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Published byToby Hodges Modified over 9 years ago
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Abstract/Objectives Better understand the effects of typical GD&T variations on Bolt Stresses in Torque Carrying Bolted Flanges Create Trend Curves for Stress vs. GD&T deviation for a given Flange Configuration – Tolerances to be studied are Hole Size and Bolt Hole True Position Flange Config to be Studied 2 shaft members Bolted w/ 8 bolts Snapped to enforce shaft alignment
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Method (Overall) Various Geometry Cases were built in order to create an array of results for the two tolerance conditions – Baseline (nominal) to determine stress/load concentrations against – 4 Hole Diameter tolerance models with tolerances ranging from 0.001” - 0.004” – 4 Hole True Position tolerance models with tolerances ranging from 0.001” - 0.004” Stress/Load Concentrations Determined by finding the Ratio of Stresses/Loads between the baseline case and tolerance case in question Hole DiameterTrue Position
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Method (Modeling) Solid Geometry was built in CAD (Unigraphics) No Symmetry was used, a full 360 FEA model was built in order to: – Avoid Over-Constraint of shafts due to symmetry boundary constraints – Be able to model the worst case condition, i.e. one hole at the worst tolerance condition instead of some fraction of holes at max tolerance Cross Section of Flange Assembly w/ BC’s3D CAD Model
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Method (Pre-Processing) 3D FEA Mesh and Boundary Conditions Created in Ansys – All solids were meshed with 8 noded bricks (solid 45’s) – Most contacts modeled as surface to surface, one side of the bolt to flange face was modeled bonded in order to add stability to the model – Preload was applied to the bolts, a torque load was applied to one shaft’s free end, while the other shaft’s free end was locked down in all degrees of freedom – Mesh was kept as constant as possible between the various models in order to improve results consistency Assembly Cut-AwayHole Mesh Bolt Mesh
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Method (Solving) Model was Solved in Ansys An Assembly Step (Bolt Pre-Load Only) and a Running Step (Pre-load and Shaft Torque Applied) – Bolt pre-loaded by modeling an interference between the bolt head and shaft flange – Torque Applied by applying discreet circumferential forces to the nodes on the free end of shaft 2 (the sum of these moments adding to the desired total torque) Hoop Displacement (Baseline)Hoop Displacement (Hole+.002)
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Method (Post-Processing) Tensile Stresses (S1 and Von-Mises) were quoted from the critical bolt’s shank on the free side (side w/o bonded contact) Max Bearing stress (S3) and Shear Load Summations were pulled from the loaded side of the critical bolt’s free shank Bearing Stress Max Running Tensile Stress Max Von-Mises Stress Bearing Stress w/ Nodal Reaction Forces
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Results (Hole Diameter) Linear stress/load increases relative to Applied Tolerance
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Results (Hole True Position) Somewhat Linear stress/load increases relative to Applied Tolerance
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Results (Verification) A mesh Sensitivity Study was performed in order to understand what mesh density affects may be affecting the solution – Bolt Element size was Doubled (from 0.025” edge length to 0.050” edge length) in the baseline model and the True Position 0.004” model The large change in Mesh Density had a relatively small affect on the results – Coarse Model Stress/Load concentrations dropped by a delta of 10% - 14% relative to a 100% increase in element size Fine Bolt Mesh Coarse Bolt Mesh
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