Integrated FEM based package for Fatigue and … FEM-based package for Fatigue and Damage...

1

Integrated Integrated FEMFEM--basedbased packagepackagefor Fatigue for Fatigue andand Damage Damage ToleranceTolerance

--SAFESAFE

Emmanuelle ALIOS Jean-Pascal KLEINERMANN

213th-14th June 2002

ContentContent

Introduction

Airbus France tool : SAFE• General overview• Assessment of initiation life• Assessment of propagation life

Illustration : Widespread Fatigue Damage• MSD phenomenon• Modelisation principles• Example

Conclusion


IntroductionIntroduction

AIRBUS France : SAFE• integrated tool providing analytical or FE solutions• library of parameterised models

Before 1990 : analytical solutions for fatigue calculation• easy to use and short calculation time• but a limited number of possible structures

Need to develop general approaches

Aim : to conceive a tool for • specialists in fatigue but• non-specialists in FEA


Exploitation of tests results

Tests reports

Definition of certification

policy

Means of compliance

Mission building

Spectrum building

Spectrum analysis

Crack initiation calculation

Crack propagation calculation

Residual strength

settlementStress

dossier

Selection of items for analysis

Calculation of Maintenance

Program

Scatter factors

Follow up of tests

Certification processCertification process

SAFE softwareSAFE software


SAFE proceduresSAFE procedures-- Stress spectrum generation in the different aircraft zonesStress spectrum generation in the different aircraft zones-- Equivalent stress computation in initiation and propagation

Spectrum procedureEquivalent stress computation in initiation and propagation

Initiation fatigue procedure

Crack propagation procedure

No local loca

FEM FEMgeomeeome

olveretry study

No l g

try study

=> no s

=> no solv r

-- Equivalent stress as boundary conditionEquivalent stress as boundary condition-- Local stress study using FEM solverLocal stress study using FEM solver-- Specific fatigue postSpecific fatigue post--processingprocessing

-- Equivalent stress as boundary conditionEquivalent stress as boundary condition-- SIF computation using either analytical solution or FEM solverSIF computation using either analytical solution or FEM solver-- SIF computation integrated in an external crack propagation looSIF computation integrated in an external crack propagation loopp


Initiation fatigueInitiation fatigue

Models Library concept more than 30 preModels Library concept more than 30 pre--defined FE modelsdefined FE models

•• lug type modelslug type models•• plate with holesplate with holes•• U or L sectionsU or L sections•• stiffened panelstiffened panel•• drain hole in a stiffenerdrain hole in a stiffener•• etcetc……

1013th-14th June 2002


Fully parameterised models (geometry, loading, …)

1113th-14th June 2002


Models tested and validated by Airbus France

MODEL MODEL RESULTSRESULTS

Small coupon tests

………..………..………..

Large representativetests

Calculation method (full 3D model)

MODEL MODEL VALIDATIONVALIDATION

1213th-14th June 2002


Geometry inputMaterial definition

…

Local stress calculation using FEM solver (SAMCEF®)

1313th-14th June 2002


Geometry inputMaterial definition

…

Local stress calculation using FEM solver (SAMCEF®)

Critical site identification and max stress extraction

Fatigue life calculation usingAIRBUS France SA Fatigue Manual Law

Results output:• Maximum stress value• Initiation life in each critical site• Most critical site identification

1413th-14th June 2002

Joint geometry

Considered part

Numerical model

Model dedicated to bolted or riveted assembliesModel dedicated to bolted or riveted assemblies


1513th-14th June 2002

Crack propagation using either analytical or numerical SIF compuCrack propagation using either analytical or numerical SIF computationtation

Cracks propagationCracks propagation

•• Analytical SIF computation => NasgroAnalytical SIF computation => Nasgro®®•• Numerical SIF computation => SAMCEFNumerical SIF computation => SAMCEF®®

Models Library concept more than Models Library concept more than -- 30 pre30 pre--defined analytical modelsdefined analytical models-- 25 FE models25 FE models

•• Lug type modelsLug type models•• Plate with holesPlate with holes•• Stiffened panelsStiffened panels•• etcetc……

Fully parameterised models (geometry, loading, …)

Models tested and validated by Airbus France

1613th-14th June 2002

Stress intensity factors computationUsing Nasgro®

First step ?Y

N

NasgroNasgro®®

Crack length ai computation such as ∆Ni = min(∆Ni)

Crack growth step estimationai = ai + ∆ai

∆Ni computation (Elber or Modified Forman)

Input data reading

•• PrePre--defined Nasgrodefined Nasgro®® ModelsModels•• Stress intensity factors using NasgroStress intensity factors using Nasgro®®•• Elber (Paris) or Modified Forman crack growth equationsElber (Paris) or Modified Forman crack growth equations•• Corner and through crack modelsCorner and through crack models


1713th-14th June 2002

Stress intensity factors computationKI, KII and θ (Barsoum)

FEM simulation

Automatic remeshing

First step ?Y

N

SAMCEF®SAMCEF®

Crack length ai computation such as ∆Ni = min(∆Ni)

Crack growth step estimationai = ai + ∆ai

∆Ni computation (Elber or Modified Forman)

•• PrePre--defined Finite Element Modelsdefined Finite Element Models•• Stress intensity factors using FEM solver SAMCEF Stress intensity factors using FEM solver SAMCEF ®®•• Automatic remeshing with crack propagationAutomatic remeshing with crack propagation•• Elber (Paris) or Modified Forman crack growth equationsElber (Paris) or Modified Forman crack growth equations•• Through crack modelsThrough crack models

