Experimental analysis of stress and strain using photoelasticity and photogrammetry

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 has been tested for different enforcement. In each step, addition to recording the required information for photoelasticity, photos of the object have been taken by a digital camera in a fixed position and orientation. The position of the corresponding points on the object was 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 a high accuracy for photogrammetry compared to photoelasticity. Therefore, conventional methods for stress and strain measurements can be replaced by photogrammetry.