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Problem $02\mathrm{.}060-$ Thermal stresses in a composite rod

At room temperature $\backslash (\backslash$left$(20^\{\backslash$circ$\}\backslash$mathrm$\{$C$\}\backslash$right$)\backslash ),$ a $\backslash (0\mathrm{.}5-\backslash$mathrm$\{$mm$\}\backslash )$ gap exists between the ends of the rods shown. The temperature eventually reaches a value of $\backslash (131^\{\backslash$circ$\}\backslash$mathrm$\{$C$\}\backslash ).$

Problem $02\mathrm{.}060.$a $-$ Thermal stresses in a composite rod

Determine the normal stress in the aluminum rod.

The normal stress in the aluminum rod is