RESUMO
The aim of this article is to determine experimentally and numerically the influence of material degradation on the deformation of a paraglider during flight. The presented method regards numerical modeling of pressure distribution over the wing and its effect on paraglider behavior; the considerations are preceded by experiments on three types of Polyamide 6.6 paraglider fabrics, subjected and not subjected to thermal, UV and flexing degradation. Scanning electron microscope (SEM) records allowed to determine the structural characteristics of the analyzed samples. Air permeability and mechanical tests are the input data for the computational simulations. When a pressure drop of 200 Pa is applied, all the analyzed samples are impermeable, except for those damaged by flexing. Thus, flexing damage has the greatest influence on the air permeability change among all considered aging factors. Aging caused by UV radiation has the greatest influence on mechanical properties. No major influence of thermal ageing on the mechanical properties of the considered samples is observed. Safety factors of the considered materials not subjected to degradation range between 3.94 and 6.00. Safety factor of fabric no. 1 subjected to the UV degradation is equal to 1.33; this result does not secure a safe usage of the considered material. The methodology described in this research can help to predict paraglider covering materials' behavior in flight; it assumes many cases, i.e., applying a new material or the material at any point of its life cycle. Thus, the practical implications of this model supported by numerical methods may result in saving time and cost in producing prototypes, as well as potentially assessing the safety of used wings. Future research activity can introduce the application of different elastic-plastic damage models to determine the paraglider behavior during collapse.
RESUMO
The aim of paper is to determine experimentally and numerically the strength characteristics related to the paraglider wing with Fourier transform infrared spectroscopy of applied materials. The applied method consists in theoretical modeling supplemented by the tests of material parameters. First, the set of 10 lightweight fabrics was selected for the tests; the samples are representative for these structures. The materials were tested using the spectroscopy to determine the FTIR spectra. The samples differ in the content of certain characteristic groups. Air permeability change of the materials was determined for the different pressure drops. The air permeability of almost all the analyzed samples was close to zero with the exception of only one material. The tensile strength and elongation at the break of samples were determined on the testing machine. The paraglider samples were characterized by slightly decreased mechanical properties compared to the parachute fabrics. The material characteristics determined during the tests are the input data for the theoretical analysis. The numerical model of the paraglider wing is based on a 3D geometry from previous research, but the stress, strain, and deformation were determined using the ANSYS Structural program and the finite elements method. To determine the strength correctly, we introduce two basic values: the absolute maximal and the representative values that are the biggest repetitive values of stress, strain, and deformation. The stress value was determined by the main factors: (i) the thinner the material, the bigger the stresses that were accumulated; (ii) the stronger the material, the bigger the stresses that were accumulated. The results are similar for all materials and differ mainly by the values. The biggest stresses were observed inside the material contacting the ribs, whereas the biggest deformation and strain were in the regions between ribs, and the smallest were in the contact areas with the fixed supports. Their highest intensity was observed on the leading edge of the paraglider. We conclude that the obtained stresses were far from the breaking level for the wing.
RESUMO
OBJECTIVES: Sleep disorders in the form of insomnia or excessive daytime sleepiness have their health and social consequences. The aim of the study was to evaluate the frequency of sleep disorders, quality of life and the pattern of psychoactive substance use among the students of Polish universities using CAVI method. METHODS: The Athens Insomnia Scale, the Epworth Sleepiness Scale, and the Manchester Short Assessment of Quality of Life were used. The study was conducted using anonymous and voluntary questionnaires distributed via the Internet. RESULTS: Most of the respondents (N = 5,342) were women (74%). A high percentage (>51%) of sleep disorders was found in women. Daytime sleepiness occurred in 28% of respondents, which correlated with sleep disorders. The use of psychoactive drugs is very common (94%) among Polish students of both sexes and (apart from alcohol) significantly affects the quality of life (p = 0.000). In the assessment of the psychoactive substance use pattern, the students of medical universities only slightly differ from students of other majors. The quality of life of people affected by sleep disorders is much lower than of the healthy student population. CONCLUSIONS: The great scale of the sleep disorder phenomenon and the use of psychoactive substances among Polish students require further exploration with particular emphasis on preventive and therapeutic activities.