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Influence of the heat insulation layer on the thermally stressed condition of the facade wall

Basok Borys, Davydenko Borys, Koshlak Hanna, Lysenko Oksana

Production Engineering Archives

2022

Vol. 28, Iss. 2

123--131

The temperature-stress state of the concrete facade wall with a window opening, which is the external enclosing structure of the room with a steel heating device, was investigated by the method of numerical modeling. Estimated studies were performed for winter period when the heating system of the building is functioning. According to the results of solving the system of equations of thermal stress and equation of thermal conductivity, the temperature distribution over the wall volume and distribution of normal and tangential stresses were determined. Areas of the wall where these stresses are maximum were identified. The research was performed for cases of both, absence and presence of a heat-insulating layer on the outer surface of the facade wall. From comparison of the results obtained for these two options, it follows that the external thermal insulation coating not only helps to reduce dissipative heat loss through the facade wall, but also reduces the absolute values of stresses in the concrete wall arising resulting from temperature deformations. In some cases, the sign of stresses changes from stretching (wall without external insulation) to compressive (wall with insulation).

Lifetime prediction method for MEMS gyroscope based on accelerated degradation test and acceleration factor model

Liu Yao, Wang Yashun, Fan Zhengwei, Hou Zhanqiang, Zhang Shufeng, Chen Xun

Eksploatacja i Niezawodność

2020

Vol. 22, no. 2

221--231

The reliability analysis of MEMS gyroscope under long-term operating condition has become an urgent requirement with the enlargement of its application scope and the requirement of good durability. In this study we propose a lifetime prediction method for MEMS gyroscope based on accelerated degradation tests (ADTs) and acceleration factor model. Firstly, the degradation characteristic (bias instability) is extracted based on Allan variance. The effect of temperature stress on the degradation rate of bias instability is analyzed, and it shows that the degradation rate of bias instability would increase with the increase of the temperature. Secondly, the ADTs of MEMS gyroscope are designed and conducted, the degradation model of MEMS gyroscope is established based on the output voltage of MEMS gyroscope and Allan variance. Finally, the acceleration factor model of MEMS gyroscope under temperature stress is derived, and the lifetime of the MEMS gyroscope is predicted based on two group tests data under high stress level. The results show that the lifetime calculated by the acceleration factor model and mean lifetime under high stress levels is close to the mean lifetime calculated by the linear equation at normal temperature stress.

Analiza niezawodności żyroskopu MEMS w warunkach długotrwałej pracy stała się pilną koniecznością wraz z rozszerzeniem zakresu jego zastosowania i wprowadzeniem wymogu dobrej trwałości. W niniejszym artykule, zaproponowano metodę prognozowania czasu pracy żyroskopu MEMS w oparciu o testy przyspieszonej degradacji i model współczynnika przyspieszenia. W pierwszej kolejności, wyznaczono charakterystykę degradacji (niestabilność wskazań) na podstawie wariancji Allana. Analizowano wpływ naprężenia cieplnego na szybkość degradacji w zakresie niestabilności wskazań. Analiza wykazała, że szybkość degradacji wzrastała wraz ze wzrostem temperatury. Następnie, opracowano i przeprowadzono testy przyspieszonej degradacji żyroskopu MEMS, a model jego degradacji ustalono na podstawie napięcia wyjściowego żyroskopu i wariancji Allana. Na koniec, wyprowadzono model współczynnika przyspieszenia dla żyroskopu MEMS w warunkach naprężenia cieplnego, a żywotność żyroskopu prognozowano na podstawie danych z dwóch testów grupowych przeprowadzonych w warunkach wysokiego naprężenia. Wyniki pokazują, że czas pracy obliczony na podstawie modelu współczynnika przyspieszenia i średni czas pracy przy wysokich poziomach naprężeń są zbliżone do średniego czasu pracy obliczonego na podstawie równania liniowego przy normalnym naprężeniu cieplnym.

Formation of temperature cracks of concrete in high-rise buildings and the corresponding measures

Guo L.

Archives of Civil Engineering

2019

Vol. 65, nr 4

177--188

A lot of heat will generate in mass concrete after pouring to form temperature cracks, which will reduce structural stiffness. This paper briefly introduces the principle of solid heat conduction and the cause of temperature crack formation and then used COMSOL software to simulate and analyze the mass concrete. The results showed that the simulation model had enough reliability to analyze the temperature change; the internal and external temperature of concrete rose first and then decreased; the formation of temperature crack was related to the internal and external temperature difference; the internal and external temperature difference was inversely proportional to the heat conductivity coefficient of concrete and directly proportional to the pouring temperature. Then, according to the analysis results, two measures were put forward to prevent temperature cracks in mass concrete: selecting concrete materials with high thermal conductivity, i.e., selecting coarse aggregate and fine aggregate with larger heat conductivity coefficient and reducing concrete pouring temperature, i.e., selecting cement with lower hydration heat, paying attention to temperature reduction in the process of concrete stirring, and reducing the amount of cement.