Showing papers on "Paris' law published in 1991"
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TL;DR: In this article, the cyclic deformation and fatigue crack initiation in polycrystalline ductile solids was studied and a total-life approach was proposed to deal with the problem.
Abstract: Preface 1. Introduction and overview Part I. Cyclic Deformation and Fatigue Crack Initiation: 2. Cyclic deformation in ductile single crystals 3. Cyclic deformation in polycrystalline ductile solids 4. Fatigue crack initiation in ductile solids 5. Cyclic deformation and crack initiation in brittle solids 6. Cyclic deformation and crack initiation in noncrystalline solids Part II. Total-Life Approaches: 7. Stress-life approach 8. Strain-life approach Part III. Damage-Tolerant Approach: 9. Fracture mechanics and its implications for fatigue 10. Fatigue crack growth in ductile solids 11. Fatigue crack growth in brittle solids 12. Fatigue crack growth in noncrystalline solids Part IV. Advanced Topics: 13. Contact fatigue: sliding, rolling and fretting 14. Retardation and transients in fatigue crack growth 15. Small fatigue cracks 16. Environmental interactions: corrosion-fatigue and creep-fatigue Appendix References Indexes.
4,158 citations
TL;DR: In this article, an algorithm for the prediction of fatigue lives to initiation of cracks of technical sizes in case of variable amplitude loading is presented. But the results of the investigations have been merged to build an algorithm to predict the initiation of crack of technical size and the improvement in accuracy of life prediction compared to results of an existing damage accumulation concept is demonstrated for two materials and two load sequences.
Abstract: Opening and closure of short cracks has been examined experimentally using small strain gauges fixed to unnotched specimens very close to short fatigue cracks. The results of completely reversed tension-compression constant amplitude tests are that crack opening stresses decrease with increasing stress amplitude and that crack closure occurs at nearly the same strain as crack opening. In variable amplitude loading the crack is subjected to a low crack opening level resulting from larger cycles. Based on the results of this experimental investigation some simple approximation formulas are proposed with which decrease as well as increase of crack opening levels can be described. Using these formulas it is possible to compute crack opening strains for any load sequence. The findings of the investigations have been merged to build an algorithm for the prediction of fatigue lives to initiation of cracks of technical sizes in case of variable amplitude loading. The improvement in accuracy of life predictions compared to results of an existing damage accumulation concept is demonstrated for two materials and two load sequences.
165 citations
TL;DR: In this paper, the surface and the deepest point of a semi-elliptical crack in a finite thickness plate were derived from a general weight function and two references stress intensity factors.
162 citations
TL;DR: In this article, a strip crack closure model based on the original Dugdale-Barenblatt model was investigated for various aspects of fatigue crack growth behavior, and a variable constraint factor was introduced into the model to account for the 3D effect at the crack tip.
140 citations
TL;DR: In this article, mixed mode crack growth direction criteria have been applied to calculations of the loading experienced by surface-initiated rolling contact fatigue cracks growing at a shallow angle to the surface, and it was demonstrated that cracks grow on the plane of the maximum shear stress rather than perpendicular to the maximum tangential stress as occurs during conventional fatigue testing.
134 citations
TL;DR: In this paper, the fatigue behavior of a naturally aged powder metallurgy 2xxx series aluminum alloy (Alcoa MB85) and a composite made of this alloy with 15 vol pct SiCp was investigated using load-controlled axial testing of unnotched cylindrical samples.
Abstract: The fatigue behavior of a naturally aged powder metallurgy 2xxx series aluminum alloy (Alcoa MB85) and a composite made of this alloy with 15 vol pct SiCp, has been investigated. Fatigue lives were determined using load-controlled axial testing of unnotched cylindrical samples. The influence of mean stress was determined at stress ratios of −1, 0.1, and 0.7. Mean stress had a significant influence on fatigue life, and this influence was consistent with that normally observed in metals. At each stress ratio, the incorporation of SiC reinforcement led to an increase in fatigue life at low and intermediate stresses. When considered on a strain-life basis, however, the composite materials had a somewhat inferior resistance to fatigue. Fatigue cracks initiated from several different microstructural features or defect types, but fatigue life did not vary significantly with the specific initiation site. As the fatigue crack advanced away from the fatigue crack initiation site, increasing numbers of SiC particles were fractured, in agreement with crack-tip process zone models.
