报告题目：Impact Comminution of Concrete and Rock Due to Kinetic Energy of High-Rate Shear
报 告 人：Zdeněk P. Ba？ant教授
报告时间：2015年1月13日（周二）上午9:00～10：30
报告地点：新主楼会议中心第二会议室
主办单位：航空学院、研究生院
报告人简介：
美国西北大学 Zdeněk P. Ba？ant教授是在国际力学和土木工程学科享有崇高声誉的科学家。现为美国国家科学院、美国艺术与科学院和美国工程院院士，意大利、奥地利、西班牙、捷克等国家的科学院院士，欧洲科学院和欧洲科学与艺术院院士，ASCE, ASME, ACI荣誉会员，获7个荣誉博士学位。曾获美国机械工程师学会颁发的铁木钦柯奖，美国土木工程师学会颁发的冯卡门奖、Newmark奖、Biot和Croes奖、终身成就奖等，以及许多欧洲的科学奖项。Ba？ant教授在结构强度的尺度效应、非弹性分析、断裂的尺度效应、高温混凝土、混凝土徐变等方面学术成果丰硕，论文被引用39600+次，H因子96，是国际工程界公认的100个顶尖科学家之一。
讲座内容简介：
Fragmentation, crushing and pulverization of solids, briefly called comminution, has long been a problem of interest for mining, tunneling, explosions, meteorite impact, missile impact and penetration, groundshock and various kinds of industrial processes. While many semi-empirical models for impact analysis abound in the literature, and whereas the fragmentation in the so-called `Mescall' zones of impacted or shocked solids has been explained by branching of dynamically propagating cracks, a viable comminution model appears for macroscopic dynamic finite element analysis of large structures is unavailable and is proposed in this lecture. By contrast to static fracture, in which the driving force is the release of strain energy, here the central idea is that the driving force of comminution under compression at strain rates >10/s is the release of the kinetic energy of shear strain rate of forming particles, whose density can exceed the maximum possible strain energy density by several orders of magnitude. It is shown that the particle size or crack spacing should be proportional to the -2/3 power of the shear strain rate, that the comminution by high-rate shear is mathematically equivalent to an apparent shear viscosity proportional to the -1/3 power of the shear strain rate, and that the drop of the density of kinetic energy of shearing of forming particle is proportional to the 2/3 power of that rate. The proposed theory is inspired by analogy with turbulence, in which the kinetic energy of shear strain rate is analogous to the kinetic energy of rotating eddies and the fracture energy dissipation at interfaces of forming particles is analogous to the viscous energy dissipation between adjacent eddies. A dimensionless characteristic analogous to the Reynolds number, delineating classical and kinetic energy fractures, is formulated. In combination with the microplane model, the new theory greatly improves predictions of the exit velocity or penetration depth of missiles impacting concrete walls while remaining anchored in quasistatic laboratory tests of damage in concrete.
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