Date: Fri, 25 Sep 1998 20:44:30 -0400
From: Guy Buchanan <bnn@compuserve.com>
Subject: Carbon vs. Glass
Sender: Guy Buchanan <bnn@compuserve.com>
To: Blind.Copy.Receiver@compuserve.com
Message-ID: <199809252044_MC2-5AB8-AE02@compuserve.com>
Mime-Version: 1.0

Content-Type: text/plain; charset=ISO-8859-1
Content-Disposition: inline
X-Mailing-List: lancair.list@olsusa.com

          <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>
          <<  Lancair Builders' Mail List  >>
          <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> 
>>
John,
        Some data for your inquiry:

Material                Modulus         Comp.   Linear strain 
                                        Stress  to failure

Spruce perp.            1.57 msi (flex) 5.6 ksi 0.4%
to grain

E-glass/epoxy           2.4 msi (comp)  44 ksi  1.8%
equal 0/45/90/-45

E-glass/epoxy           2.72 msi (comp) 64 ksi  2.4%
equal 0/90

Low mod carbon/epoxy    5.37 msi (comp) 34 ksi  0.6%
equal 0/45/90/-45

Low mod carbon/epoxy    7.15 msi (comp) 52 ksi  0.7%
equal 0/90

Low mod carbon/epoxy    9.97 msi (comp) 64 ksi  0.6%
70% uni

        Thus, in a pure tug the spruce will fail first,
the carbon second, and the glass last. However, when
you build a sandwich panel with a symmetric laminate,
and then add higher stiffness material to one face,
you CAN shift the neutral exis faster than you 
increase the section inertia, thereby reducing the
section modulus and therefore the beam bending
strength. 
        More importantly to the fastidious, the
coefficients of thermal expansion between carbon and
glass are quite different (0.02e-6 v 8.6e-6 mm/(mm-C))
meaning that temporary, and possibly permenant,
deformations will show at each modification, making
your beautiful Lancair look, ahem, shall we say, lumpy?
(Permenant deformations occur because of shrinkage,
temporary because of temperature and humidity changes.)

Food for thought,

Guy Buchanan
Buchanan & Newcomer