ビッカース硬さ試験による高分子材の変形の局所化挙動と強度変化との関係の解明

抄録

The propagation of localized deformations is often observed as a typical deformation behavior of polymeric materials. In such cases, it has been confirmed that the necking portion of a specimen should be hardened, otherwise the deformation progress in this portion leads to the fracture of the specimen. However, actually the necking portion is softened according to the results of hardness tests. The aim of this study is to elucidate the relationship between localized deformations and strength change of Polycarbonate and ABS, that enables us to consider the causes of the contradiction. The authors conducted tensile tests of thin strip specimens and measured the axial and lateral strains by DIC method, then the deformation behavior was evaluated numerically, and the true stress was calculated from the strain values. From this result, increase in true stress during plastic deformation including necking propagation was observed. The Micro-Vickers hardness measurement for a gauge length was also performed to clarify the strength distribution of a specimen, and the results showed that the entire deformed area was softened, and the necking part was further softened. Since there was concern that the specimen might be hardened in the cross-section perpendicular to the tensile axis, the hardness of the cross-section was measured, and it was confirmed that the specimen was softened in the cross-section as well. The authors consider causes of contradictions in specimen strength as deviation from linearity at low stress in stress curve at reloading. Vickers hardness for polymeric materials may reflect this point of deviation.