bluuebunny/crossref_metadata_2025 huggingface dataset:
Exploring Twitter for CSR Disclosure: Influence of CEO and Firm Characteristics in Latin American Companies
Authors: Suárez-Rico Yuli Marcela , Gómez-Villegas Mauricio , García-Benau María Antonia
Published: July 2018

Social networks, which are characterised by accessibility and interactivity, offer great potential for dialogue between companies and stakeholders, for example as platforms for publishing information on aspects of corporate social responsibility (CSR). In this paper, we use a synthetic index to analyse levels of CSR disclosure via Twitter, and identify explanatory variables of this disclosure by studying the demographic characteristics of the Chief Executive Officer (CEO) and of the company. This synthetic index was based on data for 93 companies located in the four countries of the Pacific Alliance (Chile, Colombia, Mexico, and Peru), using categories based on the 2016 Global Reporting Initave (GRI) Standards. The tweets were compiled during a period of two months in 2017, immediately before and after the publication of each CSR report. The synthetic index was taken as the dependent variable and used as the basis for multivariate regression analysis to identify the relationship between the level of CSR disclosure on Twitter and the characteristics of the firm and its CEO. The results obtained show that firms operating in environmentally-sensitive industries present higher levels of CSR disclosure on Twitter than those in other sectors. By country of origin, the Colombian and Chilean companies offered higher levels of disclosure than those in Mexico and Peru. The regression analysis revealed a positive relationship between the firm operating in a sensitive industry and its level of CSR disclosure on Twitter, and an inverse relationship between the latter variable and the tenure of the CEO.
Are the World-Leading Primary Silver Mines Exhausting?
Authors: Ruberti Marcello , Massari Stefania
Published: July 2018

Silver is one of the rarest metals in nature and certainly among the most used ones, not only as precious good for financial investments but also for many industrial critical applications. Because it would be very difficult to analyze the situation regarding the future global availability of silver as a commodity in general, due to the necessity of a large amount of data which are hardly available, we have focused only on the mining production of primary silver. In particular, the study regards the activities of a sample consisting of twelve of the world top fifteen leading primary silver mines, which represent the 54% of the worldwide primary silver production and 16% of the global silver mining production. We have investigated the related exploitation state and trends of these twelve sites by elaborating their last ten-years statistics on silver production, ore grades, resources and reserves. The findings of this study, in short, are that the cumulative average silver ore grades, both in extracted mineral, resources and reserves, of the above selected mines, have decreased and also that the new mining fields (Dukat, San Bartolomé, Pirquitas, Saucito) have lower silver content indexes than the older ones.
A Rough Multi-Criteria Decision-Making Approach for Sustainable Supplier Selection under Vague Environment
Authors: Lu Huiyun , Jiang Shaojun , Song Wenyan , Ming Xinguo
Published: July 2018

With the growing awareness of environmental and social issues, sustainable supply chain management (SSCM) has received considerable attention both in academia and industry. Supplier selection plays an important role in the successful implementation of sustainable supply chain management, because it can influence the performance of SSCM. Sustainable supplier selection is a typical multi-criteria decision-making problem involving subjectivity and vagueness. Although some previous researches of supplier selection use fuzzy approaches to deal with vague information, it has been criticized for requiring much priori information and inflexibility in manipulating vagueness. Moreover, the previous methods often omit the environmental and social evaluation criteria in the supplier selection. To manipulate these problems, a new approach based on the rough set theory and ELECTRE (ELimination Et Choix Traduisant la REalité) is developed in this paper. The novel approach integrates the strength of rough set theory in handling vagueness without much priori information and the merit of ELECTRE in modeling multi-criteria decision-making problem. Finally, a case study of sustainable supplier selection for solar air-conditioner manufacturer is provided to demonstrate the application and potential of the approach.
Renewable Energy and Economic Growth: Evidence from European Countries
Authors: Ntanos Stamatios , Skordoulis Michalis , Kyriakopoulos Grigorios , Arabatzis Garyfallos , Chalikias Miltiadis , Galatsidas Spyros , Batzios Athanasios , Katsarou Apostolia
Published: July 2018

This paper aims at examining the relationship between energy consumption deriving from renewable energy sources, and countries’ economic growth expressed as GDP per capita concerning 25 European countries. The used dataset involves European countries’ data for the period from 2007 to 2016. The statistical analysis is based on descriptive statistics, cluster analysis, and autoregressive distributed lag (ARDL), and reveals that all variables are related; this suggests a correlation between the dependent variable of GDP and the independents of renewable energy sources (RES) and Non-RES energy consumption, gross fixed capital formation, and labor force in the long-run. Furthermore, the results show that there is a higher correlation between RES’ consumption and the economic growth of countries of higher GDP than with those of lower GDP. The obtained results are consistent with other papers reviewed in this study.
Advanced Wireless Sensor Networks for Sustainable Buildings Using Building Ducts
Authors: Yang Heekwon , Kim Byeol , Lee Joosung , Ahn Yonghan , Lee Chankil
Published: July 2018

