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Showing papers on "Fractography published in 1980"


Journal ArticleDOI
Robert P. Wei1, P. S. Pao, R. G. Hart1, T. W. Weir1, G. W. Simmons1 
TL;DR: In this article, the authors investigated the influence of water vapor on fatigue crack growth in aluminum alloys and showed that at a frequency of 5 Hz, the rate of crack growth is essentially unaffected by water vapor until a threshold pressure.
Abstract: Fracture mechanics and surface chemistry studies were carried out to develop further understanding of the influence of water vapor on fatigue crack growth in aluminum alloys. The room temperature fatigue crack growth response was determined for 2219-T851 aluminum alloy exposed to water vapor at pressures from 1 to 30 Pa over a range of stress intensity factors (K). Data were also obtained in vacuum (at < 0.50 μPa), and dehumidified argon. The test results showed that, at a frequency of 5 Hz, the rate of crack growth is essentially unaffected by water vapor until a threshold pressure is reached. Above this threshold, the rates increased, reaching a maximum within one order of magnitude increase in vapor pressure. This maximum crack growth rate is equal to that obtained in air (40 to 60 pct relative humidity), distilled water and 3.5 pct NaCl solution on the same material. Parallel studies of the reactions of water vapor with fresh alloy surfaces (produced either byin situ impact fracture or by ion etching) were made by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The extent of surface reaction was monitored by changes in the oxygen AES and XPS signals. Correlation between the fatigue crack growth response and the surface reaction kinetics has been made, and is consistent with a transport-limited model for crack growth. The results also suggest that enhancement of fatigue crack growth by water vapor in the aluminum alloys occurs through a “hydrogen embrittle ment” mechanism.

123 citations


12 Dec 1980
TL;DR: In this article, the authors examined the kinetics of crack initiation and crack propagation in both liquid metal-induced and solid metalinduced cracking in the same system for the first time in MIE using electrical potential-drop measurements along the indium-covered portion of the sample gage length.
Abstract: : Metal-induced embrittlement (MIE) of 4140 steel by indium has been studied using delayed failure tensile tests. The temperature and stress dependence of the kinetics of crack initiation and crack propagation in both liquid metal-induced and solid metal-induced cracking have been examined in the same system for the first time in MIE. This was done using electrical potential-drop measurements along the indium-covered portion of the sample gage length to record the start and progress of cracking, and also through fractographic observations. In Part I of the report on this work, the experimental results are presented and their implications with regard to crack propagation are discussed. In Part II, various mechanisms proposed in the literature for crack initiation are evaluated in the light of the experimental results and other known characteristics of MIE, and a new mechanism is proposed which, it is believed, synthesizes and rationalizes the available evidence best. (Author)

78 citations


Journal ArticleDOI
TL;DR: In this paper, the same authors examined the fracture surfaces of IMI-685 and Ti-11 with and without a 5 min load dwell and found that the crystallographic planes of the facets were near basal for the latter and more random for the former.
Abstract: Flat regions (facets) found on fracture surfaces caused by initiation and propagation of fatigue cracks through the titanium alloys IMI-685 tested with and without a 5 min load dwell and Ti-11 have been examined using selected area electron channeling. The crystallographic planes of the facets have been identified as being near basal for the IMI-685 and more random for the Ti-11. None of the dwell specimens showed a pure basal facet orientation. The plastic zone size was also assessed and found to correlate approximately with stress intensity, allowing confirmation of crack initiation sites as determined by fractography. One case of beta to alpha-beta transformation crystallography is also examined. A partial channeling map for titanium is presented.

71 citations


Journal ArticleDOI
TL;DR: In this paper, critical flaws were determined by fractography in several ceramic bodies having internal stresses due to thermal expansion anisotropy, phase transformations, or second phases, and the projected contribution of internal stresses to failure was consistent with simple estimates of their levels as the flaw size decreases to about the grain size.
Abstract: Critical flaws were determined by fractography in several ceramic bodies having internal stresses due to thermal expansion anisotropy, phase transformations, or second phases. Fracture energies calculated using the observed flaw sizes and shapes agreed well with those measured by fracture-mechanics techniques at large flaw sizes. However, at smaller flaw sizes, calculated fracture energies decreased with decreasing flaw size. This decrease is attributed to internal stresses which increasingly contribute to failure as flaw sizes approach the sizes dominated by tensile components of these internal stresses. These components, in turn, are due to statistical variations of grain orientation. The projected contribution of internal stresses to failure is consistent with simple estimates of their levels as the flaw size decreases to about the grain size. Thus, application of fracture mechanics must take into account an increasing contribution of internal stresses as flaw sizes decrease in bodies in which these stresses can exist.

