MECH3110 Mechanical Engineering Design

Question:

The figure below shows a sling connected to two cantilever 250 Parallel Face Channel (PFC) welded on its 250mm wide face to rigid supports. The 250 PFC material has a yield strength of 250MPa. Space constraints restrict the joint area to extend only 150 mm in from the vertical surface of the rigid support, as shown in the figure (note the figure is not to scale). For a factor of safety of 2.5 and welding done using good practice with an E70 electrode, determine the minimum size of the weld required for the following two cases:

a. Welded along the top and bottom edges of the channel only, and

b. Welded along the top, bottom and rear edges of the channel.

For both cases, check the tearing stress in the parent material using the same factor of safety.

The figure below shows a plate held to a solid foundation via 4 bolts. A load of 10 kN is applied horizontally onto the centreline of the cylindrical section – see the figure below for details. For a factor of safety of 3, determine the minimise size of SAE 4.6 bolt to hold the base to its foundations. The bolts are not pre-tensioned.

Determine the minimum nominal diameter for the rotating drive shaft illustrated below using;

(a) the maximum shear stress theory applying Soderberg’s fatigue criterion, and

(b) the distortion energy theory applying Goodman’s fatigue criterion.

The shaft is to be manufactured using quenched and drawn (over 200 Bhn) alloy steel with Sut = 850 MPa and Sy = 700 MPa. The torque is transmitted as shown below and has parallel belt pulls with the tension on the loose side of Pulley 4 being 20% of the tension on the tight side. Assume both pulleys are keyed to the shaft using profiled keyways. A shaft nominal reliability of 95% is desired with a safety factor of 2.