bluuebunny/crossref_metadata_2025 huggingface dataset:
¿Una rima perdida de Gustavo Adolfo Bécquer?
Authors: Caparrós Esperante Luis
Published: June 2019

El artículo da cuenta del hallazgo de un poema atribuido a Gustavo Adolfo Bécquer, publicado en el número 5 del periódico soriano Juventud, con fecha de 10 de enero de 1910. Para justificar esta atribución, se estudian primero las circunstancias que enmarcan la publicación, coincidente con la estancia allí de Antonio Machado, quien dejó testimonio de algún autógrafo becqueriano hasta hoy perdido, como lo haría posteriormente Gerardo Diego. En segundo término, se estudia el texto en busca de coincidencias que lo liguen al conjunto de la obra lírica de Bécquer.
Students Model in Different Learning Styles of Academic Achievement at the University of Phayao, Thailand
Authors: Nuankaew Pratya , Nuankaew Wongpanya , Phanniphong Kanakarn , Imwut Sasithon , Bussaman Sittichai
Published: June 2019

Attitudes and learning styles can affect academic achievement at different levels. While analyzing attitudes and learning styles can not only use basic statistics, using advanced tools to analyze the students' in-depth elements is discussed. Therefore, this research offers an appropriate method for clustering academic achievement (GPA) that support student’s attitudes and learning styles. At the same time, this research is aimed to study the level of attitudes towards learning styles in different academic achievement of students at the University of Phayao. The data collection was conducted from 195 students from 17 schools and colleges at the University of Phayao, Thailand. The results show that there is a variety of cluster in students’ attitudes and learning styles with a significant pattern (types of success) of the students’ model, while the model performance has a very high efficiency to the model. In future work, it will be applied with other universities in Thailand and also used in developing applications for providing a program recommended for appropriate educational programs.
Intelligent Knowledge Service System Based on Depression Monitoring of College Students
Authors: Yu Huina , Zhang Guihong , Liu Jiali , Li Kai
Published: June 2019

The number of college students suffering from depression has increased in recent years. In order to help the college student administration departments understand students' psychological state of depression better and keep college students mentally healthy through mental health services, this paper studies an intelligent monitoring system for depression. Different from previous researches, this study, based on the cloud services platform, incorporates three indicators closely related to depression-sleeping, exercise and heart rate-into the monitoring database subsystem and establishes a relatively macroscopic intelligent knowledge service system for depression monitoring of college students. It uses the Mobile Material Link Device (MMLD) to collect data and information to monitor and analyze the changes in the depression status of college students dynamically, which also provides timely warnings and a chain of personalized intelligent knowledge services based on individuals’ depression status.
Automatic Generation and Evolution of Personalized Curriculum Based on Genetic Algorithm
Authors: Duan Xiaocong
Published: June 2019

In order to solve the automatic generation and evolution of personalized curriculum, the method of using genetic algorithm to realize the evolution of personalized learning content is proposed to solve the dynamic personalized needs of users. Through the research and implementation of personalized curriculum generation technology, firstly, the structures of curriculum generation, genetic algorithm and curriculum scene, as well as the method and technology of personalized curriculum generation and evolution system framework are described in detail. Then, the framework structure based on genetic algorithm is determined, and the user model is updated. Finally, experiments are carried out based on genetic algorithm. The research on the experiment of automatic generation and evolution of personalized curriculum shows that the application of genetic algorithm in the process of curriculum generation and evolution makes students' learning content evolve with the change of their knowledge state in the process of learning, effectively promotes students' interest in learning, and improves learning efficiency and effect.
Heat Transfer Model to Predict Human Skin Temperature under Comfort Level by using Bioheat Equation
Authors: Zainol Zaina Norhallis , Tap Masine Md. , Kamar Haslinda Mohamed , Kamsah Nazri
Published: June 2019

Thermal comfort is the human subject perceived satisfaction to the environmental condition. The human comfort level is affected by skin temperature. Currently to determine the human skin temperature by using human experiment in a controlled environment. However, the experiment is very rigorous and exhaustive. This study was conducted to predict human skin temperature under comfort level with using the finite element method and the bioheat equation. The bioheat equation is used to predict the initial value of human skin temperature with the influence of the metabolic heat generation and the blood perfusion. It is discovered the skin temperature of the human subject experiment fluctuates. However, the result obtained from the model remains unchanged until the simulation ends. The predicted results from the model were well in agreement with the experimental results with an acceptable error of 1.05%.
Determining the Priority of Medical Equipment Maintenance with Analytical Hierarchy Process
Authors: Hutagalung Alfa Omega , Hasibuan Sawarni
Published: June 2019

