bluuebunny/crossref_metadata_2025 huggingface dataset:
A Modified Distributed Tuned Mass Damper Design Approach
Authors: Yang Fan , Sedaghati R. , Esmailzadeh E.
Published: March 2014

A modified Distributed Tuned Mass Damper (DTMD) design approach was proposed in this study. In the traditional DTMD or TMD design, the general approach is to focus on the attached spring (s) and damper (s) under predefined mass (distribution). In this study, the DTMD design approach is to focus on the attached masses in the DTMD system. The numerical examples will be presented to illustrate the validity and effectiveness of the proposed DTMD design approach.
A Comprehensive Evaluation Method on Dynamic Simulation Accuracy of Power System
Authors: Zheng Hui Ping , Xue Min , Zhao Yan , Liu Xin Yuan , Han Yu
Published: March 2014

In order to overcome the shortcomings of the present accuracy assessment methods of power system dynamic simulation, this paper focuses the permanent single phase short-circuit fault which occurs in a large probability in power grids,and selects the typical electrical quantities which is very concerned in engineering after the fault happened. A time-scale based error criteria on simulation validation is proposed, and a comprehensive error criteria according to the average errors between simulation data and actual data is proposed to evaluate objectively the simulation accuracy of the typical electrical quantities. Considering the variation characteristics of the electrical quantities, the simulation accuracy evaluation of a single electrical element is expended to the simulation accuracy evaluation of the entire network, so not only the comprehensive evaluation about the model and its parameters but also the information for model modification and parameter correction can be obtained. The effectiveness of the proposed method is verified by the numerical results on the New England 10 Unit 39 Bus powers system.
A Comparative Study on Solar Refrigeration Technology
Authors: Zhang Hua , Ji Xu , Li Ming , Wang Qiang , Song Xiang Bo
Published: March 2014

This paper performed a comparative study on solar photovoltaic refrigeration technology and solar adsorption refrigeration technology. The experimental results showed that in sunny day, COP of the solar fin pipe adsorption refrigerator was 0.13, and was higher than 0.12, COP of the photovoltaic refrigerator. With the solar radiation enhancement within a certain range, the COP of solar adsorption refrigerator increased faster than COP of solar photovoltaic refrigerator. From the aspects of economy, with the same refrigerating capacity, the cost of the adsorption refrigerators was 30% higher than that of the photovoltaic refrigerators.
Environmental Turbulence Analysis of the Wind Power Industry Chain
Authors: Li Cun Bin , Chen Hong Yi , Zhu Jiang , Zhao Zhen Yu
Published: March 2014

Chinese wind power industry needs to raise the flexibility level to adapt the dynamic and complex environment. It is imperative to help the wind power industry to alleviate the influence of environmental turbulence. This paper established an analysis structure for environmental turbulence types including technological dynamic, supply and demand complexity, competitiveness confrontation and policy uncertainty. A questionnaire was designed and used to investigate the main influencing components in different types from experts in the field of wind power industry. By using the method of factors analysis, 19 main components are identified as having a significant influence on the environmental turbulence. The results revealed that the stabilization of wind power industry requires a combined effort from the enterprises and government.
Heat Integration of Solid Oxide Fuel Cell System
Authors: Srisiriwat Nawadee , Wutthithanyawat Chananchai
Published: March 2014

As solid oxide fuel cell (SOFC) has operating temperatures ranging between 973 K for intermediate temperature operation and 1273 K for high temperature operation, an advantage of the hot exhaust gas from SOFC can be used to drive a fuel processor for hydrogen production. In this study, the heat integration of a SOFC integrated with ethanol steam reformer, which is very highly endothermic reaction needed the large amount of energy supply, has been performed to improve the efficiency of SOFC system. In the conceptual design for heat integration, the pinch analysis is used. Under 1200 K of SOFC operating temperature and 973 K of reformer temperature, the hot exhaust gas leaving the SOFC is sufficient for heating requirements for the heat exchanger network and for the additional electricity generation from gas turbine. An energy integrated SOFC system presents a total electricity generation from SOFC and GT of 818 kW of which 386 kW is required for air compressor so an overall electricity production and efficiency are 432 kW and 35.0%, respectively.
Preparation of Terephthalic Acid (TPA) and Dioctyl Terephthalate (DOTP) by Anthracite's Alkali Oxygen Oxidation
Authors: Du Kun , Lian Ming Lei , Fan Zhi Fang , Li Yu
Published: March 2014

TPA was synthesized by a two step reaction. Firstly, water-soluble coal acids (CA) was obtained by oxygen-oxidation at 260°C in all aqueous solution of potassium hydroxide, and then crud TPA was got by isomerization of the CA with the existence of CdCO3 catalyst and CO2 pressure. The optimum reaction conditions to get crude TPA were 4% amount of CdCO3 catalyst, and reacted at 420°C with initial 3.0MPa CO2 pressure. Pure TPA was obtained by a separation step and the yield of pure TPA is 37.16% (based on CA). Furthermore, DOTP was synthesized by the refined TPA and isooctanol. The influence of mole ratio of TPA and isooctanol, amount of catalyst and reaction time on the final yield of DOTP were discussed. The purity of TPA was detected by HPLC and DOTP was detected by FT-IR, 1H-NMR to get confirmatory results.
Design of Desalination Reverse Osmosis System Power-Supplied by PV and Wind Energy
Authors: Liu Yin , Wang Shi Ming
Published: March 2014

