Yonosuke Murayama1, Kazuo Obara1 and Eihachiro Tanaka1
1The Research Institute for Iron, Steel and Other Metals, Tohoku University, Sendai
Uniaxial tensile tests and hydraulic bulge tests were carried out for two differently textured sheets of pure titanium. The sheets were previously examined for the orientation distribution of grains, containing the orientation relation between neighboring grains. The deformation behaviour of the titanium sheets were examined in connection with the effect of the orientation difference between neighboring grains on the deformation mechanism of grains.
In the case of the uniaxial tensile test, the correlation in the 0.2% proof stress among the differently textured sheets and the different test directions can be explained by the preffered orientation of the sheets. However, the stress-strain curves are influenced by the orientation difference between neighboring grains. In the sheets rolled unidirectionally at 1173 K, the orientation difference of the c-axis between neighboring grains is distributed uniformly in the whole range from 0 to π/2. The anisotropy of the flow stress is smaller than that of the 0.2% proof stress, and the slope of the stress to the strain is larger than that of the sheets cross rolled at 873 K.
Stress-strain curves and effective stress-effective strain curves of the two differently textured titanium sheets, which were estimated from the hydraulic bulge test using the Hill's theory for the anisotropy, were examined. In the case of the sheets cross rolled at 873 K, since the preferred orientation is (0001)[10\bar10] and the orientation difference of the c-axis between neighboring grains is small, the deformation mechanism of grains is extremely different between the uniaxial tensile test and the biaxial tensile test. Therefore, as pointed out previously, the over estimation of the anisotropy by the r value takes place. In the case of the sheets rolled unidirectionally at 1173 K, though the r values are high (from 2 to 5), the difference in the deformation mechanism of grains between different loading conditions is small because of the plastic constraint among neighboring grains. As a result, the estimation of the anisotropy by the r value is not so irrelevant.
biaxial tensile test, anisotropy of sheet, texture, titanium, relation of the orientation between neighboring grains
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