196,491 research outputs found
Crack path and notch fatigue strength of Ti-6Al-4V ELI additively manufactured via selective laser melting: Defect sensitivity
No full textThe present work is aimed at exploring the applicability of the theory of critical distances (TCD) to the notch fatigue prognosis of the biomedical titanium Grade 23 (aka Ti-6Al-4V ELI) additively manufactured via selective laser melting (SLM). Particular attention is paid on investigating how the defectiveness influences the material critical length as well as the path followed by the fatigue cracks after nucleation. This latter aspect is of crucial importance, as the notch-crack equivalence postulated by TCD is reasonable only when the position selected for the critical point or the stress-averaging length reflects the actual path of the crack emanating from the notch tip. Specifically, fully-reversed axial fatigue tests are carried out on notched samples. Notches are either directly introduced into the samples via SLM or post-sintering machined via turning. The critical distance lengths are estimated according to critical distance inverse search procedure recently proposed by the authors (Santus et al., Int. J. Fatigue, vol.106 (2018) pp.208-218)
Experimental determination and sensitivity analysis of the fatigue critical distance obtained with rounded V-notched specimens
No full textThe critical distance inverse search procedure, recently proposed by the authors (Santus et al., 2018), was experimentally applied in this work to 42CrMo4+QT steel and 7075-T6 aluminium alloy for fatigue load ratios R = −1 and R = 0.1. The inverse search lengths were in good agreement with the critical distances derived from the crack threshold. The Point Method lengths were higher than the Line Method values since the relatively low stress distribution second derivative. However, this difference is compensated for when the corresponding Method, Point or Line, is then used for the fatigue strength assessment of another specimen or a component. The fatigue predictions and comparisons with the experiments are reported in an accuracy chart, showing that a small radius notched specimen is recommended to determine the critical distance and thus obtain an accurate strength assessment of a blunter specimen. This critical distance determination was then extended to the fatigue finite life, again obtaining accurate predictions, especially for the aluminium alloy. The online version of this paper is provided with MATLAB scripts which contain examples for the critical distance inverse search and the direct problem for the fatigue stress concentration factor calculation
Analysis of the contact between cubic profiles
No full textThe contact between cubic profiles with continuous relative curvatures has been analyzed and solutions in closed form were obtained for both symmetric and non-symmetric conditions. Analytical solutions have allowed a complete parametric study to be performed, showing the effects of the gradient of relative curvature. The accuracy of approximate 'equivalent' Hertzian solutions has been verified
An application of the weight function technique to inclined surface cracks under rolling contact fatigue, assessment and parametric analysis
No full textThis paper proposes the use of the weight function technique to calculate mode I and mode II stress intensity factors for a shallow surface crack typical of rolling contact fatigue, that experiences the detrimental effects of the pressurization of lubricating fluid. The weight function technique was able to easily take the pressurization into account just by adding the pressure term to the nominal stress component which is then integrated. The crack closure was also modeled by introducing an assumption for the distribution of the contact pressure on the crack face. The results were validated with the literature data and finite element analyses. Parametric simulations were performed showing that mode I and mode II stress intensity factors strongly depend on the crack angle with respect to the surface, and almost linearly on the size of the crack. In addition, the proposed algorithm was able to include any residual stress distribution. Compressive residual stress hinders pressurization and promotes the crack closure. This effect was parametrically investigated and it was found that cracks, and especially small ones, can even remain closed, with the opening effect of the pressurization completely suppressed
Notch fatigue and crack growth resistance of Ti-6Al-4V ELI additively manufactured via selective laser melting: A critical distance approach to defect sensitivity
No full textThis work is aimed at exploring the applicability of the theory of critical distances to the notch fatigue prognosis of Ti-6Al-4V ELI additively manufactured via selective laser melting. Particular attention is paid on investigating how the defectiveness influences the material critical length and the path followed by the fatigue cracks after nucleation. Fully-reversed axial fatigue tests are carried out on notched specimens of different severity and macrocrack growth tests are performed to determine the crack growth threshold ΔKth. The critical distance lengths are estimated according to a critical distance inverse search procedure and compared with the value deduced from ΔKth
Mean stress and plasticity effect prediction on notch fatigue and crack growth threshold, combining the theory of critical distances and multiaxial fatigue criteria
No full textIn the present work, we propose a robust calibration of some bi-parametric multiaxial fatigue criteria applied in conjunction with the theory of critical distances (TCD). This is based on least-square fitting fatigue data generated using plain and sharp-notched specimens tested at two different load ratios and allows for the estimation of the critical distance according to the point and line method formulation of TCD. It is shown that this combination permits to incorporate the mean stress effect into the fatigue strength calculation, which is not accounted for in the classical formulation of TCD based on the range of the maximum principal stress. It is also shown that for those materials exhibiting a low fatigue-strength-to-yield-stress ratio σfl,R = −1/σYS, such as 7075-T6 (σfl,R = −1/σYS = 0.30), satisfactorily accurate predictions are obtained assuming a linear-elastic stress distribution, even at the tip of sharp notches and cracks. Conversely, for any materials characterized by higher values of this ratio, as quenched and tempered 42CrMo4 (σfl,R = −1/σYS = 0.54), it is recommended to consider the stabilized elastic-plastic stress/strain distribution, also for plain and blunt-notched samples and even in the high cycle fatigue regime still with the application of the TCD
Building the Kitagawa-Takahashi diagram of flawed materials and components using an optimized V-notched cylindrical specimen
No full textThe present technical note illustrates a novel procedure for building the Kitagawa-Takahashi diagram of a flawed material and of notched components made of the same material. The novelty of the method over the existing technical literature is the use of a rounded V-notched cylindrical specimen, whose geometry was optimized to maximize the intensity of the asymptotical notch stress term. In this way, the sensitivity to experimental uncertainties is reduced and no cumbersome fracture mechanics tests are requested to determine the crack threshold of the defect free of the defect-free material counterpart. The only experimental input are the high-cycle fatigue strength and the mean size of the critical defect at the notch tip of three specimen batches differing in the size of the critical defect and/or in the notch root radius. The potentiality of the method is checked for an additively manufactured Ti-6Al-4V alloy
Statistical properties of threshold and notch derived estimations of the critical distance according to the line method of the theory of critical distances
No full textThe theory of critical distances is based on the definition of a material-dependent length L. Here, we investigate the statistical properties of L deduced from the crack threshold or a suitable notched specimen geometry. Monte Carlo simulations are done for best-fitting analytical functions to express mean, standard deviation and skewness of L. Standard-deviation-to-mean ratio is the lowest for the threshold-derived L estimation and decreases with notch sharpness. The minimum notch severity to achieve the desired accuracy in L estimation is identified. The impact of these statistical properties on the prediction of independent notched and cracked configurations is evaluated
Recensione a: M. Catto, "La Compagnia divisa. Il dissenso nell'ordine gesuitico tra ‘500 e ‘600", Morcelliana, Brescia 2009
No full textRecension
Corrigendum to “Healthcare costs of the SATisfaction and adherence to COPD treatment (SAT) study follow-up” (Respiratory Medicine (2019) 153 (68–75), (S0954611119301763), (10.1016/j.rmed.2019.05.017))
No full textThe authors regret that the affiliations of two authors were incorrectly reported. The right affiliation of Fabiano di Marco is: “Department of Health Science, University of Milan, Respiratory Unit, Pope John XXIII Hospital, Bergamo, Italy”; the right affiliation of Pierachille Santus is: “Department of Biomedical and Clinical Sciences (DIBIC), University of Milan, Milan, Italy”. The authors would like to apologise for any inconvenience caused
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