JNTU
JNTU B.Tech II DESIGN OF MACHINE MEMBERS – I Previous Question Paper (April - 2018 - R16)
Note: This question paper contains two parts A and B. Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks and may have a, b, c as sub questions. Illustrate your answers with NEAT sketches wherever necessary
Part A
Define the following: Impact stresses, Fracture toughness.
Answer
Impact stresses are stresses produced in a member when a load is applied suddenly or with significant velocity, resulting in higher stress levels than a static load of the same magnitude. Fracture toughness is a material property that describes the ability of a material containing a crack to resist further crack propagation under an applied stress.
Explain the design considerations for strength and rigidity.
Answer
Design for strength ensures that the component can withstand the applied loads without failure, such as yielding or rupture, by keeping induced stresses below the allowable stress of the material. Design for rigidity (or stiffness) ensures that the component maintains its shape and dimensions under load, limiting elastic deformations (deflection or twist) to levels that do not interfere with the functional performance of the assembly.
Explain the following: Fatigue failure, Endurance limit.
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Explain the difference between Goodman’s line, Soderberg’s line, Modified Goodman’s line.
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Define the following in riveted joints: Row pitch, and Diametral pitch. Give their standard values in terms of the rivet diameter.
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What are bolts of uniform strength? Explain with a sketch.
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Give the uses of internal and external circlips.
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Write the applications of different types of keys.
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Distinguish between rigid couplings and flexible couplings.
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Explain briefly the important types of mechanical springs.
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Part B
Explain about ‘Preferred numbers’. What are the different series of Preferred numbers, and how are they obtained? A circular steel bar is subjected to a load of 9800 N. The load is parallel to the axis of the bar, but is displaced from it by 25 mm. The permissible stress for the material of the bar is 80 N / mm2. Find the suitable diameter of the bar.
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What is k1c fracture toughness? Why is fracture toughness important? What is stress-intensity factor (K) which is used to determine the fracture toughness of most materials? A round bar of length L, tapers uniformly from radius r1 at one end to radius r2 at the other. Show that the extension produced by a tensile axial load P is (PL)/(2*pi*E*r1*r2), if r2 = 2 r1.
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What is Notch sensitivity? Why it is required? What are its extreme values for fully sensitive and no sensitive material to notch effects? A rotating bar is made up of steel 45C8 having ultimate tensile stress 630 N/mm2 is subjected to completely reversed bending stresses. Calculate the fatigue strength of the bar for a life of 90000 cycles, if the corrected endurance limit is 315 N/mm2.
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A 50 mm diameter shaft is made from Carbon steel having ultimate tensile strength of 600 MPa. It is subjected to a torque which fluctuates between 2000 N-m to (-900) N-m. Using Solderberg method, calculate the factor of safety.
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A double riveted lap joint is made between 15 mm thick plates. The rivet diameter and pitch are 25 mm and 75 mm respectively. If the ultimate stresses are 400 MPa in tension, 320 MPa in shear and 640 MPa in crushing, find the minimum force per pitch which will rupture the joint. If the above joint is subjected to a load such that the factor of safety is 4, find out the actual stresses developed in the plates and the rivets.
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A bracket is attached to the ceiling with the help of two steel bolts, the bracket carries a load of 25 kN and the allowable stress for bolt material in tension is 90 MPa. The distance of first bolt from the leftmost edge is 100 mm, the distance between two bolts is 120 mm and the distance between leftmost edge and the line of application of load is 150 mm (Eccentricity). Find the size of the bolt to take this load. Take the load direction is parallel to the bolt axis.
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Two bars are connected by a knuckle joint, and the bars are subjected to a tensile load of F. List all the possible modes of failure and the governing relationship to determine the dimension of the elements.
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The shaft of an axial flow rotary compressor is subjected to a maximum torque of 2 kNm and a maximum bending moment of 4 kNm. The combined shear and fatigue factors in torsion and bending may be taken as 1.5 and 2 respectively. Determine the diameter of the shaft, if the shear stress in the shaft material shall not exceed 5 MN / m2. Discuss the effect of keyways in shafts.
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Design a clamp coupling to transmit 30 kW at 100 r.p.m. The allowable shear stress for the shaft and key is 40 MPa and the number of bolts connecting the two halves are six. The permissible tensile stress for the bolts is 70 MPa. The coefficient of friction between the muff and the shaft surface may be taken as 0.3. Sketch the coupling.
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One helical spring is nested inside another. Both the springs have the same free length, and carry a total load of 2500 N. Determine the: a) Maximum load carried by each spring, b) Total deflection of each spring, c) Maximum stress in each spring. (Given: Outer spring: coils=6, wire dia=12.5mm, mean coil dia=100mm; Inner spring: coils=10, wire dia=9mm, mean coil dia=70mm)
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