Fibreglass vs Aluminium Impact Strength

[europaflyer]

Fiberglass vs Aluminum - YouTube

(Skip to 2:00)

Interesting. I always believed that since fibreglass is more brittle than aluminium (or steel) it would shatter in an impact, while aluminium would only bend. Here, we seem to see a similar size hole (although they claim no penetration of the GRP), but with much greater deformation in the aluminium. What do we reckon, true comparative test or not? Cheating and using a heavier sheet of GRP? Exotic fibres? Or have I just always been indoctrinated by metal boat owners? If the test is genuine, it's a good advert for modern resin-infused composites...

[minaret]

Having seen and repaired professionally a great deal of damage in boats of all sorts, I find this video totally plausible and it doesn't surprise me one bit. I have always seen the way a fiberglass laminate catastrophically fails as one of it's strongest points. I can't count the number of boats with major impacts that would have holed and sunk an alloy boat I've seen limp in with shattered fiberglass that just leaked heavily instead of a hole or crack or failed weld. I've also seen major damage to cored panel hulls that totally destroyed the outer skin, and delaminated the inner skin and lots of bulkhead tabbing, without actually penetrating the core and inner skin. I think it's a question of how much deflection the given material can withstand without failing in a way that causes the boat to sink. A heavily fractured glass laminate will still keep most of the water out. On the other hand an alloy hull is more rugged, and will generally survive non catastrophic impacts with less damage to repair, ie delaminated bulkhead tabbing or other structural members. The damage tends to be much more localized and hence much easier to fix. As long as it doesn't get a hole in it.

If anything is unfair about this test, it's probably that the accompanying framing is not taken into account. An aluminum hull would have a much more robust framing system than a glass one. On the other hand that glass panel looks pretty thin, certainly much thinner than the average solid glass boat hull, while 4mm alu is fairly common for hull thickness.

[Stumble]

Europa,

It's a pretty fair test. I have seen similar results from a number of different testing labs, and they all say the same thing.

And be careful when talking about brittle materials. From an engineering standpoint brittle means that there is a relatively small difference between the yield and tensile strength of something, it has nothing to do with what those strengths are. Or that there is little or no plastic deformation to an object when broken.

For instance, aluminium has a yield strength of 28Kpsi and a tensile strength of 38Kpsi. So the delta is 10kpsi. When comparing this the delta is more than 33% the yield making it a pretty maliable metal.

Grade 5 titanium on the other hand has a yield strength of 128Kpsi, and a tensile strength of 138kpis. Again we have a 10kpsi difference, but because the yield strength is so much higher there is only a 8% delta, making it 'brittle' in engineering terms.

This is one of those areas where an very technical term like brittle has lead to the general public being a little confused about a material. Simple because in common parlance brittle has a connotation of not requiring much force to break something, while in an engineering sence there is no connotation about the force required.

Other brittle materials include:
Granite
Cast iron
Brick

[europaflyer]

Thanks for the technical explanation Stumble.

So... are we saying that while metal boats are more abrasion resistant, when things get really serious the higher specific strength of GRP gives it the edge?

[Cheechako]

Originally Posted by europaflyer

Thanks for the technical explanation Stumble.

So... are we saying that while metal boats are more abrasion resistant, when things get really serious the higher specific strength of GRP gives it the edge?

Maybe not metal boats, but aluminum ones! Did they say how thick the glass was? Glass lam is amazing really, it's heavy, but my guess is not quite as heavy as aluminum...? Glass lam without core is very bendy though, more so than aluminum and alum is much more so than steel.

[delmarrey]

We started building composite parts for airplanes over 30 years ago because they hold up better to impact. Now they're building whole planes from composites. Plastics/composites are great stuff along as they don't end up in the land fills. Ships are still steel b/c of the cost of materials, and the cost of assembly/labor.

[europaflyer]

Originally Posted by minaret

I have always seen the way a fiberglass laminate catastrophically fails as one of it's strongest points. I can't count the number of boats with major impacts that would have holed and sunk an alloy boat I've seen limp in with shattered fiberglass that just leaked heavily instead of a hole or crack or failed weld.

Originally Posted by minaret

that glass panel looks pretty thin, certainly much thinner than the average solid glass boat hull, while 4mm alu is fairly common for hull thickness.

Originally Posted by delmarrey

We started building composite parts for airplanes over 30 years ago because they hold up better to impact.

So why have we put up with all the noise from metal boat owners about impact strength?

[Cheechako]

Originally Posted by europaflyer

So why have we put up with all the noise from metal boat owners about impact strength?

