Microstructure and properties of A357 aluminium alloy treated by pulsed magnetic field

This study examined the effects of a pulsed magnetic field (PMF) on the solidified microstructure and properties of A357 aluminium alloy. Results showed that the solidified microstructure of the alloy treated by a PMF was refined. The treated alloy in the T6 state had superior mechanical properties, with the ultimate tensile strength, yield strength and elongation increasing by 48?MPa (18.5%), 46?MPa (16.4%) and 4.8% (142%), respectively, when compared with the untreated alloy. When testing at room temperature, with a strain amplitude of 1?×?10^?4 and at a frequency of 1?Hz, the damping capacity value was 14.2?×?10^?3 for the alloy subjected to a PMF treatment, which increased by nearly 170% when compared with the untreated alloy.     

硅合金化ZA27合金的阻尼性行为

硅合金化ZA27合金具有良好的耐磨性能,但其阻尼性能(Q-1)研究尚不深入.本文利用多功能内耗仪研究了铸态ZA27合金和向ZA27合金中加入4%Si的合金(下称ZA27-4%Si合金)的阻尼行为和相对动态模量,分析了两种合金的阻尼机理.结果表明两种合金的阻尼性能随频率降低和温度升高而增大,阻尼值不随应变振幅变化.ZA27合金和ZA27-4%Si合金具有较高的阻尼性能,在0.1Hz下,合金的室温阻尼分别为6.87×10-3与5.83×10-3.合金的相对动态模量随应变频率提高而增大.100℃以下,ZA27-4%Si合金的相对动态模量不随温度变化.研究表明合金的阻尼是由合金晶界和相界面滑动、位错振荡以及各相的热膨胀系数和弹性模量间差造成的微塑性变形共同造成的.认为ZA27-4%Si合金具有良好耐磨性能和减振性能和强度,适合作为滑动轴承合金材料.     

Remarkable improvement of damping capacity in FeMn-based alloys by a long annealing

ABSTRACT

Effects of a long annealing up to 10?h were investigated on damping capacity and phase evolutions in FeMn-based alloys. The damping capacity in the Fe17.5Mn alloy rose with the annealing time. A highest damping capacity was obtained in the Fe16.5Mn10.5Cr alloy after 2?h annealing. The highest damping capacity was comparable in Fe17.5Mn and Fe16.5Mn10.5Cr alloys. A positive relationship between the damping capacity and the stacking faults existed in both the Fe17.5Mn and Fe16.5Mn10.5Cr alloys annealed for above 2?h. To reduce the amount of α′-martensites was favourable to the further improvement of damping capacity. The α′-martensites clustered locally in the Fe17.5Mn alloy, but they distributed inside the ?-martensite bands in the Fe16.5Mn10.5Cr alloy.     

高应变率下阻尼铝合金的动态力学性能研究

针对航空用高阻尼铝合金在高应变率载荷下的服役特征,研究了两种高阻尼铝合金在高应变率下的动态力学性能.采用分离式霍布金森(Hopkinson)压杆对高阻尼铝合金进行了动态压缩实验,获得了应变率(140,275,500s-1)对材料应力-应变曲线的影响规律,并同普通铸造铝合金ZL101A的动态压缩力学性能进行比较分析.结果表明:高阻尼铝合金在高应变率下的力学性能明显优于普通铸造铝合金;第一种高性能阻尼铝合金的动态压缩力学性能优异.第二种高性能阻尼铝合金随着应变率的提高,材料的弹性模量和应力均有所下降,但是形变强化效果显著.     

High Damping Indium-Tin Alloys

This research is directed toward the development of materials of high stiffness and high mechanical damping for the purpose of damping vibrations in structures and machinery. To this end, indium-tin alloys are considered. Cast In-Sn exhibits substantial damping for a metal. Quenching substantially improved the damping of indium-tin alloy but the effect gradually disappeared due to aging. Cold work of 1.3% permanent shear strain had the effect of moderately increasing the damping of indium-tin, and 10–100% permanent strain substantially increased the damping of tin, with 30% giving the largest damping below 5 Hz. This revised version was published online in August 2006 with corrections to the Cover Date.     