The communication technology ZigBee has been widely adopted in wireless sensor networks (WSNs) for a wide range of industrial applications. However, although ZigBee provides low-power, low-cost mesh networking, it cannot guarantee steady and predictable network performance as channels are time-variant and highly attenuated by man-made obstacles. The networks also suffer from interference, especially in the important 2.4 GHz industrial, scientific, and medical (ISM) band. These degraded channel characteristics increase the number of hops, thus increasing both the packet error rate and transmission delays. In this paper, we report the deployment of a ZigBee-based WSN inside an existing building duct system utilized for intelligent waste collection in an industrial environment. The Received Signal Strength (RSS) and path losses were measured, revealing that the duct communication channel acts as a very effective waveguide, providing a more reliable and consistent network performance than conventional free space channels.
Winter Weather Anomalies and Individual Destination Choice
Authors: Falk Martin , Hagsten Eva
Published: July 2018

Recently, several winter seasons in the European Alps have been unexpectedly warm. In the Austrian mountains, December 2015 was the warmest since weather records began, with a temperature deviation of +6.6 °C compared to the long-term average. By use of data on 6200 individual trips from the Austrian travel survey, a multinomial Logit model is employed to estimate if weather anomalies affect the choice of winter trips. A substitution for more distant trips may create additional environmental burdens, given that they require longer travels or alternative transportation modes. Estimation results reveal that the choice of a mountain destination is not yet affected by extreme winter weather conditions. The result is valid for December 2015, as well as for the total winter season 2015/2016. However, December 2015 and 2016 exhibit a separate development with a significant increase in the likelihood of trips to non-mountains in Europe (mostly city breaks), although no traces of a direct substitution effect can be found. Younger and older people, as well as women, are less likely to go on a winter trip to the mountains. Residents with a tertiary degree and students are more interested in this, as well as large travel groups.
Phylogenetic Analysis and Characterization of the Complete Hepatitis E Virus Genome (Zoonotic Genotype 3) in Swine Samples from Mexico
Authors: Sotomayor-González Alicia , Trujillo-Ortega María E. , Taboada-Ramírez Blanca I. , Sandoval-Jaime Carlos , Sarmiento-Silva Rosa E.
Published: July 2018

Hepatitis E virus (HEV) is an emerging public health problem with an estimated 20 million infections each year. In Mexico, Orthohepevirus A, genotype 2, has been reported in humans, but genotype 3 has only been reported in swine (zoonotic). No diagnostic tests are publicly available in Mexico, and only partial sequences have been reported from swine samples. Hence, research is necessary to determine circulating strains, understand the features and dynamics of infection on pig farms, determine how to implement surveillance programs, and to assess public health risks. In this study, a next-generation sequencing (NGS) approach was applied to obtain a complete genome of swine HEV. Liver, feces, and bile samples were taken at slaughterhouses and a farm in Mexico. RT-PCR was used to determine positive samples and confirmed by Sanger sequencing. Of the 64 slaughterhouse samples, one bile sample was positive (B1r) (1.56%). Of 21 sample pools from farm animals, 14 were positive (66.66%), representing all stages of production. A complete sequence strain MXCDg3_B1c|_2016 was obtained from the bile of a domestic swine in the fattening stage. In addition, two partial sequences—MXCDg3_H2cons|_2016 (1473 nt) and MXCDg3_C3Acons|_2016 (4777 nt)—were obtained from sampled farm animals. Comparison with all reported genome HEV sequences showed similarity to genotype 3 subgenotype a (G3a), which has been previously reported in acute cases of human hepatitis in the US, Colombia, China, and Japan.
Induction of Oxidative DNA Damage in Bovine Herpesvirus 1 Infected Bovine Kidney Cells (MDBK Cells) and Human Tumor Cells (A549 Cells and U2OS Cells)
Authors: Zhu Liqian , Fu Xiaotian , Yuan Chen , Jiang Xinyi , Zhang Gaiping
Published: July 2018

Bovine herpesvirus 1 (BoHV-1) is an important pathogen of cattle that causes lesions in mucosal surfaces, genital tracts and nervous systems. As a novel oncolytic virus, BoHV-1 infects and kills numerous human tumor cells. However, the mechanisms underlying the virus-induced cell damages are not fully understood. In this study, we demonstrated that virus infection of MDBK cells induced high levels of DNA damage, because the percentage of comet tail DNA (tailDNA%) determined by comet assay, a direct indicator of DNA damage, and the levels of 8-hydroxyguanine (8-oxoG) production, an oxidative DNA damage marker, consistently increased following the virus infection. The expression of 8-oxoguanine DNA glycosylase (OGG-1), an enzyme responsible for the excision of 8-oxoG, was significantly decreased due to the virus infection, which corroborated with the finding that BoHV-1 infection stimulated 8-oxoG production. Furthermore, the virus replication in human tumor cells such as in A549 cells and U2OS cells also induced DNA damage. Chemical inhibition of reactive oxidative species (ROS) production by either ROS scavenger N-Acetyl-l-cysteine or NOX inhibitor diphenylene iodonium (DPI) significantly decreased the levels of tailDNA%, suggesting the involvement of ROS in the virus induced DNA lesions. Collectively, these results indicated that BoHV-1 infection of these cells elicits oxidative DNA damages, providing a perspective in understanding the mechanisms by which the virus induces cell death in both native host cells and human tumor cells.
The Mechanical Properties of High Strength Reinforced Cured-in-Place Pipe (CIPP) Liner Composites for Urban Water Infrastructure Rehabilitation
Authors: Ji Hyun Wook , Yoo Sung Soo , Kim Jonghoon , Koo Dan Daehyun
Published: July 2018

