Showing papers on "Paris' law published in 2008"
TL;DR: In this paper, the effect of hydrogen on fatigue crack growth behavior of three stainless steels has been investigated from the viewpoint of microscopic fatigue mechanisms, martensitic transformation and hydrogen content.
208 citations
TL;DR: In this article, the basic mechanism of hydrogen embrittlement of stainless steels under fatigue loading is revealed as microscopic ductile fracture, resulting from hydrogen concentration at crack tips leading to hydrogenenhanced slip.
Abstract: The basic mechanism of the hydrogen embrittlement (HE) of stainless steels under fatigue loading is revealed as microscopic ductile fracture, resulting from hydrogen concentration at crack tips leading to hydrogen-enhanced slip. Fatigue crack growth rates in the presence of hydrogen are strongly frequency dependent. Nondiffusible hydrogen, at a level of 2 to approximately 3 wppm, is contained in ordinarily heat-treated austenitic stainless steels, but, over the last 40 years, it has been ignored as the cause of HE. However, it has been made clear in this study that, with decreasing loading frequency down to the level of 0.0015 Hz, the nondiffusible hydrogen definitely increases fatigue crack growth rates. If the nondiffusible hydrogen at O-sites of the lattice is reduced to the level of 0.4 wppm by a special heat treatment, then the damaging influence of the loading frequency disappears and fatigue crack growth rates are significantly decreased.
197 citations
TL;DR: In this article, the effects of FSW induced residual stresses, as well as changes in the microstructure, are presented on fatigue crack propagation in friction stir welded AA2050.
184 citations
TL;DR: In this paper, the concept of an equivalent stress intensity factor (SIF) range corresponding to R = 0 and a modified Wheeler model are introduced, which lead to a fatigue life prediction model that depends mainly on the stress ratio and the plastic zone size ahead of the crack tip.
172 citations
TL;DR: In this paper, a double-acting tool consisting of outer flat shoulder and inner retractable probe was used to re-fill probe hole of the joints, which increased effective cross sectional area of the nugget, resulting in higher tensile strength.
149 citations
TL;DR: In this article, the authors investigated the failure modes of spot friction welds made by a flat tool in lap-shear specimens of aluminum 6111-T4 sheets based on the approach presented in Part 1.
140 citations
15 Jul 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the authors present results from a systematic study linking material microstructure to monotonic and fatigue properties of NiTi shape memory alloys, including hot-rolled and cold-drawn materials.
Abstract: We present results from a systematic study linking material microstructure to monotonic and fatigue properties of NiTi shape memory alloys We consider Ni-rich materials that are either (1) hot rolled or (2) hot rolled and cold drawn In addition to the two material processing routes, heat treatments are used to systematically alter material microstructure giving rise to a broad range of thermal, monotonic and cyclic properties The strength and hardness of the austenite and martensite phases initially increase with mild heat treatment (300 °C), and subsequently decrease with increased aging temperature above 300 °C This trend is consistent with transmission electron microscopy observed precipitation hardening in the hot-rolled material and precipitation hardening plus recovery and recrystallization in the cold-drawn materials The low-cycle pseudoelastic fatigue properties of the NiTi materials generally improve with increasing material strength, although comparison across the two product forms demonstrates that higher measured flow strength does not assure superior resistance to pseudoelastic cyclic degradation Fatigue crack growth rates in the hot-rolled material are relatively independent of heat treatment and demonstrate similar fatigue crack growth rates to other NiTi product forms; however, the cold-drawn material demonstrates fatigue threshold values some 5 times smaller than the hot-rolled material The difference in the fatigue performance of hot-rolled and cold-drawn NiTi bars is attributed to significant residual stresses in the cold-drawn material, which amplify fatigue susceptibility despite superior measured monotonic properties
132 citations
TL;DR: In this article, the effects of the stress ratio (R ), overloading, underloading, and high-low sequence loading on fatigue crack growth rate were investigated and significant R -ratio effect was identified.
119 citations
TL;DR: An over 20-fold reduction in the fatigue crack propagation rate for the nanocomposite epoxy compared to the baseline (unfilled) epoxy is demonstrated.
