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。     

橡胶薄片共振结构吸声机理及性能研究

本文用驻波管法研究了橡胶薄片共振吸声结构的吸声机理及橡胶薄片厚度、空气层厚度和声波频率对其吸声性能的影响。实验结果表明,橡胶薄片共振结构与普通板共振结构在吸声机理和吸声效果方面均有所不同,前者的吸声效果优于后者;在共振状态,前者的吸声作用主要在于柔性橡胶薄片在声波作用下弹性振动,引起后面腔体内空气压强的变化,因空气层的吸声作用而损耗声能,后者主要依赖于板的内摩擦吸声作用。橡胶薄片共振的吸声系数随空气层厚度的变化而出现一极大值,随着声波频率的增加,达到共振状态所需的空气层厚度减小,随着橡胶薄片厚度的增大,其最大吸收峰向低频方向移动。     

水下吸声材料研究进展

概述了以聚氨酯基体为主要应用的水下吸声材料,主要阐述了水声机理、常用的水声吸声材料与结构,以及以局域共振声子晶体为基础衍生出的新型水下吸声材料结构,如声子晶体、局域共振声子木堆、超材料吸声结构,为未来水声吸声材料的发展提供了更广阔的发展空间及方向。     

增强橡胶界面层对材料力学性能影响的RVE计算

炭黑粒子与橡胶间相互作用的界面层对弹性体复合材料力学性能有重要影响。通过建立包含炭黑、橡胶基体及其界面层在内的三维RVE模型,借助有限元计算,研究了不同界面层厚度、界面层与基质不同模量比情况下弹性体复合材料的力学性能。研究发现,在一定范围内,界面层厚度及界面层模量与基质模量比值的变化都对复合材料体系的应力和模量有影响,计算条件下各组分承受应力由大到小的顺序为:颗粒内部应力界面层应力基体应力。     

改性PP基吸声体吸声性能的研究

本文以自行研制的乙现橡胶（ＥＰＲ）改性聚丙烯（ＰＰ）基阻燃泡沫材料制成吸声体,研究其吸声特性及规律。结果表明：该吸声体在中低频区域最大吸声系数可达到０．９９,在１２５～２０００ＨＺ频率内平均吸声系数为０．７２。     

深水下的吸声材料

由于丁基橡胶的基本结构具有多足虫状，它的粘弹性损耗因子比其他几种通用橡胶都高。因此，水下吸声材料多采用丁基橡胶。当吸声橡胶在水下处在0．5MPa的压力下，即变成了透声橡胶。国外有人用SOAB吸声橡胶做过声管试验，在0．7MPa下声波几乎完全透过，故SOAB在高静水压下则失去吸声作用。SOAB吸声产品是丁基橡胶加入铝粉制成。我国的吸声橡胶产品是由丁基橡胶加蛭石粉制成的，同样也只适用于常压下工作。     

聚乙烯醇/纤维素复合气凝胶材料的制备及其声学性能

利用绿色溶剂NaOH/尿素水溶液溶解微晶纤维素,引入交联剂环氧氯丙烷,通过溶胶-凝胶法将聚乙烯醇（PVA）均匀分散在纤维素溶液中。最后,通过冷冻干燥法,制得复合纤维素气凝胶。研究了PVA的含量对纤维素气凝胶骨架密度、孔隙率间的关系,分析了PVA含量及厚度对样品吸声性能的影响。结果表明,随着PVA的加入增多,样品内部孔强度得以提升;当纤维素与PVA比为3:2时,吸声系数最高可达到0.95以上;随着样品厚度的增加,样品吸声系数最高峰向较低频移动,2000 Hz后的吸声系数略有下降,但平均吸声系数仍在0.6以上。     

汽车顶棚用热塑性半硬质聚氨酯泡沫的吸声性能研究

通过驻波管传递函数法测试了不同条件下汽车顶棚用热塑性半硬质聚氨酯泡沫的吸声性能。研究结果表明:泡沫吸声系数随密度增加而提高;泡沫厚度对中低频区吸声性能影响较大,吸声系数随厚度增加而提高;高异氰酸酯指数情况下泡沫吸声性能较好;硅藻土的引入可有效提高泡沫的吸声性能;高回弹聚氨酯泡沫与半硬质聚氨酯泡沫复合且高回弹聚氨酯泡沫为吸声面时吸声效果较好。     

基于局域共振型声子晶体在机舱内低频隔声特性

提出了一种正八边形孔状局域共振声子晶体结构,通过有限元法分析了该结构的带隙产生机理、带隙宽度影响因素以及隔声特性。结果表明:共振频率是由局域共振单元与弹性波耦合作用的结果,耦合程度直接影响带隙宽度和弹性波衰减速度,进而影响隔声特性;隔声量取决于正八边形孔状芯体和包覆层的结构特性参数。增大芯体质量,减小正八变形框的边长,同时减小包覆层弹性模量和增大包覆层密度,则带隙宽度增大,第一隔声峰处的隔声量增大,同时第一隔声峰向低频移动。表明通过优化结构参数,可以达到良好的隔声效果,在大型军机舱室低频段降噪具有重要的理论意义。     

