This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

This thesis is concerned with the accurate numerical simulation of localized deformation that can develop into necking and failure, induced by combined bending and tension in aluminum alloy shell structures. The study is motivated by the need to establish the onset and evolution of such failures in imploding underwater cylindrical aluminum alloy shell structures. However, failure under combined bending and tension is also of concern in sheet metal forming. Such localized zones of deformation are shown to develop under controlled conditions in specially designed crushing experiments of Al-6061-T6 cylindrical shells. In these experiments shells of finite length and radially constrained ends are crushed laterally by rigid punches. The crushing, which is conducted under displacement control, causes the shell to develop bending and stretching stresses that lead to arcs of localized wall thinning to appear near the radially constrained locations. The local wall thinning develops into depressions with a width of the order of the shell wall thickness. As crushing progresses the depressions deepen, increase their span, become neck-like and develop inclined failures. The crushing was terminated when the first of four such depressions ruptured. After unloading, the shell was sliced along the principal plane of crushing and the most deformed cross sections of the necks were measured using an optical microscope. The crushing experiments were simulated numerically using solid FE models. The material was modeled as a finitely deforming elastic-plastic solid that hardens isotropically using three constitutive models: the first is based on the von Mises yield function, the second on the non-quadratic isotropic Hosford yield function and the third on the anisotropic Yld04-3D yield function. The models were calibrated to the same stress-strain response and to data from a set of radial biaxial experiments conducted on the same alloy tubes. The overall structural response was reproduced well by all models. Apparently such global responses smear out local differences introduced by the shape of the yield function adopted. However, differences between the three constitutive models were observed in the evolution of localization in the depressions. For the von Mises yield function, the localized deformation was significantly milder than in the experiments. The isotropic Hosford yield function produced necks that were closer to the experimental ones, while Yld04-3D produced results that were very close to the measurements. Clearly, and in concert with other applications, the adoption of a non-quadratic yield function is necessary for reproduction of localization and other challenging deformation histories in Al alloys. The addition of anisotropy in such models improves further the predictions. The results also demonstrated that accurate simulation of the evolution of the depressions in the presence of normal contact stresses requires the use of solid elements. Localization is clearly a three-dimensional phenomenon and shell elements reproduce most of the structural response well, but not the depressions and their evolution that eventually cause failure. / text

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Crop emergence is a major factor limiting crop yield, especially in hot climates where soil dries quickly after rainfall or irrigation. Problems with the emergence of cotton in Pakistan are of particular importance because of the high value of the crop and its contribution to national economy. A complex interaction of factors involving climate, seed properties, soil physical properties and soil management determine crop emergence and hence establishment. This means modelling of emergence is an important way of determining the combination of conditions at which emergence becomes limited. The studies reported here show the effect of temperature, matric potential and mechanical impedance on pre-emergent root and shoot growth of cotton variety MNH-147. The effect of osmotic potential and temperature on time to germination and cumulative germination of cotton is also described with some preliminary work on wheat. Finally a small field experiment was performed in Pakistan to identify major factors limiting emergence and provide data for future validation of a computer model of emergence. Time to germination was found to be a function of temperature and metric potential. It reduced with increase in temperature and osmotic potential. A linear relationship between temperature and germination rate (1/time to germination) indicated a base temperature of 9.8 °C. Germination rate also decreased linearly with decreasing osmotic potential between zero and -500 kPa. Thus the concept of hydrothermal time can be used to model germination and parameters to fit this model were determined. Root and shoot lengths of pre-emergent cotton seedling increased with increase in temperature from 22 to 32 °C but were reduced with a further increase to 38 °C. At any temperature, lengths increased linearly with time at a rate controlled by temperature. During the first 192 h after germination, growth was divided into two distinct phases: a linear increase with time followed by no further growth.

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Recently a new x-ray absorption spectroscopy (XAS) called inverse partial fluorescence yield (IPFY) has been developed that is bulk sensitive and free of saturation effects, which also provides a direct measure of total absorption coefficient. However, IPFY was originally formulated for smooth bulk samples, but XAS is often performed on rough samples. To test the applicability of IPFY on rough surfaces, a model is presented and the calculations based on this model are compared to the experimental results measured on NdGaO3. It is shown that the correspondence between calculated and experimental intensities of IPFY is sufficient to corroborate this model a means of estimating the maximum allowable surface roughness size and the optimal detection geometry.

This study aimed to investigate the response of lentil genotypes to different water regimes, providing guide lines, through partitioning the variation, for a selection program for adaptation to irrigated conditions. The research was divided into two main areas; 1) The overall variation in the crop was partitioned into genotypic, environmental and genotype-environmental components in an analysis of adaptation over seasons, irrigation regimes and locations; 2) The genotypic variation was partitioned into its various genetic components in an inheritance study using the dial lei mating system. Pronounced progress should be expected from selection for number of pods/plant, 100 seed weight and straw yield/plant traits, which showed high estimates of h(^2)(_b.s), C.G.V. and G.S. The two former traits correlated strongly and positively with seed yield, which allowed their use in indirect selection for seed yield. The 35 genotypes used in this study showed wide genetic diversity, allowing selection of high yielding genotypes under irrigation. Environmental variation in water supply, temperature and soil type was found to exert a profound effect on variation in characters measured. This suggests the possibility of raising yield levels through improved management practices. In this study, irrigation repeated twice increased seed yield by 19% over no irrigation, at the same location, and increased the yield by 300% in comparison with a dry location. Seed protein quality was influenced by environments and genotypes. Electrophoretic studies showed that the number and position of the bands could be used to identify genotypes. Four genotypes showed response to irrigation and could be recommended as promising entries. An anatomical study showed that large air spaces formed in the roots of a responsive genotype:, which could be used as a selection criterion for positive response to irrigation. Seed yield/plant exhibited 31.8% heterosis and showed a predominant role of non-additive genetic variance. Due to the significance of the non-additive effect, the superior F(_1)'s may be expected to throw out desirable transgressive segregants, provided that the complementary genes and epistatic effects included in the non-additive component are coupled in the same direction to maximize seed yield. Five F(_2) crosses showed superiority in seed yield and SCA effects. These crosses should be carried forward in lentil breeding programs.

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