Elastoplastic Mechanical Properties Of Heterogeneous Material With Nanosized Voids Or Inclusions

The mechanical properties of heterogeneous material with nanosized voids or inclusions are attracting more and more attentions of Chinese and foreign scholars.The nanoscale interfacial elasticity and weaken interface including interfacial sliding have great effects on the macroscopic properties of nanocomposites.By utilizing the micromechanics models,this thesis primarily investigates the overall elasto-plastic properties of the two typical heterogeneous materials,i.e.,nanoporous aluminum and graphite nanoplatelet or graphene oxide platelet reinforced ceramics by using micromechanics models,and examines the effects of interface elasticity,heterogeneity size and imperfect interfaces on the homogenized elasto-plastic properties of the nanocomposites.The following results are obtained.(1)The micromechanics model for predicting the effective elastic properties of composites with rotational ellipsoidal heterogeneities and the micromechanics model based on field fluctuation method and second-order stress moment for evaluating the plastic properties are derived.Taking the closed-cell porous aluminum as an example,the predicting results of the macroscopic elasto-plastic behaviors based on the micromechanics model show its veracity and reliability,by comparison with finite element modeling results.(2)For the general nanoporous materials with rotational ellipsoidal voids,the Mori-Tanaka micromechanics model is used to formulate the explicit expressions of the effective elastic parameters with surface/interface elasticity,void shape and size for such materials with randomly oriented ellipsoidal voids and surface/interface effects.It stressfully analyzes effects of the nano-void shape and size on the effective elastic parameters.Furthermore,the micromechanics model based on the field fluctuation method and second-order stress moment is utilized to investigate effects of the interface elasticity,the size and shape of ellipsoidal voids on the unidirectional tension-compression elasto-plastic behaviors and yield surfaces of such materials.(3)For the graphene nanoplatelets or graphene oxide nanoplatelets reinforced ceramic matrix nanocomposites,the Mori-Tanaka micromechanics model is used to formulate the explicit expressions of the effective elastic parameters with interfacial sliding parameter for such materials with randomly oriented nanoplatelets and slightly weakened interface(imperfect interface).A comparative analysis is conducted for effects of graphite nanoplatelet and graphene oxide platelet on the effective elastic parameters of the ceramic matrix nanocomposites with slightly weakened interfaces.In addition,the micromechanics model based on the field fluctuation method and second-order stress moment is adopted to comparatively investigate effects of the graphite nanoplatelet and graphene oxide platelet on the macroscopic elasto-plastic mechanical behaviors,and the influences of interfacial sliding parameters characterizing the slightly weakened interfaces are also addressed.