Showing papers in "Journal of Nondestructive Evaluation in 2005"

Measurement Models and Scattering Models for Predicting the Ultrasonic Pulse-Echo Response From Side-Drilled Holes

Abstract: A side-drilled hole (SDH) is a commonly used reference reflector in ultrasonic nondestructive evaluation. In this paper, we will develop reciprocity-based measurement models along with scattering models that allow us to predict the ultrasonic response from a SDH in a pulse-echo immersion setup. Two measurement models will be derived, one suitable for large SDHs where variations of the incident fields over the cross section area of the SDH are considered, and a second model which neglects those variations. Two scattering models are also used along with these measurement models. These include an explicit model based on the Kirchhoff approximation, as well as an exact model obtained using the separation of variables method. Examples of the model-based received waveforms and peak-to-peak voltage responses are presented for a number of SDHs of different sizes and compared with experimentally determined SDH responses.

Dynamic Piezoresistivity Calibration for Eddy Current Nondestructive Residual Stress Measurements

Abstract: It has been recently demonstrated [M. P. Blodgett and P. B. Nagy, J. Nondestruct. Eval. 23, 107 (2004)] that eddy current conductivity measurements can be exploited for near-surface residual stress assessment in surface-treated nickel-base superalloy components. To quantitatively assess the prevailing residual stress from eddy current conductivity measurements, the piezoresistivity coefficients of the material must be first determined using known external applied stresses. These calibration measurements are usually conducted on a reference specimen of the same material using cyclic uniaxial loads between 0.1 and 10Hz, which is fast enough to produce adiabatic conditions. Therefore, the question arises whether dynamic calibration measurements can be used or not for accurately assessing the sensitivity of the eddy current method for static residual stress. It is demonstrated in this paper that such dynamic calibration measurements should be corrected for the thermoelastic effect, which is always positive, i.e., it increases the conductivity in tension, when the material cools down, and reduces it in compression, when the material heats up. For low-conductivity titanium and nickel-base engine alloys the thermoelastic corrections are relatively modest at ≈5–10%, but for high-conductivity aluminum alloys the difference between the adiabatic and isothermal properties could be as high as 50%.

Limitation of Acoustic Emission for Identifying Seeded Defects in Gearboxes

Abstract: Acoustic Emissions (AE) is gaining ground as a Nonestructive Technique (NDT) for health diagnosis on rotating machinery. Vast opportunities exist for development of the AE technique on various forms of rotating machinery, including gearboxes. This paper reviews recent developments in application of AE to gear defect diagnosis. Furthermore, experimental results are presented that examine and explore the effectiveness of AE for gear defect diagnosis. It is concluded that application of AE to artificially seeded gear defect detection is fraught with difficulties, particularly for fault identification. In addition, the viability of the AE technique for gear defect detection by making observations from nonrotating components of a machine is called into question. Nevertheless, guidance is offered on applying the technique for monitoring the natural wear of gears.

Parametric Analysis of Acoustic Emission Signals for Evaluating Damage in Composites Using a PVDF Film Sensor

Abstract: With the increased utilization of advanced composites in strategic industries, the concept of Structural Health Monitoring (SHM) with its inherent advantages is gaining ground over the conventional methods of NDE and NDI. The most attractive feature of this concept is on-line evaluation using embedded sensors. Consequently, development of methodologies with identification of appropriate sensors such as PVDF films becomes the key for exploiting the new concept. And, of the methods used for on-line evaluation acoustic emission has been most effective. Thus, Acoustic Emission (AE) generated during static tensile loading of glass fiber reinforced plastic composites was monitored using a Polyvinylidene fluoride (PVDF) film sensor. The frequency response of the film sensor was obtained with pencil lead breakage tests to choose the appropriate band of operation. The specimen considered for the experiments were chosen to characterize the differences in the operation of the failure mechanisms through AE parametric analysis. The results of the investigations can be characterized using AE parameter indicating that a PVDF film sensor was effective as an AE sensor used in structural health monitoring on-line.

Automatic Detection of Annual Growth Units on Picea abies Logs Using Optical and X-Ray Techniques

Abstract: The aim of this study was to evaluate the number and location of annual growth units (GU) in Norway Spruce logs to have an information on the past growth of trees and thus a better knowledge of wood properties like density and knottiness. Two devices were used: an optical device which gives an accurate, description of the external log shape and a medical CT scanner which, in addition, gives information about the internal density of log. For each device, a specific method was developed to detect annual GU. The “optical method” was based on variations of the cross-section surface along the logs and the “X-ray method” on variations in the density profile. The optical method provided an accurate evaluation of the number of GU. The “X-ray method”, more sensitive to the presence of lammas shoots, generally overestimated the number of GU but provided a very good location of knotty areas inside the logs.

Investigation of Uncooled Microbolometer Focal Plane Array Infrared Camera for Quantitative Thermography

Abstract: Thermal nondestructive evaluation has shown promise as a potential NDE technology for next generation US Army rotorcraft structures because it is rapid, noncontacting, and able to inspect complex geometries. To successfully apply thermal inspection systems for field use, the cost and size must be lowered. The infrared camera is a major factor contributing to the overall cost of commercially available thermal inspection systems. Recent advances in uncooled microbolometer focal plane array detectors have resulted in low cost, small size/weight, and low power consumption cameras. These attributes make this technology well suited for portable low cost thermal inspection systems. The purpose of this paper is to investigate the capabilities of the new microbolometer infrared cameras for quantitative thermal nondestructive evaluation. Quantitative thermal diffusivity and thickness images are obtained by minimizing the squared difference between the data and a thermal model on samples with fabricated defects. Critical infrared camera features such as spatial and temperature resolution, detector response time, and detector stability are studied by comparing results to a conventional thermal imaging camera using a cooled InSb focal plane array detector. Finally several techniques are presented to improve the camera’s performance. These techniques include temporal background subtraction, use of a synchronized electronic shutter system, and cyclic flash heating.

