Question

SECTION A Q1. (a) The standards for testing the fracture toughness of materials define the shape and proportion of the specimens but not their size. Explain why this is and why it is necessary to use specimens of different sizes for these tests. [5 marks] (b) You are testing samples of steel with a yield stress of 1200 MPa. Initial results show that the fracture toughness is 120 MPavm. The specimens are 10 mm thick. Determine whether the specimens are thick enough or if further tests are needed. [5 marks] (c) The steel you have tested is to be used to make a pressure vessel as part of a chemical plant. The vessel will be 1 m in diameter with a wall thickness of 50 mm. If the maximum flaw size that can be detected is 20 mm, determine the pressure at which the vessel will fail either by yielding or by brittle fracture. Take into account the effect of the plastic zone at the crack tip. [10 marks) (d) In the event that the vessel fails, it is important that it leaks in a controlled way rather than exploding catastrophically. What wouid be the maximum safe working pressure to ensure that the vessel leaks before it bursts? [5 marks] 25 marks

Answer 1

In material science fracture tauyhmun is a property which describes the ability of a material to resist fracture, and is one of the most important property of any material for many design application. The linear elastic fracture laughers of material in electrified from stress intensity factor k at which a thin crack in material begin grow. it is denoted by k_Ic and has the unit as pe squreroot m or psi squreroot ln denoted by J_IC with the units as s/cm^2 or lb t - in/m^2 and is a measurement of energy required to grow thin crash.