液体 He 温度での 316L ステンレス鋼のΔK_<th>近傍疲労き裂進展特性

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Near-threshold fatigue crack growth tests on SUS 316L stainless steel were conducted at liquid helium temperature(4 K) and a reference temperaure of 300 K. The crack length and the crack closure point in CT-specimens in a cryostat were automatically calculated by a 16-bit computer system based on the compliance theory. The initial ΔK(ΔK_O) and the normalized ΔK gradient during ΔK-decreasing were varied on reference to the ASTM E647 standard. Constant ΔP tests, or ΔK-increasing tests, were also conducted to find the practical and appropreate ΔK-decreasing rule. It was found possible tu use higher ΔK_O and smaller increment of crack length(Δa) in the 4 K tests. However, the tests at 300 K raised some problems concerning the ASTM standard. Through the ΔK-range tested, two curves of the da/dn vs. ΔK relation at R=0.4 and 0.7 lied almost parallel at both temperatures of 4 and 300 K, but they showed a complex temperature dependence. With a decrease of temperature from 300 to 4K, the ΔK_<th>, corresponding to da/dn=10^<-7> mm/cycle, increased from 3.4 MPa√<m> to 6.5 MPa√<m> at R=0.4, and did from 2.8 MPa√<m> to 5.5 MPa√<m> at R=0.7. By taking the crack closure effect into consideration, the da/dn vs. ΔK_<eff> relation was also discussed. These values of ΔK_<th> and ΔK_<eff,th> for SUS 316L were compared with those of other 300-series ausenitic stainless steels. SEM fractographs and micrographs of cross-sectional view indicated that the fracture surface appearing at 4 K was much smoother than that at 300 K.
社団法人日本材料学会の論文
1989-11-15

液体 He 温度での 316L ステンレス鋼のΔK_<th>近傍疲労き裂進展特性

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