A method for measuring strain in a sample of material. A reference image is obtained of a surface of the sample. A test machine is used to apply a load to the sample, as determined by a control signal from a system processor. A measurement image is then obtained, and test points on the reference image are located on the measurement image, using an image processor programmed to perform machine vision. The displacements between the location of the test points on the two images are determined. These displacements are used to calculate strain. Each new strain value may be used by the system processor to determine a next load value, so that the load is adjusted in terms of strain parameters.
David L. Davidson;Steven B. Seida