JNTU
JNTU B.Tech II DESIGN OF MACHINE MEMBERS - I Previous Question Paper (February - 2024 - R16)
Note: i) Question paper consists of Part A, Part B. ii) Part A is compulsory, which carries 25 marks. In Part A, answer all questions. iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions. iv) Assume suitable data, if necessary.
PART - A
What is the role of ergonomics in machine design?
Answer
Ergonomics in machine design ensures that the equipment is compatible with the physical and cognitive capabilities of the human operator. Its primary role is to enhance safety, improve efficiency, and increase comfort by minimizing operator fatigue, reducing the risk of musculoskeletal disorders, and preventing human error through intuitive control layouts and interface design.
State the distortion energy theory of failure. Where do you use it?
Answer
The Distortion Energy Theory, also known as the von Mises-Hencky theory, states that failure occurs when the distortion strain energy per unit volume at a point in a stressed material exceeds the distortion strain energy per unit volume at the yield point in a simple tension test. Mathematically, for a three-dimensional stress state with principal stresses σ₁, σ₂, and σ₃, the condition for yielding is:
This theory is primarily used for ductile materials, such as mild steel, because it provides the most accurate predictions for yielding under complex loading conditions. It is widely preferred in engineering design for ductile components because it is less conservative than the maximum shear stress theory and aligns closely with experimental data.
What is modifying factor to account for stress concentration?
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Distinguish between fluctuating stress, repeated stress, and reversed stress.
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What is lock nut? What is the principle of lock nut?
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What are the different types of rivet heads? Give their applications.
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Why is cotter provided with a taper? Why is a taper provided only on one side?
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Define equivalent torsional moment and equivalent bending moment. State when these two terms are used in the design of shafts.
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What is the difference between coupling and clutch?
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Why do we consider Wahl’s factor for the design of helical compression springs?
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PART - B
What are impact stresses? When are they encountered?
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A steel shaft ABCD having a total length of 3.5 m consists of three lengths having different sections as follows: AB is hollow having outside and inside diameters of 100 mm and 62.5 mm respectively, and BC and CD are solid. BC has a diameter of 100 mm and CD has a diameter of 87.5 mm. If the angle of twist is the same for each section, determine the length of each section. Find the value of the applied torque and the total angle of twist, if the maximum shear stress in the hollow portion is 47.5 MPa and shear modulus C = 82.5 GPa.
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Compare the weights of equal lengths of hollow shaft and solid shaft to transmit a given torque for the same maximum shear stress. The material for both the shafts is the same, and inside diameter is 2/3 of outside diameter in case of hollow shaft.
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A cantilever beam of square section supports an electric motor weighing 1000 N at a distance of 400 mm from the fixed end. If the allowable stress of beam material is 100 N/mm2, determine the section of beam.
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Explain the effect of the following factors on the type of fatigue failure: (i) Type of material (ii) Stress distribution.
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A shaft made of steel having ultimate tensile strength of 700 MPa and yield point 420 MPa is subjected to a torque of 2000 N-m clockwise to 600 N-m anti-clockwise. Calculate the diameter of the shaft if the factor of safety is 2 and it is based on the yield point and the endurance strength in shear.
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Explain impact factor.
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A 50 mm diameter steel shaft with a 20 mm transverse hole is simultaneously subjected to a bending stress which varies from + 100 MPa to – 70 MPa. and a torsional stress which varies from + 80 MPa to -50 MPa. Find the factor of safety for infinite life assuming the following properties. Ultimate strength in tension 800 MPa, Yield strength 550 MPa. Surface correction factor = 0.85, size factor = 0.85 and Notch sensitivity factor = 0.9. Use maximum distortion energy theory.
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Prove that the plane, where maximum shear stress is induced, is inclined at 67.5° to the leg dimension in the case of transverse fillet weld of equal legs.
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A plate as shown in figure below is subjected to an eccentric force (P) of 15 kN with an eccentricity (e) of 450 mm from the CG of the bolts. The center distance between bolts 1 and 2 is 210 mm, and the center distance between bolts 1 and 3 is 150 mm. All the bolts are identical. The bolts are made from plain carbon steel 25C8 and the factor of safety is 2.5. Find the size of the bolts.
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Show by neat sketches the various modes of failure of riveted joint.
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A plate 100 mm wide and 12.5 mm thick is to be welded to another plate by means of parallel fillet welds. The plates are subjected to a load of 50 kN. Find the length of the weld so that the maximum stress does not exceed 56 MPa. Consider the joint first under static loading and then under fatigue loading.
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Distinguish between torsional rigidity and lateral rigidity of shaft.
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Two rods are connected by means of a knuckle joint. The axial force acting on the rods is 25 kN. The rods and the pin are made of plain carbon steel 45C8 (Syt = 380 N/mm2) and the factor of safety is 2.5. The yield strength in shear is 57.7% of the yield strength in tension. Calculate: (i) the diameter of the rods, and (ii) the diameter of the pin.
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Write the difference in procedure in the design of hollow shaft on the basis of torsional rigidity and on the basis of strength.
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A rectangular sunk key 14 mm wide, 10 mm thick and 75 mm long is required to transmit 1200 N-m torque from a 50 mm diameter solid shaft. Determine whether the length is sufficient or not if the permissible shear stress and crushing stress are limited to 56 MPa and 168 MPa respectively.
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Explain the two important features of flexible bush coupling, which are different from rigid flange coupling.
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A close coiled helical compression spring of 16 active coils has a spring stiffness of 10 N/mm. It is cut into two springs having 7 and 9 turns. Determine the spring stiffness of resulting springs.
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Explain the design procedure of springs under fluctuating load.
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Design a muff coupling to connect two shafts transmitting 40 kW at 120 rpm. The permissible shear and crushing stresses for the shaft and key material (mild steel) are 30 MPa and 80 MPa respectively. The material of muff is cast Iron with permissible shear stress of 15 MPa. Assume that the maximum torque transmitted is 25 percent greater than mean torque.
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