Esta tese apresenta a análise teórica e experimental da detecção de onda de Lamb em sólido isotrópico, através da utilização de um interferômetro óptico tipo Mach-Zehnder heterodino. Foi desenvolvida uma formulação para analisar a interação acusto-óptica superficial que utiliza a onda de Lamb, levando-se em consideração ambas as componentes de deslocamento acústico geradas pela onda de Lamb. Os resultados dessa análise revelaram que, ao contrário do que é regularmente divulgado na literatura, existem situações onde a difração acusto-óptica decorre também devido à componente horizontal do deslocamento acústico gerado pela onda de Lamb. A formulação desenvolvida também proporciona uma abordagem rigorosa para o estudo das técnicas de detecção síncrona e assíncrona aplicadas à detecção óptica de onda acústica. Os resultados obtidos possibilitam uma compreensão detalhada da dependência das características do sinal elétrico obtido na saída do circuito de detecção, em função da posição do ponto de interação com relação à região de geração da onda de Lamb, bem como da influência da fase e amplitude do oscilador local nas características medidas do espectro do sinal de saída do interferômetro. Na parte experimental, a detecção óptica de onda de Lamb é investigada através da utilização do interferômetro na condição onde o feixe óptico incidente sobre o corpo de prova apresenta diâmetro significativamente menor que o comprimento de onda acústico. As medidas realizadas, utilizando as técnicas de detecção síncrona e travamento de fase, PLL, revelaram o comportamento periódico que o sinal detectado apresenta como função da distância do ponto de interação à região de geração da onda de Lamb. Os resultados experimentais incluem ensaios com onda de Lamb variando harmonicamente como o tempo. Através deles, foi possível determinar a velocidade de fase da onda de Lamb gerado pelo transdutor piezoelétrico.

In the UK annual lamb mortality rates range between 10-30% with the majority of deaths occurring within the first three days of life, however research has shown that lambs that stand and suck quickly are more likely to survive. Modern breeding strategies have led to breeds of sheep, such as the Suffolk, which despite greater lean muscle growth, show slower behavioural development and are less able to thermoregulate in the neonatal period than relatively unselected breeds, such as the Scottish Blackface. The reason for this is unclear however fast growing strains of pigs and cattle have been shown to have a greater proportion of fast-twitch fibres to slow fibres in their muscles, but it is still unknown as to whether these changes in fibre proportions affect muscle function and behaviour. Thus the aim of this project is to investigate whether selection for lean muscle growth in sheep has altered muscle development by affecting the proportions of different fibre types and determine what effect this may have on the animal’s ability to perform certain behaviours, such as neonatal progression to standing and sucking. As muscle fibre development occurs very early in gestation (starting around day 32) it was also hypothesised that there may also be a relationship between muscle fibre characteristics, and foetal behaviour and presentation at birth. A further hypothesis to be addressed was that maternal undernutrition of 75% of requirements for ewe maintenance and foetal growth for the first 90 days of gestation would have a greater negative effect on muscle fibre development in genotypes selected for lean muscle growth. It was found that Suffolk foetuses (genotype selected for lean growth) were significantly less active at days 56 and 77 of gestation than Blackface foetuses (genotype relatively unselected for growth) while nutritionally restricted foetuses were more active at day 56 than control foetuses. A subsequent study found that there was a negative relationship between foetal activity at day 56 and neonatal activity while activity at day 98 of gestation was positively associated with neonatal activity. A relationship was also found between foetal activity and presentation at birth with malpresented lambs being less active as foetuses at day 77 of gestation than normally presented lambs. Suffolk foetuses had lower proportions of slow twitch (SO) fibres and higher proportions of fast-oxidative-glycolytic (FOG) fibres in the soleus (postural muscle) than Blackface foetuses and SO fibre proportions were positively correlated with foetal activity at days 56 and 77 of gestation while fast twitch (FOG and FO) and transitional (Trans) fibre proportions were negatively correlated with foetal activity at each scanning period. Suffolk lambs showed significantly slower neonatal behavioural development than Blackface lambs and there was an interaction between breed and nutritional treatment with prenatally undernourished Suffolk lambs consistently being less active and prenatally undernourished Blackface lambs being more active than all other groups of lambs. At slaughter at 164 days old, Suffolk lambs had lower proportions of SO fibres and higher proportions of fastglycolytic (FG) fibres in the soleus muscle while also having a lower proportion of FG fibres in the plantaris (muscle involved in movement of the limb) than Blackface lambs. SO fibre proportions in the soleus muscle were found to be positively correlated with total duration standing and walking in the early neonatal period while proportion of FG fibres in the plantaris was negatively correlated with duration of lying laterally following birth. The results from this study indicate that divergent breeding strategies have led to differences in muscle fibre proportions within certain muscles in sheep and also that there may be a relationship between muscle development and both foetal and neonatal lamb behaviour. This research has added to our understanding of the consequences of selection for growth on the function of the animal and it is hoped that it will lead to the development of broader breeding goals which incorporate welfare characteristics.

