CHAPTER 8
(Quiz 4 will be based on this assignment, course notes from sections 7 and 8 (excluding creep related questions) and associated chapters of
the textbook)
8.1
What is the magnitude of the maximum stress that exists at the tip of an internal crack having a radius of curvature of 2.5
10
4
mm (10
5
in.) and a crack length of 2.5
10
2
mm (10
3
in.) when a tensile stress of 170 MPa (25,000 psi) is applied?
8.2
Estimate the theoretical fracture strength of a brittle material if it is known that fracture occurs by the propagation of an
elliptically shaped surface crack of length 0.25 mm (0.01 in.) and having a tip radius of curvature of 1.2
10
3
mm when a
stress of 1200 MPa is applied.
8.5
A specimen of a 4340 steel alloy having a plane strain fracture toughness of
45 MPa m
(
41 ksi in
.
) is exposed to a
stress of 1000 MPa (145,000 psi).
Will this specimen experience fracture if it is known that the largest surface crack is 0.75
mm (0.03 in.) long?
Why or why not?
Assume that the parameter Y has a value of 1.0.
8.6
Some aircraft component is fabricated from an aluminum alloy that has a plane strain fracture toughness of
35 MPa m
(31.9 ksi in.
).
It has been determined that fracture results at a stress of 250 MPa (36,250 psi) when the maximum (or
critical) internal crack length is 2.0 mm (0.08 in.).
For this same component and alloy, will fracture occur at a stress level of
325 MPa (47,125 psi) when the maximum internal crack length is 1.0 mm (0.04 in.)?
Why or why not?
8.7
Suppose that a wing component on an aircraft is fabricated from an aluminum alloy that has a plane strain fracture
toughness of
40 MPa m
(36.4 ksi in.
).
It has been determined that fracture results at a stress of 365 MPa (53,000 psi)
when the maximum internal crack length is 2.5 mm (0.10 in.).
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 Spring '10
 John
 Tensile strength, Fracture mechanics, Fracture toughness, Charpy impact test, strain fracture toughness, plane strain fracture

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