The most popular renewable energy are solar and wind. As the problems of energy shortage and environment pollution become more serious, hybridizing energy sources turn to be a crucial solution to reach sustainable development. The present work theoretically concentrates on teasing out a set of complete and clear calculation method for deigning a seawater RO desalination unit powered by Wind-PV energy systems to produce potable water. This paper suggests a series of simple estimation models to help optimize the matching of wind and solar desalination modules.
Numerical Fatigue Analysis for Twin Roll Cast Magnesium Sheet Metal Structures
Authors: Dallmeier Johannes , Huber Otto , Saage Holger
Published: March 2014

In cyclic stress and strain controlled tests, the fatigue life was determined for twin roll cast AM50 magnesium alloy sheet metals. Different stress and strain ratios were applied to cover the technical relevant load range. The investigated sheet metal shows a strong basal texture which leads to twinning in compression parallel to the sheet plane direction. Accordingly, at low cycles to failure Nf the cyclic plastic deformation is dominated by twinning and detwinning. In this study an energy based approach for lifetime estimation is presented and compared with the Smith-Watson-Topper damage model as well as with experimental test results. The energy based approach shows a comparatively high correlation at all investigated stress and strain ratios in a wide cycle range (20< Nf <1.000.000) and is adequate for the lifetime prediction at various mean stresses.
Pseudo Fatigue Testing for Rapid Certification to Service
Authors: Molent Lorrie , Barter Simon A. , Gordon Matthew , Weibler Liam
Published: March 2014

Aircraft full-scale fatigue tests are expensive to conduct and they are a critical item on the certification path of any aircraft design or modification. Two aspects that contribute to the cost of a test are its duration and the loads spectrum development process. This paper provides a summary of a proposed supplemental pseudo full-scale fatigue test (FSFT) aimed at rapid certification. In this instance the method was developed with the aid of extant FSFTs that were found to be deficient. The proposed process involves the development of proof loads, damage size estimates, a loads application rig, insertion of the target damage or modifications and conducting proof testing. As all locations with a propensity to crack are known, the process is considered to be the equivalent of having conducted a representative fatigue test for the required service life target and then demonstrating adequate residual strength (i.e. proof testing the damage state at the end of a FSFT).
C-130H Centre Wing Lower Surface Tang Blend Repair Management
Authors: Stewart Ross , Ng Alvin , Trezise Stuart , East Phillip , Jackson Kevin
Published: March 2014

The RAAF found significant corrosion on the C-130H fleet Centre Wing Lower Surface (CWLS) panels at the tangs adjacent to the rainbow fittings. Repair of this corrosion involves blends and spot facing, and often requires the addition of a doubler to reinforce the region. All RAAF C-130H aircraft had various combinations of spot faces, blends and in some cases doublers at this location. Due to the number and combination of repairs, providing fleet wide management advice is problematic.
The fleet condition was assessed from damage maps, repairs and previous analyses. From this a number of worst case configurations were determined. A Finite Element Model was developed and used to determine the bearing and by-pass loads in each fastener row of the panel tangs. Stress intensity correction factors were developed for cracks growing from or to a spot face using Stress Check. These correction factors were applied on top of geometry factors for the baseline configuration.
A Damage Tolerance Assessment (DTA) was performed to assess the impact of spot face and blend repairs on the centre wing lower surface panel tangs, in order to develop a fleet wide management strategy. Based on the results for the repair cases, it was shown that the repairs identified in the damage maps could be managed within the existing safety by inspection program.
Study of the Effects of Two-Step Ageing Heat Treatment on Fatigue Crack Growth on an AA7050 Aluminum Alloy
Authors: Ribas Lima Luis Otavio , Jacumasso Sheila Cristina , Ruchert Cassius Olivio Figueiredo Terra , Martins Juliana Paula , Moreira Carvalho André Luis
Published: March 2014

Aluminum alloys are the first chosen materials for aircraft structures since 1930 due to their high ratio between properties and density. Currently, aircraft industries use Al-Zn-Mg-Cu alloys, with T7451 temper, which it shows high strength, fatigue and corrosion resistance. The improvements properties are result from the η’ phase formation, MgZn2. The aim the present work is to propose an alternative route for ageing heat treatment at one AA7050 aluminum alloy, the manner which the formation of η’ phase particles at lower temperatures and longer periods of treatment is obtained. According to the literature, ageing treatments at low temperatures and longer periods optimize the usage of the solution atoms, favoring the growth and nucleation particles. As a result, there is an increase in the density of the particle improving the alloy properties. These improvements show a decrease up to 13% in the crack propagation rate for moderate ΔK levels, keeping the same levels of Vickers hardness but with decay of 12% of ultimate tensile strength.
Material Scatter in Crack Growth Rates of 7075-T7351 under Spectrum Loading
Authors: Hu Wei Ping , Krieg Beau , Torregosa Ribelito F.
Published: March 2014