Experimental Evaluation of Dynamic Test Methodologies for Assessing the Elastic Constants of Granitic Rocks

Abstract: Two dynamic test methodologies, the resonance method and the ultrasonic method, are used for assessing the elastic behaviour of granitic rocks. The experimental results obtained using two types of specimens: (i) rectangular beams (parallelepiped specimens); and (ii) cylindrical specimens (rod specimens); show that the resonance method used in this work is more adequate when both Young's modulus and Poisson's ratio are to be determined in these types of rocks. Moreover, it is demonstrated that test results obtained by resonance techniques are less dependent on specimen's geometry, size, and even surface roughness.

An NDE Methodology to Predict Density in Green-State Powder Metallurgy Compacts

Abstract: Extensive work at PMRC has established a clear correlation between green-state density and electric conductivity of P/M parts. By monitoring a static electric current flow through the pre-sintered P/M sample and recording the voltage response over its surface, sufficient information can be gathered to predict the density profile throughout the sample volume. In this paper, the formulation and implementation of a novel numerical forward and inverse formulation will be presented that is capable of relating DC voltage measurements to green-state density distributions. It will be shown that this methodology is applicable to both lubricated and lubricant-free compacts. We will present a general forward solution that enables the calculation of three-dimensional surface voltages for a given set of boundary conditions and a known conductivity/density distribution throughout the P/M sample. This formulation is particularly useful for the development of new sensors and measurement arrangements, since it permits the optimization of current injection patterns and voltage probe locations. Our novel inverse solution adjusts the conductivity/density profile so as to determine the conductivity distribution that matches most closely a given set of voltage data on the surface. Practical measurements with a range of green-state P/M samples will underscore the success and usefulness of this modeling approach.

Nondestructive Evaluation of Ceramic Candle Filter with Various Boundary Conditions

Abstract: Nondestructive evaluation (NDE) using a dynamic characterization technique was conducted to study ceramic candle filters Ceramic candle filters are hollow cylindrical structures made of porous ceramic materials used to protect gas turbine in coal-fired power plants Deterioration and failure of ceramic filters occurs after being exposed to high-temperature and high-pressure operational environment over a period of time This paper focuses on the development of an NDE method that can predict the in-situ structural stiffness of the candle filters while still being attached to the plenum A combination of laboratory testing, theoretical analysis, and finite element method (FEM) simulations are presented The candle filters were tested using a laser vibrometer/accelerometer setup with variable boundary restraints A variable end-restraint Timoshenko beam equation was derived to determine the dynamic response of the candle filters with simulated in-situ boundary conditions Results from the FEM simulation were verified with the analysis to determine the stiffness degradation of the candle filters as well as the boundary conditions Results from this study show that the vibration characteristics can be used effectively to evaluate both the structural stiffness and the in-situ boundary restraints of the ceramic candle filters during field inspections

Finite Element Evaluation of Acoustic Energy Penetration of Partially Submerged Tube Bundles

Abstract: In this paper, the finite element software ANSYS is used to model ultrasonic waves propagating through a liquid volume containing partially submerged tubes. An immersible transducer is used to generate the waves. The goal of the investigation is to find an appropriate excitation frequency in order to perform ultrasonic cleaning of the tubes. Modal analysis of the coupled tubes–liquid system is conducted to evaluate the dynamic behavior of the tube structures under ultrasonic wave excitations. The frequency at which the acoustic waves efficiently penetrate the tube array with least energy loss and least deformation to tube structures is obtained, and will be used to probe the capability and the potential of utilizing ultrasonic energy as a non-destructive technique for cleaning tube bundles.

Nondestructive Quality Assurance of Ceramic Filters Using Noncontact Dynamic Characterization

Abstract: Ceramic candle filters are stiff cylindrical structures arranged in rosettes in a hot gas vessel. Custom-made with strong composite materials, these filters are designed to withstand heating and cooling cycles of very high temperature gradients during coal energy production processes. To ensure consistency in the manufactured filters, noncontact dynamic characterization using laser vibrometry is proposed as a factory quality control technique. To evaluate the proposed technique, a sensitivity study using both contact and noncontact vibration measurements is first conducted. The shift in natural vibration frequencies is used as a quality indicator for likely manufacturing variables. Six candle filters are tested using dynamic impact tests. Contact and noncontact results are compared with theoretical natural frequency values, which show that laser results were “noisier” due to dropout from speckle noises. The results are used to establish the sensitivity of the technique, which indicates that dynamic characterization is a valid nondestructive testing technique for quality assurance of the ceramic filters, provided that the manufactured filters have a quality variation greater than 3.21%.

Dynamic Nondestructive Control of Electronic Component by Liquid Crystal

Abstract: The work presented in this paper describes an electrothermal bench based upon a liquid crystal sensor. Firstly, general characteristics of the bench are presented. A detailed attention is devoted to the problem of calibration and to the algorithm that permit the determination of the temperature. The validation of this bench has been realized by comparison with infrared microscope measurements. An example of the application is given for a hybrid electronic component. To finish we show that this nondestructive control has permitted us the detection of a design defect in the component.