Extending the annular in-plane torsional shear test specimen to applications at high strain rates.

The in-plane torsion test is a well-established test used for the characterisation of sheet metals. The specimen is intended to deform in planar simple shear and is designed to be machined with a continuous annular shear zone. As a result, there are no “edge effects” or geometric discontinuities to generate instabilities, thus large true strains up to 1 can be achieved. Before this research, the specimen had only been used for material characterisation in the quasi-static regime. The aim of this research was to conduct further quasi-static testing using the in-plane torsion test and to extend its use into the dynamic regime. Quasi-static tests were performed on a quasi-static torsional (QST) system that was designed to be integrated onto a Zwick universal testing machine. Dynamic tests were performed on a modified torsional split Hopkinson bar(TSHB) system. The TSHB system adopted a nested configuration which allowed for a longer incident bar, and thus larger obtainable strains. Two quick-release mechanisms were used, one using a novel reusable wedge and the other using fracture-pins. All specimens were manufactured from Al 1050 H14. Typical results agreed with material test data available in the literature. Both systems attained large strains at near-constant strain rates and together, allowed for material characterisation over a large range of strain rates. Near-uniform deformations were observed for specimens with lower strain gauge widths. An added feature of the specimen was the flat reverse face, which together with the nested configuration of both systems allows for the possibility for full-field DIC measurement in the future. An estimation method for steady-state flow stress is presented with the steady-state flow stress found to be rate dependant. Finally, a relationship between the steady-state flow stress and strain rate for all experimental results is proposed.

平面扭转试验是一种广泛应用于板材性能表征的成熟测试方法。试样旨在平面简单剪切中发生变形，并设计为具有连续的环形剪切区域，因此不存在导致不稳定的“边缘效应”或几何不连续性，从而可以实现高达1的真应变。在此研究之前，试样仅用于准静态条件下的材料表征。本研究旨在进一步利用平面扭转试验进行准静态测试，并将其应用扩展至动态领域。准静态测试是在一个旨在集成于Zwick万能试验机的准静态扭转（QST）系统上进行的。动态测试是在一个改进的扭转分裂霍普金森棒（TSHB）系统上进行的。TSHB系统采用嵌套配置，这允许更长的入射棒，从而获得更大的可获取应变。使用了两种快速释放机制，一种采用一种新型的可重复使用的楔形块，另一种采用断裂销。所有试样均由Al 1050 H14制成。典型结果与文献中可用的材料测试数据一致。两个系统均在大约恒定的应变率下实现了大应变，共同允许在广泛的应变率范围内进行材料表征。对于应变片宽度较低的试样，观察到近均匀的变形。试样的一个附加特点是平坦的翻转面，与两个系统的嵌套配置相结合，为未来进行全场数字图像相关（DIC）测量提供了可能性。提出了一种稳态流动应力估计方法，并发现稳态流动应力与应变率相关。最后，针对所有实验结果，提出了稳态流动应力与应变率之间的关系。