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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.

Structural members and components of a vehicle during service are subjected to varying loads which are random in nature. For structural members subjected to loads of constant amplitude, it is possible to describe the load with explicit mathematical relationship, and thereby, the life span can be estimated. Whereas, for structural members subjected to varying loads with time, there is no satisfactory method to estimate their life span. This paper describes a method for the estimation of life span of a gear in the gear box of a fighting vehicle subjected to fluctuating loads. For this purpose, it is assumed that the load spectrum corresponds to Gaussian (normal) distribution, and the life has been worked out by applying linear cumulative damage theory.

En steel, in untreated and thermal treated conditions, with and without shot peening, were tested in a back-to-back gear test rig. Their contact fatigue characteristics were studied and S-N curves have been established. Contact fatigue strength of shot peened gears for a given life showed an improvement in relation to unpeened gears. ? 1998 Elsevier Science Ltd. All rights reserved.

It is possible that fatigue cracks may appear in turbomachine blades which are subjected to extreme conditions during operation. Such cracks may become the cause of failure. The feasibility of considering the natural frequency as a parameter for detecting full depth cracks has been considered earlier. The present paper not only compares the result for full depth cracks with the previous work but also presents results for partial depth cracks. It concludes with the suggestion that the natural frequency is too poor a parameter for the diagnosis of partial depth cracks. However, experimental verification is suggested and a cautionary note about extrapolation of conclusions to rotating structures is also provided. ? 1997 Academic Press Limited.

Thermo-mechanical fatigue (TMF) tests and strain to crack (SC) tests at elevated temperature are important aspects to the total fatigue life for many engineering applications. During a TMF test, crack inspections are commonly done in a disruptive manner using an acetate replication method; and post-test crack evaluations are done using both optical and scanning electronic microscopy methods. Similarly, inspections during a typical SC test are also performed in a disruptive manner. This paper demonstrates that infrared imaging can be used as an in-situ inspection approach to detect crack during TMF and SC tests at high temperature. It is also demonstrated that this technique allows for the reduction or elimination of the need for downtime that is typically required for disruptive inspection. The results obtained by induction thermography are compared to those obtained via traditional methods and post-test evaluation. The induction thermography inspections were carried out at several temperatures and showed that the temperature used during the test does not influence the crack detection capability. It is demonstrated that induction thermography can detect cracks smaller than 500 μm and has potential for monitoring and generating a crack growth curve. © 2013 SPIE., Thermosense: Thermal Infrared Applications XXXV, April 30 - May 1, 2013, Baltimore, MD, USA, Series: Proceedings of SPIE; no. 8705

This study presents a model for estimating the fatigue life of magnesium and aluminium non-penetrated butt-welded joints using Artificial Neural Network (ANN). The input parameters for the network are stress concentration factor Kt and nominal stress amplitude sa,n. The output parameter is the endurable number of load cycles N. Fatigue data were collected from the literature from three different sources. The experimental tests, on which the fatigue data are based, were carried out at the Fraunhofer Institute for Structural Durability and System Reliability (LBF), Darmstadt - Germany. The results determined with use of artificial neural network for welded magnesium and aluminium joints are displayed in the same scatter bands of SN-lines. It is observed that the trained results are in good agreement with the tested data and artificial neural network is applicable for estimating the SN-lines for non-penetrated welded magnesium and aluminium joints under cyclic loading. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In this article, the occurrence of secondary cyclic hardening (SCH) and its effect on high-temperature cyclic deformation and fatigue life of 316LN Stainless steel are presented. SCH is found to result from planar slip mode of deformation and enhance the degree of hardening over and above that resulted from dynamic strain aging. The occurrence of SCH is strongly governed by the applied strain amplitude, test temperature, and the nitrogen content in the 316LN SS. Under certain test conditions, SCH is noticed to decrease the low cycle fatigue life with the increasing nitrogen content. � The Minerals, Metals & Materials Society and ASM International 2013.

The current investigation proposes a novel method for simultaneous assessment of the electrochemical and structural fatigue properties of nickel-titanium shape memory alloy (NiTi SMA) wires. The design and layout of an in situ electrochemical cell in a custom-made bending rotation fatigue (BRF) test rig is presented. This newly designed test rig allows performing a wide spectrum of experiments for studying the influence of fatigue on corrosion and vice versa. This can be achieved by performing ex situ andor in situ measurements. The versatility of the combined electrochemicalmechanical test rig is demonstrated by studying the electrochemical behavior of NiTi SMA wires in 0.9 NaCl electrolyte under load. The ex situ measurements allow addressing various issues, for example, the influence of pre-fatigue on the localized corrosion resistance, or the influence of hydrogen on fatigue life. Ex situ experiments showed that a pre-fatigued wire is more susceptible to localized corrosion. The synergetic effect can be concluded from the polarization studies and specifically from an in situ study of the open circuit potential (OCP) transients, which sensitively react to the elementary repassivation events related to the local failure of the oxide layer. It can also be used as an indicator for identifying the onset of the fatigue failure. � 2013 American Institute of Physics.

