bluuebunny/crossref_metadata_2025 huggingface dataset:
SHORT CRACK FATIGUE BEHAVIOUR IN A MEDIUM CARBON STEEL
Authors: Rios E. R. de los , Tang Z. , Miller K. J.
Published: April 2007

The initiation stage and short crack behaviour in torsional fatigue of a 0.4% C steel was investigated by a replication technique.

The fatigue cracks initiated and propagated in the ferrite phase which is located at the prior austenite grain boundaries in the form of long allotriomorphs. At this stage of crack development it is proposed that crack growth rate depends on the extent and intensity of plasticity at the tip of the crack. Crack growth per cycle is correspondingly proportional to the strength of the slip band. The ferrite‐pearlite boundaries are strong barriers to crack propagation, which is manifested by a deceleration of growth and possible arrest. On raising the stress level the previously non‐propagating cracks may continue to grow by branching or joining with other cracks in the ferrite phase. This process is repeated until the stress fields of one or more dominant cracks attain a critical value to sustain continued growth that leads to failure.
CYCLIC DEFORMATION OF A1‐4%Cu ALLOY POLYCRYSTALS CONTAINING θ″ PRECIPITATES
Authors: Horibe Susumu , Lee Jia‐Kuen , Laird Campbell
Published: April 2007

The cyclic deformation of polycrystalline A1‐4%Cu alloy containing θ precipitates was investigated by strain controlled tests, and compared to monocrystalline cyclic behavior. The cyclic deformation of the polycrystals was found to depend on the grain size, and in coarse‐grained material (grain diameter = 1 mm) a definite plateau was observed in the cyclic stress‐strain (CSS) curve. In order to explore the relationship of cyclic behavior between single crystals and polycrystals, three available orientation factors were examined. This relationship can be interpreted by selection from the different types of orientation factors (Taylor factor, Sachs factor and Maximum Schmid factor), which operate to different degrees depending on the magnitude of the strain amplitude and the grain size.
FATIGUE GROWTH OF SURFACE CRACKS IN THE ELASTIC‐PLASTIC REGION
Authors: Obrtlík K. , PolÁk J.
Published: April 2007

Surface crack growth has been studied in centre notched and smooth panels of low carbon steel under symmetric axial elastic‐plastic cyclic straining. The crack shape, followed by heat tinting, has been found to be approximately semi‐circular for crack radii 0.3–5 mm. Both smooth and notched specimens have been fatigued until fracture. The smallest notches of 0.1 mm in radius and depth approximately represent defects of a critical size under present loading conditions. Crack propagation rates have been measured and plotted vs ΔJ. Both present part through‐crack data and previous long through‐crack data in the elastic and the elastic‐plastic regions are compatible. A single dependence of dl/dN vs ΔJ is obtained.
EFFECTS OF AIR AND INERT ENVIRONMENTS ON THE NEAR THRESHOLD FATIGUE CRACK GROWTH BEHAVIOR OF ALLOY 718
Authors: Yuen J. L. , Schmidt C. G. , Roy P.
Published: April 2007

The near threshold fatigue crack growth behavior of alloy 718 was studied in air and helium environments at room temperature and at 538°C. Tests were performed at 100 Hz and at load ratios of 0.1 and 0.5. At room temperature and at 538°C, the ΔKth values in helium were lower than in air. The ΔKth values in air decreased with increasing load ratio. These results can be explained with a model that involves the accumulation of oxide in the crack which enhances crack closure. In the air tests, the oxide build‐up on the fatigue fracture surfaces at ΔKth was of the order of magnitude as the crack tip opening displacement. In the helium tests, no significant build‐up of oxide on the fracture surface at threshold was found.
THE VARIATION OF CRACK OPENING STRESS INTENSITY WITH TIME
Authors: Lei Ming jun , Yu Weikang , Gerberich W. W.
Published: April 2007

It was found that crack opening stress intensities are not constant after holding for various times in the unloaded state for iron and a sequence of Fe‐Si binary alloys. The crack opening level decreased with time first because of asperity creep and substructure relaxation, and then increased again with time due to reverse plastic zone relaxation allowing a new set of asperities to come into contact. It is demonstrated that the crack closure phenomenon is not only a result of residual plasticity, oxidation and asperities, but also is due to asperity creep and reverse plastic zone relaxation at the crack tip for low strength materials.
ANALYTICAL AND GRAPHICAL AIDS FOR THE FATIGUE DESIGN OF WELDMENTS
Authors: Yung J.‐Y. , Lawrence F. V.
Published: April 2007

There are four important attributes of weldments which, together with the magnitude of the fluctuating stresses applied, determine their resistance to metallic fatigue: the ratio of the applied or self‐induced axial and bending stresses; the severity of the discontinuity or notch which is an inherent property of the geometry of the joint; the notch‐root residual stresses which result from fabrication and subsequent use of the weldment; and the mechanical properties of the notch‐root material in which fatigue crack initiation and growth takes place. A simple version of a more elaborate analytical model of the fatigue behavior of weldments [1] is presented here which provides analytical and graphical design aids for design.
FATIGUE CRACK GROWTH UNDER MIXED MODES I AND II
Authors: Yokobori A. Toshimitsu , Yokobori Takeo , Sato Kiyoshi , Syoji Kazuo
Published: April 2007

Fatigue crack growth behaviour under mixed modes I and II was studied by applying in‐phase alternating tensile and torsional loading to a thin‐walled hollow cylindrical specimen with an initial crack.

