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In vehicle crash events there is the potential for fracture to occur at the processed edges of structural components. The ability to avoid these types of fractures is desired in order to minimize intrusion and optimize energy absorption. However, the prediction of edge cracking is complicated by the fact that conventional tensile testing can provide insufficient data in regards to the local fracture behavior of advanced high strength steels. Fracture prediction is also made difficult because there can be inadequate data on how the cutting processes used for hole piercing and blanking affect the edge condition. In order to address these challenges, research was undertaken to analyze edge fracture in simple test pieces configured with side notches and center holes. Test specimens were made from a number of advanced high strength steels including 590R (C-Mn), 780T (TRIP), 980Y (dual phase) and hot stamp 1500 (martensitic). Edges were prepared by three different cutting processes: shearing, laser, and water jet ablation. The specimens were pulled to failure and local fracture strains were measured by digital image correlation. Component level tests were also done on simple hat sections that featured a notch cut into the flange and side wall by either water jet or punching. These hat sections were made from select steel grades and were deformed in a three-point bend crush mode to initiate failure at the notch. The results indicate that edge fracture in high strength steels is highly influenced by both edge condition and specimen geometry. In addition, it was concluded that certain material grades can be more notch or punch sensitive than others depending on their metallurgical structure.A prime example of this type of complication is the possibility for AHSS components to fracture at cut edges during crash deformation. This susceptibility can evolve from the limited ductility of the steel, the pre-existing damage from the edge cutting process, and the geometrical stress effect of the feature itself. The potential for edge fracture can be a consideration when developing body structures. If the cracking is not accounted for in the overall design, the load paths through the vehicle frame can be misdirected and the resultant intrusion levels can exceed target levels. It is beneficial if fracture prone areas can be identified in early design layouts through FEM modeling, as opposed to expensive and time-consuming crash tests. However, establishing the proper material data and analytic methods needed for edge fracture prediction has been one of the challenges in the advent of advanced high strength steel. The basic aim of this research was to broaden the understanding of edge cracking by analyzing how different material compositions, geometrical stress states, and edge process conditions affect fracture limits. The investigation promotes the use of new optical measurement techniques, such as digital image correlation (DIC), as an innovative method to acquire strain data in a localized area.

Aluminum alloys are increasingly used in automotive manufacturing to save weight. The drawability of Al 5182-O has been proven at room temperature (RT) and it is also shown that formability is further enhanced at elevated temperatures (ETs) in the range of 250–350 °C. A cost effective application of ET forming of Al alloys can be achieved using heated blank and cold dies (HB–CD). In this study, the material behavior of Al 5182-O is characterized using tensile test and viscous bulge test at RT. The nonisothermal finite element model (FEM) of deep drawing is developed using the commercial software pamstamp. Initially, deep drawing simulations and tests were carried out at RT using a 300 ton servo press, with a hydraulic cushion. The predictions with flow stress curves obtained from tensile and bulge tests were compared with experimental data. The effect of punch speed and temperature rise during forming at RT is investigated. The warm forming simulations were carried out by combining material data at ETs obtained from the literature. The coupled effects of sheet temperatures and punch speeds are investigated through the finite element analysis (FEA) to provide guidelines for ET stamping of Al 5182-O.

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