Damage development in GF/PET composite sheets with different fabric architecture produced of a commingled yarn

Glass fiber (GF) fabric-reinforced poly (ethylene terephthalate) (PET) composite sheets with various reinforcement architecture were produced by the autoclave bagging technique from a commingled yarn with a GF content of 65 wt% (similar to 50 vol%). The composite sheets were reinforced by swirl mat (SM), plane weft knitted (WK) and woven fabrics (WF), respectively, all of them containing continuous GF. The damage development and growth in the composites were studied on single-edge notched tensile loaded specimens (SEN-T) by location of the acoustic emission (AE) and by infrared thermography (IT). Both techniques are suitable to conclude the damage zone and assess the fiber structuring caused mechanical anisotropy. SM and WF proved to be isotropic reinforcements, whereas WK exhibited a strong dependence on the loading direction. The damage zone derived from the AE study was considerably larger than that from IT inspection. it was argued that the latter technique is sensitive only for detection of the process zone, which is a part of the overall damage. Assuming that the mechanical strength correlates with the size of the damage zone, the following ranking was concluded for the textile reinforcements incorporated: WK in course direction (90 degrees) less than or equal to SM < WK in wale direction (0 degrees) < WF.