玩具抛绳枪稳态构型的动力学分析

玩具抛绳枪通过迫使绳环高速切线运动,创造出柔绳悬浮在空中的错觉.利用动静法进行力学分析,推导了稳态悬浮时绳环的形状方程,给出了抛绳枪能够正常工作的条件.研究表明,发射角度使绳环上下对称时,水平跨度最大;最大跨度与阻力和重力之比正相关.     

Unified proof to oscillation property of discrete beam

The oscillation property （OP） is a fundamental and important qualitative property for the vibrations of single span one-dimensional continuums such as strings, bars, torsion bars, and Euler beams. Any properly discretized continuum model should keep the OP. In literatures, the OP of discrete beam models is discussed essentially by means of matrix factorization. The discussion is model-specific and boundary-condition- specific. Besides, matrix factorization is difficult in handling finite element （FE） models of beams. In this paper, according to a sufficient condition for the OP, a new approach to discuss the property is proposed. The local criteria on discrete displacements rather than global matrix factorizations are given to verify the OP. Based on the proposed approach, known results such as the OP for the 2-node FE beams via the Heilinger- Reissener principle （HR-FE beams） as well as the 5-point finite difference （FD） beams are verified. New results on the OP for the 2-node PE-FE beams and the FE Timoshenko beams with small slenderness are given. Through a simple manipulation, the qualitative property of discrete multibearing beams can also be discussed by the proposed approach.     

无网格方法施加本质边界条件的主从自由度法

以SPH(smoothed particle hydrodynamics)方法为例,把无网格法中的本质边界条件和复合材料界面连续条件视为多点约束(multi-point constraint,MPC),用主从自由度法(master-slave method)来处理.典型的基体-夹杂复合材料的线弹性问题算例结果表明,与罚函数法相比,采用主从自由度法的精度更高,适用范围更广.     

模拟滚弯非稳态过程的虚拟载荷法

采用传统的拉格朗日有限元模型模拟三辊滚弯的非稳态过程时,受到网格数量和接触算法的影响,计算效率难以提高.受计算流体力学的启发,将滚弯机跨内空间视作一维流场,工件挠曲线视作流场中的变量,采用欧拉观点建模,可以大大减小网格数量,同时降低接触处理的难度.将欧拉观点控制方程中的迁移项归结成一个附加的虚拟载荷,将其定义为型材空间构型不变而材料流动导致的内力不平衡量.通过引入该载荷,在经典平面梁单元的基础上稍加修改,得到适于小曲率滚弯模拟的欧拉单元平衡方程.算例表明,在相同网格尺寸下,虚拟载荷法和传统的有限元模拟结果均与理论解吻合良好;但前者的计算效率更高,结果更加光滑可靠.     

CFRP复合材料构件胶接特性及失效规律研究

对不同铺层方式和不同胶层厚度的复合材料胶接单搭结构(SLJs)的连接性能进行了研究。使用内聚力模型模拟了SLJs的胶层退化及失效过程，通过与实验对比验证了数值模型的有效性；基于改进后的三维Hashin失效准则，模拟了复合材料层合板的损伤演化。结果表明：胶层的退化形态及失效规律与胶层粘连的复合材料铺层角度密切相关，当胶层两侧粘连的复合材料铺层角度为0°时，胶层会退化形成椭圆环状；当胶层两侧粘连的复合材料铺层角度为45°或-45°时，胶层会退化形成上下中心对称的水滴状；当胶层两侧粘连的复合材料铺层角度为90°时，胶层会退化成沙漏状。0°铺层与胶层相邻时，结构的极限失效载荷最大，此时复合材料未出现损伤；当90°铺层与胶层相邻，结构的极限失效载荷最小且复合材料出现基体损伤、纤维损伤和分层损伤。胶层厚度在0.05～0.5mm时，复合材料胶接单搭结构的连接性能最好，当胶层厚度大于0.5mm,结构的连接性能会大幅下降。