bluuebunny/crossref_metadata_2025 huggingface dataset:
The stress ratio effect on plastic dissipation during fatigue crack growth
Authors: Quan H. , Alderliesten R.C. , Benedictus R.
Published: May 2018

Plastic energy dissipation is inevitable during fatigue crack growth. There have been previous attempts reported in literature to correlate the plastic dissipated energy (dW/dN) to fatigue crack growth rate (da/dN). However, at a given dW/dN, the da/dN changes with the ratio of minimum and maximum loads, known as the stress ratio. This paper describes an experimental study carried out on 2024-T3 central crack tension specimens to quantify the relation between dW/dN and da/dN. By selecting different stress ratios in the individual tests, the experiments reveal the influence of the stress ratio on this relationship. It is evident that dW/dN has no unique relationship with da/dN valid for the tested stress ratios. Instead, the relationship for each stress ratio is different. This is illustrated with the value of plastic dissipation per unit of fatigue crack growth (dW/da), representing the effective resistance to the crack increment. This value is not a constant, but changes with the stress ratios and da/dN values. Hence the plastic energy dissipation cannot be used directly for predicting crack growth.
In-situ SEM and optical microscopy testing for investigation of fatigue crack growth mechanism under overload
Authors: Zhang Wei , Cai Liang
Published: May 2018

In this paper, the in-situ scanning electron microscope (SEM) and optical microscopy experiments are performed to investigate the crack growth behavior under the single tensile overload. The objectives are to (i) examine the overload-induced crack growth micromechanisms, including the initial crack growth acceleration and the subsequent retardation period; (ii) investigate the effective region of single overload on crack growth rate. The specimen is a small thin Al2024-T3 plate with an edge-crack, which is loaded and observed in the SEM chamber. The very high resolution images of the crack tip are taken under the simple variable amplitude loading. Imaging analysis is performed to quantify the crack tip deformation at any time instant. Moreover, an identical specimen subjected to the same load condition is observed under optical microscope. In this testing, fine speckling is performed to promote the accuracy of digital imaging correlation (DIC). The images around the crack tip are taken at the peak loads before, during and after the single overload. After that, the evolution of local strain distribution is obtained through DIC technique. The results show that the rapid connection between the main crack and microcracks accounts for the initial crack growth acceleration. The crack closure level can be responsible for the crack growth rate during the steady growth period. Besides that, the size of retardation area is larger than the classical solution.
Influence of orientation and temperature on the fatigue crack growth of directionally solidification superalloys DZ125
Authors: Shi Yi , Yang Xiaoguang , Yang Didi , Miao Guolei , Shi Duoqi
Published: May 2018

The influence of orientation and temperature on the fatigue crack growth of a directionally solidification superalloys named DZ125 were investigated in this study. The specimens were designed based on ASTM E647 standard and the compliance method was employed to monitor the crack growth. Tests were conducted at room temperature, 760°C and 850°C respectively. The longitudinal and transverse orientation were both studied in this tests. Results show that the orientation dependence is weak at elevated temperature compared with that at room temperature. However, the temperature influences the fatigue crack growth rate significantly and the largest difference can be an order of magnitude on the da/dN-ΔK graph. But the reduction in higher ΔK area of elevated temperature can still be observed. Potential reasons and hypothesis were explained in this paper. In addition, the crack growth mode appears to transfer from type I with the increase of temperature which also reflects the influence of temperature.
Strain energy-and stress-based approaches revisited in notch fatigue of ductile steels
Authors: Atzori Bruno , Ricotta Mauro , Meneghetti Giovanni
Published: May 2018

The constant amplitude, zero-mean stress, axial-fatigue behaviour of plain and bluntly notched AISI 304 L stainless steel specimens is investigated in terms of strain energy density. Concerning plain material, it was found that at the fatigue knee the plastic strain energy density is 1.49 times higher than the elastic strain energy density. In the authors’ opinion, the presence of plasticity at the fatigue knee is responsible for the unsuitableness of classical stress - based approaches to synthesise the fatigue behaviour of this material. On the contrary, the elastic-plastic strain energy density was found an efficient parameter to rationalise in a single scatter band fatigue data of plain and bluntly notched specimens. Based on this result, the classic stress-and the point stress-based approaches were revisited taking into account the presence of plasticity at the fatigue knee, by introducing an equivalent fully elastic material having a linear elastic strain energy density at the fatigue knee equal to that of the actual material. Accordingly, a coefficient of plasticity Kp was successfully introduced to modify the classical definition of fatigue strength reduction factor, Kf.
Continuum damage mechanics based approach to the fatigue life prediction of cast aluminium alloy with considering the effect of porosity
Authors: Wang Xiaojia , Hu Weiping , Meng Qingchun
Published: May 2018