The best quality of services provided by health care facilities can be realized if medical devices are in a reliable and safe condition. A large number of medical devices and the use of various types of medical devices have been a problem for hospital management to decide the level of priority in carrying out medical equipment maintenance. The purpose of the maintenance is to increase their availability and to reduce maintenance costs. This study aims to show how to determine the priority level of medical device maintenance based on the calculation of the criticality scores of medical devices. The criticality scores are obtained based on the assessment of criteria, sub-criteria, and grade by using the method of Analytical Hierarchy Process (AHP). The devices with higher critical weight take higher priority for maintenance than devices with lower critical weight. The approach was applied for 20 medical devices at the Out Patient Department of Eye Hospital in Jakarta to describe how to prioritize the maintenance of medical devices.
Influence of Initial Fibre Length and Content Used in the Injection Moulding of CFRP on the Properties of C/C and C/C-SiC Composites
Authors: Ahmad Husam , Stiller Jonas , Päßler Erik , Nestler Daisy , Wagner Guntram , Kroll Lothar
Published: June 2019

The production of C/C-SiC composites comprises a three-stage process: forming (CFRP-composite), pyrolysis (C/C-composite) and liquid silicon infiltration (C/C-SiC). A new promising approach for the manufacturing of CFRP intermediate composites is the injection moulding of customised granulates (novolac resin, hardener, processing additives and short carbon fibre) produced by compounding technique. To date, a direct dosing of short carbon fibre into the compounder was technically not realisable due to fibre separation and electrostatic charging in the hopper. A possible substitute solution has been the direct feeding of a carbon fibre bundle from a roving into the compounder. However, this is associated with a severe damage of the fibres and an inaccurate adjustment of the fibres content. In the present article, new chopped carbon fibres provided with an adapted sizing to be directly dosed into the compounder are used. The fibres possess a predefined length of 3 and 6 mm and their content amounts to 50 and 58 wt.%. The influence of the initial fibre length and fibre content on the physical and mechanical properties of the resulting CFRP-, C/C-and C/C-SiC-composites is presented and discussed. In addition, the impact of fibre feeding procedure at the compounding stage on the microstructure is considered
Metal Polymer Connections: Laser-Induced Surface Enlargement Increases Joint Strength
Authors: Woitun Dominic , Roderus Michael , Bein Thilo , Kroner Elmar
Published: June 2019

The trend towards hybrid materials consisting of metals and polymers is strongly driven by requirements such as weight reduction and improved functionality. A crucial step towards new hybrid materials is the advancement of joining technology. While metals and polymers are currently often joined using adhesives, this technology has major drawbacks such as long process cycle time, low robustness with regard to changes of the material composition, and are almost impossible to recycle, a point which is becoming increasingly important. A promising joining method is thermal direct joining of metals and thermoplastic polymers due to its fast cycle time, its robustness of the process and the absence of duroplastic adhesives. Direct joining requires surface treatment of the metallic joining partner prior to the thermal joining process to achieve a sufficiently high contact strength. It is known that laser-induced topologies on the metal surface are beneficial with regard to contact strength of the joints. Designing a joint based on laser structured metals requires a fundamental understanding of the interface interactions. The present paper focuses on the influence of surface enlargement on the joint strength. Laser pretreatment was utilized to generate surface structures with specific surface enlargement on the metallic joining partner. The pretreated metallic parts were subsequently joined with a thermoplastic polymer by injection molding. The joint strength was investigated in single lap shear tests. The key finding is that the contact strength increases almost linearly with the surface area within the tested parameter range, while the structure geometry parameters have only a minor influence. This may help as a design guideline for future adhesive-free hybrid material joining technologies.
Influence of Process Parameters, Surface Topography and Corrosion Condition on the Fatigue Behavior of Steel/Aluminum Hybrid Joints Produced by Magnetic Pulse Welding
Authors: Mrzljak Selim , Gelinski Nikolai , Hülsbusch Daniel , Schumacher Eugen , Boehm Stefan , Walther Frank
Published: June 2019

In this study, magnetic pulse welded steel/aluminum hybrid joints are investigated with the aim of optimizing the process parameters regarding the fatigue behavior. Changes in discharge current, acceleration distance, welding geometry as well as influences of surface topography and corrosion, are examined regarding fatigue life and damage mechanisms. Instrumented multiple amplitude tests combined with constant amplitude tests are carried out for assessing structure-property-relations in a resource-efficient manner. Stress-induced change in strain and alternating current potential drop measurement are well suited for reliable detection of damage initiation and estimation of the fatigue limit. Results reveal that the fatigue properties primarily depend on the imperfections of the weld seam, which are affected mostly by the discharge current and the surface topography. Corrosion shows to be a relevant factor since it decreases fatigue performance. Suitable process parameters are achieved when the fatigue strength of the weld seam lies above the weaker hybrid joint (aluminum). For S235JR and EN AW1050A-H14 (Al99.5) a suitable discharge current was found to be 349 kA at an acceleration distance of 1.5 mm.
Sintered Connection - A Steel/CFRP Connection Module
Authors: Marx Alexander , Hutsch Thomas , Schiebel Patrick , Feltin Dirk , Hoffmeister Frank , Babbel Andreas , Weißgärber Thomas , Herrmann Axel
Published: June 2019

