Abstract Concertina folding of tubes used for impact mitigation bends the tube section to tight curvatures that can lead to failures on the tensioned side of the folds. This paper reports results from such axial crushing experiments on Al-6061-T6 circular tubes in which cleft-like features were also observed on the compressed sides of folds. Microscopic examination of the compressed sides of sectioned folds at different stages of bending revealed the following. Compression leads to surface wrinkles that are initiated by small initial surface roughness. Further bending increases the amplitude of the wrinkles, and at even higher bending the wrinkles morph into folds, creases, and sharp discontinuities. Metallographic examination of these surface undulations revealed that surface wrinkles encompass several grains, which deform conforming to the imposed local geometric changes. With this in mind, the axial crushing was simulated at the continuum level via an axisymmetric finite element analysis coupled with a suitably calibrated non-quadratic elastic-plastic constitutive model. A sufficiently refined mesh and representative initial surface imperfections enabled monitoring of the evolution of surface instabilities on the compressed sides of folds. Surface wrinkles appear at compressive strains of about 50%. As the local bending increases, their amplitude grows, and subsequently they evolve into local folds, and creases that resemble surface features observed in the experiments.

中文翻译：

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轴向破碎铝管中的弯曲引起的起皱和折痕

摘要 用于减轻冲击的管的六角形折叠将管部分弯曲成紧密的曲率，这可能导致折叠的张紧侧出现故障。本文报告了在 Al-6061-T6 圆管上进行此类轴向挤压实验的结果，其中在折叠的压缩侧也观察到裂缝状特征。在不同弯曲阶段对分段折叠的压缩侧进行显微镜检查，结果如下。压缩会导致表面皱纹，这是由小的初始表面粗糙度引发的。进一步弯曲会增加皱纹的幅度，在更高的弯曲度下，皱纹会变成褶皱、折痕和尖锐的不连续性。这些表面起伏的金相检查显示表面皱纹包含几个颗粒，其变形符合强加的局部几何变化。考虑到这一点，通过轴对称有限元分析与适当校准的非二次弹塑性本构模型相结合，在连续介质水平上模拟了轴向挤压。足够细化的网格和具有代表性的初始表面缺陷能够监测褶皱压缩侧的表面不稳定性的演变。表面皱纹出现在约 50% 的压缩应变下。随着局部弯曲的增加，它们的振幅增加，随后它们演变成局部褶皱和类似于实验中观察到的表面特征的折痕。通过轴对称有限元分析和适当校准的非二次弹塑性本构模型，在连续体水平上模拟轴向挤压。足够细化的网格和具有代表性的初始表面缺陷能够监测褶皱压缩侧的表面不稳定性的演变。表面皱纹出现在约 50% 的压缩应变下。随着局部弯曲的增加，它们的振幅增加，随后它们演变成局部褶皱和类似于实验中观察到的表面特征的折痕。通过轴对称有限元分析和适当校准的非二次弹塑性本构模型，在连续体水平上模拟轴向挤压。足够细化的网格和具有代表性的初始表面缺陷能够监测褶皱压缩侧的表面不稳定性的演变。表面皱纹出现在约 50% 的压缩应变下。随着局部弯曲的增加，它们的振幅增加，随后它们演变成局部褶皱和类似于实验中观察到的表面特征的折痕。表面皱纹出现在约 50% 的压缩应变下。随着局部弯曲的增加，它们的振幅增加，随后它们演变成局部褶皱和类似于实验中观察到的表面特征的折痕。表面皱纹出现在约 50% 的压缩应变下。随着局部弯曲的增加，它们的振幅增加，随后它们演变成局部褶皱和类似于实验中观察到的表面特征的折痕。