Most urban areas in the world have water infrastructure systems, including the buried sewer and water pipelines, which are assessed as in need of extensive rehabilitation. Deterioration by many other factors affects structural integrity. Trenchless technologies such as Cured-in-Place Pipe (CIPP) are now applied in numerous projects while minimizing disturbance in an urban environment. The main purpose of this study is to develop a high strength CIPP material using various composite materials (e.g., glass fiber, carbon fiber, polyester felt, unsaturated polyester resin, and others). Composite samples were made of the materials and tested using three-point bend apparatus to find mechanical properties, which include the flexural modulus, strength, and deflection. A composite combination with glass fibers with thin felt layers shows the best results in mechanical properties. Flexural modulus is a key factor for CIPP liner thickness design. Glass fiber composite yields between four and nine times higher values than the minimum value specified in the American Society for Testing and Materials (ASTM) F1216. This study provides a fundamental baseline for high strength CIPP liners that are capable of using conventional curing technologies.
Nonlinear Simulation of Wave Train Impact on a Vertical Seawall
Authors: Ning Dezhi , Li Xiang , Zhang Chongwei
Published: July 2018

A 2D nonlinear numerical wave flume is developed to investigate the wave train impact on a vertical seawall. Fully nonlinear kinematic and dynamic boundary conditions are satisfied on the instantaneous free surface. Cases of single-, double- and multi-crest wave trains are discussed. For single-crest wave train cases, the present nonlinear results are compared with the solution of the Serre-Green-Naghdi (SGN) model, showing good agreement. For double-crest wave train cases, the SGN model underestimates the maximum wave run-up along the vertical seawall. Compared with the linear results, the nonlinearity for double-crest cases can lead to an evident increase of the wave run-up and high-frequency free-surface oscillations. Through a fast Fourier analysis, evident nonlinear characteristics of the time series of the wave run-up and wave load during the wave impact process are confirmed. For multi-crest wave train cases, irregular wave run-ups can be observed. In some cases, the wave run-up along the vertical seawall can reach about 6 times that of the incident wave, which should be considered carefully in a practical design.
An amphiphilic pseudo[1]catenane: neutral guest-induced clouding point change
Authors: Ogoshi Tomoki , Akutsu Tomohiro , Yamagishi Tada-aki
Published: July 2018

The hydrophobic/hydrophilic ratio in a molecule largely affects its assembled properties in aqueous media. In this study, we synthesized a new bicyclic compound which could dynamically change its hydrophobic/hydrophilic ratio by chemical stimulus. The bicyclic compound consisted of amphiphilic pillar[5]arene and hydrophobic alkyl chain rings, and formed a self-inclusion structure in aqueous media, which was assigned as a pseudo[1]catenane structure. The hydrophobic chain ring was hidden inside the pillar[5]arene cavity in the pseudo[1]catenane structure, thus the bicyclic compound was soluble in water at 20 °C with a clouding point at 24 °C. The pseudo[1]catenane was converted to the de-threaded structure upon addition of the neutral guest 1,4-dicyanobutane, which displaced the alkyl chain ring from the inside to the outside of the cavity. The hydrophobic alkyl chain ring was now exposed to the aqueous media, causing aggregation of the hydrophobic alkyl chain rings, which induced insolubilization of the bicyclic compound in aqueous media at 20 °C and a decrease in its clouding point.
First record of Scopula orientalis (Alphéraky, 1876) (Lepidoptera, Geometridae) in Romania, at the northern limit of the Balkans
Authors: Dincă Vlad , Székely Levente
Published: July 2018

The geometrid mothScopulaorientalis(Alphéraky, 1876) has an apparently disjunct distribution in Europe, with local populations in the Balkans (Macedonia, Bulgaria and Albania where recently discovered), as well as in Ukraine and southern European Russia. In this study, based on morphological and mitochondrial DNA (cytochrome c oxidase subunit 1 – COI) data, we report the presence ofS.orientalisin south-eastern Romania (Dobrogea), at the northernmost limit of the Balkans. The flight time (September) of the recorded specimen, is the latest seasonal record for the Balkans, supporting the presence of at least a partial second generation. The Romanian specimen represented a unique COI haplotype which is differentiated by seven mutations from its genetically closest population in Sivas province, Turkey. The presence ofS.orientalisin Romania reduces the distributional gap between the known Balkan and Ukrainian populations and highlights the potential for a more widespread distribution that needs documentation based on directed studies.
Ten new species of the spider genus Althepus Thorell, 1898 from Southeast Asia (Araneae, Ochyroceratidae)
Authors: Li Fengyuan , Liu Chang , Li Shuqiang
Published: July 2018

Spiders of the genus Althepus Thorell, 1898 are found throughout Southeast Asia, notable for their long walking legs. Ten new species are reported in this paper from China, Indonesia, Laos and Myanmar: A.chengmenensis Li & Li, sp. n. (♂♀), A.cheni Li & Li, sp. n. (♂♀), A.gouci Li & Li, sp. n. (♂♀), A.hongguangi Li & Li, sp. n. (♂♀), A.phousalao Li & Li, sp. n. (♂♀), A.qianhuang Li & Li, sp. n. (♂♀), A.qingyuani Li & Li, sp. n. (♀), A.sepakuensis Li & Li, sp. n. (♂♀), A.xuae Li & Li, sp. n. (♂♀) and A.yizhuang Li & Li, sp. n. (♂♀). These species were found in cave entrances and among tree-buttresses, indicating the spiders have a preference for dark and moist environments. All types are deposited in the Institute of Zoology, Chinese Academy of Sciences in Beijing, China (IZCAS).
The Development of Mobile Culinary Recommendation System Based on Group Decision Support System
Authors: Dewi Ratih Kartika , Ananta Mahardeka Tri , Fanani Lutfi , Brata Komang Candra , Priandani Nurizal Dwi
Published: July 2018

