bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fatigue limit evaluation of notches, small cracks and defects: an engineering approach
Authors: LIVIERI P. , TOVO R. 
Published: August 2010

ABSTRACTIn this paper, the average stress method for the fatigue limit evaluation of stress raising geometrical features is revised and extended. In particular, an analytical close‐form approach was used and the linear elastic stress equations were modified by taking into account the effect of nominal stress on the local stress distribution. Hence, the average tangential stress was correctly evaluated over a distance of 2a0, where a0 was El Haddad's short crack constant, for long and small notches as well as for crack‐like notches. When this model is applied to a wide range of geometrical features subjected to mode I fatigue loading, the classical shape of the curves of the Kitagawa–Takahashi diagram was obtained for changes in crack‐like notch size. Similarly, notch sensitivity was estimated by reducing the notch tip radius. The accuracy of the proposed method in predicting fatigue limits was then checked by using experimental data taken from the literature and generated on testing specimens weakened by rounded and sharp notches as well as by small artificial defects.
Can pure mode III fatigue loading contribute to crack propagation in metallic materials?
Authors: POKLUDA J. , PIPPAN R. 
Published: August 2010

ABSTRACTThe possibility of pure mode III crack growth is analysed on the background of theoretical and experimental results obtained in the last 20 years. Unlike for modes I and II, there is no plausible micromechanistic model explaining a pure mode III crack growth in ductile metals. In order to realize ‘plain’ mode III fracture surface, we propose the propagation of a series of pure mode II cracks along the crack front. Fractographical observations on crack initiation and propagation in a low alloy steel under cyclic torsion support such a model. The authors have not seen any clear indication of a pure mode III crack growth micromechanism in metals until now.
Parametric study of oblique edge cracks under cyclic contact loading
Authors: BEGHINI M. , BERTINI L. , FONTANARI V. 
Published: August 2010

ABSTRACTThe problem of a two‐dimensional elastic body, carrying an inclined edge crack and loaded by a cylinder rolling on the surface, is solved by the weight function method. The load induced by the cylinder on the cracked body was represented by the Hertzian pressure distribution, and the nominal stress distribution in the uncracked body was numerically evaluated by the superposition principle. The crack opening displacement components were obtained by an analytical Green's function. The partial crack closure was considered and the influence of the mutual forces between the crack faces included in the analysis, by which the effective stress intensity factors KI and KII could be evaluated. By considering different friction conditions between the crack surfaces and several crack inclinations, the evolutions of the effective KI and KII during typical loading cycles were analysed.
Prediction of crack opening stress levels for 1045 quenched and tempered steel under service loading spectra
Authors: KHALIL M. , TOPPER T. H. 
Published: August 2010

ABSTRACTThe opening stresses of a crack emanating from an edge notch in a 1045 quenched and tempered steel specimen were measured under two different Society of Automotive Engineers (SAE) standard service load histories having different average mean stress levels. The two spectra are the Grapple Skidder history (GSH), which has a positive average mean stress, and the Log Skidder history (LSH), which has a zero average mean stress. To capture the behaviour of the crack opening stress in the material, the crack opening stress levels were measured at 900X using an optical video microscope, at frequent intervals for each set of histories scaled to two different maximum stress ranges.A crack growth analysis based on a fracture mechanics approach was used to model the fatigue behaviour of the steel specimens for the given load spectra and stress ranges. Crack growth analysis was based on an effective strain‐based intensity factor, a crack growth rate curve obtained during closure‐free loading cycles and a local notch strain calculation based on Neuber's rule.The crack opening stress (Sop) was modelled and the model was implemented in a fatigue notch model, and the fatigue lives of the specimens under the two different spectra scaled to several maximum stress levels were estimated. The average measured crack opening stresses were between 6 and 12% of the average calculated crack opening stresses. In the interest of simplifying the use of Sop in design, the average Sop was correlated with the frequency of occurrence of the cycle reducing the Sop to the average crack opening stress level. The use of an Sop level corresponding to the cycle causing a reduction in Sop to a level reached once per 10 cycles gave a conservative estimate of average crack opening stress for all the histories.
Analysis of fatigue crack behaviour based on dynamic response simulations and experiments for tensile‐shear spot‐welded joints
Authors: SHANG D.‐G. , BARKEY M. E. 
Published: August 2010

