摘 要

The mechanical properties of high strength structural steel (HSSS) at elevated temperatures are the basis for fire-resistant design of HSSS members and structures. Previous studies on the mechanical properties of HSSS at elevated temperatures were mainly conducted on QT (Quenched and Tempered) HSSS, while few studies were conducted on TMCP (Thermo-Mechanical Controlled Process) HSSS. In order to identify the effect of manufacturing process on the mechanical properties of HSSS at elevated temperatures, an experimental study was carried out by steady-state method on TMCP Q690 HSSS, considering nine elevated temperatures ranging from 200 to 800 °C. Results showed that the elastic modulus and strength of TMCP Q690 HSSS decreased significantly as the temperature increased over 400 °C, while the ultimate elongation increased as the temperature increased above 500 °C. Formulas for calculating the reduction factors of mechanical properties of TMCP Q690 HSSS at elevated temperatures were proposed. Comparing the results of TMCP Q690 HSSS with those of QT Q690 HSSS previously studied, it can be found that the reduction on elastic modulus and strength was more severe for TMCP Q690 HSSS than QT Q690 HSSS in most cases, which was explained in the microstructure level of HSSS.

摘 要

The conditional moment closure (CMC) method is applied in combination with large eddy simulations (LES-CMC) to the UMD line burner configuration. This corresponds to a low-strain, buoyant diffusion flame. The low strain rate conditions are representative of fire conditions and the aim of the study is to evaluate LES-CMC results, including radiative effects. Only conditions far from extinction are studied. The weighted sum of grey gases model (WSGGM) for radiation is applied in mixture fraction space. Results are compared to what is obtained when radiation is taken into account as a local loss term in the conditional heat release rate, with prescribed radiative fraction. It is shown that the conditional scalar dissipation rate (CSDR) profile in mixture fraction space and the spatial terms in the transport equations for the conditional quantities have a major impact with the non-local WSGGM approach, while this is not the case in adiabatic simulations, nor in the radiative fraction approach. In the latter, only the value of the CSDR at stoichiometric is important, making this approach less sensitive. However, the latter are not well suited for extinction simulations.

摘 要

This paper aims to further explore the frosting and defrosting performance of coatings applied to microchannel heat exchangers. A visualization cycle experiment of hydrophilic, desiccant and hydrophobic coated microchannel heat exchangers was performed, and compared with the uncoated sample, under frosting condition. The results show that the delayed frost formation of the hydrophilic coating and the desiccant coating is not obvious. Even worse, the average heat transfer of the hydrophilic coating sample is 19% lower than that of the uncoated coating. By contrast, in the first round, the hydrophobic coating has a significant anti-frost effect, with a 24% reduction in pressure drop and a 40% increase in heat transfer. But it attenuated the most after four cycles. Taken together, the application potential of hydrophobic coatings is the greatest, but the horizontal fins and crest and trough structures, making drainage difficult, are key factors that limit its superior performance. Additionally, when evaluating the frosting performance of the coating of the microchannel heat exchanger, it is not recommended to use the frosting amount alone or the index of thickness and pressure drop, but to comprehensively consider the heat exchange effect.

摘 要

We present a simple, efficient and easy-to-use finite element (FE) model for the simulation of progressive damage in quasi-isotropic IM7/8552 carbon fibre reinforced composites under low velocity impact loading. The sub-laminate based continuum-discrete model in the commercial FE software LS-DYNA consists of built-in tools to facilitate modelling and analysis. The coupled plastic-damage material card MAT81 describes intralaminar damage in tension and compression which is calibrated using digital image correlation in over-height compact tension and compact compression tests to extract damage properties such as strain softening curves and size of the failure process zone. The cohesive interface formulation is virtually calibrated leading to realistic zones of delamination. The proposed model was applied to a wide range of impact loadings and compared to results obtained from experimental testing and high-fidelity FE models. Besides the good correlation between simulation and experiments, we demonstrate how to quantify different energy dissipation mechanisms during impact events.

摘 要

Many signboards are installed on the rooftops of low- and middle-rise buildings in Japan, which are often damaged by strong winds. However, there are no specifications of wind force coefficients for such signboards in the Japanese building codes and standards. In the present study, wind tunnel experiments were conducted to collect data on wind force coefficients under various conditions, including building shapes, as well as signboard shapes and locations. The distributions of the maximum peak wind force coefficients were obtained at various wind angles. Based on the results, the variation of the maximum peak wind force coefficient with wind angle was investigated. It was found that very large wind forces occurred near the edges of the signboard at oblique wind angles ranging from 30° to 60° with respect to the outside surface of the signboard. The present study focuses on such conditions that cause large wind forces on signboards. The results indicate that the building shape significantly affects the maximum peak wind force