DAMAGE AND FAILURE MECHANISMS OF CONTINUOUS GLASS-FIBER REINFORCED POLYPHENYLENE SULFIDE

The damage that accompanies flexural deformation of a unidirectional glass fiber composite of polyphenylene sulfide was examined by acoustic emission (AE) and scanning electron microscopy (SEM). These complementary techniques were used to identify damage mechanisms at the micro-scale and correlate them with the macroscopic stress state in four-point bending. The AE location technique made it possible to extend this approach to analysis of damage in more complex stress states than previously. A pair of AE sensors was used to determine the location of specific AE events in relation to the loading points. The flexural stress-strain curve was nominally linear to about 1.0% strain, but the onset of damage detectable by AE occurred at 0.3% strain. Two peaks in the AE amplitude distribution were observed at 35dB and 60dB. Low amplitude events were detected along the entire length of the specimen, and correlation with direct observations of damage made by deforming the composite on the SEM stage suggested that these events arose from matrix cracking and fiber debonding concentrated at flaws in the composite. High amplitude events occurred primarily in the region of highest flexural stress between the inner loading points, they were attributed to fracture of glass fibers on the tension side and surface damage on the compressive side.