bluuebunny/crossref_metadata_2025 huggingface dataset:
OPTIMIZATION OF STEEL HARDNESS USING NANOFLUIDS QUENCHANTS
Authors: Hussein Abbas , Abbas Laith , Hassan Wisam
Published: February 2019

The goal of this study is to specify the optimal factors for the hardening process (tempering temperature, the percentage of nanoparticles, type of base media, nanoparticles type and tempering time) in order to maximize the hardness of medium carbon steel by using Taguchi technique. An (L18) orthogonal array was chosen for the design of the experiment. The optimum process parameters were determined by using signal-to-noise ratio(larger is better) criterion. The important levels of process parameters on hardness were obtained by using analysis of variance which applied with the help of (Minitab17) software to investigate the effect of parameters on the hardness. Percentage of volumetric fractions of nanoparticles with three different levels (0.01, 0.03 and 0.08%) was prepared by dispersing nanoparticles that are (α-Al2O3, TiO2 and Cuo) with base fluids (De-ionized water, salt solution, and engine oil). Medium carbon steel specimens were suffered to hardening and tempering heat treatment process. Tempering temperature was (400℃, 550℃) for (30,45and 60 minutes). Results ended up with a conclusion that tempering temperature (400℃) had the major influence on hardness behavior then type of nanoparticles (TiO2) followed by time tempering (30min) then base media (salt solution) and finally volume fraction of nanoparticles (0.03%).
Análise de livro didático e a prática pedagógica do professor que ensina Matemática
Authors: Januario Gilberto
Published: February 2019

Neste artigo, evidenciamos o recorte de um projeto de pesquisa que teve por objetivo o estudo das contribuições da análise de livro didático para a prática pedagógica do professor que ensina Matemática. Em sua prática pedagógica, dentre outras ações, cabe ao professor conceber um tratamento adequado aos conteúdos matemáticos para que esses possam se tornar potencialmente significativos aos alunos. Porém, quais elementos teóricos estão à disposição do professor para selecionar e desenvolver o rol de conteúdos matemáticos? De que modo essa ação contribui para a sua prática pedagógica? Essas questões nos motivaram a analisar, pela perspectiva da Teoria Antropológica do Didático, como três livros didáticos abordam o conceito de Função para alunos do 9º ano do Ensino Fundamental e que elementos promovem a (re)construção da prática pedagógica do professor que ensina Matemática
O perfil dos conselheiros na Baixa Idade Média Ibérica: O Libro del Consejo e de los Consejeros
Authors: Lima Douglas Mota Xavier de
Published: February 2019

Tendo em vista a crescente importância do Conselho para as monarquias medievais, este artigo propõe analisar o perfil dos conselheiros na Idade Média ibérica, a partir dos espelhos de príncipes, gênero que se afirma no Ocidente medieval desde o século XIII com origens na tradição textual greco-romana, cristã e muçulmana. Para o estudo discute-se o Libro del Consejo e de los consejeros, de Maestre Pedro, primeiro tratado conhecido na Península Ibérica destinado aos conselheiros régios. O trabalho busca demonstrar como o texto constrói um perfil dos conselheiros pautado em vícios e virtudes, criando uma pedagogia política aos homens que passavam a orientar as monarquias do período.
Três formas de amar: a construção da imagem de Neymar Jr no mercado brasileiro de revistas
Authors: Ferraz Luís Henrique Mendonça , Marques José Carlos
Published: February 2019

Este artigo tem como finalidade analisar a construção discursiva realizada pela imprensa brasileira a respeito de Neymar Jr., futebolista que iniciou sua carreira no Santos FC e que atualmente defende o Paris Saint-Germain e a Seleção Brasileira. Nosso objetivo é abordar, por meio da Análise do Discurso de linha francesa, como o mercado brasileiro de revistas construiu a imagem do atleta nas publicações de 2010 a 2012, período de consolidação da carreira como craque bem-sucedido no Brasil. Nestes anos, Neymar Jr. esteve presente em pelo menos 22 capas de revistas brasileiras, de diferentes gêneros e temáticas, a partir de uma construção discursiva sistêmica, eufórica e convergente. Com sua ida para o exterior em 2013, o processo de exposição nas capas de revistas brasileiras reduziu-se, ao mesmo tempo em que o atleta ganhou nova dimensão no mercado global futebolístico.
PENYUSUNAN PROGRAM APLIKASI INVENTARISASI POHON DI JALAN KH. RD. ABDULLAH BIN NUH BOGOR
Authors: Sulistyantara Bambang , Rahmatullah Heru
Published: February 2019

