关键词： 三明治结构   阻尼复合材料   微结构设计   拓扑优化   连接的  

摘要： 三明治阻尼复合结构的力学性能取决于阻尼层材料的性能,综合考虑该结构的阻尼性能和可制造性要求,提出了一种面向结构宏观性能并考虑连接性的三明治阻尼复合结构拓扑优化设计方法。以最大化结构模态阻尼比为目标,考虑微结构刚度相材料的连接性,通过组合强制性连接约束法和非线性扩散法,构建了连接性约束下的阻尼复合材料微结构的优化设计模型,并结合3D打印技术实现了三明治阻尼复合结构的制造。运用所提方法对典型结构进行优化设计,得到了刚度相保持连接的阻尼复合结构,且优化后的结构阻尼变大,结构的频率响应变小,实现了三明治阻尼复合结构材料结构设计制造协同优化设计。仿真和实验结果表明,在微结构上存在最优的阻尼材料体积分数使优化后的三明治结构频率响应最小。

关键词： 混凝土   水泥基材料   低温   孔结构   抗拉性能   钢纤维  

摘要： 低温环境中混凝土的抗拉性能是影响"全混凝土"液化天然气储罐长期安全服役的重要因素。本文研发了一种新型耐低温高性能水泥基材料(CHC),利用拉伸试验机研究了低温循环(20~-165℃)前后CHC的抗拉性能,借助压汞孔隙率测试和核磁共振测试分析了CHC的孔结构特征。结果表明,相比于C60混凝土,CHC的总孔隙率较低,抗拉强度较大,峰后变形能力较强。低温循环后,微裂缝的出现和总孔隙率的增加导致CHC和C60混凝土的峰值应力下降。相比于C60混凝土,CHC中裂缝的宽度较小,总孔隙率的增加量较少,故CHC峰值应力的下降幅度较低。本研究证实低温循环前后CHC的抗拉性能均优于C60混凝土,这源于CHC优异的孔结构和钢纤维的掺入。

关键词： spark plasma sintering(SPS)   Cu/Invar bi-metal composite   microstructure   interface diffusion   mechanical property   thermal property  

摘要： An orthogonal experiment scheme was designed to investigate the effects of the Cu content,compaction pressure,and sintering temperature on the microstructures and mechanical and thermal properties of(30−50)wt.%Cu/Invar bi-metal matrix composites fabricated via spark plasma sintering(SPS).The results indicated that as the Cu content increased from 30 to 50 wt.%,a continuous Cu network gradually appeared,and the density,thermal conductivity(TC)and coefficient of thermal expansion of the composites noticeably increased,but the tensile strength *** increase in the sintering temperature promoted the Cu/Invar interface diffusion,leading to a reduction in the TC but an enhancement in the tensile strength of the *** compaction pressure comprehensively affected the thermal properties of the *** 50wt.%Cu/Invar composite sintered at 700℃ and 60 MPa had the highest TC(90.7 W/(m·K)),which was significantly higher than the TCs obtained for most of the previously reported Cu/Invar composites.

关键词： 脆性断裂   显微结构   缺陷   裂纹   压痕   韧性   强度   增韧机制  

摘要： 本文系统地回顾了自Griffith的经典性工作发表一个世纪以来在陶瓷材料断裂行为方面所取得的研究进展,着重强调了脆性断裂的显微结构效应。

关键词： Na2Co1-xFexSiO4   Sodium-ion batteries   Cathode material   Doping   Grinding effect   Electrochemical properties  

摘要： Sodium-based orthosilicates are considered promising candidates as positive electrode materials for rechargeable sodium-ion batteries (SIBs). Na2Co1-xFexSiO4 (NCFS), with x = 0.1 and 0.2 cathode materials have been synthesized by low cost method (improved solid-state). The effects of Fe substitution and grinding process on the structural, morphological, and electrochemical properties of Na2Co0.9Fe0.1SiO4 (NCFS1) and Na2Co0.8Fe0.2SiO4 (NCFS2) are deeply investigated. The prepared Na2Co1-xFexSiO4 cathodes are indexed based on the orthorhombic system with Pca21 space group with a slight difference in lattice parameters. The morphological properties are strongly determined by the suspension formalism, which has an impact on the electrochemical performances. The ball-milling process leads to enhanced electrochemical performance and higher reversible capacity although with capacity fading after 100 cycles. Na2Co0.8Fe0.2SiO4 demonstrated an initial discharge capacity at C/50 of 131.4 mAh.g -1 (1C = 272.7 mA.g -1) that is two times higher than that of the Na2Co0.9Fe0.1SiO4 (54.6 mAh.g -1 (1C = 272.27 mA.g -1)). All the above features and insights make the new materials highly promising for use as potential cathode material for SIBs.

关键词： 聚氨酯/短切碳纤维/碳纳米管复合材料   模压成型   倒金字塔微结构阵列   柔性传感器   灵敏度  

摘要： 采用模压成型方法制备了2种柔软性不同的热塑性聚氨酯/短切碳纤维/碳纳米管(TPU/SCF-CNT)复合材料复制物,其表面上具有倒金字塔微结构阵列,内部有SCF与CNT共同构成的导电通路.将复合材料复制物和相应的复合材料平整片封装成柔性传感器.结果表明,压力作用下传感器内复制物和平整片之间的接触电阻因倒金字塔底棱的形变而显著降低.对使用柔软性较高的复合材料封装的传感器,虽然其相对迟滞稍大,但压力作用下倒金字塔底棱形变量较大,且复制物和平整片内导电通路增加量较大,因此其在0~2.5 kPa的线性区内具有较高的灵敏度(0.32 kPa^(‒1)).制备的2种传感器均具有快速响应特性,且能在500 s(约1580次)的循环压缩/释放测试(峰值压力约3 kPa)中保持较稳定的电阻响应.研究表明,利用模压成型的表面倒金字塔结构复合材料复制物封装成的柔性压力传感器具有良好的传感性能.

