Model-Based Characterization of Planar and Focused Immersion Ultrasonic Transducers

Advanced ultrasonic nondestructive evaluation techniques require well characterized transducers. This need may arise, for example, because modern, cost-efficient fabrication procedures necessitate high reliability inspection through non-planar surfaces and for which careful control of the beam pattern in needed. An example of this is the developing procedure for inspection of titanium billet material for subtle flaws, such as hard-alpha inclusions [1]. Large aperture, bicylindrical focusing transducers are being developed, and characterization procedures are also being formulated for that activity. Methods are required to relate design parameters, such as crystal and lens shape, to the ultrasonic fields that will be generated in the billet. Advanced signal processing methods, such as characterization of noise due to ultrasonic scattering from grains, require precise knowledge of probe characteristics, as well. For example, model-based approaches to calculating a grain scattering “figure of merit” [2] require the ability to deconvolve transducer effects from measured noise signals. Knowledge of transducer characteristics is also essential for the application of ultrasonic measurement models [3,4] to the prediction of flaw signal amplitudes as measured through curved component surfaces and in a variety of materials. This geometry and material transferrability issue is of great importance in new methods applied to designing for inspectability

Ultrasonic Sizing of Cracks in Web Geometries

Evaluation of the critical nature of interior cracks in turbine rotor component web regions in order to assess the remaining service life of the parts requires accurate determination of the crack sizes in order to perform fracture mechanics analysis. This analysis is important both in order to retire critically defective parts and in order to return components to service if detected flaws are sub-critical. The purpose of this paper is to evaluate several techniques for sizing internal cracks in planar geometries

Distance Amplitude Correction Factors for Immersion Ultrasonic Measurements through Curved Surfaces

Near net-shaped forgings offer significant advantages for component manufacture, including less material waste and reduced costs for machining to final shape. However, curved entry surfaces on near net shape forgings create complications for ultrasonic inspection methods. In immersion ultrasonic testing, entry surface curvature causes ultrasonic beam focusing or defocusing, which affects the detection sensitivity to interior material flaws, such as voids and inclusions, as compared to inspection through planar surfaces

Suppression of Classical and Quantum Radiation Pressure Noise via Electro-Optic Feedback

We present theoretical results that demonstrate a new technique to be used to improve the sensitivity of thermal noise measurements: intra-cavity intensity stabilisation. It is demonstrated that electro-optic feedback can be used to reduce intra-cavity intensity fluctuations, and the consequent radiation pressure fluctuations, by a factor of two below the quantum noise limit. We show that this is achievable in the presence of large classical intensity fluctuations on the incident laser beam. The benefits of this scheme are a consequence of the sub-Poissonian intensity statistics of the field inside a feedback loop, and the quantum non-demolition nature of radiation pressure noise as a readout system for the intra-cavity intensity fluctuations.Comment: 4 pages, 1 figur

Effects of System’s Limitations on the Accuracy of Measured Ultrasonic Correlated Signal

Within a highly attenuating material, it is often difficult to identify relevant target signals due to the system’s white noise that is elevated by high gains on a conventional ultrasonic system. Ultrasonic pulse compression technique resolves such problem. The ultrasonic pulse compression technique permits an ultrasonic system to operate with long transmitted pulses for an increased detection range, but without sacrificing the depth resolution by signal correlation. Moreover, the time integral involved in the cross-correlation further suppresses the system’s white noise, and hence it produces an improved signal-to-noise ratio (SNR)

Anisotropic Gauss-Hermite Beam Model Applied to through-Transmission Inspections of Delaminations in Composite Plates

Manufactured parts containing composite materials can present challenging ultrasonic inspection problems. The inherent anisotropy of such materials acts to distort propagating ultrasonic beams, leading in turn to an associated distortion of defect images. Such distortions complicate the task of estimating the physical dimensions of a defect from its ultrasonic image. In the present work we demonstrate how these difficulties can be overcome by appropriately modelling the ultrasonic inspection process, and using the model to analyze defect images. To illustrate the approach, we consider a normal incidence through-transmission inspection of a flat uniaxial composite plate with an internal delamination. We begin by reviewing our model of the inspection process which incorporates the Gauss-Hermite model for beam propagation in anisotropic materials. The inspection model requires as inputs certain parameters which characterize the transducers, and others which characterize the composite material. We demonstrate how these parameters can be obtained from simple beam-mapping experiments. We then present experimental C-scan images of a seeded circular delamination in a composite plate, and compare these to images predicted by the model. Finally, we demonstrate how the model can be used to accurately size a delamination from its ultrasonic image

Evaluation of Ultrasonic Beam Models for the Case fo a Piston Transducer Radiating Through A Liquid-Solid Interface

In order to accurately predict the performance of immersion ultrasonic inspection techniques, it is necessary to have a model for the transducer radiation process. This model should include the case of propagation of the ultrasonic beam at oblique incidence through liquid-solid interfaces of complex geometries. Included should be the effects of diffraction, refraction, focussing and aberrations upon the beam shape

A Model for the Ultrasonic Scattering from Multi-Branched Cracks

The ultrasonic detection (discrimination from geometrical reflectors) and sizing of intergranular stress corrosion cracks (IGSCC’s) is an essential element in the continued safe operation of nuclear power plants. Unfortunately, these ultrasonic tests are rendered difficult by the complex topography of the cracks, which may include multiple facets and branches which scatter ultrasound in a nearly independent fashion. Thus, the waveforms reflected from such flaws exhibit complex shapes which may not be related to the overall extent of the flaw in a simple fashion