Abstract: Fatigue is one of the primary reasons for failure in structural materials It has been demonstrated that carbon nanotubes can suppress fatigue in polymer composites via crack-bridging and a frictional pull-out mechanism However, a detailed study of the effects of nanotube dimensions and dispersion on the fatigue behavior of nanocomposites has not been performed In this work, we show the strong effect of carbon nanotube dimensions (ie length, diameter) and dispersion quality on fatigue crack growth suppression in epoxy nanocomposites We observe that the fatigue crack growth rates can be significantly reduced by (1) reducing the nanotube diameter, (2) increasing the nanotube length and (3) improving the nanotube dispersion We qualitatively explain these observations by using a fracture mechanics model based on crack-bridging and pull-out of the nanotubes By optimizing the above parameters (tube length, diameter and dispersion) we demonstrate an over 20-fold reduction in the fatigue crack propagation rate for the nanocomposite epoxy compared to the baseline (unfilled) epoxy
105 citations
TL;DR: In this paper, a comparative study between fatigue crack growth behavior of friction stir welds of 6082-T6 and 6061T6 aluminium alloys is carried out. Fatigue crack growth curves were determined for cracks growing in different locations of the weldments, including the base material, the heat affected zone and the welded material.
102 citations
TL;DR: In this paper, a numerical simulation of plasticity-induced fatigue crack closure is performed using the finite element method and the authors show that increasing the number of load cycles between node releases has a strong effect on the opening stresses, particularly, under plane strain conditions and 3D fatigue cracks.
TL;DR: In this article, the results about the fatigue properties and the fatigue crack growth behavior of dissimilar 2024-7075 jointed aluminium sheets are presented for FSW butt welds, produced with different positions of the tool with respect to the weld line.
TL;DR: In this article, the relationship between the area of the crack face and fatigue crack growth behavior was investigated, and it was shown that the change in area can be predicted by assuming the extension of crack front based on evaluated stress intensity factor at each position along the front.
TL;DR: In this article, a self-healing material consisting of a microencapsulated vinyl-terminated poly(dimethylsiloxane) resin containing platinum catalyst compounds and a micro-encapped initiator (methylhydrosiloxane).
TL;DR: In this paper, the effect of the radial size of crack front elements and crack propagation on crack closure level is analyzed, and an extrapolation model is proposed, with excellent results.
TL;DR: In this article, the results of a joint research project between the Politecnico di Milano, Italy, and the GKSS Research Centre Geesthacht, Germany, within an activity of ESIS-TC24 (Technical Committee on the Integrity of Railway Structures).
TL;DR: Evaluating fatigue crack growth in human enamel and compares that to the fatigue response of sintered hydroxyapatite (HAp) with similar crystallinity, chemistry and density shows that enamel has a sensitivity to crack growth similar to bone and lower than that of human dentin.
TL;DR: In this paper, a two-parameter (ΔKtot, Kmax,tot) driving force based on the elasto-plastic crack tip stress-strain history has been proposed.
TL;DR: In this article, three different ferritic-pearlitic ductile cast irons, characterized by different ferrite/pearlite volume fractions, and an austempered cast iron were considered.
TL;DR: In this article, the authors investigated the fatigue behavior of aluminum 5754-O and 6111-T4 spot friction welds in lap-shear specimens based on experimental observations and two fatigue life estimation models.
TL;DR: In this paper, the authors investigated the 3D fatigue crack growth behavior in 3PB-specimens or in cantilever beam specimens under bending or torsion loading, with inclined planes for the initial crack, by the dual boundary element method (DBEM).
TL;DR: In this paper, several examples for fatigue crack growth in machines and components are shown, and the reason for failures can be found in misconstructions, inappropriate fatigue strength calculations as well as material and manufacturing imperfections.
TL;DR: In this article, the dimensional analysis approach by Barenblatt and Botvina is generalized to explore the functional dependencies of m and C on more dimensionless parameters than the original dimensionless analysis, and experimental results are interpreted for a wider range of materials including both metals and concrete.
