JEC COMPOSITES MAGAZINE - Issue #68 Special JEC Asia - October 2011 - 86

filament winding
glued interface between boss and liner was calculated in order to foresee potential separation between the surfaces, seeing that the peel strength of the adhesive is 4 MPa. The subsequent illustrations indicate the results of the simulation. In particular, it was found that, in the fillet radius of the threaded boss (1 mm), the Von Mises stress (Figure 6) is somewhat higher than the yield stress of the Fig. 6: Von Mises stress of the threaded material. boss (up), pressure at the interface However, it can be noted between the threaded boss and the liner (down) that the concentration of the stresses is extremely localised in the threaded boss fillet radius (Figure 6). For this reason, and considering that the loads are steady, the contribution of the stress concentration to increasing the local stress level could be ignored, on the condition that the material is sufficiently ductile. In fact, ductile materials present a wide plasticity range and in reality, the stresses reach values equivalent to the material’s yield stress, to the detriment of local plasticising with a redistribution of the same stresses. The pressure behaviour at the boss-liner interface confirms that the adhesive is compressed between the two surfaces (Figure 6). Even the laminate was found to be far from the breaking limit, as the Tsai-Wu parameter does not exceed 0.2 at any point (the laminate fractures when this parameter is equal to 1) (Figure 7).

(the component was developed in collaboration with Technologycom in Brindisi). To encase the nozzle into the booster, a collapsible mandrel was designed and produced (Figure 8) in order to allow fixing the nozzle before starting the winding process. Therefore, the winding surface is a combination of a cylindrical portion and a portion having as a profile the external surface of the nozzle.

Booster design

Definition of the winding path The booster is composed of a carbon-fibre cylindrical chamber encasing the converging-diverging shaped nozzle, where the expansion of the combustion gas takes place. The nozzle is produced by autoclave technology, utilizing a carbon fibre prepreg and an appropriate resin resistant to the temperatures reached in this area, found to be in excess of 3000°C

jec composites magazine / No68 October 2011

Fig. 7: Application of the Tsai-Wu failure criterion for loading condition 2

An in-house-developed program was used to define the fibre winding path for the mandrel. The mandrel shape used to obtain the winding is represented in Figure 9. In particular, it can be seen that there are some points where the winding angle α needs to be 90°. Indeed, there are two internal points (A and B in Figure 9) where the profile of the mandrel is concave with sharp edges, and two external points (C and D) where the fibre path needs to come back in order to achieve a continuous winding.

Fig. 9: Shape of the mandrel used for the booster and identification of the geometrical constraints for the fibre path Fig. 10: Definition of the fibre path on the mandrel used for the booster

Fig. 8: CAD model (left) and a picture of the mandrel used to wind the booster (right)

The resulting path is shown in Figure 10, where the requested friction coefficient μ is also represented. Experimental measurements showed that the available friction coefficient is somewhat higher than the maximum requested friction coefficient (0.2), so that the fibre cannot slip during the winding process.

JEC COMPOSITES MAGAZINE - Issue #68 Special JEC Asia - October 2011

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #68 Special JEC Asia - October 2011