ASM Metals HandBook Vol. 8 - Mechanical Testing and Evaluation
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Fig. 12 Schematics of test apparatuses using piezo-electric ceramics to generate fatigue loading of
ceramic beam specimens. Source: Ref 75, 76
Cyclic fatigue test results indicate substantial changes in the mechanism controlling crack growth (i.e.,
cyclically induced versus environmentally induced) for different materials. Fatigue behavior for a given
ceramic (e.g., silicon nitride) depends on factors such as the grain boundary phase, grain size, and the fracture
mode (transgranular versus intergranular). Thus, fatigue testing needs to consider both environmentally induced
and cyclically induced crack growth.
References cited in this section
1. C. Gurney and S. Pearson, Fatigue of Mineral Glass under Static and Cyclic Loading, Proc. R. Soc. A.,
Vol 192, 1948, p 537–543
15. DD ENV 843-3 Advanced Technical Ceramics—Monolithic Ceramics—Mechanical Properties at
Room Temperature, Part 3: Determination of Subcritical Crack Growth Parameters from Constant
Stressing Rate Flexural Strength Tests, British Standards Institution, London, 1997
16. “Testing Method for Bending Fatigue of Fine Ceramics,” JIS R 1621, Japanese Standards Association,
Tokyo, Japan, 1996
17. “Standard Test Method for Determination of Slow Crack Growth Parameters of Advanced Ceramics by
Constant Stress-Rate Flexural Testing at Ambient Temperature,” C 1368, Annual Book of ASTM
Standards, ASTM, Vol 15.01, 1999, p 706–714
18. “Test Methods for Static Bending Fatigue of Fine Ceramics,” JIS R 1632, Japanese Standards
Association, Tokyo, Japan, Dec 1998
19. Standard Practice for Constant-Amplitude, Axial Tension-Tension Cyclic Fatigue of Advanced
Ceramics at Ambient Temperatures,” C1361, Annual Book of ASTM Standards, ASTM
22. F. Gigu, Cyclic Fatigue of Polycrystalline Alumina in Direct Push-Pull, J. Mater. Sci. Lett., Vol 13 (No.
6), 1978, p 1357–1361
23. M.V. Swain, Lifetime Prediction of Ceramic Materials, Mater. Forum, Vol 9 (No. 1–2), 1st and 2nd
Quarter 1986, p 34–44
24. H. Kawakubo and K. Komeya, Static and Cyclic Fatigue Behavior of a Sintered Silicon Nitride at Room
Temperature, J. Am. Ceram. Soc., Vol 70 (No. 6), 1987, p 400–405
25. R.H. Dauskardt, W. Yu, and R.O. Ritchie, Fatigue Crack Propagation in Transformation Toughened
Zirconia, J. Am. Ceram. Soc., Vol 70 (No. 10), 1987, p C-248–C-252
26. G. Grathwohl, Fatigue of Ceramics under Cyclic Loading, Mater. Sci. Technol., Vol 19 (No. 4), April
1988, p 113–124 (in German)
27. M.J. Reece, F. Guiu, and M.F.R. Sammur, Cyclic Fatigue Crack Propagation in Alumina under Direct
Tension-compression Loading, J. Am. Ceram. Soc., Vol 72 (No. 2), 1989, p 348–352
28. Y. Mutoh, M. Takahashi, T. Oikawa, and H. Okamoto, Fatigue Crack Growth of Long and Short Cracks
in Silicon Nitride, Fatigue of Advanced Materials, R.O. Ritchie, R.H. Dauskardt, and B.N. Cox, Ed.,
Material and Component Engineering Publications, Ltd., Edgbaston, U.K., 1991, p 211–225
29. S. Horibe and H. Hirahara, Cyclic Fatigue of Ceramics Materials: Influence of Crack Path and Fatigue
Mechanisms, Acta Metall. Mater., Vol 39 (No. 6), 1991, p 1309–1317
30. M. Okazaki, A.J. McEvily, and T. Tanaka, On the Mechanism of Fatigue Crack Growth in Silicon
Nitride, Metall. Trans. A, Vol 22A, 1991, p 1425–1434
31. T. Tanaka, N. Okabe, H. Nakayama, and Y. Ishimaru, Fatigue Crack Growth of Silicon Nitride with
Crack Wedging by Fine Fragments, Fatigue Fract. Eng. Mater. Struct., Vol 17 (No. 7), 1992, p 643–
653
32. R.O. Ritchie, C.J. Gilbert, and J.M. McNaney, Mechanics and Mechanisms of Fatigue Damage and
Crack Growth in Advanced Materials, Int. J. Solids Struct., Vol 37, 2000, p 311–329
