JNTU
JNTU B.Tech III PRINCIPLES OF MACHINE DESIGN Previous Question Paper (October - 2020 - R15)
Answer any five questions. All questions carry equal marks.
Main
Enumerate the most commonly used engineering materials and state at least one important property and one application of each.
Answer
Commonly used engineering materials include:
- Mild Steel: High ductility and weldability. Used in structural steelwork and machine parts.
- Cast Iron: Excellent compressive strength and vibration damping. Used for machine tool beds and engine blocks.
- Aluminum Alloys: High strength-to-weight ratio and corrosion resistance. Used in aerospace components and automotive parts.
- Copper: High electrical and thermal conductivity. Used in electrical wiring and heat exchangers.
- Stainless Steel: High corrosion resistance. Used in chemical equipment and surgical instruments.
A bar 3 m long is made of two bars, one of copper having E = 105 GN/m2 and the other steel having E = 210 GN/m2. Each bar is 25 mm broad and 12.5 mm thick. This compound bar is stretched by a load of 50 kN. Find the increase in length of the compound bar and the stress produced in the steel and copper. The length of copper as well as of steel bar is 3 m each.
Answer
Given: Length (L) = 3 m = 3000 mm, Width (b) = 25 mm, Thickness (t) = 12.5 mm. Area of each bar (A) = 25 × 12.5 = 312.5 mm2. Load (P) = 50 kN = 50000 N. Es = 210 GPa, Ec = 105 GPa.
Since the bars are in parallel, the extension (δL) is the same for both. The total load is shared: P = Ps + Pc.
Substituting the values:
Stress in steel (σs):
Stress in copper (σc):
The load on a bolt consists of an axial pull of 10 kN together with a transverse shear force of 5 kN. Find the diameter of bolt required according to:
a) Maximum principal stress theory
b) Maximum shear stress theory
c) Maximum principal strain theory
d) Maximum strain energy theory
e) Maximum distortion energy theory.
Answer
Sign in to view the complete answer paper.
Draw a cotter joint to connect two mild steel rods for a pull of 30 kN. The maximum permissible stresses are 55 MPa in tension; 40 MPa in shear and 70 MPa in crushing. Draw a neat sketch of the joint designed.
Answer
Sign in to view the complete answer paper.
A steam boiler is to be designed for a working pressure of 2.5 N/mm2 with its inside diameter 1.6 m. Give the design calculations for the longitudinal and circumferential joints for the following working stresses for steel plates and rivets: In tension = 75MPa; In shear = 60 MPa; In crushing = 125 MPa. Draw the joints to a suitable scale.
Answer
Sign in to view the complete answer paper.
It is stated that the speed at which a belt should be run to transmit maximum power is that at which the maximum allowable tension is three times the centrifugal tension in the belt at that speed. Prove the statement.
Answer
Sign in to view the complete answer paper.
State the advantages and disadvantages of the chain drive over belt and rope drive.
Answer
Sign in to view the complete answer paper.
Design a chain drive to actuate a compressor from 15 kW electric motor running at 1000 RPM the compressor speed being 350 RPM. The minimum centre distance is 500 mm. The compressor operates 16 hours per day. The chain tension may be adjusted by shifting the motor on slides.
Answer
Sign in to view the complete answer paper.
Design a pair of helical gears for transmitting 22 kW. The speed of the driver gear is 1800 rpm and that of driven gear is 600 rpm. The helix angle is 30° and profile is corresponding to 20° full depth system. The driver gear has 24 teeth. Both the gears are made of cast steel with allowable static stress as 50 MPa. Assume the face width parallel to axis as 4 times the circular pitch and overhang for each gear as 150 mm. The allowable shear stress for the shaft material may be taken as 50 MPa. The form factor may be taken as 0.154 – 0.912/TE, where TE represents the equivalent number of teeth. The velocity factor may be taken as 350/(350+v), where ‘v’ is pitch line velocity in m/min. the gears are required to be designed only against bending failure of the teeth under dynamic condition.
Answer
Sign in to view the complete answer paper.
Select a single row deep groove ball bearing for a radial load of 4000 N and an axial load of 5000 N, operating at a speed of 1600 RPM for an average life of 5 years at 10 hours per day. Assume uniform and steady load.
Answer
Sign in to view the complete answer paper.
Explain how the following factors influence the life of a bearing: i) Load ii) Speed iii) Temperature iv) Reliability
Answer
Sign in to view the complete answer paper.