FRANC3D Workshop/Training

FRANC3D Workshop/Training May 7, 2012 Drs. Paul “Wash” Wawrzynek, Bruce Carter, Tony Ingraffea, and Omar Ibrahim

Objectives • General introduction to FRANC3D: - capabilities and limitations • Present theory and approaches to computational fracture mechanics built into the program. • Hands-on sessions give participants a chance to try the code with tutors here to help. • Opportunity for participants to ask questions.

Agenda • Introduction to FRANC3D • Demo/Hands-on: build an uncracked model • Overview of the crack insertion process • Demo/Hands-on: insert initial crack and run analysis • Stress Intensity Factor (SIF) computation - theory • Demo/Hands-on: SIF computation - practice • Crack growth - theory • Demo/Hands-on: Crack growth - practice • Demo/Hands-on: Student generated models

FRANC3D Product FRANC3D (FRacture ANalysis Code3-D) uses finite element method to simulate crack growth analysis Adaptively remeshes a finite element model to simulate crack growth. Has several elements to be used for modeling the crack front

FRANC3D Product Designed to work in conjunction with a commercial finite element solvers: ANSYS ABAQUS NASTRAN The FRANC3D program has a programming interface that is an extension to the Python programming language. Written in the C++ programming language Support the following operating systems: Windows Linux

FRANC3D Development History 1988 to 1994 FRANC3D v1.0 BEM only 1994 to 2001 FRANC3D v2.0 BEM & Thin Shell FEM 2001 to 2005 FRANC3D v3.0 BEM & Thin Shell & Solid FEM (ANSYS) 2005 to 2009 FRANC3D v4.0 Solid FEM only (ANSYS, ABAQUS, NASTRAN) Completely new code written in C++ 2009 to 2010 FRANC3D v5.0 – Additional enhancements 2010 to 2011 FRANC3D v6.0 – Fretting Fatigue, Fatigue Life, Post-processing & other enhancements 2012 FRANC3D v7.0 is under development

FRANC3D Development History Development of FRANC3D was funded by: USA Air Force USA Navy NASA Others

What Does FRANC3D Do? • insert a flaw into an existing finite element mesh and remesh locally, using special crack-front elements. • compute stress intensity factors (SIF’s) for all nodes along a crack front for isotropic and anisotropic materials. • predict how a crack will grow (relative extension and angle) using engineering growth criteria, and will then extend the crack geometry and remesh locally.

What FRANC3D is NOT • not a general finite element pre-processor or post-processor. External codes are required to build uncracked FE models and to visualize results (FRANC3D can display deformations). • not a finite element analysis program. An external FE code is required (e.g., ANSYS or ABAQUS) to perform stress analysis. • not a general purpose fatigue life prediction code, although some basic life prediction models are available. An external lifing code (e.g., AFGRO, NASGRO or DARWIN) can be used.

remainder of model FRANC3D Typical Work Flow ANSYS/ABAQUS/NASTRAN ANSYS/ABAQUS/NASTRAN Full 3D FE Model Stress Analysis portion to be cracked Combine portions FRANC3D Define crack(s) geometry Insert crack(s) into portion of model and remesh displacements, temperatures, crack surface tractions Compute stress intensity factors Extend crack(s) geometry

Global and Sub-models “sub-model” crack growth region “global” model FE package (e.g., ANSYS or ABAQUS) is used to define a global model and a sub-model. The sub-model should encompass the crack growth region with ‘space’ for remeshing.

FRANC3D FRANC3D Modifies the Sub-model uncracked model after crack insertion FRANC3D modifies the sub-model, inserting a crack and remeshing the model locally. It outputs an input file that combines the global and sub-model (ABAQUS) or it outputs the sub-model and a macro command file that will combine the models (ANSYS).

FRANC3D Maintains Compatibility mesh compatibility FRANC3D can retain surface meshes on “cut” surfaces so that there is FE compatibility between the global and sub-model. This is the preferred approach. However, FRANC3D can also instruct the FE program to insert constraint equations.

Combined (Full Model) Analysis FRANC3D does not use a global/local approach. The FE analysis is performed with the full combined model. (However, a global/local approach can be used.)