In the linear region of a log‐log plot where da/dN=A(ΔK)m, da/dN at first decreases with increasing ΔK110 component and then approaches a minimum close to the value of ΔK110/ΔK10∼ 0.58; here ΔK110/ΔK10 is the ratio of the initial ΔKII to the initial ΔK1., When ΔK110/ΔK10 increases further, da/dN increases. Under shear mode, da/dN becomes higher than that under mode I. The ΔK1, and ΔK11 components during fatigue crack growth under mixed mode loading increase and decrease, respectively, with an increase in da/dN In the low crack growth rate region the fatigue crack growth rates accelerate with an increase of the initial ΔK11 component, ΔK110. Fatigue life increases with increase of ΔK110/ΔK10 under the test condition of equivalent stress range being kept constant and the pre‐crack length being the same.
STRESS INTENSITY FACTORS FOR CRACKS IN NOTCHED FINITE PLATES SUBJECTED TO BIAXIAL LOADING
Authors: Xiao S. T. , Brown M. W. , Miller K. J.
Published: April 2007

Stress intensity factors were calculated, based on Bueckner's principle for cracks in both infinite and finite plates with notches subjected to biaxial loading. Approximate Green's functions have been obtained by modifying two existing Green's functions, originally for unnotched plates. Values of stress intensity factors calculated using Bueckner's principle with the approximate Green's functions are in good agreement with published stress intensity factors for cracks in both infinite and finite plates containing a circular notch or an elliptical notch, previously found by the method of boundary collocation.
THE APPLICATION OF FRACTURE MECHANICS TO FRETTING FATIGUE
Authors: Nix K. J. , Lindley T. C.
Published: April 2007

Abstract—A fracture mechanics model of fretting fatigue has been developed. This enables the calculation of the critical size of defect which can grow under fretting conditions. The model has been applied to the fretting of aluminium alloy 2014A fatigue specimens in contact with 3.5NiCrMoV steel fretting contact pads. The input parameters to the model include externally applied stresses, contact pressure between pad and specimen and frictional forces between the two contacting surfaces. The latter have been measured using a strain gauge technique. Small fretting defects in the fatigue specimens have been investigated metallographically and fractographically. There is good agreement between their size and critical defect sizes calculated using the fretting model.
FATIGUE FAILURE AT STRESSES BELOW FATIGUE LIMIT
Authors: Iwasaki C. , Ikai Y.
Published: April 2007

In the present study, the authors have focused attention on the internal stress in a material. A stress applied to a specimen does not fully act to deform the material. The effective stress which actually acts on dislocations depends on the internal stress in the material. The origin of the internal stress is attributed here to the dislocation structure. From this viewpoint, fatigue tests were carried out and the following results were obtained:

(1) The origins of the internal stress and the effective stress were clarified by means of a dislocation model.

(2) The behaviour of the internal stress during the fatigue process showed clear differences between over‐stressed and under‐stressed states.

(3) The concept of internal and effective stresses assists in our understanding of the fatigue phenomenon.

(4) The mechanism of fatigue failure in the under‐stressed fatigue state was also studied, and the concept of an internal stress was applied to instances of practical fatigue situations.
NON‐DAMAGING NOTCHES IN FATIGUE*
Authors: Lukáš P. , Kunz L. , Weiss B. , Stickler R.
Published: April 2007

The fact that very small notches (cavities, holes, scratches, etc.) have no effect on the fatigue limit of metallic materials is well known. This paper presents both a qualitative explanation for the existence of non‐damaging notches and a quantitative derivation of their critical sizes. The condition for a notch (characterized by the stress concentration factor Kt and the notch root radius ρ) to be non‐damaging in a metallic material (characterized by a critical crack size l0) is

(K2t− 1)ρ≤ 4.5 l0.

The critical crack size can be expressed with good approximation in terms of the threshold stress intensity for fatigue crack growth and the plain fatigue limit. Therefore the above relation can be applied for an engineering evaluation of non‐damaging notches. Test results obtained for copper and a pressure vessel steel demonstrate the applicability of the proposed method.
LIMITATIONS OF LINEAR ELASTIC FRACTURE MECHANICS IN RESPECT OF SMALL FATIGUE CRACKS AND MICROSTRUCTURE
Authors: Tokaji Keiro , Ogawa Takeshi , Harada Yukio , Ando Zenji
Published: April 2007

The growth characteristics of small fatigue cracks were investigated under rotary bending in a low alloy steel prepared with two prior austenite grain sizes of 15 μm (fine grain) and 91 μm (coarse grain). The influence of grain boundaries on crack growth rate and the crack aspect ratio was examined, and the critical crack length above which linear elastic fracture mechanics (LEFM) is applicable was evaluated for a growing small crack. When the surface crack length is shorter than three grain diameters (3d), crack growth rates decrease near the grain boundaries. Aspect ratios are also affected by the microstructure and thus vary widely. Cracks longer than 3d are not influenced by the microstructure, but they grow faster than would be expected based on LEFM until their lengths reach 3d+ 150 μm. This behaviour may be attributed to the difference in crack closure between small cracks and large cracks. If the contribution of crack closure to the growth of small cracks can be established experimentally or analytically, the critical crack length above which LEFM is applicable would be 3d. However, because it is difficult to evaluate crack closure, 3d+ 150 μm is considered to be the critical crack length for engineering applications.
A SIMPLIFIED RESIDUAL STRESS MODEL FOR PREDICTING FATIGUE CRACK GROWTH BEHAVIOR AT COLDWORKED FASTENER HOLES
Authors: Su X. , Gu M. , Yan M.
Published: April 2007

This paper presents an investigation of the fatigue crack growth (FCG) behavior at fastener holes in a high strength steel, 30CrMnSiNi2A, before and after a cold‐expansion process. The fatigue life of coldworked specimens was significantly increased compared to non‐coldworked ones and increased the lower applied stress level.

