PSG College of Technology, Coimbatore 641 004Department of Production Engineering

08P601 Design of Machine Elements, Tutorial – II

1. A metal has strength of 689 MPa at its elastic limit and the strain at that point is 0.006. What is its modulus of elasticity? What is the strain energy at the elastic limit? Assume the test specimen is 12.827 mm diameter and has a 50.8 mm gage length. Can you define the type of metal based on the given data?

2. Steel has yield strength of 414 MPa, an ultimate tensile strength of 689 MPa, and an elongation at fracture of 15%. What is its approximate modulus of toughness? What is its approximate modulus of resilience?

3. Which of the aluminum alloys shown in Figure 1 would you choose to obtain (a) Maximum strength (b) Maximum modulus of resilience (c) Maximum modulus of toughness (d) Maximum stiffness

Figure 1

4. For each of the stress states listed below, find principal normal and shear stresses. Draw a complete Mohr’s circle diagram and label all points of interest.

(a) σx = −80 MPa, σy = −30 MPa, τxy = 20 MPa cw

(b) σx = 30 MPa, σy = −60 MPa, τxy = 30 MPa cw

(c) σx = 40 MPa, σz = −30 MPa, τxy = 20 MPa ccw

(d) σx = 50 MPa, σz = −20 MPa, τxy = 30 MPa cw

5. The cantilevered bar in the Figure 2 is made from a ductile material and is statically loaded with Fy = 890 N and Fx = Fz = 0. Analyze the stress situation in rod AB by obtaining the following information.

(a) Determine the precise location of the critical stress element.(b) Sketch the critical stress element and determine magnitudes and directions for all stresses acting on it. (Transverse shear may only be neglected if you can justify this decision.)

(c) For the critical stress element, determine the principal stresses and the maximum shear stress.

Figure 2