Effect of contact geometry on the contact stresses in a flat with rounded edge contact
08 Mar 2019-Vol. 13, Iss: 48, pp 630-638
TL;DR: In this paper, a 2-D elastic and elasto-plastic finite element analysis has been carried out for a rounded contact geometry to study the influence of the radius of the corners "R" and length of the flat region "2a".
Abstract: The blade-disc dovetail interface in an aero-engine compressor is characterized by a non-uniform pressure distribution which can be obtained by an equivalent flat with round edge-on-plate configuration. The contact tractions for a mating pair are affected by many parameters which include, contact geometry, loading conditions, and material properties; with contact geometry being one of the prominent factors. In the present work, a 2-D elastic and elasto-plastic finite element analysis has been carried out for a rounded contact geometry to study the influence of the radius of the corners ‘R’ and length of the flat region ‘2a’. It is observed that the peak tensile stress in the fretting direction was found to decrease with increasing ‘a’ (for constant ‘R’) which is likely to delay the crack initiation. Also, as compared to elasto-plastic analysis, elastic analysis overestimates peak tensile stress and possibly give a conservative estimate for the fretting fatigue life. Further, the effect of modelling elastic-plastic behaviour is significant for low a/R ratio (for constant ‘R’). However, opposite trend was observed when ‘R’ was varied keeping ‘a’ constant. Also, it is found that the effect of contact geometry cannot be characterized using a single parameter like a/R ratio or contact area.
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01 Jan 2008
TL;DR: In this article, the authors classified the contact conditions at the pad-to-rotor interface as a conformal dry s-drone interface and showed that the contact condition depends strongly on contact conditions.
Abstract: Passenger car disc brakes are safety-critical components whose performance depends strongly on contact conditions at the pad-to-rotor interface. The interface can be classified as a conformal dry s ...
108 citations
TL;DR: In this article, the influence of counter surface roughness and lay on the tribological behavior of three bearing materials used in hydropower applications was investigated using a linear reciprocating flat-on-flat configuration under high contact pressure and low sliding speed.
Abstract: In Kaplan turbines, the most critical components are the self-lubricating polymer composite bearings used to control the guide vanes and the turbine blades. Reducing the sliding wear and friction of these bearings can benefit both the economy and the environment, including longer useful life, lower operational costs, and higher efficiency. In this study, the influence of stainless-steel counter surface roughness and lay on the tribological behaviour of three bearing materials used in hydropower applications were investigated using a linear reciprocating flat-on-flat configuration under high contact pressure and low sliding speed. The surface roughness was measured using white light interferometry. SEM and EDS analysis were used to investigate the worn surfaces. Results from this study show that overly smooth surfaces result in higher friction and wear of the counter surface, while rougher surfaces have a negative effect on the wear of the polymers. Highest surface coverage using protective transfer layers is found on the steel surfaces with the perpendicular lay and is accompanied with a lower coefficient of friction compared to the parallel lay. The dominant wear mechanism of the bearing materials changes from delamination wear to abrasive wear between the lowest and the intermediate roughness for steel surfaces with the parallel lay. It can be concluded that counter surface topography has a significant influence on the tribological behaviour of these bearing materials and that the effect differs between the self-lubricating polymer composites.
1 citations
TL;DR: In this paper , the effect of the design parameters of BCR TKA knee implants on the mechanics of knee joints and optimise and individualise the knee implant design parameters using the Taguchi method incorporating finite element analysis.
Abstract: Total knee replacement has become a viable option for treating severe knee arthritis. The demand for more kinematically functional implants that better replicate natural knee kinematics led to the development of total knee arthroplasty (TKA), including bi-cruciate-retaining (BCR) TKA. However, optimised design parameters of BCR TKA knee implants that can help achieve a long-term prosthetic survival rate remain unknown. Therefore, this study aimed to investigate the effect of the design parameters of BCR TKA knee implants on the mechanics of knee joints and optimise and individualise the knee implant design parameters using the Taguchi method incorporating finite element analysis. Herein, experimental factors and levels were selected and nine finite element models of BCR TKA knee implants were developed to optimise the design of the following parameters: the curvature ratio on the sagittal plane, curvature ratio on the coronal plane, and tibial slope. In addition, finite element analysis was used to determine the effect of the design parameters on the peak contact stress on ultra-high-molecular-weight polyethylene (UHMWPE) and its deformation. Consequently, among the three parameters that affect the peak contact stress and its deformation, the curvature ratio on the sagittal plane had the greatest effect (range = 10.96), followed by the curvature ratio on the coronal plane (range = 3.54), and the tibial slope (range = 2.56). The optimal design parameters for the BCR TKA knee implant were a curvature ratio of 1.5 on both the sagittal and coronal planes and a tibial slope of 5°. Under these conditions, the peak contact stress and deformation were 25.80 MPa and 0.0835 mm, respectively. The optimisation method based on finite element analysis and the Taguchi method can produce one of the highest-performing BCR TKA knee implant designs, thereby reducing the peak contact stress and deformation. This method sheds fresh light on the development of the BCR TKA knee implant as well as biomechanical decision-making to implant the TKA prosthesis correctly.
TL;DR: In this paper , the effect of pad radius on the contact parameters such as: contact pressure, shear traction, stresses, sliding, size of contact line and crack nucleation and its location along the contact line of aeronautical Al2024 alloy under fretting fatigue loading was analyzed.
