Abstract: Non-metallic inclusions significantly influence the properties of steels. Take heavy rail steel as an example, Al2O3 inclusions can become fatigue source under cyclic stress, resulting in the rupture of the steel. Existing technologies and equipment can effectively reduce the amount and harm brought about by such inclusions, but they cannot guarantee the complete removal of large-sized and high-melting-temperature inclusions. Large-sized non-metallic inclusions give rise to instability in high-quality steels; as such, they are one of the bottlenecks in the development of steel. In the steel-making process, refractories in close contact with molten steel are a main source of large-sized non-metallic inclusions. Therefore, adopting appropriate ladle-lining refractories for refining and alloying is vital. This paper summarized the current research and latest developments in refractories used as ladle linings, and analyzed the application background and existing problems of traditional ladle lining refractories. Based on this discussion, future research directions regarding refractories suitable for the smelting of ultra-low-oxygen steel (or clean steel) as well as approaches to precisely control refractory properties via the reasonable selection of material components and structures were then provided. Novel ladle-lining refractories must possess not only excellent thermomechanical properties but also the ability to purify molten steel.
Abstract: Bone cutting is a basic and vital clinical operation in surgery. Traditional mechanical processing methods such as drilling, grinding, and milling, are widely applied in bone surgery. Bone is a hard biological tissue with a complex structure. The compact bone structure is similar to a brittle fiber-reinforced composite. It is easy to damage bone tissue and reduce bone activity during cutting. The quality and efficiency of bone cutting are related to the therapeutic and rehabilitative outcomes of patients. A correct understanding of bone-cutting processes and mechanisms, optimizing the process parameters of bone cutting, and developing advanced bone-cutting surgical tools are important ways to reduce cutting-induced thermal-mechanical damage from bone cutting and improve the postoperative rehabilitation of patients. This article reviewed published works related to constitutive models of bone tissue, bone cutting processes, and the cutting mechanisms used in different bone-cutting surgeries, with a main focus on the effect of machining parameters and tool design. The latest techniques and challenges in ultrasonic bone cutting were also discussed. Finally, it is concluded that bone-cutting research should address the following aspects: (1) improving the constitutive model for numerically simulating bone cutting; (2) constructing a systemic bone-material-cutting theory that explains the cutting mechanism as it relates to the chip morphology of bone material; (3) further refining the development of cutting tools for bone materials; (4) recognizing the advantages of ultrasonic bone cutting, including high safety levels, less damage, and faster healing, which will guide the development trends of future clinical bone-cutting operations.
Abstract: In recent years, low-salinity waterflooding has become the focus of research in the petroleum industry owing to its enormous advantages, including high efficiency in displacing oils, ease of injection into oil-bearing formations, easy access and operation of water, and low investment and pollution, all of which are more cost-effective compared to other enhanced oil recovery methods. Numerous experimental studies and field trials of sandstone and carbonate rocks have proven that low-salinity waterflooding can enhance oil recovery effectively due to various mechanisms, including fines migration and mineral dissolution, increased pH effect and reduced interfacial tension, multicomponent ion exchange, and double-layer expansion. As an important mechanism of low-salinity waterflooding, fines migration induced by lowering injected water salinity can effectively change reservoir quality and injection profile, thereby achieving equilibrium displacement and enhance oil recovery. Several models and mathematical equations that describe particle release and capture have been proposed by many scholars in previous studies, and the maximum retention concentration function of fine particles is considered to be the most effective method for describing fines migration. Based on the Derjaguin-Landau-Verwey-Overbeek theory and electric double-layer theory of colloid stability, the effect of injected water salinity and ion valence on the clay particle force and particle migration concentration were analyzed from the microcosmic view in this paper, and the relationship between the particle migration concentration and the permeability impairment was established through maximum concentration of attached fine particles. Aiming at the problem of interlayer interference in vertically heterogeneous reservoir, the numerical simulation of low-salinity waterflooding was carried out in high water-cut stage. Force analysis and numerical simulation results show that the high-permeability layer with high injected water flow rate will cause the hydration, expansion, migration, and clogging of a large amount of clay particles, leading to a marked permeability decline in the high-permeability layer. More injected water is diverted into low-permeability and middle-permeability layer with low sweep efficiency. The injection profile and interlayer interference is relieved. Therefore, the production degree of reservoirs and cumulative oil recovery improve by approximately 3% beyond conventional seawater flooding.
