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Cold extrusion is a process commonly used to manufacture drive train components in the automotive industry. Large plastic strains can be applied during this operation (up to 1.5) and greatly changes the mechanical properties of the resulting material. This study focuses on the impact of cold extrusion process parameters on the multiaxial fatigue behaviour of steel components. A specific set of forward rod extrusion tools was developed to get original fatigue specimen able to characterise the effect of the manufacturing process on the fatigue behaviour. The specimens were extruded from two different initial diameters, giving two different reductions in cross-section of 18% and 75% respectively. To understand the influence of cold extrusion, the following analyses have been undertaken for each condition and on the initial material: monotonic tensile properties, microstructure, EBSD, residual stresses and hardness. Simulation of the forming process and microstructural observations show that the plastic strain is homogeneous in the specimen section. For both reduction factors, the forming process has a positive effect on the components properties: induced residual stresses in compression and improved hardness and roughness (Ra decreasing). Tension, plane bending and torsion fatigue tests show that the fatigue strength is about 30% higher for the batch with 75% reduced cross-section. All investigations show that strain hardening is the principal material parameter responsible for the increase in fatigue strength. A multiaxial fatigue criterion taking into account the effects of the forward rod extrusion process was also developed. This work has been performed within the ANR (National Research Agency) DEFISURF project, in a partnership including several industrial (Ascometal, Cetim, PSA, Transvalor, Atelier des Janves, Gévelot) and academic (INSA Lyon MATEIS, ENSMP-CEMEF, Arts et Métiers ParisTech LAMPA) institutions.

In this cross-sectional study associations were examined between eight shift schedule characteristics with shift-specific sleep complaints and need for recovery and generic health and performance measures. It was hypothesized that shift schedule characteristics meeting ergonomic recommendations are associated with better sleep, need for recovery, health and performance. Questionnaire data were collected from 491 shift workers of 18 companies with 9 regular (semi)-continuous shift schedules. The shift schedule characteristics were analyzed separately and combined using multilevel linear regression models. The hypothesis was largely not confirmed. Relatively few associations were found, of which the majority was in the direction as expected. In particular early starts of morning shifts and many consecutive shifts seem to be avoided. The healthy worker effect, limited variation between included schedules and the cross-sectional design might explain the paucity of significant results. © 2016 Elsevier Ltd and The Ergonomics Society.

This study investigated the mechanical properties of aluminum matrix functionally graded material (FGM) reinforced by integration of aluminum 2014 alloy (AlCu4SiMg) and 15 vol% SiC. The specimens were obtained by centrifugal casting technique, followed by aging treatment. The variations that occurred in microstructure, hardness, Young's modulus, tensile strength, yield strength, elongation, fatigue, and fretting fatigue behaviors were analyzed. In both cast and aged conditions, it was observed that hardness values and mechanical properties changed between SiC-rich and aluminum-rich regions. Fatigue and fretting fatigue data were similar. It was determined that greater wear was occurring on the pad surfaces compared to that occurring on the sample surfaces. © 2015 Institution of Mechanical Engineers.

Retardation is a load sequence effect, which causes a reduced fatigue crack growth rate after an overload is encountered. Retardation can be cancelled when the overload is followed by an underload. The net effect is beneficial to the fatigue lifetime of Offshore Wind Turbines (OWTs). To be able to take this into account, computationally demanding cycle-by-cycle approaches are required. This paper presents a methodology which aims at reducing a very long variable amplitude stress signal, such that it can be used to estimate the cycle-by-cycle fatigue damage, without jeopardizing accuracy. Filtering and reduction techniques are combined, based on typical events seen in the loading pattern of an OWT, e.g. during a storm. The effectiveness of the method is shown by comparing the number of cycles and the fatigue damage estimation, before and after reducing.

In the present study, the results of the monotonic tension tests and low cycle fatigue tests performed on aluminium alloy EN AW-2024-T3 under various operating temperatures are presented in order to assess the fatigue behaviour of the aluminium alloy under evaluated temperatures. Monotonic tests were performed to determine the influence of temperature on mechanical properties of the material. The aim of cyclic tests was to acquire the parameters required for Manson-Coffin equation in order to plot strain-fatigue life curves. Moreover, stress-strain behaviour of the alloy and the cyclic hardening behaviour were evaluated using Ramberg-Osgood equation. Finally, PSWT-damage parameters for each temperature have been calculated for further investigation of the effects of the temperature on fatigue life using acquired data while taking the account of mean stress effect into calculations. Variations in the experimental data due to various test temperatures are presented for both monotonic and cyclic tests. © 2015 Wiley Publishing Ltd.

