FAILURE MODE AND DAMAGE ZONE DEVELOPMENT IN A GMT-PP BY ACOUSTIC-EMISSION AND THERMOGRAPHY

The failure behavior and the damage zone growth in a glass fiber mat-reinforced thermoplastic polypropylene (GMT-PP) were studied on static tensile loaded single-edge notched (SEN-T) and compact-tension (CT) specimens at room temperature by using different techniques, such as light microcopy (LM), acoustic emission (AE) and infrared thermography (IT). In the knowledge of the assignation of the AE parameters to the individual failure events the failure sequence was concluded. It was established by AE that the failure mode, and especially the onset of fiber fracture, strongly depends on the fiber content (V-f) of the GMT-PP. This was attributed to an impediment in the mesh-type deformability of the reinforcing mat by increasing V-f. The size of the damage zone was considerably underestimated when deduced from the stress-whitened zone in the LM pictures taken during the loading of the specimens (diameter approximate to 5 mm). Location of the AE by a four sensors array resulted in much higher values (diameter approximate to 30mm) being practically unaffected by V-f in the studied range (V-f approximate to 20 to 30 vol.%). The damage zone size derived from IT layed between those of LM and AE (diameter approximate to 11-16 mm). The occurrence of such a large damage zone clearly demonstrates that reliable mechanical data on GMTs can be determined only by using specimens of adequate size (width). It was assumed that the whole damage zone (encompassing a process and a dissipation part) is assessed by AE during the whole fracture process, whereas LM and IT reflect mostly its process zone constituent in the crack initiation and propagation stages, respectively.