ASM Metals HandBook Vol. 8 - Mechanical Testing and Evaluation
Подождите немного. Документ загружается.
32. “Plastic—Determination Of Charpy Impact Properties: Part 2—Instrumented Impact Test,” ISO-179-2,
International Organization for Standardization
33. Impact Testing of Metals, STP 466, ASTM, 1970
34. Instrumented Impact Testing, STP 563, ASTM, 1974
35. C.E. Turner, in Advanced Seminar on Fracture Mechanics, EURA-TOM-ISPRA Courses, 1975
36. Dynamic Fracture Toughness, The Welding Institute and The American Society for Metals, 1976
37. E.C.J. Buys and A. Cowan, Interpretation of the Instrumented Impact Test, Weld. World, Vol 8 (No. 1),
1970, p 70–76
38. Pressure Vessel Research Committee/Metal Properties Council Working Group on Instrumented
Precracked Charpy Testing, “Instrumented Precracked Charpy Testing: Report I—Recommended
Testing Procedure, Report II—Associated Test Program,” Westinghouse Research Laboratory,
Pittsburgh, PA, 1974
39. R.A. Wullaert, Ed., CSNI Specialist Meeting on Instrumented Precracked Charpy Testing, Nov 1980,
EPRI NP-2102-LD, Electric Power Research Institute, 1981
40. “ESIS Instrumented Charpy V-Notch Standard,” Proposed Standard Method for the Instrumented
Charpy-V Impact Tests on Metallic Materials, Draft 10, ESIS, Jan 14, 1994
41. E. Lucon, Instrumented Impact Testing of Sub-Size Charpy-V Specimens: The Activity of the ESIS
TC5 Working Party, ECF 11—Mechanisms and Mechanics of Damage and Failure, Vol 1, Elsevier,
1996, p 621
42. T. Kobayashi and I. Yamamoto, Progress and Development in the Instrumented Charpy Impact Testing
Method, Bull. Jpn. Inst. Met., Vol 32 (No. 3), 1993, p 151–159 (in Japanese)
43. W.L. Server, Impact Three-Point Bend Testing for Notches and Precracked Specimens, J. Test. Eval.,
Vol 6 (No. 1), 1978, p 29–34
44. D.M. Norris, D. Quiñones, and B. Moran, Computer Simulation of Plastic Deformation in the Charpy
V-Notch Impact Test, What Does the Charpy Test Really Tell Us?: Proceedings of the American
Institute of Mining, Metallurgical and Petroleum Engineers, American Society for Metals, 1978, p 22–
32
45. T.M.F. Ronald, J.A. Hall, and C.M. Pierce, Usefulness of Precracked Charpy Specimens for Fracture
Toughness Screening Tests of Titanium Alloys, Metall. Trans., Vol 3, April 1972, p 813–818
46. G.M. Orner and C.E. Hartbower, Transition-Temperature Correlations in Construction Alloy Steels,
Weld. J., Vol 40 (No. 9), Oct 1961, p 459s
47. J.H. Gross, The Effect of Strength and Thickness on Notch Ductility, Weld. J., Vol 48 (No. 10), Oct
1969, p 441s
48. W.L. Server, D.R. Ireland, and R.A. Wullaert, “Strength and Toughness Evaluations from an
Instrumented Impact Test,” ETI TR-74-29R, Effects Technology, Inc., Santa Barbara, CA, Nov 1974
49. H.J. Saxton et al., Load Point Compliance of the Charpy Impact Specimen, Instrumented Impact
Testing, STP 563, ASTM, 1974, p 30–49
50. W.L. Server, R.A. Wullaert, and J.W. Sheckherd, “Verification of the EPRI Dynamic Fracture
Toughness Testing Procedures,” ETI TR 75–42, Effects Technology, Inc. Santa Barbara, CA, Oct 1975
51. W.L. Server, W. Oldfield, and R.A. Wullaert, “Experimental and Statistical Requirements for
Developing a Well-Defined KIR Curve,” EPRI NP-372, Electric Power Research Institute, Palo Alto,
