A Strain Field Measurement Method for Surfaces with Out-of-plane Deformations

A Strain Field Measurement Method for Surfaces with Out-of-plane Deformations

This paper presents the progress of a follow-up development of the ImPro Strain, an image-based surface strain field measurement system. The ImPro Strain assumes that the measurement regions are planes. In this work, an alternative surface deformation measurement method is prototyped so that it is also suitable to measure out-of-plane deformation. The photography hardware is based on commodity digital cameras and their accessories. The software prototyped in this work is based on open source toolkits. Image template matching is performed on image pairs taken by a dual-camera facility. Four-node finite element shape functions are adopted for image reconstruction during sub-image template matching to decrease the geometric distortion induced by the viewing angle differences between two cameras. To evaluate the accuracy of this system, a set of zero-strain tests are carried, and the photos of an RC-wall experiment performed and a steel braced frame are used in this work. The results show that this system is capable to capture out-of-plane deformation and its strain fields.