Acousto-ultrasonic nondestructive evaluation of materials using laser beam generation and detection

The acousto-ultrasonic method has proven to be a most interesting technique for nondestructive evaluation of the mechanical properties of a variety of materials. Use of the technique or a modification thereof, has led to correlation of the associated stress wave factor with mechanical properties of both metals and composite materials. The method is applied to the nondestructive evaluation of selected fiber reinforced structural composites. For the first time, conventional piezoelectric transducers were replaced with laser beam ultrasonic generators and detectors. This modification permitted true non-contact acousto-ultrasonic measurements to be made, which yielded new information about the basic mechanisms involved as well as proved the feasibility of making such non-contact measurements on terrestrial and space structures and heat engine components. A state-of-the-art laser based acousto-ultrasonic system, incorporating a compact pulsed laser and a fiber-optic heterodyne interferometer, was delivered to the NASA Lewis Research Center

Optical Detection of Acoustic Emission Signals

Piezoelectric transducers, long used in the generation and detection of ultrasonic waves, have more recently been the detector of choice for acoustic emission signals. Optical probing methods, however, have several important advantages for acoustic emission studies: (1) they have an inherent broad frequency response, free from mechanical resonances, (2) they do not interfere with the acoustic waves. (3) since the focused optical beam diameters are typically only a few hundredths of a millimeter, optical methods can probe very close to a crack or a twin, (4) they can probe internally in transparent media, and (5) they can be used over a very wide temperature range. In this paper we compare the response of an optical probe with that of a commercial acoustic emission transducer. Since the optical probe permits absolute calibration, we can not only measure acoustic emission amplitudes, but also determine the quantitative response of the piezoelectric transducer to known acoustic disturbances of various kinds over a range of frequencies. We include measurements of real acoustic emission from twinning in two metals and stress corrosion cracking in steel

Determination and Monitoring of through Hole Diameters in Thin Plates Using Acoustic Diffraction

In this paper, we describe a method to monitor changes in the diameter of through holes in thin plates. The method has the potential for applications in the industry

Adaptive Control Allocation for Powered Descent Vehicles

The following work details a study into real-time failure adaptive control allocation method for powered descent vehicle systems. The motivation for this work is to enable future human and robotic missions utilizing a powered descent system to tolerate engine failures in flight without the loss of crew or assets. This study is conducted using a six degree-of-freedom trajectory simulation of a PDV (Powered Descent Vehicle) experiencing either a loss of thrust or an engine stuck full on failure scenario. Sequential least squares in the frequency domain is used on-board to process inertial measurement unit (IMU) data and generate an estimate of the PDV plant model, which is then fed to the guidance and control system. Data used by the sequential least squares method is generated from an in-flight maneuver. The work herein focuses on determining a maneuver that is least impactful to the PDV trajectory and enables a suitable plant model estimate. A 1.5-second-long maneuver with an amplitude of 5 percent throttle is determined to provide suitable data for the sequential least squares method to estimate a plant model. A PDV implementing this method can adapt to a single engine failure and continue to reach its touchdown conditions

White Beam Synchrotron X-Ray Topography of Gallium Arsenide

The defect structure of gallium arsenide is being examined using white beam transmission topography. The specimens under examination are cut-and-polished, three inch diameter, single crystal substrates from various suppliers in the “as received” condition. The goal of this continuing program is to first document the existence of various crystallographic defect structures and then to establish their effect on the performance of microwave integrated circuits subsequently fabricated on the wafers. Success in establishing such a correlation might permit the use of an x-ray diffraction measurement to screen incoming material, eliminating marginal substrates and achieving a corresponding increase in yield

Acousto-ultrasonic nondestructive evaluation of materials using laser beam generation and detection

Presented in viewgraph format, the possibility of using laser generation and detection of ultrasound to replace piezoelectric transducers for the acousto-ultrasonic technique is advanced. The advantages and disadvantages of laser acousto-ultrasonics are outlined. Laser acousto-ultrasonics complements standard piezoelectric acousto-ultrasonics and offers non-contact nondestructive evaluation

Reviews

Christianity and the Detective Story. Ed. Anya Morlan and Walter Raubicheck. Reviewed by Melody Green. The Shamanic Odyssey: Homer, Tolkien, and the Visionary Experience Robert Tindall with Susana Bustos. Foreword by John Perkins. Reviewed by Emily E. Auger. Gaining a Face: The Romanticism of C.S. Lewis. James Prothero and Donald T. Williams. Reviewed by Crystal Hurd. The A-Z of C.S. Lewis: An Encyclopedia of His Life, Thought and Writings. Colin Duriez. Reviewed by Andrew Stout. Under The Mercy: Charles Williams & The Holy Grail. Robert Peirano. Reviewed by Eric Rauscher. Tolkien and the Modernists: Literary Responses to the Dark New Days of the 20th Century. Theresa Freda Nicolay. Reviewed by Robert T. Tally Jr. Tolkien at Exeter College: How an Oxford undergraduate Created Middle-Earth. John Garth. Reviewed by Mike Foster Fastitocalon: Studies in Fantasticism Ancient to Modern. Editors in Chief Thomas Honegger and Fanfan Chen. Reviewed by Janet Brennan Croft. TOLKIEN Studies XI Editors: Michael D.C. Drout, Verlyn Flieger, and David Bratman. Reviewed by Janet Brennan Croft

Optical Propagation and Communication

Contains an introduction and reports on three research projects.Maryland Procurement Office Contract MDA 903-94-C6071Maryland Procurement Office Contract MDA 904-93-C4169U.S. Air Force - Office of Scientific Research Grant F49620-93-1-0604U.S. Air Force - Office of Scientific Research Grant F49620-96-1-0028U.S. Army Research Office Grant DAAHO4-95-1-0494U.S. Air Force - Office of Scientific Research Grant F49620-96-1-0126U.S. Army Research Office Grant DAAHO4-93-G-018

Optical Propagation and Communication

Contains an introduction and reports on three research projects.Maryland Procurement Office Contract MDA 903-94-C6071Maryland Procurement Office Contract MDA 904-93-C4169U.S. Air Force - Office of Scientific Research Grant F49620-93-1-0604U.S. Air Force - Office of Scientific Research Grant F49620-96-1-0028U.S. Army Research Office Grant DAAH04-95-1-0494U.S. Air Force - Office of Scientific Research Grant F49620-95-1-0505U.S. Air Force - Office of Scientific Research Grant F49620-96-1-0126U.S. Army Research Office Grant DAAH04-93-G-0399U.S. Army Research Office Grant DAAH04-93-G-018