bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of mucins in lung homeostasis: regulated expression and biosynthesis in health and disease
Authors: Symmes Breanna A. , Stefanski Adrianne L. , Magin Chelsea M. , Evans Christopher M.
Published: May 2018

In humans and mice, the first line of innate defense against inhaled pathogens and particles in the respiratory tract is airway mucus. The primary solid components of the mucus layer are the mucins MUC5AC and MUC5B, polymeric glycoproteins whose changes in abundance and structure can dramatically affect airway defense. Accordingly, MUC5AC/Muc5ac and MUC5B/Muc5b are tightly regulated at a transcriptional level by tissue-specific transcription factors in homeostasis and in response to injurious and inflammatory triggers. In addition to modulated levels of mucin gene transcription, translational and post-translational biosynthetic processes also exert significant influence upon mucin function. Mucins are massive macromolecules with numerous functional domains that contribute to their structural composition and biophysical properties. Single MUC5AC and MUC5B apoproteins have molecular masses of >400 kDa, and von Willebrand factor D-like as well as other cysteine-rich domain segments contribute to mucin polymerization and flexibility, thus increasing apoprotein length and complexity. Additional domains serve as sites for O-glycosylation, which increase further mucin mass several-fold. Glycosylation is a defining process for mucins that is specific with respect to additions of glycans to mucin apoprotein backbones, and glycan additions influence the physical properties of the mucins via structural modifications as well as charge interactions. Ultimately, through their tight regulation and complex assembly, airway mucins follow the biological rule of ‘form fits function’ in that their structural organization influences their role in lung homeostatic mechanisms.
Neuroprotection via AT2 receptor agonists in ischemic stroke
Authors: Bennion Douglas M. , Steckelings U. Muscha , Sumners Colin
Published: May 2018

Stroke is a devastating disease that afflicts millions of people each year worldwide. Ischemic stroke, which accounts for ~88% of cases, occurs when blood supply to the brain is decreased, often because of thromboembolism or atherosclerotic occlusion. This deprives the brain of oxygen and nutrients, causing immediate, irreversible necrosis within the core of the ischemic area, but more delayed and potentially reversible neuronal damage in the surrounding brain tissue, the penumbra. The only currently approved therapies for ischemic stroke, the thrombolytic agent recombinant tissue plasminogen activator (rtPA) and the endovascular clot retrieval/destruction processes, are aimed at restoring blood flow to the infarcted area, but are only available for a minority of patients and are not able in most cases to completely restore neurological deficits. Consequently, there remains a need for agents that will protect neurones against death following ischemic stroke. Here, we evaluate angiotensin II (Ang II) type 2 (AT2) receptor agonists as a possible therapeutic target for this disease. We first provide an overview of stroke epidemiology, pathophysiology, and currently approved therapies. We next review the large amount of preclinical evidence, accumulated over the past decade and a half, which indicates that AT2 receptor agonists exert significant neuroprotective effects in various animal models, and discuss the potential mechanisms involved. Finally, after discussing the challenges of delivering blood–brain barrier (BBB) impermeable AT2 receptor agonists to the infarcted areas of the brain, we summarize the evidence for and against the development of these agents as a promising therapeutic strategy for ischemic stroke.
Leflunomide counter

akt

s cardiac hypertrophy
Authors: Pescatore Luciana A. , Laurindo Francisco R.M.
Published: May 2018

Cardiac hypertrophy (CH) is a major independent risk factor for heart failure and mortality. However, therapeutic interventions that target hypertrophy signaling in a load-independent way are unavailable. In a recent issue of Clinical Science (vol. 132, issue 6, 685-699), Ma et al. describe that the anti-inflammatory drug leflunomide markedly antagonized CH, dysfunction, and fibrosis induced by aortic banding or angiotensin-II in mice or by agonists in cultured cells. Unexpectedly, this occurred not via anti-inflammatory mechanisms but rather via inhibtion of Akt (protein kinase B, PKB) signaling. We further discuss the mechanisms underlying Akt activation and its effects on CH and review possible mechanisms of leflunomide effects. Despite some caveats, the availability of such a newly repurposed compound to treat CH can be a relevant advance.
Design and analysis of a new HTS modular flux‐switching linear machine for rail transit
Authors: Li Xianglin , Wang Xiaoyang , Wang Yubin , Ma Wenzhong
Published: May 2018

This study proposes a new high‐temperature superconductor (HTS) modular flux‐switching linear machine for rail transit, in which the armature windings and HTS field windings are placed on the short mover, while the long stator is only made of segmented low‐cost iron. The key is to adopt a modular mover consisting of three separate phase modules whose positions are mutually 120° electrical degrees apart to greatly offset the cogging force for suppressing the thrust force ripple, accompanied with the features of high‐fault tolerance. Also, the HTS excitation can produce stronger magnetic field than permanent magnet excitation to obtain a high force density; meanwhile, it easily regulates the air‐gap flux density for achieving flexible high‐speed constant‐power operation. The operation principle and general design method of the proposed machine with concerning the HTS‐excitation pattern are described in details. By using the finite element analysis, the machine performances are comparatively analysed with its counterpart without using modular mover to verify its validity. The results show that the proposed machine can offer more sinusoidal back electromotive force, better fault tolerance, higher thrust force and smaller force ripple.
Digital compensation of the sideband-rejection ratio in a fully analog 2SB sub-millimeter receiver
Authors: Rodriguez R. , Finger R. , Mena F. P. , Alvear A. , Fuentes R. , Khudchenko A. , Hesper R. , Baryshev A. M. , Reyes N. , Bronfman L.
Published: May 2018

Context. In observational radio astronomy, sideband-separating receivers are preferred, particularly under high atmospheric noise, which is usually the case in the sub-millimeter range. However, obtaining a good rejection ratio between the two sidebands is difficult since, unavoidably, imbalances in the different analog components appear.

