Trans RINA, Vol 152, Part B1, Intl J Small Craft Tech, 2010 Jan-Jun


Silicone rubber coated electric heating blankets were chosen to heat the repair region. This choice was made because of their flexibility and relatively high power density of 7.75 kW·m-2, Trials were conducted to determine whether a good quality repair could be achieved with single-sided heating or whether it would be necessary to heat the repair with blankets on both sides. It was found that, with these heaters, only two- sided heating provided complete consolidation over the full thickness of a 12mm laminate. With single-sided heating the maximum temperature achievable on the cold side of the repair was 150ºC, somewhat short of the PP melting point of 165ºC and the desirable processing temperature of >180ºC. It is worth noting that, unlike the original manufacturing process for the


craft, which


involved impregnation of a commingled fibre mixture, no significant impregnation was expected to take place during the repair process: only bonding and consolidation of previously impregnated material.


Prior to carrying out the fusion bonding process,


damaged and delaminated material was removed from the hull, using the results of the NDE study as a guide. Material removal included some intact internal structure because of the space needed for disposables and vacuum arrangement on both sides of the panel. The reason for this is that the vacuum bag coverage must include both sides of the whole area to be repaired, plus the space required for the sealant tape, to provide the necessary pressure and air-removal from the repair joint. Inside the boat, the area to be covered is likely to intersect internal structure elements, as occurred in this work. Paint and dirt were sanded away and the edges were prepared with 35 mm long scarfs, giving a scarf angle of roughly 17º. Scarf lengths larger than this were not possible, due to space restrictions.


The flat panel was manually fitted in place. On both sides of it, layers of disposables and the heaters were applied and kept in place with spray adhesive. Although a one- stage process is achievable, in this work the fusion bonding of the panel joints was performed in four stages, corresponding to the four sides of the panel. In each processing stage, two heater blankets of the same size were used, one on the outside surface of the hull and the other on the inside. As a result, the intersections of the heated areas were processed twice. As the four sides of the panel were fusion bonded to the hull, the former matched the double curvature of the latter by means of the ambient pressure on the vacuum bag. The final curvature of the panel corresponded approximately to a 20 mm deflection over 500 mm long panel. Figures 7 and 8 show the final repair results.


The processing time for the panel joints was 30 min at 185ºC. The heating and cooling periods on either side of the processing zone were around 30 min each, a typical temperature profile being shown in Figure 9.


Figure 7: Panel fusion-bonded to the hull. Pre-made panel


The Atlantic 85 RIB includes spray rails to increase lift force and reduce


hydrodynamic resistance.


These


comprise three longitudinal V-shaped thin, step-like members along the hull, as shown in Figures 1, 2, 4, 7 and 8. Spray rail repair was not included in this work, as it was understood that it would require the use of a mould.


Fusion bonded joints


2.3


Figure 8: Panel curvature observed after bonding REPAIR CHARACTERISATION


2.3 (a) Micrography Samples cut from the repairs


were polished and


examined using optical microscopy. Figures 10-12 show that good consolidation had occurred along the length of the joint. The achievable vacuum was around 0.7 bar, due to some leakage through the bagging tape due to the spray rails which can be seen in Figures 7 and 8. This was poorer than would have been desirable. Figure 13 shows that, in addition to well-consolidated regions there are occasional voids, apparently evenly distributed over the original laminate, the repair laminate and the joint. The overall repair void content was 5-10%, compared to the lower value of 0.5% in the original laminate. .


©2010: The Royal Institution of Naval Architects


B-37


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