BISMAP: A Non-Contact Biaxial Displacement Measurement System

The development and validation of a prototype BISMAP (Biaxial Displacement Measurement by Machine Vision Processing) system is described. The non-contact biaxial displacement measurement system adapts machine vision technology to create a unique extensometer. The BISMAP system is built around a vision processing system that tracks and recognizes surface texture features around specific control points by using a normalized correlation technique. The system has numerous advantageous features including non-contact measurement in two-dimensions, variable gage length, direct surface measurement (no attached target) and real-time measurement of multiple, discrete points. The performance of the system is demonstrated with evaluations of the monotonic (and in some cases cyclic) stress-strain response for four different materials: aluminum, LEXAN, rubber and baboon tendon. The system has a measured accuracy of 370 μ∈ with ′50 μ∈ variability when compared to a strain gage. It is best-suited for measuring strains in excess of 5000 μ∈ and there is no practical upper limit on the measurable strain with retraining. The BISMAP system shows promise for development from prototype into a laboratory instrument capable of measuring strains in pliable or delicate materials.