STRAIN-HARDENING AND INSTABILITY IN BIAXIALLY STRETCHED SHEETS
STRAIN-HARDENING AND INSTABILITY IN BIAXIALLY STRETCHED SHEETS
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DOI：
10.1007/bf02645615
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发表时间：
1973-01-01
期刊：
影响因子：
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通讯作者：
BACKOFEN, WA
中科院分区：
文献类型：
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作者：
GHOSH, AK;BACKOFEN, WA
这项工作涉及双轴拉伸板材中两种不同的失效极限模式的起源，最近在参考文献中对此进行了描述。 1：极限应变对应变状态不敏感的黄铜类型，以及铁素体钢类型，其中极限应变随着施加应变比 ρ = ε2/ε1 从零（平面应变张力）向统一（平衡双轴张力）变化而增加。早期提出的不同滑移模式（即铁氧体中的波状与黄铜中的平面）可能导致这些失效极限差异的提议被发现是无效的。主要实验程序有两个部分：通过在 ρ= 0 和 ρ= 1 之间的不同路径上按比例加载对小片材进行预应变，然后进行拉伸测试，以及在 ρ ≅ — 1/2（单轴拉伸）和 ρ= 0 之间更直接地测量应变硬化和不稳定性。主要发现是，总体硬化率（基本上如材料的有效应力-应变曲线中所示）随加载路径而变化。在α黄铜中，当p从∼1/2增加到1时，它会衰减；在铁素体钢中，它增加；而对于铝来说，它受到的影响很小。硬化率的这种变化会导致材料稳定流动的能力发生类似的变化。反过来，稳定流是在达到观察到的失效极限时添加准稳定流增量（当 ρ > 0 时）的基础。因此，与ρ相关的高度的底可以解释失效极限模式。对于硬化率与 ρ 的相关性，目前还没有任何解释。
This work is concerned with the origins of the two different patterns of failure limits in biaxially stretched sheets which were recently described in Ref. 1: the brass-type in which the limit strain is insensitive to strain state, and that of ferritic steel in which the limit strain increases as the imposed strain-ratio, ρ = ε2/ε1, changes from zero (plane-strain tension) toward unity (balanced biaxial tension). An earlier proposal that different slip modes,i.e.wavy in ferrite vs planar in brass, might have contributed to these failurelimit differences was found not to be valid. There were two parts to the main experimental program: the prestraining of small sheets by proportional loading on different paths betweenρ= 0 andρ= 1, followed by tension testing, and a more direct measurement of strain hardening and instability between ρ ≅ — 1/2 (uniaxial tension) andρ= 0. The principal finding was that the overall hardening rate, essentially as it appeared in the material’s effective stress-strain curve, changed with the loading path. Inαbrass it decayed as p was increased from ∼—1/2 to 1; in ferritic steel it increased; and in aluminum it was affected very little. Such changes in hardening rate cause similar changes in the material’s capacity for stable flow. The stable flow, in turn, is the base to which a quasistable-flow increment (whenρis >0) is added in reaching the observed failure limit. Thus a base ofρ-dependent height can account for the failure-limit patterns. There is still no explanation for the ρ dependence of the hardening rate.