39. M. Masuda, T. Soma, M. Matsui, and I. Oda, Fatigue of Ceramics, Part 1: Fatigue Behavior of Sintered
Silicon Nitride under Tension-Compression Cyclic Stress, J. Ceram. Soc. Jpn. Int. Ed., Vol 96, 1988, p
275–280
40. A. Steffen, R.H. Dauskardt, and R.O. Ritchie, Cyclic Fatigue Life and Crack Growth Behavior of
Microstructural Small Cracks in Magnesia-Partially-Stabilized Zirconia Ceramics, J. Am. Ceram. Soc.,
Vol 74 (No. 6), 1991, p 1259–1268
43. S.M. Weiderhorn, Prevention of Failure in Glass by Proof-Testing, J. Am. Ceram. Soc., Vol 56 (No. 4),
1973, p 227–228
45. A.G. Evans and E.R. Fuller, Crack Propagation in Ceramic Materials under Cyclic Loading Conditions,
Metall. Trans. A, Vol 5 (No. 1), 1974, p 27–33
56. “Test Method for Flexural Strength (Modulus of Rupture) of Fine Ceramics,” JIS R 1601, Japanese
Standards Association, Tokyo, Japan, 1995
57. J.E. Ritter, Jr., Assessment of Reliability of Ceramic Materials, Fracture Mechanics of Ceramics, Vol 6,
R.C. Bradt et al., Ed., Plenum Press, 1983, p 227–251
58. J.E. Ritter, Jr., Engineering Design and Fatigue Failure of Brittle Materials, Fracture Mechanics of
Ceramics, Vol 4, R.C. Bradt et al., Ed., Plenum Press, 1978, p 667–685
59. E.B. Haugen, Probabilistic Mechanical Design, John Wiley & Sons, 1980
60. N.N. Nemeth, L.M. Powers, L.A. Janosik, and J.P. Gyekenyesi, “Durability Evaluation of Ceramic
Components Using CARES/LIFE,” ASME Paper 94-GT-362 and NASA-TM 106475, ASME/IGTI Gas
Turbine Conference, June 1994
61. A.D. Peralta, D.C. Wu, P.J. Brehm, J.C. Cuccio, and M.N. Menon, Strength Prediction of Ceramic
Components under Complex Stress States, Proceedings of the International Gas Turbine and
Aeroengine Congress and Exposition, 5–8 June 1995 (Houston, TX), American Society of Mechanical
Engineers, 1995; Allied Signal Document 31-12637, 1995
62. “Fatigue Crack Growth Program NASA/Flagro 2.0,” JSC 22267A, NASA Johnson Space Flight Center,
May 1994
63. J.E. Ritter, N. Bandyopadhyay, and K. Jakus, Am. Ceram. Soc. Bull., Vol 60, 1981, p 798
64. “Standard Test method for Flexural Strength of Advanced Ceramics at Ambient Temperature,” C 1161,
Annual Book of ASTM Standards, ASTM, Vol 15.01, 1999, p 309–315
65. H.A. Linders and B. Caspers, Method for Determining Life Diagrams of Mechanoceramic Materials
DKG/DKM-Joint Experiment, Ceramics in Science and Practice, Mechanical Properties of Ceramic
Construction Materials, G. Grathwohl, Ed., DGM Information Association, Verlag, Germany, 1993, p
191–195 (in German)
66. S. Freiman, “Pre-Standardization and Standardization Activities in the USA in Mechanical Property
Testing of Advanced Structural Ceramics,” presentation at the 7
th
CIMTEC World Ceramics Congress,
Montecatini Terme, Italy, 23 June 1990
67. S.W. Freiman and E.R. Fuller, Versailles Project on Advanced Materials and Standards, VAMAS TWA
3 Bulletin 8, July 1988
68. W.P. Byrn and R. Morrell, “Results of the UK Interlaboratory Strength Test Exercise,” NPL Report
DMM (D) 72, National Physical Laboratory, Teddington, Middelsex, U.K., Crown Copyright, Dec 1990
69. “Standard Test Method for Tensile Strength of Monolithic Advanced Ceramics at Ambient
Temperatures,” C 1273, Annual Book of ASTM Standards, Vol 15.01, ASTM, 1999, p 671–678
70. Cyclic Fatigue Testing of Silicon Nitride, Ceramics (newsletter), Ceramics Division of IIT Research
Institute, Chicago, IL, 42, March 1978; Ceram. Eng. and Sci. Proc. of the 18th Annual Conference on
Composites and Advanced Ceram. Mater.-A, Part 1 of 2, 9–14 Jan 1994, Vol 15 (No. 4), July–Aug 1994
(Cocoa Beach, FL), Am. Ceram. Soc., Westerville, OH, 1994, p 32–39
71. H.N. Ko, Cyclic Fatigue Behavior of Ceramics under Rotary Bending, Materials Research Society
International Meeting on Advanced Materials, Materials Research Society, Vol 5, 1989, p 43–48
