Additive manufacturing is an important and promising way to realize the structural-functional integration of diamond abrasive tools. In the presented study, the porous diamond grinding heads with different pore structure and porosity were designed and fabricated by selective laser melting (SLM). By analyzing the stress distribution of overall structures and pore units, the 50 %-porosity square-pore structure with lowest stress concentration degree was optimized. The porous composite samples had good SLM formability, including good integrity and connectivity of pore units, and the diamond abrasives were evenly distributed and exhibited good retention and protrusion height. The high retention was attributed to the multiple interfacial system composed of carbide layer and solid solution strengthening layer. Compared with other porous samples, the 50 %-porosity square-pore structured sample with frame supporting unit and uniform stress distribution showed high deformation resistance of 430 MPa in yield strength and energy absorption capacity of 56.4 MJ/m 3 , which well verified the simulation results. The wear and grinding tests showed that the sharpness and self-sharpening ability of porous samples were significantly superior to the full-dense sample, and the grinding ratio increased with the increasing of the porosity.

The quality of metal parts fabricated by selective laser melting (SLM) is strongly depended on the manufacturing process parameters. The establishment of relationship between manufacturing parameters and the formability is the effective way to obtain forming parts with high density, defect-free and excellent mechanical properties by SLM. In this study, the effect of SLM process parameters on the relative density (RD) and mechanical properties of FeCoCrNi high entropy alloys (HEAs) were systematically investigated, involving single tracks, single layers and block samples. By optimizing the laser power, scanning speed and hatching space, the highest RD of 99.85% was obtained under the moderate energy density of 95.24 J/mm3, with no defect as prosity, cracks, un-melted powders and spheroidization under other SLM parameters. The tiny changes in RD significantly affected the mechanical properties of FeCoCrNi HEAs. The highest RD sample corresponded to the optimal comprehensive mechanical properties of 585 MPa in yield strength, 714 MPa in ultimate strength and 45.30% in elongation. The elevation of mechanical properties attributed to the high RD, defect-free, grain refinement and the unique cellular substructure.

Macrosegregation at the interface in Multi-Material (MM) structures fabricated by Selective Laser Melting (SLM) has evidenced deleterious effects on interfacial bonding reliability, but its fundamental understanding is less revealed. Therefore, this work vertically prepared MM parts of H13 tool steel and IN625 superalloy by SLM, as an example, to explore the interfacial macrosegregation mechanism. According to the mechanism, a liquid layer of unmixed H13 can exist at the molten pool bottom due to the no-slip boundary condition in fluid mechanics and solidifies as an H13 macrosegregation beach. Considering the higher liquidus temperature of H13 (1483 degrees C) than IN625 (1300 degrees C), a region cooler than the H13 solidification temperature exists within the IN625 molten pool; therefore, when the melted but unmixed H13 liquid is entrained into the cooler region by fluid flows, it can solidify quickly, forming H13 macrosegregation peninsulas/islands. The laser melting+remelting strategy developed to mitigate interfacial macrosegregation reveals its significant contribution to efficient migration of H13 into IN625 molten pools in a layer-by-layer manner, forming a broad interface. As the direct reflection of interfacial macrosegregation, the microstructure experiences a cellular-columnar-cellular transition across the H13/IN625 interface. Even a peninsula with H13 microstructural features is observed in an IN625 molten pool, verifying the rapid solidification of intruded H13 in IN625. Finally, the microhardness values with varying standard deviations across the interface successfully evaluate the interfacial macrosegregation on a macro-scale. These results can provide theoretical support to mitigate interfacial macrosegregation and benefit the development of MM structures with good interfacial bonding reliability by SLM.