cited By 0; International audience; The intent of this paper is to identify the damage phenomena controlling the life of composites at high temperatures (> 600°C), and to measure the kinetics of these phenomena during mechanical tests. The analysis of AE data provides a classification into groups of signals having similar characteristics that can be afterward associated to one or to several damage mechanisms. A method of unsupervised classification was used to differentiate the signals resulting from various mechanisms of damage and from failures. Then, a method of supervised classification was developed, so as to establish a classification in real-time whatever the temperature, the applied constraint and the mode loading (static or cyclic). © 2013 Lavoisier.

cited By 0; International audience; The fracture of fibres dictates the fracture of composites reinforced by long fibres. The ceramic matrix composites that are made of a ceramic matrix reinforced by ceramic fibres, display features that are interesting to address lifetime issues. The flaws they contain have a random distribution, and act as stress concentrators. The resistances to failure display a statistical distribution. The effects of microstructural defects on lifetime are discussed in the present paper. A multi scale approach based on modelling of the damage modes in the matrix and the fibers is outlined. The models integrate facture probabilities owing to stochastic phenomena induced by the statistical distribution of microstructural flaws. © 2013 Lavoisier.

A spatial non-uniformity of the switching properties during the fatigue cycling in lead zirconate titanate ceramics was investigated by a quasi-static piezoelectric and a polarization switching measurements. The agreement between the local piezoelectric properties and the switching behavior of segmented samples was demonstrated. The observed spatial variation of the properties and its evolution with cycle number provides clear evidence of the presence of heterogeneous regions that possess a local fatigue state and the local switching behavior. These results can be explained as a result of the build-up of the spatially non-uniform field and the formation of frozen domains in the ceramics during cycling. The statistical analysis of spatial variation of the switching properties and its evolution with cycle number provides the evidence that the heterogeneity of the switching properties during the fatigue cycling in lead zirconate titanate ceramics is mostly related to the non-uniform change of the local characteristic switching time. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

There has been a number of studies on the influence of ultrasonic vibrations on various metallurgical phenomena. In the present study, however, some investigations have been carried out on a relatively less familiar aspect of ultrasound, viz. its application towards bringing about a rapid fatiguing effect on materials under resonant conditions. Intense ultrasound was given to materials under resonance conditions to produce fracture in them by what is known as ultrasonic fatigue. The failure time was usually of the order of a few minutes and, sometimes, only a few seconds. Some well-known common materials such as commercially pure aluminium, age-hardenable aluminium alloys and armco iron in different heat-treated conditions were chosen for this study. The specimens were of dumb-bell shape conforming to resonance. The complete equipment for this purpose was designed, developed and fabricated in-house. Some aspects of the damage under these conditions are discussed here, primarily through fractography. The fractures appear to be different from conventionally produced fractures. The influence of ultrasonic loading (short of fracture) in affecting the strength of age-hardenable alloys is also discussed briefly, X-ray line broadening analysis seems to indicate a strong recovery of the matrix due to the rapid fatiguing effect.

The fatigue life of MIG welded cruciform joint failing from root (LOP) region was successfully predicted using new fracture mechanics equations. These equations were developed by combining Paris' law and ΔK i -endurance equation and incorporating an integral factor ( I p ) obtained by integrating Paris' equation. In the numerical formulation of the equation, the initiation life ( N i ) and propagation life ( N p ) of the joint were accounted for to obtain the total fatigue life ( N f ). The initiation life was obtained experimentally using crack “Initiation Criteria”. The propagation life was evaluated using the numerically developed equations. The method outlined successfully predicted the fatigue life of the joint from its crack growth parameters. To test the accuracy of the method, the predicted data were compared with the experimental data. It was found that the predicted data compared quite well with the experimental data. This method is simple and can be applied easily for other joint geometries.

When the material yields local stress and strain behaviour changes, especially if there is a notch, determination of the local strain value can be difficult. Therefore it is not easy to predict the life of mechanical components in the low-cycle region. In the present work pressure vessels are considered and fatigue tests carried out. The most stressed zones, which are at the connections between the nozzles and the vessel, are subjected to cyclic loads with subsequent repeated plastic strains that cause nucleation and propagation of fatigue cracks. The life of such a mechanical component under low cycle fatigue can be predicted by utilizing the life strain curves e − N f or the energy approach (plastic strain and total strain energy density). In the present work, life prediction is performed by considering several different approaches. The results are compared with the experimental results obtained by fatigue testing pressure vessel nozzles. The material considered is Fe 510 B UNI 7070-72 steel.