125 citations
TL;DR: In this paper, the effect of varying amounts of Laves phase on the mechanical properties of wrought and cast + HIP Inconel718 is discussed, and methods for controlling Laves phases in cast+HIP+INconel 718 are discussed.
Abstract: The effect of varying amounts of Laves phase on the mechanical properties of wrought and cast + HIP Inconel718 is discussed. When present as a continuous or semicontinuous grain boundary network in wrought Inconel718, Laves phase dramatically reduces room temperature tensile ductility and ultimate tensile strength, with room temperature impact and fracture toughness properties and elevated temperature ductility also reduced. Laves may also act as a preferred crack initiation and propagation site, resulting in reduced low cycle fatigue (LCF) p blty d ca a i i an accelerated fatigue crack growth rates. Laves present as large globular aggregates in cast+HIP Inconel 718 significantly reduces room temperature tensile and elevated temperature stress rupture properties. In addition, the phase acts as a preferred crack initiation and propagation site, resulting in significant reductions in smooth and notch LCF capability and an accelerated fatigue crack growth rate. Methods for controlling Laves phase in wrought and cast +HIP Inconel 718 are discussed. Superalloys 718,625 and Various Derivatives Edited by Edward A. JJxia The Minerals, Metals & Materials Society, 1991
121 citations
TL;DR: In this article, a number of modifications are introduced to the linear elastic approach to establish a new parameter which is capable of correlating both long crack and short crack fatigue crack growth data.
110 citations
TL;DR: In this paper, a hybrid composite (CARALL) consisting of thin layers of carbon fiber/ epoxy prepreg sandwiched between aluminium sheets was developed, and it was shown that this class of materials offers higher modulus, higher tensile strength and lower density than 2024-T3 alloy in the longitudinal direction.
103 citations
TL;DR: In this article, a fracture mechanics analysis for the strain energy release rate associated with 90° ply matrix crack formation and growth has been developed and compared with experimental results, where the authors focused on fatigue mechanisms of matrix cracking in carbon/epoxy cross-ply laminates.
77 citations
01 Apr 1991
TL;DR: Fatigue Crack Growth (NASA/FLAGRO) computer program developed as aid in predicting growth of preexisting flaws and cracks in structural components of space systems and provides fracture-mechanics analyst with computerized method of evaluating "safe-crack-growth-life" capabilities of structural components.
Abstract: Fatigue Crack Growth (NASA/FLAGRO) computer program developed as aid in predicting growth of preexisting flaws and cracks in structural components of space systems. Is enhanced version of FLAGRO4 and incorporates state-of-the-art improvements in both fracture mechanics and computer technology. Provides fracture-mechanics analyst with computerized method of evaluating "safe-crack-growth-life" capabilities of structural components. Also used to evaluate tolerance to damage of structure of given design. Designed modular to facilitate revisions and operation on minicomputers. Written in FORTRAN 77.
TL;DR: In this article, a computer simulation is carried out to study the influence of the number of dislocations, the friction stress and the critical stress intensity, k e, to emit a dislocation.
Abstract: The stress intensity range ΔK below which no cyclic plastic deformation at the crack tip, and hence, no fatigue crack propagation occurs is investigated. The emission of dislocations from the crack tip is assumed as mechanism for the dislocation generation. For a mode III crack, a computer simulation is carried out to study the influence of the number of dislocations, the friction stress and the critical stress intensity, k e , to emit a dislocation. If during loading only one dislocation is emitted, the return of this dislocation to the crack tip and the emission of a dislocation with an opposite sign and the recombination with the first dislocation are possible during unloading. The ΔK necessary for both mechanisms is about 2 k e . If during loading more than one dislocation is emitted, during unloading at first a certain number of disclocations return to the crack tip before a dislocation of opposite sign is emitted. The necessary ΔK to move one dislocation back to the crack tip during unloading decreases with increasing number of dislocations and reaches a constant values of about 1.1 k e . This value of ΔK then is roughly independent of the friction stress and k e .
TL;DR: In this article, the effect of colony size on ΔK th, ΔK eff,th and K cl,th has been investigated as a function of Widmanstatten microstructures and it has been found that crack growth rates are strongly affected by the size of microstructural features such as colonies and α laths.
