Numerical Study Of Stress Intensity Factors For 3D-T-Type Crack

Coating /interlayer / substrate layered structure have been increasingly widely used, and this makes the research of their fracture strength, not only has theoretical significance, but also provides analysis basis for the design and preparation of layered structure. Coating/interlayer/substrate layered structure will produce a higher stress concentration in interfacial area under external or temperature loads due to material mechanics and thermal properties mismatch, resulting in interface debonding and cracking. And another type of interface failure mode, that is, cracks occurred in the direction perpendicular to interface, such failure is prone to occur in the adhesive, coating and coated materials, ceramic composite materials, and microelectronic materials. Even in the production and use of these materials, these two types of failure mode may occur at the same time. This paper performs numerical study on subsurface transverse median crack and elliptical interface crack in layered structure using the general-purpose finite element software package ABAQUS, with an emphasis on the stress field and stress intensity factors of the crack front.(1) A type of crack system, subsurface transverse median crack system in coating/interlayer/substrate layered structure under Hertz spherical indenter is studied using finite element method. Firstly, the finite element mesh of the crack front is designed, and the mesh design technical is verified with reference to Newman-Raju empirical equation, then the transverse median crack system is analyzed using three-dimensional J-integral method taking the elastic parameters of material layers, semi-elliptical crack aspect ratio, the ratio of interlayer thickness to coating thickness into account.(2) Ellipitical interfacial cracks buried between dissimilar material interfaces are investigated. Firstly, the complex stress intensity factors of the interfacial crack are analyzed and then extracted using interaction energy integral method. The complex stress intensity factors and two types of phase angle (ψand ?) of the interface crack are discussed when the ratio of bimaterial elastic parameters, aspect ratio of elliptical interface crack varies.(3) A new type of crack system, that is, when elliptical interface crack and subsurface transverse median crack occur at the same time (call it'3D-T-type crack'for short), is also studied. The stress intensity factors of 3D-T-type crack under remote side uniform tension are investigated, taking the ratio of elastic parameter of dissimilar layers and characteristic geometry of the crack front into account, and then some unique properties are concluded.