•FE analysis of fretting wear induced multiaxial-stresses in thin steel wires.•Implementation of the SWT critical-plane approach in a 3D FE fretting wear model.•Novel damage accumulation method for ...3D FE fretting wear simulation models.•Analysis of different methods for the fatigue coefficients estimation of wires.•Comparison the predicted lives with those obtained in fretting wear tests.
This paper studies the effect of fretting on fatigue life reduction of thin steel wires, using the frictionally-induced multiaxial contact stresses obtained from a finite element wear model, validated in previous work. The fatigue life prediction model uses a critical-plane SWT approach in a 3D crossed cylinder problem. A new damage accumulation methodology for the adaptive mesh simulation, based on the cyclic material removal, has been developed. Four methods (Manson’s universal slope, Muralidharan modified universal slopes, medians and fatigue S–N curves) for estimation of the fatigue coefficients of the wire have been used. Manson’s method and medians method give lives closer to those obtained from fretting wear tests in thin steel wires. The other methods are more conservative. The methodology predicts correctly the life reduction of this component due to the increase of normal load (contact pressure), while it is not clearly predicted that an increase of the stroke reduces the life of these components as shown in the experimental testing. Guidelines for developing a more robust methodology are proposed.
► 3D FE implementation of continuum damage mechanics for multiaxial fatigue. ► Validation for uniaxial and notched fatigue and fretting fatigue for Ti–6Al–4V. ► Automatic incrementation scheme for ...efficient computation of damage accumulation. ► Captures effect of contact slip on fatigue life for round-on-flat fretting geometry. ► Comparisons with critical-plane multiaxial fatigue approach for fretting.
The three-dimensional finite element implementation of a continuum damage mechanics formulation for multiaxial fatigue is presented, incorporating elastic modulus reduction due to fatigue damage. The implementation is validated against theoretical and published experimental results for uniaxial and notched multiaxial fatigue under different combinations of mean and alternating stresses for Ti–6Al–4V. An automatic incrementation scheme is developed for efficient computation of damage accumulation and hence stress redistribution. The method is also implemented in two-dimensional, plane strain for fretting fatigue and is shown to successfully capture the effect of contact slip on fatigue life for a round-on-flat fretting geometry. Comparisons are also made with a critical-plane multiaxial fatigue approach for fretting. The work is a first step towards a more general fatigue damage approach to unify wear and fatigue prediction for fretting.
Tidal turbine blades are subjected to significant thrust and torsional loadings due to the high density of the seawater in which they operate. These thrust loadings lead to high bending moments at ...the blade root, which can prove to be a serious design constraint for these devices and can have implications with respect to cost-effectiveness and scalability. This work presents a combined hydrodynamic-structural design methodology for a commercial scale (1.5 MW) tidal turbine. A hydrodynamic analysis of the blade is carried out to determine force distributions along the blade span under normal and extreme operating conditions. Using output from the hydrodynamic model, a pre-processor for computing blade structural properties is used to determine the strain distribution along the blade spar caps. The strain distributions from this analysis are then compared with a finite element model of the blade which is then used to compare the structural performance of glass fibre reinforced polymer (GFRP) and carbon fibre reinforced polymer (CFRP) as spar cap materials.
► Combined hydrodynamic-structural design methodology for a tidal turbine blade is presented. ► Comparison of glass fibre and carbon fibre as blade construction materials. ► High bending moments are likely to restrict up-scaling of composite designs. ► Predicted spar cap thickness has significant cost implications for production.
A finite element-based method is presented for simulating both the fretting wear and the evolution of fretting variables with number of wear cycles in a cylinder-on-flat fretting configuration for ...application to aeroengine transmission components. The method is based on a modified version of Archard’s equation and is implemented within a commercial finite element code. Fretting tests are employed to determine the coefficient of friction (COF) and the wear coefficient applicable to the contact configuration and loading conditions. The wear simulation technique is incremental in nature and the total simulation time has been minimised via mesh and increment size optimisation. The predicted wear profiles have been compared with profilometer measurements of fretting test scars.
Fatigue crack nucleation in polycrystal ferritic steel is investigated through experimental observation of multiple large-grained, notched, four-point bend tests combined with explicit ...microstructural representation of the same samples using crystal plasticity finite element techniques in order to assess fatigue indicator parameters, together with the roles of elastic anisotropy and length scale effects in slip development, and hence in crack nucleation.
Elastic anisotropy has been demonstrated to play a pivotal role in the distribution and magnitude of polycrystal slip relative to observed crack nucleation sites in the context of constrained cyclic microplasticity. Length scale effects were found not to alter substantively the distributions or magnitudes of slip relative to the observed crack nucleation site, but in detailed analyses of an experimental sample, the location of highest magnitude of geometrically necessary dislocations was found to coincide precisely with the position of predicted peak plasticity and the experimentally observed crack nucleation site.