Nowadays, carbon fiber reinforced plastics (CFRP) are present in a variety of applications. However, it is still possible to maximize the potential of CFRP by creating multi-material designs of CFRP and metal. The key to success for multi-material designs is the joining technology. In this work a metal/carbon fiber connection module was develop. Carbon fibers (CF) were integrated with stainless steel by using a powder metallurgy approach. After this, the created connection module was integrated in a fiber layup, which was infiltrated with epoxy resin by a Resin Transfer Molding (RTM) process. Leveraging from this technology, a M6 thread-forming screw was chosen and added in the sintered body. The screw press out test indicated that the strength between the screw and the sintered body was above 11 kN, which can be still enhanced for future by thread optimization. Microscopic cut images and computer tomography (CT) were used to characterize the CF in the sintered steel body and to examine the border area between the two materials.
Analysis of the Macroscopic Behaviour of PMI Foam
Authors: Nagler Michaela , Thor Michael , Peyrer Peter , Schneiderbauer Gernot , Sendner Franz M. , Wolfahrt Markus , Hinterhölzl Roland
Published: June 2019

o accurately simulate the foam core in composite parts on a macroscopic scale the morphology, the characterisation, and the nonlinear behaviour of thefoam must be understood properly. Accounting for the heterogeneity and the mechanical properties of the foam core affects the dimensioning of the final part.In the present study the microstructure of the foam samples were characterized using scanning electron microscopy. To determine the bulk material behavior and the strength limitations of the nonlinear foam, shear and compressions tests are performed. All numerical calculations were carried out on the macroscopic level.A basic challenge in the finite element modelling of hyperelastic materials by means of test data is the identification of material model coefficients which are appropriate to describe the behaviour of the considered foam.
Ultrasonic Assisted Thermal Direct Joining of Thermoplastic Composites and Aluminum for Multi Material Design
Authors: Roderus Michael , Woitun Dominic , Kroner Elmar
Published: June 2019

The trend towards multi material design is strongly driven by improved functionality and decreased total weight of hybrid parts. Conventional joining techniques for metals and polymers usually require a complex process and are thus time consuming and expensive. A novel technique addressing these shortcomings is ultrasonic assisted thermal direct joining of metals and thermoplastic polymers. The metallic joining partner is laser pre-treated to generate a specific surface topology. The subsequent joining process is a combination of thermal direct joining and ultrasonic joining. This hybrid joining process results in short cycle times, and the maximum heat input is localized to the joining area. The joint performance was measured by lap shear tests, resulting in strength values exceeding 18 MPa, while the duration of the joining process was about 1.5 seconds. The relevant joining parameters were identified and a process window was obtained. The results indicate that there may be an optimum energy range for successful joining. An appropriate energy map may allow a deeper understanding of the process and enables prediction of process windows for various material combinations.
Influence of Composition on Mechanical Properties of Additively Manufactured Composites Reinforced with Endless Carbon Fibers
Authors: Czasny Mathias , Goerke Oliver , Kaba Onur , Koerber Stephan , Schmidt Franziska , Gurlo Aleksander
Published: June 2019

Additive manufacturing of endless carbon fiber-reinforced composites is a technology which produces parts with mechanical properties similar to those of additively-manufactured metallic parts. In this work, the influence of layer height and width on mechanical properties of additively-manufactured carbon fiber-reinforced polymer composites has been studied. Two different 3k carbon fibers have been used as reinforcement. The composites are printed by material extrusion technology with layer heights of 0.2, 0.3, and 0.4 mm and layer widths of 1.0, 1.2, and 1.7 mm. The composites possess higher flexural strength at smaller layer height and the flexural modulus is dependent on the fiber volume content. The formation of voids/defects decreases the mechanical properties of composite and should be optimized.
Surface Topography Influences on the Fatigue Behavior of Composite Joints
Authors: Thäsler Torsten , Holtmannspötter Jens , Gudladt Hans Joachim
Published: June 2019

The surface condition of carbon fibre reinforced plastic (CFRP) substrates is decisive to obtain high bond strength and lifetime of adhesively bonded parts. Those surfaces were adjusted in terms of their microscopic topography by means of peel plies and release foils. The subsequent surface treatment via atmospheric pressure plasma jet or vacuum blasting allowed the modification of the microscopic roughness as well as the surface chemistry. Those configuration were assessed using surface analytic methods as well as quasi-static and cyclic fracture tests on single lap shear specimens. The microscopic surface roughness, if at all, only showed a small influence on the bond strength. Despite release agent residues, fracture was found within the fiber-matrix interface, which caused difficulties in evaluating the effect of surface pretreatments on the adhesion strength. Fatigue tests revealed a lifetime reduction of uneven microscopic rough surfaces, which was assigned to stress concentrations at the tip of asperities. The crack propagation was accelerated in case of release agent residues. If surfaces were free of contaminations, no differences between microscopically smooth and slightly structured surfaces were found. Overall, fatigue testing on single lap shear specimens showed an increased sensitivity with regard to the assessment of surface morphology.
Influence of Carbon Roving Strain Sensory Elements on the Mechanical Properties of Carbon Fibre-Reinforced Composites
Authors: Weißenborn Oliver , Haentzsche Eric , Nocke Andreas , Geller Sirko , Cherif Chokri , Modler Niels
Published: June 2019

