bluuebunny/crossref_metadata_2025 huggingface dataset:
Fatigue behaviour of AA6061-T6 alloys in the corrosive environment
Authors: Vu Nguyen Ngoc , Li Peifeng
Published: May 2018

The combined effects of corrosion and fatigue are known to be hazardous threats to structural integrity of aluminium alloys that are being extensively used in marine applications. This work investigated the fatigue crack initiation and growth behaviour of AA6061-T6 alloys in 3.5 wt% NaCl simulated seawater using scanning electron microscope and electron backscatter diffraction characterisation techniques. It was found that the fatigue resistance of AA6061-T6 is drastically downgraded when subjected to the corrosive environment of 3.5 wt% NaCl solution. High stress concentration at both sides of a pit mouth in conjunction with attacked grain boundaries facilitates fatigue crack nucleation, while the presence of hydrogen formed by corrosion reactions causes crack tip embrittlement and thus increases crack growth rate. Fractographic analysis reveals that there is a change in fatigue crack growth mechanism of AA6061-T6 alloys tested in the NaCl solution. At short crack length, the crack develops transgranularly along crystallographic planes due to hydrogen-enhanced decohesion process. Further crack growth is dominated by adsorption induced dislocation emission process, resulting in the mixed mode of intergranular and transgranular crack growth.
A finite element and experimental analysis of durability tested springs
Authors: Wang Ying , Soutis Constantinos , Gagliardi Lorenzo
Published: May 2018

Ageing of vehicles has become a major concern as the vehicles reach the end of their original design life. Corrosion is part of long-term ageing and forms one of the critical degradation processes affecting the mechanical properties, such as stiffness, affecting the structural integrity and life of key components. In this study, a finite element and experimental analysis was carried out to investigate the response of corroded springs in relation to the morphology of a corroded surface. An FE model was created using ABAQUS that correlates the stiffness changes with ageing. The analysis of corrosion-induced stress is then performed to determine the stress fields within the corrosion region. The durability tested springs were analysed with a microscope to identify the morphology of corrosion pits; the measured pattern was adopted in the subsequent FE simulations. A spring test machine was employed to perform the mechanical tests. The load-deflection behaviour of durability tested springs was recorded and then was used to validate the FE simulations.
A cyclic slip irreversibility based model for fatigue crack initiation of nickel base alloys
Authors: Ho Hsin Shen , Risbet Marion , Feaugas Xavier
Published: May 2018

The opportunity to define a microscopic law of fatigue crack initiation using Manson-Coffin law formulated in terms of cyclic slip irreversibility deduced from AFM measurements is discussed for a polycrystalline superalloy with different grain sizes and precipitate sizes. The results show that the modified Manson-Coffin law, relating cyclic slip irreversibility parameter to fatigue crack initiation life, is sustained through a two-parameter power law: ε′f and c. The analysis suggests that the exponent c-value can be related to the degree of plastic strain incompatibility between grains, and the cumulative irreversible cyclic plastic strain to crack initiation is a relevant damage indicator for crack initiation. Consequently, our approach allows giving a physical base of engineering law.
Metastability and fatigue behavior of austenitic stainless steels
Authors: Smaga Marek , Boemke Annika , Daniel Tobias , Klein Matthias W.
Published: May 2018

This study presents the results of a detailed investigation of metastability and susceptibility to deformation induced α’-martensite formation of several austenitic steels (AISI 304, AISI 321, AISI 348 and two batches from AISI 347) in the solution-annealed state. Besides conventional characterization of metastability by calculating stacking-fault energy and threshold temperature (designated as MS and Md30), the present work introduced a new method for determining susceptibility to α’-martensite formation. The method was based on dynamically applied local plastic deformation and non-destructive micro-magnetic measurement of α’-martensite content. The parameter Iξ was established, which correlated very well with the grade of α’-martensite formation during cyclic loading. The cyclic deformation and phase transformation behavior of cyclically loaded specimens from different metastable austenitic steels were investigated in total-strain and stress controlled fatigue tests with load ratio R = -1 at ambient temperature. The influence of the strain rate on the cyclic deformation and phase transformation behavior was also examined. During the fatigue tests, besides stress-strain hysteresis and temperature measurement, in situ micro-magnetic measurements were performed. Using the compressive measured data, the influence of plastic induced self-heating of the specimen and the strain rate on α’-martensite formation was analyzed.
Comparison of fatigue crack initiation behavior in different microstructures of TC21 titanium alloy
Authors: Tan Changsheng , Sun Qiaoyan , Xiao Lin , Zhao Yongqing , Sun Jun
Published: May 2018

