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本文首先根据失稳的定义,对现有的分散性失稳(diffuse instability)和局部性失稳(localized instability)的准则进行了评述。同时对失稳变形的形式、以及在σ_2>σ_1/2的应力状态下局部性失稳产生的条件和失稳微体在分散性失稳发展到局部性失稳过程中具有的状态进行了讨论。然后在所得结论的基础上,以板材濒临出现吕德斯(Luders)线为许用变形的限度,提出了一种不同于根据斯韦夫脱(Swift,H.W.)失稳准则预测板材成形极限图右部曲线的新方法。实验验证表明,根据本文所提方法得出的预测曲线,与实验数据相当接近,其符合程度远比按现有其它理论预测的结果为佳。
Based on the definition of instability, the dissertation first reviews the existing criteria of diffuse instability and localized instability. At the same time, the forms of instability deformation, the conditions of local instability in the stress state of σ_2> σ_1 / 2, and the state of the unstable micro-body in the process of dispersion instability development to the local instability are discussed . Based on the conclusions obtained, the limit of allowable deformation of Lumber line is approached, and a new method is proposed to predict the sheet forming limit according to Swift (HW) instability criterion The new method of the right curve. Experimental results show that the prediction curves obtained according to the proposed method are quite close to the experimental data, which is far better than the prediction based on other existing theories.