Mobile based culinary recommendation system has received significant attention in recent mobile application research . Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) has regained popularity in supporting multi-criteria decision making due to this method allowing inclusion of many factors and criteria into the decision making process. Previous works on mobile based scenario culinary recommendation system reveal that TOPSIS stand out from other recommendation approaches like AHP and Fuzzy by providing a lightweight computation algorithm that have promising performance in time complexity. However, computing a culinary recommendation using TOPSIS has own limitations especially in the menu judgment processes due to the alternatives priority only include personal preferences for recommendation. In such a culinary recommendation system scenario, users more likely search culinary menus in group instead of alone. This research aims to develop a culinary recommendation system based on group decision support system (GDSS) using TOPSIS that possible to calculate a recommendation by using group preferences instead of personal preferences. The experimental results show that the overall functional of proposed GDSS gives better recommendation result. GDSS using TOPSIS have 100% rank consistency for 6 group of users with 5 combination of menus. The accuracy testing shows that 83,33 % recommendation of GDSS TOPSIS are match with real user preferences. Furthermore, it can be run well in various type of Android smartphone.
Multi-Criteria Analysis and Advanced Comparative Study between M-learning Development Approaches
Authors: Zidoun Youness , Dehbi Rachid , Talea Mohamed
Published: July 2018

With the great advances in the world of mobile learning, development approaches are a very important challenge in designing an M-learning platform for instructors. The development can quickly become a handicap to the integration of certain functionalities and features if the approach is not very well thought and adapted to the pedagogical model designed for the platform. The purpose of this article is to clarify certain comparative aspects between the various methods of development of mobile learning platforms, their ordering and processing and the advantages and disadvantages of each approach. The authors present a multi-criteria analysis which can help instructors in decision-making by assisting their choice of the mobile development approach according to the most important criteria. This paper constitutes an overview of the m-learning platforms from design implementation point of view and will help researchers implement the pedagogical design model described in previous work.
Ghosts Happen
Authors: Delaplace Grégory
Published: July 2018

What is it that happens when the dead appear, when ghosts manifest? Beyond the variety of contexts, eras and approaches presented here, this volume considers ghosts not only as things that are believed in (or not), but also – and above all – as things that happen, as events. By the institutions they set in motion, the doubts they stir, or the solutions they inspire, these events generate solidarity, rekindle old conflicts, and define the borders of communities; in short, they force the living to recompose their world anew. Documenting an apparition invites us not only to ask what appears – that is, the forms that ghosts may take around the world – but also what it is that the apparitions themselves make appear; what is made visible as a result of a ghost’s manifestation.
Percepções da família acerca do cuidado ao homem com alguma condição crônica/ Family perceptions about care for men with chronic conditions
Authors: Arruda Guilherme Oliveira de , Leal Luzia Borges , Peruzzo Hellen Emilia , Nass Evelin Matilde Arcain , Reis Pamela Dos , Marcon Sonia Silva
Published: July 2018

O objetivo deste estudo foi conhecer as percepções da família acerca do cuidado a homens com condições crônicas e dependentes de cuidados domiciliares. Estudo de natureza qualitativa, realizado junto a 17 familiares de homens em adoecimento crônico, que adotou os referenciais do Cuidado Centrado na Família e Gênero. Os dados foram coletados em 2014, por meio de entrevistas abertas, realizadas nos domicílios dos familiares, e submetidos à Análise de Conteúdo, modalidade temática. Os resultados mostram que a maior parte dos familiares cuidadores era do sexo feminino, tinha idade entre 49 e 83 anos e também apresentava alguma condição crônica. Os homens cuidados tinham, em sua maioria, hipertensão arterial, diabetes mellitus e conseqüências de acidente vascular cerebral. Os cuidados referidos foram desde o auxílio no banho até o manejo de dispositivos mais complexos — traqueostomia e gastrotomia. Os familiares apontaram diferentes motivos comportamentais pelos quais, acreditam eles, os homens adoeceram;  relataram que realizavam os cuidados necessários, embora  os homens manifestassem resistência em recebê-los. Conclui-se ser importante considerar diferenças de gênero em relação ao adoecimento crônico e à dependência de cuidado familiar no domicílio, como subsídio para fundamentar o planejamento e a prestação de um cuidado centrado nas necessidades do homem e sua família.
Continuous Dynamic Recrystallization in Dual-Phase Titanium Alloy in Superplasticity
Authors: Sekiguchi Keita , Masuda Hiroshi , Tobe Hirobumi , Sato Eiichi
Published: July 2018

A new class of superplastic titanium alloy, Ti–4.5Al–2.5Cr–1.2Fe–0.1C–0.3Cu–0.3Ni, was deformed at 1073 K with strain rates of 1×10−4–1×10−1 s−1, and microstructures in the condition between superplastic regions II and III (= 1×10−2 s−1) were observed using scanning electron microscope and electron back-scattered diffraction. Continuous dynamic recrystallization was observed, resulting in grain refinement both in α and β phases. The grain size decreased significantly in α phase at the early stage of the deformation and in β phase at the later stage. In the recrystallized microstructure, the major sub-boundaries formed perpendicularly to slip directions <11−20> in α phase and parallel to slip planes {110} in β phase, which might be caused by the difference in the symmetry of the crystal structures.
Superplasticity in Fine Grain Ti-6Al-4V Alloy: Mechanical Behavior and Microstructural Evolution
Authors: Despax Laurie , Vidal Vanessa , Delagnes Denis , Dehmas Moukrane , Geyer Morgane , Matsumoto Hiroaki , Velay Vincent
Published: July 2018

