bluuebunny/crossref_metadata_2025 huggingface dataset:
Repairing and Preserving Bridge and Steel Structure Using an Innovative Crack Arrest Repair System
Authors: Reid Len
Published: March 2014

Cracking in steel road or rail bridges is a major concern for continued safe operation of the bridge. Traditional crack arrest hole (CAH) or drill stops placed at the end of the detectable crack have been shown to be ineffective in stopping cracks. A method adapted from the aerospace industry, which utilizes a high interference fit bushing expanded into the CAH, has been tested in large A36 steel coupons under typical cyclic bridge loading. Expansion of the bushing into the hole yields the surrounding steel and induces a residual compressive stress around the hole to shield it from the cyclic load and prevent further crack growth. Not only did this method completely arrest the crack with a life improvement factor exceeding 60:1 over the conventional CAH but it also increased the load factor capability of the coupon by over 20%. This paper will describe the methodology, present the results of the test program and show how this innovative method dramatically increases the effectiveness of a typical CAH that could forestall major structural failure.
Proposal of an Eigen-Strain Estimation for Determination of Residual Stresses Considering the Influence of Machining
Authors: Ogawa Masaru
Published: March 2014

In order to assure structural integrity for mechanical structures, it is indispensable to estimate three-dimensional residual stresses quantitatively to asses a crack growth rate of an observed crack. Now, the neutron diffraction method and the DHD (Deep Hole Drilling) method have been proposed to evaluate stress gradient in the thickness direction. However, estimated stresses by these methods can not be input to the FEM (Finite Element Method) model that has been widely used at design time for the assessment of the structural integrity. Then, the eigen-strain method has been proposed. In this method, three-dimensional residual stresses are calculated by an elastic FEM analysis from eigen-strains those can be evaluated quantitatively by an inverse analysis from released strains measured by strain gauges while the geometric boundary condition or material properties of the object has been changed. However, inelastic strains are newly created on the machined surface, the estimation accuracy of this method becomes relatively poor because the eigen-strains before and after measurements have to be the same. In this study, a calculation technique to evaluate not only initial eigen-strains but also processing strains is shown, and effectiveness of this method is demonstrated numerically in the bead flush method based on the eigen-strain method. Although estimation accuracy of processing strains was poorer, three-dimensional residual stresses for whole region could be evaluated accurately from measured strains without measurement errors.
Influence of Cyclic Deformation Induced Phase Transformation on the Fatigue Behavior of the Austenitic Steel X6CrNiNb1810
Authors: Sorich Andreas , Smaga Marek , Eifler Dietmar
Published: March 2014

The austenitic steel X6CrNiNb1810 (AISI 347) was investigated in isothermal total strain-controlled tests at ambient temperature and T = 300 °C in the LCF-and HCF-range. The phase transformation from paramagnetic austenite (fcc) into ferromagnetic α´-martensite ́(bcc) leads to cyclic hardening and to an increase in fatigue life. At 300 °C no α´-martensite formation was observed in the LCF-range and the cyclic deformation behavior depends basically on cyclic hardening processes due to an increase of the dislocation density, followed by cyclic saturation and softening due to changes in the dislocation structure. In the HCF-range an increase in fatigue life was observed due to ε- and α´-martensite formation. Measurements of the mechanical stress-strain-hysteresis as well as temperature and magnetic properties enable a characterization of the cyclic deformation behavior and phase transformation in detail. The changes in the physical data were interpreted via microstructural changes observed by scanning-and transmission-electron-microscopy as well as by x-ray investigations. Additionally electromagnetic acoustic transducers (EMATs) developed from the Fraunhofer Institute of Non-destructive Testing (IZFP) Saarbrücken were used for an in-situ characterization of the fatigue processes.
Preliminary Study on the Acoustic Emission Wave Velocity on Filament Wound Glass Fiber Reinforced Polymer Pipes and its Correspondence with the Winding Angle
Authors: Ortenzi Altibano , Corvi Andrea , Virga Antonio
Published: March 2014

In this study, three types of filament wound glass fiber reinforced epoxy composite specimens were tested according to the ASTM standards to evaluate preliminary, the acoustic emission wave velocity. The pipe specimens had 300.0 mm of length, 50.5 mm of diameter and 3.5 mm of wall thickness. Ten points were marked over the imaginary central circle on the pipe middle, from zero degree up to 90º with nine divisions of 10º each one and an additional point representing the crossing of plies. Next, there are positioned two collinear acoustic emission (AE) sensors along the length, positioned at 35 mm from middle, axially. After the specimen preparation, took place the HSU-NIELSEN or pencil lead break (PLB) tests to analyze the signal wave time for both sensors, by means of the 0.3mm – 2H graphite lead brake. The results were compared to considering the angular variation and the velocity for each winding angle. It was evident that the procedure above can determine with good precision the variations occurred on the acoustic emission velocity on filament wound composite pipes, regarding the three angular variations compared. This study was the parameter of control to proceed with the acousticemission evaluation over tensile tests in further studies to predict the fatigue and the damage propagation on this typology of laminates.
Scattering Phenomena of Edge Guided Waves at and around Notches
Authors: Nadarajah Nithurshan , Vien Benjamin Steven , Chiu Wing Kong , Rose L.R. Francis
Published: March 2014