Abstract: Barenblatt and Botvina with elegant dimensional analysis arguments have elucidated that Paris’ power-law is a weak form of scaling, so that the Paris’ parameters C and m should not be taken as material constants On the contrary, they are expected to depend on all the dimensionless parameters of the problem, and are really “constants” only within some specific ranges of all these In the present paper, the dimensional analysis approach by Barenblatt and Botvina is generalized to explore the functional dependencies of m and C on more dimensionless parameters than the original Barenblatt and Botvina, and experimental results are interpreted for a wider range of materials including both metals and concrete In particular, we find that the size-scale dependencies of m and C and the resulting correlation between C and m are quite different for metals and for quasi-brittle materials, as it is already suggested from the fact the fatigue crack propagation processes lead to m = 2 – 5 in metals and m = 10 – 50 in quasi-brittle materials Therefore, according to the concepts of complete and incomplete self-similarities, the experimentally observed breakdowns of the classical Paris’ law are discussed and interpreted within a unified theoretical framework Finally, we show that most attempts to address the deviations from the Paris’ law or the empirical correlations between the constants can be explained with this approach We also suggest that “incomplete similarity” corresponds to the difficulties encountered so far by the “damage tolerant” approach which, after nearly 50 years since the introduction of Paris’ law, is still not a reliable calculation of damage, as Paris himself admits in a recent review
TL;DR: In this article, the influence of the interaction on the growth of semi-elliptical/semi-circular surface cracks in the parallel position was investigated, and the authors concluded that the simulation can estimate the crack growth of interacting cracks and the replacement can be carried out when the offset distance is less than the crack depth.
TL;DR: In this article, the effects of crack closure at various load ratios, R, will be considered as it might impact this conclusion, and the presence of closure will be explored for a range of transition sizes from small to long crack as well as various load ratio.
TL;DR: In this paper, the tensile properties of AA 6061 are determined as basic information for conducting fatigue test and fractographic analysis is performed to predict the life of the component through fatigue crack growth rate graph.
TL;DR: In this paper, load-controlled fatigue tests are conducted for four positive R values on a low-alloy TRIP steel for two different heat treatments: an optimal treatment leading to a multiphase microstructure containing retained austenite, ferrite, bainite and martensite, and a non-optimally treated (ferritic-martensitic) steel.
TL;DR: In this paper, thermal mechanical fatigue tests with controlled thermal gradients (TGMF-tests) were performed on coated tubular specimens, which were made from directionally solidified nickel base superalloy IN100 DS and the coating system comprised a NiCoCrAlY bond coat and a ceramic top coat from partially stabilized zirconia.
TL;DR: In this article, the effect of frequency, environment, and temperature on S-N behavior of E319 cast aluminum alloy can be predicted by use of a general version of a modified environmental superposition model.
Abstract: The fatigue stress-life (S-N) behavior of E319 cast aluminum alloy was studied by using both ultrasonic and conventional fatigue techniques in order to understand the potential effect of frequency on fatigue behavior of cast aluminum alloys. It was observed that, at the investigated temperature (20 °C, 150 °C, and 250 °C), fatigue life in air at 20 kHz is 5 to 10 times longer than that at 75 Hz. The difference in fatigue life between 20 kHz and 75 Hz is attributable to an environmental effect on fatigue crack growth rate. The effect of frequency, environment, and temperature on S-N behavior of E319 cast aluminum alloy can be predicted by use of a general version of a modified environmental superposition model. Environmental effects need to be considered when ultrasonic fatigue is used for estimating fatigue lives of aluminum alloys that are under cyclic loading at lower frequencies in service. It is possible to extrapolate ultrasonic fatigue data to conventional fatigue behavior for an E319 cast aluminum alloy based on the environmental superposition model.
TL;DR: In this paper, the role of residual stress on the propagation of fatigue cracks orthogonal to the weld direction in a friction stir welded Ti-6Al-4V joint was investigated.
Abstract: Recent studies have illustrated a predominant role of the residual stress on the fatigue crack growth in friction stir welded joints. In this study, the role of the residual stress on the propagation of fatigue cracks orthogonal to the weld direction in a friction stir welded Ti-6Al-4V joint was investigated. A numerical prediction of the fatigue crack growth rate in the presence of the residual stresses was carried out using AFGROW software; reasonable correspondence between the predictions and the experimental results were observed when the effects of residual stress were included in the simulation.