60 citations


Journal ArticleDOI
TL;DR: In this paper, the fracture surface energy was determined for boron carbide specimens with 0 to 15% porosity in a cylindrical pore model, and the fracture energy appeared to be independent of porosity but was inversely related to temperature.
Abstract: Young's modulus at room temperature and the fracture surface energy, up to 1200°C, were determined for boron carbide specimens with 0 to 15% porosity. Sonic modulus measurements indicated that the Young's modulus decreased as porosity increased in a manner characteristic of the cylindrical pore model. The fracture surface energy appeared to be independent of porosity but was inversely related to temperature. Fractography supported the low values of fracture surface energy that were obtained.

51 citations



Journal ArticleDOI
TL;DR: In this article, the influence of the presence or absence of elastic mismatch between the dispersed and matrix phases on local crack particle interactions in brittle composites was investigated, and the role of interfacial bond strength was also investigated in the presence of elastic stress concentrations.
Abstract: The influence of the presence or absence of elastic mismatch between the dispersed and matrix phases on local crack particle interactions in brittle composites is reported. The role of interfacial bond strength is also investigated in the presence of elastic stress concentrations. The optimum toughness possible for a brittle composite results when G i⩽G m, (G i, G m — elastic rigidity moduli for inclusion and matrix), and the interfacial bond strength is sufficient to allow plastic deformation of the dispersed phase. The dispersion of a ductile second phase with high interfacial bond strength but G i>G m, reduces effective crack/particle interactions. To increase the toughness in this case, weak interfacial bonding is necessary. Ultrasonic fractography was used to verify the local crack/particle interactions in detail.

32 citations


Journal ArticleDOI
01 Jan 1980-Carbon
TL;DR: In this paper, the fracture toughness and slow crack growth behavior of polycrystalline graphites, oxidized to 5, 10 and 20% weight losses, were measured in air at room temperature.

31 citations


01 Apr 1980
TL;DR: In this paper, an experimental program was conducted to investigate the possible degradation in mechanical properties of silicon-based ceramics exposed to high temperature oxidizing environments, including flexural stress rupture at 1200 C and stepped temperature stress rupture (STSR) experiments.
Abstract: : An experimental program was conducted to investigate the possible degradation in mechanical properties of silicon-based ceramics exposed to high temperature oxidizing environments. Thirteen materials were studied, all with potential for use in energy conversion devices such as the gas turbine. The materials ranged from some of the better known silicon nitrides and carbides to experimental grades. Testing included flexural stress rupture at 1200 C and stepped temperature stress rupture (STSR) experiments. The latter test was devised for this study and is a variation of the stress rupture test in which a range of temperatures is employed. The purpose of the STSR test is to explore the potential stress/temperature regimes of static fatigue failure. In addition, a combined cycle durability sequence was applied to selected materials. This procedure is a simple service simulation involving static heat soaks and rapid thermal cycling on bend bars. In nearly all cases, material degradation and/or time-dependent failure was observed. Extensive fractography was conducted to identify mechanisms of failure.

23 citations


Journal ArticleDOI
01 Jan 1980-Carbon
TL;DR: In this paper, the authors measured subcritical crack growth in polycrystalline graphites in air at room temperature and found that the crack growth was correlated with processing conditions and microstructure.