Crack Growth after 21 steps of crack growth Crack growth is simulated by FRANC3D repeatedly reading and modifying the initial sub-model. At each step, the global and modified sub-model are re-combined and the full model is analyzed.

Sub-models for “free” meshes “free mesh” cut surfaces It is possible to cut out a FRANC3D sub-model from a “free” (unstructured) mesh. (However, surface facets of tetrahedral elements with poor aspect ratios can cause local meshing problems.)

FRANC3D Tutorials Using ANSYS: Using ABAQUS: simple global model vs sub-model with global model through-crack extract sub-model automated crack growth crack insertion & automated growth crack face traction vs far-field loading crack face traction vs far-field loading

FRANC3D Tutorials • Step 1: Build the FE model • Step 2: Extract small portion from the full FE model • Step 2.1: Separate element components • Separate the FE model into a small portion (local model) and the remaining of the FE model (global model) • Local FE model will be used for fracture analysis Local Model Global Model

FRANC3D Tutorials • Step 2.2: Create node component for cut-surface • Select the nodes on the cut surfaces of each component and save a node component. For the 3x3x3 ‘local’ model, name this node component CUT_SURF. • Step 2.3: Save local and global • Archive each element component as a separate model for the local and other for global • Global model, which consists of the exterior elements, will include the boundary conditions and material properties • Local model will include the CUT_SURF node component and FRANC3D will use this information to retainthose mesh facets

FRANC3D Tutorials • Step 3: Read the local FE model into FRANC3D • Step 3.1: Reading Local FE Model • Start with the FRANC3D graphical user interface • Select File and Open • Switch File Filter in the Open Model File dialog box to proper file extension name and select the file name for the local model • Click Accept.

FRANC3D Tutorials • Step 3.2: Selecting the Retained Items in the Local FE Model • Material, mesh facet groups, contact/constraint & residual stress

FRANC3D Tutorials • Step 3.3: Selecting Cut Surface Nodes • Lists the node components present in the local FE model file

FRANC3D Tutorials • Step 3.4: Importing and Displaying the Local FE Model • User can turn on the surface mesh and manipulate the view

FRANC3D Wizardfor Defining the Crack Type and Meshing Process for the Cracked Portion of the FE Model

Current Crack Type Options in FRANC3D • Elliptical Crack • Through-the-thickness • One crack front • Two crack fronts • Long-shallow surface crack shape • Elliptical crack shape with two fronts • User-defined crack

Defining Crack Geometry • Crack geometry and location can be prescribed either by: • Interactively using the Graphical User Interface (GUI) • Using FRANC3D extensions to the Python programming language

Crack Insertion Wizard (Elliptical Flaw) crack size/shape parameters Define the crack surface geometry, position and orient crack crack-front template parameters

Crack Insertion Wizard – Flaw Library

User Defined Crack Front Points User-defined flaw allows an analyst to define an arbitrary (planar) shape by entering (or reading from a file) a series of points that define the vertices of a polygon. Crack front vertices should be flagged.

Surface Meshes after Crack Insertion crack surface mesh

Crack-Front Template Element Types tetrahedral elements are used for the bulk of the volume quarter-point singular wedge crack-front elements pyramids enforce compatibility between brick and tetrahedral elements two or more “rings” of brick elements

Crack Insertion: Input Sub-model Mesh The first major input to the crack insertion procedure is a finite element mesh. Usually this is a sub-model, but a full model mesh is acceptable. In the case of a sub-model, the cut surfaces are flagged. sub-model cut surface cutting planes This model has brick elements only. However, brick, wedge, pyramid, and tetrahedral elements of both first and second order are okay. Currently, FRANC3D can handle ANSYS, ABAQUS and NASTRAN models.

Crack Insertion: Approximate Surface Geometry Curved surface geometry is approximated from the faceted surface of the input finite element mesh. Locally refined meshes near flaws will fall on the curved surface rather than on the faceted finite element input. Step 1: compute weighted average normals at all nodes. Step 2: define 1 or 2 triangular Bezier patches for each FE facet. Step 3: identify “topological” edges and group together facets that form logical faces. Bezier patches Note that FE facets on the cut surfaces are retained for compatibility Topological edges and logical faces

Crack Insertion: Flaw Definition The second major input to the crack insertion procedure is a description of a flaw shape and location. FRANC3D has tools to define and place a flaw interactively. Flaws can be zero volume (cracks) or finite volume (voids). The crack above appears to have a piecewise linear crack front, but that is a just a display artifact. Flaw surfaces are defined as Bezier patches and can have curved crack fronts. In theory, initial flaws can be non-planar, but there is currently no practical user-interface for such a capability.

