Return-Path: Sender: (Marvin Kaye) To: lml@lancaironline.net Date: Mon, 29 Mar 2004 04:17:23 -0500 Message-ID: X-Original-Return-Path: Received: from imo-d04.mx.aol.com ([205.188.157.36] verified) by logan.com (CommuniGate Pro SMTP 4.2b1) with ESMTP id 3132577 for lml@lancaironline.net; Mon, 29 Mar 2004 01:30:30 -0500 Received: from Newlan2dl@aol.com by imo-d04.mx.aol.com (mail_out_v37_r1.2.) id q.84.2574ce50 (4312) for ; Mon, 29 Mar 2004 01:30:26 -0500 (EST) From: Newlan2dl@aol.com X-Original-Message-ID: <84.2574ce50.2d991c82@aol.com> X-Original-Date: Mon, 29 Mar 2004 01:30:26 EST Subject: Re: [LML] e-glass vs carbon fiber X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1080541826" X-Mailer: 9.0 for Windows sub 5017 -------------------------------1080541826 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Normally, a fillet of carbon or glass is transfering loads along a secondary surface such as a spar being attached to a rib so there is a lot more to do with geometry and dispersing loads than just mixing various moduii of the materials. In all cases, you have a stiff area that transitions to a more flexible area and you are trying to avoid making a hinge. By this I mean look at what the BIDS are doing. They are attaching a rib to a spar or something like that, which already has vastly stiffer properties due to its geometry than a carbon laminate when the loads are applied edge on. And that completely ignores the effects of resin which can be huge. Jeffco and others make toughened epoxies that are a family of resins that are better in impact, peel, flex and aging in general. That is much higher performance than what we currently use and for the relatively few extra dollars, is surprising we haven't done it....But then again, you don't see a lot of Lancairs falling out of the sky because the epoxied in tabs fatigued and failed from flexing after a collision. Obviously the existing system is adequate, even though there are options at no extra weight that are stronger. So in general, I am less concerned about that than miss-using mixed modulus fabrics in structures. For example, a cool looking fabric I did some laminates of was a braided tube of Kevlar and carbon. It looked great! The yellow and black looked like a snake skin. The problem is if it comes under severe stress, the higher modulus fiber will take the strain before the lower on will. This is always the case. So I have a good looking tough skin over a carbon laminate that I don't rely on to take major loads. As an example, take a laminate of 50% carbon and 50% Eglass. the modulus of "standard" T-700 type carbon is 33 million. and the glass is about 1/3 of that. In other words, the glass will stretch about 3 times as much before it fails. So if you pull a rope made of the stuff to where the carbon strarts braeaking, the glass has only contributed 1/3 of its ultimate to the rope. It may add a lot of toughness thoug so there are potentially synergistic effects but you need to test it. One thing that surprises me is that I haven't seen anywhere in the manual that tells you to taper the laminate. It's something I always do since structurally, a taper is more efficient at distributing a load. For example, if a fillet is to have two layers of 2" glass tape, it's better to have one 1.75" and the other 2.25" since you reduce the tendancy to have a hard spot. Those of us that are anal may also lightly grind the edge to get rid of non structural (and finger biting) nibs. Cosmetically better too of course. On some of the boats I've built, the test is to run your wife's nylons over the surface and if it snags, do some sanding. I HATE fishing in the bilge for something that's gotten loose and in the search come up with hands that look like they tangled with a cheese grater. Happy laminating and grinding! Dan -------------------------------1080541826 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
Normally, a fillet of carbon or glass is transfering loads along a seco= ndary surface such as a spar being attached to a rib so there is a lot more=20= to do with geometry and dispersing loads than just mixing various moduii of=20= the materials.  In all cases, you have a stiff area that transitions to= a more flexible area and you are trying to avoid making a hinge.  By t= his I mean look at what the BIDS are doing.  They are attaching a rib t= o a spar or something like that, which already has vastly stiffer properties= due to its geometry than a carbon laminate when the loads are applied edge=20= on.  And that completely ignores the effects of resin which can be huge= .  Jeffco and others make toughened epoxies that are a family of resins= that are better in impact, peel, flex and aging in general.  That is m= uch higher performance than what we currently use and for the relatively few= extra dollars, is surprising we haven't done it....But then again, you don'= t see a lot of Lancairs falling out of the sky because the epoxied in tabs f= atigued and failed from flexing after a collision.  Obviously the exist= ing system is adequate, even though there are options at no extra weight tha= t are stronger.
 
So in general, I am less concerned about that than miss-using mixe= d modulus fabrics in structures.  For example, a cool looking fabric I=20= did some laminates of was a braided tube of Kevlar and carbon.  It look= ed great!  The yellow and black looked like a snake skin.  The pro= blem is if it comes under severe stress, the higher modulus fiber will take=20= the strain before the lower on will.  This is always the case.  So= I have a good looking tough skin over a carbon laminate that I don't r= ely on to take major loads. 
 
As an example, take a laminate of 50% carbon and 50% Eglass.  the=20= modulus of "standard" T-700 type carbon is 33 million. and the glass is abou= t 1/3 of that.  In other words, the glass will stretch about 3 times as= much before it fails.  So if you pull a rope made of the stuff to wher= e the carbon strarts braeaking, the glass has only contributed 1/3 of its ul= timate to the rope.  It may add a lot of toughness thoug so there are p= otentially synergistic effects but you need to test it.
 
One thing that surprises me is that I haven't seen anywhere in the manu= al that tells you to taper the laminate.  It's something I always do si= nce structurally, a taper is more efficient at distributing a load.  Fo= r example, if a fillet is to have two layers of 2" glass tape, it's better t= o have one 1.75" and the other 2.25" since you reduce the tendancy to have a= hard spot.  Those of us that are anal may also lightly grind the edge=20= to get rid of non structural (and finger biting) nibs.  Cosmetical= ly better too of course.  On some of the boats I've built, the test is=20= to run your wife's nylons over the surface and if it snags, do some sanding.=   I HATE fishing in the bilge for something that's gotten loose and in=20= the search come up with hands that look like they tangled with a cheese grat= er.
 
Happy laminating and grinding!
 
Dan
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