CA, May 1977
52. J.D.G. Sumpter and C.E. Turner, Method for Laboratory Determination of J
c
, Cracks and Fracture, STP
601, ASTM, 1976, p 3–18
53. D.J.F. Ewing, Calculations on the Bending of Rigid/Plastic Notched Bars, J. Mech. Phys. Solids, Vol
16, 1968, p 205–213
54. W.L. Server, General Yielding of Charpy V-Notch and Precracked Charpy Specimens, J. Eng. Mater.
Technol. (Trans. ASME), Vol 100, April 1978, p 183–188
55. Committee on Safety of Nuclear Installations Specialist Meeting on Instrumented Precracked Charpy
Testing, EPRI NP-2102-LD, Electric Power Research Institute, Palo Alto, CA, Nov 1981
56. F.J. Loss, Ed., “Structural Integrity of Water Reactor Pressure Boundary Components,” Progress Report
Ending Feb 1976, NRL Report 8006, Naval Research Laboratory, Washington, D.C., Aug 1976
57. T. Nicholas, “Instrumented Impact Testing Using a Hopkinson Bar Apparatus,” AFML-TR-75-54, Air
Force Materials Laboratory, Wright-Patterson Air Force Base, Dayton, OH, July 1975
58. J.F. Kalthoff et al., “Measurements of Dynamic Stress Intensity Factors in Impacted Bend Specimens,”
Committee on Safety of Nuclear Installations Specialist Meeting on Instrumented Precracked Charpy
Testing, EPRI NP-2102-LD, Electric Power Research Institute, Palo Alto, CA, Nov 1981
59. J. Woolman and R.A. Mottram, The Mechanical and Physical Properties of the British Standard DN
Steels, Vol 1, Appendix UI, The British Iron and Steel Research Association, 1964, p 442
60. J.H.J. Giovanola, One-Point Bend Test, Mechanical Testing, Vol 8, ASM Handbook, 1985, ASM
International, p 271–275
61. L.S. Costin, J. Duffy, and L.B. Freund, Fracture Initiation in Metals Under Stress Wave Loading
Conditions, Fast Fracture and Crack Arrest, STP 627, G.T. Hahn and M.F. Kanninen, Ed., ASTM,
1977, p 301–318
62. R.H. Hawley, J. Duffy, C.F. Shih, Dynamic Notched Round Bar Testing, Mechanical Testing, Vol 8,
ASM Handbook, 1985, ASM International, p 275–284
63. G.R. Irwin, J.W. Dally, X.-J. Zhang, and R.J. Bonenberger, Lower-Bound Initiation Toughness of
A533-B Reactor-Grade Steel, Rapid Load Fracture Testing, STP 1130, ASTM, 1991, p 9–23
Evaluation of Environmentally Assisted Crack
Growth
Y. Katz, N. Tymiak, and W.W. Gerberich, University of Minnesota
Introduction
ENVIRONMENTALLY ASSISTED CRACK GROWTH is a special form of mechanical degradation that
occurs when the combined effect (or interaction) of environment and applied or residual stresses causes
subcritical crack growth or fracture. Materials ranging from metals and alloys to glasses, plastics, composites,
and ceramics can be susceptible. Even materials such as very pure metals, which were once considered not
susceptible to environmentally assisted cracking, have usually, on more detailed investigation, proven to be so.
Relevant crack propagation rates from environmentally assisted cracking can range from more than 10 to less
than 10
-10
mm/s depending on the environment, load condition, and material.
In broad terms, environmentally assisted cracking includes stress-corrosion cracking, hydrogen embrittlement,
and corrosion fatigue. Although these phenomena represent distinct forms of cracking, they also overlap to
some degree, as the interaction of mechanical loads and environmental conditions has common mechanisms of
degradation across a spectrum of loading conditions and materials. Thus, the choice between the term stress-
corrosion cracking and corrosion fatigue may be somewhat arbitrary, as they may both refer to the same
underlying degradation phenomenon. However, not all aspects of environmentally assisted crack advance are
identical in all cracking systems. Therefore, phenomenological categories are still useful divisions in the
evaluation of environmentally assisted crack growth.