From a study of the residual stress distribution near the edge of the hole, it was found that the experimental residual compressive stresses in absolute values were much less than the calculated values derived by previous analytical methods. Thus, a simplified residual stress model for describing the FCG behavior at coldworked fastener holes is proposed, from which, the δKeff and fatigue lives of specimens after cold‐expansion can be predicted satisfactorily for engineering applications.
THE EFFECTS OF MOISTURE ON THE FATIGUE CRACK GROWTH BEHAVIOUR OF A LOW ALLOY STEEL NEAR THRESHOLD
Authors: Smith P.
Published: April 2007

Abstract— The influence of moisture on the fatigue crack growth behaviour near threshold of a 2NiCrMoV rotor steel has been investigated. At a high stress ratio (R= 0.6), moisture enhances fatigue crack growth rates by approximately 60% compared with the growth rate in dry air. The effect would appear to be due to the influence of hydrogen which is confined to a volume of material at the crack tip considerably smaller than the plastic zone. At a low stress ratio (R= 0.14), the growth rates in moist air can be very much lower than in dry air. This difference is closely associated with the formation of oxides on the fracture surface—moisture modifying the type and extent of oxidation which is observed. Observations of transient crack growth following environmental changes, suggest that fracture surface oxides within approximately 0.3 mm of the crack tip exert a strong retarding influence on crack growth although oxides up to at least 3 mm from the tip may also have some retarding effect.
THE EFFECTS OF CATHODIC POTENTIAL AND CALCAREOUS DEPOSITS ON CORROSION FATIGUE CRACK GROWTH RATE IN SEA WATER FOR TWO OFFSHORE STRUCTURAL STEELS
Authors: Murakami R. , Ferguson W. G.
Published: April 2007

The effects of cathodic protection potential, corrosion products and stress ratio on corrosion fatigue crack growth rate have been studied on offshore structural steels. These materials were cathodically polarised in seawater and 3% sodium chloride solution at three potentials of ‐0.8, ‐1.0 and ‐1.1 V(SCE). The corrosion fatigue crack growth rate in seawater was greater than that in air and increased with more negative potentials. The maximum acceleration of crack growth rate in seawater was observed at the crack growth plateau which was independent of ΔK.Calcareous deposits precipitated within the cracks resulted in an increase of crack opening level and contributed to a reduction of the corrosion fatigue crack growth rate. Such a corrosion‐product‐wedging effect could be evaluated by using an effective stress intensity range, ΔKeff. The estimation of corrosion fatigue crack growth rate in terms of ΔKeffclarified the effect of hydrogen embrittlement under a cathodic potential. Thus the processes of cracking in seawater at cathodic potentials resulted from mechanical fatigue and hydrogen embrittlement with calcareous deposits reducing the crack growth rate. All these three mechanisms were mutually competitive.
EFFECT OF FATIGUE CRACK CLOSURE ON NEAR‐THRESHOLD CRACK RESISTANCE OF STRUCTURAL STEELS
Authors: Romaniv O. N. , Tkach A. N. , Lenets Yu N.
Published: April 2007

Abstract— The present paper is an attempt to clarify conditions for plasticity‐induced and oxide‐induced crack closure as well as to evaluate the effect of crack closure on near‐threshold fatigue crack behaviour.

The autocatalytic character of oxide formation at the crack tip has been elucidated in this study. An increase of plastic constraint at the crack tip is shown to intensify the fretting oxide formation process on the fracture surface and thus to cause an increase of the stress intensity factor range controlling the fatigue crack propagation rate. The proposed concept of stress state influence on crack closure allows us to explain the effect of specimen thickness on ΔKth.
FATIGUE CRACK CLOSURE OF CORNER CRACKS LOCATED AT HOLES LOADED IN TENSION OR BENDING
Authors: Ray S. K. , Perez R. , Grandt A. F.
Published: April 2007

Abstract— The objective of this paper is to report fatigue crack growth and closure behavior for corner cracked holes. An optical interference technique is employed with transparent polymer specimens to determine the three‐dimensional crack surface displacement field. The local crack closure behavior is examined along the crack front under remote tension and pure bending conditions. It was observed that the crack opening loads along the hole and the free surface were significantly higher than the opening values at interior crack locations.
NON‐ISOTHERMAL FATIGUE CRACK GROWTH IN HASTELLOY‐X
Authors: Marchand N. J. , Pelloux R. M. , Ilschner B.
Published: April 2007

