101,963 research outputs found
A review of analytical aspects of fretting fatigue, with extension to damage parameters, and application to dovetail joints
No full textRecent 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
Elastic multiscale contact of rough surfaces: Archard's model revisited and comparisons with modern fractal models
No full textStress field near sharp notches
No full textThe correct description of the stress field of a two dimensional linear elastic domain with sharp notches and under complex load conditions can be obtained using the superposition of two elementary stress fields having respectively symmetric and anti-symmetric displacements. On the free boundaries of a sharp notch, the distance between the singularity and the points where the radial stresses have the same values for both the elementary stress fields, can be used for a complete description of the stress distribution of domains with the same shape and different sizes. This distance is proportional to the intrinsic defect introduced by the shape of the domain. An example of application of the described approach has been performed with regard to the parametric analysis of the stress field and of the intrinsic defect in an idealised model of a welded butt join
Numerical methods for the optimisation of specific sliding, stress concentration and fatigue life of gears
Get PDFPresented in this paper is a set of modern tools for the design of gearing: kinematic optimisation (minimisation and balancing of specific sliding), static stress analysis (to minimise stress concentrations) and crack propagation studies (to estimate fatigue life under a pre-existing defect). All three aspects are integrated in a software package developed by the authors. In particular, Boundary Element (BE) and Finite Element (FE) grids are automatically generated corresponding to gears manufactured by means of user defined tools with known shape and cutting parameters. BE models are used for a complete and automatic subcritical propagation analysis of cracks. FE models are used mostly for cases without crack propagation but requiring a greater versatility.Tests conducted on cases found in the literature demonstrate the accuracy of the methods used and the effects of rack shift factors and of rim thickness are studied in example cases.It is found that the fatigue life depends significantly on the cracking path mode, which in turn is particularly sensitive to the rim thickness in gears manufactured on thin hollow shafts as are typical in aeronautical applications. Further, the rack shift factors significantly change the stress concentrations (and therefore the maximum torque transmittable, in general in a beneficial manner). However, for designs with same concentration factor the fatigue life is considerably different, and in particular is lower on gears with a low number of teeth. This clearly indicates that the use of a complete crack propagation analysis from the early stages of the design process is highly recommended
On non-symmetrical plane contacts
Get PDFPlane elastic contact problems are considered, with particular emphasis on asymmetrical punch profiles, in the case of ‘complete’, ‘partially complete’ and ‘incomplete’ contact. An explicit, analytical solution is presented for the case of a single area of contact where the overlap is described by a generic spline function, and examples presented. The interior stress field and strength of the contact, under full or partial slip conditions, are also discussed, and some example shown for representative cases. It is found also that the direction of sliding has a significant effect for the strength of non-symmetrical contacts
On the extraction of notch stress intensity factors by the post-processing of stress data on the free edges of the notch
No full textFollowing on the lines of a previous paper dedicated to cracked components by Ciavarella et al., here the case of a notch of semi-angle alpha is considered. Contrary to the crack case (alpha = 180°), the free edges of the notch are easily accessible to experimental analysis; moreover they provide information about all the terms of the Williams series expansion of the stress field about the notch apex, including the most important, i.e. the symmetric and antisymmetric singular term notch stress intensity factors (N-SIFs), whereas for the crack case the mode I N-SIFs cannot be extracted from those stresses. Another important different feature is that symmetric and antisymmetric N-SIFs have different singularities, and in several cases they are so close that their contributions tend to overlap. Therefore, a simple procedure is here proposed to use radial stresses, to separate their symmetric and antisymmetric contributions a priori by computing the sum and difference of the stresses on the two edges, to post-process these quantities in the 'asymptotic region' with standard least-squares techniques and to extract the N-SIFs. The method is applied to a simple case known in the literature and solved by means of a boundary element code, and the results are almost coincident with previous results, even with quite coarse mesh discretizations
Elastic multiscale contact of rough surfaces: Archard's model revisited and comparisons with modern fractal models
Get PDFOn the extraction of notch stress intensity factors by the post-processing of stress data on the free edges of the notch
No full textFollowing on the lines of a previous paper dedicated to cracked components by Ciavarella et al., here the case of a notch of semi-angle alpha is considered. Contrary to the crack case (alpha = 180 degrees), the free edges of the notch are easily accessible to experimental analysis; moreover they provide information about all the terms of the Williams series expansion of the stress field about the notch apex, including the most important, i.e. the symmetric and antisymmetric singular term notch stress intensity factors (N-SIFs), whereas for the crack case the mode I N-SIFs cannot be extracted from those stresses. Another important different feature is that symmetric and antisymmetric N-SIFs have different singularities, and in several cases they are so close that their contributions tend to overlap. Therefore, a simple procedure is here proposed to use radial stresses, to separate their symmetric and antisymmetric contributions alpha priori by computing the sum and difference of the stresses on the two edges, to post-process these quantities in the 'asymptotic region' with standard least-squares techniques and to extract the N-SIFs. The method is applied to a simple case known in the literature and solved by means of a boundary element code, and the results are almost coincident with previous results, even with quite coarse mesh discretizations
A review of analytical aspects of fretting fatigue, with extension to damage parameters, and application to dovetail joints
No full textRecent advances by the authors in analytical methods for the analysis of plane fretting fatigue (FF) contact problems are described, acid 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 hat one, or an intermediate one. (C) 2001 Elsevier Science Ltd. All rights reserved
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