Influence of the Experimental Setup on the Damping Properties of SLM Lattice Structures

Background: Metal lattice structures obtained through Selective Laser Melting may increase the strength-to-weight ratio of advanced 3D printed parts, as well as their damping properties. Recent experimental results showed that AlSi10Mg and AISI 316L lattices are characterized by higher Rayleigh damping coefficients with respect to the fully dense material. However, some unclear or contradictory results were found, depending on the experimental setup adopted for modal analysis. Objective: In this work the influence of the experimental setup when performing modal analysis on different SLM AISI 316L lattice structures was deeply investigated. The study provides a critical comparison of various experimental modal analysis approaches, allowing to evaluate the influence of external damping sources and material internal damping phenomena. Methods: The dynamic behaviour of SLM AISI 316L specimens incorporating lattice structures was estimated by means of pulse testing and sinusoidal excitation through an electromagnetic shaker. The validity of the viscous damping model was assessed by means of sinusoidal excitation with different levels of vibration velocity. Moreover, the influence of experimental setup on modal analysis results was critically evaluated, by considering different actuators, contact and non-contact sensors and boundary/clamping conditions. Results: The classical viscous damping model describes with good approximation the damping properties of SLM lattice structures. When exciting single specimens in free-free conditions, those embedding lattice structure and unmelted metal powder filler were characterized by superior internal damping properties with respect to the specimens incorporating the lattice structure without any filler, which was however more effective than the full density equivalent material. Most of the other experimental setups introduced additional external damping sources, that could alter this important outcome. Conclusions: SLM lattice structures embedded into 3D printed components provide superior damping properties against mechanical and acoustic vibrations and the metal powder filler does significantly enhance such damping capacity. A correct estimation of material internal damping was achieved by applying non-contact sensors and free-free boundary conditions, whereas other experimental setups were partly inadequate

GHB: farmaco, sostanza d’abuso e droga da stupro: diverse tipologie di uso, differenti problematiche analitico-forensi

L’acido gamma-idrossibutirrico (GHB) è un neurotrasmettitore con effetti gaba-mimetici; si tratta di un composto endogeno, ma notoriamente usato per le applicazioni terapeutiche come anestetico per via endovenosa, come sedativo e per il trattamento della narcolessia. Dagli anni ‘80 è comune sostanza usata come doping, quindi emerge come droga da “tempo libero” nei rave-party; più recentemente, i supposti effetti afrodisiaci e la reale capacità di induzione di amnesia retrograda ne hanno indotto l’utilizzazione quale sostanza in grado di ridurre la capacità di resistenza della vittima di uno stupro annoverandola tra le cosiddette “date rape drugs” (Drug facilitated sexual assault, DFSA), e cioè sostanze psicoattive usate per lo stupro cosiddetto “dopo appuntamento”1. Nel presente contributo si riporta l’approccio metodologico relativamente a due differenti scenari di interesse forense: l’abuso del GHB con quadro di dipendenza patologica e l’uso del GHB come droga da stupro; gli Autori illustrano le modalità di indagine per determinare il GHB nelle differenti matrici biologiche. Conclusioni: gli scenari d’abuso qui presentati rafforzano il concetto che l’analitica tossicologica rivolta alla determinazione del GHB, per tutte le evenienze riguardanti l’uso/abuso e le possibili implicazioni legali, deve realizzarsi secondo canoni analitici convalidati

Passive chatter suppression of thin-walled parts by means of high-damping lattice structures obtained from selective laser melting

Chatter vibrations arising during machining operations are detrimental for cutting process performance, since they may cause poor surface quality of the machined part and severe damages to machine tool elements. Passive approaches for chatter suppression are based on the integration of special mechanical components with high-damping properties within the machining system. They represent a good solution to this problem thanks to their intrinsic simplicity. Recently, the application of metallic lattice structures inside 3D printed parts obtained from the Selective Laser Melting technology have proven superior damping properties with respect to the same full density material. Here, this idea is further explored by considering the novel configuration where the unmelted powder grains are retained inside the lattice structure by an external shell, acting as a multiplicity of microscopic mechanical dampers. This concept is applied for passive chatter suppression of thin-walled parts that are of particular relevance for industry. Preliminary experimental investigation was first carried out on simple beam-like specimens, and then on thin-walled benchmarks that were identified through modal analysis and tested under real cutting conditions. The main conclusion is that the novel proposed configuration (lattice plus unmelted powder) has higher damping properties with respect to the full density and lattice alternatives. Accordingly, it may be successfully applied for passive chatter suppression in real machining operations

Mercury emissions and stable isotopic compositions at Vulcano Island (Italy)

