Thanks, Joe, for clearing that up. @ Mr. Bayly: Now, THAT is an engineer speaking! The previous explanation (mine) is merely an engineering geologist attempting to explain some physics that he learned many years ago! ;-D
Ron Holcomb, CEG > Date: Fri, 23 Dec 2011 11:31:16 -0500 > Subject: [alfa] RE: Little to zip Alfa glue question - Stress, Strain, Shear > From: [email protected] > To: [email protected] > > Actually, strain is defined as the ratio of that linear measurement > (deformation) to the initial dimension of the material, so strain is > unitless. (To help answer Stefano's question, the stress/strain > relationship is typically linear up until the point at which the material > yields, which is to say it won't return to its original shape when the load > is removed.) The classic example is 10" long strip of metal that is loaded > in tension such that it gets 0.01" longer. 0.01"/10" = 0.001. That's your > strain. Or 0.1% if you prefer. > > I still haven't found time to look up a photo of Biba's chair, so I'm not > 100% certain what we're talking about here, but as far as shear stress > goes, the shear strain is typically defined as the ratio of tangential > deformation divided by the thickness of the material. So if you have two > parts joined by a 0.05" thick layer of glue, and the applied load causes > the parts to shift 0.001" relative to each other, your shear strain is > 0.001"/0.05" = 0.02 or 2%. Of course, if one of those parts is a > relatively flexible rubber block, it will undergo much greater strain. If > it's an inch thick, and under load the glued surface moves 0.1" relative to > the other surface (viewed from the side, that's a rectangle being deformed > into a parallelogram with 84 and 96 degree interior angles), your shear > strain in the rubber block is 0.1"/1.0" = 0.1 or 10%. > > To relate shear strain to the more common tensile strain in my first > example (and the associated published material property data) you need to > imagine a cube-shaped element of the material tilted 45 degrees from the > shear plane. That element will see a tension load when the actual part is > loaded in shear, with tensile stress and strain roughly 1.4 times (divide > by the sine of 45 degrees) greater than the calculated values for shear > stress and strain. So if you were imagining a cube shape element of the > rubber block 0.1" wide in each dimension, oriented 45 degrees relative to > the block, the shear load that deformed the block into the aforementioned > parallelogram shape will have stretched your imaginary 45 degree 0.1" cube > element into a rectangular solid 0.114" x 0.093" x 0.093" for a tensile > strain of (0.114" - 0.1")/0.1" = 0.14 or 14% equivalent tensile strain. > > Joe Elliott, PE > > > > > Date: Fri, 16 Dec 2011 23:03:21 +0000 > > From: ron holcomb <[email protected]> > > Subject: RE: [alfa] RE: Little to zip Alfa glue question - Stress, Strain, > > Shear > > > > Stress/Strain relationships are dependent upon the material involved. > > Stress > > will not be equal to strain since the units are different. Stress = force > > per > > area (i.e. pounds per square inch). Strain is a linear measurement (i.e. > > one > > eighth of an inch). > > > > > > > Date: Fri, 16 Dec 2011 08:31:11 -0800 > > > Subject: [alfa] RE: Little to zip Alfa glue question - Stress, Strain, > > Shear > > > From: [email protected] > > > To: [email protected] > > > > > > >So, when a Shear Stress is applied to the glued bond between the metal > > and > > the > > > >wood, the Strain will probably be great enough to separate the block > > from > > the > > > >frame of the chair. > > > > > > So will the value of Shear Stress and Strain be equal at the time of > > separation? > > > Or are they not related in this way? > > > > > > And thanks to all that answered me about my Speedo cable question! > > > > > > Stefano > > > Concord, CA > > > -- > > > to be removed from alfa, see http://www.digest.net/bin/digest-subs.cgi > > > or email "unsubscribe alfa" to [email protected] > -- > to be removed from alfa, see http://www.digest.net/bin/digest-subs.cgi > or email "unsubscribe alfa" to [email protected] -- to be removed from alfa, see http://www.digest.net/bin/digest-subs.cgi or email "unsubscribe alfa" to [email protected]
