Join Date: Feb 2012
Location: New Orleans Louisiana
Thanked 126 Times in 120 Posts
Rep Power: 6
Re: Chain Plate Material
G10, like bronze, aluminium, and all fiberglass has fatigue issues. There is a definite life cycle number that will eventually break the part. The stronger the part is from inception, the higher the number, but it is still a definite number.
Steel including stainless varieties eventually have a logarithmic flattening of the fatigue cycles needed to break the part. As the loads go below some % of tensile strength of the part, it takes progressively more cycles to fail. For steel (including stainless) this occurs around 30 and 40% MBL though it is alloy specific, so to know exacally what the failure point is will require knowing exacally what alloy you have.
Like steel titanium has a flat lined fatigue cycle curve, but generally titanium flatlined earlier than steel does (40-50%) MBL. Again it is alloy specific, and the actual calculations are pretty complicated (beyond my abilities certainly).
In practice what happens is that a designer will spec a stainless chainplate of X size, which is chosen to get the fatigue limit into the flatline, and assumes some amount of corrosion degrading over time. By switching to titanium you acomplish a few things.
1) the part itself is roughly twice as strong for the same size (most replacements are done size for size, not strength for strength).
2) the fatigue limit is higher for the titanium
3) the corrosion allowance used for the 316 can be ignored in the Ti.
So the result is a part that is honestly massively overbuilt for the expected loads. Because in the ways that matter the titanium is actually stronger across the board than the steel. Effectively this gives a titanium replacement a nearly infinite fatigue cycle as compared to a 316 replacement.
Bronze on the other hand does not have a logarithmic flattening of the fatigue cycle curve, which means as the loads go down, the number of cycles it can endure do go up, but at a roughly linear rate. By sizing bronze for a definite life cycle, and making a number of assumptions about how many cycles it will see in a given period it is possible (and has been done for years) to design a part that will last for some given time. But it has to be larger and stronger than a comparable part out of steel or Ti.
Fiberglass including G10 has a very steep fatigue cycle life, and while it can be used for chainplates, the number of cycles it can absorb is like bronze much lower. This requires the part to either be replaced more often, or to be build significantly oversized. G10, is also prone to fracturing and shattering from impact loads, like carbon fiber it has massive physical properties, but these are offset by real limitations. Again, it is doable, but it really isn't the best material for the job. Though like titanium it is effectively immune to corrosion and is very light.
Honestly if you design it right you could make chainplates from just about anything. But there are certain materials that are more suited than others. Stainless of course has been the go to for a long time, and will be used a lot in the future as well, with very good results. New fiberglass/composite chainplates are showing interesting promise, but are held together with titanium or stainless pins and bushings.
Titanium is coming on the market is a big way, and it's easy to see why. Sadly the price is still quite high compared to stainless, though we are working on getting the prices down to comparable with stainless. Honestly it isn't even the material price difference, it is the cost of fabrication. People don't buy it because it is expensive, which keeps the price up, when things go into mass production, our cost is only about 20% more than a stainless part. This is why we are trying so hard to get manufacturers to install them OEM. Figure it would add $100-$300 to the purchase price of a boat for them to install titanium as opposed to stainless, and effectively remove them as an issue to worry about.
Last edited by Stumble; 07-13-2012 at 09:40 PM.