Just about every product has several parts connected by bolts, screws, or pins. One assembly task often calls for sizing bolts and finding the effect of the connection on the whole assembly. Analysis experts generally acknowledge that it's difficult to model bolt behavior in a finite-element simulation, as indicated in several recent articles (MACHINE DESIGN, December 12,2004 and February 3,2005). "Simulating bolts in finite-element assemblies requires a great deal of knowledge and time," says Ramesh Ramalingam, a product manager with Solid-Work's Cosmos division in Los Angeles. "Those doing analyses are asked to do more and so need help with these problems. The good news is that the latest simulation software handles a lot of the former complexity. For example, rather than having to manually define bolt behavior, software such as Cosmos, has virtual-bolt connectors that make it easier and faster to analyze assemblies that contain bolts and screws. Virtual connections consider the effects of bolt pretension and shear, especially when the bolt diameter is the same as the bolt-hole diameter in the flange. Users can also find axial and shear reactions at the bolt to determine its size, or whether clamping force generated by the bolt and the tightening torque is sufficient to overcome external loads," says Ramalingam. The concepts behind virtual-bolt connectors are the same as those used by dedicated analysts. "The program takes no shortcuts in accuracy. Rather, it offers a simple interface, calling for straightforward input, while handling many tasks in software that were performed by analysts," he adds.
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