Browsing by Author "Mendes, R."
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- Effect of explosive mixture on quality of explosive welds of copper to aluminiumPublication . Loureiro, A.; Mendes, R.; Ribeiro, J.B.; Leal, Rui; Galvão, I.The aim of this research is to investigate the influence of explosive ratio and type of sensitizer on the quality of explosive welds between copper and aluminium alloy plates. The welds were performed on a partially overlapping joint configuration using an emulsion explosive (EE) with two different sensitizers, hollow glass microspheres (HGMS) and expanded polystyrene spheres (EPS). Welds with an improved surface were achieved by using the HGMS sensitizer. A higher wave amplitude was registered in welds produced with the EPS sensitizer. In turn, the dimension of the molten pockets was influenced by the explosive ratio, increasing in size with increases in the values of this parameter. The intermetallic content of these zones varied according to the sensitizer type.Unlike the CuAl2 phase, the Cu-richer phases CuAl and Cu9Al4were only identified inwelds performed using the EPS sensitizer. An increase in hardness was observed at the interface of all welds, which resulted from both the presence of intermetallic phases and the plastic deformation of the materials promoted by the impact. This effect was most evident on the aluminium alloy side. All the welds had a greater strength than copper, i.e. the weakest material of the joint.
- Effect of the flyer material on the interface phenomena in aluminium and copper explosive weldsPublication . Carvalho, G.H.S.F.L.; Mendes, R.; Leal, R. M.; Galvão, I.; Loureiro, A.The effect of physical and mechanical properties of three different flyers on the interface phenomena of partially overlapped explosive welds, using the same base plate material, was studied. Flyers of Copper Cu-DHP and aluminium alloy 6082 (tempers T6 and O) were welded to AA6082-T6 base plates. The morphology of the weld interface is strongly influenced by the physical and mechanical properties of the flyer. In the interface of the aluminiumwelds, the use of a flyer of lower hardness and yield strength than the base plate results in asymmetrical waves, with bigger amplitude and smaller wavelength than the weld series of similar temper, and higher mechanical properties. The copper-aluminium welds presented flat interfaces, mainly because of the significant differences inmelting temperature and density between the copper flyer and the aluminiumbase plate. Considering these results and analysing several dissimilar welds carried out by other authors itwas found thatwhen the product of density and melting temperature ratios between the flyer and the base plate exceeds a certain value, there is no formation of waves at the interface of the metals. Furthermore, for the Cu-Al welds, the CuAl2 (θ) intermetallic phase was formed on the bond zone.
- Explosive welding of aluminium to stainless steel using carbon steel and niobium interlayersPublication . Carvalho, G.H.S.F.L.; Galvão, I.; Mendes, R.; Leal, R. M.; Loureiro, A.This work aimed to study aluminium to stainless steel explosive welds produced using two different interlayers: carbon steel and niobium. The use of each interlayer was analysed and compared microstructurally and mechanically using many characterisation techniques. The final joints using both interlayers presented favourable interfacial microstructure: waves on both interfaces. However, the joint using the carbon steel interlayer showed the best mechanical properties compared to the joints using the niobium interlayer. All interfaces found on both welds were wavy. However, depending on the metallic alloy combination, the shape of the wave is completely different. The results suggest that the shape of the waves is influenced by the shock impedance mismatch of the materials being welded. The impedance mismatch parameter (IMP) developed for explosive welding in this work proved to be a compelling method to order metallic combinations in a single axis to estimate the tendency to form typical or curled waves. Typical symmetrical waves tend to develop less quantity of IMCs than curled waves. However, the mechanical tests performed did not detect differences that could have been caused by this difference.
- Formation of intermetallic structures at the interface of steel-to-aluminium explosive weldsPublication . Carvalho, G.H.S.F.L.; Galvão, I.; Mendes, R.; Leal, Rui; Loureiro, A.The formation of intermetallic structures at the interface of carbon steel to 6082 aluminium alloy explosive welds and their influence on the weldability of these two materials were studied. The morphology, the microstructure, the chemical and phase compositions of the welds were characterised by several types of microscopy techniques. The interface characterisation proved that explosive mixtures with a lower detonation velocity were revealed as being more suitable for achieving consistent welds since jet entrapment was prevented and continuous molten layers were not formed at the weld interface. It was also found that the physical properties of the intermetallic phases generated at the weld interface have a strong influence on the weldability of steel-to-aluminium explosive welds. Specifically, it was shown that the formation of aluminium-rich intermetallic phases at the weld interface increases the solidification time of the interfacial molten material, decreasing the weldability of these two materials. The formation of these intermetallic compounds should be avoided by reducing the interaction between the flyer and the baseplate as well as by avoiding excessive molten layers.
