Determination of crack-initiating defects in cast aluminium alloys by Non-destructive Testing

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By Yakub Tijani (Fraunhofer Institute for Structural Durability and System Reliability LBF)

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Determination of crack-initiating defects in cast aluminium alloys by Non-destructive Testing

  1. 1. Determination of Crack-Initiating Defects in Cast Aluminium Alloys by Non-destructive Testing AVIZO EUGM, 30 May - 1 June, 2012, Bordeaux, FranceAVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France Yakub Tijani and André Heinrietz 1 © Fraunhofer
  2. 2. Outline  Pores in cast aluminium components  Influence of defects on cast aluminium  Development of a parametric model for fatigue life  Non-destructive evaluation by computer tomography using AVIZO FIRE  Finite element models of cast poresAVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France  Correlation between FE models, experiments and parametric model  Summary 2 © Fraunhofer
  3. 3. AVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France Cast aluminium alloys in automobile industry: Motor engine  Good strength-weight ratio  Castability of complex geometries  Cheap to produce Porsche Cayenne V8 Motor Volvo 5 cylinder engine block Ref: www.vdg.de Source: Müller-Weingarten 3 © Fraunhofer
  4. 4. Pores in cast aluminium alloy Components Cast Aluminium alloys: Process Chain in 3 Steps Liquid Aluminium + - Mould Filling Alloying Elements - Cooling End Products + - Solidification HeatingAVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France Die Casting Automotive Investment Casting Aerospace Sand Casting Transport [….] Mechanical Engineering Energy, Environment, Health 4 © Fraunhofer
  5. 5. Pores in cast aluminium alloy Components - Turbulence - Temperature difference - Mould Filling - Change in Solubility - Cooling - Solidification (Liquid  Solid) - Oxidation [….] IfGAVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France Material matrix is no longer homogenous  Pores and/or Oxides may be present  Unwanted notch effect in the material leads to crack initiation  Reduction in fatigue life  Processes to reduce pores lead to increase in cost 5 © Fraunhofer
  6. 6. Influence of defects on cast alloys: State of the art Defects in the components interior increase the notch effect in the loaded section Influence of porosity on fatigue strength is scientifically proven, but not quantitatively predictable based on measured variablesAVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France  Poor explicit correlation between fatigue strength and pore size/morphology  Difficult to experimentally measure the effect of mechanical stress on pores  The radiographic quality assurance is carried-out by comparison with reference catalog  Cast products will be unnecessarily scrapped in the event of pores  The cast simulation cannot quantitatively predict porosity 6 © Fraunhofer
  7. 7. Influence of defects on cast alloys: Fatigue experiment 170 160 AlSi8Cu3 Ingot Pü = 50% 150 AlSi8Cu3 with pores 140 Pü = 50% 130 120 Continous Stress amplitude, MPa 110 casting-ingot 100 90 80 40% reduction inAVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France 70 fatigue strength at N=107 60 σ(N=1e7) PV (MPa) Tσ k (mm³) 50 < 0.5 - 4 54 1:1.34 9.7 Ingot 90 1:1.10 15.6 Ref: Tijani et al., TMS 2012, Orlando FL 40 Int. J. Fatigue (in Review) 3 4 5 6 7 8 10 10 10 10 10 10 Number of cycles to failure [ ] 7 © Fraunhofer
