Fatigue strength of a material can not be increased by

ANS:B - hot working

Hot working is a metalworking process that involves shaping or forming metal while it is in a heated state, typically above its recrystallization temperature but below its melting point. This process is carried out to alter the shape, size, and properties of metals and alloys, and it is commonly used for materials like steel, aluminum, copper, and titanium. Here's how hot working works and why it's used:

1. Heating: The metal or alloy is heated to an elevated temperature to make it more malleable and easier to deform. The temperature range for hot working varies depending on the material being processed and the desired outcome, but it is typically above the recrystallization temperature. Heating can be done in furnaces, induction heaters, or other specialized equipment.
2. Deformation: Once the metal reaches the desired temperature, it is subjected to mechanical forces such as compression, rolling, forging, extrusion, or pressing. These processes help reshape the material into the desired form, whether it's sheets, plates, bars, rods, tubes, or complex shapes.
3. Advantages:
   • Reduced deformation forces: Heating the metal reduces its yield strength and increases its ductility, allowing for easier deformation with lower applied forces.
   • Improved workability: Hot working enables complex shapes to be formed more easily without the risk of cracking or other defects.
   • Grain refinement: The high temperature during hot working promotes recrystallization and grain growth, resulting in a finer grain structure and improved mechanical properties.
   • Stress relief: Hot working can relieve residual stresses that may have accumulated in the material during previous processing steps.
   • Improved surface finish: Hot working can produce smoother surfaces compared to cold working processes due to the higher temperatures and reduced strain hardening.
4. Applications: Hot working is used in various industries such as aerospace, automotive, construction, and manufacturing for producing components like engine parts, structural beams, piping, shafts, and automotive body panels.

Overall, hot working is a versatile metal forming technique that offers numerous benefits in terms of shaping, refining microstructure, and enhancing mechanical properties of metals and alloys. It is an essential process in modern manufacturing for producing high-quality components with precise dimensions and desired properties.