振动疲劳对压电悬臂板电激励响应的影响

针对压电智能结构的动力学设计,研究振动疲劳对双晶压电悬臂板电激励响应的影响。在电压激励下,测试压电悬臂板的自由端位移、致动层根部应变和传感层发电电压随振动循环次数的变化,分析激励电压幅值和电压波形对位移、应变及发电电压的影响,讨论位移响应、应变响应和发电电压响应随振动疲劳的变化情况。结果表明:在45~50 V的激励电压下,激励电压幅值越大,压电悬臂板的电致响应幅值下降越多,疲劳损伤速率越快;正弦波电压激励相较于三角波电压激励更容易导致振动疲劳;由于振动疲劳损伤的非线性,压电悬臂板疲劳损伤前后的位移?应变曲线斜率不再一致,而且疲劳损伤后共振时压电悬臂板根部应变降低。试验结果可为压电智能结构的动力学设计提供数据支撑。     

双激励压电悬臂梁的力电响应分析

压电能量收集器因其结构简单、能量密度高、不受电磁干扰、能够在较低的频率收集振动能等优点,在机械、电子和航空航天等领域具有良好的应用前景。针对提高压电振动能量收集器发电效率的动力学设计,旨在研究双激励环境下压电悬臂梁的力电响应特性。根据Euler-Bernoulli梁理论、压电材料本构关系以及克希霍夫定律,建立双激励压电悬臂梁的机电耦合动力学模型。在此基础上,应用Galerkin法与模态叠加原理推导压电悬臂梁的力电响应表达式,建立根部应变与输出电压的关系模型。测试不同参数下单/双激励压电悬臂梁的力电响应特性,验证理论推导的合理性。最后,分析相位对双激励下压电悬臂梁输出电压的影响。结果表明：压电悬臂梁在双激励下的应变幅频响应变化规律与电压响应规律基本吻合;双激励下压电悬臂梁的力电响应曲线均呈现先增大,在接近共振频率达到极值时减小的变化趋势;激励幅值的增大导致压电悬臂梁的刚度和共振频率降低,试验测得的压电悬臂梁最大频率降为1.5 Hz;调节2种激励信号的相位,会影响输出电压响应,而且在一个周期内呈先减小后增大的趋势。     

压电悬臂梁的力电响应及疲劳寿命分析

压电悬臂梁的力电响应与疲劳寿命是制约振动能量收集器深层次应用的关键。基于分布式参数建模方法,建立了压电悬臂梁的动力学模型,求解了压电悬臂梁的力电响应的解析解;借助有限元方法,开发了压电悬臂梁的仿真模型;通过实验验证了理论模型与有限元模型的准确性;应用仿真模型,分析了压电悬臂梁的几何尺寸、基体层厚度、陶瓷层厚度对力电响应的影响;基于估算的压电材料SN曲线,探讨了各参数对压电悬臂梁疲劳寿命的影响。结果表明：当宽度、基体层和陶瓷层厚度分别从16～24 mm、0.16～0.24 mm线性增加时,压电悬臂梁的疲劳寿命近乎呈现指数形式增加,而压电悬臂梁的长度由48 mm增加到56 mm,其疲劳寿命显著降低。     

并联结构d_(15)模式PZT-51悬臂梁的俘能性能

利用高剪切压电系数,设计并制作并联结构d15模式PZT-51悬臂梁装置,测量其在不同负载电阻下输出峰-峰值电压和输出功率随频率变化的关系以及不同负载电阻下共振瞬时输出电压和振动激励电压与输出峰-峰值电压关系。当频率为96 Hz、负载电阻为100 k?时,该PZT-51悬臂梁装置的输出峰-峰值电压最大值为1.96 V,输出功率达到最大为19.21μW。随着振动激励电压的增大,并联结构d15模式PZT-51悬臂梁装置的输出峰-峰值电压随之增大,并联结构d15模式PZT-51悬臂梁俘能特性的研究可为设计d15模式压电俘能器提供指导。     

