Browsing by Author "Kakandar, Ebiakpo"

Now showing 1 - 5 of 5
  • Thumbnail Image
    ItemOpen Access
    Comparison of the low and high/very high cycle fatigue behaviors in Ni microbeams under bending
    (Springer, 2021-02-16) Barrios, Alejandro; Kakandar, Ebiakpo; Castelluccio, Gustavo M.; Pierron, Olivier N.
    The present work demonstrates a micromechanical technique to investigate the low cycle fatigue (LCF) behavior of Ni microbeams under fully reversed bending loadings. The technique extends the range of measured fatigue lives from the previously reported technique for high and very high cycle fatigue (HCF/VHCF) characterization in the same microbeams. The results highlight significant differences in the slope of stress and strain-life behavior and crack propagation rates that differ from an average of 10–12 m/cycle in HCF/VHCF to an average of 10–8 m/cycle in LCF. These results, in addition to postmortem fractography work, suggest that the mechanisms follow the conventional mechanisms of crack tip stress intensification in the LCF regime. This is in stark contrast to the void-controlled mechanisms that were previously identified in the HCF/VHCF regime. These results demonstrate that the transition in governing mechanisms from void-controlled to conventional mechanisms is highly influenced by the size effects present in the microbeams.
  • Thumbnail Image
    ItemOpen Access
    A computational and experimental comparison on the nucleation of fatigue cracks in statistical volume elements
    (Elsevier, 2020-04-05) Kakandar, Ebiakpo; Barrios, Alejandro; Michler, Johann; Maeder, Xavier; Pierron, Olivier N.; Castelluccio, Gustavo M.
    The failure of micron-scale metallic components presents significant variability as a result of their size being comparable to microstructural length scales. Indeed, these components do not represent the bulk of the material but correspond to statistical volume elements (SVEs). This work investigates the role of SVEs on fatigue crack nucleation with a novel comparison between microbeam experiments and microstructure-sensitive simulations. We recreate multiple microstructural computational realizations to estimate fatigue crack nucleation lives and orientations by means of physics-based crystal plasticity models. We demonstrate a unique approach to validate microstructure sensitive models and quantify the fatigue crack stochasticity associated with small volumes.
  • Thumbnail Image
    ItemOpen Access
    Computational and experimental study of crack initiation in statistical volume elements
    (EDP Sciences, 2019-12-02) Kakandar, Ebiakpo; Castelluccio, Gustavo M.; Barrios, Alejandro; Pierron, Olivier; Maeder, Xavier
    Fatigue crack formation and early growth is significantly influenced by microstructural attributes such as grain size and morphology. Although the crystallographic orientation is a primary indicator for fatigue cracking, the neighbourhood conformed by the first and second neighbour grains strongly affect the fatigue cracking driving force. Hence, two identical grains may result in different fatigue responses due to their interactions with their microstructural ensemble, which determines the fatigue variability. Naturally, macroscopic samples with millions of grains and thousands of competing microstructural neighbourhoods can effectively resemble a representative volume element in which fatigue failure may seem deterministic. However, when considering systems in which fatigue failure is controlled by hundreds or less of grains, fatigue failure is stochastic in nature and the samples are not a representative but a statistical volume. This work studies fatigue crack nucleation in micron-scale Ni beams that contain a few hundred grains. This work presents 3D crystal plasticity finite element models to compute stochastic distribution of fatigue indicator parameters that serve as proxies for crack nucleation in statistical volume elements. The integration of experiments with models provides a method to understand the irreversible deformation at the grain level that leads to fatigue cracking. Our results explain the role of grain morphology of crack nucleation distribution
  • Thumbnail Image
    ItemOpen Access
    A Simulation Based Approach to Model Design Influence on the Fatigue Life of a Vented Brake Disc
    (Elsevier, 2017-03-02) Kakandar, Ebiakpo; Roy, Rajkumar; Mehen, Jorn
    The brake disc is considered a safety critical components in vehicles, hence the growing concern on its service life performance. Brake disc performance is measured by several criteria of which prominent amongst these criteria is fatigue life and disc thermal deflection. This study considers the influence of geometric design features of a vented brake disc on its fatigue life at particular sections of the brake disc which are considered critical and its deflection due to thermal inputs. A parametric study is carried out with CAE/FEA using Taguchi design of experiment. The study identified the geometric design features that significantly influence the studied performance measures. Sensitivity plots were also obtained to show the manner these design factors affect the fatigue life at these points as well as the disc thermal deflection. Two design features, the inboard plate thickness and the length of the effective offset are observed to contribute majorly to the fatigue life of the brake disc as well as its thermal deflection. Hence, design effort should be concentrated on these features for optimal fatigue life design at these points of interest in this study.
  • Thumbnail Image
    ItemOpen Access
    Study of the dependencies between in-service degradation and key design parameters with uncertainty for mechanical components.
    (2017-08) Kakandar, Ebiakpo; Roy, Rajkumar; Mehnen, Jorn
    The design features of machine components can impact significantly in its life while in-service, and only relatively few studies which are case specific have been undertaken with respect to this. Hence, the need for more understanding of the influence of geometric design features on the service life of a machine component. The aim of this research is to develop a methodology to assess the degradation life of a mechanical component due to geometric design influence in the presence of uncertainties and its application for the optimisation of the component in the presence of these uncertainties. This thesis has proposed a novel methodology for assessing the thermal fatigue life, a degradation mechanism based on the influence of design features in the presence of uncertainties. In this research a novel uncertainty analysis methodology that is able to handle simultaneously the presence of aleatory and epistemic uncertainties is proposed for a more realistic prediction and assessment of a components thermal fatigue degradation life estimated using finite element analysis. A design optimisation method for optimising the components design in the presence of mixed uncertainty, aleatory and epistemic uncertainties is also proposed and developed. The performance of the proposed methodology is analysed through the use of passenger vehicle brake discs. The novel uncertainty quantification methodology was initially applied on a solid brake disc, and validated for generalisability using a vented brake disc which has more complex design features. While the optimisation method as proposed was applied on the vented brake disc. With these this research proposes a validated set of uncertainty and optimisation methodology in the presence of mixed uncertainties for a design problem. The methodologies proposed in this research provide design engineers with a methodology to design components that are robust by giving the design with the least uncertainty in its output as result of design parameters inherent variability while simultaneously providing the design with the least uncertainty in estimation of its life as a result of the use of surrogate models.