Fabric reinforced cementitious matrix (FRCM) is a relatively new material system recently developed for the repair, retrofit, and rehabilitation of reinforced concrete (RC) and masonry structures. Concrete structures such as bridges experience high traffic volumes and varying vehicle axle weights causing repeated cyclic loading throughout their lifetime. Cyclic loading may cause damage to the structure, a phenomenon known as fatigue. Due to the novelty of FRCM technology, there is a lack of research regarding the long-term performance of FRCM systems for RC strengthening. This study aims to investigate experimentally the parameters that most influence the flexural fatigue performance of Polyparaphenylene benzobisoxazole (PBO) FRCM strengthened RC beams. For members subject to cyclic loading, a stress ratio vs. the number of cycles (S-N) curve is developed with the objective of defining the endurance limit of the strengthened beams. Failure mode and fatigue life of the beams during cyclic loading are investigated and discussed. 2016 International Committee of the SCMT conferences. All rights reserved. The project was made possible with the financial support received from the University Transportation Center RE-CAST and the Qatar National Research Fund (a member of Qatar Foundation) under NPRP grant # 7-1720-2-641. The statements made herein are solely the responsibility of the authors. Scopus

This article attempts to relate ultrasonic second harmonic generation to dislocation structures in fatigued materials. By focusing on the fact that asymmetric dislocation motion is required to generate the second harmonic, a theoretical derivation of the non-linearity parameter (ratio of the amplitude of second harmonic to square of the amplitude of the fundamental) from dislocation pile-ups is presented. In order to verify the theory, harmonic generation was measured along a failed fatigue sample of DA718, a nickel base superalloy that exhibits planar slip, and consequently dislocation pile-ups. TEM studies along the length of the failed fatigue sample revealed a banded dislocation structure, composed of pile-ups near the fracture zone and a sparse dislocation network closer to the grip region. The non-linearity parameter was found to increase by between 90% and 140% from the grip region to the fracture zone and this correlated well with the calculations based on theoretical expressions derived here. � 2007 Elsevier Ltd. All rights reserved.

The objective of the present work is to study the influence of magnetic arc oscillation and current pulsing on the fatigue behavior of alloy 718 tungsten inert gas (TIG) weldments in two different post-weld heat treatment conditions. For reference base metal data have also been presented. As the base metal did not have undesirable Laves phase, it exhibited superior fatigue resistance than the weldments. In the direct aged condition, continuous current weldments (made without magnetic arc oscillation or current pulsing) exhibited the highest fatigue resistance. This was attributed to lower % Nb in Laves of these welds despite the welds had lumpy and large amount of Laves with more interconnectivity. As magnetic arc oscillated welds had refined and lower amount of Laves with less interconnectivity, they had better fatigue resistance than the pulsed current weldments. In the solution treated and aged condition, in spite of having more Laves with higher % Nb, the continuous current weldments exhibited the highest fatigue resistance due to lesser number of ?-needles. As pulsed current welds had the largest amount of Laves with high % Nb and ?-needles, they exhibited the least fatigue resistance. As relatively higher heat input was used in pulsed current technique in the present study to get full penetration welds, the benefits of current pulsing were not realized. � 2006 Elsevier B.V. All rights reserved.

AISI 304 austenitic stainless steel samples were plasma nitrided at 420��C for 6�h in vacuum atmosphere by glow discharge technique, in the presence of nitrogen gas. Plain fatigue and fretting fatigue tests were carried out on unnitrided and plasma nitrided samples. Plasma nitrided samples exhibited higher surface hardness, compressive residual stresses at the surface and lower surface roughness compared with unnitrided samples. However, plasma nitrided samples exhibited inferior plain fatigue and fretting fatigue lives compared with unnitrided samples. This was attributed to segregation of chromium at the grain boundaries of plasma nitrided specimens which might have weakened the regions near grain boundaries resulting in early crack initiation and accelerated crack propagation. � 2006 Elsevier B.V. All rights reserved.

