Showing papers on "Paris' law published in 2006"
TL;DR: In this paper, a comprehensive study was carried out on series of nanocomposites containing varying amounts of nanoparticles, either titanium dioxide (TiO 2 ) or aluminium oxide (Al 2 O 3 ).
766 citations
TL;DR: In this article, an extension of the celebrated Paris law for crack propagation is given to take into account some of the deviations from the power-law regime in a simple manner using the Wohler SN curve of the material, suggesting a more general ''unified law''.
Abstract: An extension of the celebrated Paris law for crack propagation is given to take into account some of the deviations from the power-law regime in a simple manner using the Wohler SN curve of the material, suggesting a more general ''unified law''. In particular, using recent proposals by the first author, the stress intensity factor K(a) is replaced with a suitable mean over a material/structural parameter length scale Da, the ''fracture quantum''. In practice, for a Griffith crack, this is seen to correspond to increasing the effective crack length of Da, similarly to the Dugdale strip-yield models. However, instead of including explicitly information on cyclic plastic yield, short-crack behavior, crack closure, and all other detailed information needed to eventually explain the SN curve of the material, we include directly the SN curve constants as material property. The idea comes as a natural extension of the recent successful proposals by the first author to the static failure and to the infinite life envelopes. Here, we suggest a dependence of this fracture ''quantum'' on the applied stress range level such that the correct convergence towards the Wohler-like regime is obtained. Hence, the final law includes both Wohler's and Paris' material constants, and can be seen as either a generalized Wohler's SN curve law in the presence of a crack or a generalized Paris' law for cracks of any size. r 2006 Elsevier Ltd. All rights reserved.
290 citations
TL;DR: In this article, the authors proposed to use the well-known Hutchinson-Rice-Rosengren (HRR) fields to represent the singularities in elastic-plastic fracture mechanics.
238 citations
TL;DR: In this paper, the authors investigated the effect of the self-same epoxy interlayer on the interlaminar fracture properties under modes I and II loadings on the bases of the fractographic observations and mechanism considerations.
232 citations
TL;DR: In this paper, the authors investigated the delamination fatigue crack growth behavior in carbon fiber (CF)/epoxy laminates with two kinds of interlayer/interleaf and found that the crack path shifted from the heterogeneous interlayer region (Stage I) to the inter-layer/base lamina interface (Stage II) with the increase of the crack length.
222 citations
TL;DR: In this paper, a tapered double-cantilever beam (TDCB) specimen for a range of microcapsule concentrations and sizes: 0, 5, 10, and 20% by weight and 50, 180, and 460 μm diameter.
Abstract: The addition of liquid-filled urea-formaldehyde (UF) microcapsules to an epoxy matrix leads to significant reduction in fatigue crack growth rate and corresponding increase in fatigue life. Mode-I fatigue crack propagation is measured using a tapered double-cantilever beam (TDCB) specimen for a range of microcapsule concentrations and sizes: 0, 5, 10, and 20% by weight and 50, 180, and 460 μm diameter. Cyclic crack growth in both the neat epoxy and epoxy filled with microcapsules obeys the Paris power law. Above a transition value of the applied stress intensity factor ΔKT, which corresponds to loading conditions where the size of the plastic zone approaches the size of the embedded microcapsules, the Paris law exponent decreases with increasing content of microcapsules, ranging from 9.7 for neat epoxy to approximately 4.5 for concentrations above 10 wt% microcapsules. Improved resistance to fatigue crack propagation, indicated by both the decreased crack growth rates and increased cyclic stress intensity for the onset of unstable fatigue-crack growth, is attributed to toughening mechanisms induced by the embedded microcapsules as well as crack shielding due to the release of fluid as the capsules are ruptured. In addition to increasing the inherent fatigue life of epoxy, embedded microcapsules filled with an appropriate healing agent provide a potential mechanism for self-healing of fatigue damage.
184 citations
TL;DR: The fatigue crack growth resistance of human dentin decreases with both age of the tissue and dehydration, and differences in the microscopic features of the fracture surfaces from the old and young dentin suggested that particular mechanisms contributing to energy dissipation and Crack growth resistance in the young hydrated dentin were not present in the old dentin.
163 citations
TL;DR: In this paper, the micro-fracture mechanisms of an UFAF pipeline steel are investigated by in situ tensile testing in a transmission electron microscope, and the results indicate that a grain-boundary-film structure composed of martensite/austenite could significantly influence the crack propagating behavior in the UfaF steel, consequently lowering the fatigue-crack growth rate by enhancing roughness-induced crack closure during cyclic loading.
