Modeling of Bolt Joint Behavior of Cast Aluminum Alloy (A380-T5) by Coupling Creep and Plasticity in Finite Element Anal
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CAST aluminum alloy A380 is widely used in die casting for structural applications because of its excellent corrosion resistance and high strength-to-weight ratio. Like other aluminum alloys, however, A380 alloy also exhibits creep behavior when exposed to high temperature and load.[1–5] In major powertrain components such as engine blocks and automatic transmission cases, the operating temperatures can be as high as 250 C and 175 C, respectively.[6] The creep of aluminum alloys cannot be neglected in the head bolt joint design, because it can have a significant influence on the head bolt-load retention and thus engine performance. Creep is known as time-dependent deformation that occurs while the stress and temperature are kept constant. The existence of creep behavior in many metals and alloys is due to the influence of thermal activation on dislocation movement, which is a function of temperature and time.[7] Therefore, creep deformation is possible at all temperatures above absolute zero and becomes more significant at the higher temperatures. CHERNG-CHI CHANG, Staff Engineer, Engine CAE, and Q.G. WANG, Senior Materials Engineer, are with the Advanced Materials Group, Powertrain Engineering, General Motors Corporation, Pontiac, MI 48340. Contact e-mail: [email protected] This article is based on a presentation given in the symposium entitled ‘‘Simulation of Aluminum Shape Casting Processing: From Design to Mechanical Properties’’ which occurred March 12–16, 2006 during the TMS Annual Meeting in San Antonio, Texas under the auspices of the Computational Materials Science and Engineering Committee, the Process Modeling, Analysis and Control Committee, the Solidification Committee, the Mechanical Behavior of Materials Committee, and the Light Metal Division/Aluminum Committee. METALLURGICAL AND MATERIALS TRANSACTIONS B
In powertrain applications, components made of cast aluminum alloys are often assembled together with other stronger and stiffer materials such as steel and cast iron using steel bolts. In most cases, the bolt-load retention behavior in the assembled structure is dominated by the creep properties of cast aluminum components, such as engine blocks and cylinder heads.[1] The creep properties of cast aluminum alloys are strongly dependent upon the quality of castings. The greater the number of defects in the castings, the lower the tensile strength and creep properties. In this article, a model of the head bolt joint in a cast aluminum engine is used to simulate the bolt-load retention behavior of the engine under thermal cycle conditions using the finite element method. In the simulation, transient thermal analysis is performed first to calculate the metal temperature at the head bolt joint as a function of time during engine thermal cycling. The temperature is then translated into thermal loading in the subsequent structural analysis to calculate its effect on the bolt-load retention. The creep property of cast aluminum alloy A380-T5 is coupled with the plasticity of other metal components in th
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