In this study, keyhole and smooth specimens, made from a low alloy pressure vessel steel (ASTM A-533 grade B), were subjected to monoaxial fatigue tests. The results show the influence of the stress concentration factor, K[sub t], on the number of cycles to failure, N[sub f]. Total strain energy per cycle, [Delta]W[sub t] = [Delta]W[sub p] + [Delta]W[sub e], was proved to be a good parameter for predicting the life of notched components. Elasto-plastic FEM analysis, utilizing the cyclic and monotonic curve of the material, showed close agreement with the experimental values.

Fatigue crack growth rate (FCGR) and dwell-FCGR tests were conducted at 704C° in a vacuum environment and compared with data obtained under lab air conditions for various microstructural conditions of ATI 718Plus Alloy (718Plus) and Waspaloy. The results indicated that environmental damage has a significant impact on the FCGR characteristics of both alloys, particularly in the near-threshold regime. The dwell fatigue crack propagation behaviour under vacuum conditions displayed identical behaviour irrespective of differences in microstructural features. The observed crack growth rates under vacuum decreased dramatically compared to lab air test results, highlighting the crucial impact of environmental damage on the dwell-fatigue crack propagation resistance of both alloys. The fracture mode for 718Plus was observed to be predominately intergranular in both the FCGR and dwell-FCGR test conditions, with the effect of long-term thermal exposure leading to a larger fraction of transgranular failure. Waspaloy fracture surfaces revealed a predominantly transgranular deformation mode. The fracture surfaces of 718Plus and Waspaloy all exhibited transgranular fracture under vacuum test conditions and were nearly indistinguishable in crack topography. Dynamic embrittlement is believed to be the governing mechanism for intergranular failure of 718Plus leading to grain boundary decohesion. Improvement of dwell-fatigue crack propagation resistance of 718Plus may be strongly related to the coarsening of the γ hardening phase, with potential further improvement via implementation of a bimodal γ heat treatment. EDX analysis showed that the 8 phase just at the crack tip becomes oxidized and may be a contributing factor in the susceptibility of the grain boundaries during the dwell-FCGR tests. The presence of Nb-rich carbides along the dwell-fatigue crack path of 718Plus was also identified. Carbides located behind the crack front were heavily oxidized and those carbides observed just ahead of the crack tip showed no oxidation. It is believed that oxidation of these NbC particles near grain boundaries may be linked to the environmental susceptibility of 718Plus during dwell-fatigue crack propagation., 12th International Symposium on Superalloys, Superalloys 2012, September 9-13, 2012, Seven Springs, PA, USA

The strength of autoclaved lightweight concrete (ALC) is evidently lower than that of normal concrete. Therefore, when movement occurs at a sealed joint between ALC panels, the sealant is required to deform and remain intact without damaging the ALC substrate. However, there is currently not sufficient information to permit evaluation of the expected performance of sealants applied to ALC substrates. In this study, static and dynamic tests were carried out in order to obtain an index that could be used to select the modulus of a sealant that can be expected to provide long-term performance when applied to an ALC substrate. To develop this index, an initial study was carried out in order to clarify actual joint movement between ALC panels of buildings; the expansion and contraction at the joint were measured, and shear joint movement was calculated based on the expected story-to-story drift of an external wall due to earthquake loads. Thereafter, in a subsequent stage of the study, five types of two-component polyurethane sealant products, of different elastic modulus, were subjected to tensile and shear tests from which the relationship between stress and the type of joint fracture was determined. The results from these tests revealed that when the stress is greater than 0.6 to 0.7 N/mm2, the ALC substrate is more easily fractured than the sealant. In a final stage of the study, the cyclic fatigue resistance of the same two-component sealants was evaluated using tensile and shear fatigue tests. Results from the fatigue tests indicated that the high modulus sealants lost adhesion from the ALC substrate at an early stage in the test. As well, the fatigue resistance of test specimens with joints having three-sided adhesion was lower than that of specimens having normally configured joints with adhesion on two sides of the sealant. Therefore, on the basis of results derived from all the studies, it was determined that a suitable sealant for use on ALC substrates is a sealant having a low modulus that is applied in the normal fashion as a two-sided joint. Copyright © 2012 by ASTM International., 4th Durability of Building and Construction Sealants and Adhesives, 16 June 2011 through 17 June 2011, Anaheim, CA

