• Journal of the Korean Society for Precision Engineering
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• v.13 no.8
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• pp.80-87
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• 1996

The present paper will give some results of the fatigue behavior of typical axi-symmetric forward extrusion die. The extrusion process is analyzed by rigid-plastic FEM and the deformation analysis of extrusion die is conducted by elasto-plastic FEM. To approach the crack problem LEFM (Linear Elastic Fracture Mechanics) is introduced. Using special element in order to conside the sigularity of stress/ strain in the vicinity of the crack tip, stress intensity factor and the effective stress intensity factor is calculated. Applying proper fatigue crack propagation criterion such as Paris/Erdogan fatigue law and maximum principal criterion to these data, then, the angle and the direction of fatigue crack propagation is simulated. In result, it is proved that the simulated fatigue crack propagates in the zigzag path along the radial direction and fatigue life of the extrusion die is evaluated by using the computed crack growth rate.

• Journal of the Korean earth science society
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• v.29 no.3
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• pp.255-262
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• 2008

Late Cretaceous to early Tertiary paleostress was evaluated by analyzing the healed microcracks in the Cretaceous granite of the Goheung area, south Korea. Healed microcracks in five granite samples (GH-1, GH-3, GH-4, GH-5, GH-8) were investigated and measured according to direction. The directions of maximum horizontal principal stress in GH-1, GH-3, and GH-4 are dominantly $N60^{\circ}W\;and\;N70^{\circ}E,\;N20^{\circ}W\;and\;N50^{\circ}W$, while minor directions are N-S and $N30^{\circ}E$. In GH-5 and GH-8, $N40^{\circ}E\;and\;N10^{\circ}E$ are the most dominant directions, while $N40^{\circ}W$ is the minor direction. Thus overall, the most dominant directions of healed microcracks in the study area are oriented $N60^{\circ}W$, while minor directions are oriented $N20^{\circ}W,\;N20^{\circ}E\;and\;N70^{\circ}E$, essentially NE. Combining the paleostress results of this study with other studies, the direction of the maximum horizontal principal stress in the study area during the late Cretaceous to the early Tertiary should perhaps be changed WNW to NE. The reason for this is thought to be the complex tectonic movements which occurred in northeast Asia at that time.

• The Journal of Korean Academy of Prosthodontics
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• v.23 no.1
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• pp.97-112
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• 1985

The purpose of this study was to evaluate the stress patterns developed in supporting structures by removable partial denture with attachment retainers. The attachments tested were Dalbo(miniature) attachment, resilient Ceka attachment, rigid Ceka attachment, precision and sleeve attachment, and R.P.I. clasp as a contrast. 3-dimensional photoelastic stress analysis was used to record the isochromatic and isoclinic fringe patterns and to calculate principal stress components at measuring points. The results showed that: 1. The maximum compressive stress on residual ridge was produced under the loading point with Dalbo and resilient Ceka attachment, distal to the loading point with rigid Ceka and precision and sleeve attachment, and mesial to the loading point with R.P.I. clasp. 2. The Dalbo attachment produced the most stress on residual ridge, and the least stress on abutment teeth. and resilient Ceka attachment showed favorable stress distribution. 3. Rigid Ceka attachment produced higher compressive stress on buccal. alveolar crest, and precision and sleeve attachment produced higher compressive stress on distal alvelolar crest and mesial surface of the root apex in abutment teeth. 4. R.P.I. clasp produced higher compressive stress on mesial alveolar crest.

• The Journal of Engineering Geology
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• v.26 no.2
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• pp.177-185
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• 2016

This work investigates whether stress changes induced by an earthquake can be estimated using the deformation measured by high-resolution borehole strainmeters. We estimate the changes in the orientation and magnitude of the principal compression stresses using borehole strainmeter data recorded before and after the M7.2 El Mayor-Cucapah earthquake on April 4, 2010. Clear differences in the stress orientations and magnitudes are apparent before and after the event. The change in stress orientation appears related to subtle increases of stress in the tectonic maximum principal orientation, which is in agreement with the earthquake focal mechanism solution. The sudden stress drop at the onset of the earthquake was 10⁻³-10⁻² MPa in the principal orientations. The Coulomb stress transfer model, which can estimate stress transfer, predicts a shear stress increase of (0.1-0.6) × 10⁻² MPa at the strainmeter site, which is in line with the measured data (0.3-0.8) × 10⁻² MPa. Overall, our results suggest that borehole strainmeter data reflect the subtle stress changes associated with earthquake occurrence, and that such data can be utilized for earthquake-related research.

• The Journal of Korean Academy of Prosthodontics
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• v.27 no.2
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• pp.79-100
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• 1989

The Purpose of this study was to investigate material differences in stress transmission among various artificial teeth and denture base materials. For this study, a two-dimensional finite element model and a two-dimensional photoelastic model of a mandible with complete denture were made. A resin tooth and a porcelain tooth were used as artificial teeth, and a resin base, a metal lined base, and a soft-liner lined base were used as denture bases. An occlusal load was applied and principal stresses generated in the supporting tissues were compared. To test the impact stress transmission, strain gauge attached to the denture base specimens made of the different materials were made in thick and thin groups. Voltage outputs from hitting the specimen with a steel ball were compared. The results were as follows : 1. In FEM, increasing the mucosal thickness reduced the maximum principal stresses in the supporting tissues, but altering the tooth materials and the base materials induced no difference in the stresses. 2. In photoelastic model study, no difference in fringe order among the specimens were observed, but the thick mucosa group and the soft-liner lined group revealed a more uniform distribution of the load. 3. In strain measuring, the impact force transmission was highest in the soft-liner lined group, and was the lowest in the metal lined group(p<0.01). 4. In the thin group using the resin base, the porcelain tooth showed higher impact stress transmission than the resin tooth(p<0.01), but no difference was observed between them in the thick group. In the soft-liner lined group, the porcelain tooth showed higher impact stress transmission than the resin tooth(p<0.01), but no difference was observed between them in the metal lined group. 5. The thick group showed lower impact stress transmission than the thin group(p<0.01).