Abstract— Non‐isothermal fatigue crack growth tests were performed on Hastelloy‐X single edge notch specimens in which strain and temperature were varied simultaneously. Conditions were selected to include nominally elastic and nominally plastic conditions and temperatures up to 925°C. The crack growth rates were first reported as a function of the strain intensity factor (δKε) derived from a crack compliance analysis. Out‐of‐phase (εmax at Tmax) cycling showed faster crack growth rates than isothermal or in‐phase (εmax at Tmax) cycling under elastic straining. Under fully plastic cycling, the opposite results was observed, i.e. crack growth rates under isothermal cycling are faster than under TMF cycling. On a δKε‐basis, a strain range effect was observed. All the results were rationalized using a corrected stress‐intensity factor (δKeff) computed from the actual load, the closing bending moment caused by the increase compliance with crack length, and with the effective opening stress. Each mode of fracture was found to be characterized by a unique crack growth rate vs δKeff curve. On a δKeff‐basis, the isothermal crack growth rates at Tmin and Tmax provide an upper and a lower bound for the TMFCG rates. The effectiveness of δKeff to correlate crack growth rates under fully plastic cycling is discussed in detail.
THE USE OF A NEW LINE‐SPRING SHELL ELEMENT FOR ELASTIC SURFACE CRACK ANALYSIS
Authors: Langre E. de , Ebersolt L.
Published: April 2007

In this paper, the Line‐Spring concept developed by Rice and Levy[l] is used to build a new elastic surface cracked shell element in the general purpose Finite Element code CASTEM 2000. The implementation is described and an energy release rate technique is proposed to arrive at more accurate Stress Intensity Factor values at the crack front‐free surface intersection. A comparison with existing accepted numerical solutions is made on various plane and cylindrical configurations and a discussion on the applicability of the model is presented.
MODELLING OF EMBEDDED FATIGUE CRACKS IN RAILROAD RAILS
Authors: Rice R. C. , Rungta R.
Published: April 2007

Abstract— A first‐generation fatigue crack growth model has been developed which realistically models the patterns of subsurface shells and detail fracture crack growth that are commonly observed in railroad rails. (These types of defects are further described in the Introduction.) The key assumptions upon which the model is based are reviewed and the input data on railroad rail residual stresses and wheel‐induced stresses are described. Examples of the predicted growth patterns for shells and detail fractures are shown and compared to actually observed growth patterns. Apparent deficiencies in the model are discussed and probable avenues for improvement in the accuracy of the crack growth life estimates are identified.
AN INVESTIGATION OF FATIGUE CRACK GROWTH IN A DUCTILE MATERIAL AT HIGH GROWTH RATES
Authors: Nix K. J. , Knee N. , Lindley T. C. , Chell G. G.
Published: April 2007

Abstract— Investigations into tearing‐fatigue have been performed using three point bend specimens made of mild steel. A computer controlled testing machine was used which could maintain constant cyclic displacement ranges, or constant cyclic energy input ranges, and hence provide a range of crack tip driving force conditions. Fatigue crack growth rates were measured and compared with the predictions of a model based on the linear summation and non‐interaction of fatigue and ductile tearing growth rates. The effects of fatigue crack growth on monotonic crack growth resistance properties were investigated. It is concluded that there is no significant interaction between these two crack propagation mechanisms in this steel. Crack growth rate equations governing propagation in the tearing‐fatigue regime are given.
A SIMPLIFIED LABORATORY APPROACH FOR THE PREDICTION OF SHORT CRACK BEHAVIOR IN ENGINEERING STRUCTURES
Authors: Herman W. A. , Hertzberg R. W. , Jaccard R.
Published: April 2007

Abstract— Conventionally determined fatigue threshold information (ASTM E647) can lead to non‐conservative estimates of fatigue lifetimes when these data are utilized in damage tolerant design assessments. The non‐conservative nature of such data can be attributed primarily to the development of excessively large amounts of crack closure at low R‐ratios, particularly at near threshold stress intensity factor levels. These high closure levels attenuate the effective stress intensity condition prevailing at the crack tip and confound attempts to predict the behavior of short cracks that exhibit limited crack closure. A modified test procedure, involving constant maximum stress intensity factor (Kcmax) test conditions, is described which identifies fatigue crack propagation (FCP) threshold behavior in the absence of detectable amounts of crack closure. These data have been generated with conventional long crack specimens for several aluminum, iron, and nickel‐based alloys and which are shown to closely simulate the FCP response of short cracks in these engineering materials. As such, the modified threshold test procedure, incorporating constant Kmax loading conditions, represents a valuable tool in the prediction of the cyclic lifetime of engineering components. The stress‐cyclic lifetime (S‐N) curve for aluminum butt‐welded beams was computed based on Kcmax data and found to be in excellent agreement with actual test results.
RESULTS OF A ROUND ROBIN ON STRETCH ZONE WIDTH DETERMINATION*
Authors: Heerens J. , Cornec A. , Schwalbe K.‐H.
Published: April 2007

Abstract— ‐A round robin on experimental stretch zone width (SZW) measurement was conducted. The SZW of eight different materials showing an SZW range of 5 to 200 μm was measured by evaluating a set of micrographs. The round robin was carried out by 14 participants from different firms and institutes. The standard deviation of the experimental SZW measurement was found to be in a range of smaller than 75% of the stretch zone average SZW. For 90% of the micrographs the standard deviation of SZW remains in a range smaller than 35% of SZW. This scatter range was not significantly influenced by the experience of the participants in measuring the individual SZW, the materials tested and the magnitude of the SZW itself. The SZW results determined in this round robin match well with a theoretical SZW determination using the recently developed blunting line equation including strain hardening: SZW = 0.4 dn* J/E.
PROPAGATION AND CLOSURE OF SHORT FATIGUE CRACKS AT NOTCHES UNDER COMPRESSIVE MEAN STRESSES
Authors: Akiniwa Y. , Tanaka K. , Taniguchi N.
Published: April 2007

