bluuebunny/crossref_metadata_2025 huggingface dataset:
A modern perspective on flow instability and shockwave phenomena in reacting gas multiphase system excited by direct current
Authors: Kurbatov Peter F.
Published: November 2019

A critical analysis of physical insights into ionization waves, plasma states, and attendant phenomena in a gas discharge plasma excited by direct current discussed in the literature is performed. A comparison between synergy bifurcation and kinetic bunching models shows that the former is undoubtedly close-to-perfect and “useful,” and it “is an accurate representation of the real world from the perspective of the intended uses of the model” in the range of gas pressures from 1 to 100 Torr, whereas the latter is obviously imperfect. The latter model is no perspective. The basic factors and ideas definitely established at the early stage of studying striations and current jumps in the discharge are briefly reviewed. The synergy aspect invoking the diffusion-reaction equations, catastrophe theory, and ionization equilibrium principle is demonstrated to permit us to better understand the physics of ionization waves and the underlying physical processes and also to establish a natural and useful link between the parameters of a physical system. Conditions and specific features of their formation and propagation directions are determined. Based on modern concepts of the physical nature of striations and current jumps, it is demonstrated that these ionization waves propagating in a gas discharge are typical ionization-diffusion shock waves.
Influence of plasma-activated nitrogen species on PA-MOCVD of InN
Authors: Ahmad Z. , Cross G. B. , Vernon M. , Gebregiorgis D. , Deocampo D. , Kozhanov A.
Published: November 2019

We report on the influence of various plasma species on the growth and structural properties of indium nitride in plasma-assisted metalorganic chemical vapor deposition. Atomic emission spectroscopy was used to quantify the molecular, neutral, and ionized nitrogen species concentrations above the growth surface. Reflectance and Raman spectroscopy and X-ray diffraction techniques were used to characterize the grown InN films. It has been found that ionized rather than molecular or neutral nitrogen species is positively correlated with the InN growth rate. We conclude that InN formation in the present case is due to the chemical combination of atomic nitrogen ions with indium.
Dielectric properties and electrocaloric effect of high-entropy (Na0.2Bi0.2Ba0.2Sr0.2Ca0.2)TiO3 ceramic
Authors: Pu Yongping , Zhang Qianwen , Li Run , Chen Min , Du Xinyi , Zhou Shiyu
Published: November 2019

Single-phase homogeneous (Na0.2Bi0.2Ba0.2Sr0.2Ca0.2)TiO3 powder with high configurational entropy was synthesized by using a solid-state method. Calculations of thermodynamic parameters and related experiments indicate that both entropy and enthalpy drive the formation of a stable system. To further research the material's performance, we sintered the powder into a ceramic, which exhibited relaxation behavior because of the disorder of the microscopic composition. In addition, an applied electric field of 145 kV/cm produces a discharge energy density of 1.02 J/cm3. Meanwhile, the adiabatic temperature is 0.63 K at 60 kV/cm. These properties suggest that the electrocaloric effect of the (Na0.2Bi0.2Ba0.2Sr0.2Ca0.2)TiO3 ceramic is attractive for applications such as solid-state refrigeration and energy storage. High-entropy perovskite oxides are also highly tolerant to ions, and their properties can be tailored by tuning their composition, making them attractive for a broad range of applications.
Long-range spin dependent delocalization promoted by the pseudo Jahn-Teller effect
Authors: Stein Benjamin W. , Dickie Diane A. , Nedungadi Sachin , Brook David J. R. , Shultz David A. , Kirk Martin L.
Published: November 2019

Strong spin-dependent delocalization (double exchange) was previously demonstrated for the complexes, NN-Bridge-SQ-Coiii(py)2Cat-Bridge-NN (where NN = S = 12 nitronylnitroxide, Bridge = 1,4-phenylene and single bond, SQ = S = 12 orthobenzosemiquinone, Coiii = low-spin d6 cobalt 3+, and Cat = diamagnetic catecholate). The mixed-valent S = 12 SQ-Coiii-Cat triad results in ferromagnetic alignment of localized (pinned) NN spins which are ∼22 Å apart (Bridge = Ph). Herein, we report similar ferromagnetic coupling of localized verdazyl (Vdz) radical spins. The origin of the magnetic exchange results from a second order vibronic effect (pseudo Jahn-Teller effect) in [Vdz-diox-Ru(py)2-diox-Vdz]0, which possesses a diamagnetic [diox-Ru-diox]0 triad by virtue of strong antiferromagnetic SQ-Ruiii exchange.
Application of proton boron fusion to proton therapy: Experimental verification to detect the alpha particles
Authors: Yoon Do-Kun , Naganawa Naotaka , Kimura Mitsuhiro , Choi Min-Geon , Kim Moo-Sub , Kim Yong-Jin , Law Martin Wai-Ming , Djeng Shih-Kien , Shin Han-Back , Choe Bo-Young , Suh Tae Suk
Published: November 2019

