bluuebunny/crossref_metadata_2025 huggingface dataset:
The Role of Surface Topography on Fatigue Behaviour of Nickel Based Superalloys
Authors: Ardi Dennise Tanoko , Li Yue Gang , Chan Kelvin Hau Kong , Blunt Liam , Bache M.R.
Published: March 2014

Advanced areal (three-dimensional) characterisation of surface topography was applied to laboratory scale fatigue test specimens manufactured from the nickel based superalloy Alloy720Li. Finishing was deliberately manipulated to offer four distinct grades of topography. Subsequent low cycle fatigue performance was then correlated to a range of parameters selected to represent the surface topography. The aim of the ongoing study is to predict fatigue performance and aid to establish correlations between topographic parameters and fatigue life.
Investigation of the Three-Dimensional Shape of Slip Bands in Fatigued Dual Phase Steel
Authors: Zellmer Lisa , Tereschenko Stanislav , Brueckner-Foit Angelika , Lehmann Peter
Published: March 2014

The formation and the three-dimensional shape of slip bands in a fatigued dual phase steel were analyzed with the purpose of understanding the relation between fatigue crack initiation and the topography development on the specimen surface. Fatigue tests with small dog-bone-shaped specimens were conducted under fully reversed axial loading (R = -1) with a constant stress amplitude and were interrupted when the first slip bands occurred and at defined numbers of load cycles, respectively. Subsequently the surface topography of the specimen was investigated with a white light interferometer with hundredfold magnification and high numerical aperture (NA = 0.9) which allows analyzing the surface of individual grains. The results were confirmed by additional atomic force microscopy measurements. Based on this analysis the height, width and length of the slip bands are known at different stages of the fatigue process. The results obtained using white light interferometry and AFM, were checked by cutting individual slip bands with the help of focused ion beam thus revealing the true shape of the slip bands.
Experimental and Theoretical Study of the Performance of Reinforced Concrete Specimen Subjected to Cyclic Loading and Aggressive Environment
Authors: Göringer Jakub , Foglar Marek
Published: March 2014

Because of the progress in cementitious composites material engineering, modern concrete structures are designed as more slender in comparison to previous years. For structures subjected to cyclic loadings it means higher stress ranges and thus higher probability of fatigue failure. These types of structures are often located in places of severe environment (bridges, crane tracks in chemical plants etc.). The paper presents an experimental research focused on the effect of coupled deterioration by aggressive environment and cyclic loading on the concrete specimens. The evaluation of the deteriorative effect of aggressive environment is based on kinetics of chemical reaction between concrete and aggressive solution of hydrochloric acid.
Low Cycle Fatigue Behaviour of a Turbine Blade Made of Nickel Base Wrought Alloy
Authors: Sahoo Benudhar , Panigrahi Sashi Kanta
Published: March 2014

Life of an aero-engine is limited by the life of the turbine blade in particular and that of hot end components in general. Design of aero-engine is always conservative in nature considering the flight safety as paramount important. Earlier engines have been assigned life in hours but the life of the component is limited by LCF cycles particularly during the start-stop cycles. In this paper LCF behaviour of a typical Russian origin nickel base wrought super alloy AP220BD used for turbine blade has been studied at room temperature (RT), 400 °C and 700 °C that corresponds to idle rating and cruise rating of a typical aero-engine. Low cycle fatigue (LCF) tests have been carried out at RT, 400°C and 700 °C at three strain amplitudes of ±0.3%, ±0.5% and ±0.8%. Hysteresis loop have been developed at each strain and temperature. It has been observed that LCF life of the nickel base wrought alloy AP220BD is not influenced significantly at strain amplitude of ±0.3% till it reaches 400° C. Reduction in LCF life with increase in strain amplitude from ±0.3% to ±0.8% is much significant compared to that of increase in temperature up to 700°c.The higher life at intermediate strain of ±0.5% may be due to DSA(dynamic strain aging) of the material. Transgranular fracture has been observed at RT & 400° C while intergranular fracture at 700° C.
High-Cycle Fatigue Properties of Carbon Steel and Work-Hardened Oxygen Free Copper in High Pressure Hydrogen
Authors: Kubota Masanobu , Kawakami Kota
Published: March 2014

The high-cycle fatigue properties of 0.35% carbon steel and work-hardened oxygen-free copper in 10MPa hydrogen were studied. The fatigue limit of the carbon steel in hydrogen was almost the same as that in air. The fatigue strength at 107 cycles of the copper was higher in hydrogen than in air. The fatigue life of both materials is longer in hydrogen than in air. The reason was the delays in the crack initiation and the early propagation of the cracks in hydrogen. For both materials, the detrimental effect on the fatigue strength due to the hydrogen environment was small, however, it was determined that hydrogen participates in the slip deformation. The morphology of the slip bands was specific in hydrogen. In the copper, the slip bands, which are non-viable in air, developed in hydrogen.
Fatigue Analysis and Design of Composite-Metal Joints in Primary Aircraft Structures
Authors: Rufin Antonio C. , Jochum Robert L.
Published: March 2014

