SYNOPSISThe effect of processing temperature on the low-speed tensile and high-speed impact properties of novel ABS/PET blends was investigated. In agreement with the conclusions from related studies of ABS/PC blends, it appears that catalytic impurities in the ABS accentuate the propensity of PET for chain scission. Due to the cocontinuous structure of the blend, the hydrolytic or thermomechanical degradation of the PET results in a dramatic loss in mechanical properties which can be explained by the entanglement theory for fracture and the Orowan brittle-ductile hypothesis. 0

AbstracL The tear resistance of multi-layered plastic films can be generally predicted from the tear resistance of individual layers by an additive rule. The most notable exception from this additive rule is the case of multi-layered films containing a polyethylene layer. The reason for this specific case is explained by the constraint on the plastic yield zone of polyethylene, which causes a dramatic drop in the tear resistance of the multi-layered film. An extensive plastic zone is generated during the tear fracture of a single layer polyethylene film. This yield zone does not appear when polyethylene is laminated with other polymer films.

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Peening is a technique commonly used to improve fatigue resistance, but it is not always appreciated that excessive peening may be detrimental to fatigue behaviour. The present work demonstrates this effect in three different alloys: a mild steel, stainless steel, and a commercial copper alloy. The dependence of fatigue behaviour on peening intensity is shown to reach a maximum beyond which high intensity peening reduces fatigue life; at very high intensities the fatigue life can be reduced below the unpeened value. This reduction in fatigue life is shown to coincide with an increase in surface roughness, as measured by the parameter Ra, and the onset of a distinct damage mechanism revealed by scanning electron microscopy. The varying effect of peening intensity in the different materials is related to their tensile, fatigue, and wear properties; a model is advanced to explain the observed behaviour, based on the change from an initiation dominated mechanism to a propagation dominated mechanism as peening intensity is increased. A limited number of results is also presented showing the effect of peening time on fatigue behaviour.

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