• Korean Journal of Metals and Materials
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• v.46 no.4
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• pp.189-198
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• 2008

The changes in microstructure and mechanical properties of AZ31 alloy subjected hot-rolling process were investigated. The AZ31 plates fabricated by horizontal continuous casting process were prepared and have hot-rolled from 30 mm to 1 mm in thickness under different processing conditions. At the rolling temperature of $400^{\circ}C$, little surface and side crack was observed up to 20% reduction rate. As total reduction and reduction rate increase to more than 75% and 20% pass, respectively, Grains were more uniformly refined through overall thickness, and particularly lots of shear bands were appeared to be inclined at less than $20^{\circ}C$ along the rolling direction. Average grain size of less than $5{\mu}m$ and tensile properties of YS ${\geq}$ 250 MPa, UTS ${\geq}$ 300 MPa and El. ${\geq}$ 13% were acquired for hot-rolled AZ31 sheets without post-heat treatment. Maximum intensity of (0002) pole figure was decreased with an increase in reduction rate, indicating the improvement of texture by means of high reduction rate.

• Journal of the Korean Society for Heat Treatment
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• v.36 no.5
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• pp.303-310
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• 2023

β titanium alloys are widely used in aerospace industry due to their excellent specific strength and corrosion resistance. In particular, mechanical properties of metastable β titanium can efficiently be controlled by various deformation mechanisms such as slip, twinning, and SIM (Stress-Induced Martensite Transformation), making it an ideal material for many industrial applications. In this study, Ti-5Mo-xFe (x=1, 2, 4 wt%) alloy was designed by adding a relatively inexpensive β element to ensure price competitiveness. Additionally, microstructural analysis was conducted using OM, SEM, and XRD, while mechanical properties were evaluated through hardness and compression tests to consider the deformation mechanisms based on the Fe content. SIMT occurred in all three alloys and was influenced by the presence of β_m (metastable beta) and beta stability. As the Fe content decreased, the α'' phase increased due to SIMT occurring within the β_m phase, resulting in softening. Conversely, as the Fe content increased, the strength of the alloy increased due to a reduction in α'' formation and the contributions of solid solution strengthening and grain strengthening. Moreover, unlike the other alloys, shear bands were observed only in the fracture of the Ti-5Mo-4Fe alloy, which was attributed to differences in texture and microstructure.

• Computers and Concrete
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• v.31 no.3
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• pp.207-221
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• 2023

In this investigation, the interaction between opening space and neighboring joint has been examined by experimental test and Particle flow code in two dimension (PFC2D) simulation. Since, firs of all PFC was calibrated using Brazilian experimental test and uniaxial compression test. Secondly, diverse configurations of opening and neighboring joint were provided and tested by uniaxial test. 12 rectangular sample with dimension of 10 cm*10 cm was prepared from gypsum mixture. One quarter of tunnel and one and or two joint were drilled into the sample. Tunnel diameter was 5.5 cm. The angularities of joint in physical test were 0°, 45° and 90°. The angularities of joint in numerical simulation were 0°, 30°, 60°, -30°, -45°, -60° and its length were 2cm and 4cm. Loading rate was 0.016 m/s. Tensile strength of material was 4.5 MPa. Results shows that dominant type of crack which took place in the model was tensile cracks and or several shear bands develop within the model. The Final stress is minimum in the cases where oriented angle is negative. The failure stress decrease by decreasing the joint angle from 30° to 60°. In addition, the failure stress decrease by incrementing the joint angle from -30° to -60°. The failure stress was incremented by decreasing the number of notches. The failure stress was incremented by decreasing the joint length. The failure stress was incremented by decreasing the number of notches. Comparing experimental results and numerical one, showed that the failure stress is approximately identical in both conditions.

• Geophysics and Geophysical Exploration
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• v.8 no.1
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• pp.26-33
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• 2005

Inversion of multi-mode surface-wave phase velocity for shallow engineering site investigation has received much attention in recent years. A sensitivity analysis and inversion of both synthetic and field data demonstrates the greater effectiveness of this method over employing the fundamental mode alone. Perturbation of thickness and shear-wave velocity parameters in multi-modal Rayleigh wave phase velocities revealed that the sensitivities of higher modes: (a) concentrate in different frequency bands, and (b) are greater than the fundamental mode for deeper parameters. These observations suggest that multi-mode phase velocity inversion can provide better parameter discrimination and imaging of deep structure, especially with a velocity reversal, than can inversion of fundamental mode data alone. An inversion of the theoretical phase velocities in a model with a low velocity layer at 20 m depth can only image the soft layer when the first higher mode is incorporated. This is especially important when the lowest measurable frequency is only 6 Hz. Field tests were conducted at sites surveyed by borehole and PS logging. At the first site, an array microtremor survey, often used for deep geological surveying in Japan, was used to survey the soil down to 35 m depth. At the second site, linear multichannel spreads with a sledgehammer source were recorded, for an investigation down to 12 m depth. The f-k power spectrum method was applied for dispersion analysis, and velocities up to the second higher mode were observed in each test. The multi-mode inversion results agree well with PS logs, but models estimated from the fundamental mode alone show f large underestimation of the depth to shallow soft layers below artificial fill.