This article briefly describes the typical test methods for the evaluation of hydrogen embrittlement, stress-
corrosion cracking, and corrosion fatigue with an emphasis on fracture mechanics methodologies for metals. A
brief overview on the environmentally assisted crack growth of nonmetallic materials is also included. In
general, the test results of environmentally assisted cracking can be influenced by a wide range of variables,
such as those listed in Table 1. In addition, because of the large contribution of environment to crack advance,
attention to experimental detail is often critical. Unless the multidisciplinary nature of these studies is
recognized, most efforts will produce seriously misleading results or outright confusion, which is perhaps most
responsible for the slow progress in quantifying and understanding environmental cracking. Familiarity with
chemical and physical metallurgy, mechanics, chemistry, electrochemistry, and corrosion also is generally
considered essential.
Table 1 Material, environmental, and mechanical variables of environmentally assisted cracking
Metallurgical variables
• Alloy composition
• Distribution of alloying elements and impurities
• Microstructure and crystal structure
• Heat treatment
• Mechanical working
• Preferred orientation of grains and grain boundaries (texture)
• Mechanical properties (strength, fracture toughness, etc.)
Environmental variables
• Temperature
• Types of environments: gaseous, liquid, liquid metal, etc.
• Partial pressure of damaging species in gaseous environments
• Concentration of damaging species in aqueous or other liquid environments
• Electrical potential
• pH
• Viscosity of the environment
• Coatings, inhibitors, etc.
Mechanical variables
• Maximum stress or stress-intensity factor, σ
max
or K
max
• Cyclic stress or stress-intensity range, Δσ or ΔK
• Stress ratio (R)
• Cyclic loading frequency
• Cyclic load waveform (constant-amplitude loading)
• Load interactions in variable-amplitude loading
• State of stress
• Residual stress
• Crack size and shape, and their relation to component size and geometry
Evaluation of Environmentally Assisted Crack Growth
Y. Katz, N. Tymiak, and W.W. Gerberich, University of Minnesota
Evaluation of Hydrogen Embrittlement
Hydrogen embrittlement is a time-dependent fracture process caused by the absorption and diffusion of atomic
hydrogen into a metal, which results in a loss in ductility and tensile strength. Hydrogen embrittlement is
distinguished from stress-corrosion cracking generally by the interactions of the specimens with applied
currents (Ref 1). Cases where the applied current makes the specimen more anodic and accelerates cracking are
considered to be stress-corrosion cracking, with the anodic-dissolution process contributing to the progress of
cracking. On the other hand, when cracking is accentuated by current in the opposite direction, the hydrogen-
evolution reactions are accelerated, and the cracking process is considered to be dominated by hydrogen
embrittlement. These two basic types of environmental conditions have different phenomenological effects on
cracking mechanisms, as briefly summarized in Table 2 for anodic and cathodic reactions.
Table 2 Corrosion/deformation cracking mechanisms including hydrogen embrittlement
Mechanism
Phenomenological implications
Anodic dissolution
Crack-tip blunting
Anodic-dissolution-formed film (oxide or
dealloyed)
Film fracture or film-induced cleavage
Passivating film removal or breakdown
Promotion of plasticity (e.g., slip reversal in fatigue)
Hydrogen enhanced crack-tip decohesion, or HEDE (brittle
fracture)
Hydrogen enhanced localized plasticity, or HELP (ductile
fracture)
Cathodic reaction
Hydrogen phase forms and fractures
In a broad sense, the key phenomenological consequence of hydrogen embrittlement is subcritical crack growth
that often produces a time-delayed fracture in production parts, sometimes even with no externally applied
stress. However, the mechanisms of hydrogen embrittlement are not entirely understood, even though hydrogen
embrittlement of metals is an old, frequently encountered, phenomenon. There are many different sources of
hydrogen, several types of embrittlement, and various theories for explaining the observed effects. These
factors make evaluation more difficult. Hydrogen embrittlement is also a complex phenomenon that probably
cannot be described by a single dominant mechanism.
