Ultrasonic techniques were investigated for non-invasive quality evaluation of selected fruits and vegetables. An ultrasonic non-destructive evaluation system was developed and used to investigate physical and acoustical property changes for the selected fruits and vegetables non-invasively. The system included a high power burst pulser, a broadband receiver, a digital storage oscilloscope, two pairs of transducers of 250 kHz and 1 MHz, and a microcomputer system, which was interfaced with the ultrasonic equipment through a General Purpose Interface Board (GPIB), for data acquisition and analysis. Using potatoes and apples, several forms of the acoustic indices were investigated using the system. Investigation of “Yukon-Gold’ potatoes concentrated on the physical and acoustical property changes during the storage period of approximately five months. The tests were conducted at regular intervals. Ultrasonic velocity, attenuation coefficient, modulus of elasticity, and tissue density were determined for each potato along two different orientations — longitudinal and transverse. Three varieties of apples, ‘Golden Delicious’, ‘Red Delicious’, and ‘Granny Smith’, were tested to detect their physiological changes with ripeness. The tests were conducted at two different stages of ripeness. In each test, ultrasonic velocity, attenuation coefficient, modulus of elasticity, and tissue density were determined along longitudinal and radial directions of the apples. Frequency analysis of the transmitted ultrasonic signals through potato and apple samples was also conducted using Fast Fourier Transform (FFT) techniques. The experimental results for the potatoes and apples indicated the measured acoustical and physical properties differed along different orientations; i.e., potato and apple tissues are anisotropic materials. Apple tissues transmitted much lower frequency components than potato tissues and the transmitted frequency range was much narrower due to the much higher percentage of intercellular void space in apple tissues (24%) than in potato tissues (2%). The ultrasonic measurements were able to detect physiological changes and physical heterogeneities in fruit and vegetable tissues. Therefore, the ultrasonic technique can be a useful and quick method for evaluating firmness as well as textural and rheological property changes during storage of fruits and vegetables. Hollow hearts in ‘Atlantic’ potatoes were successfully detected using the ultrasonic nondestructive evaluation system at 250 kHz. A objective this work was to develop a quantitative, non-invasive method for hollow heart detection in potatoes, and to provide information for designing evaluation equipment which could serve as an automatic quality control step in the production process. The analysis of the transmitted ultrasonic signals through the potatoes was carried out in both time and frequency domains. The results of the investigation of ‘Atlantic’ potatoes showed that the waveform of transmitted ultrasonic signals through a hollow heart potato differed significantly from that of a normal potato. Further, the defective potatoes could be separated on the basis of the amount of ultrasonic power transmitted through a potato. By means of digital Fourier analysis, the 0^th spectral moment, M₀, was determined from the power spectral density curve of a transmitted ultrasonic signal. The spectral moment represents the amount of ultrasonic power transmitted through a tested potato, and was chosen as the basis for quantitative, non-invasive method for hollow heart detection, since power transmission of ultrasonic wave was affected by the presence of hollow heart in potatoes. Potatoes with hollow heart transmitted much less ultrasonic power than normal potatoes — approximately 89% less on average. There was a distinct separation between the normal potatoes and hollow heart potatoes. The reliability of this method was confirmed. Among 41 ‘Atlantic’ potatoes tested, all 26 hollow-heart potatoes were identified without exception. Therefore, the parameter M₀ could provide an effective method of analyzing the ultrasonic measurements for quantitative, non-invasive evaluation of hollow hearts in potatoes. This non-invasive method could be used to identify internal quality of potatoes that is difficult to evaluate from external appearance. Such a measurement offers promises for the development of equipment that would sort potatoes with hollow heart automatically. / Ph. D.

