Introduction to Elasticity/Torsion of rectangular sections

< Introduction to Elasticity

Sample homework problem

Torsion of a bar with a rectangular cross section

Given:

A cylinder with a rectangular cross sections $a\times b$ under torison.

A bar with a rectangular cross section

Show:

Why a function of the form

\varphi = m\left(\frac{x_1^2}{a^2}-1\right)\left(\frac{x_2^2}{b^2}-1\right)

cannot be used as a Prandtl stress function for this cross section.

Solution

For compatibility, we need

\nabla^2{\varphi} = C

However, for the given $\varphi$ ,

\nabla^2{\varphi} = -\frac{2m}{a^2b^2}\left[a^2+b^2-(x_1^2+x_2^2)\right]

which is not constant. Hence, the given function cannot be used as a Prandtl stress function.

This article is issued from Wikiversity - version of the Monday, February 01, 2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.