APPLICABILITY OF FRACTURE-MECHANICS IN STRENGTH EVALUATION OF FUNCTIONALLY GRADED MATERIALS

Elastic and elastic-plastic analyses of a crack in a particulate-dispe rsed functionally graded material (FGM) have been carried out using a newly developed finite element method based on Tohgo-Chou-Weng's (1994 , 1996) constitutive relation for particulate-reinforced composites. B y setting the mechanical properties of particles and a matrix and thei r content graded in the thickness direction, FGMs and non-FGM are desi gned. From comparison of the numerical results for the FGMs and non-FG M, the influence of the gradient of the mechanical properties on a str ess intensity factor and the crack tip field is discussed. The followi ng conclusions are derived: (1) The stress intensity factor of a crack under constant boundary conditions is considerably affected by the gr adient of the mechanical properties, (2) The elastic and plastic stres s singular fields around a crack tip in a FGM are basically described by the fracture mechanics parameters (K-I and J(I)) as well as in a no n-FGM, using the mechanical properties of the material at the crack ti p. (3) The size of the singular field decreases with an increase in th e gradient of the mechanical properties. This means that the applicabi lity of fracture mechanics, such as the small-scale-yielding condition and the validity of the J-integral, is affected by the gradient.