摘要:

Sensitivity of UT methods in materials such as coarse‐grained steels depends on attenuation and noise, due to scattering by microstructural heterogeneities. Here, existing UT simulation tools developed at CEA are modified to account for experimental observations of noise and attenuation. A model‐based inversion tool is developed to estimate from experiments the parameters to input into the forward models. Example of application is given, showing the quantitative importance of these phenomena in terms of performance demonstration. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570124

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We present a study performed to model and predict the ultrasonic response of alumina inclusions in steels. The Born and the extended quasistatic approximations have been applied and modified to improve their accuracy in the framework of this application. The modified Born approximation, allowing to deal with various inclusion shapes, have been selected to be implemented in the CIVA software. The model reliability has been evaluated by comparison with Ying and Truell’s exact analytical solution. In parallel, measurements have been carried out upon both natural and artificial alumina inclusions. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570125

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Reliable nondestructive evaluation of structural/machine components fabricated from polycrystalline materials require the knowledge of attenuation and dispersion of an ultrasonic wave propagating through such microscopically inhomogeneous medium. Expected propagation characteristics of ultrasonic waves in randomly oriented equiaxed grains are relatively well understood. But when the grains are elongated and/or preferentially oriented, the wave propagation constants exhibit anisotropic behavior. The authors have published a number of research articles on propagation of ultrasonic waves in materials with macroscopic texture and elongated grains. The present paper sheds more light on the effect of grain shape on the attenuation and dispersion of ultrasonic waves in polycrystals. Specifically, theoretical results are presented showing the effects of different grain aspect ratios. It is observed that for the same effective grain volume, grain elongation has smaller effect on attenuation. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570126

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A two‐dimensional scalar model has been established to study the scattering caused by an inhomogeneous medium with granular microstructure. Time domain signals are calculated using a 64‐node PC cluster. Special test problems are set up to compare the effects of single and multiple scattering and to quantify errors introduced by the Born approximation. Computed results for backscattered RMS grain noise results are compatible with recent experimental measurements. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570127

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

In papers given in previous years in this conference, a rigorous solution has been presented and experimentally verified for the 2‐D problem of an ultrasonic wave backscattered from a periodically rough surface. While predicting experiment very well, that theory has the limitation that it is very computationally intensive and that it only can be applied to the problem of planar interfaces. Practical applications, however, call for solutions that can be evaluated more rapidly and that can be generalized to the case in which the interface is curved. Such a theory is presented in this paper. The backscattering problem is formulated as a scattering process in which the strength of the scattering from individual ridges is viewed as an unknown. By summing over all scattering events and comparing to the rigorous solution, these unknown scattering strengths can be determined. In this paper, we present the theory, compare it to the rigorous solution, and use it to make numerical predictions for the effects of curvature on the backscattered noise. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570128

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The use of ultrasound for detecting material damage from microcracks within a heterogeneous medium is discussed. The ability to detect the damage is dependent on the amount of scattering due to the microcracks relative to the scattering from the heterogeneous background. The damage is modeled in terms of penny‐shaped microcracks that are assumed to be randomly oriented and uniformly distributed. Scattering from the heterogeneous microstructure is considered in terms of two types of media: polycrystalline and two‐phase. Expressions for attenuation and backscatter coefficient are derived using stochastic wave theory for both the assemblage of microcracks and for the microstructure. Incident longitudinal and shear waves are both considered. Wave speed changes are shown to be weak indicators of damage. However, attenuation and backscatter are shown to change sufficiently for damage detection. The scattering from the microcracks is assumed independent of the microstructural scattering. Thus, the results are thought to provide a lower bound on damage detectability. The results are applicable to detection of microcracking for various applications including thermal fatigue damage in concrete and mechanical fatigue damage in metals. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570129

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Reformulation of the elastodynamics problem as a system of first‐order partial differential equations is reviewed and preliminary results are presented for isotropic and anisotropic materials that suggest that the approach will extend in a reasonable way to analysis of more general materials. The propagating fields are expressed as a sum of characteristic propagation modes of an expanded acoustic matrix, which include the stress terms as well as the displacements. Boundary projection operators for the reflection and refraction coefficients are determined and the classic Frennel coefficients are recovered as particular examples within a general theory. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570130

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

This paper investigates the interaction of the SH0 elastic wave mode with discontinuities in plates and explains some of the physical phenomena involved in this interaction. The significance of the non‐propagating modes in the scattering from thickness steps and notches is examined. A method for predicting the reflection from notches using knowledge of the reflection from steps is proposed. The limits of validity of this procedure are also investigated. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570131

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A permanently attached guided wave array for the constant monitoring of defects in plate‐like structures is designed and a prototype built. Employing the first antisymmetric Lamb wave mode A0, the condition of large areas can be monitored from a single position of the device with minimum power consumption, necessary for long term operation independent of external power sources. The performance of the piezoelectric transducer elements used for the excitation and measurement of the A0mode is studied. Preliminary measurement results on an aluminum plate containing a model defect are presented. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570132

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Numerical simulations of laser‐generated guided elastic waves in two‐layer bonded plates are presented by modeling adhesive bond layer as a spring model. The transient waveform is expressed by the two‐layer normal mode expansion method (NME), and then the sensitivity of each mode and transient waveform on the stiffness coefficients characterizing cohesive quality are analyzed in details. This method provides a new promising way for the characterization of the cohesive quality in bonded plates. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570133

出版商:AIP    

年代:1903

数据来源: AIP