Browsing by Author "Moreira, R."
Now showing 1 - 3 of 3
Results Per Page
Sort Options
- Evaluation and numerical modeling of phenomenological approach for AZ31B-F magnesium alloy under multiaxial fatiguePublication . Moreira, R.; Anes, Vitor; Freitas, M. De; Reis, L.Magnesium alloys have been attractive to use in structural components due to their high strength to weight ratio, low density and high damping capacity. However, magnesium alloys show peculiar plastic deformation mechanisms under cyclic loads (twinning and de-twinning) that causes the asymmetric material behaviour and limits their use in structural components. Recent researches indicate that this type of plastic deformation mechanism cannot be fully characterized using the typical tools used in steels. Therefore, the phenomenological Hypo-strain (HYPS) model has been developed to capture the asymmetric behaviour of magnesium alloys under uniaxial and multiaxial loadings. This study aims to evaluate the phenomenological Hypo-strain approach for AZ31B-F magnesium alloy and to implement the HYPS model on an external subroutine (UMAT) to run on Abaqus. The goal is to reach a numerical tool that can be used to accurately describe the cyclic elastic-plastic behaviour of magnesium alloys in synergy with finite element packages. In order to characterize the cyclic behaviour of AZ31B-F magnesium alloy, experimental tests were performed considering proportional and non-proportional loadings. To evaluate the implemented model in UMAT, these results were correlated with the experiments and with the analytical HYPS approach. Moreover, the estimates were also correlated with the Armstrong-Frederick model available on Abaqus/Standard 6.14 library. The results have shown that the HYPS model was successful implemented on the UMAT subroutine with a good correlation between experimental tests and the HYPS model. Some remarks between the HYPS and Armstrong-Frederick models are drawn.
- Occupational exposure to metals and PAHs: combining literature-based exposure and in vitro hazard data towards a mixture risk assessmentPublication . Tavares, A.M.; Alves, I.; Moreira, R.; Louro, H.; Ladeira, Carina; Viegas, Susana; Loureiro, S.; Santonen, T.; Göen, T.; Kortenkamp, A.; Luijten, M.; Silva, M.J.A.The environment within industrial settings is commonly characterized by the existence of a complex mixture of chemicals from different raw materials and transformation processes. Occupational co-exposure to chromium (Cr), Nickel (Ni), and Polycyclic Aromatic Hydrocarbons (PAHs) may occur in diverse workplaces, such as aeronautic and waste management, (e.g incineration) sectors. Such co-exposure raises concern in terms of occupational health, as these substances are recognized lung carcinogens and mainly act by genotoxic mechanisms, increasing the likelihood of interactive toxic effects. The fact that current regulatory practices are usually focused on single chemical substances, without integrating the possibility of combined or aggregated exposures and effects, may lead to a risk underestimation. This work, developed under the scope of HBM4EU Initiative (https://www.hbm4eu.eu), a literature-based mixture risk assessment (MRA) exercise for occupational exposure to metals and PAHs was performed. In addition, in vitro toxicity data was obtained for the same mixtures to provide support to its hazard assessment. Human biomonitoring (HBM) data on Cr(VI), Ni, and/or PAHs were extracted from occupational studies conducted in the European Union and searched in literature databases. Selected reference values were used to calculate risk quotients (RQ) for each substance based on the retrieved exposure data; the combined risk was given by the sum of the RQ, i.e., the Background Exposure Exceedance Score(BEES). In parallel, we evaluated the combined cyto- and genotoxicity of the same chemicals (assessed by the MTT and micronucleus assays) in the human alveolar A549 cell line. In most of the analyzed studies, we observed that BEES levels, estimated from the exposure to metals mixture or to metals and PAHs, exceeded RQ levels considered acceptable for the individual substances. Only two studies, conducted in hazard waste incinerator settings, presented urinary exposure levels for the three substances. They showed a value of BEES of concern (>1) for all exposure scenarios, even for workers performing activities considered of low exposure or no exposure, such as laboratory and administrative workers. In vitro assays supported that A549 cells' exposure to these substances resulted in interactive cytotoxic and genotoxic effects that may underlie health effects different from those predicted from single exposures. Our findings show the limitations of applying occupational exposure reference values defined on a single substance basis to workplaces where exposure to chemical mixtures occurs, highlighting the relevance of performing MRA as a more realistic approach to guide suitable risk management measures in occupational settings.
- Worker’s nasal swab: a tool for occupational exposure assessment to bioburden?Publication . Viegas, Carla; Santos, V.; Moreira, R.; Faria, Tiago; Ribeiro, Edna; Caetano, Liliana Aranha; Viegas, SusanaThe nose cavity is the primary portal of entry for inspired air and the first region of the respiratory tract to be in contst with bioaerosols. Nasal swab allows measurement of bioburden presence in the nose cavity and the collection is easy and painless. We intended to identify scientific papers reporting this tool as a surrogate to access exposure to microbiologic agents in occupational environments. Literature research was performed using scientific and academic databases. In 5 from 11 articles studied only one parameter was analysed, being the most common Methicillin-resistant S. aureus. Sevem studies applied cutured based-methods coupled with molecular tolls essay. Findings from two studies coroborate the use of nasal swab as a tool to complement the occupational exposure assessements, since was found association between the nasal swabs results and the occupational microbiota also assessed. Nasal swabs analyses should comprehend culture based-methods and molecular tools assay.