bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effects of Non-Metallic Inclusion on Ductile Damage of High Carbon Steel Wire in Multi-Pass Dry Drawing Process
Authors: Ji Se In , Lee Kyung Hun , Yang Yo Sep , Lee Choong Yeol , Bae Chul Min , Kim Byung Min
Published: September 2014

The objective of this study is to evaluate how the inclusion sizes influence the damage value and the maximum hydrostatic stress during multi-pass dry drawing process. It was well known that non-metallic inclusions can lead to material fracture during metal forming process, and be harmful to the quality of the final product. In multi-pass dry wire drawing, the temperature rise during deformation greatly decreases the quality of final product. In this study, the pass schedule in which initial diameter of 3.55 mm is reduced to final diameter of 2.115 mm was isothermally designed for the high carbon content steel. Spherical non-metallic inclusion of Al2O3 is located in the center of a steel rod. Influences of inclusion size, 5 μm, 10 μm, 20 μm and 50 μm in initial diameter 3.55 mm on ductile damage was investigated by FE-simulation in which material fracture was estimated using normalized Cockcroft and Latham criterion.
An Experimental and Numerical Investigation into Forming Force Reduction in Precision Gear Forging
Authors: Politis Nicholas J. , Politis Denis J. , Davies Catrin Mair , Lin Jian Guo , Dean Trevor A.
Published: September 2014

A significant factor in the cost of industrial machinery for precision forging is the maximum load required to fully forge the final shape of components. Typically in a precision forging process, the required load increases greatly towards the end of the stroke. This study focuses on reducing the final sharp increase in load encountered in a typical closed die forging setup. A technique of reducing the peak load in the forging of gears is proposed, named the Peripheral Relief (PR) method. A gear forging tool set has been designed and manufactured. A number of experimental trials have been performed using model materials to investigate the force reduction technique. An efficient and simplified FE model has been developed to evaluate the effects of the PR method. The experimental load characteristics are compared to the simulated results. The method has been found, both numerically and experimentally, to significantly reduce the peak load encountered at the end of the forging stroke compared to current closed die forging techniques.
Estimation of Strain-Hardness Correlation in Cold-Forged Austenitic Stainless Steel
Authors: Skubisz Piotr , Rumiński Maciej , Lisiecki Łukasz
Published: September 2014

The paper presents selected aspects of analysis cold micro-forging process of a screw made of austenitic stainless steel, concerning relation between strain and hardness. Strain hardening character of a material in consecutive forming operations was analyzed experimentally by the measurement of hardness distribution made on longitudinal axial sections of screws. The relationship between hardness and effective strain (hardness curve) was determined, which made it possible to obtain strain distributions in different regions of a material subjected to cold deformation on the basis of strain distribution numerically estimated with FEM simulation performed using QForm2D/3D commercial software. Conclusions were formulated concerning strain inhomogeneity and strain-hardening intensity with respect to the correlation between strain and hardness. It was also concluded, that nonuniformity of hardening rate in a bulk can lead to local variations in flow stress and eventually, to occurrence of the metal flow related defects, which was illustrated with a case study of cold heading of self-tapping screw of AISI 304Cu stainless steel, with large head diameter to shank diameter ratio. In order to validate the obtained results, the same method was used for analysis of hardness development in steel 19MnB4.
New Method for Forming Brackets with a Triangular Rib
Authors: Dziubińska Anna , Gontarz Andrzej
Published: September 2014

This paper presents the experimental research results concerning a new method of forming of brackets with a triangular rib. The forging process of products with ribs was conducted applying a three-slide forging press (TSFP) on material model in the form of lead plates. During the experiment, the influence of the process particular parameters on the obtained products quality was analyzed. On the basis of the research results the main failure modes of the material during processing were determined. The limiting value of the plate upsetting coefficient depending on its length was given. Considering conducted research works, it was stated that it is possible to form such brackets forgings in TSFP in accordance with the worked out method.
Advanced In-Process Control System for Sheet Stamping and Tube Hydroforming Processes
Authors: Manabe Kenichi
Published: September 2014

A sophisticated servo press with the digital control has been developed and attracted attention in recent years. By utilizing its high function in-process, servo presses have a potential to enhance the forming limit and to improve quality and accuracy of product not only in sheet stamping but also in tube hydroforming processes. On the other hand, in-process control and adaptive process control technologies in metal forming processes using intelligent technique and soft computing have been investigated and developed previously. Nowadays we are in a good environment to realize further advanced adaptive in-process control in metal forming process. To further advance this technology, sensing system is essential element and it should be applied to feedback control optimally in their forming operation. This paper describes the current situation on advanced intelligent process control technology for sheet stamping and tube hydroforming processes on the basis of the research results by the author.
Investigation of the Shape of a Cruciform Biaxial Tensile Specimen Intended for a Combination of Plane Strain Tensile States
Authors: Usui Hayato , Iizuka Takashi
Published: September 2014