Abstract: Absorption heat pump (AHP) system is an energy-saving technology that utilizes renewable energy or industrial waste heat for refrigeration and heating. Therefore, it has attracted much attention for use in residential and industrial buildings. The thermodynamic performance of the AHP system greatly depends on the thermodynamic properties of its working pairs. In commercial applications, LiBr/H2O is usually used as a traditional working pair. However, its shortcomings of easy crystallization and severe corrosion have significant impacts on the practical application of high-temperature AHP systems. To overcome the shortcomings of LiBr/H2O, various ionic liquids (ILs)/H2O mixtures have been recently investigated as alternative working pairs. Though ILs/H2O has a wider operating temperature range and less corrosiveness, ILs/H2O working pairs generally have very high viscosity, which restricts its practical applications. To further solve the above shortcomings of LiBr/H2O and ILs/H2O, a new ternary working pairs LiBr-[BMIM]Cl/H2O was proposed in the previous study. Compared to the traditional LiBr/H2O binary working pair, the LiBr-[BMIM]Cl/H2O ternary working pair has advantages in terms of crystallization temperature and corrosiveness. LiBr-[BMIM]Cl/H2O shows a great potential in the practical application of an AHP and refrigeration systems, especially at a high temperature. Based on the previous study, in this work, several important thermodynamic properties, including densities, viscosities, specific heat capacities, and specific enthalpies were systematically measured and correlated using the least-squares method, and the average absolute relative deviation (AARD) between the measured data and the calculated data is 0.03%, 1.10%, 0.29%, and 0.01%, respectively. In addition to the crystallization temperature and corrosiveness, viscosity is another key thermodynamic property affecting the practical application of working pairs in AHP system. The viscosity of LiBr-[BMIM]Cl/H2O is less than 25 mm2·s-1, which is well compatible with the application requirement. Moreover, the addition of LiBr in[BMIM]Cl/H2O is beneficial for improving the high viscosity of ionic liquids.
Abstract: Copper tailings are potential resources rich in iron minerals and their long-term stockpiling not only cause resource waste but also bring serious pressure to the ecological environment. Therefore, the resource utilization of copper tailings has attracted considerable attention and becomes the key to the sustainable development of the copper industry. In this study, the technology of the selective reduction of iron from copper tailings at low temperature using coal and recovery of iron from reduction pellets using magnetic separation was proposed. The effects of several factors, such as reduction temperature, reducing agent dosage, reduction time, and activator dosage, on the selective reduction and recovery of iron from copper tailings were investigated. The following optimum process conditions are determined through single-factor experiments: the reduction temperature is 1200℃, the reducing agent dosage is 25% of the mass of copper tailings, the reduction time is 2 h, and the activator dosage is 5% of the mass of copper tailings. Under the optimum process conditions, the iron mass fraction of the magnetic concentrate exceeds 90%, and the iron recovery rate is greater than 95%. The composition and structure of copper tailings, reduction pellets, and magnetic ores were determined via X-ray diffraction, optical microscopy, and scanning electron microscopy. Moreover, the mechanism of mineral phase reduction and metal phase generation/merging was revealed. The results show that increase in temperature is beneficial for the reduction, merging, and growth of the metal phase. Merging the metal particles becomes common by increasing the reducing agent dosage. Prolonging the reduction time promotes the merging of metal particles and reduction of fayalite. The activator promotes the diffusion and merging of metal particles. The merging and growth of metal particles promote the increase in particle size. The amount of slag wrapped by coarse metal particles in the magnetic concentrate is relatively small in the magnetic separation process, and the iron grade of the magnetic concentrate is significantly improved.