Abstract— Single‐edge‐notched specimens of a low‐carbon steel were fatigued under cyclic in‐plane bending with compressive mean stresses. The development of crack closure with crack growth was studied both experimentally and theoretically. The relation between the crack opening stress and the crack length was a function of the minimum (compressive) applied stress, irrespective of the maximum stress. The effective stress intensity range was a unique parameter in correlating the crack growth rate, even if the crack was embedded in the compressive plastic zone. Under a constant minimum stress, the length of nonpropagating cracks became longer with increasing maximum applied stress. A theoretical model was proposed for predicting the crack opening stress on the basis of the compressive stress distribution at the minimum applied stress. The predicted value agreed fairly well with the experimental result. The model gave upper bounds of the crack growth rate and the length of nonpropagating fatigue cracks within the plastic zone.
THE PROGRESSION OF BENDING FATIGUE IN NICKEL
Authors: Price C. E.
Published: April 2007

Abstract— The progression of fully reversed bending fatigue, in a 99.6% pure polycrystalline nickel (NO2200) at room temperature, was monitored utilizing Nomarski interference contrast microscopy in conjunction with microhardness measurements. It was found that a gradual hardening, without early saturation, occurred from about 95 to 160 HV. Similar data were obtained with indenter weights of 15–500 g, from which it was concluded that a different behaving surface layer did not develop during fatigue. Cracks initiated at coarse slip bands within the first 1% of the life, when the hardness reached 140 HV. The cracking of these bands initiated away from grain boundaries. The slow growth of these slip band cracks dominated the life subsequently. Growth of the cracks both across and beyond the initial grain was difficult. The significant hardening prior to crack initiation and the confinement of the cracking mainly to coarse slip bands, contributed to a good inherent fatigue resistence of nickel. with a fatigue limit above the yield strength. Non‐propagating cracks were not observed below the fatigue limit.
CRACK CLOSURE AND FATIGUE CRACK GROWTH RATE IN THREE POINT BEND SPECIMENS OF DIFFERENT WIDTHS
Authors: Singh U. P. , Banerjee S.
Published: April 2007

Abstract— The crack closure stress intensity factor values and fatigue crack growth rates were determined in Three Point Single Edge Bend, SE(B), specimens prepared from rails manufactured using two different grades of rail steels. The width, and correspondingly the span, of the SE(B) specimens were varied eight fold; the thickness of all the specimens being the same. It is observed that the crack closure stress intensity factor values decrease with an increase in the width of SE(B) specimens. At a given value of ΔKeff, the fatigue crack growth rate (FCGR) is independent of the width. However, at a given value of ΔKeff, the FCGR is observed to decrease with increasing width. In view of the above results, the scope of application of the FCGR laws based on an effective stress intensity factor to the life prediction of components, requires careful examination.
VECTOR CTD CRITERION APPLIED TO MIXED MODE FATIGUE CRACK GROWTH
Authors: Li Chingshen
Published: April 2007

Abstract— This work is aimed at developing a general parameter based on the deformation intensity at a mixed mode crack tip to predict crack growth behaviour, especially in the near threshold region. Being a mechanisms‐related parameter, the vector crack tip displacement (CTD) is defined as a vector summation of CTOD and CTSDc which act, respectively in the directions of mode I and mode II fatigue crack growth. The basic assumption is that both direction and rate of mixed mode fatigue crack growth are governed by the vector ΔCTD, which represents the resultant of the “driving force”at the crack tip. The analytical predictions obtained by using the vector ΔCTD are in good agreement with the reported experimental results of mixed mode I and II fatigue cracks.
A STUDY OF THE INTERACTION AND COALESCENCE OF TWO COPLANAR FATIGUE CRACKS IN BENDING
Authors: Soboyejo W. O. , Kishimoto K. , Smith R. A. , Knott J. F.
Published: April 2007

Abstract— This paper reports the results of an experimental and numerical investigation of the interaction and coalescence of two coplanar semi‐elliptical cracks. Fatigue crack growth data were obtained from a four‐point bend specimen using the direct current potential difference method and a beachmarking technique. A finite element simulation of the experimental conditions was also performed. Crack advance was computed from the Paris equation on a step by step basis. Good agreement between experimental fatigue crack growth data and the finite element predictions is demonstrated.
A RELIABILITY ANALYSIS OF FATIGUE CRACK GROWTH UNDER RANDOM LOADING
Authors: Huang X. , Hancock J. W.
Published: April 2007

Abstract— The fracture mechanics approach to the growth of fatigue cracks under random loading has been used to predict both the distribution of crack lengths after a given number of cycles, and the distribution of cycles to grow a crack to a given length. The analysis ignores interaction effects between cycles, and its predictions agree closely with the results of Monte‐Carlo simulations. These results allow a simple method of assessing the reliability of cracked components subjected to narrow or broad band random loading and the introduction of material variability allows a quantitative description of the parameters which affect the reliability of a structural component.
THE INFLUENCE OF TEST VARIABLES ON THE FATIGUE CRACK GROWTH THRESHOLD
Authors: Priddle E. K.
Published: April 2007