This work presents a computational investigation into the scattering of edge guided waves travelling by a notch. To establish a good understanding of this scattering phenomenon, the analysis was conductedon a range of length scales. The finite element analysis indicate that the edge guided surface waves are scattered by the presence of a notch which resulted in a SH0-like appearance wave radiating into the medium. This can be mistaken as a mode conversion of the fundamental lamb modes or even a source at notch tips. The phenomenon becomes harder to notice at higher frequency as increasing the frequency decreases the speed and both the bulk and surface waves travel at identical speeds. A clear understanding of this interaction furthers our knowledge in one of the most prominent interaction in the study of acoustic waves for structural health monitoring.
Durability of Embedded PZTs in Structural Health Monitoring Systems under Cyclic Loading
Authors: Yoo Sanghyun , Khatibi Akbar Afaghi , Kandare Everson
Published: March 2014

Structural Health Monitoring (SHM) systems are developed to decrease the maintenance cost and increase the life of engineering structures by fundamentally changing the way structural inspections are performed. However, this important objective can only be achieved through the consistent and predictable performance of a SHM system under different service conditions. The capability of a Piezoelectric lead Zirconate Titanate (PZT)-based SHM system in detecting structural flaws strongly depends on the sensor signals as well as actuator performance. But service conditions can change the behaviour of transducers, raising questions about long term SHM system capability. Although having a clear understanding of the reliable sensor life is important for surface mounted systems, however, this is particularly critical for embedded sensors. This is due to the fact that opportunity for replacement of sensors exists for surface bonded transducers while for the embedded systems, sensor replacement is not straightforward. Therefore, knowledge of the long term behaviour of embedded-SHM systems is critical for their implementation. This paper reports a study on the degradation of embedded PZT transducers under cyclic loadings. Carbon/epoxy laminates with an embedded PZT were subjected to fatigue loading and their performance was monitored using Scanning Laser Vibrometery (SLV). The functionality of PZT transducers under sensing and actuating modes were studied. High and low cycle fatigue tests were performed to establish strain-voltage relationships which can be used to identify critical cyclic loading parameters (number of cycles and R value) under sensing and actuating modes.
Endurance Testing of a Vibration Energy Harvester for Structural Health Monitoring
Authors: Hart Genevieve A. , Moss Scott D. , Nagle Dylan J. , Galea Steve C.
Published: March 2014

The Australian Defence Science and Technology Organisation (DSTO) is developing a variety of in-situ structural health monitoring (SHM) approaches for potential use in high value platforms across the Australian Defence Force (ADF). The implementation of SHM systems would allow the ADF to move from expensive interval based inspection and maintenance regimes for ageing platforms to more cost-effective condition-based approaches, and therefore reduce aircraft through - life support costs. One critical issue is determining the optimal means of supplying power to these in-situ SHM systems. To address this issue DSTO has developed a bi-axial vibration energy harvesting approach based on a vibrating spherical-mass, magnet and wire-coil transducer arrangement. It is important that the vibration energy harvesting devices themselves are resistant to fatigue and wear related damage as they may need to operate in service for many years. This paper examines work done on mitigating wear effects in vibration energy harvesting devices, with the goal of ensuring device longevity.
Modelling of TMF Crack Initiation in Smooth Single-Crystal Superalloy Specimens
Authors: Leidermark Daniel , Segersäll Mikael , Moverare Johan , Simonsson Kjell
Published: March 2014

In this paper the TMF crack initiation behaviour of the single-crystal nickel-base superalloyMD2 is investigated and modelled. TMF tests were performed in both IP and OP for varying mechanicalstrain ranges in the [001] crystallographic direction until TMF crack initiation was obtained. Acrystal plasticity-creep model was used in conjunction with a critical-plane approach, to evaluate thenumber of cycles to TMF crack initiation. The critical-plane model was evaluated and calibrated ata stable TMF cycle, where the effect of the stress relaxation had attenuated. This calibrated criticalplanemodel is able to describe the TMF crack initiation, taking tension/compression asymmetry aswell as stress relaxation anisotropy into account, with good correlation to the real fatigue behaviour.
Fatigue Crack Thresholds Significantly Affected by Thermo-Mechanical Loading Histories in an Austenitic and a Ferritic Low Alloy Steel
Authors: Okazaki Masakazu , Muzvidziwa M. , Iwasaki R. , Kasahara Naoto
Published: March 2014

High cycle thermal fatigue failure of pipes induced by fluid temperature change is one of interdisciplinary issues to be concerned for long term structural reliability of high temperature structural material and components in energy systems. In order to get basic understanding on this article. the fatigue crack propagation tests were carried out in a low alloy steel and an austenitic stainless steel those were subjected to typical kinds of thermo-mechanical loading histories those included a simulated weld repair process. It was shown experimentally that the thermo-mechanical histories left their individual effects along the prior fatigue crack wake, resulting in significant change in the fatigue crack threshold. Some proposes are presented to predict those history effects.
Influence of Extremum Temperatures on TMF of a Ni-Base Superalloy
Authors: Kirka Michael M. , Shinde Sachin R. , Gravett Phillip W. , Neu Richard W.
Published: March 2014

