BALANCED NON-CONTRACTING LASER EXTENSOMETER FOR BIAXIAL STRAIN MEASUREMENTS

ENHANCEMENTS TO A NON-CONTACTING, LASER BASED EXTENSOMETER FOR REAL-TIME MEASUREMENTS OF BIAXIAL STRAIN ON COMPOSITES, PLASTICS, METALS, CERAMICS, AND A VARIETY OF OTHER MATERIALS INCLUDING ELASTOMERS ARE PROPOSED. THESE ENHANCEMENTS WILL ENABLE RESEARCHERS TO STUDY MULTI-AXIAL STRAIN BEHAVIOR (I.E. AXIAL, TRANSVERSE, AND TORSIONAL) ON MATERIALS SUBJECTED TO UNIAXIAL AND MULTI-AXIAL LOADING CONDITIONS. THIS CAPABILTITY WILL SIMPLIFY CALCULATIONS OF YOUNG'S MODULUS, POISSON'S RATIO, AND OTHER MATERIAL PARAMETERS USED FOR DESIGNING COMPOSITES AND ELASTOMER MATERIALS. THE APPROACH DOES NOT REQUIRE MARKINGS ON THE SPECIMEN OR ANY SORT OF SURFACE PREPARATION AND WILL NOT INFLUENCE THE PERFORMANCE OF THE SPECIMEN DURING THE TEST. THE ENHANCEMENTS WILL INCLUDE MODIFICATIONS TO THE OPTICAL SYSTEM OF A NON-CONTACT LASER EXTENSOMETER AND THE IMPLEMENTATION OF NEW SIGNAL PROCESSING ELECTRONICS TO ADDRESS LOW RETURN SIGNALS COMMONLY SEEN ON DARK COMPOSITES AND MATERIALS THAT EXHIBIT POOR LIGHT SCATTERING PROPERTIES. TECHNICAL OBJECTIVES INCLUDE MEASUREMENT RESOLUTION ENHANCEMENTS TO 0.5 MICROSTRAIN, IMPROVED STRAIN RATE CAPABILTIY OF 50 INCHES/INCH/SECOND, AND INCREASED STANDOFF DISTANCE OF 16 INCHES FOR BIAXIAL MEASUREMENTS. STRAIN MEASUREMENTS CAN ALSO BE MADE ON MATERIALS ENCLOSED IN ENVIRONMENTAL OR THERMAL CHAMBERS AND SUBJECTED TO EXTREME TEMPERATURES, PRESSURES, OR OTHER ENVIRONMENTAL CONDITIONS.