Titanium Ti-6Al-4V alloys are known to exhibit interesting superplastic properties for different conditions of temperature and strain rate, depending on the initial grain size. Even if superplasticity is generally explained in terms of grain boundary sliding (GBS) accompanied by several accommodation mechanisms, it appears that the micromechanisms of superplasticity are still controversial especially at the grain scale and even more at lower scale. These micromechanisms, involving microstructural evolution, depend also on the SPF conditions (temperature, strain rate and initial microstructure). In this study, the flow stress in the Ti-6Al-4V alloy is investigated for different strain rate and for temperature in the range of the α/β transformation. The preferred orientation evolution of alpha phase grains for different percentage of deformation is studied for a non-optimal SPF regime (920°C-10-4 s-1) in order to highlight the microstructural evolution and so the deformation mechanisms involved. For that, mechanical interrupted test combined with Scanning Electron Microscopy (SEM) and Electron Back Scatter Diffraction (EBSD) are used.
Microstructure Evolution and Properties of Ti-6Al-4V Alloy Doped with Fe and Mo during Deformation at 800°C
Authors: Klimenko Denis , Ozerov Maxim , Suresh Santharam , Stepanov Nikita , Tikhonovsky Mikhail A. , Salishchev Gennady , Zherebtsov Sergey
Published: July 2018

Microstructure evolution and mechanical behavior of alpha/beta Ti-6Al-4V and Ti-6Al-4V-0.75Mo-0.5Fe titanium alloys during uniaxial compression to a height strain of 70% was studied. The plastic-flow response for both alloys is characterized by successive stages of strain hardening, flow softening, and steady-state flow. During compression the lamellae spheroidized to produce a globular microstructure with higher rate of globularization in Ti-6Al-4V-0.75Mo-0.5Fe. The globularization kinetics in Ti-6Al-4V-0.75Mo-0.5Fe was also found to be much faster than that in Ti-6Al-4V. This difference can be partially associated with different interphase energy due to doping of β-stabilizing elements.
Effect of Initial Microstructure on Grain Refinement and Enhanced Low Temperature Superplaticity in Friction Stir Processed Ti-6Al-4V Alloy
Authors: Zhang Wen Jing , Ding Hua , Yang Wen Jing , Li Ji Zhong
Published: July 2018

Ti-6Al-4V alloy sheet with two kinds of initial microstructure (base material (BM) and heat-treated material) was subjected to friction stir processing (FSP). These two kinds of friction stir processed (FSPed) materials show similar characteristics that the microstructure exhibited equiaxed ultrafine-grained (UFG) structure with high fraction of high angle grain boundaries (HAGBs) and random crystallographic orientations. Furthermore, slightly finer grains were observed in FSPed heat-treated material than that in FSPed BM. Superplastic tensile tests were conducted utilizing the FSPed heat-treated material in the strain rates range from 1×10-2 to 1×10-4 s-1 at 650°C, and the optimal superplasciticy with an elongation of 1220% was achieved at 1×10-3 s-1. The superplastic deformation mechanism appears to be grain boundary sliding.
Effect of Grain Refinement on the Elemental Composition and Nanohardness of the Surface Layers in AISI 316L Austenitic Steel Subjected to Ion-Plasma Hardening
Authors: Moskvina Valentina , Astafurova Elena , Maier Galina , Ramazanov Kamil , Astafurov Sergey , Melnikov Eugene
Published: July 2018

We study the effect of the grain refinement on the elemental composition and nanohardness of the surface layers in AISI 316L austenitic steel processed by ion-plasma hardening. Ion-plasma hardening of the samples with (1) grain-subgrain (with high dislocation density) and (2) coarse-grained structures causes a surface hardening and formation of the composite layers with a thickness of about 20 μm. The nanohardness and depth profiles of elemental concentration of nitrogen, carbon and oxygen in the ion-plasma hardened layers depends on pretreatment regime of the steel specimens. Cold rolling causes an increase in the grain and subgrain boundaries fraction and dislocation density in steel specimens, provides more intensive accumulation of interstitial atoms in thin surface 5 μm-layer, leads to additional surface hardening and suppress carbon diffusion into depth of the specimens as compared with coarse-grained structure.
On the Nuances in the Power Law Description and Interpretation of High Homologous Temperature Creep and Superplasticity Data
Authors: Padmanabhan K. Anantha , Balasivanandha Prabu S. , Abbas Ali A. Arsath
Published: July 2018

