Researches On Fracture And Fracture Mechanism Of A New Type Wood-Plastic Composite

This thesis studies mechanical and physical properties, fracture and the mechanisms of wood-plastic composites which make up of rice paddies and recycled PE. Mechanical and physical properties are gotten by tension test, compression test, three-point bending test, nail-holding test, rigidity test, impact test, water absorption test and so on. Fracture toughness of I fracture mode is analyzed and tested by tension test and three-point bending test. The fracture toughness is gotten and the most appropriate test way is proposed. The influence to the fracture toughness by low temperature is analyzed and tested by three-point bending test. The fracture mechanism of wood-plastic composites is gotten by analyzing fracture planes. It is testified that the wood-plastic composites belong to brittle material by tension test and compression test and that the tension elastic modulus is practically equal to the compression elastic modulus. It can result from tension, compression, and three-point bending test that the stress-strain relationship is according to Hook's Law and the typical bending-stress formula can be used for calculating bending strength. Samples with prefabricated cracks are used in fracture toughness test. The most appropriate dimensions of the samples are proposedThe bending strength and the fracture toughness of the wood-plastic composites both are weakening as the time of low temperature treatment increases. However, both of the bending strength and the fracture toughness of low-temperature-treated samples are stronger than normal samples. The fracture planes show that the fracture belongs to a kind of brittle fracture and that it is the mechanism of fracture of the material that the cracks spread at the joints of filling and prime matter. Some propositions are given in this thesis to enhance the strength and the fracture toughness of the wood-plastic composites: (1) To enhance the binding strength between the filling and the prime matter; (2) To increase the fiber content of the filling; (3) To weaken the filling coalescence.