Feasibility of proton boron fusion (PBF) reaction to radiotherapy has previously been studied using Monte Carlo simulation. Alpha particles are emitted from the fusion reaction between the proton and 11B close to the end of the Bragg peak. The generated alpha particles can theoretically induce critical damage to tumor cells due to their high linear energy transfer. Nevertheless, there has been a lack of experimental verification to detect the alpha particles and to apply in proton therapy due to the difficulty to observe the generated alpha particles with a very short range in medium. An experimental observation of the generation of alpha particles is indeed necessary for PBF to be applied to proton therapy. We have performed an experimental study using a medical proton accelerator and fine-grained nuclear emulsion films to detect tracks of alpha particles produced. These films, attached to the rear side of the natural boron containing plate located close to the end of the Bragg peak, were individually irradiated by 2 × 108 cm−2 density proton beams at an energy of 79.7 MeV. Some clear tracks of alpha particles, produced by the PBF reaction and clearly separated with those from n + 10B reaction, were observed with the use of a 3D microscope after the films were developed. Each track was analyzed, and alpha particle tracks were verified. A detailed experimental method will be presented using microscopy analysis. In conclusion, the experimental results showed that the observation of alpha particles resulted from PBF and the application feasibility of the PBF reaction to the proton therapy.
On the Noble-Abel stiffened-gas equation of state
Authors: Radulescu M. I.
Published: November 2019

The inviscid hydrodynamics of inert compressible media governed by the Euler equations of motion only require knowledge of a caloric equation of state e(p, v) for the material relating the internal energy e to the fluid pressure p and specific volume v (or density). For departures from the ideal gas behavior, simple equations of state such as the stiffened gas, Noble-Abel, or a hybrid recently generalized by Le Métayer and Saurel [“The Noble-Abel stiffened-gas equation of state,” Phys. Fluids 28, 046102 (2016)] can correctly model compressible flows in gases, liquids, and solids. However, reactive and multicomponent descriptions require a formal definition of temperature. In the present note, we formulate a general thermodynamically based method to determine the thermal equation of state T(p, v) compatible with a generic e(p, v) relation. We apply our method to the Noble-Abel Stiffened Gas equation of state and recover the closed form solution of Le Métayer and Saurel. We also show that variations of the model taking its exponent different from the ratio of specific heats do not permit to define a thermodynamic temperature.
Computing vibrational eigenstates with tree tensor network states (TTNS)
Authors: Larsson Henrik R.
Published: November 2019

We present how to compute vibrational eigenstates with tree tensor network states (TTNSs), the underlying ansatz behind the multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) method. The eigenstates are computed with an algorithm that is based on the density matrix renormalization group (DMRG). We apply this to compute the vibrational spectrum of acetonitrile (CH3CN) to high accuracy and compare TTNSs with matrix product states (MPSs), the ansatz behind the DMRG. The presented optimization scheme converges much faster than ML-MCTDH-based optimization. For this particular system, we found no major advantage of the more general TTNS over MPS. We highlight that for both TTNS and MPS, the usage of an adaptive bond dimension significantly reduces the amount of required parameters. We furthermore propose a procedure to find good trees.
Workload efficiency as a new tool to describe external and internal competitive match load of a professional soccer team: A descriptive study on the relationship between pre‐game training loads and relative match load
Authors: Grünbichler Johannes , Federolf Peter , Gatterer Hannes
Published: November 2019

The current study introduces a new index for external and internal workload, “workload efficiency”, and assesses in professional soccer the influence of pre‐match training load on match workload efficiency. External and internal workloads were determined for 44 training sessions and 16 competitive matches using a 10‐Hz global positioning system (GPS) and a 200 Hz accelerometer/heart rate monitor. Training loads were registered from day five (D‐5) to day one (D‐1) prior to each competitive match. Workload efficiency was calculated for each match as the ratio between overall external and internal load. A multiple stepwise regression analysis (including z‐transformed variables) was used to determine training load variables that predict workload efficiency of the following matches. Training load variables of the previous days explained 26.6% of the variance in workload efficiency during the following matches. Long sprinting distance on D‐3 and D‐4 and total distance on D‐1 positively influenced the players’ workload efficiency, whereas long training durations and high training load on D‐1 showed adverse effects. The present outcomes suggest that including sprint training (high sprinting distance) four and three days prior to a match, may provide a positive stimulus for the subsequent workload efficiency in matches. The negative impact of long training duration and high training load one day before the game highlights the importance of a diligent planning of the immediate competition preparation phase. This study shows that workload efficiency is a useful metric to assess match performance and that body‐worn sensor technology can be useful for tailoring training loads.
A comparison of methods for adapting

177Lu

dose-voxel-kernels to tissue inhomogeneities
Authors: Götz Th , Schmidkonz C , Lang E W , Maier A , Kuwert T , Ritt P
Published: November 2019

In

radionuclide therapies, dosimetry is used for determining patient-individual dose burden. Standard approaches provide whole organ doses only. For assessing dose heterogeneity inside organs, voxel-wise dosimetry based on 3D SPECT/CT imaging could be applied. Often, this is achieved by convolving voxel-wise time-activity-curves with appropriate dose-voxel-kernels (DVK). The DVKs are meant to model dose deposition, and can be more accurate if modelled for the specific tissue type under consideration. In literature, DVKs are often not adapted to these inhomogeneities, or simple approximation schemes are applied.

