1,721,365 research outputs found
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 Wöhler 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
Rapid evaluation of notch stress intensity factors in welded joints using the peak stress method: comparison of commercial finite element codes for a range of mesh patterns
No full textOn fatigue limit in the presence of notches: classical vs. recent unified formulations
No full textClassical formulations for the fatigue strength reduction factor of notched specimen, K-f, (such as those by Neuber, Peterson, Heywood) were developed long time ago and have found some success by introducing a material constant (dependent on the tensile strength only) in order to take into account the problem of notch sensitivity. However, being empirical fitting equations, they have serious limitations when their asymptotic behaviour is considered, or when the empirical constants are not directly calibrated with experiments. This is shown in this work by using example data taken from the literature for various steels and alloys, and various notch sizes and shapes. Furthermore, although the material constants can be modified to include fatigue threshold dependence (satisfying the requirements of fracture mechanics), only the Neuber formula has a correct functional form in the entire range of notch sizes and shapes, and indeed appears to be sufficiently conservative in the range of data considered. Improved accuracy is found with a more recent empirical criterion due to Atzori and Lazzarin based on the Smith and Miller classification of notches, and with a new criterion here obtained by making consistent the Atzori and Lazzarin with the Lukas-Klesnil, having a sound interpretation in terms of self-arrested cracks ahead of a rounded notch for which the Creager-Paris stress field is valid. A large number of experimental data are taken from the literature to compare the accuracies of the various criteri
Fracture and notch mechanics to estimate the uniaxial fatigue limit of plain and severely notched L-PBF AlSi10Mg specimens
No full textThis work discusses the applicability of the notch mechanics and linear elastic fracture mechanics to estimate the uniaxial fatigue limit of sharply notched Additively Manufactured (AMed) specimens. It is well known that the fatigue behaviour of AMed materials is influenced by defects inherent to the manufacturing process and the fatigue strength of materials weakened by defects depends on material properties, load ratio R and size of defects. While defect sensitivity on fatigue thresholds has been studied extensively in the literature for different AM materials, investigations on the effect of notches, and especially sharp notches, including notch-defect interaction and competition are still limited, leaving considerable scope for theoretical and experimental investigations. In this study, fatigue tests were conducted on plain and sharply notched specimens AMed from AlSi10Mg powders to investigate the competition between AM process-related defects and sharp notches. The investigation highlighted that AM defects are detrimental for plain specimens, while they do not impact the fatigue strength of sharp notches. A previously published model proved satisfactory to predict the fatigue limit of the plain and sharply notched specimens; the model requires two material properties, namely the plain material fatigue limit and the threshold range of the mode I stress intensity factor for long cracks
Confronto di codici commerciali agli elementi finiti per la valutazione rapida dei fattori di intensificazione delle tensioni in geometrie tridimensionali con il metodo della tensione di picco
No full textMultiaxial fatigue strength assessment of steel and aluminium welded joints using the peak stress method
No full textRapid finite element evaluation of the averaged strain energy density of mixed-mode (I + II) crack tip fields including the T-stress contribution
No full textThe strain energy density (SED) averaged over a material dependent control volume has been demonstrated to control fracture and fatigue behaviour of different materials in many engineering design situations. A method to rapidly calculate the averaged SED at the tip of long cracks under in-plane mixed mode (I + II) loading has been recently proposed. It was based on the peak stresses evaluated from finite element (FE) analyses, according to the peak stress method (PSM). The aim of this work is to extend this FE approach to short cracks. In the present paper short cracks are distinguished from long cracks by considering that the stress fields within the control volume of short cracks are no longer governed solely by the stress intensity factors (SIFs), but the contribution of higher order terms, and primarily the T-stress, becomes significant to estimate the averaged SED. Therefore the averaged SED is calculated using the linear elastic nodal stresses evaluated by FEM either at the crack tip, to account for the SIF contribution, and at selected FE nodes of the crack free edges, to include the T-stress contribution. The proposed approach is referred to as nodal stress approach. The advantage of the nodal stress approach is two-fold: there is no need of mesh refinements in the close neighbourhood of the points of singularity, so that coarse FE meshes can be adopted; moreover, geometrical modelling of the control volume in FE models is no longer necessary. Infinite plates weakened by central small cracks subjected to mixed mode I + II loading and a lap joint geometry have been analysed taking into consideration different crack lengths, mode mixities and average finite element sizes of the employed meshes. A comparison between approximate values of the averaged SED according to the nodal stress approach and those derived directly from the FE strain energy adopting very refined FE meshes has been successfully performed within a range of applicability
The peak stress method applied to the fatigue strength assessment of steel and aluminium butt welded joints
No full textIn-Field Load Acquisitions on a Variable Chamber Round Baler Using Instrumented Hub Carriers and a Dynamometric Towing Pin
No full textIn this work, the load spectra acting in the vertical direction on the hub carriers and in the horizontal longitudinal direction on the drawbar of a trailed variable chamber round baler were evaluated. To this end, each hub carrier was instrumented with appropriately calibrated strain gauge bridges. Similarly, the baler was equipped with a dynamometric towing pin, instrumented with strain gauge sensors and calibrated in the laboratory, which replaced the original pin connecting the baler and the tractor during the in-field load acquisitions. In both cases, the calibration tests returned the relationship between applied forces and output signals of the strain gauge bridges. Multiple in-field load acquisitions were carried out under typical maneuvers and operating conditions. The synchronous acquisition of a video via an onboard camera and Global Positioning System (GPS) signal allowed to observe the behaviour of the baler in correspondence of particular trends of the vertical and horizontal loads and to point out the most demanding maneuver in view of the fatigue resistance of the baler. Finally, through the application of a rainflow cycle counting algorithm according to ASTM E1049-85, the load spectrum for each maneuver was derived
High torque density PM motor for racing applications
No full textReferring to a 4-wheel drive Formula Student Electric vehicle, a fractional-slot synchronous permanent magnet machine has been designed. Torque density has been improved adopting outer rotor topology and lightweight materials. An ironless rotor with PMs placed in an Halbach array configuration allows reduced rotor inertia to be obtained. The results described in the paper provide a quantitative assessment of the achievable torque density for small size motors
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