A damage mechanics based approach is applied for the study of fatigue behaviour of high pressure die cast ADC12 aluminium alloy. A damage coupled elastoplastic constitutive model is presented according to the concept of effective stress and the hypothesis of strain equivalence. An elastic fatigue damage model taking into account the pore-induced stress concentration is developed to investigate fatigue damage evolution of the specimens subjected to cyclic loading. The predicted lives for the specimens with different sizes of pores are consistent with the experimental data. The pore-induced fatigue damage and the variation of fatigue life along with the size of pores are also investigated.
Influence of graphite morphology on static and cyclic strength of
ferritic nodular cast iron
Authors: Gebhardt Christian , Chen Geng , Bezold Alexander , Broeckmann Christoph
Published: May 2018

High silicon alloyed nodular cast iron consists of a purely ferritic matrix and graphite nodules, mainly. Varying wall thicknesses and manufacturing conditions result in different graphite morphologies throughout a structural component. From an experimental point of view, axial fatigue and tensile tests were carried out on specimens with differently degraded graphite. From a numerical point of view, the microstructure has been modelled using a finite element (FE) approach with representative volume elements (RVE). The RVE models were built according to micrographs of fatigue specimens. The generated RVEs determine effective material properties through elasto-plastic homogenization and were subsequently analysed using a shakedown approach. In shakedown theory, the material re-enters the elastic regime after a few cycles of initial plastic deformation. This work uses the shakedown theorem to derive a lower bound estimation of the endurance limit from a non-incremental simulation. Here, the material has to be modelled elastic-perfectly plastic. The major challenge in modelling nodular cast iron is to determine suitable material parameters for the graphite and ferrite phase, revealed by parameter studies on the static and cyclic model. By using reasonable material parameters, fundamental effects, observed in the fatigue tests, were reproduced on the model level.
Evaluation of notch effects in low cycle fatigue of alloy 718 using critical distances
Authors: Eriksson Robert , Simonsson Kjell , Leidermark Daniel , Moverare Johan
Published: May 2018

Gas turbine disks contain many notch-like features acting as stress raisers. The fatigue life based on the notch root stress may be overly conservative as the steep stress gradient in front of the notch may give rise to so-called notch support. In the current work, the theory of critical distances was applied to the prediction of the total fatigue life of low cycle fatigued, notched specimens made from alloy 718. The fatigue tests were performed at 450 °C and 550 °C. It was found that, for lives shorter than 5000–10000 cycles, the notched specimens had longer lives than would have been expected based on the notch root strain. For lives longer than 5000–10000 cycles, there were no notch support. The life prediction for notched specimens could be significantly improved by basing the prediction on the strain chosen some distance from the notch (the critical distance). An expression for calculating the critical distance based on the notch root strain was suggested.
Low cycle fatigue of 316L stainless steel processed by surface mechanical attrition treatment (SMAT)
Authors: Sun Zhidan , Zhou Jianqiang , Retraint Delphine , Baudin Thierry , Helbert Anne-Laure , Brisset François , Kanouté Pascale
Published: May 2018

In this work, the effect of surface mechanical attrition treatment (SMAT) on the cyclic behaviour of a 316L stainless steel under low cycle fatigue (LCF) is investigated. The LCF results are presented in the form of cyclic stress amplitude evolution for both untreated and SMATed samples. In order to better understand the microstructure change due to cyclic loading, electron backscatter diffraction (EBSD) is used to characterize the microstructure of the SMATed samples before and after fatigue tests. A microstructure gradient is highlighted for samples after SMAT from the top surface layer in nanocrystalline grains to the interior region non-affected by impacts. Under LCF loading, new slip systems are activated in the work hardened region, whereas no plastic slip is activated in the nanostructured layer. The residual stresses generated by SMAT are measured using X-ray diffraction (XRD), and their relaxations under cyclic loading are studied by taking into account the microstructure change. The cyclic behaviour of the samples in different material states is interpreted based on these investigations.
Effects of mean strain and tensile pre-strain on torsional fatigue behaviours of duplex stainless steel SAF2205
Authors: Li Bingbing , Yu Dunji , Chen Xu
Published: May 2018

Effects of mean strain and tensile pre-strain were investigated on the torsional fatigue behaviours of duplex stainless steel SAF2205. Two equivalent strain amplitudes (0.5%,0.7 %), three strain ratios (-1, - 0.5, -0.25) and 5% tensile pre-strain were chosen. Results indicated that the mean strain had no distinct influences on the torsional fatigue behaviours in terms of cyclic stress reponse and fatigue life while tensile pre-straining made a significant increase in cyclic stress response which was mainly attributed to the cross hardening derived from the loading sequence of monotonic tension preceding to cyclic torsion and led to a reduction in fatigue life. The failure mechanisms were revealed by scanning electron microscope characterized by microcracks initiation at the extrusions in ferrite and phase boundary inhibited further propagation. Additionally, the fractography of all fatigued specimens revealed a quasi-cleavage brittle mode with features of distinct tearing ridges and cleavage facets.
Influence of the microstructure on the cyclic stress-strain behaviour and fatigue life in hypo-eutectic Al-Si-Mg cast alloys
Authors: Tenkamp Jochen , Koch Alexander , Knorre Stephan , Krupp Ulrich , Michels Wilhelm , Walther Frank
Published: May 2018

