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Metallurgical Principles and Practice of Engineering (PE) Study Guide: Question #22

It Is the Policy of The Minerals, Metals & Materials Society (TMS) to Encourage the Professional Registration of Metallurgical Engineers.

The stress intensity KI for a crack tip in a material containing a crack and subjected to tensile stress is given by:

sf(g)Ö(pa), where

s = tensile stress (psi, ksi or MPa)

f(g) = function accounting for crack geometry and structural configuration (dimensionless)

a = crack length (inches or meters)

The units of KI are usually expressed as ksiÖinch or MPaÖmeter.

The quantity KIc is called the "critical stress-intensity factor" for static loading and plane strain conditions of maximum constraint. It is a property of a material. Materials with high KIc are said to have high fracture toughness.

Which of the following is true?

(A)
Both KI and KIc are independent of temperature.
(B)
When KI exceeds KIc, a crack in the material will likely extend until the material is weakened sufficiently for an overload failure to occur.
(C)
The concepts of KI and KIc are valid only at temperatures below the ductile-to-brittle transition temperature.
(D)
The KIc of a material cannot be improved by heat treatment.


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