Crack Insertion: Crack-Front Templates Crack-front templates are generated to emplace regular well-shaped elements near crack fronts. The template elements are a combination of brick and quarter-point wedge elements. Additional processing is required where templates intersect free surfaces. Locally template element topology and geometry must be modified to conform to the surface geometry. A typical template cross-section

Crack Insertion: Intersections & Trimming Surface/surface intersections are computed for all body and flaw patches. The body and flaw patches are trimmed and combined into one composite object. Inside Outside Trimmed patches are divided into triangular sub-patches to keep the model “water-tight”.

Crack Insertion: Surface Meshing Surface meshes are generated for all “logical” model surfaces. The surface meshes are constrained to conform to the meshes on cut surfaces. retained cut surface meshes

Crack Insertion: Pyramids & Volume Meshing Pyramid elements are generated to enforce compatibility between quadrilateral facets on both the template and “cut” surfaces and triangular faces in the volume mesh. template surfaces cut surfaces An advancing front meshing algorithm* is used to generate a tetrahedral volume mesh (not shown). This algorithm respects the special case of distinct nodes on opposite sides of crack faces, which are geometrically coincident. *Neto, J.B., Wawrzynek, P.A., Martha, L.F., and Ingraffea, A.R., “An algorithm for three-dimensional mesh generation for arbitrary regions with cracks,” Engng with Comp., vol. 17, 75-91 (2001)

Volume Meshing • After completing the surface, the volume mesh starts • Options for performing volume meshing: • FRANC3D • ANSYS • ABAQUS CAE • Final mesh smoothing are used to improve the elements quality

A Sub-Volume Definition Issue Retained cut-surface facet It can be difficult to mesh a thin section that is constrained with a large quadrilateral patch on one side. There is not enough room for a well shaped pyramids and transition tetrahedral elements.

Workshop Agenda • Introduction to FRANC3D • Demo/Hands-on: build an uncracked model • Overview of the crack insertion process • Demo/Hands-on: insert initial crack and run analysis • Stress Intensity Factor (SIF) computation - theory • Demo/Hands-on: SIF computation - practice • Crack growth - theory • Demo/Hands-on: Crack growth - practice • Demo/Hands-on: Student generated models

FRANC3D Tutorials – Crack Insertion Steps • Step 1: Selecting Cracks from FRANC3D Menu • From the FRANC3D menu, select Cracks and New Flaw Wizard. The first panel of the wizard should appears. The default flaw type is Crack (zero volume flaw) and select Next.

FRANC3D Tutorials – Crack InsertionSteps • Step 2: Selecting Crack Type • The next panel allows the user to choose type of crack, hint Next after the selection.

FRANC3D Tutorials – Crack Insertion Steps • Step 3: Specify the Crack Size • The next panel allows us to specify the size of the ellipse. Select Next after the size definition.

FRANC3D Tutorials – Crack Insertion Steps • Step 4: Specify Crack Location and Orientation • The next panel allows us to specify location and orientation of the flaw. After defining the location and orientation; select Next.

FRANC3D Tutorials – Crack Insertion Steps • Step 5: Specify Crack Front Template Parameters • The next panel allows us to specify the crack front template parameters. After specifying the parameters; select Finish.

FRANC3D Tutorials – Crack Insertion Steps • Step 6: Surface and Volume Meshing of Local Model after the Crack Insertion • FRANC3D begins the process of inserting the flaw into the original model and then meshes the resulting cracked model. • Operations is displayed on the screen • When meshing is completed, the newly meshed cracked model will be displayed.

FRANC3D Tutorials – Static analysis Steps • Step 1: Select Static Crack Analysis • From the FRANC3D menu, select Analysis and Static Crack Analysis. The first panel of the wizard should appear, specify the file name for the FRANC3D database first.

FRANC3D Workshop/Training