No abstract

No abstract

Cyclic cryogenic treatment, a major cycle accompanied by zero or more subsidiary cycles, was conducted on the hardened 42CrMo steel using orthogonal design method to investigate the effect of different parameters (cryogenic temperature, holding time, and cycles number) of cryogenic treatment on wear resistance and impact toughness of the steel. Range analysis was performed to obtain the influencing order of the three parameters and their optimum values. The results show that after cryogenic treatment, the steel exhibits higher wear resistance and impact toughness, whereas no significant change in hardness. For wear resistance, the influencing order of parameters is cryogenic temperature, holding time, and cycles number, and the optimum values of the parameters are −160°C, 24 h and two cycles, respectively. For impact toughness, the influencing order of parameters is cryogenic temperature, cycles number, and holding time, and the optimum values are −120°C, 24 h and three cycles, respectively. The wear topography and fracture topography were examined using scanning electronic microscopy (SEM) to investigate the wear mechanism and fracture mechanism of the steel after cryogenic treatment, respectively. The results show that after cryogenic treatment, the wear mechanism is the combination of abrasive wear and adhesive wear with oxidative wear, and the fracture mechanism is a quasicleavage fracture. The microstructure was also examined by SEM to investigate the influencing mechanism of cryogenic treatment for improving wear resistance and impact toughness of the steel. It suggests that more precipitation of fine carbides dispersively distributed in the matrix is responsible for the beneficial effect of cryogenic treatment on wear resistance and impact toughness of the steel.

No abstract

Aiming at the floor heave of transportation concentrated roadway on the West Wing (TCRWW) of No. 1 Coal Seam in Danhou Mine, it affects underground coal transportation and mine safety production. First, the lithology and structure of the roadway floor were sampled and tested, and it was found that it contained clay minerals with high hydrophilicity. Secondly, starting from the mechanical mechanism of the roadway floor, a mechanical model of the roadway floor is established. By increasing the floor anchoring layer thickness m1, the floor deformation can be effectively controlled to guarantee the stability of the surrounding rock of the roadway. Thirdly, the FLAC3D numerical simulation analysis of the roadway deformation under the existing support scheme of the roadway is consistent with the measured deformation results on-site, thereby revealing that the existing support scheme and parameters are not reasonable. Finally, the unreasonable support scheme and parameters of the existing roadway were disclosed, and an antifloor arch structure was proposed: “quicklime bottom paving + prestressed anchor cable + concrete arc beam + metal mesh + C20 high-strength concrete filling.” This floor treatment plan is adopted for the industrial verification of the test section of TCRWW. Engineering practice shows that the optimized roadway support scheme has a better effect on the deformation control of the roof-to-floor and rib-to-rib, thereby effectively ensuring safe and efficient production in the mine.

Orebodies in the Xiadian gold deposit in the Jiaodong Peninsula, China are mainly hosted in the Mesozoic granitoids, controlled structurally by the Zhaoyuan–Pingdu Fault Zone, and occur as disseminated and cataclastic altered type. Four mineralization stages were identified as follows: quartz–pyrite stage (I), gold‐bearing fine‐grained pyrite–quartz stage (II), polymetallic sulfide–quartz stage (III), and quartz–carbonate stage (IV). Quartz was classified as including quartz granules with dentation boundaries (I), cataclastic quartz grain assemblages (II and III), and rod‐like quartz grains (IV). Petrography, laser Raman analysis, and microthermometry of fluid inclusions in these stages (in both tunnel and borehole samples) reveal (a) CO2–H2O fluid inclusions (C–H type), (b) CO2–H2O ± CH4 fluid inclusions (C–H–CH4 type), and (c) aqueous fluid inclusions (H type). Fluid immiscibility caused by fluid mixing caused rapid precipitation of gold. The ore‐forming fluid of the Xiadian gold deposit evolves from an H2O–CO2–NaCl ± CH4 system with medium temperature and salinity to an H2O–NaCl system with low temperature and salinity, from CO2‐rich to CO2‐poor in composition and from a mixture of magmatic water with increasing meteoric water as δ18OH2O values. Sulphur isotope compositions suggest a mixed source of ore metal, and the Jiaodong Group may be a major source for sulphur. Fluid parameters of borehole samples indicate that there is the same fluid system for Au precipitation at different depths and fault gouge with poor permeability may play a crucial role in forming a relatively closed semi‐open space for Au precipitation. Integrating the data obtained from the studies including regional geology, ore geology, and fluid inclusions and stable isotope geochemistry, the Xiadian gold deposit is concluded as an orogenic‐type gold deposit formed in the tectonic transition from compression to extension.

In the previous studies, the criterion for deciding the occurrence time of the fetal central sulcus (CS) on magnetic resonance imaging (MRI) is based on the observation by the eyes. There have been no existing quantitative standards or numerical criteria in this field. In this study, we reconstructed the three-dimension (3D) images of the fetal brain based on the 7.0T MR images of 45 Chinese fetal specimens from the 11 to 22 weeks of gestational age (GA). Then we obtained data by measuring the maximum depth and length of the CS so as to analyze the early developmental pattern of it. These measures, especially CS depth, can be used to quantitatively determine the time of emergence of the fetal CS during the development. Statistics show that there are no gender or interhemispheric asymmetries of the CS from GA of 11 to 22 weeks.

In this chapter, we present a detailed introduction to the factors which influence laser powder bed fusion (LPBF) on oxide ceramics. These factors can be in general divided in three main categories: laser-related factors (wavelength, power, scanning speed, hatch distance, scan pattern, beam diameter, etc.), powder-and material-related factors (flowability, size distribution, shape, powder deposition, thickness of deposited layers, etc.), and other factors (pre-or post-processing, inert gas atmosphere, etc.). The process parameters directly affect the amount of energy delivered to the surface of the thin layer and the energy density absorbed by the powders; therefore, decide the physical and mechanical properties of the built parts, such as relative density, porosity, surface roughness, dimensional accuracy, strength, etc. The parameter-property relation is hence reviewed for the most studied oxide ceramic materials, including families from alumina, silica, and some ceramic mixtures. Among those parameters, reducing temperature gradient which decreases the thermal stresses is one of the key factors to improve the ceramic quality. Although realizing crack-free ceramics combined with a smooth surface is still a major challenge, through optimizing the parameters, it is possible for LPBF processed ceramic parts to achieve properties close to those of conventionally produced ceramics.