Interbody fusion cages are key implants in spinal interbody fusion surgeries, and for the novel biodegradable interbody fusion cages that can be gradually absorbed and replaced in the body, the formulation system of the materials plays a crucial role in their long-term biocompatibility and mechanical stability. In this study, PCL/HA composites with high mass fractions (25%, 30%, 35%, 40%) hydroxyapatite (HA) and different molecular weights (50kDa, 80kDa) polycaprolactone (PCL) were fabricated. PCL/HA biodegradable interbody fusion cages of different material systems were printed by polymer melt differential three-dimensional (3D) printing technology. In vitro degradation tests were conducted in a simulated in vivo environment to quantitatively analyze the stability and degradation behavior of PCL/HA interbody fusion cages with different material compositions and molecular weights in an artificially simulated body fluid environment, as well as their mechanical properties under loads. The cytotoxicity assays of the material were also conducted. This study revealed that as the HA content increased, the degradation rate of the interbody fusion cage accelerated. The strength and stiffness of each material system exceed the minimum standard of human cancellous bone. When the HA content was the same, the degradation rate of the high molecular weight (80 kDa) interbody fusion cage was faster compared to that of the 50 kDa molecular weight cage. When the HA mass fraction was below 30wt%, the compressive strength and compressive modulus of the fusion cage increased with increasing HA content. However, when the HA mass fraction exceeded 30wt%, the mechanical properties of the fusion cage worsened with higher HA content. A comparative analysis of material properties indicates that when the HA content was 30wt%, the fusion cage exhibited a moderate degradation rate, high compressive strength and compressive modulus, and excellent 3D printing performance, making it the formulation system with the best overall performance. In addition, the PCL material which was also used in most literature exhibited different levels of cytotoxicity for different methods of cytotoxicity testing. Further animal implantation experiments of spinal fusion cages require the selection of medical-grade-implant materials.

Spinal fusion operations are often utilized to address disc degeneration, vertebral slippage, instability, and trauma, and interbody fusion cages have been widely employed in these procedures. The fundamental aim of an interbody fusion cage is to give immediate interbody support, height, and biomechanical stability of the spinal space to enable bone development in the fused area. With the aim to address shortcomings of the currently commonly used clinical spinal interbody fusion cages, such as non-osteogenic activity, non-resorbability, biomechanical mismatch, etc., composites made of polycaprolactone (PCL) were prepared in this study, with the addition of hydroxyapatite (HA) that possesses both osteoinductive properties and enhanced mechanical strength as a functional filler. An innovative bi-directional variable meso-structure scheme is proposed. The porous degradable spinal interbody fusion cage was manufactured by using polymer melt differential three-dimensional (3D) printing technology. The study of the cage's 3D structural characteristics on the degradation properties and the influence of the degradation process on its mechanical properties was carried out. Preliminary cell viability assays were also conducted. This study showed that the compressive strength of the cages increases with the aperture diameter and the number of crossing layers of the beams, and the compressive modulus is positively associated with the number of crossing layers of the beams. The degradation rate of the cage grew with the reduction of its filling rate and the rise of the number of crossing layers of the beams, i.e., the degradation rate increased with the expansion of the internal aperture. The cage with a 60% internal filling rate and containing 1 or 2 crossing layers of beams is more suited for spinal fusion, and with a pore size between 450 and 490 mu m, the fundamental structure of the cage can be preserved while maintaining strong support performance throughout degradation. In addition, the 3D printing process in this study does not cause an increase in cytotoxicity, making it a feasible bioprinting method.

