Numerical simulations of components produced by fused deposition 3D printing

Three-dimensional printing technology using fused deposition modeling processes is becoming more and more widespread thanks to the improvements in the mechanical properties of materials with the addition of short fibers into the polymeric filaments. The final mechanical properties of the printed components depend, not only on the properties of the filament, but also on several printing parameters. The main purpose of this study was the development of a tool for designers to predict the real mechanical properties of printed components by performing finite element analyses. Two different materials (nylon reinforced with glass or carbon fibers) were investigated. The experimental identification of the elastic material model parameters was performed by testing printed fully filled dog bone specimens in two different directions. The obtained parameters were used in numerical analyses to predict the mechanical response of simple structures. Blocks of 20 mm × 20 mm × 160 mm were printed in four different percentages of a triangular infill pattern. Experimental and numerical four-point bending tests were performed, and the results were compared in terms of load versus curvature. The analysis of the results demonstrated that the purely elastic transversely isotropic material model is adequate for predicting behavior, at least before nonlinearities occur

Can the effects of anthropogenic pressures and environmental variability on nekton fauna be detected in fishery data? Insights from the monitoring of the artisanal fishery within the Venice lagoon

Nekton communities in transitional ecosystems are naturally adapted to stressful conditions associated with high environmental variability. Human activities in these systems are likely to determine additional stress with a possible effect on fish fauna, hence on fisheries. In order to test the relative importance of natural and anthropogenic factors in determining changes in nekton community, catches (incl. bycatch) from artisanal fisheries (fyke nets) were monitored seasonally in different areas of the Venice lagoon (Italy) between 2001 and 2013. Changes in nekton community composition and in the biomass of target and non-target species/groups were analysed, and the results were related to temporal factors, environmental characteristics and to the variability in anthropogenic pressures. Statistical tests were carried out using a model-based analysis of both univariate and multivariate data. Results highlighted that temporal factors and environmental conditions (i.e. the main chemico-physical descriptors) are more relevant than anthropogenic pressures in explaining spatial and temporal changes in the lagoon nekton assemblage, but that several characteristics of the assemblage, in particular the biomass of some particular categories and of the whole assemblage, are sensitive to human impacts. A particularly negligible effect seemed to be associated with fishing effort, thus suggesting that the monitoring of the local artisanal fishery is suitable also to provide useful information on the evaluation of the status of nekton assemblage

Analysis of strain rate behavior of an Al 6061 T6 alloy

Abstract In order to simulate complex scenario like ballistic impact, correct material calibration is fundamental. The material in the area involved by impact can experience high deformation and damage in a very limited time. As a consequence dynamic tests on the materials are needed in order to calibrate constitutive law able to describe the material behavior in terms of hardening and in particular strain rate. According to the fact that no guidelines are available on testing methods, different types of testing techniques have been used to generate data under dynamic conditions. Several dynamic tests, are carried out on Al 6061 T6 specimens and the experimental data elaborated. The developed procedure is useful to take into account also the thermal phenomena generally affecting high strain-rate tests due to the adiabatic overheating related to the conversion of plastic work. The method presented requires strong effort both from experimental and numerical point of view; anyway it allows to precisely identifying the parameters of a material models. This could provide great advantages when high reliability of the material behavior is necessary

L’USO DI EQUAZIONI DI STATO MULTI-FASE NELLA SIMULAZIONE NUMERICA DI ONDE D’URTO

Questo lavoro è volto a mettere in evidenza l’importanza dell’utilizzo di Equazioni di Stato (EOS) multi-fase in eventi caratterizzati da onde d’urto. L’obiettivo è la descrizione del comportamento del materiale in seguito alla deposizione di energia derivante dall’impatto con un fascio di particelle subatomiche ad elevata energia. Siccome i tempi di deposizione sono talmente brevi (ns o mus) da essere inferiori al tempo caratteristico di risposta idrodinamica del sistema, nel materiale gli incrementi di energia, e di conseguenza, di temperatura e pressione avvengono con una trasformazione pressoché isocora. Il materiale tende, perciò, ad esplodere dall’interno: una volta che il processo di rarefazione inizia, il materiale, che si trova a monte del fronte di shock, è libero di espandere, e raggiunge valori inferiori di pressione e densità. Al contrario, l’arrivo del fronte di shock nel materiale inizialmente quasi indisturbato, ne causerà l’aumento di pressione e densità

