Abstract The in-plane torsion test achieves true strains far beyond 1.0 for sheet metals, especially using specimens with circular grooves. The accurate measurement of these high strains is a challenge for the conventional digital image correlation (DIC). Thus, the determination of flow curves is limited and fracture strains for very ductile materials cannot be measured. A new grooved specimen is introduced to avoid strain localization. Shear stress and shear strain along a defined area in the groove are constant so that strains can be measured independently of the DIC system setting without error due to strain localization. Furthermore, three methods for the measurement of very high shear strains in the in-plane torsion test are presented: Firstly, the limit of the optical strain measurement is extended by multiple renewal of the digital image correlation (DIC) pattern on the samples. Secondly, the shear strain for the planar specimen is calculated exactly from the rotation angle curve. Lastly, a new incremental method is presented. This method enables to determine shear strains for plane and grooved specimen exactly by only measuring the torque and the angle of rotation. All methods were applied for three steel sheet materials namely DP1000, CP1000 and DC04. The equivalent strain in a grooved in-plane torsion test of sheet steel DC04 was determined as 3.3 with the new incremental method. Such high strains far exceed conventional methods for determining the flow curve.

中文翻译：

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面内扭转试验中大剪切应变的测量方法

摘要 面内扭转试验对金属板实现了远远超过 1.0 的真实应变，尤其是使用带有圆形凹槽的试样时。这些高应变的准确测量对于传统的数字图像相关 (DIC) 来说是一个挑战。因此，流动曲线的确定是有限的，并且无法测量非常具有延展性的材料的断裂应变。引入了一个新的凹槽试样以避免应变局部化。沿凹槽中定义区域的剪切应力和剪切应变是恒定的，因此可以独立于 DIC 系统设置测量应变，而不会因应变局部化而产生错误。此外，还提出了三种测量面内扭转试验中极高剪切应变的方法：首先，通过多次更新样品上的数字图像相关 (DIC) 图案，扩展了光学应变测量的极限。其次，平面试样的剪切应变是根据旋转角曲线精确计算的。最后，提出了一种新的增量方法。该方法仅通过测量扭矩和旋转角度即可准确确定平面和凹槽试样的剪切应变。所有方法均适用于三种钢板材料，即 DP1000、CP1000 和 DC04。钢板 DC04 开槽面内扭转试验中的等效应变用新的增量法确定为 3.3。如此高的应变远远超过用于确定流动曲线的传统方法。平面试样的剪切应变是根据旋转角曲线精确计算的。最后，提出了一种新的增量方法。该方法仅通过测量扭矩和旋转角度即可准确确定平面和凹槽试样的剪切应变。所有方法均应用于三种钢板材料，即 DP1000、CP1000 和 DC04。钢板 DC04 开槽面内扭转试验中的等效应变用新的增量法确定为 3.3。如此高的应变远远超过用于确定流动曲线的传统方法。平面试样的剪切应变是根据旋转角曲线精确计算的。最后，提出了一种新的增量方法。该方法仅通过测量扭矩和旋转角度即可准确确定平面和凹槽试样的剪切应变。所有方法均适用于三种钢板材料，即 DP1000、CP1000 和 DC04。钢板 DC04 开槽面内扭转试验中的等效应变用新的增量法确定为 3.3。如此高的应变远远超过用于确定流动曲线的传统方法。所有方法均应用于三种钢板材料，即 DP1000、CP1000 和 DC04。钢板 DC04 开槽面内扭转试验中的等效应变用新的增量法确定为 3.3。如此高的应变远远超过用于确定流动曲线的传统方法。所有方法均适用于三种钢板材料，即 DP1000、CP1000 和 DC04。钢板 DC04 开槽面内扭转试验中的等效应变用新的增量法确定为 3.3。如此高的应变远远超过用于确定流动曲线的传统方法。