bluuebunny/crossref_metadata_2025_split huggingface dataset:
CRACK EXTENSION UNDER MIXED‐MODE LOADING IN AN ANISOTROPIC MODE–ASYMMETRIC MATERIAL IN RESPECT OF RESISTANCE TO FRACTURE
Authors: Kfouri A. P. 
Published: August 2010

Abstract— Recently, a crack path fracture criterion was proposed by Kfouri and Brown, based on maximum energy release rates at the tip of short kinks emanating from an existing crack when the main crack is subjected to mixed‐mode loading. Assuming a ‘mode asymmetry’ in respect of the fracture resistances of the material, KIr, and KIIr, for pure mode I and pure mode II, respectively, i.e., KIIr, differing from KIr, generally, the modified criterion proposed that the resistance to fracture is a function of the ratio q (=k2/k1) of the mode II to the mode I stress intensity factors at the tip of the kink.The aim of the present paper is to extend the modified criterion by presenting it in a form that takes into account material fracture resistance anisotropy in addition to the fracture resistance mode asymmetry previously described. Note however that the material's elastic properties are still assumed to be isotropic. A short FORTRAN computer program has been written to predict the kink angle under mixed‐mode loading for cracks in materials with mode asymmetry and material anisotropy with respect to their fracture resistance properties, and the inclination angle, θ, defining the direction of the main crack in the material. The values of four parameters, r0, r90, s and θ, described in the text, characterising the material fracture resistance asymmetrical and anisotropic properties and the orientation of the main crack, are prompted by the program, which provides, almost instantaneously, the kink angles under various loading modes and much additional relevant information. The effects of the variation of these parameters, treated singly or in combination, and the discontinuous “catastrophic” character of many of the responses at certain “transition” values of the parameters, are illustrated further. In the discussion it is recognised that the translation of the results of the analysis of a highly idealised situation to actual practical problems on real materials encountered in practice, is not straightforward but, notwithstanding, since material fracture resistance anisotropy and fracture resistance mode asymmetry may well be present in the real world, the possible influence of these factors perhaps needs to be taken into account in studies on crack paths.
Fracture analysis of composite co‐cured structural joints using decohesion elements
Authors: CAMANHO P. P. , DÁVILA C. G. , PINHO S. T. 
Published: August 2010

ABSTRACTDelamination is one of the predominant forms of failure in laminated composite structures, especially when there is no reinforcement in the thickness direction. To develop composite structures that are more damage tolerant, it is necessary to understand how delamination develops, and how it can affect the residual performance. A number of factors such as residual thermal stresses, matrix‐curing shrinkage and manufacturing defects affect how damage will grow in a composite structure. It is important to develop computationally efficient analysis methods that can account for all such factors. The objective of the current work is to apply a newly developed decohesion element to investigate the debond strength of skin‐stiffener composite specimens. The process of initiation of delaminations and the propagation of delamination fronts is investigated. The numerical predictions are compared with published experimental results.
Comparative analysis of fatigue life predictions in central notched specimens of Al–Mg–Si alloys
Authors: COSTA J. D. M. , ANTUNES F. J. V. , SILVA V. R. , FERREIRA J. A. M. 
Published: August 2010

ABSTRACTThe fatigue behaviour of an Al–Mg–Si alloy was studied using notched specimens. Fatigue tests were conducted at two stress ratios R= 0 and R= 0.4 on thin plates with a central hole. Constant and block variable loading amplitudes were applied to the specimens using a servo‐hydraulic machine. The applicability of the local strain approach method to the prediction of the fatigue life was investigated for this type of discontinuity. Two methods, the equivalent strain energy density approach and a modified stress–strain intensity field approach, were used to predict the fatigue strength. For the second one an elastic–plastic finite element analysis was carried out in order to obtain the local strain and stress distributions near the notch root. Based on Miner's rule an equivalent stress was used to correlate the fatigue lives for the variable amplitude histories. The experimental results were compared with the predicted results obtained by the two methods investigated and better agreement was found with the stress–strain field intensity approach, while the strain energy approach gave more conservative results. Miner's rule gives a good correlation between the variable amplitude and constant amplitude results.
Influence of intralaminar cracking on the apparent interlaminar mode I fracture toughness of cross‐ply laminates
Authors: De MOURA M. F. S. F. , PEREIRA A. B. , De MORAIS A. B. 
Published: August 2010

