Tensile testing of microsamples

Structural analysis has advanced rapidly to the point where lack of knowledge about the local inhomogeneity and anisotropic nature of the materials prevents the accurate prediction of the behavior; models can incorporate local material properties provided they can be experimentally determined. Conventional tensile techniques are unable to test speciments from submillimeter-sized regions, and micro-hardness measurements do not reveal directional variations. A system has been developed to perform tensile tests on microsamples that are 3.1 mm long with a gage cross section that is 0.2 mm square. The volume of the test region is roughly 500,000 times smaller than a standard half-inch diameter specimen. Tensile stress-strain curves are measured, and the yield strength, ultimate strength, modulus and elongation are calculated for each sample. Samples cut from the weld metal of undermatched welds in HY-100 plate showed a large variation in properties from the center of the weld to the outer edge, as well as anisotropy at some locations. The average mechanical properties of a group of microsamples cut from the outer region of the weldment compared favorably with measurements made using full-sized specimens; the variation in the microsample measurements reflect local variations in the material that are not measured with full-sized specimens.