The performance of two acoustooptical systems for ultrasonic materials characterization has been investigated. The first system uses an optical fiber interferometric technique to detect directly slowly varying residual stresses and both high frequency continuous and transient ultrasonic waves characteristic of acoustic emission events in composites. The potential for embedding optical fibers inside fiber composites during manufacturing makes this an attractive built-in alternative to conventional contact transducers for the nondestructive evaluation of composite materials. Experimental static and dynamic calibration as well as the frequency domain characterization of acoustic emission as detected by this system are discussed. The second system is a pulse-echo transducer system that generates an electronically focusable ultrasonic field and detects the reflected field optically. The generating transducer consists of concentric ring electrodes etched on a single x-cut quartz crystal substrate with a 1 mm circular aperture at the center. By shaping the amplitude and phase profile of the high voltage pulse applied to each ring, a focused ultrasonic field results at an adjustable distance below the transducer. If the field is focused below the surface of a specimen, energy in the wave reflected from the focal point modulates the normal and parallel components of surface displacement. Furthermore, if the sample arm of an adaptively stabilized interferometer is focused on the free surface at the transducer center aperture, the normal component of surface motion may be detected. This system has potential applications in materials characterization and evaluation as well as biomedical imaging. The design of the system is discussed with particular emphasis on the necessary sub-system interfaces required for operational flexibility. / Master of Science

New materials and manufacturing processes, and the quest for economy and user safety, have necessitated the development of nondestructive testing methods to quantify the life and reliability of a product during manufacture and service. Described herein, is a testbed to be used in the research and development of these testing methods. A brief motivation for using ultrasonics applied to nondestructive evaluation is followed by a chapter on the feasibility of using a unique testing method and animated data presentation on advanced composite materials. This testing method, conceived by the author, utilizes oblique injection of ultrasound into the specimen. Several cycles of the ultrasonic waveform radiated from the specimen downstream of the injection area is digitized and recorded. The data has three independent dimensions; cartesion location and time. The time variable is the key to the presentation of the data as an animated two dimensional image. It was this work that illustrated the need for a flexible scanning imaging research testbed, not only for the discussed method, of which it is an integral part, but for advanced development of other techniques. Software development and integration of off -the-shelf parts into a unified computer controlled testing facility is the contribution by the author in the second phase of this research. Chapters on the description of the system, an example showing the capabilities of the system analogous to traditional ultasonic C-scanning, accomplishments, and a look to the future conclude this thesis. The appendices include listings of the programs developed for the system, a manufacturer address list. A videotape of the animation data presentation is included as a second volume of this thesis. / Master of Science

Quantification of inclusions is important since it is correlated to the steel’s fatigue properties. One method that could be further developed for detection of inclusions in steel is ultrasonic testing (UST). The aim of this study is to investigate what type of inclusions, in terms of size, morphology and chemical composition, that can be detected with 25 MHz UST, and what type of inclusion that cannot be detected. This was done by firstly scanning 74 steel samples with 25 MHz UST, and then fatigue test the same samples until fracture. The inclusion that caused the fracture was then analysed with microscopy and compared with the results from the 25 MHz UST. It was found that Mn-Mg-sulphides, Ca-sulphides, oxy sulphides and complex oxides are difficult to detect with 25 MHz UST. Globular oxides can be detected with 25 MHz UST, at least down to an area of 8300 μm2 and if they are not too fragmented due to rolling. The results indicate that oxy sulphide stringers can be detected with 25 MHz UST if the inclusion have oxides in direct contact with the steel matrix, rather than oxides encapsulated by sulphides. / Kvantifiering av inneslutningar är viktigt då det korrelerar med stålets utmattningsegenskaper. En metod som kan utvecklas för detektering av inneslutningar i stål är ultraljudstestning (UT). Syftet med den här studien är att undersöka vilken typ av inneslutningar, med avseende på storlek, morfologi och kemisk sammansättning, som kan detekteras med 25 MHz UT, och vilken typ av inneslutningar som inte kan detekteras. Detta gjordes genom att först skanna 74 stålprover med 25 MHz UT och sedan utmattningstesta samma prover tills de gick till brott. Inneslutningen som orsakade brottet analyserades sedan med mikroskopi och jämfördes med resultaten från 25 MHz UT. Det visade sig att Mn-Mg-sulfider, Ca-sulfider, oxisulfider och komplexa oxider är svåra att upptäcka med 25 MHz UT. Globulära oxider kan upptäckas, åtminstone ner till en area på 8300 μm2 och om den inte har blivit för fragmenterad av valsning. Resultaten indikerar att oxisulfider kan detekteras om oxiderna är i direkt kontakt med stålmatrisen, i stället för att oxiderna är inkapslade av sulfider.