Abstract: Final electromagnetic stirring (F-EMS) is widely used in the billet and bloom continuous casting process because it effectively improves the as-cast quality. Numerous industrial trials on F-EMS have been conducted; however, the real melt flow and heat transfer characteristics at the crater end remain unclear. In this study, based on a round billet special steel continuous casting process, a coupled three-dimensional numerical model was developed to describe the F-EMS phenomenon. The flow and solidification behavior of the melt in the F-EMS region were obtained by a segmentation calculation model, and the Darcy source term method was employed to suppress the velocity within the mushy region. The effect of stirring current intensity and frequency on the electromagnetic field, melt flow, and heat transfer was investigated numerically. The model was validated using the measured data of magnetic flux density in the stirrer center and the strand surface temperature. According to the simulation results, with every 100 A increase in the current intensity, the maximal magnetic flux density increases by 19.05 mT. The electromagnetic force significantly increases with the increase in current intensity. With the increase in current frequency within 20-40 Hz, the magnetic flux density decreases slightly, whereas the electromagnetic force increases. Moreover, a swirling flow field in the stirrer region is observed under the rotary electromagnetic force, and the tangential velocity of melt increases with the increase in current intensity and frequency. Additionally, the swirling flow enhances the local melt heat transfer at the radial direction of the round strand. As the current intensity and frequency increase, the temperature of the melt in the liquid core decreases, and the center solid fraction at the F-EMS-implemented position increases accordingly.
Abstract: Ultralow-carbon steel is an important material for automobile production. Titanium is usually added in this steel grade to form a precipitant and improve the deep drawing property of the steel. However, due to the deoxidation capacity of Ti, Ti addition will directly generate Ti-bearing oxide inclusions instead of the precipitant. To reduce the amount of Ti-bearing oxide inclusions, samples were collected during the RH refining based on the basic oxygen furnace-Ruhrstahl-Heraeus reactor-continuous casting (BOF-RH-CC) ultralow-carbon steel production process, and the oxygen content and inclusion characterization after Al addition and Ti addition were analyzed. The thermodynamics calculation software FactSage was adopted to calculate the Fe-Al-Ti-O inclusion stability phase diagram. The results show that the Al2O3 inclusion usually acts as the nucleation point of the Ti-bearing oxide inclusion, which wraps the Al2O3 inclusion to form the Al-Ti-O complex inclusion. To avoid the generation of the Ti-bearing oxide inclusions, the mass fraction of dissolved Al in the molten steel should be greater than 0.01% when the Ti mass fraction is 0.1%. Furthermore, the generation and growth behavior of the Ti-bearing oxide inclusion were also studied. Based on the calculation of the growth rate and the comparison of the adhesion work of the Al2O3 inclusion and the Ti2O3 inclusion, it is concluded that the growth rate of Ti2O3 inclusion is greater than that of Al2O3 inclusion, and it is more difficult for Ti2O3 inclusions to collide with each other and to be removed at 1600℃. Therefore, the generation of Ti-bearing oxide inclusions should be strictly controlled to improve the removal rate of oxide inclusions in ultralow-carbon steels.
Abstract: Bearing steel has very strict requirements on the size, shape, and quantity of non-metallic inclusions. Even if the total oxygen content in steel is kept at very low levels, large inclusions are not completely removed. These large inclusions have a decisive effect on the fatigue life of bearing steel. To remove the large inclusions in the bearing steel as much as possible, the effect of rare earth and magnesium duplex treatment on inclusions in GCr15 bearing steel was investigated by adding moderate rare earth and magnesium to liquid steel under experimental conditions. The size, composition, and morphology of the inclusions were observed by combining Aspex inclusion automatic analysis technology and scanning electron microscope. The experimental results show that the inclusions in steel before modification are mainly composed of MnS-Al2O3, MnS, and Al2O3, and the inclusions are modified to be composed of a large number of compound inclusions containing sulfur and magnesium and a small amount of Al2O3 and magnesia alumina spinel after adding trace magnesium to steel. After complex treatment by rare earth and magnesium, the inclusions are mainly composed of Re-O-S. Al2O3, MnS, and magnesia alumina spinel vanish gradually. The inclusions are spherically distributed, and most of them have diameter less than 5 μm. Inclusions with diameters greater than 10 μm are greatly reduced. Thus, the inclusions in GCr15 bearing steel are obviously refined after rare earth and magnesium complex treatment. When the magnesium content in the steel remains unchanged, the proportion of large particle inclusions decreases with increasing content of rare earth. When the content of rare earth is similar, increasing the magnesium content in steel is beneficial to the removal of large particle inclusions. The interaction of rare earth and magnesium further promotes the refinement of inclusions.
