Elastic-plastic deformation of lightweight core-perforated sheet metal laminates and their optimum design considering strength, rigidity and formability

在这个项目中，带有穿孔核心和外壳的夹层金属板是新开发的，用于轻质壳体结构。采用铜夹层试件，通过单轴拉伸、弯曲和拉伸成形等力学试验，考察了该种板材的弹塑性力学性能。通过有限元分析，研究了该板材的弹塑性变形机理和成形极限。研究结果总结如下：(1)对夹层板(其空洞体积分数V_f=17%)、整体铜板和单穿孔板(V_f=28)的塑性流动强度进行了单轴拉伸试验。对于单孔板，其比强度(=强度除以板的密度)比整体板低28%，而对于夹层板，其比强度仅低5%。夹层板具有优良的弯曲刚度，是单孔板的2.7倍。(2)夹层板的成形极限图与单孔板的成形极限图相似。与整体板材相比，平面应变条件下的极限应变不是很小，而平衡双向拉伸条件下的极限应变明显小于单轴拉伸条件下的极限应变。通过实验观察和有限元模拟，得出夹层板的断裂是金属蒙皮应变局部化的结果。

In this project, sandwiched metal plates with perforated core and skins are newly developed for the use of lightweight shell constructions. Using copper sandwiched specimens, mechanical properties of elasto-plasticity of this type of plates were examined by performing several mechanical tests such as uniaxial tension, bending and stretch forming. Moreover, the mechanisms of elastic-plastic deformation and the forming limit of this plate were investigated by the finite element analysis. The present findings are summarized as follows:(1) The plastic-flow strength of the sandwiched plate (its volume fraction of voids V_f = 17%), as well as a monolithic copper sheet and a single perforated sheet (V_f = 28 were examined by uniaxial tension tests. For the single perforated sheet the specific strength (= strength divided by the density of the plates) is 28% less than that of the monolithic sheet, while for the sandwich plate it is only 5% less. The sandwich plate has excellent performance in bending rigidity, namely it is as high as 2.7 times of one of the monolithic plate.(2) The forming limit diagram (FLD) of the sandwiched plate is similar to one of the single perforated sheet. The limit strain under plane-strain condition is not so small compared to one of the monolithic sheet, while it under balanced biaxial stretching condition is significantly smaller than that under uniaxial tension. From the experimental observations, as well as the FE simulation, it is concluded that the fracture of the sandwich plate will occur as a result of strain localization at the skin metals.