Comparative characterisation of damping behaviour of aluminium alloy composites produced by different fabrication techniques

Abstract

There is limited information currently available on the damping behaviour of silicon carbide reinforced metal matrix composites for aerospace structural applications. Dynamic mechanical analysis is one of the thermal analysis techniques which can be used to study the damping properties. In the present investigation, a dynamic mechanical thermal analyser is used to investigate the dynamic mechanical properties as a function of temperature for aluminium alloy 2124 + 5%SiC particle reinforced composites. The formation and dissolution of precipitate phases as a function of temperature have also been characterised by the technique of differential scanning calorimetry. It was observed that in all composites, the complex modulus, loss modulus, and damping capacity increased whereas the storage modulus decreased with increasing temperature.     

Frequency effects on the fatigue behaviour on carbon fibre reinforced polymer laminates

Test frequency exerts a considerable influence on dynamic mechanical behaviour of carbon fibre reinforced materials. In this study the effect of test frequency on the fatigue behaviour of the T300/914C system, a carbon fibre/epoxy matrix composite, is examined. Tension-tension fatigue tests were carried out at various stress levels and at three test frequencies (5, 10 and 20 Hz) for three specimen orientations (unidirectional, (0)₈, crossply (0°/90°)_4s and angleply (±45°c)_4s). A number of dynamic mechanical properties were monitored throughout specimen lifetimes and subsequently analysed — stress/life behaviour, maximum strain, normalised fatigue modulus, dynamic loss modulus, damping factor and specimen temperature. Frequency effects are found to profoundly influence the fatigue behaviour of both crossply and angle ply specimens. Angleply specimen fatigue response exhibits a strong dependence on test frequency, a fact that is reflected in the dynamic mechanical property responses monitored. The data obtained for unidirectional specimens is inconclusive due to the large degree of fatigue scatter observed.     

玻璃纤维芯-铅网增强橡胶复合材料动态性能

制备了具有不同结构和界面结合强度的玻璃纤维芯2铅网增强橡胶复合材料( GF- Pb/ R) , 并通过测试复合材料的力滞回线, 研究了其在3～20 Hz 时的动态性能。结果表明, GF- Pb 网增强结构可以同时提高橡胶的动态力学性能和阻尼性能, 其中GF-Pb 网垂向增强方式的性能改善效果明显, 当GF-Pb 网体积分数为4 %时, 其动刚度和损耗因子的提高率可分别达到49 %和25 %。GF- Pb/ R 复合材料阻尼性能是材料阻尼、界面微滑移阻尼、Pb 塑性变形阻尼等多种阻尼机制共同作用的结果。界面粘结强度显著影响了复合材料的力学性能和阻尼行为: GF-Pb/ R 刚度随界面结合强度的增大而提高; 损耗因子按照界面中等强度结合、强结合、弱结合的顺序递增。      

挤压工艺对Mg-0.6Zr-0.5Y合金力学和阻尼性能的影响

系统地研究了挤压温度和挤压比对Mg-0.6Zr-0.5Y合金力学和阻尼性能的影响规律.采用光学金相显微镜、电子式万能试验机及动态机械分析仪(DMA)等手段分析合金显微组织、力学和阻尼性能的变化,并讨论了晶粒细化与合金力学和阻尼机理之间的内在联系.研究发现,合金在挤压过程中发生了动态再结晶,晶粒显著细化,使综合力学性能得...     

Influence of solution-aging treatment on damping and tensile properties of Ti-36Nb-2Ta-3Zr-0.3O alloy

High-damping alloys have been used in aerospace, automobile manufacturing and other fields due to its capacity to weaken vibration and noise. The damping and tensile properties of the Ti-36Nb-2Ta-3Zr-0.3O (wt-%) alloy were investigated by dynamic mechanical analysis and tensile tests. The results showed that aging treatment significantly improved the tensile strength. The Snoek-type relaxation was observed in the alloy with and without aging treatment, although the aging treatment exerted a negative influence on damping capacity, especially at high temperatures. This phenomenon could be related to the precipitation of the α phase and the segregation of oxygen in the α phase from the β phase during the aging process. As a result, the alloy aged at 713?K simultaneously presents excellent damping and tensile properties.     

