摘要
提出了一种计算受冲薄壁结构动力效应的显式有限元方法．采用退化四节点亮单元及快速可靠的接触搜寻法，运用基于Ｐｒａｎｄｔｌ－Ｒｅｕｓｓ塑性流动增量理论的等向强化弹塑性Ｓｙｍｏｎｄｓ应变率材料模型与合适的应力回映方法，可以准确地模拟受冲薄壁结构的动态过程．文中实例表明：已被广泛采用的Ｒｅｉｄ与Ｒｅｄｄｙ的针对薄壁圆管横向压缩中某些特殊情况而作的变形模式假设并不具有广泛适应性；对应变率敏感材料，应变率效应不仅影响受冲薄壁结构的变形特性，也影响其变形模式；此外，冲击过程中的惯性效应不容忽视．
An explicit finite element method for the evaluation of dynamic effects of thin-walledstructure in impacting processes was presented. The 4-node bilinear degenerated shell elementwith five through-the-thickness integration points which is based on the well-known definitions oflaminas and fibers is employed. A common numerical deficiency encountered in this type of shellfinite element is the transverse shear-locking phenomenon. The locking phenomenon become moreand more pronounced as the thickness of the element becomes smaller and smaller. To overcomethis locking phenomenon, a one-point integration rule is adopted. This reduced intetration ruleis also used to improve computational efficiency. To eliminate Zero-energy modes (i.e. hourglassinstabilities) introduced by the one-point integration technique, a priori stabilization procedureswhich is to add corrective terms to the nodal internal force vector prior to solving the discreteproblem is employed. A single surface contact algorithm is introduced to cope with the contactsearch and the contact force is evaluated by penalty method. The evaluation of friction force incontact area is based on the classical Coulomb law of friction. To take the strain rate effectsinto account, a Symonds strain rate model for isotropic elastic-plastic materials that based onthe Prandtl-Reuss flow rule is applied. The elastic predictor-plastic corrector method is used todeal with the stress return-mapping problem. To enforce consistency at the end of the time-stepin a manner consistent with the prescribed Prandtl-Reuss flow rule, a purely elastic trial state isfollowed by a.plastic corrector phase in this return mapping method. The explicit time integrationschemes are used to solve the dynamic equations. The satisfactory behavior of the explicit-FEMis demonstrated in several numerical examples. It has also been proved by these examples thatthe assumption which has been used extensively for a long time may become invalid for ordinarycircumstances. This assumption was made by Reid & Reddy to deal with some special conditionswhen they studied the responses of laterally compressed tubes. This assumption is that the tubewas assumed to deform in the same modes under the dynamic loads exerted by the hammer asduring quasi-static loading. In fact, the Iimitations. of the assumption are clear. There is no one byone corresponding relation between stress and strain when material be in elastic-plastic stage. Thestress-strain relations will become more complication due to strain rate effects in dynamic problem.i.e. the constitutive relations of dynamic processes are different from that of static or quasi-staticprocesses, especially for strain rate sensitive material. Examples make further indications thatboth crush characteristics and deformation mode are affected evidently for strain rate sensitivematerial and indistinctly for strain rate insensitive material by strain rate effects during impactingprocesses. But, the illustrations given in this paper indicate that inertia effects do need to beborne in mind by the thin-walled structure designers for both strain rate sensitive and insensitivematerial.
出处
《力学学报》
EI
CSCD
北大核心
2000年第1期70-77,共8页
Chinese Journal of Theoretical and Applied Mechanics
基金
国家自然科学基金
湖南省科委基金
关键词
冲击
薄壁结构
动力效应
有限元
接触
impact, thin-walled structure, dynamic effects, FEM, contact
