bluuebunny/crossref_metadata_2025 huggingface dataset:
Stress Analysis of the Human Skull due to the Insertion of Rapid Palatal Expander with Finite Element Analysis (FEA)
Authors: Culea Laurenţiu , Bratu Cristina
Published: March 2009

The study aims at analyzing the stress state of the human skull with FEA, simulating the loads due to the insertion of rapid palatal expanders with two or four arms. A 3D CAD solid model of a human skull has been created starting from CT slices. Using FEA, forces that simulate the loads developed by the expander have been applied to the solid model of the skull to determine the stress state.
On the Time-Dependent Behavior of FGM Plates
Authors: Altenbach Holm , Eremeyev Victor A.
Published: March 2009

A non-classical plate theory based on the direct approach is introduced and applied to
plates composed of functionally graded materials (FGM). The governing two-dimensional equations are formulated for a deformable surface, the viscoelastic stiffness parameters are identified assuming linear-viscoelastic material behavior. In addition, the material properties are changing in the thickness
direction. Solving some problems of the global structural analysis it can be shown that in some cases the results based on the presented theory significantly differ from the results based on the Kirchhofftype
theory.
The Effect of Geometry and Material Properties on the Load Capacity of Single-Strapped Adhesive Bonded Joints
Authors: Sandu Marin , Sandu Adriana , Constantinescu Dan Mihai , Sorohan Ştefan
Published: March 2009

Adhesive bonding is a particularly effective method of assembling complex structures, especially those made from dissimilar materials. If the joint is well designed and correctly executed, the adhesive bond ought to be one of the strongest components of the structure and most certainly should not be the reason for reducing the load capacity or fatigue life. The major factors determining the integrity of an adhesive bond are selection of the most appropriate adhesive, joint design, preparation of the bonding surfaces, strict quality control in production and monitoring in service.
This work focuses on the evaluation of the load capacity of some configurations of adhesively bonded single-strapped joints based on finite element analyses. The adhesive layer thickness, the overlap length, the adherent and strap thicknesses were varied as well as the materials properties.
Behaviour Analysis of Adhesive Joints Used in Ship Structures
Authors: Chirica Ionel , Beznea Elena Felicia , Chirica Alexandru
Published: March 2009

The paper describes the results from mechanical testing and numerical analyses for the adhesive joints used in ship structures. The work undertaken in the numerical and experimental tests of different connections (steel-glass fiber polyester resin; steel - Carbon fibre epoxy) is summarized. The numerical nonlinear calculus is done due to the nonlinear properties of the adhesive and also due to the nonlinear behaviour of the adhesive joint.
Property Assessment of Magnesium Phosphate Cement
Authors: Qiao Fei , Lin Wei , Chau C.K. , Li Zong Jin
Published: March 2009

Magnesium phosphate cement (MPC) paste is prepared by mixing dead burned magnesia powder and potassium di-hydrogen phosphate with a proper proportion of water. The superior properties such as fast setting, high early strength, low shrinkage and good bonding makes MPC suitable for applications in rapid repair of infrastructures. However, the setting time of MPC is sometimes too fast, only taking a few minutes, which causes difficulties in manipulation. How to retard and control the setting time of MPC becomes a challenging topic in both scientific and engineering fields.
It was found that the setting of MPC was greatly influenced by the reactivity of magnesia, which could be determined by a quick, accurate and convenient test method. Two kinds of magnesia, namely, high-reactivity magnesia and low-reactivity magnesia were blended in order to control the setting time of MPC. Effects of magnesia to phosphate molar ratio, blending ratio and borax addition on setting time, workability and mechanical properties of MPC cement paste were investigated. Finally, the suitable ranges of the different constitutes of MPC based repair materials with satisfied workability and strength development were proposed for the practical engineering applications.
Experimental Study on Frothing Technics with Mixed Polyurethane Materials
Authors: Gao Yi , Wei Zhuo Bin
Published: March 2009

Frothing technics with mixed polyurethane materials have been widely used in the field of civil engineering. Polyurethane has many properties, such as frothing quickly, stronger viscidity and better elasticity. Having been frothed and vulcanized, polyurethane with other hard granules can form a new kind of backfill materials which have the higher initial strength. Based on the properties of polyurethane above, the frothing technic of polyurethane materials can be applied to consolidation and backfill of concrete and roadbed structure. In this paper, on the base of the experimental research about the materials’ properties, a test simulating an actual consolidation of subsoil was processed. The stable backfill substance used as base of pavement can be formed quickly by frothing of polyurethane in the pore space of gravels. The surface of pavement can be made from gravels and some certain polyurethane. It took 2 hours to backfill the base and to make the surface. Immediately, the loading test including static and impact load was taken. The result of the test indicated that the mechanical properties of surface and base made up of polyurethane composite materials can satisfy certain standards and specifications.
Study on the Sulfate Corrosion of Concrete under the Action of Loading
Authors: Xing Feng , Huang Zhan , Dong Bi Qin , Liu Jun , Zhang Ming , Luo Shuai
Published: March 2009

