John David Young

A Multizone Technique for Billet Inspection

An ultrasonic inspection system has been developed in response to FAA recommendations for improved inspection of titanium billet [1]. This prototype system — called Multizone — has been transitioned to the factory floor and has inspected 1,000,000+ pounds of Ti billet in 1993–94. It is a real-time, PC based platform that employs custom built analog electronics using up to 8 parallel (non-multiplexed) channels, each with a remote pulser/receiver matched to the ultrasonic transducer. Scanned helically, the billet is divided into concentric zones with a focused transducer used to acquire peak detected C-Scan image data for each zone. The depth of each zone is established by the depth of focus of that transducer. C-Scan image data from all channels are displayed simultaneously on a 1024×1280 CRT and scroll as the inspection advances along the billet length. The data are written to optical storage upon completion of the inspection. The analog electronics are fully synchronous and could provide a baseline system for the acquisition of full waveforms. Custom post scan analysis software has been developed to detect flaws using signal to noise based algorithms. This software provides more reproducible results than conventional systems and greatly reduces operator fatigue and the chance for error. This paper will discuss the system architecture and operation. A companion paper in this volume discusses inspection results. [2]

Compound focus ultrasonic transducer

Improved focussing and increased bandwidth is obtained in a single-element ultrasonic transducer for non-destructive evaluation and material characterization applications. The piezoelectric ceramic element has a radius of curvature R1, and a combination lens and cover layer on its front surface has a radius of curvature R2 which is less than R1. The depth of field of the transducer is increased and the bandwidth improved; the total thickness of the lens may be selected to control bandwidth.

Recent Advances and Implementations of Flexible Eddy Current Probe Technology

GE has recently developed a family of flexible circuit eddy current sensors in an effort to provide our customers with cost effective solutions to the inspection of complexly shaped, metallic surfaces. The new family of eddy current sensors, comprised of single element and multi-element conformable probes, are lower cost derivatives of the multiple coil Eddy Current Array Probe (ECAP) previously developed by GE [1]. This paper discusses the major aspects of flexible circuit sensor optimization. These include consideration of eddy current coil orientation and geometry, operating frequency, and instrumentation.

Optimizing the Design of Multilayer Eddy Current Probes — A Theoretical and Experimental Study

General Electric developed a new eddy current probe technology in the early ‘90’s to address critical NDE needs in the aerospace industry. The technology utilizes lasers to trace out precise, multiple turn coils on a flexible substrate. The result is an eddy current probe that is capable of conforming to complex geometries and inspecting with a very high detection sensitivity. To cover large areas quickly, arrays of these coils were also fabricated and are currently in use with great success at GE inspection facilities. The newly developed probes, however, raised some unique questions and problems that needed to be addressed in order to determine the“best” probe configuration. In this paper we summarize these issues and through a combination of experimental and finite element results, we show how the design of the probe is“optimized” for various applications. Further details on the development of the technology are provided in a companion paper in these proceedings[1].

X-RADIATION ALIGNMENT OF QUARTZ CRYSTALS FOR IMPROVED HYPERSONIC PROPAGATION

The generation and detection of a large number of reverberating acoustic echoes in crystalline quartz at liquid‐hel um temperatures and at frequencies above 1 Gc/sec require and end‐face parallelism alignment less than 0.4 sec of arc for 3‐mm‐diam rods. Parallelism angles of this magnitude are beyond the present commercial capability of optical companies to process quartz rods. This paper describes an x‐radiation technique which induces a permanent bend in quartz crystals and, when applied in a specific azimuth direction, makes the end faces more nearly parallel. The acoustic response of quartz crystals at 10 Gc/sec and 4.2°K is used as an indicator of end‐face parallelism. Our experimental acoustic results show the effects of thermal annealing of quartz crystals, the effects of x radiation applied to the specimens in various directions, the effects of increasing dosage of x irradiation, and the effects of rotating the crystal while irradiating it with x rays. We have been able to improve the 10‐Gc/sec ac...

Eddy Current Arrays for Defect Detection

What was originally an inspection technique for large-scale defects has become an increasingly miniaturized method. Originally, the use of eddy currents for nondestructive evaluation was limited to gross defects in massive structures such as railroads and ship hulls; today, eddy current techniques are routinely used to detect sub-millimeter cracks. Unfortunately, the trend towards miniaturization creates a practical dilemma. To achieve greater resolution and sensitivity, eddy current probes must be made smaller. As probes become smaller, the amount of time needed to completely cover an inspection area escalates. As with other NDE modalities, one solution proposed to resolve the conflict between productivity and sensitivity is the use of eddy current arrays. An array of many elements could easily decrease the required inspection time by an order of magnitude without sacrificing the high-resolution capabilities of smaller probes. The advantages of array inspection are thus quite attractive, and interest is increasing. However, practical implementation of eddy current arrays requires careful attention to a number of details, including elementto-element uniformity, size versus sensitivity, and electrical interactions (crosstalk).

Eddy Current Probe Evaluation: Experimental Measurements and System Interaction

Eddy current testing is often considered an old and mature technology. However, the state of the art technology cannot meet the new stringent demands that the US Government has imposed on inspection of new aircraft engines under a program called ENSIP (engine structural integrity program). These demands require substantial improvements both in inspection sensitivity and speed — for instance, crack detection capability must improve by a factor of 3 over what is currently possible. In order to meet the new goals, all aspects of an eddy current inspection system must be addressed from probe selection and mechanical scanning noise to system electronics and signal processing. It has previously been shown [1,2] that imaging techniques provide improved flaw detection capability and also may be used to optimize system performance. This paper describes work that combines imaging with probe measurements to analyze eddy current probes and system performance from a practical point of view. Slightly different designs of a specific type of probe have been examined to evaluate differences in the designs and to determine how well the probe construction method is controlled. Parameters were calculated from electric measurements on the probes and plotted in an attempt to explain their significance and to provide a method for selection of probes with superior qualities. The probe/system interaction was also analyzed in order to learn why some probes with good electric properties did not perform well in the eddy current system. Finally, images were created and used to evaluate the impact of different imaging parameters on inspection performance.

Acoustic Microscopy: Materials Art and Materials Science

Significant progress has been made in acoustic microscopy and other forms of acoustic imaging over the last two decades. Originally introduced by Quate [1], this technology has been established by Weglin [2], Kino [3], Wickramasinghe [4], Bertoni [5], and Quate [6] as a powerful tool for materials characterization and development. The work described here [7] goes beyond that cited: it utilizes time-resolved acoustic signals of much greater bandwidth, and does not rely on V(z) behavior to form images. Instead only the digitized amplitudes of the spatially and temporally resolved acoustic signals are processed and displayed to form the images. Much of the progress reported here is also due to advances in computer display technology. Originally presented as posters, the included figures demonstrate various hardcopy and high-resolution raster displays incorporated in the described acoustic microscope. Keeping in mind the purpose for which each image was intended, it is instructive to compare the image quality that the different displays can produce. Six figures, containing twenty-nine separate images, make up the presentation. In their original display format, each figure was a 30 × 40 in. poster in which the individual images were displayed at the identical magnifications that were initially presented to the acoustic microscopist.