Abstract— A microcomputer controlled fatigue crack growth and threshold testing system has been used to investigate the influence of test variables on the measured values of ΔKth, the threshold for fatigue crack growth, using a C‐Mn steel. The work has examined: (1) the influence of crack length and test management; (2) the basic material scatter from repeated testing; (3) the effect of unloading rate C where C= (1/Δ/K)(d ΔK/d a); (4) the effect of step unloading; (5) the influence of minimum stress intensity factor, Kmin. Comparisons have been made between the results of this computer controlled work and those published previously but made using a manual load shedding technique. The results of ΔKth and fatigue crack growth rates are in general agreement with previous data and confirm the Kmin dependence of ΔKth and da/dn. The value of ΔKth is shown to be generally independent of the other test variables for a wide range of conditions and is reproducible with a low degree of scatter.
SURFACE CRACK GROWTH IN A PLATE UNDER THE REMOTE HIGH STRAIN‐CONTROLLED CYCLIC LOADING
Authors: Shuilong Yang , Yizhong Lu
Published: April 2007

Abstract— —Low cycle fatigue surface crack growth in a plate of finite width under remote strain‐controlled cyclic loading has been studied for a mild steel. Both crack growth in the depth direction and along the surface plane were measured. It is found that the cyclic J‐integral, estimated by Dowling and Begley's approach, can be used as the mechanical driving force to characterize crack growth rates in both directions. The maximum strain, strain ratio and strain rate have no influence on the relation between the crack growth rates and the corresponding cyclic J‐integral. The shape of the crack, idealized as a semi‐ellipse, gradually changes from shallow to deep at the beginning of a test and remains unchanged after the ratio of crack depth to thickness of the plate attains a value of 0.7. The change of crack shape is not affected by maximum strain, strain rate and strain ratio, but is dependent on the precracked shape.
FATIGUE STRENGTH OF BUTT WELDED Al–Mg ALUMINIUM ALLOY: TESTS WITH MAXIMUM STRESS AT YIELD STRENGTH
Authors: Ohta Akihiko , Mawari Toshio
Published: April 2007

Fatigue tests were carried out on type A5083P‐O Al–Mg aluminium alloy butt welded specimens by a test method which simulates the behaviour of large size welded structures having high tensile residual stresses by means of ordinary narrow specimens, containing low level residual stresses. In the tests, specimens were cycled down from a constant maximum stress of the yield strength of the material. The S–N data obtained in these tests were compared with corrected lines from S–N data for narrow specimens tested at R= 0 considering the presence of high tensile residual stresses and the proposed design curve in the draft British Standard BS 8118. It was found that the discrepancy between corrected lines and the data plots was not small and that the proposed design curve was over conservative in the high cycle region.
EFFECT OF SPECIMEN GEOMETRY ON FATIGUE CRACK GROWTH IN PLANE STRAIN—I. CONSTANT AMPLITUDE RESPONSE
Authors: Shercliff H. R. , Fleck N. A.
Published: April 2007

Abstract— The influence of specimen geometry on crack growth and crack closure response was determined for BS4360 50B steel and 6082‐T6 aluminium alloy. Specimens were sufficiently thick for plane strain conditions to prevail along most of the crack front. After an initial crack growth transient from the sharpened notch, and steady state conditions are attained, the growth rate and closure responses are independent of specimen geometry. At growth rates above the near‐threshold regime the cyclic crack openings exceed the fracture surface roughness for the steel, but are much less than the surface roughness for the aluminium alloy. This suggests that roughness‐induced crack closure plays a dominant role for the aluminium alloy but not for the steel. Finally, the effect of mean stress upon closure response is presented for the steel.
PREDICTION OF BENDING FATIGUE BEHAVIOUR BY THE REFERENCE STRESS APPROACH
Authors: Megahed M. M.
Published: April 2007

Abstract— A technique is presented for prediction of low‐cycle fatigue behaviour under bending conditions from the knowledge of uniaxial fatigue data. The technique utilizes the reference stress approach used in the analysis of creeping components. The results enable determination of nominal elastic bending stress in terms of the observed saturation stress amplitude in an uniaxial fatigue test conducted at a reference value of strain amplitude. The reference parameters are determined for beams with both rectangular and circular cross‐sections. The predictions of fatigue bending behaviour are in excellent agreement with closed form solutions reported recently. The merits of this alternative approach lie in its potential applicability to other structural situations once their reference uniaxial parameters are determined. Since the reference parameters are nearly the same for both creep and fatigue, the approach can be a useful experimental tool for relating creep‐fatigue interaction effects in structural components with uniaxial creep‐fatigue tests conducted under the reference conditions.
COMPUTER AIDED MULTIAXIAL FATIGUE TESTING
Authors: Fernando U. S. , Miller K. J. , Brown M. W.
Published: April 2007

Abstract— This paper describes a microcomputer system that controls a multiaxial fatigue test facility. The system involves interface hardware, command control units, data acquisition units, and associated software for data processing, setting‐up of test procedures and system monitoring. Without such a microcomputer system it would be impossible to acquire and analyse the vast amount of data generated by multiaxial fatigue tests, but perhaps more important, it would be impossible to control and monitor the important parameters that govern fatigue fracture behaviour of metals. This is particularly true for complex tests in which waveform shapes and out‐of‐phase angles can be changed during the course of a test. Finally, such a facility permits for the first time a detailed investigation of the effects of anisotropy on the deformation and fracture behaviour of metals.
EFFECT OF NOTCH STRESS FIELD AND CRACK CLOSURE ON SHORT FATIGUE CRACK GROWTH
Authors: Ye Tao , Jiawen He , Naisai Hu
Published: April 2007