In this paper, the sulfate resistance properties of concrete under loading action are studied. The concrete specimens with different water/cement ratio are prepared and correlative corrosive experiments are carried out under single damage factor (SDF) and multiple damage factors (MDF), which is relative with drying and wetting cycles. Dynamic elastic modulus is taken to characteristic the sulfate resistance properties of concrete under the action of loading, drying and wetting cycles and sulfate corrosion. Results show the corrosion mechanisms of sulfate attack due to single damage factor and multiple damage factors were not all the same, and multiple damage factors could indicate the concrete structure due to sulfate attack more exactly.
Study on Calculation Methods for Ultimate Moment Capacity of SRC Columns with T-Shaped Steel
Authors: Wang Qiu Wei , Shi Qing Xuan , Tang Liu Jiu
Published: March 2009

Based on the common calculation methods of normal section bearing capacity of steel reinforced concrete (SRC) columns with I-shaped steel, SRC columns containing T-shaped steel are presented and their mechanical properties and failure modes are analyzed. Combining with actual engineering and current national codes, the calculation methods and formulas of ultimate moment capacity of this column are proposed and heights of the concrete pressured region in two different situations are compared, by which it can be seen that SRC columns are easier to form large eccentric compression failure when the big flange is nearer to axial force N .The bearing capacity of one SRC column with T-shaped steel is checked using above proposed formulas and the calculation results agree well with the experimental data, and finally this numerical example shows that the suggested method has good precision and reasonable application.
Meso-Mechanics Analysis of Concrete: Generation of Random Aggregate Structure
Authors: Jiang Shao Fei , Wu Zhao Qi , Qiu Yun Fei
Published: March 2009

In this paper, a new analytical method is proposed to generate concrete random aggregate structure (RAS) in meso-scopic level. This method is particular useful for the progressive failure of concrete under various external loads. In the meso-mechanics level, the concrete is taken as the composite material consisting of aggregate, mortar and interface between them. As a result, it is generated a random aggregate structure in which the shape, size and distribution of the aggregate particles resemble real concrete in the statistical sense using the Monte Carlo random sampling principle in this paper, and the method proposed can generate both regular aggregate particles and irregular ones in 2-Dimmension. It is should be noted that vector concept and some controlling measures are also proposed to avoid generating aggregate particles not consistent with real ones. Numerical examples are simulated to validate the proposed method finally.
Behavior of Prestressed Ultra High Performance Concrete Beams
Authors: Yang Jian , Fang Zhi
Published: March 2009

An experimental program was formulated to investigate the characteristics of complete stress-strain curve of UHPC in uniaxial compression and flexural behaviors of prestressed UHPC beams. The particular focus was the influence of the partial prestress ratio and jacking stress on the flexural response of UHPC beams. The tests of beams demonstrated that the UHPC beams have an excellent behavior in load carrying capacity, crack distribution and deformability; their ultimate deflection can reach 1/34～1/42 of the span. Based on this investigation, theoretical correlations for the prediction structure response of UHPC beams are proposed.
Numerical Simulation of Temperature Effect of Concrete Hydration
Authors: Wang Lu , Li Ying Min , Liu Li Ping , Xue Shang Ling , Dai Xun , Zhang Yu , Hu Zhao Hui
Published: March 2009

Based on the improved equation of concrete heat-generation rate and an improved calculation method of temperature stress, the temperature effect of concrete hydration heat is simulated successfully in ANSYS. Comparison between the numerical simulation results and test results of a scaled model of blast furnace foundation indicates that the calculated temperature field based on the improved equation and method is much closer to that of test than which obtained by the old equation and method. By using the stress superposition principle, the temperature-stress field can be calculated with considering the change of material behavior with temperature and time.
Seismic Behaviour of Semi-Rigid Joints to Concrete Filled Steel Tubular Columns
Authors: Wang J.F. , Han Lin Hai
Published: March 2009

This paper discussed the results of experiments on bolted moment connection joints of square or circular concrete filled steel tubular (CFST) columns and H-shaped steel beam using high-strength blind bolts under cyclic loading. The objective of this work was to study the seismic performance of the blind bolted flush endplate connections to CFST columns. The test parameters varied were the column section type and the thickness of the endplate. The feasibility of the proposed beam-column connection is successfully verified by the experiments. The test results showed that under cyclic loading the tested specimens displayed large rotation ductility capacities and could satisfy the request of the structural seismic design. When subjected to cyclic loading, most of failure modes of the tested joints are similar to those under monotonic loading. Moreover, the energy dissipation of the type joints is influenced by the column section type and the thickness of the endplate.
Dynamic Behavior of Composite Beams under Impact Load
Authors: Xiao J.C. , Liu J.F. , Bai C. , Mao J.Y. , Ma Ke Jian
Published: March 2009

Impact experiment of a set of steel/RC composite beams was conducted. To consider the influence of local impact residual deformation, transient response was investigated using elastic-plastic contact law. Experiments show that the main failure mode is related to the value of potential energy of impacter and energy dissipation capacity of sand cushion. Each theoretical analysis result is slightly less than its corresponding experimental value. Experimental values and elastic-plastic contact analysis results present that the maximum displacement and the maximum steel strain on the lower layer at midspan increase with the thickness of sand cushion and the height of impacter.
Effect of Site Conditions on the Design of Removable Anti-Ram Bollards
Authors: Liu Chun Lin , Phang Siew Kheong , Sun Jian Yun
Published: March 2009