The fatigue performance of gas carburized SAE 8620 steel was evaluated as a function of case depth. To vary the case depths, different carburizing times were applied. The typical times were: 45 min, 3 and 5 h at the temperature of 940 °C. To cause failure in the rotating bending fatigue specimens, the applied load was chosen as the equivalent load at 106 cycles for the material when is subjected to bending fatigue. The characterization of the specimens was carried out using X-ray diffraction technique for stress measurement and retained austenite and optical metallographic examination. The fractured surfaces were cleaned in an ultrasonic bath and examined using scanning electron microscope (SEM) equipped with EDX to evaluate the crack initiation and growth characteristics of the materials in the core and carburized case regions of specimens. The results showed that the fatigue limit was associated with the microstructure, the case depth, the distribution of retained austenite, the depth of the internal oxidation and the compressive residual stresses near the surface. The bending fatigue strength of gas carburized specimens was showed to decrease with the increasing case depths caused by the increasing of internal oxidation and nonmartensitic transformation present at the surface. © 2006 Elsevier B.V. All rights reserved.

The present work deals with the influence of pad span on fretting fatigue behaviour of AISI 304 stainless steel. Relative slip is one of the three primary variables influencing fretting fatigue behaviour. The relative slip can be modified by changing the pad span and/or cyclic stress. In the present study, the effect of relative slip was studied at different cyclic stress levels and by using fretting pads with three different pad span values (15, 20 and 30 mm). The relative slip increased with an increase in pad span and cyclic stress. Samples tested with fretting pads having longer pad span (30 mm) exhibited longer lives. Though the specimens tested with pads having longer pad span experienced higher frictional stress and tangential force coefficient compared with those tested with pads having smaller pad span (15 or 20 mm), the relative slip values were larger in the former. Due to larger relative slip values it was assumed that small cracks initiated by fretting fatigue would have been worn away due to wear damage. Due to this the specimens tested with pads having longer pad span exhibited enhanced fretting fatigue lives. More deformation-induced martensite formed in the samples tested with pads having longer pad span owing to longer lives. � Springer Science+Business Media, LLC 2007.

The present work deals with the effect of crystallite size on the hardness and fatigue life of steel samples coated with electrodeposited nanocrystalline Ni-W alloys. The Ni-W alloys were electrodeposited on steel samples at four different current densities (0.05, 0.10. 0.15 and 0.20�A/cm2) and at a temperature of 75��C. The crystallite size of the deposit reduced (from 40 to 13�nm) with an increase in current density (from 0.05 to 0.20�A/cm2) due to an increase in the tungsten content (from 0.72 to 9.33�at.%). Ni-W alloy containing 9.33�at.% W and having a crystallite size of 13�nm exhibited the maximum hardness of 638�HV. The alloys, with the crystallite size in the range 40-13�nm, followed the direct Hall-Petch relation, i.e. hardness increased with a reduction in the crystallite size. The coated samples exhibited inferior fatigue lives compared to uncoated samples. This may be attributed to the presence of tensile residual stresses and inherent microcracks in the coatings. Among the specimens coated with Ni-W alloys, as the crystallite size decreased, the fatigue life of the specimen increased owing to the increase in hardness values. � 2006 Elsevier B.V. All rights reserved.

Optimization of the temporal aspects of task design requires a better understanding of the development of muscle fatigue in the neck and shoulder region over time. The objective of the study was to investigate this in two production companies and to determine the relationship between objective and subjective estimates of fatigue. Indicators of fatigue were obtained through electromyography (EMG) during test contractions and ratings of perceived discomfort. EMG amplitude increased during the day in both case studies while mean power frequency decreased only in one case. In both cases, a more detailed frequency analysis of the EMG signals showed an increase in lower frequency power accompanied by a decrease in higher frequency power. Local perceived discomfort in the neck and shoulder increased over the course of the day in both cases. However, no clear relationship between perceived discomfort and objective indicators of fatigue was found. Obtaining sufficient sensitivity to detect effects of temporal aspects of task design probably requires complementary or more refined methods (e.g. EMG arrays, mechanomyography).

Deformation and damage accumulation occur by fundamental dislocation and diffusion mechanisms. An integrated creep-fatigue theory (ICFT) has been developed, based on the physical strain decomposition rule that recognizes the role of each deformation mechanism and thus relate damage accumulation to its underlying physical mechanism(s). The ICFT formulates the overall damage accumulation as a holistic damage process consisting of nucleation and propagation of surface/subsurface cracks in coalescence with internally distributed damage/ discontinuities. These guiding principles run through both isothermal low cycle fatigue (LCF) and thermomechanical fatigue (TMF) under general conditions. This paper presents a methodology using mechanismbased constitutive equations to describe the cyclic stress strain curve and the non-linear damage accumulation equation incorporating i) rate-independent plasticity-induced fatigue, ii) intergranular embrittlement, iii) creep and iv) oxidation to predict LCF and TMF lives of ductile cast iron (DCI). The complication of the mechanisms and their interactions in this material provide a good demonstration case for the model, which is in good agreement with the experimental observations., ASME Turbo Expo 2015: Turbine Technical Conference and Exposition, GT 2015, 15 June 2015 through 19 June 2015

