During the first outbreak of the SARS-CoV-2 pandemic the population, focusing primarily on the risk of infection, was generally inattentive to the quality of indoor air. Spain, and the city of Madrid in particular, were among the world’s coronavirus hotspots. The country’s entire population was subject to a 24/7 lockdown for 45 days. This paper describes a comparative longitudinal survey of air quality in four types of housing in the city of Madrid before and during lockdown. The paper analysed indoor temperatures and variations in CO2, 2.5 μm particulate matter (PM2.5) and total volatile organic compound (TVOC) concentrations before and during lockdown. The mean daily outdoor PM2.5 concentration declined from 11.04 µg/m3 before to 7.10 µg/m3 during lockdown. Before lockdown the NO2 concentration values scored as ‘very good’ 46% of the time, compared to 90.9% during that period. Although the city’s outdoor air quality improved, during lockdown the population’s exposure to indoor pollutants was generally more acute and prolonged. Due primarily to concern over domestic energy savings, the lack of suitable ventilation and more intensive use of cleaning products and disinfectants during the covid-19 crisis, indoor pollutant levels were typically higher than compatible with healthy environments. Mean daily PM2.5 concentration rose by approximately 12% and mean TVOC concentration by 37% to 559%. The paper also puts forward a series of recommendations to improve indoor domestic environments in future pandemics and spells out urgent action to be taken around indoor air quality (IAQ) in the event of total or partial quarantining to protect residents from respiratory ailments and concomitantly enhanced susceptibility to SARS-CoV-2, as identified by international medical research.

A Hopkinson tensile bar has been numerically simulated by means of the commercial software ABAQUS, with different gaps between the sample and the incident and the transmitted bars. This simulated a poor adjustment in the preparation of the tests and observed the effect the measurements of the stress of the incident, reflected and transmitted bars might have in the results of the stress-time and strain-time curves, as well as in the stress-strain curve of an aluminum sample. It is verified that the gap may significantly affect the elastic limit to be obtained from the dynamic tests and the expected results of the ultimate stress and deformation, and also affect the sample stress-strain curve to a large extent. We also concluded in the importance that is necessary in the testing equipment for a dynamic characterization of materials, in this case, the equipment for dynamic tensile testing.

RESUMEN El enfoque principal de este estudio es discutir la influencia de la longitud del proyectil en los resultados de un experimento de la barra Hopkinson de tracción (SHTB). Se han realizado simulaciones por medio de elementos finitos utilizando el software comercial ABAQUS en ensayos de tracción a altas velocidades de deformación en muestras de aleación de aluminio 7017T73 variando la longitud del proyectil. Los análisis por elementos finitos se han aplicado para simular los efectos de la variación de la longitud del proyectil en las mediciones obtenidas en las barras incidente, reflejada y transmitida. Se han obtenido diferentes velocidades de deformación, al variar la longitud del proyectil permaneciendo su velocidad constante. Los resultados de la simulación muestran que la longitud del proyectil tiene un efecto significativo en la tensión obtenida en la muestra y también en la curva de tensión-deformación. Se puede concluir que la longitud del proyectil es un factor que influye en los ensayos de tracción dinámica, ya que tiene un efecto significativo en la tensión obtenida dentro de la probeta. Las simulaciones también proporcionan información complementaria a los experimentos y una comprensión profunda del comportamiento de la probeta.

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