Papers by Author: Cheng Wen Tan

Abstract: Magnesium alloys can be utilized as potential aerospace materials due to their low density, high specific strength, good vibration and shock absorption ability. This paper deals with the mechanical behavior of hot-rolled AZ31 alloy that was shock-deformed to 2.3 and 3.3 GPa. The post shock microstructure and mechanical response have been determined via full one-dimensional recovery techniques. The microstructure of deformed sample was characterized by the transmission electron microscopy (TEM) and electron back scattered diffraction (EBSD) techniques. All the shock-deformed materials showed shock-strengthening effect that was greater at higher shock pressure. The reload yield stress of the shock-deformed 2.3 GPa sample was determined to be 238 MPa while 264 MPa for the sample which shock-deformed at 3.3 GPa. It was postulated that the shock-strengthening is ascribed to a greater dislocation density and the formation of deformation twins.

Abstract: In order to research the formation and spread of adiabatic shear bands in Ti-6Al-4V targets, LS-DYNA code is used to simulate the ballistic impact process. The projectile used in the impact test is a flat-headed steel cylinder with diameter of 7.62mm and length of 39mm. The results of simulated and impact test are in good agreement. Multiple adiabatic shear bands form in Ti-6Al-4V targets under high-speed ballistic impact. Adiabatic shear bands were found to extend parallel with a certain distance. The formation and distribution of adiabatic shear bands was related to the breaking-off of projectiles, which was caused by the distribution of maximum shear stress in Ti-6Al-4V targets and projectiles.

Abstract: Supersaturated Mg-Gd-Y alloy followed by aging at 225 °C with different times were subjected to quais-static and dynamic strain rates to determine the influence of precipitate phase β′ on the strain rate sensitivity of magnesium alloy. Strain rate sensitivity (SRS) decreases with the increase of the size of β′. SRS decreases from initial condition to peak-aged condition due to the β′ increases the athermal component of flow stress. On the other hand, the influence of precipitate interfaces on dislocation generation and storage mechanisms may be responsible for the decrease of SRS from peak-aged to over-aged condition.

Abstract: Effects of anisotropy on the microstructural characteristics and mechanical behavior of shock loaded of AZ31 magnesium alloy have been investigated. Using electron backscatter diffraction, tension twinning was observed in both shock loading directions along the normal (ND) and rolling directions (RD). Compression tests were carried out along ND and RD in both as-received and post-shock conditions. It indicated that the RD samples show a more notable hardening behavior compared to the as-received conditions. Moreover, it is postulated here that detwinning results in a drop of strain-hardening rate for the ND samples under post shock reload conditions and tension twinning formed during the shock wave loading process leads to a significant moving left of the peak strain hardening rate for the RD samples under post shock reload conditions.