Dear Arthur,
Well, I understand that you are student, but not excuses, the use of engineering tools of Finite Element Analysis requires competence, anybody can use a CAD system to create a solid model of an engine, not need to be engineer, but FEA tools are powerful tools that requires experience & knowledge, and it is only a question of time ... years. Here you are some comments to your model:
1.- All the bolts (shanks, nut & washer) of your 3-D CAD model are meshed with solid tetrahedral elements, and used a surface-to-surface contact of NO PENETRATION between bolts & parts. Well, you may understand that surface-tu-surface contact avoid the penetration of wahser in nut, or washer & body, etc.., but do not prevent the separation between parts, then a singular matrix error will appear for sure!!. The problem is the approach used to model bolts AS SOLIDS: not, a better approach to model bolts is to use the Bolt Connection command. The Bolt Connection command automatically creates an element that represents the shank of the bolt and a pair of spider elements (RBE2/RBE3 NX Nastran rigid elements) that connect the ends of the element to the surrounding mesh. Please note:
• You can use the Circular Imprint command to define the surfaces around the bolt hole that are under the heads of the bolt and nut. By imprinting these surfaces, the legs of the spider elements that are created using the Bolt Connection command are automatically connected to all the nodes within the imprinted surfaces.
• With NX Nastran solver the elements representing the bolts are CBEAM or CBAR, then you can use the Bolt Pre-Load command for direct entry of bolt preload forces.
2.- You have prescribed EXTERNAL boundary conditions to the bolt solid faces of type "pinned". Not correct at all, you can´t prescribe external constraints to bolts, this should be done using "INTERNAL" 1-D connections that define relations of multi-point constraints (MPC) between components DOF. Well, these are the RBE2/RBE3 rigid elements available in NX NASTRAN, more easy & powerful, frequently used as spider elements: An R-type element is an element that imposes fixed constraints between components of motion at the grid points or scalar points to which they are connected. Thus, an R-type element is mathematically equivalent to one or more multipoint constraint equations. Each constraint equation expresses one dependent degree of freedom as a linear function of the independent degrees of freedom
in the following picture you have an example of using bolts in an assembly where an spider element is defined as a single core node that is connected to multiple leg nodes with rigid or constraint elements.
Hope it helps.
Best regards,
Blas.
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Blas Molero Hidalgo
Ingeniero Industrial
Director
IBERISA
48011 BILBAO (SPAIN)
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