Road is a unit that must be completed, efficient, and attractive. It must have a circulation, a good interaction, and an exciting experience for the pedestrian. The road is also a place to plant trees. A line of trees can be planted on the roadside and median of road. Tree is a plant with woody stem and branch. Planting trees along of the road can provide a shelter and comfortable, reduce noise, and direct pedestrian path and vehicle path. Unfortunately, trees can arise some problems such as fallen trees and broken branche. The problem has happened at Abdullah bin Nuh street, Bogor City.In order to avoid and or minimize the risk of trees problem,it is needed to construct trees database in form of inventory application program. This research found a model of database application program forinventory of trees condition at Abdullah bin Nuh street. The advantage of program is that it can be applicated up to city scale and can record the number of trees up to 99.999. Beside, the program can be applicated for other cities in Indonesia.
KUALITAS PENGAJARAN BAHASA ARAB (TEORI DAN PRAKTEK) IAIN PALOPO
Authors: IAIN Palopo Prodi_PGMI FTIK
Published: February 2019

Pembelajaran Bahasa Arab di Indonesia melalui beberapa tahapan mulai dari pembelajaran lafadz-lafadz yang digunakan dalam ibadah dan do'a, lalu berkembang menjadi sarana pembelajaran agama Islam, menjadi sebuah mata pelajaran yang diajarkan di pesantren dan lembaga-lembaga islam.
PENINGKATAN KEMAMPUAN MENULIS KARANGAN NARASI DENGAN METODE PETA PIKIRAN DALAM PEMBELAJARAN BAHASA INDONESIA
Authors: IAIN Palopo Prodi_PGMI FTIK
Published: February 2019

Peningkatan kemampuan menulis karangan narasi dengan metode peta pikiran (mind mapping) dalam pembelajaran Bahasa Indonesia pada siswa kelas V SDN 34 Palopo Kota. Penelitian ini bertujuan untuk meningkatkan kemampuan siswa menulis narasi dengan metode peta pikiran.
GERAKAN DAKWAH DI KOTA PALOPO
Authors: IAIN Palopo Prodi_PGMI FTIK
Published: February 2019

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A Reflection on Economics of Microcredit Borrowing in Rural Bangladesh
Authors: Molla Rafiqul Islam , Alam Md. Mahmudul
Published: February 2019

There is no room for denying the critical importance of microcredit for economic emancipation of rural poor in Bangladesh or any such other country. In analyzing the effectiveness of microcredit program the microcredit providers (NGOs) use accounting profit of the borrowers’ enterprises ignoring implicit costs on the plea that the opportunity cost of labor is near zero in those countries. This plea is certainly not tenable. In this research we use the principle of economic profit taking into account the implicit cost of family labor. From the results of this pilot study we get the reflection that a bulk of the microcredit is borrowed for non productive purposes. As high as 24% of borrowers used the credit exclusively for consumption and debt repayment purposes, and therefore demand for payment of interest from them is nonsensical. Only 48 % of the borrowers used the credits entirely for investment purposes. However, they are faced with very low-return investment opportunities in rural areas. About 68% of them on average had an impressive 83% net return on investment available for payment of interest and dividend. But in case of as high as 32% of them average return on investment was not enough even to cover the most minimum or tolerance level of wages for family labors. In their cases any payment of interest for capital has to be at the expense of the sacrifice of this subsistence level wages of the family labors. They are trapped in a vicious circle of loans. In the absence of a built in mechanism for debt relief they have no scope to be freed from this bondage of debt. An Islamic microcredit model based on Mudarabah principle (whereby the lender and borrower share the business surplus/profit on an agreed ratio, but in case of loss the lender alone bears the loss) may be a better alternative for them. There are indications that it requires an investment of around Tk 12,000 for creating job opportunity for one rural labor for the whole year.
Deciphering the Land: Artistic Cartography in the Illustrated Cabreo of the Congregation of the Gentlemen of the Nativity of the Virgin Mary in Tivoli, Italy (1661–1808)
Authors: Pampinella Margherita
Published: February 2019

In 1661, the Congregation of the Gentlemen of the Nativity of the Virgin Mary, a lay pious organization devoted to religious and charitable services in Tivoli, Italy, commissioned from land surveyor Gismondo Stracha an illustrated cabreo of its endowments. Cabrei were private estate records, frequently commissioned by large estate owners in Europe between the fifteenth and the nineteenth century. Illustrated cabrei, such as this one from Tivoli, were elegantly decorated and included watercolour maps and drawings of lands, vegetation, and buildings. They could indeed be works of art, perceived by the landowners not only as administrative documents, but also as artistic testimonies of the commissioners’ legacy in the territory. The private cadastral maps included in illustrated cabrei predate the implementation of land surveying and mapping in the national land registration systems in Europe in the mid-eighteenth century. Unlike public cadastral records, the maps in cabrei combine geometric accuracy with artistic flair and are accompanied by extensive annotations and regular updates to facilitate the management of the estate. The cabreo of the Congregation of the Nativity of the Virgin Mary is therefore invaluable in documenting the evolution of landscape, economy, cartography, and social life in Tivoli throughout the centuries.
Protective Effect of Curcuma Against Chromium Hepatotoxicity in Rats
Authors: Saidi M. , Aouacheri O. , Saka S.
Published: February 2019

