TiC/AZ91D composites fabricated by in situ reactive infiltration process and its tensile deformation

An innovative processing route was adopted to fabricate 42.1%(volume fraction) TiC/AZ91D magnesium matrix composites. The reinforcement TiC was in situ synthesized from elemental powders of Ti and C and the matrix magnesium alloy AZ91D pressurelessly infiltrated into the preform of Ti and C. A comparative tensile deformation tests were conducted on the as-synthesized TiC/AZ91D composites and magnesium alloy AZ91D. The true strain—stress curves were fitted by Hollomon relation and their failure mechanisms were finally analyzed. The results show that the in situ formed TiC can increase the tensile strength, and is especially effective at elevated temperatures. Theoretical calculation of the strain hardening exponent (n) for TiC/AZ91D composites indicates that the n value ranges from 0.71 to 0.82 when tensile deformation was carried out at 423?723 K and shows fracture with brittle characteristic. However, the n value of 0.11?0.32 obtained for the matrix alloy AZ91D shows typical ductile features at elevated temperatures.

The Genetic Mechanism of Wenchuan Earthquake

The genetic mechanism of the 5.12 Wenchuan Earthquake is still being debated and there is still no convincing general explanation for most of the phenomena. This is because researchers have ignored the important role of the Minshan block in the seismogenic process. The authors present a new opinion based on geological survey and comprehensive analyses. The Minshan block is a key tectonic element of the earthquake occurrence in the northwest triangle faulty block of Sichuan Province. The Minshan block is bordered by Longmen Mountain Range fractures in the south, the Huya fracture in the east, the Tazang fracture in the north and the Mounigou Valley fracture in the west. The rigidity of the block is relatively larger than those of the adjacent regions. The block's eastward movement pushed by regional maximum main geo-stress is limited when it suddenly tapers off near the east triangle end with a bottle-neck effect, and this causes geo-stress concentration around it. The shape of the block is coffin-like, wide in the upper part and narrow in the lower part. When a strong earthquake occurs along the block margins, the lock-up effect temporarily released, resulting in geo-stress transmitted to the Pingwu-Qingchuan (Motianling block) region. This transmission caused the Wenchuan earthquake's aftershocks to be concentrated in Qingchuan region. As the block moved eastward, the back of the block, i.e. the south segment of Mounigou Valley fracture, became active after the Wenchuan Earthquake. Therefore the aftershocks were concentrated along the south segment of Mounigou Valley fracture. Because the south margin is composed of the front range fracture, the geo-stress gradually released, causing many aftershocks along the Guanxian-Anxian fracture. The geological survey made after the Wenchuan Earthquake reveals that the surface ruptures in the south margin of Minshan block occur not along the Beichuan-Yingxiu fracture (central fracture) also along the front range fracture. The length of the surface rupture in the south margin ranges from several meters to several kilometers and it is distributed in en echelon (closely-spaced, parallel or subparallel, step-like surface ruptures). The vertical and horizontal displacements range from place to place and the thrusting component is dominant in the middle segment of Longmen Mountain Range structure belt. Nevertheless, the strike slip of the surface ruptures is dominant in the north segment of Longmen Mountain Range structure belt. Therefore the south margin is the original seismic structure. The sudden thrusting of the south margin of the Minshan block is the source event for the Wenchuan Earthquake.

Mechanism on simulation and experiment of pre-crack seam formation in stope roof

The pre-crack blast technology has been used to control the induction caving area in the roof. The key is to form the pre-crack seam and predict the effect of the seam. The H-J-C blast model was built in the roof. Based on the theories of dynamic strength and failure criterion of dynamic rock, the rock dynamic damage and the evolution of pre-crack seam were simulated by the tensile damage and shear failure of the model. According to the actual situation of No. 92 ore body test stope at Tongkeng Mine, the formation process of the pre-crack blast seam was simulated by Ansys/Ls-dyna software, the pre-crack seam was inspected by a system of digital panoramic borehole camera. The pre-crack seam was inspected by the system of digital panoramic borehole in the roof. The results of the numerical simulation and inspection show that in the line of centers of pre-hole, the minimum of the tensile stress reaches 20 MPa, which is much larger than 13.7 MPa of the dynamic tensile strength of rock. The minimum particle vibration velocity reaches 50 cm/s, which is greater than 30-40 cm/s of the allowable vibration velocity. It is demonstrated that the rock is destroyed near the center line and the pre-crack is successfully formed by the large diameters and large distances pre-crack holes in the roof.

Application of computer-assisted surgery techniques in the management of zygomatic complex fractures

Patients suffering from zygomatic complex fractures always present facial deformity and dyslunctions, and thereafter develop psychological and physiological problems. It is really hard to get an ideal prog- nosis for the zygomatic complex fractures because of the complicated anatomical structures. Computer- assisted surgery techniques, as the new emerging auxiliary methods, can optimize the surgical protocol, predict operation outcomes, and improve the accuracy and quality of the operation. Meanwhile the postoperative complications can be reduced effectively. This review aims to provide a comprehensive overview of the application of computer-assisted surgery techniques in the management of zygomatic complex fractures.