  8. 8. Influence of defects on cast alloys: Fatigue experiment 10 7 10 6 A i8 u In t lS C 3 go P =5 % ü 0 10 5 A i8 u P < 0 m ³ lS C 3 V .5 m 10 4 P =5 % ü 0 A i8 u P 0 m ³ - 2m ³ lS C 3 V .5 m m 10 3 P =5 % ü 0 A i8 u P 2m ³ - 4m ³ lS C 3 V m m 10 2 P =5 % ü 0 plitude, M a 10 1 P 10 0 90 VPore ~ σN=1E7 80 tress amAVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France 70 σ(N=1e7) PV (MPa) Tσ k S 60 (mm³) < 0.5 59 1:1.16 11.2 0.5 - 2 43 1:1.35 7.2 50 2-4 49 1:1.33 9 Ingot 90 1:1.10 15.6 Ref: Tijani et al., TMS 2012, Orlando FL 40 Int. J. Fatigue (in Review) 3 4 5 6 7 8 10 10 10 10 10 10 N m of cy u ber cles to failu [ ] res 8 © Fraunhofer
  9. 9. Influence of defects on cast alloys: Fractography by SEM SEM fractographic image of cast AlSi9Cu3 specimenAVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France  Crack initiated by big pore close to the surface  Image can be analyzed to determine pore parameters  Relationship between pore parameters and fatigue life is only qualitative  The approach is a destructive testing method 9 © Fraunhofer
  10. 10. AVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France Influence of defects on cast alloys: Pore shape Metallography of the fracture surface 10 © Fraunhofer
  11. 11. Influence of defects on cast alloys: Pore shape 1 4 6 7 10 11 13 2 5 8 12 3 9 1,2 1 0,8 0,6 0,4AVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France 0,2 0 1 2 3 4 5 6 7 8 9 10 11 12 13 De fe k t co n vext y f o rm f akt o r Crack-initiating pore: - Biggest pore close to the surface - Smallest values of Convexity and Shape factor 11 © Fraunhofer
  12. 12. Development of a parametric model for fatigue life A C B Kt= 2.322 Kt= 2.366 Kt= 2.420AVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France DtS Diameter Pore Volume Pore (mm) (mm) (mm³)  Different pore sizes A 0.3 1 0.524  Different pore distance to surface (DtS) B 0.45 1.5 1.767 C 0.6 2 4.189  Similar stress concentration factor Ref: Tijani et al., ECAA 2011, Bremen Same DtS-Diameter ratio Int. J. Fatigue (in Review) 12 © Fraunhofer
  13. 13. Development of a parametric model for fatigue life Effect of pores can be characterized by their stress concentration factors, Kt K t1  f (distance to surface ) K t 2  f (size) K t  f (distance to surface, size, shape ) K t 3  f (shape)  impact of characteristic material behavior is excluded Fatigue notch factor : K f  Kt  = notch sensitivity factor AVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France     1 0,71R 0,31 Diameter Kf  2,74  0,6 R    2,21 R    R 1,1 R R   6 Volume       R   Area  distance to surface R  0 pore diameter Ref: Tijani et al., MS & T 2011, Columbus OH Int. J. Fatigue (in Review) 13 © Fraunhofer
  14. 14. Non-destructive Evaluation by Computer Tomography using AVIZO FIRE  Microstructure discontinuities can be reconstructed by using AVIZO Fire on microfocus CT  Pore parameters can be determined by 3D image analysisAVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France  The crack-initiating pore can be determined from the pore Pore Volume Area DtS* Shape factor parameters (mm³) (mm²) (mm) [] 1 0.13 1.43 3.53 0.8 2 0.45 4.42 3.36 0.5 Ref: Tijani et al., TMS 2012, Orlando FL 3 0.09 1.35 3.56 0.6 Int. J. Fatigue (in Review) 4 1.56 10.92 3.12 0.5 * DtS = Distance to Surface 14 © Fraunhofer
  15. 15. Non-destructive Evaluation by Computer Tomography using AVIZO FIRE Pore Volume Area DtS* Shape factor (mm³) (mm²) (mm) [] 1 0.15 2.47 3.53 0.4 2 0.21 3.81 3.43 0.3 3 0.68 8.04 2.74 0.3 4 0.19 2.94 2.95 0.4 5 0.60 7.77 2.33 0.3 6 0.14 1.96 3.42 0.6AVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France 7 0.12 1.92 1.98 0.5 * DtS = Distance to Surface Tijani et al., Int. J. Fatigue (in Review)  A database of pore parameters can be prepared using AVIZO Fire on microfocus CT  Stress concentration factor due to each pore can be determined 15 © Fraunhofer