Significantly reducing the minimum temperature while maintaining maximum temperature of thermomechanical fatigue (TMF) cycles can reduce the life even when mechanical strain ranges are similar. This applies to in-phase (IP) and out-of-phase (OP) TMF cycles. This reduction in life has generally been attributed to a combination of changes in microstructure arising from aging and increases in the cyclic inelastic strain promoted by increases in the elastic modulus as the minimum cycle temperature is reduced. TMF cycles under both IP and OP conditions were conducted with maximum cycle temperatures within the 750-950C range and with minimum cycle temperatures of either 100 or 500C. A reduction in minimum temperature was observed to promote a decrease in TMF life by as much as a factor of ten for all TMF experiments. The reduction in TMF life is primarily controlled by increases in the inelastic strain range associated with increases in the elastic modulus that arise when the minimum temperature is reduced.
Influence of the Strain Rate on the Low Cycle Fatigue Life of an Austenitic Stainless Steel with a Ground Surface Finish in Different Environments
Authors: Poulain Thibault , Mendez José , Hénaff Gilbert , de Baglion Laurent
Published: March 2014

This paper focuses on the influence of strain rate in Low Cycle Fatigue (LCF) of a 304L austenitic stainless steel at 300 °C in different environments (secondary vacuum, air and Pressurized Water Reactor (PWR) water environment). Moreover test samples are ground to obtain a surface finish rougher than all that could be found in nuclear power plants. Different strain rates (4x10-3, 1x10-4 and 1x10-5 s-1) are studied, with a triangular waveform at a total strain amplitude of ±0.6%. The influence of strain rate on cyclic stress-strain behavior and fatigue life is firstly analyzed in secondary vacuum, considered as a non-active environment. Then, interactions between stain rate and environmental effects in Air and in PWR environment are presented. In all environments, a decrease in strain rate leads to a negative strain rate dependence of the stress response and a reduction in fatigue life. Finally, SEM observations of fatigue striations in PWR environment indicate a crack propagation rate enhancement when the strain rate is decreased.
Low Cycle and Multiaxial Fatigue Behavior of Three Al-Mg-Si Alloys
Authors: Laurito-Nascimento Denise F. , da Silva Antunes Ana Márcia Barbosa , Reis Pereira Baptista Carlos Antonio , Dias José Célio , Souza Angelo
Published: March 2014

Al-Mg-Si alloys (6xxx series) are medium strength structural alloys, with good corrosion resistance, good weldability and high damping capacity. They represent a high volumetric fraction of extruded aluminium alloys which are produced for commercial use and have been increasingly applied in the automotive industry. For structural materials, the fatigue strength is the most important factor to ensure a long-term reliability. Engineering structures such as aircrafts and automobiles usually undergo complex multiaxial loadings, which lead to changes of the principal stresses and strains directions in components during a loading cycle. In this study, fatigue tests were performed in three Al-Mg-Si alloys, namely AA 6005, AA 6351 and AA 6063, tempered and aged for the T6 condition. A comparative study was undertaken by assessing their Low Cycle Fatigue (LCF) properties and multiaxial fatigue behaviour using round smooth specimens. Strain-controlled fully reversed axial loadings and distinct combinations of axial-torsional fully reversed stress cycles, including in-phase and 90o out-of-phase loadings were adopted for the tests. The collected data are discussed in relation to some well-known multiaxial fatigue models.
Accurate Prediction of Fatigue Life under Random Loading
Authors: Takeda Norio , Naruse Tomohiro
Published: March 2014

This study focuses on the method of predicting the fatigue life of materials subjected to random loading. Since random stress caused by random loading is rigorously expressed in the frequency domain as stress power spectral density (PSD), fatigue life should be predicted using stress PSD. We propose two adjustment methods of improving the accuracy of fatigue life prediction using stress PSD in the frequency domain. The method proposed by Dirlik is widely used for predicting the fatigue life in the frequency domain; however, it overestimates fatigue damage caused by large stress amplitude when the slope of the fatigue resistance curve is large. To prevent this overestimation, we applied our two adjustment methods to fatigue life prediction for typical random stresses observed on mechanical products. As a result, the adjustment methods worked well in improving prediction accuracy. Lightweight and reliable products can be therefore designed by applying the proposed methods to the evaluation of fatigue life under random loading.
A Flexible HCF Modeling Framework Leading to a Probabilistic Multiaxial Kitagawa-Takahashi Diagram
Authors: Bellett Daniel , Pessard Etienne , Morel Franck
Published: March 2014