Aims. We describe a method to correct these imbalances without making any change in the analog part of the sideband-separating receiver, specifically, keeping the intermediate-frequency (IF) hybrid in place. This opens the possibility of implementing the method in any existing receiver.

Methods. (i) We have built hardware to demonstrate the validity of the method and tested it on a fully analog receiver operating between 600 and 720 GHz. (ii) We have tested the stability of calibration and performance versus time and after full resets of the receiver. (iii) We have performed an error analysis to compare the digital compensation in two configurations of analog receivers, with and without intermediate-frequency hybrid.

Results. (i) An average compensated sideband-rejection ratio of 46 dB is obtained. (ii) Degradation of the compensated sideband rejection ratio on time and after several resets of the receiver is minimal. (iii) A receiver with an IF hybrid is more robust to systematic errors. Moreover, we have shown that the intrinsic random errors in calibration have the same impact for configuration without IF hybrid and for a configuration with IF hybrid with analog rejection ratio better than 10 dB.

Conclusions. We demonstrate that compensated rejection ratios above 40 dB are obtained even in the presence of high analog rejection. Further, we demonstrate that the method is robust allowing its use under normal operational conditions at any telescope. We also demonstrate that a full analog receiver is more robust against systematic errors. Finally, the error bars associated with the compensated rejection ratio are almost independent of whether IF hybrid is present or not.
Functioning of the Primary Aquifer Relating to the Maider Basin, Morocco: Case of the Ordovician aquifer.
Authors: Ben-said E. , Boukdir A. , Mahboub A. , Younsi A. , Zitouni A. , Alili L. , Ikhmerdi H.
Published: May 2018

The basin of Maider is limited northly by the vast ensemble Oriental Saghro-Ougnate, from the east by the Tafilalet plain, from the west by the oriental Jbel Bani, finally from the south and south-east by the Cretaceous Hamada of Kern-Kem. During last decades, groundwater in the basin of Maider, is confronting degradation in both cases: Quantitative and qualitative, as a result of the drought, the overexploitation and the salinization. The aim of this action research is to understand the current state of water resources in the area of stady. At the end of this work, we can get the following conclusions: the general flow of the ordovician aquifer is always directed from the north to the south-east of the basin by following the principal axes of the wadis:Taghbalt, Hssiya and Fezzou. The recharge of the aquifer is primarily done, either by the underground flow, or by the surface runoff of torrential waters from the upstream of Jbel Saghro. The piezometric anomaly noticed at the level of Ait Saàdane, explained by overexploitation linked to the needs of irrigation water. The physicochemical approach for the Maider basin identifies two essential factors of the salinisation of groundwater: the dissolution of the aquifer which is rich in minerals with high temperature on the one hand, and the decrease of the piezometric surface due to the overexploitation and drought on the other hand.
Assessment of the effects rejections of feed fish on water resources.: (Ouedoumerrbia, Morocco)
Authors: Ouaissa Khadija , Kritihi Assia , Oumessoud Youness , Maychal Abdelaziz , Hasnaoui Mustapha
Published: May 2018

In order to compare the effects of three types of extruded food (A, B and C) on the growth of rainbow trout, an experimental test was conducted on June 15, 2015 at a rainbow trout farming station near river of Oumerrrabi .Morocco.

The comparison of three foods of different composition and energy is performed in isoenergetic conditions.

Six basins were used for this comparative test. These basins are fed with fresh water according to the open circuit with a renewal of twice an hour. The initial feeding conditions were the same for the three food types and the initial density of 1, 58 kg/m3(kg by volume) and an initial flow rate of 1, 04 m3/h.

Fish are fed by ratios two to three times a day depending on the magnification stage.

The sampling frequency is fortnightly, where we measure the zootechnical performance of fish and collect water samples for physicochemical analyses in order to assess the quality of the water leaving in the basins before their discharge into the river of Oum Er-Rbia.

The comparative trial of three fish foods (A, B, and C) revealed that diet B is the better formulation reflected by the zootechnical performances and low phosphate release than diet A and C.
Public services for distribution of drinking water and liquid sanitation in urban zones in Morocco Relevance of introduction the performance indicators for preservation water resources.
Authors: Habib AKKA , Abdelhamid BOUZIDI , Said HOUSNI
Published: May 2018

Because of the absence of regulations and specific national norms, the unilaterally applied indicators for performance evaluation of water distribution management services are insufficient. This does not pave the way for a clear visibility of water resources. The indicators are also so heterogeneous that they are not in equilibrium with the applied management patterns. In fact:

1- The performance (yield and Linear loss index) of drinking water networks presents a discrepancy between operators and lack of homogeneity in terms of parameters put in its equation. Hence, It these indicators lose efficiency and reliability;

2- Liquid sanitation service has to go beyond the quantitative evaluation target in order to consider the qualitative aspects of water.