17 citations


Journal ArticleDOI
TL;DR: In this article, stress corrosion cracking of aluminum alloy 7039 was investigated by following the kinetics of crack propagation as a function of environmental and metallurgical variables, including stress direction vs grain orientation, solution temperature, addition of an oxidizing inhibitor, and application of a cathodic potential.
Abstract: Stress corrosion cracking (SCC) of aluminum alloy 7039 was investigated by following the kinetics of crack propagation as a function of environmental and metallurgical variables. The variables included: stress direction vs grain orientation, solution temperature, addition of an oxidizing inhibitor, and application of a cathodic potential. Experiments were carried out in a 3.5% NaCl solution on precracked DCB specimens. The morphology of the cracking was studied by SEM fractography. The possibility of creep being the rate controlling step in crack propagation, under the specific conditions of this study, is discussed in the light of experimental results.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the mechanism of hot shortness in 12L14 + Te steels, which might lead to a hot-rolling practice to minimize the high yield losses in this grade.
Abstract: This investigation was aimed at understanding the mechanism of hot-shortness in AISI 12L14 + Te steels, which might lead to a hot-rolling practice to minimize the high yield losses in this grade. High temperature tensile tests showed a pronounced loss in ductility between 810 and 1150 °C, the embrittlement being most severe at about 980 °C. Electron microprobe studies confirmed thermodynamic stability data which indicated that tellurium occurs primarily as PbTe in this steel composition. SEM fractography revealed increasingly brittle, partially intergranular tensile fracture with a loss of ductility. Auger Electron Spectroscopy of samples quenched from the embrittlement temperature range indicated the formation of a thin film of PbTe on the grain boundary surfaces. All these results are consistent with a mechanism of liquid metal embrittlement by PbTe which has a melting point of 923 °C. Some theoretical considerations of this mechanism are discussed. The characteristic return to ductility above the embrittlement range suggests that rolling at temperatures above 1150 °C might minimize the hot-shortness problem. Results of limited hot-rolling experiments to study the incidence of surface cracking as a function of temperature support the above suggestion.

Journal ArticleDOI
TL;DR: In this article, the relationship between surface energetics and adhesion is reviewed and new data that confirm such relationships, for peel tests as well as lap shear tests, are presented.
Abstract: The relationships between surface energetics and adhesion are critically reviewed. New data that confirm such relationships, for peel tests as well as lap shear tests, are presented. The effect of hydrothermal aging of aluminum surfaces on surface energetics can be used to predict degradation in bond strength. The mechanism of failure for elastic adhesives (such as Scotch ® tape) in peel tests may be essentially the same as for more brittle adhesives (such as epoxies) in lap shear tests. This mechanism may involve brittle fracture that forms a critical flaw at the adherend-adhesive interface (on a microscopic level), followed by crack propagation which then may include considerable elastic and plastic deformation. The locus of propagation (fractography) is generally not (but may be) relevant to the problem of how to remedy mechanical weakness in an adhesive joint, since the local region of critical flaw formation rather than the general surface area determines the joint strength.

Journal ArticleDOI
TL;DR: In this paper, the effect of heat treatment on the JIC fracture toughness behavior of Alloy 718 was characterized at room temperature, 427°C and 538°C, and two different heat treatments were used: the conventional (ASTM A637) treatment, and a modified heat treatment designed to improve the toughness of alloy 718 base metal and weldments.
Abstract: The effect of heat treatment on the JIC fracture toughness behavior of Alloy 718 was characterized at room temperature, 427°C and 538°C. Two different heat treatments were used: the conventional (ASTM A637) treatment, and a modified heat treatment designed to improve the toughness of Alloy 718 base metal and weldments. The elastic-plastic JIC fracture toughness response of the modified Alloy 718 was found to be superior to the JIC behavior exhibited by the conventional material over the entire test temperature range. Metallographic and fractographic examinations of Alloy 718 fracture surfaces revealed that the inferior fracture resistance of the conventional superalloy was attributed to the presence of coarse δ precipitates throughout the conventional matrix. The increased fracture toughness response of the modified Alloy 718 was related to the dissolution of coarse δ precipitates during the high temperature solution anneal employed in the modified treatment.

Journal ArticleDOI
TL;DR: In this article, a fracture mechanics and fractographic study of stress corrosion cracking (SCC) of heat treated HY-180 M steel was undertaken over the temperature range 22 to 95 °C at applied potentials of −0.28 VSHE (−0.48 VAg/AgCl) and − 0.80 VSHH (−1.0 VAg /Agcl).
Abstract: A fracture mechanics and fractographic study of stress corrosion cracking (SCC) of heat treated HY-180 M steel was undertaken over the temperature range 22 to 95 °C at applied potentials of −0.28 VSHE (−0.48 VAg/AgCl) and −0.80 VSHE (−1.0 VAg/Agcl). Particular attention was directed toward Region II behavior, where crack propagation rates were independent of stress intensity(K l). Region II rates were always higher at the less noble potential of −0.80 VSHE than at the more noble potential of — 0.28 VSHE. However, fractography studies suggested that the basic mechanism of cracking at both potentials was the same, and involved hydrogen embrittlement. An Arrhenius analysis of Region II rates showed that crack propagation was under the control of more than one process. Consequently, the mechanistic details remained obscure.

