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Alternate choices to X-ray use in detecting foreign materials in metal assemblies are available, including negative radiography, neutron radiography, liquid-crystal inspection and ultrasonics. Advantages and disadvantages of each method are given. Report is valuable in testings and inspections, including heat exchangers and piping systems.
The techniques involved are ultrasonic scanning, neutron radiography, scanning laser acoustic microscopy, and voltage conditioning. The test capacitor, for this first phase, is a 0.47 uF, 50V capacitor style CKR06. Eighteen of 768 devices failed in voltage conditioning with elapsed times from 15 minutes to 1239 hours. Eleven of the failures were detected by ultrasonic scanning. Four failures were found by neutron radiography. Fourteen failures showed up in the acoustic microscopy test. Three failures in voltage conditioning were not detected by any of the techniques. Failures were confirmed by destructive physical analysis. There is no direct relationship between the size of the defect and electrical failure.
Radiographic, ultrasonic, scanning laser acoustic microscopy (SLAM), and thermo-acoustic microscopy techniques were used to characterize silicon nitride and silicon carbide modulus-of-rupture test specimens in various stages of fabrication. Conventional and microfocus X-ray techniques were found capable of detecting minute high density inclusions in as-received powders, green compacts, and fully densified specimens. Significant density gradients in sintered bars were observed by radiography, ultrasonic velocity, and SLAM. Ultrasonic attenuation was found sensitive to microstructural variations due to grain and void morphology and distribution. SLAM was also capable of detecting voids, inclusions and cracks in finished test bars. Consideration is given to the potential for applying thermo-acoustic microscopy techniques to green and densified ceramics. The detection probability statistics and some limitations of radiography and SLAM also are discussed.
Radiographic, ultrasonic, scanning laser acoustic microscopy (SLAM), and thermo-acoustic microscopy techniques were used to characterize silicon nitride and silicon carbide modulus-of-rupture test specimens in various stages of fabrication. Conventional and microfocus X-ray techniques were found capable of detecting minute high density inclusions in as-received powders, green compacts, and fully densified specimens. Significant density gradients in sintered bars were observed by radiography, ultrasonic velocity, and SLAM. Ultrasonic attenuation was found sensitive to microstructural variations due to grain and void morphology and distribution. SLAM was also capable of detecting voids, inclusions and cracks in finished test bars. Consideration is given to the potential for applying thermo-acoustic microscopy techniques to green and densified ceramics. The detection probability statistics and some limitations of radiography and SLAM also are discussed.
The reliability of microfocus x-radiography and scanning laser acoustic microscopy for detecting microvoids in silicon nitride and silicon carbide was statistically evaluated. Materials- and process-related parameters that influenced the statistical findings in research samples are discussed. The use of conventional x-radiography in controlling and optimizing the processing and sintering of an Si3N4-Si02-Y203 composition designated NASA 6Y is described. Radiographic evaluation and guidance helped develop uniform high-density Si3N4 modulus-of-rupture bars with improved four-point flexural strength (857, 544, and 462 MPa at room temperature, 1200 C, and 1370 C, respectively) and reduced strength scatter.
A review is presented on research and development of techniques for nondestructive evaluation and characterization of advanced ceramics for heat engine applications. Highlighted in this review are Lewis Research Center efforts in microfocus radiography, scanning laser acoustic microscopy (SLAM), scanning acoustic microscopy (SAM), scanning electron acoustic microscopy (SEAM), and photoacoustic microscopy (PAM). The techniques were evaluated by applying them to research samples of green and sintered silicon nitride and silicon carbide in the form of modulus-of-rupture bars containing seeded voids. Probabilities of detection of voids were determined for diameters as small as 20 microns for microfucus radiography, SLAM, and SAM. Strengths and limitations of the techniques for ceramic applications are identified. Application of ultrasonics for characterizing ceramic microstructures is also discussed.
The reliability of microfocus X-radiography and scanning laser acoustic microscopy for detecting microvoids in silicon nitride and silicon carbide was statistically evaluated. Materials- and process-related parameters that influenced the statistical findings in research samples are discussed. The use of conventional X-radiography in controlling and optimizing the processing and sintering of an Si3N4-SiO2-Y2O3 composition designated NASA 6Y is described. Radiographic evaluation and guidance helped develop uniform high-density Si3N4 modulus-of-rupture bars with improved four-point flexural strength (857, 544, and 462 MPa at room temperature, 1200 C, and 1370 C, respectively) and reduced strength scatter.
Neutron inspection finds deposits and defects invisible to x rays. Neutron radiography detects many low-density materials even when surrounded by larger quantities of denser materials. Materials with similar properties and densities often appear quite different when viewed by neutron radiography. Technique gives comprehensive view of hidden channels.
Process changes iterated under guidance of x-radiography. In recent work at NASA Lewis Research Center, density gradients in sintered silicon nitride, characterized by x-radiography, identified and appeared strongly dependent upon powder-processing and sintering conditions. NASA technical memorandum describes systematic investigation, based upon preliminary work, of density-gradient/flexural-strength relationships as affected by processing.