• The Journal of Korean Academy of Prosthodontics
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• v.37 no.1
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• pp.93-103
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• 1999

Stress distribution on mandibular implants supporting overdentures were registered in vitro experimental model by means of 4 rosette gauges which were placed around the implant. The overdenture attachments used in this study were the Resilient Dolder bar, Rigid Bolder bar, Round bar, Hader bar & Dal-Ro attachment. An occlusal jig was placed on the overdenture and the loading sites were 3 points which mimicked working, balancing, and median relations. With 5 and 10kg loading, strains were measured by strain indicator(P-3500, Measurement group, Raleigh, USA), and using these data, maximum and minimum principal stresses and Von Mises stress were calculated and evaluated. The results were as follows : There was a tendency of high stress concentration in the lingual side of the implant, and in the buccal side low stress was developed regardless of the attachment systems. The resilient Bolder bar concentrated highest stress among the attachment systems, and the Round bar and the Dal-Ro attachment provided comparatively low stresses around the implant. The rigid Bolder bar concentrated high stress in the mesial side, and the Dal-Ro attachment developed tensile stress patterns in the lingual and distal sides of the implant at the balancing relation.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.295-302
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• 2000

Earthquakes not only produce additional load on the structures and underlying soil, but also change the strength characteristics of the soil. Therefore, in order to analyze soil structures for stability, the behaviour after earthquake must be considered. In this paper, a series of cyclic triaxial tests and monotonic triaxial tests were carried out to investigate the undrained shear strength and liquefaction strength characteristics of Nak-Dong River sand soils which were subjected to cyclic loading. The sample was consolidated in the first stage and then subjected to stress controlled cyclic loading with 0.1Hz. After the cyclic loading, the cyclic-induced excess pore water pressure was dissipated by opening the drainage valve and the sample was reconsolidated to the initial effective mean principal stress(p/sub c/'). After reconsolidation, the monotonic loading or cyclic loading were applied to the specimen. In the results, the undrained shear strength and liquefaction strength characteristics depended on the pore pressure ratio(Ur=U/p/sub c/'). The volume change following reconsolidation can be a function of cyclic-induced excess pore water pressure and the maximum double amplitude of axial strain.

• Journal of the Korean Society of Safety
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• v.29 no.3
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• pp.1-7
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• 2014

In this study, for the evaluation of the static and fatigue joining strength of the joint, the geometry of the cross-tension specimen was adopted. The specimens were produced with optimal joining force and fatigue life of the clinch joint specimens was evaluated. The material selected for use in this study was cold rolled mild steel (SPCC) with a thickness of 0.8 mm. The maximum tensile load was 708 N for the specimen with single point. The fatigue endurance limit (=42.6 N) per point approached to 6% of the maximum tensile strength at a load ratio of 0.1, suggesting that the joints are vulnerable to cross-tension loading during fatigue. Compared to equivalent stress and maximum principal stress, the SWT fatigue parameter and equivalent strain can properly predict the current experimental fatigue life. The SWT parameter can be expressed as $SWT=2497.5N^{-0.552)_f$.

• The Journal of Advanced Prosthodontics
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• v.12 no.6
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• pp.351-360
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• 2020

PURPOSE. The aim of the present study was to compare the stress distributions on the dental implants, abutments, and bone caused by different overdenture attachment types under functional chewing forces. MATERIALS AND METHODS. The 3D finite element models of the mandible, dental implants, attachment types, and prostheses were prepared. In accordance with a conventional dental implant supported overdenture design, the dental implants were positioned at the bone level in the canine teeth region bilaterally. A total of eight models using eight different attachment systems were used in this study. All the models were loaded to simulate chewing forces generated during the centric relationship (450 N), lateral movement (400 N), protrusive movement (400 N), and also in the presence of a food mass unilaterally (200 N). Stress outputs were obtained as the maximum principal stress and the equivalent von-Mises stress. RESULTS. In all attachment types, higher stress values were observed in the abutments, dental implants, and bone in the magnet attachments in different loading conditions. The highest stress values were observed among the magnet systems in the components of the Titanmagnetics model in all loading conditions (stresses were 15.4, 17.7, and 33.1 MPa on abutment, dental implant, and bone, respectively). The lowest stress value was observed in the models of Zest and O-Ring attachments. CONCLUSION. The results of the present study implied that attachment types permitting rotation and tolerating various angles created lower stresses on the bone, dental implants, and abutments.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.111-115
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• 2001

The die design for hot forging was investigated for manufacturing precisely of scroll rotor made with Al-Si alloy. A scroll rotor is a non-symmetric 3-D shape part, having involute wraps. Disk-shaped billet of Al-Si alloy was extruded to wraps and boss simultaneously. Because the involute wraps is not axi-symmetric, the flow velocity and the stress of die is very much different at each portion. Moreover, the die in wraps portion is a cantilever beam and fractured. In this paper, the analysis of forming and die stress is investigated using the FEM tool, DEFORM-3D. The tensile strength of tool material is $250kg/mm^{2}$. From the analysis results, we can find the maximum principal stress of die is over the fracture strength and redesign the die. The prototype forged part is superior in net shaping and microstructure.