157 citations
TL;DR: In this paper, the authors investigated the fatigue behavior of as-cast and extruded AZ61 magnesium alloys in ambient air (20°C-55%RH) and found that the casting defects served as stress concentration sites for fatigue crack nucleation.
137 citations
TL;DR: Crosslinking was found to decrease the ability of UHMWPE to resist crack inception and propagation under cyclic loading, and suggested that annealing as a post-irradiation treatment may be somewhat less detrimental to FCP resistance of UhMWPE than remelting.
124 citations
TL;DR: In this article, the effect of hydrogen on the fatigue properties of alloys which are used in fuel cell (FC) systems has been investigated, and the results showed that there was a degradation in fatigue crack growth resistance due to hydrogen in the case of SUS304 and SUS316 austenitic stainless steels.
TL;DR: In this paper, the authors deal with the fatigue crack initiation under multiaxial non-proportional loadings in a natural rubber and propose two fatigue crack criteria, the first based on the first and second invariant of the Cauchy stress tensor, the second, based on micromechanisms of crack initiation, consist of a critical plane approach under large strain conditions using a micro to macro approach.
TL;DR: In this paper, experimental investigations on both mixed mode overloads, which are interspersed into a Mode I baseline level loading, and mixed mode block loadings are presented, and it is shown that the retardation effect decreases with an increasing amount of Mode II of the overload.
TL;DR: In this article, a number of modifications to the Wheeler fatigue crack retardation model were proposed to account for the delay retardation due to applied overloads, initial crack growth acceleration immediately following an overload, overload interaction and the net section yielding effect observed in the fatigue crack growth retardation behaviour of many materials.
TL;DR: In this article, the energy release rate approach is applied to describe the delamination growth rate in a fiber metal laminate such as Glare, which is accompanied by delamination at the interface between the aluminium and glass fibre/adhesive layers.
TL;DR: In this paper, the effect of an absorbent overlay on the residual stress field using this LSP setup and this energy level was evaluated and it was observed that the overlay makes the compressive residual stress profile move to the surface.
TL;DR: In this article, the results of in situ observation of fatigue crack growth in a ferrite-pearlite steel were reported, where stress intensity factor range (ΔK) decreasing/increasing and constant ΔK fatigue tests have been carried out.
TL;DR: Based on the experimental results for spot welds in square-cup, lap-shear and coach-peel specimens of dual phase, low carbon and high strength steels, kinked fatigue crack paths near spot weld was examined as discussed by the authors.
TL;DR: In this paper, the authors examined the fatigue crack growth histories, at low to mid range Δ K, for a range of aircraft aluminium alloys, test specimens and service loaded components, and concluded that there is a log-linear relationship between the apparent crack length or depth and the life (N ), respectively.
TL;DR: In this paper, the authors investigated the fatigue crack growth behavior in a stiffened thin 2024-T3 aluminum panel repaired with one-sided adhesively bonded composite patch through experiments and analyses.
TL;DR: In this article, a linkage system was developed in order to permit the variation of the K I / K II ratio by changing the loading angle, and a finite element analysis was also done to obtain the k I and K II values for the different loading angles.
TL;DR: Very long life fatigue and near-threshold fatigue crack growth behavior of 7075 and 6061 Al-alloys in T6 condition were investigated using accelerated fatigue testing at 19.5 kHz on a piezoelectric machine as mentioned in this paper.
TL;DR: In this article, a short crack growth model is presented for calculating fatigue lives to technical crack initiation in materials and structures under non-proportional multiaxial loading, which is based on an integration of the crack growth equation expressed in terms of the effective range of the cyclic J-integral.
TL;DR: In this article, the effect of Manganese sulfides (MnS) on anisotropy of forged steel components is quantified using push-pull fatigue testing in longitudinal and short transversal directions.