Abstract: In the previous studies on the microstructure and orientation of titanium alloys, the microstructural and orientational evolution of typical titanium alloys during thermal compression have been studied in depth. However, studies of the correlation between hot compression and heat treatment processes on microstructural and orientational changes have been few. It is of great significance to further study this correlation during hot treatment. For this study, during hot compression deformation and subsequent hot treatment of TC17 titanium alloy on a thermal simulator using cylindrical specimens, the microstructure, grain size change, and orientation evolution of TC17 were studied using optical microscopy and backscattered electron diffraction analysis. Grain size, texture distribution, pole figure, and reverse polarity were analyzed. Law and the relation between structure and orientation results show that the primary α-content decreases dramatically and size decreases in tandem with deformation temperature. Most of the α phase grains are dispersed and located on the trigeminal grain boundaries of the high temperature β phase grains. After heat treatment, the α phase and β phase had a clear structure and distinct boundary. The primary α phase still exists and tends to be equiaxed, and the metastable β phase changes formed a lamellar β-transformed structure. The hot deformation reduces the density of the α phase texture. Additionally, with increasing temperature, the density value of the α phase texture also becomes small. The α phase is no longer strongly textured after thermal deformation, and the orientation of the α phase grains is considerably influenced by thermal deformation, which clearly improves the uniformity of orientation. The thermal deformation also reduces the texture polar density value of the β phase, but the effect is not obvious. However, there is still a density of orientation, and the uniformity of the orientation is relatively poor.
Abstract: Many factors affect the success of dental implant surgery, such as surgical trauma, excessive chewing pressure, material performance mismatch, and improper abutment-implant connection. Among these factors, stress shielding caused by the mismatch of elastic modulus of the material is a major problem affecting the biomechanical compatibility of the implant. Also, the elastic modulus of the dental implant directly affects its binding to the surrounding support bone and stress distribution. Presently, most of the abutmentimplant systems on the market use the same material, with TC4 being popular because of its good biocompatibility. However, the elastic modulus of titanium implants is quite different from that of surrounding bone tissue; this difference can cause stress shielding. Additionally, stress concentration may cause implant surgery to fail. The abutment-implant with materials of different elastic modulus directly affect the stability and stress distribution of the bone tissue around the implant; thus, understanding the stress distribution under loading will help to establish a better elastic modulus combination of the dental implant system. In this paper, finite element analysis software was used to calculate the stress distribution of various abutments-implants under different loading conditions. Compared to other experimental abutment-implant systems, the simulation results show that Ti6Al4V abutment-(poly-ether-ether-ketone) (TC4-PEEK) can effectively reduce stress concentration, resulting in uniform stress distribution of surrounding bone tissue whose maximum stress value is 40-60 MPa. The stress level of PEEK implants in different abutment-implant systems is smaller under axial loading condition, whereas the stress level of surrounding bone tissue is larger. In the oblique direction of 45° loading condition, compared to two other abutment-implant systems, the stress level of the TC4-PEEK is lower, and the maximum stress value of the cortical and the cancellous bones in the surrounding bone tissue is 55 and 5 MPa, respectively, and the stress level is the smallest; such conditions contribute to the increase of bone deposition and bone formation, effectively improving the interface stability of the implant.
