1,721,146 research outputs found
Nocht mechanics under elastic and elastic-plastic conditions
No full textDeliberately created or inadvertently induced, notches and defects unavoidably exist in engineering components. Then, fatigue strength assessments often need linear and nonlinear stresses and strains at the notch root or in the close neighbourhood of it.
Whilst there is a large body of work on notch root stresses under tensile loading, in the previous literature there has been relatively little attention paid to torsional loading of prismatic shafts. Nevertheless, the engineering use of torque carrying shafts is extensive and they are susceptible to crack formation at notches and grooves under both static and cyclic conditions.
In this work, a comprehensive evaluation of the components of the linear and non-linear stress fields ahead various kind of mode III loaded notches is presented.
These expressions are also used to provide closed form solutions for some local parameters such as the averaged strain energy density and Rice J-integral.
Finally an assessment of fatigue strength of welded joints subjected to multiaxial loading (combined Mode I and Mode III) as well as to complex three-dimensional welded joints based on the local energy is presented.Variazioni geometriche, come fori e intagli, sono comunemente presenti nella maggior parte dei componenti meccanici. Tali discontinuità, causa di una perturbazione della distribuzione di tensione nominale, comportano un aumento locale delle tensioni e delle deformazioni. La conoscenza delle distribuzioni di tensione nelle adiacenze di tali variazioni geometriche è quindi di grande importanza nella valutazione della resistenza a fatica di componenti strutturali.
Mentre in letteratura vi sono numerose soluzioni teoriche per componenti piani soggetti a trazione o flessione, relativamente pochi sono i contributi relativi a casi di torsione in travi prismatiche o assialsimmetriche. Tuttavia, gli alberi soggetti a coppia torcente rappresentano un caso di notevole interesse applicativo, essendo potenzialmente interessati da fenomeni di innesco e propagazione di cricche di fatica dovute a effetti di intaglio di diverso tipo.
Il lavoro riporta delle soluzioni analitiche in forma chiusa per le distribuzioni di tensione generate da intagli circonferenziali in componenti assialsimmetrici soggetti a torsione, in condizioni lineari elastiche ed elastoplastiche.
Tali soluzioni sono inoltre utilizzate per determinare delle espressioni in forma chiusa per alcuni parametri locali, quali la densità di energia di deformazione e il J-integral di Rice, e per discutere dal punto di vista teorico alcuni aspetti peculiari relativi all’effetto d’intaglio in presenza di sollecitazioni torsionali.
Viene infine proposta una sintesi di un elevato numero di risultati sperimentali, tratti dalla letteratura, relativi a giunzioni saldate tridimensionali soggetti a fatica monoassiale (trazione o flessione) e multiassiale (Modo I e Modo III combinati) in termini di densità di energia di deformazione
A three-dimensional stress field solution for pointed and sharply radiused V-notches in plates of finite thickness
No full textBy making use of the generalized plane strain hypothesis, an approximate stress field theory has been developed according to which the three-dimensional governing equations lead to a system where a bi-harmonic equation and a harmonic equation should be simultaneously satisfied. The former provides the solution of the corresponding plane notch problem, and the latter provides the solution of the corresponding out-of-plane shear notch problem. The system can be applied not only to pointed three-dimensional V-notches but also to sharply radiused V-notches characterized by a notch tip radius small enough. Limits and degree of accuracy of the analytical frame are discussed comparing theoretical results and numerical data from FE models
A new version of the Neuber rule accounting for the influence of the notch opening angle for out-of-plane shear loads
No full textThe paper deals with nonlinear stress and strain distributions at the root of sharp and rounded notches with different opening angles under antiplane shear loading and small scale yielding, In order to make an easier comparison with the Neuber rule, the material is thought of as obeying the particular nonlinear law used in the past just by Neuber.
By solving the linear differential equation resulting from the use of the hodograph transformation, a new relationship linking linear and nonlinear stress and strain concentrations is found. The relationship is written also in terms of the relevant notch stress intensity factors. In contrast with the Neuber rule, this relationship strictly depends on the notch opening angle. Even when the notch opening angle is zero, it does not match the Neuber Rule, but results in an additional factor 2 which is in agreement with Hult and McClintock's Solution when the notch tip radius tends to zero and the notch becomes a crack
The strain energy density approach applied to cyclic and transient thermo-mechanical problems
No full textThree-dimensional elastic stress fields ahead of notches in thick plates under various loading conditions
No full textThe paper discusses the features of three-dimensional elastic stress distributions ahead of notches in finite thick plates under different loading conditions. It is proved that, under certain circumstances, the three-dimensional governing equations of elasticity can be reduced to a system where a bi-harmonic equation and a harmonic equation have to be simultaneously satisfied. The former provides the solution of the corresponding plane notch problem, the latter provides the solution of the corresponding out-of-plane shear notch problem. The analytical frame is applied to a number of notched geometries, and its degree of accuracy is discussed comparing theoretical results and numerical data from 3D FE models. Practical consequences on the expected crack paths are also documented for one of the considered model
Antiplane shear stresses in orthotropic plates with lateral blunt notches
No full textThis contribution investigates the stress fields in orthotropic plates featuring lateral notches under anti-plane shear loading. Four different notch geometries are considered and the relevant analytical expressions for the stress distribution are derived in closed form. For each geometry, the main features of the stress fields and the accuracy of the analytical expressions developed are discussed comparing theoretical results and numerical data from FE analyses carried out on finite plates under longitudinal shear
Torsional stress distributions in tubes with external and internal notches
No full textPractical expressions useful to assess the elastic stress distribution in a torque loaded axisymmetric tube, weakened by circumferential U- and blunt V-shaped notches, are presented. The solution is obtained as an extension of a previous analytical solution valid for axisymmetric solid shafts. It accounts for the local geometry (notch tip root radius and notch opening angle) as well as for the global geometry (inner and outer diameter of the tube). Shear stress fields are written as a function of the shear stress at the notch tip. Varying global and local geometries, the obtained equations are compared with a large bulk of finite element results, showing a good agreement
J-Integral for Deep and Shallow Notches Under Torsion
No full textJ-integral has been calculated along the free-of-stress border of deep and shallow rounded notches under torsion, under the hypothesis of a linear elastic behaviour of the material. Two exact closed-form solutions have been obtained which make it explicit the influence of the notch opening angle and the notch root radius. When the notch root radius tends to zero the proposed solution matches the expression for the corresponding pointed V-notch case
Percolation in Carbon Nanotube-Reinforced Polymers for Strain-Sensing Applications: Computational Investigation on Carbon Nanotube Distribution, Curvature, and Aggregation
Full text linkThe present article investigates the possibility of simulating the electrical conductivity of carbon nanotube-reinforced polymer composites by numerical methods. Periodic representative volume elements are generated by randomly distributing perfectly conductive reinforcements in an insulating matrix and are used to assemble an electrical network representative of the nanocomposite, where the nanotube–nanotube contacts are considered equivalent resistors modeled by means of Simmons’ equation. A comparison of the results with experimental data from the literature supports the conclusion that a random distribution of reinforcements is not suitable for simulating this class of materials since percolation thresholds and conductivity trends are different, with experimental percolation taking place before the expectations. Including nanotube curvature does not solve the issue, since it hinders percolation even further. In agreement with experimental observations, the investigation suggests that a suitable approach requires the inclusion of aggregation during the volume element generation to reduce the volume fraction required to reach percolation. Some solutions available in the literature to generate properly representative volume elements are thus listed. Concerning strain sensing, the results suggest that representative volume elements generated with random distributions overestimate the strain sensitivity of the actual composites
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