The Study Of Imperfect Interfacial Stiffness In Particle Reinforced Composites

Particle reinforced composites(PRCs) are considered as high specific modulus and strength, In general, epoxy resins, polyesters, silicones, polyurethanes, and several other polymers are used as matrix, while the reinforcements have been made of glass, carbon, ceramics, polymers, and even metals, thus applied in many manufacture industries comprehensively. The mechanical properties of composites are dependent on micro structural composition, mechanical characteristic of microstructure and interfacial bonding. However, the theoretical models considering many assumptions neglect the effects of microstructure in PRCs, the single fiber pull out experiment is not suitable for PRCs and the FEM of homogenization merely considered the imperfect interface.This thesis presents the effect of the interfacial stiffness on the effective modulus in particle reinforced composites. The mechanical properties of particle/matrix imperfect interface are defined by the cohesive zone model(CZM). Considering the Mori-Tanaka(M-T) method, dilute solution and finite element model(FEM) associated with CZM, Our results present the monotonic increasing relation curves of effective modulus and imperfect interfacial stiffness. The imperfect interfacial stiffness characterized by a unique critical point(CP) dominates the way of how volume fraction affects the effective modulus. This thesis discussed the factors influencing the position of CP. Employing the relation curves together with the experimental effective modulus leads to the estimated results of the imperfect interfacial stiffness in different kinds of composites. The parametric study of different elastic properties between matrix and particles shows that the relation curves present the regular pattern of three types for different composites.To study the relation between interfacial stiffness and effective modulus, with the 3D representative volume element(RVE) generated via Python script in ABAQUS, we built a real microstructure 3D RVE considering the interface, the different particle size, morph, geometric and material orientation using Random sequential absorption(RSA) combining with Gaussian distribution to insert the particles. This thesis studied the reasonable size of the RVE. Adopting the strain energy method, we solved the difficulty in extracting the normal stress in interface via homogenization method, and with the equilibrium equation between strain energy(including matrix, particles and interface) in FEM and the one presented by stiffness tensor components, the relation between effective elastic parameters and the interfacial stiffness in orthotropic composite materials were found. The parameters of CZM was estimated through Spruce/PP and the effect of hollow particle size on the effective elastic modulus were discussed in SiC/epoxy.The mapping of different kinds of composites such as cellular material, polymer matrix composite and metal matrix composite are obtained in the relation curves, and thus giving us the basis in interface designing.