This article describes a flexible modeling framework which leads to the construction of a probabilistic, multiaxial Kitagawa-Takahashi diagram. This framework has been developed following experimental observations that clearly indicate that two independent fatigue damage mechanisms can be activated, at the same time, in metallic materials. Specifically, one damage mechanism is associated with crack initiation and the other with crack arrest. It is postulated that these damage mechanisms are more appropriately modeled using two different fatigue criteria or, more specifically, two completely different approaches to fatigue (i.e. a classical multiaxial fatigue criterion and a LEFM type criterion). Hence, the proposed modeling framework provides the possibility of combining any two suitable criteria, in a probabilistic framework based on the weakest link hypothesis and results in the continuous description of the Kitagawa diagram for any multiaxial stress state. It is shown that under certain conditions this approach is equivalent to the classical El Haddad approach to the short crack problem encountered in LEFM. However, the proposed framework is easily extended to multiaxial loading conditions. This modeling framework is demonstrated in detail via its application to multiaxial fatigue data for data taken from the literature.
Fatigue Behaviour of Laser Beam Welded Circular Weld Seams under Multi-Axial Loading
Authors: Zimmermann Martina , Bretschneider Jörg , Kirchhoff Gunter , Stamm Uwe , Standfuss Jens , Brenner Berndt
Published: March 2014

With modern laser beam sources welding processes can be developed, that allow the joining of otherwise barely realisable material and geometrical constellations such as dissimilar welded, thick-walled shaft-hub joints for powertrain systems. Current design recommendations do not offer solutions to account for the cyclic strength under torsional loading for welded structures. In order to bridge the gap between cost and time consuming prototype testing and laboratory tests of basic homogeneous material samples, a test system combining axial and torsional loading was used. For this purpose application oriented test parts are designed to mimic the weld seam geometry, stiffness and heat dissipation conditions of the real structural part at its best. The dissimilar joints were realised for two material combinations: cast iron GJS-600-3 with case hardened steel 16MnCr5 and 42CrMo4 with 16MnCr5. The latter combination showed only a slightly higher cyclic strength compared to the cast iron/steel combination. A systematic optimization of the laser beam welding process leads to a fatigue behaviour under multi-axial loading conditions, where the cast iron/case hardened steel combination still met the strength specification required.
High-Temperature Ultrasonic Fatigue Testing at 1000°C
Authors: Furuya Yoshiyuki , Kobayashi Kazuo , Hayakawa Masao , Sakamoto Masao , Koizumi Yutaka , Harada Hiroshi
Published: March 2014

A high-temperature ultrasonic fatigue testing system was developed to evaluate the gigacycle fatigue properties of single-crystal superalloys used in aircraft engine turbine blades. In this development, a commercial ultrasonic fatigue testing machine was considerably modified to achieve high-temperature fatigue testing. The developed system took account of temperature dependency of Youngs modulus, and also had a function to evaluate the Youngs modulus. In order to protect the testing system from the heat of a specimen, straight and round rods were inserted between the testing system and the specimen. Other modifications achieved accurate control of temperature, edge displacement and resonance frequency, which were necessary for accurate control of stress amplitude. The testing system was first applied to a heat-resistant steel at 650 °C to check its accuracy, and next to SC superalloy samples at 1000 °C. In the conventional fatigue tests on the heat-resistant steel, the results were coincident in a frequency range from 1 Hz to 800 Hz, suggesting that comparable results would be obtained in ultrasonic fatigue testing at 20 kHz. In case of the SC superalloy samples, conventional fatigue tests were conducted at only 10 Hz, so the frequency effects were not clarified. In both cases, ultrasonic fatigue testing showed good agreement with conventional fatigue testing. The accuracy of the developed system is therefore high, even at 1000 °C. In these results, the SC superalloys showed no fatigue limit, indicating gigacycle fatigue tests to be necessary.
Influence of Weld Imperfections on the Fatigue Behaviour of Resistance Spot Welded Advanced High Strength Steels
Authors: Rethmeier Michael
Published: March 2014

The use of advanced high strength steels (AHSS) in the automotive body-in-white is increasing. Those steels are predominantly joined by resistance spot welding. For the performance of the whole body-in-white, the fatigue behaviour is of high interest, especially as during production, weld imperfections such as cracks and manufacturing-related gaps cannot be avoided. In this study the TRIP steel HCT690 was used as it is a typical advanced high strength steel in automotive production. The investigation into the influence of cracks was split depending on the crack location in the weld area. Surface cracks in the electrode indentation area as well as in the heat affected zone were produced during welding and analyzed. The results showed that surface cracks independent of their position have no effect on the fatigue life. The produced internal imperfections have shown only a marginal impact on the fatigue life. It was ascertained that gaps of 3 mm lead to a significant drop in fatigue life compared to gap free shear tension samples under a load ratio R of 0.1. This fact was attributed to decreased stiffness, higher transverse vibration and higher rotation between the sheets. Furthermore, FE-simulations have shown an increase in local stresses in gapped samples.
On the Effect of Electrodischarge Drilling on the Fatigue Life of Inconel 718
Authors: Bassoli Elena , Baldini Andrea , Gatto Andrea , Strozzi Antonio , Denti Lucia
Published: March 2014