To reach this aim, a reasonable enlargement of performance indicators is of paramount importance in order to better manage water resource which is becoming scarce and insufficient.
Adsorption of an anionic dye on a novel low-cost mesoporous adsorbent: kinetic, thermodynamic and isotherm studies
Authors: Msaad Asmaa , Belbahloul Mounir , Zouhri Abdeljalil
Published: May 2018

Our activated carbon was prepared successfully using phosphoric acid as an activated agent. The activated carbon was characterized by Scanning Electron Micrograph (SEM), Brunauer-Emmett- Teller (BET), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The aim of our study is to evaluate the adsorption capacity of Methyl Orange (MO) on Ziziphus lotus activated carbon. Adsorption isotherms were studied according to Langmuir and Freundlich Model, and adsorption kinetics according to pseudo-first and second-order. Results show that the maximum adsorption was reached in the first 10min at ambient temperature with a yield of 96.31%. The Langmuir isotherm shows a correlation coefficient of 99.4 % higher than Freundlich model and the adsorption kinetic model follow a pseudo-second-order with a maximum adsorption capacity of 769.23 mg/g. FTIR and X-Ray spectroscopy indicate that our activated carbon has an amorphous structure with the presence of functional groups, where BET analysis revealed a high surface area of 553 mg/g, which facilitate the adsorption process
Assessment of leachates from uncontrolled landfill: Tangier case study
Authors: Elmaghnougi I. , Afilal Tribak A. , Maatouk M.
Published: May 2018

Landfill site of Tangier City is non-engineered low lying open dump. It has neither bottom liner nor leachate collection and treatment system. Therefore, all the leachate generated finds its paths into the surrounding environment Leachate samples of landfill site were collected and analyzed to estimate its pollution potential. The analyzed samples contained a high concentration of organic and inorganic compounds, beyond the permissible limits.
From the promotion of biodiversity to the Recovery of organic waste
Authors: Jammoukh Mustapha , Mansouri Khalifa , Salhi Bachir
Published: May 2018

This article presents an empirical research to classify a new renewable resource material, as opposed to eco-composites, it has been neglected by the materials specialist. This classification is based on the typology of elastic behavior demonstrated by tensile tests. In addition, some identifying criterions of the usefulness of this material were examined. To justify the relevance of this classification, curves from the extension of tests focusing on the virgin material, illustrate significant results of the review. Obtained from waste, having a significant recycling possibilities and potential from renewable resources, bio-mechanically characterized loads will be injected into polymeric materials of different categories. All in the perspective of promoting changes in thermomechanical properties, whether static or dynamic; such as resistance to corrosion, heat, wear… They result in functional changes such as security, relief, coatings and stability…
Analysis of environmental impacts of renewable energy on the Moroccan electricity sector: A System Dynamics approach
Authors: Chentouf M. , Allouch M.
Published: May 2018

Producing electricity at an affordable price while taking into account environmental concerns has become a major challenge in Morocco. Moreover, the technical and financial issues related to renewable electricity plants are still hindering their efficient integration in the country. In fact, the energy sector (both electricity and heat) accounted for more than half of all Greenhouse Gases (GHG) emissions in the kingdom due to the major reliance on fossil fuels for answering the growing local demand. The key strategies to alleviate this critical situation include the integration of more renewable energies in the total energy mix and the enhancement of energy efficiency measures in different sectors. This paper strives to (1) evaluate the potential of carbon dioxide mitigation in Moroccan electricity sector following the actual and projected strategies and (2) highlight the policy schemes to be taken in order to achieve the ambitious carbon dioxide mitigation targets in the mid-term. A system dynamics model was built in order to simulate different scenarios of carbon dioxide mitigation policies up to 2030. The results shows that the achievement of renewable energies projects by 2030 could save 228.143 MtCO2 between 2020 and 2030 and an additional 18.127 MtCO2 could be avoided in the same period by enhancing energy efficiency measures.
Contribution of gravity data and Sentinel-1 image for structural mapping. Case of Beni Mellal Atlas and Beni Moussa plain (Morocco).
Authors: Boutirame Ikram , Boukdir Ahmed , Akhssas Ahmed , Boutirame Fatima , Manar Ahmed , Aghzzaf Brahim
Published: May 2018

The present work is a combined study of gravity and Sentine-1 data for fracture mapping in the karstic massif of Beni Mellal Atlas and the adjacent plain of Beni Moussa. In order to locate the various faults that contribute to the study area structuring, the gravimetric contacts analysis method, based on the joint use of the horizontal gradient and the upward continuation at different altitudes, has been applied to the gravity data. To optimize the structural mapping in the study area, the gravimetric lineaments obtained were completed and correlated with the lineaments got from Sentinel-1 image. Four faults families of NE-SW; E-O; N-S and NWSE directions have been highlighted. There fault families are perfectly combined with the studied area’s surface water network, moreover, they corroborate with the previous geological and structural studies.
Solar system design for water pumping
Authors: Abdelkader Hadidi , Mohammed Yaichi
Published: May 2018

