bluuebunny/crossref_metadata_2025 huggingface dataset:
Iron Isotopic Composition of Suspended Particulate Matter in Hongfeng Lake
Authors: Zheng Xiaodi , Teng Yanguo , Song Liuting
Published: February 2019

The geochemical study of iron isotopes is of great significance to comprehensively understand the surface material circulation process and its environmental effects in surface and subsurface environments. Eutrophic lakes are an important part of the surface and subsurface environment; however, knowledge of the geochemical behaviour and fractionation mechanism of iron isotopes in the biogeochemical cycling of eutrophic lakes is still scarce. In this study, a eutrophic lake with seasonal anaerobic characteristics (Hongfeng Lake) was selected as the study object to systematically analyse the iron isotope composition of suspended particles in lake water and the main tributaries in different seasons. The results show that the value of δ56Fe in Hongfeng Lake is between −0.85‰ and +0.14‰, and the value of δ56Fe has a high linear correlation with Fe/Al, indicating that the continental source material carried by the main inflow tributaries of the lake has an important influence on the source of iron in the lake. And Hongfeng Lake is moderately eutrophic lakes. Algal bloom and the content of chlorophyll a (Chl-a) are high, combined with the high correlation between Chl-a and the value of δ56Fe, which indicates that the growth of algae has an important influence on the change in the iron isotope composition of suspended particulate matter (SPM) in lake water and that the adsorption and growth absorption of Fe by algae are the main reason for the change in the value of δ56Fe; therefore, Fe isotope can be used to trace the lake’s biological action. For the lake and its inflow tributaries, δ56Fe values are higher in summer than in winter. The variation in the δ56Fe value of SPM with lake depth is more distinct in summer than in winter. In addition, there is a distinct thermocline in summer, which leads to hydrochemical stratification. Moreover, according to a linear correlation analysis, the content of dissolved organic matter (DOC) in Hongfeng Lake’s upper and lower water bodies, respectively, has a high correlation with the value of δ56Fe. Specifically, the correlation is positive in the upper water but negative in the lower water, which indicates that the difference in algae metabolism patterns between the upper and lower water bodies of Hongfeng Lake plays an important role in the iron isotope composition of SPM. The composition of the iron isotope in SPM is altered by organic adsorption and growth absorption of algae in the upper water. With an increase in depth, degradation becomes the main process. In addition, the value of δ56Fe is low and that of Fe/Al is high in the water bottom, which indicates that a “ferrous-wheel” cycle forms at the bottom of the water.
Comprehensive Utilization of Seawater in China: A Description of the Present Situation, Restrictive Factors and Potential Countermeasures
Authors: Gong Shuxin , Wang Hongrui , Zhu Zhongfan , Bai Qijie , Wang Cheng
Published: February 2019

China is a maritime power. However, as its economy develops rapidly, China lacks freshwater resources. The water resources per capita are low in China and are less than a quarter of the global mean value. The development and utilization of desalination, a new unconventional water resource in coastal areas, has gradually attracted the attention of the central and local governments. This paper introduces three aspects of the comprehensive utilization of seawater in China, including the desalination of seawater, the direct use of seawater, and the use of seawater as a chemical resource. Based on the recent status (2017) of comprehensive seawater utilization in China, the prospects for optimizing the utilization of seawater resources are presented. Furthermore, the restrictive factors and potential countermeasures for the increased use of seawater desalination are investigated. Several recommendations are presented, specifically, improving the laws, using regulations and standards related to desalination, strengthening the policies that support enterprises that use desalination, gradually improving the localization rate of key technologies and equipment, and devoting additional attention to the problems associated with brine processing. Seawater is expected to become an important supplemental source of water in coastal areas of China, and the resources needed for its use will be developed as a strategic and influential industry.
Coagulation: Determination of Key Operating Parameters by Multi-Response Surface Methodology Using Desirability Functions
Authors: Corral Bobadilla Marina , Lorza Rubén Lostado , Escribano García Rubén , Somovilla Gómez Fátima , Vergara González Eliseo P.
Published: February 2019

The clarification process removes colloidal particles that are suspended in waste water. The efficiency of this process is influenced by a series of inputs or parameters of the coagulation process, of which the most commonly used are initial turbidity, natural coagulant dosage, temperature, mixing speed and mixing time. The estimation of the natural coagulant dosage that is required to effectively remove these total suspended solids is usually determined by a jar test. This test seeks to achieve the highest efficiency of removal of the total suspended solids while reducing the final turbidity of waste water. This is often configured in iterative fashion, and requires significant experimentation and coagulant. This paper seeks to identify regression models that relate the clarification process parameters to the process outputs (final turbidity and total suspend solid) by the Response Surface Methodology (RSM) based on experiments of Central Composite Design (CCD) of experiments that involve three emerging natural coagulants. Several clarification process scenarios also were proposed and demonstrated using the Multi-Response Surface (MRS) with desirability functions. The experimental results were found to be in close agreement to what are provided by the regression models. This validates the use of the MRS-based methodology to achieve satisfactory predictions after minimal experimentation.
2D PIV Measurement of Twin Buoyant Jets in Wavy Cross-Flow Environment
Authors: Xu Zhenshan , Otoo Ebenezer , Chen Yongping , Ding Hongwei
Published: February 2019