“Power law’’ representation is used to describe minimum creep rate and “steady state” superplastic deformation. In creep isothermal log stress – log strain rate relationship is linear for so long as the rate controlling mechanism remains unchanged. During optimal superplastic flow the slope of this curve changes even when there is no change in the rate controlling mechanism, i.e. the stress exponent, n, at a constant temperature and grain size is a function of strain rate. For a constant rate controlling mechanism, in both the phenomena, n decreases with increasing temperature. Grain size has no effect on creep, but its effect is significant in superplasticity. Therefore, analyzing creep and superplasticity data by treating n for any given mechanism as a constant independent of stress and temperature is questionable. In this analysis stress is normalized with respect to a reference stress, rather than the shear modulus. The microstructure dependence comes through the Buckingham Pi theorem. When contribution from microstructure terms to isothermal strain rate is constant, Laurent’s theorem helps generate a set of values for n. It is shown that the simplest solution, viz. n is independent of stress, but is a linear function of temperature, describes steady state creep. (The case n is independent of both stress and temperature follows as a special case.) The second simplest solution, viz. n is a linear function of both temperature and stress corresponds to steady state superplasticity. Using the equations, the values of n, activation energies for the rate controlling processes and strain rates at different temperatures and stresses could be estimated for both creep and superplasticity. The analysis is validated using experimental results concerning many systems. iiThis lecture is dedicated to the sacred memory of late Prof. Oleg D. Sherby.
Influence of Temperature of Severe Plastic Deformation and Aging on Microstructure, Mechanical Properties and Electrical Conductivitiy of the Cu-Cr-Zr Alloy
Authors: Sarkeeva Elena , Abramova Marina M. , Alexandrov Igor V.
Published: July 2018

The article studies an influence of temperature of severe plastic deformation (SPD) and post-deformation heat treatment on microstructure, mechanical properties and thermal stability of the Cu-0.5Cr-0.2Zr alloy. The results demonstrate that strength is considerably increased to 900 MPa by high pressure torsion (HPT) at room temperature. Subsequent ageing at 450 °С during 1 hour leads to a decay of solid solution and an allocation of dispersion particles that further incrises strength to 900 MPa, restores electrical conductivity to 70% IACS (International annealed copper standard) and enhances thermal stability of the alloy. When deformation temperature is increased to 300°С, strength is 690 MPa that is lower than in the case of deformation at room temperature that is related to reversion process at deformation. Additional a aging does not lead to an increase of strength characteristics.
Influence of Inhomogeneity on Mechanical Properties of Commercially Pure Titanium Processed by HPT
Authors: Zhilyaev Alexander P. , Huang Yi , Cabrera Jose María , Langdon Terence G.
Published: July 2018

Already for fifteen years many researchers have been trying to discover metallic materials with unusual combinations of strength and ductility: with high strength and enhanced ductility. This combination may be achieved through different ways: alloying, nanostructuring, etc. This report is an attempt to analyze the influence of inhomogeneity of different types (structural, phase and space) on mechanical properties of commercially pure titanium (bulk and powder) subjected to high-pressure torsion. Experimental results for HPT bulk and powder titanium have demonstrated that mechanical behavior of CP titanium strongly depends on phase inhomogeneity (alpha + omega phases), structural inhomogeneity (bimodal grain size distribution) and space inhomogeneity (retained porosity) in case of cold consolidated Ti powder. High strength in HPT bulk titanium due to the formation of hard omega phase during HPT processing at room temperature was detected. The strong omega phase transforms back to nanograined alpha phase domains during short annealing at elevated temperature. HPT consolidation of titanium powder leads to the formation of brittle specimens showing high strength but almost zero plasticity.
Thirty Years of Superplastic Ultrafine-Grained Materials: Examining the Legacy of Oscar Kaibyshev
Authors: Langdon Terence G.
Published: July 2018

The occurrence of superplasticity may be traced to the classic work of Pearson conducted in the U.K. in 1934 when an elongation of 1950% was reported in a Pb-Sn eutectic alloy. Subsequently, much attention in Russia was devoted to this scientific curiosity and this led to the first book on superplasticity written by Prof. A.A. Presnyakov and published in 1964. Later, in 1985, Oscar Kaibyshev established in Ufa the Institute of Problems of Superplasticity of Metals of the Russian Academy of Sciences and this was, and remains to this day, the only institute in the world devoted exclusively to studies of the phenomenon of superplastic flow and the development through superplastic forming of complex-shaped parts. An important development occurred in 1988 with the publication of a classic report by Kaibyshev and co-workers describing the potential for achieving low temperature superplasticity in a metallic Al-Cu-Zr alloy that had been specially processed by severe plastic deformation (SPD) to produce a remarkably small grain size of only 300 nm. This report formed the basis for the later development of SPD processing as a major tool for the production of exceptional grain refinement and as a procedure for achieving large superplastic elongations that cannot be achieved using more conventional processing. This report describes this early work, the subsequent developments and the modern status of superplastic flow in ultrafine-grained metals.
On Primary Recrystallization of High-Mn Austenitic Steels
Authors: Kusakin Pavel , Tikhonova Marina , Belyakov Andrey , Kaibyshev Rustam
Published: July 2018

The grain refinement is an effective approach to strengthen high-Mn TWIP/TRIP steels. The development of recrystallized microstructure with a grain size of about one micron increases the yield strength of high-Mn steels above 500 MPa. The fine grained microstructures can be easily developed by cold rolling followed by primary recrystallization. The recrystallized grain size can be expressed by a power law function of the strain hardening during the previous cold rolling with an exponent of -2. Taking the dislocation density as the main strengthener, the grain size is an inverse proportion to the dislocation density. Then, the number density of recrystallized grains can be expressed by a power law function of dislocation density evolved during cold rolling with an exponent of about 2.
Effect of Pre-Strain Rolling on Annealing Behavior of Friction-Stir Welded AA6061-T6 Aluminum Alloy
Authors: Mironov Sergey , Malopheyev Sergey , Vysotskiy Igor , Zhemchuzhnikova Daria , Kaibyshev Rustam
Published: July 2018

