Microspecimen Tensile Tests of A533-B Steel

Miniature tensile specimens of A533-B steel were tested as part of the ASTM Cross-Comparison Exercise on Determination of Material Properties Through the Use of Miniature Mechanical Testing Techniques. The microspecimens are 3 mm long with a test section ∼0.3 mm square. Thin slices were cut from the supplied block of material by wire EDM and the microspecimens were machined from the slices with a benchtop CNC mill. Specimens were cut so that the tensile axes were in three orthogonal directions to investigate the anisotropy of the steel block.

A total of 47 microspecimens were pulled in a small test machine with an air bearing to reduce friction in the moving grip. Strain was measured directly on the specimen with a laser-based interferometric technique that used two tiny reflective indentations as gage markers. The entire stress-strain curve was recorded. In addition, five macrospecimens with cross-sections 3.2 mm square were tested in a conventional test machine using foil strain gages.

The coefficient of variation (ratio of standard deviation to mean value) of the microspecimen tests is on the order of 5% for both the yield and ultimate stresses. This sample block of A533-B steel is slightly anisotropic with regard to yield stress, but not ultimate stress. The yield stress — on the order of 440 MPa — and the ultimate stress — on the order of 600 MPa — are consistent with other results. The microspecimens showed yield and ultimate stresses approximately 5% lower than those measured on the macrospecimens.