填充蜜胺泡沫芳纶蜂窝复合芯吸声性能研究

制备了蜜胺泡沫填充芳纶蜂窝复合芯,分析了复合芯的吸声机理,考察了复合芯的密度和厚度对吸声性能的影响。结果表明,在较高频率范围内,复合芯的吸声系数高于蜜胺泡沫;随着复合芯的密度及厚度的增大,复合芯在低频下的吸声性能逐步增大;当复合芯密度和厚度分别为78 kg/m3及20 mm,其平均吸声系数可达0.61,是一种优异的工程吸声材料。     

2mm短切碳纤维吸波涂层的制备与吸波性能

基于雷达吸波涂层薄、轻、宽、强的要求,以2 mm短切碳纤维为吸收剂,水性聚氨酯为基体树脂,制备了碳纤维吸波涂层,将芳纶纸蜂窝与碳纤维吸波涂层进行匹配,并采用矢量网络分析仪测试了涂层的吸波性能。结果表明,单层碳纤维吸波涂层在厚度较薄时吸波性能较差,添加匹配层后性能有所改善。将不同碳纤维含量的吸波涂层与芳纶纸蜂窝进行匹配,制备了多层匹配碳纤维吸波涂层,涂层的吸收强度和有效吸收带宽均得到明显提升,通过调整碳纤维涂层和芳纶纸蜂窝的匹配方式,复合涂层在4.1~13.6 GHz频率范围内均能实现有效吸收。     

Effects of material and treatment parameters on noise‐control performance of compressed three‐layered multifiber needle‐punched nonwovens

The effects of material and treatment parameters on airflow resistivity and normal‐incidence sound absorption coefficient (NAC) of compressed three‐layer nonwoven composites have been studied. Material parameters included fiber size and porosity, and treatment factors included applied pressure and duration of compression. Fibers used included poly(lactic acid) (PLA), polypropylene (PP), glassfiber, and hemp. Three‐layered nonwoven composites were classified based on material content and fiber blend. LHL and PGP were sandwiched structures consisting of PLA/Hemp/PLA and PP/glassfiber/PP layers, respectively. PGI consisted of three layers of an intimate blend of PP and glassfiber. Statistical models were developed to predict air flow resistivity from material parameters and the change in air flow resistivity from compression parameters. Independent variables in the first model were porosity and fiber size and, in the latter model, were compressibility, pressure, and initial material parameters. An increase in air flow resistivity was found with increased compression. No significant effect of compression duration was detected. Two additional statistical models were developed for the prediction of sound absorption coefficient based on material and treatment parameters. The independent variables of the first model were air flow resistivity, thickness, and frequency, and those of the second model were compressibility, initial thickness, and initial density of the composite, diameter and density of the fiber, compression pressure, and frequency. A decrease in sound absorption coefficient was detected with increasing compression, while no effect of duration was detected. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

汽车隔音垫用聚氨酯软质高回弹泡沫的吸音性能研究

通过驻波管法测试不同隔音垫聚氨酯软质高回弹泡沫的吸声系数,结合显微镜对泡沫的力学特性和形态进行观察和分析。研究结果表明,泡沫在低频区的吸声系数随厚度的增加而提高,而在高频区则有所减弱;泡沫的吸声系数随密度增加而提高;泡孔形态对泡沫的吸声性能有显著影响,细密而均一的泡孔有利于声能的吸收;不同异氰酸酯由于反应性和结构上的差异,泡沫也表现出不同的吸声特性;高压发泡生产的泡沫峰值吸声频率稍向高频区移动,复合乙烯–醋酸乙烯共聚弹性体（EVA）后泡沫的峰值吸声频率稍向低频区移动。     

Characterization of AFM cantilevers coated with diamond-like carbon

The resonance frequency of AFM cantilevers depends on the elastic modulus and on the dimensions of the cantilever. As for coated cantilevers, the resonance frequency will be determined not only by the properties of the cantilever, but also by the properties of the coating (elastic modulus and thickness). We have carried out a systematic investigation of cantilevers coated with several thicknesses of the DLC films. Measurements of the resonance frequency of the cantilevers, before and after the DLC coating, were used with a model to determine the elastic modulus of the DLC. The elastic modulus obtained for the DLC, with this model, was E₂=616 GPa. The AFM tip radii were also measured after coating and were found to increase with the DLC film thickness.     