Sampling and analyses methods for determining the stable isotopic compositions of Hg in an active volcanic system were tested and optimized at the volcanic complex of Vulcano (Aeolian Islands, Italy). Condensed gaseous fumarole Hg(fum) T , plume gaseous elemental Hg(g) 0 and plume particulate Hg(p) II were obtained at fumaroles F0, F5, F11, and FA. The average total Hg emissions, based on HgT/SO2 in condensed fumarolic gases and plumes, range from 2.5 to 10.1 kg y−1, in agreement with published values [Ferrara, R., Mazzolai, B., Lanzillotta, E., Nucaro, E., Pirrone, N., 2000. Volcanoes as emission sources of atmospheric mercury in the Mediterranean Basin. Sci. Total Environ. 259(1–3), 115–121; Aiuppa, A., Bagnato, E., Witt, M.L.I., Mather, T.A., Parello, F., Pyle, D.M., Martin, R.S., 2007. Real-time simultaneous detection of volcanic Hg and SO2 at La Fossa Crater, Vulcano (Aeolian Islands, Sicily). Geophys. Res. Lett. 34(L21307).]. Plume Hg(p) II increases with distance from the fumarole vent, at the expense of Hg(g) 0 and indicates significant in-plume oxidation and condensation of fumarole Hg(fum) T . Relative to the NIST SRM3133 Hg standard, the stable isotopic compositions of Hg are δ202Hg(fum) T =−0.74‰±0.18 (2SD, n=4) for condensed gaseous fumarole Hg(fum) T , δ202Hg(g) 0 =−1.74‰±0.36 (2SD, n=1) for plume gaseous elemental Hg(g) 0 at the F0 fumarole, and δ202Hg(p) II =−0.11‰±0.18 (2SD, n=4) for plume particulate Hg(p) II . The enrichment of Hg(p) II in the heavy isotopes and Hg(g) 0 in the light isotopes relative to the total condensed fumarolic Hg(fum) T gas complements the speciation data and demonstrates a gas-particle fractionation occurring after the gas expulsion inambient T° atmosphere. A first order Rayleigh equilibriumcondensation isotope fractionation model yields a fractionation factor αcond-gas of 1.00135±0.00058

Effects of post-printing heat treatment on microstructure, corrosion and wet wear behavior of CoCrW alloy produced by L-PBF process

CoCr alloys are widely used as human implants because of both their superior corrosion resistance and superior mechanical properties (fatigue, wear resistance, etc.) respect to other metal alloys used in biomedical field. In particular, CoCrW alloys are used mainly to produce dental implants. In this study, the effects of thermal treatment on the corrosion resistance and wet wear resistance of CoCrW alloys produced via Laser-Powder Bed Fusion (L-PBF) were investigated, and the corrosion resistance and wet wear resistance of the L-PBF specimens were compared with those of the specimens obtained after forging. The heat treatment involved the solubilization of the alloy at 1150 °C in an Ar-saturated atmosphere, followed by furnace cooling. A detailed microstructural characterization of the L-PBF specimens was carried out using a light microscope and a scanning electron microscope in both the horizontal and vertical growth directions. Scanning Kelvin probe measurements were performed on the heat-treated specimens obtained by three-dimensional printing and forging. The void contents of the specimens were evaluated using the Archimedes’ method and image analysis. Vickers (HV2) hardness measurements were performed to evaluate the mechanical properties of the specimens. The corrosion properties of the specimens were evaluated by carrying out potentiodynamic tests in two different corrosive media (aqueous solution (9 g/L NaCl) at pH = 2 and 7). The corroded areas of the specimens were then examined using scanning electron microscopy (SEM). Finally, tribological tests were performed using the pin (Ti counter material)-on-flat configuration under dry and wet conditions, using the same corrosive environments as those used in the potentiodynamic tests and two different stroke lengths. The worn samples were characterized using SEM to investigate their wear mechanisms, and a stylus profilometer was used to determine the wear rates of the materials. The experimental results showed that the additively manufactured CoCrW L-PBF alloy had higher corrosion resistance than the wrought material. In addition, the additively manufactured material showed better dry and wet wear performances than the wrought material. Nevertheless, the heat treatment did not affect the properties evaluated in this study

Comparison between two different modes of non-invasive ventilatory support in preterm newborn infants with respiratory distress syndrome mild to moderate: preliminary data

Despite of improved survival of premature infants, the incidence of long term pulmonary complications, mostly associated with ventilation-induced lung injury, remains high. Non invasive ventilation (NIV) is able to reduce the adverse effects of mechanical ventilation. Although nasal continuous positive airway pressure (NCPAP) is an effective mode of NIV, traumatic nasal complications and intolerance of the nasal interface are common. Recently high flow nasal cannula (HFNC) is emerging as a better tolerated form of NIV, allowing better access to the baby's face, which may improve nursing, feeding and bonding. HFNC may be effective in the treatment of some neonatal respiratory conditions while being more user-friendly for care-givers than conventional NCPAP. Limited evidence is available to support the specific role, efficacy and safety of HFNC in newborns and to demonstrate efficacy compared with NCPAP; some studies suggest a potential role for HFNC in respiratory care of the neonate as a distinct non invasive ventilatory support. We present the preliminary data of a randomized clinical trial; the aim of this study was to assess efficacy and safety of HFNC compared to NCPAP in preterm newborns with mild to moderate respiratory distress syndrome (RDS)

Death of a 23-year-old man from cardiac conduction system injury through a blunt chest impact after a car accident.

Cardiac contusion, usually caused by blunt chest trauma, has been recognized with increased frequency over the past decades. Traffic accidents are the most frequent causes of cardiac contusion resulting from a direct blow to the chest. Myocardial contusion is difficult to diagnose; the clinical presentation varies greatly, ranging from a lack of symptoms to cardiogenic shock and arrhythmia. Although death is rare, cardiac contusion can be fatal. The Authors report a case of death due to a cardiac conduction system injury from a blunt chest impact following a car accident. The autopsy showed no external signs of thoracic trauma, no evident rib or sternum fractures. A small subendocardial hemorrhage was found in the region of the atrioventricular node. Histological examination revealed an injury of the atrioventricular node and His' bundle. The cause of the death was attributed to the arrhythmia induced by contusion of the cardiac conduction system