JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II Year DESIGN OF MACHINE MEMBERS - I Previous Question Paper (August/September - 2022 - R16)
Answer any five questions
All questions carry equal marks
Main
What are the steps involved in design of a machine element?
Answer
The design of a machine element is a systematic process involving the following steps:
- Define the problem by identifying the function, the forces acting on the member, and the motions involved.
- Select the material based on properties like strength, stiffness, wear resistance, and cost.
- Determine the modes of failure (e.g., yielding, fatigue, fracture, or excessive deflection) and calculate the forces and stresses acting on the member.
- Determine the geometric dimensions of the member by applying appropriate failure theories and safety factors.
- Modify the dimensions to accommodate standard sizes, manufacturing limitations, and assembly requirements.
- Prepare detailed design drawings and specifications, including tolerances and surface finish requirements.
What is meant by working stress and how it is calculated from the ultimate stress or yield stress of a material?
Answer
Working stress, also known as allowable or design stress, is the maximum safe stress that a material is permitted to carry under normal operating conditions to ensure the safety of the component.
It is calculated by dividing the material's failure strength by a factor of safety (FOS):
Where σ(u) is the ultimate tensile stress, σ(y) is the yield stress, and FOS is the factor of safety chosen based on the uncertainty of loads, material properties, and the consequences of failure.
A hydraulic press exerts a total load of 3.5 MN. This load is carried by two steel rods, supporting the upper head of the press. If the safe stress is 85 MPa and E = 210 kN/mm2, find:
a) Diameter of the rods, and
b) Extension in each rod in a length of 2.5 m.
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What is meant by endurance strength of a material? How do the size and surface condition of a component and type of load affect such strength?
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What is the difference between failure due to static load and fatigue failure?
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A rotating shaft, subjected to a non rotating force of 5 kN and simply supported between two bearings A and E. The shaft is machined from plain carbon steel 30C8 (Sut = 500 N/mm2) and the expected reliability is 90%. The equivalent notch radius at the fillet section can be taken as 3 mm. What is the life of the shaft?
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What is the cause of residual stresses in welded joint? How are they relieved?
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Two plates of 15 mm thick are joined by double riveted lap joint. The pitch of each row of rives is 150 mm. The permissible stresses are 160MPa in tension, 100MPa in shear and 200MPa in crushing. How the joint fails and find efficiency of joint.
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Explain the elastic analysis of bolted joints.
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The cylinder head of a steam engine is subjected to a pressure of 1 N/mm2. It is held in position by means of 12 bolts. The effective diameter of the cylinder is 300 mm. A soft copper gasket is used to make the joint leak proof. Determine the size of the bolts so that the stress in the bolts does not exceed 100 MPa.
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A hollow transmission shaft, having inside diameter 0.6 times the outside diameter, is made of plain carbon steel 40C8 (Syt = 380 N/mm2) and the factor of safety is 3. A belt pulley, 1000 mm in diameter, is mounted on the shaft, which overhangs the left hand bearing by 250 mm. The belts are vertical and transmit power to the machine shaft below the pulley. The tension on the tight and slack sides of the belt are 3 kN and 1 kN respectively, while the weight of the pulley is 500 N. The angle of wrap of the belt on the pulley is 1800. Calculate the outside and inside diameters of the shaft.
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Design and draw C.I muff coupling when shaft transmits 200 kw at 400 rpm. If the allowable shear and crushing stresses for the shaft and key material is 40 N/mm2 and 60kN/mm2. The permissible shear stress in the muff is 20 Kn/mm2 maximum torque transmitted is 20% higher than mean torque.
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Explain what you understand by A.M. Wahl’s factor and state its importance in the design of helical springs.
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