Aluminium alloys are promising candidates for energy-and cost-efficient components in automotive and aerospace industries, due to their excellent strength-to-weight ratio and relatively low cost compared to titanium alloys. As modern cast processing and post-processing, e.g. hot isostatic pressing, result in decreased frequency and size of defects, the weakest link depends on microstructural characteristics, e.g. secondary dendrite arm spacing (SDAS), Si eutectic morphology and α-Al solid solution hardness. Hereby, fatigue investigations of the effect of the microstructure characteristics on the cyclic stress-strain behaviour as well as fatigue mechanisms in the low cycle and high cycle fatigue regime are performed. For this purpose, samples of the aluminium cast alloy EN AC-AlSi7Mg0.3 with different Si eutectic morphology and α-Al solid solution hardness were investigated. To compare the monotonic and cyclic stress-strain curves, quasistatic tensile tests and incremental step tests were performed on two microstructure conditions. The results show that the cyclic loading leads to a hardening of the material compared to monotonic loading. Based on damage parameter Woehler curves, it is possible to predict the damage progression and fatigue life for monotonic and cyclic loading in hypo-eutectic Al-Si-Mg cast alloys by one power law.
Strain characteristics of non-ferrous metals obtained on the basic of different loads
Authors: Kurek Andrzej , Koziarska Justyna , Łagoda Tadeusz
Published: May 2018

The paper presents the comparison of the results of experimental fatigue tests for the 6082-T6 and 2017-T4 aluminium alloys. Tests performed under two types of load conditions. That is tensilecompressive and oscillatory bending. The results are obtained by applying the Basquin's stress-life equation and strain-life equations: Kandil’s equation, Langer’s equation and the authors’ own equation. On the basis of own experimental studies and the relevant physical relations, the stress and strain amplitudes occurring in bent rods under smooth specimens, were calculated according to the elastoplastic model. The results were then used to compare both types of loads with different types of control.
Thermomechanical fatigue behaviour of ferritic stainless steel grades for high temperatures applications
Authors: Prudhomme Cloé , Santacreu Pierre-Olivier , Evenepoel Isabelle , Proult Benoit
Published: May 2018

Nowadays high temperatures resistant materials are needed to resist to high temperature applications (up to 1000°C), such as automotive exhaust gas manifolds. Some developed stainless steel grades, including ferritic grades or austenitic refractory grades, can be used in this temperature range and both in continuous or cyclic thermal conditions. In order to predict the thermomechanical fatigue damage of stainless steel parts submitted to cyclic thermal loading and constrained bonding conditions, the elastoviscoplastic model by Chaboche is determined for a wide range of temperatures, of strain amplitudes and strain rate levels thanks to isothermal traction-compression tests. The validation procedure is performed afterward by comparison with stabilized behavior under non isothermal conditions on a dedicated thermal fatigue test performed on V-shape specimens. Results of simulation show very good fitting with the experimental curves which would lead to a more accurate fatigue life prediction. A damage model was derived from Taira’s thermal low-cycle fatigue model to include dwell-time period at high temperature and creep-oxidation effect. In this paper the example of K44X, a dedicated grade for high temperatures applications, is presented.
Performance of chosen multiaxial cycle counting method under non-proportional multiaxial variable loading.
Authors: Margetin Matus , Biro Dominik
Published: May 2018

One of the most crucial tasks in fatigue life-time estimation of components loaded with multiaxial variable amplitude loading is to correctly identify loading cycles that can be used with multiaxial damage criterions. During past years, several cycle counting methods have been proposed for multiaxial loading conditions. The aim of this text is the comparison of selected multiaxial cycle counting methods, namely Wang-Brown’s method, Modified Wang-Brown’s method, Bannantine-Socie’s method and then a critical analysis of the obtained results. For the comparison of chosen methods, a new data set, consisting of experimentally obtained results from multiaxial non-proportional variable amplitude loading tests carried on by authors, has been used. The tested specimens were made from S355J0 structural steel and the testing procedure has been carried out on the MTS Axial/Torsion servo hydraulic testing machine. Findley and McDiarmid multiaxial criterion with Palgren-Miner summation rule have been used for fatigue life-time estimation of the tested specimens.
Cost effective strategy using Kriging surrogates to compute fatigue at multiple locations of a structure: Application to offshore wind turbine certification
Authors: Huchet Quentin , Mattrand Cécile , Beaurepaire Pierre , Relun Nicolas , Gayton Nicolas
Published: May 2018

Offshore wind energy development has experienced a rapid development over the last few years encouraged by the of carbon reduction policy and the energy mix objectives of several countries worldwide. Nowadays, the offshore projects under investigation are composed of tens to hundreds of units reaching impressive dimensions with total rotor diameters from 150 to 220 meters and production capacity of 5 to 12 MW per turbine. Mechanical analyses have to be performed to validate the design regarding the solicitations it may face during its lifetime (20 years). Because of the high number of solicitation cycles the structure is confronted to, an estimation of the cumulated damage is mandatory and has to be carefully assessed. As presented in standards, this verification requires massive computation investments and is usually a challenging task for project engineers. This paper presents the “MultiSite” extension of the AK-DA numerical strategy (“Adaptive Kriging for Damage Assessment”). After being formalized, an illustration of its behaviour and performances is proposed for the validation of a design regarding its cumulated damages at different locations.
Design, service and testing grounds stress spectra and their using to fatigue life assessment of bus bodyworks
Authors: Kepka Miloslav , Kepka Miloslav
Published: May 2018

