Q1: Stretcher strains found in a low carbon sheet are associated with the

ANS:C - yield point phenomenon.

The yield point phenomenon refers to a characteristic behavior exhibited by certain materials, particularly metals, when subjected to tensile stress. It involves a sudden and temporary decrease in stress or load experienced by the material after it has begun to deform plastically. Here's a detailed explanation:

1. Elastic Deformation: When a material is initially subjected to tensile stress, it deforms elastically, meaning that it returns to its original shape once the stress is removed. This elastic deformation occurs up to a certain point called the elastic limit.
2. Plastic Deformation: Beyond the elastic limit, if the stress continues to increase, the material undergoes plastic deformation. In this phase, the material experiences permanent changes in shape or size even after the stress is removed. Plastic deformation typically proceeds gradually and uniformly in most materials.
3. Yield Point: In materials exhibiting the yield point phenomenon, such as certain types of steel, there is a distinct point on the stress-strain curve where the material experiences a sudden drop in stress after undergoing initial plastic deformation. This point is known as the yield point.
4. Stress Relaxation: At the yield point, the material undergoes a phenomenon known as stress relaxation, where the applied stress decreases momentarily while the material continues to deform. This decrease in stress is often accompanied by a reduction in the rate of strain, indicating that the material is "relaxing" or adjusting to the applied load.
5. Subsequent Deformation: After the initial stress relaxation, the material resumes its plastic deformation behavior and continues to elongate until it reaches ultimate tensile strength, where it experiences fracture or failure.
6. Reproducibility: The yield point phenomenon is usually observed in materials with specific microstructural characteristics, such as certain types of steel alloys. It is important to note that the yield point is not always well-defined and can vary depending on factors such as material composition, temperature, and rate of loading.
7. Significance: Understanding the yield point phenomenon is crucial in engineering applications, especially in designing structures and components subjected to cyclic loading or fatigue. The presence of a distinct yield point can affect the material's behavior under load, including its resistance to deformation, energy absorption capacity, and susceptibility to stress concentrations.

In summary, the yield point phenomenon refers to the sudden drop in stress experienced by a material during plastic deformation, followed by continued deformation until failure. It is a characteristic behavior observed in certain materials and has implications for their mechanical properties and performance in various applications.