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In order to study the shear mechanical properties of photovoltaic bracket member connection with the high⁃strength cold⁃formed thin⁃walled steel, 24 photovoltaic bracket connection specimens were tested for shear capacity. The mechanical properties of web and flange connected by bolts were mainly studied. The failure process and failure mode of the specimens were observed, and the load⁃displacement curve and ultimate bearing capacity of the specimens were obtained. The results show that when the peak load is reached, the self⁃drilling screw on the flange of the specimen is cut first, and then the cold⁃formed thin⁃walled steel plate near the bolt is compressed to yield, which leads to the typical bearing failure of the specimen. Compared with the specimen of the bolt on the flange, the stiffness of the specimen of the bolt on the web is larger, but the ductility is lower.Based on the relevant calculation formulas in the technical code, a modified calculation formula for calculating the bearing capacity of photovoltaic bracket member connection with the high⁃strength cold⁃formed thin⁃walled steel was proposed, and the calculation values were in good agreement with the test values. The research conclusion can provide reference for the engineering application of the photovoltaic bracket with the high⁃strength cold⁃formed thin⁃walled steel. [ABSTRACT FROM AUTHOR]

The microstructure of machined superficial layer significantly affects the mechanical properties and service life of mechanical components. Herein, to obtain a machined surface with excellent properties, a comprehensive application of theoretical calculations and test analysis research methods was conducted to investigate the influence mechanism of machining on performance and quality of machined superficial layer of high-strength alloy steel during machining, and reveal the intrinsic correlation between microstructure evolution, quality and performance of machined superficial layer. The results indicate that the machining can achieve gradient microstructure on the machined surface, which can improve the performance of machined surface greatly. From the surface to the inside region, the layers are respectively the recrystallized layer where compact nano-sized equiaxed grains are located, the rheological layer with clusters of high-density sub-grain structures, and the distorted layer with residual distorted grains. The maximum strain of superficial layer in the machined state is 2.81 times that of the original state. The grains are evidently refined and the grain size is reduced by 49.03%. The dislocation density is enhanced by 100.69%, while the number of small-angle grain boundaries (SAGB) and other substructures increase sharply, being 5.26 times that in the original state. By performance testing, the machining substantially enhances the hardness of the superficial layer of high-strength alloy steel with certain rise in toughness simultaneously, which is exactly the result of the combined effect of fine-grain strengthening and dislocation strengthening caused by the machining process above.

This article presents failure investigation on a high-strength alloy SA213-T91 super-heater tube. This failure is the first occurrence involving the material in Kapar Power Station Malaysia. The investigation includes visual inspections, hardness measurements, and microscopic examinations. The failed super-heater tube shows a wide open rupture with thin and blunt edges. Hardness readings on all the as-received tubes are used for estimating the operating metal temperature of the super-heater tubes. Microstructures of the failed tube show numerous creep cavities consisting of individual pores and chain of pores which form micro- and macro-cracks. The findings confirmed that the super-heater tube is failed by short-term overheating. Higher temperatures of the flue gas due to the inconsistent feeding of pulverized fuels into the burner is identified to cause overheating of the failed tube. [ABSTRACT FROM AUTHOR]