Residual Stresses around Individual Graphite Nodules in Ductile Iron: Impact on the Tensile Mechanical Properties

Abstract:

Residual stresses in ferritic ductile iron castings have been studied for decades. However, little attention has traditionally been given to the local residual stresses which may arise in the microstructure as a result of the thermal contraction mismatch between the matrix and the graphite nodules during solid-state cooling. Recent synchrotron X-ray measurements performed by the authors have demonstrated that in the ferritic phase these local stresses can be in the order of 100-150 MPa, hence of the same order of magnitude as the material macroscopic yield stress. This suggests that they might have a significant influence on the mechanical properties of ductile iron components. However, no systematic research appears to have been conducted so far to investigate this aspect. The present work takes a first step in this direction by presenting an integrated theoretical analysis which addresses both the formation of these local residual stresses at the microscopic level and their role during mechanical loading at the macro-scale.

• Periodical: Materials Science Forum (Volume 925)
• Pages: 465-472
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.925.465
• Online since: June 2018
• Authors: Tito Andriollo*, Jesper Thorborg, Niels Skat Tiedje, Jesper Henri Hattel
• Keywords: Cast Iron, Ductile Iron, Graphite, Mechanical Properties, Residual Stress

References

[1] 50th Census of World Casting Production, Mod. Cast. - A Publ. Am. Foundry Soc. (2016) 25–29.

[2] N.S. Tiedje, Solidification, processing and properties of ductile cast iron, Mater. Sci. Technol. 26 (2010) 505–514.

[3] T. Andriollo, J. Hattel, On the isotropic elastic constants of graphite nodules in ductile cast iron: Analytical and numerical micromechanical investigations, Mech. Mater. 96 (2016) 138–150.

DOI: 10.1016/j.mechmat.2016.02.007

[4] T. Andriollo, Graphite nodules and local residual stresses in ductile iron: Thermo-mechanical modeling and experimental validation, PhD thesis, Technical University of Denmark, ISBN: 978-87-7475-476-3, (2017).

[5] Y.B. Zhang, T. Andriollo, S. Fæster, W. Liu, J. Hattel, R.I. Barabash, Three-dimensional local residual stress and orientation gradients near graphite nodules in ductile cast iron, Acta Mater. 121 (2016) 173–180.

DOI: 10.1016/j.actamat.2016.09.009

[6] T. Andriollo, J. Thorborg, N. Tiedje, J. Hattel, A micro-mechanical analysis of thermo-elastic properties and local residual stresses in ductile iron based on a new anisotropic model for the graphite nodules, Model. Simul. Mater. Sci. Eng. 24 (2016) 055012(19pp).

DOI: 10.1088/0965-0393/24/5/055012

[7] T. Andriollo, K. Hellström, M.R. Sonne, J. Thorborg, N. Tiedje, J. Hattel, Uncovering the local inelastic interactions during manufacture of ductile cast iron: How the substructure of the graphite particles can induce residual stress concentrations in the matrix, J. Mech. Phys. Solids 111 (2018) 333–357.

DOI: 10.1016/j.jmps.2017.11.005

[8] MAGMA GmbH, MAGMA5 simulation software, (2017).

[9] M.R. Sonne, J. Thorborg, J.H. Hattel, Modelling the effect of coating on the stresses and microstructure evolution in chill casting of wind turbine main shafts, Wind Energy. (2017).

DOI: 10.1002/we.2114

[10] N. Bonora, A. Ruggiero, Micromechanical modeling of ductile cast iron incorporating damage. Part I: Ferritic ductile cast iron, Int. J. Solids Struct. 42 (2005) 1401–1424.

DOI: 10.1016/j.ijsolstr.2004.07.025

[11] C. Berdin, M.J. Dong, C. Prioul, Local approach of damage and fracture toughness for nodular cast iron, Eng. Fract. Mech. 68 (2001) 1107–1117.

DOI: 10.1016/s0013-7944(01)00010-8

[12] D. Peric, On a class of constitutive equations in viscoplasticity: formulation and computational issues, Int. J. Numer. Methods Eng. 36 (1993).

[13] J. Schneibel, M. Heilmaier, Hall-Petch Breakdown at Elevated Temperatures, Mater. Trans. 55 (2014) 44–51.

DOI: 10.2320/matertrans.ma201309

[14] D.K.L. Tsang, B.J. Marsden, S.L. Fok, G. Hall, Graphite thermal expansion relationship for different temperature ranges, Carbon N. Y. 43 (2005) 2902–2906.

DOI: 10.1016/j.carbon.2005.06.009

[15] H. Qin, Y. Sun, J.Z. Liu, Y. Liu, Mechanical properties of wrinkled graphene generated by topological defects, Carbon N. Y. 108 (2016) 204–214.

DOI: 10.1016/j.carbon.2016.07.014

[16] F.E. Faris, L. Green, C.A. Smith, The thermal dependence of the elastic moduli of polycrystalline graphite, J. Appl. Phys. 23 (1952) 89–95.

DOI: 10.1063/1.1701984

[17] D.K.L. Tsang, B.J. Marsden, S.L. Fok, G. Hall, Graphite thermal expansion relationship for different temperature ranges, Carbon N. Y. 43 (2005) 2902–2906.

DOI: 10.1016/j.carbon.2005.06.009

[18] G. Savini, Y.J. Dappe, S. Öberg, J.C. Charlier, M.I. Katsnelson, A. Fasolino, Bending modes, elastic constants and mechanical stability of graphitic systems, Carbon N. Y. 49 (2011) 62–69.

DOI: 10.1016/j.carbon.2010.08.042