辊轧机状态监测系统压电俘能自供电装置带宽自调整方法

研究了一种基于带宽自调整压电俘能供电的辊轧机状态监测装置,该装置能够根据不同的外界激励频率调整自身结构和改变自身固有频率,从而实现压电俘能装置在外界激励作用下发生共振。对该带宽自调整的压电俘能装置建立数学模型,并对其固有频率进行有限元仿真以及实验研究,通过理论研究分析了不同悬臂梁长度在不同外界激励作用下对压电俘能自供电装置的固有频率和发电电压的影响规律。研究结果表明:压电俘能装置的共振频率范围包含了设备工作时的主要振动频率范围,可以通过反复调节悬臂梁长度,使得供电装置的输出电压更加稳定。     

电压特性对压电纤维复合物驱动性能的影响

压电纤维复合物因机电响应速度快、驱动能力强和柔性佳成为智能材料领域的研究热点之一。压电纤维复合物作为驱动器时,在不同的应用领域对于驱动电压特性有不同的要求。本文通过自由应变和悬臂梁顶端位移研究压电纤维复合物在不同电压幅值、偏置、波形下的驱动应变性能。结果表明:随着驱动电压幅值增大,压电纤维复合物自由应变值和驱动性能随之增大。压电纤维复合物的横向和纵向自由应变分别随着电压偏置的增大而降低,相应的悬臂梁顶端位移量减小。当用方波驱动时压电纤维复合物的纵向自由应变值和横向自由应变值分别为2061.4×10~(-6)和574.9×10~(-6),顶端位移量为1.614mm,比正弦波和锯齿波的驱动值更大,其原因主要是电压的阶跃性导致瞬间施加在压电纤维上的电场强度较大。     

压电悬臂梁能量收集及减振研究

根据压电悬臂梁和悬臂梁-质量块振子的理论模型,针对船舶柴油机多振源、高频振动等特点,提出了一种集压电集能和减振降噪两种功能协调工作的多压电悬臂梁装置。运用COMSOL有限元分析软件建立了带质量块的多悬臂梁仿真模型。有限元仿真分析结果表明:压电悬臂梁结构振动频率接近柴油机固有频率时产生共振,振动由柴油机转移到悬臂梁装置,柴油机振动情况明显减少,压电片输出电压和功率分别为5. 88 V和3. 46 m W。压电悬臂梁减振降噪和压电能量收集实验得出:悬臂梁与振动源在频率18 Hz发生共振,振幅由19. 49 d B减少到2. 41 d B,压电片最大的输出电压约为5. 92V,集能效果和减振都较为明显。     

热超声键合压电换能器的动力学特性

基于有限元方法和试验测试,研究了芯片封装用压电超声换能器的动力学特忡。借助ANSYS压电耦合和非线性接触分析功能,对换能器自由和约束状态下的振动特性进行了分析。探讨了超声能量在空间域、时域和频域的传递规律。由模态分析得到换能器的振动形式,通过谐响应分析提取其在正弦电压激励下的振动信息,经瞬态分析获得换能器的瞬态响应。结果表明,螺栓径向尺寸和预紧力影响换能器的模态分布和动态特性,压电晶堆加载电压的频率影响超声能量传递特性。通过键合试验考察了焊点质量与螺栓径向尺寸的关系。分析和试验结果为换能器设计和键合工艺优化提供了指导。     

悬臂梁压电系统性能分析与应用研究

基于压电效应,设计了一种包含悬臂梁、压电片、磁铁和驱动马达的新型压电系统,通过对其发电性能的优化分析,将该系统应用于自行车警示灯装置中,并作为自主供电系统.首先利用ANSYS对压电悬臂梁进行结构应力和动力学分析,探讨尺寸变化对发电性能的影响,进一步利用圆盘的转动和磁力的作用使压电悬臂梁弯曲变形并增加其振幅,研究了磁铁不同间距、马达转速对输出电压的影响,并进行了电路分析实验.结果表明:将该压电系统装配在自行车上,车轮转速240 r/min,磁铁间距为15 mm时,可输出4.42 V电压,LED灯能保持稳定点亮状态,作为自行车夜间警示灯使用具有较好的效果.     

