An investigation of strain measurement on curved surface using photogrammetry with validation

Metal forming is a crucial technique for shaping sheet material to specific dimensions. Predicting strain in formed components is essential for evaluating sheet metal formability. This study investigates the measurement of major and minor strain on curved surfaces formed through a single-point incremental forming process using photogrammetry and validates the results. The aim is to measure strain on a curved surface post-forming by applying circle grids on the sheet metal before forming. A system was developed to capture deformed circle grids and compare the deformation with the original diameter to calculate strain. A Forming Limit Diagram was plotted to analyze the formability of the sheet metal. Statistical methods were used to predict the confidence interval level of the developed strain. The average percentage error of the strain obtained through 3D photogrammetry method compared to the experimental results is approximately 1.91% and 2.93% for the major and minor axes, respectively. These findings demonstrate that photogrammetry analysis of strain on curved surfaces is more accurate than traditional experimental methods.