Aircraft and pressure vessel components experience stresses that are negative biaxial or multiaxial in nature. Biaxiality is defined as the ratio of stress applied parallel and normal to the crack front. In recent years many experimental studies have been conducted on fatigue crack growth under various biaxial loading conditions. Biaxial loadings affect crack front stresses and strains, fatigue crack growth rate and direction, and crack tip plastic zone size and shape. Many of these studies have focused on positive biaxial loading cases. No conclusive study has been reported out yet that accurately quantifies the influence of negative biaxiality on fatigue crack growth behavior. Lacking validation, implementation on real life problems remains questionable. To ensure safe and optimum designs, it is necessary to better understand and quantify the effect of negative biaxial loading on fatigue crack behavior. In this paper, attempts were made to quantify the effect of biaxial load cases ranging from B = −0.5 to 1.0 on fatigue crack growth behavior. Also an attempt has been made to establish a simplified approach to incorporate the effect of biaxiality into da/dN curves generated from uniaxial loading using an analytical approach without conducting expensive biaxial crack growth testing. Sensitivity studies were performed with existing test data available for AA2014-T6 aluminum alloy. Detailed elastic–plastic finite element analyses were performed with different stress ranges and stress ratios with various crack sizes and shapes on notched and un-notched geometries. Constant amplitude loads were applied for the current work and comparison studies were made between uniaxial and different biaxial loading cases. It was observed from the study that negative biaxiality has a very pronounced effect on the crack growth rate and direction for AA2014-T6 if the externally applied load exceeds 20% of the yield strength as compared with 40% of externally applied load for alloy of steel quoted in the literature.

In this study, compressive dwell (C-D) and no-dwell (N-D) low-cycle fatigue (LCF) behaviours of several single crystal Ni-base superalloys, including CMSX-4, LSC-11 and LSC-15, were studied under strain-controlled zero-compression (RE = -co) loading at 1100°C. LSC-11 and LSC-15 are new alloys developed by 1H1 Corporation, Japan with 0.8 wt% Re and without Re addition, respectively, as reduced-cost alternatives to the second generation single crystal Ni-base superalloys. The fatigue experiments were conducted with or without a two-minute dwell (hold) in compression and total strain ranges of 0.7%, 0.6% and 0.5% on uncoated specimens in the [001] orientation. Examination of the cyclic stress-strain behavior revealed that the initially compressive mean stress relaxed to approximately zero stress in N-D tests, while compressive hold resulted in the development of a tensile mean stress during C-D fatigue. Cyclic stress softening was observed under all test conditions. Microstructural analysis of tested specimens showed that N-D fatigue promoted isotropic coarsening of the γ′ precipitates, while C-D loading resulted in the formation of discontinuous γ′ rafting parallel to the loading direction. Fatigue cracks initiated from the specimen surface from regions of localized oxide attack. All alloys were compressive dwell sensitive. C-D fatigue lives were 4-15× shorter than N-D when the same alloys were considered. CMSX-4 exhibited 1.5-3× N-D fatigue life advantage over alloys LSC-11 and LSC-15. Under C-D fatigue the life advantage of CMSX-4 was 20-50% greater than alloys LSC-11 and LSC-15. The differences in these behaviours could be attributed to Re content and oxidation., 12th International Symposium on Superalloys, Superalloys 2012, 9 September 2012 through 13 September 2012, Seven Springs, PA

An analysis of residual stress, one of the contributory factors to the crack tip driving force, is extremely important to probe the fatigue crack growth mechanism and to further develop the life prediction methodology. Since fatigue crack growth is governed by crack-tip plasticity and crack closure in the wake of the crack tip, the investigation of residual stain/stress field in both behind and in front of the crack tip is crucial. In the current work, a 304L stainless steel compact-tension specimen is pre-cracked under constant-amplitude cyclic loading. Neutron diffraction is employed to directly measure the three orthogonal residual strain fields with 1-mm spatial resolution as a function of distance from the crack tip. The mapping results show that the three orthogonal residual-strain distributions around the crack tip depend on the stress multiaxiality, not following a single Poisson relationship to each axis. © 2012 Trans Tech Publications, Switzerland., 7th International Conference on Processing and Manufacturing of Advanced Materials, THERMEC'2011, 1 August 2011 through 5 August 2011, Quebec City, QC

The fatigue behaviour of cold rolled and annealed sheet metals are influenced by the anisotropy of mechanical properties due to crystallographic texture. However, the existing fatigue strain-life models are primarily meant for isotropic material behaviour. In the present work, the Coffin-Manson equation for strain-life is modified to include the effect of anisotropy using phenomenological plasticity models. It is observed that the variation of strain hardening exponent is critical to model the strain-life behaviour. Variation of strain hardening exponent with orientation is modelled using existing anisotropic yield criteria. The prediction of fatigue life using the proposed model correlates well with the experimental results of Al6061-T6 along different orientations. The proposed model can be used to predict the fatigue properties along any orientation from the fatigue data along one orientation and monotonic mechanical properties along longitudinal, transverse and diagonal directions. � 2012 Blackwell Publishing Ltd.

