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A discussion of the impact of a 2.5 mph bumper standard on aluminum sheet and extruded bumpers is presented. Information is presented on energy management systems, bumper shape, and dentability. This information can be used to determine whether a sheet or extruded bumper is the most efficient for a particular application.

An evolutionary state variable model is used to predict failure in sheet forming. The development of damage in aluminum sheet is characterized using Bammann's plasticity model. Simulations are carried out with the commercial code LS-Dyna3D. Using the limiting dome height test as an example, the prediction of failure in straining states of draw, plane strain, and stretch is made for AA 6111-T4 sheet. The location of failure and associated major/minor strains are contrasted with experimental forming limit curves. As a further example, the drawing of a square cup from a 5000 series alloy blank is simulated and compared with experimental data. The simulations accurately predict the location of failure and show limit strains which compare favorably with experiment. The damage variable provides a method for predicting the location and time of failure in a framework that accommodates general straining paths.

Aluminum use for automotive body sheet applications is growing. This growth requires improvement of related joining processes and technology. Resistance spot welding will be one of the major joining technologies used in assembling automobiles. When spot welding aluminum, electrode tip life is limited by tip erosion and pickup of aluminum on the tip. Increasing weld current improves weld strength (to a limit), however this reduces tip life. This study examines the control variables in the resistance spot welding process and offers an improved weld schedule to achieve desired weld properties while maximizing tip life. First, the limits of weld parameters where satisfactory welds can be obtained are determined. A window of tip force and weld current is established for a given material and tip geometry. These limits are used to optimize the weld schedule in terms of tip life. Spot welds fail on the basis of shear strength, button diameter or peel rate.

Tailored blanks have been produced by a variety of welding processes. Currently, laser welding and mash seam welding are commonly used to produce steel blanks for automotive stampings. Because of the high electrical and thermal conductivity of aluminum, mash seam welding is generally not suitable for this application. Laser welding is currently in the developmental stage for welding aluminum. Reynolds Metals Company is investigating another existing welding technology -- Gas Tungsten Arc Welding (GTAW)--for welding of aluminum tailored blanks. Using the GTAW process, production weld speeds approximating those of laser systems can be obtained. Additionally, good control of weld geometry and quality can be easily attained. This study focuses on GTA welding process parameters for joining various alloys, tempers, and thickness of aluminum. Additionally, performance of welded joints in terms of strength, ductility, and formability are discussed.

Recent trends in the automotive industry toward improving fuel economy have led to the conversion of many steel applications to aluminum. The use of aluminum reduces vehicle weight while allowing the automaker to continue to use traditional fabricating methods. The primary joining technique used for steel sheet components has been resistance spot welding. While this technique is currently used to join many aluminum components, automakers are reluctant to specify this joining technique due to capital equipment cost, electrode tip life, or reliability concerns. Several alternate joining techniques have been investigated and used. These include adhesive bonding, weld bonding, resistance welding with arc cleaning (1, 2)*, GMA spot welding, clinching, and riveting. Recently, a method of riveting components without prepunching or pre-drilling holes has generated a large amount of interest. This paper is a review of this riveting technique.

One joining technique that is receiving increased attention is mechanical fastening with a steel self-piercing rivet. The use of steel rivets in direct contact with aluminum components raises questions concerning galvanic corrosion. To determine if a corrosion problem exists, aluminum samples were joined by two processes--resistance spot welding and steel self-piercing rivets. Replicate samples using two aluminum alloys were tested for 90 days by alternate immersion in 3.5% NaCl water solution. After alternate immersion exposure, the integrity of the joint was evaluated by shear testing. Joint shear strengths and the metallographic corrosion evaluations are presented in this paper.

The aluminum alloy 2036 is presently being used in the production of automotive body panels. In the study presented, specimens of 2036-T4 with varying crystallographic textures were subjected to tensile testing and limiting dome height (LDH) evaluations in an effort to gauge the effect of texture on formability and stamping performance. To describe the texture, relative magnitudes of ideal texture components were derived from the orientation distribution function. Finite element analysis was used to study the effect of anisotropic properties due to texture on thinning in the LDH test. The impact of textural character on formability is discussed.