Development of impact-resistant polymeric materials by nano structure control

点击翻译按钮获取中文摘要

New experimental techniques for evaluating the impact fracture toughness of polymers and composite materials were developed. The validity and adaptability of the techniques were then examined by testing the various materials including biodegradable polymers and composites. The techniques were also applied to these materials which changed their structures in the nano- and micro-scopic level. The impact fracture mechanism was then investigated.The impact fracture mechanism was studied by measuring the dynamic response and residual deformation of the specimen materials after fracture. The dynamic and non-elastic effects were analyzed, because the fracture toughness of polymers is generally dependent on both the viscosity of material and the dynamic effect due to the crack propagation. These two effects were taken into consideration in the impact analysis. The external work applied to the specimen was partitioned into three components : the elastic energy, non-elastic energy, and fracture energy for creating a new fracture surface. The energy release rate was estimated to examine the impact fracture mechanism in detail.The structures of biodegradable polymers and composite materials were modified by annealing, blending and/or mixing with different biodegradable materials. The fracture toughness of the specimens was measured under static and impact loadings, and the morphology of the fracture surfaces and damage zone ahead of the crack front were also examined using polarizing microscopy and scanning electron microscopy. As a fracture parameter that controls crack growth, the energy release rate was determined using a load and displacement diagram, and it was shown that the fracture toughness can be clearly improvable by controlling the structures by nano- and micro-scopic level.