Improved Fracture Characterization of High Strength Steels due to a new Test Method for Shear Tension Specimen on uniaxial Tensile Testing Machines

为了保持先进高强度钢(AHSS)在汽车工业中相对于其他轻质材料的主导地位，有必要不断开发AHSS，并更好地利用其轻量化潜力。基于有限元的成形过程数值分析为提高这一利用率提供了一种有效的方法。与传统的利用有限元描述板料成形过程中断裂应变的方法不同，基于应力的断裂模型可以用于具有非线性应变路径的成形过程和多阶段成形过程，此外，除了延性断裂之外，还可以预测剪切断裂。基于应力的断裂模型的标定还没有被标准化。因此，由于试验程序的不同以及试件断裂起始区应力状态的不同发展，文献中可用的AHSS的估算断裂应变往往因作者不同而差异很大。该项目的目标是开发一种基于剪切拉伸试验的单轴拉伸试验机程序，从而可以在广泛的应力状态下精确校准AHSS的断裂行为。为此，将使用已经开发的蝴蝶标本，并将开发一种新的测试设备。该装置可以在试验过程中连续调整试件与试验机的受力方向之间的夹角，从而保持试件的恒定应力状态。

In order to maintain the dominating position of advanced high-strength steels (AHSS) as compared to other lightweight materials in automotive industry, there is a need for continuous development of AHSS as well as a better utilization of their lightweight potential. The numerical analysis of forming processes on basis of FEM provides an effective method to improve this utilization.In contrast to the conventional method for the description of fracture strains in sheet metal forming processes with the help of FLD, stress-based fracture models can be used for forming processes with non-linear strain paths as well as multi-stage forming processes, and furthermore, besides ductile fracture also shear fracture can be predicted. The calibration of stress-based fracture models has not been standardized yet. Therefore, estimated fracture strains of AHSS available in literature often differ much from one author to another because of different testing procedures with varying developments of the stress state in the fracture initiation zone of the specimen. The objective of the project is to develop a procedure for uniaxial tensile testing machines based on shear tension tests, whereby it is possible to calibrate precisely the fracture behaviour of AHSS for a wide range of stress-states. For this purpose, an already developed butterfly specimen will be used and a new test device will be developed. This device will allow adjusting continuously the angle between the specimen and the force direction of the testing machine during the test thus a constant stress state in the specimen can be maintained.