ABSTRACTOne of the major difficulties in interlaminar fracture tests of multidirectional laminates is the high tendency for intralaminar cracking and the resulting wavy crack propagation. Experimental work showed that this occurred in double cantilever beam (DCB) tests of cross‐ply laminates having a starter crack on a 0°/90° interface. Moreover, under steady‐state propagation conditions, the apparent values of the critical strain energy release rate GIc were two times higher than those of 0°/0° specimens. In this paper, a finite‐element‐based progressive damage model was used to simulate crack propagation in cross‐ply specimens. The results showed that transverse cracking alone cannot be responsible for the above difference of GIc values. Therefore, the higher propagation GIc values for cross‐plies must be attributed to the more extensive fibre bridging observed and to plastic deformations of the 90° interfacial ply.
Elevated temperature fatigue crack growth in directionally solidified GTD‐111 superalloy
Authors: HIGHSMITH S. , JOHNSON W. S. 
Published: August 2010

ABSTRACTGTD‐111 is a General Electric proprietary nickel‐base superalloy widely employed in a growing fleet of industrial gas turbines. However, much of the published research to date has focused on creep damage and coating durability, with no available data on fatigue crack growth rate (FCGR). Accordingly, FCGR has been measured at several load ratios and an elevated temperature, 760 °C (1400 °F) corresponding to typical turbine bucket conditions. In order to account for load ratio effect, several different methods for determining Walker model parameters are discussed in terms of methodological consistency and accuracy.
A comparison of total fatigue life models for composite laminates
Authors: CHEN H. , SHIVAKUMAR K. , ABALI F. 
Published: August 2010

ABSTRACTA total fatigue life model proposed previously by the same authors for laminated composite structures subjected to mode‐I fracture loading is evaluated by two newer models. The new models differ from the original model by normalization factor and approximation of stable delamination growth rate equation. All three models include the delamination growth in subcritical (delamination initiation), linear (stable growth) and final (unstable growth) fracture domains. All three models were evaluated by comparing the total life predictions for two different block loadings. One is a normal operation of a rotor craft‐type structure and the other is an aggressive loading. Predicted results of the three models were compared with each other and with the experimental data. The material considered was woven‐roving E‐glass fibre and vinyl ester matrix and the laminate was made by vacuum assisted resin transfer molding.
Effect of mean stress on fretting fatigue of Ti‐6Al‐4V on Ti‐6Al‐4V
Authors: LOVRICH N. R. , NEU R. W. 
Published: August 2010

ABSTRACTFretting fatigue tests of Ti‐6Al‐4V on Ti‐6Al‐4V have been conducted to determine the influence of stress amplitude and mean stress on life. The stress ratio was varied from R=−1 to 0.8. Both flat and cylindrical contacts were studied using a bridge‐type fretting fatigue test apparatus operating either in the partial slip or mixed fretting regimes. The fretting fatigue lives were correlated to a Walker equivalent stress relation. The influence of mean stress on fretting fatigue crack initiation, characterized by the value of the Walker exponent, is smaller compared with plain fatigue. The fretting fatigue knockdown factor based on the Walker equivalent stress is 4. Formation of fretting cracks is primarily associated with the tangential force amplitude at the contact interface. A simple fretting fatigue crack initiation metric that is based on the strength of the singular stress field at the edge of contact is evaluated. The metric has the advantage in that it is neither dependent on the coefficient of friction nor the location of the stick/slip boundary, both of which are often difficult to define with certainty a priori.
Elastic T stress estimates for circumferential surface‐cracked cylinders*
Authors: HUH N.‐S. 
Published: August 2010

