1,570 research outputs found
On higher order terms and out-of-plane singular mode
No full textIt is well known that in a plate weakened by a through-the-thickness crack and subjected to remote anti-symmetric loading (mode II), the Poisson's effect leads to the generation of a coupled out-of-plane singular mode (mode O). Recent theoretical and numerical analyses have demonstrated that this effect also occurs in plates weakened by pointed V-notches, and it can play an important role in failure initiation especially in the case of large notch opening angles. Dealing with cracked plates the influence of higher order terms tied to mode II loading on the out-of-plane singular mode has not been investigated until now. The aim of this paper is to fill this gap with an accurate analysis of mode II higher order terms and their effects on mode O. © 2011 Elsevier Ltd. All rights reserved.F. Berto, P. Lazzarin and A. Kotousovhttp://www.elsevier.com/wps/find/journaldescription.cws_home/505659/description#descriptio
On coupled fracture modes and three-dimensional fracture mechanics
No full textA. Kotousov, P. Lazzarin, F. Berto, L.P. Poo
Fictitious notch rounding concept applied to sharp V-notches: Evaluation of the micro structural support factor for different failure hypotheses. Part I: Basic stress equations
No full textWith the aim to perform a comprehensive and accurate evaluation of the microstructural support factor of sharp V-notches (Neuber's notch rounding concept), in Part I of this contribution, the indispensable theoretical tools, especially the basic stress equations, are reconsidered and amended in respect of accuracy of results. First, the analytical solution derived by Neuber [Neuber H. Kerbsparmungslehre. 2nd ed. Berlin: Springer-Verlag; 19581 for sharp rounded V-notches with an arbitrary flank angle under tension loading is considered. The equation of the normal stress has been obtained with the restriction to the notch bisector. Using the Airy stress function suggested by Neuber, this solution is extended to the region outside the notch bisector, and the complete stress field is derived in this manner. A comparison between Neuber's solution, a more recent solution due to Filippi et al. [Filippi S, Lazzarin P, Tovo R. Developments of some explicit formulas useful to describe elastic stress fields ahead of notches in plates. Int J Solids Struct 2002;39:4543-65] and highly accurate FE results is performed. Filippi's equations which include Williams' solution [Williams ML. Stress singularities resulting from various boundary conditions in angular corners on plates in tension. J App] Mech 1952;19:526-8] for pointed V-notches, are shown to be superior
On a coupled mode at sharp notches subjected to anti-plane loading
No full textWhen a crack or sharp notch is subjected to anti-plane shear loading the boundary conditions negate the transverse shear stress components at the free surfaces and generate a coupled in-plane shear stress field, which can be singular. For sharp V-notches with zero notch opening angle (or cracks) this 3D phenomenon was known for a long period of time. However this mode was largely ignored in stress analysis of notched components. Till now it is still unclear how significant this mode is and whether it has to be taken into consideration in integrity and failure analysis of engineering structures. The present paper is aimed to investigate this singular mode by means of the 3D Finite Element method, which is applied to notched plates with different notch opening angles and plate thicknesses. The stress state associated with the coupled mode is localised and quickly decays with the distance from the notch tip. Therefore, the obtained theoretical results can be applied to a wide range of notched components provided that the boundaries are sufficiently far from the notch tip. Among these results is the effect of the plate thickness on the intensity of the coupled mode; the latter increases with the decrease of the plate thickness. Significance of these new results to failure and integrity assessments of plate and shell components with sharp notches, including through-the-thickness cracks, is discussed in the final section of the paper. © 2012 Elsevier Masson SAS. All rights reserved.Filippo Berto, Andrei Kotousov, Paolo Lazzarin, Fabio Pegori
On three-dimensional stress field and deterministic scale effect in notched plate components
No full textF. Berto, P. Lazzarin, A. Kotouso
Transverse singular effects in V-shaped notches stressed in mode II