Increasingly broader application of composite materials in commercial airplane primary structure has led to a renewed, more in-depth assessment of the effect composite elements in mechanical joints have on the durability of the metal structure to which they are mated. Thermal stresses, clamp-up loss due to composite creep, composite joint properties, and lightning and electrical grounding effects have been found to be some of the parameters most significantly affecting or limiting the fatigue performance of the metallic constituents within these hybrid joints, influencing the way joint design and analysis are approached.
Nondestructive Evaluation of Mechanically Loaded Advanced Marine Composite Structures
Authors: Ibrahim Matthew E. , Phillips Andrew W. , Ditchburn Robert J. , Wang Chun H.
Published: March 2014

Marine composite structures subject to dynamic loading typically incorporate more than one material type, and consist of laminate sections up to hundreds of millimetres in thickness. These solid hybrid laminates exhibit different behaviour in static and fatigue loading from thin aerospace composite laminates and sandwich structures. There is therefore a need to better understand the likely damage and degradation mechanisms that will occur in these thick structures and to concurrently develop nondestructive evaluation (NDE) technology to meet the consequent inspection problems. In this paper we present details of an ongoing fatigue program on marine composite blades. The challenges for ultrasonic NDE of thick composites, and emerging inspection methods using state-of-the-art inspection systems and analysis tools will be discussed.
Failure Analysis of Repeat Tooth Breakage of a 40MW Steam Turbine Load Gearbox
Authors: Liu William
Published: March 2014

A repeat premature gear tooth breakage occurred in a load gearbox of a 40MW steam turbine. Factographic examination indicated that the breakage was a complex fatigue fracture. The oil deposit on the fracture surface has been applied as an auxiliary fractographic method. The root cause of the failure was due to improper heat treatment. The insufficient surface hardness and shallow case resulted in case/core separation through main fatigue crack propagation. The very coarse detrimental tempered low carbon martensites in core resulted in cleavage fracture in final fast fracture. The fractographic morphology of the butterfly has been revealed. Hertzian stress and non-metallic inclusions are not the necessary condition of the butterfly formation. The microcracks within the butterflies did not actively play the role of the fatigue rupture.
Evaluation of Fatigue Damage by Diffraction Contrast Tomography Using Synchrotron Radiation
Authors: Shiozawa Daiki , Nakai Yoshikazu , Miura Ryotaro , Matsuda Shota
Published: March 2014

The three dimensional grain mapping technique for polycrystalline material, which is called X-ray diffraction contrast tomography (DCT) has proposed. In the present study, the measurement of DCT was conducted in SPring-8, which is the brightest synchrotron radiation facility in Japan, and the condition of measurement and data procedure are discussed. Developed technique was applied to aluminium alloy and stainless steel. The shape and location of grain could be determined by the developed three-dimensional mapping technique using the apparatus in a bending beam line of SPring-8. To evaluate plastic deformation, the grain orientation spreads of individual grains were measured. The grain orientation spread is caused by the mosaicity, which relates to the dislocation structure in a grain. The grain orientation spread was found to increase with increasing plastic strain. Fatigue damage also could be evaluated by the grain orientation spread in the DCT measurement.
Experimental Study of Relationship between Energy Dissipation and Fatigue Damage from Observation of Slip Band by Atomic Force Microscope
Authors: Shiozawa Daiki , Inaba Ken , Akai Atsushi , Sakagami Takahide
Published: March 2014

In recent years, fatigue limit estimation based on dissipated energy has been introduced in various industries because of its time and cost effectiveness. However, the mechanism of energy dissipation and the relationship between energy dissipation and fatigue damage have not been investigated well. In this study, mechanism of energy dissipation is investigated in relation with formulation of slip bands for JIS type 316L stainless steel through observation of slip bands by optical microscope and atomic force microscope.
Optimization of Numerical Analyses for Maintenance of Fuselage Skins with Rectangular Repairs
Authors: Pastoukhov Viktor , Reis Pereira Baptista Carlos Antonio , Teixeira Junior Helio De Souza , Manzoli Paulo Roberto Pereira
Published: March 2014

Greatly reduced inspection intervals of skin damage repairs pose a significant financial problem for aging commercial aircraft fleets. Such intervals for visual inspections are the result of simplified conservative repair substantiation analyses, based on the same crack propagation scenarios and curves that were established in the initial project development. These neglect the structural role of external repair (“doubler”) and consider only the increase in hidden crack path. A more refined approach to reassessing inspection intervals after a repair may keep maintenance jobs in accordance with common C-check routines in most cases. This approach, based on new crack growth simulations for worst case scenarios that could occur at the region of repair, uses respective kinetic equation and new geometric stress intensity factor functions, obtained in additional FEM (Finite Element Method) analyses. In particular, for standard rectangular repairs, the number of possible geometric configurations is astonishing considering length, width, skin and “doubler” thickness, reinforced panel dimensions, and frame and stringer cross sections. This investigation deals mainly with defining a minimum sufficient number of intermediate crack length values for FEM analyses in each propagation scenario. A conservative but efficient definition of most relevant parameters for a new numerical analysis campaign is another important issue. The results obtained are helpful for the improvement of the operational efficiency and safety of an aging fleet.
Residual Fatigue Properties of a 2024-T351 Aluminium Alloy from the Teardown of AIRBUS A320 Wing Panels after Service
Authors: Billy Fabien , Hénaff Gilbert , Benoit Guillaume , van der Veen Sjoerd
Published: March 2014

