1,721,023 research outputs found
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
On non-symmetrical plane contacts
Full text linkPlane 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
Full text linkOn 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
Stress-driven morphological instability and catastrophic failure of microdevices
No full textIn microdevices, the competition between surface energy and elastic energy could lead at the phenomenon known as stress-driven morphological instability (MI), causing an increase of Surface roughness with time. Several different mass transport mechanisms can trigger such a morphological alteration and operate simultaneously: surface and bulk diffusion, evaporation and condensation, chemical reactions. Unstable solids could eventually evolve towards crack-like surfaces thus altering mechanical, electrical and optical properties of the devices or even leading to catastrophic failures by supercritical crack propagation. In this work, a more general kinetic law is employed to estimate the onset of MI, considering the effect of the stress field on the atomic mobility. A more intuitive and straightforward approach is used to determine the stability conditions, where the rate of atomic mass motion is introduced, as a stability parameter-The critical loads and wavelengths for the onset of MI, determined as a function of material parameters alpha and beta, are compared with the limiting conditions for the supercritical crack propagation (SC) of a crack-like surface in order to asses if and under which situations catastrophic failures by SC can be observed. Two practical cases are investigated: fixed wavelength (Case I) and arbitrary rough surface with a fixed remote load (Case II). In Case I, absolute and relative threshold loads are found below which MI could never occur and a transitional wavelength over which MI would always lead to SC is introduced. In Case II, it is shown that dominant perturbation for NIT would always lead to SC given enough time for the surface to evolve towards a crack-like profile. The influence of the material properties a and on the critical parameters is also addresse
On the post-processing of data obtained from cracked components
No full textThe use of a simple singular value decomposition (SVD) technique to post-process far-field data from cracked components is discussed. The technique employs the series expansion for stress or displacements ahead of the crack tip, which is available for a wide range of configurations. The use of higher-order terms, necessary for the post-processing, is beneficial for two reasons: (a) it permits the abstraction of the maximum usable amount of information; (b) it gives a better understanding of the fracture mechanics, especially regarding crack tip plasticity and dynamic propagation. Several numerical cases are examined and a comparison is made with analytical results, permitting an evaluation to be made of the pure numerical error in the post-processing
Recent trends in structural design of ultra-light refrigerated semitrailers
No full textThe need for weight reduction has recently motivated the use of better steels to produce lighter chassis in semitrailers lorries, and the resulting chassis are also inevitably more flexible. On the other hand, body structures are made with improved composite materials, so that the weight reduction often corresponds to an increase in rigidity. The combination of these two changes has made the chassis-body ensemble design more complex than it used to be when chassis were extremely rigid, so that there was no major interaction in their structural behaviour with the bodies, and 'beam theory' (or at most 'plate theory') was more than sufficient to design safely. Here a structural analysis using the Finite Element Method (FEM) is presented, using examples with different chassis with a particular composite material body. The distribution of loads between body and chassis and the amount of structural coupling have been determined when the stiffness of the chassis is reduced. It is found that safe ultra-light designs can be achieved only with a detailed investigation of the stresses acting on the fasteners in the fifth wheel zone. Within such limits, very high global weight reduction can be achieved, with evident advantages for the payload, and at the same time increased safety margins
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