The probabilistic distribution of crack lengths at a critical location is a key input for risk assessment of structural failure of airframes due to fracture. This distribution depends on the initial surface condition of the structural component, the crack growth behaviour of the material, and the applied load history. MIL-STD-1530C suggests the use of a single master crack growth curve to derive the subsequent crack length distributions from the initial crack length distribution, without taking into consideration the well-recognized scatter in crack growth rates due to uncertainties in material properties. In this paper, we report the results of a study that aims to quantify the scatter in crack growth rates of 7075-T7351 aluminium alloy subjected to spectrum loading, and to assess its effect on risk assessment. About 80 middle-tension specimens were planned to be tested under nominally identical conditions, with the crack lengths recorded using crack cameras and direct current differential potential method. Based on the test data and the analyses, crack length distributions are developed for different times. These are then compared to the distributions derived from the master curve approach. This investigation attempts to quantitatively demonstrate the reasonableness, or otherwise, of using a single crack growth curve to derive the distributions of crack lengths for risk analyses, and the conditions under which the observations apply. The results reported here and those from other researchers show that this scatter in crack growth rates cause by variation in material properties cannot be appropriately addressed by the master crack growth curve approach for the purpose of risk analysis.
Fatigue Assessment of Large Thin-Walled Structures with Initial Distortions
Authors: Lillemäe Ingrit , Remes Heikki , Romanoff Jani
Published: March 2014

Due to economic reasons the industry is seeking new lightweight solutions for large steel structures. However, when moving from traditional steel plate thicknesses, i.e. 5 mm or larger, to thinner ones, the fatigue design becomes challenging due to larger initial distortions caused by welding. The fatigue assessment methods used for thicker welded structures are not fully validated for thinner ones. This paper deals with the fatigue assessment of large thin-walled structures starting from the global response analysis of a whole structure to the stiffened panel and finally welded joint. A modern cruise ship is used as an example case, where traditional superstructure deck plate thickness of 5 mm is replaced by 3 mm. The influence of initial distortion at different levels of structural analysis is studied using geometrically nonlinear finite element (FE) analysis. For the lowest level of analysis, i.e. small welded joint, the experiments have been carried out including geometry measurements and fatigue tests. It is shown that for a large thin-walled structure the global response analysis can be carried out with acceptable accuracy using ideally straight plates and geometrically linear FE analysis. For intermediate level of analysis, i.e. stiffened panel, the analysis can also be geometrically linear, but the actual shape of the plates influences the structural stresses near welds significantly. When analyzing small welded specimens to define experimental fatigue strength, both the actual shape and the geometrically nonlinear FE analysis are needed in order to capture the straightening effect and to obtain the correct structural stress.
Investigation on Fatigue Crack Interaction with Grain Orientation during TMF Tests in Nickel-Base Superalloy
Authors: Messé Olivier M.D.M. , Stekovic Svjetlana , Hardy Mark , Rae Cathie M.F.
Published: March 2014

Turbine discs in the gas turbine engine experience a wide range of stress and temperature during service. These result in distinct deformation mechanisms characteristic of different temperatures and stresses, and the cumulative effect of these on fatigue life is of much interest as turbines run hotter and thermal stresses rise. Thermo-mechanical fatigue tests are used to investigate performance at specific disc locations and have been performed on the alloy RR1000, a nickel based superalloy. This work describes a series of examinations to explore the interaction between temperature-loading conditions, deformation and failure mechanisms of an out-of-phase, largely compressive, thermo-mechanical cycle. Fatigue cracks initiated in the corners of the rectangular-sectioned test pieces and propagated to form approximately quarter-circle cracks. The interaction of the microstructure and deformation mechanism with the crack growth path has been investigated using Electron Backscatter Diffraction (EBSD) analysis complemented by Transmission Electron Microscopy (TEM) of specimens sampled from specific locations in the vicinity of a secondary crack.
Crack Growth of a Polycrystalline Nickel Alloy under TMF Loading
Authors: Pretty Christopher J. , Whittaker Mark T. , Williams Steve J.
Published: March 2014

Thermo-mechanical fatigue (TMF) is an important factor for consideration when designing aero engine components due to recent gas turbine development, thus understanding failure mechanisms through crack growth testing is imperative. In the current work, a TMF crack growth testing method has been developed utilising induction heating and direct current potential drop techniques for polycrystalline nickel-based superalloys, such as RR1000. Results have shown that in-phase (IP) testing produces accelerated crack growth rates compared with out-of-phase (OOP) due to increased temperature at peak stress and therefore increased time dependent crack growth. The ordering of the crack growth rates is supported by detailed fractographic analysis which shows intergranular crack growth in IP test specimens, and transgranular crack growth in 90° OOP and 180°OOP tests. Isothermal tests have also been carried out for comparison of crack growth rates at the point of peak stress in the TMF cycles.
Experiments and Interpretations of some Load Interaction Phenomena in Fatigue Crack Growth Related to Compressive Loading
Authors: Benz Christopher , Sander Manuela
Published: March 2014