ABSTRACTFatigue crack initiation and propagation behaviours were studied based on the dynamic response simulation by the three‐dimensional finite‐element analysis (FEA) and dynamic response experiments for tensile‐shear spot‐welded joints. The entire fatigue propagation behaviour from the surface elliptical cracks at the initiation stage to the through thickness cracks at the final stage was taken into consideration during the three‐dimensional FEA dynamic response simulations. The results of the simulations and experiments found that the fatigue cracks of spot‐welded joint from initial detectable crack sizes to crack propagation behaviour could be described by three stages. Approximately one‐half of the total fatigue life was taken in stage I, which includes micro‐crack nucleation and the small crack growth process; 20% of the total fatigue life in stage II, in which the existing surface crack propagates through the thickness of sheet and 30% of the total fatigue life in stage III, during which the through thickness crack propagates along the direction of plate width to the final failure. According to the relationship between the crack length and depth and the dynamic response frequency during the simulated fatigue damage process, the definition of fatigue crack initiation and propagation stages was proposed. The analysis will provide some information for the fatigue life prediction of the spot‐welded structures.
A critical plane fatigue model with coupled meso‐plasticity and damage
Authors: HUYEN N. , FLACELIERE L. , MOREL F. 
Published: August 2010

ABSTRACTThe work proposed in this paper is a possible way of modelling some local observations at the surface of mild steel specimens submitted to uniaxial and multiaxial loads. It is clearly seen that local plasticity, controlled by local microstructural heterogeneities, plays a fundamental role in microcrack nucleation and damage orientation is closely related to the applied loading mode. The framework of irreversible thermodynamics with internal variables for time‐independent, isothermal and small deformations has been used to build a critical plane damage model by assuming the existence of a link between mesoplasticity and mesodamage. Non‐associated plasticity and damage rules allow the evolution of some plastic slip before any damage nucleation, as seen during the observations. A key feature of this proposal is the capacity to reflect nonlinear damage accumulation under variable amplitude loading.
Fracture analysis using parametric meshless Galerkin method
Authors: HOSSEINI‐TOUDESHKY H. , MUSIVAND‐ARZANFUDI M. 
Published: August 2010

ABSTRACTThe recently introduced parametric meshless Galerkin method (PMGM) uses meshless shape functions which are mapped from a parametric space. The PMGM improves the efficiency of the meshless methods via the capability of using the meshless shape functions of an existing elements library and no necessity to construct all meshless shape functions in the running time. In this paper, the application of the PMGM to calculate the crack‐tip stress intensity factors (SIFs) is studied. Some modifications are performed on the original PMGM to eliminate the restrictions arisen from the compulsory use of the whole of the parametric data. In doing so, some of the mapped nodes are inactivated due to their confliction with the problem geometry or extra node patterns and some of the Gaussian cells are also replaced with new ones. Numerical examples show a computational time saving of more than 20% as well as accurate obtained SIFs.
Control volumes and strain energy density under small and large scale yielding due to tension and torsion loading
Authors: LAZZARIN P. , BERTO F. 
Published: August 2010

ABSTRACTIn the recent literature some researchers proposed the use of the mean value of the Strain Energy Density (SED) over a well‐defined control volume for static and fatigue strength assessment of components weakened by sharp V‐shaped notches. In those papers the SED was expressed in terms of Notch Stress Intensity Factors (NSIFs), whose accurate evaluation needs a very fine mesh when based on local stress determined along the notch bisector. This contribution shows that when the material behaviour is ideally linear elastic or obeys a power hardening law, the mean value of the SED over the control volume can also be precisely determined from a coarse mesh. This result is of interest in the practical application of the SED approach to real components. Eventually, NSIFs can be evaluated a posteriori, just on the basis of the local SED. While discussing some results from elastic‐plastic analyses carried out on a V‐notched plate under tension loading and on a V‐notched round bar under torsion, the different roles played by local and large scale yielding are highlighted. The result is used here to provide a justification for the different slopes, 3.0 and 5.0, reported by Eurocode 3 and other Standards in force for welded details subjected to tensile or shear stresses, respectively.
Analysis of key factors for the interpretation of small punch test results*
Authors: LACALLE R. , ÁLVAREZ J. A. , GUTIÉRREZ‐SOLANA F. 
Published: August 2010

ABSTRACTIn recent years, great advances have been made in non‐destructive or quasi‐non‐destructive test techniques for the determination of fracture toughness. One of the most interesting of these techniques is the one known as Small Punch, in which a punch acts on a small plane specimen, deforming it until fracture. From the continuous records of force and displacement of the punch taken during the test, it is possible to quantify the energy absorbed and then to determine the classic parameters of fracture mechanics such as ductile‐to‐brittle transition temperature or even the fracture toughness of the material. In this paper, fundamental aspects of the interpretation of the results of this kind of test have been studied. The effect of specimen thickness has been analysed. Moreover, a study has been carried out with the aim of clarifying the relation between the orientations in which it is possible to machine Small Punch specimens and the orientations of traditional specimens used in the determination of fracture toughness.
Tensile and fatigue behaviour of wrought magnesium alloys AZ31 and AZ61
Authors: CHAMOS A. N. , PANTELAKIS Sp. G. , HAIDEMENOPOULOS G. N. , KAMOUTSI E. 
Published: August 2010

