Creep and creep rupture of laminated graphite/epoxy composites

An incremental numerical procedure based on lamination theory is developed to predict creep and creep rupture of general laminates. Existing unidirectional creep compliance and delayed failure data is used to develop analytical models for lamina response. The compliance model is based on a procedure proposed by Findley which incorporates the power law for creep into a nonlinear constitutive relationship. The matrix octahedral shear stress is assumed to control the stress interaction effect. A modified superposition principle is used to account for the varying stress level effect on the creep strain. The lamina failure model is based on a modification of the Tsai-Hill theory which includes the time dependent creep rupture strength. A linear cumulative damage law is used to monitor the remaining lifetime in each ply

Ecology of Plant Distribution on the Salt-Deserts of Utah

The reciprocal effects of vegetation and soils have long been a subject of speculation and conjecture. In the management of any natural land area the problem of interpreting vegetational expression is especially important. The effects of native vegetation on soils and the effects of the soil on the vegetation have been studied and observed for many years. The arid-desert range lands have been studied and observed for many years. The arid-desert range lands have been studied least and as a result are not well understood. As human populations increase there will be additional need for agricultural production, and these lands may be put to higher use, perhaps even to irrigated crop production. Basic to increasing the productivity of these lands is an understanding of the vegetation they are now supporting, what they supported prior to their use by domestic livestock, and why the present vegetation grows to the exclusion of other vegetation types

High-volume pressure relief valve

Valves with counterweights to assist in opening and closing are described, which can release large volumes of gas almost instantaneously, and provide airtight seals

The Effect of a Fine Arts Program on the Intelligence, Achievement, Creativity and Personality Test Scores of Young Gifted and Talented Students

The problem of this study was to determine if young gifted and talented students who participate in a special program of the fine arts score significantly higher on tests of intelligence, language arts achievement, creativity, and personality than young gifted and talented students who do not participate in the program. For the study 102 students from kindergarten, first, second and third grades were selected. At the end of the study, ninety-seven students were posttested. Five students had moved from the school district. The students were selected for the program on the basis of teacher recommendations and on the basis of scores acquired on tests of intelligence, achievement, and creativity. Students selected for the program were additionally administered a personality pretest. Following participation in the fine arts program they were administered posttests in the four areas. The following questions were considered: (1) Does participation in a fine arts program significantly enhance the test scores of young gifted and talented students in the areas of intelligence, language arts achievement, creativity, and personality? (2) Does participation in a fine arts program and in an additional home component of the program significantly enhance the test scores of young gifted and talented students in the areas of intelligence, language arts achievement, creativity, and personality? (3) Does the basis of selection for a special program for gifted and talented students significantly influence the test scores in the area by which the student was selected? The study revealed that gifted and talented students at certain grade levels who participated in a fine arts program for a minimum of one hour per week scored significantly higher on tests of intelligence and on tests of creativity than young gifted and talented students who did not participate in the program. The study also revealed that students selected for the program on the basis of creativity showed significant increases in test scores of intelligence when compared with students selected on the basis of intelligence or language arts achievement

Numerical solution methods for viscoelastic orthotropic materials

Numerical solution methods for viscoelastic orthotropic materials, specifically fiber reinforced composite materials, are examined. The methods include classical lamination theory using time increments, direction solution of the Volterra Integral, Zienkiewicz's linear Prony series method, and a new method called Nonlinear Differential Equation Method (NDEM) which uses a nonlinear Prony series. The criteria used for comparison of the various methods include the stability of the solution technique, time step size stability, computer solution time length, and computer memory storage. The Volterra Integral allowed the implementation of higher order solution techniques but had difficulties solving singular and weakly singular compliance function. The Zienkiewicz solution technique, which requires the viscoelastic response to be modeled by a Prony series, works well for linear viscoelastic isotropic materials and small time steps. The new method, NDEM, uses a modified Prony series which allows nonlinear stress effects to be included and can be used with orthotropic nonlinear viscoelastic materials. The NDEM technique is shown to be accurate and stable for both linear and nonlinear conditions with minimal computer time

Use of hamster as a model to study diet-induced atherosclerosis

Golden-Syrian hamsters have been used as an animal model to assess diet-induced atherosclerosis since the early 1980s. Advantages appeared to include a low rate of endogenous cholesterol synthesis, receptor-mediated uptake of LDL cholesterol, cholesteryl ester transfer protein activity, hepatic apoB-100 and intestinal apoB-48 secretion, and uptake of the majority of LDL cholesterol via the LDL receptor pathway. Early work suggested hamsters fed high cholesterol and saturated fat diets responded similarly to humans in terms of lipoprotein metabolism and aortic lesion morphology. Recent work has not consistently replicated these findings. Reviewed was the literature related to controlled hamster feeding studies that assessed the effect of strain, background diet (non-purified, semi-purified) and dietary perturbation (cholesterol and/or fat) on plasma lipoprotein profiles and atherosclerotic lesion formation. F1B hamsters fed a non-purified cholesterol/fat-supplemented diet had more atherogenic lipoprotein profiles (nHDL-C > HDL-C) than other hamster strains or hamsters fed cholesterol/fat-supplemented semi-purified diets. However, fat type; saturated (SFA), monounsaturated or n-6 polyunsaturated (PUFA) had less of an effect on plasma lipoprotein concentrations. Cholesterol- and fish oil-supplemented semi-purified diets yielded highly variable results when compared to SFA or n-6 PUFA, which were antithetical to responses observed in humans. Dietary cholesterol and fat resulted in inconsistent effects on aortic lipid accumulation. No hamster strain was reported to consistently develop lesions regardless of background diet, dietary cholesterol or dietary fat type amount. In conclusion, at this time the Golden-Syrian hamster does not appear to be a useful model to determine the mechanism(s) of diet-induced development of atherosclerotic lesions