In our days, it seems to us that nobody can suspect it on the importance of water and energy for the human needs. With technological advances, the energy need does not cease increasing. This problem of energy is even more sensitive in the isolated sites where the use of the traditional resources proves often very expensive. Indeed, several constraints, like the transport of fuel and the routine maintenances of the diesel engines, return the search for an essential alternative energy source for this type of sites. It summer necessary to seek other resources of energy of replacement. Renewable energies, like photovoltaic energy, wind or hydraulic, represent a replacement solution par excellence and they are used more and more in our days more especially as the national territory has one of the solar layers highest with the world. The duration of insolation can reach the 3900 hours/year on the Sahara. The energy acquired daily on a horizontal surface of 1m2 is about 5kWh, that is to say meadows of 2263kWh/m2/year in the south of the country. The photovoltaic energy utilization for pumping of water is well adapted for more the share of the arid and semi-arid areas because of the existence in these areas of an underground hydraulic potential not very major. Another very important coincidence supports the use of this type of energy for the water pumping is that the demand for water, especially in agriculture, reached its maximum in hot weather and dryness where it is precisely the moment when one has access to the maximum of solar energy. The goal to see an outline on the general composition of a photovoltaic system of pumping, as well as the theoretical elements making it possible to dimension the current pumping stations.
Modeling and simulation of the shading effect on the performance of a photovoltaic module in the presence of the bypass diode.
Authors: Zebiri Mohamed , Mediouni Mohamed , Idadoub Hicham
Published: May 2018

In photovoltaic renewable energy production systems where production is dependent on weather conditions, maintaining production at a suitable level is more than essential. The shading effect in photovoltaic panels affects the production of electrical energy by reducing it or even causing the destruction of some or all of the panels. To circumvent this problem, among the solutions proposed in the literature we find the use of by-pass diode and anti-return diode to minimize these consequences.In this paper we present a simulation under Matlab-Simulink of the shading effect and we compare the current voltages characteristics (I-V) and power voltage (P-V) of a photovoltaic system for different irradiations in the presence and absence of diode by -pass. For modeling, we will use the diode model and the Lambert W-function to solve the implicit equation of the output current. This method allows you to analyze the performance of a panel at different shading levels.
Application of the small punch test to determine the fatigue properties of additive manufactured aerospace alloys
Authors: Lancaster Robert , Illsley Henry , Jeffs Spencer , Hurst Roger , Baxter Gavin
Published: May 2018

Additive layer manufacturing (ALM) processes are becoming increasingly prevalent in the aerospace industry as design engineers look to profit from the numerous advantages that these advanced techniques can offer. However, given the safety critical nature and arduous operating conditions to which these components will be exposed to whilst in service, it is essential that the mechanical properties of such structures are fully understood. Transient microstructures are a typical characteristic of ALM components and resulting from the thermal cycles that occur during the build operation. Those microstructures make any mechanical assessment an involved procedure when assessing the process variables for any given parameter set. A useful mechanical test technique is small-scale testing, in particular, the small punch (SP) test. SP testing is capable of localised sampling of a larger scale component and presents an attractive option to mechanically assess complex parts with representative geometries, that would not be possible using more conventional uniaxial test approaches. This paper will present the recent development of a small-scale testing methodology capable of inducing fatigue damage and a series of novel tests performed on different variants of Ti-6Al-4V.
Effect of microstructure on fatigue crack tip field of laser melting deposited Ti–5Al–5Mo–5V–1Cr–1Fe titanium alloy
Authors: Wang Kai , Bao Rui , Ren Siyuan , Liu Dong , Yan Chuliang
Published: May 2018

In this paper, experimental and simulated investigations were carried out to understand the effect of microstructure on the fatigue crack tip strain field of laser melting deposited Ti–5Al–5Mo–5V–1Cr–1Fe titanium alloy. The mechanical properties of the laser melting deposited material corresponding to different microstructure zones were measured by digital image correlation method under in-situ static stretching, and the results indicate that the direction of primary α lamellas has great influence on the mechanical property of each grain. The crack tip strain fields considering the influence of material microstructure under constant amplitude conditions were measured, and the strain field of plastic zone has significant difference. Crystal plasticity finite element simulation of the static tensile and crack tip field considering the microstructure effect had been conducted and compare with experiment results. The simulation results are in good agreement with the test results in both the static tension strain field and crack tip strain field.
The role of pores and microstructural heterogeneity on the tooth root fatigue strength of sintered spur gears
Authors: Benedetti Matteo , Fontanari Vigilio , Molinari Alberto , Valcozzena Pietro , Pahl Wolfgang
Published: May 2018

