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Weld Fatigue Analysis in ANSYS using ANSYS FatigueModule
Alexander Kielland platform accident during 1980
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Fatigue Analysis in ANSYS
Scope of presentation
ANSYS fatigue overview ANSYS nCode DesignLife
Fatigue module in ANSYS Workbench
ANSYS (classic) post1 Fatigue Module
ser ca cu a e a gue cr er a p o e us ng pos
Weld fatigue methods that can be related to WB Fatigue Module
Short notes on sub-modeling technique
Live demonstration of complete work flow from CAD to analysisresults using ANSYS WB Fatigue Module
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ANSYSnCode DesignLife
Integrated within ANSYS Workbench
environment to provide a leading solution for
advanced fatigue analysis.
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ANSYS Fatigue Module
Stress life fatigue evaluation
Strain life fatigue evaluation
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ANSYS post1 Fatigue Module
How ANSYS Calculates Fatigue
The ANSYS fatigue calculations rely on the ASME Boiler andPressure Vessel Code, Section III (and Section VIII, Division 2)for guidelines on range counting, simplified elastic-plastic
a aptations, an cumu ative atigue summation y Miner srule.
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User calculated fatigue criteria
User calculated fatigue criteria plotted using ANSYS post1
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Fatigue assessment of welds
There are a number of methods available for fatigue assessmentof welded joints
Nominal stress method
Fracture mechanics analysis
Effective Notch Method (notch stresses)
Can be used directly with ANSYS Fatigue Module when theappropriate fatigue data is input
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Fatigue assessment of welds
Effective notch stress method (R1MS)
This method consider the notch stresses in concentratedareas and require correct modeling of weld seam.
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Total stress Membrane Bending
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Non linear peak stress
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Fatigue assessment of welds
Effective notch stress method (R1MS)
For use with solid models only
Both weld root and weld toe is considered.
e met o s app ca e or p ate t c nesses arger t an mm
Misalignment, skewness of plates or other geometricimperfection must be modeled since it is not in the fatiguestrength class.
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Fatigue assessment of welds
Effective notch stress method (R1MS)
A radius of 1 mm is introduced at weld root or weld toeRadius = 1 mm
Max of principal stresses are used, but stresses should beperpendicular to the weld joint.
Fatigue evaluation is performed according to fatigue strengthclass FAT 225 according to IIW (International Institute ofWelding).
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Fatigue assessment of welds
Sub modeling technique
Effective Notch stress method require a fine mesh to capturethe notch peak stresses which makes it virtually impossible inmost practical situations to analyze large structures with alldetails required.
The solution to this is to use sub modeling technique where asmall but detailed model can use the results from a largemodel with a course mesh.
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Fatigue assessment of welds
Key points in sub modeling analysis
There is no need to know in advance if a sub model is required.
The geometry of the sub model must over lap the geometry ofthe global model.
Global modelSub model
Sub model &global model
shown together
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Fatigue assessment of welds
Workbench command objects and live demonstration
Sub modeling in ANSYS Classic environment is fairly straightforward but this capability is not implemented in WB yet, but caneasily be handled by a command object.
comman o ec s a sequence o ass c comman sthat are executed in sequence performing the tasks required.
The next demonstration will demonstrate the work flow fromCAD-model, preparation of analysis model including sub modeling
process and fatigue evaluation in the WorkBench Environment.
Influence of geometrical imperfection will be the object ofinterest in the demonstration.
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Live demo
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Live demo
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