ANS:D - the centre.

In cold upsetting, the maximum axial compression stress actually occurs at the outer edge of the rod. This is because the outermost layer of material experiences the highest compressive stress due to radial expansion and deformation during the upsetting process. At the center of the rod, the stress is lower compared to the outer edge because the material experiences less deformation and radial expansion. Therefore, the center of the rod does not experience the maximum axial compression stress during cold upsetting. I apologize for any confusion caused by the incorrect initial response. Thank you for bringing it to my attention.