LEARNING OUTCOMES

Knowledge and Understanding
1. Understand the modes of failure of materials.

Cognitive and Intellectual Skills
2. Can make selections of approprite materials for given service conditions.
3. Can select materials according to the suitability of their material properties.

Practical and Professional Skills

Key Transferable Skills
4. Apply numerical skills to enable appropriate materials selection.

1. The bracket shown in FIGURE 1 is to be used to mount an outboard motor onto the transom of a boat.
(a) Suggest two appropriate materials which will require different methods to manufacture the bracket.
(b) Discuss the implications of each of the materials and manufacturing processes you have stated in (a) on the cost and service life of the
bracket.
(c) State likely causes of failure for the materials you have chosen? Give reasons for your answer.
(d) Suggest how the manufacturer might calculate or predict the service life of the component.
(e) Suggest any treatments which may prolong the life of the bracket.

FIG. 1

2. A tensile load F is to be applied to the tie bar shown in FIGURE 2. The tie bar is 50 mm diameter. The surface of the bar has defects resulting from the manufacturing process, these have a maximum depth of 1.5 mm and have a shape factor of 1.4. If the fracture toughness of the material used is 120 MPa m-0.5, determine the maximum load which can be applied if brittle fracture is not to occur. Use a factor of safety of 3.

FIG. 2

3. Consider that we need to predict the fatigue life of the bracket shown in FIGURE 1. If we are given that the following relationship applies for the bracket:

da/dN = 4 x 10^-12(ΔK)³

where ΔK is in MPa m^1/2

and that the stress varies cyclically between 30 and 150 MPa, determine the number of cycles for a defect to grow from 1.5 mm to 4 mm.