This study was carried out to investigate the antioxidant effects of curcuma against chromium-induced alterations in hepatic indices and dysfunctions in the antioxidant system. Forty maleWistarrats were randomly divided into four groups and were treated for 30 consecutive days. The control group (0-0) received per os mineral water and normal diet. The second group (0-Cur) received mineral water and an experimental diet containing 2% of curcuma powder, whereas the third group (Cr-0) was orally fed (per os) with 15 mg/kg body weight/day of potassium dichromate and normal diet. The last group (Cr-Cur) received per os 15 mg/kg of potassium dichromate and a diet with 2% of curcuma. The treatment by chromium was found to elicit a perturbation in biochemical parameters producing a significant increase in glycemia, triglycerides, cholesterol, ALP, ALT, AST, and LDH levels. On the contrary, a significant reduction was observed in the oxidative stress-related parameters (GSH, GPx, CAT, and GST). Moreover, we noticed that liver sections of rats intoxicated with chromium showed a disrupted architecture. However, the administration of curcuma revealed an intense reduction in the oxidative stress induced by chromium, ameliorating the levels of the majority of the previous parameters. The data of this study revealed the potent antioxidant effects of curcuma in reducing oxidative stress damage induced by the hexavalent chromium.
Investigation of properties of equivalence classes of permutations by inverse Robinson — Schensted — Knuth transformation
Authors: Vassiliev N. N. , Duzhin V. S. , Kuzmin A. D.
Published: February 2019

Introduction:All information about a permutation, i.e. about an element of a symmetric groupS(n), is contained in a pair of Young tableaux mapped to it by RSK transformation. However, when considering an infinite sequence of natural or real numbers instead of a permutation, all information about it is contained only in an insertion infinite Young tableau. The connection between the first element of an infinite sequence of uniformly distributed random values and the limit angle of the recording tableau nerve was found in a recent work by D. Romik and P. Śniady. However, so far there were no massive numerical experiments devoted to the reconstruction of the beginning of such a sequence by the beginning of an insertion Young tableau. The reconstruction accuracy is very important, because even the value of the first element of a sequence can be determined only by an infinite tableau.

Purpose:Developing a software package for operations on Young diagrams and Young tableaux, and its application for numerical experiments with large Young tableaux. Studying the properties of Knuth equivalence classes and dual Knuth equivalence classes on a set of permutations by numerical experiments using direct and inverse RSK transformation.

Results:A software package is developed using the C ++ programming language. It includes functions for dealing with Young diagrams and tableaux. The dependence of values of the first element of a permutation obtained by inverse RSK transformation on the recording tableau nerve end coordinates was investigated by conducting massive numerical experiments. Standard deviations of these values were calculated for permutations of different sizes. We determined possible positions of 1 in permutations of the same Knuth equivalence class. It has been found out that the number of these positions does not exceed the number of corner boxes of the corresponding Young diagram. Experiments showed that for a fixed insertion tableau, the value of the first element of a permutation depends only on the recording tableau nerve end coordinates.
Safe control of SEMS in group interaction
Authors: Gorodetskiy A. E. , Kurbanov V. G. , Tarasova I. L.
Published: February 2019

Introduction:In control over a group of interacting smart electromechanical systems (SEMS), situations may arise when the operator’s instructions and/or the automatic control system at a higher level contradict the internal state of the controlled SEMS and/or the environment of choice. Such situations can be prevented by algorithms which check the fulfillment of conditions for the admissibility of movements. These algorithms can be based on modeling the SEMS behavior using logical-probabilistic or logicallinguistic descriptions of situations, and on non-scalar quality criteria when making decisions.

Purpose:The development of algorithms for safe control over robots based on SEMS modules with phase constraints, under incomplete certainty of the environment.

Results:Algorithms have been developed for safe control over three robots, using a mathematical description of situational control over a group of SEMS and the methodology of organizing the situational control over a group of mobile SEMS. The algorithms move the robots from certain current positions to specified terminal positions, avoiding their collisions with each other. In order to avoid collisions, the decision-making system in a robot’s central nervous system uses robot’s priorities based on the distance between the robots. An approach has been proposed to overcome uncertainty on the way (trajectory) of the robots. Uncertainties in the form of logical-probabilistic and logical-linguistic type constraints are considered. It is shown that these restrictions can be translated into a logical-interval form. This allows you to use standard mathematical programming procedures when searching for the optimal solution.

Practical relevance:The obtained algorithms can be used for decision-making in the central nervous system and when controlling robots.
Compact specification of polar codes
Authors: Morozov R. A. , Trifonov P. V.
Published: February 2019

Introduction:Practical implementation of a communication system which employs a family of polar codes requires either to store a number of large specifications or to construct the codes by request. The first approach assumes extensive memory consumption, which is inappropriate for many applications, such as those for mobile devices. The second approach can be numerically unstable and hard to implement in low-end hardware. One of the solutions is specifying a family of codes by a sequence of subchannels sorted by reliability. However, this solution makes it impossible to separately optimize each code from the family.