In the development of a road vehicle such as a bus, the input data for the assessment of the fatigue life of the body and other mechanical parts of the vehicle are gradually refined. In the initial phase of the development of a new vehicle, so-called design stress spectra are used. It is necessary to estimate the design spectrum parameters correctly. At the vehicle's prototype testing phase, the so-called service stress spectra can be evaluated. It is essential to determine the characteristic operating modes of the vehicle and to record representative stress-time histories of the critical sections of the construction nodes and vehicle components. Accelerated driving test of fatigue life can be performed on special test routes. The acceleration of such a fatigue test is dependent on the test track composition. The paper generally describes the methodology of such a process and demonstrates it using unique real-time data acquired during the development of a bus.
Fatigue Life Extension of AA2024 Specimens and Integral Structures by Laser Shock Peening
Authors: Kashaev Nikolai , Chupakhin Sergey , Ventzke Volker , Horstmann Manfred , Riekehr Stefan , Barbini Alessandro , dos Santos Jorge. F. , Keller Sören , Klusemann Benjamin , Huber Norbert
Published: May 2018

The goal of the present study is to understand the effects of laser shock peening (LSP)-induced residual stresses on the fatigue crack propagation (FCP) behaviour of the commonly used aircraft aluminium alloy AA2024 in T3 heat treatment condition. LSP treatment was performed using a pulsed Nd:YAG laser on compact tensile C(T)50-specimens with a thickness of 2.0 mm. LSP-treated specimens reveal a significant retardation of the fatigue crack propagation. The fatigue crack retardation effect can be correlated with the compressive residual stresses introduced by LSP throughout the entire specimen thickness. A possible application of the LSP process on a component like panel with three welded stringers representing a part of a fuselage structure was performed as well. The skin-stringer AA2024-AA7050 Tjoints were realised through stationary shoulder friction stir welding (SSFSW), a variant of the conventional friction stir welding process. In this relatively new process, the shoulder does not rotate and therefore does not contribute to the heat generation. Consequently, a reduced and more homogeneous heat input leads to a less affected microstructure and better mechanical properties. The efficiency of the LSP process has been demonstrated resulting in an increase of 200 – 400% in fatigue lifetime.
Influence of surface residual stresses on the fatigue life and crack propagation behavior of turned Inconel 718 super-alloy
Authors: Javadi Hamid , Jomaa Walid , Dalgaard Elvi , Brochu Myriam , Bocher Philippe
Published: May 2018

The effects of surface roughness parameters and residual stresses induced by finish turning on fatigue life and crack propagation behavior of Inconel 718 super-alloy are investigated. A criterion serving as a good indicator of surface quality is also discovered. This is carried out for some specific turning conditions in order to control surface characteristics including surface roughness and the bi-axial state of surface residual stresses and to investigate the effects of these characteristics on fatigue behavior. Rotating bending fatigue (RBF) tests are performed on the machined specimens at room temperature. Characterization techniques including X-ray diffraction (XRD), laser confocal microscopy, and opto-digital microscopy are used to investigate surface residual stresses in axial (ARS) and hoop (HRS) directions, surface roughness, and secondary fatigue cracks, respectively. The huge dispersion in fatigue life of smooth turned Inconel 718 with very low arithmetic average roughness (Ra) values indicates that surface finishing is not the only reliable criterion for quality control of machined components. Multivariate statistical analyses show that axial surface residual stress is the most important surface characteristic affecting the fatigue life of machined Inconel 718 for the conditions tested. Changing ARS from compressive to tensile increases the number of secondary cracks and also decreases the fatigue life of turned specimens.
Predictive Modeling of Arbitrary Loaded TMF Crack Growth in Superalloys
Authors: Johnson W. Steven , Neu Richard W. , Radzicki Andrew T. , Adair Benjamin S. , Barker Vincent M.
Published: May 2018

Hot sections in turbine engines are subjected to large variations in temperatures and mechanical/thermal loadings. As such, accurate predictions of fatigue crack growth must account for many physical phenomena: temperature dependent crack growth behavior, load interaction history effects, time at temperature effects, temperature history effects, and the effects of stress/temperature/time on the materials. Through extensive experimental work on superalloys, a very definite “temperature history effect” on the resulting crack growth behavior has been identified and modeled. This work also identified a Temperature Affected Zone (TAZ) that occurs ahead of the crack tip and affects subsequent crack growth rates. The size of the TAZ is dependent on temperature, hold time, and stress state. Measurements of the TAZ were made under various conditions. The changes that occur in this TAZ are a combination of oxidation and material microstructure evolution. Various simplified “hot section” engine spectra (changing temperatures and stress levels) were tested to determine resulting crack growth behavior. Correlation between the experiments and model predictions were good
and generally conservative.
Creep crack growth assessment in terms of continuum damage mechanics
Authors: Shlyannikov Valery , Tumanov Andrey
Published: May 2018