Cyclic heterogeneous deformation, slip characteristics and crack nucleation with different microstructures, such as bimodal microstructure (BM) and fine lamellar microstructure (FLM) in TC21 alloy (Ti-6Al-2Sn-2Zr-3Mo-1Cr-2Nb-0.1Si), were systematically investigated and analyzed during high cycle fatigue at room temperature. The results demonstrated that the FLM microstructure possesses higher high-cycle fatigue strength than those of the BM one. For BM, the heterogeneous plastic deformation existed within the different large primary α phase, such as equiaxed primary α and primary α lath. The cracks at interfaces and slip bands easily coalesce with each other to form large cracks in BM. However, the α laths with similar morphology and size (nanosize) distributed uniformly in FLM and could relatively deform homogeneously in micro-region, which delayed the initiation of the fatigue crack. Based on the electron-backscattered diffraction (EBSD) analysis, it found that the strain was nonuniformly distributed in BM, however, it is relatively homogeneous in FLM. Moreover, lots of straight cracks are parallel and along single intrusions within the β grain which delays the coalescence of cracks.
Effects of thermomechanical history and environment on the fatigue behavior of (β)-Ti-Nb implant alloys
Authors: Reck André , Pilz Stefan , Thormann Ulrich , Alt Volker , Gebert Annett , Calin Mariana , Heiß Christian , Zimmermann Martina
Published: May 2018

This study examined the fatigue properties of a newly developed cast and thermomechanical processed (β)-Ti-40Nb alloy for a possible application as biomedical alloy due to exceptional low Young’s modulus (64-73 GPa), high corrosion resistance and ductility (20-26%). Focusing on the influence of two microstructural states with fully recrystallized β-grain structure as well as an aged condition with nanometer-sized ω-precipitates, tension-compression fatigue tests (R=-1) were carried out under lab-air and showed significant differences depending on the β-phase stability under cyclic loading. Present ω- precipitates stabilized the β-phase against martensitic α’’ phase transformations leading to an increased fatigue limit of 288 MPa compared to the recrystallized state (225 MPa), where mechanical polishing and subsequent cyclic loading led to formation of α’’-phase due to the metastability of the β-phase. Additional studied commercially available (β)-Ti-45Nb alloy revealed slightly higher fatigue strength (300 MPa) and suggest a change in the dominating cyclic deformation mechanisms according to the sensitive dependence on the Nb-content. Further tests in simulated body fluid (SBF) at 37°C showed no decrease in fatigue strength due to the effect of corrosion and prove the excellent corrosion fatigue resistance of this alloy type under given test conditions.
Long-term durability of CFRP under fatigue loading for marine applications
Authors: Le Guen-Geffroy Antoine , Le Gac Pierre-Yves , Diakhate Malick , Habert Bertrand , Davies Peter
Published: May 2018

Composite propellers are a major new development in the marine transport industry. The use of composite materials in seawater turbines is also of great interest to the marine renewable energy industry. Those systems present similarities being both constantly immersed in seawater, under fatigue loadings, of large dimensions, and they are often designed using Carbon Fibre Reinforced Polymer (CFRP). Previous studies have shown sensitivity of some composite materials to the seawater environment mainly in the quasi-static loading domain. However, investigations now need to be performed on the behaviour of CFRP under seawater environment and fatigue loadings. In this study, CFRP samples were aged in natural seawater until saturation, in order to investigate the influence of water absorption on the fatigue properties of the material. Results showed a small decrease in fatigue lifetime under tension but a more significant drop for sample subjected to four point flexural fatigue.
A two-parameter analysis of surface fatigue crack growth behavior of fine-grained WC-Co cemented carbide at different stress ratios
Authors: Mikado Hiroko , Ishihara Sotomi , Oguma Noriyasu , Kawamura Shingo
Published: May 2018

In this study, the fatigue crack growth (FCG) characteristics of the short surface crack was studied at various stress ratios, R, using the fine grained cemented carbide. The FCG law for the material was studied using two parameters, the maximum stress intensity factorKmaxand the stress intensity factor range ΔK. It was found that the relationship between the rate of FCG,da/dNand ΔKdepends on theRvalue. In theda/dNvs.Kmaxrelation, at the region of high crack growth rate, the FCG rate was nearly constant by the value ofKmaxwithout depending on R. However, in the low FCG rate region, the FCG rate tended to accelerate as R became lower. Therefore, it was difficult to specifyda/dNas a single value at differentRratios using either ΔKorKmaxfrom the low speed region to the high-speed region. For that reason, the FCG behaviour of the material was studied based on the crack growth law,da/dN= AKmaxmΔKn. The values ofmandnwere obtained as 6.6 and 1.4, respectively. Therefore, it was found that the FCG rate of the cemented carbide was strongly dependent onKmaxrather than ΔK, like the FCG characteristics of ceramics.
Fatigue of polyamide mooring ropes for floating wind turbines
Authors: Chevillotte Yoan , Marco Yann , Davies Peter , Bles Guilhem , Arhant Maël
Published: May 2018

