Abstract: Analyzing the mechanical state of an assembly modeled by a computer aided design system includes generating a model of a fastener and a part of the assembly. The fastener model includes an engaging region and the part model includes a receiving region to fastenably receive the engaging region. The fastener and the part are each represented by finite element representations that include elastically interconnected nodes. A tightening mesh interconnecting nodes of the engaging region and nodes of the receiving region is generated and a force applied between the nodes of the engaging and receiving region is determined based on a pre-tension force occurring upon engaging the engaging region with the receiving region.