The effects of microcracking on the thermal expansion of graphite-epoxy composites

A study of the effects of thermal environment and microcracking in graphite epoxy composites was made. Research indicates that microcracking does affect the thermal expansion of composite laminates. The amount of reduction in thermal expansion was a function of the crack density. A maximum reduction of approximately 25% occurred in a quasi-isotropic specimen with a crack density of 2.05 mm 1 in the 90 deg plies. Laminate analysis with appropriate reductions in E sub 2 and Alpha sub 2 of the damaged plies appears to be capable of modeling the observe

The occurrence of the genus Maruina (Diptera: Psychodidae) in Texas

I recently collected immature stages of the aquatic dipteran genus Maruina from a spring-run located in the Big Bend region of western Texas

Finite Element Composite Analysis Program (FECAP) for a microcomputer

A special purpose finite element composite analysis program for analyzing composite material behavior with a microcomputer is described. The formulation assumes a state of generalized plane strain in a material consisting of two or more orthotropic phases. Loading can be mechanical and/or thermal. The theoretical background, computer implementation, and program users guide are described in detail. A sample program is solved showing the required user input and computer generated output

Study of vapor flow into a capillary acquisition device

An analytical model was developed that prescribes the conditions for vapor flow through the window screen of a start basket. Several original submodels were developed as part of this model. The submodels interrelate such phenomena as the effect of internal evaporation of the liquid, the bubble point change of a screen in the presence of wicking, the conditions for drying out of a screen through a combination of evaporation and pressure difference, the vapor inflow rate across a wet screen as a function of pressure difference, and the effect on wicking of a difference between the static pressure of the liquid reservoir and the surrounding vapor. Most of these interrelations were verified by a series of separate effects tests, which were also used to determine certain empirical constants in the models. The equations of the model were solved numerically for typical start basket designs, and a simplified start basket was constructed to verify the predictions, using both volatile and nonvolatile test liquids. The test results verified the trends predicted by the model

Light weight polymer matrix composite material

A graphite fiber reinforced polymer matrix is layed up, cured, and thermally aged at about 750 F in the presence of an inert gas. The heat treatment improves the structural integrity and alters the electrical conductivity of the materials. In the preferred embodiment PMR-15 polyimides and Celion-6000 graphite fibers are used

Aquatic Invertebrate Community Structure, Biological Condition, Habitat, and Water Quality at Ozark National Scenic Riverways, Missouri, 2005-2014

Ozark National Scenic Riverways (OZAR) was established to protect the corridor of the Current River and its major tributary, the Jacks Fork. The Current River is one of the few remaining free-flowing rivers in the U.S., with much of its base flow coming from several large springs. To assess the biological condition of these rivers, aquatic invertebrate community structure was monitored from 2005 to 2014. Benthic invertebrate samples and associated habitat and water quality data were collected from each of nine sampling sites using a Slack-Surber sampler. The Stream Condition Index (SCI), a multimetric index that incorporates taxa richness, EPT (Ephemeroptera, Plecoptera, Trichoptera) richness, Shannon’s diversity index, and Hilsenhoff Biotic Index (HBI), was calculated. The benthic invertebrate fauna was diverse with 155 distinct taxa identified from all sites. Mean taxa richness was high, ranging from 22 to 30 among sites. The invertebrate taxa of the Current River and Jacks Fork are largely intolerant across all taxa represented (mean tolerance value= ~4.25). Mean HBI did not exceed 3.9 in the Current River or 4.4 for the Jacks Fork. Mean SCI scores across sampling sites generally were well above 16, indicating they are not impaired. Habitat and water quality data were summarized, but they were poorly correlated with individual invertebrate metrics. Sørenson’s similarity index was used to assess community similarity among sites, and similarity scores were then analyzed using ascendant hierarchical cluster analysis. Similarity among sites was 72% or greater. Cluster analysis showed that Current River and Jacks Fork sites clustered separately and in a downstream progression. The uppermost collection site on the Current River was most unlike the other sites, which probably relates to the distinct physical features of that site compared to the others. Nonmetric Multidimensional Scaling (NMDS) was used to evaluate the relationship of invertebrate metrics to habitat and water quality. The NMDS model was found to be a good fit (stress=0.04) and specific conductance, temperature, discharge, filamentous algae and aquatic vegetation were among the most important habitat variables in defining the relationship among sampling sites. The three lower Current River and Jacks Fork sites each were closely grouped in ordination space, but the three upper Current River sites were farther apart from each other. The influence of several large volume springs near those sites is suspected of producing such disparity through press type disturbances. Although the invertebrate communities and water quality in the Current River and Jacks Fork are largely sound and have high biological condition, ongoing and projected threats to these resources remain, and those threats largely originate outside park jurisdictional boundaries. Inherent variability of invertebrate community diversity across sites and years highlights the importance of using multi-metric assessments and multiyear monitoring to support management decisions

Heart and Minds: A Social Model of U.S. Productivity Growth

macroeconomics, product growth

A Dobsonfly, Corydalus cornutus (Megaloptera: Corydalidae), from Arkansas with Aberrant Mandibles

No abstract required for general note

Combined mechanical loading of composite tubes

An analytical/experimental investigation was performed to study the effect of material nonlinearities on the response of composite tubes subjected to combined axial and torsional loading. The effect of residual stresses on subsequent mechanical response was included in the investigation. Experiments were performed on P75/934 graphite-epoxy tubes with a stacking sequence of (15/0/ + or - 10/0/ -15), using pure torsion and combined axial/torsional loading. In the presence of residual stresses, the analytical model predicted a reduction in the initial shear modulus. Experimentally, coupling between axial loading and shear strain was observed in laminated tubes under combined loading. The phenomenon was predicted by the nonlinear analytical model. The experimentally observed linear limit of the global shear response was found to correspond to the analytically predicted first ply failure. Further, the failure of the tubes was found to be path dependent above a critical load level

Thermal expansion of graphite-epoxy between 116 K and 366 K

A Priest laser interferometer was developed to measure the thermal strain of composite laminates. The salient features of this interferometer are that: (1) it operates between 116 K and 366 K; (2) it is easy to operate; (3) minimum specimen preparation is required; (4) coefficients of thermal expansion in the range of 0-5 micro epsilon/K can be measured; and (5) the resolution of thermal strain is on the order of micro epsilon. The thermal response of quasi-isotropic, T300/5208, grahite-epoxy composite material was studied with this interferometer. The study showed that: (1) for the material tested, thermal cycling effects are negligible; (2) variability of thermal response from specimen to specimen may become significant at cryogenic temperatures; and (3) the thermal response of 0.6 cm and 2.5 cm wide specimens are the same above room temperature