Abstract: The thermal insulation properties of nano-porous thermal insulating materials largely depend on thermal transport via gas phase within their pores, and this process relies on their pore structures. Therefore, investigating pore structures and thermal transport via gas phase is important to understand the heat transfer mechanism. Current research mainly focuses on the theoretical calculation and analysis from the perspective of heat transfer, and special and systematic studies based on actual materials have not been reported yet. In addition, accurate analysis of pore structures using usual techniques is difficult due to the complex pore network and the poor mechanical properties of their solid skeleton. In this study, nano-porous thermal insulating materials with different pore structures were synthesized via a sol-gel process followed by supercritical drying. The materials were then characterized by thermal conductivity tester, nitrogen adsorption-desorption, and helium pycnometer. The pore structures of the resulting materials were obtained, and the relationship between pore structures and thermal transport via gas phase was studied. Results show that the bimodal distribution of pores in the resulting materials, corresponding to gas-contributed thermal conductivity. All pores within the resulting materials can be equivalent to pores with a single diameter when the equivalent size of large pores is 10 times less than that of small pores. Similar to the pure gaseous thermal conductivity, the intrinsic gas-contributed thermal conductivity including gas-solid coupling effects rises with increasing pore diameter of the materials. The ratio of intrinsic gas-contributed thermal conductivity to pure gaseous thermal conductivity is 2.0, 1.5, and 2.0-1.5 for pores smaller than 200 nm, larger than 500 nm, and with size between 200 and 500 nm, respectively. When the equivalent size of large pores is 10 times less than that of small pores or when the equivalent size of large pores is 100-1000 times that of small pores and the contribution of large pores to the total porosity is less than 10%, the gas-contributed thermal conductivity reduction of the resulting material with decreasing gas pressure can be divided into three stages (steep decreasing stage, slow decreasing stage, and hardly changing stage) according to decreasing rate. When the equivalent size of large pores is 3000 times larger than that of small pores, the gas-contributed thermal conductivity reduction of the resulting material with decreasing gas pressure can be divided into four stages (steep decreasing stage, slow decreasing stage, steep decreasing stage, and hardly changing stage) even if the contribution of large pores to the total porosity is very low (less than 10%).
Abstract: The friction and wear behavior of NM400 and NM500 steels in the temperature range from room temperature to 300℃ were investigated, including the formation of interface oxide, wear surface morphology, and microstructures. A high-temperature sliding friction tester was used to study the behavior of sliding friction between wear-resistant steel and Al2O3 ceramic balls under different loads of 200-300 N and speeds of 100-400 r·min-1. A ball-disc friction pair containing mix-sintered Al2O3 ceramic balls with a diameter of 5 mm was mounted on the holding tool and steel plate. The friction coefficients of the two materials from room temperature to 300℃ are determined to be in a range of 0.27-0.40, whereas the average friction coefficients of NM400 and NM500 steels are found to decrease gradually from 0.337 to 0.296 and from 0.323 to 0.288. The generation of oxides is the primary reason for slight decrease in the friction coefficient at a high temperature of 300℃. The friction behavior is controlled by the abrasive wear mechanism, and then the phenomenon of pressure-into-peeling-oxidation of oxide gradually occurs at a higher temperature, which slightly reduces the wear rate. Larger amount of oxides are produced on the interface as the temperature increases, but this is not sufficient to form a continuous oxide layer. The main wear pattern at this time is still abrasive wear, although the wear rate and friction coefficient are affected by oxides. The main factors influencing the wear behavior are the hardness, oxide volume fraction, and oxidation activation energy of the wear-resistant steel, as found through the analysis of high-temperature frictional wear behavior and micro-oxidation model. In conclusion, the wear mechanisms of NM400 and NM500 steels from room temperature to 300℃ are influenced by the combined effect of abrasive wear, extrusion deformation wear, and trace oxide wear. NM500 steel exhibites better wear resistance than NM400 steel, and this can be mainly attributed to higher level of its hardness. A small amount of additional alloying elements in the high-strength microalloyed martensitic wear-resistant steel can reduce the wear rate to some extent, due to the formation of a certain amount of stable attached oxides that are produced during the high-temperature friction process.