This paper reports on investigations on the residual fatigue resistance of a 2024 aluminium alloy of an A320 aircraft at the end of life. The fatigue data (S-N and da/dN curves) are compared with data obtained on a pristine alloy using a similar procedure. The results are analysed on the basis of fracture surfaces observations and of AFGROW fatigue life computations.
Effects of Bonded Crack Retarders on Fatigue Parameters of FSWed Integral Panel
Authors: Ma Yu E , Xu Pan Fu
Published: March 2014

As known, friction stir welded (FSWed) joints are mature to be applied in aircraft structure. However, the weld creates local discontinuity in property and local tensile residual stress, which harm the damage tolerance of welded panels. So crack retarders were bonded in the weld zone to improve damage tolerance. Finite element method was used to calculate stress intensity factors by ABAQUS software. Finite element models were built to simulate the function of bonded retarder. Cohesive elements were used between the substrate panel and bonded retarder. A Fortran program was made to input residual stress to finite element models. Stress intensity factors from residual stress with and without bonded retarders were calculated and compared. Effects of residual stress on stress intensity factors and redistribution of residual stress were taken into considered. Effective R ratios were calculated with crack growing through the weld. Effects of bonded retarder on stress intensity factors were calculated. The results were compared with the experimental findings.
Effect of Ultrasonic Shot Peening on the Fatigue Strength of Stainless Cast Steel ASTM CA6NM for Hydraulic Turbine Runner
Authors: Arakawa Jinta , Kakuta Motoki , Hayashi Yoshiichirou , Tanegashima Ryota , Akebono Hiroyuki , Kato Masahiko , Sugeta Atsushi
Published: March 2014

In this paper, in order to investigate the effect of the ultrasonic shot peening (USP) treatment on fatigue characteristics of the structural materials for hydroelectric facilities, plane bending fatigue tests were carried out using stainless cast steel ASTM CA6NM performed by USP treatment. The fatigue test results showed that the fatigue strength of the USP materials was approximately 60% higher than that of the untreated materials. In order to examine the reason for that, the effect of USP treatment on fatigue crack initiation behavior was evaluated based on the Haigh's diagram. This evaluation implied that increasing the crack initiation resistance associated with high hardness and high compressive residual stress at surface by USP treatment is the major cause for the improvement of fatigue strength. Furthermore, the effect of USP treatment on fatigue crack propagation behavior was also examined by simulating the crack growth rate considering the stress intensity factor at crack tip. Crack propagation simulation results suggested that compressive residual stress leads crack growth rate slow compared with untreated material.
Hole Cold Expansion the Fatigue Mitigation Game Changer of the Past 50 Years
Authors: Reid Len
Published: March 2014

Over the past 50 years, mitigating cracks from holes has been a major focus of aerospace research, design, and stress engineers. Technology and design philosophies were developed to focus on predicting and increasing fatigue life of metal aircraft structure. One of the innovations to have the biggest impact to slow or arrest crack growth was to induce beneficial residual stresses around a hole. The zone of residual compressive stresses shields the hole from the effects of cyclic loads. The split sleeve cold expansion method was pioneered in the early 1970s by Boeing and Fatigue Technology. The split sleeve cold expansion process has become the bench mark method in mitigating fatigue cracks and enhancing durability and damage tolerance of aerospace metal structures. This paper will review the history of cold expansion methods and the evolution of this technology to the controlled and widely accepted methods used by industry today.
Fractographic Study on the Use of Rainflow Counting for Small and Long Cracks in AA7050
Authors: White Paul , Mongru David S.
Published: March 2014

Using a da/dN equation to predict fatigue crack growth for a variable amplitude loading sequence, requires converting the sequence into an equivalent series of constant amplitude cycles, which is sometimes achieved using the rainflow cycle counting technique. Rainflow counting views small intermediate cycles as an interruption to a larger cycle, in effect, the crack tip remembers the state of the larger cycle. This has been shown to be an effective technique in predicting fatigue growth rates for long cracks, but has not been extensively investigated for use in predicting the growth of small cracks. An investigation was made into the applicability of rainflow cycle counting for predicting the crack growth of small and long cracks created with variable amplitude fatigue loading in AA7050-T7451 plate, a common modern aircraft material. A series of coupons were tested with a number of different variable amplitude loading sequences which had distinct marker bands inserted to separate the individual segments of loading and enable them to be identified fractographically. For the sequences examined, which covered varying numbers of interrupted cycles and a staircase of three steps, the baseline and the rainflow loading segments within each sequence showed effectively the same rate of growth for the same stress intensity range in both the small and long crack coupons, demonstrating that rainflow cycle counting was a suitable cycle counting technique for both small and long cracks.
Helicopter Airframe Fatigue Spectra Generation
Authors: Krake Luther
Published: March 2014

