Joseph Heyman

Most ultrasonic measurements of materials involve the generation of an acoustic wave and the propagation of that wave from a transducer through a coupling medium to a specimen under test. After interacting with the specimen, the wave propagates through the coupling medium to a receiving transducer and is converted to an electrical signal. The information presented to the observer by the electrical signal depends on each element of the system. In this paper, the role that the receiving transducer plays in ultrasonic measurements is examined. The phase-sensitive nature of conventional receiving transducers has, for the most part, been neglected in nondestructive evaluations. This is shown to lead to significant data misinterpretation. A new acoustoelectric transducer (AET) has been developed which is phase insensitive. Comparative data obtained with both conventional and AET transducers are presented and discussed. The AET is shown to produce more accurate measurements for the cases investigated.

Early fatigue damage in non-unidirectional multi-ply graphite/epoxy composites is manifested by a distribution of cracks and disbonds through the bulk of the material. Such damage is subtle and is difficult to detect with conventional ultrasonic technology. Consequently, a new ultrasonic measurement technique called phase-insensitive tone-burst spectroscopy has been developed. The new technique eliminates problems associated with phase cancellation and pulse shape artifacts inherent to conventional broadband ultrasonic spectral measurement systems and produces clean spectral information irrespective of specimen inhomogeneity or irregularities in surface geometry. Application of the new technique to measurements of graphite/epoxy composites has yielded frequency-domain profiles that show distinct differences in ultrasonic attenuation, attenuation slope, and velocity for each specimen experiencing a different level of fatigue damage.

Fiber optic sensors provide the opportunity for fabricating materials with internal sensors which can serve as lifetime health monitors, analogous to a central nervous system. The embedded fiber optic sensors can be interrogated by various techniques to measure internal strain, temperature, pressure, acoustic waves and other parameters indicative of structural integrity. Experiments have been conducted with composite samples with embedded sensors to measure strain using optical time domain reflectometry, modal interference and an optical phase locked loop. Fiber optic sensors have been developed to detect acoustic emission and impact damage and have been demonstrated for cure monitoring. These sensors have the potential for lifetime monitoring of structural properties, providing real time nondestructive evaluation.

A remote radiometric technique for making quantitative thermal diffusivity measurements is described. The technique was designed to make assessments of the structural integrity of large composite parts, such as wings, and can be performed at field sites. In the measurement technique, a CO2 laser beam is scanned using two orthogonal servo-controlled deflecting mirrors. An infrared imager, whose scanning mirrors oscillate in the vertical and the horizontal directions, is used as the detector. The analysis technique used to extract the diffusivity from these images is based on a thin infinite plate assumption, which requires waiting a given period of time for the temperature to equilibrate throughout the thickness of the sample. The technique is shown to be accurate to within two percent for values of the order of those for composite diffusivities, and to be insensitive to convection losses.

This paper describes the research activities of the NASA Airframe Structural Integrity Program for the aging commercial transport fleet. Advanced analysis methods are under development to predict the fatigue crack growth in complex built-up shell structures. Innovative nondestructive examination technologies are under development to provide large area inspection capability to detect corrosion, disbonds, and fatigue cracks. The ultimate goal of this interdisciplinary program is to develop and transfer advanced technology to the airline operators and airframe manufacturers. The program is being conducted cooperatively with the FAA and the U.S. industry.

... J. Companion, PRC Kentron, Hampton VA.: Joseph S . Heyman and T. Blalock, NASA Langley Research Center, Hampton, VA.; A. Cavalier and B. Mineo, ARCUS, National Hdqts., Arlington, Tx; F. Mien and L. Fox, Med. College of VA.. Richmond, VA. Abstract ...

Abstract A potentially useful new technique for residual stress characterization in ferromagnetic material is described. The unique feature of this technique is the measurement of small changes in ultrasonic wave velocity by the application of external DC magnetic field in the material under various stress conditions. It was found, in steel, that the fractional change in the natural velocity δW/W of waves propagating along the external field direction is affected by the uniaxial stress applied in the same axis. External compression lowers the slope of the δW/W curve in the low field region, while external tension generally does the opposite. For most cases, the slope in this region falls below zero under external compression. The result of measurements in specimens with residual stress shows exactly the same tendency.

