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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.

= +

Total stress Membrane Bending

+

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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