Methodology for the Analysis of the Process Behaviour of Advanced High Strength Steels in Bending and Shearing Operations

Abstract

In the automotive sector the application of advanced high strength steels (AHSS) for structural and safety relevant components plays an important role. Typical manufacturing processes concerning these parts are bending and cutting operations. However, the forming and cutting potential of these steel grades is different compared to conventional steels, as the process behaviour is changing. For an improved workpiece quality the fundamental knowledge of the damage and failure mechanisms is essential. This study presents a methodology for the analysis of AHSS in bending and out-of-plane shearing operations. Two micro alloyed high strength steels are investigated within this work. First results are presented concerning material characterisation by tensile tests, the material performance in air bending tests and the development of a modular punching tool. The study is closed by summarizing the damage behaviour along the process chain considering both bending and cutting. This shows the applicability of the presented methodology for analysing the process behaviour with respect to occurring failure.

Numerical Prediction of Failure within Small Curvature Bending of Advanced High Strength Steels

“…A calibration of the damage model`s parameters with experiments, where observable failure occurs, usually has to be performed in this case. However, it could be shown that also a strain based identification method is appropriate to adapt the damage parameters to bending experiments, when no observable failure occurs [14]. A methodology was developed to derive the maximum major strain φ max at the outer surface of the bending edge utilizing an optical strain measurement system and the progression of the strain curve over the displacement of the punch is used as a target function for the optimisation process.…”

“…As starting values the determined parameters of the uniaxial tensile test are used and systematically varied. Within the study of [14] the methodology was proved for the micromechanical damage model of Gurson [4] and for the case that no failure in terms of cracks occurs in the bending experiments with high strength low alloyed steels with a sheet thickness of t 0 = 1.8 mm. The aim of the present study is to show that the strain based calibration method is appropriate to determine and adapt Lemaitre [3] damage parameters to bending load cases with the different steel grade AHSS and a different sheet thickness of t 0 = 1.0 mm.…”

“…In preliminary investigations different material cards were studied in order to represent the evolution of the maximum major strain φ max at the outer bending edge. The maximum major strain φ max in simulation an experiment is derived according to the methodology shown in [14]. Besides isotropic modelling of the material also the yield criteria of Hill48 [16] and Barlat91 [17] were considered as they are available for solid elements in LS-DYNA.…”

Development of a Damage Prediction System for Bending and Cutting of High Strength Steels

“…The development of a damage prediction system requires an investigation of parameters determining the process and their effect on the formability. In a first step the bendability and the cutting behaviour are analysed in new constructed model experiments [6]. Within the model tests process defining parameters can be varied and thus the damage evolution of the material can be studied in dependency of these parameters experimentally.…”

“…5. Preliminary investigations showed [6], that more critical bending conditions occur, when the bending line is orientated parallel to the rolling direct of the sheet. Consequently, the validation of the damage prediction programme is demonstrated for this parameter set.…”