Showing papers on "Paris' law published in 1978"
400 citations
TL;DR: In this paper, a simple model was proposed which qualitatively accounts for all observed notch phenomena including non-propagating cracks and size effects, and quantitatively predicts the experimental fatigue failure limit of sharply notched specimens.
267 citations
TL;DR: In this paper, the authors used the acoustic emission technique to monitor fatigue crack growth, and attributed the peak load emissions to both crack extension and deformation and fracture events occurring within the crack tip plastic zone, and these emissions have been correlated with the energy released during crack growth.
240 citations
Book•
30 Apr 1978
TL;DR: A survey of studies on fatigue changes in different metals can be found in this paper, where the authors present several methods of studying fatigue phenomena, including the thermal etching method, the Ionic bombardment method, and the fracture initiation model.
Abstract: 1 Fundamental concepts and fatigue processes.- 1.1 Fatigue stresses.- 1.2 Wohler fatigue diagrams.- 1.3 The low-cycle range.- 1.3.1 General testing methods. Fundamental formulae.- 1.3.2 The influence of various factors and testing conditions. Hardening and softening hypotheses.- 1.4 The stages in fatigue processes.- References.- 2 Fatigue phenomena.- 2.1 Introductory remarks.- 2.2 Slip bands.- 2.2.1 Slip bands in the region above the fatigue limit.- 2.2.2 Slip bands in the range below the fatigue limit.- 2.3 Extrusions and intrusions.- 2.3.1 Extrusions and intrusions in polycrystalline iron and copper.- 2.3.2 Models and hypotheses of extrusion and intrusion formation.- 2.4 Fatigue cracks.- 2.4.1 Crack sources and propagation.- 2.4.2 Microcracks in polycrystalline iron.- 2.5 Supplementary methods of studying fatigue phenomena.- 2.5.1 Fatigue phenomena and changes in physical properties.- 2.5.2 Ionic bombardment (etching) method.- 2.5.3 The thermal etching method.- 2.5.4 Fatigue phenomena and surface microroughness.- 2.6 A survey of studies on fatigue changes in different metals.- 2.6.1 Face-centered cubic metals and alloys.- 2.6.2 Body-centered cubic metals and alloys.- 2.6.3 Hexagonal close-packed metals.- 2.6.4 Microcracks initiation in electroplated steel samples.- 2.7 Theories of fatigue.- 2.7.1 General remarks and early theories.- 2.7.2 Dislocation theories and crack initiation models.- 2.7.3 Statistical theories.- 2.7.4 Energy theories.- References.- 3 Fatigue dislocation structures.- 3.1 Introduction.- 3.2 The dislocation structure in face-centered cubic metals and alloys.- 3.2.1 Copper and its alloys.- 3.2.2 Aluminium and aluminium alloys.- 3.2.3 Austenitic steels.- 3.2.4 Other metals and alloys.- 3.3 The dislocation structure in body-centered cubic metals and alloys.- 3.3.1 Iron and iron alloys.- 3.3.2 Non-ferrous metals and alloys.- 3.4 The dislocation structure in hexagonal close-packed metals and alloys.- 3.5 An attempt at a synthesis.- References.- 4 Fatigue crack growth.- 4.1 General remarks.- 4.2 Description of crack growth.- 4.3 Fundamental relations for determining the fatigue crack growth rate.- 4.4 The influence of loading conditions on fatigue crack propagation rates. Sundry problems (Examples).- 4.5 Non-propagating fatigue cracks.- References.- 5 Fatigue fractures.- 5.1 Introduction.- 5.2 Classification of fractures and their characteristic features.- 5.2.1 General classification of fractures.- 5.2.2 The fundamental types of fracture.- 5.3 The macrostructure of fatigue fractures.- 5.3.1 Specific features of fracture surfaces.- 5.3.2 The macrostructure of fractures and the loading mode (Examples).- 5.4 The microstructure of fatigue fractures.- 5.4.1 General remarks.- 5.4.2 Fatigue striations.- 5.4.3 Tire tracks.- 5.4.4 Examples of fracture microstructure and their interpretations.- 5.4.5 Concluding remarks.- References.
