JNTU
JNTU B.Tech III DESIGN OF MACHINE MEMBERS - I Previous Question Paper (July/August - 2023 - 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.
Part A
Define ‘mechanical property’ of an engineering material. State any three mechanical properties.
Answer
A mechanical property defines the behavior of a material when subjected to external loads or forces. Three common mechanical properties are strength, ductility, and hardness.
Why is it necessary to use factor of safety?
Answer
The factor of safety is necessary to account for uncertainties in material properties, variations in loading conditions, approximations in stress analysis, and the potential for unforeseen overloads or manufacturing defects, ensuring the component does not fail during its service life.
What are the methods of reducing stress concentration?
Answer
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What is the difference between the Gerber curve and Soderberg and Goodman lines?
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Discuss any four weld symbols.
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How will you designate ISO metric coarse threads?
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What type of stresses induced in keys?
Answer
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Distinguish between cotter joint and knuckle joint.
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What are flexible couplings and what are their applications?
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Discuss the various types of shafts and the standard sizes of transmissions shafts?
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Part B
Discuss the Indian standard system of limits and fits. What are the BIS codes of steel?
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What are the manufacturing consideration in design?
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State maximum shear stress theory of failure. Where do you use maximum shear stress theory of failure?
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What are preferred numbers? How many basic series are used? How will you denote them?
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A cantilever beam made of cold drawn steel 4OC8 (Sut = 600 N/mm2 and Syt = 380 N/mm2) is shown in Figure. The force P acting at the free end varies from –50 N to +150 N. The expected reliability is 90% and the factor of safety is 2. The notch sensitivity factor at the fillet is 0.9. Determine the diameter d of the beam at the fillet cross-section using Gerber curve as failure criterion.
Answer
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A rotating bar made of steel 45C8 (Sut = 630 N/mm2) is subjected to a completely reversed bending stress. The corrected endurance limit of the bar is 315 N/mm2. Calculate the fatigue strength of the bar for a life of 90,000 cycles.
Answer
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A double-riveted double-strap butt joint is used to connect two plates; each of 12 mm thickness, by means of 16 mm diameter rivets having a pitch of 48 mm. The rivets and plates are made of steel. The permissible stresses in tension, shear and compression are 80, 60 and 120 N/mm2 respectively. Determine the efficiency of the joint.
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A bolted joint is used to connect two components. The combined stiffness of the two components is twice the stiffness of the bolt. The initial tightening of the nut results in a preload of 10 kN in the bolt. The external force of 7.5 kN creates further tension in the bolt. The bolt is made of plain carbon steel 30C8 (Syt = 400 N/mm2) and the factor of safety is 3. There are coarse threads on the bolt. Calculate the tensile stress area of the bolt and specify a suitable size for the bolt.
Answer
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Describe the design procedure of a gib and cotter joint.
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Why gibs are used in a cotter joint? Explain with the help of a neat sketch the use of single and double gib.
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It is required to design a knuckle joint to connect two circular rods subjected to an axial tensile force of 50 kN. The rods are co-axial and a small amount of angular movement between their axes is permissible. Design the joint and specify the dimensions of its components. Select suitable materials for the parts.
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When the shaft is subjected to fluctuating loads, what will be the equivalent twisting moment and equivalent bending moment ?
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How does the working of a clamp coupling differ from that of a muff coupling?
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A rotating shaft, 40 mm in diameter, is made of steel FeE 580 (Syt = 580 N/mm2). It is subjected to a steady torsional moment of 250 N-m and bending moment of 1250 N-m. Calculate the factor of safety based on maximum principal stress theory.
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