This paper describes a study of the fatigue characterization of polyamide mooring ropes for floating wind turbines. Under some conditions polyester ropes, which are favoured for offshore platform station-keeping, are too stiff for wind turbine moorings, and polyamide may be a suitable alternative. While early studies on fatigue of braided nylon ropes showed very short lifetimes some recent results have indicated that it is possible to significantly enhance lifetime by modifying rope construction and improving fibre coatings [1]. The fatigue results presented here for ropes from a different supplier, confirm this result. In order to develop an accelerated evaluation of the fatigue performance, heat build-up tests have been performed, and promising first results are shown. Finally, the influence of coating is examined by microscopy and yarn-on-yarn tests, in order to improve understanding of the fatigue mechanisms leading to failure.
Methods for Structural Stress Determination according to EN 13445-3 Annex NA – Comparison with other Codes for Unfired Pressure Vessels
Authors: Trieglaff Ralf , Rudolph Jürgen , Beckert Martin , Friers Daniel
Published: May 2018

The European Pressure Vessel Standard EN 13445 provides in its part 3 (Design) a simplified method (Clause 17) and a detailed method for fatigue assessment (Clause 18). Clause 18 “Detailed Assessment of Fatigue Life” is under revision within the framework of the European working group CEN/TC 54/WG 53 – Design methods with the aim of reaching a significant increase in user-friendliness and a clear guideline for the application.

This paper is focused on the new informative annex NA ”Instructions for structural stress oriented finite elements analyses using brick and shell elements”. As an essential amendment for the practical user, the determination of structural stress ranges for fatigue assessment of welds is further specified in this new annex. Different application methods for the determination of structural stresses are explained in connection with the requirements for finite element models and analyses.

This paper will give a short overview of the proposed approaches of structural stress determination in annex NA of the revised EN 13445-3. It will present the status of the approaches based on the results of fatigue analyses according to EN 13445-3 Clause 18 for different application examples.

For verification purposes, the results of the approaches proposed in EN 13445-3 are compared with the results of other pressure vessel design codes for nuclear and non-nuclear application.
Significance of Fatigue Damage from Overload Trucks on Bridge Load Rating
Authors: Jang Bora , Mohammadi Jamshid
Published: May 2018

Overload trucks constitute a major portion of truck load populations on highways. Specific to bridges, the increase in the frequency of overloads may trigger shortening of service life of critical components because of fatigue damage, considering the fact that fatigue damage accelerates at higher loads. This is especially important to older bridges that have been designed for loads lower than the standard for current highway bridge design in the United States. As the number of requests for special permits to use bridges by overload trucks increases, the accumulated damage may substantially reduce the service life of bridges resulting in costly repair and replacements. In this paper, the significance of overloads in causing fatigue damage to bridges is discussed. Samples of truck load data have been compiled and used to determine the contribution of overloads to fatigue damage for steel girder bridges made up of welded cover plates. The paper discusses using the expected fatigue life expended (FLE) as an index to determine the impact of overloads on bridge fatigue damage. The FLE is then determined to be an important factor that can be used to modify bridge rating equations as a way of controlling the number of overload permits for a given bridge.
Introduction to the new FKM guideline which considers nonlinear material behaviour
Authors: Fiedler Melanie , Vormwald Michael
Published: May 2018

In 2018 the German Research Association of Mechanical Engineering (FKM) will present a new guideline for calculating the fatigue crack initiation life of structures and components .

The user of this guideline

… is able to calculate the fatigue life for crack initiation for structures of steel, cast steel and aluminium alloy

… has to perform an elastic FE-calculation and gets the quality of an elastic-plastic calculation

… is able to determine the cyclic material parameters and the damage parameter Wöhler curve by the ultimate tensile strength Rm

… is able to calculate the fatigue life in HCF and LCF for constant and variable amplitude loading

This paper presents the algorithms of the new guideline, gives an overview about the mechanical background and discusses the results for specimens of steel and aluminium alloys. It also shows results comparing the new to the current FKM guideline for a given steel structure.
Fatigue crack surface area and crack front length: new ways to look at fatigue crack growth
Authors: van Kuijk Jesse , Alderliesten René , Benedictus Rinze
Published: May 2018

This paper discusses the appropriateness of crack length as a reference dimension for fatigue damage. Current discussion on short crack versus long crack data is still divided between various approaches to model small crack growth. A proper physical explanation of the probable cause of the apparent differences between short crack and long crack data is not yet provided. Long crack data often comprises crack growth in constant thickness specimens, with a through crack of near constant crack front geometry. This is not true for corner cracks or elliptical surface crack geometries in the small crack regime where the crack front geometry is not symmetric or through-thickness. This affects similitude parameters that are based on the crack length. The hypothesis in this paper is that a comparison between long crack data and short crack data should be made using similar increments in crack surface area. The work applied to the specimen is dissipated in generation of fracture surface, whereas fracture length is a result. The crack surface area approach includes the two-dimensional effect of crack growth geometry in the small crack regime. A corner crack and a through crack are shown to follow the same power law relationship when using the crack area as base parameter. The crack front length is not constant, and its power law behaviour for a corner crack is shown.
Fatigue and fracture resistance of ferritic ductile cast iron: the effect of Sb and solidification time
Authors: Benedetti Matteo , Fontanari Vigilio , Lusuardi Danilo
Published: May 2018