Defects in a plastic floor material produced in Tarketts factory in Ronneby are causing waste of time and material since it is noticed too late in the production line. The objective of this thesis is to investigate if the nondestructive test method NAW®, which is developed by Acoustic Agree in Ronneby, can be a solution to find the defects at an earlier stage. Nondestructive testing mainly means what the name says; quality tests of a material can be made without causing any damage. One simple example of a nondestructive testing tool is the human eye. By looking at a product defects on the surface can be found. The method used in this thesis, NAW®, is a nonlinear acoustical method. By listening to the material, information about disturbances inside the material can be gathered and interpreted to get a picture of the quality status. Although by listening it does not in this case mean by a human ear but with special equipment since the sound used is high frequent ultrasound. For several material samples, experiments were made both for the references and with introduced defects. It was hard to get definitive results since, for example, even the results for the different reference samples were differing a lot. Nevertheless there are some results pointing in the same direction which means that there is still hope for the possibility to use NAW® as a tool in the production at Tarkett. One important problem in this work is the fact that the defect material is not actually a real defect material but an imitated one with defects made by hand in the experiments. This is a possible error and has to be considered in case of further experiments. Either the imitated defects have to be “improved” or, in the ideal case, real defective material from the factory should be used to get as reliable results as possible. / Defekter i golvmaterial i tillverkningen hos Tarkett i Ronneby orsakar slöseri med tid och material eftersom de upptäcks sent i produktionslinjen. Syftet med detta examensarbete är att undersöka om den oförstörande provningsmetoden NAW®, som utvecklats av Acoustic Agree i Ronneby, kan vara en lösning för att hitta defekterna på ett tidigare stadium. Oförstörande provning är helt enkelt materialprovning där föremålet som undersöks inte förstörs. Ett enkelt exempel på verktyg för oförstörande provning är ögat. Genom att undersöka ett föremål med synen kan man enkelt kvalificera ytan. Den metod som används i detta arbete, NAW®, är en olinjär akustisk metod. Genom att lyssna på materialet kan mycket information om störningar inuti materialet samlas ihop och tolkas för att få en bild av kvaliteten. För flera materialbitar har experiment genomförts både för referensmaterial och för material med imiterade defekter. Det var svårt att se entydiga resultat då exempelvis till och med resultaten för referensmaterialet var väldigt olika sinsemellan. Dock pekar vissa av resultaten åt samma håll vilket gör att hoppet lever kvar för att NAW® kan vara ett möjligt verktyg i produktionen hos Tarkett. Ett stort problem i arbetet var frånvaron av trovärdiga defekter. Defekterna tillverkades och introducerades i materialet för hand, och viss tveksamhet finns gällande likheten mellan imiterade och riktiga defekter. Detta ses som en möjlig felkälla och måste tas i beaktan för eventuellt fortsatt arbete. Antingen måste de imiterade defekterna ”förbättras” eller, som vore idealt, så kan riktigt defekt material från tillverkningen användas för att ge så trovärdiga och pålitliga resultat som möjligt.