72. H.N. Ko, Cyclic Fatigue Behavior of Sintered Al
2
O
3
under Rotary Bending, J. Mater. Sci. Lett., Vol 6,
1987, p 801–805
73. R. Kossowsky, “Cyclic Fatigue of Hot Pressed Silicon Nitride,” J. Am. Ceram. Soc., Vol 56, 1973, p 10,
531–535
74. Y. Matsuo, Y. Hattori, Y. Katayama, and I. Fukuura, Cyclic Fatigue Behavior of Ceramics, Progress in
Nitrogen Ceramics, F.L. Riley, Ed., Martinus Nijhoff, 1983, p 515–522
75. K. Ohya, K. Ogur, and M. Takatsu, Effect of Loading Waveform on Cyclic Fatigue Behavior of PSZ, J.
Soc. Mater. Sci., Jpn., Vol 38 (No. 425), 1989, p 144–148
76. K. Ohya, K. Ogura, and M. Takatsu, Cyclic Fatigue Testing Device for Fine Ceramics by Using Piezo-
Electric Bimorph Actuator, J. Soc. Mater. Sci., Jpn., Vol 38 (No. 424), 1989, p 44–48
Fatigue Testing of Brittle Solids
J.A. Salem, Glenn Research Center at Lewis Field; M.G. Jenkins, University of Washington
Fracture Mechanics Methods
Fracture mechanics methods or “direct” methods generally employ test specimens with relatively large, induced
cracks. Crack growth data is typically determined directly by observation of the crack or by devices that
monitor test specimen compliance, such as clip gages and strain gages (Ref 77, 78). One exception to this is the
double torsion specimen, which has a relatively constant stress-intensity factor, K
I
, over a wide range of crack
length. Thus, the K
I
can be calculated without observation of the crack length. When used in this fashion, the
method is effectively an indirect, long crack method.
Two general types of fracture mechanics specimen are employed: line loaded or flexural specimens. Line-
loaded specimens such as the double torsion (DT), double-cantilever beam (DCB), or compact tension (CT)
allow cracks to be extended over large distances. Flexural specimens such as notched and precracked beams
can be scaled so that crack length is comparatively small or large.
The main advantage of fracture mechanics specimens is that large amounts of data can be derived from a single
test specimen, and the results are not subject to the scatter associated with the natural flaw distribution that is
sampled by strength techniques. However, as the cracks are large in comparison with those developed naturally
in smooth specimens, the fatigue behavior may be different. In particular, for materials that exhibit
transformation toughening or for materials with a coarse or elongated grain structure, a strong effect of crack
length on crack growth resistance is exhibited. Figure 13 shows the effect of crack growth resistance on the
stress-intensity factor for both long and short crack lengths. Although the same range of stress-intensity factors
is measured, the rates at which resistance develops, and possibly the rate at which fatigue damages the
resistance, are very different. Thus, techniques that use different crack length scales may result in different
fatigue parameters.
Fig. 13 Crack growth resistance as a function of crack extension for alumina
The Double Torsion Method. The double torsion method, which was developed by Outwater and Gerry (Ref
79, 80) and developed further by other researchers (Ref 81, 82, 83, 84, 85, 86, 87, 88, and 89) is illustrated in
Fig. 14. Detailed experimental and analytical analyses of the specimen have been given by Fuller (Ref 88) and
Pletka et al. (Ref 89). Tests can be performed with or without a guide groove on one or both sides of the
specimen. However, the use of a guide groove can lead to errors (Ref 90, 91), and elimination of the groove can
be achieved by using thin, carefully aligned specimens. If side grooves must be used, wide grooves and thinner
specimens help to avoid interaction between the groove wall and the crack.