In this paper, we explore the effect of inoculants and solidification time on the mechanical properties of an EN-GJS-400-type ferritic ductile cast iron (DCI). For this purpose, static tensile, rotating bending fatigue, fatigue crack growth and fracture toughness tests are carried out on three different material conditions. They are produced under fast cooling (solidification time 2h45min), representative of thin walled castings, and very slow cooling (solidification time 10—13h), representative of thick walled castings, this latter with and without the addition of Sb. It has been found that the long solidification time leads to an overgrowth and degeneration of the spheroidal graphite nodules. The addition of Sb avoids the formation of chunky graphite observed in the slowly cooled condition but results in large exploded graphite nodules. These effects impact negatively on tensile strength, total elongation and fatigue strength. Conversely, the resistance to fatigue crack growth is even superior and the fracture toughness comparable to that of the fast cooled condition. Metallurgical and fractographic analyses are carried out to explain this behaviour.
The significance of microstructure heterogeneities on the fatigue thresholds of aluminum castings
Authors: Gerbe Sascha , Knorre Stephan , Krupp Ulrich , Michels Wilhelm
Published: May 2018

Industrial in-series aluminum castings contain a wide range of microstructural heterogeneities like differences in secondary dendrite arm spacing (SDAS), eutectic silicon and intermetallic precipitates of varying morphologies and diverse-shaped and-sized porosity. Regarding to technical and economic limitations, the complete elimination of them is hard to achieve, which requires conservative design, i.e., increased wall thicknesses to accommodate the failure tolerance. To improve the performance of cast aluminum products concerning safety and fatigue properties, the present work deals with the significance of such structures with respect to the threshold for crack propagation ΔKI,th under pure bending and the fatigue behaviour in the high-and very-high-cycle-fatigue regime (HCF and VHCF). Therefore, two automotive cast alloys taken from engine blocks (AlSi8Cu3) and cylinder heads (AlSi7Cu0.5Mg) and a gravity die cast set (AlSi7Mg0.3), either T6 conditioned or additionally hot isostatic pressed (HIP), were used. For in-series castings, two positions of maximal difference in cooling rate and respective microstructure were extracted. With this set of specimens, the significance of SDAS in interaction with (i) eutectic silicon regions, (ii) intermetallic precipitates in varying occurrence, (iii) the crystallographic orientation, and (iv) the porosity in correlation with the fatigue threshold is shown and compared with first results of fatigue damaging mechanisms in quasi pore-free material.
The effect of microstructural heterogeneities on the High Cycle Fatigue scatter of cast aluminium alloys: from an elementary volume to the structure
Authors: El Khoukhi Driss , Morel Franck , Saintier Nicolas , Bellett Daniel , Osmond Pierre
Published: May 2018

Cast Al-Si alloys have been widely used in automobile applications thanks to their low density and excellent thermal conductivity. A lot of components made of these alloys are subjected to cyclic loads which can lead to fatigue failure. Furthermore, the well know size effect in fatigue, whereby the fatigue strength is reduced in proportion to an increase in size, can be important. This is caused by a higher probability of initiating a crack in larger specimens (i.e. statistical size effect). This paper analyses the role of casting defects on the statistical size effect. For that, a uniaxial fatigue testing campaign (R=0.1) has been conducted using two cast aluminium alloys, fabricated by different casting processes (gravity die casting and lost foam casting), associated with the T7 heat treatment, and with different degrees of porosity. Different specimens (smooth and notched) with different stressed volumes have been investigated. The first part of this article is dedicated to the experimental characterization of the statistical size effect in both alloys via the concept of the Highly Stressed Volume. The second part investigates the effect of the Highly Stressed Volume on the critical defect size via diagram of Kitagawa-Takahashi. The results show that the presence of statistical size effect is strongly linked to the characteristics of the pore population present in the alloy. A numerical approach, linking the observed pore distribution to the volume of loaded material, is proposed and discussed.
Prediction of fatigue crack initiation life of aluminium alloy joints using cyclic elasto-plasticity FEM analysis
Authors: Seiichiro Tsutsumi , Moe Sano , Riccardo Fincato
Published: May 2018

Finite element analyses (FEA) are particularly useful for investigating fatigue problems since it is possible to carry out elasto-plastic simulations for any configuration and to predict the material behaviour for a large number of loading cycles. This study aims to investigate the fatigue life for Al-Mg alloy A5083-O joints by means of numerical simulations. The Proposed method needs to give a precise description of the elasto-plastic behaviour of the alloy together with an appropriate definition of the criteria for the fatigue crack initiation. In this paper, the elasto-plastic behaviour of the A5083-O alloy was investigated by FE analyses. On the other hand, the fatigue crack initiation criterion is provided based on strain ranges observations. In detail, the finite element analyses focused the attention on the study of the service life of a butt-weld join.
Study and modelling of anodized 2618 aluminum behavior subjected to multiaxial fatigue
Authors: Malek Benaissa , Mabru Catherine , Chaussumier Michel
Published: May 2018

