• Journal of the Korean Geotechnical Society
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• v.32 no.10
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• pp.31-40
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• 2016

In order to investigate the change in soil arch structure developed within the soil subjected to trapdoor movement, various responses in the deformed particle assembly were observed via photoelastic measurement technique. The particle assembly was composed of the regularly stacked model particles coated by thin photoelastic material. Variation of the internal structure transmitting contact forces were observed by taking images showing the photoelastic responses and compared with the change in slip lines and pressures measured by load cells placed beneath the assembly. Initial soil arch structure established immediately after the trapdoor movement collapsed progressively and meanwhile a new extended structure was developed against further movement of the trapdoor. For the sufficient movement of the trapdoor, initially identical regions bounded by the soil arch structure and slip lines were separated and the region enclosed by slip lines became a part of the region loosing the transmitting contact forces identified by photoelastic measurement.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.3
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• pp.213-220
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• 2000

The method of photoelasticity allows one to obtain principal stress differences and principal stress directions in a photoelastic model. In the classical approach, the photoelastic parameters are measured manually point by point. The previous methods require much time and skill in the identification and measurement of photoelastic data. Fringe phase shifting method has been recently developed and widely used to measure and analyze fringe data in photo-mechanics. This paper presents the test results of photoelastic fringe phase shifting technique for the stress analysis of a circular disk under compression and an edge-cracked plate subjected to tensile load. The technique used here requires four phase stepped photoelastic images obtained from a circular polariscope by rotating the analyzer at $0^{\circ}$, $45^{\circ}$, $90^{\circ}$ and $135^{\circ}$. Experimental results are compared with those or FEM. Good agreement between the results can be observed. However, some error may be included if the technique is used to general direction which is not parallel to isoclinic fringe.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.2
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• pp.189-196
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• 2001

Photoelasticity is one of the most widely used methods for whole field stress analysis. In photoelasticity, the difference and the directions of the principal stresses we given isochromatic and isoclinic fringe patterns. Conventionally, principal stress directions are measured manually by relating the polarizer and analyzer of a plane polariscope at the same time. This is known to be the Tardy compensation method. This measurement can be very tedious and time consuming in whole field analysis. It is not possible to separate isoclincs from photoelastic fringes by conventional photoelastic technique. In this study, photoelastic theory is represented by Jones matrices and 4-steps and 8-steps phase shifting methods are described A feasibility study using computer simulation is done to separate isoclincs and isochomatics from photoelastic fringes of a circular disk under diametrical compression. Fringe patterns of the disk are generated using stress optic law. The magnitudes of isoclincs and isochromatics obtained from 8-step phase shifting method are compared with those of theories. From computer simulation, it is verified to separate isoclincs and isochomatics from photoelastic fringes.

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.1
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• pp.120-131
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• 2005

Statement of problem. More than 70% of patients who need the implant supported restoration are parially edentulous. The principles of design for implant supported fixed partial denture in mandibular posterior region are many and varied. Jurisdiction for their use is usually based on clinical evaluation. There are several areas or interest regarding the design of implant supported fixed partial denture in mandibular posterior region. 1) Straight and tripod configuration in implant placement, 2) Two restoration types such as individualized and splinted restorations. Purpose. The purpose of this study was to compare the amount and distribution of stress around the implant fixtures placed in the mandibular posterior region with two different arrangements and to evaluate the effects of splinting using the photoelastic stress analysis. Material & methods. 1) Production of study model: Mandibular partially edentulous model was waxed-up and duplicated with silicone and two models were poured in stone. 2) Fixture installation and photoelastic model construction: Using surveyor(Ney, USh), 3 fixtures(two 4.0 $\times$13 mm, one 5.0$\times$10 mm, Lifecore, USA) were insta)led in straight & tripod configurations. Silicone molds were made and poured in photoelastic resin (PL-2. Measurements group, USA). 3) Prostheses construction: Four 3-unit bridges (Type III gold alloy, Dongmyung co., Korea) were produced with nonhexed and hexed UCLA abutments and fitted with conventional methods. The abutments were tightened with 30 Ncm torque and the static loads were applied at 12 points of the occlusal surface. 4) Photoelastic stress analysis : The polarizer analyzer system with digital camera(S-2 Pro, Fujifilm, Japan) was used to take the photoelastic fringes and analysed using computer analysis program. Results. Solitary hexed UCLA restoration developed different stress patterns between two implant arrangement configurations, but there were no stress transfer to adjacent implants from the loaded implant in both configurations. However splinted restorations showed lesser amount of stresses in the loaded implants and showed stress transfer to adjacent implants in both configurations. Solitary hexed UCLA restoration with tripod configuration developed higher stresses in anterior and middle implants under loading than implants with straight configurations. Splintied 3 unit fixed partial dentures with tripod configuration showed higher stress development in posterior implant under loading but there were no obvious differences between two configurations. Conclusions. The tripod configuration of implant arrangement didn't show any advantages over the straight configuration. Splinting of 3 unit bridges with nonhexed UCLA abutments showed less stress development around the fixtures. Solitary hexed UCLA restoration developed tilting of implant fixture under offset loads.