Removable Anti-ram bollards used in perimeter protection are tested to meet performance requirements of established standards such as the US Department of State specification SD-STD-02.01. Under these standards, tests are conducted in prescribed conditions that should be representative of the service installation. In actual project, conditions encountered on site may vary from the test environment and it would be expensive and time consuming to validate each deviation with a physical test. High-fidelity physics-based (HFPB) finite element modeling can provide precise simulations of the behavior of anti-ram bollards. This paper presents the use of HFPB finite element modeling, using LS-DYNA, in an actual project to evaluate the performance of an anti-ram bollard design according to the actual site condition that is different with the test requirement. The study suggests that removable anti-ram bollards must be designed and engineered to actual conditions that are found on site. It also shows that HFPB modeling can be an effective tool that supplements physical testing of anti-ram bollards.
Contact Mechanism Analysis between Soil Structure and Underground Structures under Seismic Forces
Authors: Wang Jin Li , Liu Hai Qing , Wang Xue Qing
Published: March 2009

the soil-structure appeared slipped of roadway under earthquake, using the Coulomb contact surface model and built soil-structure of roadway contact model for analyzing, and got slip rule at different direction and position under horizontal and vertical direction and pointed out the corner as the weakness position; the beneath of roadway has more slipping; the vault is vulnerable to the level of shear failure; and gave reference for roadway structure for the seismic design.
A Computer Simulation-Based Method for the Volume Fraction of Capillary Pores
Authors: Zheng Jian Jun , Pang Xian Wei , Xiong Fang Fang
Published: March 2009

In view of the importance of capillary pores to the physiomechanical properties of cement-based materials, it is essential to determine the volume fraction of capillary pores. The intention of this paper is to present a computer simulation-based method for predicting the volume fraction of capillary pores. By applying the periodic boundary conditions and introducing three physical parameters to quantify the mutual interference between neighboring cement particles, a computer simulation technique for the distribution and hydration of cement particles is described. Based on the simulated microstructure of cement paste, a numerical method is developed for the volume fraction of capillary pores. After verifying the numerical method with the experimental results obtained from the research literature, the effect of the water/cement ratio and the maximum cement diameter on the volume fraction of capillary pores is evaluated in a quantitative manner. It is found that, at a given hydration time, the volume fraction of capillary pores increases with the increase of the water/cement ratio and/or the maximum cement diameter. This paper concluded that the developed numerical method can predict the volume fraction of capillary pores with reasonable accuracy.
Subcritical Crack Growth of α/β-Sialon Ceramics in Distilled Water
Authors: Riva Marco , Oberacker Rainer , Hoffmann Michael J. , Fett Theo
Published: March 2009

Environmental-assisted subcritical crack growth on two different /-sialon ceramics is determined in static fatigue tests. The goal of these investigations was to determine the influence of delivering medium of high pressure pumps on their durability (life cycle). Therefore 4-point-bending bars were statically loaded in distilled water and subcritical crack growth was analyzed. The large number of spontaneous failure and survivals made the development of a modified testing procedure necessary in order to obtain a significant database.
Macro- and Micro-Scale Thermal Conductivities of SiC Single Crystal and Ceramic
Authors: Yamada Ikuko , Kume Shoichi , Nakano Hiromi , Watari Koji
Published: March 2009

Thermal properties of SiC at the micrometer-scale were measured quantitatively with a thermal microscope using thermo-reflectance and periodic heating techniques. In this study, SiC single crystal and polycrystal were investigated. The small values of standard deviation suggest that the SiC single crystal had constant thermal conductivities. For the single crystal, the average value of the thermal conductivity at the micrometer-scale was in good agreement with the macro-scale thermal conductivity value obtained by the laser flash technique. On the other hand, thermal conductivity of the polycrystal was heterogeneous at the micrometer-scale. An average thermal conductivity value of 257 Wm-1K-1 was obtained within an area of 50 m ×100 µm. The highest and lowest values of the thermal conductivity from the polycrystal were 300 and 220 Wm-1K-1, respectively.
Effect of HfO2 Coating Films on Oxidation Resistance of SiC Ceramics
Authors: Kasajima Miho , Akashi T. , Shimada Shiro
Published: March 2009

HfO2 coatings were deposited on sintered SiC ceramics by a sol-gel process to improve the oxidation resistance of SiC. Crack-free HfO2 coatings ~200 nm thick were obtained by 8 cycles of dip-coating process using a mixed solution of Hf(OEt)4, DEA, and ethanol. XRD analysis indicated that the monoclinic HfO2 film was formed on the SiC ceramics. The un- and HfO2-coated SiC specimens were oxidized in Ar (purity: 99.9995%) containing a trace of oxygen or H2O at 1600°C for 10 h and the weight change was monitored by thermogravimetry. The weight of the un-coated sample decreased due to the active oxidation, while the weight loss of the HfO2-coated samples was smaller than that of un-coated sample.
Applying SiC Nanoparticles to Functional Ceramics for Semiconductor Manufacturing Process
Authors: Konishi Mikio
Published: March 2009