For 26 patients, which had previously undergone a

-PSMA or -DOTATOC therapy, decay maps, mass-density maps as well as tissue-type maps were derived from SPECT/CT acquisitions. These were used for a voxel-based dosimetry based on convolution with DVKs (each of size

) obtained by four different DVK methods proposed in literature. The simplest only considers a spatially constant soft-tissue DVK (herein named ‘constant’), while others either take into account only the local density of the center voxel of the DVK (herein named ‘center-voxel’) or scale each voxel linearly according to the proper mass density deduced from the CT image (herein named ‘density’) or considered both the local mass density as well as the direct path between the center voxel and any voxel in its surrounding (herein named ‘percentage’). Deviations between resulting dose values and those from full Monte-Carlo simulations (MC simulations) were compared for selected organs and tissue-types.

For each DVK method, inter-patient variability was considerable showing both under- and over-estimation of energy dose compared to the MC result for all tissue densities higher than soft tissue. In kidneys and spleen, ‘constant’ and ‘density’-scaled DVKs achieved estimated doses with smallest deviations to the full MC gold standard (∼

underestimation). For low and high density tissue types such as lung and adipose or bone tissue, alternative DVK methods like ‘center-voxel’- and ‘percentage’- scaled achieved superior results, respectively. Concerning computational load, dose estimation with the DVK method ‘constant’ needs about 1.1 s per patient, center-voxel scaling amounts to 1.2 s, density scaling needs 1.4 s while percentage scaling consumes 860.3 s per patient.

In this study encompassing a large patient cohort and four different DVK estimation methods, no single DVK-adaption method was consistently better than any other in case of soft tissue kernels. Hence in such cases the simplest DVK method, labeled ‘constant’, suffices. In case of tumors, often located in tissues of low (lung) or high (bone) density, more sophisticated DVK methods excel. The high inter-patient variability indicates that for evaluating new algorithms, a sufficiently large patient cohort needs to be involved.
Applications of highly non-equilibrium low-pressure oxygen plasma for treatment of polymers and polymer composites on an industrial scale
Authors: Vesel A , Primc G , Zaplotnik R , Mozetič M
Published: November 2019

Scientific aspects of technologies based on application of non-equilibrium oxygen plasma are presented. Oxygen plasma is sustained by an electrodeless discharge to facilitate a high concentration of neutral reactive species, in particular O atoms. The species interact with solid materials causing surface functionalization, removal or organic impurities, nanostructuring of polymers, selective etching of polymer composites or synthesis of metal-oxide nanoparticles. The flux of O atoms onto the surface-facing plasma is often between 1020 and 1023 m−2 s−1. While the physical interaction with solid materials (i.e. heterogeneous surface recombination) does not depend much on the sample temperature, the chemical interactions (functionalization, etching, oxidation) increase significantly with increasing temperature. The key treatment parameters are therefore the fluence of O atoms onto the sample surface and its temperature. The recommended ranges of parameters for various technologies are shown in the graphical abstract.
Characterisation of the mechanical failure and fracture mechanisms of single grain Y–Ba–Cu–O bulk superconductors
Authors: Congreve Jasmin V J , Shi Yunhua , Huang Kai Yuan , Dennis Anthony R , Durrell John H , Cardwell David A
Published: November 2019

The widespread use of melt processed, single grain (RE)–Ba–Cu–O bulk superconductors [(RE)BCO], where RE = Y, Gd or Sm, is limited predominantly by the poor mechanical properties of these inherently brittle, ceramic-like materials. The high density of flaws, such as cracks and voids, within the single grain microstructure leads directly to a low fracture toughness. As a result, the Lorentz forces, generated when these materials carry current in the presence of a large magnetic field, create stresses sufficiently large to cause brittle failure. The addition of Ba–Cu–O (liquid phase) and Ag to the precursor composition prior to melt-growth has been demonstrated to be effective in improving the mechanical properties of these technologically important materials. In this work, we characterise the mechanical failure of single grain YBCO bulk superconductors in terms of a Weibull statistical distribution. In addition, differences in fracture mechanisms have been studied to provide a better understanding of how the provision of additional liquid phase and silver produces YBCO single grains with better resulting mechanical properties and how these can be improved further.
The influence of hybrid nanostructures TiC/MWCNT concentration on the properties of bulk composites based on aluminum alloy
Authors: Aborkin A V , Khorkov K S , Kremlev K V , Ob`edkov A M , Sytschev A E
Published: November 2019