Abstract: Near threshold fatigue crack growth behavior of Ti-6A1-4V alloy was investigated as function of Widmanstatten microstructures. In particular, the effect of colony size on ΔK th , ΔK eff,th and K cl,th has been studied. It has been found that crack growth rates are strongly affected by the size of microstructural features such as colonies and α laths. However, the microstructural units controlling crack growth are colonies in fast cooled microstructures consisting of fine Widmanstatten colonies while they are α laths in relatively slow cooled ones with coarse colonies. As a result, the projection in literature of increased fatigue crack growth resistance at large colony sizes in titanium alloys can not be generalized. This distinction appears to be brought about by the thick continuous interplatelet β phase present in slow cooled structures. In fast cooled structures, thin discontinuous β phase is seen to be ineffective in arresting slip or crack. However, in slow cooled ones thick β phase appears to effectively retard slip/crack in fatigue. The thickness, composition, intrinsic properties such as modulus, ductility of β phase and an added environmental effect have been suggested to be important in this respect. The crack growth rates and the magnitudes of ΔK th and ΔK eff,th can be uniquely ordered when compared in terms of the controlling microstructural units in respective microstructures. However, crack closure levels at threshold appear to be dependent on colony size. In addition, an increase in the intrinsic crack growth resistance ΔK eff,th appears to exist when the cyclic plastic zone size approaches the thickness of α laths in the microstructure.
TL;DR: In this paper, the authors compared fatigue cracks bridged by continuous fibers in titanium alloy and titanium aluminide composites with analogous observations in fiber-reinforced ceramics under monotonic loading.
Abstract: — Recent observations of fatigue cracks bridged by continuous fibers in titanium alloy and titanium aluminide composites are compared to analogous observations in fiber-reinforced ceramics under monotonic loading. Three failure modes have been identified under axial loading in each case: longitudinal failure (failure parallel to the fibers) and noncatastrophic and catastrophic mode I failure (failure normal to the fibers). The criteria for transition from one failure mode to another are reviewed. Models developed previously to describe the failure of fiber-reinforced ceramics are extended to describe the mechanics of mode I fatigue crack growth. The extension is straightforward as long as the fibers do not fail in the crack wake, i.e. the failure mode is noncatastrophic mode I failure.
TL;DR: In this article, the authors derived the da/dN-ΔK curves for small cracks from lifetimes under cyclic load, based on a method usually applied to subcritical crack growth.
Abstract: Crack-growth relations under cyclic fatigue conditions are mostly determined for long cracks. In order to determine da/dN-ΔK curves for small cracks from lifetimes under cyclic load a procedure has been derived which is based on a method usually applied to subcritical crack growth. To prove the cyclic effect and to demonstrate the procedure in detail, measurements were carried out on an Al2O3-ceramic in bending with anR-ratio ofR=−1 and two types of relatively small cracks, namely natural cracks and Knoop-cracks. It was found that both crack types exhibit the same da/dN-ΔK relation. The exponent of the Paris law for fatigue crack growth is significantly different from the exponent of the power law for subcritical crack growth.
TL;DR: In this paper, a probabilistic finite-element method and reliability analysis for mixed-mode cyclic loading with randomness in the initial and final crack lengths, initial crack angle and position, material properties, crack-growth law, crack direction law, and loading is presented.
Abstract: Fusion of the probabilistic finite-element method and reliability analysis for probabilistic fatigue-crack growth is presented. A comprehensive method for determining the probability of fatigue failure for mixed-mode cyclic loading is also presented. The loading is mixed-mode with randomness in the initial and final crack lengths, initial crack angle and position, material properties, crack-growth law, crack-direction law, and loading. The methodology consists of calculating the reliability index via an optimization procedure which is used to calculate the probability of fatigue failure. Performance of the methodology presented is demonstrated on a classical mode-I fatigue problem.
TL;DR: In this article, the authors established the steadystate, intrinsic fatigue crack propagation (FCP) rates (da/dN) in peak-aged Al-Li-Cu alloy 2090 are established by electrical potential monitoring of short cracks with programmed constant ΔK and KmaxI loading.