204 citations
TL;DR: In this paper, the authors measured the fatigue crack growth rate (FCGR) of Alloy 718 on CT type specimens at 298 and 823 K and found that a substantial increase in FCGR occurred at low stress intensity levels, as the temperature was increased from 298 to 823 k and as the frequency was decreased at 823k.
Abstract: The fatigue crack growth rate (FCGR) of Alloy 718 was measured on CT type specimens at 298 and 823 K. At 823 K, the influence of frequency was studied in the range between 5 – 10-3 Hz and 20 Hz, using a sinusoidal wave form signal. A substantial increase in FCGR occurred, particularly at low stress intensity levels, as the temperature was increased from 298 to 823 K and as the frequency was decreased at 823 K. At elevated temperature, the effect of cyclic stress wave form was equally investigated, using triangular and square wave form signals producing the same frequency of 5.10-2 Hz. The triangular load led to higher FCGR than the square wave form. In addition the hold time of 10 s both at the maximum and the minimum load associated with the square load had no significant effect on the FCGR. Electron microscopy was used to observe the substructures that developed ahead of fatigue cracks. These observations showed that in certain circumstances plastic deformation proceeded by the propagation of planar bands which were identified as twins. At room temperature, twinning was found to be abundant only in the threshold regime. At 823 K, twinning was observed in the domain of higher FCGR, particularly at low frequencies. Fractography was carried out to study the micromechanisms of crack propagation. At 823 K. intergranular cracking occurred as the frequency was decreased. The comparison between the substructures formed in low cycle fatigue and those associated with the plastic zones of propagating cracks is made. The importance of planar deformation and twinning on intergranular cracking and on the acceleration of FCGR when the loading rate is decreased at 823 K, is discussed.
119 citations
TL;DR: In this article, it is proposed that internal compressive stresses as induced by a positive local volume change can retard crack growth, and measurements of fatigue crack growth rates of specially designed austenitic alloys with test temperature T and martensite temperature Ms are used to test this hypothesis.
94 citations
TL;DR: In this article, an automated test system utilizing computer control was developed to obtain crack growth rate data down to the fatigue crack growth threshold with a decreasing stress intensity technique and compact type specimens.
Abstract: An automated test system utilizing computer control was developed to obtain crack growth rate data down to the fatigue crack growth threshold with a decreasing stress intensity technique and compact type specimens. The starting stress intensity range ΔK0 was chosen to yield crack growth rates in the range of 2.54 × 10−8 m/cycle (10−6 in./cycle) and subsequent values of ΔK are controlled to the equation ΔK = ΔK0 exp [C(a − a0)] (a0 and a are the initial and instantaneous crack lengths and C is a test variable). Crack length is continuously monitored by using the elastic compliance technique, thereby enabling ΔK to be decreased continuously. Comparison crack growth data were also obtained by the more conventional constant load amplitude or K-increasing method. Excellent agreement was observed between data obtained from the two procedures for a Society of Automotive Engineers 1045 steel at load ratios R of 0.1 and 0.5, an A356-T6 sand-cast aluminum alloy at load ratios of 0.1 and 0.8, and a 2219-T851 aluminum alloy at a load ratio of 0.1.
94 citations
01 May 1978
TL;DR: In this paper, an ASTM standard for generating, analyzing and presenting fatigue crack growth rate data is proposed. And a new mathematical representation of wide-range fatigue crack data is also proposed which has advantages over existing representations.
Abstract: : Results are presented which provide the basis for the development of an ASTM standard for generating, analyzing and presenting fatigue crack growth rate data. Comprehensive data were also obtained on the individual and combined effects of load ratio, cyclic frequency, test temperature and environment on fatigue crack growth rates in a 10Ni steel and a 2219-T851 aluminum alloy. These data are used to demonstrate the utility of the proposed test methods. A new mathematical representation of wide-range fatigue crack growth rate data is also proposed which has advantages over existing representations.
