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Tensile specimen and engineering stress–strain curve showing Young’s modulus, 0.2% proof strength, tensile strength, uniform elongation, total elongation at maximum force and reduction of area.

What Is Micro Tensile Testing?

Tensile testing is one of the most established and widely used methods for characterizing materials. The reason is simple: with a comparatively straightforward test, a large amount of information can be obtained about how strong a material is and how much it can deform before it fails. Typical…

Site-specific micro tensile specimen preparation showing a component, selected region of interest, specimen-axis alignment relative to the grinding wheel and the resulting micro tensile specimen.

How Are Round Micro Tensile Specimens Manufactured?

Manufacturing a reliable round micro tensile specimen is not simply a matter of scaling down a conventional tensile bar. When only a very small material volume is available, or when a precisely defined local region must be tested, specimen preparation becomes part of the measurement strategy…

Why Round Specimens Matter in Micro Tensile Testing

Why Round Specimens Matter in Micro Tensile Testing

Engineering stress is calculated from the applied force and the initial cross-sectional area A0 of the specimen. The cross-sectional geometry must therefore be characterized adequately to determine A0. At the microscale, this makes the difference between an idealized geometry and the real specimen…

Schematic comparison of round specimen cross sections with diameters from 1000 to 100 µm, illustrating the increasing relative proportion of a preparation-affected near-surface region as specimen diameter decreases.

Influence of Specimen Fabrication on Micro Tensile Test Results

The fabrication of a tensile specimen should ideally change its geometry without significantly changing the material that will subsequently be tested. At conventional specimen dimensions, a thin preparation-affected surface layer may represent only a small fraction of the tested material volume….

Relative contribution of diameter measurement error to calculated engineering stress versus specimen diameter for constant absolute diameter errors of 2, 5 and 10 µm.

Diameter Measurement and Stress Calculation in Micro Tensile Testing

Tensile stress is calculated from two measured quantities: the applied tensile force and the load-bearing cross-sectional area of the specimen. For a round micro tensile specimen, the cross-sectional area is determined from its diameter. This makes diameter measurement a direct part of the stress…

Stress–strain curves of an HPT-deformed nickel specimen comparing strain evaluation from cross-head movement, pulling-shoulder displacement and gauge-length displacement.

Strain and Displacement Measurement in Micro Tensile Testing

Measuring tensile force on a small specimen and measuring its deformation are two different tasks. Force can be measured directly by the load cell. Strain, however, is derived from a change in length of a defined part of the specimen. In conventional tensile testing, deformation can often be…

(Reprinted, with permission, from the Journal of Testing and Evaluation, Vol. 41, Issue 4, copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428.)

Reduction of Area in Micro Tensile Testing

During a tensile test, not only the length of the specimen changes. Its cross-sectional area changes as well. This change becomes particularly important once necking begins and the reduction in cross section becomes increasingly localized. The changing cross section is therefore an important…