This study investigates the shape of a cruciform specimen that is stretched in the normal direction of the minimum cross section using FEM. In addition, plane strain tensile states exist in the measurement region in order to determine the forming limit diagram not by an arbitrary stress ratio but by the strain ratio. We propose two types of cruciform specimens. One is a flat-type cruciform specimen, which has deep slits in the middle of the arm region in the width direction. The other specimen is a reduced measurement region type, which also has deep slits as well as a shape that is a biaxial combination of two plane strain tensile specimens. We analyze equibiaxial tensile tests of these two proposed cruciform specimen types using FEM.
Strain Analysis of Parts Produced by Multi-Pass Conventional Metal Spinning
Authors: Šugár Peter , Šugárová Jana , Petrovič Ján
Published: September 2014

Sheet metal spinning is one of the forming processes based on gradual shaping of metal blank into an axisymetric part by a roller according to a mandrel. Very significant feature of spinning is ability to produce components with high mechanical properties and high quality of surface layers. The paper brings the results of major true strains analysis of mild steel parts produced by CNC multi-pass conventional metal spinning. The influence of the spindle speed, feed rate, workpiece geometry and planar anisotropy of the blank on the strain distribution of formed part is studied by method of grain size measurement. The design of experiment using the Taguchi approach and analysis of variance (ANOVA) is applied to find optimal process parameters.
Effective Linear Friction Welding Machine Redesign through Process Analysis
Authors: Buffa Gianluca , Cammalleri Marco , Campanella Davide , Fratini Livan , Vairis Achilles
Published: September 2014

Linear friction welding is a solid-state joining process developed for non-axisymmetric components in which the joining of the specimens is obtained through reciprocating motion and pressure. In the process, the friction forces work due to the high frequency oscillation and the pressure between the specimens is converted in thermal energy. In order to design an effective machine, relevant issues derive from the high frequency and the large inertial forces involved in the process. In this study, the authors describe the redesign of a preexisting prototypal machine for LFW processes. A machine redesign is needed when welding high resistant materials, i.e. steels or titanium alloys, with high frequencies, up to 72 Hz. The sensors equipping the machine allows in process measurements of key process variables as temperatures of the specimens, tangential forces, accelerations and speeds. At the same time through the acquired data, the main weaknesses of the machine can be highlighted allowing for effective redesign.
Friction Stir Welding between Dissimilar Metalswith Circular Weld Line
Authors: Fukumoto Masahiro , Mizushima Hiroki , Yasui Toshiaki
Published: September 2014

Hybrid metallic structure, which is composed of aluminum alloy as a representative of light metal and steel as that of high strength metal, has been paid attention remarkably in these days, especially in the transportation vehicle industry from the energy saving viewpoint. To perform the hybrid structure, friction stir welding FSW has been recognized to be an effective way for the welding between dissimilar metals, like between steel and Al alloy. Based on our previous findings on the butt welding between dissimilar metals with straight weld line, welding between dissimilar metals with circular weld line has been tried to open a new application field of FSW. The objective of this research is to get a fundamental finding on the welding between dissimilar metals with circular weld line and to clarify the effect of material character of Al alloy and tool design on the FSW between dissimilar metals.
Typical results obtained in this study are summarized as follows:
1) Macroscopic defects often observed at the bottom part of the welding in case of ADC12 material. It indicates that insufficient stirring was given in the stirring zone due to the higher thermo-mechanical property of ADC12.
2) Tensile strength of the specimen welded with scroll shoulder tool was 266 MPa, while that with flat shoulder tool was 161 MPa. Tensile strength of the weld joint was improved by a factor of 1.65 by introducing the scroll onto the tool shoulder with normal thread probe.
3) High performance defect free ADC12/S45C weld structure with circular weld line could be fabricated by the tool with combination of scroll shoulder and thread probe.
High Temperature Deformation and Diffusion Brazing of INCONEL 718 Sheet
Authors: Kwon Yong Nam , Hong S.S. , Kim H.G.
Published: September 2014