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Non-Destructive Testing of industrial components carries vital importance, both financially and safety-wise. Among all Non-Destructive techniques, Long Range Ultrasonic Testing utilizing the guided wave phenomena is a young technology proven to be commercially valid. Owing to its well-documented analytical models, Ultrasonic Guided Waves has been successfully applied to cylindrical and plate-like structures. Its applications to complex structures such as multi-wire cables are fairly immature, mainly due to the high complexity of wave propagation. Research performed by the author approaches the long range inspection of overhead transmission line cables using ultrasonic guided waves. Existing studies focusing on guided wave application on power cables are extremely limited in inspection range, which dramatically degrades its chances of commercialization. This thesis consists of three main chapters, all of which approaches different problems associated with the inspection of power cables. In the first chapter, a thorough analysis of wave propagation in ACSR (most widely used power cable) cables is conducted. It is shown that high frequency guided waves, by concentrating the energy on the surface layers, can travel much further in the form of fundamental longitudinal wave mode, than previous studies have shown. Defect detection studies proved the system’s capability of detecting defects which introduce either increase or decrease in cross sectional area of the cable. Results of the chapter indicate the detectability of defects as small as 4.5% of the cross sectional area through a 26.5 meter long cable without any post-processing. In the second chapter, several algorithms are proposed to increase the inspection range and signal quality. Well-documented wavelet-denoising algorithm is optimized for power cables and up to 24% signal-to-noise ratio improvement is achieved. By introducing an attenuation correction framework, a theoretical inspection range of 75 meters is presented. A new framework combining dispersion compensation and attenuation correction is proposed and verified, which shows an inspection range of 130 meters and SNR improvement up to 8 dBs. Last chapter addresses the accurate localization of structural defects. Having proven the optimum excitation and related wave propagation in ACSR cables, a system having a more complex wave propagation characteristics is studied. A new algorithm combining pulse compression using Maximal Length Sequences and dispersion compensation is applied to multi-modal signals obtained from a solid aluminum rod. The algorithm proved to be able to improve signal quality and extract an accurate location for defects. Maximal Length Sequences are compared to chirp signals in terms of SNR improvement and localization, which produced favourable results for MLS in terms of localization and for chirp in terms of SNR improvement.

"The condensation of vapor onto a cooled surface is a phenomenon which can be difficult to quantify spatially and as a function of time; this thesis describes an ultrasonic system to measure this phenomenon. The theoretical basis for obtaining condensate film thickness measurements, which can be used to calculate growth rates and film surface features, from ultrasonic echoes will be discussed and the hardware and software will be described. The ultrasonic system utilizes a 5MHz planar piston transducer operated in pulse-echo mode to measure the thickness of a fluid film on a cooled copper block over the fluid thickness range of 50 microns to several centimeters; the signal processing algorithms and software developed to carry out this task are described in detail. The results of several experiments involving the measurement of both non-condensing and condensing films are given. In addition, numerical modeling of specific condensate film geometries was performed to support the experimental system; the results of modeling nonuniform fluid layers are discussed in the context of the effect of such layers on the measurement system."

<p>The objective of this research is to develop recommendations on calibration standards, scanning procedures, and acceptance criteria for phased array ultrasonic testing (PAUT) of complete joint penetration butt welds within the AWS D1.5 Bridge Welding Code. These recommendations include the development of a rational acceptance criteria which is based in engineering analysis and fracture mechanics. It is expected that the updated scanning procedures and acceptance criteria will result in improved reliability for bridges and improved consistency in bridge fabrication quality.</p><p><br></p> <p> </p> <p>While PAUT was included in the 2015 edition of AWS D1.5 in Annex K, the acceptance criteria for this procedure was developed as an adaptation of an existing conventional ultrasonic testing (UT) acceptance criteria in AWS D1.1. Therefore, the acceptance criteria in AWS D1.5:2015 is a workmanship-based criteria and is not based on engineering analysis of the criticality of weld flaws. The scanning procedures and application of PAUT inspections of bridge welds according to this procedure differ greatly from the scanning procedures outlined in AWS D1.5 for conventional UT inspections. Previous research has shown that differences in flaw rejection are possible for PAUT and conventional UT ultrasonic methods under the AWS D1.5:2015 approach.</p><p><br></p> <p> </p> <p>In order to develop recommendations for improved calibration standards, scanning procedures, and acceptance criteria for PAUT within AWS D1.5, this research project utilized both analytical techniques and experimental testing. This research project included determination of target critical flaw sizes for routine detection and rejection through fitness-for-service evaluations. This was followed by a round robin ultrasonic testing program in order to collect data on the variability of inspection results of eleven weld samples with nineteen weld flaws using different ultrasonic inspection techniques. Next, calibration requirements were developed to account for differences in ultrasonic attenuation and shear wave velocity between calibration blocks and test objects. Development of these requirements included experimental testing of base metals and weld metals, along with simulations of ultrasonic inspection using commercial software. Finally, minimum requirements for weld scanning procedures, reference standard reflectors, and corresponding amplitude limits for detection and rejection of target critical weld flaws were developed using ultrasonic inspection simulations and verified through experimental testing of weld samples with known weld flaws.</p>