Criterion for Crack Kinking out of the Interface of Two Orthotropic Layers Subjected to Thermal and Mechanical Loading

The problem of crack path stability along the interface between two orthotropic elastically dissimilar materials under the presence of in-plane residual stresses is analyzed using the concept of Finite Fracture Mechanics and matched asymptotic procedure. An energy based fracture criterion is introduced for this problem and it is investigated whether and how is the criterion for the prediction of crack kinking from the interface affected by residual stresses. The complex stress intensity factor and the T-stress characterizing the stress state at the crack tip are calculated both for the thermal (residual stresses) and mechanical loading using the two-state integral. The matched asymptotic procedure together with FEM is used to derive the change of the potential energy induced by the crack growth by crack increment of finite length.

Numerical Computation of Complex Stress Intensity Factors of Interface Cracks in Bi-Materials Based on Photoelastic Theory

This paper presents a new numerical method for obtaining the complex stress intensity factor with an interface crack in bi-materials using photoelastic isochromatic fringe numbers N. The theoretical solution of stress field at the crack tip was deduced from Muskhelishvilis stress function and an undetermined term σ0 which is a function of material properties was added to this theoretical solution. A partial differential iterative equation with fast convergence was formed by applying the photoelastic theory. The complex stress intensity factor K=K1+iK2 and σ0 were obtained by Newton-Raphson iteration method and K domain was discussed. The simulant photoelastic isochromatic fringe pattern could be generated through image processing and numerical calculation according to K and σ0. The simulant isochromatic fringe pattern accords with experimental photoelastic isochromatic fringe pattern, so it is practicable for this numerical method of obtaining the complex stress intensity factor.

Crack Deflection from the Interface between Two Orthotropic Materials-Effect of Higher Order Terms in Asymptotic Analysis

The problem of crack deflection from the interface between two orthotropic materials is analyzed using the concept of Finite fracture mechanics and matched asymptotic procedure. A fracture criterion based on the energy approach is introduced for this problem. The main input for such criterion is the complex stress intensity factor calculated e.g. using the two-state integral. However for more precise predictions of the crack propagation also higher order terms of the asymptotic expansion are advisable to involve in the fracture criterion. To this end a T-stress term will be calculated and considered as the second input parameter. The matched asymptotic procedure together with FEM is used to derive the change of the potential energy induced by the incremental crack growth.

Interfacial Fracture Toughness of Adhesively Bonded Joints

The aim of the present paper is to evaluate the interfacial fracture toughness of an Al/Epoxy adhesive system with a crack lying at the interface. A cracked lap shear specimen loaded in four point bending is adopted and the fracture toughness is pointed out in terms of the critical complex stress intensity factor. To this aim numerical analyses of the fracture specimen have been carried out using a commercial finite element code. In addition, fracture surfaces are analyzed and the locus of failure is discussed.

On the Partly Bonded Thermoelastic Circular Inhomogeneity

The thermoelastic problem of an infinite elastic plane containing a partly bonded circular inhomogeneity of different thermomechanical properties is considered. Based upon the solution of a perfectly bonded inhomogeneity established in the current work, the complex stress intensity factor of the interfacial crack problem is obtained for full heat-conductive conditions of an “open” crack and for a linear temperature change at infinity.

Photoelastic Determination of Stress Intensity Factor of an Interfacial Crack in a Bi-material

The stress intensity factor of an interfacial crack in a bi-material can be represented by a complex vector whose phase changes as a function of r, the radial distance from a crack tip. Two photoelasticity approaches are proposed for the determination of both the magnitude and the phase angle of this complex vector. It is shown that within the K-dominated zone the complex stress intensity factor can be determined at any r and then converted to any other r. The case of an interfacial crack under remote tension is used as an example for the illustration of the proposed techniques.