• Structural Engineering and Mechanics
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• v.86 no.4
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• pp.535-546
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• 2023

In the present paper, multiple interface cracks between a functionally graded orthotropic coating and an orthotropic half-plane substrate under concentrated loading are considered by means of the distribution dislocation technique (DDT). With the use of integration of Fourier transform the problem is reduced to a system of Cauchy-type singular integral equations which are solved numerically to compute the dislocation density on the surfaces of the cracks. The distribution dislocation is a powerful method to calculate accurate solutions to plane crack problems, especially this method is very good to find SIFs for multiple unequal cracks located at the interface. Hence this technique allows considering any number of interface cracks. The primary objective of this paper is to investigate the effects of the interaction of multiple interface cracks, load location, material orthotropy, nonhomogeneity parameters and geometry parameters on the modes I and II SIFs. Numerical results show that modes I/II SIFs decrease with increasing the nonhomogeneity parameter and the highest magnitude of SIF occurs where distances between the load location and crack tips are minimal.

• Structural Engineering and Mechanics
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• v.26 no.1
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• pp.99-109
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• 2007

A cracked composite specimen, comprised of an epoxy and an aluminium plate, was fractured under a tensile load. In this paper, two crack configurations were investigated. The first was an artificial center crack positioned in the epoxy plate parallel to the material interface. The other was for two edge cracks in the epoxy plate, again, parallel to the interface. A tensile test was carried out by gradually increasing the applied load and it was verified that the cracks always moved suddenly in an outward direction from the interface. The d/a ratio was gradually reduced to zero, and it was confirmed that the maximum stress intensity factor value for the artificial center crack, $K_{{\theta}{\theta}}^{max}$, approached that of an artificial interface crack,$K_{{\theta}{\theta}}^{ifc\;max}$ (where: 2a is the crack length and d is the offset between the crack and interface). The same phenomenon was also verified for the edge cracks. Specifically, when the offset, d, was reduced to zero, the maximum stress intensity factor value, $K_{{\theta}{\theta}}^{max}$, approached that of an artificial interface edge crack.

• Structural Engineering and Mechanics
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• v.64 no.1
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• pp.71-79
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• 2017

In this study, interaction of several interface cracks located between a functionally graded material (FGM) layer and an elastic layer under anti-plane deformation based on the distributed dislocation technique (DDT) is analyzed. The variation of the shear modulus of the functionally graded coating is modeled by an exponential and linear function along the thickness of the layer. The complex Fourier transform is applied to governing equation to derive a system of singular integral equations with Cauchy type kernel. These equations are solved by a numerical method to obtain the stress intensity factors (SIFs) at the crack tips. The effects of non-homogeneity parameters for exponentially and linearly form of shear modulus, the thickness of the layers and the length of crack on the SIFs for several interface cracks are investigated. The results reveal that the magnitude of SIFs decrease with increasing of FG parameter and thickness of FGM layer. The values of SIFs for FGM layer with exponential form is less than the linear form.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.346-351
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• 2003

In this paper, an evaluation method of fracture toughness on interface cracks has been investigated under various mixed-mode conditions of the bonded scarf joints. Two types of the bonded scarf joints with an interface crack were prepared to analyze the stress intensity factors using boundary element method(BEM) and to perform the fracture toughness test. From the results of fracture toughness experiments and BEM analysis, an evaluation method of fracture toughness on interface cracks in the bonded components of dissimilar materials has been proposed and discussed.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.4
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• pp.110-116
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• 2003

In this paper, an evaluation method of fracture toughness on interface cracks has been investigated under various mixed-mode conditions of the bonded scarf joints. Two types of the bonded scarf joints with an interface crack were prepared to analyze the stress intensity factors using boundary element method(BEM) and to perform the fracture toughness test. From the results of fracture toughness experiments and BEM analysis, an evaluation method of fracture toughness on interface cracks in the bonded dissimilar materials has been proposed and discussed.

• International Journal of Automotive Technology
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• v.6 no.3
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• pp.293-303
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• 2005

Bonded dissimilar materials are being increasingly used in automobiles, aircraft, rolling stocks, electronic devices and engineering structures. Bonded dissimilar materials have several material advantages over homogeneous materials such as high strength, high reliability, light weight and vibration reduction. Due to their increased use it is necessary to understand how these materials behave under stress conditions. One important area is the analysis of the stress intensity factors for interface cracks emanating from circular holes in bonded dissimilar materials. In this study, the bonded scarf joint is selected for analysis using a model which has comprehensive mixed-mode components. The stress intensity factors were determined by using the boundary element method (BEM) on the interface cracks. Variations of scarf angles and crack lengths emanating from a centered circular hole and an edged semicircular hole in the Al/Epoxy bonded scarf joints of dissimilar materials are computed. From these results, the stress intensity factor calculations are verified. In addition, the relationship between scarf angle variation and the effect by crack length and holes are discussed.

• Journal of the Microelectronics and Packaging Society
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• v.8 no.3
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• pp.25-30
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• 2001

The stress intensity factors for edge cracks located at the bonding interface between the semiconductor chip and the adhesive layer subjected to a uniform transverse tensile strain are investigated. Such cracks might be generated due to a stress singularity in the vicinity of the free surface. The boundary element method (BEM) is employed to investigate the behavior of interface stresses. The amplitude of complex stress intensity factor depends on the crack length, but it has a constant value at large crack lengths. The rapid propagation of interface crack is expected if the transverse tensile strain reaches a critical value.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.9
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• pp.1477-1485
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• 2003

The displacement vector field can be represented in terms of a scalar potential ${\phi}$ and a vector potential ${\phi}$. The scalar potential ${\phi}$ is related to dilatational waves and the vector potential ${\phi}$ is related to rotational waves. Using these two complex displacement potentials, the stress and displacement fields for steadily growing interface cracks in dissimilar materials are obtained. The energy release rate for steadily growing interface cracks in dissimilar materials are also obtained. And with photoelastic isochromatic patterns simulated by computer graphics, the stress intensity factors are discussed.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.14 no.3
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• pp.309-315
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• 2001

The Stress intensity factors for edge cracks located at the bonding interface between the elastic semiconductor chip and the viscoelastic adhesive layer have been investigated. Such cracks might be generated due to stress singularity in the vicinity of the free surface. The domain boundary element method(BEM) has been employed to investigate the behavior of interface stresses. The overall stress intensity factor for the case of a small interfacial edge crack has been computed. The magnitude of stress intensity factors decrease with time due to viscoelastic relaxation.

• Korean Journal of Materials Research
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• v.18 no.1
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• pp.38-44
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• 2008

The micro-structural changes, strength characteristics, and micro-fractural behaviors at the joint interface between a Sn-4.0wt%Ag-0.5wt%Cu solder ball and UBM treated by isothermal aging are reported. From the reflow process for the joint interface, a small amount of intermetallic compound was formed. With an increase in the isothermal aging time, the type and amount of the intermetallic compound changed. The interface without an isothermal treatment showed a ductile fracture. However, with an increase in the aging time, a brittle fracture occurred on the interface due mainly to the increase in the size of the intermetallic compounds and voids. As a result, a drastic degradation in the shear strength was observed. From a microshear test by a scanning electron microscope, the generation of micro-cracks was initiated from the voids at the joint interface. They propagated along the same interface, resulting in coalescence with neighboring cracks into larger cracks. With an increase in the aging time, the generation of the micro-structural cracks was enhanced and the degree of propagation also accelerated.