ABSTRACTOn the basis of detailed three‐dimensional (3D) elastic finite element (FE) analyses, this paper provides tractable approximations for elastic T stress solutions for circumferential inner‐surface cracks in cylinders. Internal pressure and global bending moment were considered. The FE model and analysis procedure employed in the analysis were verified using existing solutions for both elastic stress intensity factor and T stress. To cover a practical range, three different values of the ratio of the mean radius of cylinder to the thickness, Rm/t, were selected; furthermore, four different values of the ratio of the crack depth to the thickness, a/t, ranging from 0.1 to 0.75 and three different values of θ/π ranging from 0.1 to 0.4 were selected. On the basis of FE analyses results, polynomial approximations were proposed at three different locations: surface point, middle point and deepest point. On the basis of the detailed 3D elastic FE analysis, the solutions presented are believed to be the most accurate, and thus provide valuable information for structural integrity assessment considering a crack‐tip constraint.
Latent crack path and service life predictions for unnotched concrete under bending by digital speckle correlation method
Authors: GUO LI‐PING , SUN WEI , CARPINTERI ANDREA 
Published: August 2010

ABSTRACTThe critical factor for flexural fracture of an unnotched concrete structure is the local damage with stress concentration. The latent critical crack path on the concrete surface is difficult to inspect using ordinary experimental methods. In the present paper, the digital speckle correlation method (DSCM) is employed to obtain the latent critical crack and to calculate the strain and displacement distributions on the surface of unnotched concrete under flexural load. The relationships of static flexural load versus longitudinal strain and load‐direction displacement as well as fracture toughness are inherent material parameters. Furthermore, the cohesive energy density (CED) around the latent critical crack for unnotched concrete and the brittleness number are also determined by using the DSCM results. Then, the tensile performance of concrete and the residual service life are evaluated through the above material parameters. It is found that the latent crack path on the concrete surface depends on the strain fields after the bending force applied to the specimen reaches 30% of concrete flexural strength, and the cohesive stress does not rapidly increase until reaching 75% of concrete flexural strength. The service life of unnotched concrete without steel bars is dependent on the local cohesive performance around the latent crack path. Finally, the experimental results show that DSCM is useful to confirm the connection between the local damage of the material and the whole structure safety.
Fatigue crack propagation in tensile shear stainless steel spot welded specimens
Authors: LANCIOTTI A. , POLESE C. 
Published: August 2010

ABSTRACTFatigue tests were carried out on 4 mm thick spot welded joints; the material was stainless steel AISI 301, quarter hard. Some specimens were instrumented with a strain gauge bonded in correspondence with one of the edges of the spot weld. Strain gauge output was demonstrated to be a reliable instrument to monitor the nucleation and propagation of fatigue cracks. A good correlation was found between strain gauge output and spent fatigue life. Some fatigue tests were suspended when the strain gauge output was equal to pre‐fixed values, corresponding to fatigue life in the range from 15 to 85%. Subsequently, the specimens were dissected to observe fatigue cracks. The same correlation existed between crack depth and fatigue life. Small cracks were observed in specimens fatigue tested up to 15% of the mean fatigue life; fatigue cracks in the joints under examination would be nucleated between 5 and 10% of fatigue life.Finite Element calculations were carried out, introducing in the models cracks similar to those observed in the fatigue tests. Calculated strain at the external surface compared well with the measured strain as a function of crack depth. Calculations demonstrated that small errors in strain gauge position can be tolerated without appreciable deterioration in crack dimension prediction.
Fatigue crack growth through a residual stress field introduced by plastic beam bending
Authors: JONES K. W. , DUNN M. L. 
Published: August 2010

ABSTRACTWe present predictions and measurements of fatigue crack growth rates in plastically bent aluminium 2024‐T351 beams. Beam bending and fatigue were carefully controlled to minimize factors other than residual stress that could affect the fatigue crack growth rate, such as large plastic strains or residual stress relaxation. The residual stress introduced by bending was characterized by a bending method and by the slitting method, with excellent agreement between the two methods. Crack growth rates were predicted by three linear elastic fracture mechanics (LEFM) superposition based methods and compared to experimental measurements. The prediction that included the effects of partial crack closure correlated with experimental data to within the variability normally observed in fatigue crack growth rate testing of nominally residual stress free material. Therefore, we conclude that crack growth through residual stress fields may be predicted using the concept of superposition as accurately as crack growth through residual stress free material, provided that the residual stress is accurately known, the residual stress remains stable during fatigue, the material properties are not changed by the introduction of residual stress, and that the effect, if any, of partial crack closure is taken into account.
Fatigue life assessment for brake disc of railway vehicle
Authors: KIM D.‐J. , SEOK C.‐S. , KOO J.‐M. , WE W.‐T. , GOO B.‐C. , WON J.‐I. 
Published: August 2010

