Model Question Paper

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

##### Instructions
2. 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 = $\frac{\pi}{2} r^{4}$ m4.
5. A material has a threshold cyclic stress intensity $\Delta K_{th}$ of 2.5 MPa m1/2. 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.