The multiport diffuser effluent discharge facilities constructed beneath the coastal waters were simplified in the laboratory as twin buoyant jets in a wavy cross-flow environment. The near-field flow structure of twin jets was studied by series of experiments conducted in a physical wave–current flume. The particle image velocimetry (PIV) system was used to measure the velocity field of the jets in various cross-flow-only and wavy cross-flow environments. By means of flow visualization, the distinctive “effluent cloud” (EC) phenomenon was clearly observed and the jet penetration height was found to be notably increased compared with that of cross-flow-only environment at the downstream position. It was found that the wave-to-current velocity ratio Rwc is a very important parameter for effluent discharge. A new characteristic velocity uch and the corresponding characteristic length scale lmb for twin buoyant jets in the wavy cross-flow environment were defined. Using curve-fitting, a new equation to estimate the effects of the jet-to-current velocity ratio (Rjc), wave-to-current velocity ratio (Rwc) and Strouhal number (St) on the jet trajectory were derived to enhance understanding the physical processes underpinning the rise and the dilution of buoyant jets, which is critical to the design of discharge facilities.
Allocating Water in the Mekong River Basin during the Dry Season
Authors: Yuan Liang , He Weijun , Liao Zaiyi , Degefu Dagmawi Mulugeta , An Min , Zhang Zhaofang , Wu Xia
Published: February 2019

With population numbers increasing and anthropogenic climate change, the amount of available fresh water is declining. This scenario can lead to an increase in the occurrence of water conflicts, especially in transboundary river basins. Prevention strategies to avert water conflicts by designing a fair, efficient, and sustainable water allocation framework are needed. Taking into account the socioeconomic and environmental differences among the riparian countries is one of the most important features an allocation scheme should have. In this article, bankruptcy and bargaining games were used to construct a new weighted water allocation model. The proposed method was applied to allocate the contested water capital of the Mekong River during the dry season. The Mekong River originates in China and flows through Myanmar, Laos, Thailand, Cambodia, and Vietnam. The results of the allocation showed that, except for China and Vietnam, all the other riparian countries get their full claim of the water demand from the river. The water allocation payoffs satisfy individual rationality, Pareto optimality, and maximization of the group utility. Therefore, the allocation outputs from the proposed scheme are self-enforceable and sustainable.
A Multi-Sourced Data Retrodiction of Remotely Sensed Terrestrial Water Storage Changes for West Africa
Authors: Ferreira Vagner G. , Andam-Akorful Samuel A. , Dannouf Ramia , Adu-Afari Emmanuel
Published: February 2019

Remotely sensed terrestrial water storage changes (TWSC) from the past Gravity Recovery and Climate Experiment (GRACE) mission cover a relatively short period (≈15 years). This short span presents challenges for long-term studies (e.g., drought assessment) in data-poor regions like West Africa (WA). Thus, we developed a Nonlinear Autoregressive model with eXogenous input (NARX) neural network to backcast GRACE-derived TWSC series to 1979 over WA. We trained the network to simulate TWSC based on its relationship with rainfall, evaporation, surface temperature, net-precipitation, soil moisture, and climate indices. The reconstructed TWSC series, upon validation, indicate high skill performance with a root-mean-square error (RMSE) of 11.83 mm/month and coefficient correlation of 0.89. The validation was performed considering only 15% of the available TWSC data not used to train the network. More so, we used the total water content changes (TWCC) synthesized from Noah driven global land data assimilation system in a simulation under the same condition as the GRACE data. The results based on this simulation show the feasibility of the NARX networks in hindcasting TWCC with RMSE of 8.06 mm/month and correlation coefficient of 0.88. The NARX network proved robust to adequately reconstruct GRACE-derived TWSC estimates back to 1979.
Architecture and Protocols for Toll-Free Electric Vehicle Charging
Authors: Yaqub Raziq
Published: February 2019

This paper proposes system architecture and protocols for the deployment of a toll-free electric vehicle charging service. The architecture enables the party initiating the electric vehicle (EV) charging to have their service request authorized by the system and paid for by a third party.
Synthesis and SAR of the antistaphylococcal natural product nematophin from Xenorhabdus nematophila
Authors: Wesche Frank , Adihou Hélène , Wichelhaus Thomas A , Bode Helge B
Published: February 2019

The repeated and improper use of antibiotics had led to an increased number of multiresistant bacteria. Therefore, new lead structures are needed. Here, the synthesis and an expanded structure–activity relationship of the simple and antistaphylococcal amide nematophin from Xenorhabdus nematophila and synthetic derivatives are described. Moreover, the synthesis of intrinsic fluorescent derivatives, incorporating azaindole moieties was achieved for the first time.
Photometry and Spectroscopy of Faint Candidate Spectrophotometric Standard DA White Dwarfs
Authors: Calamida Annalisa , Matheson Thomas , Saha Abhijit , Olszewski Edward , Narayan Gautham , Claver Jenna , Shanahan Clare , Holberg Jay , Axelrod Tim , Bohlin Ralph , Stubbs Christopher W. , Deustua Susana , Hubeny Ivan , Mackenty John , Points Sean , Rest Armin , Sabbi Elena
Published: February 2019