In this work, the effect of pre-strain cold rolling on thermal stability of friction-stir welded AA6061-T6 alloy was studied. The pre-strain rolling was found to be very effective in suppression of abnormal grain growth during standard post-weld T6 heat treatment. It was also shown that the efficiency of this approach essentially depends on rolling path and the rolling along welding direction was the most effective rolling schedule.
Friction-Stir Welding of Work-Hardened Al-Mg Alloy with Nanoscale Particles
Authors: Mironov Sergey , Malopheyev Sergey , Vysotskiy Igor , Zhemchuzhnikova Daria , Kaibyshev Rustam
Published: July 2018

In this work, feasibility of friction-stir welding (FSW) for joining of heavily deformed 5083 aluminum alloy was studied. To produce work hardening condition, the commercially available material was homogenized to precipitate strengthening particles and then subjected to equal-channel angular pressing (ECAP) at 300 °C to a true strain of ~12 via BCroute and successive rolling at the same temperature to 80 pct. of thickness reduction. Despite the subsequent FSW resulted in significant microstructural changes in stir zone, joint efficiency was found to be 98 pct.
Increase of the Elasticity and Strength of the Welded Joints for the Al-Mg-Li Alloy Made by the Laser Welding by Means of the Thermal Mechanical Processing
Authors: Malikov Aleksandr , Orishich Anatolii , Karpov Evgenij , Sandalov Evgenij
Published: July 2018

The paper deals with the analysis of the effect of the thermal mechanical processing on the mechanical characteristics (elasticity and tensile strength) of the welded joints of the aluminum alloy, the system Al-Mg-Li. The microstructures of the basic alloy and welded joint before and after the thermal processing are compared by electronic microscoping. The X-ray diffraction method is used to compare the phase composition. The concentration of the strengthening phase δʹ(Al3Li) reduces in the welded joint, which results in the low mechanical characteristics. The thermal processing, namely quenching, increases the concentration of the equilibrium S1 phase (Al2MgLi) in the welded joint as compared with an unquenched joint. The elasticity of the welded joint rises significantly at the almost constant strength, the value of the relative extension lies within the range of 2.4 – 19.2 % before and after quenching, respectively. Artificial ageing applied to the welded joint after the quenching gives the structurization of the S1 phase. The full thermal mechanical processing (quenching, elastic deformation, artificial ageing) of the welded joint of the aluminum alloy (the system AL-Mg-Li) results in the tensile strength increase up to 0.95 of the basic alloy strength.
Establishment of the High Temperature Constitutive Relationship of the Haynes 230 Ni-Based Superalloy
Authors: Cheng Xiu Quan , Zhu Ning Yuan , Xia Qin Xiang , Xiao Gang Feng
Published: July 2018

The high temperature flow behavior of materials is an important basis to study their formability and to determine reasonable forming process parameters. In this work, the high temperature plane strain compression (HTPSC) tests were employed to reveal the high temperature flow behavior of Haynes 230 Ni-based superalloy under the wide range of temperatures (950°C-1200°C) and strain rates (0.01/s-10/s). The stress-strain data from the tests were applied to model the strain-compensated Arrhenius physically-based constitutive equation and considering the dynamic recovery (DRV) and dynamic recrystallization (DRX) phenomenological constitutive equation. The comparison indicated that the predictions of the two modeled constitutive equations are in good agreement with the experimental data. The prediction of the flow behavior of Haynes 230 Ni-based superalloy of strain-compensated Arrhenius constitutive equation is more accurately (average absolute relative error (AARE) is 2.84%) than that of considering DRV and DRX constitutive equation (AARE is 7.57%).
FEM Simulation of Influence of Asymmetric Cold Rolling on Through-Thickness Strain Gradient in Low-Carbon Steel Sheets
Authors: Pustovoytov Denis , Pesin Alexander , Zhilyaev Alexander P. , Raab Georgy I.
Published: July 2018

Grain refinement by severe plastic deformation can make conventional metallic materials several times stronger, but it leads to dramatic loss of their ductility. Gradient structure through the thickness of processed material represents a new strategy for producing a superior combination of high strength and good ductility. In gradient metallic materials the grain size increases gradually from nanoscale at the surface to coarse-grained in the core. Strain gradient can be considered as a mechanism of creating of such microstructures. Providing of predetermined strain gradient in the metallic materials can be achieved by asymmetric rolling (AR), when circumferential speeds of the top and bottom work rolls are different. Since the AR is a continuous process, it has great potential for industrial production of large-scaled sheets. Searching the optimal process parameters which can provide special strain gradients through sheet thickness is very important. This paper presents the distributions of the effective strain through sheet thickness of low-carbon steel AISI 1015 processed by a single-pass AR. Influence of process parameters was investigated by the finite element method with using software DEFORM 2D. Extremely high strain gradient e ≈ 4...8 through sheet thickness during a single-pass AR was found. FE analysis of the deformation characteristics, presented in this study, can be used for optimization of the AR process as a method of fabrication of metallic materials with gradient microstructures.
Modification of the Shear-Compression Specimen and Development of a Special Technique for the Physical Simulation of Asymmetric Rolling with a Large Strain
Authors: Pesin Alexander , Pustovoytov Denis , Zhilyaev Alexander P. , Raab Georgy I.
Published: July 2018

