Jun 20, 2013 - ANSYS Mechanical and Mechanical APDL use the. – Domain Integral method to calculate J-integral. – Interaction Integral method to extract the ...
2013 UGMs – ANSYS
Fracture Mechanics in ANSYS Mechanical R14.5 1
© 2013 ANSYS, Inc.
June 20, 2013
ANSYS Confidential
Introduction Traditional structural design uses a strength‐of‐material approach to assess structural integrity – does not consider the effect of flaws which can significantly degrade structural integrity
Using fracture mechanics methods that include the effect of flaws is becoming common practice in many industries
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© 2013 ANSYS, Inc.
June 20, 2013
ANSYS Confidential
Fracture Mechanics Approach Fracture mechanics describe crack behavior using concepts from both applied mechanics and material science – cracks propagate by the combined effect of stress and flaws
Commonly represented using one of 3 fracture parameters – stress intensity factors (K or SIFs) • characterizes stress state near crack tip
– J‐Integral (J or JINT) • contour‐integral around the crack tip that is equal to the change in potential energy due to incremental crack advance
– energy release rate (G) • energy required to create newly formed crack surfaces
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© 2013 ANSYS, Inc.
June 20, 2013
ANSYS Confidential
ANSYS Fracture Mechanics Capabilities ANSYS Mechanical and Mechanical APDL use the – Domain Integral method to calculate J‐integral – Interaction Integral method to extract the stress intensity factors (SIFs) from the J‐integral results • single mode and mixed‐mode – Virtual Crack Closure Technique (VCCT) to characterize the energy release rate (G) (e.g. delamination of composite structures) • only method applicable to non‐isotropic materials
Domain Integral approach calculates J‐integral at radial contours from crack tip – J‐integral is path independent – results should converge within a few contours
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© 2013 ANSYS, Inc.
June 20, 2013
ANSYS Confidential
R14.0 ANSYS Mechanical Procedure 1.
Construct FE mesh with embedded crack(s)
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Apply boundary conditions
3.
Issue MAPDL CINT commands in Command Objects – CINT is a /SOLU module command
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Solve
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Post‐process by issuing MAPDL /POST1 commands in Command Objects
ANSYS Mechanical R14.5 includes powerful new fracture mechanics features that make this process easier to use, more robust, and more efficient
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© 2013 ANSYS, Inc.
June 20, 2013
ANSYS Confidential
New Mechanical R14.5 Fracture Features Crack Object provides automated tools for embedding crack(s) into existing meshes – significant ease‐of‐use enhancement • creating well‐shaped, efficient cracked meshes can be difficult • reduces need to use tools like DM to create crack(s) in solid model
Pre‐Meshed Crack Object enables fracture mechanics calculations to be performed on cracked meshes directly within the Mechanical interface – eliminates need to use Command Objects to access the MAPDL CINT command
Fracture Tool enables post‐processing of fracture mechanics directly within the Mechanical interface – eliminates need to use Command Objects to access MAPDL /POST1 commands 6
© 2013 ANSYS, Inc.
June 20, 2013
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Fracture Folder Fracture Folder must be first inserted from the Model toolbar – Crack and Pre‐Meshed Crack Objects can then be accessed – new in R14.5
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© 2013 ANSYS, Inc.
June 20, 2013
ANSYS Confidential
Fracture Solver Control Setting To compute fracture parameters for all cracks defined under the Fracture folder, set the “Fracture” solver control to “ON” – located under Solver Controls on the Analysis Settings – inserts appropriate MAPDL CINT commands into the ds.dat
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© 2013 ANSYS, Inc.
June 20, 2013
ANSYS Confidential
Crack Object Crack Object inserts a semi‐elliptical crack into an existing non‐ cracked mesh – eliminates need to manually embed semi‐elliptical crack(s) in solid model – robust set of tools for creating well‐shaped mesh in cracked region – automatically connects cracked region to full model
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© 2013 ANSYS, Inc.
June 20, 2013
ANSYS Confidential
Using Crack Object • • • • • • • • • • •
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Create full model with non‐cracked mesh Insert Fracture Folder Insert Crack Object under Fracture Folder Identify crack location with coordinate system Specify major and minor radii for crack Specify any optional data for cracked region Generate mesh in Crack Object Set Fracture solver control to “ON” Solve Insert Fracture Tool Post‐process fracture results
© 2013 ANSYS, Inc.
