• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.4
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• pp.1263-1274
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• 1996

In this paper, as elastic-plastic fracture toughness test under mixed mode loading was proposed using a single edge-cracked specimen subjected to bending moment(M), shearing force(F), and twisting moment(T). The J-integral of a crack in the specimen is expressed in the form J=$J_I$+ $J_II$$J_III$, where $J_I$, $J_II$ and $J_III$ are the components of mode I, mode II and mode III deformation, respectively. $J_I$, $J_II$ and $J_III$ can be estimated from M-$\theta$ ($\theta$;crack opening angle), F-U(U; crack shear displacement) and T-$\alpha$ ($\alpha$;crack twisting angle). In order to obtain the the M<-TEX>$\theta$, F-U and T-$\alpha$ diagram inreal time, a new deformaiton gage for mixed mode loading was proposed using the optical position sensing device(PSD). The elastic-plastic fracture toughness test was carried out with an aluminum alloy. The loading apparatus was designed and manufactured for this experiment. For the loading condition of the crack initatio in the mixed mode, the MMT -3(mode I+ mode II+ mode III) has the lowest values out of the all specimens. This implies that MMT-3 is possible of the crackinitation at lower load, if the specimen acts on together with the torque under the same loading condition. An elastic-plastic fracture toughness test using the PSD brings a successful experimentation in measuring the crack deformation(mode I+ mode II+ mode III).

• Journal of Korea Foundry Society
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• v.15 no.5
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• pp.483-493
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• 1995

The microstructural changes during semi-solid state processing of hypereutectic Al-Si alloy has been investigated in the present study. Stirring of semi-solid slurry results in the morphological changes of the primary Si particles, i.e. from angular rod shape to near-spherical shape. Besides the spherodization of primary Si particles, the average particle size increases, especially, at much higher rate in the final stage than that in the early stage of stirring. Various microstructure characterization techniques, such as anisotropic etching, SEM imaging and ECP analysis, reveal that the spherodization of primary Si particles occurs by the combinations of the mechanisms of coalescence, fracture, and wear of the individual particles. Isothermal shearing of hypereutectic Al-Si at $580^{\circ}C$ shows that spherical ${\alpha}-Al$ particles are formed by the dissociation of Al-Si eutectic structure at the early stage of isothermal shearing. The spherical ${\alpha}-Al$ particles gradually grow by the mechanisms of Ostwald ripening and coalescence of the particles.

• Design & Manufacturing
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• v.12 no.3
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• pp.42-47
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• 2018

Recently, in the surge of global environmental issues, there has been a great attention to lightweight materials in purpose of saving energy. Magnesium alloys not only have low specific gravity, and superb specific stiffness, but are also excellent in blocking vibrations and electromagnetic waves. So demand for this material is getting bigger rapidly throughout the industry. In this study, we examined the improvement of formability of magnesium alloy AZ31 material in warm working. Drawing, bending and shearing process were carried out by varying the forming temperature and the forming speed, and the influence of the variables on each process was studied. In the experiments, the high forming temperature and low forming speed results in high formability in the drawing process and the bending process. In the shearing process, as the forming temperature increases, the length of the fracture decreases.

• Geomechanics and Engineering
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• v.22 no.6
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• pp.529-540
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• 2020

Water inrush is a major hazard for mining and excavation in deep coal seams or rock masses. It can be attributed to the coalescence of rock fractures in rock mass due to the interaction of fractures, hydraulic flow and stress field. One of the key technical challenges is to understand the course and mechanism of fluid flows in rock joint networks and fracture propagation and hence to take measures to prevent the formation of water inrush channels caused by possible rock fracturing. Several case observations of fluid flowing in rock joint networks and coupled fracture propagation in underground coal roadways are shown in this paper. A number of numerical simulations were done using the recently developed flow coupling function in FRACOD which simulates explicitly the fracture initiation and propagation process. The study has demonstrated that the shortest path between the inlet and outlet in joint networks will become a larger fluid flow channel and those fractures nearest to the water source and the working faces become the main channel of water inrush. The fractures deeper into the rib are mostly caused by shearing, and slipping fractures coalesce with the joint, which connects the water source and eventually forming a water inrush channel.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.4
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• pp.423-431
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• 2004