• The korean journal of orthodontics
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• v.24 no.3 s.46
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• pp.709-719
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• 1994

The aim of this investigation was to identify which suing is more suitable for uprighting of the 30 degree inclined lower second molar in different situations. Between four different molar uprighting springs which were A, B, C type and T-loop spring, the author tested T-loop suing as a control material and the other springs were experimental group. Each spring was fabricated from .017' $\times$ .025' TMA wire and preactivated with 40 degree tip-back bend. Stabilizing unit included from the lower right central incisor to the lower right second premolar which were made by acrylic resin. The photoelastic overview of the lower right quadrant showed that stress concentrations were observed in its photoelastic model. The obtained results were as follows. 1. Higher concentration of compression can be seen clearly at the distal curvature than the mesial of the lower second molar when A type uprighting spring was applied, which can be used as a space regainer. 2. Higher level compression was presented at the mesial root apex area than the distal of the lower second molar in B type uprighting spring, which can be used as a space closer. 3. Areas of higher compression and tension were observed about the mesial and distal root of the lower second moalr than A and B type in C type uprighting spring, which can be used as a partial space regainer.

• Transactions of the Korean Society of Mechanical Engineers
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• v.7 no.1
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• pp.1-10
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• 1983

The photoelastic determination of S.I.F. in Fracture mechanics has been regarded as one of the most effective and practical experimental methods in which stresses are read directly, except a few shortcomings involved in the process of experiment; the difficulties of making a sharp crack tip similar to the practical one and nearly impossibilities of carving an arbitrarily shaped crack on the test plate, etc. To eliminate flaws mentioned above, recently, Kitagawa and Watanabe of Tokyo Univ.developed a new method named"Teflon Insert Method". which has improved experimental accuracy to a considerable extent byt remaining still room for further improvement, that is, the elimination of bonding boundary scars which render photoelastic fringes obscure. In this paper, a newly exploited"Teflon Molding Method" was attempted for the completion of teflon-epoxy experimental method. The experimental results obtained by this method are compared with existent theoretical and experimental values to evaluate its accuracy. As result, 1-6% of margin of errors were appeared in a series of photoelastic experiments which defied any other conventional method in terms of experimental accuracy.perimental accuracy.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.11 s.170
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• pp.1904-1911
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• 1999

The most effective material in the shape memory alloy(SMA) is the TiNi alloy, because its shape recovery characteristics are very excellent. We molded the composite material with shape memory function. The fiber of it is $Ti_{50}-Ni_{50}$ shape memory alloy and matrix of it is epoxy resin(Araldite B41, Hardner HT903. Ciba Geigy), its adhesive and optical sensitivity are very excellent. It was assured that the composite material could be used as model material of photoelastic experiment for intelligent materials or structures. In this research, the composite material with shape memory function is used as model material of photoelastic experiment. Photoelastic experimental hybrid method is developed in this research, it is assured that it is useful on the obtaining stress intensity factor and the separation of stress components from only isochromatic data. The measuring method of stress intensity factor of intelligent material by photoelastic experiment is introduced. In the mode I state, we can know that stress intensity factors are decreased more than 50% of stress intensity factor of room temperature when temperature of fiber is greater than 4$0^{\circ}C$, prestrain greater than 5% and fiber volume ratio greater than 0.42% and that stress intensity factors are decreased by 100% when fiber volume ratio is greater than 0.84%, prestrain greater than 5% and temperature greater than 60 $^{\circ}C$.