The automotive industry employs a considerable amount of sintered parts, mainly as transmission and engine components. Gears are the parts that mostly benefit, in terms of cost saving, from the near net shape P/M technology. However, the porosity along with the heterogeneous microstructure can detrimentally affect the mechanical behaviour, especially the fatigue strength. The possibility of increasing sintered density up to 90% and more, the use of high strength alloys, as well as post sintering treatments have been extensively investigated obtaining consistent increases in the fatigue strength. The present study focuses on the effects of porosity and microstructure on tooth root bending fatigue of small module spur gears. The aim is to investigate the synergistic contribution of pore morphology and microstructure heterogeneity to the initiation of fatigue cracks and to the following crack paths. High density parts produced by high strength pre-alloyed powders were studied. Part of the specimens was case-hardened to obtain a martensitic/bainitic microstructure in the surface layer. Bending fatigue tests up to a fatigue endurance of three million cycles were performed. A careful fractographic analysis was conducted. The obtained results were discussed using the fracture mechanics approach of Murakami, considering the pores as pre-existing defects, whose propagation strongly depends on the microstructural heterogeneity.
Cyclic plasticity and low cycle fatigue damage characterisation of thermally simulated X100Q heat affected zone
Authors: Devaney Ronan J. , Oesterlin Heiner , O’Donoghue Padraic E. , Leen Sean B.
Published: May 2018

This paper presents the cyclic plasticity and low cycle fatigue (LCF) damage characterisation of thermally simulated heat affected zone (HAZ) for API 5L X100Q weldments. Microstructures representative of the HAZ for two cooling rates are generated using a Gleeble thermomechanical simulator for manufacture of strain-controlled cyclic plasticity test specimens. The simulated HAZ specimens are subjected to a strain controlled test programme which examines the cyclic effects of strain-range and the tensile response at room temperature. A modified version of the Chaboche rate independent plasticity model, which accounts for early stage damage is implemented to characterise the cyclic plasticity response, including isotropic and kinematic hardening effects. The constitutive parameters are fitted to experimental data using an optimisation procedure developed within a MATLAB code. The measured response of the simulated HAZ specimens is compared to that of the X100Q parent material (PM), and the simulated HAZ is shown to share the early stage fatigue damage behaviour of the PM, but exhibits significantly a higher yield and cyclic strength.
Fatigue Crack Growth Behaviour of High Strength Ferritic Steels in High Pressure Hydrogen
Authors: Saxena Ashok , Nibur Kevin
Published: May 2018

The design of safe and low-cost, high-pressure hydrogen storage systems are a critical need for harnessing clean power but must consider the propensity of hydrogen to accelerate fatigue crack growth rates in the construction materials. Design of safe pressure vessels needs robust models for predicting crack growth rates and how they are affected by variables such as loading frequency, load ratios, hydrogen pressure, gaseous impurities, temperature, and material variability. In this study, fatigue crack growth rates were measured in the liner material in 10 MPa gaseous hydrogen at various load ratios, R, in the range -1 ≤ R ≤ 0.2. The effects of varying loading frequency were investigated, and the results were pooled with those from literature for similar alloys tested in 103 MPa gaseous hydrogen pressure. The differences in crack growth rates between H2 pressures of 10 to 103 MPa as well as the effects of frequency on the environment assisted crack growth rates were assessed. Loading frequency effects tend to saturate at frequencies of 1 Hz and less. H2 pressure effects appear to saturate at pressures of 45MPa, while load ratio effects are not significant for –1 ≤R≤ 0.2 but become important for R ≥ 0.2.
Effect of hydrogen on fatigue crack growth of quenched and tempered CrMo(V) steels
Authors: Peral Luis Borja , Blasón Sergio , Zafra Alfredo , Rodríguez Cristina , Belzunce Javier
Published: May 2018

In order to select the most appropriate steel to deal with pressurized hydrogen during long times, the fatigue crack propagation rate of quenched and tempered 2.25Cr1Mo and 2.25Cr1Mo0.3V steel grades was evaluated by means of tests performed on thermally pre-charged specimens in a hydrogen reactor at 195 bar and 450°C during 21 hours. Cylindrical samples to measure the hydrogen content and their desorption kinetics at room temperature and compact tensile specimens to determine the fatigue crack growth rate were used. Finally, scanning electronic microscopy was used in the study of fracture surfaces. Using the aforementioned pre-charging conditions, significant amounts of hydrogen were introduced, being much larger in the 2.25Cr1Mo0.3V steel grade (vanadium carbides provide strong hydrogen tramps). Regarding fatigue tests, the fatigue crack growth rate was increased notably due to the presence of hydrogen in the 2.25Cr1Mo grades for frequencies lower than 10 Hz. On the other hand, the presence of vanadium carbides has significantly improved the fatigue crack propagation performance in the presence of internal hydrogen.
Hydrogen-assisted fatigue crack propagation in a pure BCC iron. Part I: Intergranular crack propagation at relatively low stress intensities
Authors: Ogawa Yuhei , Birenis Domas , Matsunaga Hisao , Takakuwa Osamu , Yamabe Junichiro , Prytz Øystein , Thøgersen Annett
Published: May 2018

The role of hydrogen on intergranular (IG) fracture in hydrogen-assisted fatigue crack growth (HAFCG) of a pure iron at low stress intensity was discussed in terms of the microscopic deformation structures near crack propagation paths. The main cause of IG fracture was assumed to be the hydrogen-enhanced dislocation structure evolution and subsequent microvoids formation along the grain boundaries. Additionally, the impact of such IG cracking on the macroscopic FCG rate was evaluated according to the dependency of IG fracture propensity on the hydrogen gas pressure. It was first demonstrated that the increased hydrogen pressure results in the larger area fraction of IG and corresponding faster FCG rate. Moreover, gaseous hydrogen environment also had a positive influence on the FCG rate due to the absence of oxygen and water vapor. The macroscopic crack propagation rate was controlled by the competition process of said positive and negative effects.
Fatigue Performance of the Novel Titanium Alloy Timetal 407
Authors: Davey William , Bache Martin , Davies Helen , Thomas Matthew
Published: May 2018

