Rock wool board (RWB) is widely used in construction of exterior insulation worldwide. Fiber diameter, solid volume fraction (SVF), and contact degree among the fibers significantly influence the RWB physical properties. Herein, the effects of these factors on the mechanical properties of RWB were investigated using the GeoDict software. First, the fiberization process resulted in a finer fiber diameter, and the SVF of RWB increased with decreasing pore sizes. In addition, both the fiber diameter and SVF significantly influenced the RWB shear strength. Furthermore, in compliance with the Chinese standards of compression, tensile, and shear strength, the SVF of RWB with a 10.5 μm fiber diameter did not exceed 4.72%, 4.04%, and 5.4%, respectively. The novel method proposed herein can be used for optimizing the RWB manufacturing process.
Employee assistance program (EAP) is a service mode for organizations to effectively manage employees’ psychology and behavior to improve their work efficiency. As the problems of teachers’ stress and mental health are so serious that cannot be ignored, in order to understand their psychological stress and the demands for EAP, a survey was conducted among 386 college teachers, on their working pressure and pressure management by self-made questionnaires. The results show that besides the interpersonal relationships, teachers in colleges and universities have greater stress and the stress sources are more various, and they are supposed to have stronger subjective needs for the EAP. However, few college teachers have received EAP services, and the teachers who received EAP services are not the most stressed people. Thus, the EAP should be promoted inside universities to provide supportive services for teachers’ career development.
This paper studied the mechanical behavior of the filament/staple fiber composite yarn and the pure cotton yarn under the isostress and isostrain of cycling tensile strength with the conditions of small deformation. And it also analyzed the elastic recovery rate, creep rate and stress relaxation rate under the different deformation rate and load. The results show that the mechanical properties of elastic recovery rate, stress relaxation and creep all keep in good range in the experiment of cycling tensile strength with low certain elongation and constant load; as the increase of certain elongation and constant load, the mechanical properties of elastic recovery rate, stress relaxation and creep have much difference, just in terms of the conformality under the cyclic tensile strength, PET/PU/cotton composite yarn shows the best, next is the PU/cotton composite yarn, and then next is the PET /cotton composite yarn, and the pure cotton yarn shows the worst.
Thermal conductivity of rock wool boards was investigated in this study. Although distribution of fibers in a realistic rock wool board is unclear, it can be simulated by computer X-ray tomography technique (CT) followed by rearrangement through the random generation-growth (RGG) model. An ideal CT-RGG structure model of rock wool boards (CT-random generation-growth model) was established by simplifying material properties based on the mesostructure parameters of the RGG model. Thermal conductivity of rock wool boards with different apparent densities and fiber diameters was studied, and the CT-RGG model was analyzed by explicit jump (EJ) diffusion equations solved by the fast Fourier transform method. We found that thermal conductivity of a single rock wool fiber can be successfully determined. Simulation and measurement results show that thermal conductivity increases consistently with the increase of apparent density and fiber diameter, particularly when the apparent density of rock wool board is greater than 140 kg m−3. Compared with the existing theoretical models, the proposed method does not depend on the empirical parameters; therefore, it is useful in designing and optimizing the thermal conductivity of rock wool boards.
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