Difficult-to cut-materials are associated with premature tool failure, most likely in the case of complex geometries and this shapes. However, Nickel-based alloys are commonly used in high-temperature and aerospace applications, where thin deep holes are often required. Then, the only viable manufacturing solution relies on non-contact processes, like electrodischarge (ED) drilling. Morphology of ED machined surfaces is significantly different than obtained by metal-cutting operation and is known to jeopardize fatigue strength, but the extent needs to be gauged and related to the process parameters. Aim of the paper is to study the effect of holes (0.8 mm diameter, aspect ratio 10) produced by ED drilling on the fatigue life of Inconel 718. Rotating bending fatigue tests are carried out on specimens drilled under two ED setups, as well as with a traditional cutting tool. Specimens free from holes are fatigued under the same conditions for comparison. Based on previous studies, extremal ED parameters are selected, giving best surface finish versus highest productivity. S-N curves show that the ED process causes a decrease of the fatigue resistance with respect to traditional drilling, whereas the effect of different ED setups is negligible. Maximum productivity can thus be pursued with no threat to fatigue performance. The fatigue limit variation is quantified by using the superposition effect principle: ED drilling causes an increase of the stress concentration factor around 25% if compared to traditional drilling. The macroscopic fatigue behavior is integrated with a study of the effects of the different drilling processes in the micro-scale, by means of a microstructural and fractographic analysis.
Fatigue and Fatigue Crack Propagation of Laser Beam-Welded AA2198 Joints and Integral Structures
Authors: Kashaev Nikolai , Chupakhin Sergey , Enz Josephin , Ventzke Volker , Groth Anne , Horstmann Manfred , Riekehr Stefan
Published: March 2014

To meet the future demands of the aerospace industry with respect to safety, productivity, weight, and cost, new materials and joining concepts have being developed. Recent developments in the metallurgical field now make it possible to use laser-weldable Al-alloys of the 2xxx series such as AA2198 with a high structural efficiency index due to their high strength and low density. AA2198 holds the promise of providing a breakthrough response to the challenges of lightweight design in aircraft applications. Laser beam welding as an efficient joining technology for fuselage structures is already established in the aircraft industry for lower fuselage panels because the welded panels provide a higher buckling strength and lower weight compared with the classical riveted designs. The key factor for the application of laser-welded AA2198 structures is the availability of reliable data for the assessment of their damage tolerance behavior. In the research presented, the mechanical properties with regard to fatigue and fatigue crack propagation of laser beamwelded AA2198 joints and four-stringer panels were investigated. It was found that the fatigue endurance limit of laser beamwelded AA2198T3 is approximately 25 % below the endurance limit of the base material. With regard to the fatigue crack propagation behavior, the laser beam welded four-stringer panels with T-joints show a fatigue life increased by a factor of 1.7 compared with the base material. This work shows that high-quality laser beam welds of AA2198 can be produced on a large scale using the laser beam welding facilities of the Helmholtz-Zentrum Geesthacht.
Reduction in Fatigue Strength of Arc Welded Aluminium 5083-H111 on Immersion in NaCl
Authors: du Toit Madeleine , Mutombo Kalenda
Published: March 2014

The design of welded aluminium structures subjected to fatigue loading is usually carried out on the basis of reference fatigue curves published in design codes. The reference curves are usually relevant to dynamic loading in ambient air and make provision for the presence of a corrosive environment by downgrading the detail category for a particular joint type. This investigation studied the corrosion-fatigue behaviour of Al 5083-H111 welded using ER5356 wire. Comparison between experimentally determined fatigue curves and reference fatigue design curves published in Eurocode 9 confirms that 5083-H111 welds display significantly lower reference fatigue strengths than unwelded base material. Immersion in a NaCl solution during testing reduced the reference fatigue strengths even further. The reduction in detail category number recommended in Eurocode 9 for aluminium butt welds on immersion in sea water appears suitable (or even marginally conservative) for the 5XXX series Al-Mg-Mn welds examined in this investigation.
The Effectiveness of Design Procedures for Fatigue Design of Welds
Authors: Price John W.H.
Published: March 2014

This paper examines the link between the design codes, good design and the prevention of field failures.
There are many design codes for the fatigue design of welds. They contain many differences influenced by the history of particular industries. Engineering may not be well served by these codes since on one hand they are normally conservative, thus creating excessively heavy structures. On the other hand the design codes often do not include the most important factors in the life expectancy of a weld namely the weld procedure, the quality of the weld and environmental effects.
The paper concludes that a thorough review and unification of the industry design codes is overdue. The issue of manufacture of welds has to be put at the centre of the consideration of fatigue design.
Influence of Heat Treatment on Fatigue Resistance of Electron Beam Welded Dissimilar Titanium Alloy Joints
Authors: Wang S.Q. , Liu Jin He , Chen Dao Lun
Published: March 2014