June 20, 2013
ANSYS Confidential
Crack Object Actions To create cracked mesh, issue “Generate All Crack Meshes” under the Fracture Folder – – – – –
clears the base mesh from the Fracture Affected Zone and Buffer Zone inserts cracked mesh template inside the Fracture Affected Zone creates radial patterned mesh around crack creates mesh in remainder of Fracture Affected Zone creates mesh in Buffer Zone • region between the Fracture Affected Zone and the base mesh – connects Fracture Affected Zone mesh to Buffer Zone mesh using MPC contact
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© 2013 ANSYS, Inc.
June 20, 2013
ANSYS Confidential
Inputs for Crack Object
Only Major and Minor radii are required
Optional input data available to control crack mesh: – – – – – – – 12
© 2013 ANSYS, Inc.
June 20, 2013
largest contour radius number of circumferential divisions number of mesh contours number of crack front divisions number of solution contours size of buffer zone Named Selections to be created ANSYS Confidential
Crack Object – Impeller Example uncracked mesh
solid model
cracked mesh
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© 2013 ANSYS, Inc.
June 20, 2013
ANSYS Confidential
Pre‐Meshed Crack Object Pre‐Meshed Crack Object performs fracture mechanics calculations on imported meshes with existing cracks Enables fracture mechanics calculations to be performed on cracks of any shape Can be used to assess cracks in 2D models – mesh connections can be used to close one side of the crack Eliminates need to issue MAPDL CINT commands from within Command Objects Allows use of Fracture Tool for post‐processing within Mechanical 14
© 2013 ANSYS, Inc.
June 20, 2013
ANSYS Confidential
Using Pre‐Meshed Crack Object • • • • • • •
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Create full FE model with embedded crack(s) Insert Fracture Folder Insert Pre‐Meshed Crack Object Set Fracture solver control to “ON” Solve Insert Fracture Tool Post‐process fracture results
© 2013 ANSYS, Inc.
June 20, 2013
ANSYS Confidential
Fatigue Tool Fracture Tool is used to post‐process fracture mechanics directly within the Mechanical interface – eliminates need to use Command Objects to access MAPDL /POST1 commands
Solution Branch > RMB > Insert “Fracture Tool” > pick result type
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© 2013 ANSYS, Inc.
June 20, 2013
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Post Processing of Fracture Results Fracture results can be plotted, graphed, and/or listed – X axis of graph and length in table is the distance along the crack front – tabular results can be exported to text files or xls file
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© 2013 ANSYS, Inc.
June 20, 2013
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Crack Object Example Create full structural model – solid model, mesh, boundary conditions, etc. – create coordinate system at crack center
Insert “Fracture” folder Insert Crack Object under Fracture Folder
Set Fracture solver control to ON 18
© 2013 ANSYS, Inc.
June 20, 2013
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Crack Object Example Specify Crack Object details Generate cracked mesh Solve Insert Fracture Tool Post‐process
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© 2013 ANSYS, Inc.
June 20, 2013
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Pre‐Meshed Crack Example Import mesh with embedded flat, through‐wall crack from MAPDL using CDB file and FE Modeler Import model from FE Modeler into Mechanical
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© 2013 ANSYS, Inc.
June 20, 2013
ANSYS Confidential
Pre‐Meshed Crack Example Specify crack coordinate system and Named Selection containing crack front nodes Insert “Fracture” folder Insert Pre‐Meshed Crack Object under Fracture Folder
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© 2013 ANSYS, Inc.
June 20, 2013
ANSYS Confidential
Pre‐Meshed Crack Example Set Fracture solver control to ON Solve Insert Fracture Tool and post‐process
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© 2013 ANSYS, Inc.
June 20, 2013
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Future Enhancements Extend crack creation capabilities for additional crack types and arbitrary crack shapes •
•
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Additional Crack Types
Corner cracks
Edge cracks
Embedded cracks
Surface cracks (e.g. non‐elliptical surface cracks)
Arbitrary Crack Shapes
Non‐elliptical cracks
Non‐planar cracks
© 2013 ANSYS, Inc.
June 20, 2013
ANSYS Confidential
