• Korean Journal of Materials Research
• /
• v.14 no.5
• /
• pp.322-327
• /
• 2004

Copper-based leadframe sheets were oxidized in two kinds of hot alkaline solutions to form brown-oxide or black-oxide layer on the surface. The oxide coated leadframe sheets were molded with epoxy molding compound (EMC). After post mold curing, the oxide-coated EMC-leadframe joints were machined to form sandwiched Brazil-nut (SBN) specimens. The SBN specimens were used to measure the fracture toughness of the EMC/leadframe interfaces under mixed-mode (mode I + mode II) loading conditions. Fracture surfaces were analyzed by various equipment to investigate failure path. The results revealed that the failure paths were strongly dependent on the oxide type. In case of brown oxide, hackle-type failure was observed and failure path lay near the EMC/CuO interface with a little inclining to CuO at all case. On the other hand, in case of black oxide, quite different failure path was observed with respect to the distance from the tip of pre-crack and phase angle. Different failures occurred with oxide type is presumed to be due to the difference in microstructure of the oxides.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1995.04a
• /
• pp.573-577
• /
• 1995

An integration method for the hypersingular kernels, in the boundary integralequations used for the solution of crack-like problems in elasticity, has been developed. To isolate the stronger singularities, the actual boundaries are replaced by the smoothly curved auxiliary boundaries which provide the detoured, non-singular integration paths. The auxiliary boundary can be interpreted as a contracted form of the actual boundaries except for the singular element where the collocating point is located. For an optimal integration path for every singular collocation point, the auxiliary boundary may have different shape depending on the position of the collocation point on the singular element.

• Journal of Korean Ophthalmic Optics Society
• /
• v.11 no.2
• /
• pp.85-89
• /
• 2006

To research of the improved mechanical properties of materials for spectacle lens cutting, SiC and TiC were used as the main powder. Also, $Al_2O_3$ and $Y_2O_3$ was included as a sintering additive. The weight ratio of the alumina($Al_2O_3$) to yttria($Y_2O_3$) was set to 1:1. The materials for spectacle lens cutting were fabricated by hot-pressing at $1810^{\circ}C$ for 1h and subsequently annealed at $1860^{\circ}C$ for 3, 6 and 12h to initiated grain growth. The longer annealing time is, the bigger the grain size is. The microstructures were observed by scanning electron microscopy (SEM). The SEM images were quantitatively analyzed by image analysis (Image-Pro Plus, Media Cybernetics, Maryland, U.S.A.). Crack deflection by elongated SiC grains was most frequently observed as the dominant toughening mechanism. Crack deflection was generally observed for elongated SiC grains with aspect ratio(AR) > 2.5 and grain thickness < $2.3{\mu}m$. Crack bridging was also observed as one of the operating toughness mechanism.

• Structural Engineering and Mechanics
• /
• v.17 no.1
• /
• pp.51-68
• /
• 2004

Since the linear elastic fracture analysis has been proved to be insufficient in predicting the failure of strain hardening materials, a number of fracture concepts have been studied which remain applicable in the presence of plasticity near a crack tip. This work thereby presents a new finite element model to predict the elastic-plastic crack-tip field and fatigue life of center-cracked panels(CCP) with ductile fracture under large-scale yielding conditions. Also, this study has been carried out to investigate the path-dependence of J-integral within the plastic zone for elastic-perfectly plastic, bilinear elastic-plastic, and nonlinear elastic-plastic materials. Based on the incremental theory of plasticity, the p-version finite element is employed to account for the accurate values of J-integral, the most dominant fracture parameter, and the shape of plastic zone near a crack tip by using the J-integral method. To predict the fatigue life, the conventional Paris law has been modified by substituting the range of J-value denoted by ${\Delta}J$ for ${\Delta}K$. The experimental fatigue test is conducted with five CCP specimens to validate the accuracy of the proposed model. It is noted that the relationship between the crack length a and ${\Delta}K$ in LEFM analysis shows a strong linearity, on the other hand, the nonlinear relationship between a and ${\Delta}J$ is detected in EPFM analysis. Therefore, this trend will be depended especially in the case of large scale yielding. The numerical results by the proposed model are compared with the theoretical solutions in literatures, experimental results, and the numerical solutions by the conventional h-version of the finite element method.

• Proceedings of the KWS Conference
• /
• 2002.10a
• /
• pp.583-588
• /
• 2002

The purpose of the study is to evaluate fracture toughness on the Laser and the electron beam welded joints of high tensile steels (HT500, HT550, HT650) by using 3-point bend CTOD and Charpy impact test. WM (weld metal) CTOD tests have been carried out using two kinds of CTOD specimen, the Laser beam welding (108mm length, and 24mm width, and 12mm thickness) and the electron beam welding (l71mm length, and 38mm width, and 19mm thickness). WM Charpy impact specimen is a standard V-notch type, and the temperature of the experiment is changed from -45 to 20 degree of centigrade. FE-analysis is also performed in order to investigate the effect of stress-strain fields on fracture characteristics. Results of the standard V-notch Charpy test are influenced by strength mis-match effect and the absorbed energy vE depends on crack path, and The transition temperature of Laser beam welded joints is more higher than that of electron beam welded joints. Results of the 3-point bend test give low critical CTOD and the crack path is in the weld metal of al specimens. These results indicate fracture toughness characteristics of the welded joints and transition temperature of HT500 are similar both a Laser beam welded joint and an electron beam welded joint. But the fracture toughness and the transition temperature of the electron beam welded joints of HT550 and HT650 are higher than those o the Laser beam welded joints.

