-®bre pull-out experiments with the measured AE energy is demonstrated. For the single-®bre fragmentation of glass ®bres and carbon ®bres, a quantitative approximation of the AE amplitudes at locations of the fragmentation sources is achieved. A new method for the selection of single transient acoustic emis- sions and the classi®cation of failure mechanisms in composites is introduced. Selected emissions are classi®ed into matrix cracking, ®bre breakage and interface processes (®bre/matrix debonding or ®bre pull-out)from their total power in de®ned frequency inter- vals of the spectral power density. A fracture-mechanics investigation of the delamination behaviour of unidirectional composites accompanied by AE examinations is discussed. The extension of the damage zone around the crack tip is quanti®ed by the location of AE events and compared with the theoretically approximated dimensions. The size of the damage zone is used for theoretical calculations of the mechanical energy release from micro-failure processes. A correlation of the AE energy-release rates with the mechanical energy-release rates from participated failure mechanisms like matrix cacking, ®bre/matrix debonding and ®bre break- age is presented.