Studies on the mechanical behaviour of squeeze-cast SiCw / Al composites have been revjewed. The results show that SiCw / Al composites exhibit improved mechan ical properties and cyclic hard ening. The reasons leadin...Studies on the mechanical behaviour of squeeze-cast SiCw / Al composites have been revjewed. The results show that SiCw / Al composites exhibit improved mechan ical properties and cyclic hard ening. The reasons leading to the above results are discussed. Localized deformation near SiC whiskers plays an important role in the initiation of microcracks in the composites, and the fracture of the composites is caused by the abrupt linking of microcracks展开更多
Ceramics constitute an integral part of highly efficient armours due to their low density, high hardness, strength and stiffness. However, they lack toughness and multi-hit capability. Therefore, zirconia toughened al...Ceramics constitute an integral part of highly efficient armours due to their low density, high hardness, strength and stiffness. However, they lack toughness and multi-hit capability. Therefore, zirconia toughened alumina is investigated. The hardness is evaluated using Vickers, Knoop and instrumented indentations, while the fracture toughness is evaluated using the indentation technique and Charpy tests. The strength is evaluated using ring-on-ring, four point bend and drop weight tests. The Young’s modulus is evaluated using the unloading instrumented indentation curves. Microstructure, porosity and density are characterised using ultrasonic scanning, Archimedes principle, optical and scanning electron microscopy. Results show an indentation size effect on all mechanical properties. A substantial improvement in toughness is achieved through retardation of crack initiation by tetragonal-to-monoclinic phase transformation in zirconia particles, crack deviation thanks to appropriate grain structure, as well as energy absorption by densification due to remaining porosity. This improved toughness is expected to promote multi-hit capability.展开更多
次最大强度训练对经过长期训练的高水平耐力运动员的运动成绩和相关生理指标的提高作用甚少。研究发现通过高强度的间歇训练(HIT)可以提高他们的运动成绩。但是,关于高水平耐力运动员 HIT 的相关生理机制并不十分清楚。本文就高水平耐...次最大强度训练对经过长期训练的高水平耐力运动员的运动成绩和相关生理指标的提高作用甚少。研究发现通过高强度的间歇训练(HIT)可以提高他们的运动成绩。但是,关于高水平耐力运动员 HIT 的相关生理机制并不十分清楚。本文就高水平耐力运动员高强度间歇训练的相关生理机制的研究进展加以总结和展望。展开更多
文摘Studies on the mechanical behaviour of squeeze-cast SiCw / Al composites have been revjewed. The results show that SiCw / Al composites exhibit improved mechan ical properties and cyclic hard ening. The reasons leading to the above results are discussed. Localized deformation near SiC whiskers plays an important role in the initiation of microcracks in the composites, and the fracture of the composites is caused by the abrupt linking of microcracks
文摘Ceramics constitute an integral part of highly efficient armours due to their low density, high hardness, strength and stiffness. However, they lack toughness and multi-hit capability. Therefore, zirconia toughened alumina is investigated. The hardness is evaluated using Vickers, Knoop and instrumented indentations, while the fracture toughness is evaluated using the indentation technique and Charpy tests. The strength is evaluated using ring-on-ring, four point bend and drop weight tests. The Young’s modulus is evaluated using the unloading instrumented indentation curves. Microstructure, porosity and density are characterised using ultrasonic scanning, Archimedes principle, optical and scanning electron microscopy. Results show an indentation size effect on all mechanical properties. A substantial improvement in toughness is achieved through retardation of crack initiation by tetragonal-to-monoclinic phase transformation in zirconia particles, crack deviation thanks to appropriate grain structure, as well as energy absorption by densification due to remaining porosity. This improved toughness is expected to promote multi-hit capability.