Compared with conventional pneumatic tyres, non-pneumatic tyres (NPTs) have various advantages such as zero-blowout risk, maintenance-free, and environment-friendliness. Instead of compressed air, NPTs employ elastic spokes as the main load-carrying structure. Honeycomb and flexible radial spokes are the commonly used types, and various spoke geometries are also continuously emerging. In this study, an innovative NPT with V-shape spokes was developed. With the specially designed V-shape spokes, the NPT can achieve better supporting performance and aerodynamic characteristics. A finite element (FE) model was constructed for the proposed NPT, and mechanical properties were studied. Prototypes of the proposed NPT were fabricated, and experimental test confirmed the fidelity of the FE model. To reveal the impact mechanism of design parameters on the mechanical properties of the proposed NPT, we used the Taguchi method for parametric analysis. Based on the verified FE model, orthogonal experimental simulations were conducted to study the interactions among the design parameters and the multi-axis properties such as the radial, longitudinal, lateral, and torsional stiffnesses. Based on the result analysis, design principles are extracted for the proposed NPT to satisfy its multi-axis mechanical property demands.

Material selection is a crucial factor in the design of non-pneumatic tyres (NPT). Most NPTs are integrally manufactured using polyurethane materials for the supports, the inner ring, and the outer ring. It is evident that designing different components with varying material hardness will have distinct impacts on NPT performance. To study the influence of material hardness on the performance of V-shaped non-pneumatic tyres (VS-NPT), we developed finite element models of VS-NPTs with different TPU materials. To validate the finite element models, we manufactured tyres with three different hardness levels and conducted performance tests. Based on this model, a design concept is proposed where different components use materials with varying hardness levels. To elucidate how material hardness affects VS-NPT performance, the Taguchi method was used for analysis. The results reveal that increased material hardness leads to higher triaxial forces and triaxial stiffness in integrally designed VS-NPTs. Regardless of variations in the structural parameters of existing VS-NPTs, the spoke material has a significant impact on triaxial stiffness and contact area. When the spoke thickness exceeds 7.3 mm, the tread material predominantly affects the contact area.

The rapid development of additive manufacturing (AM) has facilitated the creation of bionic lightweight, energy-absorbing structures, enabling the implementation of more sophisticated internal structural designs. For protective structures, the utilization of artificially controlled deformation patterns can effectively reduce uncertainties arising from random structural damage and enhance deformation stability. This paper proposed a bionic corrugated lightweight honeycomb structure with controllable deformation. The force on the onset state of deformation of the overall structure was investigated, and the possibility of controlled deformation in the homogeneous structure was compared with that in the corrugated structure. The corrugated structures exhibited a second load-bearing capacity wave peak, with the load-bearing capacity reaching 60.7% to 117.29% of the first load-bearing peak. The damage morphology of the corrugated structure still maintained relative integrity. In terms of energy absorption capacity, the corrugated lightweight structure has a much stronger energy absorption capacity than the homogeneous structure due to the second peak of the load carrying capacity. The findings of this study suggested that the combination of geometric customization and longitudinal corrugation through additive manufacturing offers a promising approach for the development of high-performance energy-absorbing structures.

Soft robots offer significant potential in various fields, including healthcare, education, and rescue operations, where actuators are critical components that influence power, precision, and environmental adaptability. However, the nonlinear properties of hyperelastic materials often necessitate reliance on empirical methods and extensive experimentation for actuator design. This study introduces a methodology for designing soft structures, exemplified by pneumatic mesh actuators. Utilizing numerical simulations to investigate deformation patterns and applying the principle of virtual work within a segmented constant curvature framework, a theoretical model was developed to describe the relationships between input air pressure, bending angle of a single airbag, and wall thickness. To validate the model's accuracy and applicability, bending tests were performed on actuators with varying wall thicknesses. A new pneumatic mesh actuator was designed and fabricated using the proposed method, with the experimental results showing a deviation of only 0.27 degrees from the target bending angle under the specified air pressure. This confirms the effectiveness of the proposed design approach. This methodology has potential applications beyond pneumatic mesh actuators, extending to other areas of soft structure design.

Ultra-fine particles are prone to agglomeration, limiting the preparation of ultra-fine powder. The aggregates' disaggregation mechanism is studied, and the proposal of improving the guide vane of a turbo air classifier is contributed to strengthen powder disaggregation based on CFD-DEM coupling and the novel local fluid domain extraction method. The results show the cylindrical tail of guide vane is conducive to the disaggregation, and the powder dispersion near the guide vane is improved. When the inlet air velocity vin is <18 m & sdot;s(- 1), the cylindrical tail of guide vane can significantly improve the powder dispersion. When the cylinder diameter is larger than or equal to 2 mm, the effect of the increase of the cylinder diameter on powder dispersion is significant. However, the increase of cylinder diameter will lead to the increase of energy consumption, so the cylinder diameter should not be too large.