The present paper addresses two issues regarding the influence of compressive loadings for fatigue crack growth. The first issue is the crack tip loading in compression. It will be verified that Kmaxand R are not suitable to account for compressive loading conditions at the crack tip. The second issue is the investigation of some basic load interaction effects in tension-compression loading. Especially loading conditions that were reported leading to an acceleration of fatigue crack growth were revisited. Numerical simulations of the experiments are used to interpret the results.
A Self-Heating Approach to Characterize Anisotropy Effects in Fatigue Behaviour: Application to a Nineteenth Century Puddled Iron from a French Railway Bridge
Authors: Gallegos Mayorga Linamaría , Sire Stéphane , Calloch Sylvain , Yang Suzhe , Dieleman Luc , Martin Jean Luc
Published: March 2014

The puddled iron is known for its extended use in monumental construction during the second half of the nineteenth century; among the structures built with such material are about half of French railway metallic bridges, most of them with over a century of service life. This scenario rises several concerns about the resistance of this material to cyclic loadings and therefore its fatigue behaviour. However, the puddled iron possesses several properties that make its mechanical characterization particularly difficult. Due to the puddling process this metal contains an important number of non-metallic inclusions that not only will turn out in a heterogeneous material but also (due to the rolling process) into an anisotropic one. In this paper a fast characterization of fatigue properties is proposed by using the self-heating method. The experimental self-heating curves obtained from specimens of the bridge of Toles (Chaumont, France) showed a scatter that was not observed in homogeneous materials (modern steel for example), this phenomenon is explained by the lack of determination of the representative elementary volume of the puddled iron. However, this data gives us important information such as the minimum and maximum boundaries of the mean fatigue limit for several orientations. An anisotropic two-scale probabilistic model for high cycle fatigue is also used to represent the orientation dependency of the results and the scatter found on the experimental data by using Hills elasto-plastic law and Weibulls distribution law to describe several characteristics of each site where the microplasticity occurs. The influence of such parameters and the limitations of the model are also discussed.
AZ31 Magnesium Alloy Multiaxial LCF Behavior: Theory, Simulation and Experiments
Authors: Reis Luís G. , Anes Vitor , de Freitas Manuel
Published: March 2014

In this work it is studied the low-cycle fatigue behavior of the magnesium alloy AZ31-B at several total strains under uniaxial and multiaxial cyclic loading conditions. Cyclic tests were carried out in a biaxial servo hydraulic machine under strain control at room temperature. Test specimens were machined in an hourglass shape from extruded rods. The total strain amplitudes started at 0,2% and ended at 1.4% regarding the von Mises equivalent strain. The particular mechanical behavior inherent to this type of materials, hexagonal closed pack microstructures, leads to conclude that it is necessary to have a numeric elastoplastic model based in experimental tests. In this paper is presented a numerical model based on stress-strain experimental data. The objective is to modulate several physical mechanisms inherent to the magnesium elastoplastic behavior. In order to validate the achieved model the numeric estimations were correlated with the experimental data and with the Jiang & Sehitoglu plasticity model. Results show that the implemented model modulation is in agreement with the experimental data. Some differences between the Jiang & Sehitoglu and the implemented model regarding the magnesium hysteresis loop modulation are pointed out.
Fundamental Concepts for Formulating Fatigue Strength Diagrams of Notched Metals
Authors: Matsuno Hiroshi
Published: March 2014

In the present paper, two fundamental concepts are discussed for formulating fatigue strength diagrams of notched metals. The first is a hypothesis of cyclic plastic adaptation that reflects mechanical behavior/property inherent in a persistent slip band. From this hypothesis, an equivalent cyclic stress ratio , which is the corresponding parameter between the cyclic stress condition of a notched and un-notched specimen, is derived. is extended to multi-axial cyclic stress conditions by use of the potential stress defined by Mises', Kawamoto's criterion, etc. The fatigue strength of a notch specimen is diagramed as a relation between and the notch root stress range . As a result, the fatigue strength is characterized into the two types of and , which can be replaced by the fatigue strength in the surface layer of the un-notch specimen and by the threshold stress of the crack specimen with the same crack depth as the notch depth, respectively. The second idea is how to express parametrically notch size factors based on a notch behavior/property map. For the type of , the notch size factor is expressed by a power function of a square root of a product of a notch root radius and a notch depth , and for the type of as a power function of the notch depth . These factors can be also applied to multi-axial cyclic stress conditions.
Notch Effects on Fatigue Behavior of Thermoplastics
Authors: Mortazavian Seyyedvahid , Fatemi Ali
Published: March 2014

An experimental study was conducted to evaluate notch effects on fatigue behavior of a neat polymer (PP impact co-polymer) and a composite made of 30 wt% short glass fibers in polybutylene terephthalate (PBT). A plate-type specimen geometry with a central circular hole was used. The experiments were conducted at room temperature in uniaxial tension-tension (R = 0.1) and tension-compression (R = -1) loading conditions. Some analytical methods including Neubers rule and the method of critical distances were used in addition to FEA to predict fatigue life of notched specimens. Neubers rule commonly used for metallic materials proved to be an accurate method for predicting the notched fatigue life of the thermoplastics considered.
Formation Mechanism of Specific Fracture Surface Region in the Sub-Surface Fracture of Titanium Alloy
Authors: Oguma Hiroyuki , Nakamura Takashi
Published: March 2014

