Background

Although accurate knowledge of material behavior in plane strain tension is important for the modelling of sheet metal forming processes, it is often overlooked in yield function calibration because of experimental characterization challenges. Plane strain notch tensile tests, though experimentally convenient, are subject to stress and strain gradients across the gauge width that complicate the analysis.

Objective

A novel experimental integration methodology was developed to exploit these stress and strain gradients to locally calibrate the arc of an anisotropic yield surface from uniaxial-to-plane strain tension.

Methods

Constraining the anisotropic yield surface at the plane strain point, to be consistent with pressure-independent plasticity, enables the local arc to be governed by a single parameter. The arc shape is largely independent of the choice of yield function and can be optimized using a cutting line approach and full-field optical strain measurements. The accuracy of the method was evaluated using finite-element simulations of isotropic and anisotropic materials with different hardening behaviors.

Results

The methodology was applied to a dual phase DP1180 steel and AA5182-O aluminum alloy in the rolling, transverse, and diagonal directions. Data along each of the three locally calibrated arcs was included in calibrations of Yld2000 and Yld2004 yield surfaces.

Conclusions

The plane strain yield strength and arc shape had significant implications on the calibration of advanced anisotropic yield criteria. The yield exponent of the DP1180 agreed with the common value of six for BCC metals while the AA5182 yield surface approximated a Tresca-shape with local yield exponents in excess of 20.

中文翻译：

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从单轴到平面应变张力表征钣金塑性的实验方法

背景

尽管平面应变张力中材料行为的准确知识对于钣金成型过程的建模很重要，但由于实验表征挑战，它在屈服函数校准中经常被忽视。平面应变缺口拉伸试验虽然在实验上很方便，但在整个规格宽度上会受到应力和应变梯度的影响，这使分析变得复杂。

客观的

开发了一种新的实验集成方法来利用这些应力和应变梯度来局部校准各向异性屈服面的弧度，从单轴到平面应变张力。

方法

约束平面应变点处的各向异性屈服面，使其与压力无关的塑性一致，使局部弧由单个参数控制。弧形在很大程度上与屈服函数的选择无关，可以使用切割线方法和全场光学应变测量进行优化。使用具有不同硬化行为的各向同性和各向异性材料的有限元模拟来评估该方法的准确性。

结果

该方法应用于双相 DP1180 钢和 AA5182-O 铝合金的轧制、横向和对角线方向。Yld2000 和 Yld2004 屈服面的校准中包含了沿三个局部校准弧中每一个的数据。

结论

平面应变屈服强度和弧形对高级各向异性屈服准则的校准具有重要意义。DP1180 的屈服指数与 BCC 金属的常用值 6 一致，而 AA5182 屈服面近似于 Tresca 形状，局部屈服指数超过 20。