数種の金属材料における疲労き裂伝ぱとJ積分およびき裂開口変位との関係

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Fatigue crack growth tests of copper, very low-carbon steel, mild steel, stainless steel and aluminum alloys were conducted by using center-cracked specimens under elastic, elastic-plastic and gross yielding conditions. The growth rate of a fatigue crack was correlated to the ranges of J integral ΔJ and crack opening displacement Δφ_<250>, where ΔJ was evaluated from the loading portion of hysteresis loops of load against crack opening displacement at the crack center and Δφ_<250> was measured at the position 250μm behind the crack tip. The growth rate da/dN was expressed as a unique power function of ΔJ or Δφ_<250&t; for each material. The variance in the da/dN-ΔJ relation with materials was found to be minimum when da/dN was correlated to ΔJ/E (E=Young's modulus). The variance was even reduced if Δφ_<250> was taken as a parameter. The exponent in the da/dN-ΔJ relation tended to decrease from 2.3 to 1.4 as the yield strength of the material increased. In the region of rates between 3×10^<-7> and 5×10^<-5>m/cycle, the fracture surfaces of copper, very low-carbon steel and stainless steel were covered almost entirely by ductile striations, whose spacing s coincided with the macroscopic growth rate da/dN. Since s was not proportional to ΔJ, the simple crack tip blunting model proposed previously was not enough to derive the fatigue crack growth law. Some discussion was made for a further refinement of the mechanics of crack growth by plastic blunting mechanism.
社団法人日本材料学会の論文
1984-04-15

数種の金属材料における疲労き裂伝ぱとJ積分およびき裂開口変位との関係

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