Fig. 14 Schematic of the double torsion test specimen. Source: Ref 88
A variety of complications associated with the test specimen have been discussed and analyzed to varying
degrees. These include crack front curvature leading to a variation in the stress-intensity factor along the crack
front; variation in the stress-intensity factor with crack length; and poor reproducibility of data for certain
conditions, particularly for polycrystalline ceramics when multiple load relaxations are performed with the
same specimens.
Most noteworthy is the last of the problems just noted, as opposite trends have been observed for different
materials. It seems that the crack-microstructure interactions, which are more prevalent for long cracks, may be
the source of discrepancy.
Despite the complication associated with the DT, it does provide a simple geometry that is easy to load and
crack. Further, for testing of opaque materials or for hostile environments, the constant stress-intensity factor is
advantageous.
The stress-intensity factor for the DT method is (Ref 89):
(Eq 30)
with:
ξ = 1 - 0.6302t + 1.20t exp (-π/t)
where P is the applied force, W
m
is half the test specimen width minus half the notch width, d is the total
thickness, d
n
is the notch depth, W is the total width, ν is Poisson's ratio, and ξ is a correction factor for thick
test specimens where t = 2d/W. It has been recommended that the crack length be maintained between W < a <
L - W, where a is the crack length and L is the length, to ensure that the crack is in the constant K
I
region (Ref
88).
Three methods of loading DT specimens have been developed: constant load, constant displacement (Ref 83,
84) and load relaxation. The load relaxation technique has the advantage that less crack extension is required to
obtain an accurate measure of crack velocity and stress intensity factor (Ref 88).
In the load relaxation technique, a precracked specimen is loaded rapidly in a displacement control mode (~0.2
to 0.5 mm/min, or ~0.01 to 0.02 in./min) to nearly the load required to cause specimen fracture. If the crack
begins to move rapidly, the displacement is halted and the load is recorded as a function of time. Once the crack
has stopped apparent movement, the test specimen is removed and the final crack length measured. The stress-
intensity factor at any load is calculated from Eq 30, and the crack velocity from the slope of the load-time
curve and either the specimen displacement or the crack length and load before or after the test (Ref 91):
(Eq 31)
(Eq 32)
where E is Young's modulus, P
i
and a
i
are the initial load and crack length values, respectively, and P
f
and a
f
are the values at the end of the relaxation.
The DCB Method. The double-cantilever beam (DCB) specimen has been used to test glass, sapphire,
magnesium fluoride, and various polycrystalline ceramics (Ref 8, 14, 91, 92, and 93). Also, a form of the DCB
specimen referred to as the compact tension has been standardized for fracture toughness testing of metals (Ref
52). A variety of methods can be used to apply load to the DCB specimen. These include wedge loading and the
application of a constant moment (Ref 94). If a constant K
I
is desired, the specimen can be tapered (Ref 95).
Often, side grooves are used to guide the crack longitudinally. For the geometry shown in Fig. 15, the stress-
intensity factor and fracture toughness can be determined from:
(Eq 33)
where P is the applied force, h is half height of the test specimen, B is the thickness of the test specimen, b is
the Web thickness, and a is the crack length. Some advantages of this geometry are the constant stress-intensity
factor for some configurations (e.g., tapered DCB or applied moment DCB), simple test specimen preparation,
efficient material usage, and the simple loading configuration. The primary disadvantages are effects associated
with the side groove and the difficulty of introducing a sharp crack.
Fig. 15 Double-cantilever beam (DCB) test specimen (Ref 8). Slots on both sides of the specimen for
restraining the crack to the midplane are not shown.
Generally, crack growth measurements are made by optical observation of the crack on the side of the
specimens while a constant load is applied. For glass, good agreement between DCB and strength
measurements (Ref 8, 91) and between DCB and DT measurements have been obtained (Ref 86, 96).
Cyclic Fatigue by Other Fracture Mechanics Methods. Cyclic fatigue measurement using the direct or fracture
mechanics approach can be classified into two crack-length regimes: long cracks made by using large
specimens that are typically applied in metals testing (e.g., compact tension) or shorter cracks generated by
indentation with Knoop or Vickers hardness indenters (Fig. 16). Both the DT and DCB, however, can be loaded
cyclically.