Reference cited in this section
1. M.G. Fontana and N.D. Greene, Corrosion Engineering, McGraw-Hill, 1978, p 113
Evaluation of Environmentally Assisted Crack Growth
Y. Katz, N. Tymiak, and W.W. Gerberich, University of Minnesota
Types of Hydrogen Embrittlement (Ref 2 and 3)
The metals processing, chemical, and petroleum industries have experienced various types of hydrogen-induced
cracking for many years. Examples include hydrogen-induced failures of parts that have been forged, heat
treated, welded, chemically milled, pickled, or exposed to paint removers. Hydrogen embrittlement is a
problem in welding, due to the complex nature of welds and the various sources of hydrogen. Hydrogen sulfide
stress cracking is also a major concern in the petroleum industry, and the aerospace industry has experienced
unexpected hydrogen embrittlement problems, principally in dealing with high-strength steels. Other examples
include hydrogen embrittlement of parts installed in boilers, pressurized-water reactors, high-pressure
hydrogenation units, and parts with cathodic protection. Hydrogen cracking has also been a serious concern
when hydrogen is used as the liquid fuel in engines.
There are three basic types of hydrogen embrittlement observed in metals:
• Internal reversible hydrogen embrittlement
• Hydrogen environment embrittlement
• Hydrogen reaction embrittlement
If specimens have been precharged with hydrogen from any source or in any manner and embrittlement is
observed during mechanical testing, then embrittlement is caused by either internal reversible embrittlement or
hydrogen reaction embrittlement. If hydrides or other new phases containing hydrogen form during testing in
gaseous hydrogen, then embrittlement is attributed to hydrogen reaction embrittlement. For all embrittlement
determined during mechanical testing in gaseous hydrogen other than internal reversible and hydrogen reaction
embrittlement, hydrogen environment embrittlement is assumed to be responsible.
Internal reversible hydrogen embrittlement has also been termed slow-strain-rate embrittlement and delayed
failure. This is the classical type of hydrogen embrittlement that has been studied quite extensively. Widespread
attention has been focused on the problem resulting from electroplating, particularly of cadmium in high-
strength steel components. Other sources of hydrogen are processing treatments, such as melting and pickling.
More recently, the embrittling effects of many stress-corrosion processes have been attributed to corrosion-
produced hydrogen. Hydrogen that is absorbed from any source is diffusible within the metal lattice. To be
fully reversible, embrittlement must occur without the hydrogen undergoing any type of chemical reaction after
it has been absorbed within the lattice.
Internal reversible hydrogen embrittlement can occur after a very small average concentration of hydrogen has
been absorbed from the environment. However, local concentrations of hydrogen are substantially greater than
average bulk values. For steels, embrittlement is usually most severe at room temperature during either delayed
failure or slow-strain-rate tension testing. This time-dependent nature (incubation period) of embrittlement
suggests that diffusion of hydrogen within the lattice controls this type of embrittlement. Cracks initiate
internally, usually below the root of a notch at the region of maximum triaxiality. Embrittlement in steel is
reversible (ductility can be stored) by relieving the applied stress and aging at room temperature, provided
microscopic cracks have not yet initiated. Internal reversible hydrogen embrittlement has also been observed in
a wide variety of other materials, including nickel-base alloys and austenitic stainless steels, provided they are
severely charged with hydrogen.
Hydrogen environment embrittlement was recognized as a serious problem in the mid-1960s when the National
Aeronautics and Space Administration (NASA) and its contractors experienced failure of ground-based
hydrogen storage tanks. These tanks were rated for hydrogen at pressures of 35 to 70 MPa (5–10 ksi).
Consequently, the failures were attributed to high-pressure hydrogen embrittlement. Because of these failures
and the anticipated use of hydrogen in advanced rocket and gas turbine engines and auxiliary power units,
NASA initiated both in-house and contractual research. The contractual effort generally has been to define the
relative susceptibility of structural alloys to hydrogen environment embrittlement. A substantial amount of
research has concerned the mechanism of the embrittlement process. There is marked disagreement as to
whether hydrogen environment embrittlement is a form of internal reversible hydrogen embrittlement or is truly
a distinct type of embrittlement.
Hydrogen Reaction Embrittlement. Although the sources of hydrogen may be any of those mentioned
previously, this type of embrittlement is quite distinct from hydrogen environment embrittlement. Once
hydrogen is absorbed, it may react near the surface of diffuse substantial distances before it reacts. Hydrogen
can react with itself, with the matrix, or with a foreign element in the matrix. The chemical reactions that
comprise this type of embrittlement or attack are well known and are encountered frequently. The new phases
formed by these reactions are usually quite stable, and embrittlement is not reversible during room-temperature
aging treatments.