Journal ArticleDOI
TL;DR: In this paper, an impact test was conducted from room temperature to 500°C to get crack initiation and propagation energies as well as dynamic fracture toughness (K1d) of SKD 62 and SKT 4.
Abstract: Impact failure of hot forging die occurrs frequently from surface cracks due to fatigue or thermal fatigue. However, useful information for failure analysis of hot forging dies is scarce because few data exist on the fracture behavior and fractography of hot forging die steels. Therefore, instrumented impact tests were conducted from room temperature to 500°C to get crack initiation and propagation energies as well as dynamic fracture toughness (K1d) of SKD 62 and SKT 4. Fractographic analyses were carried out by SEM. Measurements of the stretched zone width (SZW) on the fracture surface of hot forging die was found useful to determine the fracture toughness and temperature at the time of hot forging die failure by using the obtained relationship between K1d and temperature or SZW. Low cycle fatigue life tests on the notched round bar specimens with or without such surface hardening as ion nitriding and tuftriding were also conducted to clarify the influence of surface hardening on low cycle fatigue strength. of SKD 62. The effect of ion nitriding (500°C×30hr) was found at the stress lower than 80% ultimate tensile strength of this steel and after 3×103 cycles. Striation appeared on the fracture surface after 102 cycles.

Journal ArticleDOI
TL;DR: In this paper, the influence of prior austenite grain size, ductile-brittle transition temperature and test temperature on impact fatigue crack growth rate was investigated by means of fracture mechanics and fractography in quenched and tempered Cr-Mo alloy steel.
Abstract: — Impact fatigue tests were carried out using a rotating-disk type impact fatigue testing machine The influence of prior austenite grain size, ductile-brittle transition temperature and test temperature on impact fatigue crack growth rate was investigated by means of fracture mechanics and fractography in quenched and tempered Cr-Mo alloy steel in which the prior austenite grain size was varied from 8–3 to 25-4 μm The results in impact fatigue tests were compared to those under non-impact conditions The crack growth rates associated with striation formation were insensitive to the change in prior austenite grain size, ductile-brittle transition temperature and test temperature regardless of impact and non-impact fatigue When the material was in the brittle condition, impact fatigue gave rise to a transition from striation formation to intergranular and cleavage cracking Such a transition will result in the acceleration of crack growth rate The Paris Law exponent values in impact fatigue were reasonably expressed by the ratio of test temperature to ductile-brittle transition temperature


Journal ArticleDOI
TL;DR: In this article, the authors used the J-R curve approach to evaluate the ductile to brittle temperature performance of a high yield strength structural steel (HY130) and to demonstrate that the single specimen unloading compliance method is applicable to evaluate J Ic values and J R curves for compact specimens tested at temperatures from −192 to 150°C.

Book ChapterDOI
TL;DR: Stress-corrosion cracking (SCC) studies were conducted in the following commonly used pressure vessel steels: ASTM A533 Grade B Class 1 (A533-B-1) plate and a fabricated forging that is equivalent in chemistry and thermomechanical processing to American-made A508 Class 2 (A508-2) forgings as discussed by the authors.
Abstract: Stress-corrosion cracking (SCC) studies were conducted in the following commonly used pressure vessel steels: ASTM A533 Grade B Class 1 (A533-B-1) plate and a fabricated forging that is equivalent in chemistry and thermomechanical processing to American-made ASTM A508 Class 2 (A508-2) forgings. The purpose of these studies was to determine the response of the materials in a simulated pressurized-water reactor environment. Round tensile specimens were bolt-loaded to 75 to 80 percent of yield and left in the water at 93°C for 2000 h. At the end of this time period, the specimens were taken out of the water, unloaded, and examined by scanning electron microscopy (SEM) and by energy-dispersive X-ray analysis. The specimen cut from A533-B-1 plate did not have any cracks as a result of the SCC tests. Several cracks, some of which were visible with the unaided eye, had developed in the specimen that was cut from the A508-2 forging. The polished and etched sections of the specimen that showed SCC, when examined with the SEM, revealed the presence of many microcracks starting from the outside surface and propagating along either inclusion-matrix or carbide-matrix interfaces; the corresponding microstructure was mostly pearlitic. The microstructure of the specimen that did not crack was bainitic; it had fewer inclusions and carbide particles, and no microcracks were observed. When the fracture surfaces of the larger cracks were examined by SEM, they revealed a cleavage-like failure propagating along inclusion bands. X-rayimage scansand energy spectra of these hands showed thatthey were silicate and manganese-sulfide inclusions. A hydrogen-assisted cracking model has been proposed to explain the experimental results on A508-2 forging. Produced by a cathodic reaction and aided by the stress fields, hydrogen diffuses ahead of the crack tip to the inclusion sites. This causes a preferential decohesion at the inclusion-matrix interfaces and subsequent cracking along inclusion bands. The absence of stress-corrosion cracking in A533-B-1 plate tested under identical experimental conditions is due mainly to fewer inclusion and carbide particles and to the more refined bainitic microstructure of this steel. This type of microstructure is less susceptible than the mainly pearlitic microstructure found in A508-2 forging to hydrogen-assisted cracking.

