Question 1 (continued) (Answer all parts) (40 marks) (Compulsory) Question 1 (Answer all parts) (40 marks) (Compulsory) (a) Explain the difference between 'designing for strength' and 'designing for fatigue life'. (5 marks) (g) (b) Using the attachments to this paper, determine the endurance limit for a 22 mm diameter AISI 1050 CD steel bar that is loaded by a reversed bending force. (5 marks) A circular specimen of MgO with 5% porosity is loaded in a three-point bending test. The maximum bending moment is 48 Nm and the separation between the support points is 40 mm. Using the attachments to this paper, calculate the minimum possible radius of the specimen so that fracture will not occur. (5 marks) (h) The stress relaxation test is used to investigate a particular behaviour of polymeric materials. (c) Answer each of the following: (i) For free vibration systems with viscous damping, why is the under-damped case so important in the study of mechanical vibrations. (i) (2 marks) (ii) Draw sketches of graphs to describe the motion of each of the following: under-damped; critically damped; over-damped. (ii) (3 marks) Clearly identify the type of behaviour that is investigated by this test and its dependencies. (2 marks) Describe the manner of performing stress relaxation tests and state the experimental parameter of interest. (3 marks) (d) Consider two springs that can be used to increase the overall stiffness of a system. How should you connect them to maximise the system stiffness? Explain your answer. (5 marks) For a particular mass-spring system, m = 55 kg and k = 750 N/m. Given that % %=15 determine: (f) (i) The frequency of damped vibration. (ii) The logarithmic decrement. (3 marks) (2 marks) Contrast compression, injection, and transfer molding techniques that are used to form polymer materials. (5 marks)