| Summary: | 碩士 === 國立交通大學 === 機械工程學系 === 100 === This research aims to investigate the effect of local aggregation on tensile strength of particulate composites with an embedded crack. Particle size, volume fraction, interphase thickness and particle Young’s modulus were taken into account in the exploration. A micromechanical finite element model (FEM) accounting for the configuration of particle distribution was employed to study the particle aggregation effect on the fracture behavior of the composites. Basically, the concept of strain energy release rate anchored in the linear elastic fracture mechanics was adopted to evaluate the fracture behavior, from which the “normalized” tensile strength of the particulate composites with respective to the pure resin was determined. It is noted that all analysis was conduced based on the continuum mechanics approach in an attempt to efficiently save the computing cost. Results reveal that increasing particle size can deteriorate the tensile strength of the composites associated with the same volume fraction. Moreover, the declining behavior becomes more significant as particle aggregation taking place. Similar tendency was also observed in the composites with different volume fractions. The increase of particle volume fraction together with high extent of particle aggregation would dramatically decrease the tensile strength of composites. Basically the ratio of particle modulus to matrix modulus exhibits less influence on the normalized tensile strength of composites. In addition, the introduction of interface layer in the vicinity of particles also depicts little effect on the tensile strength of composites. When initial crack is embedded on the particle/matrix interface, the tensile strength of composite with good particle dispersion is not influenced by volume fraction. However, when the degree of aggregation increases, the rate of reduction in tensile strength is raising with the increment of particle volume fraction. Comparing the energy release rate of the composites with an embedded crack either in the matrix or on the interface revealed that when the crack size is much less than the particle diameter, the composites with crack in matrix demonstrates higher energy release rate than that with interfacial crack. On the other hand, when the crack size is compatible to that of particle size, the strain energy release rate calculated in both cases are quite close. In light of forgoing investigations, it is concluded that particle aggregation can considerably depreciate the tensile strength of composites, which is in a good agreement with experimental observations.
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