Fig. 16 Flexure test specimen with a precrack formed by Vickers indentation
Both crack-length regimes have advantages and disadvantages. The core issue for both approaches is whether
the behavior in real applications is represented. For long cracks this is basically an issue of scale, while for the
short, indentation cracks, the residual stress field about the indentation and its changes during fatigue are an
issue.
Probably the simplest method of long crack testing is the use of the single-edge-precracked-beam (SEPB)
specimen. A precrack is formed by bridge indentation (Ref 97) and loaded in three- or four-point flexure. The
crack extension can be monitored directly on the specimen sides, or by compliance measurements via
extensometers, clip gages, strain gages (Ref 77, 78), or electrical grids (Ref 98, 99).
This method has been used to generate long crack fatigue data for silicon nitride in vacuum and air (Ref 30).
The results indicate lower threshold stress-intensity factors for cyclic loading or air as compared with static
loading or vacuum. The threshold is also a function of crack length and thus related to the crack growth
resistance mechanism. No dependence on frequency was found between 0.5 and 20 Hz, however, and an effect
of R-ratio was found.
The compact tension specimen has been used frequently to test ceramics (Ref 25, 33, 100, and 101), and long-
crack data have been generated for comparison with short-crack data for materials such as SiC-whisker-
reinforced alumina, pyrolitic carbon, and magnesia-partially-stabilized zirconia.
For magnesia-partially-stabilized zirconia, fatigue measurements with long cracks indicate a threshold at ~50%
of the fracture toughness and the slowest growth rates for the materials with the most transformation
toughening. However, for short, naturally developing cracks, growth occurs below the long-crack threshold,
and, as with metals, a negative dependency of growth rate on stress intensity is exhibited.
Short fatigue crack testing of many ceramics is complicated by the infrequent development of natural cracks
and the difficulty of detecting such cracks. This difficulty can be circumvented by precracking the polished
surface of a beam with a Vickers or Knoop indenter. The crack size during static or cyclic loading in four-point
or cantilever flexure is monitored optically or via electron microscopy (Ref 29, 100, andd 101). Multiple cracks
can be placed on a single specimen.
Ideally, short cracks without the residual stress should be used, as is done in standardized fracture toughness
testing (Ref 102). This can be accomplished by polishing the specimen until a sufficient amount of the
indentation and crack has been removed.
A number of more exotic methods, such compressive cyclic fatigue of notched specimens, have also been used
to demonstrate cyclically induced fatigue in ceramics (Ref 103, 104).