PU/PMMA IPN的阻尼行为研究

采用全自动扭辫仪和驻波管对ＰＵ＝ＰＭＭＡ ＩＰＮ体系的阻尼行为进行了研究,ＴＢＡ结果表明,填料的最佳填加量为１０％,吸音系数测试表明,常温时该种结构的ＩＰＮ材料的吸音系数与频率近似成峰形,最大吸收在３０００Ｈｚ左右。最好的吸音材料的吸音系数峰值为５０％以上。     

Evaluation of styrene-butadiene latex as a vibration damping admixture for concrete: a micromechanical analysis

Abstract

The styrene-butadiene latex as an admixture for Portland cement concrete is evaluated in this study using a numerical simulation approach aided by a series of laboratory experiments conducted for material parameter determination and numerical model validation. Using the discrete element method (DEM), a three-dimensional (3D) beam of concrete was built with due consideration of the concrete microstructural features. The beam was employed to simulate the cyclic three-point flexural test at three loading frequencies: 0.2, 1 and 5 Hz and a representative in-service temperature: 25 °C. The effects of admixture usage and loading frequency on the overall damping properties of concrete were evaluated to explore the vibration-reduction mechanisms of the latex-admixtured concrete. Results show that a 20 percent usage of styrene-butadiene latex (by weight of cement) was found to significantly enhance the storage and loss moduli and the loss tangent of concrete. The developed 3D DEM model realistically accounts for the micro-structural features of concrete matrix and can potentially be used for evaluating and designing high performance concretes against detrimental dynamic loads.     

铁基阻尼材料的发展现状和趋势

铁基阻尼材料是一种具有广阔应用前景的结构-功能一体材料,它具有优良的阻尼性能、综合力学性能和冷热加工性能。本文全面地介绍了铁磁型、孪晶型和复相型三类铁基阻尼材料的阻尼机制、研究和应用现状,并对铁基阻尼材料的发展趋势进行了展望。     

High-frequency micromechanical columnar resonators

Abstract

High-frequency silicon columnar microresonators are fabricated using a simple but effective technological scheme. An optimized fabrication scheme was invented to obtain mechanically protected microcolumns with lateral dimensions controlled on a scale of at least 1 μm. In this paper, we investigate the influence of the environmental conditions on the mechanical resonator properties. At ambient conditions, we observed a frequency stability δf/f of less than 10^?6 during 5 h of operation at almost constant temperature. However, varying the temperature shifts the frequency by approximately ?173 Hz °C^{? 1}. In accordance with a viscous damping model of the ambient gas, we perceived that the quality factor of the first flexural mode decreased with the inverse of the square root of pressure. However, in the low-pressure regime, a linear dependence was observed. We also investigated the influence of the type of the immersing gas on the resonant frequency.     

Research on identification of nonlinear damping based on time frequency analysis

Abstract

According to the relationship between damping, strain and time, the piecewise linear wavelet transform and the piecewise linear short time Fourier transform methods are put forward to identify the nonlinear damping of alloy material. The overall nonlinear property of damping is derived from the piecewise local linearisation. The satisfied results obtained from simulations demonstrate that the methods presented are effective. Usually, damping measured in the non-uniform stress field is only a volumetric average. To overcome this deficiency, a trapezoid specimen with quasi-uniform stress field is developed on the basis of the traditional damping experimental equipment. The damping measurement experiment is carried out. The measurement signal is analysed by the two methods presented. The relation curve of damping versus strain has shown that the damping capacity of the alloy Al–33Zn–6Si increases with the increasing strain. The relationship between damping and strain appears obviously nonlinear.     

