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Re: S&G: Stiffness compared to strip *PIC*
By:Sam McFadden
Date: 7/1/2013, 11:54 am
In Response To: Re: S&G: Stiffness compared to strip (ancient kayaker)

You are correct, according to Gougeon's data a glass skin on both sides increases the stiffness of the ply core so much that the stiffnes of the ply core becomes virtually negligible.

I believe a better way to see the influence of core on strength and stiffness is to look at bend tests where the primary variable is wood grain direction. A while back, Nick made some samples to look at this, and we found significant difference in stiffness and strength between the parallel and cross grain direction of common strip layups. Take a look at http://www.guillemot-kayaks.com/Building/Testing/photos.html and then at http://www.guillemot-kayaks.com/Building/Testing/index.html.

In the plot below, the two groups of curves with different stiffness and strength are the result of grain orientation in samples made from 1/4 inch thick cedar with 6 oz. plain weave on both sides. Clearly, the sandwich model, where the skins provide stiffness and strength and the core contributes primarily to in-plane shear with no significant contribution to stiffness and strength, does not apply well to the strip or plywood core layups typically used for kayaks.

Sam

Messages In This Thread

S&G: Stiffness compared to strip
Dan Caouette (CSCWC) -- 6/25/2013, 2:26 pm
Re: S&G: Stiffness compared to strip
Matt Jakubek -- 6/25/2013, 2:49 pm
Re: S&G: Stiffness compared to strip
Etienne Muller -- 6/25/2013, 2:53 pm
Re: S&G: Stiffness compared to strip
Dan Caouette (CSCWC) -- 6/26/2013, 9:18 am
Re: S&G: Stiffness compared to strip
Etienne Muller -- 6/26/2013, 10:16 am
Re: S&G: Stiffness compared to strip
Malcolm Schweizer -- 6/25/2013, 3:21 pm
Re: S&G: Stiffness compared to strip
Nick Schade - Guillemot Kayaks -- 6/25/2013, 4:40 pm
Re: S&G: Stiffness compared to strip
Marc Upchurch -- 6/25/2013, 6:06 pm
Re: S&G: Stiffness compared to strip
Dan Caouette (CSCWC) -- 6/26/2013, 9:03 am
Re: S&G: Stiffness compared to strip
Nick Schade - Guillemot Kayaks -- 6/26/2013, 4:33 pm
Re: S&G: Stiffness compared to strip
ancient kayaker -- 6/26/2013, 11:32 pm
Re: S&G: Stiffness compared to strip
Nick Schade - Guillemot Kayaks -- 6/27/2013, 9:29 am
Re: S&G: Stiffness compared to strip
Bill Hamm -- 6/30/2013, 2:24 am
Re: S&G: Stiffness compared to strip
Robert N Pruden -- 6/27/2013, 4:55 pm
Re: S&G: Stiffness compared to strip
Erik -- 6/25/2013, 8:12 pm
Re: S&G: Stiffness compared to strip
ancient kayaker -- 6/25/2013, 9:01 pm
Re: S&G: Stiffness compared to strip
Dan Caouette (CSCWC) -- 6/26/2013, 9:30 am
Re: S&G: Stiffness compared to strip
Bill Hamm -- 6/30/2013, 2:21 am
Re: S&G: Stiffness compared to strip
Dan Caouette (CSCWC) -- 6/26/2013, 9:17 am
Re: S&G: Stiffness compared to strip
Bill Hamm -- 6/26/2013, 1:53 am
Re: S&G: Stiffness compared to strip
Tony G -- 6/26/2013, 9:27 am
Re: S&G: Stiffness compared to strip
Dan Caouette (CSCWC) -- 6/26/2013, 9:38 am
Re: S&G: Stiffness compared to strip
john Messinger -- 6/26/2013, 11:49 am
Re: S&G: Stiffness compared to strip
Etienne Muller -- 6/26/2013, 12:14 pm
Re: S&G: Stiffness compared to strip *PIC*
Rob Macks/Laughing Loon CC&K -- 6/26/2013, 12:20 pm
John, are you talking about boats? *NM*
Rob Macks/Laughing Loon CC&K -- 6/26/2013, 12:50 pm
Where's the tip jar?!
Dan Caouette (CSCWC) -- 6/26/2013, 1:04 pm
Re: Where's the tip jar?!
john Messinger -- 6/27/2013, 8:37 am
Re: S&G: Stiffness compared to strip
Mike Savage -- 6/27/2013, 6:34 pm
Re: S&G: Stiffness compared to strip
Kurt Maurer -- 6/27/2013, 9:35 pm
Re: S&G: Stiffness compared to strip
Mike Savage -- 6/28/2013, 4:49 pm
Re: S&G: Stiffness compared to strip
Bill Hamm -- 6/30/2013, 2:31 am
Re: S&G: Stiffness compared to strip
Mike Savage -- 7/1/2013, 4:46 pm
Re: S&G: Stiffness compared to strip
ancient kayaker -- 6/28/2013, 7:14 pm
Re: S&G: Stiffness compared to strip *PIC*
Sam McFadden -- 7/1/2013, 11:54 am
Re: S&G: Stiffness compared to strip
Bill Hamm -- 7/2/2013, 9:11 am
Re: S&G: Stiffness compared to strip
Sam McFadden -- 7/2/2013, 10:43 am
Re: S&G: Stiffness compared to strip *PIC*
ancient kayaker -- 7/2/2013, 6:43 pm
Re: S&G: Stiffness compared to strip
Etienne Muller -- 7/1/2013, 1:31 pm