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Modeling Bolts in ADINA

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Bolts are an integral part of engineering designs, and bolted structures can show a complex mechanical behavior. Not long ago, bolted structural parts were commonly treated as rigidly connected. With recent advances in computer-aided modeling and finite element analysis, engineers can now get insight into bolted connections that was previously difficult to obtain. Engineers can ask questions regarding, e.g., the bolt forces required to prevent leaking of fluid, the frequencies of a bolted structure when contact and friction play an important role, and the contribution of the bolted connections to noise and vibration. Also, there are often many bolts in assemblies that need to be tightened in a certain sequence. With the practical requirements of today’s design engineers in view, the bolt modeling capability in ADINA allows bolt tightening specified either by a force value or by a bolt shortening. The program allows bolts to be tightened in a specified sequence in order to model the actual assemblage process. To illustrate the ADINA bolt option, we present a typical bolt-type problem, a mount of an axle used in heavy machinery (courtesy of John Deere). A panoramic view of the assembly is shown in the movie above. 10-node tetrahedral elements are used to model the bulky parts, 8-node shell elements are used to model the frame, and 3D contact surfaces model the contact in the bolted parts. The entire model (shown in the movie above) has over 2.5 million degrees of freedom. About 40 bolts are tightened in a sequence using 25 steps with about 5 Newton-Raphson iterations per step. The band plots in the Figure below show some results.

Effective stress band plotsFigure 1:  Effective stress band plots after step 1(left) and step 25 (right)

The ADINA solution time per step is only about 12 minutes (elapsed time) on a quad-core PC, which is remarkable for the size of the model. Such performance is possible due to the ADINA 3D iterative solver, which can handle not only 3D solid elements but also shell and other structural elements, and contact conditions. The effective modeling of bolts in linear and nonlinear solutions, including frequency analyses, is clearly an important feature in general CAE and in the use of ADINA. Keywords: Bolt model, bolt element, contact, friction, tightening, iterative solver, axle, mount, assemblies

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