Influence of wood anisotropy on its mechanical properties in relation to the scale effect

As a construction material wood is characterized by many advantages: low density, a high degree of strength and stiffness, low thermal and electrical conductivity and chemical durability. However, it is an anisotropic material that contains structural elements of varying stiffness and strength. When moisture levels increase, it is characterized by the variability of its mechanical properties and creep resulting from rheological properties. Therefore, it is important to understand how the mechanical properties of wood vary depending on its heterogeneity, the orientation of the sample in relation to the directions of anisotropy and its natural disadvantages. The research material was obtained from the lumber of pine wood, which on the basis of the foursided planing process was divided into 2 groups: A, B. The wood was subjected to strength tests specifying for appropriate groups of samples respectively: modulus of elasticity in static bending – group A-B, static bending strength - group A-B. The influence of wood anisotropy on the elasticity and strength properties of wood was demonstrated, this results from the variability of the wood element orientation and load direction in relation to the main directions of anisotropy

Validation of Heat and Mass Transfer Model in the Protective Clothing

W artykule przedstawiono zaawansowany model matematyczny i numeryczny transportu ciepła i masy w wielowarstwowych ubraniach ochronnych, które były poddane działaniu wysokiej temperatury otoczenia lub dużych radiacyjnych strumieni ciepła emitowanych przez gorące ciała. Zaproponowany model uwzględniał przewodzenie ciepła i promieniowanie cieplne w warstwach tkaniny o spektralnych właściwościach optycznych i w szczelinach powietrznych oraz transport energii związany z dyfuzją wilgoci przez ubranie ochronne oraz z procesami sorpcji i desorpcji wody w włóknach tkaniny. Dodatkowo do modelu włączono złożone warunki bilansu energii i masy oraz warunki optyczne na granicach warstw tkaniny. Do rozwiązania równań modelowych opracowano autorski iteracyjny algorytm numeryczny, który bazował na metodzie objętości kontrolnych. Następnie przeprowadzono analizę walidacyjną zaproponowanego modelu obliczeniowego poprzez porównanie otrzymanych wyników z wynikami pomiarów eksperymentalnych dla wybranego pakietu ubrania ochronnego ogrzewanego przez krótki czas radiacyjnym strumieniem ciepła emitowanym przez promiennik podczerwieni, a następnie chłodzonego w otoczeniu. Otrzymano dobrą zgodność czasowych przebiegów temperatury, co potwierdziło wiarygodność zaproponowanego modelu.An advanced mathematical and numerical model of heat and mass transfer in the multi-layer protective clothing, which was exposed to either high temperature environment or to high incident radiative heat flux emitted by hot objects was presented in this paper. The developed model accounted for heat conduction and thermal radiation in a non -grey layers of the protective garment. Additionally, heat transport associated with water vapour diffusion through the protective clothing and with sorption and desorption of liquid water in the fabric fibres were included. Complex energy and mass balances as well as optical conditions at the external and internal interfaces between clothing layers were formulated and incorporated into the model. A novel iterative numerical algorithm which was based on the Finite Volume Method was developed to solve the system of governing equations. Finally, the validation analysis of the model was carried out for selected multi-layer clothing which was exposed for a short time to radiative heat flux emitted by an infrared emitter and then cooled down in the surroundings. The simulated and experimentally measured time variations of temperatures were in good agreement, therefore the accuracy of the proposed model was validated