Effects of Material Anisotropy on Cyclic Deformation and Biaxial Fatigue Behavior of Al-6061-T6

Abstract

Anisotropic cyclic stress-strain curves (CSSCs) and fatigue lives were obtained from fully reversed fatigue tests in strain control on two orientations of an Al-6061-T6 plate (along the rolling direction and the transverse direction). The experiments were conducted at room temperature in air under three loading conditions: tension/compression, torsion, and combined tension/torsion in-phase. Based on the CSSCs data, the anisotropic constitutive relations of the material were obtained by using Hill's anisotropic plasticity theory. Yield loci and flow behavior were determined and compared to theoretical predictions. Two anisotropic effective stress-effective strain criteria were evaluated. During the fatigue tests, fatigue cracking behavior was observed. The damage mechanism of the material was shear dominated. Four multiaxial fatigue life prediction models representing three different concepts were used to correlate the anisotropic fatigue life data of the plate under the biaxial loadings. A new shear cracking model incorporated with material anisotropy coefficients is proposed and correlated with the fatigue life data very well.

Modification of fatigue strain‐life equation for sheet metals considering anisotropy due to crystallographic texture

“…">Isotropic hardening is sufficient to characterize the initial plastic anisotropy in cyclic properties. At strain range higher than 0.002, ignoring kinematic hardening does not affect the accuracy 16 of prediction. The plastic strain ratio values ‘ R ’ estimated from monotonic tests is applicable for cyclic loads also.…”

“…Isotropic hardening is sufficient to characterize the initial plastic anisotropy in cyclic properties. At strain range higher than 0.002, ignoring kinematic hardening does not affect the accuracy 16 of prediction.…”

“…Most of the work discussed above and other similar work concentrated primarily on the experimental investigation of anisotropy effect 13–15 . Attempts to model anisotropic fatigue behaviour using constitutive plasticity equations are scarce, though not unavailable 16 . Lin and Nayeb‐Hashemi 16 modelled the cyclic stress‐strain behaviour of orthotropic Al‐6061‐T6 alloys using Hill's anisotropic yield criterion, which was subsequently extended to predict the strain‐life relation 17 .…”

“…This results in experimental determination of constants from fatigue tests for every direction of interest. Subsequent to the initial work of Lin and Nayeb‐Hashemi 16, efforts on modelling anisotropic fatigue are scarce. To overcome the above drawback of dependence on experimental constants, it is desirable to account the anisotropic effect using phenemenological constitutive relations of plasticity.…”

Pressure vessels design methods using the codes, fracture mechanics and multiaxial fatigue

“…The first approach is the stress or strain invariant approach leaded by many authors [2][3][4][5][6][7][8]. The second one is the critical plan approach leaded by Brown and Miller [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. The third one is the integral approach leaded by [29][30][31][32].…”