Deformation Behavior and Ductility in Free Forging with Convex Die.

利用凸形模具进行自由锻造，使板材产生塑性变形，从而提高了板材的弹性特性和强度。本文研究了圆柱模锻板料的变形行为和延展性。采用平面应变作用下的平板法来评价变形行为。板材的锻造面积在锻造初期随着锻造工艺的增加而增大，但在锻造中期后，其增大幅度由减小变为增大。在锻件的中心，沿纵向方向的应力是拉伸的，在许多情况下，尽管取决于刀具半径和摩擦系数，但它在接近中期时达到最大值，之后它减小并转向压缩。当最大拉应力过高时，可能产生韧性断裂。我们提出了基于塑性不稳定性的一般塑性准则，并试图预测各种金属成形的可成形性。它们对应于Swift改进的漫反射缩颈和Storen & Rice改进的局部缩颈。使用的材料是强化铝，磷青铜和不锈钢。在平面应力作用下，铝和钢的开裂发生在材料内部，而青铜的开裂发生在板材边缘。实验得到的延性极限与对铝的分析估计进行了比较，因为青铜的断裂观不同，钢和部分青铜的断裂发生在非常大的变形和非常高的静水压力下，这拒绝了任何基于现象学和塑性不稳定性提出的准则的应用。铝的塑性试验值与分析值总体上吻合较好，但实验值略高于分析值。大变形后出现的开裂应考虑到所有可能影响应力状态变化的因素，例如高压下模具的压平。少

Improvment for spring characteristic and strength of sheet metals has been brouhgt by giving them plastic deformation through free forging with convex shape dies. Here, the deformation behavior and ductility in sheet metal forging with cylindrical dies are investigated. Slab method under plane strain is used in order to evaluate deformation behavior. Forging region of a sheet increases with forging process at the early stage of forging, but after the middle stage its increase changes to decrease. At the center of the forging sheet the sterss along longitudinal direction is tensile, in many cases, thouhgh depending upon tool radius and friction coefficient, and it becomes maximum near middle stage, after which it decreases and shifts to compressive. When the maximum tensile stress is too high, ductile fracture may be possible to arise.We proposed general criteria for ductility based on plastic instability, and tried to predict the formability of various metal formings. They correspond t … More o modified diffuse necking by Swift and to modified localized necking by Storen & Rice. The materials used are strengthened aluminium, phospher bronze and stainless steel. The cracking of the aluminium and steel occurs at the interior of materials under plane strain, but that of the bronze does at sheet edge under plane stress. Ductiltiy limit obtained by experiment is compared with analytical estimation on the aluminium, because the bronze shows different view of fracture, and the fracture of the steel and a part of the bronze occurs after very large deformation where very high hydrostatic pressure arises, which rejects all of application of any criteria proposed on phenomenological basis and plastic instability.The ductility on the aluminum shows, on the whole, good agreement between experiment and analysis, though experimental values are a little higher than analytical ones. The cracking appearing after very large deformation should be inverstigated considering all possible items producing effects on the change of stress state, for example, the flatting of dies under high pressure. Less