Fatigue crack growth tests were conducted on compact, C(T), specimens made of 7249-T76511 aluminium alloy. These tests were conducted to generate crack growth rate data from threshold to near fracture over a wide range of load ratios (R). Four methods were used to generate near threshold data: (1) ASTM E-647 load reduction (LR), (2) compression pre-cracking constant-amplitude (CPCA), (3) compression pre-cracking LR, and (4) constant crack mouth opening displacement LR method. A crack closure analysis was used to develop an effective stress-intensity factor range against rate relation using a constraint factor (α = 1.85). Simulated aircraft wing spectrum tests were conducted on middle crack tension, M(T), specimens using a modified full-scale fatigue test spectrum. The tests were used to develop the constraint-loss regime (plane strain to plane stress; α = 1.85 to 1.15) behaviour. Comparisons were made between the spectrum tests and calculations made with the FASTRAN life prediction code; and the calculated crack growth lives were generally with ±10% of the test results.

In the present paper, influence of hold time on the high temperature low cycle fatigue (LCF) behavior of modified 9Cr-1Mo ferritic steel in the normalized and tempered condition is addressed. Total axial strain controlled LCF tests at 873 K with hold times at peak strain up to 10 min in tension and compression were carried out employing total strain amplitude of �0.6%. The alloy in general, showed a gradual and continuous softening regime. Fatigue life was found to decrease with increase in the duration of hold time in both tension and compression. Compression hold was found to be more damaging than the tension hold. The fatigue failure in compression hold tests were marked by extensive crack branching and formation of secondary cracks. Oxidation-assisted crack initiation and propagation contributed to life reduction at high temperatures in hold time tests. Additionally, the substructural changes of the starting microstructure were also found to be responsible for the reduction of the fatigue life. The combined effect of cyclic deformation and elevated temperature on the evolving microstructure have been evaluated. The application of hold during cycling at elevated temperature accelerates the conversion of initial heavily dislocated lath structure to equiaxed cells with low dislocation density and coarse carbides. � 2006 Elsevier B.V. All rights reserved.

Fretting fatigue is an adhesive wear mechanism caused by repetitive tangential micro-oscillation between two contacting materials pressed together under cyclic load. Bioimplants, such as hip joints and bone plates, are prone to undergo fretting fatigue failures during their service within the body. This article presents the fretting fatigue damage characterization of physical vapor deposition (PVD) TiN-coated biomedical titanium alloys (Ti-6Al-4V and Ti-6Al-7Nb) subjected to cyclic loads. The PVD TiN layer delayed the damage because of superior tribological properties compared with uncoated alloys. Delamination and abrasive wear damage of TiN at contact caused failure of the alloy. Friction coefficient curves of the PVD TiN-coated pair showed an irregular pattern caused by the influence of wear particulates and Ringer fluid at the contact. � ASM International.

In this present study fatigue properties of polypropylene gear reinforced with metallic springs was investigated. Three different springs was used as reinforcement material in the study. Involute rack gear specimens were produced with injection moulding process. Extension springs were used as reinforcement element and placed into the mould and stretched before injection of polypropylene material into the mould. After injection of polypropylene, stretched springs were loosened in order to obtain residual compression stress in the vertical section of gear tooth. Fatigue tests were performed on the produced gear. Reinforcement increased the strength of gears. Increase in the wire diameter of reinforcement spring and the amount of residual compression stress resulted in increase in service life 30 times more than that of specimens without reinforcement. At constant load cycle number, 10% increase was obtained in the strength of specimens reinforced with springs and residual compression. (c) 2004 Elsevier Ltd. All rights reserved.