References cited in this section
8. S.M. Weiderhorn and L.H. Boltz, Stress Corrosion and Static Fatigue of Glass, J. Am. Ceram. Soc., Vol
62 (No. 7–8), 1970, p 547–548
14. T.A. Michalske, B.C. Bunker, and S.W. Freiman, Stress Corrosion of Ionic and Mixed Ionic/Covalent
Solids, J. Am. Ceram. Soc., Vol 69 (No. 10), 1986, p 721–724
25. R.H. Dauskardt, W. Yu, and R.O. Ritchie, Fatigue Crack Propagation in Transformation Toughened
Zirconia, J. Am. Ceram. Soc., Vol 70 (No. 10), 1987, p C-248–C-252
29. S. Horibe and H. Hirahara, Cyclic Fatigue of Ceramics Materials: Influence of Crack Path and Fatigue
Mechanisms, Acta Metall. Mater., Vol 39 (No. 6), 1991, p 1309–1317
30. M. Okazaki, A.J. McEvily, and T. Tanaka, On the Mechanism of Fatigue Crack Growth in Silicon
Nitride, Metall. Trans. A, Vol 22A, 1991, p 1425–1434
33. R. Dauskardt, Cyclic Fatigue-Crack Growth in Grain Bridging Ceramics, J. Eng. Mater. Technol.
(Trans. ASME), Vol 115, 1993, p 115–251
52. “Standard Test Method for Plane Strain Fracture Toughness of Metallic Materials,” E 399, Annual Book
of ASTM Standards, Vol 03.01, ASTM, 1998
77. J.A. Salem, L.J. Ghosn, and M.G. Jenkins, A Strain Gage Technique to Measure Stable Crack Extension
in Ceramics, Post Conference Proceedings of the 1997 SEM Spring Conference on Experimental
Mechanics, Society for Experimental Mechanics, Bethel, CT, 1997, p 1–8
78. J.A. Salem, L.J. Ghosn, and M.G. Jenkins, Back-Face Strain as a Method for Monitoring Stable Crack
Extension in Ceramics, Ceram. Eng. Sci. Proc., Vol 19 (No. 3), 1998, p 587–594
79. J.O. Outwater and D.J. Gerry, “On the Fracture Energy of Glass,” NRL Interim Contract Report,
Contract NONR 3219(01)(x), AD 640848, University of Vermont, Burlington, VT, Aug 1966
80. J.O. Outwater and D.J. Gerry, “On the Fracture Energy, Rehealing Velocity and Fracture Energy of Cast
Epoxy Resin,” Paper 13-D, presented at the 22
nd
Society of Plastic Industry Conference, 1967; also, J.
Adhes., Vol 1, 1969, p 290–298
81. G.W. Weidmann and D.G. Holloway, Slow Crack Propagation in Glass, Phys. Chem. Glasses, Vol 15
(No. 5), Oct 1974, p 116–122
82. C.D. Beacham, J.A. Kies, and B.F. Brown, A Constant K Specimen for Stress Corrosion Cracking
Testing, Mater. Res. Standards, Vol 11, 1970, p 30
83. A.G. Evans, Method For Evaluating the Time-Dependent Failure Characteristics of Brittle Material and
Its Application to Polycrystalline Alumina, J. Mater. Sci., Vol 7 (No. 10), 1972, p 1137–1146
84. A.G. Evans and S.M. Wiederhorn, Crack Propagation and Failure Prediction in Silicon Nitride at
Elevated Temperatures, J. Mater. Sci., Vol 9, 1974, p 270–278
85. A.G. Evans, L.R. Russel, and D.W. Richerson, Slow Crack Growth in Ceramic Materials at Elevated
Temperatures, Metall. Trans. A, Vol 6A (No. 14), 1975, p 707–716
86. K.R. McKinney and H.L. Smith, Method of Studying Subcritical Cracking of Opaque Materials, J. Am.
Ceram. Soc., Vol 56 (No. 1), 1973, p 30–32
87. P.N. Thornby, Experimental Errors in Estimating Times to Failures, J. Am. Ceram. Soc., Vol 59 (No.
11–12), 1976, p 514–517
88. E.R. Fuller, Jr., an Evaluation of Double Torsion Testing: Analysis, Fracture Mechanics Applied to
Brittle Materials, STP 678, S.W. Frieman, Ed., ASTM, 1979, p 3–18
89. B.J. Pletka, E.R. Fuller, Jr., and B.G. Koepke, An Evaluation of Double Torsion Testing: Experimental,
Fracture Mechanics Applied to Brittle Materials, STP 678, S.W. Frieman, Ed., ASTM, 1979, p 19–37
90. C.G. Annis and J.S. Cargill, Modified Double Torsion Method for Measuring Crack Velocity in NC-132
Si
3
N
4
, Fracture Mechanics of Ceramics, Vol 4, R.C. Bradt et al., Ed., Plenum Press, 1978, p 737–744
91. D.P. Williams and A.G. Evans, A Simple Method for Studying Slow Crack Growth, J. Test. Eval., Vol
1 (No. 4), 1973, p 264–270
92. K.R. Linger and D.G. Holloway, Fracture Energy of Glass, Philos. Mag., Vol 18 (No. 156), 1968, p
1269–1280
93. J.A. Salem, M.G. Jenkins, M.K. Ferber, and J.L. Shannon, Jr., Effects of Pre-Cracking Method on
Fracture Properties of Alumina, Proceedings of Society of Experimental Mechanics Conference on
Experimental Mechanics, 10–13 June 1991 (Milwaukee, WI), Society for Experimental Mechanics,