SiC nanoparticles are synthesized by r.f. thermal plasma chemical vapour deposition using a chemical system of SiH4-C2H4-H2-Ar. The average particle size is about 30 nm, and its shape is nearly spherical. The product is β-SiC and high pure with total metal impurity of less than 1 ppm. High pure and fully densified SiC body can be made by hot-pressing the sub-micron sized SiC powder added SiC nanoparticles without any sintering additives. They show electrical conductivity, high thermal conductivity and better properties of thermal shock resistance and chemical resistance compared with conventional SiC ceramics. Furthermore, Al2O3-SiC nano-composite can be made by using SiC nanoparticles easily. These functional ceramics from nanoparticles are the most promising materials for the semiconductor manufacturing process. Up to now, various sintered parts, such as heater, susceptor, pulse heat tool, shower plate and electrical static chuck, etc. have been developed and widely used in the semiconductor industry.
Reaction Bonded Silicon Nitride - Silicon Carbide and SiAlON - Silicon Carbide Refractories for Aluminium Smelting
Authors: Jones Mark Ian , Etzion Ron , Metson Jim , Zhou You , Hyuga Hideki , Yoshizawa Yuichi , Hirao Kiyoshi
Published: March 2009

The widely used Si3N4-SiC sidewall refractories for aluminum smelting cells, and β SiAlON-SiC composites that can be potentially used for this purpose, have been produced by reaction bonding and their corrosion performance assessed in simulated aluminum electrochemical cell conditions. The formation of the Si3N4 and SiAlON phases were studied by reaction bonding of silicon powders in a nitrogen atmosphere at low temperatures to promote the formation of silicon nitride, followed by a higher heating step to produce β SiAlON composites of different composition. The corrosion performance was studied in a laboratory scale aluminum electrolysis cell where samples were exposed to both liquid attack from molten salt bath and corrosive gas attack. The corrosion resistance of the samples was shown to be dependent on the composition but more importantly on the environment during corrosion, with samples in the gas phase showing higher corrosion.
Synthesis of Non-Oxide Ceramic Fine-Powders from Organic Precursors
Authors: Nishimura Toshiyuki , Ishihara S. , Yoshioka Yoshiki , Tanaka Hidehiko
Published: March 2009

Synthesis of titanium carbide ceramic powders and control of particle size were tried by carbothermic reduction of a precursor, comparing synthesis of silicon carbide from a precursor. Metal alkoxides were used as a metal source and phenolic resin was done as a carbon source. Homogeneous sol-like mixture was obtained by mixing ethylsilicate and phenolic resin with alcohol. Gel-like precursor was formed by drying the sol-like mixture. Precipitation was formed by mixing titanium(IV) tetraisopropoxide and phenolic resin. The precursor was amorphous and ceramization occurred by heat treatment in argon flow. Growth of particles and phase formation were investigated.
Surface Structuring of α/β-Sialon Ceramics by Plasma-Etching
Authors: Riva Marco , Oberacker Rainer , Hoffmann Michael J. , Ziebert Carlos
Published: March 2009

Effects of plasma etching on mixed /-sialon ceramics with different /-ratiowere investigated. A mix of CF4/O2 in a ratio of 2:1 was chosen as reactive gas. Parameters such as etching time and the material composition were examined. It was shown that -grains exhibit a larger etching rate than the grain boundary glassy phase or the -grains, generating pockets in a range of few µm. The so created surfaces were characterized both by scanning electron microscopy (SEM) and by atomic force microscopy (AFM) in contact mode. These complementary techniques also enabled the determination of the bearing ratio.
Mechanisms of Al/SiC Composite Machining with Diamond Whiskers
Authors: Zhang G.F. , Zhang Bi , Deng Zhao Hui
Published: March 2009

The objective of this study is to experimentally investigate the mechanisms in machining of aluminum/silicon carbide (SiC) composite with two types of diamond whiskers. These whiskers are prepared from polycrystalline diamond compacts (PDC) and chemical vapor deposition (CVD) diamond plates which are cut into dimensions of 10×0.3×0.6 mm with an Nd:YAG (Neodymium-doped Yttrium Aluminum Garnet) laser. In order to obtain sharp and consistent cutting edges, the diamond whiskers are polished with diamond powders of the average grain sizes of 10 µm, 2.5 µm and 1 µm, respectively. A precision grinder is used to conduct machining of the aluminum/SiC composite at a depth of cut smaller than that in the conventional milling but larger than the individual grit depth of cut in grinding. Scanning electron microscopy (SEM) is utilized for observing the machined workpiece surfaces, the whisker cutting edges, and a surface profilometer for inspecting surface roughness and verifying the actual depth of cut in the machined workpiece. The study discusses the mechanisms of workpiece material removal and diamond whisker wear in machining of the aluminum/SiC composite.
A Focused Review on Enhancing the Abrasive Waterjet Cutting Performance by Using Controlled Nozzle Oscillation
Authors: Wang Jun
Published: March 2009

Increasing the performance of the abrasive waterjet (AWJ) cutting technology for engineering materials is the ultimate aim of research in this field. This paper presents a review on the studies using a controlled nozzle oscillation technique to increase the cutting performance of the AWJ cutting technology and the associated mechanisms primarily based on the work in the author’s laboratory. Primary attention is paid to the discussions of the depth of cut, the effect and selection of process parameters and the advantages by using this technique in both single- and multi-pass cutting modes.
Research on Adaptability of Slag-Based Geopolymer with Superplasticizer
Authors: Wang Qing , Li Lin , Wu Chang Peng , Sui Zhi Tong
Published: March 2009