Abstract: Early escharotomy in cases of severely burned patients can reduce infection and shorten the course of treatment. From the treatment effect, the quality of escharotomy operation is critical to the postoperative recovery of burn patients. However, the traditional burn wound escharotomy surgery easily causes bleeding as well as other related complications. Applying high-energy laser cutting can effectively reduce bleeding. Moreover, its treatment cycle is short, and it is highly precise, less prone to related complications, and leads to fast postoperative recovery. Considering that the mechatronics of medical equipment can greatly improve the treatment effect and combining the multi-degree-of-freedom motion platform with laser cutting is more convenient, accurate, and effective, this paper focuses on the key technical issues of normal automatic focusing and cutting in complex space wounds. Considering the advantages of multi-degree-of-freedom motion platform, a set of laser escharotomy control system composed of five-degrees-of-freedom motion platform and two-degrees-of-freedom laser optical path control mechanism was proposed. The degree of freedom of the parallel mechanism was analyzed and coordinate system of the whole mechanism was established. Second, inverse kinematic analysis of the laser eschar cutting parallel mechanism was carried out. Last, the position correspondence between the motion platform and the laser light path control mechanism was derived. The system could realize automatic planning of the laser trajectory and complete the automatic laser cutting by combining the derived corresponding position and the 3D scanning result of the complex wound contour. Based on the proposed laser cutting system, an eschar cutting experiment was carried out, and the experimental test results show that the laser escharotomy system can complete the 3D contour scanning and reconstruction of the human hand region well, and it can also automatically plan the laser focus spot motion track and complete the escharotomy.
Abstract: Due to the development of industrialization, low-oxygen environment has become common in the confined spaces of construction industries, chemical industries, military, urban underground spaces, and poorly ventilated crowed areas and caused a large number of hypoxic injuries. The traditional method of preventing hypoxic injuries is to monitor the oxygen concentration in the environment without considering the difference in oxygen tolerance limits when the human body is in different physiological states. Photoplethysmography (PPG) can comprehensively reflect physiological information, including heart rate, blood pressure, blood oxygen saturation, cardiovascular blood flow parameters, and respiratory rate. When the human body enters a hypoxic environment, the physiological parameters change rapidly, resulting in a change in the PPG signal. By measuring the PPG signal of the human body, the physiological state is considered to determine whether the human body reaches the oxygen tolerance limit. This study proposed a method for quickly identifying the hypoxic state of the human body using hypoxia experiment. According to the latest research on aviation medicine, mountain medicine and naval submarine medicine, 15.5% oxygen volume fraction can guarantee the basic life safety of personnel. Through the training experimental data of a constructed deep neural network, the PPG signal of a human in normal oxygen volume fraction (16% -21%) and extremely low-oxygen volume fraction (15.5% -16%) was determined to obtain the pattern recognition network of human physiological state. After testing, the recognition accuracy of the network could reach 92.8%. Using the confusion matrix and receiver operating characteristic curve analysis, the accuracy rate of training set, verification set, test set, and ensemble recognition of the confusion matrix reached 97.9%, 94.8%, 92.8%, and 96.3%, respectively. The area under the curve value is close to 1, the network classification performance is excellent, and the entire identification process could be completed within 4 s.
Abstract: The existence of concrete slab has significant influence on the local mechanical characteristic of the beam-to-column joint. In the design of beam-to-column joints, if the composite effects of steel beam and concrete slab are considered particularly as safety stock, the counteractive result of "strong column and weak beam" or "strong beam and weak column" may be produced; therefore, ignoring the influence of concrete slab affect the bearing capacity and stiffness of the joints. Based on the results of a full-scale cyclic test conducted on T-shaped beam-to-column joints, a detailed nonlinear finite element model was proposed. To completely understand the working mechanism of composite joints and further improve the experimental research, the nonlinear material properties and the shear effect of the connectors between concrete slab and steel beam were considered in the model. The results from the model agree well with the test results. Moreover, an extensive parametric study was performed to examine the seismic behavior of the joints. Parameters, such as the size effect, axial-load ratio, slab thickness, concrete compressive strength, and diameter-to-thickness ratio of the column, were investigated. The results show that the size and axial-load ratio have insignificant effect on the flexural capacity and stiffness of beam end, whereas the slab thickness, concrete compressive strength and diameter-to-thickness ratio of the column have significant effect on it. Furthermore, a calculation formula of flexural capacity was developed to estimate the flexural capacity of the beamto-column joints, considering the composite effects of the slab. The comparison between the calculation, experiment, and simulation results indicates that the proposed formula can reasonably predict the flexural strength of beam-to-column joints with concrete slab.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