In this paper, we present the results of producing bulk composite materials based on aluminum alloy AlMg2, hardened 0.1-5 wt.% MWCNT and decorated with TiC nanoparticles by powder metallurgy method. Powder and bulk composites were characterized by electron microscopy, X-ray diffraction, kinetic indentation and compression tests. The influence of hybrid nanostructures TiC/MWCNT concentration on the properties of bulk composites was studied.
Image acquisition of the test-object by the CVL-10 copper vapor amplifier and optical bunch
Authors: Arakelyan S M , Galkin A F , Zhirnova S V , Shamanskaya E L
Published: November 2019

Images of the test object surface were obtained using a laser projection microscope and an optical bunch. Images of the surface of the test object at its different location in the experiment (the test object is located at the end of the optical bunch; the test object is located in a double focus lens; the test object is located after the optical bunch and optical system of two lenses) were obtained on the screen of a laser projection microscope.
Study of the effect of scanning speed in selective laser melting on the physicomechanical properties of samples.
Authors: Voznesenskaya A. , Zhdanov A. , Morozov V.
Published: November 2019

In this work, prototypes of aluminum alloy were obtained by the method of selective laser melting at different beam scanning speeds. Images of the powder material were obtained on a scanning electron microscope and the shape and size of the particles were investigated. The microstructure and defects were studied by metallographic analysis. Diagrams of the structure-phase composition of powder materials and samples obtained by the method of selective laser melting were obtained. The physical and mechanical properties of the images were also investigated.
Control of the alexandrite lasing spectrum
Authors: Putilov A G , Antipov A A , Shepelev A E , Lotin A A , Arakelyan S M
Published: November 2019

This paper discusses the use of dispersive optical elements as control devices for the wavelength of alexandrite laser. Some types of selective resonators are considered. The losses in the resonators with dispersive elements are described. The results of a dual-wavelength alexandrite lasing with an installed birefringent filter are presented.
Modeling of electrical conductivity of labyrinth bimetallic nanofilms
Authors: Bukharov D.N. , Kucherik A.O. , Arakelyan S.M.
Published: November 2019

In the framework of this paper, the results of experimental studies on the production of thin labyrinth bimetallic films, as well as measurement of ampere characteristics from volts, are presented. In addition, the simulation of their electrically conductive properties is done.
Study of properties and strength of no-fines concrete
Authors: JiaHao L , Chin Lian F , Hejazi Farzad , Azline Noor
Published: November 2019

Nowadays, special concrete is widely adopted in construction industry. No-fines concrete is a one of the special concrete which eliminate the use of fine aggregates in concrete mixing. The application of no-fines concrete has been introduced to construction industry especially pavement construction. Due to its high porosity behavior, the relative density of no-fines concrete is lower than normal concrete of 2400kg/m3which also helps in reducing dead weight in the design. In term of strength, no-fines concrete also gave lower compressive strength compared to normal conventional concrete. The aggregate/cement ratio also found to be a factor affecting its strength as it is depending on the interlocking or the strength of bonding between aggregate and cement. Also, concrete with varies mix ratio gives different has been studied for its physical and mechanical properties. In addition, there are further study of introducing fiber materials to determine the chance of enhancement in no-fines concrete study. By elimination of fines aggregates, the development and application of no-fines concrete in the construction industry will be more economical than normal concrete. This paper reviews and studies the performance characteristics and strength of no fine concrete based on previous researcher’s outcome.
Effects of soil-structure interaction on base-isolated structures
Authors: Aden M. A. , Al-Attar Alyaa A. , Hejazi F. , Dalili M. , Ostovar Nima
Published: November 2019

Structural integrity and seismic protection of the buildings against earthquake have been challenging among structural engineers. Many studies have been devoted to development of seismic isolators to improve the seismic behavior of civil structures. This study presents the analysis of building structures with SAP2000 considering soil structure interaction and base isolation effects under El Centro. Four different models are analyzed including fixed base structure, base isolated structure, frame supported by spring representing the soil and structure with combined base isolation and spring. The seismic results are investigated in terms of displacement, shear force, axial force, moment and drift of the columns and beams. It was observed that the soil structure interaction provides some flexibility to the structure by increasing the displacements of the structure and imposing internal forces variation to the system. Therefore, modeling base isolation together with consideration of soil structure interaction leads to better prediction of structural response.
Preliminary Modelling Assessment of Hydrodynamic Simulation due to Terengganu Airport Runway Extension
Authors: Yee Ling Soh , Veerasamy K. , Hidayat Jamal Mohamad , Shahrizal Ab Razak Mohd
Published: November 2019

