Determination of temperature dependence in Modified-Mohr-Coulomb failure model for process simulation of shear cutting

Abstract

Shear cutting is a proven process for chip-less separation of metals and used as a cost-effective production method. The process design of shear cutting is usually based on time and cost intensive experimental tests. Therefore, numerical depiction of the process offers great potential to reduce these practical tests. An important aspect hereby is the representation of temperature dependency of the material. However, the classical Modified-Mohr-Coulomb (MMC) failure model does not depict this effect directly. Therefore, the objective of this paper is to investigate the temperature dependency of MMC failure model for simulating shear cutting. The required data is obtained from tensile tests on miniaturised specimens under variation of temperature on dual-phase steel DP1000, using an additional optical measurement system. To determine stress triaxiality, Lode angle parameter and plastic strain at failure, the experimental tests are simulated using the Finite-Element simulation program ABAQUS. The MMC failure surfaces are fitted using the least squares method in Matlab. With this approach, temperature dependent MMC failure model was built to be used for shear cutting simulation of DP1000 steel.

Extension of the modified Mohr-Coulomb fracture model by a strain rate and temperature dependence

“…An interesting phenomenon can be pointed out in Fig. 2 (a), which is the so called blue-brittleness [6]. It indicates, that at specific temperatures materials strength does not decrease with increasing temperature due to foreign atom diffusion at dislocations.…”

“…Additionally, an optical measurement system Aramis was applied to correctly indicate the length change at fracture by means of digital image correlation (DIC). The schematic setup of the dilatometer and its corresponding components is presented in [6]. A uniaxial and two notched specimen geometries with a radius of 3 and 10 mm were chosen as miniaturised tensile specimens, which are shown in Fig.…”

“…However, the model only describes failure in a stress based space, which is not accurate when modelling materials fracture. Nonetheless, the transformation of the equation from a solely stress based into a stress and strain based space under condition of monotonic loading allowed to define the MMC failure model in terms of equivalent plastic strain at fracture 𝜀𝜀 p f � [6]. Therefore, with 𝐴𝐴 and 𝑛𝑛 as strength and work hardening exponents of the Swift hardening law, respectively, as well as 𝑐𝑐 3 as a material constant, the MMC failure model is defined as follows [7]:…”

“…However, the MMC fracture model does not directly take the temperature nor the strain rate into account. In [6] it was shown, that DP980 changes its characteristics when exposed to higher temperatures. For this reason, in [6] it was investigated whether the temperature influence reflects on the MMC fracture model.…”

“…In [6] it was shown, that DP980 changes its characteristics when exposed to higher temperatures. For this reason, in [6] it was investigated whether the temperature influence reflects on the MMC fracture model. As a result, it was depicted that the MMC fracture model and its parameters are highly dependent on materials behaviour under increasing temperatures.…”