We present precise photometry and spectroscopy for 23 candidate spectrophotometric standard white dwarfs. The selected stars are distributed in the Northern hemisphere and around the celestial equator, and are all fainter than r ∼ 16.5 mag. This network of stars, when established as standards and together with the three Hubble Space Telescope primary CALSPEC white dwarfs, will provide a set of spectrophotometric standards to directly calibrate data products to better than 1%. In future deep photometric surveys and facilities, these new faint standard white dwarfs will have enough signal-to-noise ratio to be measured accurately while still avoiding saturation. They will also fall within the dynamic range of large telescopes and their instruments for the foreseeable future. This paper discusses the provenance of the observational data for our candidate standard stars. A comparison with models, reconciliation with reddening, and the consequent derivation of the full spectral energy density distributions for each of them is reserved for a subsequent paper.
Implications of a Hot Atmosphere/Corino from ALMA Observations toward NGC 1333 IRAS 4A1
Authors: Sahu Dipen , Liu Sheng-Yuan , Su Yu-Nung , Li Zhi-Yun , Lee Chin-Fei , Hirano Naomi , Takakuwa Shigehisa
Published: February 2019

We report high angular resolution observations of NGC 1333 IRAS 4A, a protostellar binary including A1 and A2, at 0.84 mm with the Atacama Large Millimeter/submillimeter Array. From the continuum observations, we suggest that the dust emission from the A1 core is optically thick, and A2 is predominantly optically thin. The A2 core, exhibiting a forest of spectral lines including complex molecules, is a well-known hot corino, as suggested by previous works. More importantly, we report, for the first time, solid evidence of complex organic molecules (COMs), including CH3OH, 13CH3OH, CH2DOH, and CH3CHO, associated with the A1 core seen in absorption. The absorption features mostly arise from a compact region around the continuum peak position of the A1 core. Rather than originating from a larger common envelope surrounding the protobinary, the COM features are associated with individual cores A1 and A2. Considering the signatures observed in both continuum and spectral lines, we propose two possible scenarios for IRAS 4A1: the COM absorption lines may arise from a hot-corino-like atmosphere at the surface of an optically thick circumstellar disk around A1, or the absorption may arise from different layers of a temperature-stratified, dense envelope.
A Complete Spectroscopic Census of A2029: A Tale of Three Histories
Authors: Sohn Jubee , Geller Margaret J. , Zahid H. Jabran , Fabricant Daniel G.
Published: February 2019

A rich spectroscopic census of members of the local massive cluster A2029 includes 1215 members of A2029 and its two infalling groups, A2033 and the Southern Infalling Group. The two infalling groups are identified in spectroscopic, X-ray, and weak-lensing maps. We identify active galactic nuclei (AGNs), star-forming galaxies, E+A galaxies, and quiescent galaxies based on the spectroscopy. The fractions of AGN and post-starburst E+A galaxies in A2029 are similar to those of other clusters. We derive the stellar mass (M
*)–metallicity relation of A2029 based on 227 star-forming members; A2029 members within 109
M
⊙ < M
* < 109.5
M
⊙ are more metal-rich than Sloan Digital Sky Survey galaxies within the same mass range. We utilize the spectroscopic index

, a strong age indicator, to trace past and future evolution of the A2029 system. The median

of the members decreases as the projected clustercentric distance increases for all three subsystems. The

relations of the members in A2029 and its two infalling groups differ significantly, indicating the importance of stochastic effects for understanding the evolution of cluster galaxy populations.
Forward Modeling of SDO/AIA and X-Ray Emission from a Simulated Flux Rope Ejection
Authors: Zhao 赵 Xiaozhou 小舟 , Xia Chun , Doorsselaere Tom Van , Keppens Rony , Gan Weiqun
Published: February 2019

We conduct forward-modeling analysis based on our 2.5 dimensional magnetohydrodynamics (MHD) simulation of magnetic flux rope (MFR) formation and eruption driven by photospheric converging motion. The current sheet (CS) evolution during the MFR formation and eruption process in our MHD simulation can be divided into four stages. The first stage shows the CS forming and gradually lengthening. Resistive instabilities that disrupt the CS mark the beginning of the second stage. Magnetic islands disappear in the third stage and reappear in the fourth stage. Synthetic images and light curves of the seven Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) channels, i.e., 94 Å, 131 Å, 171 Å, 193 Å, 211 Å, 304 Å, and 335 Å, and the 3–25 keV thermal X-ray are obtained with forward-modeling analysis. The loop-top source and the coronal sources of the soft X-ray are reproduced in forward modeling. The light curves of the seven SDO/AIA channels start to rise once resistive instabilities develop. The light curve of the 3–25 keV thermal X-ray starts to go up when the reconnection rate reaches one of its peaks. Quasiperiodic pulsations (QPPs) appear twice in the SDO/AIA 171 Å, 211 Å, and 304 Å channels, corresponding to the period of chaotic (re)appearance and CS-guided displacements of the magnetic islands. QPPs appear once in the SDO/AIA 94 Å and 335 Å channels after the disruption of the CS by resistive instabilities and in the 193 Å channel when the chaotic motion of the magnetic islands reappears.
Evaluating the Optical Classification of Fermi BCUs Using Machine Learning
Authors: Kang Shi-Ju , Fan Jun-Hui , Mao Weiming , Wu Qingwen , Feng Jianchao , Yin Yue
Published: February 2019