Superplastic forming has been known for the ideal process for manufacturing complex parts. Also, diffusion bonding can give a higher design flexibility, which allows a better performance with a lower overall manufacturing cost. Fine grained INCONEL 718 alloy sheet has been known to show superplastic behavior with the combination of high strength and corrosion resistance at the elevated temperatures. In the present study, high temperature deformation characteristic of INCONEL 718 sheet with 15m was investigated firstly. Then, blow forming process with cylindrical cavity was tried. Also, best diffusion brazing and bonding condition was tried to be defined in terms of temperature, pressure and time. Bonding strength was characterized by using lap shear type test and interface observation. Characteristics of deformation and diffusion bonding at high temperature were influenced greatly with grain size while Nb precipitate also played an important role.
Numerical Investigation on Dissimilar Friction Stir Welding of Aluminum and Magnesium Sheets
Authors: Buffa Gianluca
Published: September 2014

Friction Stir Welding (FSW) is a solid-state welding process used to weld difficult to be welded or unweldable materials as aluminum alloys. In the last years other materials have been successfully tested as magnesium, titanium and nickel based alloys. Mixed joints can be obtained by FSW but issues arise in the correct choice of the process parameters. In the paper a numerical model is presented for the prediction of the main field variables distribution and the occurring material flow in FSW of dissimilar AA6061 and AZ31 butt joints. Important insights are obtained on the effect of the mutual position of the two materials with respect to the advancing and retreating side of the joint has been highlighted.
Effect of SiC Addition on the Mechanical Properties of Twin-Roll-Cast AZ31 Sheet
Authors: Neh K. , Kawalla Rudolf
Published: September 2014

The effect of SiC addition on grain refinement of an AZ31 alloy was investigated. First preliminary casting tests were carried out. Different amounts between 0.25 wt% and 1,0 wt% of SiC-particles with a diameter of about 2 μm were added to an AZ31 melt and poured into a plate mould. The resulting microstructure was observed by optical microscopy. Best results were reached with the addition of about 0.25 wt% in terms of a homogeneous microstructure and a sufficient grain refinement. Higher amounts lead to coarsening and agglomeration of precipitations. Based on these results Twin-Roll-Casting (TRC) of an AZ31 alloy with the addition of SiC-particles was conducted. For the investigations a TRC-system in laboratory scale was used. This system is part of the Twin-Roll-Casting pilot plant at the Institute of Metal Forming, which is used in collaboration with the MgF Magnesium Flachprodukte GmbH. The produced TRC-strip was cut into plates, and samples for microstructure characterization and the determination of the mechanical properties were retrieved. Compared to TRC-strip without the addition of SiC-particles a microstructure with finer precipitations and a more homogeneous distribution can be observed. Furthermore, sheets with an addition of SiC offer improved mechanical properties in TRC-condition.
Flow Curve Modelling of a ZM21 Magnesium Alloy and Finite Element Simulation in Hot Deformation
Authors: Bruni Carlo , El Mehtedi Mohamad , Gabrielli Filippo
Published: September 2014

The present investigation deals with the development of a methodology to predict the flow behaviour of the ZM21 magnesium alloy in given intervals of temperature and strain rate by FEM simulation of torsion testing. Equations based on the hyperbolic sine of flow stress and on the multiple linear regression were proposed and implemented into the finite element code. The flow curve shapes obtained by simulation were compared with experimental ones that were not used in the building phase of the equations. It was found that the simulation of torsion tests allows, under given conditions of temperature, strain rate and deformation levels, to obtain flow curve shapes very similar to those obtained by experiments under conditions not included in the building of the models.
Development of Dynamic Recrystallization Model Based on Cellular Automata Approach
Authors: Sitko Mateusz , Madej Łukasz
Published: September 2014

Development of a numerical model for the dynamic recrystallization (DRX) on the basis of the Cellular Automata method and the Digital Material Representation (DMR) idea is the main goal of the present work. Basic assumptions (space definition, neighborhood type, state and internal variables) of the proposed model are presented and discussed. Particular attention is put on description of the developed transition rules used to replicate mechanisms leading to dynamic recrystallization. Finally, examples of obtained results of DRX morphology and kinetics are also presented within the paper.
Motion-Controlled Precise Stamping for Microtexturing onto Aluminum Sheet
Authors: Aizawa Tatsuhiko , Itoh Taichi , Tamaki Masahiro , Fukuda Tatsuya
Published: September 2014