Helicopter airframe fatigue cracking is a cause of significant and growing cost of ownership and operational readiness concerns for the operators of (primarily) metallic airframe helicopters. Airframe fatigue has often had relatively low priority for helicopters, with research and design concentrated on the fatigue of flight critical rotating structural components such as rotor blades and pitch links. The Australian Defence Science and Technology Organisation (DSTO) and the US Naval Air Systems Command are collaborating to develop improved methods and technologies that can be used to assess the fatigue damage endured by ageing helicopter airframes.
The flight load sequencesor fatigue spectraexperienced by a helicopter airframe in its lifetime contain many billions of load cycles due to rotor revolutions. Fatigue spectra developed for helicopter airframe certification tests are heavily simplified for reasons such as computational efficiency, test practicality and cost. Real airframe fatigue spectra are likely to be influenced by the modes of vibration that might be present on the airframe, the attenuation of the vibratory loading that is introduced at the main and tail rotors and the relative magnitudes and influences of both quasi-static (manoeuvre induced) and vibratory loading. To better capture such complexity, more realistic, higher fidelity fatigue spectra are required.
Fatigue spectra generation involves creating realistic flight-by-flight sequences of flight conditions and assigning high-fidelity flight loads data to those sequences. This paper details DSTOs development of a novel computer-automated process which pseudo-randomly generates realistic sequences of flight conditions to match a known or assumed usage spectrum.
A Modified Compliance Method for Automatically Measuring Fatigue Crack Growth In Situ during Spectrum Fatigue Testing
Authors: Zhuang Wyman , Liu Qian Chu
Published: March 2014

The fatigue critical structures of military aircraft are generally subjected to variable amplitude flight spectrum loading. Maintaining aircraft structural integrity to ensure safe operation of the fleet is critically dependent on accurate analysis and reliable prediction of fatigue crack growth in those structures under service operating conditions. To achieve this goal, laboratory experimental methods that can accurately measure and monitor fatigue crack growth under variable amplitude loading are required. This can be challenging as no test standard exists to guide the process of fatigue crack growth measurement under variable amplitude loading conditions to ensure the accuracy of the test results. This challenge was addressed by developing a modified compliance method as described in this paper. The results presented employed a modified compliance method complemented with a travelling microscope technique and marker band loads. The modified compliance method developed is able to measure in-situ, fatigue crack growth of standard compact-tension specimens under a fighter flight spectrum loading. The marker band loads and microscope readings were used to assist the post-test validation using quantitative fractography. The results from this study have demonstrated that the modified compliance method can produce consistent and accurate fatigue crack growth data under variable amplitude loading conditions.
Life Extension of F/A-18 LAU-7 Missile Launcher Housings Using Rework Shape Optimisation
Authors: Heller M. , Calero Jaime , Wescott Ron , Barter Simon A. , Choi Jireh , Surtees Greg
Published: March 2014

LAU-7 missile launcher housings, which are fitted to most Royal Australian Air Force (RAAF) F/A-18A/B aircraft, can experience cracking in the guide rail. This paper covers the design, manufacture and validation of a life extension repair for cracked launcher housings. The repair development uses DSTO's rework shape optimisation technology and fatigue testing capabilities. The rework design reduces peak stresses by 33 %, resulting in significant fatigue life enhancements, as demonstrated by representative coupon testing. A special manufacturing jig has been designed and transitioned to the RAAF, which has used it to repair housings. These housings have performed well in flight tests, with no cracking detected.
Development of New Fatigue Model for New Zealand Dense Graded Hot Mix Asphalts
Authors: Saleh Mofreh F.
Published: March 2014

The Mechanistic empirical pavement design method for flexible pavements is based on modelling certain modes of failures for different pavement materials. In the Australian and New Zealand guidelines, the mechanistic empirical pavement design is based on modelling fatigue and permanent deformation as the two major modes of failures. The Austroads guidelines use the Shell fatigue performance transfer function to model the fatigue behaviour of asphalt mixes. In this research, the fatigue behaviour of different mixes AC10, AC14 and AC20 with different types of binders 80/100 and 60/70 was thoroughly investigated. The Shell model significantly underestimated the measured fatigue life for all mixes. A wide range of properties of the examined mixes was considered; percent of air voids ranges from 1.2% to 11.4%, binder content (at optimum, ± 0.5 from optimum), and the flexural modulus ranges from 1600 to 4576 MPa. A new fatigue model was developed at the University of Canterbury. The Canterbury model was based on the bending beam fatigue results of 78 beams tested at constant strain mode at different strain levels range from 300 to 600 microstrains. The new model provides a much better matching to the measured data with no observed bias and it accounts for percentage of air voids in the total mix and the effective binder content instead of the total binder content that is currently included in the Shell Model.
A Fractographic Investigation of a Failed Precombustion Chamber Nozzle from a Large Marine Diesel Engine
Authors: Davidson Len
Published: March 2014