Purpose:Developing a method for compact specifications of polar codes and subcodes.

Results:A method is proposed for compact specification of polar codes. It can be considered a trade-off between real-time construction and storing full-size specifications in memory. We propose to store compact specifications of polar codes which contain frozen set differences between the original pre-optimized polar codes and the polar codes constructed for a binary erasure channel with some erasure probability. Full-size specification needed for decoding can be restored from a compact one by a low-complexity hardware-friendly procedure. The proposed method can work with either polar codes or polar subcodes, allowing you to reduce the memory consumption by 15–50 times.

Practical relevance:The method allows you to use families of individually optimized polar codes in devices with limited storage capacity.
Comparative characteristics of anti-collision processing of radio signal from identification tags on surface acoustic waves
Authors: Sorokin A. V. , Shepeta A. P. , Nenashev V. A. , Wattimena G. M.
Published: February 2019

Introduction:Collision of information signals is a common problem in the measurement of physical magnitudes, such as temperature, pressure, stress, etc., with acoustic-electronic sensors. This problem is caused by overlapping response signals in the time domain, which makes it difficult to interpret correctly the device identification codes or the sensor data received.

Purpose:Analysis of anticollision algorithms for radio-frequency tag code detection and identification by response information signals from acoustic-electronic devices which use the methods of time, frequency and frequency-time division of the response radio signals.

Methods:Probabilistic methods for calculating the parameters of digital detectors of radio pulse bursts with given false alarm values and gaussian white noise background; individual code group identification methods when studying the attenuation of acoustic-electric signal during their propagation in the tag substrate, taking into account the dependence of the attenuation on the tag topology.

Results:We have derived analytical expressions to calculate the probability of the correct identification of each tag, taking into account the dependence on tag topology, attenuation characteristics, the anti-collision signal processing methods and the signal-to-noise ratios. Curves which allow you to compare the advantages and disadvantages of the considered anti-collision signal processing methods are calculated and shown in the article. The analysis of the graphic charts demonstrating the correct identification probability has shown that identification tags with frequency-time coding have better ratios as compared to frequency or time methods of collision prevention.

Practical relevance:The obtained result allows you to effectively evaluate the condition of technical objects, improving the predictability and prevention of possible environmental and man-made disasters.
Evolution of multiple-access networks — cellular and non-cellular — in historical perspective. Part 4
Authors: Sergeev A. M. , Blaunstein N. Sh.
Published: February 2019

Introduction:The goal of this issue is the analysis of evolution of the current and novel wireless networks, from second generation (2G) to fifth generation (5G), as well as changes in technologies and their corresponding theoretical background and protocols — from Bluetooth, WLAN, WiFi and WiMAX to LTE, OFDM/OFDMA, MIMO and LTE/MIMO advanced technologies with new hierarchy of cellular maps design — femto/pico/micro/macro.

Methods:We use new theoretical frameworks for description of the advanced technologies, such as multicarrier diversity technique, OFDM and OFDM novel approach, MIMO aspects description based on multi-beam antennas approach, various cellular maps design based on a new algorithms of femto/pico/micro/macrocell deployment, and a new methodology of a new MIMO/LTE system integration based on multi-beam antennas.

Results:We have created a new methodology of multi-carrier diversity description for novel multiple-access networks, of usage of OFDM/OFDMA modulation to obey inter-user and inter-symbol interference in multiple-access networks, of how to obey the multiplicative noises occurring in the multiple-access wireless networks, caused by multi-ray phenomena, and finally, of how to overcome propagation effects occurring in the terrestrial communication links by use combination of MIMO and LTE technologies based on multi-beam antennas. For these purposes we present new stochastic approach that accounts for the terrain features, such as buildings’ overlay profile, buildings’ density around the base station and each user antennas, and so forth. These parameters allow us to estimate for each situation occurs at the built-up terrain area the effects of fading, as a source of multiplicative noise.

Practical relevance:New methodology of how to estimate effects of multiplicative noise, inter-user and inter-symbol interference, occurring in the terrestrial wireless networks, allows us to predict a-priory practical aspects of the current and new multiple-access wireless communication networks, such as: the users’ capacity and user’s links spectral efficiency for various configurations of cells deployment — femto, pico, micro, and macro, as well as the novel MIMO/LTE system configuration for future networks of 4th and 5th generation deployment.
Diagnostic principles of immature epileptic (proepileptic) EEG activity in rats with genetic predisposition to absence epilepsy
Authors: Sitnikova E. Yu. , Smirnov K. S. , Grubov V. V. , Hramov A. E.
Published: February 2019

Introduction:Absence epilepsy is a specific neurological disorder characterized by brief episodes of loss of consciousness (absence) accompanied by high-amplitude “spike-wave” discharges in the electroencephalogram (EEG). WAG/Rij rats with a genetic predisposition to absence epilepsy are used as a reliable model of this disease. This model is beneficial for investigating basic mechanisms of absence epilepsy, including the development of spike-wave seizures.

