Characterization of stress–strain behavior of a cast TRIP steel under different biaxial planar load ratios

Bendability of advanced high strength steels—A new evaluation procedure

In this study, a model based on a strain localization level to overcome the shortcomings of the well-established Forming Limit Diagram (FLD) in predicting the physical phenomenon of necking is introduced. An optical measurement system was used to capture the strain history of the Nakazima experiment until rupture occurred. In order to measure the fracture strain more accurately, a further method is introduced, which is based on the microscopic measurements of ruptured regions. This model is validated using a 3-point bending test. The results show the ability of the method to predict failure under bending conditions as well. Additionally, failure is investigated based on the pressure sensitivity and the Lode dependency. The results show that the triaxiality at the failure point is independent of the loading path.

Modeling of localization and fracture phenomena in strain and stress space for sheet metal forming

Models and modelling for process limits in metal forming

Deep drawing simulations using the finite element method embedding a multi-level crystal plasticity constitutive law: Experimental verification and sensitivity analysis

The investigation of bendability of sheet metal alloys is of great importance for the evaluation of process robustness in production of hemmed sheet metal assemblies. Furthermore, material cracks due to bending can also occur at deep drawing operations. This contribution focuses on the experimental determination of material’s formability at deep drawing, the characterisation of bendability especially for hemming operations and the determination of formability under combined deep drawing and bending loads, respectively.

Investigation on the effect of curvature on forming limit prediction for aluminium sheet alloys

For characterising formability of sheet metal materials several testing methods have been developed during recent years. The most common way to estimate formability of sheet metal parts is the so called Forming Limit Diagram (FLD) method. But forming limits under bending cannot be described by the conventional FLC. This contribution reveals possibilities of an experimental characterisation of material’s bendability. Furthermore, an approach concerning the characterisation of formability under simultaneous drawing and bending for various sheet thicknesses is given.

Investigation on the effect of curvature and sheet thickness on forming limit prediction for aluminium sheet metal alloys

Kurzfassung Im vorliegenden Beitrag wird uber zwei neu entwickelte Prufverfahren berichtet, mit dem die Kantenrissempfindlichkeit von hochfesten Stahlblechwerkstoffen quantifiziert werden kann. Basierend auf konventionellen Biegetests wurde das neue Prufverfahren so modifiziert, dass eine maximal mogliche Kantenbelastung aufgebracht wird. Im Beitrag wird auf die standardisierten und genormten Werkstoffcharakterisierungmethoden und -prufverfahren eingegangen und es werden Prufverfahren vorgestellt, die eine Aussage uber die Biegbarkeit von hochfesten Stahlblechwerkstoffen uber deren Kantenrissempfindlichkeit vor allem liefern konnen.

Erweiterte Werkstoffprüfverfahren zur Charakterisierung von Leichtbaublechwerkstoffen im Hinblick auf die Kantenrisssensitivität

Hang-on parts of modern passenger cars such as doors and hoods are mainly manufactured by a two-step hemming process during assembly, whereby the edge of the already deep-drawn, blanked and flanged outer panel is further bent to a hem. This hem ties together outer and inner panel of hang-on part. Owing to the bending processes during hemming, large amounts of strain occur on the outer side of the hemming rope, causing local roughening of the formed sheet surface, which may become critical in terms of the quality of the coated component. In this study, the surface roughening during bending and hemming of a typical aluminum sheet material for hang-on parts is examined. In a first step, the roughening process is determined as a function of the bending angle and plastic strain during bending and hemming. Then hemming was further investigated to describe surface roughening as a function of the flanging radius and pre-strain level. The results of the plate bending test and hemming test at identical bending angles and plastic strain levels showed different levels of surface roughening, caused by the non-congruent size and local position of the forming zone in both bending methods.

Surface roughening of an aluminum 6016 alloy during bending and hemming

Dieser Beitrag zeigt auf Basis experimenteller Untersuchungen Einflusse dehnungsinduzierter Anderungen von Werkstoffkennwerten auf die Berechnung der Grenzformanderung und die Folgen fur sowohl ein- als auch mehrstufige Umformprozesse auf. Besonderes Augenmerk liegt dabei auf den Vorteilen dieser differenzierten Betrachtung gegenuber dem in der Praxis ublichen Stand der Technik.



Effect of strain dependent material properties on formability of sheet metals



This paper describes strain induced effects on the change of material properties. Because of these effects the calculation of forming limit curve changes, too. Special attention is given to the material property caused differences between one or more stepped forming operations with main advantages in comparison to the today’s common practice.

Manfred Sindel

Papers

Investigation on the effect of curvature on forming limit prediction for aluminium sheet alloys

Investigation on the effect of curvature and sheet thickness on forming limit prediction for aluminium sheet metal alloys

Erweiterte Werkstoffprüfverfahren zur Charakterisierung von Leichtbaublechwerkstoffen im Hinblick auf die Kantenrisssensitivität

Surface roughening of an aluminum 6016 alloy during bending and hemming

Einfluss dehnungsabhängiger Werkstoffeigenschaften auf die Umformbarkeit von Blechwerkstoffen