Applicable for Civil Engineering 4th Semester
CE1259 STRENGTH OF MATERIALSUNIT III
PART-A (2 Marks)
1. Define torsional rigidity of the solid circular shaft.
2. Distinguish between closed coil helical spring and open coil helical spring
3. What is meant by composite shaft?
4. What is called Twisting moment?
5. What is Polar Modulus ?
6. Define: Torsional rigidity of a shaft.
7. What do mean by strength of a shaft?
8. Write down the equation for Wahl factor.
9. Define: Torsional stiffness.
10. What are springs? Name the two important types.
PART- B (16 Marks)
1. Determine the diameter of a solid shaft which will transmit 300 KN at 250 rpm. The
maximum shear stress should not exceed 30 N/mm2 and twist should not be more than 10 in a shaft length 2m. Take modulus of rigidity = 1x 105N/mm2. (16)
2. The stiffness of the closed coil helical spring at mean diameter 20 cm is made of 3 cm diameter rod and has 16 turns. A weight of 3 KN is dropped on this spring. Find the height by which the weight should be dropped before striking the spring so that the spring may be compressed by 18 cm. Take C= 8x104 N/mm2. (16)
3. It is required to design a closed coiled helical spring which shall deflect 1mm under an axial load of 100 N at a shear stress of 90 Mpa. The spring is to be made of round wire having shear modulus of 0.8 x 105 Mpa. The mean diameter of the coil is 10 times that of the coil wire. Find the diameter and length of the wire. (16)
4. A steel shaft ABCD having a total length of 2400 mm is contributed by three different sections as follows. The portion AB is hollow having outside and inside diameters 80 mm and 50 mm respectively, BC is solid and 80 mm diameter. CD is also solid and 70 mm diameter. If the angle of twist is same for each section, determine the length of each portion and the total angle of twist. Maximum permissible shear stress is 50 Mpa and shear modulus 0.82 x 105 MPa (16)
5. The stiffness of close coiled helical spring is 1.5 N/mm of compression under a maximum load of 60 N. The maximum shear stress in the wire of the spring is 125 N/mm2. The solid length of the spring (when the coils are touching) is 50 mm. Find the diameter of coil, diameter of wire and number of coils. C = 4.5 (16)