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Technical Paper

A Parametric Design and Formability Study of Boron Steel Bumper Beams

Among the various high strength steels available today, boron steels are finding increasing applications in bumper beams and other crash resistant structures, primarily for their high strength. However, to overcome the forming difficulty at room temperature and to achieve the microstructural changes needed for high strength, manufacturing of boron steel parts is done under hot forming conditions. In this study, the effect of three principal bumper design parameters, namely depth, thickness and corner radius on the formability of a hat section bumper beam was considered. Using a forming simulation program, 27 different combinations of these three design parameters were examined for forming limits, failure types and failure locations. The bumper beams were also examined for energy absorption in pendulum impact tests. Recommendations are made for the design of boron steel bumper beams based on both impact energy absorption and formability.
Technical Paper

Switching Losses in the Rotor of the Field Regulated Reluctance Machine

The field regulated reluctance machine is perspective for automotive transport electric drives. In this machine, the switching of a stator current is done in function of a rotor position. The massive salient rotor of the electric machine does not contain windings. The stator is fulfilled in the body and iron of serial ac induction motor. The stator winding sections, which conductors lay above between rotor poles intervals, serve as a excitation winding, and others sections, which conductors lay above rotor poles, the role of a armature winding. In most cases, the optimal winding current waveform is distinct from the sine waveform. For a case of use separate current sources for each phase, the ideal is rectangular waveform. At the rotation of the motor, the each stator section winding pass from a zone of “excitation” to a zone of “armature”. The stator has finite number of phases.
Technical Paper

A Fatigue Prediction Method for Spot Welded Joints

Generally linear finite element analysis (FEA) is used to predict fatigue life of spot welded joints in a vehicle body structure. Therefore, the effect of plastic deformation at the vicinity of the spot welded joints is not included on fatigue prediction. This study introduces a simple technique to include the plastic deformation effect without performing elastic-plastic finite element analysis. The S-N curve obtained from fatigue test results is modified to consider this effect. Tensile strength test results of spot welded joint specimens were utilized to find the load range for FEA equivalent to the applied load range for fatigue tests. To demonstrate the proposed approach, fatigue test results of advanced high strength steels (AHSS) for lap-shear and coach peel specimens were used. Both the specimen types were tested at various constant amplitudes with the load ratios of R=0.1 and 0.3.
Technical Paper

Application of Fatigue Life Prediction Methods for GMAW Joints in Vehicle Structures and Frames

In the North American automotive industry, various advanced high strength steels (AHSS) are used to lighten vehicle structures, improve safety performance and fuel economy, and reduce harmful emissions. Relatively thick gages of AHSS are commonly joined to conventional high strength steels and/or mild steels using Gas Metal Arc Welding (GMAW) in the current generation body-in-white structures. Additionally, fatigue failures are most likely to occur at joints subjected to a variety of different loadings. It is therefore critical that automotive engineers need to understand the fatigue characteristics of welded joints. The Sheet Steel Fatigue Committee of the Auto/Steel Partnership (A/S-P) completed a comprehensive fatigue study on GMAW joints of both AHSS and conventional sheet steels including: DP590 GA, SAE 1008, HSLA HR 420, DP 600 HR, Boron, DQSK, TRIP 780 GI, and DP780 GI steels.
Journal Article

The Effect of Welding Dimensional Variability on the Fatigue Life of Gas Metal Arc Welded Joints

Gas Metal Arc Welding (GMAW) is widely employed for joining relatively thick sheet steels in automotive body-in-white structures and frames. The GMAW process is very flexible for various joint geometries and has relatively high welding speed. However, fatigue failures can occur at welded joints subjected to various types of loads. Thus, vehicle design engineers need to understand the fatigue characteristics of welded joints produced by GMAW. Currently, automotive structures employ various advanced high strength steels (AHSS) such as dual-phase (DP) and transformation-induced plasticity (TRIP) steels to produce lighter vehicle structures with improved safety performance and fuel economy, and reduced harmful emissions. Relatively thick gages of AHSS are commonly joined to conventional high strength steels and/or mild steels using GMAW in current body-in-white structures and frames.