Showing papers on "Paris' law published in 2005"
TL;DR: In this article, a model for fatigue crack growth based on the elastic-plastic crack tip stress-strain history was proposed, and the model was developed to predict the effect of the mean stress including the influence of applied compressive stress.
300 citations
TL;DR: In this article, the authors deal with the complex problem of a-however initiated-crack, that is subjected to a mixed-mode loading, and present the hypotheses and concepts, which describe the superposition of Mode I and Mode II (plane mixed mode) as well as the subgroup of all three modes (Mode I, II and III) for spatial loading conditions.
Abstract: In many practical cases, the crack growth leads to abrupt failure of components and structures. For reasons of a reliable quantification of the endangerment due to sudden fracture of a component, therefore, it is of enormous importance to know the threshold values, the crack paths and the growth rates for the fatigue crack growth as well as the limiting values for the beginning of unstable crack growth (fracture toughness). This contribution deals with the complex problem of a-however initiated-crack, that is subjected to a mixed-mode loading. It will present the hypotheses and concepts, which describe the superposition of Mode I and Mode II (plane mixed mode) as well as the superposition of all three modes (Mode I, II and III) for spatial loading conditions. Those concepts admit a quantitative appraisal of such crack situations and a characterization of possible crack paths.
293 citations
TL;DR: In this paper, the authors examined two promising crack-tip shielding mechanisms during fatigue of a microcapsule toughened epoxy, and demonstrated the potential for in situ self-healing of fatigue damage.
267 citations
TL;DR: In this article, the authors studied the stress-life fatigue behavior and fatigue crack growth characteristics of pure Ni as a function of grain size spanning a range of tens of nanometer to tens of micrometer and found that grain refinement to the nanocrystalline regime generally leads to an increase in total life under stress-controlled fatigue whereas a deleterious effect was seen on the resistance to fatigue cracks growth at low and high tensile load ratio levels.
246 citations
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01 Jan 2005
TL;DR: In this article, an analytical model has been developed based on the crack opening relations, which reveals a good correlation between predicted and experimental crack growth rates, crack opening contours and delamination shapes.
Abstract: Fibre Metal Laminate Glare consists of thin aluminium layers bonded together with pre-impregnated glass fibre layers and shows an excellent fatigue crack growth behaviour compared to monolithic aluminium. The fibres are insensitive to the occurring fatigue loads and remain intact while the fatigue cracks occur in the aluminium layers. As a consequence, part of the load is transferred through the fibre layers instead of around the crack tip in the aluminium layers, reducing the crack growth rate. The major concept in this thesis is the stress intensity at a crack tip in the metal layers of a Fibre Metal Laminate being the factor determining the extension of that crack under cyclic loading. The stress intensity factor consists of a crack opening contribution of the far field stresses in the aluminium layers, similar to monolithic aluminium, and a crack closing contribution of the intact fibres in the wake of the crack. An analytical model has been developed based on the crack opening relations. Validation with a wide range of test data, reveals a good correlation between predicted and experimental crack growth rates, crack opening contours and delamination shapes
215 citations
TL;DR: In this paper, the authors examined the fatigue crack growth histories of a range of test specimens and service loaded components and concluded that in all cases, the crack growth shows, as a first approximation, a linear relationship between the log of the crack length or depth and the service history (number of cycles).
152 citations
TL;DR: In this article, the effect of welding residual stresses on fatigue crack growth in rail welds is studied using finite element analysis (FEA) to calculate residual stresses in a flash-butt welded rail.
100 citations
TL;DR: In this article, the fatigue properties of TiAl alloys, namely fatigue life, cyclic stress-strain behavior and fatigue crack growth resistance are reviewed, and the influence of different parameters (microstructure, defects, temperature and environment) on these properties is examined.
93 citations
TL;DR: In this paper, Spievak et al. used finite element methods to simulate arbitrarily shaped fatigue crack growth in a spiral bevel gear more efficiently and with much higher resolution than with a previous boundary element-based approach.
91 citations
TL;DR: In this article, the authors examined the fatigue crack growth behavior of titanium alloys using the Unified Approach developed by the authors, based on the realization that fatigue requires two load parameters for unambiguous description This requirement manifests as two fracture mechanics parameters: maximum stress intensity factor, K max, and stress intensity amplitude, Δ K .
85 citations
TL;DR: In this article, an elastic-plastic stress analysis was conducted for the cracked specimens using the finite element method and it was shown that the predicted crack opening load did not stabilize when the extended crack was less than four times of the plastic zone size.
TL;DR: In this paper, the question of the size dependence of the Paris power law is re-examined, and through comparison to a larger body of fatigue-crack growth data in steels, physical explanations why such scaling effects may exist are deduced.