The purpose of this study was to evaluate the influence of heat treatment on the microstructural change and low cycle fatigue (LCF) resistance of an electron beam welded (EBWed) dissimilar joint between Ti-6Al-4V and Ti17 alloys. The aging with solution (STA) had a more significant effect on the microstructure and hardness than aging, compared to the as-welded joint. The post-welded joints in both aging and STA conditions were basically cyclic stable at low strain amplitudes up to 0.6%, while cyclic softening occurred at higher strain amplitudes. The fatigue life in the aging condition was slightly longer than that in the STA condition at the lower strain amplitudes. Fatigue crack initiation occurred from the specimen surface or near-surface defect, and fatigue crack propagation was characterized mainly by the fatigue striations coupled with secondary cracks in both aging and STA conditions.
Three-Dimensional Porous Carbonate Apatite with Sufficient Mechanical Strength as a Bone Substitute Material
Authors: Nguyen Xuan Thanh Tram , Maruta Michito , Tsuru Kanji , Matsuya Shigeki , Ishikawa Kunio
Published: March 2014

In this study, three - dimensional porous carbonate apatite (CO3Ap) materials with the chemical compositions and structures similar to cancellous bone were produced via phosphorization of porous calcite precursor in hydrothermal condition. In order to make porous calcite precursor, negative replication of polyurethane foam that named as inverse ceramic foam method was conducted. When the polyurethane template occupied within the ceramic solid walls disappeared due to burning at high temperature, interconnected hollow pathways were produced. Polyurethane foam was used as a porogen - template firstly was coated layer by layer with synthetic resin to modify morphology and enlarge thickness of struts so as to expand porous area for satisficing cellular bioactivities. Calcium hydroxide (Ca(OH)2) slurry was then infiltrated into resin coated-polyurethane foam. Heat treatment in atmosphere of oxygen and carbon dioxide gases was carried out to eliminate polyurethane template and induce carbonation process. Ca(OH)2 was converted to calcite with the internal porous channel architecture simulating polyurethane foam struts network. That interconnected porous calcite was subsequently transformed to CO3Ap with remaining the same macroporous structure through hydrothermal treatment in phosphate solution. The porous CO3Ap materials were implanted in the tibia of Japanese male rabbits and removed after a period of 3 months. The bone formation response of the three - dimensional porous carbonate apatite in vivo has been preliminary studied using micro-computed tomography (µ-CT) scanner. The results showed that the porous implant materials have sufficient mechanical strength to provide structural support during bone remodeling and successfully bond with host bone.
A Brief Review of Fatigue Strengthening of Metallic Structures in Civil Engineering Using Fibre Reinforced Polymers
Authors: Zhao Xiao Ling , Motavalli Masoud
Published: March 2014

There is a great potential in using fibre reinforced polymer (FRP) to strengthen aging metallic structures. This paper briefly describes the benefit of using FRP to strengthen metallic structures. It then addresses how fatigue load affects the bond between FRP and steel. FRP fatigue strengthening of cracked steel plates and connections are discussed. Furthermore, effects of using prestressed FRP on flexural and fatigue behaviours of a FRP-steel composite system are addressed. Bonded and un-bonded FRP-to-steel applications, as two different approaches for steel strengthening, are discussed. Finally fatigue strengthening of metallic riveted bridges using un-bonded pre-stressed FRP plates is presented. A comprehensive list of references is provided.
Postponing Crack Nucleation in 2024 Aluminium Alloy by Dynamic Precipitation from the Supersaturated State
Authors: Mahdavi Shahri Meysam , Alderliesten Rene C. , van der Zwaag Sybrand , Schut Henk
Published: March 2014

Recently a novel strategy to improve the fatigue resistance of precipitation hardened aluminium alloys has been proposed, which is based on dynamic precipitation in partially aged material. In this paper, the effect of mean stress and alternative temperature treatments that can enhance the high cycle fatigue resistance through the mentioned mechanism were investigated. The material used is an under-aged 2024 aluminium alloy, which showed superior fatigue life compared to the peak aged condition. The recorded behaviour was observed to be more effective at lower stress amplitudes and lower R values. As the dynamic precipitation may not be able to keep up with the damage evolution, dedicated experiments were conducted to insert periods of controlled healing in a stress free state.
Review on the Fatigue of Composite Hybrid Joints Used in Aircraft Structures
Authors: Chowdhury Nabil , Chiu Wing Kong , Wang John
Published: March 2014

The use of composite materials as a replacement for commonly used metals such as aluminium and steel are increasing in the engineering industry, particularly in the aerospace sector. The move towards light weight and high stiffness structures that have good fatigue durability and corrosion resistance has led to the rapid move from metal to composites. This change allows for further flexibility in design and fabrication of various components and joints.
There are three main categories of joints used in composite materials – mechanically fastened joints, adhesively bonded joints and the combination of the two called hybrid joints. In order to adequately understand the effectiveness of these joints, substantial testing and validation is required, particularly in the use of hybrid joints for real life applications. Static testing, load distribution and parametric studies of hybrid joints have been investigated by various researchers; however further work is still required in understanding the durability and fatigue of hybrid joints and ensuring that both the adhesive and mechanical fasteners can work together effectively in producing an optimum joint.
Mechanical fastening alone in composite laminates is not a preferred joining method as they create high stress concentrations around the fastener holes. Adhesive bonding although has numerous benefits it is difficult to detect the bond defect particularly in cases where weak bonds can occur during applications and it is sensitive towards the environmental conditions. Thus hybrid joints are seen arguably as being more effective in joining composite components together and offer greater residual strength. Hence the performance, strength and long-term durability of these joints need to be further investigated and be applied to practical situations whilst assisting in repair certification.
Low-Cycle Fatigue Behavior of TWIP Steel - Effect of Grain Size
Authors: Rüsing Christian Johannes , Niendorf Thomas , Frehn Andreas , Maier Hans Jürgen
Published: March 2014

