Thanks Mariog for that great explanation. Anyway, the direct stiffness approach is a closed form of solution unlike Finite Element Approach which is approximate. So the Physics for the axial stiffness of a bar works.

I am just curious what part of the finite element approach is causing the singularity in a sharp corner as the mesh is increased. What part of the math (particular number) is causing this stress singularity?

Just correct any wrong mathematical statement I've made.

Cheers!!!