Atomic hydrogen (H) can react with the matrix or with an alloying element to form a hydride (MH
x
). Hydride
phase formation can be either spontaneous or strain induced. Atomic hydrogen can react with itself to form
molecular hydrogen (H
2
). This problem is frequently encountered after steel processing and welding; it has
been termed flaking or “fisheyes.” Atomic hydrogen can also react with a foreign element in the matrix to form
a gas. A principal example is the reaction with carbon in low-alloy steels to form methane (CH
4
) bubbles.
Another example is the reaction of atomic hydrogen with oxygen in copper to form steam (H
2
O), resulting in
blistering and a porous metal component.
Although hydrogen reaction embrittlement is not a major topic in this article, its definition is included for the
sake of completeness and in the hope of establishing a single definition for each of the various hydrogen
embrittlement phenomena to avoid problems with semantics.
Further confusion results from the relation of stress-corrosion cracking (SCC) to hydrogen embrittlement,
because the crack growth mechanism is often found to be the same. On the surface, the active corrosion process
produces the hydrogen that is the cause of the failure. In SCC, the pits or crevices (polarized anodically) are
initiation sites, and, therefore, although the growth mechanisms are the same, the method of prevention based
on initiation can be different.
References cited in this section
2. L. Raymond, Ed., Hydrogen Embrittlement Testing, STP 543, ASTM, 1972
3. L. Raymond, Evaluation of Hydrogen Embrittlement, Corrosion, Volume 13, ASM Handbook, ASM
International, 1987, p 283–284
Evaluation of Environmentally Assisted Crack Growth
Y. Katz, N. Tymiak, and W.W. Gerberich, University of Minnesota
Mechanisms and Models
Although the micromechanisms of hydrogen-related fracture have been the subject of intense interest and
review in the literature (Ref 4, 5, 6, 7, and 8), many facets of hydrogen embrittlement are still not entirely
understood. This is due, in part, to the ad hoc nature of many test methods and the large number of variables
(Fig. 1) that influence test results. Several different types of mechanisms, rather than just one dominant
mechanism, may also occur.
Fig. 1 Interaction variables in hydrogen embrittlement
Although numerous mechanisms have been proposed, there appear to be at least three distinct mechanisms of
hydrogen embrittlement in metals (Table 2):
• Hydrogen-enhanced decohesion (HEDE) mechanism, which is characterized by hydrogen decreasing
either grain boundary or cleavage plane cohesion (Ref 6, 9, 10, 11, 12, and 13)
• Hydrogen-enhanced local plasticity (HELP) mechanism, which proposes that solid-solution free
hydrogen causes dislocation unpinning, which may increase dislocation mobility and allow highly
localized deformation (Ref 7 and 8)
• Hydride formation (as previously noted, included here only for the sake of completeness)
In terms of mechanical testing and the use of fracture mechanics, the following sections describe the HEDE and
HELP mechanisms in more detail. These damage models are conceptually related to the fracture-mechanics
concepts of failure by brittle fracture or plastic collapse. In general, fracture occurs under one of three
conditions: plastic collapse, brittle fracture, or elastic-plastic fracture. These three fracture criteria are roughly
defined in the failure assessment diagram (Fig. 2) of the R-6 Method (Ref 14), where the envelope of safe
operation in the elastic-plastic region converges to either a brittle fracture condition (K/K
c
= 1) or plastic
collapse (σ/σ
c
= 1). The HEDE and HELP mechanisms are conceptually related to these basic concepts of
fracture mechanics, as illustrated in Fig. 2.
Fig. 2 Failure assessment diagram showing operative region of HEDE and HELP hydrogen degradation
Hydrogen-enhanced decohesion (HEDE) is based on brittle fracture associated with “embrittlement.” The
HEDE model has allowed considerable progress to be achieved particularly regarding fracture criteria,
including subcritical crack growth, threshold values, damage dependency on the hydrogen partial pressure,
temperature, kinetic considerations, and delayed fracture analysis.
The HEDE model actually goes back to the original hydrogen embrittlement study by Troiano (Ref 15 and 16),
which later developed in different stages. Following a comprehensive series of research activities (Ref 11 and
12), as related to brittle fracture concepts in general, further developments resulted also in the HEDE hydrogen
embrittlement model (Ref 9 and 17). Basically the initial considerations are:
• Can the near-crack-tip mechanical field be better established?