In Ti–6Al–4V alloy, fatigue properties have been widely investigated, and the origin of fatigue fracture is usually at the surface in the high stress and lower fatigue life region, whereas in low stress and longer fatigue lifetimes origins are generally sub-surface in nature. Very high cycle fatigue tests were conducted, and observation of fracture surfaces revealed that a unique fine concave and convex agglutinate (hereinafter called Granular Region) formed on the fracture surface of sub-surface fractures. The granular region was not observed on the fracture surface of surface fractures. To clarify the formation mechanism and process of forming the granular region, which is a unique phenomenon in the very high cycle fatigue, fatigue tests using specimens with an artificial surface defect were conducted in air and vacuum. The fatigue tests were based on the idea that the environment around a sub-surface fatigue crack is a vacuum-like environment. During the tests, fracture surfaces were intentionally contacted in air and vacuum under different loading conditions. Fracture surface observations revealed that repeated contact of the fracture surfaces and a vacuum environment are necessary for the formation of the granular region. A mechanism for the formation of the granular region will be proposed.
Behaviour of Friction Stir Welded Joints Made out of Two Aluminium Alloys under Cyclic Loading Conditions
Authors: Lukács János , Meilinger Ákos
Published: March 2014

The friction stir welding (FSW) is a dynamically developing version of the pressure welding processes. Nowadays, the knowing of the properties and the behaviour of the welded joints is an important direction of the investigations, especially under cyclic loading. The research work aimed (i) to demonstrate the behaviour of the friction stir welded joints under cyclic loading conditions; (ii) to determine fatigue limit or design curves for aluminium alloys and their welded joints made by FSW process. Experiments were performed on 5754-H22 and 6082-T6 aluminium alloys and their welded joints. Both high cycle fatigue (HCF) and fatigue crack propagation (FCG) tests were executed on both base materials and their welded joints. Statistical behaviour of the base materials and welded joints was represented by the cutting of the specimens and the using of different crack paths. HCF limit curves were determined based on staircase method. FCG limit curves can be determined by own developed six step method. The investigations and their results were compared with each other and with the results can be found in the literature.
Improved Fatigue Life Assessment of Lighting Poles
Authors: Hyland Clark W.K. , Ferguson W. George , Csikasz Katalin
Published: March 2014

Fatigue cracking reported in a lighting pole on an elevated bridge structure near Wellington raised the question of how to better design for and predict the fatigue life of lighting poles subject to wind induced fatigue. There have been concerns as to the reliability and currency of the methods commonly used in New Zealand.
The paper therefore reviews current international design methods and describes the development of an improved fatigue design method for lighting poles in New Zealand.
The new method uses fracture mechanics based crack growth formulations in conjunction with a modified J.D. Holmes Method for wind response analysis of the pole to varying wind speeds. Cumulative crack growth is calculated iteratively rather than using an S-N curve based Palmegran-Miner summation. Wind spectra used in the method are developed from long term meteorological records at representative locations.
Software has been prepared to enable quick assessment of the expected fatigue life of lighting poles, and associated gear openings and holding down bolts The method and software has been calibrated with reference to full scale laboratory fatigue proof testing of representative base stubs and natural wind response testing of a 12 m high lighting pole.
Role of Friction Stir Channel Geometry on the Fatigue Behaviour of AA5083-H111 at 120°C and 200°C
Authors: Vidal Catarina , Infante Virgínia
Published: March 2014

Friction StirChannelling (FSC) is an innovative solid-state manufacturing technology able toproduce, in a single step, continuous integral channels in monolithic platesthat can be used to produce conformal cooling systems as well as heatexchanging devices. FSC is based on the same principles of Friction StirWelding (FSW) process and the features of the channels produced by FSC can becontrolled by the processing parameters and tool geometry. Bending fatiguetests have been performed using friction stir channelling specimens of 5083‑H111aluminium alloy with different channel geometries. Fatigue tests have beencarried out at 120°C and 200°C in a servo-hydraulic testing machine coupledwith a furnace, in order to understand the role of channel geometry on thefatigue behaviour at elevated temperature. Results were compared with thoseobtained at room temperature. The specimens were tested until fracture or up to 3x106 cycles. For the channel geometries tested, the fatiguestrength of friction stir channelling specimens is dependent on the testingtemperature, decreasing with the temperature increased. At all temperaturesstudied, for both channel geometries, fatigue-crack always initiated into theinterior of the specimen, namely on the boundary between the channel nugget andthe thermo‑mechanically affected zone. It was observed that crack initiationhas been occurred earlier at elevated temperature than at room temperature.
Microstructure and Strain-Based Fatigue Life Approach for High-Performance Welds
Authors: Remes Heikki , Lehto Pauli , Romanoff Jani
Published: March 2014