Using slag and metakaoline as raw materials , different modules of water glass as activator ,a new type of cementitious material—slag-based geopolymer was prepared. The fluidity of slag-based geopolymer paste and optimum content of superplasticizer in slag-based geopolymer mortar being as evaluation standard, adaptablities of slag-based geopolymer to naphthalene superplasticizer and melamine superplasticizer were studied. The results have shown that both naphthalene superplasticizer and melamine superplasticizer with slag-based geopolymer were adaptable well, obvious saturated points and optimum contents to two kinds of superplasticizers were performed.
Internal Curing of Saturated Lightweight Aggregate in High Performance Combined Concrete
Authors: Zha Jin , Li Bei Xing , Li Jin Hui , Gao He , Cui Gong
Published: March 2009

This paper investigated the mechanical properties, workability, autogenous shrinkage, drying shrinkage and durability of the high performance combined aggregate concrete with the coarse aggregate replaced by the lightweight aggregate in the volume fraction from 0% to 50%. The results demonstrated that the fresh concrete with the lightweight aggregate volume fraction of 10% and 30% had good workability, but degrade with a high volume fraction of 50 %. The hardened concrete with 10% and 30% lightweight aggregate replacement had similar compressive strength and splitting tensile strength comparing to the reference concrete without adding lightweight aggregate. The concrete with 50% lightweight aggregate replacement showed decreased compressive strength and splitting tensile strength. The concrete adding lightweight aggregate exhibited less autogenous shrinkage and drying shrinkage than the reference concrete without adding lightweight aggregate. The autogenous shrinkage and drying shrinkage increased with the increasing lightweight aggregate volume fraction. The concrete containing lightweight aggregate showed good durability after 200 freezing and thawing cycles, but the chloride permeability efficiency of concrete decreased.
Study on the Influence of Admixture on Chemical Shrinkage of Cement Based Materials
Authors: Xiao Kai Tao , Yang Hua Quan , Dong Yun
Published: March 2009

The influences of fly ash, phosphorus slag powder and slag powder on the chemical shrinkage were researched in this paper. The results indicated that chemical shrinkage of cement paste was mainly relative to the mineral composition of cement, and three kinds of admixture could all make chemical shrinkage of cement paste reduce in early stages, but the chemical shrinkage of cement paste increased in later stages after mixing slag powder and phosphorus slag powder, and the activity of slag powder was higher than phosphorus slag powder, and fly ash could be used to inhibit chemical shrinkage of cement paste. The prediction model of chemical shrinkage of cement based materials was established.
Design on the Concrete Structure Durability of the Relocation of Shougang and the Steel Project Construction of Caofeidian
Authors: Ding Hong
Published: March 2009

The relocation of Shougang and the steel project construction of Caofeidian is a national major project, according to the working life of design, the environmental classification and their exposure classes, we must consider the concrete structural durability in various ways, such as the forms of concrete structures, texture measures, the concrete materials and so on. The paper has discussed the basic design regulations, the forms of concrete structures and texture measures as well as the technical requirement of concrete materials, it is example with the concrete structures of the major projects, has analyzed the effect of the durability design for the actual concrete material.
Optimising the Design of Adhesively Bonded Joints
Authors: Pearson Ian
Published: March 2009

The effect of varying certain geometric and material property parameter on the stiffness of bonded joints has been investigated for both single overlap joints and for coach (T peel) joints. An understanding of bonded joint behaviour under load has been gained from this parametric study and this insight has been used to fashion some design guidelines aimed at optimising these parameters to increase joint stiffness.
To develop these design guidelines, laboratory tensile testing of single overlap joints and coach joints, manufactured from steel and aluminium and bonded with either an epoxide or a methacrylate adhesive, was utilised to establish joint stiffness. For single overlap joints, joint stiffness was found to be sensitive to changes in adherend thickness, adherend’s Young’s modulus, bondline thickness and overlap length but indifferent to changes in adhesive material properties, unsupported length and joint width. Coach joints, stiffness was found to be sensitive to changes in adherend material, adherend thickness, fill ratio and outer radius and adhesive material.
It must be recognised that the Design of Experiments technique, used to analyse the coach joint samples may have masked some of the effects caused by changes to joint parameters.
Robot-Based Incremental Sheet Metal Forming – Increasing the Part Accuracy in an Automated, Industrial Forming Cell
Authors: Meier Horst , Buff B. , Smukala V.
Published: March 2009

This paper describes new developments in incremental, robot-based sheet metal forming (Roboforming). Roboforming is a dieless sheet metal forming process which ensures cost-effective manufacturing of prototype parts and small batches.
An approach for increasing the part accuracy in Roboforming is presented. It is developed in a cooperative project funded by the German Federal Ministry of Education and Research called Roboforming. The project concentrates on the development of an industrial applicable system design. The use of standard components allows a modular and scalable set-up. A servo loop, consisting of sensors and a programming system, represents the basis of this design and shall guarantee higher part accuracies by measuring the deviations between a formed part and its target geometry. The deviations are used to derive corrected tool paths. The correction is performed by an adjustment vector for every point on the tool path. The theory for this strategy and first results are presented in this paper.
Enhanced Formability of Ultrafine-Grained Aluminum Blanks by Local Heat Treatments
Authors: Merklein Marion , Vogt Uwe
Published: March 2009