In the third catalog of active galactic nuclei detected by the Fermi-LAT (3LAC) Clean Sample, there are 402 blazar candidates of uncertain type (BCUs). Due to the limitations of astronomical observation or intrinsic properties, it is difficult to classify blazars using optical spectroscopy. The potential classification of BCUs using machine-learning algorithms is essential. Based on the 3LAC Clean Sample, we collect 1420 Fermi blazars with eight parameters of γ-ray photon spectral index; radio flux; flux density; curve significance; the integral photon flux in 100–300 MeV, 0.3–1 GeV, and 10–100 GeV; and variability index. Here we apply four different supervised machine-learning (SML) algorithms (decision trees, random forests, support vector machines, and Mclust Gaussian finite mixture models) to evaluate the classification of BCUs based on the direct observational properties. All four methods can perform exceedingly well with more accuracy and can effectively forecast the classification of Fermi BCUs. The evaluating results show that the results of these methods (SML) are valid and robust, where about one-fourth of sources are flat-spectrum radio quasars (FSRQs) and three-fourths are BL Lacertae (BL Lacs) in 400 BCUs, which are consistent with some other recent results. Although a number of factors influence the accuracy of SML, the results are stable at a fixed ratio 1:3 between FSRQs and BL Lacs, which suggests that the SML can provide an effective method to evaluate the potential classification of BCUs. Among the four methods, Mclust Gaussian Mixture Modeling has the highest accuracy for our training sample (4/5, seed = 123).
Effect of season and behavioral activity on the hypopharyngeal glands of three honey bee Apis mellifera L. races under stressful climatic conditions of central Saudi Arabia
Authors: Ali Hussain , Alqarni Abdulaziz S. , Iqbal Javaid , Owayss Ayman A. , S. Raweh Hael , Smith Brian H.
Published: February 2019

Honey production gains are needed to deal with high demand in Saudi Arabia. The honey bee races are facing stressful hot-arid weather conditions that can affect different aspects of physiology and behavior. The hypopharyngeal glands (HPGs) of honey bees have prominent roles in various social behaviors through their secretions. The measurement of acini size and lipofuscin accumulation indicates the changes in HPGs in response to different factors including weather and behavioral castes. This research aimed to reveal how natural harsh environment of summer and winter can shape the HPGs in foragers and nurses of an indigenous bee race (Apismelliferajemenitica Ruttner) in comparison with two exotic bee races (Apismelliferacarnica Pollmann and Apismelliferaligustica Spinola). This study presents new information of significant differences in the HPGs of two behavioral castes (nurses and foragers) of indigenous and exotic bee races under harsh natural environmental conditions. HPGs of foragers have significantly higher lipofuscin accumulation and smaller acini size than nurse bees in all tested races during summer and winter seasons. A strong inverse correlation was found between acini size and lipofuscin accumulation in each race in both seasons. Smaller acini size and lipofuscin accumulation were detected in the HPGs of indigenous bees (foragers and nurses) than exotic bee races during both seasons. The acini size and lipofuscin accumulation were similar between exotic bee races but higher than that of the indigenous bee race.
The attraction of Tremex apicalis (Hymenoptera, Siricidae, Tremecinae) and its parasitoid Ibalia japonica (Hymenoptera, Ibaliidae) to the fungus Cerrena unicolor
Authors: Kuramitsu Kazumu , Ishihara Teruhito , Sugita Aki , Yooboon Thitaree , Lustig Barry , Matsumori Yuko , Yamada Hideo , Kinoshita Natsuko
Published: February 2019

Woodwasps (Hymenoptera: Siricidae) are saproxylic insects and a common forest pest. Siricid woodwasps are classified into two subfamilies: Siricinae and Tremecinae. All known symbiotic fungi of Siricinae are in the genusAmylostereumBoidin while some species of Tremecinae have been observed to have a relationship with the fungusCerrenaunicolor(Bull.) Murrill. Previous studies about the host searching behavior of woodwasps and their parasitoids have focused primarily on the subfamily Siricinae.

We analyzed the role ofC.unicolorvolatiles on the host searching behavior ofTremexapicalisMatsumura (Hymenoptera: Siricidae: Tremecinae) and its parasitoid Ibalia (Tremibalia) japonica Matsumura (Hymenoptera: Ibaliidae). The results of an olfactory response experiment indicated that the females ofT.apicalisand its parasitoid find their respective hosts using volatiles fromC.unicolor. Using DNA barcode, we identified basidiocarps on the trees infested withT.apicalis.The basidiocarps were all white-rot fungi that cause sapwood decay, includingC.unicolor. Two additional species that we identified belonged to genera closely related toC.unicolor.

