ANS:B - residual localised stresses.

Residual localized stresses, also known as residual stresses or residual strain, are internal stresses that remain in a material even after external loads or forces have been removed. These stresses can occur during manufacturing, processing, or assembly processes and can have significant effects on the performance and behavior of materials and components. Here's an explanation of residual localized stresses:

1. Formation: Residual localized stresses can arise from various sources, including:
   • Manufacturing Processes: Processes such as casting, forging, welding, machining, heat treatment, and surface treatments can introduce localized stresses into materials due to temperature gradients, phase transformations, cooling rates, or plastic deformation.
   • Assembly Processes: Joining or bonding of components, such as welding, brazing, or adhesive bonding, can induce residual stresses at the interfaces or within the joint regions.
2. Distribution: Residual localized stresses are typically non-uniform and can be concentrated in specific regions or areas of a material or component. These stresses can be tensile, compressive, or shear in nature, depending on the manufacturing or assembly processes involved.
3. Effects: Residual localized stresses can have several effects on the mechanical behavior and performance of materials and components:
   • Cracking and Fracture: High tensile residual stresses can lead to cracking or fracture initiation, particularly in regions with stress concentrations or defects.
   • Distortion and Warping: Residual stresses can cause dimensional changes, distortion, or warping of components, affecting their dimensional accuracy and fitment.
   • Reduced Fatigue and Fracture Resistance: Residual stresses can decrease the fatigue life and fracture resistance of materials by promoting crack initiation and propagation under cyclic loading conditions.
   • Stress Corrosion Cracking: Residual stresses can increase the susceptibility of materials to stress corrosion cracking, particularly in environments where corrosive agents are present.
   • Springback: Residual stresses can cause elastic deformation or springback after forming or shaping processes, affecting the final shape and geometry of components.
4. Measurement and Mitigation: Residual localized stresses can be measured using various techniques, including X-ray diffraction, neutron diffraction, strain gauges, and optical methods. To mitigate the adverse effects of residual stresses, strategies such as stress relief annealing, shot peening, mechanical or thermal stress relaxation, and design optimization can be employed during manufacturing or assembly processes.

In summary, residual localized stresses are internal stresses that remain in a material or component after external loading or processing, with potential implications for its mechanical behavior, dimensional stability, and performance. Understanding and managing these stresses are crucial for ensuring the reliability and integrity of engineered components and structures.