01 Jan 1980
TL;DR: In this article, the authors examined the fracture morphology of iron-chromium-nickel base alloys in either a hydrogen environment or in air following thermal charging with hydrogen Fracture surfaces were examined by scanning electron microscopy and were characterized by: changed dimple size, twin-boundary parting, transgranular cleavage, and intergranular separation.
Abstract: Tensile specimens of iron-chromium-nickel base alloys were broken in either a hydrogen environment or in air following thermal charging with hydrogen Fracture surfaces were examined by scanning electron microscopy Fracture morphology of hydrogen-embrittled specimens was characterized by: changed dimple size, twin-boundary parting, transgranular cleavage, and intergranular separation The nature and extent of the fracture mode changes induced by hydrogen varied systematically with alloy composition and test temperature Initial microstructure developed during deformation processing and heat treating had a secondary influence on fracture mode

01 Jan 1980
TL;DR: In this article, the same authors reported that fracture initiation appeared to be associated with subsurface flaws in high-strength specimens and both sub-surface and surface flaws in low-strength ones.
Abstract: Silicon powder wet milled in heptane was dried, compacted into test bar shape, helium-sintered, and then reaction bonded in nitrogen-4 vol% hydrogen. As-nitrided bend strengths averaged approximately 290 MPa at both room temperature and 1400 C. Fracture initiation appeared to be associated with subsurface flaws in high-strength specimens and both subsurface and surface flaws in low-strength specimens.

Journal ArticleDOI
TL;DR: In this paper, the influence of fracture mechanism on the stage 2 fatigue crack growth resistance in center-notch plate and compact type specimens of high-strength steel 4340 has been studied in relation to the different microstructure and stress intensity, particularly in a wide range of growth rate, by means of fracture mechanics and fractography.
Abstract: The influence of fracture mechanism on the stage 2 fatigue crack growth resistance in center-notch plate and compact type specimens of high-strength steel 4340 has been studied in relation to the different microstructure and stress intensity, particularly in a wide range of growth rate, by means of fracture mechanics and fractography. The fractographic examination has shown three general mechanisms of growth, namely a structure sensitive mechnism (stage 2a), a striation mechanism (stage 2b) and a pseudo-monotonic fracture mechanism like microvoid coalescence or intergranular cracking (stage 2c). Departure from the exclusively striation mechanism to include the pseudo-monotonic fracture mechanisms has been found to result in accelerated crack growth rates. The roles of microstructure, strength level and fracture mechanics parameters in promoting the different crack growth behaviour was also discussed.

Book ChapterDOI
01 Jan 1980
TL;DR: This paper illustrates that fractography is useful to both scientists and practical engineers, since it has proved valid in the interpretation of fracture processes as well as in the diagnosis of causes of failure.
Abstract: This paper reviews the techniques used in fractography, i.e. in the study of fracture surfaces, and discusses their relative advantages. It also describes the most typical fracture surface features and the information that they can provide. Finally, it illustrates that fractography is useful to both scientists and practical engineers, since it has proved valid in the interpretation of fracture processes as well as in the diagnosis of causes of failure.