ABSTRACTThe mechanical behaviour of two hot rolled magnesium alloys, namely the AZ31 and AZ61, has been evaluated experimentally under both monotonic and cyclic loading. Both longitudinal (L) and long transverse (LT) directions were evaluated. The tensile behaviour of the L and LT directions is similar and differs only in the offset 0.2% yield strength for both materials. This difference is attributed to the angular spread of basal poles toward the rolling direction and is more pronounced for the case of AZ31. A distinct hardening response is obvious in both directions. Twinning formation was observed; it is more pronounced in the longitudinal direction while the fracture mode is intergranular and equiaxed facets are present in the fracture surfaces of the specimens. The S–N curves exhibit a smooth transition from the low to high cycle fatigue regime. AZ61 exhibits an overall better fatigue behaviour compared to AZ31. A transgranular crack initiation mode is observed in all tested specimens while the propagation of the cracks is characterized as intergranular.
δ25 Crack opening displacement parameter in cohesive zone models: experiments and simulations in asphalt concrete
Authors: SONG S. H. , WAGONER M. P. , PAULINO G. H. , BUTTLAR W. G. 
Published: August 2010

ABSTRACTRecent work with fracture characterization of asphalt concrete has shown that a cohesive zone model (CZM) provides insight into the fracture process of the materials. However, a current approach to estimate fracture energy, i.e., in terms of area of force versus crack mouth opening displacement (CMOD), for asphalt concrete overpredicts its magnitude. Therefore, the δ25 parameter, which was inspired by the δ5 concept of Schwalbe and co‐workers, is proposed as an operational definition of a crack tip opening displacement (CTOD). The δ25 measurement is incorporated into an experimental study of validation of its usefulness with asphalt concrete, and is utilized to estimate fracture energy. The work presented herein validates the δ25 parameter for asphalt concrete, describes the experimental techniques for utilizing the δ25 parameter, and presents three‐dimensional (3D) CZM simulations with a specially tailored cohesive relation. The integration of the δ25 parameter and new cohesive model has provided further insight into the fracture process of asphalt concrete with relatively good agreement between experimental results and numerical simulations.
Influence of core hardness on bending strength of tooth in cylindrical gears under quasistatic loading conditions
Authors: BOZCA M. 
Published: August 2010

ABSTRACTDynamically loaded mechanical components can withstand overloading if they are designed by considering sufficient safety of margin for the static strength. In this study, the influence of core hardness on bending static strength of the tooth in cylindrical hardened gears is investigated experimentally. For this purpose, shot peened and unpeened gears having different core hardness and comparable surface hardness are tested on a pulsator test rig, which provides a quasi‐static loading condition by means of a servomotor. All test gears are made of 20MnCr5 steel and have the same geometry (module m = 5 mm). Average static load for fracture is measured. The relationship between the applied load and bending stress is known. Hardness profiles from the surface to the core of the test gears were measured. Strength is assumed to be a function of depth depending hardness to justify fracture initiation on the surface under bending static load conditions. Tooth root failures originating from the surface were observed experimentally. It is found that the shot peening treatment and core hardness have no considerable influence on the bending strength of the tooth under static loading conditions.
Dynamic stress intensity factors due to scattering of harmonic waves by a crack in an infinite medium
Authors: ESLAMI S. H. , AMINI F. 
Published: August 2010

ABSTRACTAn analytical method for calculating dynamic stress intensity factors in the mixed mode (combination of opening and sliding modes) using complex functions theory is presented. The crack is in infinite medium and subjected to the plane harmonic waves. The basis of the method is grounded on solving the two‐dimensional wave equations in the frequency domain and complex plane using mapping technique. In this domain, solution of the resulting partial differential equations is found in the series of the Hankel functions with unknown coefficients. Applying the boundary conditions of the crack, these coefficients are calculated. After solving the wave equations, the stress and displacement fields, also the J‐integrals are obtained. Finally using the J‐integrals, dynamic stress intensity factors are calculated. Numerical results including the values of dynamic stress intensity factors for a crack in an infinite medium subjected to the dilatation and shear harmonic waves are presented.
Alcohol consumption enhances antiretroviral painful peripheral neuropathy by mitochondrial mechanisms
Authors: Ferrari Luiz F. , Levine Jon D. 
Published: August 2010