The stress, strain rate, and process zone with respect to the creep-crack growth in compacttension C(T) specimen is analyzed by employing damage-evolution equations. The damage model for the fracture of the process zone is represented using a stress based formulation. Both damage free and defective creeping solids have been studied. The variations in the creep stress/strain and crack-tip governing parameter in terms of the creep stress intensity factors with respect to time and the evolution of creep damage are analyzed using an FE model for C(T) specimen. The creep-fatigue crack growth rate tests were performed on special designed program test-cycle. The interpretation of the experimental creep crack growth rate data was given in terms of introduced creep stress intensity factors based on undamaged and damaged stress/strain fields.
Cyclic viscoplastic deformation modeling of a nickel-based single crystal superalloy with [001] orientation
Authors: Wang Rongqiao , Zhang Bin , Hu Dianyin , Jiang Kanghe , Mao Jianxing , Jing Fulei
Published: May 2018

Accurate simulations of cyclic viscoplastic deformation behaviors of single crystal superalloys which are widely used for the manufacture of gas turbine blades are important for the effective design and safety assessment in practice. In this context, based on the in-phase thermomechanical fatigue (IP TMF) and out-of-phase thermomechanical fatigue (OP TMF) experiments of the nickel-based single crystal superalloy with [001] orientation, a modified constitutive model has been developed to describe the deformation behavior under thermomechanical loadings. The TMF experiment results indicate that stable hysteresis
loops with remarkable ratcheting appear in both IP TMF and OP TMF. And it’s worth noticing that the ratcheting growth direction of IP TMF and OP TMF are opposite. By introducing a Schmid stress rate related term to the back stress evolution equation, the slip-based Walker’s constitutive model is modified in this study. And the simulation results of the deformation behavior reveal good agreement with the experiments under different IP TMF and OP TMF conditions.
High cycle thermal fatigue of austenitic stainless steel
Authors: Wang Yanjun , Charbal Ali , Hild Françis , Vincent Ludovic
Published: May 2018

A new experimental setup called FLASH (THErmal Fatigue by LASer or Helium pulses) has been developed to perform thermal fatigue tests on materials used in structures of Sodium-cooled Fast Reactors (SFRs). A set of thermal loadings ranging from 150°C to 200°C prescribed by a high energy laser has been applied to A316L(N) stainless steel samples. Thermal fatigue tests are performed until a macrocrack is formed. The 3D displacement fields of the surface impacted by the laser beam are measured by a hybrid multiview system. A thermomechanical model is used to compute displacement fields that are compared with correlation measurements. These results are compared in terms of strain levels to the fatigue curve determined from standardized isothermal uniaxial mechanical fatigue tests.
The influence of tension mean stress to the crack initiation process at the very high cycle fatigue regime for a high strength steel
Authors: Rohm Thomas , Lang Karl-Heinz , Korn Marcus
Published: May 2018

Strain controlled tests were performed on a high strength steel to investigate the influence of tension mean stress to the crack initiation process at the very high cycle fatigue regime. It is supposed that the variation of stress the state in the vicinity of a non-metallic inclusion results in a change to the energy transferred to the surrounding metallic matrix. To prove this, incremental step tests on cylindrical specimen were realized in which the tension mean stress was stepwise increased. It could be verified that the hysteresis area, which is a criterion of the work transferred to the specimen, decreases with increasing tension mean stress. The test results provide a reasonable physical model to estimate the influence of tension mean stress to the crack initiation process in the very high cycle fatigue regime.
The influential factors on very high cycle fatigue testing results
Authors: Wen-jie PENG , Huan XUE , rui GE , zhou PENG
Published: May 2018

When the fatigue cycle is extended from high cycle (105~107) to very high cycle (107~109), the fatigue testing results will be more sensitive to the influential factors such as specimen size, specimen surface roughness and the inclusion size. The influential factors on the very high cycle fatigue testing results are investigated in the present paper. Firstly, the design and control method for ultrasonic fatigue test were introduced for several specimen shapes. The effect of the shape, size and the surface roughness of specimen on the ultrasonic fatigue test results are investigated. Meanwhile, the effect of test frequency and the size of the inclusion on the fatigue test results are also investigated. It is concluded that: 1. the test results of specimen with different shape and size differ with each other, due to the risk volume is different. 2. There is a critical roughness for the specimen, depending on the hardness of tested metallic material. A larger roughness than the critical one will lead to a premature fracture. 3. The frequency effect is obvious for the low strength steel, however, is prone to vanish for the very high strength steel. 4. The very high cycle fatigue will be more sensitive to the inclusion size as the strength increases and the S/N curve character is strongly related to the size of the inclusion.
Changing in Fatigue Life of 300 M Bainitic Steel After Laser Carburizing and Plasma Nitriding
Authors: Abdalla Antonio J. , Santos Douglas , Vasconcelos Getúlio , Baggio-Scheid Vladimir H. , Silva Deivid F.
Published: May 2018

