Feature 2 | MARINE COMPOSITES
and widths up to 3m. It is not feasible to have too thick reinforcements because the overlaps at the joints of structures larger than the maximum width of the reinforcements will be too thick. Tis will cause problems when vacuum infusing and also have a negative effect on the strength of the laminate. For practical reasons it is also not feasible to have many reinforcements with different weights and special reinforcements for one type of laminate is usually not cost effective. Since some of the specified minimum weights are dependant on the size of the ship special reinforcements weight are not desirable if building more than one type of ship at the same time. Standard carbon-fibre multi-axial
reinforcements are usually between 400 and 600g/m2
and have fibre in two directions,
but with today’s weaving technology the exact weight can easily be changed without extra cost. Lower weights will be more expensive per kilo simply because the stitching machines produce fewer kilos per hour compared to heavier reinforcements.
Carbon Fibre Laminate: 1600g/m2 Core: 130kg/m2
Figure 5. Compression strength of carbon-fibre laminates with different reinforcements.
Making laminates with low-weight reinforcements will also take more time because there will be more layers to place. What is needed is a limited number of
=>1.8mm , t=20mm Fibre fraction: 50 vol% Cost (x/m2 Carbon fibre Resin core 86 Resin laminate 8 5.2
Core material 60 Total
159.2
) Weight (kg/m2
3.2 2
1.3 2,6 9.1
) Weight (kg/m2
Resin laminate 4.4 2.6
Resin core
Core material 60 78
Total 38
4.8 2.2 1.3 2.6
10.9 )
54 5 3
3.8 100
Table 6. Cost and weight breakdown of carbon-fibre sandwich panel. Cost (x/m2
% Cost ) Glass fibre 11
14 6 3
77 100 Table 7. Cost and weight breakdown of glass-fibre sandwich panel.
44 20 12 24
100
35 22 14 29
100 % Weight
Glass Fibre Laminate: 2400g/m2 Core: 130kg/m2
reinforcements that still gives the flexibility to make laminates with many different weights. Tis can be done by choosing two weights that are not directly dividable, for example 400 and 550g/m2
. For 2-6 layers =>1.9mm , t=20mm Fibre fraction: 50 vol% % Cost % Weight
it is possible to combine reinforcements to make 25 unique weights from 800 to 3300g/ m2
. If 400 and 600 are used it is only possible
to get 15 unique combinations for the same number of layers.
Cost and weight breakdown of a bottom panel In tables 6 and 7 is a breakdown of the different components in a sandwich panel. One panel with carbon-fibre laminates and one with glass-fibre laminates are given as examples. Tese sandwich panels are bottom panels. DNV rules states that the core must have a density of at least 130kg/m3
. For a sandwich panel with carbon-fibre
laminates the carbon fibre is the dominating cost but the core still represents about 70% of the cost of the fibre. Te resin cost is negligible. Te effort of reducing cost should therefore be concentrated on the fibre in the first place but since the minimum weight is specified there might not be much that can be done except to try and get as close as possible to that weight. Te core must also be targeted when trying to reduce cost. If the weight is the most critical all three components are equally important to scrutinise, but the resin absorption of the core is in fact the only weight that can be reduced. Tis is not only the surface absorption of the core material but also the configuration with
Ship & Boat International July/August 2010
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