Coastal erosion is a naturally phenomenon occurring result of the coastal hydrodynamic process. It is referring to the process of diminution, crafting and unloading of materials in coastal areas by agents such as waves, wind and tides. Erosion process becomes faster when there is activity on the waterfront development. To identify potential erosion caused by development, a study was conducted at the Terengganu Airport Runway extension. In this study, numerical modelling analyses were conducted to represent hydrodynamics using MIKE-21 software. The MIKE-21 is a comprehensive coastal modelling of software that simulates hydrodynamic, wave action, wind and tides. Modelling data input were obtained from National Hydraulics Research Institute Malaysia (NAHRIM) for the period of November 2009. Collected marine data were used as base for model calibration. Model calibration is with-in the acceptable confident level. Then, the calibrated model is used to predict the potential impact due to the Kuala Terengganu Airport runway extension.
Developing a Knowledge-based Decision Support System for Prefabricated Prefinished Volumetric Construction
Authors: Li Y S , Hwang B G , Shan M , Looi K Y
Published: November 2019

Prefabricated prefinished volumetric construction (PPVC) has a lot of advantages, including environmental protection, saving money, reducing on-site manpower and so on. Many countries advocate the development of PPVC, the decision making of PPVC construction becomes critical important. This study aims to developing a scoring approach based on Knowledge-Based Decision Support System (KBDSS) for PPVC implementation. To achieve this goal, 19 key decision-making factors (DMFs) were identified from literature reviews first, subsequently, a questionnaire survey was conducted on 41 construction organizations in Singapore and using a five-point rating scale. Then create a PPVC scoring approach by using the data from the questionnaire, this scoring approach will developing a program named KBDSS-PPVC, by using the Microsoft Excel and Microsoft Visual Basic for Applications (VBA). Finally, four industry experts will be invited to validate the feasibility of KBDSS-PPVC and scoring their current construction projects, this program can also give corresponding recommendations according the score. The results of validation showed the developed system really could provide some available suggestions for industry practitioners on the decision-making for PPVC implementation, this study complements the current knowledge system on PPVC decision-making and provides the basis for further research.
A S.W.O.T. Analysis of Green Procurement Implementation in Construction Projects
Authors: Bidin Z A , Bohari A A M , Rais S L A , Saferi M M
Published: November 2019

Green-related practices are widely implemented in various countries to ensure that problems related to the environment can be reduced. The concept of green-related practices and strategies were introduced and identified in providing the green procurement can be fully implemented in the Malaysian construction project. Green procurement concept is presented as one of the initiatives to support in reducing environmental issues throughout construction execution. Hence, this paper focuses on analysing the strengths and weaknesses of green procurement as well presented the opportunities and threats towards construction. Focus group discussion was conducted among green expert's participant who shares their experiences and point of views related to green procurement. The outcomes of this research findings offer plans and a clearer picture for practitioners in implementing green procurement practices in construction execution.
What are the factors behind the distinct character of Mosques in Turkey and Iran?
Authors: Kelly Tamara
Published: November 2019

Cities or its urban fabric and the characteristics architecture in many regions during various timescale is shaped by numerous factors. Among those factors are intangibles as political motivation, inspirations from other civilizations, religious influence. Whereas physical sways such as climate or geographical consideration or availability of materials and skilled labor are behind other great architecture creation. Therefore this article examines the impact of these factors in shaping the religious architecture in two vast neighboring countries Iran and Turkey. Iran is an immense country and its weather is variable and key factors in shaping a specific type of architecture while in Turkey, other influences are more dominant. The methodology of this paper is based on a literature review of various references and a theoretical analysis of several case studies in Iran and Turkey. This paper is an attempt to help students and researchers to understand how architects creates distinct architecture by acknowledgement of intangible forces.
Themes and Factors of Construction Safety Management for System Dynamic Model Interactions: A Systematic Review
Authors: Jasni Nur Azalini , Nordin Rumaizah Mohd , Ismail Zulhabri , Abdul Aziz Nurul Ayuni
Published: November 2019

The construction industry has always been regarded as a dangerous industry to work in, and the Malaysian construction industry is not exempted. Most safety and health studies conducted in this industry only view the overall factors contributing to the accidents or focus only on the main factor such as human behaviour. However, accidents actually happen based on the interaction between all the factors of the accidents at a construction site, and thus this study is conducted to identify the factors contributing to the accidents happening at construction sites and to classify them into their themes by using a systematic review method. This method is used to gather the empirical evidence regarding construction safety management by assessing academic journals mostly searched using keywords ‘construction safety management’, ‘themes of accidents’, ‘factors of accidents’ and ‘System Dynamic’ on academic journal databases known as ‘Google Scholar’, ‘Science Direct’ and ‘Academia’. The findings of this study identified 18 factors that contribute to the accidents and are classified into four (4) main themes which are human factors, management factors, technical factors and also environmental factors. The themes and factors identified in this study would contribute to develop a construction safety management system using System Dynamic model that will show the complex interactions between all the factors according to their themes.
Prediction of mechanical behaviour of an ultra-thin sheet metal under non-proportional loading using a crystal plasticity model
Authors: Bong H. J. , Lee J. , Lee M.-G.
Published: November 2019