Woodwasp species are known to carry symbiotic fungi in a pair of specialized sacs called mycangia. Notably we found that mycangia-like structures were absent in the abdomens ofT.apicalisfemales. To the best of our knowledge,Xerisspectrum(Linnaeus) (Hymenoptera: Siricidae) is the only reported example of woodwasp species that do not contain symbiotic fungi in their bodies.

Our results suggested that: (1)T.apicalisfemales search for host wood that is already infected with sapwood decaying fungus using volatile compounds; (2)T.apicalis’ female parasitoid also uses volatile compounds from fungus to locate wood that is infested with its potential host.
Effect of Magnetized Water on the Mechanical Properties of Concrete Containing Recycled Waste Glass Aggregate
Authors: Ngene Ben U. , Olofinnade Oluwarotimi M. , Agomo Chidiebere E.
Published: February 2019

Concrete use is fundamental to most infrastructural development plan of humanity today. This underscores the need to understand the strength characteristics of concrete made with crushed glass aggregate as partial replacement for fine aggregate and mixed with magnetic field treated water (MFTW). This study investigates the mechanical properties of concrete mixes prepared and cast into cubes of varying constituents such as concrete mixed with normal water, concrete mixed with MFTW, concrete with varying degree of crushed glass as replacement of fine aggregate from 15 to 45% with or without MFTW. The cubes were thereafter crushed after 7, 14, 28 and 56 days of curing to determine their compressive and tensile strengths. From the results obtained, it was observed that the optimum percentage partial replacement of sand with crushed glass aggregate is 15% to attain a suitable using MFTW in the mixing of the concrete. At this percentage replacement, it was observed that both the compressive and tensile strengths of the concrete mixed with MFTW improved by 25-30% relative to the conventional concrete. The study therefore recommend the use of MFTW in place of normal water in concrete production and use especially when partially replacing fine aggregate with crushed glass aggregate.
Electro-Magnetic Forming of Fiber Metal Laminates
Authors: Glushchenkov Vladimir , Chernikov Dmitrii , Erisov Yaroslav , Petrov Ilia , Alexandrov Sergei , Lang Li Hui
Published: February 2019

The paper presents the results of forming rifts in five-layer metal polymer laminates by electro-magnetic forming. During the experimental studies the discharge energy of the electro-magnetic machine was varied in such a way as to achieve different depths of the rift. Samples obtained by electro-magnetic forming were compared with control samples obtained by forming using a rubber pad under static loading. The strain state of the samples was analyzed using an digital image correlation system Vic-3D.
Forming Limit in the Nosing Process of Micro Copper Cups
Authors: Chang Chao Cheng , Pan Shuo Kai , Yu Kuan Te
Published: February 2019

This study used finite element simulations and experiments to investigate the forming limit in the nosing process of micro copper cups, and to establish the limit nosing curves in terms of nosing ratio, die angle, and friction factor. Two-stage processes, including backward extrusion and nosing processes, were considered in simulations and experiments at micro scale. The copper billets with 1 mm diameter and length were backwards extruded to produce the 1 mm diameter cups with 0.1 mm wall thickness. The cups were later used in the nosing processes under different forming conditions. By analysing the results of the nosed cups from the simulations, it is possible to identify the safe and failure forming conditions and establish the limit nosing curves for the nosing process. The simulation results show that the limit nosing ratio increases as the die angle or friction factor decreases. Two predicted results for poor and well lubricated conditions have been examined and are in good agreement with those from experiments. The study not only explores the characteristics of the noise process of copper cups at micro scale but also establishes the limit nosing curves which could be the guidelines for the design of micro metal components.
Thermal Deformation Behavior and Formability of High Temperature with Corrosion Resistance Alloy
Authors: Jeong Gyeong Uk , Park Jun , Jin Chul Kyu , Moon Young Hoon , Kang Chung Gil
Published: February 2019

The aim of present wor is, therfore, to investigated the effect of the damage value prediction equation on the formability of compression specimen and find the optimize forming condition.Although Inconel 625 alloys are excellent materials, Ni-base alloy cannot be formed at room temperature owing to limitation of formability. To improve the formability of Inconel 625, it is necessary to investigate the formability at a high temperature range.A high temperature compression test is performed with a Gleeble 3500 testing machine at various temperatures (approximately 900 1200°C) and strain rates (10/s and 30/s) to obtain high temperature deformation characteristics of Inconel 625. Furthermore, high temperature tensile tests results are used to measure elongations and reductions in the area of Inconel 625.A rigid-plastic finite element simulation is applied to the high temperature compression process to obtain the damage valueThe results of the hot deformation experiment and analysis are presented for various conditions of temperatures and strain rates, and it is expected that damage value will be used in hot forming processes such as hot extrusion and rolling process.
Stress Compensation Method for Structural Shakedown Analysis
Authors: Peng Heng , Liu Ying Hua
Published: February 2019