This paper presents the results of an investigation into the three-dimensional stress field around an interference fit fastener hole. Understanding the stress variations in the vicinity of the hole during the entire loading sequence from the fastener set-up process to the tensile-loading stage is extremely useful for the design and builing of a high-fatigue performance joint. Two specimens were tested, each specimen consisted of a single aluminum sheet and an interference fit fastener. A photoelastic coating was bonded to the outer surface (fastener head side) on one specimen and the inner surface (nut side) of the other. An interference fit fastener was installed in a single sheet and then photoelastic analysis was used to measure the strains under different tensile loads. Four different three-dimensional finite element (FE) models of the sheet and fastener/nut structure with and without a coating were generated. A numerical technique is proposed to analyze the fastener-clamping torque, which was employed in the contact numerical simulations. Multiple-load steps in the FE models were used to simulate the entire joining and then tensile-loading stages. A good correlation was achieved between the experimental results and the finite element predictions for the maximum shear strain. The full-field contours of the maximum principal stress under different clamping values and tensile loads were also studied., available, unclassified, unlimited

The purpose of this study has been to investigate the effect of dilation on the some mechanical properties of several types of warp-knitted vascular grafts. The structures of warp knit vascular grafts used in the experiments were reverse locknit, locknit, and Tricot. Various mechanical properties of these grafts were determined using devices developed for the purpose. Clinical data obtained were compared with experimental results of warp knit vascular grafts. The most important mechanical properties are found to be creep extension, bursting strengths, and compliance. Preliminary results indicate that vascular grafts are non-compliant and exhibit creep which is predictive of the long term dilation that has been noted in the clinical results. It is found that there is a positive correlation between experimental data and clinical results for at least the grafts tested.

Based on the concept proposed by Kitagawa and Takahashi, an attempt was made to generate different stress (S) vs. crack length (a) plots for a ferritic steel weld metal. Traditionally, Kitagawa-Takahashi (KT) diagrams have been obtained for the threshold fatigue life, i.e., infinite life cycles. Attempts were made in the present work to obtain these types of plots for various finite life cycles. These plots may be used for the prediction of stress levels for the material with different initial flaws to achieve the desired finite fatigue lives. ? 2004 Elsevier B.V. All rights reserved.

Fatigue cracks initiate at stress raisers such as notches, discontinuities, and surface defects. Many of the field failures that indicate the presence of a fatigue crack at failure can be traced to crack initiation from one or more crack initiation sites and merger of cracks over a period of service. Substantial service life is spent in the growth of small cracks from an initial size of few micrometres before they coalesce and grow to critical dimensions that cause fracture. This paper summarizes research that was carried out in order to understand the kinetics of crack growth of small cracks at notches under simulated FALSTAFF service loading. This paper also presents a method used to understand crack growth kinetics in a pin-loaded lug joint through a crack-front-mapping technique.

The phenomenon of ratchetting is defined as constant accumulation of plastic strain or deformation under combined steady state and cyclic loading. It can reduce the fatigue life or can cause failure of piping components or systems subjected to seismic or other cyclic loads. The uniaxial ratchetting characteristics of SA333 Gr.6 steel have been investigated at room temperature in the present paper. The specimens were subjected to cyclic axial stress with a constant mean stress of 200 MPa and a varying amplitude stress of 149, 174, 199 and 224 MPa. Tests were also performed on 203.2 mm, Sch 80, SA333 Gr. 6 carbon steel straight pipe. The pipe was subjected to a constant internal pressure of 18 MPa and a cyclic bending load. The effects of amplitude of load on the rate of ratchetting have also been investigated in the present paper. The uniaxial experiments showed that specimens exhibited shakedown at low stress amplitude after some strain accumulation. However, specimens experienced continuous ratchetting at higher stress amplitudes with no shakedown before failure. Ovalization of the pipe cross-section was observed when the pipe was subjected to constant internal pressure and cyclic point load. Local bulging was observed at higher loading. The pipe did not show any shakedown behaviour for the given cycles of loading and exhibited continuous ratchetting under the varying amplitude loading., © Elsevier

Currently, prediction of crack initiation by corrosion pits is only possible by assuming regular geometrical shapes, such as semi-spheres or semi-ellipsoids. Moreover, typical fatigue life diagrams associate the crack initiation life with geometrical features, such as pit depth or aspect ratio, often leading to unsatisfactory correlations due to high pit shape variability and data scatter. In the context of blade-disc fixation in aero engine turbines, this limitation translates into highly conservative life estimations. Therefore, a new crack initiation predictor is formulated based on experimental testing and numerical analysis of 28 artificial corrosion pits. A low-cycle fatigue test campaign is conducted using three-point bending test specimens to simulate maximum takeoff operation conditions of the aero engine and the associated loading of the blade root designed as firtree. An artificial pit is located at the critical point of each test specimen, respectively. The prediction criterion is based on finite element analysis and is formulated as the lowest plastic strain of a plastic region with a certain volume in the corrosion pit. This reference volume is varied until an optimum correlation with experimental crack initiation life is obtained. The criterion shows a superior correlation with crack initiation life compared to pure geometrical parameters such as pit depth.

