La propagation des ondes élastiques dans les structures périodiques infinies est décrite par la théorie de Floquet-Bloch. Les contraintes expérimentales conduisant nécessairement à des cristaux phononiques de taille finie, des écarts à la théorie sont donc envisageables. Par ailleurs, le comportement expérimental des ondes élastiques au sein de ces milieux périodiques est mal décrit à ce jour, car déduit du signal transmis. Ainsi, un grand nombre de phénomènes, n'existant qu'au sein des cristaux, ne peuvent être mis en évidence. La première partie de ce travail expérimental vise à mieux appréhender la dispersion des ondes élastiques se propageant au sein de cristaux phononiques bidimensionnels. Ces derniers sont composés d'inclusions d'air obtenues par photolithographie et attaque chimique de plaques minces de silicium. Un montage "ultrasons-laser", permettant la génération et la détection d'ondes élastiques en tout point de la surface de l'échantillon, a été mis au point. L'analyse des champs de déplacements de surface a permis la mise en évidence de la décomposition des vecteurs d'onde telle que prédite par la théorie de Floquet-Bloch. Une observation des modes à vitesse de groupe nulle en bord de gap a également été réalisée. Enfin, l'influence de la dissymétrie des inclusions sur l'ouverture de gap intra-bande a été étudiée. La seconde partie de ce travail est consacrée à l'observation expérimentale de la réfraction négative d'ondes élastiques, de Lamb et de Rayleigh, par des cristaux phononiques à deux dimensions et à matrices solides (silicium et silice). Le lien entre la propagation des ondes au sein du cristal phononique et leur réfraction à l'interface avec le milieu homogène est établi.

In one of the non-destructive testing techniques, Lamb waves, because of its ability to propagate a long distance and being hard to attenuate, can detect a wide range of area. However, due to its multimodal and dispersive characteristics, identifying the signals of defects during the test is often difficult. Time reversal method, a self-focusing technique, can offset the dispersion of Lamb waves and effectively focus on the spatial and temporal domain. This study applies the finite element method to stimulate the propagation of Lamb waves on an aluminum plate, selecting four sets of frequency-thickness products and two excitation types to excite the single-mode or multimode Lamb waves. This study aims to discuss the effects of modal and dispersion on the focus of the time reversal methods. The results show that 2 MHz-mm and in-plane excitation can produce numerous, more dispersive modals with the best focus effect. If we applied the time reversal method to testing the defects of Lamb waves, and the defects are circular and longitudinal notches, then, according to the results, the reflection signal amplitude of the circular defects can be highly increased. According to the test results of small-sized notches, the time reversal method cannot effectively improve the detecting ability of this defect.

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The primary objective of this study was to increase net farm income in the Highland Sourveld of Natal by developing pasture based fat lamb production systems. Secondary objectives included (a) determination of the most suitable pasture species or species mixture; (b) determination of the optimum level of N fertilization; (c) establishment of biological and economic optimum stocking rates; (d) projection of expected profit and (e) verification of proposals on a farm scale. Midmar Italian ryegrass was compared to selected legumes alone, and in mixtures with ryegrass in a small plot trial conducted over two years at a 3- and 6-week harvesting frequency under irrigation. Ryegrass in combination with red and white clover provided the highest yields for both harvesting intervals in both years. When this pasture was subsequently compared to ryegrass alone under grazing, no significant difference could be detected in lamb gains at 20 and 28 ewe-lamb units/ha, but at 36 ewe-lamb units/ha the lambs on ryegrass started losing weight at 30 kg, while those on ryegrass + clover continued to gain until a market weight of 40 kg was achieved. In a small plot trial little response was detected to added N above 175 kg N/ha on ryegrass + clover, and under grazing, no significant difference was observed between 275; 375 and 4,75 kg N/ha over two single year periods. Relationships between average daily gain (ADG) and stocking rate, ADG and disc meter height, and stocking rate and disc meter height were mostly well described by linear functions. Expected pre-weaning AOG was 150 g higher (p ≤ 0,01) than post-weaning ADG (100 g) in the first year, and a similar difference was observed in the second year. For the period common to all stocking rates an average maximum gain/ha of 824 kg was achieved at a stocking rate of 33,5 lambs/ha and a disc meter height of 4,5 cm. By lambing in April, lambs could be marketed in September at 40 kg and more weaned lambs could be grazed on the pasture and marketed in December, leading to an expected gain/ha of 1400 to 2200 kg, and expected profit/ha of R 1254 to R 2771, depending on stocking rate. When evaluated under farm conditions, this system produced 2060 kg live weight/ha and a profit of R 3206/ha. It is concluded from the present study that the fat lamb production system based on irrigated ryegrass + clover pastures can be recommended with confidence to farmers in the Highland Sourveld of Natal. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1986.