随机振动加载条件下铝合金加筋板的疲劳行为(英文)

基于基础激励对固支的3类铝合金加筋板进行振动测试。测试过程中采用应变片监测试样的动态响应。在应变历程的基础上用雨流计数法和Miner线性累积模型得到时域内加筋板的疲劳累积损伤。利用固有频率的改变,拟合用于预测板结构疲劳损伤的新模型,改进先前固有频率下降5%的失效判据。同时,还研究了筋条截面形状与筋间距对铝合金板振动疲劳行为的影响。结果表明,加装T型或L型截面的铆接筋条后铝板的疲劳寿命延长,对于筋条截面积大小相同的筋条,T型截面筋条的加筋板其疲劳寿命长于L型的。此外,振动疲劳寿命表现出对筋间距的敏感性。     

磁流变阻尼器动态响应分析

磁流变阻尼器的动态响应决定了其实时控制效果,为了增加磁流变阻尼器响应速度和减小响应时间,对其动态响应影响因素进行分析。针对某型号磁流变阻尼器,定义其响应时间的组成,建立时滞模型。建立了两级线圈同向串联、反向串联、同向并联、反向并联的电流及磁场响应模型,分析磁流变液两阶段的流变响应模型,得到反向串联与反向并联的电磁响应时间较小,且流变响应仅与间隙与动力黏度有关。并基于瞬态有限元磁场分析,从平均有效剪切屈服强度的角度来衡量阻尼器的动态响应过程,得到了不同磁路结构对阻尼器响应时间的影响及其影响原因。     

方坯连铸过程中结晶器内的热响应及振动响应

采用热电偶测温系统以及在线振动监测系统对方坯连铸机进行了长时间的在线监测,结果表明:结晶器内铸坯凝固状态与铜管温度场及振动状态存在一定的相关关系:结晶器铜管温度场的不稳定往往伴随着结晶器振动的不稳定;浇注初期坯壳凝固状态不稳定,温度波动大,振动偏摆大;拉速增大坯壳温度不均匀倾向增大,采用浸入式水口保护浇铸与敞开式油润滑浇注方式相比,结晶器换热效率更高,温度场更稳定。     

低合金超高强度钢研究进展

低合金超高强度钢是超高强度钢中最早开发钢种之一,因其强度高、冲击性能好、热加工性能好和生产成本低而受到广泛重视。本文回顾了该类钢的发展历程,介绍了国内外该类钢常见钢种,重点综述国内外关于该类钢在合金化、冶炼与轧制、热处理等方面对其静态响应方面的研究进展,并简单阐述了该类钢在高应变速率下的动态响应方面的研究。     

Dielectric response of carbon coated TiC nanocubes at 2-18 GHz frequencies

Microwave frequency (2-18 GHz) dielectric response has been investigated in the carbon-coated cubic TiC nanoparticles embedded in paraffin matrix with different weight fractions. DC conductivity measurements showed that the TiC nanocubes/paraffin composites have a percolation threshold of about 30 wt%. Absorption property was found to be improved with increasing mass ratio in the present system, up to a mass ratio of 50 wt%. Reflection loss exceeding −20 dB in the frequency range of 6-16 GHz, with layer thicknesses from 2 to 4 mm, was found in the 50 wt% loaded sample. TiC nanocube/paraffin composite with a proper mass ratio can be very good prospective microwave absorption agent.     

多层压电晶体型电——机械转换器动态特性研究

本文设计了多层压电晶体型电—机械转换器及其驱动电路，并对其进行了阶跃响应和频率响应特性的实验。     

Low-loss microwave dielectrics using rock salt oxide Li2MgTiO4

Rock-salt-structured Li₂MgTiO₄ ceramic was prepared by the conventional mixed oxide route and its microwave dielectric properties were investigated. The microstructures of the ceramics were characterized by SEM. The dielectric properties of the ceramics exhibited a significant dependence on the sintering condition and crystal structure. A new microwave dielectric material, Li₂MgTiO₄ sintered at 1360 °C has a dielectric constant (?_r) of ∼17.25, a Q × f of ∼97,300 GHz (where f = 9.86 GHz, is the resonant frequency) and a τ_f of ∼-27.2 ppm/°C. The microwave dielectric properties of the ceramic are reported for the first time.     

