爆炸科学与技术国家重点实验室9月16日学术报告预告

报告题目：Smooth dynamics of oblique impact with friction
报告时间：2013年9月16日（星期一）下午2:30
报告地点：爆炸科学与技术国家重点实验室计算与仿真中心（9号教学楼617房间）
报告人：Prof. W.J. Stronge（University of Cambridge）

报告摘要:
　　Effects of friction during impact between hard bodies can be analyzed as a continuous function of the normal component of impulse p;  i.e. by considering the normal component of impulse as an independent variable.  The resulting expressions for changes in relative velocity at the contact point C, are obtained as a continuous function vC(p).  Any sliding during contact is opposed by Coulomb friction.  In this analysis the terminal normal component of impulse pf separates into an initial ‘period’ of compression or approach followed by a ‘period’ of expansion or restitution. For planar impact where initial slip is brought to rest before termination of impact, the tangential component of impulse separates into a ‘period’ of initial sliding and a subsequent ‘period’ of either reverse sliding or stick.
　　For oblique planar impact in general, initial sliding can continue in the original direction or else slow and come to rest before separation.  After initial sliding is brought to rest, subsequently either the direction of sliding reverses or, with a sufficiently large coefficient of friction, the contact sticks.  Regions for each pattern of sliding are mapped as functions of the initial angle of incidence, the coefficient of friction and the inertia properties of the colliding bodies.  This mapping employs two non-dimensional parameters; (1) a normalized initial angle of incidence and (2) a parameter which depends on the unbalance of the configuration as well as the coefficient of friction. With these new impact parameters, terminal velocities and energy dissipation are calculated as functions of the normalized angle of incidence but independent of the impact speed.  Furthermore, specific relationships are obtained between the kinematic, kinetic and energetic coefficients of restitution. For frictional impact, it is shown that these definitions are equivalent only if the direction of sliding does not change.

报告题目：Impact Response of Polymer Metal Laminates
报告时间：2013年9月16日（星期一）下午4:00
报告地点：爆炸科学与技术国家重点实验室计算与仿真中心（9号教学楼617房间）
报告人：Dr. Graham McShane（University of Cambridge）

报告摘要:
　　Polymer coating is beginning to emerge as an efficient and economical solution for enhancing the blast and impact resistance of metallic plates. Coating materials such as polyurea can be sprayed onto existing structures, curing in-situ, offering a convenient retro-fit solution. However, the key mechanisms of energy dissipation for polymer-metal hybrid systems, and hence the optimal configurations, have not been clearly identified to date. The aim of this investigation is to identify the mechanisms by which a polymer coating is able to alter the perforation energy of a thin metallic plate. Although polyurea-steel is a practical material combination for many amour applications, this investigation considers first the use of polyethylene for the polymer layer. Polyethylene systems such as LDPE, HDPE and UHMWPE permit a wide range of microstructure and mechanical properties without significantly changing the density, allowing the relevant phenomena to be studied in a systematic and repeatable manner. Similarly, aluminum alloy is used for the metallic layer, permitting a range of mechanical properties to be achieved at fixed density via heat treatment. The findings from the extensive aluminum alloy-polyethylene study are finally compared with selected results from the more realistic steel-polyurea system, to assess their validity.
　　The investigation is presented in two parts.  First, the perforation response of monolithic polymer plates is investigated. The deformation and failure modes are identified, and some key material characteristics governing energy absorption are determined. Secondly, polymer-metal bi-layer targets are considered comprising Al alloy 6082 (in both T6 and T4 tempers) for the metallic layer, and polyethylene sheets with a range of mechanical properties (LDPE, HDPE and UHMWPE) for the polymer layers. In both parts of the investigation, three contrasting nose shapes are considered: blunt, hemispherical and conical. Quasi-static indentation experiments are first performed in order to identify the phases of the indentation response, including both deformation and perforation, in the absence of significant inertia and strain rate effects. In order to investigate the dynamic effects, a gas gun apparatus is also used to apply impact loading. The influence of layer order (i.e. polymer or metal facing the indenter) and layer thicknesses are identified.
 

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