Showing papers on "Paris' law published in 1984"
TL;DR: In this paper, a general crack opening stress equation is presented which may be used to correlate crack growth rate data for various materials and thicknesses, under constant amplitude loading, once the proper constraint factor has been determined.
Abstract: A general crack opening stress equation is presented which may be used to correlate crack growth rate data for various materials and thicknesses, under constant amplitude loading, once the proper constraint factor has been determined. The constraint factor, alpha, is a constraint on tensile yielding; the material yields when the stress is equal to the product of alpha and sigma. Delta-K (LEFM) is plotted against rate for 2024-T3 aluminum alloy specimens 2.3 mm thick at various stress ratios. Delta-K sub eff was plotted against rate for the same data with alpha = 1.8; the rates correlate well within a factor of two.
761 citations
01 Jan 1984
TL;DR: In this paper, a Symposium was organized specifically to concentrate on the concepts underlying the fatigue crack growth threshold, including the roles of composition, microstructure, environment, temperature, crack closure, crack size, and variable amplitude loading.
Abstract: This symposium was organized specifically to concentrate on the concepts underlying the fatigue crack growth threshold. Research has led to an improved understanding of the many mechanisms influencing the near-threshold behavior of fatigue crack growth in engineering materials. These proceedings deal with many aspects of near-threshold fatigue crack growth including the roles of composition, microstructure, environment, temperature, crack closure, crack size, and variable amplitude loading. The current level of knowledge of fatigue thresholds is accurately reflected by the contents of the manuscripts.
200 citations
TL;DR: In this article, the role of microstructure and environment in influencing ultra-low fatigue crack propagation rates has been investigated in 7075 aluminum alloy heat-treated to underaged, peak-aged, and overaged conditions and tested over a range of load ratios.
Abstract: The role of microstructure and environment in influencing ultra-low fatigue crack propagation rates has been investigated in 7075 aluminum alloy heat-treated to underaged, peak-aged, and overaged conditions and tested over a range of load ratios. Threshold stress intensity range, ΔK0, values were found to decrease monotonically with increasing load ratio for all three heat treatments fatigue tested in 95 pct relative humidity air, with ΔK
0 decreasing at all load ratios with increased extent of aging. Comparison of the near-threshold fatigue behavior obtained in humid air with the data forvacuo, however, showed that the presence of moisture leads to a larger reduction in ΔK0 for the underaged microstructure than the overaged condition, at all load ratios. An examination of the nature of crack morphology and scanning Auger/SIMS analyses of near-threshold fracture surfaces revealed that although the crack path in the underaged structure was highly serrated and nonlinear, crack face oxidation products were much thicker in the overaged condition. The apparent differences in slow fatigue crack growth resistance of the three aging conditions are ascribed to a complex interaction among three mechanisms: the embrittling effect of moisture resulting in conventional corrosion fatigue processes, the role of microstructure and slip mode in inducing crack deflection, and crack closure arising from a combination of environmental and microstructural contributions.
146 citations
TL;DR: In this article, the authors investigated the influence of a preferred crystallographic orientation on mechanical properties of textured Ti-6Al-4V material and found that high cycle fatigue and fatigue crack growth were performed in vacuum, laboratory air, and a 3.5 pct NaCl solution.
Abstract: Tensile properties, high cycle fatigue strength, and fatigue crack propagation behavior were evaluated on highly textured Ti-6Al-4V material to investigate the influence of a preferred crystallographic orientation on mechanical properties. Thermomechanical treatments were used to develop three different textures: a basal, basal/transverse, and transverse type, all of which exhibited the same homogeneously equiaxed microstructure. The Young’s modulus was found to vary between 107 and 126 GNm-2, and yield strength changed from 1055 to 1170 MNm-2. Ductility was only slightly affected by texture. High cycle fatigue and fatigue crack growth measurements were performed in vacuum, laboratory air, and a 3.5 pct NaCl solution. It is shown that laboratory air can be regarded as a quite corrosive environment. In vacuum the highest fatigue strength values were measured whenever loads were perpendicular to basal planes. However, these conditions had the highest susceptibilities to air and 3.5 pct NaCl solution environments. Nearly no influence of texture on fatigue crack propagation was found in vacuum, but in a corrosive environment crack growth parallel to (0002)-planes was much faster than perpendicular to these planes. To explain the corrosive effect on the fatigue properties of the textured material hydrogen is thought to play a key role.
