Robert R. Mayer

Crashworthiness of Aluminium Tubes; Part 1: Hydroforming at Different Corner‐Fill Radii and End Feeding Levels

The automotive industry, with an increasing demand to reduce vehicle weight through the adoption of lightweight materials, requires a search of efficient methods that suit these materials. One attractive concept is to use hydroforming of aluminium tubes. By using FE simulations, the process can be optimized to reduce the risk for failure while maintaining energy absorption and component integrity under crash conditions. It is important to capture the level of residual ductility after forming to allow proper design for crashworthiness. This paper presents numerical and experimental studies that have been carried out for high pressure hydroforming operations to study the influence of the tube corner radius, end feeding, material thinning, and work hardening in 76.2 mm diameter, 3 mm wall thickness AA5754 aluminium alloy tube. End feeding was used to increase the formability of the tubes. The influence of the end feed displacement versus tube forming pressure schedule was studied to optimize the forming process operation to reduce thinning. Validation of the numerical simulations was performed by comparison of the predicted strain distributions and thinning, with measured quantities. The effect of element formulation (thin shell versus solid elements) was also considered in the models.

Theoretical Effects of Hydroforming on Crashworthiness of Straight Sections

This paper considers the effect of hydroforming on the downstream crashworthiness for tubes. Three types of aluminum tubes were chosen as examples. Hydroforming will affect both strains and thickness of a tube, which will have opposite effects on the tubes mean crush load for crashworthiness. For hydroforming, the theoretical assumptions of no friction versus sticking friction will result in very different values for thickness, strains, stresses and mean loads when the corner radius is less than half the original tube radius. The theoretical effect on mean crush load can be as much as 25% different than without considering forming effects.Copyright

The Effect of Tempering (Artificial Aging) on the Crashworthiness Performance of Mass-Efficient Extruded Aluminum Structures

The effect of tempering (artificial aging) on the axial crush strength of four cell extruded rectangular aluminum alloy (AA) 6061 and 6063 tubes is developed in this report. Increasing the aging time from the press quenched condition increases the flow strength of the material and also increases the axial energy absorbed up to a point when the material showed fracture. Good predictions were made between experimental, theoretical, and numerical mean crush loads for various tempers of AA6061 and AA6063, except in the cases where a large amount of fracture was present. A recommended temper time of three hours was obtained for AA6063, with an increase in mean crush load of 60%. A recommended temper time of six hours was obtained for AA6061 with an increase in mean crush load of 40%. These results will be useful in future aluminum automotive body projects, both for their predictive capability, and for the temper recommendations.Copyright

Automated Finite Element Modeling of Tube Frame Structure Parametric Design

This research was intended to address the last step in the development of a tube-frame (termed B2B) parametric crashworthiness model - automated finite element modeling of the parametric design. We have added the generation of finite element models to the previously built Unigraphics Version 16 (UG V16) parametric model, so that finite element models could be quickly built. UG/WAVE was used to design the vehicle parametrically and UG/SCENARIO, a pre- and post-processor integrated in UG, was used to automatically construct the finite element mesh. We established the quality of the finite element meshes, generated for two new designs, which were created by changing overall dimensions of the vehicle. This was done using objective criteria for the finite element mesh. The component data was added to the automatically generated mesh, and the results from the crashworthiness analysis of this model compared favorably with the ‘hand-built’ model using traditional model building techniques. The results from this work will be useful in the development of the parametric design process. The use of automatically generated finite element meshes will also be useful for the automated evaluation of these parametric designs.© 2002 ASME

Crashworthiness Performance of Mass-Efficient Extruded Structures

Theoretical, numerical and experimental studies were conducted on the axial crushing behavior of traditional single-cell and innovative four-cell extrusions. Two commercial aluminum alloys, 6061 and 6063, both with two tempers (T4 and T6), were considered in the study. Testing coupons taken from the extrusions assessed the nonlinear material properties. A theoretical solution was available for the one-cell design, and was developed for the mean crushing force of the four-cell section. Numerical simulations were carried out using the explicit finite element code LS-DYNA. The aluminum alloy 6063T4 was found to absorb less energy than 6061T4, for both the one-cell and four-cell configurations. Both 6061 and 6063 in the T6 temper were found to have significant fracture in the experimental testing. Theoretical analysis and numerical simulations predicted a greater number of folds for the four-cell design, as compared to the one-cell design, and this was confirmed in the experiments. The theoretical improvement in energy absorption of 57% for the four-cell in comparison with the one-cell design was confirmed by experiment. The good agreement between the theoretical, numerical and experimental results allows confidence in the application of the theoretical and numerical tools for both single-cell and innovative four-cell extrusions. It was also demonstrated that these materials have very little dynamic strain rate effect.Copyright

