Performance enhancement of wing-based piezoaeroelastic energy harvesting through freeplay nonlinearity

We investigate experimentally how controlled freeplay nonlinearity affects harvesting energy from a wing-based piezoaeroelastic energy harvesting system. This system consisits of a rigid airfoil which is supported by a nonlinear torsional spring (freeplay) in the pitch degree of freedom and a linear flexural spring in the plunge degree of freedom. By attaching a piezoelectric material (PSI-5A4E) to the plunge degree of freedom, we can convert aeroelastic vibrations to electrical energy. The focus of this study is placed on the effects of the freeplay nonlinearity gap on the behavior of the harvester in terms of cut-in speed and level of harvested power. Although the freeplay nonlinearity may result in subcritical Hopf bifurcations (catastrophic for real aircrafts), harvesting energy at low wind speeds is beneficial for designing piezoaeroelastic systems. It is demonstrated that increasing the freeplay nonlinearity gap can decrease the cut-in speed through a subcritical instability and gives the possibility to harvest energy at low wind speeds. The results also demonstrate that an optimum value of the load resistance exists, at which the level of the harvested power is maximized.     

偏置磁场对磁致伸缩纵向导波换能器效能的影响研究

为提高磁致伸缩导波换能器的激励效能,本文研究了磁场结构参数对偏置磁场空间分布的影响。基于COMSOL有限元仿真平台,对磁致伸缩换能器磁场分布特性进行了数值计算,研究了磁路结构形式、磁路和永磁铁数量等对偏置磁场分布的影响,最后优化出适合纵向导波激励的磁场结构参数。检测实验结果表明,随着偏置磁场磁路数量的增加,偏置磁场强度增大,磁场径向均匀性更好,磁致伸缩换能器的效能也相应提高;在相同磁路数量的条件下,永磁体数量的改变对换能器效能影响较小,四磁路偏置磁场最优;轭铁中部增加永磁铁后的磁路结构的偏置磁场的轴向均匀性更高,其激励效能更好。     

具有弱界面特性叠层压电球壳的自由振动

针对具有弱界面的叠层压电球壳自由振动,引入两个位移和应力函数,从三维压电弹性理论基本方程出发建立了分别对应于两类振动形式的独立状态方程,并通过球面谐函数展开技术以及近似层合模型将其化为关于径向坐标的常系数状态方程。采用弱界面模型建立状态向量的界面传递关系,与层内传递关系得到球壳内外状态变量的整体传递关系。最后考虑球壳内外边界自由条件, 得到了两类振动形式的频率方程。通过与已有精确解的比较验证了本文解的准确性,数值详细表明弱界面弹性柔性系数的大小对叠层球壳自振频率有较大影响,但弱界面导电性的高低对自振频率的影响不大。     

Improving performance of polymer solar cell by adjusting crystallinity and nanoscale phase separation

In this paper, we report a high-performance P3HT/PCBM bulk-heterojunction solar cell with a power conversion efficiency of 4.85% fabricated by adjusting polymer crystallinity and nanoscale phase separation using an ultrasonic irradiation mixing approach of the polymer. The results of grazing incidence X-ray diffraction, UV/Vis spectroscopic, and atomic force microscopic measurements of the P3HT/PCBM blend films reveal that the P3HT/PCBM film fabricated by ultrasonic irradiation mixing P3HT and PCBM solutions for 10 min has higher degree of crystallinity, higher absorption efficiency, and better phase separation, which altogether account for the higher charge transport properties and photovoltaic cell performance.     

Fatigue life assessment of a high strength steel 300 M in the gigacycle regime

The fatigue behavior of a high strength steel 300 M in the gigacycle regime was investigated. Fully reversed tension — compression fatigue tests at ambient temperature were performed using an ultrasonic fatigue system operating at 20 kHz. The staircase test method was employed to obtain accurate values of the mean fatigue strength corresponding to fixed numbers of cycles up to 10⁹. These results were compared to the curve which is estimated by the data tested in the mid-long life regime on conventional servo hydraulic test machine at 20 Hz. Results indicate that the fatigue strength determined from ultrasonic fatigue testing is lightly higher than conventional testing in the range of 10⁶–10⁷ cycles. It is obvious that nucleations of fractures tend to occur below the surface, if fractures happen after more than 10⁷ cycles. All the fractured specimens fails from internal SiO₂ inclusions or smaller carbides and carbide clusters.     

Current understanding of ultra-high cycle fatigue

The fatigue life of numerous aerospace, locomotive, automotive and biomedical structures may go beyond 10⁸ cycles. Determination of long life fatigue behavior becomes extremely important for better understanding and design of the components and structures. Initially, before the invention of ultrasonic fatigue testing, most of the engineering materials were supposed to exhibit fatigue life up to 10⁷ cycles or less. This paper reviews current understanding of some fundamental aspects on the development of accelerated fatigue testing method and its application in ultra-high cycle fatigue, crack initiation and growth mechanisms of internal fracture, S-N diagram, fatigue limit and life prediction, etc.     

Energy harvesting by two magnetopiezoelastic oscillators with mistuning

We examine an energy harvesting system of two magnetopiezoelastic oscillators coupled by electric circuit and driven by harmonic excitation. We focus on the effects of synchronization and escape from a single potential well. In the system with relative mistuning in the stiffness of the harvesting oscillators, we show the dependence of the voltage output for different excitation frequencies.     

4-羟基-3-(2-亚氨基乙基)-2H-苯并吡喃-2-酮类化合物的超声辐射合成

以乙醇为溶剂,4-羟基-3-乙酰基香豆素和胺为原料,对甲苯磺酸为催化剂,在超声波作用下合成一系列4-羟基-3-(2-亚氨基乙基)-2H-苯并吡喃-2-酮类化合物,产率62%~94%。 对产物进行了IR、1H NMR及HRMS表征,对化合物3c进行了X射线衍射分析。 该方法具有反应产率高、时间短、反应条件温和及操作简单等优点。     

氧化铁掺杂对PMnS-PZN-PZT压电陶瓷性能的影响

通过对晶体结构与压电、介电性能测试,探讨了Fe_2O_3掺杂对PMnS-PZN-PZT陶瓷压电性能的影响.结果表明,PMnS-PZN-PZT陶瓷结构位于三方、四方相共存的MPB区间,Fe_2O_3掺杂导致晶体三方、四方相结构含量发生变化.当Fe_2O_3掺杂含量为0.45 wt;时,晶体结构位于准同型相区间偏四方相结构的位置,压电与介电性能达到最佳:tanδ=0.12;,d_(33)=356 pC · N~(-1),k_p=0.60,Q_m=745,在230 ℃以下的温度范围具有很好的频率温度稳定性.