Low-firable high-K dielectric in the Zrx(Zn1/3Nb2/3)1−xTiO4 ceramic system

Composite ceramics in the solid solution of Zr_x(Zn_1/3Nb_2/3)_1−xTiO₄ (x = 0.1-0.4) have been prepared by the mixed oxide route. Formation of solid solution was confirmed by the X-ray diffraction patterns. The microwave dielectric properties, such as dielectric constant (?_r), Q × f value and temperature coefficient of resonant frequency (τ_f) have been investigated as a function of composition and sintering temperature. With x increasing from 0.1 to 0.4, the dielectric constant decreases from 70.9 to 43.2, and the τ_f decreases from 105 to 55 ppm/°C. The Q × f value, however, increases with increasing x value to a maximum 26,600 GHz (at 6 GHz) at x = 0.3, and then decreases thereafter. For low-loss microwave applications, a new microwave dielectric material Zr_0.3(Zn_1/3Nb_2/3)_0.7TiO₄, possessing a fine combination of microwave dielectric properties with a high ?_r of 51, a high Q × f of 26,600 GHz (at 6 GHz) and a τ_f of 70 ppm/°C, is suggested.     

The effect of non-stoichiometry on the microstructure and microwave dielectric properties of the Mg1+δTiO3+δ ceramics

The microwave dielectric properties and microstructure of Mg_1+δTiO_3+δ (−0.05 ≤ δ ≤ 0.05) ceramics prepared via the conventional solid-state route were investigated. A slight deviation from stoichiometry does not practically affect the relative permittivity and temperature coefficient of resonant frequency of the specimen. However, the Q × f value is very sensitive to the composition and it shows a non-linear variation corresponding to a relative amount of Mg. A very high Q × f can be achieved for specimen with single MgTiO₃ phase, which can be obtained within the compositional range −0.02 ≤ δ ≤ 0.02. In addition, a low Q × f measured for specimens at δ < −0.02 can be attributed to the presence of second phase MgTi₂O₅. An extremely high Q × f of ∼357,600 GHz (at 10 GHz) together with an ?_r of ∼18.3 and a τ_f of ∼−50 ppm/°C can be found for specimen using Mg_1.02TiO_3.02.     

Effect of CaTiO3 addition on microwave dielectric properties of Mg2(Ti0.95Sn0.05)O4 ceramics

The microwave dielectric properties of CaTiO₃-added Mg₂(Ti_0.95Sn_0.05)O₄ ceramics prepared by the mixed oxide route have been investigated. The combination of spinel-structured Mg₂(Ti_0.95Sn_0.05)O₄ and perovskite-structured CaTiO₃ forms a two-phase system (1 − x)Mg₂(Ti_0.95Sn_0.05)O₄-xCaTiO₃, which was confirmed by the XRD patterns and the EDX analysis and it also leads to a zero τ_f. The microwave dielectric properties of the ceramics can be effectively controlled by varying the x value. For practical applications, a new microwave dielectric material 0.91Mg₂(Ti_0.95Sn_0.05)O₄-0.09CaTiO₃ is suggested and it possesses a good combination of dielectric properties with an ?_r of ∼18.01, a Q × f of ∼92,000 GHz, and a τ_f of ∼0 ppm/°C, which makes it is a very promising candidate material for high frequency applications.     

High-dielectric-constant and low-loss microwave dielectric in the (1 − x)La(Mg0.5Ti0.5)O3-x(Ca0.8Sr0.2)TiO3 solid solution system

The microwave dielectric properties and microstructures of (1 − x)La(Mg_0.5Ti_0.5)O₃-x(Ca_0.8Sr_0.2)TiO₃ ceramics, prepared by a mixed oxide route, have been investigated. The forming of solid solutions was confirmed by the XRD patterns and the measured lattice parameters for all compositions. A near zero τ_f was achieved for samples with x = 0.5, although the dielectric properties varied with sintering temperature. The Q × f value of 0.5La(Mg_0.5Ti_0.5)O₃-0.5(Ca_0.8Sr_0.2)TiO₃ increased up to 1475 °C, after which it decreased. The decrease in dielectric properties was coincident with the onset of rapid grain growth. The optimum combination of microwave dielectric properties was achieved at 1475 °C for samples where x = 0.5 with a dielectric constant ?_r of 47.12, a Q × f value of 35,000 GHz (measured at 6.2 GHz) and a τ_f value of −4.7 ppm/°C.