A theoretical crystal plasticity model to predict mechanical responses of ultra-thin (<0.1 mm thick) sheet metal under non-proportional loading, which are difficult to measure experimentally due to premature buckling in simple shear or compression-tension test, was developed. In the model, three different dislocation density components, namely, forward, reverse and latent dislocations, were incorporated in the crystal plasticity model. The model was applied for 100 μm thick ultra-thin ferritic stainless steel sheet to predict mechanical responses under two-step tension, and the predicted results were compared with the experimental data.
Local fracture strain measurement in AHSS uniaxial flat tensile tests considering specimen geometry and fracture morphology
Authors: Larour P , Wagner L , Felbinger A , Angeli J
Published: November 2019

The local formability of AHSS sheet steels can be estimated by means of the relative average reduction of cross section area (or thickness) at fracture in flat tensile specimens. A 2D/3D characterization of tensile fracture shapes is performed with an optical stereo microscope for various typical fracture shapes. The initial width to thickness ratio (w0/t0) of flat tensile samples quantifies their non-proportionality behavior. A charpy like lower and upper shelf region with a highly scattered transition zone in between at a critical w0/t0 ratio is observed when plotting the fracture area or thickness reduction versus w0/t0 ratio. The higher the w0/t0 ratio of tensile specimens (samples wider, material thinner) the higher the local fracture strain level. The higher the material work hardening ability (n-value), the higher the critical w0/t0 ratio below which high scattering in thickness - and area reduction occurs. The local tensile fracture strain is therefore strongly dependent on specimen thickness, width and work hardening behavior. This is a severe drawback for a broader use of such tensile test based fracture strain measurements.
Effect of kinematic hardening on the yield surface evolution after strain-path change
Authors: Yang Yanfeng , Baudouin Cyrille , Balan Tudor
Published: November 2019

Abrupt strain path changes without elastic unloading have been used to investigate the yield surface of sheet metals, both experimentally and theoretically. These investigations emphasized an apparent non-normality phenomenon, following such a strain-path change. Subsequently, these results inspired the development of plasticity models including non-associated flow rules and non-normality theories. In this study, this type of abrupt strain-path changes is investigated using kinematic hardening models in the context of associated plasticity. The aim is to emphasize the contribution of kinematic hardening ingredient to the apparent violation of the normality condition. The results show that kinematic hardening slope and curvature of the material have a strong influence to contribute to this apparent non-normality.
Blockchain for forming technology – tamper-proof exchange of production data
Authors: Frey P , Lechner M , Bauer T , Shubina T , Yassin A , Wituschek S , Virkus M , Merklein M
Published: November 2019

An increasingly connected production in the sense of Industry 4.0 allows completely new possibilities in regard to improved and more efficient production and higher product quality. But a key factor to Industry 4.0 is a consistent data flow along the production chain. However, the exchange of data, especially between companies, still is a major obstacle to overcome in order to achieve the aforementioned advantages. Currently, there are increasing efforts to record and analyse data. But there is a lack of a holistic system to handle data, therefore commonly company databases or other inefficient methods are used. These solutions are limited with regard to data exchange since the ownership of data cannot be proven, production data has no unforgeable timestamp, which in turn hinders the generation of complete production history from the final product (e.g., car door) back to the semi-finished product (e.g., steel sheet). As a result, there is insufficient to no data exchange along the production chain. In order to solve these problems blockchain is a promising approach. At the Institute of Manufacturing Technology, an operational blockchain system was developed and implemented using standard production machines. With the combination of a quarto rolling mill and a 400t - press, representing the sheet metal supplier and a forming company, respectively, the typical process chain of sheet metal processing is represented, which allows the detailed investigation of the established blockchain in this field of application. Within this contribution, the conceptual approach of a blockchain system for forming technology will be presented. The nature and the classification of occurring data throughout the production chain will be addressed.
Local formability of AHSS: Measurement technique, specimen types and robustness
Authors: Gruenbaum M , Aydin G , Dettinger T , Heibel S
Published: November 2019

The recently proposed classification scheme for AHSS with global and local formability enables a material specific process development, allows a designation based on mechanical properties, as well as an assessment of various properties: deep drawability, edge-crack sensitivity, bendability, damage tolerance and fracture toughness. Local formability is measured by local fracture strains, e.g. area reduction at fracture or true thickness strain at fracture. Based on investigations of AHSS with strengths between 600 and 1000 MPa from different steel suppliers, this contribution addresses the influence of the measurement technique, of different specimen types and different sheet thicknesses on the measure for local formability. Furthermore, the correlation between true thickness strain at fracture and hole expansion ratio and also the hardness difference of the microstructure, as well as no correlation between local formability and bending angle according to VDA 238-100 are confirmed. It is shown that the influence of the measurement technique for true thickness strain at fracture is neglectable regarding the differentiation between the investigated grades. Using “uniaxial” tensile tests with specimen types 2 and 3 according to ISO 6892-1 one can obtain similar local fracture strains. Same states for the notched tensile tests with radii of 4 mm and 5 mm. The values gained by the smaller A30 mm specimen show slightly lower values compared to the “uniaxial” tensile specimen types. With increasing sheet thickness, a slight decrease in true thickness strain at fracture resulting from the combination of a changing width-to-thickness ratio of the tensile specimen and different microstructures can be seen. The large range of the measure for local formability using materials from different suppliers and different sheet thicknesses motivates the definition of requirements for material specifications and source approvals.
Characterizing damage and fracture of sheet metal materials using large scale test specimen
Authors: Jurendic Sebastijan , Anderson David
Published: November 2019