In this work 300M steel samples is used. This high-strength steel is used in aeronautic and aerospace industry and other structural applications. Initially the 300 M steel sample was submitted to a heat treatment to obtain a bainític structure. It was heated at 850 °C for 30 minutes and after that, cooled at 300 °C for 60 minutes. Afterwards two types of surface treatments have been employed: (a) using low-power laser CO2 (125 W) for introducing carbon into the surface and (b) plasma nitriding at a temperature of 500° C for 3 hours. After surface treatment, the metallographic preparation was carried out and the observations with optical and electronic microscopy have been made. The analysis of the coating showed an increase in the hardness of layer formed on the surface, mainly, among the nitriding layers. The mechanical properties were analyzed using tensile and fatigue tests. The results showed that the mechanical properties in tensile tests were strongly affected by the bainitic microstructure. The steel that received the nitriding surface by plasma treatment showed better fatigue behavior. The results are very promising because the layer formed on steel surface, in addition to improving the fatigue life, still improves protection against corrosion and wear.
Notch effect of welded joint
Authors: Chmelko Vladimír , Margetin Matúš , Harakal’ Michal
Published: May 2018

In general, the welded joints are multifactorial notches. This study is focused to separate the geometrical influence (when the weld can be seen on the surface) and technological factors (internal defects of the weld, structural changes of the material and residual stress) on its fatigue life. Proposed methodology of this separation comes out from the cyclic test of three specimens – group with existing weld, group without weld joint (base material) and another group where was removed outer geometry of the weld.
A numerical analysis to investigate the spot weld local influence
Authors: Mainnemare Florian , Delattre Benoit , Raoult Ida , Villars Olivier , Boucard Pierre-Alain , Guidault Pierre-Alain
Published: May 2018

Relations between existing spot-weld finite element models and the mechanical behaviour of spot-weld are investigated for fatigue design application. Specifically, the different zones that constitute the numerical model are interrogated with respect to physical observation. In order to identify the Mechanical Influence Area of the Spot-Weld here designated as “MIASW” we propose a methodology to determine numerically its size. Hence, we develop a finite element coupon representing a spot-weld under a basis of four unit load cases. The coupon provides mechanical quantities of interest that allows us to characterize the spot-weld response that shell element are unable to represent. This response is crucial to be captured for further fatigue analysis.
Seam weld shell element model for thin walled structure FE fatigue design
Authors: Turlier D. , Facchinetti M.L. , Wolf S. , Raoult I. , Delattre B. , Magnin A. , Grimonprez N.
Published: May 2018

In automotive industry, the FE fatigue analysis of mechanical structures made of steel thin walled parts and seam welded assemblies uses a dedicated technique based on shell element modelling for components and on 1D rigid elements for welds. This method has been validated with several intensive fatigue test campaigns using gas metal arc welded samples with different assemblies, for both bending and torsional loads. The fatigue results are relative to crack initiation at the weld toe with bending normal stress or with longitudinal shear stress for several load ratios. The purpose of the current work is the transposition of the initial method to another FE welded model. In a recent IIW guideline for the assessment of weld root fatigue, a shell element weld model has been proposed for seam weld fatigue assessment in case of weld root crack initiation. The idea is to analyse the possible extension of this FEA weld element model for weld toe fatigue analysis and several comparisons of stress results are detailed and discussed. Different fatigue criteria are used to verify the correlation with the fatigue test results. First, the approach is based on maximum shear stress, then structural stress is calculated and results are compared to IIW S/N curves.
Undercut tolerances in industry from a fracture mechanic perspective
Authors: Steimbreger Ceferino , Chapetti Mirco
Published: May 2018

Fatigue is an important damage mechanism that particularly affects welded components, since they are likely to present residual stresses, inhomogeneities and stress raisers. Assessment of cyclic load effects on welds has concerned both industries and scientist for decades; unexpected failure must be prevented and at the same time, structures must withstand design loads with minimum requirements of material. All these facts together with economic issues have lead to the creation of normative that rule designing and construction of welded components. Particularly, toe undercuts are generally found in large structures, and large scatter and disagreement exists towards their significance and effects. Documents usually limit only their depth without considering radius, width or length, and there is currently no explanation to that fact. Understanding the damaging process will also help to set less conservative tolerances, with consequent cost reduction due to less demanding inspection. The present paper deals with a fracture mechanic approach that uses the Resistance Curve concept to predict fatigue limit of welded components with undercuts. Results revealed that depth is the most influencing variable, and it can be used as the limiting parameter in design regulations. Moreover, good correlation was obtained with FAT values normally assigned to this kind of defect.
Failure Assessment Diagram (FAD) analysis of fatigue test results for X65 welded joints
Authors: Jen Hoh Hsin , Pang John Hock Lye , Tsang Kin Shun
Published: May 2018

