1,721,036 research outputs found
Estimation of the fatigue strength of welded joints by an equivalent notch stress analysis
No full textIn this work the well known local approach to predict the fatigue strength of sharply notched components, based on the analytic
expressions of the local stress field as proposed in literature, is applied to welded joints in aluminium alloys in a simplified form
oriented to practical applications. A particular value of the general expression of the local stress field parameter is taken into
account, which the fatigue strength depends on. Then a simple model is proposed by the authors in order to estimate such a
parameter, based on the calculation of a geometric (or structural) contribution to the local stress field, depending on the overall
joint geometry, and a local contribution evaluated by considering a specimen with lateral V-notches characterised by the same weld
toe profile and a depth proportional to the weld throat thickness. Doing so, the estimation of the fatigue strength of a welded joint
can be reduced to the estimation of the fatigue strength of the equivalent V-notch subjected to a remote stress equal to the structural
stress (that can be regarded as a ‘hot spot’ stress). Finally a simple fatigue strength diagram, in the form recently proposed by
Atzori and Lazzarin and calibrated on experimental fatigue test results, is proposed, so that one can estimate the fatigue strength
of a welded joint, in terms of structural stress at a given number of cycles, as a function of the equivalent V-notch depth. By
considering this diagram, the scale effect and the effectiveness of the methods to improve the fatigue strength by smoothing the
weld toe radius are also taken into account
High-cycle fatigue crack paths in specimens having different stress concentration features
No full textThis paper summarises an attempt to study the high-cycle fatigue cracking behaviour in specimens of low carbon steel
weakened by U-notches. The specimens were tested under uniaxial fatigue loading with a load ratio equal to 0.1, and the
considered Kt values, calculated with respect to the gross area, ranged from 3.8 up to about 25. The generated crack paths
were quite irregular showing a propagation occurring in alternate trans- and intra-crystalline mode: in many cases, this
made difficult to unambiguously measure orientation and length of Stage 1 planes. In spite of these experimental difficulties,
the observed material cracking behaviour seemed to suggest that a Stage 1-like process could always be assumed to be
representative of the crack initiation phenomenon, and this held true independently of the notch sharpness. In light of the
fact that, at a mesoscopic level, crack initiations never occurred on material planes parallel to the notch bisector, we
attempted to investigate whether it was possible to use a critical plane approach to estimate high-cycle fatigue damage
in notched components under uniaxial fatigue loading. In more detail, the generated results have initially been re-analysed
by using the Modified Wo ̈ hler Curve Method re-interpreted in terms of the Theory of Critical Distances [Susmel L. A unifying
approach to estimate the high-cycle fatigue strength of notched components subjected to both uniaxial and multiaxial
cyclic loadings. Fatigue Fract Eng Mater Struct 2004;27:391–411]. The accuracy in predicting the high-cycle fatigue behaviour
of the considered multiaxial fatigue method was then compared to the accuracy of two other uniaxial approaches: the
classical one by Smith and Miller [Smith RA, Miller KJ. Prediction of fatigue regimes in notched components. Int J Mech
Sci 1978;20:201–206] and the one recently proposed by Atzori and co-workers [Atzori B, Lazzarin P, Meneghetti G. A
unified treatment of the mode I fatigue limit of components containing notches or defects. Int J Fract 2005;133:61–87]
and based on the use of some classic LEFM concepts. In particular, this comparison was performed considering virtual
specimens having the same geometries as the ones investigated in the present study, but assuming that they were made
of materials having mechanical properties known from the literature. This exercise allowed us to see that the high-cycle
fatigue damage in notched specimens under uniaxial fatigue loading can satisfactorily be predicted not only using Mode
I-crack based methods, but also using multiaxial fatigue criteria modelling the crack initiation phenomenon
A novel engineering method based on the critical plane concept to estimate lifetime of weldments subjected to variable amplitude multiaxial fatigue loading
No full textThis paper summarizes an attempt at proposing a new engineering method suitable for estimating the fatigue lifetime of steel- and aluminium-welded connections subjected to variable amplitude multiaxial fatigue loading. In particular, the proposed approach is based on the use of the so-called Modified W ̈ ohler Curve Method (MWCM), i.e. a bi-parametrical critical plane approach, whose accuracy has been checked so far solely in addressing the constant amplitude multiaxial fatigue problem. In order to extend the use of our criterion to variable amplitude situations, the critical plane is suggested here as being determined by taking full advantage of the maximum variance concept, that is, such a plane is assumed to be the one containing the direction along which the variance of the resolved shear stress reaches its maximum value. The main advantage of such a strategy is that the cycle counting can directly be performed by considering the shear stress resolved along the maximum variance direction: by so doing, the problem is greatly simplified, allowing those well-established cycle counting methods specifically devised to address the uniaxial variable amplitude problem to be extended to those situations involving multiaxial fatigue loading. The validity of the proposed methodology was checked by using two different datasets taken from the literature and generated by testing both steel and aluminium tube-to-plate welded connections subjected to in-phase and 90◦ out-of phase variable amplitude bending and torsion. This new fatigue life assessment technique was seen to be highly accurate allowing the estimates to fall within the calibration scatter bands not only when the constants in the governing equations were calculated by using the experimental uniaxial and torsional fully reversed fatigue curves, but also when they were determined by using the reference curves supplied, for the investigated geometry, by the available standard codes. These results seem to strongly support the idea that, thanks to its peculiar features, our method can be considered as an effective engineering approach capable of performing multiaxial fatigue assessment under variable amplitude loading which fully complies with the recommendations of the available standard codes
A simple and efficient reformulation of the classical manson-coffin curve to predict lifetime under multiaxial fatigue loading. Part I: plain materials.