Abstract: The Paris power law, which relates fatigue-crack growth rates to the applied stress-intensity range, is an example of a scaling law with the inherent property of incomplete similarity. Previous considerations of dimensions and self-similarity have suggested that the assumed 'materials constants' in this law are also a function of specimen size. In this note, the question of the size-dependence of the Paris law is re-examined, and through comparison to a larger body of fatigue-crack growth data in steels, physical explanations why such scaling effects may exist are deduced.
TL;DR: In this paper, both similarity methods and fractal concepts are used to derive a crack-size dependent Paris law, which is based upon the assumption of an incomplete self-similarity in the fatigue crack growth phenomenon or, on the other hand, the modelling of crack surfaces as selfsimilar invasive fractals.
TL;DR: In this paper, the elastic-plastic finite element analysis was used to model the fatigue crack growth under variable amplitude loading in a real structure and showed that due to an overload depending on the overload ratio R ol and the mode I/mode II ratio plastic deformations occur, which on the one hand reduce the near-tip closure and cause a far-field closure.
TL;DR: In this paper, the effects of ductile reinforcement (titanium alloy) type, thickness, and volume fraction on fatigue crack propagation in metal-intermetallic laminate (MIL) composites were systematically investigated in both arrester and divider orientations.
Abstract: Fatigue crack propagation (FCP) has been studied in a new class of materials termed metal-intermetallic laminate (MIL) composites (Ti-Al3Ti). Due to ease of fabrication and control over layer makeup, these MIL composites can be tailored to optimize the constituent properties for structural and higher performance aerospace applications. Effects of ductile reinforcement (titanium alloy) type, thickness, and volume fraction were systematically investigated in both arrester and divider orientations. Stress intensity (Kmax) values as large as 40 MPa√m were observed in the higher crack growth regime, indicating that the fracture toughness of the MIL composites is comparable to common structural metals. In both divider and arrester orientations, the overall fatigue crack growth rate showed an improvement with increasing Ti volume fraction and with increasing Ti thickness (at constant ductile-phase volume fraction). It is noted that the fatigue resistance of monolithic Al3Ti was improved by an order of magnitude by incorporating just 20 vol pct ductile Ti. In the divider orientation, toughening is obtained through plastically stretching the intact ductile Ti ligaments that bridge the crack wake, thus reducing the crack driving force. By virtue of its morphology, the arrester orientation provides toughening by trapping the crack front entirely at the metallic-intermetallic interfaces, thus requiring the crack to renucleate at each interface. Results are compared with specific crack growth rates of conventional monolithic alloys and other composite systems such as TiNb/γ-TiAl and Nb/Nb3Al. Owing to their low density (∼3.8 g/cc), Ti-Al MIL composites exhibited specific crack growth rates (da/dN vs ΔK/ρ) on par with tougher, but relatively denser, ductile metals such as Ti alloys and high-strength steels.
TL;DR: In this paper, a relatively novel approach to the estimation of the life of the fleet, utilising a probabilistic approach, and considering the wing attachment bulkheads of a specific fighter aircraft, is presented.
TL;DR: In this paper, the authors used FRANC3D, a state-of-the-art crack propagation software developed at Cornell University, which uses boundary elements and linear elastic fracture mechanics.
TL;DR: In this article, a fracture mechanics-based model was developed to simulate the observed multiple crack growth process, and an interactive effect with corrosion exposure duration and fracture interaction effects were investigated.
TL;DR: In this paper, a study on the behavior of crack propagation rate as a function of R ratio, from negative to positive stress ratios, is made, where both the effect of P max and of R ratios are taken into consideration.
TL;DR: In vitro cyclic fatigue experiments were conducted over a range of cyclic frequencies on elephant dentin in order to quantify fatigue-crack growth behavior from the perspective of understanding the mechanism of fatigue in dentin, finding results obtained to be of importance for an improved understanding of fatigue-related failures in teeth.
TL;DR: In this article, the authors investigated the fatigue crack growth rate in ultrafine grained (UFG) Al-7.5Mg and compared it to powder-metallurgy (P/M) Al−7Mg, ingot-mechanical (I/M), and I/M Al−6Mg.
TL;DR: In this article, the effects of frequency on the fatigue behavior of S2 glass fiber-vinylester reinforced sandwich composites with two different PVC cores have been investigated, and it was observed that the fatigue strength increased with core density, and the number of cycles to failure, N f, increased with increase in frequency.
01 Aug 2005
TL;DR: In this article, the authors developed a database of fatigue crack growth data in three usable formats: (1) NASGRO equation parameters, (2) Walker equation parameters and (3) tabular data points.
Abstract: The objective of this project was to begin the process of developing a fatigue crack growth database (FCGD) of metallic materials for use in damage tolerance analysis of aircraft structure. For this initial effort, crack growth rate data in the NASGRO (Registered trademark) database, the United States Air Force Damage Tolerant Design Handbook, and other publicly available sources were examined and used to develop a database that characterizes crack growth behavior for specific applications (materials). The focus of this effort was on materials for general commercial aircraft applications, including large transport airplanes, small transport commuter airplanes, general aviation airplanes, and rotorcraft. The end products of this project are the FCGD software and this report. The specific goal of this effort was to present fatigue crack growth data in three usable formats: (1) NASGRO equation parameters, (2) Walker equation parameters, and (3) tabular data points. The development of this FCGD will begin the process of developing a consistent set of standard fatigue crack growth material properties. It is envisioned that the end product of the process will be a general repository for credible and well-documented fracture properties that may be used as a default standard in damage tolerance analyses.