Objective Currently, traditional engineering materials are facing the contradiction between strength and toughness. Several organisms in nature have comprehensive high strength and toughness properties owing to the long-term evolution of heterogeneous characteristics; thus, they have become a model for people to imitate. However, achieving heterogeneous forming using the traditional manufacturing process is difficult; the selective laser melting (SLM) with high degree of freedom and precision provides a new opportunity for forming parts with this feature. Currently, the heterogeneous forming of SLM is mainly achieved through multimaterial and different-layer forming. However, the studies regarding the same-layer forming are inadequate, and the same-layer formed parts' performance is poor compared with different-layer formed parts. The reason is that the laser penetration is reduced in the same-layer forming, and the overlapping efficiency of the melt pool at the boundary is poor, leading to poor bonding quality between heterogeneous materials, making it difficult to achieve metallurgical bonding. Therefore, this study improved the interface bonding quality of SLM316 L/IN718 heterogeneous parts with the same layer based on optimizing the laser remelting process. In addition, the mechanical properties of the remelted parts were significantly improved compared with those without remelting, making further innovation and expansion to form SLM bionic structure materials. Methods The metal materials used in this study are atomized 316L and IN718 powders. After laser remelting, the top surface morphology and roughness of 316L were observed and measured using a laser confocal microscope. For heterogeneous forming of different layers 316L/IN718, the sequence of 316L - IN718 - 316L was used, and the upper surface of each material was remelted after forming. For heterogeneous forming of the same-layer 316L/ IN718, the intermediate IN718 was formed after forming both sides of 316L, and laser remelting was performed at the interface joint. Scanning electron microscope ( SEM) and energy dispersive spectrometer ( EDS) were used to observe the microstructure and element distribution of the interface. The tensile test was performed at room temperature using DDL100 electronic universal testing machine at a strain rate of 3 mm/min, and the tensile strength and elongation were measured. Finally, SEM was used to observe and analyze the fracture morphology of tensile specimens. Results and Discussions The effect of different laser remelting parameters (laser power, scanning speed, and remelting times) on the surface roughness of 316L is different (Fig. 5). When the laser power is 300 W, scanning speed is 250 mm/s, and remelting times is 5, the surface roughness exhibits the lowest values of 2. 4, 2. 4, and 2.7 mu m. After laser remelting, the surface quality of 316L parts is effectively improved, indicating that this optimization process is expected to improve the interface bonding quality of heterogeneous parts, and the interface transition zone of 316L/IN718 heterogeneous layer becomes smoother with a width of 450 mu m (Fig. 7). However, the interface bonding quality of the 316L/IN718 heterogeneous layer is poor without remelting and the pore diameter is approximately 0. 18-0. 35 mm. Moreover, after remelting, the spheroidization and pores in the transition zone almost disappear, and the interface bonding quality is improved (Fig. 8). EDS analysis results show a gradient trend in the element diffusion of same-layer 316L/IN718 heterogeneous parts after laser remelting. Consequently, the distribution of Fe, Ni, and other elements is more uniform (Figs. 9 and 10). The tensile test results in Fig. 11 show that the tensile strength of remelted sample increases from (104. 77 +/- 45. 26) to (507. 33 +/- 58. 3) MPa and the elongation is approximately 11%. This proves that the laser remelting optimization process improves the performance of SLM 316L/IN718 heterogeneous components. The fracture morphologies of same-layer 316L/IN718 tensile parts before and after remelting were observed (Fig. 12). The crack was found to deflect at the poor joint, leading to rapid fracture failure of the sample without remelting; however, no obvious transition was observed at the fracture after remelting optimization, indicating that 316L and IN718 exhibit good metallurgical bonding. Both samples exhibit brittle fracture in macroscopic view. However, numerous dimples and tearing edges are observed at the fracture of remelted specimens, indicating that the fracture mode is brittle and ductile fractures. Conclusions After remelting, the surface roughness of 316L decreases from 7. 1 to 2. 7 mu m by 62%; the flat micromorphology and good element diffusion of the 316L/IN718 transition zone exhibit the effect of remelting in improving the bonding quality of the 316L/IN718 heterogeneous interface. The increase in tensile strength of the sample from (104.77 +/- 45.26) MPa before optimization to (507.33 +/- 58. 3) MPa after optimization also verifies the feasibility of the optimized process. Both the unremelted and remelted same-layer 316L/IN718 heterogeneous tensile parts exhibit brittle fracture characteristics in the macroscopic view. Simultaneously, the interface joints of the remelted samples exhibit obvious dimple fracture characteristics and no secondary cracks and unmelted powders were observed, indicating that laser remelting can considerably improve the quality of interface bonding.