Purpose:Establishing diagnostic principles for immature forms of spikewave activity in EEG (so-called proepileptic activity) of WAG/Rij rats.

Results:Diagnostic criteria are proposed for proepileptic EEG activity in rats, based on time-frequency analysis with the continuous wavelet transform and skeletons of wavelet surfaces. The algorithm was tested in “epileptic” and “asymptomatic” individuals. Rats with the “epileptic” phenotype demonstrated a decrease in number of proepileptic patterns between 5 and 7 months of age in parallel to an increase in the number of epileptic discharges that might relate to the transformation of proepileptic activity to epileptic. In rats with the “asymptomatic” phenotype, the age-related decline in the number of proepileptic patterns was not accompanied by the occurrence of spike-wave discharges. A decrease in the instantaneous frequency was found in a larger number of proepileptic patterns in “epileptic” WAG/Rij rats as compared to “asymptomatic” individuals.

Practical relevance:A similar approach can be used for early diagnosis of absence epilepsy at the preclinical stage in patients with genetic predisposition.
A review of thermographic techniques for damage investigation in composites
Authors: Vergani Laura , Colombo Chiara , Libonati Flavia
Published: February 2019

The aim of this work is a review of scientific results in the literature, related to the application of thermographic techniques to composite materials. Thermography is the analysis of the surface temperature of a body by infrared rays detection via a thermal-camera. The use of this technique is mainly based on the modification of the surface temperature of a material, when it is stimulated by means of a thermal or mechanical external source. The presence of defects, in fact, induces a localized variation in its temperature distribution and, then, the measured values of the surface temperature can be used to localize and evaluate the dimensions and the evolution of defects. In the past, many applications of thermography were proposed on homogeneous materials, but only recently this technique has also been extended to composites. In this work several applications of thermography to fibres reinforced plastics are presented. Thermographic measurements are performed on the surface of the specimens, while undergoing static and dynamic tensile loading. The joint analysis of thermal and mechanical data allows one to assess the damage evolution and to study the damage phenomenon from both mechanical and energetic viewpoints. In particular, one of the main issues is to obtain information about the fatigue behaviour of composite materials, by following an approach successfully applied to homogenous materials. This approach is based on the application of infrared thermography on specimens subjected to static or stepwise dynamic loadings and on the definition of a damage stress, ?D, that is correlated to the fatigue strength of the material. A wide series of experimental fatigue tests has been carried out to verify if the value of the damage stress, ?D, is correlated with the fatigue strength of the material. The agreement between the different values is good, showing the reliability of the presented thermographic techniques, to the study of composite damage and their fatigue behaviour.
The application of the infrared thermography on titanium alloy for studying fatigue behavior
Authors: Hou P. , Fan J. , Guo Q. , Guo X.
Published: February 2019

The infrared thermography is an attractive tool for studying the fatigue behavior of materials. Based on two theoretical models of fatigue damage indicators, this work studied the fatigue properties of the virgin Ti- 6Al-4V alloy. According to the two damage indicators and the energy theory, the relationship between the macro-phenomenon and the micro-structural evolution during fatigue process was discussed. The fatigue limit of the titanium alloy was rapidly determined based on the measured temperature increment signals. The capability of the infrared thermographic method on the evaluation of fatigue properties was validated.
Energy dissipation and storage in iron under plastic deformation (experimental study and numerical simulation)
Authors: Kostina A. , Iziumova A. , Plekhov O.
Published: February 2019

The work is devoted to the experimental and numerical investigation of thermodynamic aspects of the plastic deformation in Armco iron. Dissipation and stored energies was calculated from processed experimental data of the surface temperature obtained by infrared thermography. An original mathematical model describing the process of mesoscopic defects accumulation was used for numerical simulation of the quasistatic loading of iron samples and for calculation of theoretical value of the stored energy. Experimental and modeled values of the stored energy are in a good agreement.
Fatigue behavior of lubricated Ni-Ti endodontic rotary instruments
Authors: Brotzu A. , Felli F. , Lupi C. , Vendittozzi C. , Fantini E.
Published: February 2019

The use of Ni-Ti alloys in the practice of endodontic comes from their important properties such as shape memory and superelasticity phenomena, good corrosion resistance and high compatibility with biological tissues. In the last twenty years a great variety of nickel-titanium rotary instruments, with various sections and taper, have been developed and marketed. Although they have many advantages and despite their increasing popularity, a major concern with the use of Ni-Ti rotary instruments is the possibility of unexpected failure in use due to several reasons: novice operator handling, presence manufacturing defects, fatigue etc. Recently, the use of an aqueous gel during experimental tests showed a longer duration of the instruments. The aim of the present work is to contribute to the study of the fracture behavior of these endodontic rotary instruments particularly assessing whether the use of the aqueous lubricant gel can extend their operative life stating its reasons. A finite element model (FEM) has been developed to support the experimental results. The results were rather contradictory, also because the Perspex (Poly-methyl methacrylate, PMMA) cannot simulate completely the dentin mechanical behavior; however the results highlight some interesting points which are discussed in the paper.
micromechanical approach for the micropolar modeling of heterogeneous periodic media
Authors: De Bellis M.L. , Addessi D.
Published: February 2019