139 citations
TL;DR: In this paper, the effects of slip character and grain size on the intrinsic material and extrinsic closure contributions to fatigue crack growth resistance have been studied for a 7475 aluminum alloy.
Abstract: The effects of slip character and grain size on the intrinsic material and extrinsic closure contributions to fatigue crack growth resistance have been studied for a 7475 aluminum alloy. The alloy was tested in the underaged and overaged conditions with grain sizes of 18 μm and 80 μm. The fracture surface exhibited increased irregularity and planar facet formation with increased grain size, underaging, and tests in vacuum. These changes were accompanied by an increased resistance to fatigue crack growth. In air the 18 μm grain size overaged material exhibited relatively poor resistance to fatigue crack growth compared with other microstructural variants, and this was associated with a lower stress intensity for closure. All materials exhibited a marked improvement in fatigue crack growth resistance when tested in vacuum, with the most significant difference being ˜1000× at a ΔK of 10 MPa m1/2 for the 80 μm grain size underaged alloy. This improvement could not be accounted for by either an increase in closure or increased crack deflection and is most likely due to increased slip reversibility in the vacuum environment. The intrinsic resistance of the alloy to fatigue crack growth was microstructurally dependent in vacuum, with large grains and planar slip providing the better fatigue performance.
136 citations
TL;DR: In this paper, Fatigue crack growth rates have been determined on standard specimens containing long cracks and on specimens containing two-dimensional short cracks (∼0.10-0.50mm).
Abstract: Fatigue crack growth rates have been determined on standard specimens containing long cracks (∼5–10mm) and on specimens containing two-dimensional short cracks (∼0.10–0.50mm). Large differences have been observed indicating that at a given stress intensity factor short cracks propagate much faster than long cracks. Mouth opening displacement measurements for both specimen geometries have shown that the crack closure effect is largely responsible for the observed effect. These results are used to rationalize the behaviour of short cracks initiated from natural sites which were either graphite nodules or microshrinkage pores. The three-dimensional aspect of these natural small cracks is analysed and discussed in detail.
117 citations
TL;DR: The relative fatigue crack propagation resistance of plain and carbon fiber‐reinforced ultrahigh molecular weight polyethylene (UHMWPE) was determined from cyclic loading tests performed on compact tension specimens machined from the tibial components of total knee prostheses.
117 citations
TL;DR: Aramid reinforced aluminium laminates show excellent fatigue crack growth properties as discussed by the authors, due to the restraint on the crack opening by uncracked fibres in the wake of the crack.
69 citations
TL;DR: The influence of temperature and frequency on the crack propagation behavior of a single crystal superalloy has been investigated in this article, where failure at all temperatures is associated with the fracture of script carbides ahead of the crack tip.
Abstract: The influence of temperature and frequency on the crack propagation behavior of a single crystal superalloy has been investigated. At applied stress intensities approaching the fracture toughness, failure at all temperatures is associated with the fracture of script carbides ahead of the crack tip. At low and intermediate levels of ΔK the fatigue crack growth behavior is influenced by the temperature and frequency. At room temperature crack growth is found to occur by failure on {111} planes; at 600 °C and 850 °C crack growth is parallel to {100} . It has been shown that this behavior is not attributable to environmental interactions but arises from the morphology and distribution of the strengthening γ’ precipitate. Dislocations within the crack tip plastic zone are contained within the matrix, and crack propagation occurs primarily within the γ matrix by plasticity-controlled failure.
65 citations
TL;DR: In this article, fatigue crack growth data are presented for different microstructures of typical nickel base superalloys used in gas turbine engines, i.e., from the short crack through to the long crack propagation regime, described for each microstructural condition and discussed in terms of current theories of fatigue crack propagation.
Abstract: The use of engineering materials in critical applications necessitates the accurate prediction of component lifetime for inspection and renewal purposes. In fatigue limited situations, it is necessary to be able to predict the growth rates of cracks from initiation at a defect through to final fracture. To this end, fatigue crack growth data are presented for different microstructures of typical nickel base superalloys used in gas turbine engines. Crack growth behaviour throughout the life history of the crack, i.e. from the short crack through to the long crack propagation regime, is described for each microstructural condition and discussed in terms of current theories of fatigue crack propagation.