From 1998 until 2001 a series of engine failures occurred in a fleet of large marine diesel engines due to the failure of precombustion nozzles. The nozzles are screwed into the head of the engines and are held in place by a tightening torque and a high temperature ceramic adhesive. The preliminary findings of an engineering investigation after one such failure concluded that cracking occurred in the nozzle at the time of the installation, due to poor installation technique, and that this cracking resulted in the loss of tightening torque causing the nozzle to become loose. However, the investigation also recommended that fractography be undertaken to verify the cause of failure since this would influence the engineering solution. The current paper focuses on the fractography that was conducted on the failed nozzle to determine its mode of failure and provides a reminder of the importance of fractography in failure analysis.
Modelling of Fatigue Crack Growth in Inconel 718 under Hold Time Conditions - Application to a Flight Spectrum
Authors: Lundström Erik , Simonsson Kjell , Månsson Tomas , Gustafsson David
Published: March 2014

Gas turbine operating cycles at high temperatures often consist of load reversals mixed with hold times; the latter occurring either as cruise for aero engines or at continuous power output for land based turbines, but also at low frequency loading conditions, e.g. slow “ramp up” of engine thrust. The hold time conditions cause the crack to grow by intergranular fracture due to material damage near the crack tip, thus rapidly increasing the crack growth rate. Since the damaged zone will affect the crack propagation rate due to cyclic loadings as well, the complete load history of a component therefore has to be considered. The crack propagation model presented in this paper is based on the damaged zone concept, and considers the history effect in the form of damaged zone build up during hold times, and subsequent destruction as the crack propagates onwards by rapidly applied load reversals. By incorporating crack closure for handling different R-values, an aero engine component spectrum is evaluated for a surface crack at 550 °C. The result shows a good correlation to model simulation, despite the complexity of the load spectrum.
A Cohesive Zone Model to Simulate Fatigue Crack Propagation under High Pressure Gaseous Hydrogen
Authors: Bilotta Giovambattista , Moriconi Clara , Hénaff Gilbert , Arzaghi Mandana , Halm Damien
Published: March 2014

In this study we focus on the effect of hydrogen gas on the cracking resistance of metals. The main objective is to predict the fatigue crack propagation rates in the presence of hydrogen. For this purpose, a Cohesive Zone Model (CZM) dedicated to cracking under monotonic as well as cyclic loadings has been implemented in the ABAQUS finite element code. A specific traction-separation law, adapted to describe the gradual degradation of the cohesive stresses under cyclic loading, and sensitive to the presence of hydrogen is formulated. The coupling between mechanical behaviour and diffusion of hydrogen can be modelled using a coupled temperature - displacement calculation available in ABAQUS.
The simulations are compared with fatigue crack propagation tests performed on a 15-5PH martensitic stainless steel. They show that while the proposed model is able to predict a lower resistance to cracking in presence of hydrogen, at this stage it cannot fully account for the detrimental effect induced by high pressure of gaseous hydrogen.
Rainflow-on-the-Fly Methodology: Fatigue-Crack Growth under Aircraft Spectrum Loading
Authors: Newman James C.
Published: March 2014

Crack-growth-rate tests were conducted on compact, C(T), specimens made of 7075-T7351 aluminum alloy over a wide range of constant-amplitude loading (R = Pmin/Pmax = 0.1 to 0.9) to establish the baseline crack-growth-rate curve for life-prediction analyses. Both compression precracking and load-reduction methods were used. A crack-closure analysis was used to collapse the ΔKeff-rate data into a fairly narrow band over many orders of magnitude in rates using an appropriate plane-strain constraint factor. Life predictions were made on C(T) specimens using the FASTRAN Version 5.42 life-prediction code. Some improvements had been made in the code and the predictions were made under cycle-by-cycle simulations. Life predictions under Christmas-Tree-type loading using the rainflow-on-the-fly methodology were very good. And the predicted results on three different aircraft spectrum loading histories (a modified Falstaff, modified Mini-TWIST (Level III), and a modified Wing-Gust-Maneuver spectrum), agreed to within 20% of the test data.
Numerical Simulation of Fatigue Crack Growth Rate and Crack Retardation due to an Overload Using a Cohesive Zone Model
Authors: Silitonga Sarmediran , Maljaars Johan , Soetens Frans , Snijder Hubertus H.
Published: March 2014

In this work, a numerical method is pursued based on a cohesive zone model (CZM). The method is aimed at simulating fatigue crack growth as well as crack growth retardation due to an overload. In this cohesive zone model, the degradation of the material strength is represented by a variation of the cohesive traction with respect to separation of the cohesive surfaces. Simulation of crack propagation under cyclic loads is implemented by introducing a damage mechanism into the cohesive zone. Crack propagation is represented in the process zone (cohesive zone in front of crack-tip) by deterioration of the cohesive strength due to damage development in the cohesive element. Damage accumulation during loading is based on the displacements in the cohesive zone. A finite element model of a compact tension (CT) specimen subjected to a constant amplitude loading with an overload is developed. The cohesive elements are placed in front of the crack-tip along a pre-defined crack path. The simulation is performed in the finite element code Abaqus. The cohesive elements behavior is described using the user element subroutine UEL. The new damage evolution function used in this work provides a good agreement between simulation results and experimental data.
Stress Intensity Factor Solutions for Narrow Plates
Authors: Hammond Matthew J. , Fawaz Scott A.
Published: March 2014

