Ultrasonic NDE Techniques Research Articles

Nondestructive Evaluation of Austenitic Stainless Steel Welds

The paper presents advanced ultrasonic and eddy current NDE techniques developed in the authors laboratory for nondestructive evaluation of austenitic stainless steel welds. The paper discusses the performance and comparison of 2D discrete wavelet transform (DWT) and de-noising methods applied on eddy current images obtained from stainless steel weld pad with machined longitudinal notches and a systematic approach for eddy current defect characterisation in weld pads by neural network. The simulation and experimental results on the effect of elastic anisotropy on ultrasonic phased array inspection in austenitic stainless steel weld are also discussed. A guided wave based ultrasonic method developed for detection of defects in stainless steel welds and its validation with complimentary techniques such as radiography and in-situ metallography are also presented.

Influence of stresses on grain size and attenuation parameters in ultrasonic scattering models

Recent findings have shown the dependence of material stresses on the strength of ultrasonic backscatter. The stress dependence arrives when considering the covariance of effective elastic moduli of a medium with a randomly oriented grain structure. In some instances, the change in magnitude of the scattered response due to stress is significant and can be utilized as a technique for NDT stress monitoring. Conversely, ignoring the stress sate could result in significant error when attempting to extract micrsotructural parameters using ultrasonic NDE techniques. This presentation touches on the error generated in estimating the average grain size when using ultrasonic scattering models which include stress dependent backscatter coefficients. Results are given for three scattering modes; longitudinal to longitudinal, shear to shear, and (mode converted) longitudinal to shear under a variety of loading configurations. Furthermore, the stress dependence in the covariance influences common multiple echo attenuation measurements when grain scattering is present. Theoretical attenuation values of the different modes are given for various stress-states. Understanding how stress influences these parameters can potentially improve existing ultrasonic NDT techniques. [Research supported by the Federal Railroad Administration.]

Nondestructive sizing and localization of internal microcracks in fatigue samples

A large number of fatigue experiments on standardized samples is required for the development of databases of the fatigue properties of specific material systems. To facilitate such studies, different visual monitoring methods for surface fatigue cracks have been used; however, the problem of monitoring internal fatigue crack initiating during cold dwell fatigue of Ti is much more complicated. This paper describes the development and integration of several nondestructive evaluation methods for monitoring and sizing microcracks in titanium fatigue samples. For in situ monitoring of crack initiation and evolution ultrasonic Lamb wave signals are excited and acquired in the sample continuously during fatigue tests at different levels of fatigue load using a high-speed data acquisition system. Localization of the secondary cracks is done by both the in situ ultrasonic method and an ultrasonic immersion scanning method here referred to as “vertical C-scan” (VC-scan). The VC-scan is developed for imaging small cracks aligned normal to the fatigue sample axis. Microradiography has been performed on fatigue samples to confirm the localization and sizing of the detected cracks with other ultrasonic NDE techniques. The fusion of data from different NDE techniques provides useful information on the initiation, location, shape, size and growth history of fatigue cracks.

Porosity estimation of concrete by ultrasonic NDE

The increasing number of concrete structures with symptoms of premature deterioration due to environmental action demands procedures to estimate the durability of this type of component. Concrete durability is related to porosity, which determines the intensity of interactions of the material with aggressive agents. The pores and capillaries inside the structure facilitate the destructive processes that generally begin in the surface. In this work, an ultrasonic NDE technique to estimate the porosity of concrete is developed. The method is based on the analysis of the mechanical behaviour of mortar probes built with calibrated sand, in which the concentration of water–cement mixture has been varied. In this sense, data of sound velocity are correlated with data of porosity, which have been previously measured by destructive measurements.

Nondestructive evaluation of BWR internal attachment welds : Anon Electric Power Research, Institute, Palo Alto, California (United States), TR-101760, 56pp. (Dec. 1992)

Some BWR RPV internal components are attached with welds that contain Inconel 182 and may be susceptible to IGSCC. Through fabrication and examination of attachment weld mockups, ultrasonic and eddy current NDE techniques were developed to detect and characterize cracking if it occurs. Crack detection reliability was high for both methods. Crack depths were measured ultrasonically within 0.03 inch of their intended fabrication depths. Position of the pad/base metal interface was measured within 0.01 inch of its true position, so that base metal penetration by the cracking can be assessed with only a 0.04-inch-wide band of uncertainty. Further work will use mockups with less optimized geometry and surface conditions.

Matrix techniques for modeling ultrasonic waves in multilayered media

Research into ultrasonic NDE techniques for the inspection of multilayered structures relies strongly on the use of modeling tools which calculate dispersion curves and reflection and transmission spectra. These predictions are essential to enable the best inspection strategies to be identified and their sensitivities to be evaluated. General purpose multilayer modeling tools may be developed from a number of matrix formulations which have evolved in the latter half of this century and there is now a formidable number of publications on the subject. This paper presents a review of the main developments of the matrix techniques, and their use in response and modal models, with emphasis on ultrasonics applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Ultrasonic NDE of 3-D textile composites

Three-dimensional (3-D) textile composites provide a unique challenge to current ultrasonic NDE techniques. In 3-D textile composites, through-the-thickness stitching or tows provide reinforcement against delamination, which is common cause of failure in traditional aligned fiber laminates. However, standard nondestructive techniques for quality control and inspection are made less effective by the complex scattering created by the multidirectional fiber architecture. Although no single method will be suitable for detecting all potential defects and damage, the extent to which any given method is applicable is still relatively unexplored. The present research investigates the benefits of using plane waves to detect defects near the through-thickness reinforcements. Preliminary results will be presented on the effect of various structural parameters (e.g., interlaminar spacing, interlacing density, tow size, etc...) on the ultrasonic signal response.

A new technique for time-domain ultrasonic NDE of thin plates

A new time-domain ultrasonic NDE technique is reported in this paper for the measurement of the thickness (given the wavespeed) or wavespeed (given the thickness) of thin plates; by thin we mean the thickness is less than the wavelength. By introducing a retrieve function the incident field can be reconstructed from the transmitted (reflected) field by a two-term (three-term) summation. A systematic sensitivity analysis of this technique has been carried out. The new technique has been used to measure the thickness or the wavespeed of aluminum plates with thickness ranging from 0.089 to 6.426 mm using (low frequency) 1-MHz transducers: 0.014≤(thickness/wavelength)≤1.0. The measurement error was found to be about 1% for thickness and 3% for the wavespeed.

Dark-field magneto-elastic nondestructive testing technique

In the field of nondestructive testing, great advantages can be obtained if a dark-field technique can be achieved. A magneto-elastic technique generating sound waves only on the presence of a defect and from the defect is described (no defect—no sound waves in the material under test). The magneto-elastic technique generates three-dimensional information about the defect location, dimensions, and characteristics, unlike conventional ultrasonic NDE techniques where the defect is used as a scatterer of incident ultrasonic waves. Eddy currents are generated in the material under test with a current carrying conductor. A magnet is placed such that its magnetic field is parallel to the current carrying conductor. Elastic waves are generated in the conductive material under test only at the crack edges from the interaction of the magnet with transverse eddy currents flowing around the defect. The generated elastic waves are detected with an ultrasonic receiver transducer coupled to the material. An array of receivers may be used to triangulate on the defect and also to characterize the properties of the defect from the 3-D information. Conventional EMAT (electromagnetic acoustic transducers) are used to generate elastic waves in the materials even when no defects are present; the magneto-elastic technique depends on the presence of a defect to create the elastic waves. Preliminary experimental results are presented together with other potential application of the new concept.