Papers by Keyword: Interface Crack

Abstract: Basing on the theoretical study on the stress intensity factor (SIF) of the crack parallel to and lying on the interface of the cermet cladding part, the finite element analysis (FEA) of the crack’s SIF is made. The change laws of the SIF with the load action angleψ, the load Q, the clad thickness ratio h1/h and the elastic modulus ratio E1/E2 are obtained. The research results have theoretical and steering significance on the wide application of the cermet cladding part.

Abstract: This paper presents the simple method to determine the complex stress intensity factor of interface crack problem by the finite element method. The proportional method is extended to the interface crack problem. In the present method, the stress values at the crack tip calculated by FEM are used and the stress intensity factors of interface crack are evaluated from the ratio of stress values between a given and a reference problems. A single interface crack in an infinite bi-material plate subjected to tension and shear is selected as the reference problem in this study. The accuracy of the present analysis is discussed through the results obtained by other methods. As the result, it is confirmed that the present method is useful for analyzing the interface crack problem.

Abstract: In this study, a rectangular interfacial crack in three dimensional bimaterials is analyzed. First, the problem is formulated as a system of singular integral equations on the basis of the body force method. In the numerical analysis, unknown body force densities are approximated by the products of the fundamental density functions and power series, where the fundamental density functions are chosen to express a two-dimensional interface crack exactly. The calculation shows that the present method gives smooth variations of stress intensity factor along the crack front for various aspect ratios. The present method gives rapidly converging numerical results and highly satisfied boundary conditions throughout the crack boundary. It is found that the stress intensity factors K1 and K2 are determined by bimaterials constant e alone, independent of elastic modulus ratio and Poisson's ratio.

Abstract: The interface strength of low-dimensional nano-components such as films and islands formed on substrates has been investigated in this project, and the focus is put on the mechanics of crack initiation from the free interface edge and propagation along the interface. The series of experiments elucidates the applicability of fracture mechanics concept on the structures. We proposed experimental methods for evaluating the initiation strength of an interface crack in submicron films and islands deposited on substrates. The initiation is governed by the singular stress field, and the criterion is prescribed by the stress intensity parameter. Using special loading apparatus built in a TEM, we developed a crack initiation method for nano-components and the role of plasticity on the delamination is clarified. Subcritical crack growth along an interface between submicron films under fatigue was also investigated by modified four-point bend method.

Abstract: Polymeric materials such as epoxy are widely used as coating layers for the containment building of the nuclear power plant. These layers may be damaged through a hygrothermal process and residual stresses can reach significant levels near the free edges, possibly leading to interface debonding or delamination. Interfacial stress singularities induced in a laminate model consisting of the epoxy coating layer and the concrete substrate is investigated using the time-domain boundary element method. The epoxy layer is assumed to be a linear viscoelastic material and moisture effects are assumed to be analogous to thermal effects. The overall stress intensity factor for the case of a small interfacial edge crack of length a has been computed.

Abstract: Some numerical parameters-sensitivity analysis has been conducted to evaluate the stability and propagation of the interface cracks at heel of concrete gravity dam. In this paper, utilizing the software ANSYS to simulate the stress and displacement fields of the tip of the interface cracks between concrete gravity dam and foundation, the stress intensity factor (SIF) of the interface crack is analyzed using facture mechanics. Three impacting factors have been discussed, such as the crack length, the angle of crack, and the water height. Critical length and loads of interface crack propagation are obtained using composite fracture criteria. The results indicate that the coarse interface retards the propagation of interface crack, and redounds to stability of gravity dam. It is found that the interface crack often propagates alone the interface between dam and foundation, simultaneously the branch crack kinks to foundation at the specific condition.

Abstract: The fracture of the functionally graded thermal barrier coating (TBC) under the thermal loads is a key for the engineering application of this kind of materials. In the previous studies, the functionally graded TBC is usually simplified into a laminate by homogenizing the material of each interlayer as an isotropic layer. Nevertheless, this method is a macro equivalent method, which neglected the microstructure characteristics of materials. In this paper, the computational micromechanics method (CMM) is employed to study the fracture problem of the functionally graded TBC with the interface crack. Essentially, CMM is a finite element analytical method based on the real microstructure of materials, which combines the digital image processing technique, the auto mesh generation technique with the finite element method. Firstly, the microstructure photos of the functionally graded TBC are required. Secondly, the digital image processing technique and the auto mesh generation technique are used to construct the finite element model. Finally, the finite element method is utilized for the fracture analysis of the functionally graded TBC under the thermal shock loads. Moreover, the problem is also analyzed using the macro equivalent method and the results from the two methods are compared. The temperature field obtained using CMM is basically consistent with the one obtained from the macro equivalent method and the influences of the interface crack on the temperature fields are limited in a local region. But results of the driving forces for the crack propagation, J-integrals, from the two methods are quite different. Comparing with the CMM results, J-integrals from the macro equivalent method are smaller. It means that the macro equivalent method tends to underestimate the driving force of the interface crack. On the other hand, the prediction of the critical location of the interface crack from the two methods is also different. Since the influence of the microstructure is taken into account by CMM, results of the present work may suggest that CMM is a more useful and accuracy method for the fracture analysis of the functionally graded TBC.

Abstract: The main sources of error in the determination of stress intensity factors (SIFs) for an interface crack in a bi-material by conventional photoelasticity are the measurement of the positional co-ordinates of the data point and the fringe order. In the present work, use of two digital photoelasticity methods for collecting these data is discussed. SIFs are evaluated using constant radius method and a least squares approach based on the singular stress field equation. The need for developing a multi-parameter stress field solution for evaluating SIF is highlighted.

Abstract: A strategy of coupling length scales from atomistic to continuum is investigated on the basis of quasicontinuum model for interface fracture problems. In the model, an atomistic region of the interest is discretized by finite elements and the positions of atoms are prescribed by means of nodal displacements of the elements with shape function for the reduction of the degrees of freedom. Total energy of the system consists of interatomic potentials, and minimized through variational method employed in conventional finite element formulation. In this study, we deal with the fracture behavior of Cu-Fe interface crack in two dimensional problems, and investigate the adequate discretization manner around the crack tip in use of quasicontinuum method.

Abstract: The crack propagation along the bond coat / topcoat interface of a TBC system has been studied in a previous work under a certain mode ratio (K2/K1). In order to discuss a parameter that describes the crack propagation, the growth behavior of a crack has to be studied under various K2/K1 ratios. In this work, BEM was used to determine the modifications that change K2/K1 ratios of the specimen employed in the previous study. Six characteristics of the specimen were modified: location of the applied load; height; length, position and direction of the notch, and its separation from the bond coat / topcoat interface. Among these modifications, the change of location of load point can effectively change K2/K1 ratio to values greater and smaller than those of the previous study. Crack propagation tests with three different positions of load point were performed using specimens with topcoat porosity of 5%, 15% and 20%. The results indicated that, independently of K2/K1 ratio, the parameter Ki dominated the crack growth behavior for an interface crack under mixed mode.