64 citations
TL;DR: In this article, a power relation between the fatigue crack propagation rate d a/d N and the J integral range ΔJ was obtained for OFHC copper, 0.04%C steel and stainless steel (Type 304).
01 Apr 1984
TL;DR: In this paper, the authors predicted crack growth patterns and crack growth lives for aluminum alloys using linear-elastic fracture mechanics concepts that were modified to account for crack-closure behavior, using stress intensity factor equations for these crack configurations and the fatigue crack-growth (delta K against rate) relationship for the material of interest.
Abstract: Fatigue crack growth patterns and lives for surface cracks, surface cracks at holes, and corner cracks at holes in three dimensional bodies were predicted using linear-elastic fracture mechanics concepts that were modified to account for crack-closure behavior. The predictions were made by using stress intensity factor equations for these crack configurations and the fatigue crack-growth (delta K against rate) relationship for the material of interest. The crack configurations were subjected to constant-amplitude fatigue loading under either remote tension or bending loads. The predicted crack growth patterns and crack growth lives for aluminum alloys agreed well with test data from the literature.
TL;DR: In this article, the micromechanical theory of fatigue crack nucleation is applied to stage I fatigue crack growth observed in high-strength alloys, and it is further extended to the near-threshold growth of a long fatigue crack.
TL;DR: In this paper, the size and density of individual contacts can be estimated from acoustic measurements, which is useful to provide the static stress across a partially closed crack as well as the effective stress intensity range which activates fatigue crack propagation.
Abstract: The partial contact of two rough fatigue crack surfaces leads to transmission, reflection, diffraction, and mode conversion of an acoustic signal at those contacts. This paper reviews recent experimental and theoretical efforts to understand and quantify such contact on actual fatigue cracks in greater detail. It is shown that the size and density of individual contacts, or asperities, can be estimated from acoustic measurements. Furthermore, it is shown that this information is useful to provide the static stress across a partially closed crack as well as the “effective” stress intensity range which activates fatigue crack propagation.
Book•
01 Oct 1984
TL;DR: In this article, a fracture model for Iodine Stress Corrosion Crack Propagation in Zircaloy Tubing was presented. And the authors used a constant /Delta/kappa/ test method in the investigation of fatigue crack growth in 288/sup 0/C water environments.
Abstract: These proceedings collect papers on metal fracture mechanics. Titles include: A Fracture Mechanics Model for Iodine Stress Corrosion Crack Propagation in Zircaloy Tubing; Evaluation of SCC Test Methods for Inconel 600 in Low-temperature Aqueous Solutions; Automated Corrosion Fatigue Crack Growth Testing in Pressurized Water Environments; and use of a constant /Delta//kappa/ test method in the investigation of fatigue crack growth in 288/sup 0/C water environments.
TL;DR: In this paper, the authors examined the fatigue crack propagation behavior of aluminum alloy 2020 (AlCuLiMnCd) in the peak strength temper over a wide range of growth rates (from 10 −6 to 10 −11 m cycle −1 ).
01 Jan 1984
TL;DR: In this paper, a considerable amount of research on elastic-plastic fracture mechanics has been conducted during the last five years, and the use and application of fracture mechanics to practical problems is discussed.
Abstract: During the last five years a considerable amount of research on elastic-plastic fracture mechanics has been conducted. The aim of this book is to show the use and application of fracture mechanics to practical problems. The book deals with the following aspects: basic problems and concepts; mechanisms of fracture and crack growth; the elastic crack-tip stress field; the crack tip plastic zone; the energy principle; dynamics and crack arrest; plane strain fracture toughness; plane stress and transitional behaviour; elastic-plastic fracture; fatigue crack propagation; fracture resistance of materials; fail-safety and damage tolerance; determination of stress intensity factors; practical problems; fracture of structures; stiffened sheet structures; and prediction of fatigue crack growth. (TRRL)
TL;DR: In this paper, the influence of microstructure on the low cycle fatigue behavior in a model single crystal superalloy has been measured for aligned as well as randomly oriented crystals, and a model was developed to predict this phenomenon.