No full textThis paper summarises an attempt to devise an engineering method suitable for predicting fatigue lifetime of metallic materials subjected to both proportional and non-proportional multiaxial cyclic loading. The proposed approach takes as a starting point the assumption that the plane experiencing the maximum shear strain amplitude (the so-called “critical plane”) is coincident with the micro/meso-crack initiation plane. In order to correctly account for the presence of both non-zero mean stresses and non-zero out-of-phase angles, the degree of multiaxiality/non-proportionality of the stress state damaging crack initiation sites is suggested here to be evaluated in terms of the ratio between maximum normal stress and shear stress amplitude relative to the critical plane. Such a ratio is used then to define non-conventional Manson-Coffin curves, whose calibration is done through two strain-life curves generated under fully-reversed uniaxial and under fully-reversed torsional fatigue loading, respectively. The accuracy and reliability of our approach was systematically checked by using approximately 350 experimental data taken from the technical literature and generated by testing 13 different materials under both in-phase and out-of-phase loading. Moreover, the accuracy of our criterion in estimating lifetime in the presence of non-zero mean stresses was also investigated. Such an extensive validation exercise allowed us to prove that the fatigue life estimation technique formalised in the present paper is a reliable tool capable of correctly evaluating fatigue damage in engineering materials subjected to multiaxial cyclic loading paths
Fracture behaviour of grain refined A356 cast aluminium alloy: tensile and Charpy impact specimens
No full textThe excellent combination of high strength/weight ratio, high impact toughness, very good castability, low thermal expansion coefficient and corrosion resistance make Al-Si cast alloys suitable for the production of components like rims, engine and gear parts. Even though it is well-known that mechanical properties are closely related to secondary dendrite arm spacing (SDAS), the influence of grain size has to be considered as well. A fine and equiaxial grain structure is generally obtained through specific products, called grain refiners, which are added to the melt alloy in form of cans, bars, tabs, waffles, ingots and granulated fluxes. In this study three commercial Ti-B based grain refiners were added to the A356 (Al-Si-Mg) aluminium alloy. A number of 20 castings was obtained through permanent mould casting, n°5 for each experimental condition, named Reference (not refined), GR1, GR2 and GR3. Tensile and Charpy impact specimens were drawn by means of machining, T6 heat-treated and then tested. The influence of the grain refiners was assessed according to the experimental data of tensile and impact tests. Experimental results were compared to OM and SEM fracture observations, pointing out the effect of the different grain refiners on fracture mechanism. Although both impact and tensile specimens showed a mixed transgranular-intergranular fracture mode, it was found that impact samples were deeply influenced by the refiner added, while this effect was less pronounced for the tensile ones. Fractographic observations also revealed the role of Fe based intermetallic compounds in terms of fracture behaviour
Notch and Mean Stress Effect in Fatigue as Phenomena of Elasto-Plastic Inherent Multiaxiality
No full textThe present paper summarises an attempt of estimating fatigue lifetime of notched metallic
materials by directly accounting for the degree of multiaxiality of the local elasto-plastic
stress/strain-fields acting on the fatigue process zone. In more detail, the proposed
approach takes as its starting point the assumption that Stage I is the most important stage
to be modelled to accurately estimate fatigue damage, and this holds true independently of
the sharpness of the assessed geometrical feature. According to this initial idea, and by taking
full advantage of the so-called Modified Manson-Coffin Curve Method (MMCCM), the
hypothesis is then formed that the crack initiation plane is always coincident with that
material plane experiencing the maximum shear strain amplitude. Subsequently, to devise
an efficient design method capable of taking into account the detrimental effect of stress/
strain gradients arising also from severe stress/strain concentration phenomena, the
MMCCM is suggested here as being applied in terms of the Theory of Critical Distances
(TCD), the latter being used in the form of the Point Method (PM). Further, in light of the
well-known fact that the value of the mean stress/strain components in the vicinity of
the stress/strain raisers’ apices can be different from the corresponding nominal values
due to the actual elasto-plastic behaviour of the material being assessed, it is shown,
through the MMCCM itself, that also the mean stress effect can directly and accurately
be treated as a problem of inherent multiaxiality. Finally, as a preliminary validation, the
accuracy and reliability of the proposed approach is checked through several experimental
results taken from the literature and generated by testing, under uniaxial fatigue loading,
samples containing a variety of geometrical features, the effect of different nominal load
ratios being investigated as well
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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