Abstract: Abstract The fatigue process under fretting conditions is characterized by small oscillatory movements due to vibrating or cyclic loads between two surfaces in contact. Two phenomena can arise as a consequence: the surface wear of the bodies in contact, giving rise to the so-called fretting wear. The second phenomenon concerns crack nucleation in the contact region, causing a reduction in the fatigue strength of the component subjected to cyclic loading. This process is called “fretting fatigue”. In the present study, finite element models (2D-FEM) are provided to demonstrate the effect of pad radius on the contact parameters such as: contact pressure, shear traction, stresses, sliding, size of contact line and crack nucleation and its location along the contact line of aeronautical Al2024 alloy under fretting fatigue loading. Six numerical models are utilized to describe the effect of changing pad radii on contact stresses and damage of crack nucleation. The Ruiz parameter criterion should be used to predict the location of crack initiation in the contact zone. Comparison of the finite element results shows that there is a good agreement between the numerical modeling predictions with those analytical results. The stress field, relative slip, and damage parameters in fretting fatigue loading were highlighted. The pad radius substantially affects the distribution of contact parameters. Particular attention must be taken into consideration to this variable when analyzing the structure in fretting fatigue.
References
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TL;DR: In this article, a numerical approach to simulate fretting wear, based on a modified version of the Archard equation, is applied to a cylinder-on-flat fretting configuration for gross sliding and partial slip conditions.
Abstract: A numerical approach to simulate fretting wear, based on a modified version of the Archard equation, is applied to a cylinderon-flat fretting configuration for gross sliding and partial slip conditions. The evolution of contact geometry, surface contact variables, including, contact pressure and relative slip, and sub-surface stresses are predicted. Surface wear damage is predicted to have a significant effect on the near-surface tangential and shear stress distributions for both slip regimes, with significant differences between the partial slip and gross slip cases. The implications of these effects are discussed with respect to fatigue prediction, leading to new insight into experimentally observed effects of slip regime on crack initiation. The more detrimental effects of partial slip conditions, with respect to cracking risk, are demonstrated quantitatively. In addition, the results suggest an explanation for the observed variations in location of crack initiation within the slip zone under partial slip conditions. The work establishes a basis for direct incorporation of the effect of slip amplitude on fretting fatigue life prediction. 2003 Elsevier Ltd. All rights reserved.
175 citations
"Effect of contact geometry on the c..." refers background in this paper
...These elements are generally preferred over second-order elements which give fluctuating pressure distribution for contact problems with friction [15]....
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01 Apr 1998
TL;DR: In this paper, the contact problem and stress state for indentation by a flat punch with rounded edges are studied, and analytical solutions for both surface pressure and interior stress fields are obtained for both normal indentation and frictional contact.
Abstract: The contact problem and stress state for indentation by a flat punch with rounded edges is studied. For the contact problem itself analytical solutions are obtained for both surface pressure and interior stress fields. Cases of normal indentation and frictional contact, the latter in both sliding or partial slip conditions, are all treated. The transition from the Hertzian configuration to the contact between a nominally flat pad and contacting flat surface is discussed, and it is found that the strength of the contact decays surprisingly slowly. Regarding the von Mises yield parameter, there is a range of configurations for which the strength is actually higher than the Hertzian one, and the strength decays only when the corner radii are very small. The present solution is therefore a realistic alternative to the classical rigid-flat punch idealization, and has particular application to fretting fatigue tests.
168 citations
"Effect of contact geometry on the c..." refers background in this paper
...This results in a non-uniform pressure distribution with constant pressure at the center and pressure peaks at the corners [9]....
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...[9] which is a scaled-down model and represents the contact pressure distribution for a real blade-disc dovetail interface....
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...[9-11] in one of their seminal works, proposed the analytical solution for the contact tractions in the case of partially flat contacts subjected to oscillating tangential and bulk load....
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TL;DR: In this paper, the authors analyzed the impact of plane fretting fatigue contact problems and derived new consequences for FF damage, showing that the surface damage parameters decrease, but the tensile stress concentration increases, suggesting that for cracks eventually initiated, the likelihood of self-arrest is higher than in the equivalent Hertzian case with same loads.
Abstract: Recent advances by the authors in analytical methods for the analysis of plane fretting fatigue (FF) contact problems are described, and new consequences for FF damage are derived. Constant normal load and oscillating tangential load (the celebrated Cattaneo–Mindlin case) are considered with in-phase oscillating moderate bulk stresses, for an arbitrary spline rotated geometry and, in particular, the flat punch with rounded corners in view of application to the dovetail joints. Extremely simple, new results are found for initiation parameters such as tangential microslip and frictional energy, which have been used under certain conditions as threshold parameters for FF. Finally, it is shown that for an “almost flat” geometry, the surface damage parameters decrease, but the tensile stress concentration increases, although it becomes more localized, suggesting that for cracks eventually initiated, the likelihood of self-arrest is higher than in the equivalent Hertzian case with same loads. This seems to interpret recent experiments, although it is not clear whether the optimal geometry in terms of FF life is the perfectly flat one, or an intermediate one.
115 citations
01 Jan 2008
TL;DR: In this article, the authors classified the contact conditions at the pad-to-rotor interface as a conformal dry s-drone interface and showed that the contact condition depends strongly on contact conditions.
Abstract: Passenger car disc brakes are safety-critical components whose performance depends strongly on contact conditions at the pad-to-rotor interface. The interface can be classified as a conformal dry s ...
108 citations