抄録
In order to study the behavior of lattice defects during low-cycle fatigue tests with strain-amplitude change, electrical resistivity was measured on wire (0.55mm in dia.) of polycrystalline aluminium (99.999%) which had been torsionally fatigued at 77K. Two different total surface-strain amplitudes, 1.8 and 4.4%, were used.
The dislocation density in metal during cyclic straining after changing the strain amplitude was given by
ρ1/2=ρs1/2[1-[1-ρi1/2β/α]e]-(β/2)γ
ρs=(α/β)2
where α is a constant, β is a constant depending on strain-amplitude, γ is the cumulative plastic strain, and ρi is the dislocation density prior to the strain-amplitude change. In this study, the constant β was estimated from the peak torque versus cumulative plastic strain curve for fatigued metal.
The concentration of point defects in metal during cyclic straining at 77K was represented as follows:
C=Cs[1-1-P/K2-β/2[K2e-(β/2)γ-β/2-K2P/1-Pe-K2γ]]+Cie-K2γ
Cs=K1α2/K2β, P=ρi1/2β/α
where K1 and K2 are constants, Cs is the concentration of saturated point defects, and Ci is the concentration of point defects prior to the strain-amplitude change.
The experimental data was analysed on the assumption that the increment in resistivity in fatigued metal is related to the number of dislocations and point defects as
ΔR/ΔRs=mρ/ρs+mC/Cs, m+n=1
where ΔRs is the saturation value in resistivity, ΔR is the increment in resistivity, and m and n are constants.