Journal ArticleDOI
TL;DR: In this paper, the influence of ductile-brittle transition temperature and test temperature on the impact fatigue crack growth rate was investigated by means of fracture mechanics and fractography in quenched and tempered Cr-Mo alloy steel in which the prior austenite grain size was varried from 8.3 to 25.4μm.
Abstract: The impact fatigue tests were carried out using a rotating disk type impact fatigue testing machine. The influence of ductile-brittle transition temperature and test temperature on the impact fatigue crack growth rate was investigated by means of fracture mechanics and fractography in quenched and tempered Cr-Mo alloy steel in which the prior austenite grain size was varried from 8.3 to 25.4μm, and the results of impact fatigue tests were compared with those of non-impact fatigue tests. The results obtained were as follows.(1) The impact fatigue and non-impact fatigue crack growth rates associated with striation formation at stage IIb were insensitive to the change in ductile-brittle transition temperature and test temperature.(2) In impact fatigue, it was found that the impact loading gave rise to transition of dominant fracture appearance from striation formation at stage IIb to intergranular cracking and cleavage at stage IIc as the Charpy impact value was decreased.(3) In impact fatigue, the transition of dominant fracture appearance from exclusively striation formation to intergranular cracking and cleavage was found to result in the acceleration of crack growth rate. The relation between the m value in Paris's equation and the ratio of test temperature, T, to ductile-brittle transition temperature, TM, was expressed as follows.m=1.12(T/TM)-1.99.

ReportDOI
01 Apr 1980
TL;DR: In this article, the microstructural aspects that influenced the room temperature and elevated temperature fatigue-crack propagation response of Alloy 718 fracture surfaces were studied, and the fracture surfaces exhibited a faceted appearance at low-Delta levels, which is indicative of crystallographic fracture along intense inhomogeneous slip bands.
Abstract: The microstructural aspects that influenced the room temperature and elevated temperature fatigue-crack propagation response of annealed, conventional, and modified heat-treated Alloy 718 were studied Electron fractographic examination of Alloy 718 fatigue fracture surfaces revealed that operative crack growth mechanisms were dependent on heat treatment, heat-to-heat variations, temperature, and prevailing crack tip stress intensity level In the low temperature regime (below 538{sup 0}C), all fracture surfaces exhibited a faceted appearance at low {Delta} levels, which is indicative of crystallographic fracture along intense inhomogeneous slip bands The facets in the modified Alloy 718, however, were found to be rather poorly defined since the modified heat treatment tends to promote more homogeneous slip processes Under progressively higher stress intensity levels, the room temperature and elevated temperature fatigue fracture surfaces exhibited striations, followed by a combination of striations and dimple rupture at the highest {Delta} values Striation spacing measurements in all three heat-treated conditions were generally found to be in agreement with macroscopic growth rates at 24 and 538{sup 0}C Under high temperature conditions (above 538{sup 0}C), evidence of intergranular fracture was also detected on the fatigue fracture surfaces, particularly at low stress intensity levels This intergranular failure mechanism was found to be more extensive in the modified heat-treated Alloy 718 17 figures


Book ChapterDOI
01 Jan 1980
TL;DR: In this article, the Mises hypothesis was applied to the tensile adhesive joint as the fracture criterion and the ultimate tensile properties of the joint were found to be associated with the viscoelastic nature of the adhesive rather than with a thermodynamic criterion.
Abstract: The present investigation was undertaken to verify the criterion of the interfacial bond failure. The time-temperature superposition, the failure envelope, the dependence of the tensile bond strength on the degree of crystallinity and the fractography of the interfacial region of the adhesive were observed by the use of steel-nylon 12-steel cross lap joint. The ultimate tensile properties of the joint were found to be associated with the viscoelastic nature of the adhesive rather than with a thermodynamic criterion. The experimental results suggest that the Mises hypothesis can be applied to the tensile adhesive joint as the fracture criterion.

Journal ArticleDOI
TL;DR: In this paper, the crack propagation of a 304 stainless steel under repeated load at elevated temperatures was examined using specimens of different size to clarify the successful correlating parameter, and the results were discussed in the light of electron fractography.
Abstract: The crack propagation of a 304 stainless steel under repeated load at elevated temperatures was critically examined using specimens of different size to clarify the successful correlating parameter, and the results were discussed in the light of electron fractography. The crack propagation rate at 250 and 500°C where creep is not significant in this material was correlated with the stress intensity