ABSTRACTThe brake disc of a railway should have stability. After long‐term use, the brake disc may be seriously damaged by thermal fatigue cracks on the frictional surface. In this study, fatigue tests were carried out for a brake disc material (GC25). Furthermore, in order to determine the cause of the thermal fatigue cracks, contact pressure and thermal stress analyses were performed. From these results, the linear relation between temperature and stress variations was obtained, and the remaining life assessment of the brake disc of a railway vehicle was performed by using it.
Adenosine drives recycled vesicles to a slow‐release pool at the mouse neuromuscular junction
Authors: Perissinotti Paula P. , Uchitel Osvaldo D. 
Published: August 2010

AbstractThe effects of adenosine on neurotransmission have been widely studied by monitoring transmitter release. However, the effects of adenosine on vesicle recycling are still unknown. We used fluorescence microscopy of FM2‐10‐labeled synaptic vesicles in combination with intracellular recordings to examine whether adenosine regulates vesicle recycling during high‐frequency stimulation at mouse neuromuscular junctions. The A1adenosine receptor antagonist (8‐cyclopentyl‐1,3‐dipropylxanthine) increased the quantal content released during the first endplate potential, suggesting that vesicle exocytosis can be restricted by endogenous adenosine, which accordingly decreases the size of the recycling vesicle pool. Staining protocols designed to label specific vesicle pools that differ in their kinetics of release showed that all vesicles retrieved in the presence of 8‐cyclopentyl‐1,3‐dipropylxanthine were recycled towards the fast‐release pool, favoring its loading with FM2‐10 and suggesting that endogenous adenosine promotes vesicle recycling towards the slow‐release pool. In accordance with this effect, exogenous applied adenosine prevented the replenishment of the fast‐release vesicle pool and, thus, hindered its loading with the dye. We had found that, during high‐frequency stimulation, Ca2+influx through L‐type channels directs newly formed vesicles to a fast‐release pool (Perissinottiet al., 2008). We demonstrated that adenosine did not prevent the effect of the L‐type blocker on transmitter release. Therefore, activation of the A1receptor promotes vesicle recycling towards the slow‐release pool without a direct effect on the L‐type channel. Further studies are necessary to elucidate the molecular mechanisms involved in the regulation of vesicle recycling by adenosine.
Src family kinases mediate the inhibition of substance P release in the rat spinal cord by μ‐opioid receptors and GABABreceptors, but not α2adrenergic receptors
Authors: Zhang Guohua , Chen Wenling , Marvizón Juan Carlos G. 
Published: August 2010

AbstractGABAB, μ‐opioid and adrenergic α2receptors inhibit substance P release from primary afferent terminals in the dorsal horn. Studies in cell expression systems suggest that μ‐opioid and GABABreceptors inhibit transmitter release from primary afferents by activating Src family kinases (SFKs), which then phosphorylate and inhibit voltage‐gated calcium channels. This study investigated whether SFKs mediate the inhibition of substance P release by these three receptors. Substance P release was measured as neurokinin 1 receptor (NK1R) internalization in spinal cord slices andin vivo. In slices, NK1R internalization induced by high‐frequency dorsal root stimulation was inhibited by the μ‐opioid agonist DAMGO and the GABABagonist baclofen. This inhibition was reversed by the SFK inhibitor PP1. NK1R internalization induced by low‐frequency stimulation was also inhibited by DAMGO, but PP1 did not reverse this effect.In vivo, NK1R internalization induced by noxious mechanical stimulation of the hind paw was inhibited by intrathecal DAMGO and baclofen. This inhibition was reversed by intrathecal PP1, but not by the inactive PP1 analog PP3. PP1 produced no effect by itself. The α2adrenergic agonists medetomidine and guanfacine produced a small but statistically significant inhibition of NK1R internalization induced by low‐frequency dorsal root stimulation. PP1 did not reverse the inhibition by guanfacine. These results show that SFKs mediate the inhibition of substance P release by μ‐opioid and GABABreceptors, but not by α2receptors, which is probably mediated by the binding of G protein βγ subunits to calcium channels.
Eccentric exercise induces chronic alterations in musculoskeletal nociception in the rat
Authors: Alvarez Pedro , Levine Jon D. , Green Paul G. 
Published: August 2010