External DC magnetic field induced changes in natural velocity of Rayleigh surface waves have been measured in steels under various stress conditions. Curves representing t he fractional changes in ultrasonic natural v elocity propagating along the external field direction show distinct slopes under uniaxial stress applied in the same axis. The simultaneous measurements of magnetic induction confirm that the stress effect on the natural v elocity curve is dominant in the domain wall motion region. The initial slopes of curves under compression, exceeding about one third of the yield stress, fall below zero in all the steel specimens with different carbon contents. The slopes under tension vary among different steels but remain positive under all conditions. R esults of measurements with residual stress show exactly the same tendency. A physical interpretation of these phenomena is given based on the stressinduced ferromagnetic domain structure change and the AE-effect.

Achieving accurate preload in threaded fasteners is an important and often critical problem which is encountered in nearly all sectors of government and industry. Conventional tensioning methods which rely on torque carry with them the disadvantage of requiring constant friction in the fastener in order to accurately correlate torque to preload. Since most of the applied torque typically overcomes friction rather than tensioning the fastener, small variations in friction can cause large variations in preload. An instrument called a pulsed phase locked loop interferometer, which was recently developed at NASA Langley, has found widespread use for measurement of stress as well as material properties. When used to measure bolt preload, this system detects changes in the fastener length and sound velocity which are independent of friction. The system is therefore capable of accurately establishing the correct change in bolt tension. This high resolution instrument has been used for prec...

High-resolution sensor fast, portable, does not require permanent bonding to structure. Sensor measures nondestructively type (compressive or tensile) and magnitude of stresses and stress gradients present in class of materials. Includes precise high-resolution acoustic interferometer, sending acoustic transducer, receiving acoustic transducer, electromagnet coil and core, power supply, and magnetic-field-measuring device such as Hall probe. This measurement especially important for construction and applications where steel is widely used. Sensor useful especially for nondestructive evaluation of stress in steel members because of portability, rapid testing, and nonpermanent installation.

This invention relates to an apparatus for measuring strain in a structure. In particular, the invention detects strain in parts per million to over ten percent along an entire length (or other dimension) of a structure measuring a few millimeters to several kilometers. By using a propagation path bonded to the structure, the invention is not limited by the signal attenuation characteristics of the structure and thus frequencies in the megahertz to gigahertz range may be used to detect strain in part per million to over ten percent with high precision

Space transportation propulsion systems symposium is discussed. The following subject areas are covered: overall goals; main issues; materials characterization; reduction of manufacturing defects; standards and certification; advanced NDE techniques; designing for inspectability; candidate programs/milestones; and NDE technology potentials

Quantitative Nondestructive Evaluation (QNDE) is the technology of measurement, analysis, and prediction of the state of material/structural systems for safety, reliability, and mission assurance. QNDE has impact on everyday life from the cars we drive, the planes we fly, the buildings we work or live in, literally to the infrastructure of our world. Here, researchers highlight some of the new sciences and technologies that are part of a safer, cost effective tomorrow. Specific technologies that are discussed are thermal QNDE of aircraft structural integrity, ultrasonic QNDE for materials characterization, and technology spinoffs from aerospace to the medical sector. In each case, examples are given of how new requirements result in enabling measurement technologies, which in turn change the boundaries of design/practice.

In proposed method of obtaining information on strain at surface of material specimen, magnetic coat (like that on magnetic tape) or optical coat (like that on compact disk) applied to all or part of surface monitored. Coating layer and associated measuring equipment, taken together, constitute system called "material strain monitor" (MSM). MSM important in research in materials and mechanics; in particular, expected to compete strongly with systems based on image-analysis and laser techniques now being developed to obtain information on strain fields.

Recent advances in nondestructive evaluation (NDE) at NASA Langley Research Center and their applications that have resulted in quantitative assessment of material properties based on thermal and ultrasonic measurements are reviewed. Specific applications include ultrasonic determination of bolt tension, ultrasonic and thermal characterization of bonded layered structures, characterization of composite materials, and disbonds in aircraft skins.

Advanced aerospace structures are discussed that will very likely be fabricated with integral sensors, actuators, and microprocessors for monitoring and dynamic control of configuration. The concept of 'smart structures' integrates fiber-optic sensor technology with advanced composite materials, whereby the optical fibers are embedded in a composite material and provide internal sensing capability for monitoring parameters which are important for the safety, performance, and reliability of the material and the structure. Along with other research facilities, NASA has initiated a cooperative program to design, fabricate, and test composite trusses, tubes, and flat panels with embedded optical fibers for testing and developing prototype smart structures. It is shown that fiber-optic sensor technology can be combined with advanced material and structure concepts to produce a new class of materials with internal sensors for health monitoring of structures.

