Consider a bar which is fixed at one of the ends. I increase the temperature of the bar by $\Delta T$. The sources I'm referring to say that stress developed in the bar will be zero because the bar is free to expand.
However the bar is free to expand only in the longitudinal direction not in the lateral ones. So how the stress can be zero.
If the bar would've rested on a frictionless surface then the stress would've been zero. But how in this case?