表面切り欠きを有する丸棒の脆性破壊強度評価

抄録

The brittle fracture strength of surface notched round bar (SNRB) has been investigated theoretically and experimentally. Firstly, the stress intensity factors for SNRB subjected to axial load and bending, K_A and K_B, respectively, have been analyzed with the aid of the finite element method. Secondly, the brittle fracture test under axial load has been conducted on SMn443 and SCM440 specified in, JIS. The curve showing the relationship between net section stress at fracture, σ_{n, F}, and testing temperature. T, covers two regions macroscopically. One is called Region I where σ_{n, F}, diminishes with decreasing T, and the other is Region II, where σ_{n, F}, is nearly constant irrespectively of T. The effect of diameter, D, and notch depth, α, on σ_{n, F} in Region I can be evaluated on the basis of linear elastic fracture mechanics technology. σ_{n, F} in Region II shows little change with D, and diminishes with an increase in relative notch depth, α/D. σ_{n, F} in Region II can be approximately estimated on the basis of semi-experimental equation derived from general yielding stress level of SNRB. Lastly, the fracture test under combined load of tension and bending has been conducted on PMMA. The fracture stress under combined load can be estimated from the following criterion, K_A+K_B=K_C where K_C. is fracture toughness.