Xin Lan

Single and double edge interface crack solutions for arbitrary forms of material combination

In this paper interfacial edge crack problems are considered by the application of the finite element method. The stress intensity factors are accurately determined from the ratio of crack-tip-stress value between the target given unknown and reference problems. The reference problem is chosen to produce the singular stress fields proportional to those of the given unknown problem. Here the original proportional method is improved through utilizing very refined meshes and post-processing technique of linear extrapolation. The results for a double-edge interface crack in a bonded strip are newly obtained and compared with those of a single-edge interface crack for different forms of combination of material. It is found that the stress intensity factors should be compared in the three different zones of relative crack lengths. Different from the case of a cracked homogeneous strip, the results for the double edge interface cracks are found to possibly be bigger than those for a single edge interface crack under the same relative crack length.

Effect of arbitrary bi‐material combination and bending loading conditions on stress intensity factors of an edge interface crack

Purpose – The purpose of this paper is to compute the stress intensity factors (SIFs) of single edge interface crack for arbitrary material combinations and various relative crack lengths, and compare with those for the bonded plates subjected to tensile loading conditions. It aims to discuss the results of the shallow edge interface crack on the basis of the singular stress near the free‐edge corner without the crack.Design/methodology/approach – In this study, the SIFs of interface crack in dissimilar bonded plates subjected to bending loading conditions are analyzed by the finite element method and a post‐processing technique. The use of post‐processing technique of extrapolation reduces the computational cost and improves the accuracy of the obtained result.Findings – The empirical expressions are proposed for evaluating the SIFs of arbitrary material combinations.Originality/value – Empirical functions can be used to obtain the SIFs for arbitrary material combinations for the bending loading conditio...

The Effect of Geometric Configurations on the Elastic Behavior of an Edge-Cracked Bonded Strip

Interface cracks often initiate around the bonding free-edge corner due to the high-stress concentration. In this research, the elastic behavior of an edge-cracked dissimilar bonded strip subjected to remote tensile load is investigated using the proportional crack tip opening displacement method based on FE analysis for arbitrary material combinations. The stress intensity factor, energy release rate, and mode mixity are computed and compared systematically with varying geometrical configurations and material combinations. Then, the combined effects of the relative height of the bonded component and material combination are discussed for the typical engineering materials.

A novel method of computing the Stess intensity factors of the interfacial cracks

Bi-material interface and multi-layer systems are widely observed in modern microelectronic applications. When the external load reaches a critical level, the crack either extends along the interface or kinks out of the interface, and finally leads to the catastrophic failure. In fracture mechanics, stress intensity factor, mode mix ratio and strain energy release rate are normally used as parameters to evaluate the adhesive toughness and failure prediction of bi-material interfaces. In this research, a new efficient method based on the finite elements and the extended proportional method using nodal-displacement behind the crack tip was introduced to obtain the stress intensity factors, then the strain energy release rate could be computed by using its relationship with the stress intensity factors. The robustness and accuracy of the current proposed method was discussed by comparing the solution results proposed by other researchers. It was found that the average error is less than 1% for the stress intensity factors, and it can get accurate results with rather coarse finite element meshes. Furthermore, the current method is fairly efficient and less computational resource consuming. The current method could be used as an effective tool in the reliability analysis of the bonded multi-layers in microelectronics.

Effects of resin thickness on the stress intensity factors of edge-cracked adhesive joints

The effects the thickness of epoxy resin on the stress intensity factors (SIFs) of the edge-cracked adhesive joints subjected to external loads are investigated in the current paper. The three-layered joints composed of Silicon, epoxy resin and FR-4.5 are widely seen in the package solutions of CSP/FBGA for electronic devices. Cracks or delaminations from resin-substrate interface or resin-silicon interface are the common failure modes in plastic IC packages. However, it is difficult to determine the exact stress state of a bi-material interface due to the oscillatory singularity. In this paper, the SIFs of the single edge-cracked joints are determined accurately by using the Crack Tip Stress Method. Then, the effects of resin thickness on the SIFs of various edge interface cracks under uniform tension are investigated by varying the resin thickness and crack length. It was found that the SIFs grow with the increment of resin thickness and reach constants when the resin thickness is larger than the width of the joint.

Stress Intensity Factor of a Central Interface Crack in a Bonded Strip under Arbitrary Material Combination

Although a lot of interface crack problems were previously treated, few solutions are available under arbitrary material combination. This paper deals with one central interface crack and numerical interface cracks in a bonded strip. Then, the effects of material combination on the stress intensity factors are discussed. A useful method to calculate the stress intensity factor of interface crack is presented with focusing on the stress at the crack tip calculated by the finite element method. For one central interface crack, it is found that the results of bonded strip under remote uni-axial tension are always depending on the Dunders’ parameters , and different from the well-known solution of the central interface crack under internal pressure that is only depending on . Besides, it is shown that the stress intensity factor of bonded strip can be estimated from the stress of crack tip in the bonded plate when there is no crack. It is also found that when , when , and when . For numerical interface cracks , values of and with arbitrary material combination expressed by , are obtained.

Single and Double Edge Interface Cracks in a Bonded Plate under Arbitrary Material Combination

Although a lot of interface crack problems were previously treated, few solutions are available under arbitrary material combinations. This paper deals with a single edge interface crack as well as a double edge interface crack in a bonded plate. Then, the effects of material combination on the stress intensity factors are discussed. A useful method to calculate the stress intensity factor of interface crack is presented with focusing on the stresses at the crack tip calculated by the finite element method. Then, the stress intensity factors are indicated in charts under arbitrary material combinations. Specifically, some necessary skills as refined mesh and extrapolations of the stress intensity factors are used to improve the accuracy of the calculation. It has been proved that the values shown in this paper have at least 3-digit accuracy. For the edge interface crack, it is found that the dimensionless stress intensity factors are not always finite depending on Dunders’ parameters , . For example, they are infinite when . And they are finite when , and zero when .

Stress Intensity Factors of a Crack on the Interface of Adhesive and Adherents

Adhesive joints are widely used as the joints with the same or different adherents, such as in engineering and electric devices. However, because of mismatch of different materials properties, failures due to crack initiation and propagation are often observed on the interface between adhesive and adherents. Therefore, it is important to analyze stress intensity factor of crack on the interface. In this paper, the effect of material combination of adhesive and adherents on stress intensity factor and effect of the thickness of adhesive on stress intensity factor are discussed. A useful method to calculate the stress intensity factor of interface crack is presented with focusing on the stresses at the crack tip calculated by finite element method. The stress intensity factors are indicated in charts under different thickness of adhesive . It is found that the intensity of singular stress first increases with increasing , then decreases from about , and keeps constant from about , when is the width of adhesive. These results are helpful to design dimensions of devices and choose appropriate materials when adhesives are used inside of them.