The application of laser generated ultrasonics was first demonstrated in the mid-seventies and has shown good potential when applied to isotropic materials. However, its use with composite materials is still in the early stages of development. This study explores the potential for application of laser generated Rayleigh and Lamb waves in graphite/epoxy composites. Numerical results are obtained by the solution of the wave equations using assumed solutions, and enforcing the boundary conditions. Experimentally, Rayleigh and Lamb waves were generated by a Q-switched ruby laser in the ablation regime and detected by piezoelectric pinducers which permitted accurate phase velocity measurements. The Rayleigh wave velocity was measured at various directions relative to the fiber direction and results were found to agree closely with numerical predictions. The increase of surface wave velocity using thin plates could be useful for the application of delamination detection in thick composites and an increase of Rayleigh wave attenuation could indicate damages caused by impact. Also, surface waves can reflect from small surface cracks. Therefore, laser generated surface waves, particularly along the fiber direction, have high potential for application in non-destructive testing. Lamb wave experiments were conducted in aluminum plates and gave distinctive signals, but there were some difficulties in detecting the precise arrival of each Lamb wave mode for the graphite/epoxy composite plates. / Graduation date: 1992

Thesis (Ph. D.)--University of Pennsylvania, 1932. / Bibliography: p. 233-238.

Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Jacobs, Laurence; Committee Member: Kim, Jin-Yeon; Committee Member: Qu, Jianmin. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Laurence J. Jacobs; Committee Member: Jianmin Qu; Committee Member: Jin-Yeon Kim. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Orientador: Américo Garcia da Silva Sobrinho / Banca: Emanuel Almeida de Oliveira / Banca: Iraides Ferreira Furusho Garcia / Resumo: Objetivou-se avaliar as características da carcaça e de seus não componentes em cordeiros alimentados com fenode amoreira (FA) no concentrado em substituiçãoao farelo desoja e milho,além das características qualitativas de hambúrguerese linguiças elaboradas com fígadoovino. Foram utilizados 24 cordeiros com 15,48 ±0,07 kg de peso corporal alojados em baias individuais eabatidos aos 32,20 ± 0,49 kg. Os tratamentos foram: 0%FA: cana forrageira + concentrado, 12,5%FA: cana forrageira + concentrado + 12,5% defeno de amoreira na MS e 25%FA: cana forrageira + concentrado + 25%de feno de amoreirana MS. Os hambúrgueres e linguiças foram elaborados com carne de cordeiros provenientes do tratamento controle do experimento acima anterior, sem ou com (15 e 30%) inclusãode fígado ovino em substituição à carne de pescoços e costelas desossadas. Odelineamento experimental foi o inteiramente casualizadosendo os dados submetidos à análise de variância e regressãopelo programa estatístico Sisvar a 5% de significância.A inclusão do fenodeamoreira promoveu efeito linearcrescente para a profundidade do tórax, índice de musculosidade da perna e relaçãomúsculo:osso eefeito linear decrescente, para o índice de compacidade da carcaça,peso da paleta, área de olho de lombo obtida pelo ultrassom, peso e comprimento do fêmur, peso dapele e pesoe porcentagemdas extremidades dos membros. Houve efeito linear crescentepara teoresde sódio no fígado, potássio no coração e sódio, potássio, cálcio, ferro e cobre na língua de cordeiros recebendo feno de amoreira.A inclusão do fígado nos processados comcarne ovina promoveu aumento na luminosidade e efeitoquadrático para a intensidade de vermelho. As variáveis pH, capacidadede retenção de água, força de cisalhamento, oxidação lipídica no dia 0 e 45 dias, teor de gordura e sabor dos hambúrgueres tiveram efeito quadrático... / Abstract: The aim of this study was to evaluate non-components and carcass traits of lambs fed concentrate containing mulberry hay (FA) as a substitute for soybean and corn. Further, qualitative traits of hamburgers and sausages made with sheep liver were evaluated. Twenty-four lambs with 15.48 ± 0.07 kg live weight were allotted in individual pens and slaughtered at 32.20 ± 0.49 kg. The treatments were: 0%FA: sugarcane forage + concentrate, 12.5%FA: sugarcane forage + concentrate + 12.5% mulberry hay, dry basis and 25%FA: sugarcane forage + concentrate + 25% mulberry hay, dry basis. The hamburgers and sausages were elaborated with lamb meat from the control treatment of the experiment cited above, with the inclusion (15 and 30%) or not of sheep liver as a substitute for neck and ribs. A completely randomized design was used and data were submitted to an analysis of variance and regression analysis using the Sisvar software with a 5% significance level. A linearly increasing for chest depth, leg muscularity and muscle: bone ratio were observed with the inclusion of mulberry hay and a linearly decreasing for carcass compactness index, palette weight, loin-eye area through ultrasound, femur weight and length, skin weight and limb percentages. A linearly increasing effect for sodium levels in the liver, potassium in the heart and sodium, potassium, iron and cupper in the tongue were observed in the lambs fed mulberry hay. An increasing luminosity and a quadratic effect for red intensity were observed with the inclusion of liver in the meat products of sheep meat. The pH, water-holding capacity, shear force, lipid oxidation at 0 and 45 days, fat level and the flavor of hamburgers showed quadratic effects... / Mestre