Q1: The most serious manufacturing defect from fracture toughness point of view is

ANS:D - crack

The most serious manufacturing defect from a fracture toughness point of view is a crack. Explanation:

1. Surface roughness: Surface roughness refers to irregularities or unevenness on the surface of a material. While excessive surface roughness can affect the performance and aesthetics of a product, it does not significantly impact fracture toughness. Surface roughness is generally considered a surface quality issue rather than a structural defect affecting the bulk material properties.
2. Pores: Pores are small voids or cavities within a material that may result from incomplete filling during casting or solidification processes. While pores can reduce the strength and ductility of a material, they typically do not pose as significant a threat to fracture toughness as cracks. Proper engineering practices can often mitigate the effects of pores through quality control measures and material selection.
3. Spherical inclusions: Spherical inclusions are non-metallic particles or contaminants embedded within a material. While inclusions can act as stress concentration points and reduce the fracture toughness of a material, they are generally less severe than cracks in terms of their impact on fracture behavior. Inclusions can be managed through material purification techniques and control of processing parameters.
4. Crack: A crack is a structural defect characterized by a sharp discontinuity or fracture surface within a material. Cracks can propagate under applied stress, leading to catastrophic failure without warning. From a fracture toughness perspective, cracks are the most serious defect as they significantly reduce the ability of a material to resist fracture and tolerate applied loads. Proper defect detection, prevention, and mitigation strategies are essential to address cracks and maintain the fracture toughness of manufactured components.