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Overall Bending Stiffness of a Tube Rod Assembly

Overall Bending Stiffness of a Tube Rod Assembly

Overall Bending Stiffness of a Tube Rod Assembly

(OP)
A polymer tube 2.5mm diameter with a Youngs Modulus = 2 GPa that contains a metal rod diameter 0.75mm with a Young's modulus of 107 GPa. I need to know the overall bending stiffness of the assembly.

If both materials were touching it would be simple i.e.

k = EI , where I = 2nd moment of area. and just add the two stifness values.

However, i need to know how to calculate the stiffness for the above conditions i.e. material not touching.

RE: Overall Bending Stiffness of a Tube Rod Assembly

It is difficult to know for sure without knowing the end conditions, however, you seem to have a
condition similar to springs in parallel, eg. two extension springs side by side bearing a single
load. In this condition the k values are additive, k total = k1 + k2 + k3... If the rods were
stacked end to end you would have springs in series 1/k total = 1/k1 + 1/k2... (the inverse of
electrical resistors) Hope this helps.

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