Low temperature strength and notch sensitivity of glass mat polypropylene

Literature on the effects of lowered temperature on the toughness of random short fiber composites have neither offered a clear trend nor explained the mechanisms of failure. In this work, unnotched and notched strengths at room temperature and -30 degrees C of two glass melt polypropylenes with different fiber architectures are investigated. Observations are explained based on models for Young's modulus and notch sensitivity. Increases in strength and stiffness with Lowered temperature are caused by increased matrix modulus and yield stress. Fiber bridging operating in a damage zone of substantial length was the major toughening mechanism and forms the basis for the modeling approach for notch sensitivity. Increased notch toughness at low temperature is caused by increased work of fracture in the damage zone. The increased matrix modulus and yield stress lead to an increased toughening efficiency of short fibers.