Over the last decade, carbon fibre-reinforced composites (CFRP) are increasingly used as lightweight material for various industrial applications. Due to the anisotropic material structure and its corresponding properties, novel design concepts and processing technologies were developed to further harness the material inherent lightweight potential. However, the material degradation in long-term use and failure behaviour is still considered a challenging issue for material scientists and engineers in particular. Therefore, concepts for structural health monitoring and their suitable implementation is still a major research topic. Among others, one solution uses the conductivity of carbon fibre yarns and their suitability to act as in-situ strain sensors. In the present work, the measurement principle bases on the usage of the piezo-resistive effect, meaning that every mechanical strain of the roving filaments causes a correlative change of the measurable electrical resistance. Since, these sensory elements need shielding from their surrounding carbon filaments of the composite structure, suitable fibre-based dielectric jackets have been developed with a wide range of suitable materials and textile processing technologies. In this contribution, the influence of the integrated carbon fibre sensors on the resulting mechanical performance of the composite structure is evaluated using an analysis of variances approach. Beyond that, the local composite morphology is analysed to evaluate the composite microstructure.
BN-Based Fiber Coatings by Wet-Chemical Coating
Authors: Maier Jonathan , Nöth Andreas , Schönfeld Katrin
Published: June 2019

Fiber coatings for BN/SiC-and BN/Si3N4-bilayer systems were developed for the use in SiC/SiC composites. All coatings were produced with high process velocities of 500 m/h by a continuous roll-to-roll dip-coating process. The fiber surface was fully covered with a homogeneous coating and without fiber bridging. Tensile tests of fiber bundles were used to examine potential degradation of the fiber properties due to the application of the coatings. The coated fiber bundles showed a reduction of the maximum tensile load to 90.0 % for the BN/Si3N4 and to 86.7 % for the BN/SiC coating in comparison to the fiber bundle in the as-received state. A thermal treatment of the coated fiber bundles up to 1650 °C led to no reduction of their maximum tensile load. SiC/SiC composites were fabricated by polymer infiltration and pyrolysis. The flexural strength and strain of composites with BN/SiC fiber coating were improved to 467 MPa and 0.42 % in comparison to the composites without fiber coating. The composites with BN/SiC coating showed toughened fracture behavior with fiber pull-out effects.
Chemical Vapor Deposition of AlZrN Coatings by the Reaction of In Situ Produced ZrCl4 and AlCl3 with NH3
Authors: Rauchenwald Elisabeth , Lessiak Mario , Weissenbacher Ronald , Haubner Roland
Published: June 2019

Ternary transition metal nitrides are commonly used as protective coatings on cutting tools, owing to their excellent mechanical and wear properties. While AlTiN is a very well-studied material, little is known about AlZrN, in part due to the large miscibility gap in the phase diagram of AlN-ZrN. In this study, AlZrN thin films were prepared using chemical vapor deposition. By the reaction of metallic aluminum and zirconium with HCl gas under elevated temperature, AlCl3 and ZrCl4 were produced in situ and subsequently transported into a heated coating reactor with a carrier gas. Due to the high temperatures and the separately introduced mixture of NH3 and N2, AlZrN coatings were deposited. By varying the experimental conditions, such as the ratio between ZrCl4 and AlCl3, we studied the influence of these parameters on the coating thickness and morphology as well as the microstructure. Additionally, the impact of different sample positions in the coating reactor on the deposited coatings was investigated. Furthermore, the generated samples were characterized by scanning electron microscopy, energy dispersive x-ray spectroscopy and transmission electron microscopy.
Thermal Stability of Natural Fibers via Thermoset Coating for Application in Engineering Thermoplastics
Authors: Vellguth Natalie , Rudeck Tanja , Shamsuyeva Madina , Renz Franz , Endres Hans Josef
Published: June 2019

An effective integration of natural fibers into engineering thermoplastics requires sufficient thermal stability of natural fibers during processing, since melting temperature of engineering thermoplastics lies above 200 °C. The aim of the work was to protect natural fibers from the heat of the molten thermoplastic via coating with a modified epoxy resin, thus enabling manufacture of natural fiber-reinforced engineering thermoplastic composites with minimized thermal degradation of the fibers. Processing temperature comprised the range of engineering thermoplastic polyamide 6 (PA6), which was 225 °C. Flax fabrics were spray coated with partially bio-based epoxy resin and incorporated via hot press technique into a PA6 matrix. The composite samples including spray coated flax fibers as well as the reference flax fibers without coating were characterized with regard to their mechanical properties, namely bending and tensile tests, thermal properties with differential scanning calorimetry (DSC) as well as thermogravimetric analysis (TGA) and optical via scanning electron microscopy (SEM) and computer tomography (CT). The results show that this approach enables manufacture of composites with reproducible mechanical properties, i.e. bending and tensile properties as well as enhanced thermal stabilities.
Efficient Characterization and Modelling of Material Behaviour of LFT for Component Simulations
Authors: Grimm-Strele Hannes , Kabel Matthias , Köbler Jonathan
Published: June 2019