- High-pressure range shock wave data for syntactic foamsPublication . Ribeiro, J.; Mendes, R.; Plaksin, I.; Campos, J.; Capela, Carlos; Elert, Mark; Furnish, Michael D.; Anderson, William W.; Proud, William G.; Butler, William T.Syntactic foams [SF] are a porous composite material resulting from the mixture of Hollow Glass Micro Spheres [HGMS] with a polymeric binder. Beyond a set of technological advantages over the polymer considered alone, SF present as an essential feature the possibility to control in wide limits the amount, the shape and the size of the pores and for that reason are being used for benchmarking in the area of shock wave [SW] behavior of porous materials. In this paper, SW loading experiments of SF samples were performed in order to assess the high-pressure range Hugoniot equation of state as a function of the SF initial density. Hugoniot data were assessed coupling the SW velocity within the SF samples with the SW velocity in a reference material or with manganin gauge results. The results obtained present a significant variation with the initial specific mass and can be described with appreciable precision by the Thouvenin/Hofmann Plate Gap model, while the concordance between the experimental results and the Gruüneisen model seems to be very dependent on the Gruüneisen coefficient values.
- Influence of base material properties on copper and aluminium–copper explosive weldsPublication . Carvalho, G. H. S. F. L.; Galvão, I.; Mendes, R.; Leal, Rui; Loureiro, A.The influence of base material properties on the interfacial phenomena in copper and aluminium–copper explosive welds was studied. Two explosive mixtures with different detonation velocities were tested. Sound aluminium–copper joints with effective bonding were achieved by using an explosive mixture with a lower detonation velocity. High energy explosives led to extensive interfacial melting, preventing the production of consistent dissimilar welds. Unlike to the similar copper joints, the aluminium–copper welds presented very asymmetrical interfacial waves, rich in intermetallic phases and displaying a curled morphology. The interaction of the materials in dissimilar welding was found to be completely different depending on the positioning of each alloy in the joint, i.e. positioned as the flyer or as the baseplate.
- Mental Health Status and Fear of COVID-19 in Young Adult Male Inmates in PortugalPublication . Laranjeira, C.; Baccon, W.; Mendes, R.Introduction Incarcerated individuals are subject to a heightened risk of both mental and physical ailments. Hence, it is important to conduct regular assessments of their mental well-being and other potential health hazards. Objectives The aim of this study is to examine the subjective experience of fear related to COVID-19 and the psychological consequences of the pandemic among a cohort of young adult male convicts. Methods A research design using an institutional-based quantitative cross-sectional approach was used. The data collecting period was from July to September 2022, during which data was gathered at a juvenile correctional facility located in the center area of Portugal. The researchers used questionnaires to gather data pertaining to demographic and health attributes, fear related to COVID-19, as well as measures of depression, anxiety, stress, and resilient coping. Results The study included a cohort of 60 incarcerated males who had been imprisoned for a duration exceeding 2 years. The prevalence of stress was found to be the highest among offenders, with around 75% reporting this symptom. Anxiety was the second most often reported symptom, with 38.3% of inmates experiencing it, followed closely by depression, which was reported by 36.7% of the inmate population. The average score on the Fear of COVID-19 Scale was 17.38 ± 4.80, suggesting that participants generally reported mild levels of fear. A total of 38 subjects, accounting for 63.3% of the sample, had low scores in resilience. The participants’ responses indicated that their perceptions of mental health were within a fairly high range, with an average score of 3.62 ± 0.87. Similarly, their perceptions of physical health were also moderately high, with an average score of 3.73 ± 0.95. In terms of global health, participants reported a slightly lower average score of 3.27 ± 0.82 for the preceding month. The Pearson correlation matrix revealed statistically significant associations between fear of COVID-19 and characteristics linked to mental health, with the strength of these associations ranging from moderate to high (p < 0.001). The identification of predictive variables for fear of COVID-19 was accomplished by the use of a multiple linear regression model. Four predictors were identified in the study, namely age, perception of mental health, and overall levels of anxiety and stress. These predictors together account for about 49.7% of the variance in the outcome variable. Conclusions The findings of our research indicate a significant prevalence of stress among incarcerated individuals, accompanied by moderate levels of anxiety and depression. Our research has the potential to provide valuable insights for policymakers, mental health professionals, public health specialists, and other relevant stakeholders in the identification and effective management of pandemic-induced anxieties and mental health symptoms.