様々な金属材料を用いた断続引張試験とBridgman の式による破断直前までの真の応力ーひずみ関係の推算

摘要

True stress (σ)-true strain (ε) relationships until just before fracture, i.e., the plastic deformation limit, were estimated by the stepwise tensile test and the Bridgman equation for various metals and alloys with different crystal structures. The estimated σ-ε relationships were different from the nominal stress-strain curves including the conventional tensile properties. In the relationships between the true stress (σ_(pdl)) and true strain (ε_(pdl)) at the plastic deformation limit, SUS304 and SUS329J4L indicated a better σ_(pdl)-ε_(pdl) balance. On the other hand, SUS329J4L, tempered martensite, and an ultrafine-grained steel showed superior results in the yield strength-ε_(pdl) balance. The estimated σ-ε relationship for the ultrafine-grained steel suggests that grain refinement strengthening can improve σ and ε up until the plastic deformation limit. The value of ε_(pdl) became larger with increasing the reduction in area and a decrease in the fracture stress. The products of σ_(pdl) and ε_(pdl) became larger with increasing work-hardening rate at the plastic deformation limit.%応力ーひずみ関係は金属材料の塑性変形挙動を議論する際に重要な役割を果たし，この関係を得るための引張試験ほ代表的な機械的試験として広く用いられている．また，超微細粒材料の楔械的特性も応力ーひずみ曲線を用いて検討が行われている．引張試験結果としては荷重と伸びより得られる公称応力ーひずみ曲線が示されることが一般的だが，局所伸びや全伸びは試験片形状により大きく変化する．