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The risk of skid lines for Class A panels has to be assessed before releasing the die development for hard tooling. Criteria are needed to predict skid lines in the formability evaluation stage to avoid expensive changes to tooling and process for resolving skid line issue in production. In this study, criteria using three different measured parameters were developed and validated. A draw-stretch-draw (DSD) test procedure was developed to generate skid lines on lab samples for the physical evaluation. This was done using tooling with various die entry radii and different draw beads. The skid line severity of lab samples was rated by specialists in the inspection of automotive outer panel surface quality. The skid line rating was correlated with geometric measurements of the lab samples after the DSD test. The sensitivity of the appearance of skid lines to tooling and process parameter variations was identified.

Static and dynamic strength tests were performed on spot welded specimens made of dual-phase (DP) 780 and mild steels (DQSK). Lap-shear (LS) and cross-tension (CT) as well as a new mixed mode specimen were studied using MTS hydraulic universal testing machine for static tests and drop weight tower for dynamic tests. Three weld nugget sizes were made for each steel and CT and LS. DP780 with one weld size was also tested in mixed mode. Load and displacement as functions of time and fracture mode of the spot welds were recorded. Representative data are reported in this paper.

The fatigue performance of gas metal arc welding (GMAW) joints of advanced high strength steels (AHSS) are compared and analyzed. The steel studied included a number of different grades of AHSS and baseline mild steels: DP600, DP780, DP980, M130, M220, solution annealed boron steel, fully hardened boron steels, HSLA690 and DR210 (a mild steel). Fatigue testing was conducted under a number of nominal stress ranges to obtain the S/N curves of the weld joints. A two-phase analytical model is developed to predict the fatigue performance of AHSS welds. It was found that there are appreciable differences in the fatigue S/N curves among different AHSS joints made using the same welding practices, suggesting that the local microstructure in the weld toe and root region plays non-negligible role in the fatigue performance of AHSS welds.

Rollover crash is one of the important fatal crash modes in highway accidents. To protect occupant safety, the National Highway Traffic Safety Administration (NHTSA) has proposed a higher roof strength requirement in the upcoming new federal regulation. Meanwhile fuel efficiency and environmental friendliness demands that the safety cage design should have the minimum weight while providing the sufficient roof crush strength. These requirements pose a challenge to automotive design engineers. In this paper, Advanced High Strength Steels (AHSS) are introduced as an enabler to support this challenging task. The advantages of different types of AHSS for vehicle crashworthiness are presented. The criteria to select materials to improve the roof crush performance are discussed in detail.

Increasingly stringent requirements for auto safety, fuel consumption and environmental friendliness require lightweight and efficient vehicle designs. Advanced High Strength Steel (AHSS) tubes, including hydroformed tubular parts, are one of the key enablers used today. However, conventional tube joint designs, in general, are difficult to utilize with spot welding processes, a preferred and commonly used assembly process in North America's automotive industry. This is particularly true for light gauge tubes. In this paper, a new tube joint design is proposed and this new proposed joint is applicable for spot welding, adhesive bonding, and other joining methods. From a performance perspective, this joint design utilizes the advantages of the box joint, which distribute load more uniformly through the whole joint structure, and thus it provides better stiffness and stability to the vehicle structure.

Weldability is one of the manufacturing concerns for the application of newly developed advanced high strength steels, which have tensile strengths above 440 MPa. The successful utilization of advanced high strength steels depends on not only the steel product development, but also car body and structure design consideration and optimization. The resistance spot weldabilities of five different material combinations, DP500EG/CRS to DP500EG/CRS, DP500EG to Mild EG, and Mild EG/CRS to Mild EG/CRS, were investigated in this study. An optimized welding schedule was established for each material combination. In addition, a methodology to determine the minimum button size was proposed to accommodate the existing commercial practice in the resistance spot welding specifications. A brief review with simple failure mode estimation formulas of standard tensile shear and cross tension tests was also introduced and discussed to aid AHSS applications.