The differences of damage initiation and accumulation of DP steels: a numerical and experimental analysis

Abstract

Many studies have examined the damage behaviour of dual-phase steels already. It is a topic of high interest, since understanding the mechanisms of damage during forming processes enables the production of steels with improved properties and damage tolerance. However, the focus was rarely on the comparison between representatives of this steel class, and the numerical simulation for the quantification of damage states was not thoroughly used. Therefore, this study compares the damage initiation and accumulation of two dual-phase steels (DP800 and DP1000), which are used in the automotive industry. Additionally, parameter sets of a phenomenological damage mechanics model with coupled damage evolution are calibrated for each material. The combined analysis reveals an earlier initiation of damage for the DP800, where the damage accumulation phase is prolonged. For DP1000 the damage nucleates only shortly before material failure. The material model is able to correctly predict the behaviour, while experimental analysis confirms the prediction via light optical and SEM metallography.

Stand der Untersuchungen zu Werkstoffanforderungen hochfester Stähle S700 bis S960 – FOSTA‐Forschungsverbund HOCHFEST

“…Im Bai‐Wierzbicki‐Modell ist zusätzlich ein Kriterium zur probabilistischen Spaltbruchmodellierung eingefügt. Das Modell zur Beschreibung des duktilen Verhaltens bei Raumtemperatur und der duktilen Schädigung wird als MBW‐np‐19 bezeichnet und kann neben der Modellierung von Schädigung und Versagen auch für nicht proportionale Lastpfade verwendet werden [20]. Das Modell kann je nach Material auch ungekoppelt eingesetzt werden, d. h. ohne die Modellierung des Einflusses von Schädigung auf das Kraftniveau.…”

A new method for the toughness assessment of mobile crane components based on damage mechanics

“…However, according to the research of Bai and Wierzbicki, stress triaxiality and Lode angle should be taken into account to define the equivalent strain to ductile fracture [16]. The modified Bai-Wierzbicki model (MBW model) in its most recent formulation [17][18][19][20] derives the possible activation of the cleavage or ductile fracture mechanism based on local stress variables, where both stress-and strain-based criteria are used. To quantify these local parameters, the model is embedded in a numerical stress analysis based on FEM.…”

“…A load cell in the eight years have resulted in a far more complex model formulation that allows features such as non-proportional strain paths or the concurrence between cleavage and ductile fracture mechanisms to be considered. The most recent model release for ductile fracture [19,20] is therefore briefly described in the following. By relying on the invariants of the stress tensor (I 1 , I 2 , I 3 ) and the deviatoric stress tensor (J 1 , J 2 , J 3 ), it uses the stress triaxiality h (Eq.…”

3D Multilevel Modeling of Surface Roughness Influences on Hole Expansion Ratios

“…Therefore, attempts are made to replace these experiments by meaningful numerical simulations, in which typically damage mechanics models are applied to allow for predicting damage and fracture. Recently, the modified Bai-Wierzbicki (MBW) model [3,4,6] has been presented and proven able to provide accurate damage and fracture predictions even for complex strain paths. The MBW model is a macroscopic phenomenological ductile damage mechanics model.…”