In order to assess the remaining life of gas turbine critical components, it is vital to accurately define the aerothermodynamic working environments and service histories. As a part of a major multidisciplinary collaboration program, a benchmark modeling on a practical gas turbine combustor is successfully carried out, and the two-phase, steady, turbulent, compressible, reacting flow fields at both cruise and takeoff are obtained. The results show the complicated flow features inside the combustor. The airflow over each flow element of the combustor can or liner is not evenly distributed, and considerable variations, ±25, around the average values, are observed. It is more important to note that the temperatures at the combustor can and cooling wiggle strips vary significantly, which can significantly affect fatigue life of engine critical components. The present study suggests that to develop an adequate aerothermodynamics tool, it is necessary to carry out a further systematic study, including validation of numerical results, simulations at typical engine operating conditions, and development of simple correlations between engine operating conditions and component working environments. As an ultimate goal, the cost and time of gas turbine engine fleet management must be significantly reduced. © 2012 Leiyong Jiang and Andrew Corber.

Extruded 2024, 6065 and 7075 alloys were subjected to Strain Induced Melt Activated (SIMA) process and average of 80 μm spherical grains were obtained. T6 solution heat treatment was carried out to all alloys. In addition to the typical water quenching at 20°C, temperature controlled bath was used where the water was set to 80°C and some samples were quenched in that water. High mean stress values were selected (0.9, 0.8 and 0.7UTS) and load stress ratio (R) was selected to be 0.1. The fatigue test results were analyzed by Weibull and the distributions were compared with metal quality. SEM analysis was carried out on the fracture surface. A good correlation was found between bifilm index and the fatigue properties; as the quality was lowered, the scatter of the test results was increased.

The effect of electron beam surface treatment (EBST) on fatigue crack growth (FCG) resistance of an austenitic steel has been investigated. The EBST results in significant improvement in the FCG resistance. The beneficial effect is attributed to extensive crack closure as a result of residual stresses originating during EBST. A comparison with the FCG data of the alloy surface treated with other high-energy beam sources such as lasers reveals that EBST could provide similar improvements in the FCG resistance.

The aim of this investigation was determining the fatigue behaviour of welded aluminium joints and so the appertaining SN-lines by application of Artificial Neural Network (ANN) architectures. For this, fatigue data obtained with aluminium welded joints subjected to constant amplitude loading were used. The main benefit of ANN is the good description of the effects of different factors on fatigue life. The results determined by the ANN method for four aluminium alloys are displayed in scatter bands of SN-lines. It is observed that the trained results are in good agreement with the tested data and enable the estimation of SN-lines. Ziel der Untersuchungen war es die Abschatzung des Schwingfestigkeitsverhaltens von Aluminiumschweisverbindungen und somit der zugehorigen Wohlerlinien mit Hilfe von Kunstlichen Neuronalen Netzen (KNN). Hierzu wurden Ergebnisse zugrunde gelegt, die mit Aluminiumschweisverbindungen aus vier verschiedenen Legierungen unter Einstufenbelastungen ermittelt wurden. Der Vorteil von KNN liegt darin, dass verschiedene Einflussgrosen auf die Lebensdauer zutreffend beschrieben werden konnen. Die mit dieser Methode berechneten Ergebnisse sind in Wohlerlinienstreubandern dargestellt. Durch KNN trainierte und getestete Daten zeigen eine gute Ubereinstimmung und bestatigen den Nutzen dieses Verfahren.

In order to qualify residual stress relaxation as an indicator of mechanical overloading of machined parts, an individually designed residual stress profile has to be allocated. Even though numerous investigations have been carried out in the past, residual stress profiles cannot be predicted to a satisfactory degree. For this reason, essential studies on the reproducibility of residual stress profiles for several external cylindrical turning parameters are conducted and it is demonstrated that identical residual stress profiles can be induced successfully. Subsequently, specimens with defined residual stress profiles are loaded in bending tests with various numbers of test cycles. The amount of residual stress relaxation in the specimen's surface layer is measured to determine the influence of theapplied load on the stress relaxation. By applying single tensile and compressive loads below and above thematerial's yield and ultimate strength, the stress relaxation can be evaluated in detail. DFG/CRC/SFB/653