The single fiber pull-out test analysis: influence of a compliant coating on the stresses at bonded interfaces

The mechanical properties at the fiber/matrix interface play a significant role in controlling the fracture resistance of fiber-reinforced composites. By coating the fiber with sizing and coupling agents, these interfacial properties can be modified. The aim of the present analysis was to examine the effects of the coating thickness and modulus on the stresses at the bonded interfaces between the fiber, coating, and matrix. Using the fiber pull-out test as the analytical model, the stresses are first obtained by minimizing the total complementary energy in the coated fiber/matrix composite. The analytical results show that the interfacial shear stress between the fiber and the coating is higher than that between the matrix and the coating. Also, a thin and compliant coating reduces substantially the peak interfacial shear stress but not the interfacial radial stress due to Poisson's effect on the fiber. Furthermore, the shear stress transfer from the fiber to the matrix across the coating layer is found to be more uniform. The implications of these findings are discussed.     

Internal friction of capsule-free HIPed porous alumina

Porous alumina were sintered by conventional sintering and capsule-free Hot Isostatic Pressing (HIPing), at temperatures between 800 and 1500 °C under pressures 0.1 MPa or 200 MPa for 1 h or 50 h. Young’s modulus and internal friction of samples were measured by resonance method. The results show that Young’s modulus is mainly dominated by porosity of material. Capsule-free HIPed porous materials have slightly higher Young’s modulus than conventionally sintered ones at the same porosity. Internal friction is governed by both porosity and specific surface area. Capsule-free HIPed porous alumina has lower internal friction coefficient than conventionally sintered ones at the similar porosity or at the similar specific surface area. Enhanced surface-self diffusion under high gas pressure reduces internal friction coefficient, and affects internal friction more than Young’s modulus.     

双变频共振阻垢、除垢技术在电石渣上清液中的应用

介绍了双变频共振除垢、阻垢技术在电石渣上清液中的应用情况:使用变频防垢、除垢器1个月后拆下管道,发现垢层得到明显控制,清洁管道中的垢层厚度约1 mm,以前结垢的管道中几乎没有新的垢层生成,而且垢层有一定程度的减少;使用半年后,管道中的垢层未超过3 mm。     

压敏胶带Loop Tack试验方法初探

以SBS(苯乙烯-丁二烯-苯乙烯嵌段共聚物)弹性体为热熔型压敏胶(PSA)的基体树脂,采用Loop Tack(环形或胶圈初粘力)法和斜面滚球法测定PSA的初粘力,并探讨了胶层厚度、PSA的储能模量以及黏贴材料的种类等对PSA初粘力测试结果的影响。结果表明:Loop Tack法中基材因折痕作用力给胶层施加了瞬间应力;在储能模量相差不大的情况下,斜面滚球法测试结果不理想的胶体却在Loop Tack测试中表现出良好的初粘力值;同一PSA在玻璃面板上测得的最大剥离力均大于镜面钢板上测得的数据(两者相差2.56%～6.12%)。     

Sound absorption performance of a lightweight ceramic foam

Porous materials can be effective for sound absorption and noise reduction. A kind of lightweight cellular ceramic foam with bulk density of 0.38–0.56 g cm^-3 was successfully prepared by conventional molding with pore forming agent. The porosity is from 76.4% to 83.7% for the sample with relatively large pores (the average pore size: 5.3–5.6 mm), and from 74.1% to 81.1% for the sample with relatively small pores (the average pore size: 1.5–1.7 mm). The effects were investigated for processing parameters on the structure of samples, and for the pore size, sample thickness and porosity on the sound absorption performance of samples. The results show that the absorption performance of the ceramic foam product with relatively large pores may be superior to that with relatively small pores in the case of the approximately same porosity. The first absorption peak moves from a higher frequency to a lower frequency with the increase of sample thickness. When the porosity increases, the average sound absorption coefficient increases for all of the samples, and the first absorption peak moves from a higher frequency to a lower frequency for the sample with relatively large pores but does not change for that with relatively small pores.     

Properties and mechanism of a novel metallic-hollow-spheres/polyurethane acoustic composite

In this article, 316L stainless steel hollow spheres (316L HS) and polyurethane (PU) resins were used to prepare a novel metallic-hollow-sphere/polyurethane (MHSP) acoustic composite by casting. The acoustic experimental results of this composite revealed that compared to monolithic PU, the sound transmission loss of the composites increased and the maximum sound absorption peak shifted to lower frequency with the change of acoustic impedance and resonance frequency. When the surface of metallic hollow sphere used in MHSP composite was modified by silane coupling agent, the sound insulation and sound absorption performance of MHSP composites were further improved. This is related to the addition of the molecular layer of coupling agent between MHSP matrix. In addition, the addition of silane coupling agent creates PU foaming in matrix, resulting in a large number of pores and gaps that can increase the sound waves energy loss through air friction and heat exchange.