• How can far-field stresses from fracture mechanics be related to theoretical calculations that established
that hydrogen does decrease the cohesive strength of cleavage planes and grain boundaries?
The latter finding emerged from embedded-atom (Ref 18 and 19) and full-energy (Ref 20) calculations.
Following these developments, the connection between the local stress intensity, k
tip
, and the far field, K
I
, has
been found (Ref 17 and 21). This was then coupled to the decrease in resistance associated with localized
hydrogen concentrations. Moreover, this approach turned out to be very consistent experimentally with the
ability to accommodate the principal common features related to the decrease of the threshold value, K
Ith
, and
the substantial increase of the crack growth rate with increasing K
I
. Note that the high sensitivity of high-
strength materials to hydrogen embrittlement becomes the dominant process in the more general framework of
SCC.
Hydrogen-enhanced local plasticity (HELP) is based on the localized loss of load-bearing capacity from “shear”
decohesion. The HELP model proposes the notion that solid-solution free hydrogen in metals causes dislocation
underpinning, which increases dislocation mobility and allows highly localized deformation. Moreover, such
enhanced plasticity has been claimed to result in localized softening, which enhances plastic failure in contrast
to the usual sense of embrittlement. Enhanced ductile processes due to hydrogen interaction had first been
suggested by Beachem (Ref 22), later joined by others (Ref 7 and 23). In fact, the direct relation between H
solute causing enhanced dislocation mobility and fracture has been shown using in situ environmental cell
transmission electron microscopy (TEM) measurements (Ref 24, 25, and 26). Nevertheless, observations of
deformation behavior and fracture under such plane-stress conditions leave significant issues unresolved. At
least two major questions still remain:
• What is the exact sequence of events causing fracture in the bulk?
• Even observed, how do hydrogen solutes result in slip localization? Is this related to hydrogen-induced
slip localization or to low-energy dislocation structures? Can local internal strains be separated from the
role of any concurrent internal stress field?
Thus, in contrast to the HEDE model, the localized plasticity part of the HELP mechanism suggests
alternatively that hydrogen promotes “shear” decohesion along slip planes. The HELP model still has limited
predictive capability that needs to be developed.
References cited in this section
4. K. Sieradzki, Atomistic and Micromechanical Modeling Aspects of Environment-Induced Cracking of
Metals, EICM Proc., R.P. Gangloff and M.B. Ives, Ed., National Association of Corrosion Engineers,
1990, p 125
5. W.W. Gerberich and S.-H. Chen, Environment-Induced Cracking of Metals, Fundamental Processes:
Micromechanics, Int. Conf. Environmentally Induced Cracking, Oct 1988, National Association of
Corrosion Engineers, 1990, p 167–187
6. W.W. Gerberich, P. Marsh, J. Hoehn, S. Venkataraman, and H. Huang, Hydrogen/Plasticity Interactions
in Stress Corrosion Cracking, Corrosion-Deformation Interactions, CD1 '92, Les Editions de Physique
les Ulis, T. Magnin, Ed., 1993, p 325–343
7. H.K. Birnbaum, Mechanism of Hydrogen-Related Fracture of Metals, EICM Proc., R.P. Gangloff and
M.B. Ives, Ed., National Association of Corrosion Engineers, 1990, p 21
8. H.K. Birnbaum, I.M. Robertson, D. Sofronis, and D. Teter, Mechanism of Hydrogen-Related Fracture—
A Review, CDI '96, T. Magnin, Ed., The Institute of Materials, 1997, p 172
9. M.-J. Lii, X.-F. Chen, Y. Katz, and W.W. Gerberich, Dislocation Modeling and Acoustic Emission
Observation of Alternating Ductile/Brittle Events in Fe-3wt%Si Crystals, Acta Metall., Vol 38, 1990, p
2435–2452