The fatigue performance of composite joints is one of the major concerns for the extensive application of composites in aircraft structures. Accurate assessment of the fatigue life behaviour is crucial and valuable to this end. A wearout model was used to characterize the fatigue life behaviour of composite joint structures. The fatigue data used were selected from the open literature. A data fitting tool, which could deal with small fatigue data sample cases, was developed. The tool could accurately replicate the fitting parameters for S-N curves of single-piece composite cases and was used to study the fatigue life behaviour of adhesively bonded and bolted composite joint cases. Recommendations are made for improving the fatigue assessment capability in composite joint structures using the wearout model., 26th Annual Technical Conference of the American Society for Composites 2011 and the 2nd Joint US-Canada Conference on Composites, 26 September 2011 through 28 September 2011, Montreal, QC

The fatigue crack growth of commercial AA2219 has been examined under different aging treatments, namely, naturally aged (NA), under aged (UA), peak aged (PA) and over aged (OA) conditions. From the near threshold stress intensity range (?KNTH), the alloy in the NA condition is found to have the highest resistance to fatigue crack initiation. The crack growth rate increases and the near threshold stress intensity range decreases with advancing aging. This observation is found to be consistent with lower levels of crack closure and decreasing levels of tortuosity in crack path for PA and OA tempers. The inhomogeneous transcrystalline slip in the UA condition results in the slower crack growth at low stress intensity range (?K). The fracture morphology changes from crystallographic facets near the threshold region to clearly developed ductile striations in the Paris power-law regime to microvoid coalescence in the high ?K regions. � 2011 Elsevier B.V.

In order for new composite materials like fiber metal laminates (FML) to gain acceptance in the aerospace field, it is important to understand the effect on them of common manufacturing techniques such as riveting and cold expansion. A comprehensive research program was initiated using two advanced strain measurement techniques; digital image correlation and thermoelastic stress analysis, to understand the failure mechanisms in FML materials that had been fatigue cycled after having undergone hole cold expansion or riveting. Prior theoretical work has shown the potential for improvement in fatigue life of FMLs, so one standard grade of FML (FML 4-3/2) and a novel FML variant were manufactured and tested. Thermoelastic stress analysis was employed to measure strains on the mandrel exit face while digital image correlation was used to measure strains on the mandrel entry face in the coupons and additional insight was gained regarding the effect of the cold expansion process and of riveting on fatigue crack growth. The results also highlighted the effect of material design on fatigue life as well as the interaction between residual strains and fatigue crack growth. ©2010 Society for Experimental Mechanics Inc., 2010 Annual Conference on Experimental and Applied Mechanics, 7 June 2010 through 10 June 2010, Indianapolis, IN

A new superalloy, ATI 718Plus alloy (718Plus), has been developed to have a 55°C higher temperature capability over the traditionally used alloy 718, while maintaining favourable processing characteristics and intrinsic raw material costs. The fatigue and dwell fatigue behaviour of four microstructural variations of 718Plus are evaluated and compared with Waspaloy: standard heat treated condition (HT1), standard heat treated condition with thermal exposure at 732°C (1350°F) for 1000 h (HT2), fine grain condition with a modified d phase (HT3) and fine grain overaged through modified heat treatment (HT4). Fatigue crack growth rate tests were performed at 649°C (1200°F) and 704°C (1300°F) under constant amplitude loading at 10 Hz or with a 100 s tension dwell. The results show that the steady state fatigue crack growth rates of each microstructural variation and both alloys are identical, with all of the 718Plus variations showing a clear advantage over Waspaloy in the fatigue crack threshold regime. The 718Plus variants HT1 and HT3 exhibited the highest fatigue crack growth threshold, followed closely by HT4 and finally HT2. At 649°C (1200°F), the 718Plus alloys had average threshold values ranging from 8·8 to 10·4 MPa m1/2 whereas the Waspaloy material was 6·1-7·5 MPa m1/2. At 704°C (1300°F), the advantage increased with the 718Plus alloys having average threshold values ranging from 10·1 to 11·6 MPa m1/2 compared with Waspaloy, which exhibited average threshold values of 6·6-7·7 MPa m1/2. Dwell fatigue results show that Waspaloy has better resistance to crack propagation under dwell conditions; however, optimisation of the precipitate phase (HT2) shows vast improvement in the dwell fatigue resistance of 718Plus. © 2011 Canadian Institute of Mining, Metallurgy and Petroleum.

Laser surface treatment (LST) results in significant improvement in fatigue crack growth resistance of an FeMnAl austenitic steel. The observed benificial effect is attributed to extensive crack closure as a result of compressive residual stresses originating from LST. The structure-sensitive nature of the crack growth operative in the base microstructure at low ΔK levels (up to ∼ 40 MPa m 1 2 with LST.