Computational homogenization is adopted to assess the homogenized two-dimensional response of periodic composite materials where the typical microstructural dimension is not negligible with respect to the structural sizes. A micropolar homogenization is, therefore, considered coupling a Cosserat medium at the macro-level with a Cauchy medium at the micro-level, where a repetitive Unit Cell (UC) is selected. A third order polynomial map is used to apply deformation modes on the repetitive UC consistent with the macro-level strain components. Hence, the perturbation displacement field arising in the heterogeneous medium is characterized. Thus, a newly defined micromechanical approach, based on the decomposition of the perturbation fields in terms of functions which depend on the macroscopic strain components, is adopted. Then, to estimate the effective micropolar constitutive response, the well known identification procedure based on the Hill-Mandel macro-homogeneity condition is exploited. Numerical examples for a specific composite with cubic symmetry are shown. The influence of the selection of the UC is analyzed and some critical issues are outlined.
Effects of large amounts of hydrogen on the fatigue crack growth behavior of torsional prestrained carbon steel
Authors: Matsuda Yuta , Nishiguchi Hiroshi , Fukuda Takayuki
Published: February 2019

The effects of large amounts of hydrogen on the fatigue crack growth properties of torsional prestrained ferritic–pearlitic low-carbon steel were investigated. Hydrogen-precharged specimens were produced by conducting cathodic charge to the virgin material and to torsional prestrained JIS-S10C and JISS25C steels (hereafter S10C and S25C steels). Rotating bending fatigue tests were conducted in air at room temperature. Hydrogen content, CH, increased with torsional prestrain for both S10C and S25C steels; the CH of the torsional prestrained S25C steel precharged with hydrogen was lower than that of S10C at the same torsional prestrain. No clear difference between the maximum CH values of the torsional fractured S10C and S25C hydrogen-precharged steel specimens. With respect to crack initiation, there was no obvious difference between the uncharged and precharged specimens in spite of the large amount of CH induced by torsional prestrain. The acceleration of fatigue crack growth by hydrogen was the main cause of the decreased fatigue life. For the virgin material, hydrogen had no obvious effect on the fatigue crack growth rate. In contrast, for the torsional prestrained materials, the acceleration ratios, {(da/dN)H/(da/dN)U}, increased with the torsional prestrain and CH. However, {(da/dN)H/(da/dN)U} did not exceed the value of about 30, even when a large amount of hydrogen was charged (10.0 ? CH ? 30.3 mass ppm). A hydrogen content threshold was found; hydrogen content above this limit enhances the growth of the non-propagated crack, even for metals with lower hardness (HV < 200).
Mechanism of crack branching in the fatigue crack growth path of 2324-T39 Aluminium alloy
Authors: Songsong Lu , Rui Bao , Ting Zhang , Binjun Fei
Published: February 2019

The crack growth behavior in 2324-T39 aluminium alloy was experimentally investigated. Two types of crack branching were observed. The mechanism of an uncommon crack branching which results from the link up of secondary crack with the main crack was focused on. The crack paths were observed with optical microscope and in-situ SEM. Finite element crack tip simulation was performed to investigate the relationship between plastic zone size and the location of the secondary crack. Tests and analysis results indicate that the secondary crack initiates near the plastic zone boundary and from the subsurface. The mechanism of this kind crack branching relates to the interaction of grain size and plastic zone size.
Microstructure dependence of fatigue crack propagation behavior in wrought magnesium alloy
Authors: Morita S. , Fujiwara S. , Hori T. , Hattori N. , Somekawa H. , Mayama T.
Published: February 2019

This paper deals with the fatigue crack propagation behavior of rolled AZ31B magnesium alloy (grain size: approximately 40 ?m). Fatigue crack propagation tests were performed on single edge notched tension specimens at a stress ratio of R = 0.1 and a frequency of 10 Hz at room temperature. Loading axes were parallel to the rolling direction; fatigue cracks propagated parallel to the transverse direction (L-T specimen), parallel to the short transverse direction (L-S specimen). Loading axis was perpendicular to the rolling direction; fatigue cracks propagated parallel to the transverse direction (S-T specimen). The crack growth rate (da/dN) of the L-S specimen was several times lower than that of the L-T specimen in the examined stress intensity factor range (?K). Fracture surfaces of the L-T and L-S specimens showed many steps parallel and perpendicular, respectively, to the macroscopic crack growth direction. The da/dN of the S-T specimen was higher than that of the L-T and L-S specimens in the examined ?K. The fracture surface was covered by quasi-cleavage facets independent of macroscopic crack growth direction, and the fracture surface roughness at low ?K was larger than that at high ?K.
A non-linear procedure for the numerical analysis of crack development in beams failing in shear
Authors: Bernardi P. , Cerioni R. , Michelini E. , Sirico A.
Published: February 2019