提出一种基于机器视觉的莲子去芯位置定位的方法,并搭建试验平台进行去芯验证.采集4个产地、不同尺寸的莲子,用2个相互垂直的摄像头采集凹槽内莲子图像,对图像进行裁剪和灰度处理后,通过莲子头部和尾部的灰度特征差异识别莲子朝向;对沿长轴尾部向上的莲子图像进行二值化处理,经腐蚀运算以消除边缘杂质,缩放以增大特征点的曲率,利用角点检测确定莲子去芯位置坐标后进行坐标换算,计算机械手移动距离,实现莲子去芯作业.试验表明:莲子理想去芯位置为莲子尾部凸点,莲子朝向判别成功率约97％,尾部凸点识别准确率约97％,整体识别成功率约94％,去芯成功率约93％,单颗莲子图像处理平均时间约78 ms,平均去芯时间约0.5 s.若以尾部凸点识别成功数为基数计算,则莲子去芯成功率可达98.9％.

The inorganic coating of Al2O3 was introduced on nanoparticles to weaken their tendency of agglomeration in electroless plating bath. The influence of the coating on interaction energy and interaction forces between the coated particles was evaluated in this study. The Al2O3-coated diamond particles were prepared by the heterogeneous nucleation process. The attractive interaction and repulsive interaction between the coated particles in electroless nickel (EN) solution were calculated by the classical DLVO theory. Sedimentation tests were conducted to verify the modelling. The calculation predictions are well in agreement with the experimental results. The Al2O3 coating could reduce van der Waals attraction by enlarging the surface separation distance of diamond particles, and could increase electrical double layer repulsion by increasing the surface potentials in EN solution. Consequently, it could weaken the net attractive interaction, whose net attractive force decreased from −3.77×10−2N/m between bare particles to −1.12×10−2N/m between the coated ones, a reduction by 70%, at the separation distance of 1κ−1. The coated diamond particles in EN solution show a slower settling rate than bare ones. The Al2O3 coating contributes to the high dispersability of the coated particles under the agitation condition.

This paper presents the influence of an inorganic Al2O3 layer over MoS2 particles on the tribological performance of electroless Ni–P–MoS2/Al2O3 composite coatings fabricated without using surfactants. The Al2O3-coated MoS2 particles were prepared by a heterogeneous nucleation process. The dry sliding tests of the composite coatings were tested against a WC ball. SEM was used to observe the surface morphology of particles, composite coatings, and worn surfaces. The results indicate that the coverage of an Al2O3 coating on MoS2 particles significantly affects the surface morphology, frictional coefficient and wear loss of the composite coatings. The incorporation of Al2O3-coated MoS2 particles with lower coverage (up to 7% of Al2O3) could obtain compact surface structure of composite coatings, which contribute to reduced wear loss. However, higher coverage would lead to loose surface structure of the composite coatings, and thus increase their wear loss.

Nickel iodate tetrahydrate (Ni(IO3)(2)?4H(2)O) particles with different morphology and size were synthesized by precipitation method (PM) and electrospray precipitation method (EPM). The electrospray was used in chemical precipitation to synthesize nanoscale metal iodate particles with a narrow size distribution. The thermal decomposition mechanism of Ni(IO3)(2)?4H(2)O at different heating rates, ignition, and combustion of Al/Ni(IO3)(2)?4H(2)O nanothermites was studied by thermogravimetry?differential scanning calorimetry?mass spectrometry, T-jump and time-of-flight mass spectrometry, T-jump equipped with high-speed camera, and combustion cell test. The Al/Ni(IO3)(2)?4H(2)O prepared by EPM had a lower ignition temperature (587 ? 14?C) and a shorter burn time (159 ?s). The ignition processes of Al/Ni(IO3)(2)?4H(2)O nanothermites prepared by EPM and PM were solid?solid and gas?liquid reactions, respectively. The rate-determining step of their combustion processes was the burning of aluminum powder and the decomposition of Ni(IO3)(2)? 4H(2)O, respectively.

