Effects of real-time thermal aging on graphite/polyimide composites

As part of a program to evaluate high-temperature advanced composites for use on supersonic cruise transport aircraft, two graphite/polyimide composites have been aged at elevated temperatures for times up to 5.7 years. Work on the first, HT-S/710 graphite/polyimide, was started in 1974. Evaluation of the second polyimide, Celion 6000/LARC-160, began in 1980. Baseline properties are presented, including unnotched and notched tensile data as a function of temperature, compression, flexure, shear, and constant-amplitude fatigue data at R = 0.1 and R = -1. Tensile specimens were aged in ovens where pressure and aging temperatures were controlled for various times up to and including 50,000 hours. Changes in tensile strength were determined and plotted as a function of aging time. The HT-S/710 composite aged at 450 F and 550 F if compared to the Celion 6000/LARC-160 composite aged at 350 F and 450 F. After tensile testing, many of the thermal aging specimens were examined using a scanning electron microscope. Results of these studies are presented, and changes in properties and degradation mechanisms during high-temperature aging are discussed and illustrated using metallographic techniques

Time-temperature-stress capabilities of composite materials for advanced supersonic technology application, phase 1

Implementation of metal and resin matrix composites into supersonic vehicle usage is contingent upon accelerating the demonstration of service capacity and design technology. Because of the added material complexity and lack of extensive service data, laboratory replication of the flight service will provide the most rapid method of documenting the airworthiness of advanced composite systems. A program in progress to determine the time temperature stress capabilities of several high temperature composite materials includes thermal aging, environmental aging, fatigue, creep, fracture, and tensile tests as well as real time flight simulation exposure. The program has two parts. The first includes all the material property determinations and aging and simulation exposures up through 10,000 hours. The second continues these tests up to 50,000 cumulative hours. Results are presented of the 10,000 hour phase, which has now been completed

Registration of N30-N56, N741, N743, N745, N747, U362, U363, U367, U369-U374, U389-U394, U396-U398, and U500 Sweetclover Genetic Stocks

Forty-nine white-flowered sweetclover (Melilotus alba Medik.) genetic stocks [N30-N45 (Reg. GS-1–16, PI 549120–549135); N46-N53 (Reg. GS-17–24, PI 557503–PI 557510); N54-N55 (Reg. GS-25–Reg. GS-26, PI 629289–PI 629290); N741, N743, N745, N747 (Reg. GS-27–GS-30, PI 557511–PI 557514); U362, U363, U367 (Reg. GS-31, Reg. GS-32, Reg. GS-33, PI 557515–PI 557517); U369-U374 (Reg. GS-34–GS 39, PI 557518–PI 557523); U389-U394 (Reg. GS-40–GS 45, PI 557524–PI 557529); U396- U398 (Reg. GS-46–GS 48, PI 557530–PI 557532); U500 (Reg. GS-49, PI 557533)] (Table 1); and N56 (Reg. no. GS-50, PI 634019), a yellow-flowered sweetclover [Melilotus officinalis (L.) Lam.] genetic stock, were developed jointly by USDA- ARS and the Agricultural Research Division, Institute of Agriculture and Natural Resources, University of Nebraska-Lincoln and were jointly released in May 2004. The genetic stocks, which contain unique combinations of genes and traits, were developed over more than three decades of cooperative sweet- clover genetic research

Registration of N30-N56, N741, N743, N745, N747, U362, U363, U367, U369-U374, U389-U394, U396-U398, and U500 Sweetclover Genetic Stocks

Forty-nine white-flowered sweetclover (Melilotus alba Medik.) genetic stocks [N30-N45 (Reg. GS-1–16, PI 549120–549135); N46-N53 (Reg. GS-17–24, PI 557503–PI 557510); N54-N55 (Reg. GS-25–Reg. GS-26, PI 629289–PI 629290); N741, N743, N745, N747 (Reg. GS-27–GS-30, PI 557511–PI 557514); U362, U363, U367 (Reg. GS-31, Reg. GS-32, Reg. GS-33, PI 557515–PI 557517); U369-U374 (Reg. GS-34–GS 39, PI 557518–PI 557523); U389-U394 (Reg. GS-40–GS 45, PI 557524–PI 557529); U396- U398 (Reg. GS-46–GS 48, PI 557530–PI 557532); U500 (Reg. GS-49, PI 557533)] (Table 1); and N56 (Reg. no. GS-50, PI 634019), a yellow-flowered sweetclover [Melilotus officinalis (L.) Lam.] genetic stock, were developed jointly by USDA- ARS and the Agricultural Research Division, Institute of Agriculture and Natural Resources, University of Nebraska-Lincoln and were jointly released in May 2004. The genetic stocks, which contain unique combinations of genes and traits, were developed over more than three decades of cooperative sweet- clover genetic research

Quality Traits in Forage Sorghum Harvested at Early Head Emergence and at Physiological Maturity