89 citations
TL;DR: In this article, the authors determined fatigue crack growth rates for Ti-6Al-4V alloys with respective oxygen contents of 0.06, 0.18 and 0.20 wt pct.
Abstract: Fatigue crack growth rates have been determined for beta-annealed Ti-6Al-4V alloys with respective oxygen contents of 0.06, 0.11, 0.18 and 0.20 wt pct. For each of these alloys, transitional crack growth behavior has been observed which appears to correlate with a critical value of the reversed plastic zone size,viz the Widmanstatten packet size. Moreover, growth rates below transitional levels order in terms of packet size, with lower growth rates associated with larger packets. The present results suggest that intersti-tial oxygen content and prior beta grain size significantly affect fatigue crack growth rates through control of the Widmanstatten packet size.
74 citations
TL;DR: In this article, a mechanism of retardation is proposed, deriving from metallographic observations, for aluminum alloys, based on the rate of overload and its intensity, but other factors such as the number of overloads and the frequency of the test are considered.
65 citations
TL;DR: In this paper, the authors compared the strain intensity factor for both linear elastic and high strain fatigue crack growth tests in cast Cr-Mo-V steels at 550 °C and found that there was a good correlation of rates in air and under vacuum in terms of strain intensity factors in conditions where there was no significant creep damage.
TL;DR: In this article, it was shown that the /3-transus-transformer is more stable when the ratio of the number of /3transus to the length of the transition is higher than 0.01 to 0.25 mm.
Abstract: The m i c r o s t r u c t u r e s r e su l t i ng f rom /3-processing or /3-annealing of a +/3 t i t an ium al loys have r ecen t ly been cons idered for room and elevated t e m p e r a t u r e appl ica t ions of ae rospace components . These m i c r o s t r u c t u r e s offer improved creep, 1 f r ac tu r e toughness and fatigue c rack propagat ion e p rope r t i e s over those of a 4,13 p roces sed and heat t r ea ted m i c r o s t r u c t u r e s . The potent ia l cost reduc t ion due to lower p r e s s load r e q u i r e m e n t s and be t t e r shape def in i t ions s'a make the m i c r o s t r u c t u r e s r e su l t i ng f rom s u p e r t r a n s u s forging an a t t r ac t ive choice for many eng inee r ing appl ica t ions . When cooled f rom above the /3transus t empe ra tu r e , the /3-phase t r a n s f o r m s into ~ -p l a t e l e t s separa ted by f i lms of/3. Between the a ma t r ix and the /3 f i lms , e lect ron mic roscopy r evea l s an in te r face phase, the na ture Of which was invest igated by Rhodes and Will iams.S The a p la te le t s can be a r r a n g e d in a basketweave mor phology 6 or in packets of s i m i l a r l y a l igned p la te le t s cal led colonies. The mean in te rcep t d i ame te r of the colonies may va ry in s ize f rom 0.01 to 0.25 mm. The tendency to t r a n s f o r m into large colonies of c~-platelets will i n c r e a s e with the dec rea se in the content of/3 s tab i l i z ing e lements , with the i n c r e a s e of the /3-solut ion t r e a t m e n t t e m p e r a t u r e and t ime, with the dec rea se of the amount of /3-work and with d e c r e a s i n g cooling r a t e s . The re fo re the la rge colony s t r uc tu r e is more l ikely to occur in th ick sec t ions of fi-worked or /3-annealed near -a t t i t an ium al loys like Ti-112 and IMI6857 (Fig. 1). An inves t iga t ion of the p r o p e r t y m i c r o s t r u c l u r e r e l a t i onsh ips in these two al loys showed that the s ize and the c rys ta l lograph ic o r ien ta t ion of the colon ies a re the con t ro l l ing e l emen t s in d e t e r m i n i n g prope r t i e s such as fatigue life and fatigue c rack growth ra te . The fatigue c racks in this m i c r o s t r u c t u r e tend to in i t ia te and propagate in s t ra igh t l ines a c r o s s the pla te le t colonies as shown in Fig. 1 for an IMI-685 fatigue c rack growth spec imen . This type of c rack ing is r e l a t ed to the in tense shear bands observed in the same spec imens ac ros s the colonies . 