composites analysis using nastran/patran by dr. faeq m. shaikh

Composite AnalysisUsing NASTRAN / PATRAN

Dr. Faeq M. Shaikh

Seattle, Washington, USA

(Seattle is home of Boeing Jets)

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• Pre‐Requisites for Today’s Seminar

Basic understanding of Finite Element Analysis

Working Knowledge of Laminate Plate Theory

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• NASTRAN & PATRAN are products of McNeal Schwendler Corporation (MSC)

• PATRAN = Pre & Post Processor• NASTRAN (NASA Structural Analysis)= Solver

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PATRAN

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• Summary of PATRAN Modeling CapabilitiesLine (Bar) Elements:

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• Summary of PATRAN Modeling CapabilitiesLine (Beam) Elements:

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• Summary of PATRAN Modeling CapabilitiesSurface (Shell) Elements:

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• Summary of PATRAN Modeling CapabilitiesSurface (Shell) Elements:

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• Summary of PATRAN Modeling CapabilitiesSolid Elements:

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• Summary of PATRAN Results ‐ Deformation

Animate Deformation

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• Summary of PATRAN Results ‐ Deformation

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• Summary of PATRAN Results ‐ Stresses

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• Process of Finite Element Analysis:Set database units (British or Metric)Define or Import (from CAD tools) GeometryCreate finite element meshDefine materials (isotropic, orthotropic, anisotropic)Define laminate / sandwich materialsApply materials to element propertiesApply loads and boundary conditionsPerform analysis (Linear, Non‐Linear, Buckling, etc)Access ResultsCreate fringe and deformation plots

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• Shell (Plate) vs. Solid ElementsMesh Using Shell

Elements:• Can model bending.•Usually much smaller model size• Elements are created on a surface (area)• Limited thru‐thickness results

Mesh Using Solid Elements:

•Do not have bending capability•Much larger model size• Elements are created on a volume• Thru‐thickness result capabilities

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• Examples of Models with Shell & Solid Elements:

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• Composites can be modeled using both shell and solid elements. Choice depends on:Computing power (large vs. small models) What kind of results are required (2D vs. 3D state of stress in‐plane vs. thru‐thickness)Importance of interfaces (fitting attachments, etc.) IF

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• 2D vs. 3D State of Stress

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• Composites can also be modeled as a hybrid of shell and solid elements

Model facesheet as shell elements

Model facesheet as shell elements

Model core as solid elements

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• Materials – Isotropic:

3D Constitutive Relationship

Plane StressConstitutive Relationship

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• Materials – Orthotropic:MAT3 Orthotropic materialis defined for Solid elements.

MAT8 orthotropic materialis defined for shell elements.

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• Materials – Anisotropic:

The MAT2 is used to define 2D anisotropic constitutive stress-strain relationship using the anisotropic material matrix.

The MAT9 is used to define 3D orthotropic constitutive stress strain relation using the anisotropic material matrix.

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• Laminate Plate Theory – Overview

The laminate consists of perfectly bonded laminae.The bonds are infinitesimally thin and nonshear‐deformable; i.e., displacements are continuous across laminae boundaries so that no lamina can slip relative to another.Each of the lamina is in a state of plane stress.

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• Modeling composites:Laminated composites are a "stack" of laminae with different orientations

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• Modeling composites‐what do we need?Lamina properties (E, G, etc)OrientationThicknessStacking sequence

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• Modeling composites‐what do we need?Data RecoveryDisplacementsForcesPly StressesPly StrainsMargin of Safety / Failure Indices

FI < 1, the lamina is assumed safe.FI > 1, the lamina is assumed to have failed.

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• Failure Indices:Isotropic Materials: Strength is independent of orientation of body under loadLaminated Composites (orthotropic ): Strength is a function of body orientation relative to load.Minimum Allowables Required:

Tensile stress/strain in material 1 & 2 directionsCompressive stress/strain in material 1 & 2 directionsShear stress/strain in principal material direction.

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• Failure Theories in NASTRAN / PATRAN:

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• Start a project:

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• PATRANModeling Window

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• PATRANApplication Form

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Creating Geometry: 1

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• Creating Mesh: 1

2 3

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• Materials:

1

2

3

4Creating Uni‐Directional Tape(for 2D Shell Elms)

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• Materials:

1

2

3

4Creating Honeycomb Core(for 2D Shell Elms)

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• Materials:

1

2

3

4

Creating Honeycomb Core(for 2D Shell Elms)

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• Materials:

1

2

Laminate Constants(for 2D Shell Elms)

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• Element vs. Material Coordinate System:

For 2D shell elements, ECS from Node 1 to Node 2Element Forces come out in Element Coordinate Sys

MCS defines the 0 deg fiber directionPly Strains & Stresses come out in ply fiber directions / Material Coordinate System

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• Properties:

1

2

3

4

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• Geometry:

1. Create Points2. Create Surface

3. Create solid (for 3D analysis)

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• FEMs:

1. Create Nodes & Elements (2D)

2. Create solids (for 3D analysis)

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• Apply Loads: 1

2

3

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• Apply Boundary Conditions: 1

23

4

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• Analyze:1

2

3

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• 3D Modeling:

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• 3D Modeling:

Facesheets modeled with 2D Shell Elements

Honeycomb Core modeled with 3D Solid Elements

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• 3D Anisotropic Material:

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• Results – Deformation plot:

1

2

3

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• Ply‐1 (bottom) x‐direction strain fringe plot:

1

2

3

4Compressive strain

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• Ply‐13 (top) x‐direction strain fringe plot:

1

2

3

4Tensile strain

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• Printed Output File – Displacements:

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• Printed Output File – Element Forces (2D Shell):

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• Printed Output File – Reactions at Support:

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• Printed Output File – Ply Strains (2D Shell):

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• Printed Output File – Stresses (3D Solid):

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• Word of Caution ‐ Use of Offsets:

–Modeling with 2D shell elements–Meshing surface is the bottom surface– How do we model varying thicknesses?

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• Word of Caution ‐ Offsets:

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Thank You.

For questions, please contact me at:[email protected]

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composites analysis using nastran/patran by dr. faeq m. shaikh

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