Information about the extent of variation in quality traits among plants sampled at the same developmental stage but on different dates would be useful to forage researchers. The primary purpose of this study was to obtain such information for five forage sorghum [Sorghum bicolor (L.) Moench] cultivars. Percent dry matter, crude protein, and in vitro dry matter disappearance of leaf, stem, and whole plant samples were determined for field-grown samples harvested on three different days during early head emergence (EHE) and once during physiological maturity (PM) for each cultivar. Orthogonal comparisons between EHE and PM sampling stages and among the• EHE samples were made. Results of the 2-year study indicated that statistically significant differences existed among EHE samples and between EHE and PM samples. However, differences among EHE samples were generally much smaller than those between EHE and PM samples and may be of little importance for some applications

Variability for Traits Used to Estimate Silage Quality in Forage Sorghum Hybrids

The variation among 49 F1 forage sorghum [Sorghum bicolor (L.) Moench.] hybrids from a 7 X 7 cross-classified design was explored in 1979 and 1980 for the following silage traits: dry matter (DM), crude protein, in vitro dry matter disappearance (IVDMD), neutral detergent fiber, acid detergent fiber, acid detergent lignin, ammonia, lactate, and Brix of the juice from fresh stalks. Wider ranges generally were found for male than for female parental means. Means for most traits were significantly different among entries. Significant differences among hybrid means over males and over females were found for only DM, IVDMD, and Brix. Interactions with years existed for most traits. Genetic ratios calculated from the mean squares indicated that general combining ability was important for DM, IVDMD, and Brix. Simple correlation coefficients between traits measured on silage and on fresh-dried samples from the same hybrids were all significant. In view of the effort required to make and evaluate silage samples, initial selection for traits used to estimate quality in fresh-dried samples appears to be the best approach for improving the quality of forage sorghum silage

Variability for Traits Used to Estimate Silage Quality in Forage Sorghum Hybrids

The variation among 49 F1 forage sorghum [Sorghum bicolor (L.) Moench.] hybrids from a 7 X 7 cross-classified design was explored in 1979 and 1980 for the following silage traits: dry matter (DM), crude protein, in vitro dry matter disappearance (IVDMD), neutral detergent fiber, acid detergent fiber, acid detergent lignin, ammonia, lactate, and Brix of the juice from fresh stalks. Wider ranges generally were found for male than for female parental means. Means for most traits were significantly different among entries. Significant differences among hybrid means over males and over females were found for only DM, IVDMD, and Brix. Interactions with years existed for most traits. Genetic ratios calculated from the mean squares indicated that general combining ability was important for DM, IVDMD, and Brix. Simple correlation coefficients between traits measured on silage and on fresh-dried samples from the same hybrids were all significant. In view of the effort required to make and evaluate silage samples, initial selection for traits used to estimate quality in fresh-dried samples appears to be the best approach for improving the quality of forage sorghum silage

Curvature invariants in type N spacetimes

Scalar curvature invariants are studied in type N solutions of vacuum Einstein's equations with in general non-vanishing cosmological constant Lambda. Zero-order invariants which include only the metric and Weyl (Riemann) tensor either vanish, or are constants depending on Lambda. Even all higher-order invariants containing covariant derivatives of the Weyl (Riemann) tensor are shown to be trivial if a type N spacetime admits a non-expanding and non-twisting null geodesic congruence. However, in the case of expanding type N spacetimes we discover a non-vanishing scalar invariant which is quartic in the second derivatives of the Riemann tensor. We use this invariant to demonstrate that both linearized and the third order type N twisting solutions recently discussed in literature contain singularities at large distances and thus cannot describe radiation fields outside bounded sources.Comment: 17 pages, to appear in Class. Quantum Gra

Breathers in the weakly coupled topological discrete sine-Gordon system

Existence of breather (spatially localized, time periodic, oscillatory) solutions of the topological discrete sine-Gordon (TDSG) system, in the regime of weak coupling, is proved. The novelty of this result is that, unlike the systems previously considered in studies of discrete breathers, the TDSG system does not decouple into independent oscillator units in the weak coupling limit. The results of a systematic numerical study of these breathers are presented, including breather initial profiles and a portrait of their domain of existence in the frequency-coupling parameter space. It is found that the breathers are uniformly qualitatively different from those found in conventional spatially discrete systems.Comment: 19 pages, 4 figures. Section 4 (numerical analysis) completely rewritte

Kinks in dipole chains

It is shown that the topological discrete sine-Gordon system introduced by Speight and Ward models the dynamics of an infinite uniform chain of electric dipoles constrained to rotate in a plane containing the chain. Such a chain admits a novel type of static kink solution which may occupy any position relative to the spatial lattice and experiences no Peierls-Nabarro barrier. Consequently the dynamics of a single kink is highly continuum like, despite the strongly discrete nature of the model. Static multikinks and kink-antikink pairs are constructed, and it is shown that all such static solutions are unstable. Exact propagating kinks are sought numerically using the pseudo-spectral method, but it is found that none exist, except, perhaps, at very low speed.Comment: Published version. 21 pages, 5 figures. Section 3 completely re-written. Conclusions unchange