2'7 An inves t igat ion of fatigue c rack propagat ion in ex t r eme ly large colonies of T i l l s showed that in tense shear bands always precede the a c r o s s the colony fatigue f r a c t u r e . Unstable shear r e l a t ed f r ac tu r e s in monotonic loading have been observed in other /3 -processed Ti a l loys such as the T i -6A1-2Sn-4Zr -2Mo n e a r ~ al loy. 1~ It is be l ieved that this deformat ion mode is r e spons ib l e for the reduc t ion in the t ens i l e duct i l i ty of f l -annealed mic r o s t r u c t u r e s . The shear r e l a t ed f r ac tu r e domina tes the fatigue c rack in i t ia t ion (Location A in Fig . 1), as well as the fatigue c rack propagat ion (Location B), at low and in t e rmed ia t e s t r e s s in tens i ty r anges . The shear re la ted fatigue in i t i a t ion c rack in la rge colonies can cause a seve re life reduc t ion as was observed for /3-annealed Ti 6A1-4V. 9 On the other hand the shear
TL;DR: In this paper, the authors measured fatigue crack growth rates over wide ranges of stress intensities (from threshold to nearly critical stress intensity) on HY130 steel in 3.5% sodium chloride aqueous solution at several cyclic frequencies, stress ratios, and potentials.
Abstract: Fatigue crack growth rates over wide ranges of stress intensities (from threshold to nearly critical stress intensity) were measured on HY130 steel in 3.5% sodium chloride aqueous solution at several cyclic frequencies, stress ratios, and potentials. The growth rates are compared with reference data measured in laboratory air. The growth rate curves for both environments can be approximated by two linear sections converging at low stress intensity ranges to the same threshold, which depends only on the stress ratio. The upper parts of the lines with lower slopes converge again to the point where maximum stress intensity approaches its terminal value. As a result, the maximum environmental acceleration of crack growth appears at intermediate stress intensities, and it increases with decreasing frequency and potential. Data indicate a relatively low susceptibility of HY130 steel to corrosion fatigue. With increasing stress ratio R the fatigue crack growth threshold is shifted to lower stress intensity ranges by the same amount in both air and salt water environments. The effect of R on growth rate can be introduced into a power law expression.
TL;DR: In this article, the effects of microstructure on the fatigue and creep crack growth of Waspaloy and P/M Astroloy were evaluated at 650°C.
Abstract: The effects of microstructure on the fatigue and creep crack growth of Waspaloy and P/M Astroloy were evaluated at 650°C. In Waspaloy, changes in γ′ size and distribution did not markedly affect fatigue crack growth. An increase in fatigue crack growth rate occurred at low test frequencies and was associated with a transition to intergranular crack propagation. In P/M Astroloy, a coarser grain size lowered the fatigue crack growth rate. Serrated grain boundaries, though beneficial under creep loading, have no effect in fatigue.
TL;DR: In this article, the authors examined the factors influencing the occurrence of intergranular fracture during fatigue crack growth tests of quenched and tempered steels and found that failure along prior austenite grain boundaries may be divided into two types.
Abstract: The factors influencing the occurrence of intergranular fracture during fatigue crack growth tests of quenched and tempered steels have been examined. It is found that failure along prior austenite grain boundaries may be divided into two types. One type is found at high proof strength levels in steels in which impurities have segregated to the grain boundaries and is responsible for increased fatigue crack growth rates. The other is confined to environments containing water vapour and does not appear to significantly influence crack growth rates. The occurrence of the latter mode is thought to be related to hydrogen derived from the water vapour. A model describing hydrogen diffusion to regions of hydrostatic stress ahead of the crack tip can account for the observed variation of intergranular failure with crack velocity, mean load, and steel purity levels.
TL;DR: In this paper, a model of fatigue crack growth is proposed that utilizes the recent developments in notch analysis of fracture and a concept of size effect that results from the changes in the critically stressed volume ahead of a crack tip.
