The determination of material properties for very small specimens such as biological cells or semiconductor microchips is extremely difficult and has been a challenging issue for several decades. One important constraint during these measurements is not to harm the specimens during the test process because the specimens, biological cells in particular, are vulnerable to the test itself even during a short period of testing time.Nondestructive evaluation (NDE) is the only suitable precess for such applications. It is fast, causes no disturbance and can give a real time response while being cost effective. Many NDE methods are available today, such as, laser based techniques, Radiography, Magnetic techniques, High resolution photography and other optical techniques, MRI, acoustic and ultrasonic techniques to name a few. Ultrasound is the most popular tool for NDE. As specimens become smaller, the need for shorter wave length ultrasound increases dramatically.The use of acoustic waves in microscopy technology provides many more benefits than its conventional optical microscope counterpart. One such benefit is its ability to inspect a specimen in dark. Another is the capability to see inside an optically opaque specimen. Today, very high frequency, higher than 1 Giga Hertz (109 Hz), ultrasound is being used. This technology has improved at the same pace as the development of electronics and computer science. In acoustic microscopy experiments wave speed and wave attenuation in the specimen are measured by the V(f) technique. A specimen's density, Poisson's ratio and Young's modulus are directly related to the wave speed. V(f) method, as discussed in this dissertation, has some advantages over the more commonly used V(z) method. In order to correctly estimate the wave speed and attenuation in the specimen, the transducer modeling should be completed first. The Distributed Point Source Method (DPSM) is used in this dissertation to model a 1 GHz acoustic microscope lens. Then the model-predicted pressure field is used in a FORTRAN program to calculate the thickness profile and properties of biological cell specimens from experimental data.Transducer modeling at 1 GHz has rarely been attempted earlier because it requires an immense amount of computer time and memory. In this dissertation 1 GHz transducer modeling is conducted by taking advantage of the axisymmetric geometry of the acoustic microscope lens. This exploitation of symmetry in the modeling process has not been attempted prior to this dissertation.

No description available.

Gas Metal Arc welding (GMAW) is one of the primary techniques used to join structural components together. The major obstacle precluding full closed-loop control of GMAW has been the lack of robust techniques using non-destructive and non-contact sensors capable of operating in high temperature and harsh environments typical of GMAW processes. This research uses laser generated ultrasound and electromagnetic acoustic transducer (EMAT) to receive ultrasound. Previous research has focused on ultrasonic shear wave time of flight (TOF) techniques to determine weld penetration depth, a key measure of weld quality. The objective of this research was to use a new technique, frequency modulation of a laser phased array (FMLPA), to determine weld penetration depth. Theoretical background of the FMLPA was developed. An analytical model of the FMLPA was derived and validated through experimentation. The FMLPA was experimentally validated. However, both the FMLPA and shear wave TOF techniques have proven to be impractical for real-time control. These techniques are impractical because the required ultrasonic waves are difficult to acquire due to attenuation and interference from other waves. A new type of wave called the RGLS wave was discovered during the course of this research. The RGLS wave was used to create a new RGLS TOF method for measuring weld penetration depth. The RGLS TOF method for measuring weld penetration depth has proven to be highly accurate, precise, and repeatable. The RGLS TOF method for measuring weld penetration depth has been demonstrated to work both off-line after welding and real-time during welding. Although the FMLPA and shear wave TOF technique was proven to be impractical, the RGLS TOF method has met the ultimate goal of this research area. Other new methods such as the RGSL, RGLL, and RGSS TOF methods related to the RGLS TOF method was also developed. The RGLS TOF method is suited for non-destructive and non-contact sensing. It will help future researchers achieve closed-loop control and automation of the GMAW process, which will help to improve quality and efficiency of welding, and also reduce waste and cost of welding parts together.

In the design of cryogenic fuel tanks for the next generation Reusable Launch Vehicles (RLVs), the permeability of liquid hydrogen (LH2) across the thickness of the tank is a critical issue. The rate of permeation of LH2 is largely dependent on the internal damage state of the composite tank wall. Damage in the form of matrix cracks in the composite material of the tank is responsible for the through-the-thickness permeation of LH2. In this context, the detection of matrix cracks takes on an unprecedented significance. In this work, an ultrasonic technique for the ply-by-ply detection of matrix cracks in laminated composites is developed. Experimental results are presented for graphite/epoxy laminates with different lay-ups and laminate thicknesses. Matrix cracks in each of the plies of the laminated composites were detected even when there was a rather high density of cracks in all of the plies. The ultrasonic data were calibrated by comparing them with the corresponding results obtained by using the traditional methods of optical microscopy and penetrant enhanced X-radiography. Excellent quantitative correlation was observed between the results obtained with ultrasonics and the traditional methods.

In the design of cryogenic fuel tanks for the next generation Reusable Launch Vehicles (RLVs), the permeability of liquid hydrogen (LH2) across the thickness of the tank is a critical issue. The rate of permeation of LH2 is largely dependent on the internal damage state of the composite tank wall. Damage in the form of matrix cracks in the composite material of the tank is responsible for the through-the-thickness permeation of LH2. In this context, the detection of matrix cracks takes on an unprecedented significance. In this work, an ultrasonic technique for the ply-by-ply detection of matrix cracks in laminated composites is developed. Experimental results are presented for graphite/epoxy laminates with different lay-ups and laminate thicknesses. Matrix cracks in each of the plies of the laminated composites were detected even when there was a rather high density of cracks in all of the plies. The ultrasonic data were calibrated by comparing them with the corresponding results obtained by using the traditional methods of optical microscopy and penetrant enhanced X-radiography. Excellent quantitative correlation was observed between the results obtained with ultrasonics and the traditional methods.