Abstract— The growth rate of a short fatigue crack that is partly or wholly embedded within the notch plastic zone, is affected by the extent and intensity of the elastic‐plastic notch stress field and closure effect. The notch stress—strain field and plastic zone were analysed by the Finite Element Method (FEM). The growth rate and the closure curve for a short fatigue crack emanating from the notch root were measured. Based on the experimental and numerical analyses, a modified Linear Elastic Fracture Mechanics (LEFM) parameter is proposed for a short through‐thickness crack emanating from a notch root under elastic—plastic loading conditions.
FATIGUE MICROCRACKS IN TYPE 304 STAINLESS STEEL AT ELEVATED TEMPERATURE
Authors: Suh C. M. , Lee J. J. , Kang Y. G.
Published: April 2007

Microcracking of type 304 stainless steel at 538°C has been studied, in particular, the initiation, growth and coalescence, of fatigue microcracks on smooth specimens via surface replicas and photomicrographs. Quantitative information, such as, initiation period, growth and coalescence behaviour, statistical distributions of crack length, density of cracks, distribution patterns and crack growth properties, were obtained. Knowledge of these parameters is critical for the application of fracture mechanics to fatigue life assessment and the damage evaluation of structures at elevated temperature.
SHORT AND LONG FATIGUE CRACK GROWTH IN A SiC REINFORCED ALUMINIUM ALLOY
Authors: Kumai Shinji , King Julia E. , Knott John F.
Published: April 2007

Fatigue crack growth behaviour in a 15 wt% SiC particulate reinforced 6061 aluminium alloy has been examined using pre‐cracked specimens. Crack initiation and early growth of fatigue cracks in smooth specimens has also been investigated using the technique of periodic replication. The composite contained a bimodal distribution of SiC particle sizes, and detailed attention was paid to interactions between the SiC particles and the growing fatigue‐crack tip. At low stress intensity levels, the proportion of coarse SiC particles on the fatigue surfaces was much smaller than that on the metallographic sections, indicating that the fatigue crack tends to run through the matrix avoiding SiC particles. As the stress intensity level increases, the SiC particles ahead of the growing fatigue crack tip are fractured and the fatigue crack then links the fractured particles. The contribution of this monotonic fracture mode resulted in a higher growth rate for the composite than for the unreinforced alloy. An increase in the proportion of cracked, coarse SiC particles on the fatigue surface was observed for specimens tested at a higher stress ratio.
DESIGN AND GROWTH RULES FOR BIOLOGICAL STRUCTURES AND THEIR APPLICATION TO ENGINEERING
Authors: Mattheck C.
Published: April 2007

Starting from the well‐accepted but not proved hypothesis that biological load carrying structures are highly optimized by growth, some examples are given and their degrees of optimization are demonstrated. Especially branch joints, deer antlers, branch holes in trees and modelling growth of trees loaded by contact stresses are discussed. On the basis of the knowledge that biological structures always try to avoid localized stress peaks (notch stresses), and that they try to grow into a locally homogeneous surface stress state, a new method of CAO (computer aided shape‐optimization) is proposed which relies on biological growth. Its efficiency and success are demonstrated for two‐ and three‐dimensional structures with very homogenous stress states after optimization.
THE CREEP/FATIGUE BEHAVIOUR OF TYPE 316 STEEL UNDER REVERSE BENDING CONDITIONS
Authors: Wood D. S. , Banks P.
Published: April 2007

Abstract— Reverse bending creep/fatigue tests have been performed on Type 316 steel at temperatures of 550 and 600°C for test durations of up to 12,000 h. It is shown that endurances obtained are comparable to those observed under push‐pull conditions and that the introduction of a hold period can significantly reduce the endurance. Detailed fractography indicates that creep/fatigue in tension is more damaging than creep/fatigue in compression. The crack initiation behaviour is shown to be temperature dependent and may result from the combination of tensile and shear stresses, the relative importance of which will depend on the precise conditions of temperature, stress level and possibly microstructure.
FATIGUE BEHAVIOUR OF AUSTENITIC Cr‐Mn‐N STEELS
Authors: Panzenböck M. , Ebner R. , Löcker U. , Aigner H. , Pohl H.
Published: April 2007

Abstract— Solid solution hardening and strain hardening are the dominating strengthening mechanisms to achieve a high yield stress and ultimate tensile strength in Cr‐Mn‐N steels for drill collars. The fatigue limit can be improved more effectively by solid solution hardening than by strain hardening, but the attainable hardness due to soluble elements is restricted by other metallurgical demands. Strain hardening significantly increases the strength and the fatigue limit is improved too, but to a lesser extent. The reason for this behaviour is the introduction of internal stresses of the I, II and III kind by forging the drill collars. This results in macroscopic stresses which are varying over the cross section and in stresses of a microscopical scale which lead to an early loss of linearity in the elastic line of the stress strain curve and to the well known Bauschinger effect. Cyclic softening and hardening is accompanied by a rearrangement of the dislocation structure as revealed by transmission electron microscopy. The results indicate that a multiaxial and homogeneous cold working to produce a stable dislocation structure and to avoid large directional internal stresses is extremely important to achieve high fatigue strengths. Crack growth and crack closure measurements were performed for determination of the effective cyclic threshold stress intensity range for evaluation of the influence of the grain size on the fatigue limit.
THE USE OF COMPLIANCE TO INVESTIGATE FATIGUE CRACK RETARDATION BY COVER PLATES
Authors: Han M. S. , Smith R. A. , Kim S. C.
Published: April 2007