Reports indicate that the joint geometry and loading configuration affect the crack growth behaviour of specimens. In an attempt to study the above effect, three specimen geometries are selected; cruciform joint under tension (CJT), side end notch under tension (SENT) and under three-point bending (SENB3) load. Results show that all three geometries have different fatigue strength and fracture mechanics parameters, although their weld-metal chemistry and mechanical properties are the same. Further tests are needed to establish this relationship quantitatively.

A FORTRAN code and the algorithm for identification of tubular joints of types T, Y, X, K, KT and SKT from structural data of a jacket is presented. This task arises in fatigue analysis of all joints in the structure where identification of all possible joints is not feasible without a code. ? 1994.

With the increasing utilization of braze repair in the gas turbine industry, the properties of braze joints under simulated service conditions become vital in selecting braze repair over other processes. While braze repair has often been claimed to deliver mechanical properties equivalent to that of the parent material, this is largely based on the results of tensile or accelerated creep tests for most gas turbine hot section components failure occurs as a result of thermal fatigue or thermomechanical fatigue. The damage that occurs under such conditions cannot be assessed from tensile or creep testing. This study was undertaken to characterize the fatigue properties of narrow and wide gap brazed X-40 cobalt-based superalloy and compare these properties to that of the X-40 parent material. Butt joint narrow gap and wide gap specimens were vacuum brazed using BNi-9 braze alloy. X-40 and IN-738 were used as additive materials in wide gap braze joints. To characterize the fatigue properties of the braze joints and parent material, isothermal fatigue tests were conducted at 950°C and under load control using a fully reversed sinusoidal wave form having stress amplitude of 75% of the yield strength of the parent material. The braze specimens were fatigue tested in the as-brazed condition. The fatigue test results showed that the fatigue lives of the brazed specimens were lower than that of the parent material, particularly for the narrow gap samples and wide gap samples containing IN-738 additive alloy. All fatigue failures in the brazed samples occurred in the braze joints. An analysis of the fracture surfaces using a scanning electron microscope revealed that porosity was the major contributing factor to fatigue failures in the wide gap braze joints. The testing life debit observed in the narrow gap braze samples can be attributed to the presence of brittle boride phases in the braze joint. This study also included examination of techniques for reducing the aforementioned porosity and presence of brittle intermetallic phases. © 2011 American Society of Mechanical Engineers.

International audience; Forged components exhibit good mechanical strength, particularly in terms of high cycle fatigue properties. This is due to the specific microstructure resulting from large plastic deformation as in a forging process. The goal of this study is to account for critical phenomena such as the anisotropy of the fatigue resistance in order to perform high cycle fatigue simulations on industrial forged components. Standard high cycle fatigue criteria usually give good results for isotropic behaviors but are not suitable for components with anisotropic features. The aim is to represent explicitly this anisotropy at a lower scale compared to the process scale and determined local coefficients needed to simulate a real case. We developed a multi-scale approach by considering the statistical morphology and mechanical characteristics of the microstructure to represent explicitly each element. From stochastic experimental data, realistic microstructures were reconstructed in order to perform high cycle fatigue simulations on it with different orientations. The meshing was improved by a local refinement of each interface and simulations were performed on each representative elementary volume. The local mechanical anisotropy is taken into account through the distribution of particles. Fatigue parameters identified at the microscale can then be used at the macroscale on the forged component. The linkage of these data and the process scale is the fiber vector and the deformation state, used to calculate global mechanical anisotropy. Numerical results reveal an expected behavior compared to experimental tendencies. We proved numerically the dependence of the anisotropy direction and the deformation state on the endurance limit evolution

