• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.3
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• pp.200-206
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• 1999

This paper describes the stress analysis of a curved beam by using photoelasticity. In order to measure accurate isochromatic fringe orders at certain locations. fringes are doubled and sharpened by digital image processing. After fringe multiplication and sharpening. fringe orders can be read as a quarter order interval (N=0, 1/4, 2/4, 3/4,...). The results obtained from photoelastic experiment are compared with those calculated by using theory. Two results are agreed well even though there are some scatter bands with maximum 8 percent for the results of photoelastic measurements and theoretical calculation. Difference may be occurred due to the slight misalignment of the direction to which axial load is applied in photoelastic experiment. It is confirmed that accurate measurement of stress distribution can be possible by using the techniques of fringe multiplication and sharpening in photoelasticity.

• The korean journal of orthodontics
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• v.34 no.2 s.103
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• pp.121-129
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• 2004

The purpose of this study was to photoelastically visualize 4he distribution of fortes transmitted to the alveolus and surrounding structures using three different types of headgear for the distal movement of the upper molars. A photoelastic maxillary model was made and three different directional forces applied, which were high-pull, straight-pull, and cervical-pull. Stress distribution was recorded through circular polariscope, and two-dimensional photoelastic stress analysis was performed according to isochromatic fringe characteristics. The results were as follows: 1. In the case of high-pull headgear bodily movement occurred in the medium- length outer bow, stress distribution in the apical region was 1st molar, 2nd premolar, lst premolar in sequence and there was no apparent difference. 2. In the case of straight-pull headgear, bodily movement occurred in the long outer bow and stress distribution in the apical region was heavy in the 1st molar, 2nd premolar, 1st premolar in sequence. But. there were no apparent differences according to the length of the outer bow. 3. In the case of cervical- pull headgear, bodily movement also occulted in 4he long outer bow, and apical stress of the premolar region was heaviest among other cases and apical stress of the 2nd premolar was heaviest in the short outer bow. In clinical situations, to achieve bodily movement of the upper 1st molars without modifying outer bow height, applying an outer bow length as long as the inner bow length in high-pull headgear and applying an outer bow length longer than the inner bow length in straight-pull, cervical-pull headgear are recommended.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.2
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• pp.148-154
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• 2014

Photoelasticity is a useful technique for obtaining the differences and directions of principal stresses in a model. In conventional photoelasticity, the photoelastic parameters are measured manually point by point. Identifying and measuring photoelastic data is time-consuming and requires skill. The fringe phase shifting method was recently developed and has been found to be convenient for measuring and analyzing fringe data in photo-mechanics. This paper presents an experimental study on the stress distribution along a horizontal line that passes the central point of a rhombus plate made of Photoflex (i.e., type of urethane rubber). The isoclinic fringe and/or principal stress direction is constant on this horizontal line, so a four-bucket phase shifting method can be applied. The method requires four photoelastic fringes that are obtained from a circular polariscope by rotating the analyzer at $0^{\circ}C$, $45^{\circ}C$, $90^{\circ}C$ and $135^{\circ}C$. Experimental measurements using the method were quantitatively compared with the results from FEM analysis; the results from the two methods showed comparable agreement.