The traditional energetic materials are insufficient to sterilize the deleterious microorganisms carried by biological weapons completely. Three kinds of biocidal energetic composites were investigated herein: (1) aluminum/manganese iodate/nitrocellulose (Al/Mn(IO3)2/NC) composite microspheres prepared by electrospray, (2) Al/Mn(IO3)2/NC nanocomposites prepared by physical mixing, and (3) Al/Mn(IO3)2 nanothermites prepared by physical mixing. The thermal decomposition process of Mn(IO3)2 was studied by thermogravimetry–differential scanning calorimetry-mass spectrometry (TG/DSC-MS) at a low heating rate of 5 °C min−1, and T-jump/time-of-light mass spectrometry (T-jump/TOFMS) at a high heating rate of ~ 5×105 °C s−1. The ignition temperatures of three energetic composites were measured in a T-jump gas chamber (Ar, 1 atm) by a high-speed camera. The combustion performance of three energetic composites was investigated in a constant-volume combustion cell. The results show that Al/Mn(IO3)2/NC composite microspheres prepared by electrospray have a better ignition (lower ignition temperature) and combustion (higher pressurization rate and peak pressure) performances than the other two prepared composites. The thermal performances of these composite microspheres also overshadow the documented energetic composites such as Al/AgIO3, Al/KIO4, and Al/NaIO4 nanothermites. The MS results at high heating rates demonstrate the production of I2 from the thermite reaction, potentiating Al/Mn(IO3)2/NC as an energetic formulation for biocidal applications.

The multi-material selective laser melting (SLM) technology has been widely studied in recent years. In this paper, 316L stainless steel (316SS) and Inconel 718 (IN718) multi-material parts were manufactured by SLM and their interfacial characteristics and mechanical properties were investigated by optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, electronic universal testing machine and microhardness tester. The interface metallograph and higher comprehensive mechanical performance with elasticity modulus (103 +/- 3 MPa), elongation (28.1 +/- 2%) and ultimate tensile strength (596 +/- 10 MPa) proved good metallurgical bonding at the interfaces (similar to 100 mu m) between 316SS and IN718. Nevertheless, some cracks and holes, which were found at or near the interfaces, suggested special SLM processing parameters (such as laser power, laser scanning speed, layer thickness, hatch spacing, remelting, fabrication sequence and layers of interface) should be applied at the interfaces.

A strategy for the preparation of bioactive poly-ether-ether-ketone/hydroxyapatite (PEEK/HA) composites was proposed in this study with the aim of controlling the biological and mechanical properties of different parts of the composites. The strategy integrated solvent-based extrusion freeforming 3D printing technology in order to print high-resolution HA scaffolds and compression molding processes for the production of bioactive PEEK/HA composites. To this end, an optimized model, established using response surface methodology, was employed to optimize the extrusion process parameters on the basis of accurate characterization of the extrusion pressure, and the effects of the filament/pore sizes on the PEEK infiltration depth into the HA scaffold were investigated. The results of scanning electron microscopy and computed tomography analyses revealed that the PEEK/HA composites exhibited a uniform microstructure and a good interface between the HA filaments and the PEEK matrix following the optimization of the process parameters. The HA scaffolds were fully infiltrated by PEEK in both vertical and lateral directions with an infiltration depth of 3 mm while maintaining the HA network structure and uniformity. The biological and mechanical performance test results validated that the PEEK/HA composites possessed excellent biocompatibility as well as yields and compressive strengths within the range of human cortical bone suitable for load-bearing applications.