Anodized Aluminum alloys are widely used in aeronautic construction due to their specific mechanical properties. However, anodization process often leads to a decrease of the fatigue resistance of the alloys. In order to identify and characterize the different mechanisms involved in the detrimental effect of anodization of 2618-T851 alloy on its fatigue life and to determine the impact of loading nature, several tests have been performed on specimens with different surface states at various stress ratios. It was found that roughness of machining has no effect unlike the stress ratio or mean stress in tensile tests. The tests on the pickled, anodized, impregnated and sealed specimens showed it was the anodic oxidation step which was the more detrimental for fatigue resistance under tensile loading comparing to the other steps. It has been also observed that no such detrimental effect occurred under torsion loading. Concerning the prediction of fatigue life, two critical plane-based analysis approaches have been used (Morel and Fatemi-Socie criteria) to make fatigue life prediction for uniaxial and multiaxial fatigue test. Comparisons showed that both criteria gives overestimated fatigue life for uniaxial tensile loading under compression mean stress and underestimated fatigue life for tensile-torsion in phase loading.
Automotive cylinder heads: recent advances on Thermal-Mechanical Fatigue design and upcoming challenges
Authors: Szmytka Fabien , Osmond Pierre , Rémy Luc , Masson Pierre-Damien , Forré Agathe
Published: May 2018

Through the peculiar case of an automotive cylinder head, actual and forthcoming challenges for low-cycle and thermal-mechanical fatigue design in an industrial context are presented. A special focus is applied on variable loadings, constitutive models and their interaction with the environment, fatigue criteria and structure validations.
Effect of surface compressive residual stress introduced by surface treatment on fatigue properties of metallic material
Authors: Arakawa Jinta , Hanaki Tatsuya , Hayashi Yoshiichirou , Akebono Hiroyuki , Sugeta Atsushi
Published: May 2018

This study considers shakedown in evaluating the fatigue limit of metals with compressive residual stress at the surface. We begin by applying tension-compression fatigue tests to ASTM CA6NM under conditions of controlled load and displacement to obtain fatigue limit diagram in compressive mean stress. The results imply that shakedown occurs under the condition of controlled displacement, therefore, shakedown should be considered when evaluating the fatigue limit of metals with compressive residual stress at the surface.
Thermomechanical fatigue crack initiation in disc alloys using a damage approach
Authors: Leidermark Daniel , Eriksson Robert , Rouse James P. , Hyde Christopher J. , Stekovic Svjetlana
Published: May 2018

A fatigue crack initiation model based on damage accumulation via a fatigue memory surface in conjunction with a plastic strain energy parameter was evaluated for thermomechanical fatigue loading in a gas turbine disc alloy. The accumulated damage in each hysteresis loop was summed up, and it was assumed that the damage at the stable state is repeated until failure occurs. Crack initiation occurs when enough fatigue damage has been obtained, and the number of cycles can thus be directly determined. The fatigue damage is highly coupled to the constitutive behaviour of the material, where the constitutive behaviour was modelled using a non-linear hardening description. Based on this, a stable state was achieved and the obtained damage could be extracted. A user-defined material subroutine was implemented, incorporating both the constitutive description and the fatigue damage accumulation. The framework was adopted in a finite element context to evaluate the thermomechanical fatigue crack initiation life of the disc alloy RR1000. From the evaluation it could be seen that a good prediction of the thermomechanical fatigue life was achieved compared to performed experiments.
Acceleration techniques for the numerical simulation of the cyclic plasticity behaviour of mechanical components under thermal loads
Authors: Srnec Novak Jelena , De Bona Francesco , Benasciutti Denis , Moro Luciano
Published: May 2018

Numerical simulations of components subjected to cyclic thermo-mechanical loads require an accurate modelling of their cyclic plasticity behaviour. Combined models permit to capture monotonic hardening as well as cyclic hardening/softening phenomena, that occur in reality. In principle the durability assessment of a component under thermal loads can be performed only if the cyclic behaviour is simulated until complete material stabilization. As materials stabilize approximately at half the number of cycles to failure, it follows that in case of small plastic strains a huge number of cycles must be considered and an unfeasible simulation time would be required. Accelerated models have thus been proposed in literature. The aim of this work is that of comparing the different acceleration techniques in the case a round mould for continuous casting loaded thermo-mechanically. It can be observed that the usual approach of using the stabilized stress-strain curve already from the first cycle could lead to relevant errors. An alternative method is that of increasing the value of the parameter that controls the speed of stabilization in the combined model. This approach permits the number of cycles to reach stabilization to be drastically reduced, without affecting the overall mechanical behaviour. Based on this approach, a simple design rule, that can be adopted, particularly when relatively small plastic strains occur, is finally proposed.
Numerical Simulation of the Fatigue Behaviour of a Friction Stirred Channel Aluminium Alloy
Authors: Vidal Catarina , Baptista Ricardo , Infante Virgínia
Published: May 2018

