Return-Path: Sender: (Marvin Kaye) To: lml@lancaironline.net Date: Tue, 30 Mar 2004 09:00:02 -0500 Message-ID: X-Original-Return-Path: Received: from [207.177.12.3] (HELO mebbs.com) by logan.com (CommuniGate Pro SMTP 4.2b1) with ESMTP-TLS id 3136209 for lml@lancaironline.net; Tue, 30 Mar 2004 07:10:32 -0500 Received: from denny63ea7z29i ([207.177.12.97]) by mebbs.com (mebbs.com [207.177.12.3]) (MDaemon.PRO.v6.8.5.R) with ESMTP id 1-md50000000620.tmp for ; Tue, 30 Mar 2004 06:11:48 -0600 X-Original-Message-ID: <001401c4164f$f5ed8cf0$610cb1cf@denny63ea7z29i> From: "Denny" X-Original-To: "Lancair Mailing List" References: Subject: Re: [LML] Re: e-glass vs carbon fiber X-Original-Date: Tue, 30 Mar 2004 06:10:07 -0600 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0011_01C4161D.A6529870" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1158 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 X-Spam-Processed: mebbs.com, Tue, 30 Mar 2004 06:11:48 -0600 (not processed: message from trusted or authenticated source) X-MDRemoteIP: 207.177.12.97 X-Return-Path: d.duello@www.mebbs.com X-MDaemon-Deliver-To: lml@lancaironline.net This is a multi-part message in MIME format. ------=_NextPart_000_0011_01C4161D.A6529870 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Dan, Please tell us what you mean by, "designed to 50% of it's design limit", = in your second paragraph . Denny ----- Original Message -----=20 From: Newlan2dl@aol.com=20 To: Lancair Mailing List=20 Sent: Monday, March 29, 2004 11:11 PM Subject: [LML] Re: e-glass vs carbon fiber Hi Rob Yes, that's true for materials like steel that have a yield so I = should have stated that in the first place. And yes, it is a simplistic = example. Carbon and glass both have pretty much a straight strain to = failure so my example was only valid for that sort of material. The = elastic limits are also pretty much linear and close to 100% except at = the extreme strain where some fibers start to fail individually or the = matrix resin starts failing. The only non-linearity is on the initial = strain but once under load, the stress/strain is virtually a straight = line. One thing you can observe is that laminates with a high void = content have a lot more little "burbs" along the plot since they tend to = have microfracturing which can lead to failures particularly in cycling. = But those tend to be at the high end also. =20 One rule that we had on a submarine I worked on was that the sub = should be designed to 50% of it's design limit since compression is the = worst case for composites since it is virtually unavoidable to prevent = kinks. And virtually all compression failures start at a kink in the = fiber. If we designed it too close, it would fail on the next dive even = though outwardly there were no signs of failure. We found that a = microphone could pick up the sound of fiber/resin fracturing which = turned out to be a good way to tell if you submarine was toast. Since = almost all resins shrink, it can't be helped (note there are some resins = that have zero shrink but they are poor structurally). You can find "Deep Flight" on a websearch if you're interested. Dan ------=_NextPart_000_0011_01C4161D.A6529870 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Dan,
 
Please tell us what you mean by, "designed to 50% of it's design = limit", in=20 your second paragraph .
 
Denny
----- Original Message -----
From:=20 Newlan2dl@aol.com
Sent: Monday, March 29, 2004 = 11:11=20 PM
Subject: [LML] Re: e-glass vs = carbon=20 fiber

Hi Rob
 
Yes, that's true for materials like steel that have a yield so I = should=20 have stated that in the first place.  And yes, it is a simplistic = example.  Carbon and glass both have pretty much a straight = strain to=20 failure so my example was only valid for that sort of material.  = The=20 elastic limits are also pretty much linear and close to 100% except at = the=20 extreme strain where some fibers start to fail individually or = the=20 matrix resin starts failing.  The only non-linearity is on = the=20 initial strain but once under load, the stress/strain is virtually a = straight=20 line.  One thing you can observe is that laminates with a high = void=20 content have a lot more little "burbs" along the plot since they tend = to have=20 microfracturing which can lead to failures particularly in = cycling.  But=20 those tend to be at the high end also. 
 
One rule that we had on a submarine I worked on was that the sub = should=20 be designed to 50% of it's design limit since compression is the worst = case=20 for composites since it is virtually unavoidable to prevent = kinks.  And=20 virtually all compression failures start at a kink in the fiber.  = If we=20 designed it too close, it would fail on the next dive even though = outwardly=20 there were no signs of failure.  We found that a microphone could = pick up=20 the sound of fiber/resin fracturing which turned out to be a good way = to tell=20 if you submarine was toast.  Since almost all resins shrink, it = can't be=20 helped (note there are some resins that have zero shrink but they are = poor=20 structurally).
 
You can find "Deep Flight" on a websearch if you're = interested.
 
Dan
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