Model Question Paper

**AML 883: Properties and Selection of Engineering Materials**

**Instructions**

- Please answer all the questions
- Please answer the questions in your own words; out and out copying from your textbook will not get you any credits
- For numerical examples, please give all the steps; wherever needed, draw neat diagrams and graphs with proper labelling; explain all the symbols; give the answers in proper units
- This is an open book exam; use the book for data that might be needed (unless specified otherwise); write down the page number in brackets next to the data that you are taking from the book
- Each question carries 20 marks. The maximum marks are 100.

**Questions**

- Water has a density of 1000 kg/m
^{3}. [1] What is the hydrostatic pressure at a depth of 100 m? [2] Consider a component made using polypropylene (PP) foam of relative density 0.2. Given that the Young's modulus of PP is 1.5 GPa, and, assuming that the foamy material is elastically isotropic with a Poisson's ratio of (1/3), what is the minimum depth to which the component be immersed under water to undergo permanent deformation. Assume that we have, somehow, made sure that water does not enter the pores of the foamy material. [3] Comment on the usability of such a water-proof foam under water in the sea given the fact that the deepest point in ocean is only 11 km deep. - Derive the material index for a torsion bar with a solid circular section. The length L and the (torsional) stiffness S* are specified, and the torsion bar is to be as light as possible. Given the moment K = $\frac{\pi}{2} r^{4}$ m
^{4}. - Assume that a thin column of material is loaded in compression. [1] Which modulus of the material is relevant for stiffness-limited design of this column? [2] Which modulus is relevant for strength-limited design of this column? [3] If the column if loaded in tension, which modulus of the material is relevant? In each of the cases, justify your answer with a few lines of explanation.
- [1] Why are the point defects equilibrium defects? [2] Why are they called point defects even when they do occupy a certain volume? [3] What is Taylor factor? [4] Are elastic modulus and elastic section modulus related? [5] What is redundant work in a metal working operation?
- A material has a threshold cyclic stress intensity $\Delta K_{th}$ of 2.5 MPa m
^{1/2}. If it contains an internal crack of length 1mm will it be safe (meaning, no failure) if subjected to continuous cyclic range of tensile stress $\Delta \sigma$ of 50 MPa. Justify your answer.

page revision: 5, last edited: 05 Feb 2009 13:20