A model for predicting the fracture strength of homogeneous materials is proposed. Impacted FWC samples were evaluated using ultrasonic testing and an X-ray dye penetration method. The ability of the model to measure fracture strength was also examined. The relation between attenuation and velocity measurements is studied. It is observed that the X-ray method is not useful for predicting fracture strength because the dye could not penetrate the matrix. It is noted that fracture strength predictions derived from the fracture mechanical model and the ultrasonic measurements correlate well with actual measured fracture strengths.

Uniaxial stress effects on the low-field magnetoacoustic interaction have been studied using bulk compressional waves and Rayleigh surface waves in numerous steel samples having various impurity concentrations (Namkung et al., 1984). The results invariably showed that the initial slope of acoustic natural velocity variations, with respect to net induced magnetization parallel to the stress axis, is positive under tension and negative under compression. The results of current measurements in railroad rail steel having about 0.68 wt percent carbon content are typical for medium range carbon steels. The low-field natural velocity slope in this particular type of steel, which is almost zero when unstressed, becomes steeper with increased magnitude of stress in both directions. Hence, the nondestructive determination of the sign of residual stress in railroad wheels and rails is possible using this technique. This paper discusses the basic physical mechanism underlying the experimental observations and presents the results obtained in railroad rail steel.

Purpose: To develop and test 1) fully digital μK‐resolution ultrasonicthermometer for non‐invasive measurements of absorbed radiation dose in water;2) rapid ultrasonic 2D temperature mapping system for precise characterization of radiation beam intensity profiles. Method and Materials: Monitoring tiny phase shifts of ultrasonic signals in water heated by ionizing radiation allows assessing water temperature changes at the μK level. Instead of the analog frequency‐driven Pulsed Phase‐Locked Loop (PPLL) used in the earlier work to track signal phase, the current system relies on fast digital phase algorithms that extract signal delay with resolution of 100ppb and better. Another ultrasonic system was built to produce 2D temperature maps in water. This system contains a 128‐element, 14″‐diameter circular transducer array operating in a tomographic fan‐beam data acquisition mode. The system acquires temperature maps in seconds and allows monitoring evolution of thermal processes in time. Results: The single‐channel digital ultrasonicthermometer demonstrated resolution equivalent or better than analog PPLL‐based prototype at overall lower noise level. The 2D temperature mapping system was constructed and went though a preliminary testing round. It monitored evolution of temperature profile in the cylindrical tank every 3–4 seconds acquiring each time a 64‐projection data set with 45 rays per projection. After extracting phase information from the acoustic waveforms the system reconstructed a sequence of phase shift images and converted them to temperature maps using newly developed calibration procedure. The maps were combined into movies to watch temperature evolution dynamics. Conclusion: The digital high‐resolution ultrasonicthermometer demonstrated performance improvement and will replace its analog predecessor in the radiation‐testing lab. The 2D ultrasonic temperature mapping system was successfully tested with a light radiation heating source. We plan to continue characterizing its spatial and temperature resolution and incorporate all findings into a next‐generation prototype for ionizing radiationtesting. Research sponsored by NIST.

Simple, inexpensive, and portable ultrasonic device accurately measures acoustic properties of liquids, gases, and solids, using pseudo-continuous wave responses from samples to measure change in resonant frequency or amplitude in acoustic signal.

Graphite/epoxy tubes were fabricated with embedded optical fibers to evaluate the feasibility of monitoring strains with a fiber optic technique. Resistance strain gauges were attached to the tubes to measure strain at four locations along the tube for comparison with the fiber optic sensors. Both static and dynamic strain measurements were made with excellent agreement between the embedded fiber optic

A remote radiometric technique for making quantitative thermal diffusivity measurements is described. The technique was designed to make assessments of the structural integrity of large composite parts, such as wings, and can be performed at field sites. In the measurement technique, a CO2 laser beam is scanned using two orthogonal servo-controlled deflecting mirrors. An infrared imager, whose scanning mirrors oscillate in the vertical and the horizontal directions, is used as the detector. The analysis technique used to extract the diffusivity from these images is based on a thin infinite plate assumption, which requires waiting a given period of time for the temperature to equilibrate throughout the thickness of the sample. The technique is shown to be accurate to within two percent for values of the order of those for composite diffusivities, and to be insensitive to convection losses.

