钝圆柱头质量对简支梁的弹性次碰撞研究

该文采用赫兹碰撞理论、三维动力有限元方法和自行研制的次碰撞实验装置，研究了钝圆柱头质量一次坠落碰撞简支钢梁过程的次碰撞现象、次碰撞过程的持续时间和次碰撞发生的条件．实验测试和数值模拟均清楚地观察到了复杂的次碰撞现象．研究结果表明：（1）当梁初始处于静止状态时，将实验测试和数值模拟结果与理论分析结果对比后发现，首个次碰撞过程由局部接触变形主导，并可以采用 Hertz弹性碰撞理论来描述；（2）实验和数值模拟结果展现了与首个次碰撞过程特征迥异的后续次碰撞过程，后续次碰撞过程的持续时间出现大范围的随机变化；（3）进一步分析发现，后续次碰撞过程由局部接触变形和梁的整体变形运动共同主导，梁的整体变形运动使得碰撞力响应变得异常复杂；（4）通过数值计算结果发现，当出现次碰撞现象时，碰撞位移响应中的一阶模态幅值占比会突然降低，相位角发生明显的变化；（5）数值计算结果表明，次碰撞发生的条件与质量比、碰撞初速度、碰撞动量、碰撞位置、测试梁长度和厚度等有关；（6）次碰撞发生的条件若用质量比来度量，则发现存在一个质量比阀值．上述研究表明，局部接触变形和梁的整体变形运动相互作用，产生了复杂的耦合效应，使得次碰撞现象呈现了丰富的力学行为．因此，进一步通过理论、实验和数值仿真研究复杂的次碰撞现象，对于深入理解柔性结构的碰撞行为很有必要．

STUDY ON ELASTIC SUB-IMPACTS OF SIMPLY SUPPORTED STEEL BEAM STRUCK BY ROUND-NOSED MASS

The sub-impact behavior of a simply supported beam struck by a round-nosed mass, including the sub-impact phenomenon, sub-impact durations and sub-impact conditions, were tested by a set of sub-impact experimental device self-designed, simulated numerically by the three-dimensional dynamic finite element method and analyzed by the Hertz impact theory. The sub-impact phenomenon was observed by the tests and simulations. By comparing the results of test, simulation and theoretical analysis, it is found that the first sub-impact process is dominated by local impact-contact deformation and can be described by the Hertz impact theory. The subsequence sub-impacts have much different characteristics from the first sub-impact, and their impact durations vary random in large ranges. The further investigation has found that the processes of the subsequence sub-impacts are dominated together by the local impact-contact deformation and the beam vibrations, and the impact force responses become complicated because of the beam vibrations. The numerical simulations show that the first vibration mode of the beam decreases its amplitude suddenly and changes its phase angle obviously when sub-impacts taken place. The numerical simulations also show that the sub-impact conditions relate to the ratio of the round-nosed mass to the beam equivalent mass, initial impact velocity, impact position, initial impact momentum, length and thickness of test beam. It is found that the sub-impact conditions can be represented by a mass ratio threshold. The present investigation illustrates that the couple mechanical effect of local impact deformation and structural vibration make a plenty of sub-impact behavior. It is necessary to further investigate the phenomenon of sub-impact by test, numerical simulation and theoretical analysis, so as to have a comprehensive understand of impact behavior of flexible systems.