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./lecture_slides/MMME2053 SE L1 Slides.pdf, ./lecture_slides/MMME2053 SE L2 Slides.pdf, ./lecture_slides/MMME2053 SE L3 Slides.pdf ] +lecture_notes: [ ./lecture_notes/Strain Energy Methods Notes.pdf ] +worked_examples: [ ./worked_examples/MMME2053 SE WE Slides.pdf ] +exercise_sheets: [ ./exercise_sheets/Strain Energy Methods Exercise Sheet.pdf, ./exercise_sheets/Strain Energy Methods Exercise Sheet Solutions.pdf ] +--- + +# Strain Energy Definition + +This section refers to the first two slide sets. + +Strain energy in a body is equal to the work done on the body by the applies loads: + +$$U = \int_0^u P\mathrm du$$ + +![](./images/vimscrot-2023-02-16T14:19:48,580021845+00:00.png) + +## Bending + +\begin{equation} +U = \int_0^\Phi M\mathrm d\Phi = \int^L_0\frac{M^2}{2EI}\delta s +\label{eqn:bendingeqn1} +\end{equation} + +![](./images/vimscrot-2023-02-16T14:22:41,358964129+00:00.png) + +If this material represents an element of a larger beam of length $L$ and curvature of radius $R$ + +![](./images/vimscrot-2023-02-16T14:41:32,526245370+00:00.png) + +The strain energy within this element will be: + +$$\delta U = \frac12 M\delta \Phi$$ + +From the elastic beam bending equation we know: + +$$\frac MI = \frac ER$$ + +and as the angle subtended by the element is equal to the change in slope, the expression for the +arc created by the element is: + +$$\delta s = R\delta \Phi$$ + +Eliminating $R$ from the above two equations and rearranging gives + +$$\delta \Phi = \frac{M}{EI}\delta s$$ + +This can be substituted into \label{eqn:bendingeqn1} (left and middle) to get + +$$\delta U = \frac{M^2}{2EI}\delta s$$ + +Integrate over full length of beam to get total strain energy: + +$$U = \int^L_0\frac{M^2}{2EI}\delta s$$ + +## Torsion + +$$U = \int_0^\theta T\mathrm d\theta = \int^L_0 \frac{T^2}{2GJ} \delta s$$ + +Derivations for the equation above is analogous to those for bending and axial loads, and can be +found in the second lecture slide set (p9-p11). + +![](./images/vimscrot-2023-02-16T14:23:06,415583742+00:00.png) + +## Elastic Axial Loading + +\begin{equation} +U = \frac12 Pu = \int^L_0\frac{P^2}{2EA}\delta s +\label{eqn:elasticaxialloading1} +\end{equation} + +![](./images/vimscrot-2023-02-16T14:26:48,809335151+00:00.png) + +If this material represents an element, of length $\delta s$, of a larger beam of length $L$, and +the change in length of this element due to the applied load $P$ is $\delta u$ ten the strain energy +within the element is + +$$\delta U = \frac12 P\delta u$$ + + +![](./images/vimscrot-2023-02-16T14:40:43,750030500+00:00.png) + +> Note that there are transverse strains/displacements due to Poisson's effects but there are no +> transverse stresses/loads, thus there is no work done in the transverse direction. + +Axial strain is: + +$$\epsilon = \frac{\delta u}{\delta s}$$ + +Equating this to Hooke's law yields: + +$$\delta u = \frac{P}{EA}\delta s$$ + +which can be substituted into equation \ref{eqn:elasticaxialloading1} (left and middle) to get + +$$\delta U = \frac{P^2}{2EA}\delta s$$ + +Integrate over full length of beam to get total strain energy: + +$$U = \int^L_0\frac{P^2}{2EA}\delta s$$ + +# Castigliano's Theorem + +This section refers to the third slide set. + +