Integrated FEM-based. package for Fatigue and Damage Tolerance - SAFE

Transcription

1 Integrated FEM-based package for Fatigue and Damage Tolerance - SAFE Emmanuelle ALIOS Jean-Pascal KLEINERMANN 1

2 Content 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 2

3 Introduction 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 AIRBUS France : SAFE integrated tool providing analytical or FE solutions library of parameterised models 3

4 Certification process Definition of certification policy Means of compliance Selection of items for analysis Mission building SAFE software Spectrum building Spectrum analysis Crack initiation calculation Crack propagation calculation Scatter factors Calculation of Maintenance Program Residual strength settlement Stress dossier Follow up of tests Exploitation of tests results Tests reports 4

5 SAFE procedures Spectrum procedure - Stress spectrum generation in the different aircraft zones - Equivalent stress computation in initiation and propagation No local l geome try study => no FEM solvs olvere r Initiation fatigue procedure - Equivalent stress as boundary condition - Local stress study using FEM solver - Specific fatigue post-processing processing Crack propagation procedure - Equivalent stress as boundary condition - SIF computation using either analytical solution or FEM solver - SIF computation integrated in an external crack propagation loop 5

6 Initiation fatigue Models Library concept more than 30 pre-defined FE models lug type models plate with holes U or L sections stiffened panel drain hole in a stiffener etc 6

7 Initiation fatigue Models Library concept more than 30 pre-defined FE models lug type models plate with holes U or L sections stiffened panel drain hole in a stiffener etc 7

8 Initiation fatigue Models Library concept more than 30 pre-defined FE models lug type models plate with holes U or L sections stiffened panel drain hole in a stiffener etc 8

9 Initiation fatigue Models Library concept more than 30 pre-defined FE models lug type models plate with holes U or L sections stiffened panel drain hole in a stiffener etc 9

10 Initiation fatigue Fully parameterised models (geometry, loading, ) 10

11 Initiation fatigue Models tested and validated by Airbus France Calculation method (full 3D model) Small coupon tests.. Large representative tests MODEL RESULTS MODEL VALIDATION 11

12 Initiation fatigue Geometry input Material definition Local stress calculation using FEM solver (SAMCEF ) 13th-14th June

13 Initiation fatigue Geometry input Material definition Local stress calculation using FEM solver (SAMCEF ) Critical site identification and max stress extraction Fatigue life calculation using AIRBUS France SA Fatigue Manual Law Results output: Maximum stress value Initiation life in each critical site Most critical site identification 13

14 Initiation fatigue Model dedicated to bolted or riveted assemblies Joint geometry Considered part Numerical model 14

15 Cracks propagation Crack propagation using either analytical or numerical SIF computation Analytical SIF computation => Nasgro Numerical SIF computation => SAMCEF Models Library concept more than - 30 pre-defined analytical models - 25 FE models Lug type models Plate with holes Stiffened panels etc Fully parameterised models (geometry, loading, ) Models tested and validated by Airbus France 15

16 Cracks propagation Pre-defined Nasgro Models Stress intensity factors using Nasgro Elber (Paris) or Modified Forman crack growth equations Corner and through crack models Input data reading Nasgro Stress intensity factors computation Using Nasgro Crack growth step estimation a i = a i + a i First step? Y N N i computation (Elber or Modified Forman) Crack length a i computation such as N i = min( N i ) 16

17 Cracks propagation Pre-defined Finite Element Models Stress intensity factors using FEM solver SAMCEF Automatic remeshing with crack propagation Elber (Paris) or Modified Forman crack growth equations Through crack models Input data reading SAMCEF FEM simulation Automatic remeshing Stress intensity factors computation KI, KII and θ (Barsoum) Crack growth step estimation a i = a i + a i First step? Y N N i computation (Elber or Modified Forman) Crack length a i computation such as N i = min( N i ) 17

18 Cracks propagation Numerical SIF computation methods Methods available in SAMCEF : Node displacement method u v Virtual Crack Extension method J-Integral method: Classical RICE formulation Equivalent Domain Integral method (NIKISHKOV-ATLURI) 2D crack SIF computation methods available for 3D corner crack 3D through crack 3D surface crack 2D elements in 3D membranes 3D Midlin shells 3D volume elements 18

19 Cracks propagation Numerical SIF computation methods Method used in SAFE: 2D and 3D through crack using Nodal displacement method Volumic Barsoum element 2D Barsoum element Volumic Barsoum elements integrated in shell plate L crack Meshing = dedicated mesh on crack tip + free mesh around this zone To ease automatic remeshing during crack propagation 19

20 Cracks propagation Automatic remeshing 20

21 Cracks propagation Problem definition PANEL WITH 7 STIFFENERS ( SAFE CENTRAL STIFFENER ) Run SAFE procedure K=f(a) a=f(n) Automatic remeshing FEM Simulation Stress intensity factors computation N computation (Elber) Crack length correction New crack step estimation Output results 21

22 Widespread 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 aircrafts Need of a MSD calculation tool 22

23 WFD : MSD Phenomenon Multiple Site Damage : aircraft = assembly of riveted joints great number of critical sites Example of WFD in a longitudinal lap joint Method developed for the A300 life extension 23

24 WFD : 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 remeshing Use of the block concept 24

25 WFD : Modelisation Block concept? 11 possible blocks : right, middle and left block intact, cracked or broken block A B C D E F G H I J K Example with the right block N = Ninit Propagation Failure block 1 block 2 block 2 block 3 25

26 WFD : Modelisation Model creation by blocks assembly Pre-defined blocks Blocks stuck together Blocks stuck to the rest of the structure 26

27 WFD : Methodology Building of the structure Random selection of initiated sites N = N + N NO (re-)meshing by blocks NO Numerical simulation Fracture of the link? YES Fracture of the structure? Post-processing (crack sizes calculation) END YES 27

28 WFD : Example Modelisation 2D membrane model linear solver Precise calculation method : interactions taken into account Barsoum elements on cracks tips SIF computation using SAMCEF Free meshing zone 28

29 WFD : Example Local stress computation on a joint Local stress Stress Intensity Factor Post-processing Local stress initiation or not Stress intensity factor crack propagation 29

30 WFD : Example 30

31 Conclusion SAFE is an integrated tool dedicated to Fatigue and Damage Tolerance dedicated to fatigue specialists but not FE specialists from complex spectrum analysis to initiation and propagation fatigue life calculation using linear and non-linear FE solver from SAMCEF computing SIF either from NASGRO (analytical) or from SAMCEF (numerical) SAFE is the AIRBUS France software developed by SAMTECH France under AIRBUS specifications distributed by SAMTECH SAFE is an industrial software distributed to more than 15 companies in 7 countries 31

32 Future developments Semi-global models development Numerical study of 3D corner cracks Automatic bifurcation of cracks regarding SIH deviation angle frame Crack length stringers frame straps splice stringers 32

33 Future developments Semi-global models development Numerical study of 3D corner cracks Automatic bifurcation of cracks regarding SIH deviation angle 33

34 Future developments Semi-global models development Numerical study of 3D corner cracks Automatic bifurcation of cracks regarding SIH deviation angle 34