# Presentation: 614322

## Meshing For Crack Propagation Simulation:

**Meshing For Crack Propagation Simulation:**
**Problems....**** **

**... ****from Within ...**

**...****and Without**

- A. R. Ingraffea
- With a lot of help from his friends in the
- Cornell Fracture Group
- And
- ASP/ITR Project

- IMR 2002

## Outline of Presentation

-  The crack propagation problem:
- 	Definitely evolutionary geometry, but
- 	need it be evolutionary meshing?
-  The problem within: examples of current simulation capability.
- 	And shortcomings.
-  The problem without:
- 	The meshfree methods are here, and more coming!
- 	Are they just a challenge, or a revolution?

- IMR 2002

## Crack Propagation is a Problem of National Significance

- An aging (>40 years old) military aircraft dies...

- IMR 2002

## Predicted Curvilinear Fatigue Crack Growth: 

- _Predicted Curvilinear Fatigue Crack Growth: _
- _Adaptive Remeshing for Shell FEM_

- IMR 2002

## Early Damage Tolerance Testing

-  on B-707 Fuselage

- Single Bay Flaps

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## An aging (>21 years old) civilian aircraft kills...

- Fatigue crack growth coupled
- with corrosion in lap joints in skin

- Ductile Tearing

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## Aging Dams are Cracking

- Oops!

- Fontana Dam
- North Carolina,
- USA

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## NY State Thruway, I90, Bridge Collapse

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## Killer crack

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## Let’s Dissect The Meshing Process with a Simple 2D Problem

- Before...

- After...

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## Requirements for an Advancing-Front- Based 3D Mesher for Crack Problems

-  Produce well-shaped elements
- 	Of course
-  Conform to an existing, triangular surface mesh on region boundary
- 	Especially in small regions around extending crack front
- 	Allows fast, local remeshing
- 	Minimize information transfer between old and new meshes
-  Transition well between regions with elements of highly varying size
- 	As much as 2 orders of magnitude difference in crack problems
-  Accommodate geometrically coincident, arbitrarily shaped crack surfaces
-     Discriminate between nodes on opposite crack faces

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## Mesh Model of SH 60 Seahawk Power Transmission Spiral Bevel Gear

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## Initial Flaw Size and Location

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## Comparison: Simulated versus Observed

- Observed

- Simulated

- Crack Trace on the Face of Tooth

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## Comparison: Simulated versus ObservedFracture Surfaces

- Observed

**Comparison: Simulated versus Observed****Fracture Surfaces**

- Simulated

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## Comparison: Simulated versus ObservedCrack Trace on Gear Hub

- Observed

- Simulated

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## Mesh Detail on Tooth Surface

- Initial Flaw/Mesh

- Later Stage of Simulation

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## An OpenDX and SQL Server-BasedMesh Analysis Tool

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## The “Nanotechnology” Revolution is Creating Interesting Meshing Demands

- 2D Representations of Crack Initiation in a Metallic Polycrystal

- 0.5 mm

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## Things Get Tough in 3D

- 50 m cube
- Only 100 Grains
- 6,271,419 DOF
- 1,519,816 10-noded tets

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## Mesh Analysis and Improvement Tool Even More Necessary

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## Problems from Without:The Meshless Methods ChallengeorIs It a Revolution?

- Money, interest, and PhD’s are flowing to meshless methods. Why?
- Can they:
- 	Solve problems that can’t be solved with meshed methods?
- 	For problems solvable with meshed methods, can meshless
- 	methods solve them:
- 	More efficiently?
- 	With better physics and mechanics?

- IMR 2002

## Is This the BIG LIE, or ....

- “...The development of a technique that does not require the
-  generation of a mesh for complicated 3D domains is still
- very appealing.  The problem of mesh generation is
-  that the time remains unbounded, even using the most
-  sophisticated mesh-generator...”
- From Oñate *et al.* “Meshless Finite Element Ideas”,
- keynote at the
- 5th World Conference on Computational Mechanics, Vienna, July 2002.

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## Sessions at 5th World Conference on Computational Mechanics on

**Sessions at 5****th**** World Conference on Computational Mechanics on**
**	****Meshless Methods:  8**
**	****Mesh Generation:    0**

- IMR 2002

## Summary

- For meshed approach with explicit representation of crack geometry:
-  Work underway on guaranteed-quality, Delaunay-based, 3D,
-   mesher, with ideal crack front features for simulation of crack
-   propagation: DMESH
-  Ditto, minus the guarantees, with an advancing-front-based
-   approach: JMESH
-  Both benefiting from a suite of quality assessment/improvement
-   tools using a SQL Server/ OpenDX basis.

- Meshfree appoaches with/out explicit representation of crack geometry:
-  They are here, in droves!
-  Are they a revolution, or just a challenge?

- IMR 2002