This paper presents a novel direct method called the stress compensation method (SCM) for structural shakedown analysis. Being different from the popular direct method of mathematical programming, the SCM just carries out some iterative calculations. Making full use of static shakedown theorem, the residual stress field is constructed via solving the modified global equilibrium equations. An effective and robust iteration control technique is adopted to generate a sequence of decreasing load multipliers. The numerical procedure is incorporated into the ABAQUS platform via some user subroutines. The shakedown problems for a cantilever beam, a symmetric continuous beam and a practical shell with nozzles are effectively solved and analyzed. These results are compared to the analytical solutions and those found in literatures. Both the incremental collapse mechanism and the alternating plasticity mechanism are revealed to determine the shakedown boundaries. Numerical examples show that the SCM is of numerical stability, good accuracy, high computational efficiency, and can effectively perform shakedown analysis of large-scale practical engineering structures.
Experimental Study on Crushing Resistance of Square CFRP Frusta under Axial Loading
Authors: Pang Tong , Sun Guang Yong , Ruan Dong , Huang Xiao Dong , Lu Guo Xing
Published: February 2019

Fibre-reinforced composite materials and structures have been extensively used as energy dissipating components in industries. The crashworthiness of square and circular CFRP (Carbon Fiber Reinforced Plastics) tubes have been widely studied. This paper investigates the deformation and energy absorption of square CFRP frusta under axial quasi-static crushing. The effects of various geometry parameters such as height-to-mean width (H/B) and thickness-to-mean width (t/B) ratios on the crushing resistance for square CFRP frusta with an apical angle of 10 ° have been examined experimentally. Finally the crashworthiness metrics of square CFRP frusta and square tube are compared and evaluated. The results show that the experimentally observed deformation mode of CFRP square frusta can be classified into three types, namely progressive folding collapse; splaying crushing mode characterized by a combination of progressive splaying and transverse shearing failure; and transition mode respectively. The initial peak force, mean crushing force and energy absorption of square CFRP frusta deformed in splaying mode increase with the increasing of wall thickness and width. For the desirable progressive splaying mode, three energy dissipated mechanisms have been identified as crack propagation, transverse shearing and friction energy.
Meshfree Analysis of Higher-Order Gradient Crystal Plasticity Using Nodal Integration
Authors: Niiro Tota , Tadano Yuichi
Published: February 2019

The size effect of metallic materials is one of the important factors for understanding characteristics of material. The higher-order gradient crystal plasticity is a powerful model for describing the size effect. However, it is known that the finite element method sometimes provides an improper solution. In this study, we analyze the higher-order gradient crystal plasticity model using a meshfree method, and a nodal integration scheme is introduced to improve the analysis accuracy. The effectiveness and stability of the meshfree method for the higher-order gradient crystal plasticity model are quantitatively discussed.
Development of Bifurcation Analysis Method for Rate Dependent Materials
Authors: Towata Daiki , Tadano Yuichi
Published: February 2019

In this study, a novel numerical method to analyze the bifurcation problemof a rate dependent material using the finite element method is proposed. The consistent stiffness matrix, which is required for a bifurcation analysis using the finite element method, for a rate dependent material is generally hard to compute, therefore, a computational method to calculate the tangent stiffness matrix based on a numerical differential is introduced so that exact bifurcation analyses for the rate dependent material can be conducted. A numerical example of the proposed method is demonstrated, and the adequacy of the proposed method is discussed.
Forming Limit Analysis of Hexagonal Metal Considering Volume Fraction of Deformation Twinning
Authors: Koga Tomoaki , Tadano Yuichi
Published: February 2019

In the plastic deformation of hexagonal metals, deformation twinning plays an important role as well as slip deformation. Therefore, a modelling of deformation twinning is essential in the crystal plasticity modeling. In this study, a model considering the volume fraction of deformation twinning is presented in the framework of crystal plasticity, and it is combined with a finite element-based homogenization scheme to represent the polycrystalline behavior. The presented model is adopted to a sheet necking formulation. Plastic flow behaviors under several strain paths are evaluated using the present framework, and the effect of volume fraction of deformation twinning on the formability of hexagonal metal is discussed.
Three Dimensional Finite Element Simulation of Strip Shape and Flatness of High Strength Steel
Authors: Xie Hai Bo , Li Lian Jie , Liu Tian Wu , Wang En Rui , Liu Xu , Jiang Zheng Yi
Published: February 2019

High-strength steel is a type of alloy steel that provides better mechanical properties or greater resistance to corrosion than carbon steel. Strip shape is an important factor affecting the strip quality significantly for the rolled products. Because of the complex influence factors of plate shape and profile, shape detection and control technology have not been solved, especially for high strength steel rolling. In this paper, a novel three dimensional finite element simulation of the strip shape and flatness of high strength steel has been proposed. The material constitutive model has been built up based on experimental results through the Gleeble 3800 Thermal Simulator under different temperatures and stain rates. The modelling of roll elastic deformation system, roll gap profile and edge drop has been set up systematically considering the influence of the work roll transverse shifting and roll bending. Results have shown that both higher bending force and more roll shifting will significantly reduce the strip crown, and obtain improved edge drop distribution as well. The proposed numerical model has been validated through hot rolling experiments in 4-high rolling mills.
Finite Element Calculation of Anisotropy of Hole Expansion in a Thin Steel Sheet with Six Degrees Polynomial Yield Function
Authors: Yang Seung Yong , Tong Wei
Published: February 2019