In this work, a consistent formulation for the representation of concrete behavior before and after cracking has been implemented into a non-linear model for the analysis of reinforced concrete structures, named 2D-PARC. Several researches have indeed pointed out that the adoption of an effective modeling for concrete, combined with an accurate failure criterion, is crucial for the correct prediction of the structural behavior, not only in terms of failure load, but also with reference to a realistic representation of crack initiation and development. This last aspect is particularly relevant at serviceability conditions in order to verify the fulfillment of structural requirements provided by Design Codes, which limit the maximum crack width due to appearance and durability issues. In more details, a constitutive model originally proposed by Ottosen and based on non-linear elasticity has been here incorporated into 2D-PARC in order to improve the numerical efficiency of the adopted algorithm, providing at the same time an accurate prediction of the structural response. The effectiveness of this procedure has been verified against significant experimental results available in the technical literature and relative to reinforced concrete beams without stirrups failing in shear, which represent a problem of great theoretical and practical importance in the field of structural engineering. Numerical results have been compared to experimental evidences not only in terms of global structural response (i.e. applied load vs. midspan deflection), but also in terms of crack pattern evolution and maximum crack widths.
Surface crack growth subject to bending and biaxial tension-compression
Authors: Shlyannikov V. , Tumanov A. , Zakharov A. , Gerasimenko A.
Published: February 2019

Fatigue surface crack growth and the in-plane and out-of-plane constraint effects are studied through experiments and computations for aluminium alloy D16T. Subjects for studies are cruciform specimens under different biaxial loading and bending central notched specimens with external semi-elliptical surface crack. Both the optical microscope measurements and the crack opening displacement (COD) method are used to monitor and calculate both crack depth and crack length during the tests. The variation of crack growth rate and surface crack paths behaviour is studied under cyclic pure bending and biaxial tension-compression fatigue loading. This work is centered on the relations between crack size on the free surface of specimen considered configurations, COD and aspect ratio under different fatigue loading conditions. For the experimental surface crack paths in tested specimens the T-stress, the local triaxiality parameter h, the out-of-plane TZ factor and the governing parameter for the 3D-fields of the stresses and strains at the crack tip in the form of In-integral were calculated as a function of aspect ratio by finite element analysis to characterization of the constraint effects along semi-elliptical crack front. The plastic stress intensity factor approach is applied to the fatigue crack growth on the free surface of the tested bending and cruciform specimens as well as the deepest point of the semi-elliptical surface crack front. As result fatigue surface crack paths or crack front positions as a function of accumulated number of cycle of loading are obtained.
Welding sequence effects on residual stress distribution in offshore wind monopile structures
Authors: Mehmanparast Ali , Adedipe Oyewole , Brennan Feargal , Chahardehi Amir
Published: February 2019

Residual stresses are often inevitably introduced into the material during the fabrication processes, such as welding, and are known to have significant effects on the subsequent fatigue crack growth behavior of welded structures. In this paper, the importance of welding sequence on residual stress distribution in engineering components has been reviewed. In addition, the findings available in the literature have been used to provide an accurate interpretation of the fatigue crack growth data on specimens extracted from the welded plates employed in offshore wind monopile structures. The results have been discussed in terms of the role of welding sequence in damage inspection and structural integrity assessment of offshore renewable energy structures.
Damage and failure modeling of lotus-type porous material subjected to low-cycle fatigue
Authors: Kramberger J. , Sterkuš K. , Glodež S.
Published: February 2019

The investigation of low-cycle fatigue behaviour of lotus-type porous material is presented in this paper. Porous materials exhibit some unique features which are useful for a number of various applications. This paper evaluates a numerical approach for determining of damage initiation and evolution of lotus-type porous material with computational simulations, where the considered computational models have different pore topology patterns. The low-cycle fatigue analysis was performed by using a damage evolution law. The damage state was calculated and updated based on the inelastic hysteresis energy for stabilized cycle. Degradation of the elastic stifness was modeled using scalar damage variable. In order to examine crack propagation path finite elements with severe damage were deleted and removed from the mesh during simulation. The direct cyclic analysis capability in Abaqus/Standard was used for low-cycle fatigue analysis to obtain the stabilized response of a model subjected to the periodic loading. The computational results show a qualitative understanding of pores topology influence on low-cycle fatigue under transversal loading conditions in relation to pore orientation.
Fatigue crack initiation and propagation in lotus-type porous material
Authors: Glodež S. , Dervaric S. , Kramberger J. , Šraml M.
Published: February 2019