Timetal 407 (Ti-407) is a novel titanium alloy formulated as a lower strength, more malleable alloy offering a range of cost reduction opportunities compared with Ti-6-4 (Ti-6Al-4V). An investigation of the room temperature, high cycle and low cycle fatigue properties of Ti-407 is presented. The effect of thermo-mechanical processing on microstructure is characterised and the fatigue properties of a microstructure containing 30-40% primary alpha volume fraction are presented and discussed. The Ti-407 results are compared with data generated from Ti-6-4 processed to provide a similar microstructure, to demonstrate both superior HCF endurance strength and ductility of the former.
Effect of local anisotropy on fatigue crack initiation in a coarse grained nickel-base superalloy
Authors: Engel Benedikt , Beck Tilmann , Moch Nadine , Gottschalk Hanno , Schmitz Sebastian
Published: May 2018

In the present work, theoretical approaches, based on grain orientation dependent Young’s modulus and Schmid factor are used to describe the influence of local grain orientation on crack initiation behaviour of the coarse grained nickel base superalloy René80. Especially for strongly anisotropic crystal structures with large grain size, such as the investigated material, the local elastic properties must be taken into account for assessment of fatigue crack initiation. With an extension of Schmid’s law, the resulting shear stress amplitude, which triggers local cyclic plastic deformation, can be calculated depending on local Young`s modulus and Schmid factor. A Monte Carlo simulation with 100,000 samples shows how random grain orientation affects these parameters. Furthermore, the product of Young`s modulus and Schmid factor (called E·m) is used as a parameter to determine how grain orientation influences resulting shear stress amplitude for given total strain amplitude. In addition to the theoretical work using that approach, this model is also validated using isothermal LCF experiments by determining local grain orientation influence on the crack initiation site using SEM-EBSD analyses.
The setup and application of the multi-scale in-situ test system for fatigue damage analysis
Authors: Shi Yi , Yang Xiaoguang , Miao Guolei , Shi Duoqi
Published: May 2018

This essays aims at introducing the setup for the multi-scale in-situ test system which is applied
for the fatigue crack initiation test. The setup of the experiment system is first introduced, including the
image capturing system, optical path system, image acquisition and storage system and the three-axis
mobile platform. Then the preparation of micro speckle and the corresponding technique for spatial
adjustment are improved to realize the DIC measurement in micro scale. Finally three experiments from
macro-meso scale to macro scale: fatigue initiation test, the observation of micro crack and the fatigue crack
growth rate in macro scale were conducted to verify the application of the system. The test result can
indicate the location of crack initiation, the crack growth rate and the evolution of displacement/strain field,
etc.
3D characterization of the fracture mechanisms of a Fe-rich Al-Si-Cu alloy
Authors: Brueckner-Foit Angelika , Bacaicoa Inigo , Luetje Martin , Wicke Marcel , Geisert Andreas , Fehlbier Martin
Published: May 2018

The effect of the defect size and morphology on the fatigue damage evolution was analysed in a recycled Al-Si-Cu alloy by micro-computed tomography and scanning electron microscopy. Fatigue tests were performed and the different crack initiation scenarios were characterized and classified. The interaction between shrinkage and gas pores was the key crack initiation mechanism and the ß-Al5FeSi particles did not play any role in the crack initiation phase. However, crack path analysis indicated that there is a certain amount of crack advance by brittle fracture of the β-phase particles. This is in accordance with the findings of tensile tests in which the ductility depended strongly on the iron content.
Early damage and fatigue crack initiation at ambient and elevated temperatures in heat resistant austenitic steel
Authors: Polák Jaroslav , Mazánová Veronika , Petráš Roman , Heczko Milan
Published: May 2018

Fatigue damage at ambient and at elevated temperature has been studied in advanced heat resistant austenitic steel. Cylindrical specimens were subjected to constant strain rate cycling and cycling with dwell in the tensile part of the cycle with different strain amplitudes. Surface relief evolution and initiation of surface and internal cracks were studied using high resolution SEM, FIB cutting, EBSD analysis, foil preparation and STEM imaging.
Effect of micro-notches on fatigue strength of electrodeposited nanocrystalline nickel thin films
Authors: Tanaka Keisuke , Murase Yuta , Kimachi Hirohisa
Published: May 2018

