Return-Path: Sender: (Marvin Kaye) To: lml@lancaironline.net Date: Sat, 03 Apr 2004 22:39:34 -0500 Message-ID: X-Original-Return-Path: Received: from imo-d21.mx.aol.com ([205.188.144.207] verified) by logan.com (CommuniGate Pro SMTP 4.2b1) with ESMTP id 3144509 for lml@lancaironline.net; Sat, 03 Apr 2004 21:16:00 -0500 Received: from Newlan2dl@aol.com by imo-d21.mx.aol.com (mail_out_v37_r1.2.) id q.27.54d7fac5 (3940) for ; Sat, 3 Apr 2004 21:15:56 -0500 (EST) From: Newlan2dl@aol.com X-Original-Message-ID: <27.54d7fac5.2da0c9dc@aol.com> X-Original-Date: Sat, 3 Apr 2004 21:15:56 EST Subject: Re: [LML] Re: e-glass vs carbon fiber X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1081044956" X-Mailer: 9.0 for Windows sub 5017 -------------------------------1081044956 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Hi Steve Sorry to take so long to get back but I was on the road. What would probably increase the dispersion of the loads better than carbon BIDS would be to make a larger radius on the fillet. However, for the same radius fillet, the carbon will be stiffer at pretty much the same weight as glass, (given the previously mentioned admonishment about carbon being bulkier and thus holding more matrix resin for the same ariel weight). A larger fillet can certainly help on the loads but I suspect deeper flanges would be better than either carbon tape or even larger fillets. Or you may want to add some extra core thickness. In fact, for almost all structures, a little bit of thickness makes a much bigger difference than carbon vs. glass. Remember that a laminate gets stiffer by the cube of the thickness from the neutral axis. For carbon and glass which are very close to balanced, i.e. the compressive strength and modulus are very close, the neutral axis is near the center of the laminate. For Kevlar and Spectra which are unbalanced having much higher tensile strength and modulus, the neutral axis in nearer the tension (higher modulus) side. Note this relates to why a balanced laminate is structurally superior for a given weight since the neutral axis is closer to the center. One thing I wanted to mention too is that you do want to make sure you have a fillet for most of this tabbing. I first started repairing boats when I was 14 and sort of became the Cal 40 fleet repair kid (I was to find out I was the only one stupid enough to grind fiberglass inside a wet gear closet). The Cal 40 was a fast boat for it's time but cored structures weren't well understood at that time. Anyway, the Cal 40 had their main bulkhead butted against the hull which was uncored (and thus relatively flexible) so the flexing ended at the bulkhead. This effectively became a hinge so the Cal 40's could expect to have their main bulkhead tabbing replaced every few years. That was unless you cut the bulkhead away from the hull by about an inch and placed a trapezoidal foam piece between it and the hull then lamionated your tabs which made smoother transition of the load from the flexing hull to the stiff bulkhead. Yet a cored hull would be lighter and wouldn't have had any trouble since the flexing is generally almost nonexistant. So the short of it is, try and use core rather than just extra solid laminate since it is really the outside of the laminate doing the work. Dan -------------------------------1081044956 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable

Hi Steve

Sorry to take so long to get back but I was on the road. What wou= ld probably increase the dispersion of the loads better than carbon BIDS wou= ld be to make a larger radius on the fillet. However, for the same radius fi= llet, the carbon will be stiffer at pretty much the same weight as glass, (g= iven the previously mentioned admonishment about carbon being bulkier and th= us holding more matrix resin for the same ariel weight). A larger fill= et can certainly help on the loads but I suspect deeper flanges would b= e better than either carbon tape or even larger fillets. Or you m= ay want to add some extra core thickness. In fact, for almost all stru= ctures, a little bit of thickness makes a much bigger difference than carbon= vs. glass. Remember that a laminate gets stiffer by the cube of the t= hickness from the neutral axis. For carbon and glass which are very cl= ose to balanced, i.e. the compressive strength and modulus are very close, t= he neutral axis is near the center of the laminate. For Kevlar an= d Spectra which are unbalanced having much higher tensile strength and modul= us, the neutral axis in nearer the tension (higher modulus) side. Note= this relates to why a balanced laminate is structurally superior for a give= n weight since the neutral axis is closer to the center.

One thing I wanted to mention too is that you do want to make sure you=20= have a fillet for most of this tabbing. I first started repairing boat= s when I was 14 and sort of became the Cal 40 fleet repair kid (I was to fin= d out I was the only one stupid enough to grind fiberglass inside a wet gear= closet). The Cal 40 was a fast boat for it's time but cored structure= s weren't well understood at that time. Anyway, the Cal 40 had their m= ain bulkhead butted against the hull which was uncored (and thus relatively=20= flexible) so the flexing ended at the bulkhead. This effectively becam= e a hinge so the Cal 40's could expect to have their main bulkhead tabbing r= eplaced every few years. That was unless you cut the bulkhead away fro= m the hull by about an inch and placed a trapezoidal foam piece between it a= nd the hull then lamionated your tabs which made smoother transition of the=20= load from the flexing hull to the stiff bulkhead. Yet a cored hull wou= ld be lighter and wouldn't have had any trouble since the flexing is general= ly almost nonexistant.

So the short of it is, try and use core rather than just extra solid la= minate since it is really the outside of the laminate doing the work.

Dan

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