Failure mechanisms and damage model of ductile cast iron under low-cycle fatigue conditions

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Proceedings titleSAE Technical Papers
ConferenceSAE 2013 World Congress and Exhibition, 16 April 2013 through 18 April 2013, Detroit, MI
SubjectFractographic observations; Inelastic deformation; Intergranular embrittlement; Nonlinear interactions; Stress strain behaviours; Synergetic interactions; Temperature conditions; Thermo-mechanical damages; Coalescence; Constitutive models; Embrittlement; Fatigue damage; Plasticity; Strain rate; Surface defects; Textures; Creep
AbstractStrain-controlled low-cycle fatigue (LCF) experiments were conducted on ductile cast iron at total strain rates of 1.2/min, 0.12/min and 0.012/min in a temperature range of RT 800°C. An integrated creep-fatigue (ICF) life prediction framework is proposed, which embodies a deformation mechanism based constitutive model and a thermomechanical damage model. The constitutive model is based on the decomposition of inelastic deformation into plasticity and creep mechanisms, which can describe both rate-independent and rate-dependent cyclic responses under wide strain rate and temperature conditions. The damage model takes into consideration of i) plasticity-induced fatigue, ii) intergranular embrittlement, iii) creep and iv) oxidation. Each damage form is formulated based on the respective physical mechanism/strain. The overall damage accumulation follows a nonlinear interaction mechanism that represents the nucleation and propagation of a surface crack in coalescence with internally distributed damages (cracks/voids). For ductile cast iron (DCI), the model predicates that the room temperature deformation and LCF life are primarily driven by cyclic plasticity; but at 400°C, albeit the deformation is mainly plasticity, its LCF is limited by intergranular embrittlement. When the temperature is increased above 600°C, rate-dependent stress-strain behaviour manifests due to creep, and the synergetic interaction of creep with oxidation dominates the LCF process. As a result of such interaction, a crossover-behaviour between room temperature and high-temperature (>600°C) strain-life relationships may occur, as observed in the experiments. The model prediction corroborates with the LCF test results and fractographic observations on the test coupons, which further substantiates the validity of the model.
Publication date
PublisherSAE International
AffiliationNational Research Council Canada; Aerospace
Peer reviewedYes
NPARC number21270627
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Record identifier5c5b967b-1277-4d66-9c42-f13846cb6a46
Record created2014-02-17
Record modified2016-05-09
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