Abstract
The complicated constitutive behaviour of cast iron, involving a non-linear elastic regime, tension-compression stress asymmetry, varying elastic modulus and an inflection in the tension-to-compression hardening curve, is investigated using a micromechanical modelling approach. In this way, it is demonstrated that the abnormalities observed in the constitutive behaviour are qualitatively and quantitatively explained by the interaction behaviour between the matrix and graphite constituents. In initial tension, the absence of linearity is rationalised by the successive loss in load-carrying capacity of the graphite phase due to debonding, which in subsequent cycling, results in the opening and re-contact of the matrix-graphite interface. This effect is demonstrated to result in tension-compression asymmetry in stress and elastic modulus, as well as the inflection in tension-to-compression loading. The given model of explanation is validated by comparison to the experimentally acquired microscopic strain field in EN-GJV-400 at locations where stress concentrations are generated due to the matrix-graphite debonding, using high-resolution digital image correlation of scanning electron images.
Highlights
Cast iron is a wide family of materials frequently employed in various engineering applications, for instance in the automotive industry (Trampert et al, 2008; Dawson, 2009; Ekström and Jonsson, 2014), due to their favourable castability, thermal conductivity and cost
There is at present a lack of consistent experimental evidence of the micromechanisms causing the mentioned abnormalities, and a unified model of explanation of the cyclic elastoplastic constitutive behaviour of cast iron has not previously been presented. The objective of this investigation is to render a qualitatively general model which rationalises the mechanical constitutive behaviour of cast iron in uniaxial cyclic loading. This is done by employing a micromechanical approach in order to relate the macroscopic mechanical behaviour with the underlying microscopic behaviour, which is experimentally validated using high-resolution digital image correlation (HRDIC) of scanning electron microscopy (SEM) images (Di Gioacchino and Quinta Da Fonseca, 2015; Efstathiou et al, 2010; Sutton et al, 2007a,b)
The observed agreement is good in both figures except for the first tensile loading sequence, which will be the topic of the section
Summary
Cast iron is a wide family of materials frequently employed in various engineering applications, for instance in the automotive industry (Trampert et al, 2008; Dawson, 2009; Ekström and Jonsson, 2014), due to their favourable castability, thermal conductivity and cost. More sophisticated yield functions have been considered, such as the Drucker-Prager (Altenbach et al, 2001; Ali et al, 2017) or the Gurson-Tveergard-Needleman yield function (Berdin et al, 2001; Seifert and Riedel, 2010) in order to reproduce the stress asymmetry The latter approach consists of investigating the averaged mechanical behaviour of a constructed volume element representing the microstructure, i.e. a homogenisation procedure (Zaoui, 2002). The objective of this investigation is to render a qualitatively general model which rationalises the mechanical constitutive behaviour of cast iron in uniaxial cyclic loading This is done by employing a micromechanical approach in order to relate the macroscopic mechanical behaviour with the underlying microscopic behaviour, which is experimentally validated using high-resolution digital image correlation (HRDIC) of scanning electron microscopy (SEM) images (Di Gioacchino and Quinta Da Fonseca, 2015; Efstathiou et al, 2010; Sutton et al, 2007a,b). A greater understanding of these materials has been achieved which is of great value for future development of cast iron constitutive models
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