High strength aluminum blanks can be obtained by grain-refinement due to an Accumulativ Roll Bonding (ARB) process, in which two sheets are iteratively brushed, stacked on top of each other and subsequently rolled together. The high shear stresses during the rolling cycles result in an ultrafine-grained microstructure with an average grain size ranging between 200 to 1000 nm. Whereas the grain-refinement causes a drastically increased strength of the aluminum material, the formability of the ARB-blanks made of industrially used aluminum alloys such as the AA6016 deteriorates to the same degree as the strength rises. In this context, a local heat treatment of the ARB-blank reducing the material’s strength and increasing its ductility in specific zones will allow to recover the blank’s formability again.
The research work presented in this paper studies the microstructural effects of a short-term heat treatment on the mechanical properties of ARB-blanks made of AA6016. Experimental investigations including hardness measurements, tensile tests as well as microscopic analyses show that heat treatments of only several seconds already result in significant increases of the material’s ductility and decreases of the material’s strength. By applying these microstructural mechanisms in terms of a specific heat treatment layout, functional gradients of strength and ductility adapted to the succeeding forming operation can be setup significantly enhancing the ARB-blank’s formability.
Interlaboratory Comparison of Forming Limit Curves for Hot Stamping of High Strength Steels
Authors: Pellegrini Daniele , Lechler J. , Ghiotti Andrea , Bruschi Stefania , Merklein Marion
Published: March 2009

The paper presents the approaches followed by two labs – LFT at the University of Erlangen-Nuremberg (Germany) and DIMEG at University of Padua (Italy) – in evaluating formability limits of 22MnB5 sheets when processed under hot stamping conditions. Details about the two testing apparatuses and the testing procedures are outlined, and the results in terms of Forming Limit Curves FLC compared and critically commented.
Development of the Hot Gas Bulging Process for Aluminium Alloy Tube Using Resistance Heating
Authors: Maeno Tomoyoshi , Mori Kenichiro , Fujimoto Kouji
Published: March 2009

A hot gas bulging process of an aluminium alloy tube using resistance heating, set into a forming machine, was developed. The tube was rapidly heated by the electrifying to increase the formability and to decrease the flow stress. The tube was bulged by thermally expanding the air sealed in the tube without control of internal pressure during the forming. Hot gas bulging of an aluminium alloy tube without and with axial feeding was performed. The effects of the initial internal pressure and the current on the expansion ratio of the tube were examined. The decrease in temperature around the contact with the electrode was prevented by inserting a stainless steel ring having low thermal conductivity and high heat generation between the copper electrode and tube, and thus the bulging length was increased. It was found that the hot gas bulging is effective in heightening the formability of the aluminium alloy tubes.
Prediction of Path Deviation in Robot Based Incremental Sheet Metal Forming by Means of an Integrated Finite Element – Multi Body System Model
Authors: Meier Horst , Laurischkat Roman , Bertsch C. , Reese Stefanie
Published: March 2009

The main influence on the dimensional accuracy in incremental sheet metal forming results from the compliance of the involved machine structures and the springback effects of the workpiece. This holds especially for robot based sheet metal forming, as the stiffness of the robot’s kinematics compared to a conventional machine tool is low, resulting in a significant deviation of the planned tool path and therefore in a shape of insufficient quality. To predict these deviations, a coupled process structure model has been implemented. It consists of a finite element (FE) approach to simulate the sheet forming and a multi body system (MBS) modeling the compliant robot structure. The forces in the tool tip are computed by the FEA, while the path deviations due to these forces can be obtained using the MBS model. Coupling both models gives the true path driven by the robots. Built on this path prediction, mechanisms to compensate the robot’s kinematics can be implemented. The current paper describes an exemplary model based path prediction and its validation.
A Neural Network Based Approach for the Design of FSW Processes
Authors: Buffa Gianluca , Fratini Livan , Micari Fabrizio
Published: March 2009

Friction Stir Welding (FSW) is an energy efficient and environmentally "friendly" welding process. The parts are welded together in a solid-state joining process at a temperature below the melting point of the workpiece material under a combination of extruding and forging. This technology has been successfully used to join materials that are difficult-to-weld or ‘unweldable’ by fusion welding methods. In the paper a neural network was set up and trained in order to predict the final grain size in the transverse section of a FSW butt joint of aluminum alloys. What is more, due to the relationship between the extension of the “material zones” and the joint resistance, the AI tool was able to furnish indications for the design of the welding process. Experimental tests and subsequent microstructure observations were developed in order to verify the numerical predictions.
A New Description of Yield Loci Based on Polycrystal Plasticity for High Strength Steels
Authors: An Yu Guo , Vegter Henk , Carless Louisa
Published: March 2009