Modeling failure and progressive damage of long fibre reinforced thermoplastics (LFT) presents a challenging task since local inhomogeneities, anisotropic fibre orientations, and strain-rate dependence must be taken into account also on the microscale. We show that for simple geometries, the material behaviour of the composite can be modelled using layered geometrical models. But for more complex geometries, this approach fails since the fibre orientation distribution is inhomogeneous. In this case, multiscale methods allow the accurate and efficient prediction of the material behaviour with the local fibre orientation taken from an injection molding simulation. This material model can be extended to viscoplasticity and integrated into the NTFA-TSO method from Michel & Suquet (2016). In this way, we can obtain an accurate and efficient multiscale method for the realistic modelling of LFT.
RecyCarb: Process Optimization and On-Line Monitoring in the Recycling of Carbon Fibre Waste for the Re-Use in High-Grade Fibre Reinforced Plastics
Authors: Hofmann Marcel , Fischer Holger , Heilos Katharina , Miene Andrea
Published: June 2019

Within the project ‘RecyCarb’ a qualified value-added chain for recycled carbon fibres (rCF) to enable their high-quality and sustainable re-use in sophisticated fibre-reinforced composites was established. A team of four industrial partners and two research institutes closed the technological gap between the actual rCF available on the market and the functional re-use as reinforcing elements in high-quality components. Process optimisation, initiation of a reliable scheme of quality assurance and a process integrated quality monitoring were the main aspects of this project. Besides different kinds of carbon fibre waste, different nonwoven processes (web formation and bonding methods) and an online fibre orientation analysis were investigated. This project focuses a variety of several application markets, e.g. sports equipment, medical technologies or automotive, shown by developed demonstrators.
Textile-Integrated Elastomer Surface for Fiber Reinforced Composites
Authors: Semar Jan Eric , May David
Published: June 2019

Elastomer layers offer a wide range of surface functionalization options for fiber-reinforced polymer composites (FRPC), e.g. erosion protection or increased impact resistance. Goal of this study was to investigate if it is possible to prepare a textile-based semi-finished product with elastomeric surface, which can easily be used as outermost layer in different liquid composite molding (LCM) processes. For this purpose, different types of elastomer were pressed and vulcanized onto a biaxial glass fiber fabric. Target of this procedure was to reach partial immersion of the elastomer into the textile with remaining dry textile areas. The dry areas of the textile can later be impregnated with a thermoset resin system. The strategy is to have the transition region between elastomer and thermoset within one textile layer and to give a robust and easy to handle semi-finished-product in order to achieve a maximum bonding strength of the elastomer surface to the final composite part.
It could be shown by micrographs and computer tomography that the elastomer only penetrates the textile at its boundary. A remarkable microimpregnation of individual filaments within the rovings does not take place. Concerning the manufacturing, since water evaporates during vulcanization, a sufficient process pressure must be maintained throughout the entire vulcanization process to ensure a pore-free elastomer. Peel-off tests similar to DIN EN 28510-1 on the finished composite showed a failure in the laminate and not in the boundary layer between laminate and elastomer, so that the desired high joint strength could be demonstrated.
Liquid Metal Embrittlement of Copper Brazed Plate Heat Exchangers
Authors: Haubner Roland , Strobl Susanne , Bichler Lorenz Pinkas , Linhardt Paul
Published: June 2019

Plate heat exchangers are widely used for heating and cooling activities in domestic and industrial applications. The plates of all these components were made of stainless steel (e.g. type X2 CrNiMo 17-12-2) and they were brazed with pure copper. After cutting and metallographic preparation, the samples were investigated by light optical microscopy (LOM) to measure the depth of copper penetration into the plates (liquid metal embrittlement (LME)). For seven heat exchangers the penetration depth was between 25 and 60 μm, but for one the depth was about 150 μm. At the steel-copper interfaces an additional phase was identified as chromium-rich ferrite by electron beam micro analysis (EBMA). To get information about the sensitivity against corrosion electrochemical tests were performed in two electrolytes (HCO3- + SO42- and HCO3- + SO42- + Cl-). It can be summarized that in the Cl- free electrolyte the copper was attacked mainly. In case of the Cl- containing electrolyte beside the copper braze, the LME zones in the steel were corroded additionally.
Microscopic Measurement of Strain Fields with Digital Image Correlation and Comparison to Finite Element Modelling
Authors: Korkisch Marco , Sause Markus G.R.
Published: June 2019