新型BTG塑料合金关于温度-频率-振幅的动态阻尼性能模型

建立了描述一种新型BTG塑料合金的温度-频率-振幅的动态阻尼性能数学模型。通过动态热分析仪DMA242, 获取了BTG塑料合金的频率扫描、温度扫描和幅值扫描的动态阻尼损耗因子实验数据。通过分析实验数据, 将温度扫描的阻尼损耗因子量分离为仅与频率相关以及与频率、温度均相关的两个分量, 并分别用Kelvin分数导数的阻尼损耗因子模型和高斯函数模型来表达这两个分量, 再以此为基准, 考虑振幅对阻尼损耗的影响, 由此建立了综合考虑温度-频率-振幅的阻尼损耗数学模型。结果表明, 所建立的综合考虑温度-频率-振幅的阻尼损耗数学模型能准确描述实验数据。      

Low frequency damping properties of a NiMnTi shape memory alloy

The present study investigated the low frequency damping properties of a NiMnTi shape memory alloy (SMA) for the first time. The NiMnTi SMA had a high β?θ′ internal friction peak at approximately 125 °C and a low relaxation peak at approximately − 45 °C in the dynamic mechanical analysis cooling tan δ curve. The relaxation peak possessed an activation energy of 0.64 ± 0.03 eV and its damping capacity gradually decreased with the increase of thermal cycling. The NiMnTi SMA also had a good inherent internal friction with tan δ = 0.009 at approximately 140 °C and is a promising high damping alloy for high temperature applications.     

新型叠层结构瓦楞纸板设计及其动态性能研究

目的 设计一种新型叠层结构瓦楞纸板,解决传统瓦楞纸板耐反复冲击性能较差等问题,获得缓冲及防振性能提升的包装用新型瓦楞纸板。方法 首先设计新型纸板芯纸结构;其次设定新型纸板和传统纸板参数,并手工制作试样;最后对这2种纸板分别进行动态缓冲性能试验和随机振动试验,对比分析2种纸板性能。结果 动态缓冲性能对比试验表明,在不同跌落高度下新型纸板的缓冲性能优于传统纸板;在反复冲击条件下,新型纸板的累积缓冲性能亦优于传统纸板的。随机振动试验表明,新型纸板的减振区间为63.4～200 Hz,而传统纸板在5～200 Hz内无减振现象;新型纸板在40 Hz左右的振动传递率达到峰值4.2,传统纸板的固有频率为163 Hz,新型纸板在此频率下弹性模量相对较小;新型纸板用于公路、铁路运输包装设计时应避开40Hz的共振频率。结论 与传统纸板相比,新型纸板的动态缓冲性能及减振性能均有提升。     

基于主动阻尼的屈曲梁准零刚度隔振技术研究

准零刚度(QZS)隔振系统具有高静刚度-低动刚度的特性,能够对低频振动进行有效抑制,而主动阻尼能够显著降低系统的共振峰值同时保持系统高频传递特性不变。因此,将准零刚度隔振系统与主动阻尼相结合,可以有效提升系统的超低频隔振性能。以屈曲梁准零刚度隔振器为研究对象,基于系统动力学模型,引入主动阻尼控制策略,通过理论分析研究了主动阻尼对屈曲梁准零刚度隔振系统传递率的影响,并利用SIMULINK工具开展扫频、正弦和随机扰动条件下的屈曲梁准零刚度-主动阻尼隔振系统仿真研究。仿真结果表明:在超低频段(≤0.1 Hz)该系统能够产生8~32 dB的隔振效果;在高频段(≥10 Hz)隔振效率不低于36 dB,且对随机扰动响应的隔振效率为36 dB。     

阻尼板材在高架轨道箱梁结构噪声控制中的应用研究

为探讨高架桥梁结构噪声的控制措施,以京沪高铁32 m无砟轨道箱梁结构为原型,设计制作1/10的模型试验系统。通过将TD09型高性能阻尼板材分别敷设于箱梁翼缘板、腹板等位置,进行多工况的桥梁结构噪声降噪的模型试验研究。结果表明:高架轨道箱梁结构噪声峰值频段为200~1000 Hz,敷设阻尼板材在峰值频段内具有一定的降噪效果。阻尼板材对桥梁结构降噪效果与阻尼板材的敷设位置有关,其在桥梁结构噪声控制中有一定的应用价值。在峰值频率500 Hz处,翼缘板敷设阻尼板材对翼缘板下侧降噪效果最好,降噪约为1.6 dB(A);腹板敷设阻尼板对底板处的降噪效果最好,降噪可达3.8 dB(A);腹板及翼缘板同时敷设阻尼板材也对底板处的降噪效果最好,降噪可达3 dB(A)。