The capabilities were investigated of projection microfocus x-radiography, ultrasonic velocity and attenuation, and reflection scanning acoustic microscopy for characterizing silicon carbide specimens. Silicon carbide batches covered a range of densities and different microstructural characteristics. Room temperature, four point flexural strength tests were conducted. Fractography was used to identify types, sizes, and locations of fracture origins. Fracture toughness values were calculated from fracture strength and flaw characterization data. Detection capabilities of radiography and acoustic microscopy for fracture-causing flaws were evaluated. Applicability of ultrasonics for verifying material strength and toughness was examined.
The capabilities were investigated of projection microfocus X-radiography, ultrasonic velocity and attenuation, and reflection scanning acoustic microscopy for characterizing silicon carbide specimens. Silicon carbide batches covered a range of densities and different microstructural characteristics. Room temperature, four point flexural strength tests were conducted. Fractography was used to identify types, sizes, and locations of fracture origins. Fracture toughness values were calculated from fracture strength and flaw characterization data. Detection capabilities of radiography and acoustic microscopy for fracture-causing flaws were evaluated. Applicability of ultrasonics for verifying material strength and toughness was examined.
New developments in x-ray radiography that may be applicable to containerless experimentation are presented. The two features discussed are the use of radiography to determine the position and shape of the solid-liquid interface and, with the aid of appropriate markers, the flow patterns in either the surface or bulk of the liquid state. Both surface energy and fluid viscosity measurements can be made with the aid of the described radiographic system.
The research accomplishments under this grant were very extensive in the areas of the development of engineering tomography for monolithic and composite materials and components. Computed tomography was used on graphite composite pins and bushings to find porosity, cracks, and delaminations. It supported the following two programs: Reusable Launch Vehicle (RLV) and Southern Research institute (SRI). Did research using CT and radiography on Nickel based Superalloy dogbones and found density variations and gas shrinkage porosity. Did extensive radiography and CT of PMC composite flywheels and found delamination and non-uniform fiber distribution. This grant supported the Attitude Control Energy Storage Experiment (ACESE) program. Found broken fibers and cracks of outer stainless steel fibers using both radiographic and CT techniques on Pratt and Whitney fuel lines; Supported the Pratt & Whitney and Aging Aircraft engines program. Grant research helped identify and corroborate thickness variations and density differences in a silicon nitride "ROTH" tube using computed tomography.
The accuDEXA(R) Bone Mineral Density Assessment System, manufactured by Schick Technologies, Inc., utilizes "camera on a chip" sensor technology invented and developed by NASA's Jet Propulsion Laboratory. Schick's accuDEXA system offers several advantages over traditional osteoporosis tests, which assess bone density loss in the hip and spine, and require specialized personnel to conduct. With accuDEXA, physicians can test the entire body's bone density at a peripheral site, such as the finger, without applying gels or having patients remove garments. Results are achieved in 30 seconds and printed out in less than a minute, compared to the estimated exam time of 15 minutes for hip and spine density analyses. Schick has also applied the CMOS APS technology to a new software product that performs dental radiography using up to 90 percent less radiation exposure than conventional X-rays. Called Computed Dental Radiography(R), the new digital imaging product utilizes an electronic sensor in place of X-ray film to generate sharp and clear images that appear on a computer screen within 3 seconds, and can be enlarged and enhanced to identify problems.
Transverse matrix cracking in cross-ply gr/ep laminates was studied with advanced acoustic emission (AE) techniques. The primary goal of this research was to measure the load required to initiate the first transverse matrix crack in cross-ply laminates of different thicknesses. Other methods had been previously used for these measurements including penetrant enhanced radiography, optical microscopy, and audible acoustic microphone measurements. The former methods required that the mechanical test be paused for measurements at load intervals. This slowed the test procedure and did not provide the required resolution in load. With acoustic microphones, acoustic signals from cracks could not be clearly differentiated from other noise sources such as grip damage, specimen slippage, or test machine noise. A second goal for this work was to use the high resolution source location accuracy of the advanced acoustic emission techniques to determine whether the crack initiation site was at the specimen edge or in the interior of the specimen.In this research, advanced AE techniques using broad band sensors, high capture rate digital waveform acquisition, and plate wave propagation based analysis were applied to cross-ply composite coupons with different numbers of 0 and 90 degree plies. Noise signals, believed to be caused by grip damage or specimen slipping, were eliminated based on their plate wave characteristics. Such signals were always located outside the sensor gage length in the gripped region of the specimen. Cracks were confirmed post-test by microscopic analysis of a polished specimen edge, backscatter ultrasonic scans, and in limited cases, by penetrant enhanced radiography. For specimens with three or more 90 degree plies together, there was an exact 1-1 correlation between AE crack signals and observed cracks. The ultrasonic scans and some destructive sectioning analysis showed that the cracks extended across the full width of the specimen. Furthermore, the locations of the cracks from the AE data were in excellent agreement with the locations measured with the microscope. The high resolution source location capability of this technique, combined with an array of sensors, was able to determine that the cracks initiated at the specimen edges, rather than in the interior. For specimens with only one or two 90 degree plies, the crack-like signals were significantly smaller in amplitude and there was not a 1-1 correlation to observed cracks. This was similar to previous results. In this case, however, ultrasonic and destructive sectioning analysis revealed that the cracks did not extend across the specimen. They initiated at the edge, but did not propagate any appreciable distance into the specimen. This explains the much smaller AE signal amplitudes and the difficulty in correlating these signals to actual cracks in this, as well as in the previous study.
