Tests were conducted to determine whether aircraft flight conditions change moisture absorption behavior in graphite-epoxy composites. Flight temperature profiles were simulated for a subsonic mission, -65°F (-54°C) for 90 minutes, and for a flight involving a subsonic segment with a supersonic dash. The simulated dash involved rapid heating to a peak of 300°F (149°C) followed by rapid cooling. These simulated dashes or thermal spikes caused small, temporary drying effects. However, they also caused permanent changes in the subsequent moisture diffusion behavior of the graphite-epoxy. Both the amount and rate of moisture absorption were significantly increased. Subsonic temperatures, however, caused no detectable change in diffusion behavior.
Fiber-reinforced epoxy laminates were exposed to several combinations of temperature and relative humidity. The purpose was to determine rates and extent of moisture absorption. Diffusion rates varied with temperature, and equilibrium moisture contents varied with relative humidity. Data analysis provided values for the material properties that determined diffusion behavior. A nonlinear diffusion model containing these values was shown to describe and predict absorption behavior for any combination of temperature and humidity. The model also describes desorption and correlates well with experimental data from changing humidity conditions.
Data are presented on the thermomechanical response and electrical conductivity of two commonly used epoxy materials, Narmco 5208 resin and RB 398 adhesive, as a function of increasing temperature. The overall conformity of the results shows that the second-order Ehrenfest-type glass transition temperature, designated as T2, governs the onset and evolution of changes in viscoelastic and electrical response as well as thermal expansion. The general features of this behavior are described with a five-element spring-and-dashpot model. The values of T2, and two other Williams-Landel-Ferry (WLF)-type parameters for the description of viscoelastic response above T2, can thus be derived from a single thermomechanical or electrical conductivity experiment conducted at constant heating rate.
Preliminary to conducting a collaborative study on a method for copper in serum, methods used by a selected group of laboratories were surveyed. The responding laboratories were supplied with a Youden pair of bovine serum samples and requested to use their current method for serum copper. Results of the analyses and the methods used were evaluated; hypotheses were developed in our laboratory to explain some of the interlaboratory variation. For the AAS method chosen, each of 12 collaborating laboratories analyzed one blind duplicate and 2 Youden pair of serum samples. A commercially available external control serum with a certified level of copper and a 1000 mg copper/L standard were also submitted. The method requires the serum to be diluted 1 + 1 with distilled water and the standards to be diluted with 10% glycerin to approximate the viscosity of the diluted serum. The intralaboratory coefficients of variation (CV) ranged from 2.24 to 4.40% and the interlaboratory CV ranged from 2.56% to 6.05%. The method has been adopted official first action.
Professor Barlow has shewn, in a Report to the Directors of the London and Birmingham Railway Company, that the deflection of rails between their points of support, occasions a considerable resistance to the progress of carriages upon them at high velocities.
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