Microstructure and pre-existing surface flaws in smooth notch geometries significantly affect the fatigue life of welded joints. Traditionally, a welded joint is assumed to incorporate crack-like defects and the crack propagation dominates the total fatigue life. For a smooth weld notch geometry, the macro crack initiation period becomes more significant, and this difference cannot be modelled with the existing stress or fracture mechanics ‑based approaches. In this paper, a microstructure and strain ‑based fatigue life approach is presented. In the approach, the fatigue damage process is modelled as a repeated crack initiation process within a material volume related to the microstructure. The novelty of the developed approach is that the size of the damage zone is defined from the grain size statistics without using fracture mechanics. The approach is able to consider the changes in the stress gradient, stress triaxiality and plasticity during the fatigue crack initiation and growth. The developed approach has been validated with experiments on submerged-arc and laser-hybrid welded joints. The predicted fatigue life, crack growth path and rate showed good agreement with the experiments. For a welded joint with smooth and favourable notch shape, the short crack growth, i.e. macro crack initiation period is dominant and it has a significant influence on the fatigue life.
Comparison of High Cycle Fatigue in 4340 and 300M Steel Welded with Fiber Laser
Authors: de Souza Martins Cardoso Andreia , Abdalla Antonio Jorge , Reis Pereira Baptista Carlos Antonio , de Lima Milton Sergio Fernandes
Published: March 2014

The AISI/SAE 4340 steel and 300M have been used in severe conditions where high strength and toughness are necessary. Since there is a particular interest in the aerospace industry, they are being used in aircraft landing gear, rocket engines vessels and satellite launch vehicles. Therefore, the understanding of the weldability of these steels has been the subject of special interest. This study aims to evaluate and compare the microstructure and mechanical strength by tensile and fatigue in steel sheets of 4340 and 300M steels after laser welding and tempering heat treatments. The results showed that the welds had high hardness and small heat affected zones. Nevertheless, there was not a decrease in the uniaxial tensile properties for the 300M and 4340 steels. The decrease in fatigue life due to the welding process, compared to the unwelded condition, was small, indicating that the parameters welding were adequate and that this process is viable.
The Effect of Manufacturing Defects on the Fatigue Behaviour of Ti-6Al-4V Specimens Fabricated Using Selective Laser Melting
Authors: Liu Qian Chu , Elambasseril Joe , Sun Shou Jin , Leary Martin , Brandt Milan , Sharp Peter Khan
Published: March 2014

Additive Manufacturing (AM) technologies are considered revolutionary because they could fundamentally change the way products are designed. Selective Laser Melting (SLM) is a metal based AM process with significant and growing potential for the manufacture of aerospace components. Traditionally a material needs to be listed in the Metallic Materials Properties Development and Standardization (MMPDS) handbook if it is to be considered certified. However, this requires a considerable amount of test data to be generated on the materials mechanical properties. Therefore, the MMPDS certification process does not lend itself easily to the certification of AM components as the final component can have similar mechanical properties to wrought alloys combined with the defects associated with traditional casting and welding technologies. These defects can substantially decrease the fatigue life of a fabricated component. The primary purpose of this investigation was to study the fatigue behaviour of as-built Ti-6Al-4V (Ti64) samples. Fatigue tests were performed on the Ti-6Al-4V specimens built using SLM with a variety of layer thicknesses and build (vertical or horizontal) directions. Fractography revealed the presence of a range of manufacturing defects located at or near the surface of the specimens. The experimental results indicated that Lack-of-Fusion (LOF) defects were primarily responsible for fatigue crack initiation. The reduction in fatigue life appeared to be affected by the location, size and shape of the LOF defect.
Weld Toe SCF and Stress Distribution Parametric Equations for Tension (Membrane) Loading
Authors: Hellier Alan K. , Brennan Feargal P. , Carr David G.
Published: March 2014

The results of linear elastic finite element analyses of stress concentration factor (SCF) and through-thickness stress distribution for 80 weld toe T-butt plate geometries are presented in parametric form for tension (membrane) loading. The closed-form solutions, which describe the stress state of the two-dimensional plane stress models studied in terms of weldment angle, weld toe radius, weld attachment width and plate thickness, are accurate and wide ranging. The SCF is presented in full parametric form and also as a simple reduced expression, quantifying the degree of error from raw data in each case. An expression for the stress distribution through the potential Mode I crack plane of the uncracked geometries is also presented in full parametric form. It is anticipated that these HBC equations will be particularly useful in the calculation of weight functions for stress intensity factors (SIFs) of fatigue cracks emanating from weld toes in T-butt welded joints, especially in the presence of known residual stresses, or those resulting from peening.
Rolling Contact Fatigue and Wear Behavior of Rail Steel under Dry Rolling-Sliding Contact Condition
Authors: Seo Jung Won , Jun Hyun Kyu , Kwon Seok Jin , Lee Dong Hyeong
Published: March 2014

Rolling contact fatigue and wear of rails are inevitable problems for railway system due to wheel and rail contact. Increased rail wear and increased fatigue damage such as shelling, head check, etc. require more frequent rail exchanges and more maintenance cost. The fatigue crack growth and wear forming on the contact surface are affected by a variety of parameters, such as vertical and traction load, friction coefficient on the surface. Also, wear and crack growth are not independent, but interact on each other. Surface cracks are removed by wear, which can be beneficial for rail, however too much wear shortens the life of rail. Therfore, it is important to understand contact fatigue and wear mechanism in rail steels according to a variety of parameters. In this study, we have investigated fatigue and wear characteriscs of rail steel using twin disc testing. Also the comparative wear behavior of KS60 and UIC 60 rail steel under dry rolling-sliding contact was performed.
Modeling Reliability of Critical Infrastructures with Application to Port Oil Transportation System
Authors: Kołowrocki Krzysztof
Published: March 2014

