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


structure. This way, an NDE-measured thickness smaller than the material thickness would mean a discontinuity inside the laminate, delamination in this case.


Despite the mentioned calibration, significant differences between NDE- and physically-measured hull thicknesses were observed, being the marked 18 mm approximately corresponding to 12 mm as confirmed with a vernier caliper. However, thicknesses were measured up to where they stabilised, which was indicated by a line containing the damaged region as seen in Figure


Therefore, the overall comparative aspect of the NDE analysis was considered


reliable with regard to the


identification of internal delaminations. 2.2 FUSION BONDED PATCH REPAIR


An emergency procedure was developed, which could be applied in the field, i.e. wherever remotely the hull damage takes place. This was aimed, not at achieving a cosmetic repair, but at restoring the water-tightness and structural integrity. Other, more comprehensive repair methods are possible, but these require the return of the craft to a centre with manufacturing capabilities. The technique tested involved


fusion bonding and the


application of a vacuum to the repair region during the heating and cooling cycle. This provided an effective uniform external pressure approaching 1 bar [3, 5 & 7]. The layout of the process is shown in Figure 6.


Fusion bonding is the technique of first choice for joining and repair of thermoplastic composites [11] because it gives greater strength and durability than adhesive bonding. The procedure is, in principle, simple: the surfaces to be joined pass through a cycle of heating,


The need for easy storage and portability restricted the equipment that could be used to simple heating blankets, a portable vacuum pump and some conventional vacuum processing disposables. In this work, these comprised a breather layer, Airbleed 33; a 50 μm thick release film, A5000 and a 50 μm thick vacuum bag, Capran 526, all of them from Aerovac. The vacuum bag was sealed to the hull by means of a sealant


SM5127. The layout of these disposables is shown in Figure 6. Because the region of hull


tape, Schnee Morehead to be damaged


would not have been foreseeable in advance, it was not felt appropriate to use any rigid tooling to shape the repaired region. The ‘no-tool’ repair that was developed involved a


12 mm thick flat PP-glass laminate,


previously manufactured from four layers of white non- woven Twintex® T PP 60 and two layers of black woven Twintex® T PP 60. The contrasting shades were chosen to assist in the later microscopic examination of the bond region. The hull


laminate was pigmented black. The


arrangement of the materials used in the repair is shown in Figure 6..


fusion and cooling, while being held together to achieve molecular inter-diffusion in the resin and maintain consolidation of the composite. Relatively little surface preparation, other than cleaning, is needed, the process can be rapid, and the long-term storage of the materials to be used in the repair requires no special conditions. The main disadvantage is that, as in many other welding processes, the local heating involved


can cause 5.


distortions and leave residual stresses. There is also a risk that, due to the melting involved, previously well- consolidated regions of the laminate may de-consolidate if not constrained to maintain their shape.


Figure 6: Repair layout diagram. Further insulation was laid up on top of the vacuum bags on both sides to prevent heat flowing outwards.


B-36 ©2010: The Royal Institution of Naval Architects


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