10. S.-H. Chen, Y. Katz, and W.W. Gerberich, Crack Tip Strain Fields and Fracture Microplasticity in
Hydrogen Induced Cracking of Fe-3wt%Si Single Crystals, Philos. Mag. A, Vol 63 (No. 1), 1990, p
131–155
11. W. Zielinski and W.W. Gerberich, Crack-Tip Dislocation Emission Arrangements for Equilibrium: Part
I—In situ TEM Observations of Fe-2wt%Si, Acta Metall. Mater., Vol 40, 1992, p 2861–2871
12. H. Huang and W.W. Gerberich, Crack-Tip Dislocation Emission Arrangements for Equilibrium: Part
II—Comparisons to Analytical and Computer Simulation Models, Acta Metall. Mater., Vol 40, 1992, p
2873–2881
13. P. Marsh, W. Zielinski, H. Huang, and W.W. Gerberich, Crack-Tip Dislocation Emission Arrangements
for Equilibrium: Part III—Applications to Large Applied Stress Intensities, Acta Metall. Mater., Vol 40,
1992, p 2883–2894
14. R.P. Harrison, K. Loosemore, I. Milne, and A.R. Dowling, CEGB R/H/R6 Rev 2, General Electricity
Generating Board, United Kingdom, 1986
15. E.A. Steigewald, F.W. Schaller, and A.R. Troiano, Trans. Metall. Soc. AIME, Vol 218, 1960, p 832
16. A.R. Troiano, Trans. ASM, Vol 52, 1960, p 54
17. H. Huang and W.W. Gerberich, Quasi-Equilibrium Modeling of the Toughness Transition During
Semibrittle Cleavage, Acta Metall. Mater., Vol 42 (No. 3), 1994, p 639–647
18. M.S. Daw and M.I. Baskes, Phys. Rev. B, Vol 29, 1984, p 6443
19. N.R. Moody, J.E. Angelo, S.M. Foiles, M.I. Baskes, and W.W. Gerberich, Atomistic Simulation of the
Hydrogen-Induced Fracture Process in an Ion-Based Superalloy, Sixth Israel Materials and Engineering
Conf., D. Itshak, D. Iliezer, and J. Haddad, E., Ben-Gurion University of the Negev, 1993, p 444
20. C.L. Fu and G.S. Painter, J. Mater. Res., Vol 6, 1991, p 719
21. X. Chen, T. Foecke, M. Lii, Y. Katz, and W.W. Gerberich, The Role of Stress State on Hydrogen-
Induced Cracking in Fe-Si Single Crystals, Eng. Fract. Mech., Vol 35 (No. 6), 1989, p 997–1017
22. C.D. Beachem, Metall. Trans., Vol 3, 1972, p 437
23. S.P. Lynch, Environmentally Assisted Cracking, Overview of Evidence for an Adsorption Induced
Localized Slip Process, Acta Metall., Vol 20, 1988, p 2639
24. G. Bond, I.M. Robertson, and H.K. Birnbaum, The Influence of Hydrogen on Deformation and Fracture
Processes in High Strength Aluminum, Acta Metall., Vol 35, 1987, p 2289
25. T. Matsumoto, J. Eastman, and H.K. Birnbaum, Direct Observations of Enhanced Dislocation Mobility
Due to Hydrogen, Scr. Metall., Vol 15, 1981, p 1033
26. T. Tabata and H.K. Birnbaum, Direct Observations of the Effects of Hydrogen on the Behavior of
Dislocations in Iron, Scr. Metall., Vol 17, 1993, p 947
Evaluation of Environmentally Assisted Crack Growth
Y. Katz, N. Tymiak, and W.W. Gerberich, University of Minnesota
Hydrogen Embrittlement Tests
Hydrogen embrittlement testing includes a wide variety of industrial and research methods. Industrial methods
are often directed toward the prevention and control of hydrogen embrittlement from processing operations
(such as plating) process and maintenance chemicals. These procedures are covered in ASTM F 519, “Standard
Method for Mechanical Hydrogen Embrittlement Testing of Plating Processes and Aircraft Maintenance
Chemicals.” Other industrial methods include sustained or step-load stress tests to evaluate the effectiveness of
the hydrogen embrittlement relief treatments on hardware such as springs or structural fasteners.
With the development of fracture mechanics, conventional test methods have been modified for measurements
in terms of crack nucleation, crack growth rate, and threshold stress-intensity values. Many research techniques
have also been developed in order to obtain a more fundamental understanding of hydrogen embrittlement.
Examples of research methods include:
• Measurement of threshold values under monotonic/cyclic loads (Ref 6, 27, 28, 29, 30, and 31)