Rubber's dissipated energy quantification used in vibratory insulation and protection systems

In vibratory protection and insulation systems, the major problem consist to choose suitable passive elements (spring, damper, others), which are inserted between the resonator and the exciter which have the role of preventing or reducing the transmission of dynamic forces. This work consists of characterizing a synthetic rubber (SR) sample of hollow circular shape (design requirement) by determining the coefficient of energy dissipation at an average ambient temperature of 20°C with a humidity of 25%. The mechanical load and discharge tests make it possible to draw hysteresis curves through which the dissipation coefficient will be determined, the load values is between 500 and 1000 N, with 30, 60, and 90 mm/min loading speeds and a number of cycles 2, 3, and 5, these values have been chosen so as not to cause the effect of cyclic hardening and softening and also to take into consideration, that the vibration limits movement at 3 cycles, which makes this test different from other tests such as fatigue. The processing of different curves, allows to determine energy dissipation coefficient of rubber specimen and also to examine its variation as a function of load, loading speed, and number of cycles; it is possible to determine other characteristics from this coefficient, such as, damping ratio, dynamic amplification factor, and so on, necessary to study efficiency of protection systems, design, and manufacture, based on the curve of transmissibility of dynamic forces to evaluate performance rubber conditions use.     

双包覆层局域共振声子晶体带隙特性研究

从理论上提出了一种双包覆层局域共振声子晶体结构,结合有限元对该结构带隙产生的机理、影响因素以及隔声特性进行深入分析。结果表明：带隙上边界频率主要由双包覆层弹性模量大的材料决定;下边界频率主要由基体密度小的材料决定。该声子晶体在低频范围具有良好的隔声特性,为声子晶体的结构设计提供理论指导。     

导热绝缘复合材料的研究进展

介绍了聚合物基导热绝缘复合材料的概况,阐述了常用基体材料与导热填料各自的特点,讨论分析了其导热机理和导热理论模型,综述了该类复合材料的研究进展和应用现状。最后,展望了导热绝缘复合材料研究与应用前景及发展趋势。     

Prolong the durability of La2Zr2O7/YSZ TBCs by decreasing the cracking driving force in ceramic coatings

Service lifetime and thermal insulation performance are both crucial for the application of thermal barrier coatings (TBCs). In this study, layered structure design under equivalent thermal insulation conception is introduced to lower the cracking driving force in TBCs, and with the goal of prolonging TBCs lifetime. Three groups of layered LZO/YSZ TBCs were designed with same thermal insulation of 500?μm YSZ, the LZO layers were deliberately designed with different initial elastic modulus. Virtual crack closure technique (VCCT) calculation result showed that the energy release rates at the crack tips are 28.2, 22, and 18.8?N/m corresponding to the initial elastic modulus of 70, 60, and 50?GPa. After gradient thermal cyclic tests with surface temperature of 1300?°C, TBCs with lowest initial elastic modulus showed the longest lifetime, and more than double of pure YSZ TBCs. This study provides a new option for the improvement of TBCs lifetime.     

Nomex纸蜂窝增强酚醛泡沫的制备及性能研究

本文以自制酚醛树脂发泡制备的酚醛泡沫为基体,Nomex纸蜂窝为增强体,采用特定的发泡制备工艺制得了Nomex纸蜂窝增强酚醛泡沫.通过对该材料微观形貌、力学性能和热性能的表征,初步探讨了材料基体和界面效应对其力学性能和隔热性能的影响.研究结果发现,填充了酚醛泡沫后,Nomex纸蜂窝增强酚醛泡沫的力学性能显著提高,导热系数显著降低.分析认为,良好的强结合界面保障了酚醛泡沫对Nomex纸蜂窝增强酚醛泡沫力学性能和隔热性能的贡献,该材料是一种综合性能较好的隔热、阻燃材料.     