Accurate quantification of crack tip stress intensity values is paramount in the analysis of damage tolerant structures. The present analytical investigation seeks to determine the stress intensity solutions for crack geometries outside the existing valid solution space and expand the analysts ability to capture representative crack growth behavior. The focus of this investigation is to calculate the stress intensity factors of single quarter-elliptical corner cracks emanating from centrally located holes in finite width plates under various loading conditions (remote tension, bending, and pin loading). Many of the available finite width corrections are singled valued and universally applied to all locations along the crack front. Early investigations into the validity of this application indicated that this correction procedure produces stress intensity values +/- 30% from new solutions. The crack depth to length ratio and depth to thickness ratio can also significantly influence the accuracy of historical finite width solutions and corrections. The analytical investigation utilizes the three dimensional virtual crack closure technique and well-structured, completely hexahedral, element meshes. Stress intensity values are generated for a wide range of ratios for crack depth to crack length, crack depth to sheet thickness, hole radius to sheet thickness, and sheet width to hole diameter. This effort is being executed under a US DoD Technical Corrosion Collaboration program.
A Deviatoric Stress-Strain Function for Fatigue Life Analysis
Authors: Sree Phani C.R. , Kujawski Daniel
Published: March 2014

The Smith-Watson-Topper (SWT) parameter was originally suggested and is still widely used to account for mean stress effects in fatigue life analysis. It is well recognized however, that the SWT parameter might be non-conservative for cyclic loads that involve relatively large compressive mean stresses. Such large compressive mean stresses can develop in notches after overloads. An energy interpretation of the SWT parameter is presented first. Based on analogy with the Neuber’s rule a new deviatoric formulation of the SWTD parameter is proposed. It is found that for positive mean stresses and moderate negative mean stresses the original SWT parameter and the proposed deviatoric SWTD parameter yield similar results. At large compressive mean stresses and non-proportional biaxial fatigue, the deviatoric SWTD parameter demonstrates a fairly good correlation to test data while the original SWT parameter results in wide scatter.
Fatigue Assessment of Existing Shiploaders
Authors: Gatto Frank
Published: March 2014

Shiploaders are used to load bulk material onto vessels. They can experience a large number of loading cycles during their design life. As a consequence, fatigue damage is an important consideration when assessing the useful life of an existing shiploader. This paper presents the results of the fatigue assessment of an existing shiploader. The shiploader is used to load coal onto bulk carriers; it is over 30 years old and the operator wishes to continue to use the facility for at least another 25 years. The results from the fatigue assessment form part of the decision making process for replacement or refurbishment of the shiploader. This assessment includes data from finite element analysis, strain gauging and measurements from on-board monitoring equipment. The results from the fatigue assessment were used to calculate the probability of fatigue damage for continued use.
Constitutive Modeling for Cyclic Behavior of AZ31B Magnesium Alloy and its Application
Authors: Behravesh Seyed Behzad , Jahed Hamid , Lambert Steve B. , Chengji Mi
Published: March 2014

Fatigue testing was conducted on AZ31B-H24 magnesium alloy in strain-control condition. An unusual asymmetric shape of the hysteresis loop was the key feature of the cyclic behavior. A continuum-based cyclic plasticity model was developed to follow the asymmetric hardening behavior of wrought magnesium alloys. The proposed model was implemented in a UMAT subroutine to run with Abaqus/Standard. It was demonstrated that the UMAT was able to follow the cyclic hardening behavior of AZ31B under uniaxial loading. An energy-based damage parameter was proposed for estimating the fatigue crack initiation life. The developed UMAT along with the proposed damage parameter were used for fatigue modeling of an automotive substructure made of magnesium. It was shown that the proposed asymmetric model was more promising than a symmetric model.
The Energy Based Approach to Fatigue
Authors: Ranganathan Narayanaswami
Published: March 2014

This paper presents the energy based approaches developed to describe different aspects of fatigue. Different topics covered include fatigue crack initiation, crack initiation at a notch, multiaxial fatigue and fatigue crack propagation. Specific examples treated include, crack initiation at a notch, cracking at solder joint in electronic application, fatigue life estimation in a synthetic rubber and fatigue crack propagation in a metallic material.
Assessing Structural Safety of Bolted Joints Subject to Cyclic Loading Using Advanced Nonlinear FEA
Authors: Alden John Miles , Brand Peter Hendrik
Published: March 2014

The concepts of structural safety embedded in recognised international standards for the fatigue design of bolted joints, such as VDI 2230 Part 1, are examined and challenged. This is done by means of theoretical investigation of the behaviour of bolted joints using non-linear finite element analysis. Potential differences between actual bolted joint parameters and behaviour, and implicit design assumptions, are reviewed and their effect on the structural safety of bolted joints in operating equipment examined. An approach to the fatigue design of bolted joints is presented which incorporates alternative concepts of structural safety and uses advanced CAE methods as part of the standard design process.
Physically-Based Simulations of the Cyclic Behavior of FCC Polycrystals
Authors: Sauzay Maxime , Liu Jia , Rachdi Fatima , Signor Loic , Ghidossi Thomas , Villechaise Patrick
Published: March 2014