Digital Image Correlation (DIC) has become more and more important in the field of material characterization and research, especially for strongly anisotropic fiber reinforced materials. Its big advantage over the conventional methods like strain gauges or point based video-extensometers is the full field strain and displacement measurement and the ability to analyze three-dimensional displacements. Although theoretically, the concept of the DIC as a pure image-based method allows it to work on every imaginable scale, its main field of application is in the range, where the region of interest (ROI) has a size between 10 −2 m to 10 −1 m. In this case, imaging is accomplished with the use of high-resolution black and white digital cameras. This work is focused on a smaller scale with ROI sizes between 10 −4 m to 10 −3 m, where a digital microscope is used to create the images. The innovative idea behind this work is using the natural surface structure of a polished carbon fiber reinforced Polyamide-6 sample, produced by automated fiber placement, as a statistical pattern instead of the usual speckle pattern applied to the area to be investigated. This way the stress and strain distributionin different regions of the investigated sample area can be evaluated and displayed, while the sample is exposed to an increasing mechanical load in form of a three-point bending test. The resulting strain and displacement fields are compared to finite element modeling of the ROI. To provide an accurate model, the image of the sample is first segmented into fiber, matrix and voids using “Trainable Weka Segmentation” and the resulting phases mapped with the corresponding material properties. To compute the resulting strains in the sample, the measured displacements from the DIC on the edges of the ROI were used as boundary conditions for the simulation. Simulation and experimental results clearly point out the inhomogeneity of the strain field in these samples. Due to the presence of fiber rovings and the presence of voids, local strain values exceed the global average by up to 4 %.
Region-of-Interest X-Ray Tomography for the Non-Destructive Characterization of Local Fiber Orientation in Large Fiber Composite Parts
Authors: Zabler Simon , Schladitz Katja , Dremel Kilian , Graetz Jonas , Dobrovolskij Dascha
Published: June 2019

To detect and characterize materials defects in fiber composites as well as for evaluatingthe three-dimensional local fiber orientation in the latter, X-ray micro-CT is the preferred methodof choice. When micro computed tomography is applied to inspect large components, the method isreferred to as region-of-interest computed tomography. Parts can be as large as 10 cm wide and 1 mlong, while the measurement volume of micro computed tomography is a cylinder of only 4 − 5 mmdiameter (typical wall thickness of fiber composite parts). In this report, the potentials and limits ofregion-of-interest computed tomography are discussed with regard to spatial resolution and precisionwhen evaluating defects and local fiber orientation in squeeze cast components. The micro computedtomography scanner metRIC at Fraunhofer‘s Development Center X-ray Technology EZRT deliversregion-of-interest computed tomography up to a spatial resolution of 2 μm/voxel, which is sufficientfor determining the orientation of natural or synthetic fibers, wood, carbon and glass. The mean localfiber orientation is estimated on an isotropic structuring element of approximately 0.1 mm length bymeans of volume image analysis (MAVI software package by Fraunhofer ITWM). Knowing the exactlocal fiber orientation is critical for estimating anisotropic thermal conductivity and materials strength.
Model-Based Quality Control System for Error Reduction in the Thermoforming Process
Authors: Vocke Richard , Stempin Johannes , Schiebel Patrick , Herrmann Axel , Fischer Andreas
Published: June 2019

Model-based quality control has the potential to reduce the reject rate in the production of fiber-reinforced plastics (FRP) components. After all the cross-market establishment of FRP, undesirable quality deviations often occur with new materials or component shapes. The quality control uses the component quality (e.g. component angle, crystallinity, fiber orientation, pore content) as the control variable. As a key component of the control, a process model is developed to link the process parameters (press pressure, press duration and tool temperature) with the quality parameters. Knowledge of the process-determining cause-effect relationships is necessary to ensure that different quality parameters are in the target value at the same time. Based on experimental tests, these interrelationships are determined using methods of statistical test planning and serve as the basis for model-based quality control. As a result, it has been shown that the targeted control of the component angle is possible in a range of about ±1° by using the control parameters, tool temperature and pressure, which have a significant influence on the quality. In the next step, further quality characteristics are included in the control system in order to demonstrate the ability to control the quality of complex component specifications. Model-based quality control is particularly promising for the reduction of the process run-in phase and thus for the reduction of the reject rate.
Controlling Moisture Content of Natural Fibres in RTM-Process
Authors: Salzmann Moritz , Schledjewski Ralf
Published: June 2019

The quality of composite materials based on natural fibres is highly influence by humidity content of the fibres. For a high product quality in the resin-transfer-moulding (RTM) process a constant humidity content has to be achieved. As the humidity content of the fibres can change relative quickly depending on the humidity, measuring humidity content in the mould is beneficial. Near-Infrared-Spectroscopy (NIR) is a widely used tool for humidity content measurement allowing determination of the moisture content within seconds. To do so a calibration model with good accuracy is required. To generate the calibration model a dry flax woven fabric is placed in a climate chamber and weight change is recorded as well as NIR-Spectra. By correlating the spectra with the weight increase a model can be developed allowing to assign the spectra with unknown weight. This allows not only monitoring the moisture content of natural fibres with in the mould. Also can the moisture content reduced to an aspired value by applying vacuum to the preheated mould, before starting the resin infusion.
High-Speed Laser Melt Injection of Tungsten Carbide in Highly Conductive Copper Alloys
Authors: Warneke Philipp , Seefeld Thomas
Published: June 2019