A sixth order yield function was used to analyze the anisotropic plasticity behavior of sheet metal forming. Based on a complete sixth order homogenous polynomial in plane stress, the yield function was implemented as user material subroutines in the FE code ABAQUS Explicit and Standard. The associated flow rule and isotropic hardening were assumed. Material parameter values in the yield function were decided by uniaxial yield stresses and plastic strain ratios along 7 different loading orientations and plane strain yield and equal biaxial stresses and plastic strain ratio. To show the superiority of the sixth order yield function, the hole expansion test by Kuwabara et al.[1] was considered. The results of finite element simulation using the sixth order yield function showed a better agreement with the test results than YLD2000-2D yield function with M=6.
Data-Driven Compensation for Bulk Formed Parts Based on Material Point Tracking
Authors: Maier Daniel , Hartmann Christoph , Till Michael , Büdenbender Christoph , Behrens Bernd-Arno , Volk Wolfram
Published: February 2019

Currently, common inefficient trial-and-error procedures are used in designing bulk forming dies. Numerous iterations, consisting of numerical simulations and subsequent real tests, are needed to achieve accurate parts. During the compensation cycles, manual redesign in CAD environments is necessary to transform discrete data into parametric descriptions causing approximation errors. Automation of these surface reconstruction processes is barely possible. To address these issues, different data-driven numerical strategies have been deduced based on either displacement or force. In this work, a material point tracking method in forming simulation between die and part geometry is presented. Based on this, enhanced displacement-based and stress-based methods for compensation of bulk forming parts are compared. The convergence behavior of both methods is analyzed with respect to the compensation factor. Finally, the material point tracking approach is validated and verified by compensating a two-dimensional bulk-formed component.
An Analytical Solution of the Subsequent Drawing Force on Multistage Deep Drawing of Cylindrical Cup
Authors: Lin Qi Quan , Wang Zhen Zhu , Peng Yan Rong , Hu Cheng Wu , Dong Wen Zheng , Wang Ying Le
Published: February 2019

In multistage deep drawing process, the subsequent drawing force (SDF) is a key reference value, which plays a significant role on the practical die structure design. In the present study, an analytical calculation of the radial stress at the die exit as well as the SDF in cylindrical cup drawing process are proposed, considering the previous strain hardening in the first drawing, normal anisotropy, frictional coefficient and die arc radius. As a result, the calculated maximum subsequent drawing force (MSDF) is in good agreement with experimental result. Besides, the MSDF decreases as normal anisotropy value increases, while increases as frictional coefficient and strain hardening exponent increases respectively.
Investigation of Stamping Tool Wear Initiation at Microscopic Level Using Acoustic Emission Sensors
Authors: Shanbhag Vignesh V. , Rolfe Bernard F. , Arunachalam Narayanan , Pereira Michael P.
Published: February 2019

Stamping tools are prone to an adhesive wear mode called galling. Adhesive wear on stamping tools can degrade the product quality and can affect the mass production. Even a small improvement in the maintenance process is beneficial for the stamping industry. Therefore, this study will focus on understanding and detecting the initiation of tool wear at the microscopic level in sheet metal stamping using acoustic emission sensors. Stamping tests were performed using a semi-industrial stamping process, which can perform clamping, piercing, stamping and trimming in a single cycle. The stamping test was performed using a high strength low alloy sheet steel and D2 tool steel for dry and lubricated conditions. The acoustic emission signal was recorded for each stamped part until severe wear on the dies was observed. These acoustic emission signals were later analyzed using time and frequency domain features. The time domain features such as peak, RMS, kurtosis and skewness could identify significant changes in the acoustic emission signal only when the severe wear was observed on the stamped parts for both dry and lubricated conditions. However, this study has identified that a frequency feature – known as mean-frequency estimate – could identify early stages of wear initiation at the microscopic level. Evidence of this early stage of wear on the part surfaces was not clearly visible to the naked eye, and could only be clearly observed via surface measurement instruments such as an optical profilometer. The sidewalls of the stamped parts corresponding to the initial change in AE mean-frequency trend were qualitatively correlated with 3D profilometer scans of the stamped parts, to show that AE mean-frequency can indicate the initial minor scratches on the sidewalls of the stamped parts due to the galling wear on the die radii surfaces. The results from this study can be used to develop a methodology to determine the very early stages of stamping tool wear, providing a strong basis for condition monitoring in the stamping industry.
Ultra-Thin Sheet Forming Analyses Considering Size Effects
Authors: Ghoo Bon Young , Son Jun Ho , Umezu Yasuyoshi , Hirashima Tei , Watanabe Yuko
Published: February 2019

Based on robust numerical formulations and various material models, finite element (FE) analysis becomes a powerful tool in conventional sheet metal forming process. Unfortunately, the present constitutive equations irrelevant to thickness that describe well conventional sheet deformation modes have difficulties being applied directly to ultra-thin sheet deformation modes. In the present study, a constitutive equation considering size effect is established by introducing a scale factor that represents size effects through thickness and width directions. Uniaxial tensile tests were used to evaluate the scale factor of different thicknesses together with the parameter identification. The developed constitutive equation reveals that thickness is the most important factor effecting on the constitutive relation of ultra-thin sheet. 2D draw forming process of C7035 ultra-thin sheet is analyzed using JSTAMP/NV introducing the developed constitutive equation. The analysis results show that there are obvious differences in the punch forces and loading geometries according to the size effect through thickness direction. Specimen width has slight effect on the flow stress although specimen thickness has strong effect on the flow stress. It is expected that the proposed constitutive equation gives good applicability to FE analysis of micro-scale forming.
Evaluation of Effect of Sample Size and Layer Direction on Mechanical Property of Specimen Manufactured by FDM-Type 3D Printer
Authors: Akiyama Hiroyuki , Uchida Makoto , Kaneko Yoshihisa
Published: February 2019

