Surface integrity of additive manufacturing parts: a comparison between optical topography measuring techniques

Additive Manufacturing (AM) presents significant industry-specific advantages allowing the creation of complex geometries and internal features that cannot be produced using conventional manufacturing processes. However, a current limitation of AM is the degraded dimensional control and surface integrity of specific surfaces. The parts are constructed through layer-by-layer approach, each layer presenting a characteristic ‘fingerprint’. The functional performance of the final part is influenced by the morphology of the outer surface as well as by the surface quality introduced at intermediate layers. Surface texture metrology therefore can play an enabling role in AM-related manufacture and research. The use of optical topography measurement instrumentation allows for a high level of detail in the acquisition of topographic information. Some of the most commonly used optical measuring instruments are Vertical Scanning Interferometry (CSI), Imaging Confocal Microscopy (CONF), and Focus Variation (FV), each one has benefits and drawbacks in terms of acquisition time and measurement resolution. AM surfaces overall present complex topographical features, requiring the acquisition of large surface areas and large z-scans which considerably increases the acquisition time. Speed is a key factor in industrial practice, and time optimization is required for quality control and surface analysis before down-stream processes. This paper reports on the measurement and characterisation of the surface texture of metal powder bed fusion AM parts. All measurements were performed in the same SENSOFAR S-NEOX instrument using the commonly used optical technologies (CSI, CONF, and FV) and the latest step in confocal measurement technology called Continuous Confocal (C-CONF). The resolution and acquisition time of each technique is analysed in order to check the suitability of each method to characterize and describe the AM surface microstructures in a time-efficient way

Critical analysis of the suitability of crack propagation direction criteria for 2D cylindrical plain fretting contact

[EN] In this work the suitability of the criterion of maximum effective amplitude of the normal stress (Delta sigma(n,eff))(max) and the criterion of minimum shear stress range (Delta tau)(min) for 2D cylindrical plain fretting contact condition has been analysed. The numerical analysis has been performed by means of the extended finite element method, which takes into account the contact between crack faces during the closing part, and the results have been compared with experiments reported in the literature. Results show that overall the (Delta tau)(min) criterion predominates in intermediate stage, while the (Delta sigma(n,eff))(max) shows less deviation in the final stage. However, the predicted crack path by the latter criterion shifts toward the outer side, which do not correlate with the experimental results reported in the literature. Additional studies should investigate the variables that are affecting this change in the behaviour along the crack in order to set a criteria that is able to predict the plain fretting condition crack paths accurately.This work was financially supported by the the Basque Government under the "Proyectos de Investigacion Basica y/o Aplicada" (Project NUSIMCO: Ref. PI2013-23), the Spanish Ministry of Science, Innovation and Universities (grant number DPI2017-89197-C22-R) and the Generalitat Valenciana (Programme PROMETEO 2016/007). Furthermore, the authors gratefully acknowledge the financial support given by the Spanish Ministry of Economy and Competitiveness and the FEDER program through the project DPI2014-56137-C2-2-R and the FPI subprogram associated to the project with the reference BES-2015-072070.Llavori, I.; Giner Maravilla, E.; Zabala, A.; Infante, D.; Aginagalde, A.; Rodríguez-Flórez, N.; Gómez, X. (2019). Critical analysis of the suitability of crack propagation direction criteria for 2D cylindrical plain fretting contact. Engineering Fracture Mechanics. 214:534-543. https://doi.org/10.1016/j.engfracmech.2019.04.035S53454321

Influence of fluoride content and pH on corrosion and tribocorrosion behaviour of Ti13Nb13Zr alloy in oral environment

© 2015 Elsevier Ltd. CpTi and Ti6Al4V alloy are the most widely used materials for implant application, but the release of toxic elements (. e.g. Al and V) and the so-called stress-shielding effect are still a concern. In recent years, β and near-. β titanium alloys have been developed, which overcome these issues with reduced modulus of elasticity and biocompatible alloying elements. However, literature is scarce studying the tribocorrosion behaviour of these alloys for dental implantology. The present work studies the tribocorrosion behaviour of the near-. β Ti13Nb13Zr alloy in oral environment, using CpTi4 for comparison purposes. To that end, the influence of the pH and fluoride concentration in artificial saliva was analysed. Reciprocating sliding corrosion tests were carried out under open circuit potential and potentiostatic conditions. Results reveal a negative influence of the increase of fluoride concentration and the acidified artificial saliva on the material degradation. Moreover, some light has been shed on the different tribocorrosion mechanisms of Ti13Nb13Zr and CpTi4 in simulated oral environment.This work was partially supported by Basque Department of Economic Development and Competitivity, S-PE13MU016, and Spanish Ministry of Economy and Competitivity, MAT2013-48224-C2-1-R-MUNSUTI.Peer Reviewe

Critical analysis of the suitability of crack propagation direction criteria for 2D cylindrical plain fretting contact.

In this work the suitability of the criterion of maximum effective amplitude of the normal stress (Delta sigma(n,eff))(max) and the criterion of minimum shear stress range (Delta tau)(min) for 2D cylindrical plain fretting contact condition has been analysed. The numerical analysis has been performed by means of the extended finite element method, which takes into account the contact between crack faces during the closing part, and the results have been compared with experiments reported in the literature. Results show that overall the (Delta tau)(min) criterion predominates in intermediate stage, while the (Delta sigma(n,eff))(max) shows less deviation in the final stage. However, the predicted crack path by the latter criterion shifts toward the outer side, which do not correlate with the experimental results reported in the literature. Additional studies should investigate the variables that are affecting this change in the behaviour along the crack in order to set a criteria that is able to predict the plain fretting condition crack paths accurately

Resident physician duty hours, resting times and European Working Time Directive compliance in Spain: a cross-sectional study

Abstract Background There is a growing interest in understanding the impact of duty hours and resting times on training outcomes and the well-being of resident physicians. However, to this date no state-wide analysis exists in any European country. Objectives Our aim is to describe the shift work scheduling and to detail the degree of compliance with the Spanish legislation and the European Working Time Directive (EWTD) of Spanish resident physicians, focusing on territorial and specialty distribution. Material and methods A descriptive cross-sectional analytical study was designed through an online survey adapted from the existing literature. Results Out of the 2035 surveyed resident physicians undergoing PGT in Spain, 80.49% exceeded the 48 h per week limit set by the EWTD and 13% of them did not rest after a 24-h on-call shift. The mean number of on-call shifts in the last 3 months was 15.03, with the highest mean reported in Asturias, La Rioja, and Extremadura. 51.6% of respondents had a day-off after a Saturday on-call shift. Significant differences are observed by region and type of specialty. Conclusion Resident physicians in Spain greatly exceed the established 48 h/week EWTD limit. Likewise, non-compliance with labor regulations regarding mandatory rest after on-call duty and minimum weekly rest periods are observed