Improved ultrasonic spectroscopy methods for characterization of dispersive materials

Transmission ultrasonic spectroscopy method has been successfully implemented for the characterization of piezoceramics at high frequencies. There are, however, still some intrinsic error sources that limit the accuracy of the method. In this paper, two improved ultrasonic spectroscopy methods are presented, which can reduce the number of pre-required parameters and reduce another error source. The two improved methods were used to measure the frequency dispersion of phase velocity and attenuation of doped piezoceramic lead zirconate titanate (PZT-5A); results were compared with those obtained from the conventional method. The advantages and limitations of each method are discussed     

Demodulation of Fiber-Optic Sensors for Frequency Response Measurement

The neural-network-based processing of extrinsic Fabry-Perot interferometric (EFPI) strain sensors was investigated for the special case of sinusoidal strain. The application area is modal or cyclic testing of structures in which the frequency response to periodic actuation must be demodulated. The nonlinear modulation characteristic of EFPI sensors produces well-defined harmonics of the actuation frequency. Relationships between peak strain and harmonic content were analyzed theoretically. A two-stage demodulator was implemented with a Fourier series neural network to separate the harmonic components of an EFPI signal and a backpropagation neural network to predict the peak-to-peak strain from the harmonics. The system performance was tested using theoretical and experimental data. The error for high-strain cases was less than about 10% if at least 12 harmonics were used. The frequency response of an instrumented cantilever beam provided the experimental data. The demodulator processing closely matched the actual strain levels     

光弹调制式反射差分光谱仪的理论分析

反射差分光谱仪是一种测量灵敏度和精度较高的研究表面／界面的新型分析仪器，但微弱的反射差分信号易受到各种噪声的干扰．作者利用Jones表示法，对光弹调制式反射差分光谱仪构建了包含器件自身缺陷和安装误差的数学模型，通过确立误差源与测量结果的联系，分析出各误差源对测量结果的影响，特别是起偏器、光弹调制器和样品的安装误差以及位相调制误差，这些系统误差经过标定可得到补偿．     

Velocity bias and fluctuation in the standard dual beam Doppler reconstruction algorithm

Bias and fluctuation of the standard velocity reconstruction algorithm for dual beam vector Doppler velocity estimation systems are analyzed; both magnitude and angle properties are considered. Bias can arise from any of the error sources known to affect single beam systems in addition to both translation and angle misregistration between the two sample volumes; standard deviation is the result of random temporal fluctuations in Doppler frequency estimates in each beam. Approximate closed-form expressions for both biases and standard deviations of the velocity estimates are derived, and the performance of a typical practical dual beam system is discussed as an illustration of the theory.     

一般阵列误差情况下信号二维方向角和多普勒频率的联合估计

针对平面阵列，推导出基于一般阵列误差模型的信号时空DOA矩阵，采用总体最小二乘法（TLS）估计出多个信号的方位角。俯仰角和多普勒频率，解决了大多数估计算法的性能因阵列误差而严重下降和“频率兼并”问题。此算法对噪声不敏感，不需进行谱峰搜索，仿真结果表明了此算法的有效性。     

半主动变刚度TLCD减振控制的研究

为改进被动式调频TLCD的减振特性,提出了半主动变刚度TLCD减振系统,基本原理是将调频TLCD的弹簧设置成可调谐状态,在振动过程中,根据减振系统的需要适时调整调频弹簧的开关状态。减振系统的刚度由两部分组成,一部分是液体振动的恢复力,另一部分由变刚度装置的弹簧提供。由Lagrange方程建立起半主动变刚度TLCD的运动方程,以一个单自由度结构体系为算例,分析了可变刚度对系统控制性能的影响。外荷载频率与结构的频率比取不同值,比较了被动TLCD、半主动变阻尼TLCD和半主动变刚度TLCD的减振频带。考虑TLCD的频率和结构的实际频率之间存在一定的误差时,研究了半主动变刚度TLCD的减振性能。最后,通过一个五层结构的算例,分别在谐波和地震波作用下,验证了半主动变刚度TLCD对多自由度结构体系的减振特性。研究结果表明,半主动变刚度TLCD具有更宽的减振频带,在TLCD的频率和结构振动的频率存在误差时,仍能保持较好的减振效果。     

The density deficit in stretching shaped charge jets

A thorough review of the pertinent literature supports the conclusion that there is an unexplained density deficit of at least 6.5%, in the stretching, unparticulated shaped charge jet, after all known sources of error are evaluated and all contributing factors (e.g. heating due to plastic work) are considered. It is suggested that a “vacancy avalanche” mechanism, which is operating only during the highest strain — rate interval, preceding particulation, can generate the high transient vacancy concentrations, required to explain the observed density deficit.     

Experimental errors in the application of photoelastic coatings on human femurs with uncemented hip stems

The investigation of the stress distribution in the proximal femur is of primary relevance when testing hip prostheses. Most of the in-vitro research to date, has been conducted with strain gauges. However, the photoelastic coatings provide a field vision of the state of strain and of the most stressed points. The purpose of this work was to validate the application of photoelastic coatings to intact and implanted human femurs. Coatings of various thickness were bonded to two regions: the surface of the diaphysis, and the resection surface of the neck. A theoretical study was conducted on a geometrical model of the diaphysis to quantify some of the experimental errors. The reinforcing effect was found to be far the most important source of error for the coating of the diaphysis. Other possible sources of error such as Poisson's coefficient mismatch, incorrect light incidence angle and uneven coating thickness were also examined. Due to the uneven distribution of such errors, any correction seems impossible. The results must therefore be considered only qualitatively, as a complement to the strain gauging. The coating of the resection surface of the neck of the femur suffers much less from the reinforcing effect, but the coating is more sensitive to Poisson's coefficient mismatch. In this second application, quantitative results can be satisfactorily obtained.     

Cyclic stress–strain response and crystal plasticity finite element analysis of AISI 9310 steel in biaxial fatigue loading

There are still many gaps in the research on the multiaxial fatigue failure mechanism of the gear shaft. In this paper, cyclic stress–strain response and biaxial fatigue damage characteristics of gear steel AISI 9310 were investigated. The specimens showed obvious cyclic softening characteristics at all phase angles, and the softening rate was directly associated with the initiation and propagation of cracks. The fractographies at different phase angles revealed that the specimens under out-of-phase loading suffered fatigue failure caused by a single crack source on the surface, while the fatigue crack under in-phase loading was gathered together by the propagation of different crack sources. Finally, the established crystal plastic finite element model showed a good prediction of the plastic strain energy density at different phase angles, and the maximum error was 13.03%. Furthermore, a biaxial fatigue life prediction method was proposed, with a maximum error of 39.5%.     

Bounds on frequency response estimates derived from uncertain stepresponse data

The frequency response of a system can be estimated from measurements of its step response; however, many error sources affect the accuracy of such estimates. This paper investigates the effects of uncertainty in the knowledge of the step response. Methods for establishing uncertainty bounds for the frequency response estimates are developed, based on the corresponding time-domain uncertainties associated with the measured step response. Two methods are described. One method produces bounds that are often very conservative. The other method produces bounds that are more realistic. End effects that influence the bounds are also considered. A simulation example and an application of the bounds are presented