JNTU
JNTU B.Tech III DESIGN OF MACHINE MEMBERS - I Previous Question Paper (March - 2024 - R13)
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
What is a fit? Write its significance.
Answer
A fit is the relationship between two mating parts (hole and shaft) based on the difference in their sizes before assembly. Its significance lies in determining the nature of the assembly, such as whether the parts can move relative to each other (clearance fit), require force to assemble (interference fit), or have a small range of overlap (transition fit), which is critical for functional performance and interchangeability.
What is notch sensitivity?
Answer
Notch sensitivity is a measure of how susceptible a material is to the weakening effect of stress concentrations, such as notches, holes, or fillets. It is defined as the ratio of the actual fatigue strength reduction to the theoretical stress concentration factor, indicating how much a material's fatigue life is reduced by geometric irregularities.
What do you understand by the term riveted joint?
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What are the assumptions made in the design of welded joint?
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What are different types of Cotter joints?
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How are keys classified?
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What are the requirements of good shaft coupling?
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What type of stresses is induced in shafts?
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What is the function of a spring?
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Discuss the materials and practical applications for the various types of springs.
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PART - B
Explain the steps involved in general machine design process.
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Briefly explain the Fatigue stress concentration factor.
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What do you understand by preferred numbers? Explain fully.
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Explain how the factor of safety is determined under steady and varying loading by different methods.
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Find the efficiency of the following riveted joints: Single riveted lap joint of 6 mm plates with 20 mm diameter rivets having a pitch of 50 mm. Assume Permissible tensile stress in plate = 120 MPa, Permissible shearing stress in rivets = 90 MPa, Permissible crushing stress in rivets = 180 MPa.
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A double riveted double cover butt joint in plates 20 mm thick is made with 25 mm diameter rivets at 100 mm pitch. The permissible stresses are: σt = 120 MPa; τ = 100 MPa; σc = 150 MPa Find the efficiency of joint, taking the strength of the rivet in double shear as twice as that of single shear.
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A steel plate is subjected to a force of 3 kN, and fixed to a vertical channel by means of four identical bolts, as shown in figure. The bolts are made of plain carbon steel 45C8 (Syt = 380 N / mm2), and the factor of safety is 2. Find the diameter of the shank. (All dimensions in the figure are in mm).
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Draw a neat labeled sketch of Knuckle joint. List its various elements and state their Functions.
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Design the rectangular key for a shaft of 50 mm diameter. The shearing and crushing stresses for the key material are 42 MPa and 70 MPa.
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A 45 mm diameter shaft is made of steel with yield strength of 400 MPa. A parallel key of size 14 mm wide and 9 mm thick made of steel with a yield strength of 340 MPa is to be used. Find the required length of key, if the shaft is loaded to transmit the maximum permissible torque. Use maximum shear stress theory and assume a factor of safety of 2.
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Describe any two types of shaft couplings, with sketches.
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A solid shaft is to transmit 1000 kW at 120 rpm. Find the shaft diameter if the permissible shear stress is 80 N/mm2. If the shaft is made hollow, find the inside and outside diameters when the ratio of inside to outside diameters is 0.5.
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Design and draw a protective type of cast iron flange coupling for a steel shaft transmitting 15 kW at 200 r.p.m. and having an allowable shear stress of 40 MPa. The working stress in the bolts should not exceed 30 MPa. Assume that the same material is used for shaft and key and that the crushing stress is twice the value of its shear stress. The maximum torque is 25% greater than the full load torque. The shear stress for cast iron is 14 MPa.
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Find the maximum shear stress and deflection induced in a helical spring of the following specifications, if it has to absorb 1000 N-m of energy. Mean diameter of spring = 100 mm; Diameter of steel wire, used for making the spring = 20 mm; Number of coils = 30; Modulus of rigidity of steel = 85 kN/mm2.
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A closely coiled helical spring is made of 10 mm diameter steel wire, the coil consisting of 10 complete turns with a mean diameter of 120 mm. The spring carries an axial pull of 200 N. Determine the shear stress induced in the spring neglecting the effect of stress concentration. Determine also the deflection in the spring, its stiffness and strain energy stored by it if the modulus of rigidity of the material is 80 kN/mm2.
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Design a helical spring for a spring-loaded safety valve (Ramsbottom safety valve) for the following conditions: Diameter of valve seat = 65 mm; Operating pressure = 0.7 N/mm2; Maximum pressure when the valve blows off freely = 0.75 N/mm2; Maximum lift of the valve when the pressure rises from 0.7 to 0.75 N/mm2 = 3.5 mm; Maximum allowable stress = 550 MPa; Modulus of rigidity = 84 kN/mm2; Spring index = 6. Draw a neat sketch of the free spring showing the main dimensions.
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