Thermal stress occurs when expansion is restricted. Fixed rods build stress on heating!

When a metal rod is heated, it naturally wants to expand. If the rod is free, this expansion happens without any problem and no stress is developed. But when the rod is fixed at both ends, expansion is restricted. This restriction generates internal compressive stress known as thermal stress. This concept is extremely important in mechanical and civil engineering because uncontrolled thermal stress can lead to failure of structures. That’s why expansion joints are provided in bridges, pipelines, railway tracks, and buildings. Understanding thermal stress helps engineers design safer and more reliable structures