Physical simulation of the stress-strain state and microstructure evolution, which are similar to that occurring during asymmetric rolling with a large strain, is very important for design of technologies of producing ultra fine grained metallic materials. This paper presents the results of optimization of specimen geometry and a special multi-cycle shear-compression technique for the physical simulation of asymmetric rolling with a large strain up to e ~ 4. The specimen consisted of a parallelepiped having an inclined gauge section created by two diametrically opposed semi-circular slots which were machined at 45°. The specimen was compressed between two flat dies during shear-compression testing in accordance to the special multi-cycle scheme. Each cycle of the shear-compression testing consisted of two steps. The first step included height reduction of specimen, after that specimen was rotated by 90º. The second step included length reduction of the specimen for getting the quasi original shape of a parallelepiped. The specimen provided simultaneous pure and simple shear in an inclined gauge-section. The level of effective strain was controlled through adjustment of the specimen geometry, height reduction, load application direction and number of cycles of shear-compression. Gauge thickness, width and radius of the specimen were optimized by FEM with using of software DEFORM 3D. Numerical simulation and comparison of the stress-strain state during shear-compression testing and asymmetric rolling of low-carbon steel AISI 1010 were performed. Results of FEM analysis of the applicability of the multi-cycle shear-compression testing to the modeling of asymmetric rolling were discussed.
Mechanisms of Superplasticity in Titanium Alloys: Measurement, In Situ Observations and Rationalization
Authors: Alabort Enrique , Barba Daniel , Reed Roger
Published: July 2018

Surface observations are used to elucidate the deformation mechanisms responsible forsuperplasticity in the Ti-6Al-4V and Ti-4Al-2.5V-1.5Fe titanium alloys. First, stress relaxation testsare used to quantify the difference in superplastic behaviour of each alloy. Then, high-temperature insitutensile tests are performed in the scanning electron microscope at 700, 800, and 900°C to relatedifferences in formability to micro-mechanisms. These are found highly dependent on: (i) the grainsize; (ii) the alpha-to-beta volume fraction; (iii) the crystallographic texture; and (iv) the nature and angle ofthe dominant grain boundaries.
Room Temperature Superplasticity in Fine/Ultrafine-Grained Zn-Al Alloys with Different Phase Compositions
Authors: Demirtas Muhammet , Yanar Harun , Saray Onur , Pürçek Gençağa
Published: July 2018

Three Zn-Al alloys, namely Zn-22Al, Zn-5Al and Zn-0.3Al, were subjected to equal-channel angular pressing (ECAP), and the effect of ECAP on their microstructure and room temperature (RT) superplastic behavior were investigated in detail referring to previous studies reported by the authors of the current study. ECAP remarkably refined the microstructures of three alloys as compared to their pre-processed conditions. While the lowest grain size was achieved in Zn-22Al alloy as 200 nm, the grain sizes of Zn-5Al and Zn-0.3Al alloys were ~540 nm and 2 µm, respectively, after ECAP. After the formation of fine/ultrafine-grained (F/UFG) microstructures, all Zn-Al alloys exhibited superplastic behavior at RT and high strain rates. The maximum superplastic elongations were 400%, 520% and 1000% for Zn-22Al, Zn-5Al and Zn-0.3Al alloys, respectively. It is interesting to point out that the highest RT superplastic elongation was obtained in Zn-0.3Al alloy with the largest grain size, while Zn-22Al alloy having the lowest grain size showed the minimum superplastic elongation. This paradox was attributed to the different phase compositions of these alloys. The formation of Al-rich α/α phase boundaries, where grain boundary sliding is minimum comparing to Zn-rich η/η and η/α phase boundaries of Zn-Al alloys, is the lowest level in Zn-0.3Al alloy among all the alloys. Therefore, it can be concluded that if it is desired to achieve high superplastic elongation in Zn-Al alloys at RT, keeping Al content at a possibly minimum level seems to be the most suitable way.
Poly(Vinyl Alcohol) Fiber Reinforced High Density Poly(Ethylene) Composites: Melting and Crystallization Behavior
Authors: Rofiqah Umi , Chafidz Achmad , Kistriyani Lilis , Kaavessina Mujtahid , Rizal Muhammad , Al Zahrani Saeed M.
Published: July 2018

In the present study, high density poly(ethylene) (HDPE)/poly(vinyl alcohol) (PVA) fiber composites were prepared via melt blending technique using a co-rotating twin screw extruder (TSE). The effect of four different PVA fiber concentrations (i.e. 0, 5, 10, 20 wt%) on the melt and crystallization behavior of the HDPE/PVA fiber composites were investigated. The surface morphology of the composites was analyzed by a scanning electron microscopy (SEM). Whereas, the melt and crystallization behavior of the composites were analyzed by a differential scanning calorimetry (DSC). The SEM analysis on the cryo-fractured surface of the HDPE/PVA fiber composites exhibited that the PVA fibers were well blended/distributed in the HDPE matrix. Additionally, the DSC test results showed that the addition of PVA fiber in the HDPE matrix did not significantly change the melting peak temperature (Tm) of the composites. Furthermore, a slight decrease of the crystallization peak temperature (Tc) can be observed when the PVA fiber was incorporated in the HDPE matrix, which indicated a weak nucleation ability of the PVA fibers in the HDPE crystallization process. The same trend was also observed for the crystallinity index (Xc). The crystallinity index of the composites decreased with increasing PVA fiber loadings.