Acoustic emission study of impact-damaged GRP pipes

Acoustic emission monitoring techniques have been used to investigate the effects of external damage on the structural integrity of GRP pipes. The pipes were 100 mm bore and 5.5 mm wall thickness, and were of wrapped chopped strand mat glass/polyester construction. Damage caused by severe impacts, of net energies up to 43 J, exerted a marked influence on the observed acoustic emissions from pipes subsequently pressurized to failure, but even though severe microstructural damage was caused by these impacts, they did not reduce the load-bearing capacity of the pipes in any way. The presence of stress concentrators in the form of axial saw-cuts resulted in a changing response to loading roughly in accordance with fracture mechanics predictions, and the results help to explain to some extent the apparently conflicting conclusions from the impact damage studies. Thus, although AE analysis was, for these materials, able to provide a clear indication of the presence of microstructural damage, it is clear that such indications can only be of value in detecting loss of structural integrity (load-bearing ability) when considered in conjunction with other information about the materials involved. Filament-wound pipes, for example, do not behave in the same manner. Amplitude analysis of the AE signals does not appear to be of significant value in giving indications of the nature of the impact damage.