Two homogeneization approaches are used in order predict the cyclic elastic-plastic behaviour of 316L(N) polycrystals, either
Fatigue Crack Development in Epoxy Coatings on Steel Substrate: The Role of Coating and Substrate Properties in Determination of the Onset of Fatigue Cracks
Authors: Wu Tong Yu , Ayre David , Irving Philip E. , Zhao Fang Ming , Jackson Paul
Published: March 2014

Development of service cracks in epoxy based corrosion protective coatings limits the life of the substrate structure. If cracks develop, corrosion protection is lost and costs of repair and re-protection of large marine structures can be crippling. Factors controlling development of cracks in the coating are poorly understood, and predictions of coating lifetime approximate. For bulk tanker applications service strains imposed on coatings arise from both low frequency thermal mismatch strains and mechanical strains from wave action. In this work the number of cycles to crack initiation has been measured during strain controlled fatigue of two selected 300 μm thick coatings applied to a 5.5 mm thick steel substrate. Cycling was performed at frequencies of 1 Hz, and strain amplitudes between ±0.16% and ±0.5%. Coating crack development was monitored optically. It was found that cycles to crack initiation depended on both strain amplitude and on the static ductility of the coating. After initiation crack growth rates in the coating reduced with increasing surface crack length. The significance of the results is considered in the light of requirements for quantitative models for service life prediction of coatings on metallic substrates.
Dependence of Static Fatigue Tests on Experimental Configuration for a Crystalline Rock
Authors: Kear James , Bunger Andrew P.
Published: March 2014

This paper presents static fatigue laboratory experiments conducted in three different configurations. The experiments are designed so as to cause delayed tensile failure in dry Gabbro specimens after the sustained application of a static subcritical load. Results from the static fatigue experiments give a time to failure of the specimen related to the applied static load. In the presented experiments, results spanning up to six orders of magnitude of time to failure were collected for three-point bending, four-point bending, and indirect tensile (Brazilian) specimens. The data supports an exponential relationship between tensile stress and time to failure, noting that a power law relationship is also supported by the data. The salient difference among the configurations is hypothesized to be the size of the region of the specimen that is subjected to a close approximation of the maximum tensile stress. The time to failure at a given nominal tensile stress, the decrease in time to failure associated with a given increase in stress (i.e. the slope in a semi logarithmic plot), and the magnitude of the scatter of the data about the best-fit curve are all observed to correlate inversely with the nominal size of the region subjected to the maximum tensile stress.
Large-Scale Deformation Patterning in Geomaterials Associated with Grain Rotation
Authors: Esin Maxim , Dyskin Arcady V. , Pasternak Elena
Published: March 2014

Modelling of large-scale deformation patterning in geomaterials is important for predicting instabilities and failures in the Earths crust. Shear band formation and the evolution of the bands is a predominant mechanism of deformation patterning. Independent rotations of separate grains/particles can affect the pattern formation by adding the effect of rotational degrees of freedom to the mechanism of instability. To model this mechanism we use a special experimental technique based on digital image correlation in order to recover both displacement and independent rotation fields in 2D physical models of granular material. In the physical model the particles are represented by smooth steel monodispersed disks with speckles painted on them to enable the rotation reconstruction. During the loading the deformation pattern undergoes stages of shear band formation followed by its dissolution due to re-compaction and particle rearrangement with the subsequent formation of multiple shear bands merging into a single one and the final dissolution. Also, patterns of rotations are observed at an intermediate scale between the scale of the particles and the scale of the shear band.
Fatigue Stress Ratio Effect on Fretting-Fatigue Crack Nucleation: Comparison between Multi-Axial and Uni-Axial Predictions
Authors: Gandiolle Camille , Fouvry Siegfried
Published: March 2014

This research focuses on high cycle fretting fatigue crack nucleation prediction. A plastic steel/steel cylinder/plane contact was investigated keeping constant the normal force and the maximum fatigue stress ratio but varying the fatigue stress ratio (RF=0.6 to 1). The evolution of the crack length as function of the applied fretting tangential force amplitude at 106 cycles allows us to formalize the crack nucleation condition. It shows that the threshold tangential force marking the crack nucleation (i.e. bp_th=0μm) is not affected by the fatigue stress ratio. However an increase of the fatigue stress amplitude sharply increases the crack extension. To model the experiments, a 2D plastic plain strain FEM modeling is performed. As expected the computed stress field description is mesh dependent. However we demonstrate that a representative stress description is obtained at the 3rd node (i.e. 2nd node below the surface). By coupling this mesh condition and non-local critical distance approach, reliable prediction of the crack nucleation risk can be achieved either considering a Crossland multi-axial fatigue analysis or using a basic uni-axial Haighs description.
Description of Small Fatigue Crack Propagation in ODS Steel
Authors: Hutař Pavel , Kuběna Ivo , Šmíd Miroslav , Ševčík Martin , Kruml Tomáš , Náhlík Luboš
Published: March 2014