Theoretical analysis has shown that material anharmonic properties are strongly coupled to the material stress state. In this paper, a specific theory is presented along with experimental verification that the temperature dependence of the natural velocity (thermal acoustic constant) can be used to determine changes in stress in isotropic materials. Data will be presented for both pulsed phase locked loop and leading edge time-of-flight ultrasonic velocity measuring techniques. Tests were performed using 2.25 MHz longitudinal waves in an axially stressed rod of polycrystalline aluminum over the temperature range 25OC-65OC and the stress range 0-175 MPa. The data show a linear relationship with a greater than 8% change in thermal acoustic constant with respect to stress up to the tested value of 175 MPa. A comparison of the present data with previous results obtained by Salama and Ling suggests the potential application of this technique to measurements of material stress.

Several planned United States Air Force (USAF) and National Aeronautics and Space Administration (NASA) space systems such as Space Based Radar (SBR), Space Based Laser (SBL), and Space Station, pose serious vibration and control issues. Their low system mass combined with their large size, precision pointing/shape control and rapid retargetting requirements, will result in an unprecedented degree of interaction between the system controller and the modes of vibration of the structure. The resulting structural vibrations and/or those caused by foreign objects impacting the space structure could seriously degrade system performance, making it virtually impossible for passive structural systems to perform their missions. Therefore an active vibration control system which will sense these natural and spurious vibrations, evaluate them and dampen them out is required. This active vibration control system must be impervious to the space environment and electromagnetic interference, have very low weight, and in essence become part of the structure itself. The concept of smart structures meets these criteria. Smart structures is defined as the embedment of sensors, actuators, and possibly microprocessors in the material which forms the structure, a concept that is particularly applicable to advanced composites. These sensors, actuators, and microprocessors will work interactively to sense, evaluate, and dampen those vibrations which pose a threat to large flexible space systems (LSS). The sensors will also be capable of sensing any degradation to the structure. The Air Force Astronautics Laboratory (AFAL) has been working in the area of dynamics and control of LSS for the past five years. Several programs involving both contractual and in-house efforts to develop sensors and actuators for controlling LSS have been initiated. Presently the AFAL is developing a large scale laboratory which will have the capacity of performing large angle retargetting manuevers and vibration analysis on LSS. Advanced composite materials have been fabricated for the last seven years, consisting mostly of rocket components such as: nozzles, payload shrouds, exit cones, and nose cones. Recently, however, AFAL has been fabricating composite components such as trusses, tubes and flat panels for space applications. Research on fiber optic sensors at NASA Langley Research Center (NASA LaRC) dates back to 1979. Recently an optical phase locked loop (OPLL) has been developed that can be used to make strain and temperature measurements. Static and dynamic strain measurements have been demonstrated using this device.' To address future space requirements, AFAL and NASA have initiated a program to design, fabricate, and experimentally test composite struts and panels with embedded sensors, actuators, and microprocessors that can be used to control vibration and motion in space structures.

A broadband capacitive electrostatic acoustic transducer (ESAT) has been developed for use in a liquid environment at megahertz frequencies. The ESAT basically consists of a thin conductive membrane stretched over a metallic housing. The membrane functions as the ground plate of a parallel plate capacitor, the other plate being a dc biased electrode recessed approximately 10 mum from the electrically grounded membrane. An ultrasonic wave incident on the membrane varies the membrane-electrode gap spacing and generates an electrical signal proportional to the wave amplitude. The entire assembly is sealed for immersion in a liquid environment. Calibration of the ESAT with incident ultrasonic waves of constant displacement amplitude from 1 to 15 MHz reveals a decrease in signal response with increasing frequency independent of membrane tension. The use of the ESAT as a broadband ultrasonic transducer in liquids with a predictable frequency response is promising.

We discuss work in progress on the development of a power sensitive transducer. Using this transducer in conjunction with current echo equipment, one should be able to obtain substantially improved echocardiograms. Since echocardiography relies heavily on pattern recognition, the ease and certainty with which diagnostic information can be derived should improve markedly with the generation of sharper and clearer echograms.

