Outgassing and dimensional changes of polymer matrix composites in space

A thermal-vacuum outgassing model and test protocol for predicting outgassing times and dimensional changes for polymer matrix composites is described. Experimental results derived from a 'control' sample are used to provide the basis for analytical predictions to compare with the outgassing response of Long Duration Exposure Facility (LDEF) flight samples

Evaluation of closed cubic failure criterion for graphite/epoxy laminates

An analytical method has been developed to ensure closure of the cubic form of the tensor polynomial strength criterion. The intrinsic complexity of the cubic function is such that special conditions must be met to close the failure surface in three-dimensional stress space. These requirements are derived in terms of non-intersecting conditions for asymptotes and an asymptotic plane. To demonstrate the validity of this approach, closed failure surfaces were derived for two graphite/epoxy material systems (3M SP288-T300 and IM7 8551-7). The agreement of test data with this model clearly shows that it is possible to use a higher order cubic failure theory with confidence

Analysis of LDEF micrometeoroid/debris data and damage to composite materials

This report presented published LDEF micrometeoroid/debris impact data in a nomogram format useful for estimating the total number of hits that could be expected on a space structure as a function of time in orbit, angular location relative to ram, and exposed surface area. Correction factors accounting for different altitudes are given. These are normalized to the average LDEF altitude. Examples on how to use the nomograph are also included. In addition, impact data and damage areas observed on composite laminates (experiment AO 180) are discussed

Electron-impact excitation of diatomic hydride cations I: HeH+^+, CH+^+, ArH+^+

{\bf R}-matrix calculations combined with the adiabatic nuclei approximation are used to compute electron-impact rotiational excitation rates for three closed-shell diatomic cations, HeH$^+$, CH$^+$, ArH$^+$. Comparisons with previous studies show that an improved treatment of threshold effects leads to significant changes in the low temperature rates, furthermore the new calculations suggest that excitation of CH$^+$ is dominated by $\Delta J =1$ transitions as is expected for cations with a large dipole moment. A model for ArH$^+$ excitation in the Crab Nebula is presented which gives results consistent with the observations for electron densities in the range $2-3\times 10^3$~cm$^{-3}$.Comment: MNRAS submitted 7 pages, 9 figure

Evaluation of failure criterion for graphite/epoxy fabric laminates

The development and application of the tensor polynomial failure criterion for composite laminate analysis is described. Emphasis is given to the fabrication and testing of Narmco Rigidite 5208-WT300, a plain weave fabric of Thornel 300 Graphite fibers impregnated with Narmco 5208 Resin. The quadratic-failure criterion with F sub 12=0 provides accurate estimates of failure stresses for the graphite/epoxy investigated. The cubic failure criterion was recast into an operationally easier form, providing design curves that can be applied to laminates fabricated from orthotropic woven fabric prepregs. In the form presented, no interaction strength tests are required, although recourse to the quadratic model and the principal strength parameters is necessary. However, insufficient test data exist at present to generalize this approach for all prepreg constructions, and its use must be restricted to the generic materials and configurations investigated to date

R-matrix calculation of electron collisions with electronically excited O2 molecules

Low-energy electron collisions with O$_2$ molecules are studied using the fixed-bond R-matrix method. In addition to the O$_2$ ${X}^3\Sigma_{g}^-$ ground state, integrated cross sections are calculated for elecron collisions with the ${a}^1\Delta_{g}$ and ${b}^1\Sigma_{g}^+$ excited states of O$_2$ molecules. 13 target electronic states of O$_2$ are included in the model within a valence configuration interaction representations of the target states. Elastic cross sections for the ${a}^1\Delta_{g}$ and ${b}^1\Sigma_{g}^+$ excited states are similar to the cross sections for the ${X}^3\Sigma_{g}^-$ ground state. As in case of excitation from the ${X}^3\Sigma_{g}^-$ state, the O$_2^-$ $\Pi_u$ resonance makes the dominant contribution to excitation cross sections from the ${a}^1\Delta_{g}$ and ${b}^1\Sigma_{g}^+$ states. The magnitude of excitation cross sections from the ${a}^1\Delta_{g}$ state to the ${b}^1\Sigma_{g}^+$ state is about 10 time larger than the corresponding cross sections from the ${X}^3\Sigma_{g}^-$ to the ${b}^1\Sigma_{g}^+$ state. For this ${a}^1\Delta_{g}$ $\to$ ${b}^1\Sigma_{g}^+$ transition, our cross section at 4.5 eV agrees well with the available experimental value. These results should be important for models of plasma discharge chemistry which often requires cross sections between the excited electronic states of O$_2$.Comment: 26 pages, 10 figure

Experimental energy levels of the water molecule

Experimentally derived energy levels are presented for 12 248 vibration–rotation states of the H2 16O isotopomer of water, more than doubling the number in previous, disparate, compilations. For each level an error and reference to source data is given. The levels have been checked using energy levels derived from sophisticated variational calculations. These levels span 107 vibrational states including members of all polyads up to and including 8v. Band origins, in some cases estimates, are presented for 101 vibrational modes