Measurement of local strain: machine vision and finite element method

Abstract

Determining the material deformation behavior including local strain data is very useful for analyzing the forming processes. In order to measure strain properties, the uniaxial tensile test was used. More than 10 important mechanical properties were obtained from the uniaxial tensile test. However, through this test, only one strain in the tensile direction can be reported. Obtaining strain at various points in the transverse and longitudinal directions can provide important information about anisotropy, the Poisson’s ratio and material heterogeneity. In this study, machine vision method along with graphical programming were used for automatic strain calculations. Also, an innovative numerical method was developed based on machine vision procedure. In this new method, a number of circles were carved as a matrix pattern on the finite element model. Removing the limitations of the machine vision method, including its sensitivity to vibration, is the most important advantage of this numerical model. The results of the finite element method were evaluated in comparison with the tensile test and the machine vision procedure.