Several approaches to characterizing damage evolution and fracture behaviour of sheet metal materials are currently in existence. These are based on different testing methodologies and test specimen designs, some of which, when combined with higher sheet thicknesses used for aluminium alloys in the automotive field, can reach and exceed geometrical limits required for the plane stress assumption commonly applied to numerical modelling of sheet metal materials. Furthermore, if shell elements are to be used in modelling of such structures, the characteristic length of the element should be larger than the thickness of the modelled sheet material. In order to allow for element sizes accounting for the two considerations outlined above, new test specimen geometries covering a range of stress triaxialities have been developed with a deformation region significantly larger than that of other commonly used test specimen designs. The geometries have been manufactured and tested on an automotive grade AA6xxx series aluminium alloy with DIC strain measurement to determine failure strains. The results were then applied to finite element models using various element sizes and the behaviour of the numerical models compared to the test results.
The effects of shear affected zone on edge crack sensitivity in dual-phase steels
Authors: Habibi N. , Beier T. , Richter H. , Könemann M. , Münstermann S.
Published: November 2019

Dual phase steels offer good combination of mechanical properties which is attractive for automotive industry. However, some challenges still remain and suppress using them widely. One of these challenges is the formation of premature cracks at shear-cut edges during the subsequent forming processes, which cannot be predicted by the conventional finite element methods. Therefore, the present study aims to propose a numerical tool to predict edge cracks in DP steel components. In this regard, the hole expansion method was applied as an edge crack detection technique on DP1000 steel sheets. To elaborate the study, parallel finite element simulations were performed as well. The simulation method considered the whole hole piercing process and the following hole expansion test as a one-stroke two-step strategy. The hole piercing process was applied in the first step on the sheet and a hole was cut. The results reveal that this process forms some surface irregularities and applies a special amount of damage at the cut edge, which both could have effects on the edge crack sensitivity. To study these effects, the subsequent hole expansion test was simulated on the manufactured hole. Thus, the effects of both surface irregularities and residual damage from hole piercing process were investigated in different case studies with all possible combinations of these effects. This strategy provides possibilities to numerically separate effects of surface quality and residual damage. The contribution shows on the one hand the experimental investigations and on the other hand deals with the numerical influence analyses.
Forming behaviour of stainless steel sheets at different material thicknesses
Authors: Lehmberg A , Sunderkoetter C , Glaesner T , Brokmeier H-G
Published: November 2019

The austenitic stainless steel X5CrNiMo17-12-2 in thickness ranging from 0.2 mm to 1.0 mm was examined in regard to the mechanical properties and microstructure. The aim was to investigate the suitability of conventional test methods for thin material down to 0.2 mm. Within these investigations, all used thicknesses were characterized by conventional tensile tests and X-ray diffraction. The results were subsequently compared with each other. The material specific vertical anisotropy r and forming limit curve showed a strong dependence on material thicknesses. The results of anisotropy pointed out different values depending on the test methods performed. In addition, the results of microstructure analysis show a decrease of grain size with lower material thickness caused by the formation of twins and probably heat treatments during the manufacturing process.
Developing smart multi-sensor monitoring for tool wear in stamping process
Authors: Shanbhag V.V. , Pereira M.P. , Voss B. , Ubhayaratne I. , Rolfe B.F.
Published: November 2019

Tool wear and galling are of significant concern in the automotive stamping industry, due to the increase in use of higher strength sheet steels in automotive structures and reduced lubrication during stamping production. There are many methods explored in the literature and applied in industry to combat wear in stamping, including new die materials and coatings, alternative lubrication systems and better predictive models. However, smart condition monitoring will continue to be relevant in conjunction with these methods because it can provide further opportunities for production quality and cost improvements, despite the advancements of these other methods. This paper explores the use of multiple sensors and multiple signal processing techniques, aimed at developing a smart multi-sensor method to monitor galling wear. The three main sensors and corresponding signal processing techniques examined are: (i) measurement of punch force signatures analyzed via Principal Component Analysis (PCA); (ii) acoustic emissions signals measured via wideband sensors and examined using time and frequency domain features; (iii) measurement of audio signals in the audible frequency range analyzed via blind signal separation techniques. For all techniques, a semi-industrial stamping test was used to provide realistic production-type conditions, albeit with accelerated wear rates. The relationship between the key outputs from the three sensor/analysis methods were directly compared to a new quantitative measure of galling wear severity. Based on these results, it was observed that a multi-sensor approach for wear condition monitoring provides an opportunity for the development of a smart monitoring tool that can actively track the progression of wear.
A type of cruciform specimen applied to evaluate forming limits for boron steel under hot stamping conditions
Authors: Zhang R , Shao Z , Lin J
Published: November 2019