The effect of different grain sizes on the fatigue performance of high manganese TWIP steel (Twinning-Induced Plasticity) in the low-cycle fatigue regime was investigated. The average grain sizes in the fine grained condition were 2 5 μm and after heat treatment in the coarse grained condition about 80 μm were obtained. Pronounced twin-dislocation interactions especially in small grains strengthen the steel during monotonic deformation. Twin boundaries act as obstacles for dislocation slip, and thus, further reduce the effective grain size, which affects the fatigue response as well. The samples were monotonically and cyclically deformed at room temperature. The results reveal that the grain size has a significant influence on the mechanical as well as on the cyclic performance. Especially under cyclic loading differences in the resulting stress levels and cyclic stability can be observed. To clarify the microstructure evolution before and after fatigue with different constant strain amplitudes the samples were analyzed by means of transmission electron microscopy (TEM).
Modelling the Effect of Particle Size Distribution in Multiphase Flows with Computational Fluid Dynamics and Physical Erosion Experiments
Authors: Wong Chong Yau , Boulanger Joan , Short Gregory
Published: March 2014

It is known that particle size has an influence in determining the erosion rate, and hence equipment life, on a target material in single phase flows (i.e. flow of solid particles in liquid only or gas only flows). In reality single phase flow is rarely the case for field applications in the oil and gas industry. Field cases are typically multiphase in nature, with volumetric combinations of gas, liquid and sand. Erosion predictions of multiphase flows extrapolated from single phase flow results may be overly conservative. Current understanding of particle size distribution on material erosion in multiphase flows is limited. This work examines the effect of particle size distribution on material erosion of a cylindrical aluminium rod positioned in a 2" vertical pipe under slug and distributed bubble regimes using various water and air volume ratios. This is achieved through physical erosion experiments and computational fluid dynamics (CFD) simulations tailored to account for particle dynamics in multiphase flows.
Cyclic Deformation Behavior of a New N+C Alloying Austenitic Manganese Steel
Authors: Kang Jie , Zhang Fu Cheng , Yang Zhi Nan , Long Xiao Yan
Published: March 2014

The cyclic deformation behavior and fatigue characteristics of a new austenitic manganese steel with composition FeMn18Cr7C0.8N0.2 (wt%) have been explored and analyzed based on the partition of hysteresis loops linked with microstructure by low cycle testing in the total strain amplitudes 0.3% - 1.0%. The new N+C austenitic manganese steel exhibited immediate cyclic softening for small strain amplitude and initial hardening at the onset of fatigue life followed by softening for medium and high strain amplitudes. For low and high strain amplitudes the evolution of internal stress and effective stress partitioned from the hysteresis loop with the prolonged cycles both corresponded to the change in the total stress amplitudes. With the exception of 316LN0.2 austenitic stainless steel, the effective stress and internal stress made a contribution to the cyclic deformation behavior with similar effect. The markedly improved contribution of effective stress in the new N+C austenitic manganese steel was attributed to the enhanced short range order caused by N+C alloying whereas the decreasing of effective stress with the number of cycles was because of this broken short range interaction. TEM observations showed that the significantly increased planar dislocation structures due to the presence of N+C were responsible for the strong tendency to cyclic softening, in association with the decrease of effective stress and internal stress simultaneously. Moreover the fatigue short crack could be observed on the fractured sample surface at high strain amplitude.
Lifetime Improvement of AlSi6Cu4 Cylinder Head Alloy
Authors: Kliemt Christian , Wilhelm Franz , Hammer Joachim
Published: March 2014

Efficiency increase of combustion engines in automotive development is directly related to improved material performance at high temperatures. In particular, the interaction of complex thermal and mechanical forces under service loading is one of the major factors affecting the lifetime. In this paper the aluminium cylinder head alloy AlSi6Cu4 is characterized concerning the high temperature low cycle fatigue (LCF) and thermo-mechanical fatigue (TMF) behaviour. Experiments were performed in air at temperatures between 200 and 400°C. The influence of the initial heat treatment and microstructure, testing temperatures, strain amplitudes and strain rates is reported. Two heat treatment modifications (i.e. overaged condition, T7, and a modified combined heat treatment, hot iso-static pressing (HIP), prior to peak hardening according to T6) are compared to the T6 standard used in service. The strain amplitudes ranged between 0.2 to 0.7%. For the standard T6 heat treatment LCF results at 400°C indicate increased ductility and longer lifetimes compared to 200°C. For the overaged microstructure and the modified treatment HIP + T6 under TMF exposure clear lifetime enhancements are observed which are significantly highest for the HIP + T6 version. Thus, the elimination of almost any microporosity reduces local stress concentrations and early crack initiation promoting failure. Special attention is focussed on microstructural changes during high temperature exposure.
Biaxial Specimen Design for Structures Subjected to Multi-Axial Loads
Authors: Chowdhury Nayeem Tawqir , Chiu Wing Kong , Wang John
Published: March 2014