Abstract: A model of fatigue crack growth is proposed that utilizes the recent developments in notch analysis of fracture and a concept of size effect that results from the changes in the critically stressed volume ahead of a crack tip. Accordingly, the fatigue crack growth mechanism involves local stresses reaching the theoretical cohesive strength and causing brittle fracture of atomic bonds at nominal stresses near the threshold, whereas slip-plane decohesion and plastic blunting and resharpening of the crack tip process may occur at stresses above the threshold range. The model contains three material parameters σFF nF, and ρF, that conveniently extend continuum analysis to situations where inhomogeneity of the material structure can influence the behavior appreciably. The analytical expression from the model was found to correlate fatigue crack growth data reasonably well in the low and intermediate stress ranges in Al 2024-T3, Al 7075-T6 and 250 grade maraging steel. The fracture modes observed are in agreement with the predictions from the model. The same fatigue crack growth model can be extended to estimating the threshold stress intensity factor range, ΔKo and fatigue notch sensitivity of different materials.
TL;DR: In this paper, the effect of R (minimum load/maximum load) on fatigue crack growth in tests on CMoV steels at 550°C was investigated under oxidising conditions.
TL;DR: In this paper, the effect of microstructures produced by different ingot processing techniques on the fatigue properties of a 7050 aluminum alloy was investigated, and the results showed that total fatigue life, both low and high cycle, were not greatly affected by the grain structures of the experimental materials.
Abstract: A study was undertaken to determine the effect of microstructures produced by different ingot processing techniques on the fatigue properties of a 7050 aluminum alloy. The different microstructures investigated were produced by hot-rolling to simulate commercial processing (CP) methods or intermediate thermomechanical treatments (ITMT). Characterization of the microstructures revealed that the CP 7050 material was partially recrystallized (<50 pct) due to the use of hot-rolling as the final deformation step. The ITMT materials were examined in the as-recrystallized (AR) condition or in AR + hot rolled condition (AR + HR). Results of the investigation showed thattotal fatigue life, both low and high cycle, were not greatly affected by the grain structures of the experimental materials. However, metallographic studies indicated that crack initiation is probably more difficult in the fine-grained AR material. The results of fatigue crack growth tests showed that higher crack growth rates observed at low ΔK values for ITMT {dy7050} were most likely due to the detrimental effects of undissolved Al2CuMg particles. These particles, which also contribute to low fracture toughness and higher crack growth rates at high ΔK levels, are formed during a furnace-cooling step in the ITMT processing schedule.
TL;DR: The relationship between m and log C of Paris law for fatigue crack growth in a commercial low-alloy steel was examined over a range of material variables (microstructure, yield stress, toughness) and of experimental variables (thickness, load ratio, frequency).
TL;DR: In this article, the authors present sources of fracture toughness and fatigue crack growth data for metallic alloys, and present a three volume report on the fracture toughness, fatigue crack, and fracture crack growth of alloys.
Abstract: This Technical Memorandum presents sources of fracture toughness and fatigue crack growth data for metallic alloys. This is Part 3 of a three volume report.
TL;DR: In this article, the influence of steady mode III loading on the fatigue crack growth behavior of a Ti-5Al-2·5 Sn alloy subjected to mode I fatigue loading has been determined using circumferentially notched specimens.
Abstract: The influence of steady mode III loading on the fatigue crack growth behaviour of a Ti-5Al-2·5 Sn alloy subjected to mode I fatigue loading has been determined using circumferentially notched specimens. It was found that the superimposition of a constant torque (mode III) on the alternating tensile load (mode I) always gave rise to a very significant decrease in crack propagation rate. This decrease could reach two orders of magnitude for the highest values of KIII/∆KI. Moreover, a change in fracture path was shown to be associated with combined mode loading. While under mode I loading the crack was essentially transverse to the tensile axis, under combined mode I + mode III loading the crack front divided into facets inclined to the tensile loading axis. This change in fracture path is tentatively explained in terms of the influence of KImax and ∆KI on the fatigue crack growth rate of this alloy. Several factors which could contribute to the reduction in crack propagation rate observed under comb...