Offshore pipelines transfer oil and gas from seabed to production facility on the surface. The long pipelines are formed by welding of pipe segments, where these welded joints are a source of stress concentration and defects from which fatigue cracks can grow. This work aims to study the behaviour of deep fatigue cracks. In this current work, finite-element based on a parametric study of four-point bending is used to assess the stress intensity factors (SIFs) of deep surface cracks in X65 specimens, while considering local limit load the remaining load bearing ligament. These deep cracks take on a non-regular shape and have widths that exceed that of the specimen. They will be compared to empirical expressions from derived standards such as British Standards BS7910, which may be more conservative. The existing large flaw is also assessed via the failure assessment diagram (FAD). The effects of limit load solutions and reference stresses used to determine the FAD diagram will be discussed.
Low-cycle fatigue behavior of extruded Al-7Zn-2Mg-1.5Cu-0.2Sc-0.1Zr alloy at room and low temperatures
Authors: Qingyan Zhu , Lijia Chen , Chengji Xu , Xin Che , Feng Li
Published: May 2018

Due to the low density and high specific strength, aluminum alloys have been considered for automotive and aerospace applications. The aluminum components usually service in the conditions of low temperature and dynamic loading. Therefore, the research on the low temperature fatigue performances of Al alloys has great significance. The lowcycle fatigue tests for the extruded Al-7Zn-2Mg-1.5Cu-0.2Sc-0.1Zr alloy subjected to solution plus aging treatment have been conducted at 25°C and -40°C, respectively. The strain ratio and cyclic frequency applied in the low-cycle fatigue test were -1 and 0.5Hz, respectively. The experimental results show that at 25°C, the alloy exhibits the cyclic hardening at the total strain amplitudes of 1.0% and 1.2%, and the cyclic stabilization at the total strain amplitudes of 0.4%, 0.6% and 0.8%. At -40°C, however, the cyclic stability is observed during whole fatigue deformation at the total strain amplitudes of 0.4%, 0.5%, 0.6%, 0.7% and 0.8%. The relationship between the elastic strain amplitude, plastic strain amplitude and reversals to failure can be described by Basquin and Coffin-Manson equations, respectively. In addition, the observation results of fatigue fracture surfaces reveal that the cracks initiate at the free surface of fatigue specimen and propagate in a transgranular mode.
Effects of Elevated Temperatures on Mechanical’s concrete specimen behaviour
Authors: Khodja Nesrine , Hadjab Hadda
Published: May 2018

This paper presents an experimental study on the performance of concrete, subjected to high temperatures. Investigation was carried out by using two mixtures: an Ordinary Concrete (OC) and High Performance Concrete (HPC) with 10% of Silica Fume (SF) replaced of cement weight and 1,5% of super plasticizer, the water-binder (w/b) ratio used was 0,5 and 0,32 respectively. The produced concrete specimens are heated at a rate of 7 °C/min up to different temperatures (150, 300, 450, 600 and 900°C). In order to ensure a uniform temperature through the specimen, the temperature is held constant at the temperature stage for one hour before cooling. Mechanical properties at ambient temperature and residual mechanical properties after heating have already been determined. We examined also the effect of high temperature on the aggregate-cement paste interface and aggregate microstructure of the concrete specimens by scanning electron microscopy (SEM) method to reveal changes occurred after the cycle of heatingcooling. The results revealed that relative strength of the concrete specimens decreased as the exposure temperature increased and reaches about a quarter of its initial strength at 900°C. Moreover SEM examinations showed that, increasing temperature caused weakening of the adherence of aggregate and cement matrix by the appearance of cracks and micro cracks.
Design Optimization and Fatigue Analysis for Seal Joint of Control Rod Drive Mechanism
Authors: Xuejiao Shao , Dujuan
Published: May 2018

Two kinds of seal joint thickness of control rod drive mechanism seal house were analyzed on stress and fatigue by using finite element method, and it provides analytical basis for equipment optimization, design manufacturing and problem handing. In the fatigue computing, all the transients were grouped into several groups, so as to separate the transients not at the same stage obviously. Meanwhile, the transients can be respectively combined in every group to reduce the redundant conservatism of computation. The elastoplastic strain correction factor was modified by analyzing thermal and mechanical load separately referring the rules of RCC-M 2002.By comparing the stress of two thickness joints, the results are found that the fatigue results of the thinner thickness are safer, but this is contrary to the rule of other results. The fatigue usage factor can be reduced by using modified elastoplastic strain correction factor when the amplify of the primary and secondary stress is large produced by both thermal load and mechanical load.
20 kHz 3-point bending fatigue of automotive steels
Authors: Sadek Mohamed , Bergström Jens , Hallbäck Nils , Burman Christer
Published: May 2018