为探究几何相似涡流空气分级机环形区流场的分布特性,建立不同尺寸的涡流空气分级机模型,提取关键结构的几何参数,通过数值模拟分析尺寸比例因数对分级机环形区流场分布的影响.模拟结果表明,在相同进口风速下,几何相似分级机模型环形区内切向速度呈准自由涡的分布.模型尺寸增大,环形区内柱面面积加权平均切向速度增大,环形区切向速度分布不均匀.转笼内外缘切向速度越接近,环形区内近转笼外缘处切向速度产生的波动越小.几何相似分级机模型环形区内径向速度分布符合点汇流动的规律,除了在靠近转笼外缘处径向速度数值有较大差异外,环形区其余位置柱面面积加权平均径向速度不随比例因数变化而变化.以几何相似分级机模型数值模拟数据作为训练样本拟合分级机环形区内柱面面积加权平均切向速度和径向速度预测公式,并建立测试样本分级机模型对预测公式进行验证.柱面面积加权平均切向速度和径向速度预测值与模拟值的最大误差分别为3.5%和1.8%.此外,通过对几何相似涡流空气分级机模型环形区流场运动相似和动力相似分析,得出几何相似分级机模型流场具有相似性.

向电磁线圈通入交流电可对用于轮胎硫化的金属内模具实现感应生热,该方法升温快、功率损耗率低、可独立调控.为进一步提升电磁硫化轮胎鼓瓦的温度均匀性,提高胎坯硫化质量,借助COMSOL Multiphysics软件对电磁线圈加热鼓瓦的温度场进行数值模拟,分析通入的电流方向、交流电大小、交流电频率和线圈匝数等多个参数对加热工件的温度和功率的影响.采用正交试验法探寻多个参数的最佳水平组合,由极差分析和方差分析得出一致结论:影响鼓瓦温度均匀性的因素次序为交流电大小＞线圈匝数＞交流电频率.在此基础上,分别从加热方式和线圈分布结构两方面对线圈鼓瓦模型进行优化,以进一步降低温差,提升硫化均匀性.研究工作可为轮胎硫化中电磁加热金属内模技术提供有意义的参考.

The design and manufacture of the green and low-carbon polyurethane non-pneumatic tire were introduced,and the energy saving mechanism was analyzed. Aiming at the problem of poor energy saving of existing non-pneumatic tires,in order to improve the roundness,this non-pneumatic tire was composed of the carcass,rim,dovetail convex structure with misalignment of splayed formation,cord, and spoke support structure. The carcass was made of polyurethane/rubber powder composite material,the outer mold was assembled with the wheel hub with a convex structure,and the hub and carcass were molded together using integrated casting process. Since polyurethane material was used for this non-pneumatic tire instead of rubber material,the tire had a high recycling rate. At the same time,high strength carcass could ensure the roundness of the tire,reduce fuel consumption and wear of the tire,and extend the service life of the tire.

塑料机械是现代制造业的"生产母机",塑机行业同时也是高分子材料产业链中资金密集、人才密集和技术密集的"钻石产业".为满足我国高速发展的塑料机械行业对于高端专业人才的迫切需求,探索建立企业高度参与的创新人才培养新模式,中国塑料机械工业协会与北京化工大学启动"中国塑机创新专业人才培养计划",建设"中国塑机创新人才培养基地".该教学实践针对机械设计制造及其自动化学科,以创新应用性强的机械创新设计课程为例,依托于"中国塑机创新人才培养基地"多种多样的工程教育资源,以注塑机"五点斜排肘杆式"注塑机合模机构的方案创新设计为题,应用项目化教学方法,在理论教学的同时,使学生们带着工程实践问题进行学习、思考、分析和研究,鼓励学生将多门机械类专业基础课程所学知识进行创新结合与灵活运用,有效地促进学生们创新创造能力的发展,探索培育应用型创新人才的新模式.

