Effects of hygrothermal aging on the fracture and failure behavior in short glass fiber‐reinforced, toughened poly(butylene terephthalate) composites

Abstract The fracture response of injection molded short glass fiber (GF) reinforced and rubber‐toughened poly(butylene terephthalate) (PBT) composites has been characterized by the fracture toughness (K_c) and energy (G_c), measured on static‐loaded compact tension (CT) specimens. The related failure of the composites with 30 wt% GF reinforcement in as‐received (AR), hygrothermally aged (HA) and re‐dried (RD) states, respectively, was studied by acoustic emission (AE) and fractography. Tougheners were functionalized ethylene/acrylate (EAF), crosslinked acrylate (XAR) and core‐shell type (CSR) rubbers, at 20 wt% in the composites. It was shown that both K_c and G_c decrease with hygrothermal aging at 90°C, and their values cannot be restored by subsequent drying. This is attributed to severe hydrolysis degradation of the PBT matrix. Deterioration in the fracture parameters was affected by the composition of the rubbery toughener: The toughness retention by EAF was superior to the other modifiers. The difference in the failure mode of the GF‐PBT composites before and after hygrothermal aging was revealed by viewing the fracture surface of the CT‐specimens in scanning electron microscope (SEM). Based on the fractographic results, changes in the AE amplitude envelopes are interpreted and discussed.