Prediction of the Fatigue Life of Cast Steel Containing Shrinkage Porosity

A simulation methodology for predicting the fatigue life of cast steel components with shrinkage porosity is developed and validated through comparison with previously performed measurements. A X-ray tomography technique is used to reconstruct the porosity distribution in 25 test specimens with average porosities ranging from 8 to 21 pct. The porosity field is imported into finite element analysis (FEA) software to determine the complex stress field resulting from the porosity. In the stress simulation, the elastic mechanical properties are made a function of the local porosity volume fraction. A multiaxial strain-life simulation is then performed to determine the fatigue life. An adaptive subgrid model is developed to reduce the dependence of the fatigue life predictions on the numerical mesh chosen and to account for the effects of porosity that is too small to be resolved in the simulations. The subgrid model employs a spatially variable fatigue notch factor that is dependent on the local pore radius relative to the finite element node spacing. A probabilistic pore size distribution model is used to estimate the radius of the largest pore as a function of the local pore volume fraction. It is found that, with the adaptive subgrid model and the addition of a uniform background microporosity field with a maximum pore radius of 100 μm, the measured and predicted fatigue lives for nearly all 25 test specimens fall within one decade. Because the fatigue lives of the specimens vary by more than four orders of magnitude for the same nominal stress amplitude and for similar average porosity fractions, the results demonstrate the importance of taking into account in the simulations the distribution of the porosity in the specimens.

[1]  Y. Murakami.  Metal Fatigue: Effects of Small Defects and Nonmetallic Inclusions , 2002 .

[2]  R. Peterson,et al.  Stress Concentration Factors , 1974 .

[3]  David L. McDowell,et al.  Multistage Fatigue Modeling of Cast A356-T6 and A380-F Aluminum Alloys , 2007 .

[4]  Edward J. Garboczi,et al.  Elastic Properties of Model Porous Ceramics , 2000, cond-mat/0006334.

[5]  Q. Wang,et al.  Prediction of Fatigue Performance in Aluminum Shape Castings Containing Defects , 2007 .

[6]  Avinash C. Kak,et al.  Principles of computerized tomographic imaging , 2001, Classics in applied mathematics.

[7]  Bjørn Skallerud,et al.  Fatigue life assessment of aluminum alloys with casting defects , 1993 .

[8]  G. G. Stokes.  "J." , 1890, The New Yale Book of Quotations.

[9]  C. Beckermann,et al.  Analysis of ASTM X-ray shrinkage rating for steel castings , 2001 .

[10]  Richard A. Hardin,et al.  Fatigue of 8630 cast steel in the presence of porosity , 2004 .

[11]  Metall , 1897 .

[12]  Sankaran Mahadevan,et al.  Multiaxial fatigue reliability analysis of railroad wheels , 2008, Reliab. Eng. Syst. Saf..

[13]  David L. McDowell,et al.  Microstructure-based fatigue modeling of cast A356-T6 alloy , 2003 .

[14]  G. Bezine,et al.  Multiaxial fatigue limit for defective materials: mechanisms and experiments , 2004 .

[15]  Avinash C. Kak,et al.  7. Algebraic Reconstruction Algorithms , 2001 .

[16]  David Taylor,et al.  Prediction of fatigue failure location on a component using a critical distance method , 2000 .

[17]  C. M. Sonsino,et al.  Fatigue strength and applications of cast aluminium alloys with different degrees of porosity , 1993 .

[18]  R. Stephenson.  A and V , 1962, The British journal of ophthalmology.

[19]  P. Heuler,et al.  FATIGUE BEHAVIOUR OF STEEL CASTINGS CONTAINING NEAR‐SURFACE DEFECTS , 1993 .

[20]  P. Baicchi,et al.  A methodology for the fatigue design of notched castings in gray cast iron , 2007 .

[21]  D. Apelian,et al.  Fatigue behavior of A356-T6 aluminum cast alloys. Part I. Effect of casting defects , 2001 .

[22]  Sankaran Mahadevan,et al.  Fatigue crack initiation life prediction of railroad wheels , 2006 .

[23]  Yves Nadot,et al.  Influence of casting defects on the fatigue limit of nodular cast iron , 2004 .

[24]  F. Nilsson,et al.  Fatigue life estimation of cast components , 2001 .

[25]  Soon-Bok Lee,et al.  A critical review on multiaxial fatigue assessments of metals , 1996 .

[26]  Alain Nussbaumer,et al.  Fatigue design of cast steel nodes in tubular bridge structures , 2008 .

[27]  E. M. Lui,et al.  Fatigue and Fracture , 2005 .

[28]  L. Coffin,et al.  A Study of the Effects of Cyclic Thermal Stresses on a Ductile Metal , 1954, Journal of Fluids Engineering.

[29]  K. Carlson,et al.  Modeling the Effect of Finite-Rate Hydrogen Diffusion on Porosity Formation in Aluminum Alloys , 2007 .

[30]  Henrik Nilsson,et al.  The influence of porosity on the fatigue life for sand and permanent mould cast aluminium , 2006 .

[31]  P. C. Paris,et al.  A Critical Analysis of Crack Propagation Laws , 1963 .

[32]  S. Manson.  Behavior of materials under conditions of thermal stress , 1953 .

[33]  T. Topper,et al.  Fatigue of casting flaws at a notch root under an SAE service load history , 2000 .

[34]  E. Maire,et al.  Experimental study of porosity and its relation to fatigue mechanisms of model Al–Si7–Mg0.3 cast Al alloys , 2001 .

[35]  Richard A. Hardin,et al.  Effect of Porosity on the Stiffness of Cast Steel , 2007 .

[36]  Yves Nadot,et al.  Fatigue failure of suspension arm: experimental analysis and multiaxial criterion , 2004 .

[37]  J. Allison,et al.  A Probabilistic Model of Fatigue Strength Controlled by Porosity Population in a 319-Type Cast Aluminum Alloy: Part I. Model Development , 2007 .

[38]  H. O. Fuchs,et al.  Metal fatigue in engineering , 2001 .

[39]  Michel Rappaz,et al.  Modeling of casting, welding and advanced solidification processes-V : proceedings of the fifth International Conference on Modeling of Casting and Welding Processes, held in Davos Switzerland, September 16-21, 1990 , 1991 .