Aluminum aint steel...... I think the jury is out on composites in Aircraft ... the big benefit being weight savings....every ounce is huge in aircraft so the companies are willing to pay the 5-7 times cost. Long term durability is in question though and manufacturing process perfection are critical to actual results.
"
"The Airbus A350 represents a breakthrough in aircraft design because more than 50% of the aircraft's weight is composite parts. However, recent Airbus crashes which have shocked the world again raise questions about the long term durability of carbon-resin components.
Composites -
Composites have been used in aircraft design for many years. They significantly reduce aircraft weight and the fuel savings that result are extremely important. Boeing, Airbus, and the USAF are the largest design and manufacturing entities that are integrating composite parts into new aircraft at a rapid pace. If widespread use of composites does not comprise aircraft structural integrity, then everyone wins. The costs of freight transport, travel and fighting in the air drop significantly, and crew and passenger safety have not been compromised. The real world situation, however, is not that straightforward. Composite aircraft parts have come under intense scrutiny and criticism from pilots, air security professionals and aeronautical engineers.
updated 3:56 p.m. MT, Fri., Aug 14, 2009
Boeing Co. has discovered another problem with its long-delayed 787 jetliner,
prompting the aircraft maker to halt production of fuselage sections at a factory in Italy.
The Chicago-based company found microscopic wrinkles in the skin of the 787’s
fuselage and ordered Italian supplier Alenia Aeronautica to stop making sections on
June 23, spokeswoman Lori Gunter said Friday. Boeing has started patching the areas.
The plane, built for fuel efficiency from lightweight carbon composite parts, is a priority
for Boeing as it struggles with dwindling orders amid the global recession."

[atoll]

in reality most boats are sunk from groundings,and wave action rather than hitting object's in the water.

a metal boat will survive for "days" in these conditions,a glass boat "hours",
a good marketing angle for speed boats,but not really applicable to cruising vessels,cruising tropical waters with step-to reefs...........

[europaflyer]

Originally Posted by Cheechako

Aluminum aint steel......

True...

Aluminum Strength vs Steel Strength

According to this guy, an aluminium yacht is 'stronger' by at least 50% kilo for kilo.

[Cheechako]

Originally Posted by atoll

in reality most boats are sunk from groundings,and wave action rather than hitting object's in the water.

a metal boat will survive for "days" in these conditions,a glass boat "hours",
a good marketing angle for speed boats,but not really applicable to cruising vessels,cruising tropical waters with step-to reefs...........

When I was building aluminum powerboats, an Alaska customer wanted a quote on fixing his 26 footer and send video to assess it.. It had come loose in a winter storm, drifted away and been battered on the coast and ended up on a rocky beach for days before they found it. The damn thing looked like a banana it was so bent up. It had no leaks whatsoever and actually floated fine. It was a total loss however.... these boats were primarily 3/16 and 5/32 aluminum.

[europaflyer]

Originally Posted by Cheechako

"However, recent Airbus crashes which have shocked the world again raise questions about the long term durability of carbon-resin components."

Can't begin to imagine what events they're talking about here... To the best of my knowledge the number of fatal structural failures in Airbus aircraft is 0. Failures of aluminium brackets in the wings of the A380 have been a problem recently though. If anything composite structures in aircraft have a longer fatigue life than aluminium alloys. I've always believed that aircraft composites were virtually fatigue-free, like wood, ie. could be stressed to the yield strength repeatedly without altering the material.

Composite Materials: Airbus and Boeing Aircraft Structural Composites, ductile failure, structural composites

But here we go off topic!

[daddle]

Some FRP boats have Kevlar laid-up in the bows and other impact zones. That must help tremendously in toughness and penetration resistance.

Aluminum boats are tough ... but noisy/hot/cold while one is sailing around waiting to hit something.

[delmarrey]

The problem with aluminum is next to each weld there is a small seam of metal that is weaker then the rest. If there are stresses in that area, it will crack. Stress areas need to be over built to compensate, like stanchions, hull/deck joints, appendage fittings and super structure joints.

But F-glass can delaminate if not laid right.

[Cheechako]

Originally Posted by europaflyer

True...

Aluminum Strength vs Steel Strength

According to this guy, an aluminium yacht is 'stronger' by at least 50% kilo for kilo.

yeah, it isnt all about published strength numbers though. Cycle fatigue is terrible in common aluminums compared with steel, as is crack propagation etc. etc Kilo for kilo it may make sense.... steel is nearly 3 times as heavy!

"The problem with aluminum is next to each weld there is a small seam of metal that is weaker then the rest. If there are stresses in that area, it will crack. Stress areas need to be over built to compensate, like stanchions, hull/deck joints, appendage fittings and super structure joints."
Yeah, no doubt about it, I think Fiberglass is pretty forgiving as far as manufacturing goes and aluminum is noisy as heck.