Finite Strain Analysis by Image Processing: Smoothing Techniques

The digital image processing technique can be successfully used to quickly measure surface deformations with good accuracy. In a previous paper the authors [1] described a method to measure large strain fields, which is based on digital images processing. A dot grid, previously marked on the surface of the workpiece, is acquired by two CCD cameras from two different view-points. The data are then processed by a stereoscopic procedure, which returns the dot locations in a three-dimensional space. A similar method was developed by Zheng Tan, Merlin and Magnusson [2] in 1992. They evaluated the spatial location of many points, placed in a square grid on the surface of the specimen, by a photogrammetry derived technique. The co-ordinates of the identified are then processed using a method proposed by Sowerby et alii [3, 4], which calculates the principal strain values and directions within triangular elements, whose strain fields is assumed to be constant.