2 Replies Latest reply on Dec 4, 2011 5:25 PM by Frank Emerson

    Material properties for unusual materials

    Frank Emerson

      I design pianos.  The materials I use are foreign to virtually every other modern industry. Besides specifying material properties for orthotropic materials, such as wood species, the problem is even greater in determining static and dynamic frictional coefficients for material combinations including buckskin, felt, graphite-coated hornbeam and other wood species.  My immediate roadblock is accurately defining frictional variables for rigid body motion analysis.

       

      Another problem relates to thermal dynamics.  Relatively slight temperature changes have the opposite effect on “tonewood,” as would be expected of other materials.  Soundboard spruce does have an expansion thermal coefficient, but higher temperatures reduce moisture content in the wood.  The lower moisture content overpowers the expansion due to temperature, resulting in dimensional contraction, mostly across the grain.

       

      When I bring these issues up with SW tech support, they “look at me” like I have three heads!  Is there anyone out there who has dealt with these issues?

       

      Thanks,

      George F Emerson

      pianoguru@cox.net

        • Re: Material properties for unusual materials
          Jerry Steiger

          Frank, (or is it George?),

           

          I can readily imagine that the folks at SW tech support are not going to be able to help much! And I'm afraid you probably aren't going to find too many people who deal with similar materials. I certainly can't be of much help.

           

          For static and dynamic friction coefficients, I think you are going to have to do your own experiments. Get a force gage and some weights. Make a sled to hold the weights and face the bottom or contact points on the bottom with one of your materials and drag or push it across the materials you want to check it with. Vary the weights to see how much the coefficient varies with pressure. You'll be the world's leading expert in no time!

           

          Being from a lumber producing state, I know that University professors have done a fair amount of work on the properties of the big commercial woods, like Douglas Fir and Yellow Pine, but I suspect you are not going to find much data on your woods, with the possible exception of Spruce. (You might find lots of old data on the types of Spruce used in early aviation.)

           

          Jerry Steiger

            • Re: Material properties for unusual materials
              Frank Emerson

              Jerry,

               

              Thanks for your reply.  I have done some rudimentary tests, such as you suggest.  What I have not done is vary the weight.  I will do that.  Another thing I have tried is to create motion studies to emulate a variety of tests for friction that piano technicians use in servicing these components.  If I can get my model to behave as the real parts do in the real world, I can have a greater degree of confidence in the coefficient values.

               

              George F. (Frank) Emerson

              (I answer to either name.)