不同工艺状态的玻璃布/酚醛复合材料防隔热特性研究

玻璃布/酚醛复合材料有较好的耐烧蚀和隔热特性,被广泛用于工业耐高温设备以及高速飞行的航天器防隔热设计上,但是不同的成型工艺表现出的耐烧蚀及隔热特性却存在差异。将不同玻璃布厚度、不同缠绕工艺、不同固化方式、以及有机纤维与玻璃纤维混编工艺获得的玻璃布/酚醛制品,取样进行风洞条件下的耐烧蚀、隔热性能试验,试验测量了各模型的质量烧蚀率及背面温升,用于评估其相应的防隔热性能。试验结果显示倾斜缠绕工艺耐烧蚀及隔热性能最优,与理论预期一致,可为工程应用提供参考。     

Dielectric,impedance and piezoelectric properties of (K0.5Nd0.5)TiO3-doped 0.67BiFeO3-0.33BaTiO3 ceramics

A novel (0.67-x)BiFeO₃-0.33BaTiO₃-x(K_0.5Nd_0.5)TiO₃ (KNT100x, x = 0.0, 0.02, 0.04, 0.06, 0.08 mol%) ceramics were fabricated and their microstructure and electrical properties were studied. All samples displayed a pseudo-cubic symmetry, and adding of KNT had little effect on grain size. The dielectric analysis displayed the dispersion increases with the addition of KNT compositions, showing strong relaxor properties. Besides, high dielectric constant (ε’) of 23000 and dielectric peak temperature (T_m) of 390 °C remain at 1 kHz in the x = 0.02 sample while the dielectric loss (tanδ) dropped below 0.5 in the range of 30–400 °C, showing excellent electrical insulation performance. In addition, doping of KNT had obvious influence on the strain, and a large strain (Smax) of 0.26% was obtained at x = 0.02 due to the increase of electrical insulation. More importantly, the strain at 50 kV cm^?1 enhanced significantly with temperature increasing, reaching a maximum strain of 0.75% with a small hysteresis coefficient of 30% at 110 °C. Particularly, KNT02 exhibited excellent fatigue resistance within 10⁵ fatigue cycles. Presumably these results are attributed to the coexistence of ferroelectric and non-ergodic relaxor domains and the thermally activated domain wall motion.     

Opacifier embedded and fiber reinforced alumina-based aerogel composites for ultra-high temperature thermal insulation

A novel method was developed to uniformly disperse sub-micron TiO₂ opacifier into fiber reinforcements using agar and silica as binders via freeze drying. TiO₂ opacifier/ fiber/ alumina-based aerogel ternary (TFA) composites with high strength and excellent high-temperature thermal insulation were successfully prepared by sol-gel route, impregnation process and supercritical fluid drying. The microstructure, mechanical and thermal insulation properties of TFA composites were investigated comprehensively. The results show that the mechanical property of TFA composites can be significantly enhanced by mullite fiber felt and the incorporation of SiO₂ binder. The effect of TiO₂ opacifier on the high-temperature thermal conductivity was studied by adjusting the content of TiO₂ from 0 to 15 wt%. The obtained TFA composites exhibit high Young's modulus of up to 3.58 MPa and low high-temperature thermal conductivities of 0.129 W/m·K at 800 °C and 0.168 W/m·K at 1000 °C, respectively. The mechanism of heat transfer in TFA composites at high-temperature was also analyzed.     

变压器中绝缘纸纤维素降解化学指示剂的综述

对油浸变压器中绝缘件化学降解和热降解、故障机理、状态监测方法及寿命预测进行综述。对不同油纸环境中评估绝缘寿命的寿命预测模型进行研究。对变压器油中化学指示剂浓度的系统测试证明糠醛及其相关产物可用于检测绝缘纸裂解的程度。     

耐1500℃超高温轻质高效隔热材料的制备及性能的初步表征

针对新型高速飞行器对超高温热防护材料的需求,以超细直径耐高温陶瓷纤维和高温粘结剂为主要原料,通过纤维短切-湿法成型-高温热处理等工序制备了轻质高效隔热材料。对高温隔热材料的微观结构、热物理性能及力学性能进行了表征和分析。结果表明:短切纤维在隔热材料内部无序排列,形成了三维网络结构,具有较高的孔隙率,而且纤维与纤维搭接处具有良好的节点,因而材料具有一定的力学性能。材料在1500℃/h处理后,线收缩2%,密度为0.35g/cm3的隔热材料厚度方向压缩强度1MPa,室温热导率0.07 W/m·K。