TL;DR: In this article, the theory of the numerical determination of the intersection angle γ r is briefly described and the influence of the 3D corner singularity on fatigue crack growth is experimentally investigated.
TL;DR: In this paper, small fatigue crack propagation in two cast aluminum alloys (W319-T7 and A356-T6) was investigated by initiating cracks from micronotches.
TL;DR: In this paper, the authors investigated the fatigue and damage tolerance behavior of pre-corroded 2024 T351 aluminum alloy specimens and compared to the behaviour of the uncorroded material.
TL;DR: In this paper, specialized finite element (FE) and fatigue life assessment software are used to solve the problem of estimating the crack path and associated stress intensity factors (SIF) of kinked and bifurcated cracks.
25 Sep 2005-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the results of a combined experimental and mechanistic modeling approach to the study of dwell fatigue in Ti-6242 were presented, where crack shape evolution, depth and surface crack growth rates were established using beachmarking, acoustic emission and scanning electron microscopy (SEM) techniques.
Abstract: This paper presents the results of a combined experimental and mechanistic modeling approach to the study of dwell fatigue in Ti-6242. Crack shape evolution, depth and surface crack growth rates are established using beachmarking, acoustic emission and scanning electron microscopy (SEM) techniques. The underlying crack nucleation and fatigue fracture modes are elucidated for three microstructures: equiaxed (microstructure 1), elongated (microstructure 2) and colony (microstructure 3) of Ti-6242. The dominant crack nucleation mode is shown to involve a Stroh-type dislocation mechanism, where sub-surface cracks are characterized by prominent facetted fracture modes in the near-threshold regime. Subsequent fatigue crack growth occurs by fatigue striations and ductile dimples or cleavage-like static modes at higher stress intensity factor ranges. The long crack growth data are similar for both dwell and pure fatigue. However, the dwell fatigue crack growth rates are shown to be much greater than those due to pure fatigue in the short crack growth regime. The differences between the dwell crack growth rates and the pure fatigue crack growth rates in the short regime are attributed to possible creep effects that give rise to a mean stress effect in the case of dwell fatigue. Subsequently, the measured crack growth rates are incorporated into a fracture mechanics framework for the estimation of fatigue life in the three microstructures. The implications of the predictions are discussed for the modeling of dwell fatigue.
TL;DR: In this article, a micro-sized Ni-P amorphous thin film was used for fracture toughness tests and the results indicated that the fracture life of micro-size specimens is dominated by a crack initiation process and that even a small surface flaw may be an initiation site for fatigue cracks.
Abstract: Fracture and fatigue tests have been performed on micro-sized specimens for microelectromechanical systems (MEMS) or micro system technology (MST) applications. Cantilever beam type specimens with dimensions of 10 x 12 x 50 μm 3 , approximately 1/1000th the size of ordinary-sized specimens, were prepared from a Ni-P amorphous thin film by focused ion beam machining. Fatigue crack growth and fracture toughness tests were carried out in air at room temperature, using a mechanical testing machine developed for micro-sized specimens. In fracture toughness tests, fatigue pre-cracks were introduced ahead of the notches. Fatigue crack growth resistance curves were obtained from the measurement of striation spacing on the fatigue surface, with closure effects on the fatigue crack growth also being observed for micro-sized specimens. Once fatigue crack growth occurs, the specimens fail within one thousand cycles. This indicates that the fatigue life of micro-sized specimens is mainly dominated by a crack initiation process, also suggesting that even a micro-sized surface flaw may be an initiation site for fatigue cracks which will shorten the fatigue life of micro-sized specimens. As a result of fracture toughness tests, the values of plane strain fracture toughness, K IC , were not obtained because the criteria of plane strain were not satisfied by this specimen size. As the plane strain requirements are determined by the stress intensity, K, and by the yield stress of the material, it is difficult for micro-sized specimens to satisfy these requirements. Plane-stress-and plane-strain-dominated regions were clearly observed on the fracture surfaces and their sizes were consistent with those estimated by fracture mechanics calculations. This indicates that fracture mechanics is still valid for such micro-sized specimens. The results obtained in this investigation should be considered when designing actual MEMS/MST devices.
TL;DR: In this article, the fatigue behavior of a T-jointed blade in a hydraulic turbine runner is analyzed both experimentally and numerically, and it is shown that structural component geometry does not remarkably influence the stress-intensity factor (SIF) values, provided that the stress field in the vicinity of the crack is approximately the same.