Conventionally, strain has been measured using scribed, etched, or printed grids together with a ruler and dividers or a graduated, transparent Mylar® overlay. Touch trigger probe equipped Coordinate Measuring Machines (CMMs) are used to measure geometry. More recently, stereo computer vision has been proposed, but, because accuracy quickly diminishes with camera distance to the part, application has been limited to small test samples. On CMMs, laser digitizers are growing in use. To date, however, accurate, simultaneous measurement / analysis of both strain and geometry has not been reported. This paper presents two new CMM based research methods that address this. The laser digitizer method uses a circle grid, and the stereo computer vision approach uses a square grid. Parallel computing is used to accelerate computer processing time. A dual thickness tailor welded steel test dome, an aluminum test dome, and a wrinkled double layer truck part illustrate practical application.
Angiographic film substraction using a laser digitizer and computer processing