Calculation of the effect of pressurizing gases on the resonant modes of single-crystal parallelepiped

Resonant ultrasound spectroscopy provides for an experimental determination of the elastic moduli of a solid sample. The moduli are extracted by matching a theoretically computed resonant spectrum to the experimental vibrational spectrum. To determine the pressure dependence of the moduli, the vibrational spectrum can be taken with the sample in a pressurizing gas. Then the extraction of the intrinsic, pressure dependent moduli requires a theoretical treatment which permits removal of the perturbation of the spectrum due to the surface loading by the pressure and shear waves in the gas. In order to illustrate a treatment which accomplishes this removal, the theoretically computed frequency shifts and the quality factors are reported for two single-crystal parallelepiped pressurized by noble gases.     

Sub-gigahertz laser resonant ultrasound spectroscopy for the evaluation of elastic properties of micrometric fibers

The cross-section eigenmodes of micrometric cylinders were measured in the range of several tens of MHz to about 0.5 GHz. The vibrations were excited using subnanosecond laser pulses. The cross-section eigenmodes were simulated using finite element modeling in a 2D geometry. Using the method of resonant ultrasound spectroscopy, the vibration spectrum of an aluminum wire of diameter 33μm served to determine Young’s modulus and Poisson’s ratio with a precision of 0.7% and 0.3%, respectively. The calculated and measured frequencies of cross-section eigenmodes were fitted with a precision better than 0.5% in the 50–500 MHz range.     

一种基于超声共振谱的低Q值材料共振频率提取方法

超声共振谱技术通过测量样本在超声激励下产生的固有共振频率来计算弹性参数,而共振频率的提取是整个测量过程的关键.低$Q$值(品质因数)材料由于其衰减特性,导致共振谱平缓并无法直观地从谱图上观察得到共振频率,为从中提取更为有效的共振频率, 本文提出了一种新的共振频率提取方法.采用经验模态分解法将材料频率响应自适应分解为有限个具有特殊振荡特性的固有模态函数分量,根据材料的超声共振谱先验信息选择具有共振频率特性的固有模态函数分量,并从中提取共振频率. 以短切纤维环氧树脂材料(仿骨材料, $Q \approx$25)为例, 通过实验与传统线性预测方法进行对比,计算弹性系数和工程模量. 实验结果表明新方法的计算效率高,对弱激发模态更为敏感,共振频率的匹配数量(26)多于传统方法(21)且满足5倍于弹性系数的估计要求,优化后的弹性模量更接近标准值.新方法可从低$Q$值材料平缓的频谱中提取数量足够且有效的共振频率,不仅有效提升了力学参数估计的可靠性,而且拓展了超声共振谱技术的应用范围.