Jawaharlal Nehru Technological University Hyderabad B. Tech III BASIC MECHANICAL ENGINEERING FOR CIVIL ENGINEERS Previous Question Paper (September - 2021 - R18)

Annealing is a heat treatment process where a metal is heated to a specific temperature (usually above the critical range), held at that temperature for a sufficient time, and then cooled slowly, typically inside the furnace. The primary purpose is to relieve internal stresses, soften the material, and improve ductility.

The process involves three stages: 1) Heating to the required temperature, 2) Soaking (holding at temperature to ensure uniform structure), and 3) Slow cooling. The resulting changes in properties include:

• Increased Ductility: The slow cooling rate allows for the formation of a coarse, equilibrium microstructure, which increases the material's ability to undergo plastic deformation.
• Reduced Hardness and Strength: By eliminating internal strains and refining the grain structure, the material becomes softer and easier to machine.
• Stress Relief: Internal residual stresses caused by prior cold working or rapid cooling are removed, preventing distortion or cracking in service.
• Improved Homogeneity: Chemical segregation is reduced, leading to a more uniform material composition.

Given: Plate thickness (t) = 20 mm, Rivet diameter (d) = 25 mm, Pitch (p) = 100 mm, σt = 120 MPa, τ = 100 MPa, σc = 150 MPa.

1. Strength of solid plate per pitch length (P):

2. Tearing resistance of plate (Pt):

3. Shearing resistance of rivets (Ps): Since it is a double riveted double cover butt joint, there are 2 rivets per pitch length, each in double shear.

4. Crushing resistance of rivets (Pc):

5. Strength of the joint (min of Pt, Ps, Pc) = 150,000 N.

6. Efficiency (η):