Structures with variable stiffness during deformation are of great importance in many fields. The solid-liquid transformation method using low melting point alloys (LMPA) is a promising method to control structural deformation. In this study, a coaxial filamentary feature consisting of pure LMPA surrounded by thermoplastic polymer (TP) is three-dimensionally printed and deformable structure can be constructed. The Polymer/LMPA structure can reveal special and valuable performances: The flexural modulus of the printed TPU/LMPA unit is about 1152 MPa, which is almost 330 times that of TPU and it can achieve large-scale stiffness changes by regulating temperature. Due to its reversibility and variable stiffness, the structure can achieve drive response perturbations under large bias loads. The maximum output force of the TPU/LMPA composite structure is 8.5 N and the maximum driving displacement is 18.5 mm. The fundamental frequency variation of the structure is achieved during the heating of the structure and the change of temperature can change the damping effect according to adjusting the frequency. This study has an important role in the future design of controllable stiffness structures.

The high overpotential of the oxygen evolution reaction (OER) is the main obstacle to water electrolysis for green hydrogen production. NiFe-based materials are the potential non -precious metal electrocatalysts for the OER, but their poor stability and limited activity have been of concern. Herein, a three-dimensional self-supporting NiFe electrode is prepared by direct writing 3D printing using spherical powders of Ni and Fe metals followed by hydrothermal treatment at 130 degrees C in urea and NH4F mixed solution. The fabricated 3D micro-nano-structured NiFe electrode presents an excellent OER activity of 220 mV overpotential to reach 100 mA cm-2 with a Tafel slope of 49.1 mV dec-1 and stability up to 100 h in continuous or intermittent power supply. The hydrothermal treatment produces in situ growth of flower-like clusters of NiFe2O4 nanoneedles wrapped with FeOOH nanosheets on the surface of the 3D NiFe bimetal microsphere network, and the outstanding OER activity is attributed to a wide variety of interfaces and heterojunctions among metal microspheres, metal oxides, and hydroxides. This study provides an approach for preparing high-performance self-supporting electrodes for electrochemical processes.

In‐space manufacturing draws great attentions due to its potential applications in space exploration. However, the high‐vacuum and microgravity environment introduces extrascientific and technical challenges. Biological experiments in the International Space Station show that spiders can build webs under microgravity conditions, which indicates that the spiderweb building could be independent of gravity. Herein, inspired by the spiderweb, a strategy for additive manufacturing in space, that is, building a 3D structure composed of metallic ribbons and bonded joints, is proposed. Several kinds of 3D metallic structures are manufactured and the flexibility and strength of the obtained jointed‐ribbons are tested. It is showed in the results that the tensile strength of the 3D metallic structures reaches about 70% of that of the raw materials, while their hardness almost keeps unchanged. Herein, an effective method to realize the manufacturing of the complex metallic structures in space is provided.

Purpose The purpose of this study was to fabricate silicone products that had different hardnesses and moduli, thus partially addressing the limitations of homogeneous materials whose deformation depends on altered structure or dimensions, and to provide new dimensions for the design of silicone soft structures. Design/methodology/approach A soft material three-dimensional printing platform with a dual-channel printing capability was designed and built. Using the material extrusion method, material screening was first performed using single-channel printing, followed by dual-channel-regulated printing experiments on products having different hardness and modulus values. Findings The proportion of additives has an effect on the accuracy of the printed product. Material screening revealed that Sylgard 527 and SE 1700 could be printed without additives. The hardness and mechanical properties of products are related to the percentage in their composition of hard and soft materials. The hardness of the products could be adjusted from 26A to 42A and the Young’s modulus from 0.875 to 2.378 Mpa. Originality/value Existing silicone products molded by casting or printing are mostly composed of a single material, whose uniform hardness and modulus cannot meet the demand for differentiated deformation in the structure. The existing multihardness silicone material printing method has the problems of long material mixing time and slow hardness switching and complicated multi-extrusion head switching. In this study, a simple, low-cost and responsive material extrusion-based hardness programmable preparation method for silicone materials is proposed.