High cycle fatigue failure is likely to occur when a rather undamped offshore installation is operated over a long period of time. Especially welded parts are vulnerable to fluctuating stress ranges, if the structural components, such as the small bore side branches, are loaded in resonance. In particular, the welded connections at e.g. tie-in points can be critical. Therefore, it is important to know what the current status of existing welded connections is and how long they can still be operated at any specific operating condition without failure. This paper describes an advanced fatigue assessment method to determine the cumulative damage in the critical parts of the system. The method is developed for industrial applications where the available information is limited. The method comprises of a mechanical analysis and a fatigue assessment based on a fracture mechanics crack growth model. The method enables determination of inspection intervals and at the same time layout optimization for a long term safe operation. This paper pays special attention to complex, braced small bore side branches. Standard fatigue stress assessment methods can be conservative for the fatigue assessment of high frequent stress ranges with relatively low stress ranges. The current paper shows the effect of the fracture mechanics procedure for an example of a braced side branch connected to the main piping: both a fracture mechanics model and a detailed 3D FE model are made. With these models, the hot spot stress in the welds is evaluated and tailor-made S-N-curves are derived. With information of the operating history, the cumulative damage is determined for the weld detail. This knowledge on the current damage status is crucial for future operations.

High cycle fatigue failure is likely to occur when a rather undamped offshore installation is operated over a long period of time. Especially welded parts are vulnerable to fluctuating stress ranges, if the structural components, such as the small bore side branches, are loaded in resonance. In particular, the welded connections at e.g. tie-in points can be critical. Therefore, it is important to know what the current status of existing welded connections is and how long they can still be operated at any specific operating condition without failure. This paper describes an advanced fatigue assessment method to determine the cumulative damage in the critical parts of the system. The method is developed for industrial applications where the available information is limited. The method comprises of a mechanical analysis and a fatigue assessment based on a fracture mechanics crack growth model. The method enables determination of inspection intervals and at the same time layout optimization for a long term safe operation. This paper pays special attention to complex, braced small bore side branches. Standard fatigue stress assessment methods can be conservative for the fatigue assessment of high frequent stress ranges with relatively low stress ranges. The current paper shows the effect of the fracture mechanics procedure for an example of a braced side branch connected to the main piping: both a fracture mechanics model and a detailed 3D FE model are made. With these models, the hot spot stress in the welds is evaluated and tailor-made S-N-curves are derived. With information of the operating history, the cumulative damage is determined for the weld detail. This knowledge on the current damage status is crucial for future operations.

We propose a new laser-based fabrication process of small-sized riblets on PWA1483 coated on a 3 mm-thin sputtered Ni/Cr/Ni multilayer. Laser ablation was used for local material removal. Subsequent oxidation was used to provide an optimal riblet dimensions for a drug reduction and oxidation resistance. As a result of the heat treatment, a 7 mm oxide film was formed. The oxide film consists of two different oxide layers: while the upper one is formed of a dense Cr2O3 layer with NiO, Cr2NiO4, and TiO2 inclusions, the bottom one mainly consists of alpha-Al2O3. Between the riblets, a TiO2 layer was formed on the top of Cr2O3 layer. First mechanical tests showed a promising riblet stability under the low-cycle fatigue load, under tension, and under quasi-cyclic bending load. The riblets also exhibit no severe failure by applying a quasi-cyclic bending stress of 900 MPa for 200 times. Furthermore, cyclic tensile loading with a mean load of 500 MPa and an amplitude of 220 MPa corresponding to a strain range of 0.35% (stress level of R = 0.35) led to no damage of the riblet structure.

Railway bridges are subjected to dynamic loadings. Dynamic loads impart additional impact force on bridges. The deformations and stress ranges are differing on these bridges. The stress ranges depends on speed of the train, intensity of loading on the bridge and number of cycles of same loading at different speed and different loads at same speed. Hence the failure of loads happens at lesser load than that of actual ultimate load carrying capacity of bridge material. Design of bridges at higher load than the fatigue failure load becomes expensive, uneconomical and less durable. Hence it is necessary to understand the fatigue behavior of bridges to ascertain the life of existing bridge in years and to arrive at the optimized cost effective cross sections of new bridges for varying loads and speeds. Variation of remaining life of bridge with respect to loads and speed are discussed in this paper considering the structural details, loading history and material specifications of bridge. � 2015 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.

