• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.25 no.6
• /
• pp.907-915
• /
• 2001

Application of bonded dissimilar materials in many industries are increasing. When these materials are to be used in structures, it needs to evaluate the failure strength applying fracture mechanics. Al/Epoxy bonded dissimilar materials with an interface crack and an interface crack emanating from an edge semicircular hole were prepared, experiment of fracture toughness were carried out. Stress intensity factors of interface cracks in bonded dissimilar materials were computed with boundary element method(BEM) and the fracture criteria of mixed mode crack were analyzed. From the results, the fracture criteria and the method of strength evaluation by the fracture toughness in Al/Epoxy bonded dissimilar materials were proposed.

• Structural Engineering and Mechanics
• /
• v.30 no.3
• /
• pp.317-330
• /
• 2008

Stress intensity factors for a planar crack parallel to a bimaterial interface are considered. The formulation leads to a system of hypersingular integral equations whose unknowns are three modes of crack opening displacements. In the numerical analysis, the unknown displacement discontinuities are approximated by the products of the fundamental density functions and polynomials. The numerical results show that the present method yields smooth variations of stress intensity factors along the crack front accurately. The mixed mode stress intensity factors are indicated in tables and figures with varying the shape of crack, distance from the interface, and elastic constants. It is found that the maximum stress intensity factors normalized by root area are always insensitive to the crack aspect ratio. They are given in a form of formula useful for engineering applications.

• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.1109-1114
• /
• 2003

The initial crack often occurs on the bonded interface and it is the general cause of the interface fracture. It is very significant to establish the measurement method of interfacial crack by applying the ultrasonic technology into the interface of bonded dissimilar materials. In this paper, the interfacial crack length was measured by ultrasonic attenuation coefficient in the Al/Epoxy bonded dissimilar materials of double-cantilever beam(DCB). The energy release rate, G, was obtained by the experimental and Ripling's equation measurement of compliance. The experimental results represent that the relation between interfacial crack length for the ultrasonic attenuation coefficient and energy release rate is increased proportionally. From the experimental results, a measurement method of the interfacial crack length by the ultrasonic attenuation coefficient was proposed and discussed.

• Journal of the Korean Society of Safety
• /
• v.16 no.3
• /
• pp.26-30
• /
• 2001

Creep crack growth lift of high temperature pressure equipments was assessed for various crack locations and for various material properties. Surface cracks at the inner and outer surface of the vessel in the axial and circumferential directions were considered. The crack was located in the weld metal, in the parent metal or at the weld interface. Results shored that the crack at the weld interface was the most dangerous one. The crack located outside is weaker than that located inside. Safety factors of the case in which improper material properties were used the to unavailability of the correct material properties were discussed.

• Magazine of the Korea Concrete Institute
• /
• v.8 no.6
• /
• pp.235-243
• /
• 1996

The mechanical behavior ot concrete is strongly influenced by various scenarios of crack initiation and crack propagation. Recently. the study of the interface fracture and cracking in interfacial regions is emerged as an important field, in the context of the developement of high performance concrete composites. The crack path criterion for elastically homogeneous materials is not valid when the crack advances at an interface because. in this case, the consideration of the relative magnitudes of the fracture toughnesses between the constituent materials and the interface are involved. In this paper, a numerical method is presented to obtain the values of two interfacial fracture parameters such as the energy release rate and the phase angle at the tip of an existing interface crack. Criteria based on energy release rate concepts are suggested for the prediction of crack growth at the interfaces and an hybrid experimental-numerical study is presented on the two-phase beam composite models containing interface cracks to investigate the cracking scenarios in interfacial regions. In general, good agreement between the experimental results and the prediction from the criteria is obtained.

• Journal of the Korean Society for Precision Engineering
• /
• v.22 no.2
• /
• pp.164-171
• /
• 2005

This study aims to examine an effect of stacking sequence and curvature on the penetration characteristic of a composite laminated shell. For the purpose, we manufactured specimens with different stacking sequences and curvatures, and conducted a penetration test using an air-gun. To examine an influence according to stacking sequence, as flat plate and curvature specimen had more plies, their critical penetration energy was higher, Critical penetration energies of specimen A and C with less interfaces somewhat higher than those of B and D with more interfaces. The reason that with less interfaces, critical penetration energy was higher is pre-impact bending stiffness of composite laminated shell with less interfaces was lower than that of laminated shell with more interfaces, but bending stiffness after impact was higher. And it is because interface, the weakest part of the composite laminated shell, was influenced by transverse impact. As curvature increases, critical penetration energy increases linearly. It is because as curvature increases, resistance to in-plane deformation as well as bending deformation increases, which need higher critical penetration energy. Patterns of cracks caused by penetration of composite laminated shells include interlaminar crack, intralaminar crack, and laminar fracture. A 0$^{\circ}$ply laminar had a matrix crack, a 90$^{\circ}$ply laminar had intralaminar crack and laminar fracture, and interface between 0$^{\circ}$and 90$^{\circ}$laminar had a interlaminar crack. We examined crack length and delamination area through a penetration test. For the specimen A and C with 2 interface, the longest circumferential direction crack length and largest delamination area were observed on the first interface from the impact point. For the specimen B and D with 4 interface, the longest crack length and largest delamination area were observed on the third interface from the impact point.

• Proceedings of the KSME Conference
• /
• 2001.11a
• /
• pp.299-303
• /
• 2001

Adherend-adhesive interface failure will occur on a macroscale when surface preparation or material quality are poor. It is well known that the stress singularity occurs at the edges of interface between the adhernds and the adhesive, and that crack will initiate from these positions. Also if bubbles are created and remained in the adhesive layer during the bonding process, the stress concentrates around these hole defects. In this paper, the effects of the hole defects on the SIF of interface crack were examined. From results, SIF increased with the hole defects near the interface crack and increased with an decreae in the upper adherend thickness, an increase in the center adhesive thickness.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1997.04a
• /
• pp.655-659
• /
• 1997

The analysis of cracks at the interface between dissimilar materilar has received a great deal of attention in recent years. In this paper we conducted the static tensile test for the aluminum bonded single lap-joint with the interface edge crack. Comparing this results, that is ultimate load and strain value of aluminum adherend by strain gauge with the fracture mechanics parameters, compliance and stress intensity factors acquied from the boundary element analysis, we concluded that there are critical value of crack length to provoke the interface fracture.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 1998.03a
• /
• pp.287-292
• /
• 1998

In this study behavior of fatigue crack and fatigue fracture is observed under rotary bending fatigue testing in friction welded dissimilar materials. Fatigue fracture most occurred in SM15C heat affected zone around Interface. In case of fatigue test, stress is reduced the position of fracture gradually moves to the welded Interface. Micro crack of heat affected zone surface on SM15C is observed at any different stress.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.15 no.4
• /
• pp.171-177
• /
• 2007

In this paper, an evaluation method of fracture toughness on interface cracks was investigated in friction welded dissimilar materials with interfacial edge cracks. To establish a reasonable strength evaluation method and fracture criterion, it is necessary to analyze stress intensity factor under the load and residual stress condition on friction welded interface between dissimilar materials. The friction welded specimens with an edged crack were prepared for analysis of stress intensity by using the boundary element method (BEM) and the fracture toughness. A quantitative fracture criterion for friction welded STS 304/SM 45C with interface crack is suggested by using stress intensity factor, F and the results of fracture toughness experiment.