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Flexural strength as length shrinks

  1. Sep 23, 2009 #1
    I'm currently compiling a report on the strength of balsa woods planks under a three point test.

    Thus far i've found that maximum load shrinks as length does, upto a point, beyond which max load increases. This doesn't fit with the proscribed flex. strength = 3FL/2bd^2 formula.

    Is there any concurrent formula that can make allowance for this?
  2. jcsd
  3. Sep 23, 2009 #2


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    The first major issue I see is that you are trying to use a relation based on isotropic materials on a non-isotropic material. Working with wood requires some special process requirements, most notably is the control of moisture content in the wood and grain orientation.
  4. Sep 23, 2009 #3


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    That formula also assumes things like small deflections, and certain aspect ratios of the beam. For very short beams, the forumla cannot apply because the forces in the beam will not be pure bending, but rather a combination of bending and compression.

    In short, the formula may not be at all applicable to the tests you are performing.
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