The authors reviewed the applications and limitations of computed tomography (CT) and magnetic resonance (MR) imaging in the assessment of the most common hip disorders. Magnetic resonance imaging is the most sensitive technique in detecting osteonecrosis of the femoral head. Magnetic resonance reflects the histologic changes associated with osteonecrosis very well, which may ultimately help to improve staging. Computed tomography can more accurately identify subchondral fractures than MR imaging and thus remains important for staging. In congenital dysplasia of the hip, the position of the nonossified femoral head in children less than six months of age can only be inferred by indirect signs on CT. Magnetic resonance imaging demonstrates the cartilaginous femoral head directly without ionizing radiation. Computed tomography remains the imaging modality of choice for evaluating fractures of the hip joint. In some patients, MR imaging demonstrates the fracture even when it is not apparent on radiography. In neoplasm, CT provides better assessment of calcification, ossification, and periosteal reaction than MR imaging. Magnetic resonance imaging, however, represents the most accurate imaging modality for evaluating intramedullary and soft-tissue extent of the tumor and identifying involvement of neurovascular bundles. Magnetic resonance imaging can also be used to monitor response to chemotherapy. In osteoarthrosis and rheumatoid arthritis of the hip, both CT and MR provide more detailed assessment of the severity of disease than conventional radiography because of their tomographic nature. Magnetic resonance imaging is unique in evaluating cartilage degeneration and loss, and in demonstrating soft-tissue alterations such as inflammatory synovial proliferation.
Foam loss on the External Tank (ET) during launch can be caused by a number of factors. Voids are the best understood mechanism of foam loss, although it is known that delaminations, cracks and crushed foam can also lead to liberation of foam. Shortly after the Columbia accident, work began on non-destructive evaluation of foam targeted at finding voids and delaminations. After several months of searching for candidate methods capable of inspecting ET foam, the five most promising techniques were taken through a blind test and narrowed down to two methods to develop and use for inspection of the ET. These methods were backscatter radiography and terahertz imaging. The backscatter radiography system measures a test part by detecting Compton backscattered x-ray energy generated by a collimated beam of x-rays directed at the test subject. This collimated beam is scanned across the subject, recording scatter intensity data one pixel at a time until the area of interest is covered. The resulting data can be used to generate an image similar to a radiograph. Some depth information can be gathered utilizing apertures or collimation on the detectors. The detectors are located around the collimated source, making this a single sided inspection. The void detection limit with the currently utilized system is around 0.5 inches in diameter by 0.2 inches high. The terahertz imaging system inspects a test part by utilizing a transceiver to emit a pulse focused at the aluminum skin of the ET, which reflects it back to the transceiver where it is analyzed. The transceiver is scanned across the area of interest until a measurement has been taken at every location. Amplitude, time delay and frequency content are examined to note any discontinuities which may be the result of a void or other type of defect. The pulse currently utilized is in the millimeter wave regime. The void detection limit with this system is around 0.5 inches in diameter by 0.2 inches high. With increased interest in other causes of foam loss following the flight of Discovery in July 2005, laser shearography was added to the techniques used for inspecting ET foam. The shearography method records a sheared image of a laser speckle pattern projected on a test part before And after some sort of excitation. The resultant fringe pattern allows the slope of the out of plane displacement to be measured. For crushed and delaminated foam applications, a non-contact air coupled acoustic force is used to excite the surface of the foam. Regions without defects tend to respond differently to the sound energy than do regions with defects, generating a map of the foam integrity. Foam crushed to a depth of about 0.1 inches is detectable with shearography even after it has relaxed to its original shape.
Don Rosenthal, a former Ames Research Center computer scientist who helped design the Hubble Space Telescope's scheduling software, co-founded Allocade Inc. of Menlo Park, California, in 2004. Allocade's OnCue software helps hospitals reclaim unused capacity and optimize constantly changing schedules for imaging procedures. After starting to use the software, one medical center soon reported noticeable improvements in efficiency, including a 12 percent increase in procedure volume, 35 percent reduction in staff overtime, and significant reductions in backlog and technician phone time. Allocade now offers versions for outpatient and inpatient magnetic resonance imaging (MRI), ultrasound, interventional radiology, nuclear medicine, Positron Emission Tomography (PET), radiography, radiography-fluoroscopy, and mammography.