Abstract: Anisotropy of forged steel components is especially adverse when it concerns rotationally symmetric components. Manganese sulfides (MnS) in steels may be desired for their improvement of machining properties; however, they also deteriorate fatigue behavior. A quantification of the effect of MnS on anisotropy is necessary to find an optimum for component dimensioning. To isolate the influence of MnS on anisotropy only, high cleanness of the test material is required. The test material in the current investigation was molten in a vacuum furnace to high-cleanness composition. Materials with two different S levels were produced to detect variations in anisotropy according to amount, shape, and distribution of the MnS inclusions. The two batches were cross-rolled to plates with a deformation ratio of 4.5. The MnS phase constitutes, upon forging or rolling, pancake-shaped inclusions. In the case of cross-rolling, an in-plane rotational symmetry of the inclusions could be created. The shape and size of these inclusions are essential for the mechanical behavior of the material. Push-pull fatigue testing was performed in longitudinal (in plane) and short transversal directions relative to the rolling plane. The results showed strong anisotropy of the fatigue behavior with inferior performance in short transverse directions where the principal stress is perpendicular to the flattened inclusions. The anisotropy was somewhat more pronounced for the high-S material, resulting from a different fatigue crack growth mechanism.
TL;DR: In this article, the stress field in a structural component depends on the possible presence of a notch, and fatigue life may strongly be affected by geometric discontinuities, and the effect of the stress concentration on the SIF values is discussed for the considered crack configurations.
TL;DR: In this article, the authors present the cracking process of small fatigue cracks and the influence of higher temperatures and vacuum conditions on the growth behavior of these cracks in cast AM50 magnesium alloy.
TL;DR: In this article, the authors provide experimental, testing, and mathematical techniques to account for residual-stress effects on crack growth rate data, together with two methods for eliminating residual stresses in crack growth test specimens.
Abstract: The fatigue crack growth (FCG) behavior of various types of alloys is significantly affected by the presence of residual stress induced by manufacturing and post-manufacturing processes. There is a qualitative understanding of the effects of residual stress on fatigue behavior, but the effects are not comprehensively quantified or accounted for. The difficulty in quantifying these effects is largely due to the complexity of residual-stress measurements (especially considering that parts produced in similar conditions can have different residual-stress levels) and the lack of mathematical models able to convert experimental data with residual stress into residual-stress-free data. This article provides experimental, testing, and mathematical techniques to account for residual-stress effects on crack growth rate data, together with two methods for eliminating residual stresses in crack growth test specimens. Fracture-mechanics concepts are used to calculate, in simple and convenient ways, stress-intensity factors caused by residual stresses. The method is advantageous, considering that stress-intensity factors are determined before the actual test is conducted. Further on, residual-stress-intensity factors are used to predict the residual-stress distribution in compact tension (CT) specimens prior to testing. Five cast Al-Si-Mg alloys with three Si levels (in unmodified (UM) as well as Sr-modified (M) conditions) were analyzed both with and without residual stress. Fatigue cracks are grown under both constant stress ratio, R=0.1, and constant maximum stress-intensity factor, K
max = const., conditions. The mechanisms involved in crack growth through residual-stress fields are presented.
25 Jul 2006-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the effect of boron on the fatigue crack growth rate in Inconel 718 (IN 718) was studied at room temperature (RT) and 650°C.
Abstract: The effect of boron on the fatigue crack growth rate (FCGR) in Inconel 718 (IN 718) was studied at room temperature (RT) and 650 °C The results showed that the addition of B improved the fatigue crack propagation resistance of IN 718 The higher the B concentration, higher was the fatigue threshold at 650 °C While the FCGRs increased as the test temperature increased from RT to 650 °C in the Paris regime, a rapid drop in the FCGRs in the near-threshold regime and a higher fatigue threshold at 650° were observed due to the oxide-induced crack closure The fracture surfaces were observed to exhibit transgranular cracking with fatigue striations in specimens tested at RT, and a mixture of transgranular and intergranular cracking at 650 °C The fracture mode changed from intergranular cracking to transgranular cracking and plastic deformation marks increased with increasing B concentration at 650 °C The micromechanism of improvement in the fatigue crack growth resistance due to B addition was further studied via observations of crack growth path, fractography and TEM examination of the plastic zone ahead of the crack tip The plastic deformation mode within the crack tip plastic zone was planar slip, along with twinning, on {1 1 1} planes A crystallographic cracking model was, thus, proposed on the basis of restricted slip or twinning The improvement in the fatigue crack growth resistance in IN 718 due to B addition was mainly attributed to the increase in the grain boundary cohesion via minimizing the deteriorative effect of oxygen and the increase in the resistance to the dislocation movement at the crack tip
TL;DR: In this article, the authors investigated the near-threshold crack growth behavior of hypoeutectic and eutective Al-Si-Mg cast alloys for both long and short cracks.
TL;DR: In this article, a numerical model of fatigue crack growth retardation in polymers induced by artificial crack closure is proposed, which relies on the combination of cohesive modeling and a contact algorithm incorporated in the wake of the advancing crack.