Friction stir channelling (FSC) is one of the most promising innovations based on the friction stir concepts. FSC uses a non-consumable tool, similar to that used to perform the friction stir welding (FSW) process, to produce continuous and integral channels, with any path, in monolithic aluminium alloys components in a single step. This paper presents the mechanical behaviour of friction stirred channel components in particular the fatigue resistance of the channels analysed. Finite element analyses were performed taking into account the maximum stress values applied in experimental fatigue tests of the aluminium components. The energy release rate for different crack lengths was obtained using the software ABAQUS. The fatigue crack growth curve was established according to the Paris Law, and the crack propagation direction was calculated using the maximum tangential stress (MTS) criterion. During the analysis it was observed that the critical areas are located in the vicinity of the channels corners, as it was observed in the fracture surfaces of the experimental fatigue test results.
High Temperature Fatigue Crack Growth Rate Studies in Stainless Steel 316L(N) Welds Processed by A-TIG and MP-TIG Welding.
Authors: Thomas Manuel , Prakash Raghu V. , Ganesh Sundara Raman S , Vasudevan M.
Published: May 2018

Welded stainless steel components used in power plants and chemical industries are subjected to mechanical load cycles at elevated temperatures which result in early fatigue failures. The presence of weld makes the component to be liable to failure in view of residual stresses at the weld region or in the neighboring heat affected zone apart from weld defects. Austenitic stainless steels are often welded using Tungsten Inert Gas (TIG) process. In case of single pass welding, there is a reduced weld penetration which results in a low depth-to-width ratio of weld bead). If the number of passes is increased (Multi-Pass TIG welding), it results in weld distortion and subsequent residual stress generation. The activated flux TIG welding, a variant of TIG welding developed by E.O. Paton Institute, is found to reduce the limitation of conventional TIG welding, resulting in a higher depth of penetration using a single pass, reduced weld distortion and higher welding speeds. This paper presents the fatigue crack growth rate characteristics at 823 K temperature in type 316LN stainless steel plates joined by conventional multi-pass TIG (MP-TIG) and Activated TIG (A-TIG) welding process. Fatigue tests were conducted to characterize the crack growth rates of base metal, HAZ and Weld Metal for A-TIG and MP-TIG configurations. Micro structural evaluation of 316LN base metal suggests a primary austenite phase, whereas, A-TIG weld joints show an equiaxed grain distribution along the weld center and complete penetration during welding (Fig. 1). MP-TIG microstructure shows a highly inhomogeneous microstructure, with grain orientation changing along the interface of each pass. This results in tortuous crack growth in case of MP-TIG welded specimens. Scanning electron microscopy studies have helped to better understand the fatigue crack propagation modes during high temperature testing.
Hysteresis Analysis of Prestressed Brick Frame with Strawbale Masonry Infill Subjected to Seismic Loads
Authors: Adedeji Adeola A. , Adedeji Abiola , Ibiyeye Aminu
Published: May 2018

This study looks at designing and evaluating strength of typha strawbale wall cross section rather than the assumption of edge column acting as axially loaded members that should resist all vertical members from the loads acting on the wall. Based on the aforementioned claim, the objective of this work is to provide the average design thickness for the cement-plastered typha strawbale that stiffens the prestressed brick frame. Data on strength and deformation of the structure are the input for the analytical models. Pseudo-dynamic earthquake response tests, of a one quarter (¼) scale model low rise storeys prestressed brick frames stiffened with cement plastered strawbale masonry was conducted. The structure is idealized as plane frames. The analysis utilised the hysteresis models for members’ models as timeindependent. The force-displacement relationship of the members’ models has been evaluated by the approximate method on the basis of the material properties and structural geometry. A model was investigated with straw bale infill panel to determine the hysteretic parameters, stiffness deterioration and strength degradation due to seismic forces.
Investigation of fatigue crack growth under loading sequence effects using in-situ SEM testing
Authors: Jiang Shan , Zhang Wei , Cai Liang , Wang Zili
Published: May 2018

Fatigue damage is one of the most important failure mechanisms in engineering components. The excited structures are usually subjected to spike loads in the fatigue weakness area during their service lives. The nonlinear loading sequence effects due to overloads are significant in the crack propagation process. In this paper, an in-situ scanning electron microscope (SEM) testing is performed to analyse the mechanisms of nonlinear fatigue crack growth affected by the load sequence. The crack tip behaviours under constant amplitude loading cycles superimposed by tensile overload were observed. The SEM experiment results reveal that the overload effects include the transient weakened area (shear bands and micro-cracks) and the relatively long-term retardation. Additionally, the observation loading sequence influence region is larger than the theoretical value. According to these SEM testing analyses, the Willenborg is modified considering the nonlinear loading sequence effects. In this approach, the damage zone concept is introduced to account for the instantaneous acceleration. Moreover, the loading sequence effect area is defined as the whole plastic zone due to overload rather than part of it. The proposed algorithm is validated by experiment data of 350WT steel and Al 2024-T351 specimens under constant loading with overloads. Good agreements are observed.
Thermo-mechanical fatigue prediction of a steam turbine shaft
Authors: Nesládek Martin , Bartošák Michal , Jurenka Josef , Papuga Jan , Růžička Milan , Měšt’ánek Petr , Džugan Jan
Published: May 2018

