クリープき裂の伝ぱ : き裂伝ぱ速度に関する実験結果

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The experiments on crack propagation in tensile creep were conducted using the center notched thin plate specimens of an 18Cr-8Ni stainless steel (SUS304) at the test temperature of 650℃. The material was highly ductile and the wedge-shaped crack was propagated in the contracted section in nearly plane stress state. The crack propagation rate was given as a function of the crack length, the net section stress or the elastic stress intensity factor. It was found that the crack propagation rate changed approximately linearly against the net section stress for the true net section area, area,σ_<net>', or against the elastic stress intensity factor, K_I, in the log-log diagram, and the non-dimensional relationship: (dl*)/(dt)/(Bσ_g^α)/(ε*_f)=A_n'((σ_<net>')/(σ_g))^α or ((K_I*)/(σ_g))^α was obtained, where l*=2l/W_0, l is the half crack length, W_0 is the initial specimen width, Bσ_g^α is the creep rate under the gross section stress, σ_g, ε*_f is the fracture strain and is about constant for the same fracture mode, α is the stress exponent of creep in smooth specimens and is nearly equal to α_<loc> or the exponent of stress in the stress-rupture life relation, K_I*=(K_I)/(√<πW_0/2=σ_g>)√<l*sec(πl*/2)>, and A_n' and A_K are material constants. The experimental results substantiated the validity of the result of the finite element analysis based on the finite deformation theory reported in the previous paper. The result of the finite element analysis suggested that the crack propagation rate would be proportional to the α_<loc>'th power of the net section stress,σ_<net>=σ_g/(1-l*), in the material with low ductility or in the state of plane strain. Double edge cracks in the plate specimens and circumferential cracks in the bar specimens of a 1Cr-1Mo-1/4V steel at 600℃ exhibited the grain boundary fracture with little reduction of area, and their propagation rates were expressed by the following non-dimensional relation. (dl*)/(dt)/bσ_g^<α_<loc>>=A_n((σ_<net>)/(σ_g))^<α_<loc>> or ((K_I*)/(σ_g))^<α_<loc>>' where bσ_g^<α_<loc>> is the mean rate of fracture under σ_g, being equal to 1/t_r; t_r is the time to rupture the smooth specimens, and the value of α_<loc>' is a little smaller thanα_<loc>. The results on two kinds of materials tested indicated the possibility of application of the net section stress or the elastic stress intensity factor for the mode I crack propagation in creep.
社団法人日本材料学会の論文
1976-08-15

クリープき裂の伝ぱ : き裂伝ぱ速度に関する実験結果

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