Based on the micromechanical framework for particle-reinforced composites of Ju and Chen and Qu's one-order modified Eshelby tensor for slightly weakened interfaces,a general micromechanical method for effective modulus prediction of elastic multi-phase composites containing randomly dispersed slightly weakened interfacial heterogeneities was proposed with pair-wise particle interactions.Through the ensemble-volume averaged procedure,a set of micromechanical constitutive equations were presented.Effective elastic properties of multi-phase composites without pair-wise particle interactions and effective elastic properties of two-phase composites with particle interactions were derived,respectively,by taking imperfect interfaces into consideration.Furthermore,explicit expressions of the effective elastic moduli,which could be degraded to the classical micromechanical estimates with perfect interfaces,were also given to those with slightly weakened interfaces for several special composites.Results of the present method,with the consideration of pair-wise particle interactions,coincide with experiment data exactly,showing the validity of the present method.

Based on the 3D visco-elastic constitutive equations of composite,a finite element model was proposed for the damage analysis of fiber reinforce composite laminates under high velocity impact.The cohesive elements were involved between layers to simulate delaminations and the 3D-Hashin failure criteria were used to predict the in-plane damage.Damage area of laminates with no boundary stress is the large,these with two opposite stress faces are intermediate,and those with one stress faces and three stress faces are the small.The residual velocity remains unchanged and the damage area increases first and then decreases when the impact velocity keeps invariable but the boundary stress increases.On the other hand the residual velocity increases linearly and damage area first increases and then decreases when impact velocity increases and boundary stress keeps constant.

Finite element-finite difference method is applied to the transient heat conduction analysis of two-directional graded plates under heat flux and convection boundaries.A continuous gradient model is established based on 8-node high-order two-directional graded elements with varying thermal properties described by the micromechanical method and rules of mixture.The response history and spatial distribution of temperature field at different times with temperature-dependent properties are calculated and compared to the counterparts with temperature-independent properties.Effects of several parameters on the transient temperature field are discussed finally.It can be concluded that the temperature-dependence of properties has few effects on the transient temperature field when the temperature is low.The temperature gradation obviously exits both along x and y directions under heat flux in y direction only.The duration time for transient heat transfer,absolute x-and y-temperature gradation and steady-state temperature field all raise as increasing the distribution coefficient of constitution volume fraction in x direction,while the reverse is true as increasing the distribution coefficient of constitution volume fraction in y direction.