2013 ugms ansys - · pdf file2013 ugms – ansys fracture mechanics in ansys mechanical...

$: 2013 UGMs ANSYS - · PDF file2013 UGMs – ANSYS Fracture Mechanics in ANSYS Mechanical R14.5 . ... 2013 ANSYS Confidential Fracture Tool is used to post-process fracture mechanics$
1 © 2013 ANSYS, Inc. May 3, 2013 ANSYS Confidential © 2013 ANSYS, Inc. May 3, 2013 ANSYS Confidential

2013 UGMs – ANSYS

Fracture Mechanics in ANSYS Mechanical R14.5


Introduction

Structural design traditionally uses a strength-of-material approach to assess structural integrity

– does not consider the effect of flaws which can significantly degrade structural integrity

Including the effect of flaws with fracture mechanics approaches is becoming common practice in many industries


Fracture Mechanics Approach

Fracture mechanics describe crack behavior using concepts from both applied mechanics and material science, because 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


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)

Domain Integral approach calculates J-integral at radial contours from crack tip

– J-integral is path independent

– results should converge within a few contours


R14.0 ANSYS Mechanical Procedure

1. Construct FE mesh with embedded crack(s)

2. Apply boundary conditions

3. Issue MAPDL CINT commands in Command Objects

4. Solve

5. 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


New Mechanical R14.5 Fracture Features

Crack Object provides automated tools for embedding crack(s) into existing meshes

– significant ease-of-use enhancement, because creating well-shaped efficient cracked meshes can be difficult and time-consuming

– 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


Fracture Folder

Crack Object and Pre-Meshed Crack Object are accessed from the Fracture Folder

– new in R14.5

– must be first inserted from the Model toolbar and then it can be accessed from the Outline tree


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

– only visible if the Fracture folder exists

Fracture Setting


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

Crack Object


• 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

Using Crack Object


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

Crack Object Actions


Inputs for Crack Object

Only Major and Minor radii are required

Optional input data available to control crack mesh:

– 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


Pre-Meshed Crack Object performs fracture mechanics calculations on meshes with existing cracks

Similar approach as R14.0, except that the MAPDL CINT commands no longer need to be issued in Command Objects

Pre-Meshed Crack Object


• 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

Using Pre-Meshed Crack Object


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

Fracture Tool

Solution Branch > RMB > Insert “Fracture Tool” > pick result type

– insert fracture result item


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


ANSYS Mechanical Example

Create full structural model

– solid model, mesh, boundary conditions, etc.

Specify coordinate system at center crack Insert “Fracture” folder Insert Crack Object under Fracture Folder Set Fracture solver control to ON


ANSYS Mechanical Example

Specify Crack Object details Generate cracked mesh Solve Insert Fracture Tool Post-process


Future Enhancements

Extend crack creation capabilities for additional crack types and arbitrary crack shapes

• 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 ugms ansys - · pdf file2013 ugms – ansys fracture mechanics in ansys mechanical...

Documents