Overall Bending Stiffness of a Tube Rod Assembly

[xpert999]

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. <br>
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If both materials were touching it would be simple i.e. <br>
<br>
k = EI , where I = 2nd moment of area. and just add the two stifness values. <br>
<br>
However, i need to know how to calculate the stiffness for the above conditions i.e. material not touching.

 

[lyletk]

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