The effect of micro-notches on the fatigue strength of nickel thin films was studied. Two types of thin films with 10 μm thickness were produced by electrodeposition using sulfamate solution without and with brightener: ultra-fine grained film (UFG) with the grain size of 384 nm and nano-crystalline grained film (NCG) with that of 17 nm. Micro-sized notches introduced by FIB had the width of 2 μm and various depths from 8 to 150μm. Fatigue tests were conducted under the stress ratio of 0.1. The fatigue strength decreased with increasing depth of notches. NCG had much higher strength than UFG compared at the same notch depth. Notches as small as 8μm did reduce the fatigue strength of both UFG and NCG. The fatigue limit was controlled by the initiation of cracks and no non-propagating crack was observed in specimens fatigued below the fatigue limit. A model of fictitious crack successfully predicted the reduction of the fatigue limit due to micro-notches. The characteristic crack length of NCG was much smaller than the UFG, while the fatigue strength of defect-free NCG was larger than that of UFG. SEM observation of fracture surfaces was conducted to reveal micromechanisms of fatigue crack initiation.
Mechanical Integrity of Steel Discs with Corrosion Pits
Authors: Urbano Jose , Golowin Andrej , Löhnert Stefan , Bestle Dieter
Published: May 2018

Currently, prediction of crack initiation by corrosion pits is only possible by assuming regular geometrical shapes, such as semi-spheres or semi-ellipsoids. Moreover, typical fatigue life diagrams associate the crack initiation life with geometrical features, such as pit depth or aspect ratio, often leading to unsatisfactory correlations due to high pit shape variability and data scatter. In the context of blade-disc fixation in aero engine turbines, this limitation translates into highly conservative life estimations. Therefore, a new crack initiation predictor is formulated based on experimental testing and numerical analysis of 28 artificial corrosion pits. A low-cycle fatigue test campaign is conducted using three-point bending test specimens to simulate maximum takeoff operation conditions of the aero engine and the associated loading of the blade root designed as firtree. An artificial pit is located at the critical point of each test specimen, respectively. The prediction criterion is based on finite element analysis and is formulated as the lowest plastic strain of a plastic region with a certain volume in the corrosion pit. This reference volume is varied until an optimum correlation with experimental crack initiation life is obtained. The criterion shows a superior correlation with crack initiation life compared to pure geometrical parameters such as pit depth.
Low and high cycle fatigue of heat resistant steels and nickel based alloys in hydrogen for gas, steam turbines and generators applications
Authors: Balitskii Alexander , Eliasz Jacek , Balitska Valentina
Published: May 2018

It has been established that, at some region of hydrogen pressure and strain rate exists a maximum influence of hydrogen on the plasticity, low cycle fatigue and cyclic crack resistance of Ni-Co alloys and high nitrogen steels. The drop of plasticity of the dispersion-hardening materials within the temperature range of intense phase transformations is caused by the localization of strains on the grain boundaries due to the intense redistribution of alloying elements in the boundary regions. Moreover, the increase in plasticity observed at higher temperatures is caused both by partial coagulation of hardening phases and possible dissolution of small amounts of finely divided precipitations. The effect hydrogen on short-term strength and plasticity, high- and low-cycle durability of 15Cr12Ni2MoNMoWNb martensitic steel, 10Cr15Ni27Ti3W2BMo austenitic dispersion-hardened steel, heat resistant 3,5NiCrMoV rotor steel, 04Kh16Ni56Nb5Mo5TiAl and 05Kh19Ni55Nb2Mo9Al Ni-base superalloys in range of pressures 0–30 MPa and temperatures 293–1073 K was investigated. In the case of 15Cr12Ni2MoNMoWNb steel and 04Kh16Ni56Nb5Mo5TiAl alloy the dependence of low-cycle durability (N) and characteristics of plasticity (δ and φ) on the hydrogen pressure consists of two regions. In the first region (low pressures), the N, δ and φ abruptly drops, and in the second, the negative action of hydrogen becomes stable or decrease negligibility.
Experimental and numerical investigation of strain distribution of notched lead fatigue test specimen
Authors: Johanson Audun , Viespoli Luigi Mario , Nyhus Bård , Alvaro Antonio , Berto Filippo
Published: May 2018

The work here presented focuses on the test methodology related to effect of stress concentrators in strain controlled structures. Cable sheathing as used in subsea power cables are investigated by cyclic fatigue testing, Digital Image Correlation (DIC) and 3D Finite Element Analysis. Focus is put on the strain distribution in conventional specimen geometries and under the presence of artificial notches. It is evident that standardized fatigue testing provides limited input to the final fatigue life of strain controlled power cable sheathing both accounting for expected and unintended stress concentrators. The limitations can be explained by measured strain distribution inherent in most fatigue test specimens. The use of DIC and 3D FEM provides valuable insight into both the theoretical and practical stress and strain distribution. This can help in understanding and overcoming geometrical test constraints, when compared to the actual component loading mode.
Experimental and Numerical Study on Plastic Zone Variation ahead of Fatigue Crack Tip
Authors: Wei Zhang , Daoqing Zhou , Liang Cai
Published: May 2018