For the first time, metal matrix composite (MMC) layers on parts made of highly conductive copper alloys have been generated by laser melt injection (LMI). In order to ensure a sufficient absorption efficiency, different kinds of surface modification were investigated. Welding speeds up to 7.5 m/min can be obtained. When increasing the dispersing rate, the process efficiency, which is the product of absorption efficiency and thermal efficiency, increases. At high dispersing rates, some spherical fused tungsten carbide (SFTC) particles are slightly deformed or partly fused together without decreasing the hardness.
Study on the Possibility of One-Step Method Processing for Poly(p-Phenylene Terephthalamide) Fiber
Authors: Zhang Xing Ke , Li Na , Hu Zu Ming , Wang Yan , Zhu Jing , Yu Jun Rong
Published: June 2019

In this paper, the low molecular weight poly (p-phenylene terephthalamide) (LMW-PPTA) solutions with different end group were obtained through changing molar ratio of monomers. Then, the high molecular weight PPTA (HMW-PPTA) polymer was synthesis by Secondary copolymerization. At that time, the PPTA fiber may be produced by means of reaction spinning in one step. Hence, the possibility of one-step method processing for PPTA fiber was studied by investigating the polymerization degree and gelling time of secondary copolymerization under different situations. The one-step method processing for PPTA fiber is not only free from the dependence on concentrated sulfuric acid, but also able to be controllable easily. Remarkably, the facile procedure, lower cost and better environmental protection are significant for the manufacture of PPTA fiber.
Effect of Li2O-Al2O3-Bi2O3-SiO2 Glass on Electromagnetic Properties of Ni0.16Cu0.22Zn0.62Fe2O4-BaTiO3 Composites at Low Sintering Temperature
Authors: Zhao Qiang , Zhang Huai Wu , Li Jie
Published: June 2019

In the present work, the composite material Ni0.16Cu0.22Zn0.62Fe2O4-BaTiO3 (NCZF-BTO, in a 10:1) was synthesized with different additive amounts of Li2O-Al2O3-Bi2O3-SiO2 (LABS) glass using a traditional solid-state reaction method and sintered at 900 °C. The synthesized composites were then comparatively investigated; in addition to their phases and density, their magnetic and dielectric properties, which include the saturation magnetization(4πMs), coercivity (Hc), permeability (μ'), quality factor (Q), dielectric constant (ε')and dielectric loss (tan δ) were characterized. In contrast to the undoped composites, the performance of the LABS-doped samples were enhanced. The optimal performance was obtained when the LABS glass content reached 1.0wt%. At this level of doping, the bulk density increased from 4.883 g/cm3 to 5.021g/cm3, the saturation magnetization (4πMs) increased from 3819.5 to 4113.6Gs, the coercivity (Hc) decreased from 111 to 106.5A/m, the permeability (μ') at 10 MHz increased from 25.8 to 61.1, and the dielectric constant (ε') at 10 MHz increased from 18.9 to 23.4. On further increasing the LABS glass content to1.5 wt%, the performance of the composite generally deteriorated, except for the dielectric constant,which increased to 27.1. In short, the optimal LABS glass doping ratio was determined to be 1.0 wt%.
A Theoretical Investigation on Second-Order NLO Properties of Organic Substitutions of [Mo6O19]2- and [MoW5O19]2-
Authors: Li Qi , Yuan Xiu Hua
Published: June 2019

In this study, density functional theory (DFT) was used to calculate second-order polarizabilities and second-order polarizabilities densities of a series of organic substitution for Lindqvist-type polyoxometalates (POMs), and the nonlinear optical (NLO) properties was also analyzed. We found that βzzz has the main contribution to β value. The expansion of molecular structure on z-axis greatly increased second-order polarizabilities. Both the size of the organic segments and metal hybridization exert an influence on β value. The analysis on the second-order polarizabilities density is used to explain the NLO phenomenon. In the present investigation, metal hybridization and π-conjugation changed the contribution of βzzz value from different parts. The results of this work will contribute to the potential applications in high-performance NLO materials.
Fatigue Property of Friction Stir Welded Butt Joints for 6156-T6 Aluminum Alloy
Authors: Chen An , Yang Jun , Chen Xian Min , Dong Deng Ke
Published: June 2019

This study was conducted to investigate fatigue behavior of friction stir welding (FSW) butt joints for 6156-T6 aluminum alloy. The detail fatigue rating (DFR) values of 6156-T6 FSW joints is obtained based on statistical analysis of fatigue tests. The micrographs of weld structure were observed by optical microscope (OM), Fatigue fractography was researched under scanning electron microscope (SEM). The results indicate that DFR value of 6156-T6 FSW joints is 153.31MPa. Fatigue property of FSW butt joints is sensitive to the microstructural features, such as nugget zone (NZ), thermo mechanically affected zone (TMAZ) and heat affected zone (HAZ). The hardness distributions of the FSW joints reveal W-shaped profiles. Fractography shows that fatigue cracking is initiated at weak-bonding defects, which are located at the root site of the butt joint. The weak-bonding defects have obvious influence on the fatigue properties of friction stir welding.
Effect of Intermediate Thermomechanical Treatment on Microstructure and Mechanical Properties of 2A97 Al-Li Alloy
Authors: Yu Juan , Lu Zheng , Xiong Yan Cai , Li Guo Ai , Feng Zhao Hui
Published: June 2019