In this review paper, the definition of the tissue engineering (TE) was comprehensively explored towards scaffold fabrication techniques and applications. Scaffold properties and features in TE, biological aspects, scaffold material composition, scaffold structural requirements, and old and current manufacturing technologies were reported and discussed. In almost all the reviewed reports, the TE definition denotes renewal, development, and repairs of damaged tissues caused by various factors such as disease, injury, or congenital disabilities. TE is multidisciplinary that combines biology, biochemistry, clinical medicine, and materials science whose application in cellular systems such as organ transplantation serves as a delivery vehicle for cells and drug. According to the previous literature and this review, the scaffold fabrication techniques can be classified into two main categories: conventional and modern techniques. These TE fabrication techniques are applied in the scaffold building which later on are used in tissue and organ structure. The benefits and drawbacks of each of the fabrication techniques have been described in conjunction with current areas of research devoted to deal with some of the challenges. To figure out, the highlighted aspects aimed to define the advancements and challenges that should be addressed in the scaffold design for tissue engineering. Additionally, this study provides an excellent review of original numerical approaches focused on mechanical characteristics that can be helpful in the scaffold design assessment in the analysis of scaffold parameters in tissue engineering.

食品3D打印作为一项新兴技术近年来获得了广泛应用.针对流体型食品3D打印的成型特点,采用模块化设计思想构建了设备的设计方案,运用Pro/E软件建立了设备的三维模型,再将模型导入到Ansys Workbench软件中,对设备进行了有限元静态分析和模态分析,静态分析结果显示其最大应力小于许用应力,强度符合要求.提取了设备模态分析的前六阶振型图,并在软件仿真的基础上搭建了食品3D打印实验平台,对食品3D打印设备进行了动态特性实验和出料实验,通过对比动态特性实验结果与仿真结果,验证了有限元分析的有效性,且出料精度达到相应标准,表明所设计的食品3D打印设备满足设计要求.

Different fabrication methods from traditional chemical engineering methods to advanced additive manufacturing (AM) are used for fabrication of tissue engineering (TE) scaffolds. The traditional techniques are subjected to limitations such as manual intervention, and inconsistent and inflexible processing procedures. In addition, the traditional techniques usually cannot control pore size, pore geometry, and spatial distribution of pores properly. To complement these limitations, there has been a trend in recent years to fabricate TE scaffolds using AM processes directly (3D printing of final scaffold) or indirectly (making negative scaffold to be used as a mold). In particular, extrusion-based AM systems have been widely used for fabrication of TE scaffolds due to their ability of processing different biomaterials, their possibility of manufacturing scaffolds in a cell-friendly environment, their high reproducibility and flexibility, and their simple process control in comparison with other AM techniques. In this chapter, the applications of extrusion-based 3D printing techniques are reviewed. In addition, an in-depth discussion on solvent-based extrusion freeforming (SEF) method, recent advances in printing bioceramic scaffolds, and its new application to make polyether-ether-ketone (PEEK)-based composites are presented.

The traditional machine tool design method with metal materials makes large-scale moving structures very heavy, which seriously impacts dynamic performance and results in significant energy consumption. Using sandwich structures of composite materials to replace metal materials is an important strategy for lightweight large-scale moving structures. However, this kind of substitution is generally believed to be difficult because foam-filled sandwich structures usually show nonlinear characteristics and must balance the moving mass, material costs, and structural stiffness. In the present study, we proposed a design optimization approach for a large-scale moving framework in a large 5-axis machining center (L5AMC) considering large dimensions in the x, y, and z work space and high machining speed with the aim of minimizing the displacements of the milling head. An improved approach, named the 3-step design optimization, was executed to obtain the optimum framework structures to solve the contradiction between the moving mass, material costs, and structural stiffness. This approach was based on multi-objective optimization and finite element analysis. The structural stiffness of the framework after optimization increased by 89% compared with before optimization although the mass increased by 6% and the material costs increased by 9%. A finite element simulation under four given operational loads showed that the displacements of the milling head were all less than the design requirement of 0.25 mm. The results indicated that the proposed 3-step design optimization approach for the optimal design of a large-scale moving framework was feasible and successful. A 40 m × 6 m × 4 m L5AMC prototype was manufactured, and the actual verification results indicated that the large-scale moving framework fully met the design requirements of the L5AMC and reduced energy consumption.