16 Aug 1978
TL;DR: In this paper, a ½Cr-½Mo-¼V steel heat treated to produce a range of microstructures was investigated for fatigue crack propagation in the threshold region, and large grain size precipitation-hardened ferritic micro-structures were found to give the highest threshold, the threshold being lower for higher strength bainitic or martensitic micro structures.
Abstract: Fatigue crack propagation in the threshold region has been investigated in a ½Cr-½Mo-¼V steel heat treated to produce a range of microstructures. Large grain size precipitation-hardened ferritic microstructures were found to give the highest threshold, the threshold being lower for higher strength bainitic or martensitic microstructures. Microstructure-sensitive fracture paths, intergranular failure, and Stage IIa crack growth were observed as the threshold was approached. S/N tests on the ½Cr-½Mo-¼V steel and a simple Fe-1V-0.2C alloy showed that the precipitation-hardened ferritic microstructures gave lower fatigue limits than tempered martensite. This indicates that there are conflicting microstructural requirements for resistance to fatigue crack initiation and to fatigue crack growth in these microstructures.
TL;DR: In this article, the effect of dwell-time at peak load on the fatigue crack propagation of a near-α alloy (Ti-11) and on α + β alloy(Ti-6A1-4V) was investigated.
Abstract: The effect of dwell-time at peak load on the fatigue crack propagation of a near-α alloy (Ti-11) and on α + β alloy (Ti-6A1-4V) was investigated. Several composition, microstructure and texture conditions were studied under fatigue cycling with a 5 min dwelltime. Three different product forms of Ti-6A1-4V were used: cross-rolled plate, highly textured plate and highly textured low interstitial plate. No deleterious effect on fatigue crack growth rate was observed for the 5 min swell cycling when compared to a 6 Hz baseline data for any of the material variables studied. In fact, for some of the microstructures studied, the dwell cycling resulted in a significantly lower fatigue crack growth rate. This deceleration can be explained on the basis of the observed increase in crack path tortuosity associated with the dwell cycling. This increased tortuosity may be the result of a crack tip blunting process which occurs during the dwell period of the load cycle.
TL;DR: In this paper, the effects of different austenitization treatments on the plane strain fracture toughness KIC, the stress corrosion threshold stress intensity factor KISCC, the fatigue crack growth rate, and the transverse tensile properties of 300M bar have been investigated over the tempering range 230°-560°C.
Abstract: The effects of different austenitization treatments on the plane strain fracture toughness KIC, the stress corrosion threshold stress intensity factor KISCC, the fatigue crack growth rate, and the transverse tensile properties of 300M bar have been investigated over the tempering range 230°–560°C. Rapid austenitization and high-temperature austenitization treatments have been compared with the conventional heat treatment, since these treatments have been reported to increase the KIC of medium-carbon steels without impairing their tensile strengths. For the standard 320°C temper, rapid austenitization decreased KIC but increased the tensile strength and 0·2% proof stress, whereas high-temperature austenitization treatments increased KIC up to 30%, slightly decreased the 0·2% proof stress, and above 1130°C caused a 50% decrease in the reduction in area. Neither the KISCC nor the fatigue crack growth rates in 1M NaCl, were affected by austenitization treatment. Reasons for the observed KIC variations...
TL;DR: In this paper, the authors investigated the delayed retardation phenomena in three steels and two aluminum alloys and confirmed that the model proposed by Matsuoka et al. was in good agreement with the experimental data for these materials when the stress state at the overloading was satisfied with the small scale yielding condition.
01 Jan 1978
TL;DR: The critical crack size is a function of the fracture toughness of the material and the component geometry and can be calculated from a fracture mechanics analysis as mentioned in this paper, and the fatigue life is determined by the time required to initiate and/or propagate a crack to critical size.
Abstract: Fatigue failure is a process of crack initiation, crack propagation, and fracture. Fracture occurs when the crack propagates to a critical size, and the structural component is no longer able to support the applied stress. The critical crack size is a function of the fracture toughness of the material and the component geometry and can be calculated from a fracture mechanics analysis. The fatigue life is determined by the time required to initiate and/or propagate a crack to critical size.