Total axial strain controlled fatigue tests have been conducted in air at 823 and 923 K to ascertain the influence of cold work on LCF behaviour of a 15Cr-15Ni, Ti modified austenitic stainless steel, designated as Alloy D9. The LCF behaviour of the 20% cold worked alloy was compared with that of solution annealed alloy. A symmetrical triangular waveform at a constant strain rate of 3?10-3 s-1 was employed for all the tests performed over the strain amplitude in the range of �0.25 to �1.00%. The cyclic stress response varied as a complex function of microstructure, temperature and strain amplitude. The cyclic stress response of solution-annealed alloy was generally characterized by initial hardening to the maximum stress followed by a regime of nearly stable peak stresses. The degree of initial hardening was higher at 823 K due to dynamic strain ageing effects. The cold worked alloy displayed a gradual softening prior to the attainment of saturation stress respon se stage. The plastic strain fatigue resistance of the cold worked alloy was inferior compared to that in solution-annealed condition at both 823 and 923 K. At low strain amplitudes, the cold worked alloy exhibited better total strain fatigue resistance at 923 K. The observed variations in fatigue life and cyclic stress response behaviour have been explained on the basis of crack initiation, development of substructure, precipitation behaviour and evolving changes in plastic strain during cycling. ? 2001 Elsevier Science Ltd. All rights reserved.

Evaluation of fatigue crack growth behavior in Nb-H alloys was done using the Unified Approach to Fatigue Crack Growth developed earlier. It shows that the mechanism of hydrogen embrittlement changes with crack growth rate, load ratio and hydrogen concentration. The analysis provides an example where the changes in the governing mechanisms can be easily followed using the ?K* vs K max* trajectory map discussed in the Unified Approach. Published by Elsevier Science Ltd.

This paper has investigated the possibility of applying nondestructive evaluation technique for finding the defects in electroplated materials. Planar meander and mesh type magnetic sensors have been considered and their relative performance have been compared based on a single criterion that the effective area of the material surface covered by each type of sensor is same.

A new finite element assembly, to account for the structural behaviour of the region surrounding a spot weld, is developed. The formulation derives from the analytic solution of two circular sheets externally clamped, with a central rigid core connecting them (representing the spot weld). The effective modelling strategy of the above mentioned region makes use of equivalent beam elements; therefore, the implementation is possible in any structural code. The aim is to use this assembled element for the region around the spot: two assembled elements, connected by a link, form the spot weld connection between two metal sheets. The analytic solution is provided for any possible typology of loading acting on a spot weld (shear, bending and orthogonal loads). Moreover, the link connecting the two sub elements may be considered rigid as well as deformable, this can be very useful to evaluate fatigue damage evolution in structures jointed with many spot welds. Using these assembled elements for the spot weld region, an important increase in the accuracy is reached, as demonstrated in the example. However, the accuracy does not imply an increase in the total number of degrees of freedom of the whole model.

Grain size reduction in weld fusion zones confers the advantages of an increased resistance to solidification cracking and an improvement in mechanical properties. Oscillation of the welding arc through an imposed alternating magnetic field is one of several approaches to modify weld solidification structures. In this study, gas tungsten arc welds were produced in two high strength, age hardenable aluminum alloys with and without an external magnetic field. Metallographic characterization revealed the degree of structural refinement produced by magnetic arc oscillation. The decrease in grain size was found to increase tensile elongation, while the effect on strength and age hardening response was only meager. The improvement in ductility was partially maintained in the peak aged condition also.

The effect of weld size on fatigue life of flux cored arc welded (FCAW) cruciform joints containing lack of penetration (LOP) defect has been analysed by using the strain energy density factor (SEDF) concept. Moreover, new fracture mechanics equations have been developed to predict the fatigue life of the cruciform joints. Load carrying cruciform joints were fabricated from ASTM 517 ‘F’ grade steel. Fatigue crack growth experiments were carried out in a vertical pulsar (SCHENCK 200 kN capacity) with a frequency of 30 Hz under a constant amplitude loading ( R =0). It was found that the crack growth rates were relatively lower in the larger welds fabricated by the multipass welding technique than the smaller welds fabricated by the single pass welding technique.

Three statistical techniques have been used to optimise some of the factors affecting fatigue life of Flux Cored Arc Welded (FCAW) cruciform joints containing Lack of Penetration (LOP) defects. High strength, quenched and tempered steel (ASTM 517 ‘F’ Grade) has been used as the base material throughout the investigation. Design of Experiments (DoE) concept has been used to optimise the required number of experiments. Fatigue experiments have been conducted in a mechanical resonance pulsar, under constant amplitude loading. The techniques described in this paper are fairly simple and economical to optimise the time consuming fatigue tests.

