Control of laminate quality for parts manufactured using the resin infusion process

Resin infusion is a manufacturing process used to produce fibre-reinforced thermo-set polymer components. This process is utilised in a range of industries such as aerospace, automotive, marine, rail and defense and is a cheaper method when compared to other closed mould or autoclave manufacturing methods, particularly as the size of the parts increases. In this study, wet compaction characteristics and behaviour of three glass fibre reinforcements were analysed, and 2D panels were manufactured with a selection of inlet and vent pressure combinations during both the filling and post-filling stages of the process to achieve control of the final fibre volume fractions. Reinforcement thickness and resin pressure were monitored throughout each experiment and the achieved fibre volume fractions were measured post-manufacture. Void content was analysed microscopically and related to the respective experimental parameters set. The compaction result fairly predicted the achieved fibre volume fraction of the manufactured part. The possibility of controlling the fibre volume fraction through control of the post-filling pressure was demonstrated. Even though there was a risk of increased void content with some post-filling configurations, the fibre volume fraction could still be controlled without creating voids with careful application of post-filling conditions.

Texture of Electrodeposited Nanocrystalline Ni-Fe with Banded Structure

Optical microscopy on the etched cross-section of a nanocrystalline Ni-18 wt.% Fe electrodeposit revealed the existence of a banded structure perpendicular to the growth direction. To evaluate if the banded structure is affecting grain growth and texture development, EBSD orientation maps were obtained after annealing for 30 min at 300, 350, and 400°C. Grown grains were found to be random in shape and no preferential sites for grain growth were observed. The texture of the grown grains is changing upon annealing and the final fibre texture parallel to growth direction of the electrodeposit can be obtained from texture components found at lower annealing temperatures when performing one or two consecutive twinning operations.

Resolving the energy paradox of chaperone/usher-mediated fibre assembly

Periplasmic chaperone/usher machineries are used for assembly of filamentous adhesion organelles of Gram-negative pathogens in a process that has been suggested to be driven by folding energy. Structures of mutant chaperone–subunit complexes revealed a final folding transition (condensation of the subunit hydrophobic core) on the release of organelle subunit from the chaperone–subunit pre-assembly complex and incorporation into the final fibre structure. However, in view of the large interface between chaperone and subunit in the pre-assembly complex and the reported stability of this complex, it is difficult to understand how final folding could release sufficient energy to drive assembly. In the present paper, we show the X-ray structure for a native chaperone–fibre complex that, together with thermodynamic data, shows that the final folding step is indeed an essential component of the assembly process. We show that completion of the hydrophobic core and incorporation into the fibre results in an exceptionally stable module, whereas the chaperone–subunit pre-assembly complex is greatly destabilized by the high-energy conformation of the bound subunit. This difference in stabilities creates a free energy potential that drives fibre formation.

Characterization of the inhibition of fibrin assembly by fibrinogen fragment D

Fragment D (Mr 100 000) prepared from a terminal plasmin digest of fibrinogen was isolated and used to study its effect on fibrin formation. Increasing amounts of fragment D added to a solution of fibrinogen and thrombin decrease the rigidity of the resultant gel (10% of control at 2 mol of fragment D/mol of fibrinogen). Half-maximal inhibition is achieved at 1 mol of fragment D/mol of fibrinogen for non-cross-linked clots and at 1/2 mol of fragment D/mol of fibrinogen for cross-linked clots. ‘Clottability’ decreases concomitantly with the rigidity. Only small amounts of fragment D (less than 10% for non-cross-linked gels) are incorporated into the gel. Light-scattering shows an increase in the final fibre thickness at fragment D concentrations up to 2 mol of fragment D/mol of fibrinogen, from 60 molecules/cross-section for the control to 120 molecules/cross-section. Higher fragment D concentrations lead to a decrease in the final fibre thickness. The limit fibre thickness is 8 nm, with a length of 80 nm, which is equivalent to a fibrin trimer. On the basis of results of synthetic-substrate and fibrinopeptide-release assays, it is clear that thrombin inactivation is not responsible for this effect. These data suggest that fragment D may inhibit fibrin formation by blocking the bimolecular polymerization of activated fibrin monomer molecules to form protofibrils, although additional effects on subsequent assembly steps may also be involved.