The 20 kHz load frequency enables fatigue tests for very high cycle fatigue life, 109-1013 cycles, within conveniently short time. In automotive applications, many components are subjected to flexural loading and hence bending fatigue is an important test mode. Ultrasound fatigue test instruments have been used successfully in several assessments of fatigue strength and more commonly in uniaxial loading. Here, a 3-point bending fatigue test rig operating in resonance at 20 kHz load frequency has been designed to test plane specimens at R=0.1 loading. The test rig design and stress calculations are presented. Testing for fatigue strength was conducted using the staircase method with 15 specimens of each steel grade, specimens reaching 108 cycles were considered run-outs giving fatigue strength at 108 cycles. Additional 15 specimens of each grade were tested for S-N curves with the upper limit above 109 cycles. Two different common automotive steels, 38MnSiV5, a micro-alloyed ferritic-pearlitic steel, and 16MnCr5, a carburizing martensitic steel, were tested. The fatigue strengths achieved from the staircase testing are 340 and 419 MPa stress amplitudes for the 38MnSiV5 and 16MnCr5 steels, respectively. The S-N curves of the steels appear to be quite flat in the tested life range 107 – 109.
Fatigue Tests – Important Part of Development of New Vehicles
Authors: Kepka Miloslav , Kepka Miloslav , Zlabek Pavel , Heller Petr , Chvojan Jan , Mentl Vaclav
Published: May 2018

In city of Pilsen (Czech Republic) modern transport engineering is developed. The Skoda Transportation (production company) has successfully been producing rail and road vehicles for many years (electric locomotives, trams, metro cars, trolleybuses, battery buses). This producer cooperates in developing these vehicles with the Research and Testing Institute (commercial research institute) and with the University of West Bohemia (public university). Fatigue tests are carried out by the Dynamic Testing Laboratory at the Research and Testing Institute and by the Regional Technological Institute, the research center of the Faculty of Mechanical Engineering at the university. The paper describes various fatigue tests and presents their practical realization in the mentioned laboratories.
Influence of Weld Toe Radii on Fatigue Life Prediction
Authors: Tsang Kin Shun , Pang John H. L. , Hoh Hsin Jen
Published: May 2018

A study was carried out to investigate the influence of the weld toe radii on the fatigue strength of butt welded joints loaded in bending and tension. Fatigue analysis starting from weld toe cracks in marine and offshore welded pipe specimens were conducted using cut-out four-point bend fatigue test specimens. Fatigue life can be enhanced by reducing the local stress concentration generated by weld toe radius effects. This study investigated the effect of different weld toe radii on the stress intensity factor at the region of the weld toe through Finite Element Analysis (FEA). FEA was used to model a butt welded steel plate extracted from a pipe subject to tension and four-point bend loading. Semi-elliptical surface (SESC) cracks were modeled at the weld toe region with different SESC crack depth and surface crack length. Four weld toe radii and two modes of loading were investigated. The stress intensity factors, weald toe magnification factors, or Mkc and Mka are reported and used for fatigue life prediction.
Big data analytics - towards the enrichment of content tourism for revitalization of Japanese rural area
Authors: Bakdur Ali , Masui Fumito , Ptaszynski Michal
Published: May 2018

Japan's domestic travel and tourism industry expenditure has been declining gradually since 1998 (from 33.5 in 1998 to 21.6 trillion JPY in 2016). Our research purpose is to construct a data analysis model to transform the collected data to a meaningful graphical format by using big data analytics techniques to discover anomalies and sustainable development possibilities for economy and tourism of Japan's rural areas, with a particular focus on the prefecture of Hokkaido, subprefecture of Okhotsk. To strengthen the reliability of this model we apply popular Monte Carlo simulation combined with Bayesian statistic and implement it on an Apache Spark platform to acquire results within the span of the study. Through this research, we focus on observing and analyzing interests, expectations and tendencies of Japanese people living in rural areas. From such collected information, we can obtain reasons for the decline of this sector’s impact on Japan’s economy. Measuring public awareness has become more efficient since the content generator role has been passed on to ordinary people. Therefore, the analysis of Big Data with the use of data science techniques has become important to comprehend human behavior from multiple points of view, including the scientific, economic, political, historical and sociological.
Thermal analysis on potential risk of cosmetic materials by DSC
Authors: Chen Yi-Feng , Huang An-Chi , Huang Chung-Fu , Shu Chi-Min
Published: May 2018

To explore the potential risk of usage on daily chemicals, the product which most contact for human directly, cosmetics, were selected as study object. In this study, common cosmetic materials, such as propylene glycol, ethanolamine, silicon dioxide, iron oxide, and copper oxide were discussed for potential hazard. According to results of differential scanning calorimetry experiments, the apparent activation energy and SADT were calculated out as 779.22 kJ mol-1 and 45°C, respectively.
New design of grab mechanism in plastic glove machine
Authors: Hsu Wei-Chun , Jiang Ming-Jin , Liu Gui-Liang
Published: May 2018

The aim of this study is to design a new type of grab mechanism for plastic bags machine in order to tear apart the plastic gloves from the plastic bags and stack them into a pile automatically. A grab mechanism with four bar linkage is developed and the main part of the grab mechanism is the clip which will pick up the plastic gloves and drag them to the other side. After a distance of drag, the clip will drop the plastic gloves to the collecting plate. The clips are fixed on the connecting rod of the four-bar linkage and the path of the clip can be traced by the position analysis of the four bar linkage. The path of the clip can be tracked by determination of the four links’ lengths. This path tracking will be one of the advantages of this new mechanism because it provides the different drag distance to grab difference size of plastic gloves by simply adjusting the lengths of four links.