In the present study, we investigate the effect of the sample size and layer direction on mechanical properties of the specimen fabricated by the FDM-type 3D printer under 4-point bending test. Acrylonitrile-butadiene-styrene (ABS) was employed as a source material. Bending tests were performed under several experimental conditions of layer direction, dimension of the specimens and supporting distance. The relationship between bending load and displacement depended strongly on the layer direction. Young’s modulus increased with increasing supporting distance, particularly, when the filaments were parallel to the loading direction. The strain distribution during the bending test was evaluated by DIC. When the supporting distance was short, strain distribution obtained from DIC became different from the theoretical distribution. This result indicated that the prominent shear deformation occurs in the bending of the printed material when the supporting distance is short. Subsequently, FEM analysis was performed to remove the error in the estimation of Young’s modulus due to the shear deformation, and the correcting equation was proposed.
Assessment of Newly Developed Ductile Fracture Criteria for Lightweight Metals
Authors: Chai Ru Gang , Lou Yan Shan , Yoon Jeong Whan
Published: February 2019

This paper assesses various newly developed ductile fracture criteria including modified Mohr-Coulomb (MMC), DF2012, DF2014, DF2016, Hu-Chen and Mu-Zang, which were all proposed in the last decade. The AA2024-T351 is used for the assessment by comparing the predicted fracture limits to the experimental results both in strain and stress spaces. Fracture loci are also constructed by these criteria to evaluate their characteristics. The evaluation demonstrates that the Lode parameter and stress triaxiality should be properly coupled for reasonable modeling of ductile fracture in wide loading conditions. This study also shows that the coupling of the Lode parameter can also be realized by introducing the effect of the largest shear stress in fracture criteria.
Development and Validation of Multiscale Thermo-Elasto-Viscoplastic Analysis Method for Plain-Woven Composites
Authors: Kubo Gai , Matsuda Tetsuya , Nagaoka Hiroma , Sato Yoshihiko
Published: February 2019

In this study, the analysis method for thermomechanical properties of plain-woven composites is developed, and applied to thermoelastoviscoplastic analysis of plain-woven glass fiber-reinforced plastic (GFRP) composites. For this, a time-dependent constitutive equation depending on temperature for matrix materials is incorporated into the micro/meso/macro-scale thermo-elastic homogenization method for plain-woven composites developed by our research group. This method enables us to analyze thermoelastoviscoplastic properties in not only fiber bundles but also fibers and matrix materials in fiber bundles, as well as macroscopic thermal properties. This method is then applied to the thermal expansion analysis of a plain-woven GFRP composite subjected to a macroscopic temperature change from 25°C to 80°C before it is cooled to 25°C. Comparing the analysis results with experimental data, we validate the present method. It is also shown that the present method can evaluate themal residual stress and strain in the composite.
Development of a Decoupled Multiscale Analysis Method for Woven Composites
Authors: Nagaoka Hiroma , Matsuda Tetsuya , Ogaki Tsubasa
Published: February 2019

In this study, development of a decoupled multiscale analysis method for woven composites is conducted. To this end, an elastic-viscoplastic macroscopic constitutive model which is able to express strong anisotropy of composites is introduced, and the material parameters in the constitutive model are determined based on the results of triple-scale homogenization analysis. Moreover, the constitutive model is implemented in the finite element analysis code LS-DYNA. The developed method is applied to 3-point bending analysis of plain-woven carbon fiber-reinforced plastic (CFRP) composites with various types of laminates configurations. It is shown that the present method can analyze their different behavior depending on the laminate configuration with greatly reduced computational costs.
Constitutive Equations for Rubber under Abrupt Change in Strain Rate Direction
Authors: Tomita Yoshihiro , Uchida Makoto
Published: February 2019

We proposed constitutive equations for the strain rate and temperature-dependent behavior of rubber by employing the nonaffine molecular chain network theory and reptation theory. The finite element homogenization method along with the proposed constitutive equations have the capability of predicting the deformation behaviors of particle-filled rubber under changes in volume fractions, distribution patterns, and size heterogeneity of the particles without additional parameters. The only existing problem is the modest estimation of the stiffness of rubber immediately after the abrupt change in strain rate direction (ACSD) as can be seen in the cyclic deformation behavior. We restricted our attention to the generalization of our nonaffine molecular chain network theory to overcome the problems associated with ACSD. We consider the effect of the delay of deformation in surrounding chains on the elasticity modulus by introducing an amplification parameter dependent on the current chain stretch and direction of strain rate immediately after ACSD. The potential of the proposed constitutive equations is examined against the predictability of the experimentally obtained deformation exhibiting ACSD.