AbstractEccentric muscle exercise is a common cause of acute and chronic (lasting days to weeks) musculoskeletal pain. To evaluate the mechanisms involved, we have employed a model in the rat, in which eccentric hind limb exercise produces both acute mechanical hyperalgesia as well as long‐term changes characterized by enhanced hyperalgesia to subsequent exposure to an inflammatory mediator. Eccentric exercise of the hind limb produced mechanical hyperalgesia, measured in the gastrocnemius muscle, which returned to baseline at 120 h post‐exercise. When nociceptive thresholds had returned to baseline, intramuscular injection of prostaglandin E2 (PGE2) induced hyperalgesia that was unattenuated 240 h later, much longer than PGE2‐induced hyperalgesia in unexercised rats (4 h). This marked prolongation of PGE2 hyperalgesia induced by eccentric exercise was prevented by the spinal intrathecal injection of oligodeoxynucleotide antisense to protein kinase Cε, a second messenger in nociceptors implicated in the induction of chronic pain. Exercise‐induced hyperalgesia and prolongation of PGE2 hyperalgesia were inhibited by the spinal intrathecal administration of antisense for the interleukin‐6 but not the tumor necrosis factor α type 1 receptor. These findings provide further insight into the mechanism underlying exercise‐induced chronic muscle pain, and suggest novel approaches for the prevention and treatment of exercise‐ or work‐related chronic musculoskeletal pain syndromes.
Autaptic cultures of single hippocampal granule cells of mice and rats
Authors: Rost Benjamin R. , Breustedt Jörg , Schoenherr Anke , Grosse Gisela , Ahnert‐Hilger Gudrun , Schmitz Dietmar 
Published: August 2010

AbstractWhen a single neuron is grown on a small island of glial cells, the neuron forms synapses onto itself. The so‐called autaptic culture systems have proven extremely valuable in elucidating basic mechanisms of synaptic transmission, as they allow application of technical approaches that cannot be used in slice preparations. However, this method has been almost exclusively used for pyramidal cells and interneurons. In this study, we generated autaptic cultures from granule cells isolated from the dentate gyrus of rodent hippocampi. Our subsequent morphological and functional characterisation of these cells confirms that this culture model is suitable for investigating basic mechanisms of granule cell synaptic transmission. Importantly, the autosynaptic connectivity allows recordings of pure mossy fibre miniature EPSCs, which are not possible in slice preparations. Further, by fast application of hypertonic sucrose solutions it is possible to directly measure the readily releasable pool and to calculate the probability of vesicular release.
Are parasites ‘‘prudent’’ in space?
Authors: Lion Sébastien , Boots Mike 
Published: August 2010

Ecology Letters(2010)AbstractThere has been a renewed controversy on the processes that determine evolution in spatially structured populations. Recent theoretical and empirical studies have suggested that parasites should be expected to be more ‘‘prudent’’ (less harmful and slower transmitting) when infection occurs locally. Using a novel approach based on spatial moment equations, we show that the evolution of parasites in spatially structured host populations is determined by the interplay of genetic and demographic spatial structuring, which in turn depends on the details of the ecological dynamics. This allows a detailed understanding of the roles of epidemiology, demography and network topology. Demographic turnover is needed for local interactions to select for prudence in the susceptible‐infected models that have been the focus of previous studies. In diseases with little demographic turnover (as typical of many human diseases), we show that only parasites causing diseases with long‐lived immunity are likely to be prudent in space. We further demonstrate why, at intermediate parasite dispersal, virulence can evolve to higher levels than predicted by non‐spatial theory.