Mass production of heat radiation devices requires for fine stamping of micro-textured patterns in the order of micro-meters in dimension onto the sheet product. In this duplication of micro-textured patterns, an original mother micro-pattern in the convex type has to be transferred onto the metallic sheet in the concave type with sufficient accuracy. The authors have proposed a micro texturing of original micro patterns onto the DLC coated mother die-and mold-unit. Once this unit is inserted and fixed in the stiff cassette die-set, the CNC-controlled stamping system works well for progressive stamping process to duplicate the original micro-patterns onto aluminum sheet. In the present paper, two kinds of motion in the stamper were designed to investigate the effect of loading and unloading sequences on the geometric accuracy in micro-texturing. Both the macroscopic and microscopic plastic deformations were described by SEM observation. First, high density oxygen plasma etching method was introduced to explain how to fabricate the micro-textured DLC-die unit. The constant-load motion control was employed as a normal motion in CNC-stamping to describe the microscopic metal flow by piercing the DLC micro-punch into the aluminum sheet. Deep micro-cavities with 3.5x3.5x3 μm3 were successfully formed by application of high pressure in stamping. The pulse-wise motion control was further used to improve the geometric accuracy in the present duplication of original micro-texturing pattern onto the aluminum sheet. Owing to the incremental loading in this motion control, the micro-friction was significantly reduced to activate the microscopic metal flow in formation of micro-cavities.
Multiscale Modelling of Mechanical Properties of Steel Deformed in Semi-Solid State – Experimental Background
Authors: Hojny Marcin
Published: September 2014

The paper reports the results of experimental and theoretical work leading to the construction of a multiscale mathematical model describing the phenomena accompanying the steel deformation in semi-solid state as well as at extra-high temperatures. Conducted experiments and simulations confirms the need to seek new methods to obtain precise characteristics in the context of detailed computer simulations. The investigations presented in the current paper has shown, that temperature distribution inside the controlled semi-solid volume is strongly heterogeneous and non-uniform. Axial-symmetrical model (core of the old methodology) does not take into account all the physical phenomena accompanying the deformation. Finally, the error of the predicted strain-stress curves can still be improved. The proposed solution of the presented problem is application of both fully three-dimensional solution and more adequate solidification model taking into consideration evolution of forming steel microstructure. Contrary to the current model the new approach should allow to better capture the physical principles of semi-solid steel deformation in micro-scale. Additionally, the new complex methodology should allow to transfer the characteristics of the material behaviour between the micro-and macro-scale. As a consequence the final results should be more precise and accurate.
Micro Rotary Plunge-Swaging of Stainless Pipes
Authors: Lin Heng Sheng , Lee Chung Ching , Lin Ying Chieh , Li Chia Hsien
Published: September 2014

Micro parts like medical catheters or end effectors require micro rotary swaging to process forming or joining. Higher strength or sophisticated inner features can be achieved through micro rotary swaging which are difficult for the micro machining or grinding process. This work focuses on examining the formability of micro pipes of AISI 304 stainless steel with micro rotary plunge-swaging. Both as-received and vacuum-annealed pipes with both furnace-cooling and water-cooling were tested. The micro hardness and grain size of the as-received and vacuum-annealed pipes were measured. The result shows that the as-received micro pipes need be annealed to be suitable for the micro swaging process. Best swaging result was obtained when annealing with a holding time of 45 minutes and furnace-cooling were used. The G2 workpiece is better than the G1 and the G3 workpieces. This is because the G1 workpieces experience more deformation due to thicker walls, and insufficient grain layers were formed in the G3 workpiece during the annealing.
A Novel Forming Process for Powder Metallurgy of Superalloys
Authors: Bai Qian , Lin Jian Guo , Tian Gao Feng , Balint Daniel S. , Zou Jin Wen
Published: September 2014

Powder metallurgy (PM) of nickel-based superalloys has been used for a wide range of products owing to their excellent special properties in processing and applications. Typical processes for high performance PM superalloys include hot isostatic pressing, hot extrusion and hot isothermal forging. Hot isostatic pressing is normally conducted at a high temperature, by using a low pressure for a long time in a closed vessel, resulting in high cost and low product efficiency. In this paper a novel forming process, i.e. direct powder forging for powder metallurgy of superalloys has been proposed. In this process, the encapsulated and vacuumed powder is heated up to the forming temperature and forged directly to the final shape, by using a high forming load for a very short time. Direct powder forging is a low-cost and energy-saving process compared to conventional PM processes, and in addition, press machines of conventional forging can be used for direct powder forming process. In direct powder forging it is important to control the relative density of the deformed part since the existence of voids could reduce the mechanical strength and fatigue life. In this paper, feasibility tests of direct powder forging are presented. Microstructure, relative density and hardness of the formed specimen were studied.
Effect of Grain Size on Cross Wedge Rolling of Micro Copper Rod
Authors: Chang Chao Cheng , Hsiao Yao Sheng
Published: September 2014

