Materials problems in space

This paper is intended to be a short survey of the materials problems associated with spacecraft design and manufacture. The space environment is first described and compared with the “Spacecraft Environment”, which is dependent upon the characteristic features of each individual vehicle.

Some areas of spacecraft technology, where materials properties are critical, are briefly described; the problems which can arise are then underlined. They are divided between “Classical” problems, not different from those which appear in a number of Earth technologies, and “Specific to Space” problems which are mainly created by vacuum exposure, radiation fluxes and thermal stresses.

The conclusions clearly indicate the necessity for proper methods of materials and processes selection for space applications and show that close cooperation between design engineers and materials specialists is absolutely essential.     

Structural and dimensional stabilities of tin-bismuth fusible cores

Eutectic tin-bismuth alloys, used as fusible cores for high polymer injection moulding, were studied in order to identify structural and dimensional modifications during ageing at temperatures ranging from 4 to 110°C. Optical and scanning electron microscopies together with X-ray diffraction were used to observe the coarsening of the eutectic structure and to plot an isothermal transformation diagram. Thermal cycles around the eutectic temperature promoted the dissociation of the eutectic structure into light tin dendrites at the top of the ingots and heavy bismuth crystals at the bottom. Differential scanning calorimetry and thermomechanical analysis were performed to observe possible phase transformations.     

Influence of alleles of apolipoprotein E on restenosis after coronary angioplasty in women

Galanin is a 29-amino acid peptide and widely distributed in the brain, although its significance in the control of neural activities is undefined. In the present study, we describe the effects of galanin on the electrically evoked release of dopamine in the rat central nervous system. In addition, to elucidate a possible role of galanin in the regulation of dopaminergic transmission in hypertension, we examined whether the effect of galanin on dopamine release might be altered in the central nervous system of spontaneously hypertensive rats (SHR). Galanin (1 x 10(-8) to 1 x 10(-7) mol/L) inhibited the stimulation (1 Hz)-evoked [3H]dopamine release by a comparable amount in striatal slices of Sprague-Dawley rats, although the basal release of dopamine was not affected by the peptide. In the striatum of SHR, the electrical stimulation (1 Hz)-evoked [3H]dopamine release was significantly smaller than in the striatum of Wistar-Kyoto (WKY) rats. However, the inhibitory effect of galanin on the stimulation-evoked [3H]dopamine release was significantly more pronounced in SHR than in WKY rats. These results show that galanin significantly reduced the release of dopamine in rat striatum. Furthermore, the greater inhibitory effect of galanin on dopamine release in SHR suggests that galanin might actively participate in the regulation of dopaminergic nerve activity in hypertension.     

Application of linearized power system model to selection of PST controller input signal

This paper presents a selection method for phase shift transformer PST controller input signal. Simple conditions of input signal selection are obtained using frequency response analysis. The proposed method requires a suitable modeling of power system including PST device. The two types of power system models described in this paper are the nonlinear equations system model and the linearized model. The linearized model is represented as a block diagram transfer function model and as a state space representation model. The block diagram model presented in this paper has been used for the PST feedback input signal selection. Five locally available measurements at the switching node of the PST are considered. The results of frequency domain tests have confirmed that the block diagram transfer function model is a useful tool for power system analysis. The LQR method is used to achieve the final verification and the choice of input control signal.     

Yield surface of polyurethane and aluminium replicated foam

It has been proposed in the literature, based on theoretical considerations and on finite-element calculations, that all three stress tensor invariants govern the yield surface of cellular materials. Recent experiments on 75 μm pore size aluminium replicated foams (Combaz E, Bacciarini C, Charvet R, Dufour W, Mortensen A. Multiaxial yield behaviour of Al replicated foam, submitted for publication) showed such a dependence of the yield surface in axisymmetric tests. This study explores the yield behaviour of 400 μm pore size aluminium replicated foams: experiments confirm the influence of the third invariant on the yield surface shape, together with the observations that (i) the yield surface shape does not depend on relative density and (ii) measured flow vectors conform with normality. A simple parabolic model fitting data in the previous study also captures well the present data under all tested stress states (biaxial, axisymmetric and Π-planes in stress space). Biaxial and axisymmetric tests are also performed on 400 μm pore size polyurethane (PU) replicated foams with a similar mesostructure. Results show yield to occur at a value lower than predicted by micromechanical models for both matrix materials (aluminium and PU). This suggests that the “knock-down” factor usually observed between predicted and observed stress values probably cannot be explained by a lowered yield stress in the material making the foam. The data also suggest an influence of the matrix nature on the yield surface geometry.     

Gamma Radiolysis of Starches Derived from Different Foodstuffs. Part II. Study of Induced Acidities

The foodstuff from which the studied starches (maize, amylomaize, waxymaize, manioc, bread-wheat, potato, rice and haricot bean) derive only has little influence upon the quantities of gamma radio-induced acids. The ratios r between the maximal and minimal found values are respectively 2.5 and 3.2 for formic acid and total acidity. If r is equal to 13.6 for free acidity, it is only due to the very small values in haricot bean, potato and rice starches.     

Use of PFGE typing for tracing contamination with Listeria monocytogenes in three cold-smoked salmon processing plants

The sites of Listeria monocytogenes contamination in three cold-smoked salmon (Salmo salar) processing plants were detected by sampling salmon and the plant's environment and equipment at different production stages. Of the 141 samples collected from three processing plants, 59 (42%) were contaminated with L. monocytogenes. The rates of contamination varied as to the plant and the sample source. L. monocytogenes isolates from 17 various contaminated seafood products (fresh, frozen and smoked fishes, cooked mussels) were also studied. A total of 155 isolates from the three plants and the various seafoods were characterized by genomic macrorestriction using ApaI and SmaI with pulsed-field gel electrophoresis (PFGE) and 82 isolates were serotyped. Macrorestriction yielded 20 pulsotypes and serotyping yielded four serovars: 1/2a, 1/2b, 1/2c, 4b (or e), with 77 (93%) belonging to serovar 1/2a. One clone of L. monocvtogenes predominated and persisted in plant I and was the only pulsotype detected in the final product although it was not isolated from raw salmon. No L. monocytogenes was detected in the smoked skinned salmon processed in plant II, even though 87% of the raw salmon was contaminated. All the smoked salmon samples collected in plant III were contaminated with a unique clone of L. monocytogenes, which may have occurred during slicing. In the three plants, the contamination of final products did not seem to originate from the L. monocytogenes present on raw salmon, but from the processing environment.     

Etude des mécanismes de formation de quelques produits identifiés après irradiation gamma de l'amidon de maïs

Studies of the Formation Processes of Some Identified Radiolysis Products after Gamma Irradiation of Maize Starch . From the variations in the concentrations of different starch radiolysis products, studied as function of starch water content and of oxygen pressure, it has been possible to suggest different formation processes. The initied break of the C O C linkages as well as the further rearrangement of the radicals formed or their reactions with water and oxygen explain the observed rearrangements. Water generally has a protector effect, which can be interpreted as an inhibition of primary radical transformation. As for oxygen, its fixation on a carbon radical may account for the generally stimulating action of this gas.