Nondestructive Evaluation System Research Articles

Reconstruction of flaw geometry in ultrasonic non-destructive testing

A microcomputer-based ultrasonic non-destructive evaluation system capable of reproducing the shape of an unknown straight-edged planar flaw is described. The system utilizes the theory of replica pulses as well as a scanning procedure to define the coordinates of the flaw extremities. A software coordinate transformation package which allows the flaw image to be rotated about any axis has also been developed. Experimental results which illustrate the potential of the system for identification of flaw geometry are given.

Fiber optic sensing for ultrasonic NDE

An innovative approach to nondestructive evaluation (NDE) using noncontacting optical sensors has demonstrated. In this effort a single mode optical fiber interferometer (OFI) was used to sense the presence and form of Rayleigh waves traveling along the surface of a steel test bar at a velocity of nearly 3mm/µs. Acousto-optic time-domain data was successfully used to detect the presence and locate the position of a test “flaw” (a machined slot) in the bar, and spectrum analysis was used to estimate its geometry and size. This approach has many potential applications in the ultrasonic evaluation of real flaws in structures with complex geometries. Coupled with the authors' earlier work demonstrating the feasibility of generating acoustic waves in metals using laser light pulses transmitted through the fiber optic probes, this latest achievement points to the development of a fully noncontacting, fiber optic based thermal-acousto-photonic (TAP) NDE system, with potential applications to the reliability testing of many important structures where composition, scale, geometry, or restricted access preclude the use of conventional NDE techniques.

A New Method of Exciting Focused Surface Acoustic Waves Using an Interdigital Transducer

Methods of exciting and focusing surface acoustic waves on a sample material are described. In the field of nondestructive evaluation, it is beneficial to excite and focus a surface acoustic wave to detect small cracks on the sample surface. An interdigital transducer deposited on a piezoelectric substrate can excite surface acoustic waves on a sample surface making it useful as an acoustic wave source in a nondestructive evaluation system. In this paper, we describe a new method of exciting focused surface acoustic waves using a Fresnel-phase-plate type interdigital transducer with a gel couplant.

Fatigue reliability of gas turbine engine components under scheduledinspection maintenance

A probabilistic method is developed for the fatigue reliability analysis of gas turbine engine components under scheduled inspection maintenance in service. Various statistical uncertainties involved in the complex design system of gas turbine engine components have been taken into account, including the time to crack initiation, fatigue crack propagation, service loads, crack modeling, stress concentration factor, nondestructive evaluation (NDE) etc. It is demonstrated that the service inspection maintenance can be used to improve the reliability of fatigue-critical components significantly. Such an improvement in fatigue reliability is shown to depend on the capability of the NDE system employed. An example for the third stage turbine disk of TF33 jet engine has been worked out to demonstrate the application of the analysis methodology developed herein.

New Ultrasonic Standard Design Criteria

Abstract : The purpose of this effort was to identify, on solid theoretical grounds, an alternative approach, to the standardization and calibration of ultrasonic nondestructive evaluation (NDE)systems, which would overcome the limitations of the commonly employed flat bottom hole standards, and to design and fabricate a laboratory prototype device to demonstrate the alternative approach to NDI standards. After establishment of the performance criteria to be met by the alternative standard, an approach based on a software programmable electronic standard simulator was selected for the design and construction of the prototype demonstration device. The resulting device has the capability of assisting the user in: equipment checkout and calibration, set-up on reference standards and diagnosis of equipment malfunctions. The ultrasonic standard simulator may be used in either an automatic mode, to perform pre-programmed tests or in a manual mode to evaluate and/or calibrate either the ultrasonic electronic equipment on the entire inspection system including both electronics and transducers.

Analysis and design considerations for a real-time system for non-destructive evaluation in the nuclear industry

This paper studies the feasibility of implementing a real-time system for non-destructive evaluation of nuclear reactors based on the principles of synthetic aperture processing. A detailed analysis of the computational requirements and simulation and benchmarking work on several computers seems to suggest the design of a special purpose processor as the most viable solution to the problem. The paper concludes with a discussion of the parameters affecting field design and some preliminary design considerations of the overall system.