Effect of intermediate thermomechanical treatment on tensile properties at short-transverse direction, fracture mechanism and microstructure of 2A97 Al-Li alloy thick plate were studied by tensile testing, SEM, EBSD and TEM.The results show that with the increasing of compression deformation, the strength and elongation of the alloy increase first and then decrease slightly. The fracture mode of the alloy changes from quasi-cleavage fracture to high energy ductile fracture. When the compression deformation rises to 20%, the elongated structure are replaced by a more uniform and equiaxial structure. The distribution of δ phase distribute more homogeneously in the grains.
Effects of Original Microstructure on Hot Deformation Behavior and Microstructure of a P/M Ni-Base Superalloy
Authors: Wang Chao Yuan , Song Xiao Jun , Zou Jin Wen
Published: June 2019

The hot deformation behavior and microstructure of a powder metallurgy (P/M) Ni-base superalloy with different original microstructure were studied by isothermal compression tests. The isothermal compression tests were conducted on Gleeble-3500D simulator with the temperature range of 1000°C~1100°C and the strain rate of 0.001s-1~0.1s-1. The results showed that the flow stress of the specimens with fine grains (10μm) and ultrafine grains (3μm) gained by hot extruding (HEX) were much less than the that with the average grain diameter of 30μm by hot isostatic pressing (HIP). At the strain rate of 0.001s-1，the as-HIPed specimens with the average grain diameter of 30μm showed steady-state deformation at 1100°C only， whereas the as-HEXed specimens with the average grain diameter of 10μm and 3μm showed steady-state deformation both at 1050°C and 1100°C. The flow stress showed decreasing trend as the average grain diameter decreasing. The activation energy of hot deformation decreased form 622.79 kJ·mol-1 to 302.36 kJ·mol-1 as the average grain diameter decreased from 30μm to 3μm. When the as-HEXed specimen with the average grain diameter of 3μm was deformed at the condition of (1050°C, 0.001s-1), the flow stress was lower than that at the condition of (1100°C,0.001s-1), and the former also gained much finer and uniform grain, the later gained mixed grains.
Publication characteristics of studies published in the The Spine Journal from 2005 to 2015
Authors: Park Joseph , Gil Joseph A. , Kleiner Justin , Eltorai Adam E.M. , Daniels Alan H.
Published: June 2019

BACKGROUND CONTEXT: There is a growing demand for evidence-based- practices and informed clinical decision making supported by reliable, high-quality research.PURPOSE: To analyze trends in the level of evidence of publications and to evaluate the publication characteristics that influence the quality of research in The Spine Journal (TSJ)STUDY DESIGN: Comprehensive publication assessment.SAMPLE: All studies published in TSJ from the years 2005, 2007, 2009, 2011, 2013, and 2015 were reviewed and analyzed.OUTCOME MEASURES: Level of evidence, study type, funding source, author country, author department, and number of citations.METHODS:  Multivariable logistic regression, and multivariable linear regression analyses, and chi square tests were used to analyze the trends of published studies level of evidence, study type, the specialties of authors, author countries, number of citations, and funding sources.RESULTS: A total of 1,456 articles were evaluated. There was a decrease in the percentage of high level evidence (level 1 and 2) studies from 73.6% in 2005 to 49.8% in 2015 (p=0.0045). There was a significant increase in the percentage studies with reporting funding support (p<0.0001). Funded studies were more likely to have a higher level of evidence (p<0.0001). The percentage of studies from international authors increased from 17.8% in 2005 to 69.1% in 2015 (p<0.0001). The percentage of studies with orthopedic authors decreased from 67% in 2005 to 44.9% in 2015 with a corresponding increase in the percentage of studies with neurosurgeon authors from 14.4% in 2005 to 23.2% by 2015, as well as an increase in the percentage of studies with a collaboration of authors from both specialties from 5.1% in 2005 to 8.7% in 2015 (p = 0.0007). Orthopedic and neurosurgery collaboration in authorship did not affect the level of evidence of the studies nor the number of citations of the studies (p=0.7583). Earlier studies had a higher SCOPUS citation number but were not affected by the level of evidence (p=0.2515) nor the department of the author(s) (p=0.9107).CONCLUSIONS: The publication characteristics of articles in TSJ have evolved between 2005 and 2015 with a 3.9-fold increase in International authorship and a 32% decrease in the proportion of Level I and Level II studies. Inter-departmental collaboration, funding source, and country of origin may affect level of evidence and number of citations. Continued efforts to increase level of evidence should be considered.
Global variability in orthopedic surgery training
Authors: Sobel Andrew D. , Hartnett Davis , Hernandez David , Eltorai Adam E. M. , Daniels Alan H.
Published: June 2019

Medical and orthopaedic training varies throughout the world. The pathways to achieve competency in orthopaedic surgery in other countries differ greatly from those in the United States. This review summarizes international educational requirements and training pathways involved in the educational development of orthopaedic surgeons. Understanding the differences in training around the world offers comparative opportunities which may lead to the improvement in education, training, and competency of individuals providing orthopaedic care.