Equal Channel Angular Pressing (ECAP) is currently being widely investigated because of its potential to produce ultrafine grained microstructures in metals and alloys. A sound knowledge of the plastic deformation and strain distribution is necessary for understanding the relationships between strain inhomogeneity and die geometry. Considerable research has been reported on finite element analysis of this process, assuming threedimensional plane strain condition. However, the two-dimensional models are not suitable due to the geometry of the dies, especially in cylindrical ones. In the present work, three-dimensional simulation of ECAP process was carried out for six outer corner radii (sharp to 10 mm in steps of 2 mm), with channel angle 105¶Çü▒, for strain hardening aluminium alloy (AA 6101) using ABAQUS/Standard software. Strain inhomogeneity is presented and discussed for all cases. Pattern of strain variation along selected radial lines in the body of the workpiece is presented. It is found from the results that the outer corner has a significant influence on the strain distribution in the body of work-piece. Based on inhomogeneity and average strain criteria, there is an optimum outer corner radius., {"references":["V. M. Segal, \"Material Processing by simple shear\", Mater. Sci. Eng. A\n197 (1995) 157-164.","V. M. Segal, \"Equal channel angular extrusion: from macromechanics to\nstructure formation\", Mater. Sci. Eng. A 271 (1999) 322-333.","Y. Iwahashi, J. Wang, Z. Horita, M. Nemoto, T. G. Langdon, \"Principles\nof equal channel angular pressing of ultra-fine grained materials\",\nScripta Mater. 35 (2) (1996) 143.","Yi-Lang, Shyong Lee, \"Finite element analysis of strain conditions after\nequal channel angular extrusion\", J. Mater. Tech. 140 (2003) 583-587.","S. Li, M. A. M. Bourke, I. J. Beyerlein, D. J. Alexander, B. Clausen,\n\"Finite element analysis of the plastic deformation zone and working\nload in equal channel angular extrusion\", J. Mater. Eng. A 382 (2004)\n217-236.","Hl-Heon Son, Jeong-Ho Lee, Yong-Taek Im, \"Finite element\ninvestigation of equal channel angular extrusion with back pressure\", J.\nMater. Process. Technol. 171 (2006) 480-487.","C. J. Luis-Perez, R. Luri-Irigoyen, D. Gaston-Ochao, \"Finite element\nmodeling of an Al-Mn alloy by equal channel angular extrusion\", J.\nMater. Process. Tech. 153-154 (2004) 846-852.","Raghavan Srinivasan, \"Computer simulation of the equal channel\nangular extrusion (ECAE) process\", Scripta Mater. 44 (2001) 91-96.","H. S. Kim, \"Finite element analysis of equal channel angular pressing\nusing a round corner die\", Mater. Sci. Eng. A 315 (2001) 122-128.\n[10] A. V. Nagasekhar and Yip Tick-Hon, \"Optimal tool angles for equal\nchannel angular extrusion of strain hardening materials by finite element\nanalysis\", Comp. Mater. Sci. 30(3-4) (2004) 489-495\n[11] H. S. Kim, M. H. Seo and S. I. Hong, \"Finite element analysis of equal\nchannel angular pressing of strain rate sensitive metals\", J. Mater.\nProcess. Tech. 130-131 (2002) 497-503\n[12] A. V. Nagasekhar, Y. Tick-Hon, S. Li and H. P. Seow, \"Effect of acute\ntool-angles on equal channel angular extrusion/pressing\", Mater. Sci.\nEng. A 410-411 (2005) 269-272.\n[13] Fuqian Yang, Aditi Saran, K. Okazaki, \"Finite element simulation of\nequal channel angular extrusion\", J. Mater. Process. Tech. 166 (2005)\n71-78.\n[14] S. C. Yoon, P. Quang, S. I. Hong, H. S. Kim, \"Die design for\nhomogeneous plastic deformation during equal channel angular\npressing\", J. Mater. Process. Tech. 187-188 (2007) 46-50\n[15] C. W. Su, L. Lu and M. O. Lai, \"3D finite element analysis on strain\nuniformity during ECAP process\", Mater. Sci. Tech. 23-6 (2007) 27-\n735.\n[16] Hong Jiang, Zhiguo Fan, Chaoying Xie, \"3D finite element simulation\nof deformation behavior of CP-Ti and working load during multi-pass\nequal channel angular extrusion\", Mater. Sci. Eng. A (2007).\n[17] Tao Suo, Yulong Li, Qiong Deng, \"Yuanyong Liu, Optimal pressing\nroute for continued equal channel angular pressing by finite element\nanalysis\", Mater. Sci. Eng. A 466 (2007) 166-171.\n[18] J. K. Kim, W. J. Kim, \"Analysis of deformation behavior in 3D during\nequal channel angular extrusion\", J. Mater. Process. Tech. 176 (2006)\n260-267.\n[19] ABAQUS User-s Manual, Version 6.5.1, Hibbitt, Karisson & Sorensen\n2006.\n[20] C. Xu, K. Xia and T. G. Langdon, \"The role of back pressure in the\nprocessing of pure aluminum by equal-channel angular pressing\", Acta\nMater., 55 (2007) 2351-2360\n[21] D. Nagarajan, \"Processing of an aluminium alloy by ECAE prior to cold\nextrusion\", M.S. Thesis, Indian Institute of Technology Madras, India,\n2005, 47.\n[22] Patil Basavaraj V. Uday Chakkingal, T.S. Prasanna Kumar, \"Study of\nchannel angle influence on material flow and strain inhomogeneity in\nequal channel angular pressing using 3D finite element simulation\", Jl.\nof Mater. Process. Tech. 209 (2009) 89-95."]}