An understanding of the generation of higher harmonics in Lamb waves is of critical importance for applications such as remaining life prediction of plate-like structural components. The objective of this work is to use nonlinear Lamb waves to experimentally investigate inherent material nonlinearities in aluminum plates. These nonlinearities, e.g. lattice anharmonicities, precipitates or vacancies, cause higher harmonics to form in propagating Lamb waves. The amplitudes of the higher harmonics increase with increasing propagation distance due to the accumulation of nonlinearity while the Lamb wave travels along its path. Special focus is laid on the second harmonic, and a relative nonlinearity parameter is defined as a function of the fundamental and second harmonic amplitude. The experimental setup uses an ultrasonic transducer and a wedge for the Lamb wave generation and laser interferometry for detection. The experimentally measured Lamb wave signals are processed with a short-time Fourier transformation (STFT) and a chirplet transformation-based algorithm, which yield the amplitudes of the frequency spectrum as functions of time, allowing the observation of the nonlinear behavior of the material. The increase of the relative nonlinearity parameter with propagation distance as an indicator of cumulative second harmonic generation is shown in the results for two different aluminum alloys. The difference in inherent nonlinearity between both alloys as determined from longitudinal wave measurements can be observed for the Lamb wave measurements, too.

Engineering industries usually require nondestructive evaluation (NDE) methods to ensure quality control, safety, and optimized use of resources. Among potential NDE techniques, ultrasonic wave methods are widely used because of their versatility and affordability. For applications to layered structures, ultrasonic guided waves are naturally excited and detected, so these guided waves are the preferred choice when compared to conventional bulk waves. The main advantage of guided waves over bulk waves for layered structures is that these guided waves can propagate a much farther distance, and thus they enable long range inspection. It is important to note that guided waves are multi-mode, so a preferred mode can be selectively used, although it is sometimes more efficient to use multiple wave modes. The characteristics of guided waves, namely dispersive propagation and attenuation, are directly related to the properties of the system in which they are propagating, so the measurement of these wave characteristics can be used for material characterization and condition monitoring. Despite a number of successful techniques to experimentally measure propagation characteristics of guided waves, there is a lack of a standard procedure to obtain attenuation characteristics. This research develops such a quantitative and systematic procedure to extract attenuation characteristics from real guided wave time-domain signals. This research considers multiple wave-modes, and focuses on broadband attenuation measurements with laser ultrasonic techniques. The analytical model of guided waves with attenuation is studied in general cases, and a numerical simulation is developed to model the point source/receiver laser measurement system. The attenuation extraction technique is developed using synthetic signals generated by the simulation. Finally, this research demonstrates the use of experimentally-measured attenuation data for material characterization and condition monitoring by developing an inversion scheme to back-calculate material properties for a number of practical cases.

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Nutrient profiles of distillers grains are primarily affected by the type of grain used for ethanol production, but the feeding value of triticale-based dry distillers grains plus solubles (TDDGS) has not been extensively studied. The first study showed that, compared to 20% corn- or wheat-based distillers grains diets, 20% TDDGS diet increased cis-9 trans-11 linoleic acid concentration in carcass fat without affecting growth performance of lambs. In the second study, lamb growth performance was not affected by the addition of up to 60% TDDGS in the diet, but the risk of urinary calculi increased at higher inclusion levels. Lambs fed 20% TDDGS had higher cold carcass weights and grade rules than lambs fed 40 or 60% TDDGS. Increasing TDDGS decreased diet digestibility, and increased nitrogen and phosphorus excretion. In conclusion, TDDGS can be used in diets for growing ruminants, and its utilization efficiency may be optimized at 20% dietary inclusion. / Animal Science

Frankfurt (Main), Univ., Diss., 2009 / Erscheinungsjahr an der Haupttitelstelle: 2008