Page 320 - Materials Science and Engineering An Introduction

292 • Chapter 8 / Failure

surface crack is 0.5 mm (0.02 in.) long? Why or why Fracture Toughness Testing
not? Assume that the parameter Y has a value of 1.0. 8.13 The following tabulated data were gathered from
8.6 An aircraft component is fabricated from an alumi- a series of Charpy impact tests on a tempered
num alloy that has a plane-strain fracture toughness 4340 steel alloy.
of 40 MPa1m (36.4 ksi1in.). It has been deter-
mined that fracture results at a stress of 300 MPa Temperature ( C) Impact Energy (J)
(43,500 psi) when the maximum (or critical) internal 0 105
crack length is 4.0 mm (0.16 in.). For this same com- 25 104
ponent and alloy, will fracture occur at a stress level
of 260 MPa (38,000 psi) when the maximum internal 50 103
crack length is 6.0 mm (0.24 in.)? Why or why not? 75 97
8.7 Suppose that a wing component on an aircraft is fabri- 100 63
cated from an aluminum alloy that has a plane-strain 113 40
fracture toughness of 26.0 MPa1m (23.7 ksi1in.). 125 34
It has been determined that fracture results at a
stress of 112 MPa (16,240 psi) when the maximum 150 28
internal crack length is 8.6 mm (0.34 in.). For this 175 25
same component and alloy, compute the stress level 200 24
at which fracture will occur for a critical internal
crack length of 6.0 mm (0.24 in.). (a) Plot the data as impact energy versus
8.8 A structural component is fabricated from an al- temperature.
loy that has a plane-strain fracture toughness of (b) Determine a ductile-to-brittle transition
62 MPa1m. It has been determined that this com- temperature as the temperature corresponding
ponent fails at a stress of 250 MPa when the maxi- to the average of the maximum and minimum
mum length of a surface crack is 1.6 mm. What is the impact energies.
maximum allowable surface crack length (in mm)
without fracture for this same component exposed to (c) Determine a ductile-to-brittle transition
a stress of 250 MPa and made from another alloy with temperature as the temperature at which the
impact energy is 50 J.
a plane-strain fracture toughness of 51 MPa1m?
8.14 The following tabulated data were gathered from
8.9 A large plate is fabricated from a steel alloy a series of Charpy impact tests on a commercial
that has a plane strain fracture toughness of low-carbon steel alloy.
82.4 MPa1m (75.0 ksi1in.). If the plate is ex-
posed to a tensile stress of 345 MPa (50,000
psi) during service use, determine the minimum Temperature ( C) Impact Energy (J)
length of a surface crack that will lead to fracture. 50 76
Assume a value of 1.0 for Y. 40 76
8.10 Calculate the maximum internal crack length al- 30 71
lowable for a Ti-6Al-4V titanium alloy (Table 8.1) 20 58
component that is loaded to a stress one-half its
yield strength. Assume that the value of Y is 1.50. 10 38
8.11 A structural component in the form of a 0 23
wide plate is to be fabricated from a steel al- 10 14
loy that has a plane-strain fracture toughness of 20 9
98.9 MPa1m (90 ksi1in.) and a yield strength of 30 5
860 MPa (125,000 psi). The flaw size resolution limit
of the flaw detection apparatus is 3.0 mm (0.12 in.). 40 1.5
If the design stress is one-half the yield strength and
the value of Y is 1.0, determine whether a critical (a) Plot the data as impact energy versus tem-
flaw for this plate is subject to detection. perature.
8.12 After consultation of other references, write a (b) Determine a ductile-to-brittle transition
brief report on one or two nondestructive test temperature as the temperature corresponding to
techniques that are used to detect and measure the average of the maximum and minimum impact
internal and/or surface flaws in metal alloys. energies.