A new approach to reliability investigations of multistate complex systems with dependent components at variable operation conditions called critical infrastructures is proposed. The multi-state reliability function of the critical infrastructure system is defined and determined for an exemplary m out of l critical infrastructure. In the developed model, it is assumed that the system components have the multistate exponential reliability functions with dependent departures rates from the subsets of the reliability states. The model is adopted to reliability prediction of an oil piping transportation system operating at maritime port.
Optimizing Reliability of Critical Infrastructures with Application to Port Oil Piping Transportation System
Authors: Soszyńska-Budny Joanna
Published: March 2014

A new approach to reliability optimization of multistate complex systems with dependent components at variable operation conditions called critical infrastructures is proposed. The reliability function of the critical infrastructure system is introduced and optimized. Further, the procedure of the critical infrastructure reliability optimization using the linear programming method is proposed and adopted to reliability optimization of an oil piping transportation system operating at maritime port.
Finite Element Simulation of Stable Fatigue Crack Growth Using Critical CTOD Determined by Preliminary Finite Element Analysis
Authors: Chu Seok Jae , Liu Cong Hao
Published: March 2014

Finite element simulation of stable fatigue crack growth using critical crack tip opening displacement (CTOD) was done. In the preliminary finite element simulation without crack growth, the critical CTOD was determined by monitoring the ratio between the displacement increments at the nodes above the crack tip and behind the crack tip in the neighborhood of the crack tip. The critical CTOD was determined as the vertical displacement at the node on the crack surface just behind the crack tip at the maximum ratio. In the main finite element simulation with crack growth, the crack growth rate with respect to the effective stress intensity factor range considering crack closure yielded more consistent result. The exponents m in the Paris law were determined.
Mechanics of Fatigue Crack Propagation in Submicron-Thick Freestanding Copper Films
Authors: Hirakata Hiroyuki , Kondo Toshiyuki , Sakihara Masayuki , Minoshima Kohji
Published: March 2014

The dominant mechanics and mechanisms of fatigue crack propagation in approximately 500-nm-thick freestanding copper films were evaluated at three stress ratios, R = 0.1, 0.5, and 0.8. The fatigue crack propagation rate (da/dN) versus stress intensity factor range (ΔK) relation was dependent on the stress ratio (R): da/dN increased with increasing R. Plots of da/dN versus the maximum stress intensity factor (Kmax) exhibited coincident features in the high-Kmax region (Kmax 4.5 MPam1/2) irrespective of R, indicating that Kmax was the dominant factor in fatigue crack propagation. In this region, the fatigue crack propagated in tensile fracture mode, or chisel-point fracture, irrespective of the R value. In contrast, in the low-Kmax region (Kmax < 4.5 MPam1/2), da/dN increased with decreasing R. In this region, the fracture mechanism depended on R. At the higher R value (R = 0.8), the fatigue crack propagated in the tensile fracture mode similar to that in the high-Kmax region. On the other hand, at the lower R values (R = 0.1 and 0.5), a characteristic mechanism of fatigue crack propagation appeared: within several grains, intrusions/extrusions formed ahead of the crack tip along the Σ3 twin boundaries, and the fatigue crack propagated preferentially through the intrusions/extrusions.
Analysis of the Fatigue Stress on Welded Joints of the U-Rib in an Orthotropic Steel Deck
Authors: Hong Sung Nam , Park Jon Gin , Park Sun Kyu , Choi Jin Woong
Published: March 2014

With the improvement in the quality of steel materials, the issue of fatigue cracking has become more important for steel bridges than the failure of the material itself. In this study, the Pelikan-Esslinger method was used to determine the fatigue stress of an orthotropic steel deck. A parametric study was then conducted with the steel deck components as the parameters. Based on the results, the effect of the diverse components of the steel deck on the fatigue stress was analyzed.
Effect of Microscopic Structure on High-Cycle Fatigue Behavior in Nano-Components
Authors: Sumigawa Takashi , Matsumoto Kenta , Kitamura Takayuki
Published: March 2014

In order to investigate the effect of microscopic structure on fatigue behavior of nanoscale components, a resonant fatigue experiment is conducted using a nanocomponents specimen where the test section is composed of a single crystalline Si substrate, a 200 nm thickness Cu polycrystalline film and a SiN amorphous layer. In the specimen, only the Cu portion plastically deforms because the yield stress is lower than those of other materials. The shape and the crystalline orientation of each grain on the surface of Cu portion are specified by means of EBSD. Although crystallographic slip bands with a width of a few tens of nanometers appear only in a grain of Cu portion, the grain is different from that expected by the Schmid factor. A FEM analysis, which takes into account the deformation anisotropy of grains, reveals that shear stress to generate slip bands is concentrated on the grain owing to the deformation constraint by neighboring crystals and components.
Prediction of Fatigue Crack Growth of Aged Hardening Al-Alloys under Variable Amplitude Loading
Authors: Benachour Mustapha , Zeggai Boumedienne , Benachour Nadjia , Benguediab Mohamed , Belmokhtar Abdelkader
Published: March 2014