We are testing a high-resolution ultrasonic thermometer with a noise floor at the µK level to improve the accuracy of radiation dosimetry methods that rely upon water calorimetry as a primary standard. Conventional water calorimeters, based upon the original design of Domen, detect temperature changes in irradiated water with thermistors that are sealed inside a thin sheath of glass. Recovering absorbed dose to water from these measurements requires the application of correction factors to compensate for the effects of self-heating of the thermistors, of excess heat induced in nonwater materials by the radiation, and of heat transfer due to dose gradients within the phantom. The ultrasonic approach dispenses with nonwater materials inside the water phantom, thereby eliminating or reducing sources of excess heat and the corresponding dose gradients. The prototype instrument, which involves a single ultrasonic transducer and an analog pulsed phase-locked loop, has been tested in 60 Co...

The invention is a device that provides a high resolution measurement of the change in optical phase length from the device optical system source to an optical reflector. The invention consists of a optical phase locked loop that uses a laser beam as a carrier of an intensity modulated energy source. The novelty of the invention appears to lie in the overall combination of elements which provide high resolution without loss of wide dynamic range. The invention does not depend on coherent reflection from a target, and thus can measure targets that do not have special preparation or corner reflectors. The use of carrier modulation achieves high resolution without the problems of high speed pulse duration systems. Thus the invention has the advantages of simplicity, low cost, and small size without sacrificing resolution.

TOUS is capable for measuring very small changes in acoustic attenuation and phase velocity. Its high sensitivity to small changes in ultrasonic absorption results in part from operation under marginal conditions. In spite of high sensitivity, TOUS system is relatively simple, inexpensive, and compact.

PLOPS system designed to provide high-resolution measurement of change in optical length from optical-system source to any optical reflector, including diffuse reflector. Serves as adjustable optical ruler, providing high resolution in measurements of small and large changes in distance to target. Use is broad and includes most measurement situations requiring information on length, vibration, and their derivatives. Applications include building dynamics, remote sensing of vibrations in such systems as turbine-based machinery, monitoring of structural dynamics, noncontacting sensing of surface contours, measurement of large strains as in earthquake monitoring, measurement of atmospheric dynamics and turbulence, high-resolution sensing of humidity, detection of surface acoustic waves by optical microscopy, and related areas.

ABSTRACT A device and method for the rapid quantification of an internal property of a material are described which are typified by embodiments for rapidly quantifying the amount of urine in the bladder of a human subject. An ultrasonic transducer, which is positioned on the subject in proximity to the bladder, is excited by a logic-controlled pulser/receiver to introduce an acoustic wave into the patient. This wave interacts with the bladder walls and is reflected back to the ultrasonic transducer, whence it is amplified and processed by the pulser/receiver. The resulting signal is digitized by an analog-to-digital converter under the command of the logic system and is stored in a memory. The software in the logic system determines the amount of urine in the bladder as a function of propagated ultrasonic energy based on programmed scientific measurements and past history of the specific subject. The system then sends out a signal to turn on any or all of the audible alarm, the visible alarm, the tactile alarm, and the remote wireless alarm.

Purpose: To develop a μK‐resolution ultrasonicthermometer for non‐invasive measurements of absorbed radiationdose in water and to characterize the intensity profile of radiation beams used for medical treatment.Method and Materials: Subtle temperature changes in water were measured by monitoring the phase of an ultrasonic disturbance propagating in it. The current system includes a thermally insulated water tank, an ultrasonic transducer, a frequency counter, and a Pulsed Phase‐Locked Loop connected to a PC. The alpha‐prototype was initially tested and characterized experimentally with time‐controlled light pulses, and was subsequently evaluated with radiation heating from a therapy‐level Co‐60 source. The system was subjected to 30 one‐minute, 50% duty cycle radiation exposures; the temperature history was recorded and analyzed. Results: Preliminary Fourier analysis of the temperature changes caused by periodic radiation heating showed that the absorbed dose rate corresponds to 1.80 Gy/min, deduced from a 0.43 mK (±3% 1 ) per cycle temperature rise in water. The estimated nominal dose rate at 81.6 cm from the source and 3.2 cm below the water surface is estimated to be 1.65 Gy/min. The discrepancy can be attributed to the non‐standard water tank size and incomplete temperature calibration of the alpha prototype at test time. We expect to resolve these issues by equipping the system with a standard water tank and implementing a more advanced calibration procedure. Conclusions: The alpha prototype has been tested in Co‐60 radiation and produced reasonable results. The feedback from these tests has recently been incorporated into the design of a beta prototype. The new system routinely detects less than 10 μK temperature changes in water and shows great promise for precise dose measurements and beam profile characterization. The new calibration procedure does not require external sensors and makes the system more portable and fully self‐contained. Research sponsored by NIST.