Flexural strength as length shrinks

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SUMMARY

The discussion centers on the flexural strength of balsa wood planks under a three-point bending test. It is established that maximum load decreases with length reduction up to a certain point, after which it increases, contradicting the flexural strength formula \( \sigma = \frac{3FL}{2bd^2} \). The participants highlight that this formula is based on isotropic materials, while wood is non-isotropic, necessitating consideration of factors such as moisture content and grain orientation. The formula's applicability is questioned for short beams due to the presence of combined bending and compression forces.

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  • Understanding of flexural strength and its calculation
  • Knowledge of isotropic vs. non-isotropic materials
  • Familiarity with moisture content control in wood
  • Basic principles of beam mechanics and loading conditions
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  • Research alternative formulas for non-isotropic materials in bending tests
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Researchers, materials scientists, and engineers involved in wood testing, particularly those focusing on the mechanical properties of balsa wood and other non-isotropic materials.

princeyprince
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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?
 
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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.
 
princeyprince said:
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.

That formula also assumes things like small deflections, and certain aspect ratios of the beam. For very short beams, the formula 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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