Measurement of pressure change of elastic moduli of materials constituting the earth's interior

将谐振法中的一种新的数据采集方法--傅里叶变换方法应用于实际，该方法将脉冲输入馈入样本，采集响应波形作为数字时间序列数据，并通过傅立叶变换获得频谱。结果表明，具有合适脉冲宽度的SiNx/x型脉冲产生了理想的光谱。对于带有样品-气腔容器组件的球形钢样，在氦气压力下，测量了特征频率的压力变化，最高可达100 Mpa。得到了0T4、1T1和0T5三个环向模式和1S2、1S3和1S4三个球面模式的频率导数*f/*P的数据。环状模式的*f/*P直接产生刚度的压力导数G_0‘=2.0(1)。为了使球状模式的*f/*P降低体积弹性模量K_0’的压力导数，将样品-气腔-容器系统视为球状三层结构，用DISPER80(Saito，1988)计算固有频率作为压力的函数，并求出不同的K_0‘值。将计算的*f/*P与实测值比较，得出K_0‘=8-9。这比K_0‘=4-5的值大一倍，K_0’=4-5是通过忽略球面模与测深之间的耦合而减小的。这一结果表明，在从球模的*f/*P约化K_0‘时，有必要将样品组件视为球面三层结构。通过已有的降低K_0‘的成果，建立了一种测量各向同性固体弹性模量压力导数的新方法--腔谐振法。测量了稀有气体和WC合金、腔容器的压力介质和材料在压力作用下的弹性性质，并将其用于球模的分析。

A new data acquisition method, FT method, in the resonance method was put into practical use, where impulse input is fed to the sample and the respondent wave form is acquired as digital time series data, and the spectrum is obtained as Fourie transform. It was found the sinx/x-type impulse with suitable pulse width yields desirable spectra.For a spherical sample of steel with the sample-gas-cavity container assembly, the pressure changes of eigenfrequencies were measured up to 100MPa under helium gas pressure. The data of pressure derivative of frequency, *f/*P,were obtained for three toroidal modes, 0T4,1T1 and 0T5, and three spheroidal modes, 1S2,1S3 and 1S4. The *f/*P's of toroidal modes yields immediately the pressure derivative of rigidity, G_0'=2.0 (1).In order to reduce the pressure derivative of bulk modulus K_0' from *f/*P of spheroidal modes, the sample-gas-cavity container system was regarded as a spherical three-layd structure, and the eigenfrequencies were computed as a function of pressure by means of DISPER80 (Saito, 1988), asuuming various values of K_0'. Comparing the computed *f/*P with the measured one, we have K_0'=8-9. This is twice as large as the value K_0'=4-5 which was reduced by neglecting the coupling between the spheroidal modes and the soundings. This result demonstrates that it is necessary to treat the sample assembly as a spherical three-layrd structure in the reduction of K_0'from *f/*P of spheroidal modes. Through the present achievement to reduce K_0', the cavity resonance method has been established as a new method to measure pressure derivatives of elastic moduli of isotropic solids.Elastic properties of rare gases and WC alloys, the pressure medium and the material of the cavity container, were measure under pressure and used in the present analysis of spheroidal modes.