Crashworthiness of Aluminium Tubes; Part 2: Improvement of Hydroforming Operation to Increase Absorption Energy

The motivation to reduce overall vehicle weight within the automotive sector drives the substitution of lightweight materials such as aluminium alloys for structural components. Such a substitution requires a significant amount of development to manufacture structurally parts such that the energy absorption characteristics are not sacrificed in the event of crash. The effects of the manufacturing processes on the crash performance of automotive structural components must be better understood to ensure improved crashworthiness. This paper presents results of an experimental and numerical investigation of the crash response and energy absorption properties of impacted hydroformed aluminium alloy tubes. Crash experiments on hydroformed tubes were performed using a deceleration sled test at the General Motors Technical Center. Results from axial crush testing showed that an important parameter that influences the energy absorption characteristics during crash was the thickness reduction caused by circumferential expansion of the tube during hydroforming. It was found that that the energy absorption decreased as the corner radius decreased, which results because of increased thinning. Sensitivity studies of end feeding parameters, such as end feed level and profile, were carried out to evaluate their impact on the energy absorption of the aluminium tubes.

S-Rail Sled Testing With Deceleration Sled

This paper considers the effects of rotary draw bending on structural crashworthiness. We impacted tested aluminum alloy tubes in s-rail bending, using either 2.0 mm or 3.5 mm thickness, and bend radius of either 152.4 mm or 191 mm. This report documents and summarizes the test setup using the GM R&D Deceleration Sled to achieve this, with emphasis on later correlation with numerical simulation. Theoretical and numerical analyses were used to help with design setup. Forces and moments found in the tests were very consistent, suggesting good test setup design. We also found that using the longest tube section at the constrained end prevents inboard rotation and contact between the two s-rails.© 2005 ASME

Math-Based Performance Evaluation of an Experimental Car: Frontal Impact Crashworthiness

This study used finite element models to assess potential benefits of selected unconventional features, implemented in an experimental car, for vehicle crashworthiness in frontal impact. These safety features include: structural energy-absorbing bumper, hood lockdown with optimized hood and extendable bumper. The A-pillar intrusion and the effective acceleration of the vehicle were used as the parameters for measuring frontal impact crashworthiness performance.Copyright

S-Rail Sled Testing of Rotary Draw Bent and Hydroformed Aluminum Tubes

This report provides detailed test results for the aluminum S-rail form & crash project. We considered the effect of rotary draw bending, and rotary draw bending plus hydroforming, and their effect on mean crush force, maximum crush force, and maximum bending moment for aluminum s-rails. The use of our sled test setup resulted in accurate, repeatable test results with no end plate welding. The R/D (center bend radius/tube diameter) used were 1.5, 2.0, and 2.5. Tubes were hydroformed from the circular shape into a square tube with rounded corners. Annealed tubes were used to isolate the forming effects to thickness changes alone.

Axial Crush Drop Tower Testing of Hydroformed Sections

This report summarizes the drop tower testing of initially circular straight aluminum tubes that had been hydroformed to a square section with round corners. Drop tower test conditions and test setup were determined for the AlMg3.5Mn aluminum alloy circular (76.2 mm outside diameter) tubes of either 2.0 or 3.5 mm thickness, which had been hydroformed into a square tube with corner radii of 38.1 (unformed), 33, 30, 27 and 24 mm. To initiate test setup, theoretical equations were found to be reasonable indicators of displacement and load cell requirements. Four-lobe symmetric modes were found for the square tubes, and three-lobe asymmetric modes for the circular tubes. The number of folding half-waves of seven for 3.5 mm tubes, and thirteen for 2 mm tubes, was generally overpredicted by theory. Aluminum end plates that were welded onto the tube ends allowed for fast test setup, but may have resulted in some sliding and tipping of the drop tower. The tubes were found to have decreasing average crush force with smaller corner radii, esp. for the 3.5 mm thick tubes.Copyright