Abstract: Deleterious environmental effects on steady-state, intrinsic fatigue crack propagation (FCP) rates(da/dN) in peak-aged Al-Li-Cu alloy 2090 are established by electrical potential monitoring of short cracks with programmed constant ΔK andKmaxI loading. Such rates are equally unaffected by vacuum, purified helium, and oxygen but are accelerated in order of decreasing effectiveness by aqueous 1 pct NaCl with anodic polarization, pure water’ vapor, moist air, and NaCl with cathodic polarization. Whileda/dN depend on ΔK4.0 for the inert gases, water vapor and chloride induce multiple power laws and a transition growth rate “plateau.” Environmental effects are strongest at low ΔK. Crack tip damage is ascribed to hydrogen embrittlement because of acceleratedda/dN due to parts-per-million (ppm) levels of H2O without condensation, impeded molecular flow model predictions of the measured water vapor pressure dependence ofda/dN as affected by mean crack opening, the lack of an effect of film-forming O2, the likelihood for crack tip hydrogen production in NaCl, and the environmental and ΔK-process zone volume dependencies of the microscopic cracking modes. For NaCl, growth rates decrease with decreasing loading frequency, with the addition of passivating Li2CO3 and upon cathodic polarization. These variables increase crack surface film stability to reduce hydrogen entry efficiency. Small crack effects are not observed for 2090; such cracks do not grow at abnormally high rates in single grains or in NaCl and are not arrested at grain boundaries. The hydrogen environmental FCP resistance of 2090 is similar to other 2000 series alloys and is better than 7075.
30 May 1991-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the influence of grain size and cold working on the threshold of fatigue crack growth was studied in ARMCO iron (grain size, 3-3000 μm; degree of cold working, 0-90%).
Abstract: The influence of grain size and cold working on the threshold of fatigue crack growth was studied in ARMCO iron (grain size, 3–3000 μm; degree of cold working, 0–90%). The role of crack tip shielding due to crack closure mechanisms and crack deflection was examined.
The fracture surface roughness is influenced by the grain size and especially by the degree of cold working. However, the effective threshold ΔKeff th for all the microstructures is about 2.75 MPa m12. The increase in ΔKth with increasing grain size at R = 0.1 is attributed to the increase in crack tip shielding due to crack closure.
TL;DR: In this paper, detailed micromechanical analyses of fatigue crack growth have been performed on a composite with 15 vol. pct particulate SiC in a peak-aged 2014 aluminum alloy matrix.
Abstract: Detailed micromechanical analyses of fatigue crack growth have been performed on a composite with 15 vol. pct particulate SiC in a peak-aged 2014 aluminum alloy matrix. This composite was manufactured by the Dural Aluminum Composites Company, San Diego, CA, by casting and extrusion. About 3 pct intermetallic particles were found in the matrix alloy in addition to those expected for this material. Fatigue cracks were grown from approximately threshold to rapid fracture. Analyses of the crack tips were performed by stereoimaging at low and intermediate stress intensities and just prior to the onset of rapid fracture. Detailed maps of strain were derived, and a considerable influence of SiC particles on strain was found. Analyses of microcracks near the main crack were made and found to have only a small influence on fracture. Fatigue threshold was explained on the basis of measured and calculated crack closure.
TL;DR: In this paper, a mechanism for the formation of microcracks caused by a wedge effect which develops during the unloading portion of a cycle is discussed and evaluated, which arises due to the roughness of the intergranular fracture surface as well as to debris trapped between the opposing fracture surfaces.
Abstract: The mechanism of fatigue crack growth in silicon nitride under the experimental conditions utilized is found to be of a cyclic nature, as contrasted to a form of static fatigue observed in some other ceramic systems. Conventional methods of analysis of the rate of fatigue crack growth in terms of ΔKeff are not applicable, because the results of the experimental portion of this investigation show that ΔKeff can decrease as the rate of fatigue crack growth increases. A mechanism which involves the formation of microcracks caused by a wedge effect which develops during the unloading portion of a cycle is discussed and evaluated. The wedge effect results from crack closure, which arises due to the roughness of the intergranular fracture surface as well as to debris trapped between the opposing fracture surfaces. In the proposed mechanism, the extent of crack advance per cycle is limited because of the decrease in stress intensity factor with crack advance in a given cycle associated with the wedge effect. The quantitative results of a semiempirical analysis of tests carried out in either air or vacuum are in agreement with some unusual experimental trends.
30 Oct 1991-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the authors measured the fatigue crack growth behavior of the aluminum alloy 2024-T3 in the very low threshold regime (down to approximately 10−13 m per cycle), using the high frequency (20 000 Hz) technique of ultrasonic resonance fatigue.