As for the uneven heating of the working medium in direct absorption solar collector (DASC),this paper proposed the method of optimizing the flow pattern in DASC by inserting combined rotors into the collector tube to improve the heat collection performance. The working medium used in this paper is Chinese ink nanofluid. The heat collection performance of the collector was studied, and the enhanced mechanism was explained through simulations. Results demonstrated that inserting rotors improved the temperature rise rate in the circuit, and the temperature of the medium after inserting rotors increased by about 56 % compared with that before inserting rotors when the mass fraction of nanoparticles was 0.2 %. In some cases, a small number of rotors can achieve an enhancement effect similar to that of enormous rotors, and improve the economic performance of the system. The numerical simulation results showed that the high-temperature medium in the plain tube is concentrated near the light side, while the medium in the centre and backlight side of the tube cannot easily absorb solar radiation. After rotors were inserted into the tube, the back-side and light-side media were displaced and mixed by the turbulence of rotors, which can improve heat collection.

Active reinforcement technology is an effective means to improve the efficiency of heat collectors.This study systematically investigated the effects of irradiation intensity,nanofluid concentration,rotor speed,number and arrangement of rotors,rotor color and type on the heat collection performance of water-based carbon black nanofluids under the action of swirling flow using a tubular active enhanced heat collection device.The results show that the photothermal conversion efficiency significantly increases with the increase of irradiation intensity.The addition of carbon black collagen protein increased the full range photothermal conversion efficiency of the medium by 56.6%to 216.7%during the same time period.The water-based carbon black nanofluid with a mass fraction of 0.005%had the highest photothermal conversion efficiency and higher energy efficiency ratio.At a rotor speed of 150 r/min,the full range photothermal conversion efficiency ultimately increased by 30.32%,and further increasing the rotor speed will not increase the heat collection efficiency of the nanofluid.When the rotors are evenly arranged,reducing the number of rotors by half will hardly affect the heat collection efficiency.The combination of rotor color and type has a synergistic effect on the heat collection efficiency of different concentrations of nanoluids.Black low flow resistance rotors have better heat collection effects in pure water and high concentration nanofluids,while the two white blade rotors have better heat collection effects in medium and low concentration nanofluids.This study clarifies the rules that affect the heat collection performance of nanofluid under rotor swirling flow,and provides new ideas for solar photothermal utilization.

To probe into the separation process of coarse and fine particles in the classifiers,based on the particle-eddy interaction model and the discrete element soft sphere model,the influence of turbulent fluctuation in the turbo air classification flow field on particle motion and cut size d50 are investigated.The distribution laws of particles in the classification process are also explored.Turbulent fluctuation mainly influences the trajectory of small particles.It has little effect on the trajectory of large particles,and has no significant effect on cut size d50.At an inlet air velocity of 12 m·s-1 and a rotor cage rotating speed of 1200 r·min-1,for the radial distribution,the fine particles less than 20 μm are mainly distributed in the rotor cage area,particles with size near d50 move with swirling flow in the annular region,and the coarse particles larger than 25 μm gather in the area near the guide blade.Due to the interaction between particles,some fine particles may be mixed with the coarse particles,resulting in a"fish-hook effect".For the axial distribution,the fine particles less than 20 μm are mainly distributed in the classifier near the top area,the coarse particles gradually settle downward and the larger the particle size the faster the settlement.

利用Abaqus软件对225/40R18轮胎阶梯式直压硫化内模具(简称内模具)的结构强度进行研究.结果表明:内模具在4.6 MPa的硫化压力下,最大应力出现在宽鼓瓦楔块滑块上,远小于滑块材料铍青铜的许用应力;内模具机构的最大变形位移为0.140 7 mm,其变形为弹性变形,对机构运动和轮胎质量不会产生影响;内模具的各零件的结构强度均满足设计要求.该研究可为阶梯式直压硫化内模具的工业化应用提供参考.