Fracture Mechanics Analysis Of Viscoelastic Functionally Graded Materials

Functionally graded materials (FGMs) are typical nonhomogeneouscomposite materials which have a continuous gradient nature of the gradualchange in microscopic detail. Some FGMs which have special purpose inengineering tend to show the nature of the creep and stress relaxation because itscomponent materials belong to viscoelastic materials such as the hightemperature metals, asphalt concrete, polymer, human and animal tissue.Especially, the viscoelastic effects in the field of high temperature technologyusually cannot be ignored. Fracture mechanics research of viscoelasticfunctionally graded materials (VFGMs) is a main part of the fracture mechanicsof FGMs. The investigations of the fracture behavior of VFGMs with differentstructures and loading conditions play an important role in guiding the structuraldesign, optimization, and security.This thesis assumes that the material has a typical shear modulus of thestandard linear solid model. Based on the piecewise-exponential model for FGMswith arbitrary elastic properties, the analytical procedure for solving the stressand displacement fields of VFGMs is given. The stress intensity factor of theVFGMs strip with a crack parallel to the gradient direction is studied.This thesis studies the dimensionless stress intensity factor (SIF) under threetypical loading conditions which are distributed loads, constant strain loads andthe concentrated load acting at the infinite ends of the VFGMs strip witharbitrary gradient properties. The loading conditions at the far ends can bereduced to those acting at the crack faces. The factors influencing the time effectand trends of the SIF are also described.In this thesis, the rules of the SIF with crack length are provided. For theembedded crack with fixed-length, the effects of the crack location on the SIFare discussed. Moreover, by adjusting the modulus ratio between the upper andlower surfaces, the difference and trends of both crack-tip SIFs are analyzed.Considering the characteristics of arbitrary gradient properties, four kinds oftypical distribution functions (including the exponential function, linear function,quadratic and square root function) are chosen and the corresponding SIFs arediscussed, which is of great significance to the manufacturing and optimizationof the actual VFGMs.