• Journal of Korea Foundry Society
• /
• v.21 no.4
• /
• pp.239-245
• /
• 2001

Microstructure and mechanical properties of Sn-3.1 wt.%Ag-6.9 wt.%Bi system solders on Cu-substrate were studied. The Sn3.1 wt.%Ag-6.9 wt.%Bi alloy was designed by phase diagram and chemical properties and was prepared by melting in argon atmosphere. The mechanical properties of solder/Cu joints were examined by shear strength test, and also creep test. The microstructure of Sn-3.1 wt.%Ag-6.9 wt.%Bi alloy consists of Bi-rich phase and $Ag_3Sn$ precipitate in {\beta}-Sn$ matrix phase. The shear strength of the joint was decreased with aging treatment. Crack path under shear test was through the solder. Similar crack path change mode was observed at the creep test of solder/Cu joint. The creep behavior of Sn-3.1 wt.%Ag-6.9 wt.%Bi alloy represented the inverse primary creep behavior at all test condition. It is suggested that the inverse primary creep behavior is induced from Bi solute atoms in Sn-matrix. The creep resistance of Sn-3.1Ag-6.9Bi alloy is better than that of Sn-3.5 wt.%Ag alloy at all test conditions.

• Journal of the Korean Ceramic Society
• /
• v.28 no.1
• /
• pp.19-19
• /
• 1991

Fracture of Al2O3 tubes for different loading path under combined tension/torsion was investigated. Macroscopic directions of crack propagation agreed well with the maximum principal stress criterion, independent of the loading path. However, fracture strength from the proportional loading test(τ/σ= constant) showed either strengthening or weakening compared to that from uniaxial tension, depending on the ratio τ/σ. The Weibull theory was capable to predict the strengthening of fracture strength in pure torsion, but not the weakening in the proportional loading condition. The strengthening or weakening of fracture strength in the proportional loading condition was explained by the effect of shear stresses in the plane of randomly oriented microdefects. Finally, a new empirical fracture criterion was proposed. This criterion is based on a mixed mode fracture criterion and experimental data for fracture of Al2O3 tubes under combined tension/torsion. The proposed fracture criterion agreed well with experimental data for both macroscopic directions of crack propagation and fracture strengths.

• Composites Research
• /
• v.32 no.6
• /
• pp.327-334
• /
• 2019

The delamination is a special mode of failure occurring in composite laminates. Several numerical studies with finite element analysis have been carried out on the delamination behavior of unidirectional composite laminates. On the other hand, the fracture for the multi-directional composite laminates may occur not only along the resin-fiber interface between plies known as interply or interlaminar fracture but also within a ply known as interyarn or intralaminar fracture accompanied by matrix cracking and fiber bridging. In addition, interlaminar and intralaminar cracks appear at irregular proportions and intralaminar cracks proceeded at arbitrary angle. The probabilistic analysis method for the prediction of crack growth behavior within a layer is more advantageous than the deterministic analysis method. In this paper, we analyze the crack path when the mode I load is applied to the cross-ply carbon/epoxy composite laminates and collect and analyze the probability data to be used as the basis of the probabilistic analysis in the future. Two criteria for the theoretical analysis of the crack growth direction were proposed by analyzing the stress field at the crack tip of orthotropic materials. Using the proposed method, the crack growth directions of the cross-ply carbon/epoxy laminates were analyzed qualitatively and quantitatively and compared with experimental results.

• Structural Engineering and Mechanics
• /
• v.11 no.6
• /
• pp.591-604
• /
• 2001

In this paper, a finite element with embedded displacement discontinuity which eliminates the need for remeshing of elements in the discrete crack approach is applied for the progressive fracture analysis of concrete structures. A finite element formulation is implemented with the extension of the principle of virtual work to a continuum which contains internal displacement discontinuity. By introducing a discontinuous displacement shape function into the finite element formulation, the displacement discontinuity is obtained within an element. By applying either a nonlinear or an idealized linear softening curve representing the fracture process zone (FPZ) of concrete as a constitutive equation to the displacement discontinuity, progressive fracture analysis of concrete structures is performed. In this analysis, localized progressive fracture simultaneous with crack closure in concrete structures under mixed mode loading is simulated by adopting the unloading path in the softening curve. Several examples demonstrate the capability of the analytical technique for the progressive fracture analysis of concrete structures.

• Composites Research
• /
• v.24 no.2
• /
• pp.1-8
• /
• 2011

Interfacial fracture toughness under various mixed-mode loading is measured to provide a mixed-mode fracture criterion of a composite/metal bonded joint. Experimental fracture characterization tests were carried out using a SLB (single leg bending) specimen, which controls mode ratio with the specimen thickness. The experimental result of the SLB test conforms that interfacial fracture toughness increases as the mode II component increases. The effect of loading mode on interfacial crack growth is investigated on the basis of crack path observation using microscopic image acquisition technique. The influence of interfacial roughness on adhesion strength is also discussed.