The increasing demands on the flexibility of steam turbines due to the use of renewable energy sources substantially alters the fatigue strength requirements of components of these devices. This paper presents Thermo-Mechanical Fatigue (TMF) design calculations for the steam turbine shaft. The steam turbine shaft is exposed to complex thermo-mechanical loading conditions during the operating cycle of the turbine. An elastic-plastic structural Finite Element Analysis (FEA) of the turbine shaft is performed for the turbine operating cycle on the basis of calculated temperature fields obtained in a previous transient thermal FEA. The temperature dependent material parameters, which are used in the elastic-plastic FEA, are obtained from the uniaxial tests. Consequently, the TMF is predicted for the steam turbine shaft. Several fatigue criteria are used for the identifications of the critical domain and for the TMF damage assessment of the turbine shaft.
Ability of multiaxial fatigue criteria accounting for stress gradient effect for surface defective material
Authors: Niamchaona Wichian , Pennec Fabienne , Tihay Kévin , Duchet Michel , Weber Bastien , Robert Jean-Louis
Published: May 2018

New high strength steels are widely used nowadays in many industrial areas as in automotive industry. These steels are more resistant and provide higher fatigue limits than latter ones but they are also more sensible to small defects. Natural defects that outcome from metallurgy (as shrinkage, inclusion, void) are not considered in this study. We focus on small manufacturing defects such as cutting edge defects generated by punching or other surface defects due to stamping. These defects are harmful on the material fatigue behaviour due to high stress concentration at defects root. They also generate stress gradient that is beneficial from the fatigue strength point of view. This study focusses on the stress gradient (it does not account for the size effect) from cylindrical defect on specimen edge. Practically a normal stress gradient is added in multiaxial fatigue criteria formulation. Both critical plane approach and integral approach are involved in the present study. This gradient is calculated from stress states at defects root by using FEM. Criteria fatigue function at N cycles is used to assess the material fatigue strength. Obviously multiaxial fatigue criteria accounting for stress gradient give more precise fatigue functions than criteria that do not consider the gradient influence.
Safety margin against the fatigue fracture under random loading
Authors: Garan Martin , Chmelko Vladimír , Schafer Ervin
Published: May 2018

The fatigue lifetime of the structure in operation is express in the number of working cycles, kilometers or time depending units. By harmonic process of loading is possible to express the safety margin as reserve against the required lifetime in the form of number cycles or amplitude of loading. By nonharmonic character of loading process in operation is difficult to express the level of safety margin as the reserve of loading (safety margin in loading). On the case of towing trailer will be discussed more ways of expression the reserve (safety margin) of structure against the fatigue fracture for required fatigue lifetime. For experimental acquired loading process in the most loaded cross-section will be discussed concept of determination of the level safety as reserve in the form of loading parameters. In the case, when the peaks of loading process exceeding the material yield stress (in the most loaded point of the structure) will be discussed concept of expression of loading in the form of time-varying process of strain. By using the cyclic material properties obtained in mode with controlled total strain is possible the safety margin to express also as the multiple of process loading parameters.
A new local approach model for cleavage fracture in ferritic steels and its validation
Authors: Qian Guian , Lei Wei-Sheng , Niffenegger Markus
Published: May 2018

The paper discusses and applies a statistical approach to correlate the fracture behavior of a notched and fracture mechanics specimen. The method can be used for fatigue analysis. The random nature of cleavage fracture process determines that both the microscopic fracture stress and the macroscopic properties including fracture load, fracture toughness and the ductile to brittle transition temperature are all stochastic parameters. This understanding leads to the proposal of statistical assessment of cleavage induced notch toughness of ferritic steels according to a new local approach to cleavage fracture. The temperature independence of the two Weibull parameters in the new model induces a master curve to correlate the fracture load at different temperatures. A normalized stress combining the two Weibull parameters and the yield stress is proposed as the deterministic index to measure notch toughness. This proposed index is applied to compare the notch toughness of a ferritic steel with two different microstructures.
A research on the calculation method of car proportion based on image processing
Authors: Xiao Hong-Wei , Jiang Chang-Jiang , Zhai Jia-Xing , Chen Jing-Wei
Published: May 2018

The proportion of the car is one of the important parts of car styling design. The study of the car proportion is of great significance. The proportion of the car is determined by the technical conditions, functions and aesthetics. At present, there're not many studies on the area proportion of the car .There're studies on the line relationship and length, width, height proportion of the car. This paper uses computer image processing method to calculate the projected area proportion of the hatchback car. And it provides a new thinking and method for the car proportion study. The result shows that the projected area proportion values of the hatchback cars of European, American, Japanese, Korean and Chinese series on the market have a difference, but are close. And the total average projected area proportion values of car window and car body of the hatchbacks have been calculated.
Numerical and experimental diagnosis of complex rotor system by time-frequency techniques
Authors: Tchomeni Bernard Xavier , Alugongo Alfayo
Published: May 2018