Numerical simulations of tungsten targets hit by LHC proton beam

The unprecedented energy intensities of modern hadron accelerators yield special problems with the materials that are placed close to or into the high intensity beams. The energy stored in a single beam of LHC particle accelerator is equivalent to about 80 kg of TNT explosive, stored in a transverse beam area with a typical value of 0.2 mm×0.2 mm. The materials placed close to the beam are used at, or even beyond, their damage limits. However, it is very difficult to predict structural efficiency and robustness accurately: beam-induced damage for high energy and high intensity occurs in a regime where practical experience does not exist. The interaction between high energy particle beams and metals induces a sudden non uniform temperature increase. This provokes a dynamic response of the structure entailing thermal stress waves and thermally induced vibrations or even the failure of the component. This study is performed in order to estimate the damage on a tungsten component due to the impact with a proton beam generated by LHC. The solved problems represent some accidental cases consequent to an abnormal release of the beam: the energy delivered on the components is calculated using the FLUKA code and then used as input in the numerical simulations, that are carried out via the FEM code LS-DYNA

Gamma-ray burst observations with new generation imaging atmospheric Cerenkov Telescopes in the FERMI era

After the launch and successful beginning of operations of the FERMI satellite, the topics related to high-energy observations of gamma-ray bursts have obtained a considerable attention by the scientific community. Undoubtedly, the diagnostic power of high-energy observations in constraining the emission processes and the physical conditions of gamma-ray burst is relevant. We briefly discuss how gamma-ray burst observations with ground-based imaging array Cerenkov telescopes, in the GeV-TeV range, can compete and cooperate with FERMI observations, in the MeV-GeV range, to allow researchers to obtain a more detailed and complete picture of the prompt and afterglow phases of gamma-ray bursts.Comment: 9 pages, two figures. Proceeding for the 6th "Science with the New Generation of High Energy Gamma-Ray Experiments" worksho

Evidence Gaps in Assessments of the Healthiness of Online Supermarkets Highlight the Need for New Monitoring Tools: a Systematic Review

Purpose of Review: Online grocery shopping is increasingly popular, but the extent to which these food environments encourage healthy or unhealthy purchases is unclear. This review identifies studies assessing the healthiness of real-world online supermarkets and frameworks to support future efforts. Recent Findings: A total of 18 studies were included and 17 assessed aspects of online supermarkets. Pricing and promotional strategies were commonly applied to unhealthy products, while nutrition labelling may not meet regulated requirements or support consumer decision-making. Few studies investigated the different and specific ways online supermarkets can influence consumers. One framework for comprehensively capturing the healthiness of online supermarkets was identified, particularly highlighting the various ways retailers can tailor the environment to target individuals. Summary: Comprehensive assessments of online supermarkets can identify the potential to support or undermine healthy choices and dietary patterns. Common, validated instruments to facilitate consistent analysis and comparison are needed, particularly to investigate the new opportunities the online setting offers to influence consumers

An innovative machine learning approach to predict the dietary fiber content of packaged foods

Underconsumption of dietary fiber is prevalent worldwide and is associated with multiple adverse health conditions. Despite the importance of fiber, the labeling of fiber content on packaged foods and beverages is voluntary in most countries, making it challenging for consumers and policy makers to monitor fiber consumption. Here, we developed a machine learning approach for automated and systematic prediction of fiber content using nutrient information commonly available on packaged products. An Australian packaged food dataset with known fiber content information was divided into training (n = 8986) and test datasets (n = 2455). Utilization of a k-nearest neighbors machine learning algorithm explained a greater proportion of variance in fiber content than an existing manual fiber prediction approach (R2 = 0.84 vs. R2 = 0.68). Our findings highlight the opportunity to use machine learning to efficiently predict the fiber content of packaged products on a large scale