No full textThe concept of a stress singularity is a cornerstone of modern fracture mechanics. A new mode of stress singularity, the out-of-plane singular mode or K O mode, was recently identified for V-shaped notches subjected to in-plane loading. This new mode is coupled with the shear mode and related to Poisson’s effect. The previous studies based on the first order plate theory focused on the derivation of a characteristic equation describing the strength of this singularity and provide no information regarding the intensity, extent and relevance of this mode to practical problems. This paper aims to fill this gap. The approach utilises the 3D finite element method and a standard regression technique for characterisation of the notch singular modes. A comprehensive study of the influence of Poisson’s ratio, plate thickness and notch opening angle on the value of the notch stress intensity factor associated with this mode is conducted for infinite plates. Additionally, to demonstrate the relevance of this new singular mode to practical problems an investigation of the out-of-plane mode and associated three-dimensional effects are presented for the case of a welded lap joint. Main areas of further research are also identified.Steven Harding, Andrei Kotousov, Paolo Lazzarin and Filippo Bert
Three dimensional finite element mixed fracture mode under anti-plane loading of a crack
No full textThe 3D Finite Element method is applied to mixed fracture under anti-plane loading of a straight through-the-thickness crack in a linear elastic plate. This coupled fracture mode represents one of three-dimensional phenomena, which are currently largely ignored in numerical simulations and failure assessment of structural components weakened by cracks. It arises due to the boundary conditions on the plate free surfaces, which negate the transverse shear stress components corresponding to classical mode III. Instead, a new singular stress state in addition to the well-known 3D corner singularity is generated. This singular stress state (or coupled fracture mode) can affect or contribute significantly to the fracture initiation conditions. The coupled singular mode exists even if the applied anti-plane loading produces no singularities (KIII=0). In this case there is a strong thickness effect on the intensity of the coupled fracture mode. © 2013 Elsevier Ltd.Andrei Kotousov, Filippo Berto, Paolo Lazzarin, Fabio Pegori
A review of the volume-based strain energy density approach applied to V-notches and welded structures
No full textA large bulk of experimental data from static tests of sharp and blunt V-notches and from fatigue tests of welded joints are presented in an unified way by using the mean value of the Strain Energy Density (SED) over a given finite-size volume surrounding the highly stressed regions. When the notch is blunt, the control area assumes a crescent shape and R(0) is its width as measured along the notch bisector line. In plane problems, when cracks or pointed V-notches are considered, the volume becomes a circle or a circular sector, respectively. The radius R(0) depends on material fracture toughness, ultimate tensile strength and Poisson's ratio in the case of static loads; it depends on the fatigue strength Delta sigma(A) of the butt ground welded joints and the Notch Stress Intensity Factor (NSIF) range Delta K(1) in the case of welded joints under high cycle fatigue loading (with Delta sigma(A) and Delta K(1) valid for 5 X 10(6) cycles). Dealing with welded joints characterised by a plate thickness greater than 6 mm, the filial synthesis based on SED summarises nine hundred data taken from the literature while a new synthesis from spot-welded joints under tension and shear loading, characterised by a limited thickness of the main plate, is presented here for the first time (more than two hundred data). Dealing with static tests, about one thousand experimental data as taken from the recent literature are involved in the synthesis. The strong variability of the non-dimensional radius R/R(0), ranging from about zero to about 1000, makes the check of the approach based on the mean value of the SED severe
Singolarita fuori-piano indotte da effetti tridimensionali in prevalente modo 2
No full textIn the application of the Strain Energy Density (SED) approach for fatigue strength assessments of welded joints a well-defined control volume is considered. This volume surrounds the weld root or weld toe, both modelled like sharp (zero radius) V-notches with different opening angles. The volume becomes a circular sector under plane strain conditions, with the radius being about 0.3 mm for welded joints made of structural steel. The mean value of the SED mainly depends on the singular stress fields when the main plate thickness is large enough, whereas the influence of the T-stress component cannot be neglected in the case of thin-walled welded joints. Both contributions are directly accounted for by using finite element models, also when the relevant meshes are quite coarse. This fact makes the application of the SED approach easier than any stress-based approach in the case of complex structures. Due to three-dimensional effects, a non conventional out-of-plane singular mode can be present, in addition to mode I and mode II stress singularities according to Williams’ solution. This out-of-plane mode, which has recently been presented by Kotousov, is discussed here with reference to welded (seam) lap joints under tensileshear loads.P. Lazzarin, F. Berto, A. Kotousov and S. Hardin
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