The objective of this work has been to study the origin of surface failures in UHMWPE tibial bearings of total knee replacements. Earlier examination of hundreds of retrieved prostheses, along with analysis of the properties of UHMWPE material from retrieved bearings, had shown that a large number of the bearings suffered from subsurface oxidation. This oxidation was related to the gamma irradiation used to sterilize the tibial bearings. Mechanical properties of the polymer were significantly deteriorated in the oxidized region, with the most severe reduction of strength and ductility occurring about 1 mm beneath the contact surface. In this work the contact stress distribution in the bearings was analyzed, and tribotesting of the bearing materials was carried out under simulated service conditions. Fatigue cracks and delamination developed in bearings tested in a knee simulator and in rolling/sliding test specimens, and the damage was similar to that found in retrieved tibial bearings. The fatigue cracks invariably initiated in the embrittled oxidized layer, and the depth of that layer determined the depth at which the cracks began. The stress analysis showed that the maximum shear stress and von Mises equivalent stress reached high levels in the subsurface oxidized zone where the delamination and contact fatigue failures initiated. [S0742-4787(00)04401-5]

International audience; Crack propagation during Stage I, in terms of crack initiation sites and growth directions and crack branching mechanisms under fretting conditions, is investigated using both experimental and theoretical approaches. Fretting tests were conducted on an aeronautical aluminum alloy. Two crack types are observed during Stage I corresponding, respectively, to specific mode I and II conditions. Transition from Stage I to Stage II is characterized for both crack types by a crack branching towards a new propagation direction of ≈65° to the specimen surface. Specific parameters linked to mode I and II propagation driving forces are proposed. Crack location and initial growth directions during Stage I are predicted in accordance with these parameters, and are in very good agreement with experimental observations. The conditions governing the transition from Stage I to Stage II are then identified. It is shown that under fretting conditions, cracks branch along a new direction, thereby maximizing the crack-opening amplitude.

A new mathematical model is developed to predict the fatigue life of Shielded Metal Arc Welded (SMAW) cruciform joints containing Lack of Penetration (LOP) defect. High strength, quenched and tempered steel (ASTM 517 'F' Grade) is used as the base material throughout the investigation. Four factors, five level, central composite, rotatable design matrix is used to optimise the required number of experiments. Fatigue experiments have been conducted in a mechanical resonance pulsator, under constant amplitude loading. The model is developed by Response Surface Method (RSM). Analysis of Variance (ANOVA) technique is applied to check the validity of the model. Student's t-test is utilised to find out the significant factors. The effect of joint dimensions on fatigue life have been analysed in detail.A new mathematical model is developed to predict the fatigue life of Shielded Metal Arc Welded (SMAW) cruciform joints containing Lack of Penetration (LOP) defect. High strength, quenched and tempered steel (ASTM 517 'F' Grade) is used as the base material throughout the investigation. Four factors, five level, central composite, rotatable design matrix is used to optimise the required number of experiments. Fatigue experiments have been conducted in a mechanical resonance pulsator, under constant amplitude loading. The model is developed by Response Surface Method (RSM). Analysis of Variance (ANOVA) technique is applied to check the validity of the model. Student's t-test is utilised to find out the significant factors. The effect of joint dimensions on fatigue life have been analysed in detail.

A new method was developed to optimise the dimensions of shielded metal arc welded (SMAW) cruciform joints, containing lack of penetration (LOP) defects, to attain maximum fatigue lives. High strength, quenched and tempered steel (ASTM 517 F grade) was used as the base material throughout the investigation. Design of experiments (DoE) concept was used to optimise the required number of experiments. Fatigue experiments were conducted in a mechanical resonance pulsator, under constant amplitude loading. The optimisation procedure was incorporated by (i) response table and response graph, (ii) normal probability plot, and (iii) analysis of variance (ANOVA) techniques.A new method was developed to optimise the dimensions of shielded metal arc welded (SMAW) cruciform joints, containing lack of penetration (LOP) defects, to attain maximum fatigue lives. High strength, quenched and tempered steel (ASTM 517 F grade) was used as the base material throughout the investigation. Design of experiments (DoE) concept was used to optimise the required number of experiments. Fatigue experiments were conducted in a mechanical resonance pulsator, under constant amplitude loading. The optimisation procedure was incorporated by (i) response table and response graph, (ii) normal probability plot, and (iii) analysis of variance (ANOVA) techniques.