The investigation of fatigue strength of lotus-type structure with nodular cast iron as a base material using computational model is analysed in present study. The irregular pores distribution in transversal and longitudinal direction, regarding the external loading, is considered in the computational models. The complete fatigue process of analyzed porous structure is then divided into the crack initiation (Ni) and crack propagation (Np) period where the total fatigue life (N) is defined as: N = Ni + Np. The crack initiation period is determined using strain life approach where elastic-plastic numerical analysis is performed to obtain the total strain amplitude in the critical stress fields around the pores. The simplified universal slope method is then used to determine the number of stress cycles, Ni, required for formation of initial cracks. The number of stress cycles, Np, required for crack propagation from initial to the critical crack length is also numerically determined using finite element (FE) models, in the frame of Abaqus computation FEM code. The maximum tensile stress (MTS) criterion is considered when analyzing the crack path inside the porous structure. The performed computational analyses show that stress concentrations around individual pores are higher when external loading is acting in transversal direction in respect to the pore distribution. Therefore, further computational analyses regarding crack initiation and crack propagation period have been done only for pores distribution in transversal direction.
Experimental estimation of the heat energy dissipated in a volume surrounding the tip of a fatigue crack
Authors: Meneghetti G. , Ricotta M.
Published: February 2019

Fatigue crack initiation and propagation involve plastic strains that require some work to be done on the material. Most of this irreversible energy is dissipated as heat and consequently the material temperature increases. The heat being an indicator of the intense plastic strains occurring at the tip of a propagating fatigue crack, when combined with the Neuber’s structural volume concept, it might be used as an experimentally measurable parameter to assess the fatigue damage accumulation rate of cracked components. On the basis of a theoretical model published previously, in this work the heat energy dissipated in a volume surrounding the crack tip is estimated experimentally on the basis of the radial temperature profiles measured by means of an infrared camera. The definition of the structural volume in a fatigue sense is beyond the scope of the present paper. The experimental crack propagation tests were carried out on hot-rolled, 6-mm-thick AISI 304L stainless steel specimens subject to completely reversed axial fatigue loading.
Crack initiation and fracture features of Fe–Co–B–Si–Nb bulk metallic glass during compression
Authors: Lesz S. , Januszka A. , Griner S. , Nowosielski R.
Published: February 2019

The aim of the paper was investigation crack initiation and fracture features developed during compression of Fe-based bulk metallic glass (BMG). These Fe-based BMG has received great attention as a new class of structural material due to an excellent properties (e.g. high strength and high elasticity) and low costs. However, the poor ductility and brittle fracture exhibited in BMGs limit their structural application. At room temperature, BMGs fails catastrophically without appreciable plastic deformation under tension and only very limited plastic deformation is observed under compression or bending. Hence a well understanding of the crack initiation and fracture morphology of Fe-based BMGs after compression is of much importance for designing high performance BMGs. The raw materials used in this experiment for the production of BMGs were pure Fe, Co, Nb metals and nonmetallic elements: Si, B. The Fe–Co–B–Si–Nb alloy was cast as rods with three different diameters. The structure of the investigated BMGs rod is amorphous. The measurement of mechanical properties (Young modulus - E, compressive stress - ?c, elastic strain - ?, unitary elastic strain energy – Uu) were made in compression test. Compression test indicates the rods of Fe-based alloy to exhibit high mechanical strength. The development of crack initiation and fracture morphology after compression of Fe-based BMG were examined with scanning electron microscope (SEM). Fracture morphology of rods has been different on the cross section. Two characteristic features of the compressive fracture morphologies of BMGs were observed. One is the smooth region. Another typical feature of the compressive fracture morphology of BMGs is the vein pattern. The veins on the compressive fracture surface have an obvious direction as result of initial displace of sample along shear bands. This direction follows the direction of the displacement of a material. The formation of veins on the compressive fracture surface is closely related to the shear fracture mechanism. The results of these studies may improve the understanding on the fracture features and mechanisms of BMGs and may provide instructions on future design for ductile BMGs with high resistance for fracture.
Crack path in aeronautical titanium alloy under ultrasonic torsion loading
Authors: Nikitin A. , Bathias C. , Palin-Luc T. , Shanyavskiy A.
Published: February 2019

This paper discusses features of fatigue crack initiation and growth in aeronautical VT3-1 titanium alloy under pure torsion loading in gigacycle regime. Two materials: extruded and forged VT3-1 titanium alloys were studied. Torsion fatigue tests were performed up to fatigue life of 109 cycles. The results of the torsion tests were compared with previously obtained results under fully reversed axial loading on the same alloys. It has been shown that independently on production process as surface as well subsurface crack initiation may appear under ultrasonic torsion loading despite the maximum stress amplitude located at the specimen surface. In the case of surface crack initiation, a scenario of crack initiation and growth is similar to HCF regime except an additional possibility for internal crack branching. In the case of subsurface crack, the initiation site is located below the specimen surface (about 200 µm) and is not clearly related to any material flaw. Internal crack initiation is produced by shear stress in maximum shear plane and early crack growth is in Mode II. Crack branching is limited in the case of internal crack initiation compared to surface one. A typical ‘fish-eye’ crack can be observed at the torsion fracture surface, but mechanism of crack initiation seems not to be the same than under axial fatigue loading.