The plastic deformation ahead of crack tip is of great significance to analysis of the fatigue crack growth behaviour. Using the in-situ microscopy experiment technique, the variation of strain field in the vicinity of crack tip is investigated within load cycles at the small time scale. The contours of plastic zones are measured through the in-situ observation and digital image correlation (DIC). Finite element method (FEM) is also used to simulate the plasticity ahead of the crack tip. Furthermore, the numerical studies are extended to the single overload case to analyse the effect of large plastic zone on the subsequent crack growth. The evolution of residual stress is extracted by FEM simulation to explore the influence of plastic deformation before, during and after the single overload applied on the following crack propagation. Based on the FEM analysis, a model is proposed to approximate the size of the overload effect zone. Finally, some experimental data and numerical simulations are employed to validate this model.
Investigating the fatigue behavior of grain-oriented Fe-3%Si steel sheets using magnet-optical Kerr microscopy and micromagnetic multiparameter, microstructure and stress analysis
Authors: Deldar Shayan , Smaga Marek , Beck Tilmann
Published: May 2018

Fatigue is considered as a reason for a significant number of mechanical failures of engineering materials. Conventionally, microstructural investigations along with stress-strain hysteresis measurements are performed to understand and characterize the fatigue behavior of metallic materials. Moreover, further physical data like temperature, electrical resistance and, in the case of ferromagnetic materials, magnetic properties can be used for a comprehensive characterization of fatigue process. The present work has employed Magneto-Optical Kerr Effect (MOKE) microscope and Micromagnetic Multiparameter, Microstructure and stress Analysis (3MA) system to illustrate magnetic domain structure and various intrinsic magnetic properties including magnetic Barkhausen noise (MBN) of the investigated material. In order to investigate the influence of the mechanical deformation processes on the magnetic parameters, samples were produced out of the grain-oriented electrical steel sheets and were subjected to a tensile test as well as a cyclic strain increase load test with R = 0 at ambient temperature.
Fatigue life improvement of cast ZK60 Mg alloy through low temperature closed-die forging for automotive applications
Authors: Karparvarfard SMH. , Shaha S.K. , Behravesh S.B. , Jahed H. , Williams B.
Published: May 2018

The influence of low-temperature closed-die forging on the quasi-static and cyclic behaviour of as-cast ZK60 magnesium alloy was investigated. As-cast ZK60 billets were forged at a ram speed of 20 mm/sec and a temperature of 250 °C. While the yield strength of the starting alloy was 139 MPa, the forging process improved the yield strength significantly by ~68% to 234 MPa. Moreover, the stresscontrolled push-pull fatigue tests at the stress amplitudes of 140 MPa to 180 MPa revealed that the fatigue life was enhanced by an order of magnitude. Microstructural analyses besides the texture measurements at different locations of the forged part manifested partial grain refinement and texture modification strengthening mechanisms. It is believed that the fatigue life improvement is achieved in the wake of the grain refinement and the subsequent material strengthening.
Experimental monitoring of the self-heating properties of thermoplastic composite materials during tensile and cyclic tests
Authors: Muller Laura , Roche Jean-Michel , Hurmane Antoine , Peyrac Catherine , Gornet Laurent
Published: May 2018

The sizing of industrial structures with a given material requires to understand completely its fatigue behaviour. Yet, the full estimation of the fatigue lifetime of a material requires time-consuming and expensive fatigue testing campaigns, and a huge number of samples. An alternative experimental procedure is based on the monitoring of the self-heating properties of the studied material. The aim is to correlate the fatigue limit with a change of the thermal behaviour of the material during the self-heating tests. The main advantage of these tests is that they need only a limited number of mechanical cycles, and require few samples to test. Ultimately, self-heating tests lead to an accelerated estimation of the fatigue behaviour. The purpose of the present paper is to validate this approach for a woven carbon/thermoplastic composite material.
Fatigue behaviour of open-hole samples and automotive mini-structures made of woven glass-fibre-reinforced polyamide 6,6
Authors: Malpot Amélie , Touchard Fabienne , Bergamo Sébastien , Peyrac Catherine , Montaudon Richard , Blumenfeld Jean-Baptiste
Published: May 2018

In the automotive industry, the integration of thermoplastic composite components represents a high-potential solution to the mass reduction challenge. In this study, a woven glassfibre-reinforced composite with a polyamide 6,6 matrix is considered for the purpose of being integrated into automotive parts. Tension-tension fatigue tests were conducted on [(0/90)3] openhole samples. These tests were instrumented with non-destructive techniques, namely acoustic emission and infrared thermography. Acoustic emission results showed fibre-matrix debonding and fibre breakages in open-hole samples, located around the hole. Furthermore, 3-point bending fatigue tests were performed on “omega” mini-structures. A semi-empirical model was used in order to predict the fatigue lives of both open-hole coupons and automotive mini-structures. Predictions of the model for open-holes samples underestimate experimental fatigue lives. Nevertheless, the semiempirical model showed good results for the fatigue life prediction of composite mini-structures.
Rapid evaluation of S-N curve for composite laminates on thermographic approach
Authors: Huang Jia , Garnier Christian , Pastor Marie-Laetitia , Gong Xiaojing
Published: May 2018

A new fatigue life prediction model is developed for composite laminates based on both infrared thermographic data and stiffness degradation process. The fatigue limit is firstly determined by the improved thermographic method and then a two-parameter function is proposed to describe the normalized stiffness degradation of specimens subjected to various maximum loading stresses. These two parameters can be calibrated by the stiffness degradation data and stabilized temperature data. Thereafter, the calibrated model can be used to predict S-N curve. The proposed model is applied the experimental data from literature and the results show that the predicted S-N curve has a well agreement with the experimental one.