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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
EFFETTO DELLA MICROSTRUTTURA SULLE CARATTERISTICHE A FATICA DI GETTI IN LEGA DI ALLUMINIO
No full textA 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
Effects of matrix reinforcement properties on low-and high-cycle fatigue behaviour of particulate reinforced MMCs
No full textHigh Cycle Fatigue Strength of Severely Notched Cast Iron Specimens under Tension and Torsion Loading Conditions
No full textThe work deals with multi-axial fatigue strength of severely notched cast iron. Circumferentially V-notched specimens were tested under combined tension and torsion loading, both in-phase and out-of-phase, with two nominal load ratios, R=-1 and R=0.The geometry of all axi-symmetric specimens was characterized by a constant notch tip radius (less than 0.1 mm), a notch depth of 4 mm and V-notch opening angle of 90. The results from multi-axial tests are discussed together with those obtained under pure tension and pure torsion loading from notched specimens with the same geometry. Altogether more than eighty new fatigue data (10 fatigue curves) are summarised in the present work. .
All fatigue strength data are presented here in terms of the local strain energy density averaged in a specific control volume surrounding the V-notch tip. The dependency of the control volume size as a function of the loading mode is investigated
Analisi sperimentale della resistenza a fatica di particolari costruttivi in lega leggera saldati
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