Observations of Tension/Compression Asymmetry in the Cyclic Deformation of Aluminum Alloy 7075

Abstract

The cyclic deformation of AA7075 in the T6 and T651 tempers has been investigated at room temperature under plastic strain control at amplitudes from 0.1% to 1.0%. Although both tempers represented peak aged conditions, their cyclic deformation behavior differed. The T6 material exhibited a slight amount of cyclic hardening to saturation, with softening evident only at the highest amplitudes. At low amplitudes, the peak compression stresses were higher than the tension peaks throughout the test. The extent of this asymmetry in peak stresses diminished at higher amplitudes. In contrast, the peak compression stresses for the T651 temper were initially lower than the tension peaks. The tension peaks remained relatively stable throughout each test, but the compression peaks exhibited hardening such that they became greater in magnitude than the tension peaks. A nonlinear elastic strain contribution is shown to account for asymmetries in hysteresis loop shape, but not the asymmetric peak stresses. We hypothesize that the tension/compression asymmetry results from strain localization caused by the inhomogeneous microstructure created during quenching and aging. In addition, stretching prior to aging gives rise to the unusual behavior of the T651 material. A = asymmetry factor E, = linear elastic modulus ED = differential elastic modulus k = nonlinear elastic strain constant N,,,, = number of cycles to crossover of tension and compression peak stresses 2Nf = number of reversals to failure ce, = elastic strain E~ = plastic strain AeJ2 = plastic strain amplitude u, = compression peak stress ut = tension peak stress

Strain-hardening behavior and microstructure development in polycrystalline as-cast Mg-Zn-Y alloys with LPSO phase subjected to cyclic loading

“…2 in the tensile peak stress. While asymmetric cyclic hardening has been reported for a number of materials including aluminum alloys [31,32] and magnesium alloys [33], the asymmetry in the present results is particularly significant. Secondly, cyclic softening at tensile peak was not found in wrought alloys.…”

Dynamic strain ageing and dynamic precipitation in AA7030 during cyclic deformation

“…This leads to the observation that the stress amplitude at half-life is essentially temperature independent. Most commercial 7000 aluminium alloys in the peak-aged (T6) condition exhibit initial cyclic hardening, followed by saturation [24][25][26][27][28][29]. In the present investigation, on the other hand, softening commences after about 20-30% of the fatigue life, progressively decreasing the stress amplitude until failure.…”

“…where t and c are the true peak stresses, corrected for the Poisson effects, in tension and compression in a cycle and m is the mean stress [25,32]. Consequently, a positive value of A in a given cycle indicates that the peak stress is higher in compression in that cycle, and vice versa.…”

Strain ratcheting and stress relaxation around interference‐fitted single‐holed plates under cyclic loading: experimental and numerical investigations

“…Ohno-Wang Model parameters determined from uniaxial hysteresis curve and uniaxial ratcheting experiment 35 are presented in Table 2. Ohno-Wang Model parameters determined from uniaxial hysteresis curve and uniaxial ratcheting experiment 35 are presented in Table 2.…”

“…where C i , γ i and m i are the model parameters and M (here M = 4) is the number of segments required for multilinear representation of the uniaxial stress-strain curve. Ohno-Wang Model parameters determined from uniaxial hysteresis curve and uniaxial ratcheting experiment 35 are presented in Table 2.…”