Abstract

In this work, the onset of failure induced by severe strain at elevated temperature was numerically estimated with cross-formed empirical hardening law describing material softening. The hardening law can replicate the rate-sensitive behavior of aluminum alloy 7075 sheets (thickness of 2.0 mm) with initial hardening and progressive material deterioration caused by dynamic recrystallization, dynamic recovery, and micro-void development. The characterized material was applied to the two-step hybrid forming process consisting of a drawing at 400 °C followed by a pneumatic forming at 470 °C to produce a shock absorber housing with an extremely complex shape. The user-defined subroutine codes, VUMAT (ABAQUS/Explicit) and UMAT (ABAQUS/Standard), were sequentially utilized for the drawing and the pneumatic forming, respectively. The identified hardening parameters based on uniaxial tensile tests were validated by simulating the two-step hybrid forming process and compared with the conventional Voce type law (converging function) and the combined Swift-Voce type law (ever-increasing function) since they play a key role in accurately predicting the onset of failure induced by severe strain localization. Finally, simulation results are reasonably well matched with experiments in terms of the moment of failure occurrence, failure location, final blank shape, and thickness distribution.

Graphic Abstract

中文翻译：

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高温下7075铝合金板的应变局部失效及其在两步混合成形中的应用

摘要

在这项工作中，通过描述材料软化的十字形经验硬化定律，对在高温下由严重应变引起的破坏的发生进行了数值估计。硬化定律可以复制7075铝合金薄板（厚度为2.0 mm）的速率敏感性行为，并具有由于动态再结晶，动态恢复和微孔发展而引起的初始硬化和逐渐的材料劣化。将特征材料应用于两步混合成型工艺，该工艺包括在400°C下进行拉伸，然后在470°C下进行气动成型，以生产形状极为复杂的减震器外壳。用户定义的子程序代码VUMAT（ABAQUS / Explicit）和UMAT（ABAQUS / Standard）分别用于绘图和气动成型。通过模拟两步混合成型过程，验证了基于单轴拉伸试验确定的硬化参数，并与传统的Voce型定律（收敛函数）和组合的Swift-Voce型定律（不断增加的函数）进行了比较，在准确预测由严重应变局部化引起的失效开始中的关键作用。最后，在故障发生的时刻，故障的位置，最终的毛坯形状和厚度分布方面，仿真结果可以与实验很好地匹配。

图形摘要