In this investigation, variable amplitude loading effect was studied on aged hardening Al-alloys in series 2000 and 7000. Generalised Willenborg model was used in order to show loading interaction effects (overload effects). Variable amplitude loading under different form of spectrum has affected highly the fatigue life and fatigue crack growth rates. Fatigue lives were increased and fatigue crack growth rates (FCGRs) were decreased in increasing of overload ratio in single overload case. In application of overload band, the fatigue lives and FCGRs were affected by band overload and R-ratio of them when level in FCGRs was increased.
Fatigue Life Prediction for Caliper Guide Pin under Random Vibrational Loading
Authors: Antar Bilal I. , Kang Hong Tae
Published: March 2014

A fatigue life prediction tool was developed for caliper guide pins under random vibrational loading. The Pie-Slice model was designed to provide detailed information about the failure location, orientation, and damage magnitude. A component test fixture was developed to determine the strain-life curve for a given guide pin design. Statistical analysis was conducted to insure the repeatability of the failure mode and the robustness of the setup. Weibull analysis was performed to the measured guide pin strain-life in order to insure that the developed strain-life data to insure that developed strain-life curve will account for all the manufacturing process variations, from a component, assembly, and a system level to a certain level of reliability and confidence. Rainflow cycle count was used to bin the damaging and non-damaging cycles based on their stain level. Fatigue life calculation was performed using the Smith-Watson-Topper strain-life approach. The predictive tool was able to accurately estimate the cumulative fatigue damage for guide pins under random loading conditions. The Pie-Slice model was also able to predict the failure location and orientation of a crack, as well as the damage magnitude. Both tools were validated using a pre-designed random block-load sequence at constant amplitude..
The Influence of Orthotropy and Taper Angle on the Compressive Strength of Composite Laminates with Scarfed Holes
Authors: Patel Mitesh , Daynes Stephen , Wang Chun H.
Published: March 2014

The residual strengths of laminated composites containing notches or holes depend on the characteristic dimension of the notches as well as the laminate properties. This paper presents an experimental and computational investigation of the effect of orthotropy as well as scarf notch angles on the compressive strength of composite laminates made of seven different stacking sequences with the number of plies ranging between 20 and 24. Specimens containing scarfed holes of different scarf angles (6° and 10°) and straight holes of two different diameters (3.175mm and 6.35mm) were tested for comparison. Experimental results of the compressive strengths, normalised by the respective un-notched compressive strength show that the extent of orthotropy, defined as the laminate stiffness ratio along and perpendicular to the main loading direction, has a major effect. Computational modelling was carried out using the finite element method to quantify the residual strength; in which ply fracture is modelled using the continuum damage mechanics approach.
Numerical Analysis of the Effect of Slip Ratio on the Fatigue Crack Initiation Life in Rolling Contact
Authors: Lee Dong Hyong , Seo Jung Won , Kwon Seok Jin
Published: March 2014

This paper presents a numerical analysis of the effect of slip ratio on the fatigue crack initiation life, considering the tangential traction on the rolling contact surface. The distribution of tangential traction and contact stresses on the contact surface, when rolling contact occurs between two cylindrical test specimens, are obtained using three-dimensional finite element analysis. The effect of slip ratio on the fatigue crack initiation life was evaluated by applying multiaxial fatigue criteria based on critical plane approaches. As a result, the 3D-FE model developed well represent the distribution of tangential traction and contact stresses on the contact surface at stick-slip condition, which is differ from the static or full sliding contact condition. As the slip ratio increases, the maximum tangential traction also increases in slip zone and the location of maximum stress closer to the contact surface in stick zone. The fatigue strength decreased with the increase in the slip ratio. Therefore, it is clear that the slip ratio has an important role in prediction of fatigue crack initiation life on the rolling contact surface.
Modelling Fatigue Crack Growth Rates in Aluminium Plates Reinforced by Bonded Fibre-Metal Laminates for Fatigue Life Extension
Authors: Doucet Jeremy , Zhang Xiang , Irving Philip E.
Published: March 2014

Aircraft structural design and manufacture is moving towards lighter structures that have extended lives and improved damage tolerance. Hybrid structures are a possible solution to improve damage tolerance. They are a combination of metallic structure locally reinforced with adhesively bonded damage tolerant straps. In the present study a 3D finite element model has been developed with a bond line delamination growing under a fatigue law. A series of fatigue delamination tests on bonded aluminium were performed to provide input data. An iterative model for crack and debonding growth was developed to describe how debonding influence crack stress intensity and crack profile, which in turn influence debonding. The model predicts decrease in stress intensity on the bonded face and an overall retardation of fatigue crack growth rates. The stress intensity factor was predicted to vary through the thickness of the substrate due to the phenomenon of secondary bending and also the bridging effect caused by the presence of the reinforcing strap.