This paper describes the application of Discrete Wavelet Transform (DWT) to identify various types of nonlinear damage caused by, unbalance, rotor-stator contact and a breathing crack in rotating machinery. Multiple faults have been investigated based on numerical and experimental signal analysis using Fast Fourier Transform (FFT) and DWT. A four degree of freedom fully coupled model of the rotor-stator system that includes the nonlinear damage in the rotor vibrations was established using Energy principles. Existence of high system nonlinearity could not allow exhaustive discrimination of rub and crack by classical FFT. Therefore, the DWT was employed. The results provide detailed feature analysis of the fault signals. Practical vibration measurements through a data acquisition system interfaced with Rotor Kit-4 and crack simulator provided the test data. Experimental Time-Frequency analysis gave more realistic faults responses with variable faults features. Irregularity of orbit, harmonic peaks in the presence of rub and crack were unique and distinguished periodic motion from other types of motion. The presence of a crack shifted the critical speed location and exhibited sub-harmonic components, which were more prominent with rub in vibration response. The detailed decomposition signal by DWT method established inherent feature patterns that effectively discriminated the multiple faults.
Safety analysis for integrated modular avionics based on blueprints
Authors: Chu Jiayun , Bao Xiaohong , Zhao Tingdi , Ren Fuchun
Published: May 2018

The Integrated Modular Avionics System (IMA) has been a core technology for the new generation of aircrafts in recent years. It consists of a set of reusable and interoperable common functional modules. However, the highly coupled relationship of resources makes it difficult to identify and control dangers. As an effective and efficient way, the blueprints are used to describe and manage the IMA system. Owing to the system management functions provided by the blueprints, we can accurately determine the system resources configuration status, which is very crucial for safety analysis. In this paper, we explore the possibilities to conduct safety analysis based on blueprints. A safety analysis method based on blueprints is proposed, which applies mathematical logic to describe the logical relationship between targets and resources provided by the blueprints and uses semi-tensor product of matrix theory to simplify the logical expressions. Based on the mathematical model, we can conduct the fail safety analysis and identify resources failures that may undermine the IMA system safety.
Apply data mining to analyze the rainfall of landslide
Authors: Lee Chou-Yuan , Lee Zne-Jung , Peng Bin-Yu , Lin Chen-chen , Huang Hsiang
Published: May 2018

Taiwan is listed as extremely dangerous country which suffers from many disasters. The disasters from the landslide result in the loss of agricultural productions, life and property and so on. Many researchers concern about the disasters of landslide, but there are few discussions for the threshold of rainfall for landslide. In this paper, data mining is applied to establish rules and the threshold of rainfall for landslide in Huafan University, Taiwan. These used variables include rainfall, insolation, insolation rate, averaged humidity, averaged temperature, wind speed, and the tilt of inclinometer. The inclinometer is an important instrument for measuring tilt, elevation or depression of an object with respect to gravity. There are 26 inclinometers in Talun mountain area of Huafan University. In this research, the used data were collected from January 2008 to July 2014. In the proposed approach, the regression analysis is used to predict rainfall first. Then, decision tree is used to obtain decision rules and set the threshold of rainfall for landslide. The output of this approach can provide more information for understanding the change of rainfall. The threshold of rainfall could also provide useful information to maintain the security for Huafan University.
Application of passive damping fixture to the improvement of CNC drilling
Authors: Hsia Shao-Yi , Chang Chen-Chung , Huang Di-Hung
Published: May 2018

High precision and high efficiency are the essential competition conditions for multi-axis machine. However, machine vibration problems are always plagued by equipment manufacturers. This study focuses on solving or eliminating the multi-angle drilling vibration of processing machines. By the design and experiment combining CNC multi-axis machine tools with vibration tables, the surface roughness in the multi-angle drilling holes is discussed for the reference of the industry or the academia. The results indicated that adding proper vibration factors could effectively improve the bore surface roughness and smoothness. Roughness Ra with the vibration interval time 0.5 sec, could improve the surface roughness 48.95% of the processing hole, comparing to it without vibration. Besides, the resonance phenomenon disappears at the feed to generate good effect. It is expected to reduce various vibration problems faced by processing with machine tools in order to enhance the international competitiveness of processing tool manufacturers.
Experimental study and finite element analysis on shear lag effect of thin-walled curved box beam under vehicle loads
Authors: Lu Hailin , Cai Heng , Tang Zheng , Nan Zijun
Published: May 2018

Shear lag effects of curved box beam under vehicle loads are investigated by using three-dimensional finite element method, where 4 parameters of vehicle loads, load size, vehicle speed, vehicle load position, load types, are considered. The change rules of stress distribution and shear lag coefficients of upper flange at mid-span are obtained when the loads move to the mid-span. The results indicate that under vehicle loads, the peak shear lag coefficients is at the junction between the flange and web, shear lag effect is prominent, shear lag effect is greatly influenced by vehicle speed and vehicle load position, while load size and load types almost don’t affect shear lag coefficients but do affect the stress. The model experiment of a cantilever curved box beam is carried out to compare with finite element analysis, and the error between them is small, which testify the validity and reliability of finite element model.