アルミニウム合金基短繊維強化複合材料の中高温域におけるき裂進展挙動について

Abstract

In order to clarify the fatigue crack growth mechanism of an alumina short fiber reinforced aluminum alloy (FRM), fatigue crack growth tests were carried out at several stress ratios on the center cracked tension (CCT) specimens at room and elevated temperatures. Aluminum alloy, A6061-T6 was also used as a reference material. Comparison of fatigue crack growth rate curves determined for A6061-T6 and FRM specimens indicated that the effect of temperature on the crack growth rate curves was much smaller for FRM than that for A6061, and the crack growth property of FRM was superior to A6061 in the region of low crack growth rate including the threshold, when the comparison was made on Kmax and ΔK. By estimating the values of ΔKeff, it was shown that the fatigue crack growth rates of A6061 and FRM at each temperature were governed by ΔKeff and KmaxαΔKeff(1-α), respectively. Moreover, the detailed evaluation indicated that the fatigue crack growth rates of A6061 and FRM at different stress ratios and temperatures could be expressed by introducing new parameters, excepting in the threshold region, as follows:da/dN=C1{UR(1-R)/UR=0.1Kmax(Eσ0.2)-1/2}m1 for A6061da/dN=C2{{UR(1-R)/UR=0.1}(1-α)Kmax(Eσ0.2)-1/2}m2 for FRMwhere R is the stress ratio, UR is the crack opening ratio at stress ratio R, UR=0.1 is the value of U at R=0.1, E and σ0.2 are Young's modulus and 0.2% proof stress at each temperature, and C1, C2, m1 and m2 are material constants.