  16. 16. Finite Element Models of Cast Pores EPOS/9125D/1 EPOS/9125D/6 EPOS/9125D/5AVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France EPOS/9125D/4 EPOS/9125D/2 EPOS/9125D/7 16 © Fraunhofer
  17. 17. FE-Model of Specimen with Pores (AlSi8Cu3)  Linear elastic calculation  Nominal stress, σn = 90 MPa  Max. principal stress σ = 681.5 MPa  Kt (FEM) = 7.6  Kt (Par. Model) = 8.0AVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France EPOS/9125D/3 Pore structure from Mikrofocus CT Ref: Tijani et al., MS & T 2011, Columbus OH Int. J. Fatigue (in Review) 17 © Fraunhofer
  18. 18. FE-Model of Specimen with Pores (AlSi7Mg0.3)  Linear elastic calculation  Nominal stress, σn = 90 MPa  Max. principal stress, σ = 571.7 MPa  Kt (FEM) = 6.4  Kt (Par. Model) = 6.9AVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France EPOS/8239A Pore structure from Mikrofocus CT Ref: Tijani et al., TMS 2012, Orlando FL Int. J. Fatigue (in Review) 18 © Fraunhofer
  19. 19. Correlation between FE Models and Parametric Model 8 7 [] KtKt , FE models (FEM Berechnung) 6 R2 = 0,9805 5 4AVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France 3 Tijani et al., Int. J. Fatigue (in Review) 2 Tijani et al., TMS 2012, Orlando FL. 2 3 4 5 6 7 8 Tijani et al., MS & T 2011, Columbus OH KKt , Parametric model t (Par. Berechnungsmodell) [] Tijani et al., ECAA 2011, Bremen Good correlation between results of FE Model and computed stress concentration Kt obtained by using parameters from AVIZO Fire 19 © Fraunhofer
  20. 20. Validation with industrial SN Curves 1000 Experiment Pu=50% Parameter model Pu=50% Stress Amplitude, MPa Fatigue SN k strength σk at Curve 100 N = 107 Exp. 5,3 74 MPaAVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France Model 5,3 78 MPa Tijani et al., Int. J. Fatigue (in Review) Tijani et al., TMS 2012, Orlando FL. 10 Tijani et al., MS & T 2011, Columbus OH 1,00E+03 1,00E+04 1,00E+05 1,00E+06 1,00E+07 1,00E+08 Tijani et al., ECAA 2011, Bremen No of Cycles to Failure [ ] Good correlation between experimental and computed fatigue life results obtained by using parameters from AVIZO Fire 20 © Fraunhofer
  21. 21. Summary  The presence of defects reduces fatigue strength  By using Avizo Fire, the crack-initiating pores can be determined in a microstructure  Fatigue life of cast aluminum alloy components based on non-destructive analysis can be calculated  The obtained parameters provide reliable predictions over the range of conditions found in industrial castings, where pores are among the major driving forces forAVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France reduction of structural durability  This approach will reduce production costs and is expected to improve control mechanisms within the scope of quality assurance 21 © Fraunhofer
  22. 22. Acknowledgement The presented work is a part of the research project IGF 295 ZN of the Research Association Casting Technology (FVG), Sohn-straße 70, 40237 Düsseldorf, Germany. It was sponsored by the German Federation of Industrial Research Associations (AiF) under the program for the promotion of joint industrial research and development (IGF) of the Federal Ministry of Economics and Technology (BMWi)AVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France due to a decision of the German Parliament. Dr.-Ing. Yakub Tijani Dipl.-Ing. André Heinrietz Fraunhofer Institute for Structural Durability Fraunhofer Institute for Structural Durability and System Reliability, Darmstadt, Germany. and System Reliability, Darmstadt, Germany. yakub.tijani@lbf.fraunhofer.de andre.heinrietz@lbf.fraunhofer.de tijani@szm.tu-darmstadt.de 22 © Fraunhofer
  23. 23. Thank You For Your AttentionAVIZO EUGM 2012. 31.5.-1.6.2012, Bordeaux, France Source: Honsel via www.vdg.de 23 © Fraunhofer

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