In this research, through-transmission ultrasonic (TTU) Acoustography was applied to measure and quantify porosity levels in carbon fiber reinforced polymer (CFRP) composite laminates. This study employed several CFRP specimens with wide ranges of porosity prepared by altering the curing pressure during the manufacturing process. The Acoustography method, operating at 5 MHz, was able to show contrast in ultrasonic images obtained for composite laminates with varied porosity levels. Porosity levels in composite laminates were quantified using destructive methods: acid digestion and microscopy. Also, strength analysis tests were conducted to investigate the effect porosity has on the laminate’s structural integrity. From the results obtained, it was demonstrated that the mechanical properties, interlaminar shear strength (ILSS), and flexural strength of CFRP decreased with the increasing void content. In addition, Acoustography absorption coefficient measurements were related to varied porosity levels in the composite laminates. As the porosity content increased within the laminates, the acoustic absorption coefficient increased. These findings are significant because Acoustography is being developed as a faster alternative to traditional ultrasonic inspection of composites and porosity is an important anomaly to quantify utilizing NDE methods.

Advanced nondestructive inspection techniques like stress wave timing and resistance microdrilling have been used to successfully inspection timber bridges, but it is most effective on girder style bridges. There is a noted need to develop additional inspection techniques for longitudinal deck/slab timber bridges, which comprise about 20% of the national bridge inventory. One technique that holds potential is ground penetrating radar, a recognized nondestructive testing technique that has been used effectively for many different environmental and transportation applications. It has been utilized successfully to identify buried objects, internal defects and material changes. The objective of this research was to assess the potential for using GPR to identify and assess simulated deterioration in longitudinal timber deck timber bridges. GPR scans were completed in the longitudinal and transverse directions of a screwlaminated timber bridge deck before and after a bituminous layer was added to assess embedded defects that simulated voids, decay, insect damage and horizontal shear splitting. Assessment of the GPR wave energy signal was completed using visualization software that was provided with the commercial GPR unit used for the testing. The radar signal was analyzed in both the longitudinal direction (antenna front to back) and the transverse direction (antenna side to side). Interpretation of the radar signals allowed for the identification of various internal defects present in the deck. Based on the results, GPR has the potential to identify internal defects in timber bridge decks before and after a bituminous layer was added. Large, rectangular void defects (at least 6? by 12? by 5 in. (15.2? by 30.4? by 12.7 cm)) that were hollow, filled with foam, or filled with sawdust/adhesive were most easily identified under all scanning conditions. The addition of a bituminous layer, common to slab bridge construction, damped the signal response and made it more difficult to identify defects. Several smaller defects that were found in the deck without a bituminous layer were not identified in scanning completed after the bituminous layer was added.

No description available.

An experimental study was conducted to characterize Portland cement concrete (PCC), to detect deterioration induced by freeze/thaw and alkali-silica reaction, and to detect chloride presence in PCC using ultrasonic waves. The experimental program was initiated to investigate the effect of water to cement (w/c) ratio, aggregate type, and air entrainn1ent on measured ultrasonic wave velocity and signal energy. Three w/c ratios (0.35, 0.45, and 0.55) were evaluated. Two aggregate types, quartzite and limestone, were included in the PCC mixes separately. Mixes were prepared as non-air entrained and air entrained. Thus, a total of twelve batches were prepared to evaluate PCC using ultrasonic waves at two frequencies, 54 and 340 kHz. The experimental program to investigate freeze/thaw (FT) damage included the effect of curing time, w/c ratio, and aggregate type. The effect of curing time was investigated by exposing PCC specimens cured for 3 and 7 days to FT. Two w/c ratios were considered, 0.45 and 0.55. The effect of aggregate on detecting FT damage was investigated using two types of crushed stone aggregate, quartzite and limestone. Alkali-silica reaction (ASR) damage was investigated uSIng two w/c ratios, 0.35 and 0.45. Embedded composite strain gages were used to monitor the ASR deleterious deterioration. High alkali cement and active silica aggregate were used to produce ASR. / Ph. D.

The objective of this thesis is to present analysis techniques that quantify the scattering of angle-beam ultrasonic waves from through-holes in plates. This topic is of interest because increased understanding of the scattering of ultrasonic waves by a defect is important for the development of many nondestructive evaluation (NDE) applications. Angle-beam techniques are commonly used in industry to detect and characterize defects, and many structures of concern have plate-like components. Scattering from through-holes is particularly important because cracks tend to form around fastener holes, which have high stress concentrations. In addition, varying boundary conditions within a fastener hole can change over the course of a structure’s lifetime and may have significant effects on NDE results. In this research, two signal processing techniques are developed to obtain scattering information from through-holes for a variety of fill conditions, including epoxy and complete and partial filling with metal inserts, using experimentally acquired wavefield measurements. Experimental procedures for acquiring wavefields, which measure the out of plane motion of ultrasonic waves on the surface of a specimen and allow for the visualization and characterization of propagating waves, are presented. Methods for obtaining radial and directional energy maps, which quantify scattering as a function of scattered angle and phase velocity, are described. In addition, baseline subtraction is used to obtain scattering patterns for both methods, which quantify scattering as a function of polar angle for each wave mode present in the wavefield. These techniques are applied to wavefield measurements from through-holes with various fill conditions to investigate the effects of boundary conditions on ultrasonic scattering. A comparison of the radial and directional energy mapping techniques, discussing the strengths and weaknesses of each approach, is provided, and recommendations are made for future work.