Abstract: The environmental influence of humid air, dried air and vacuum on the fatigue crack growth behavior of the aluminum alloy 2024-T3 was measured in the very low threshold regime (down to approximately 10−13 m per cycle), using the high frequency (20 000 Hz) technique of ultrasonic resonance fatigue. The crack growth curves, (Δa/ΔNvs. Kmax relationship) obtained in humid air were characterized by a plateau-like regime (regime with reduced slope of crack growth curve) between 10−9 and 10−10 m per cycle and a threshold value of 2.1 MPa m 1 2 . The threshold in vacuum was 3.3. MPa m 1 2 and no plateau-like regime occurred. In dried air, the curve was very close to that in vacuum, when the Kmax values were high enough; at the very lowest Kmax values, however, the curve approached that for humid air, and an almost identical threshold stress intensity value (2.3 MPa m 1 2 ) was found. The fracture morphology reflected the changing cracking mechanisms: ductile fracture with more plastic deformation and some crystallographic and intercrystalline features were observed for “high” Kmax values, whereas less plastic deformation and no crystallographic or intercrystalline features were characteristic of the threshold regime. Hydrogen embrittlement is assumed to be the main mechanism responsible for the observed corrosion fatigue behavior of alloy 2024-T3 in humid air.
TL;DR: In this paper, a model was developed for predicting residual stresses and crack growth in residual stress fields, and the application of the model to crack growth from cold-worked fastener holes in thick section aircraft components.
Abstract: This paper describes a model developed for predicting residual stresses and crack growth in residual stress fields, and the application of the model to crack growth from cold-worked fastener holes in thick section aircraft components. Comparison with experimental results demonstrates that the model can provide useful predictions of critical crack length, and a capability for correctly predicting the maxima and minima in the crack growth rate for cracks from cold-expanded holes. It also permits the observed asymmetry in cracking from cold-worked fastener holes to be better understood.
TL;DR: Several theories have been proposed to explain the transient fatigue crack growth decelerations and accelerations which follow overloads, e.g., residual stress, crack deflection, crack closure, strain hardening, and plastic blunting/resharpening as discussed by the authors.
TL;DR: In this paper, the effect of mean shear stress on the plastic deformation at stage II crack tips is discussed, which illustrates the mean-shear effect on the transition between stage I and stage II short crack growth.
Abstract: Torsional tests under different mean shear stresses were conducted at room temperature using a 1.99% NiCrMo steel. A technique was developed to control both the mean and the alternating shear stresses. It is shown that the mean shear stress plays a fundamental role in promoting stage I, mode II short crack growth. The effect of mean shear stress on the plastic deformation at stage II crack tips is discussed, which illustrates the mean shear effect on the transition between stage I and stage II crack growth. The polarity of mean shear stress is found to have no effect on the fatigue crack growth rate and the fatigue lifetime of an isotropic material. A model is proposed to account for the effect of mean shear stress on the fatigue lifetime under torsional loading.
TL;DR: In this paper, Voorwald and Pinto, C.C.E.C., discuss the effects of materials and technology on the performance of the Pinto project in Brazil.
TL;DR: In this article, the experimental and theoretical results obtained from mixed mode (I and II) fatigue crack growth tests in Jethete at 550°C were described and compared with the pure mode I data using a stress intensity factor range.
TL;DR: In this article, the fatigue crack growth properties of an aluminium AA 6061 alloy containing 15 vol.-% particulate SiC and of the corresponding matrix alloy with the same grain size were investigated.
Abstract: The fatigue crack growth properties of an aluminium AA 6061 alloy containing 15 vol.-% particulate SiC and of the corresponding matrix alloy with the same grain size were investigated. The composit...
TL;DR: In this article, the generalized driving force attached to a fatigue crack tip is in the first instance re-examined with the introduction of a new cyclic J-integral.
30 May 1991-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the results of a recent investigation of fatigue crack growth in the γ-based Ti48at.%Al alloy are presented, including room-and elevated-temperature fatigue crack data obtained at two stress ratios and temperatures.
Abstract: The results of a recent investigation of fatigue crack growth in the γ-based Ti48at.%Al alloy are presented. These include room- and elevated-temperature fatigue crack growth and closure data obtained at two stress ratios and temperatures. The possible role of oxide-induced closure at elevated temperatures is explored by use of a previously reported theoretical model,scanning Auger microscopy, and X-ray diffraction techniques. The results of deformation studies of the crack-tip region are also presented, and the micromechanisms of fatigue crack growth are elucidated.