Recently, many flexible constitutive equations have been proposed for sheet forming simulations. However, various mechanical tests are required to determine the many material parameters needed for such models. In the present work, effort has been made to investigate the correlation between the polycrystal plasticity based yield loci and those determined from mechanical tests, in order to define yield functions easily and accurately with minimum amount of experimental work. The results for different materials indicate that, in many cases, the Hill’48 deviates significantly from the measured yield loci. The yield loci derived from measured texture and polycrystal plasticity perform better than the Hill’48 yield function in general. Based on the two yield loci derived from the Taylor full constraint model and the Pancake model, a new combined model is proposed. The new model uses the averaged biaxial points of the two models but keeps the shape of the yield loci derived from the Taylor full constraint model in the stretching regime. The stress factors in the uniaxial and shear mode are calculated by averaging the stress factors of the two models. The proposed new description has been validated using several steel grades.
Bendability of Ultra-High-Strength Steel
Authors: Väisänen Anu , Mäntyjärvi Kari , Karjalainen Jussi A.
Published: March 2009

Utilisation of ultra-high-strength (UHS) steels is rapidly spreading from the automotive industry into many other application areas. It is necessary to know how these materials behave in common production processes such as air bending. The bendability of UHS steels is much lower compared to normal and high-strength construction steels. In this work, experimental tests were carried out using complex phase (CP) bainitic-martensitic UHS steels (YS/TS 960/1000 and 1100/1250) and S650MC HS steel in order to inspect material bendability and possible problems in the bending process. Mechanical and geometrical damages were registered and classified. The bending method used was air bending and press brake bending with an elastic lower die. The FE analysis was used to understand the stress state at different points in the material and build-up of failure. As UHS steels cannot stand large local strains, a large radius must be used in air bending. The results show that even when a large radius is used in air bending, the strain is not evenly distributed; there is a clear high strain area in the middle of the bend. It was also possible to simulate the other phenomena occurring in experimental tests, such as losing contact with the punch and ‘nut-like’ geometry, using FE analysis. Experimental test results also show that by using an elastic lower die, it is possible to avoid unwanted phenomena and obtain an almost 50% smaller punch radius, but the required force is 50% bigger than that required in air bending.
Prediction of Roll Profile Wear in the Cold Roll Forming Process
Authors: Galakhar Alexander S. , Daniel William J.T. , Meehan Paul A.
Published: March 2009

This paper presents a model for prediction of forming roll profile wear during the cold roll forming process. The method is based on contact pressure distribution, geometrical description of the initial forming roll profile and NURBS representation of the contact area.
Aluminum Alloy Tube Welding by Means of High Power Diode Laser
Authors: Quadrini Fabrizio , Squeo Erica Anna , Tagliaferri Vincenzo
Published: March 2009

A process innovation is proposed by the authors to weld aluminum alloy tubes by means of a high power diode laser. In order to make the temperature profile uniform along the entire welding line, multiple passes of the laser source along the welding path can be performed at very high scan speeds. In the current study, this effect is achieved by focusing the standstill laser spot on the external surface of the aluminum alloy tubes which were put in rotation at high speed. The tubes were clamped together by using a threaded rod passing inside the tubes. Experimental tests were performed by changing the aluminum alloy heat treatment (6060 T1 and 6060 T5), the length of the samples to weld (80 and 100 mm), and the laser power (ranging from 800 to 950 W). The outer diameter of the tube was 10 mm, the thickness was 1 mm, and the rotational speed was kept constant at 1000 rpm. The welding time was monitored during the tests and ranged from 30 to 100 s in dependence on the material and process parameters. Specimens were extracted from the joints to perform tensile tests so as to measure the tensile strength. In the best condition, a high tensile strength was obtained (about 140 MPa).
Thickness Determination of Thin Polycrystalline Films by Grazing Incidence X-Ray Diffraction
Authors: Lhotka J. , Kužel Radomír , Cappuccio G. , Valvoda V.
Published: March 2009

The thickness measurement based on absorption of X-rays in thin films has been tested on a polycrystalline titanium nitride films deposited on a tungsten carbide substrate. Intensities of three reflections from each material were measured for incidence angles of the primary beam ranging from 0.5° to 35°. After experimental correction for texture effects, data from the TiN film and the WC substrate were fitted by known functions using least squares
routines. The substrate reflection intensities were found to be more suitable for determining the thickness of the overlaying thin film. The average thickness of TiN film (2.00± 0.17 µm) determined from the substrate reflections was in fair agreement with the average value obtained from optical microscopy (2.2± 0.8 µm). The thickness values determined from the TiN thin film reflections are very unreliable due to a high sensitivity of measurements to disturbing
instrumental and sample effects at small angles.
XRD Line Broadening Analysis with Ball Milled Palladium
Authors: Lucks I. , Lamparter P. , Xu Jian , Mittemeijer Eric Jan
Published: March 2009

