JNTU
JNTU B.Tech III PRINCIPLES OF MACHINE DESIGN Previous Question Paper (January/February - 2023 - R18)
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
List the properties of the materials to be considered while selecting a material for a machine element.
Answer
The key material properties to consider are physical properties (density, melting point), mechanical properties (strength, ductility, hardness, toughness, stiffness), and manufacturing/service properties (weldability, machinability, corrosion resistance, and fatigue strength).
Explain why the maximum shear stress theory is more suitable for ductile material in comparison to the maximum principal stress theory.
Answer
Ductile materials fail due to yielding caused by slip along planes of maximum shear stress. The maximum principal stress theory (Rankine's theory) is based on brittle failure (fracture) and ignores the yielding phenomenon. The maximum shear stress theory (Guest's theory) accurately predicts the onset of plastic deformation in ductile materials by focusing on the shear component, which aligns with experimental observations of slip bands in ductile metals.
The tearing, shearing and crushing efficiency of a riveted joint are 75%, 65% and 60% respectively. Find the joint efficiency.
Answer
Sign in to view the complete answer paper.
What is the effect of keyways on the strength of the shaft?
Answer
Sign in to view the complete answer paper.
What is the effect of centrifugal tension on power transmission of belts?
Answer
Sign in to view the complete answer paper.
Describe construction of a wire rope with a sketch.
Answer
Sign in to view the complete answer paper.
Differentiate between circular pitch, diametrical pitch, and module of a gear.
Answer
Sign in to view the complete answer paper.
Explain Lewis form factor. What are the parameters, which affect its value?
Answer
Sign in to view the complete answer paper.
Classify the bearings according to lubricant pressure.
Answer
Sign in to view the complete answer paper.
Describe the construction of a ball bearing with the help of a neat sketch.
Answer
Sign in to view the complete answer paper.
Part B
A 50 mm diameter non-rotating shaft is subjected to a moment of 100 N-m in addition to the torque. Find the permissible torque that can be applied in addition to moment if the factor of safety is to be 2 using von-Mises theory and maximum shear stress theory. Assume yield strength of the material as 400 MPa.
Answer
Sign in to view the complete answer paper.
What do you mean by stress concentration? How is it accounted for in the design of machine elements?
Answer
Sign in to view the complete answer paper.
A solid circular pin is subjected to completely reversed bending moment of 5 N-m. The ultimate strength of the pin material is 350 MPa. Assuming the notch sensitivity and stress concentration factor as 0.85 and 1.50 respectively, determine the diameter of the pin at 90% reliability. Consider the factor of safety as 2.0.
Answer
Sign in to view the complete answer paper.
A 200 mm long hollow circular shaft of external diameter 80 mm and internal diameter 50 mm is welded to a plate along its circumference. The shaft carries a concentrated load of 15 kN at free end perpendicular to the axis of the shaft. If the permissible weld strength is 140 MPa, determine the weld size. Also discuss the nature of stresses developed on the weld.
Answer
Sign in to view the complete answer paper.
A shaft is supported by two bearings 400 mm apart and carries a bevel gear of 200 mm pitch diameter at one end that is overhanging beyond the nearer bearing by 150 mm. The gear produces a radial load of 10 kN and a thrust load of 3 kN when the speed is 600 rpm. Determine the shaft diameter if the shaft is made of steel with allowable shear stress of 40 MPa. Also determine the angle of twist and deflection at the bevel gear location if the modulus of rigidity is 80 GPa and the modulus of elasticity is 210 GPa.
Answer
Sign in to view the complete answer paper.
A pump is driven by an electric motor using an open type flat belt. Determine the width and length of belt for the following data: Power transmission = 15kW; Rotational speed of the motor=1,440 rpm; Motor pulley diameter = 250 mm; Pump pulley diameter = 500 mm; Center distance between the pulleys = 1.2 m; Thickness of the belt = 5 mm; Density of belt material = 1,000 kg/m3; Allowable stress for the belt material = 2 MPa; Coefficient of friction for motor pulley = 0.26; Coefficient of friction for pump pulley = 0.22.
Answer
Sign in to view the complete answer paper.
Sketch the cross-section of the V-belt and label its parts. How these belts are designated?
Answer
Sign in to view the complete answer paper.
Explain the various steps involved in the selection of a V-belt for a given power to be transmitted and the speed of the faster pulley.
Answer
Sign in to view the complete answer paper.
A pinion of width 12 m with 24 full depth teeth of 20 degree pressure angle transmits 30 kW at 1200 rpm. The form factor for 20 degree full depth involute is 0.12. Using Lewis equation, find the module and face width of the pinion. Assume safe bending stress 200 MPa.
Answer
Sign in to view the complete answer paper.
Discuss Buckingham’s equation for dynamic loads in spur gear.
Answer
Sign in to view the complete answer paper.
A helical gear transmits 20 kW with pinion of 20 teeth and module 5 running at 1200 rpm. Pressure angle is 20 degree and helix angle 25 degree. Determine tangential force, radial force and axial thrust force. Assume suitable positions of gear and direction of rotation accordingly draw a force component diagram.
Answer
Sign in to view the complete answer paper.
Explain the term equivalent number of teeth of a helical gear. How is it related with the actual number of teeth?
Answer
Sign in to view the complete answer paper.
A bearing of bore 35 mm and length 30 mm supports a vertical load of 1500 N at 1800 rpm. Radius to clearance ratio is 700. Oil of viscosity 30 mPa-s is used as lubricant. Calculate the friction coefficient. Use McKee equation. Also calculate heat generated.
Answer
Sign in to view the complete answer paper.
Write a note on the selection of parameters for a hydrodynamic bearing design.
Answer
Sign in to view the complete answer paper.
A ball bearing has a life of 2 million revolutions with 90 per cent reliability. Calculate its life with 95 per cent reliability. How much is reduction in life with this increased reliability.
Answer
Sign in to view the complete answer paper.
Write the procedure to design a rolling bearing.
Answer
Sign in to view the complete answer paper.