Mini-samples technique in tensile and fracture toughness tests of nano-structured materials

Abstract

Samples dimensions defined in standards for tensile and fracture toughness tests may be too large in the case of modern materials produced in small volumes, e.g. nano-structured metals. Also, dimensions of irradiation tests samples are frequently not appropriate for standardized samples. In such situations so called mini-samples need to be used. The paper presents methodology and the results of tensile and fracture toughness tests which were carried out on mini-samples with a few millimeter dimensions. These samples were made of nano-structured metals processed by hydro extrusion (HE) and equal channel angular pressing (ECAP). Due to small size of specimens optical method of strain measurement - digital image correlation (DIC) - was applied. DIC twopoint- tracing mode was used as an optical extensometer in the tensile tests. The inverse method was applied for precise determining stress intensity factors and crack tip positions from displacement fields acquired by DIC. Comparison of the results of the tensile and fracture toughness tests which were carried out on standardized and mini-samples made of the same materials is also presented and the results are discussed in terms of the applicability of mini-samples technique in the studies of nano-metals.