Damage tolerance in glass reinforced polymer laminates

Ten glass-reinforced, rubber-toughened polymer laminate panels were tested in 3-point bending in a series of loading–unloading cycles, with increasing deflection. Damage was quantified by the stiffness decrease, hysteresis and residual strain. The threshold for unacceptable damage occurred when the strain reached ca. 0.6%. Acoustic emission (AE) was monitored by four sensors on the compressive side of the samples; the correspondence between the damage threshold and different AE measures was explored, with hit strength (i.e., the measured area under the rectified signal envelope, or MARSE) providing the clearest correlation. Separating events with AE hits that were recorded by all four sensors (“associated”) from those recorded by three or fewer sensors (“unassociated”), distinguished matrix from fiber damage. Viscoelastic effects were identified by separating hits that occurred during loading from those that occurred during hold and unloading.