Material grain noise analysis by using higher-order statistics

It is well recognized that the ultrasonic method is one of the most common and reliable nondestructive testing (NDT) methods for the quantitative estimation of defects in welded structures. However. NDT techniques applying for adhesively bonded joints have not been clearly established yet. In this paper. the detection of interface crack by the ultrasonic method was applied for the measurement of interfacial crack length in the adhesively bonded joints of double-cantilever beam (DCB). An optimal condition of transmission coefficients and experimental accuracy by the ultrasonic method in the adhesively bonded joints have been investigated and discussed. The experimental values are in good agreement with the computed results by boundary element method (BEM) and Ripling's equation.

Ultrasonic detection of interface crack in adhesively bonded dcb joints

In medicine, Ultrasound (US) is generally used for diagnostic purposes through Doppler and Ultrasonography exams. The former type of exam is mainly used, for example, to detect the causes of circulatory complications, such as stenosis. The latter type of exam, based on bidimensional images of biological tissues, provides informations like size and tissue structure of some organs. In this case, the diagnostic accuracy degrades if the image becomes corrupted by some artifact, that can be caused, for instance, by US reverberation — more than one reflection on the same interface (Fish, 1990). The possibility of identifying reverberating echoes may allow image corrections with a chance for improved diagnostic accuracy.

A Method to Identify Reverberation Echoes in Multilayered Homogeneous Media

We consider a simplified ultrasonic material model and obtain the theoretic third order cumulant. Assuming that the scattering distribution can be modeled with a random variable A/spl tilde//sub n/, we show the third order cumulants dependence on the probability density function of A/spl tilde//sub n/. Simulations of the model are also presented in order to validate it and to check the number of points needed in the estimation process.

Ultrasonic characterization of scattering media by higher order spectra: a cumulant derivation

: In this paper, the compensation of ultrasonic scattering on interface crack depending on thickness variations of Al/Epoxy bonded dissimilar components was applied to improve measuring accuracy by using ultrasonic attenuation coefficient. The optimum conditions of theoretical value and experimental measuring accuracy by the ultrasonic method in Al/Epoxy bonded dissimilar components have been investigated. From the experimental results, the measurement method of interfacial crack lengths by using ultrasonic attenuation coefficient was proposed and discussed. After the ultrasonic scattering compensation depending on thickness variations of bonded dissimilar components was carried out, the measuring accuracy of interfacial crack length was improved by 5%. Key words : Bonded dissimilar components(이종 접합부재), Double-cantilever beam(이중 외팔보), Interface crack(계면균열), Transmission coefficient(통과율), Ultrasonic attenuation coefficient(초음파 감쇠계수), Ultrasonic scatter(초음파 산란), Ultrasonic test(초음파 탐상)

Measurement of Interfacial Crack Length by Ultrasonic Scattering Compensation Depending on Thickness Variations of Bonded Dissimilar Components

The ultrasonic nondestructive characterization of heterogeneous media is difficult due to their inherent inhomogeneity. Using high‐frequency ultrasonic waves, one gets very high spatial resolutions, and the characterization of heterogeneous materials appears then feasible. However, the echographic signal processing involves a new approach, different from the classical deterministic one. Due to the random nature of the scatterers distribution, a stochastic model allows the determination of the structural parameters, like the spacings between heterogeneities (mean value and probability density function). An identification process is used to define the most convenient values for the mathematical parameters involved in the probabilistic scatterers distribution law and enables one to deduce the local concentration of scatterers. The theoretical models have been confirmed through measurements on synthetic inhomogeneous media and on two different kinds of composite materials: Metal matrix composites and carbon e...

Z. Derouiche

Papers

Ultrasonic characterization of heterogeneous materials using a stochastic approach