The ability to optimise structures requires a thorough understanding of the loadsthat they are subjected to. Many composite materials in use today are subjectedto complex loading patterns that exhibit multi-axial stress and straincharacteristics. It is not sufficient to model material data for thesestructures based purely on uniaxial information. Unlike the well understoodfailure criteria of materials when subjected to uniaxial loads; biaxial failureenvelope has not been defined with sufficient experimental data particularly inthe tensile load region. There has not been any standard specimen geometrydefined for biaxial testing. Also the effective area when subjected to loadingis not as easily known as is the case in uniaxial loading. Thus biaxial testspose a greater level of difficulty when establishing failure stresses for thematerial. The authors look at establishing a specimen geometry that is suitablefor use preliminarily in isotropic materials. These specimen geometries must beable to ensure failure at the anticipated gauge region. Investigation into thefirst quadrant of the biaxial failure envelope under tension-tension is lookedat with insight into matrix failure as the dominant mode of failure. Numerical resultsand preliminary experimental results for FM355 epoxy specimens are presentedand compared with existing failure models such as Von Mises criterion and thefailure criterion used in Strain Invariant Failure Theory.
A Study on Estimation of S-N Curves for Structural Steels Based on their Static Mechanical Properties
Authors: Mukoyama Kazutaka , Hanaki Koushu , Okada Kenji , Sakaida Akiyoshi , Sugeta Atsushi , Nishikawa Izuru , Ueno Akira , Sakai Tatsuo
Published: March 2014

The aim of this study is to develop a statistical estimation method of S-N curve for iron and structural steels by using their static mechanical properties. In this study, firstly, the S-N data for pure iron and structural steels were extracted from "Database on fatigue strength of Metallic Materials" published by the Society of Materials Science, Japan (JSMS) and S-N curve regression model was applied based on the JSMS standard, "Standard Evaluation Method of Fatigue Reliability for Metallic Materials -Standard Regression Method of S-N Curve-". Secondly, correlations between regression parameters and static mechanical properties were investigated. As a result, the relationship between the regression parameters and static mechanical properties (e.g. fatigue limit E and static tensile strength σB) showed strong correlations, respectively. Using these correlations, it is revealed that S-N curve for iron and structural steels can be predicted easily from the static mechanical properties.
Crack Growth Study of Dissimilar Steels (Stainless - Structural) Butt and Overlap Welded Unions under Cyclic Load
Authors: Fuentes Andrés L. García , del Rosario Alberto Velásquez
Published: March 2014

This study describes the mechanisms of emergence and propagation of fatigue cracks caused by mechanical tension stress fluctuations in dissimilar steels butt and overlap welded joints under axial tension fatigue loads. A structural (ASTM A537, class I) and a stainless (ASTM A240, 304L) were soldiers through GMAW, Argon as protecting gas and a stainless (ASTM A240, 308L) as a supplier material, not being submitted to pre and post welding thermal treatment. Microstructures (Scanning Electron Microscopy, SEM) were contrasted in different zones of each joint, focus on Heat Affected Zone (HAZ) and fusion lines. Samples were inspected by not destructive test (penetrating liquids and ultrasound), to discard surface and internal defects. The following mechanical tests were compared between both welding joint (WJ): Vickers hardness profile, tension, bending, impact, axial fatigue, and speed of propagation of fatigue cracks. Vickers show high values of micro hardness in the HAZ, near the fusion line between weld and stainless. Tension and axial fatigue tests indicated similar behavior between WJ and structural (butt joint); and similar behavior between WJ and stainless (overlap joint). Pre-cracked test evidence a faster growth of crack in the fusion line between structural steel and stainless. Dissimilar unions (butt and overlap) have mechanical and microstructure properties, which can be considered adequate to withstand the mechanical requirements in service conditions, despite relatively high values of hardness in the HAZ, particularly in the fusion line between the welding cord and the stainless 304L, as well as inclusions between the structural and the stainless one.
On the Development of a Prediction Methodology for Crack Growth in Fibre Metal Laminates with MSD Scenario
Authors: Wang Wan Dong , Alderliesten Rene C. , Benedictus Rinze
Published: March 2014

Multiple-site Damage (MSD) is a dangerous scenario for aircraft structures due to the interaction of adjacent cracks in one structural element. Despite their excellent fatigue crack growth resistance, Fibre Metal Laminates (FMLs) may also encounter this damage scenario. However, only few studies on fatigue crack growth in presence of MSD in FMLs has been reported. An overview of the relevant methods for predicting the crack propagation properties of MSD in FMLs is given and discussed in this paper. The fatigue crack growth of MSD in FMLs was experimentally studied and is reported in this paper. A new analytical methodology, based on the superposition principle and displacement compatibility method, is proposed.