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Technical Paper

Crash Performances of Advanced High Strength Steels of DP780, TRIP780 and DP980

Advanced high strength steels (AHSS), such as dual phase (DP) and transformation induced plasticity (TRIP) steels, have been increasingly used in automotive industry. One of the major advantages of AHSS is the excellent crash energy absorption capability. In this study, crash performances were evaluated for four AHSS including DP980, DP780, TRIP780 (780T), and TRIP590 (590T). Axial crush and bending crush tests were performed to evaluate the material crush performance. High strain rate tension test results for those materials were also presented. FEA analyses with parameter sensitivity studies were conducted including strain rate sensitivity effect, part geometry effects, welding models and forming effects. Good correlations between simulation and experimental data were achieved.
Technical Paper

Hydroforming Performance of Laser Welded and Electric Resistance Welded High Strength Steel Tubes

The tubular hydroforming process has been used to reduce the weight of body-in-white (BIW) components by consolidating parts and eliminating weld flanges. Electric resistance welding (ERW) is the primary joining method for hydroformed tubes made of mild steels and some conventional high strength steels. Due to recently introduced Advanced High Strength Steels (AHSS), such as dual phase and TRIP steels, laser welded (LW) tubes have also been considered for hydroforming applications, particularly for thin-wall, large-diameter tubes. In this study, LW and ERW tubes are evaluated in a free-expansion hydroforming process using various strength steels including AHSS. The LW tubes made from both DP590 and TRIP590 steels were successfully hydroformed to a 64% expansion ratio(the maximum for the die cavity), an improved performance over the ERW TRIP590 tubes. The ERW tubes made from C-Mn440 and lower strength grades were also free-expansion hydroformed successfully to the maximum die cavity.
Technical Paper

Hydroforming Simulation for High Strength Steel Tubes

Tubular hydroforming is being used extensively for manufacturing various automotive structural parts due to its weight reduction and cost saving potentials. The use of a thin wall advanced high strength steel (AHSS) tube offers great potential to further expand hydroforming applications to upper body components. In this study, numerical and experimental investigations are conducted on a free expansion hydroforming case using various AHSS thin wall tubes. The results are also compared with tubes made from conventional steels and different tubing processes. The appropriate use of the forming limit in hydroforming is also discussed. In numerical study, a new simulation method is developed and validated to handle tube material properties input. Good correlations to the experimental data have been obtained. The new method only requires the flat sheet stress–strain curves as the basic material property. Tube and weld properties are modeled as a pre-strained tubular blank.