Bethel, CT, 1991, p 762–769
94. S.W. Freiman, D.R. Mulville, and P.W. Mast, J. Mater. Sci., Vol 8 (No. 11), 1973, p 1527–1533
95. S. Mostovoy, P.B. Crosley, and E.J. Ripling, Use of Crack-Line-Loaded Specimens for Measuring
Plane-Strain Fracture Toughness, J. Mat., Vol 2 (No. 3), Sept 1967, p 661–681
96. A.G. Evans and H. Johnson, The Fracture Stress and Its Dependence on Slow Crack Growth, J. Mater.
Sci., Vol 10, 1975, p 214–222
97. T. Sadahiro, Transverses Rupture Strength and Fracture Toughness of WC-Co Alloys, J. Jpn. Inst. Met.,
Vol 45, 1981, p 291–295
98. D.J. Martin, K.W. Davido, and W.D. Scott, Slow Crack Growth Measurement Using an Electric Grid,
Am. Ceram. Soc. Bull., Vol 65 (No. 7), 1986, p 1052–1156
99. P.K. Liaw, H.R. Hartmann, and W.A. Lodgson, A New Transducer to Monitor Fatigue Crack
Propagation, J. Test Eval., Vol 11 (No. 3), 1983, p 202–207
100. R.H. Dauskardt, R.O. Ritchie, J.K. Takemoto, and A.M. Brendzel, Cyclic Fatigue in Pyrolytic
Carbon-Coated Graphite Mechanical Heart-Valve Prostheses: Role of Small Cracks in Life Prediction,
J. Biomed. Mater. Res., Vole 28, 1994, p 791–804
101. R.H. Dauskardt, M.R. James, J.R. Porter, and R.O. Ritchie, Cyclic Fatigue-Crack Growth in a
SiC-Whisker-Reinforced Alumina Ceramic Composite: Long- and Small-Crack Behavior, J. Am.
Ceram. Soc., Vol 75 (No. 4), 1992, p 759–771
102. “Standard Test Methods for Fracture Toughness of Advanced Ceramics,” C 1421, Annual Book
of ASTM Standards, ASTM, Vol 15.01, 2000, p 631–662
103. L. Ewart and S. Suresh, Dynamic Fatigue Crack Growth in Polycrystalline Alumina under
Cyclic Compressive Loads, J. Mater. Sci., Vol 5, 1986, p 774–778
104. L. Ewart and S. Suresh, Crack Propagation in Ceramics under Cyclic Loads, J. Mater. Sci., Vol
22, 1987, p 1173–1192
Fatigue Testing of Brittle Solids
J.A. Salem, Glenn Research Center at Lewis Field; M.G. Jenkins, University of Washington
Comparison of Indirect and Direct Methods
Several researchers (Ref 105, 106, and 107) have noted that indirect techniques, such as dynamic fatigue, can
result in large errors in the estimated fatigue parameters of polycrystalline ceramics exhibiting environmentally
induced crack growth when the failure times are relatively short. Further, such methods cannot be used to
accurately predict the life of components unless some precautions are taken. For example, for a mullite with a
region I fatigue parameter of n = 41 as measured with the double-torsion method, the use of stress rates greater
than 1 MPa/s resulted in an estimated value of n = 19 (Ref 105). For a silicon nitride with a parameter of n =
66, the values estimated from dynamic fatigue was n = 100. Similar differences were shown to exist between
flexural data and double torsion data for magnesium alumina silicate (n = 51 versus 84) (Ref 89, 107).
This is a result of the fact that indirect methods average all three regions of the fatigue curves into a single
region, and for short duration tests, all the regions are significant. However, in a component with a long life,
region I is dominant.
One exception to this is static fatigue tests, in which the failure times tend to be long and the crack growth
dominated by region I. The dynamic fatigue test might be made more applicable to the generation of design
data for long-term applications by using stress rates that are sufficiently slow.
References cited in this section
89. B.J. Pletka, E.R. Fuller, Jr., and B.G. Koepke, An Evaluation of Double Torsion Testing: Experimental,
Fracture Mechanics Applied to Brittle Materials, STP 678, S.W. Frieman, Ed., ASTM, 1979, p 19–37
105. F. Sudreau, C. Olagnon, and G. Fantozzi, Lifetime Prediction of Ceramics: Importance of Test
Method, Ceram. Int., Vol 10, 1994, p 125–135
106. E.M. Rockar and B.J. Pletka, Fracture Mechanics of Alumina in a Simulated Biological
Environment, Fracture Mechanics of Ceramics, Vol 4, R.C. Bradt et al., Ed., Plenum Press, 1978, p
725–735
107. Pletka and Wiederhorn, Subcritical Crack Growth in Glass-Ceramics, Fracture Mechanics of
Ceramics, Vol 4, R.C. Bradt et al., Ed., Plenum Press, 1978, p 745–759