343 Example Questions Midterm 2

Name: Q1

MAE343 Fall 2007 Final

A fully stabilized, cubic polycrystalline ZrO2 sample has a fracture toughness of 7.5 MPa – m1/2 when tested on a four-point bend test. (a) If the sample fails at a stress of 450 MPa, what is the size of the largest surface flaw? Assume Y=pi1/2 (b) The same test is performed with a partially stabilized specimen. This sample has been transformation toughened and has a fracture toughness of 12.5MPa-m1/2. If this material has the same flaw size distribution as the fully stabilized what is the stress required to cause failure.

Q2 From the steel phase diagram below: (a) a 3 % C Austenite Steel is cooled slowly from 1000° C to a temperature of 800° C determine the weigh percent austenite in the steel. (b) What structural change occurs in iron at 723° C. (c) Define the following phases in Steel (i) austenite, (ii) α Ferrite(iii) cementite.

Q3

A Binary Peritectic Alloy of iridium and osmium of average composition 70 wt % Osmium is melted to 3000° C. What phases are present at (a) 2600° C, (b) 2665+∆ T° C and (c) 2665-∆ T° C. What are the compositions of each phase at these temperatures? What is the amount of each phase? Identify any three phase invariant reactions with composition and Temperature.

Q4

A Binary Eutectic Alloy of copper and silver of average composition 80% is melted to 1000° C. What phases are present at (a) 1000° C, (b) 800° C and (c) 600° C. What are the compositions of each phase at these temperatures? What is the amount of each phase?