For the fracture mechanics analysis of cracks in welds of dissimilar steels, residual stress analysis and fracture analysis must be performed simultaneously. The standard definition of the J -integral leads to a path dependent value in the presence of a residual stress field. And unlike cracks in homogeneous materials, a bimaterial interface crack always induces both opening and shearing modes of stress in the vicinity of the crack tip. Therefore, it is necessary to develope a path independent J-integral definition for a crack in a residual stress field generated by welding of dissimilar steels. This paper addresses the modification of the Rice-J-integral to produce a path independent J -integral when residual stresses due to welding of dissimilar steels and external forces are present. The residual stress problem is treated as an initial strain problem and the J-integral proposed for this class of problems is used. And a program which can evaluate the J -integral for a crack in a weld of dissimialr steels is developed using proposed J integral definition.

• Design & Manufacturing
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• v.11 no.1
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• pp.26-29
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• 2017

Burrs generated during shear forming such as notching and piercing may cause lifting during product assembly, which may deteriorate the productivity and quality of products. In this study, various shear angles and variable clearances between the punch and the die were applied in experimental notching tests to investigate the shear fracture surface and the burr height due to various conditions. The experimental results show that the clearance has the greatest effect on shear and fracture surfaces. It is considered that the height of the shear section increases slightly as the shear angle increases.

• Journal of Welding and Joining
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• v.18 no.1
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• pp.52-58
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• 2000

Spot welding, namely a kind of electric resisting welding has been used widely in field of automobile and aircraft industries because of easiness to apply. Specimens used in this study was a mild steel of 1.2mm thickness and the electrode was a Cu-Cr alloy of 6mm diameter. The surface sheared of specimens after testing of tensile shear was observed by SEM(scanning electron microscope) after ultrasonic cleaning for 10min., and microstructures and grain size of all specimens were measured with using of O.M.(Optical microscope). By the means of measurement and observations of tensile shear load, fatigue strength and share surface, the weldability of spot welding was evaluated. When tensile shearing testing, fracture starting point in all specimens was took place at the bond between HAZ(Heat affected zone) and nugget. With increasing in number of layers, fatigue strength was decreased. With increasing in electric current, grain size in the HAZ became more fine.

• Journal of Korean Neurosurgical Society
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• v.41 no.4
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• pp.272-274
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• 2007

Bilateral traumatic hemorrhage of the basal ganglia is an extremely rare neuropathologic entity. This report describes a 50year-old man with bilateral basal ganglia hemorrhage with occipital fracture of the skull after head trauma. The mechanism of development of traumatic hemorrhage of the basal ganglia has been not clear. But, it is presumed to be secondary to rupture of the lenticulostriate or anterior choroidal artery by shearing as a result of acceleration/deceleration forces. We briefly summarize our uncommon case and discuss its possible mechanisms.

• Journal of Korean Foot and Ankle Society
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• v.10 no.2
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• pp.271-273
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• 2006

In closed calcaneus fractures, the occurrence of FHL interposition in subtalar joint is relatively rare and difficult to diagnosis preoperatively. But careful physical examination and significant radiologic findings could be useful tools to diagnosis preoperatively. This findings is shearing off a superior medial fragment made up of the sustentaculum talus connected to a significant portion of the medial wall and medial aticular surface of the posterior facet.

• Journal of Power System Engineering
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• v.15 no.5
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• pp.67-71
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• 2011

Fine blanking is a specialized form of blanking where there is no fracture zone when shearing. This is achieved by compressing the whole part and then an upper and lower punch extract the blank. This allows the process to hold very tight tolerances, and perhaps eliminate secondary operations. In the present study, tensile test and numerical simulation has been performed to investigate distribution of deformation and stress of car seat recliner. The commercial ABAQUS/Explicit software was applied for analyzing the stress and strain of the recliner. In analysis, three lock gear has reached the maximum moment on rotational degree of 2.27. This is more than two times than maximum moment of same size recliner, and can be used safely. Therefore, these can use as criterion of actual structural design.