• Structural Engineering and Mechanics
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• v.26 no.1
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• pp.87-97
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• 2007

Some mixed mode fracture criterion may be converted in to elliptical or ellipsoidal formula with the aid of mathematical translation. Hence, the crack initiation in mixed mode fracture I+II emanating from notches, has been studied using notched circular ring specimens. On the basis of Irwin (1957) theory, a new criteria in mixed mode fracture I+II, based fracture elliptic criterion and notch stress intensity factors has been developed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.1
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• pp.113-120
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• 2002

Experimental procedure to measure fracture toughness (J$_{c}$) under mixed mode loading using CTS(Compact Tension-Shear) specimens is described. It\`s loading angle ranges from 0$^{\circ}$ to 45$^{\circ}$ with interval of 157. The general outline of experimental procedure is similar to that of ASTM E8l3-89 fur mode I fracture. Equations fur determining J-integral is quoted from the authors' previous works. The relation between unloading compliance and physical crack size was calibrated. As an example, fracture toughness of aluminum alloy 2024p-7361 was measured and some reasonable results of J$_{c}$ with various loading angles were obtained.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.3
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• pp.212-218
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• 1996

To clarify the influence of precipitation microstructure and inclusion on the monotonic tensile fracture behaviors in 2090 alloy aged at $180^{\circ}C$, the detailed measurement of hardness, tensile strength, elongation and the observation of scanning electron micrography, transmision electron micrography have been carried out. The transgranular shear ductile fracture has been observed in specimen quenched after solution treatment at $500^{\circ}C$ for 45min. While the under-aged specimen was fractured in both transgranular shear ductile and intergranular fracture mode, the fracture mode of peak-aged and over-aged alloy was predominantly intergranular fracture. The fracture behavior of each ageing condition was influenced by the change of precipitation microstructural features. In the case of peak-aged and over-aged alloys, the coarse and heterogeneous slip band caused by both shearable nature of the ${\delta}^{\prime}(Al_3Li)$ precipitates and PFZ along the high angle grain boundary aid the localization of deformation, resulting in low energy intergranular fracture. It was also estimated that the fractured T-type intermetallic phases (inclusion) and the equilibrium ${\delta}$(AlLi) phases which were formed at grain boundaries palyed an important role in promoting intergranular fracture mode.

• Steel and Composite Structures
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• v.28 no.1
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• pp.111-121
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• 2018

It has been argued that fracture energy of composite laminates depends on their thickness and number of layers. In this paper a modified direct energy balance approach (DEBA) has been developed to evaluate the mode-II shear fracture energy for E-glass/Epoxy laminates from finite element model at an arbitrary thickness. This approach considers friction and damage/plasticity deformations using cohesive zone modeling (CZM) and nonlinear finite element modeling. The presence of compressive stress and resulting friction was argued to be a possible cause for the thickness dependency of fracture energy. In the finite element modeling, CZM formulation has been developed with bilinear cohesive constitutive law combined with friction consideration. Also ply element have been developed with shear plastic damage model. Modified direct energy balance approach has been proposed for estimation of mode-II shear fracture energy. Experiments were performed on laminates of glass epoxy specimens for characterization of material parameters and determination of mode-II fracture energies for different thicknesses. Effect of laminate thickness on fracture energy of transverse crack tension (TCT) and end notched flexure (ENF) specimens has been numerically studied and comparison with experimental results has been made. It is shown that the developed numerical approach is capable of estimating increase in fracture energy due to size effect.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.2
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• pp.121-127
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• 2014

An atomistic-based finite bond element model for predicting the tearing mode (mode III) fracture of a single-layer graphene sheet (SLGS) is developed. The model uses the modified Morse potential for predicting the maximum strain relationship of graphene sheets. The mode III fracture of graphene under out-of-plane shear loading is investigated with extensive molecular mechanics simulations. Molecular mechanics is used for describing the displacements of atoms in the area near a crack tip, and linear elastic fracture mechanics is used outside this area. This work shows that the molecular mechanics method can provide a reliable and yet simple method for determining not only the shear properties of SLGS but also its mode III fracture toughness in the armchair and the zigzag directions; the determined mode III fracture toughness values of SLGS are $0.86MPa{\sqrt{m}}$ and $0.93MPa{\sqrt{m}}$, respectively.

• Steel and Composite Structures
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• v.23 no.3
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• pp.263-271
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• 2017

A theoretical study was carried-out of mode II delamination fracture behavior of the End Loaded Split (ELS) functionally graded beam configuration with considering the material non-linearity. The mechanical response of ELS was modeled analytically by using a power-law stress-strain relation. It was assumed that the material is functionally graded transversally to the beam. The non-linear fracture was investigated by using the J-integral approach. Equations were derived for the crack arm curvature and zero axes coordinate that are needed for the J-integral solution. The analysis developed is valid for a delamination crack located arbitrary along the beam height. The J-integral solution was verified by analyzing the strain energy release rate with considering material non-linearity. The effects of material gradient, non-linear material behavior and crack location on the fracture were evaluated. The solution derived is suitable for parametric analyses of non-linear fracture. The results obtained can be used for optimization of functionally graded beams with respect to their mode II fracture performance. Also, such simplified analytical models contribute for the understanding of delamination fracture in functionally graded beams exhibiting material non-linearity.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1998.10a
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• pp.254-260
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• 1998

Application of bonded dissimilar materials in various industries are increasing. When these materials are used in structures, it needs to investigate strength evolution applying fracture mechanics. Al/Epoxy bonded dissimilar materials with an interface crack and an interface crack emanating from an edge semicircular hole were prepared for the static tests so that 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 criterion of mixed mode crack were analyzed. From the results, the fracture criterion and the method of strength evolution by the fracture toughness in Al/Epoxy bonded dissimilar materials were proposed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.9 s.180
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• pp.2174-2183
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• 2000

In this paper, the evaluation method of interfacial fracture toughness to apply the fracture toughness was investigated in adhesively bonded joints of AI/Ced./A1. Four types of adhesively bonded double-cantilever beam(DCB) joints with the interface crack were prepared for the test of interfacial fracture toughness. The experiments to measure the interfacial fracture toughness were performed under the various mixed-mode conditions. The critical energy release rate, Gc, was obtained by the experimental measurement of compliances. From the experimental results, the interfacial fracture toughness for the mixed-mode specimens is well characterized by the energy release rate, and the method of strength evaluation by the interfacial fracture toughness was discussed in adhesively bonded joints.

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

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.256-259
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• 2005

Mixed-mode interlaminar fracture toughness of carbon fabric/epoxy composites, which are applicable to tilting train carbody, was evaluated through the MMB (Mixed-mode bending) test. Specimens were made of CF3327 plain woven fabric with epoxy and a starter delamination at one end was made by inserting Teflon film with the thickness of 12.5 μ m. Mixed-mode interlaminar fracture test was conducted for 6 types of specimens with the mode II ratio of 20 ,35, 50, 65, 80, 90%. Also crack propagating behaviors and fractured surfaces were examined through an optical travelling scope and a scanning electron microscope, respectively.