The ultra-high strength boron steel has been intensively used in the hot stamping process to produce complex-shaped structural components in transportation industries. Forming limit diagram (FLD) is a fundamental and useful tool to evaluate the formability of metallic materials under various forming conditions. Since the standardized Nakajima test and Marciniak test are not applicable to perform formability tests for hot stamping applications due to the complex heating and cooling processes required, an in-plane testing method, in which cruciform specimens are deformed under hot stamping conditions in a Gleeble materials simulator combined with a multi-axial tensile rig to convert an input force to an output biaxial force, has been successfully applied to assess the formability of aluminium alloys at elevated temperatures. However, it is challenging to apply this in-plane testing method for boron steel due to higher nonuniformity of temperature distribution in gauge region of the cruciform specimen at a higher temperature. In this paper, a new type of cruciform specimen, together with a new specimen heating strategy, has been proposed to improve the temperature distribution in the gauge region. The dimensions of the newly-designed cruciform specimen have been optimised by a thermo-electrical finite element model embedded with a UAMP subroutine in ABAQUS to improve the uniformity of temperature distribution in the gauge region. In order to validate the new design of cruciform specimen, biaxial tensile tests were conducted under hot stamping conditions by using the in-plane testing method.
New Multiphase CP and DP 1000 MPa strength level grades for improved performance after hot forming
Authors: Lahaije C T W , Rana R , Sunderkoetter C , Pérez Iñaki , Arribas Maribel , Aranguren Iñigo , Caro Daniele De
Published: November 2019

Pure martensitic steels have after hot forming limited performance in terms of rest ductility which limits the application in crash relevant parts. New steel grades were designed in the EU project HOTFORM including the corresponding process routes. These steel grades have ferritic-martensitic dual phase (DP) and martensitic-bainitic complex phase (CP) microstructures after hot forming process. The laboratory tests show an improved formability after hot forming. The basic concepts of the new alloys are explained. Furthermore, for validation of upscaling purposes a semi-industrial test is carried out and the results are discussed. The main application is for vehicle safety. This is evaluated by comparing the crash performance of these hot formed grades with cold rolled DP1000 and CP1000 for crash cans in a drop tower test.
Formability study on stamping an engine hood with aluminum alloy sheet
Authors: Lin Chien-Wei , Chen Fuh-Kuo
Published: November 2019

The formability of stamping an engine hood with aluminum alloy sheet was examined in the present study. In the stamping process, except that aluminum alloy would crack easily, a small elastic modulus makes the aluminum alloy easier to produce a significant springback defect, which would lead to variation of accuracy and is hard to grapple with. In the present study, the cyclic tension-compression reversal tests were first conducted to obtain the stress-strain relations and the Bauschinger effect exhibited in the aluminum alloy sheet was noted. The finite element simulations were then preformed for V-bending and U-hat drawing of aluminum alloy sheet, and the results of springback and side-wall curl were compared with those obtained from experiments. It is concluded from the comparison that the material model which includes the Bauschinger effect renders a more consistent result with the experimental data. In order to investigate the difference of forming characteristics between conventional steel and A6181-T4 in the stamping process of an engine hood, the effects of process parameters on the stamping formability were systematically analyzed by the finite element simulations. The finite element simulation results were validated by the production engine hood and the characteristics of A6181-T4 formability investigated in this study were confirmed.
Comprehensive understanding of effective parameters on edge cracking sensitivity of hot-rolled complex phase steels
Authors: Goncalves J , Alibeigi S , Sarkar S
Published: November 2019

Good stretch-flangeability is an essential property for forming complex press-formed automotive parts such as chassis, suspension and control arm components. Continuous research is ongoing in developing materials that could improve the performance of Advanced High Strength Steels (AHSS) during industrial stretch-flangeable operations. Consequently, there is a great interest in investigating the sheared edge stretchability and determining the factors, critically influencing the product edge formability. The objective of the present research is to obtain a comprehensive understanding of effective parameters on the cut-edge behaviour of Hot-Rolled (HR) stretch-flangeable Complex Phase (CP) steels. The role of microstructural damage on the edge stretchability of CP steels was evaluated employing hole punching and Hole Expansion (HE) tests. The influence of product microstructure and inclusions were highlighted. A correlation between the Lankford coefficients (‘r’ value), strain hardening exponent (‘n’ value) and Hole Expansion Rate (HER) was investigated. Finally, a new specific testing procedure combining a shearing test followed by tensile test is proposed to correlate with hole punching and HE operations and to develop in-depth understanding.