chicago comprehensive guide to bolt modeling in ansys 15 0
DESCRIPTION
Bolt modeling simplifications and good pratices form mechanical simulation.Introduction• Bolt Modeling- Bolt Modeling Method 1 – 3D bolt representation- Bolt Modeling Method 2 – 3D bolt representation- Bolt Modeling Method 3 – bolt thread contact- Bolt Modeling Method 4 – bolt thread contact- Bolt Modeling Method 5 – screw joint- Bolt Modeling Method 6 – line body representation- Bolt Modeling Method 7 – line body representation- Bolt Modeling Method 8 – beam connection• Result ComparisonTRANSCRIPT
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2011 ANSYS, Inc. May 28, 2014 1
An overview of methods for modelling bolts in ANSYS V15
Dragana Jandric ANSYS Inc Technical Support Engineer
Presented at the 2014 ANSYS Regional Conference Chicago May 23, 2014
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2011 ANSYS, Inc. May 28, 2014 2
Introduction
Bolt Modeling - Bolt Modeling Method 1 3D bolt representation
- Bolt Modeling Method 2 3D bolt representation
- Bolt Modeling Method 3 bolt thread contact
- Bolt Modeling Method 4 bolt thread contact
- Bolt Modeling Method 5 screw joint
- Bolt Modeling Method 6 line body representation
- Bolt Modeling Method 7 line body representation
- Bolt Modeling Method 8 beam connection
Result Comparison
Summary
Outline
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2011 ANSYS, Inc. May 28, 2014 3
Bolted connections are common to many industries
Basic requirements of a bolted connections are:
Bolt should transfer the load realistically across the connecting elements
Bolt must have adequate strength
Joint must remain intact
Connection must have adequate fatigue and fraction life
Bolted analysis is no different than any other FEA calculation
This presentation shows different approaches of modeling bolted connection using full 3D models to beam models
It also explores examples and best practices and explains enhancements in ANSYS v15
Introduction
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2011 ANSYS, Inc. May 28, 2014 6
To demonstrate different ways to model bolts, a simple eight bolt flange is taken. In the following slides following aspects will be considered:
Geometry Meshing Contact Pre-tension loading Post processing
Bolt modeling
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2011 ANSYS, Inc. May 28, 2014 7
Bolt modeling
Bolt can be modeled as:
- Solid body - Line body - Beam connection
Solid Body + Most accurate + All contact details available + Easy post-processing - Geometry preparation - Mesh refinement - High computational time
Line Body + Easy to set up + Low computational time + Some post-processing tools - Creating line bodies - No contact detail - No stress detail in flange
Beam Connection + Easy to set up + Low computational time + No geometry required - No stress detail in flange - No contact detail - APDL post-processing
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2011 ANSYS, Inc. May 28, 2014 8
Approach to modelling the bolts usually involve making engineering decisions about the following:
Prepare geometry
Bolt and flange
Mesh
Minimum DOF for best representation
Consider contact areas for load transfer/stress
Hex / tet
Three step analysis:
Step 1: preload by load or adjustment
Step 2: fix the pretension, release any temporary restraining boundary conditions
Step 3: Apply in-service loads
Model and analysis considerations
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2011 ANSYS, Inc. May 28, 2014 9
Eight sectors, each has a different method of modelling the bolt
Upper / lower flanges are multi-body, sweep-able parts
All contacts are asymmetric & bonded
Analysis settings:
Upper / lower flanges fixed at pipe OD
2 step (load/lock ), linear analysis
500N pre-load to all bolts
Overview of model
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2011 ANSYS, Inc. May 28, 2014 10
Key features of this approach:
No/very little geometry preparation
Full thread on bolt and nut
Good geometric representation of stiffness of bolt/nut will be captured if mesh is dense enough
Contact areas give accurate representation of bolt head and nut contact area to flange
Most cases will produce a tetrahedral mesh, check element quality
Bolt model 1:
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2011 ANSYS, Inc. May 28, 2014 11
Key features of this approach:
Some geometry preparation, threads removed on bolt and nut
Care should be taken not to alter bolt shank stiffness as this will affect bolt deflection and load transfer in the system during pre-tension and in-service loading
Contact areas give accurate representation of bolt head and nut contact area to flange
Load between bolt and nut is transferred via bonded contact.
Most cases will produce a tetrahedral mesh, check element quality
Bolt model 2:
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Key features of this approach:
Geometry same as bolt model 2
New V15 bolt thread contact applied (recommended 4 elements span 1 thread width)
Contact sizing option to increase number of elements in thread area
Contact results show helical load transfer at threads
Bolt model 3:
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Key features of this approach:
Significant amount of geometry preparation on bolt and nut
De-feature, respecting size of contact area under bolt head/nut and bolt shank diameter
Decompose to sweep-able bodies
Multi-body back together
Prepare 1 fastener and use pattern to replace others
Can take quite a few mesh controls to get a good quality mesh
Bodies are modified to mesh them with hex mesh.
New V15 bolt thread contact applied (recommended 4 elements span 1 thread width)
Bolt model 4:
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2011 ANSYS, Inc. May 28, 2014 14
Key features of this approach:
Geometry and mesh same as bolt 4
Bolt thread contact replaced with a cylindrical joint
APDL commands to redefine joint as a screw joint
Bolt model 5:
keyo,_jid,1,17 sectype,_jid,joint,screw,_wbjoint pi=acos(-1) secjoin,,12 pas=1 secjoin,pitch,(pas/2/pi)
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2011 ANSYS, Inc. May 28, 2014 15
Key features of this approach:
Geometry preparation
Bolt/nut geometry replaced with a line body
Line body meshed as beam elements, model size significantly reduced
Contact, end of bolt to cylindrical edge of bolt hole, MPC couple U-Rot inside pinball, note: for edge contacts WB automatically extends spider out 1 element for load transfer
Bolt model 6: