Deformation Behavior and Ductility in Free Forging with Convex Die.

通过凸模自由锻造使板材发生塑性变形，提高了板材的弹簧性能和强度。本文研究了圆筒形模锻造板料的变形行为和塑性。采用平面应变下的板法对变形行为进行了评价。在锻造初期，板材的锻造区域随锻造工艺的增加而增加，但在锻造中期以后，其增加的幅度逐渐减小。在锻造板材的中心，沿纵向的轴向是拉伸的，但在许多情况下，这取决于刀具半径和摩擦系数，在接近中间阶段时达到最大值，之后减小并转变为压缩。当最大拉应力过高时，有可能出现延性断裂。基于塑性失稳提出了塑性判据，并尝试对各种金属成形的成形性进行预测。它们对应于…更多的是由Swift改进的弥漫性颈缩和由Storen&Rice改进的局部颈缩。所用材料为强化铝、磷青铜和不锈钢。在平面应变作用下，铝和钢的开裂发生在材料内部，而在平面应力作用下，青铜的开裂发生在板边。将实验得到的塑性极限与铝的分析估算进行了比较，因为青铜表现出不同的断口观点，而钢和部分青铜的断裂是在产生很高的静水压力的很大变形后发生的，这排除了所有基于唯象基础上提出的判据和塑性不稳定性的应用。铝的塑性总体上表明，实验和分析之间有很好的一致性，尽管实验值略高于分析值。对于极大变形后出现的裂纹，应综合考虑所有可能对应力状态变化产生影响的因素，如模具在高压下的压扁等。较少

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