a b s t r a c tIn this study, the work-hardening and twinning behaviors in a commercially pure titanium sheet were examined under various loading paths including reverse loading. The yield stress was identical between tension and compression, while the work-hardening was slightly larger during compression than during tension. These tendencies were the same in both the rolling and transverse directions. When the sheet was subjected to reverse loading, the Bauschinger effect was observed during both tension-compression and compression-tension. The tendency in the Bauschinger effect was nearly independent of the strain path tested in the present study. Concerning the twinning, the activities of f1012g tensile twinning, f1122g compressive twinning, and f1121g tensile twinning were observed during tension. Alternatively, during compression, the activity of f1012g tensile twinning was observed and was much larger than that during tension. When the sheet was subjected to tension following compression, detwinning occurred. Although the trend in the activity of twinning was similar to that of a magnesium alloy sheet, the behavior observed in the stress-strain curves was quite different from that of a magnesium alloy sheet. Based on the results presented, the effect of twinning and detwinning activities on the work-hardening behavior was discussed.

Highlights  Deformation behavior in a CP-Ti sheet was studied using crystal-plasticity FEM.  The material parameters were determined based on the role of each deformation mode.  The deformation under various strain paths was predicted well using the simulation.  The deformation mechanism was examined numerically from a mesoscopic viewpoint.

In this study, the anisotropic deformation behavior in commercially pure titanium Grade 1 and Grade 2 sheets under various strain paths was examined. A small but sharp stress peak arose during tension following compression in the Grade 1 sheet when loaded in the rolling direction, and the occurrence of a stress peak was retarded when the sheet was subjected to cyclic loading; however, such behavior did not occur in the Grade 2 sheet. Similarly, the work-hardening rate was different between the initial and latter stages of compression following tension. These behaviors did not arise when the sheets were loaded in other directions. The type of active twin mode was different depending on the loading path. When loaded in the rolling direction in both Grade 1 and Grade 2 sheets, <101 � 2> twinning and detwinning were active, respectively, during compression and tension following compression, whereas <112 � 2> twinning and detwinning were active during tension and compression following tension. The twinning activity was much more pronounced in the Grade 1 sheet than in the Grade 2 sheet. The abovementioned stress-strain responses were presumed to result from twinning and detwinning activities as for magnesium alloy sheets.However, we concluded that the effect of twinning activity on the stress-strain curves was much smaller in the titanium sheet than in magnesium alloy sheets.

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In the present study, work-hardening behavior under various loading paths of a commercially pure titanium JIS Grade 1 sheet was investigated. The following tension-compression asymmetry was presented. The yield stress was smaller under compression than under tension, whereas the subsequent work-hardening was larger under compression than under tension. When the sheet was subjected to reverse loading from compression to tension, strong Bauschinger effect was exhibited. Thereafter, a concave curve followed by a small stress peak appeared, which was not presented under monotonic tension. Microstructure observations suggested that this characteristic behavior would be owing to the the activities of twinning and detwinning respectively during compression and following tension.