Ship & Boat International: eNews March/April 2018
Considering future trends for the application of composites, Dr Richard Collins, technology analyst at research firm IDTechEx, comments: “We see a big trend away from ‘dumb’ materials to ones that could be used for monitoring structural health”. It’s a prediction that also includes vessels that suffer from repetitive stresses, such as workboats.
Certainly, it’s been helped by the blossoming of cheap, readily available sensor technologies over the last few years. However, rather than building a structure and bolting on sensors as an afterthought, “introducing them into the manufacturing process itself is a much better solution," Collins says. "That way, there is no impact on the mechanical properties, as you can weave thin wires into the fibre mesh that will send a warning when there’s delamination or some other structural compromise.”
Of course, it does mean having a proven set of sensor solutions and a carefully controlled lay-up process – and a very robust commissioning process. But it’s all fairly ‘do-able’ he says, adding that other industries are already running with the idea: “The aerospace sector is already using sensors on wings and other stress joints.”
Moreover, Collins explains, these sensor meshes could also generate the tiny current they need by turning some of this weave into a piezoelectric grid. This would take advantage of the small electric charge that accumulates in certain solids in response to mechanical pressure. However, he adds, there are also energy-harvesting solutions that could take advantage of solar power, wind, friction, waves, vibrations and so on. “You could top up the battery like this – or even go battery-less,” he points out.
More developments are afoot. Take Phase IV’s LF RFID wireless, non-electrical sensors: these have onboard MEMS pressure and temperature readings but can also be tailored for another input. Most importantly, they are small enough to fit inside a honeycomb cell, the low-frequency magnetic waves penetrating the semi-conductive carbon fibre to allow it to be read, even years later.
While these sensors are presently being used in the aerospace industry and could make it into more general composites, they have another application that might prove useful: they can monitor the temperature and pressure inside vacuum curing processes.
However, Collins has another interesting point to make about more prosaic materials. “There are some areas on vessels where, ideally, people would like to be using carbon fibre, but the costs are prohibitive,” he says. However, he continues, the price of carbon fibre is set to come down over the next 10 years as the automotive sector (along with others) continues its search for ways to lose weight. Further, there are commercial innovations underway, such as using microwaves and plasma oxidation ovens, which have been trialled in the tow synthesis and which are “proving more efficient than traditional ovens”.
As a result, Collins predicts that bobbins of heavy tow, the coarser kind of carbon fibre, should drop to US$12 per kg from a starting price of US$14, but the better quality, lighter tow (which gives more surface area for the matrix to ‘grip’) looks like plunging from a present price of US$22/23 per kg to below US$17. This still won’t make it cheap, “but it will help the whole industry to move on in terms of use,” he says.
Subsequently, he believes that there will be a greater number of hybrid builds with high-stress areas being made of carbon, aramid or s-glass (“good for repetitive, low impacts”), these bones being sunk into a less expensive structure of standard glass composite.