Abstract— This paper develops the compliance approach to the problem of load sharing between a cracked plate and a cover plate used to bridge the crack. The theory is validated by using calculated stress intensity factors for the covered and uncovered cases to reduce experimentally observed growth rates to a common base. Calculations are then made on the effect of cover plate width on fatigue crack retardation in order to demonstrate the predictive capability of the technique.
FATIGUE CRACK INITIATION LIFE PREDICTION FOR WELDED JOINTS BY LOW CYCLE FATIGUE APPROACH
Authors: Skorupa Malgorzata
Published: April 2007

Abstract— Analytical procedures based on low cycle fatigue theory are used to estimate the fatigue crack initiation life (Ni) for a cruciform welded joint in mild steel under constant amplitude tensile cyclic loading; the fatigue crack initiating at the weld toe. Effects due to welding such as residual stresses, geometrical variability and changes in material properties are handled. It is shown that for high mean stresses the discrepancies observed between the Ni estimates provided by commonly used analytical procedures exceed an order of magnitude. For the base metal (BM) the discrepancies become negligible if cyclic relaxation of notch mean stress is taken into consideration. The differences betwen the Ni estimates for heat affected zone (HAZ) material (where fatigue cracks at the weld toe usually initiate) and for BM are quantified. The applicability of HAZ material properties, estimated from hardness, to Ni prediction is evaluated.
GROWTH OF FATIGUE CRACKS EMANATING FROM NOTCHES IN SiC PARTICULATE ALUMINUM COMPOSITE
Authors: Biner S. B.
Published: April 2007

Abstract— The initiation and growth of cracks emanating from blunt notches in 6061‐Al alloy reinforced with 25% particulate Sic metal matrix composite were investigated. To elucidate the role of aging condition of the matrix on the fatigue behavior, the studies were carried out at T6 and overaged conditions. The results show that the number of cycles required for initiation of fatigue cracks are not influenced with the notch severity and the aging condition of the matrix. The overaging heat treatment resulted in slower fatigue crack growth rates. The failure of the Sic particles during the fatigue process is given as the reason for the both observed initiation and crack growth characteristics. It is also shown that the growth rate of cracks emanating from blunt notches can be accurately described by an equivalent stress intensity factor range ΔKeq. This could provide an adequate engineering method for design against fatigue failure from various stress concentrations for this composite system.
CALCULATION OF THE STRESS INTENSITY FACTOR FOR A PARTIAL CIRCUMFERENTIALLY CRACKED TUBE LOADED IN BENDING BY USING THE SHELL LINE‐SPRING MODEL
Authors: Dai Y. , Rödig M. , Altes J.
Published: April 2007

Abstract— In this paper the line‐spring model (LSM) developed by Rice and Levy is used to obtain an approximate solution of the stress intensity factor for a partial circumferential, externally cracked tube under axial tension and four point bending. The calculation is based on the work done by Delale and Erdogan for cylindrical shells containing a circumferential or an axial semi‐elliptical, part‐through crack. The range of utility of their analysis is enlarged to thicker wall tubes with nonelliptic and longer part‐through circumferential cracks. Values of K1 calculated by the LSM are compared with those from a finite element analysis for remote tensile loading and bending cases, which shows fairly good agreement. The calculations are also applied to a fatigue crack growth test in a tube in four point bending to correlate the da/dN vs λK1 data.
CRACK GROWTH IN A TITANIUM ALUMINIDE ALLOY UNDER THERMAL MECHANICAL CYCLING
Authors: Mall S. , Nicholas T. , Pernot J. J. , Burgess D. G.
Published: April 2007

Abstract— The fatigue crack growth behavior in a titanium aluminide (Ti3Al) alloy under thermo‐mechanical loading as well as under elevated temperature conditions was investigated. The thermal mechanical fatigue crack growth behavior appears, in a general sense, to follow the same trends observed in similar data obtained in tests on nickel‐base superalloys. However, crack growth in Ti3Al appeared to be influenced by blunting of the crack tip due to creep in addition to a cyclic‐dependent contribution together with time dependent or environmental enhanced degradation. This complex phenomenon in Ti3Al is unlike that in nickel‐base superalloys where crack growth was found to be due to a linear combination of cycle and time dependent contributions. Thus, the linear cumulative modelling technique is not applicable to the tested Ti3Al.
NOTCHED FATIGUE BEHAVIOUR OF TWO COLD ROLLED STEELS
Authors: Yu M. T. , DuQuesnay D. L. , Topper T. H.
Published: April 2007

Abstract— A SAE1010 plain carbon steel and a SAE945X HSLA steel were cold rolled to various thickness reductions. Centre notched specimens were tested under stress control at a stress ratio of—1. The effect of loading direction on the fatigue strength was examined. The notched specimen fatigue strength was only slightly increased by cold rolling, since two opposing factors: the smooth specimen fatigue strength and the notch sensitivity, were increased by cold rolling. The notched specimen fatigue strength in the transverse direction was approximately the same as that in the longitudinal direction. An empirical equation and equations derived from fracture mechanics and Neuber's rule were applied to predict the fatigue notch factor for the sharp and blunt notch geometries examined. A reasonable agreement between the predictions and the experimental results was observed for the sharp notches. For the blunt notches, the predicted fatigue notch factors were conservative.