The oxide dispersion strengthened (ODS) steels are widely studied as possible candidate material for fission and fusion technology. Due to application of the ODS materials, mainly low cycle fatigue is important. Therefore, small crack initiation and propagation for rather high stress amplitude are in focus. The main aim of the presented work is description of the small fatigue crack propagation for ODS-EUROFER steel. Due to limited quantity of ODS steel special miniaturized cylindrical specimens for fatigue testing were designed. Crack propagation law based on plastic part of J-integral is presented and applied for mentioned material. The resulting fatigue crack propagation rates for ODS-EUROFER steel and EUROFER 97 are compared and discussed.
Investigation of Fatigue Crack Propagation in Nickel Superalloy Using Diffraction Contrast Tomography and Phase Contrast Tomography
Authors: Messé Olivier M.D.M. , Lachambre Joel , King Andrew , Buffière Jean Yves , Rae Cathie M.F.
Published: March 2014

Evaluation of superalloy component life in turbine engines requires a detailed understanding of how fatigue crack initiation and short crack propagation contribute to fatigue life. However most investigations have been carried out post-mortem and in two dimensions. New techniques are able to fully resolve cracks propagating in four dimensions (space and time), enabling characterisation of their local environments and allowing a much deeper understanding of fatigue mechanics.
Nickel-based superalloys experiencing high cycle fatigue have shown a high sensitivity to microstructure during initiation and short crack propagation. Using high energy X-rays and the combination of Diffraction Contrast Tomography (DCT) and Phase Contrast Tomography (PCT), we followed a fatigue crack initiated from a Focused Ion Beam (FIB) milled notch at room temperature. Analyses have been carried out to fully characterise the crack and its environment. We tracked the evolution of the crack and interactions with the microstructure. Subsequently, post-mortem investigations have been carried out to corroborate results obtained from the tomographs and to provide more local information of fatigue crack propagation.
An Investigation of the Extent of Crack Closure for Crack Growth in an Aluminium Alloy
Authors: Barter Simon A. , Burchill Madeleine , Jones Michael
Published: March 2014

The corrections incorporated in fatigue crack growth prediction programs for crack closure are usually tested by their ability to predict retardation following an overload and for the accuracy of their prediction lives for long cracks greater than about 1mm. They should, however, be examined on their ability to predict the life of cracks that grow from small sizes, such as small inherent material discontinuities, to failure, which is more typical of service situations and the growth produced by small cycles as well as the larger cycles. To examine the extent of crack closure in aluminium alloy 7050-T7451 and the prediction of that growth, quantitative fractography measurements of short periods of fatigue crack growth produced with a specially engineered spectrum were conducted and are reported here. The spectrum contained bands of constant amplitude loads with diminishing mean stress designed to examine the extent of closure. The quantitative fractography results are compared to predictions by the common analytical programs FASTRAN and AFGROW and further with a basic effective stress intensity calculation method at a crack depth of about 1mm. The results showed that the analytical programs were able to predict the presence of closure; however, the extent of the closure was not accurately predicted.
Thermographic Investigation of Fatigue Crack Propagation in a High-Alloyed Steel
Authors: Bär Jürgen , Seifert Stefan
Published: March 2014

Crack propagation experiments under constant stress intensity conditions were performed on SEN specimen of a high-alloyed steel. The experiments were accompanied by thermo elastic stimulated lock-in thermography investigations. The experiments showed that the crack propagation rate decreases with increasing crack length. Concurrent an increase in the dissipated energy in an area beside the crack flanks as well as in front of the crack tip was observed. The size of the plastic zone was also determined by thermographic measurements and was found to be constant during the crack propagation experiment. The increase of the dissipated energy doesnt reflect in the size of the plastic zone but seems to be responsible for the decrease of the crack propagation rate.
Effect of Hydrogen Gas on the Growth of Small Fatigue Crack in JIS-SCM435
Authors: Itoga Hisatake , Matsunaga Hisao , Matsuoka Saburo
Published: March 2014

The fatigue crack growth (FCG) from a small hole in a low alloy steel JIS-SCM435 round bar was investigated using tension-compression fatigue tests in 0.7 MPa hydrogen gas and ambient air. In the higher FCG rate regime (e.g. da/dN > 108 m/cycle), FCG was accelerated in hydrogen gas compared to in air. On the other hand, in the lower FCG rate regime (e.g. da/dN < 108 m/cycle), FCG in hydrogen was rather slower than that in air. There was no noticeable difference in fatigue limits between these two atmospheres. The FCG in the respective atmospheres showed a typical small crack behavior, i.e. the da/dN for small cracks were much greater than those for large cracks obtained by compact tension (CT) specimen when they were compared at the same ΔK level. In order to unify such a discrepancy of FCG behavior between small crack and large crack, the strain intensity factor range ΔKε was adopted. As a result, the da/dN data for various crack sizes was gathered in a narrow band, i.e. the small crack effect was successfully evaluated with the strain intensity. Moreover, the crack growth life was predicted based on the da/dN-ΔKε relation. The reproduced S-N curve showed a conservative agreement with the fatigue life obtained by experiments.