关键词： Pressing   Extrusion   Alumina   Titania   Aluminum titanate   Mechanical properties  

摘要： The present investigation compares for the first time the effect of the addition of TiO2 on Al2O3 ceramic materials prepared by uniaxial pressing and extrusion technique. The properties of the disc- and tubular-shaped materials were investigated using different experimental tests, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Archimedes porosity, linear shrinkage, mechanical performance and scanning electron microscopy (SEM). The XRD analysis revealed the formation of Al2TiO5 phase at 1400 degrees C for discs and tubes, and became more evident when the sintering was performed at 1500 degrees C. The increase of TiO2 loading did not affect the open porosity at a given temperature for the tubular- and disc-shaped samples. The addition of 1 wt % TiO2 led to a remarkable increase of tensile strength for the disc-shaped materials heat treated at all temperatures due to the formation of aluminum titanate. However, a further addition on the TiO2 loading appears to decrease the tensile strength of the disc-shaped samples heat treated at 1400 degrees C and 1500 degrees C. For instance, the flexural strength of the tubes improved with increasing TiO2 loading and sintering temperature from 1300 degrees C to 1500 degrees C. This effect was attributed to the occurrence of a more effective formation of Al2TiO5 on the ceramic tubes. Furthermore, the addition of TiO2 played a key role in controlling the open porosity and the microstructure as confirmed by the SEM images in ceramics obtained by uniaxial pressing and extrusion processing.

关键词： Microstructure   Melt spinning-spark plasma sintering   Phase conversion mechanism   Thermoelectric properties   CoSb3 thermoelectric materials  

摘要： Skutterudite CoSb3 thermoelectric materials were synthesized by a combination of melt spinning (MS) and consolidation by spark plasma sintering (SPS). Microstructural analysis was carried out on the MS-SPS samples using various analytical techniques such as XRD, SEM, EBSD and DSC/TGA. In the melt-spun ribbons, the initial microstructure consisted of a multiphase mixture of Sb and CoSbx (x = 1, 2, or 3) where CoSb3 is the only thermoelectric phase. Subsequent SPS processing caused conversion of other phases present (Sb, CoSb and CoSb2) into single-phase CoSb3 and recrystallization concurrently. The phase conversion mechanism has been explained in the present work using a thermodynamic interpretation. Thermoelectric transport measurement results show that the thermal conductivity of MS-SPS sample was significantly decreased as compared with that of the sample prepared by traditional methods combined with SPS (TM-SPS) due to the reduction of its grain size. Compared with TM-SPS sample, MS-SPS sample has a high ZT value at room temprerature because of its high electrical conductivity and low lattice thermal conductivity.

关键词： nonlinear guided waves   metamaterial   Bragg scattering   local resonance   structural health monitoring  

摘要： Nonlinear guided waves (NGWs) exhibit extraordinary sensitivity to microstructural changes in materials which are often considered as damage precursors in many structural health monitoring (SHM) applications. However, these changes are usually very small at the microstructural level, thus generating weak nonlinear wave components which are prone to or even overwhelmed by other deceptive and non-damage-related nonlinear sources present in a monitoring system. This may jeopardize the practical implementation of the NGW-based SHM methodology. To tackle this problem, this paper proposes a metamaterial filter (meta-filter (MF)), in the form of a patch to be surface-mounted over the structure under inspection. The MF is designed to purify the probing waves during propagation before reaching the inspection area through tactical elimination of non-damage-related nonlinear components from the actuation. Considering different bonding conditions and the lattice symmetry of the MF, two types of bandgaps, corresponding to Bragg scattering and local resonances, alongside their respective band properties are analyzed. Time-domain finite element simulations are carried out to assess the efficacy of the MF in terms of wave purification in the context of SHM, supported by experimental validations. The designed MF is deployed in an aluminum strip to detect the material microstructural changes induced by a thermal ageing treatment. Results demonstrate the designed MF significantly enhances the detection ability of NGW-based SHM system. Both locally resonant and Bragg bandgaps can, in principle, be used for wave purification. While the former requires precise control of the bonding quality of the MF, the latter relies on symmetrical installation of the MF to ensure a reasonably wide wave filtering range. Considering variability factors in the implementation of the MF and better immunity to the nonlinearity of the bonding layers, preference is given to Bragg bandgap for NGW-based SHM app

关键词： 国防科技   科研骨干   科研成果   爆炸力学   任务驱动   高压物理   工程技术发展   航空航天  

摘要： 动态加载下材料的响应行为是高压物理、爆炸力学等学科领域关注的重要科学问题之一,也是支撑国防科技和工程技术发展的关键基础,在航空航天、能源环境、交通安全等国民经济领域具有重要的应用价值。20世纪50年代后期,在相关任务驱动下,我国老一代科学家在极其困难的条件下开始了该领域的研究工作。经过半个多世纪的不懈努力,取得了很多重要的科研成果,培养了一大批优秀的中青年科研骨干,有力地支撑了我国国防科技和民生安全事业的发展。