• Journal of Dental Rehabilitation and Applied Science
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• v.24 no.3
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• pp.253-267
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• 2008

The purpose of this study was to evaluate the pattern and the magnitude of stress distribution in the supporting tissues surrounding implant fixture with different diameter of implant fixtures(3i implant, Ø4.0, Ø5.0, Ø6.0mm and UCLA abutments(Ø4.1, Ø5.0, Ø6.0mm using photoelastic stress analysis. Photoelastic model was made with PL-2 resin(Measurements Group, Raleigh, USA) and three implants of each diameter were placed in the mandibular posterior edentulous area distal to the canine. Individual crowns were fabricated using UCLA abutments. Photoelastic stress analysis was carried out to measure the fringe order around the implant supporting structure under simulated loading conditions(15 lb, 30 lb). The results were as follows; 1. The more the diameter of implant fixture was increased, the less the stress concentration on cervical area of fixture was observed under loading. 2. Increasing mesiodistal diameter of implant superstructure had no much influence on stress distribution around implant fixture. 3. The use of smaller abutment had no influence on stress distribution around implant fixture. The use of smaller abutment diameter than that of implant fixture had no favorable effect on implant supporting tissue at biomechanical consideration.

• The Journal of Korean Academy of Prosthodontics
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• v.30 no.3
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• pp.379-400
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• 1992

The purpose of this study was to analyze the magnitude and distribution of stress using a photoelastic model from the mandibular distal extension removable partial dentures with the mesial or distal placement of the occlusal rest and the mesial or distal connection in the back-action clasp with the five various designs of the back-action clasp, that is, the mesial connection and the distal rest, the distal connection and mesial rest, the mesial connection and mesial rest, the distal connection and the mesial and distal rest, and the mesial connection, and the mesial and distal rest. A photoelastic model was made of the epoxy resin(PC-1) and the hardner(PLH-1) with the acrylic resin teeth used and was coated with the plastic cement-1 at the lingual surface of the model and then five kinds of the removable partial dentures on the photoelastic model were set. A unilateral vertical load of 12.5 kg was applied on the central fossa of the first molar with the use of specially designed loading device and the pattern and distribution of the stress of the photoelastic model under each condition was analyzed by the reflective circular polariscope. The following results were obtained. 1. In the back-action clasp with the mesial connection and mesial rest of the case 3, the effect of the stress distribution was the most favorable. 2. In the back-action clasp with the mesial and distal rest, of the case 4 and 5, the stress distribution was more greatly showed in the terminal abutment. 3. Generally, the stress distribution was more favarable in the mesial connection than in the distal connection. 4. In the back-action clasp with the mesial connection of the case 1, 3 and 5, the stress distribution was the most favorable in the mesial rest.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.10a
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• pp.127-133
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• 2001

Photoelastic isochromatic fringes related to the difference of principal stresses have some bandwidth whose light intensities are not constant and unsymmetrical in experimental image. Hence it is difficult to measure fringe order accurately at a data point by visual observation. In this study, the method of fringe sharpening, which can extract sharpened lines from both full-and half-order fringes by digital image processing, is developed. To test the method, various simple photoelastic fringe patterns are simulated and their image are processed to yield sharpened lines. The method is than applied to general problem such as image of a circular disk compressed by concentrated loads and a cylinder subjected to internal pressure. The procedure is proved to be capable of extracting sharpened lines accurately from photoelastic isochromatic fringes.