Measurement and experimental analysis of stress and strain of enforced objects are crucial in the fields of mechanics and civil engineering. The PHOTOELASTICITY as a conventional method for measurement and analysis suffers from some limitations such as the need for specific transparent material, appropriate equipment and enough experience. In this research, photogrammetry was introduced for the experimental analysis of stress and strain measurement because of its high accuracy, ease and independence to the material of the object. To compare the accuracy of photogrammetry and PHOTOELASTICITY, a crane hook-shaped object from Araldite epoxy was tested for different enforcement. In each step, in addition to recording the required information for PHOTOELASTICITY, photos of the object were taken by a digital camera in a fixed position and orientation. The positions of the corresponding points on the object were measured with an accuracy of 0. 01 pixel using digital image processing and least square image matching techniques. The measured stress and strain using PHOTOELASTICITY and photogrammetry were compared with analytical stress and strain measurement method. The results indicated high accuracy for photogrammetry compared to PHOTOELASTICITY. Therefore, conventional methods for stress and strain measurements can be replaced by photogrammetry.

Background and Aim: When a complete denture is replaced with an overdenture supported by implant, masticatory efficiency will be improved. There are a lot of controversies on the use of the best attachments in overdentures. The aim of this study was to compare the stresses transferred to the implant supported overdentures in mandible with bar, ball and zaag attachments using photoelastic technique.Materials and Methods: In this descriptive in - vitro study, stresses transferred to the implants supported over dentures with bar, ball and zaag attachments were analyzed using photoelastic method. Two implants were installed in the canine area 8 mm from the midline. Vertical and oblique loads of 30Thwere applied to the first molar unilaterally. Resultant stress distribution with ball, bar and zaag attachments were evaluated.Results: The bar attachments exhibited the most stress transferred to the implants on the loaded side and opposite side. When the model was subjected to the posterior vertical load. The oblique load transferred to the implants was more than the vertical load. The ball and zaag attachments transferred the vertical load to both implants and edentulous area. These both attachment systems exhibited more stress on implants in oblique load where as the edentulous ridge was stress tree.Conclusion: Bar attachments transferred more stress to the implant bodies than ball and zaag attachments in both oblique and vertical loads and zaag attachments transferred more stress to the implant as compared with the ball ones.

A two dimensional finite model with inclined crack at different crack angles are being analyzed in mixed mode condition using photo elasticity method for the determination of Stress Intensity Factors. The well-known Sih’s equation and three points deterministic approach is used for the determination of stress intensity factors. The effects of biaxial load factor, crack angle, size factors were studied and a regression model was developed for geometry correction to predict Stress Intensity Factors. The results give a good compromise to the theoretical one. The experimental result also gives significant data for the two dimensional mixed mode loading conditions.

Two methods of PHOTOELASTICITY and finite element were employed to analyze contact stresses in bolted joints. Samples were made up of photoelastic materials. Photos were taken when samples were loaded with Polaris cope. Finite element models were analyzed using ANSYS 5.6 software. To verify the model, finite element results were compared with those of the experimental ones. The comparison led to an acceptable agreement between the two, with a correlation coefficient (R2) of 0.99. After a validation of the finite element model, the effect of number of engaged threads and different moduli of elasticity of bolt and nut were investigated, using ANSYS software. According to the results obtained, increasing the number of engaged threads in bolted joints resulted in a decrease of load concentration percentage in the first thread, and then smoother load distribution was observed to be accomplished. Of course, the behavior of load distribution in "bolt and nut" is not the same as in "body and stud" arrangement, but in either cases, when the number of engaged threads passed 20, this didn't affect stress distribution. For body and stud, the most uniform load is obtained when the Young's modulus ratio of body and stud is in the range of 0.5-1, while this value for nut and bolt is observed to be about 0.1.

Introduction: Many studies have been performed to evaluate the stress distribution around endodontic posts; those which compared posts composed of different materials are rare. The aim of this study was to compare stresses induced in dentin by three structurally different posts using PHOTOELASTICITY method.Materials and Methods: Nine blocks of PSM-5 Photoelastic material with 45x45x10 mm dimension were prepared. In each block, a canal 9 mm in length and 0.8 mm in width was drilled. Blocks were divided into 3 groups of three each. In the first group, the canals were prepared for insertion of Fiber Post with 1.25 mm width. In the second group, the canals were prepared for insertion of ParaPost with 1.25 mm width and the canals in the third group were prepared for casting post similar to the above samples. Casting Post pattern was made by Duralay resin and casted by Ni-Cr alloy. All posts were cemented in canals with Panavia cement. The stresses were evaluated in the polariscope under three different conditions: 1) without load, 2) with 135 N vertical load, and 3) with 90 N oblique load (26o inclination to post long axis). The fringe orders in the cervical, middle and apical regions of the posts were evaluated and compared with each other.Results: Application of the vertical load induced a high stress concentration (FO=4) in the apical region of the ParaPost, while lower stress was observed in the middle (FO=2) and cervical region (FO=2+). Fiber Post and Casting Post showed even stress distribution (FO=2+). High stress concentration was detected with the application of oblique force in the cervical region of ParaPost (FO=5) and Casting Post (FO=3+). Fiber Posts fractured before reaching 90-N loading force.Conclusion: The stress distribution around Fiber Post and Casting Post were constant in comparison with ParaPost. Fiber Post with 1.25 mm width was not recommended in situations with high oblique stresses.