On Fracture Mechanics Problems In FGMS By Using Layered Material Boundary Element Method

It is important to treat the fracture damage when functionally graded materials(FGMs) are designed. Since the micro-cracks will appear during the molding of material and the usage of the functionally graded materials, then these micro-cracks will grow and incorporate into main cracks. The result will affect the service life and incur safety hazard. So the problems of fracture mechanics in functionally graded materials have been become the vital research direction and hot topics.This paper examines the stress intensity factors and growth of a penny-shaped crack perpendicular to graded Interfacial zone of bonded bi-materials by using boundary element method based on the general Kelvin solution(GKS-BEM), the following achievements have been gained:The numerical value validation to GKS-BEM has been made. The modified multi-region method and traction-singular element are respectively used to treat the co-planar crack problem and the singularity elimination of the stress of crack front. And the layer discretization technique is utilized to approximate the depth material non-homogeneity of FGM interface zone. The result shows that the GKS-BEM can be effectively used to research the fracture mechanics problem in FGMs.The stress intensity factors of the penny-shaped crack are researched in detail. The graded interfacial zone is treated as a non-homogeneous interlayer with its elastic modulus varying in thickness direction. The crack surfaces are subject to either uniform normal traction or uniform shear traction. The non-zero stress intensity Tactors are examined by taking into account the effects of the non-homogeneity parameter of the graded interfacial zone, the crack distance to the graded interfacial zone, and the thickness of the graded interfacial zone. For the normal tractions, the non-zero stress intensity factor values of the mode I fracture are presented. For the shear traction, the non-zero stress intensity factor values of the modes II and III fracture are presented.When the growth of the crack under inclined tension and compression loads by taking into account the effect of a functional graded material interfacial zone is examined, we utilize the stress intensity factors of the penny-shaped crack under the action of a uniformly normal and shear stresses. The stress intensity factor values are incorporated into the strain energy density factor criterion for prediction of crack growth. The paper then presents the most possible direction and location of the crack growth under inclined tensile and compression loads. The paper further presents results of the critical external loads that would cause the crack to grow at the most possible location and along the most possible direction. The paper also examines the effects of external load direction and material and geometrical parameters on the critical loads.