AbstractA major dose‐limiting side effect of human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) chemotherapies, such as the nucleoside reverse transcriptase inhibitors (NRTIs), is a small‐fiber painful peripheral neuropathy, mediated by its mitochondrial toxicity. Co‐morbid conditions may also contribute to this dose‐limiting effect of HIV/AIDS treatment. Alcohol abuse, which alone also produces painful neuropathy, is one of the most important co‐morbid risk factors for peripheral neuropathy in patients with HIV/AIDS. Despite the prevalence of this problem and its serious impact on the quality of life and continued therapy in HIV/AIDS patients, the mechanisms by which alcohol abuse exacerbates highly active antiretroviral therapy (HAART)‐induced neuropathic pain has not been demonstrated. In this study, performed in rats, we investigated the cellular mechanism by which consumed alcohol impacts antiretroviral‐induced neuropathic pain. NRTI 2′,3′‐dideoxycytidine (ddC; 50 mg/kg) neuropathy was mitochondrial‐dependent and PKCε‐independent, and alcohol‐induced painful neuropathy was PKCε‐dependent and mitochondrial‐independent. At low doses, ddC (5 mg/kg) and alcohol (6.5% ethanol diet for 1 week), which alone do not affect nociception, together produce profound mechanical hyperalgesia. This hyperalgesia is mitochondrial‐dependent but PKCε‐independent. These experiments, which provide the first model for studying the impact of co‐morbidity in painful neuropathy, support the clinical impression that alcohol consumption enhances HIV/AIDS therapy neuropathy, and provide evidence for a role of mitochondrial mechanisms underlying this interaction.
Cortical cholinergic abnormalities contribute to the amnesic state induced by pyrithiamine‐induced thiamine deficiency in the rat
Authors: Anzalone Steven , Vetreno Ryan P. , Ramos Raddy L. , Savage Lisa M. 
Published: August 2010

AbstractAlthough the key neuropathology associated with diencephalic amnesia is lesions to the thalamus and/or mammillary bodies, functional deactivation of the hippocampus and associated cortical regions also appear to contribute to the memory dysfunction. For example, there is loss of forebrain cholinergic neurons and alterations in stimulated acetylcholine (ACh) levels in the hippocampus and cortex in animal models of diencephalic amnesia associated with thiamine deficiency. In the present study, the pyrithiamine‐induced thiamine deficiency rat model was used to assess the functional relationships between thalamic pathology, behavioral impairment, ACh efflux and cholinergic innervation of the hippocampus and cortex. In pyrithiamine‐induced thiamine deficiency‐treated rats, ACh efflux during behavioral testing was blunted to differing degrees in the hippocampus, medial frontal cortex and retrosplenial cortex. In addition, significant reductions in cholinergic fiber densities were observed in each of these regions. However, only hippocampal cholinergic fiber density correlated significantly with ACh efflux in the same region, suggesting that the reduction in cortical ACh efflux in cases of diencephalic amnesia cannot be fully explained by a loss of cholinergic fiber innervation. This notion supports the emerging theory that the functional consequences of the distal effects of lesions go beyond simple deafferentation. Specifically, some frontal cortical regions exhibit hypersensitivity to deafferentation that is only detected during behavioral and/or physiological demand.
Effects of antiepileptic drugs on associative LTP‐like plasticity in human motor cortex
Authors: Heidegger Tonio , Krakow Karsten , Ziemann Ulf 
Published: August 2010

AbstractAntiepileptic drugs (AEDs) are used extensively in clinical practice but relatively little is known on their specific effects at the systems level of human cortex. Here we tested, using a double‐blind randomized placebo‐controlled crossover design in healthy subjects, the effects of a single therapeutic oral dose of seven AEDs with different modes of action (tiagabine, diazepam, gabapentin, lamotrigine, topiramate, levetiracetam and piracetam) on long‐term potentiation (LTP)‐like motor cortical plasticity induced by paired associative transcranial magnetic stimulation (PAS). PAS‐induced LTP‐like plasticity was assessed from the increase in motor evoked potential amplitude in a hand muscle contralateral to the stimulated motor cortex. Levetiracetam significantly reduced LTP‐like plasticity when compared to the placebo condition. Tiagabine, diazepam, lamotrigine and piracetam resulted in nonsignificant trends towards reduction of LTP‐like plasticity while gabapentin and topiramate had no effect. The particularly depressant effect of levetiracetam is probably explained by its unique mode of action through binding at the vesicle membrane protein SV2A. Enhancement of gamma‐amino butyric acid‐dependent cortical inhibition by tiagabine, diazepam and possibly levetiracetam, and blockage of voltage‐gated sodium channels by lamotrigine, may also depress PAS‐induced LTP‐like plasticity but these mechanisms appear to be less relevant. Findings may inform about AED‐related adverse effects on important LTP‐dependent central nervous systems processes such as learning or memory formation. The particular depressant effect of levetiracetam on LTP‐like plasticity may also relate to the unique properties of this drug to inhibit epileptogenesis, a potentially LTP‐associated process.