The distributions of microplasticity within polycrystal samples were found to change quite significantly between the first yield and after multiple cycles. As a result, the effective plastic strain per cycle was found to be a better indicator of fatigue crack nucleation than peak effective plastic strain. In nine independently tested and analysed polycrystal samples, the cyclic effective plastic strain and crystallographic system peak accumulated slip were found to be good indicators of a fatigue crack nucleation site.
► Elastic anisotropy is pivotal in polycrystal slip and observed HCF crack nucleation. ► Peak GND density coincides with experimentally observed crack nucleation site. ► Microplasticity distribution changes between first yield and multiple cycles. ► Peak accumulated slip and cyclic effective plastic strain are good FIPs. ► Crack growth path not determined by dominant slip direction.
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•Development of a dislocation-based cyclic softening model.•Development of a precipitate strengthening material model.•Prediction of microstructure size effects of laths and ...precipitates.•Application to 9–12Cr steels for different strain-rates and temperatures.
A dislocation-based model for high temperature cyclic viscoplasticity in 9–12Cr steels is presented. This model incorporates (i) cyclic softening via decrease in overall dislocation density, loss of low angle boundary dislocations and coarsening of the microstructure and (ii) kinematic hardening via precipitate strengthening and dislocation substructure hardening. The effects of the primary micro-structural variables, viz. precipitate radii, dislocation density and martensitic lath width on cyclic viscoplasticity, reveal a size effect of initial precipitate radii and volume fraction, with smaller radii and a higher density of precipitate producing a stronger material. A similar effect is also predicted for initial martensitic lath width at temperatures below 500°C. The model is intended for microstructure sensitive design of high temperature materials and components for next generation power plant technology.
Absorbable metal stents (AMSs) are an emerging technology in the treatment of heart disease. Computational modelling of AMS performance will facilitate the development of this technology. In this ...study a physical corrosion model is developed for AMSs based on the finite element method and adaptive meshing. The model addresses a gap between currently available phenomenological corrosion models for AMSs and physical corrosion models that have been developed for more simple geometries than those of a stent. The model developed in this study captures the changing surface of a corroding three-dimensional AMS structure for the case of diffusion-controlled corrosion. Comparisons are made between model predictions and those of previously developed phenomenological corrosion models for AMSs in terms of predicted device geometry and mechanical performance during corrosion. Relationships between alloy solubility and diffusivity in the corrosion environment and device performance during corrosion are also investigated.
A unique insight into damage formation in CF/PEEK laminates before, during and after cryogenic cycling, using optical microscopy and 3D X-ray computed tomography (CT), is presented. Thicker laminates ...were found to exhibit significantly greater microcrack density and delamination when compared to thinner laminates, with lay-up and material type also being important contributing factors. Thermal residual stress induced microcracking was also found in thicker laminates post-processing. 3D rendering software was used to prove the presence of through thickness crack networks within the laminates, as well as the extent of cracking through the specimen width. Crack opening in inner and off-axis ply groups was found to be significantly less than outer plies, implying the importance of these plies in limiting laminate permeability. The presence of voids was found to influence crack nucleation and growth paths within the laminates, with full void volume characterisation presented.
In this study a numerical model is developed to predict the effects of corrosion on the mechanical integrity of bioabsorbable metallic stents. To calibrate the model, the effects of corrosion on the ...integrity of biodegradable metallic foils are assessed experimentally. In addition, the effects of mechanical loading on the corrosion behaviour of the foil samples are determined. A phenomenological corrosion model is developed and applied within a finite element framework, allowing for the analysis of complex three-dimensional structures. The model is used to predict the performance of a bioabsorbable stent in an idealized arterial geometry as it is subject to corrosion over time. The effects of homogeneous and heterogeneous corrosion processes on long-term stent scaffolding ability are contrasted based on model predictions.
► Development of a cyclic sinh unified viscoplasticity constitutive model. ► Model applied to P91 steel under high temperature, cyclic loading conditions. ► Novel calibration technique for the ...identification of the viscoplastic parameters. ► sinh model allows the strain rate effect of 9Cr steels to be modelled accurately.
An improved unified cyclic viscoplastic material model for high temperature fatigue of P91 steel is presented. The primary enhancement over existing models is in relation to strain-rate independence of parameters, for accurate interpolation and extrapolation across a range of strain-rates and stress regimes, as relevant to flexible operation of high temperature power generation plant. The model combines a hyperbolic sine constitutive equation with anisothermal cyclic evolution of isotropic and kinematic hardening variables. The material model is developed from a thermodynamic framework and is implemented in multi-axial form within a user material subroutine. The user material subroutine is calibrated and validated for P91 steel across a range of cyclic (isothermal fatigue and thermo-mechanical fatigue) and non-cyclic high temperature loading conditions. A novel method for the identification of the cyclic viscoplastic material parameters is also presented.