The present study proposes a characterization approach for the extrusion process of hydroxyapatite (HA) paste considering the nonlinear characteristics of bioceramics materials with the aim of printing high-resolution ceramic scaffolds using low-temperature extrusion 3D printing technology. A novel method named the three-point experimental extrapolation was executed to analyze the necessary extrusion pressure in relation to the extrusion velocity. This new approach presented a higher analytical accuracy as compared to previous methods. The optimum layout of the 3D printer was obtained by the comparative analysis of four typical topological constructions. On this basis, three main factors affecting the extrusion pressure of bioceramics materials, namely paste formulation (solvent content), nozzle length-to-diameter ratio, and the extrusion velocity, were selected as the control factors, and a series of experiments were performed using the L-27 (3(13)) orthogonal array. The results indicate that all the control factors significantly affected the extrusion pressure, of which the length to-diameter ratio of nozzle exhibited the greatest effect. The scaffold printed using low-temperature extrusion 3D printing technology exhibited a uniform microstructure following the optimization of the printing parameters, which validated the ability of the process to accurately control the microstructure. The results of the study can be considered as a guide for the 3D printing of high-resolution bone tissue engineering scaffolds and can be employed to further compression mold bioactive polyetheretherketone/hydroxyapatite (PEEK/HA) composites.

The present study proposes a back propagation artificial neural network (BPANN) to provide improved precision for predicting the material removal rate (MRR) in ultrasonic machining. The BPANN benefits from the advantage of artificial neural networks (ANNs) in dealing with complex input-output relationships without explicit mathematical functions. In our previous study, a conventional linear regression model and improved nonlinear regression model were established for modelling the MRR in ultrasonic machining to reflect the influence of machining parameters on process response. In the present work, we quantitatively compare the prediction precision obtained by the previously proposed regression models and the presently proposed BPANN model. The results of detailed analyses indicate that the BPANN model provided the highest prediction precision of the three models considered. The present work makes a positive contribution to expanding the applications of ANNs and can be considered as a guide for modelling complex problems of general machining.

As some deficiencies such as uneven distribution of convergence in population, poor global searching ability, easily to run into partial optimization appeared in classic non-dominated sorting genetic algorithm Ⅱ(NSGA-Ⅱ), this paper proposes an improves algorithm by introducing orthogonal crossover strategy and hybrid mutation operator into the NSGA-Ⅱ. The experiments on a series of test functions show that the improved NSGA-Ⅱ has better performance than NSGA-Ⅱ both in convergence and diversity. The research about optimization of processing parameters of 6061 aluminum alloy in precision turning based on improved algorithm and classic NSGA-Ⅱ, reveal that the improved algorithm has better convergence rate and accuracy than the classic NSGA-Ⅱ, which means the improved algorithm is more effective in solving the multi-objective optimization problems of machining parameters.

Ion transport in a confined conical nanochannel with high solution concentrations was studied using molecular dynamics simulation. The simulation results indicated that the ion current rectification appeared at high solution concentrations, even without electrical double layer (EDL) overlapping, which was still influenced by both the solution concentration and surface charge properties as it would be in a low solution concentration. With solution concentrations increasing from 0.41 to 2.08M, a maximum rectification ratio was obtained. This phenomenon was attributed to the competition between the axial binding energy gradient arising from the confined conical geometry intensifying the ion axial asymmetric concentration polarisation and the decreasing thickness of the EDL weakening the concentration polarisation.