TL;DR: In this article, the susceptibility of coarse-grained A533B to "one-step-temper-embrittlement" when tempered at 290°C was assessed using fracture toughness testing at −120°C.
TL;DR: In this article, the effective threshold stress intensity was obtained by subtracting the closure portion from the fatigue threshold, which was found to correlate very well to the thermal component of the flow stress.
Abstract: It is shown that closure mechanisms alone cannot fully explain increasing fatigue thresholds with decreasing test temperature for a sequence of Fe-Si binary alloys and an HSLA steel. Implications are that fatigue crack propagation near threshold is a thermally activated process. The effective threshold stress intensity, which was obtained by subtracting the closure portion from the fatigue threshold, was examined. This effective stress intensity was found to correlate very well to the thermal component of the flow stress. A detailed fractographic study of the fatigue surface was performed. Water vapor in the room air was found to promote the formation of oxide and intergranular crack growth. At lower temperature, a brittle-type cyclic cleavage fatigue surface was observed but the ductile process persisted even at 123 K. Arrest marks were found on all three modes of fatigue crack growth. The regular spacings between these lines and dislocation modeling suggested that fatigue crack growth was controlled by the subcell structure near threshold. A model based on the slip-off of dislocations was examined. From this, it is shown that the effective fatigue threshold may be related to the square root of (one plus the strain rate sensitivity).
TL;DR: In this paper, the cyclic and monotonic plastic zone sizes were measured in a medium strength ferrite-pearlite steel (BM 45) tested in fatigue at 25 Hz at room temperature.
TL;DR: In this article, a model for estimating crack growth at near-threshold rates has been proposed using concepts previously suggested by Hornbogen and Zum Gar, Neumann and others.
TL;DR: In this article, the linear part of the fatigue crack growth diagram is divided into Stages IIa and IIb by the point O whose coordinates K∗ and A are dependent on the physical and structural characteristics of the material.
TL;DR: In this article, the effects of microstructure on ambient temperature mechanical properties were examined on AISI 1018 and Fe2Si-0.1C steels with duplex ferrite-martensite (DFM) microstructures.
TL;DR: In this article, a model based on the hysteresis strain energy density is proposed for predicting fatigue crack growth, whose growth rates are obtained by specifying the number of cycles, Δ N, for each growth step.
TL;DR: In this paper, the influence of oxidation kinetics on the near threshold fatigue crack growth behavior of a nickel base precipitation hardened superalloy was studied in air from 427° to 649 °C.
Abstract: The influence of oxidation kinetics on the near threshold fatigue crack growth behavior of a nickel base precipitation hardened superalloy was studied in air from 427° to 649 °C. The tests were conducted at 100 Hz and at load ratios of 0.1 and 0.5. The threshold ΔK values were found to increase with temperature. This behavior is attributed to oxide deposits that form on the freshly created fracture surfaces which enhance crack closure. As determined from secondary ion mass spectrometry, the oxide thickness was uniform over the crack length and was of the order of the maximum crack tip opening displacement at threshold. Oxidation kinetics were important in thickening the oxide on the fracture surfaces at elevated temperatures, whereas at room temperature, the oxide deposits at near threshold fatigue crack growth rates and at low load ratios were thickened by an oxide fretting mechanism. The effect of fracture surface roughness-induced crack closure on the near threshold fatigue crack growth behavior is also discussed.
TL;DR: In this paper, it was shown that the early crack growth occurs in stage I along persistent slip bands both in air and in vacuum, and that transitions from stage I to stage II crack growth and vice versa could be induced at arbitary crack lengths by appropriate increases or reductions in the amplitude.
TL;DR: A generalized B-model which includes this dependence is presented whose parameters are estimated via first and second moments including covariance, motivated by application to problems in reliability and maintainability.
TL;DR: In this article, the authors investigated the room temperature crack growth response in water vapor for annealed Ti-5.5.%Al-2.5wt.%Sn alloy and for Ti-6.4.%V alloy at room temperature.
TL;DR: In this paper, an Al-Cu alloy under specially designed complex load sequences was used to investigate the propagation of fatigue crack propagation in a rain-flow cycle counting model, which was applied to the analysis of fatigue fracture growth under complex load sequence.