Effect of Loading Rate on Dynamic Fracture Toughnes of Structural Steel

Experiments of Circumferentially Notched Round Bar Specimen

Abstract

One of problems relating to the dynamic fracture toughness of heary section, structural steel plates is the effects of looding rate on it. The authors have studied experimentally on the dynamic fracture phenomena in high speed tensile test using notched round bar specimens. The results obtained were as follows.
1) The stress ratio of σN_et/σy has transition phenomerna against test temperature. This transition temperature shifts to higher side for higher notch acuity and for faster tensile rate.
2) An increase of σN_et/σY value for increasing tensile rate was smaller for fatigue cracked (FC) specimen than for machine notched (MN) specimen. While an increase of transition temperature was smaller for MN specimen than for FC specimen.
3) The critical dynamic COD value δ^d_c defined at fibrous crack initiation for both FC and MN specimens was observed to remain approximately constant up to tensile rate of 20 m/sec and δ^d_c increased ahrupthy for larger tensile rate than 30 m/sec.
4) There are following relationships between transition temperatures for dynamic and static test for FC specimen.
T^d_S-T_S(0.2)≅20 T^d_S=-40°C
T^d_J-T_J(10)≅30 T^d_J=-50°C
The authors can also estimate the transition temperature of FC specimen from the data of MN specimen.