Fatigue Properties of Hot-Dip Galvanized AISI 1020 Normalized Steel in Tension–Compression and Tension–Tension Loading

Since hot-dip galvanizing causes a heat effect on cold-worked steel substrate and produces a coating layer comprised of distinct phases with varying mechanical properties, the fatigue mechanism of hot-dip galvanized steel is very complex and hard to clarify. In this study, AISI 1020 steel that has been normalized to minimize susceptibility to the heat effect was used to clarify the effect of the galvanizing layer on the tensile and fatigue properties. The galvanizing layer causes a reduction in the yield point, tensile strength, and fatigue strength. The reduction in the fatigue strength was more significant in the high cycle fatigue at R = 0.5 and 0.01 and in the low cycle fatigue at R = 0.5. The galvanizing layer seems to have very little effect on the fatigue strength at R = −1.0 in the low and high cycle fatigue. Since the fatigue strengths at R = 0.01 and −1.0 in the low cycle fatigue were strongly related to the tensile strength of the substrate, the cracking of galvanized steel was different than that of non-galvanized steel. The fatigue strength of galvanized steel at R = 0.5 dropped remarkably in the low cycle fatigue in comparison to the non-galvanized steel, and many cracks clearly occurred in the galvanizing layer. The galvanizing layer reduced the fatigue strength only under tension–tension loading. We believe that the findings in this study will be useful in the fatigue design of hot-dip galvanized steel.

Artificial lightning strike tests and coupled electrical–thermal analysis on roofing glazed tiles of ancient buildings

Lightning strike is one of the natural disasters to the roof components of ancient buildings. To investigate the causes and damage effects of lightning strikes on the roofing glazed tiles of ancient buildings, artificial lightning strike tests were carried out on glazed tiles. Based on the experiment results, a coupled electrical–thermal finite element model of mortar-containing glazed tiles was established and the Joule heat effect of lightning current was further investigated. The results show that when the lightning channel is attached to the surface of the enamel and body with a low electrical conductivity, the lightning current is mainly released in the form of surface flashover, and a minor damage is induced along the flashover path; when the lightning channel is attached to the mortar with a high electrical conductivity, the lightning current is injected into the mortar, resulting in significant tile damage. The spatial distributions of the temperature present clear gradient characteristics. The high-temperature area appears in the mortar while the high–thermal–stress area appears in the body connected to the grounding rail. As the peak of the lightning current increases, both the high-temperature and high–thermal–stress areas of the glazed tiles expand. The combination of the experiments and the numerical analysis results demonstrate that the damage mechanism of lightning Joule heat effect to glazed tiles may include two aspects. One is the internal explosive force generated from the sharp vaporization and expansion of the moisture inside the tiles due to rapid temperature increase, and the other is the thermal stress caused by the uneven temperature distribution.

A Study on the Heat Effect and Kinetics During Magnesiothermic Reduction of Porous SiO2

Magnesiothermic reduction reaction (MRR) is an effective method to synthesis Si nanoparticles. In this paper, the heat effect and MRR kinetics were investigated by real-time temperature monitoring and analyzing the DSC curve of the MRR. It was found that the MRR onset temperature is about 465 °C, and the system temperature rose sharply at 535 °C. After the disappearance of the magnesium phase, the system temperature remained consistent with the set value. The exothermic peak lags and the spike decreases when adding NaCl into the system. The MRR was chemical reaction control, corresponding with the apparent activation energy was 193.456 kJ·mol-1 (without NaCl) and 191.434 kJ·mol-1 (with NaCl) in the temperature interval 465 °C −700 °C, respectively. NaCl affects the reaction mechanism by lowering the temperature of the system. Our work successfully prepared the spherical Si nanoparticles, which average grain size increased from 25 nm to 40 nm with the extended reaction duration. The conversion rate of porous SiO2 precursor was as high as 92%.