Palladium powder was deformed by ball milling under an argon atmosphere in two types of mills for different milling times. Two methods for X-ray diffraction line profile analysis, the Williamson-Hall method and the Warren-Averbach method, yielded similar trends, but different quantitative results for crystallite sizes (column lengths) and microstrains. With both methods, from the anisotropic line broadening for planetary milled Pd smaller crystallite sizes and larger
microstrains were obtained along the <100> direction than along <111>. Milling in a shaker mill causes microstrain higher by a factor of about two than milling in a planetary mill. The evolution of the crystallite size upon milling was discussed in terms of bimodal size distributions.
Small Angle X-Ray Scattering with Cobalt Radiation for Nanostructure Characterization of Fe-Based Specimen
Authors: Erlacher Kurt , Görgl R. , Keckes Jozef , Jakob Hannes F. , Bruegemann L. , Doppler P. , Bergmann A. , Leitner Heinz , Marsoner S. , Fratzl Peter
Published: March 2009

A laboratory system (NanoSTAR) based on a combination of specially designed X-ray multilayer optics (Göbel Mirrors) with optical bench, pinhole collimators, sample changer and primary beam stop as well as a two dimensional multiwire detector (HI-STAR) was equipped with a sealed cobalt X-ray tube. This solution was chosen because the CoKα has a wavelength close to that of copper but allows to overcome the problem of excessive fluorescence in Fe-samples.
Various measurements were performed using this configuration of the NanoSTAR to demonstrate the performance of SAXS using cobalt radiation. A comparison is given to the primary beam intensity of the NanoSTAR with Co radiation with respect to the Cu radiation. Examples for the use of the Co radiation are given by investigating the coarsening behavior of precipitates in several Fe-based alloys. The change in size and shape of these precipitates under different heat treatment conditions are characterized.
Fitting of Reciprocal Space Maps of Thin Films with Texture and Stress
Authors: Šimek D. , Kužel Radomír , Kub J. , Kunc F.
Published: March 2009

Textured thin film of PbTiO3 on glass and both textured and stressed films of TiB2 on iron substrate were investigated by two-dimensional reciprocal space mapping. The texture and residual stress parameters were found by fitting of the measured intensity in the reciprocal space map by the simulated data. Two different types of texture were found in TiB2 for different values of residual stress. The relevance of resulting parameters was checked using different models. Simulation of the data involved a proper empirical texture correction, the Pearson VII profile function, the irradiated volume correction giving a possibility of the film thickness determination,
the background, and other correction factors (Lorentz, polarisation).
Effect of Short-Term Annealing on the Crystalline Structure of Metallic Multilayers with a TiB2 Anti-Diffusion Layer on GaAs Substrate
Authors: Kryshtab T.G.
Published: March 2009

The structural characteristics of Au-TiB 2/GaAs and Au-Mo-TiB2-AuGe/GaAs device structures after deposition and short-term thermal annealing (STTA) were investigated. The multilayer contacts with TiB2 anti-diffusion layer were magnetron sputtered on (001) GaAs substrates. The structures were STTA in a stream of hydrogen at temperatures of 400°C, 600°C, and 800°C during 60 seconds. The X-ray diffraction techniques and atomic force microscopy were used for investigation. At STTA a reduction of residual strain in multilayer metallic films, an increment of film grain size, a change of grains preferred orientation in the Au polycrystalline film and a transformation of surface morphology of the upper Au film were observed. These
processes do not have monotonic temperature dependence. For Au-TiB2/GaAs a minimum value of residual strains was observed at T=600°C while for Au-Mo-TiB2-AuGe/GaAs it was observed at T=400°C. The roughness of Au film monotonically increased at annealing of Au-TiB2/GaAs structure at T=400°C and T=600°C and corresponded to the initial value at T=800°C. A strong change of Au film roughness was observed at annealing of Au-Mo-TiB2-AuGe/GaAs structure at T=600°C. The XRD pattern from a Au-TiB2 metal film denoted a quasi-amorphous structure in the initial state and an increment of micrograins size at STTA. In the initial state the crystalline structure of Au film in Au-Mo-TiB2-AuGe/GaAs structure had some preferred orientation in the <111> direction, which was reduced after STTA at T=600°C. The polycrystalline structure of Au film was partially deteriorated after STTA at T=800°C as TiB2 layer was destroyed and lost its diffusion protecting properties.
Self-Organization in Semifluorinated Polymers
Authors: Jehnichen D. , Pospiech D. , Häußler L. , Friedel P. , Gottwald A. , Kummer S.
Published: March 2009

Alkyl-perfluoroalkyl compounds are known to form a microphase-separated structure due to the thermodynamic immiscibility between the fluorinated and the protonated segments [1,2]. Many similarities between bulk and surface structures of such polymers were found in the past [2,3,4] which can be explained by both microphase separation in the bulk as well as surface segregation of the fluorinated parts. Basing on this concept, polymers with chemically different main chains were attached with alkylperfluoroalkyl side chains (particularly, oxydecylperfluorodecyl chains, -O-(CH2) 10-(CF 2) 9-CF 3). Combined investigations by means of
temperature-dependent X-ray scattering, molecular modeling and DSC measurements were performed to characterize the bulk structure in dependence on the flexibility of the main chain as well as the density of side chains. The polymers under investigation show one or more phase transitions in the temperature range from room temperature to 300 °C which can be assigned as transitions between different smectic structures. These phases are characterized to have positive as
well as negative expansion coefficients, respectively, indicating changes of the tilt angle of the side chains and/or the degree of interdigitation. The polymer melts feature a high memory behavior evidenced by reversed imaging of the scattering patterns in the heating and cooling runs.