Input data reading


1813th-14th June 2002

Cracks propagationCracks propagationNumerical SIF computation methodsNumerical SIF computation methods

Methods available in SAMCEF®:

1 2 3

u

v

Node displacement method

Virtual Crack Extension method

J-Integral method:• Classical RICE formulation• Equivalent Domain Integral method (NIKISHKOV-ATLURI)

2D crack 2D elementsSIF computation methods available for 3D corner crack in 3D membranes

3D through crack 3D Midlin shells3D surface crack 3D volume elements

1913th-14th June 2002

Cracks propagationCracks propagationNumerical SIF computation methodsNumerical SIF computation methods

Method used in SAFE: 2D and 3D through crack using Nodal displacement method

Volumic Barsoum element

L crack

Meshing = dedicated mesh on crack tip + free mesh around this zoneTo ease automatic remeshing during crack propagation

Volumic Barsoum elements integrated in shell plate2D Barsoum element

2013th-14th June 2002

Cracks propagationCracks propagationAutomaticAutomatic remeshingremeshing

2113th-14th June 2002


K=f(a)a=f(N)

PANEL WITH 7 STIFFENERS ( SAFE CENTRAL STIFFENER )Problem definition

Run SAFE procedure

• Automatic remeshing• FEM Simulation• Stress intensity factors

computation

• ∆N computation (Elber)• Crack length correction• New crack step

estimation

Output results

2213th-14th June 2002

Widespread Fatigue DamageWidespread Fatigue Damage

1988 : Aloha Airlines Boeing 737 accident

Manufacturers must consider WFD to • better design the future aircrafts• propose adapted inspection programs• justify service life extension

Airbus is going to have more and more ageing aircraftsNeed of a MSD calculation tool

2313th-14th June 2002

WFD : MSD PhenomenonWFD : MSD Phenomenon

great number of critical sites

Multiple Site Damage : aircraft = assembly of riveted joints

Example of WFD in a longitudinal lap joint

Method developed for the A300 life extension

2413th-14th June 2002

WFD : MSD PhenomenonWFD : MSD Phenomenon

3 evolution phases for each critical site :• crack initiation • crack propagation • crack link up (fracture between 2 holes)

then : fracture of the whole structure

Particularity : some cracks initiate while others propagate

Necessity of an automatic remeshingUse of the “block concept”

2513th-14th June 2002

WFD : WFD : ModelisationModelisation

Block concept

?

11 possible blocks :• right, middle and left block• intact, cracked or broken block

A B C

D E F G H

J KI

Example with the right block

block 1

Propagation

block 2 block 2 block 3

N = Ninit Failure

2613th-14th June 2002

WFD : WFD : ModelisationModelisation

Model creation by blocks assembly

Blocks stucktogether

Blocks stuck tothe rest of the structure

Pre-defined blocks

2713th-14th June 2002

WFD : MethodologyWFD : Methodology

Fracture of the link ?

Building of the structure

Post-processing(crack sizes calculation)

Numerical simulation

(re-)Meshing by blocks

Random selectionof initiated sites N = N + ∆N

END

Fracture of the structure ?

YES

YES

NONO

2813th-14th June 2002

WFD : ExampleWFD : Example

Modelisation

Free meshing zone

• 2D membrane model – linear solver• Precise calculation method : interactions taken into account • Barsoum elements on cracks tips• SIF computation using SAMCEF

2913th-14th June 2002

WFD : ExampleWFD : Example

Local stress computation on a joint

Local stress

Stress Intensity Factor

Post-processing

Local stress initiation or notStress intensity factor crack propagation

3013th-14th June 2002

WFD : WFD : ExampleExample

3113th-14th June 2002

ConclusionConclusion

dedicated to Fatigue and Damage Tolerancededicated to Fatigue and Damage Tolerancededicated to fatigue specialists but not FE specialistsdedicated to fatigue specialists but not FE specialistsfrom complex spectrum analysis to initiation and propagation fafrom complex spectrum analysis to initiation and propagation fatigue life calculationtigue life calculationusing linear and nonusing linear and non--linear FE solver from SAMCEF®linear FE solver from SAMCEF®computing SIF either from NASGRO® (analytical) or from SAMCEF® computing SIF either from NASGRO® (analytical) or from SAMCEF® (numerical)(numerical)

developed by SAMTECH France under AIRBUS specificationsdeveloped by SAMTECH France under AIRBUS specificationsdistributed by SAMTECHdistributed by SAMTECH

distributed to more than 15 companies in 7 countriesdistributed to more than 15 companies in 7 countries

SAFE is an integrated toolSAFE is an integrated tool

SAFE is the AIRBUS France softwareSAFE is the AIRBUS France software

SAFE is an industrial softwareSAFE is an industrial software

3213th-14th June 2002

Future developmentsFuture developments

Semi-global models developmentNumerical study of 3D corner cracksAutomatic bifurcation of cracks regarding SIH deviation angle

Crack lengthstringers

frame

stringers

frame

straps

splice

3313th-14th June 2002


Semi-global models development

Automatic bifurcation of cracks regarding SIH deviation angleNumerical study of 3D corner cracks

3413th-14th June 2002


Semi-global models developmentNumerical study of 3D corner cracksAutomatic bifurcation of cracks regarding SIH deviation angle

Integrated FEM based package for Fatigue and … FEM-based package for Fatigue and Damage...

Documents

Transcript of Integrated FEM based package for Fatigue and … FEM-based package for Fatigue and Damage...