This study investigated the effect of grain size on the cross wedge rolling of micro copper rod. Annealing techniques and equal channel angular extrusion were employed to refine the grains of copper, after which the treated copper was machined to prepare the cylindrical billets with 1 mm diameter for conducting experiments. The billets were rolled between a pair of the dies fixed in a developed cross wedge rolling system to form micro copper rods. The results show that the developed system was able to successfully produced micro copper rods. The grain refinement led to a higher hardness and thus a greater forming load. The rod with fine grans had a larger concave curvature radius of the end face. The grain size clearly influences the material flow in the cross wedge rolling processes of the micro copper rod.
Finite Element Modeling of Shear Strain in Rolling with Velocity Asymmetry in Multi-Roll Calibers
Authors: Pesin Alexander , Chukin Mikhail , Korchunov Alexey , Pustovoytov D.O.
Published: September 2014

Severe plastic deformation is now recognized the most efficient way of producing ultrafine grained metals and alloys. At the present time a lot of severe plastic deformation methods have been proposed and developed. They differ in the deformation schemes. Unlike such severe plastic deformation methods as high pressure torsion and equal-channel angular pressing, rolling with the velocity asymmetry is a continuous process. It helps to solve the problem of the limited length of manufactured bars with semi ultrafine structure. Rolling process with roll velocity asymmetry generates high shear strain necessary for obtaining ultrafine structures of the processed material. A new process of asymmetric rolling of profiles in multi-roll passes has been developed. This process can be used for production of high-strength profiles such as circles, hexagons, wire rods, etc. Compression of the bar in multi-roll passes can be done not only from two, as usual, but from three or four sides. In case of a multi-crimped bar, a uniform compression scheme with large hydrostatic pressure is created in the deformation zone. It enhances the ductility of the material and allows increasing the strain intensity. Simulation in DEFORM 3DTM proved that the process of asymmetric rolling in multi-roll calibers allows to obtain higher values of shear strain and strain effective.
Measurement of Residual Stresses in Work and Backup Rolls for Strip and Plate Mills and its Effect on the Final Load Situation
Authors: Hinnemann Michael , Mauk Paul Josef , Goryany Vyacheslav , Zybill Christian , Braun Rolf
Published: September 2014

Internal stresses or residual stresses remain in almost every part after manufacturing and/or further processing. Even if the entire stress state inside a system is in an equilibrium, single stresses due to their direction and strength may have positive or negative influences to the properties of a body. Especially in big parts, the residual stress state is relatively unknown, because it can only be determined by destructive methods as sectioning or slitting. The possibility of the use of non destructive measuring methods is only given for surface near regions or thin parts and not useful for the specification of the entire residual stress state inside a large compound work roll. This paper outlines an approach for the determination of residual stresses in centrifugal casted work rolls with an indefinite chill double poured or high speed steel shell. In several steps, different measurement techniques are tested and the results are to be presented. Beside the residual stress state, which is caused by manufacturing or heat treatment, these work rolls with different shell and core material differ in their thermophysical and elastic properties.
These parameters in combination with the residual stress state and the thermal and load stresses, which arise during the hot rolling process, are causing a complex stress field that is presented by a combined model for work and backup rolls in operation.
Research on the Minimum Rolled Thickness of Strip Steel in Cold Tandem Rolling
Authors: Wu Shou Min , Wei Lie Sheng , Huang Gang
Published: September 2014

In consideration of the zone between rolls and deformed area where friction at roll-sheet interface is lower than predetermined value of Coulomb friction in rolling process of ultrathin strip steel, fully integrated with equipment and process features of cold tandem mills, after a large number of field experiments and theoretical studies, on the basis of the improvement of ultrathin strip steel rolling force model, with the allowable rolling pressure and production efficiency as constraint condition, a new calculated theory about the minimum rolled thickness was put forward. What’s more, the theory will be used in the productive practice of 1220 five-rack cold tandem mills of China. The technique has the value to be further popularized.
Numerical Simulation and Experimental Investigation of Damage Behaviour on Al6061 Laser Welded Joints
Authors: Tu H.Y. , Schmauder Siegfried , Weber Ulrich
Published: September 2014

The ductile damage behaviour of an aluminium laser welded joint is studied experimentally and numerically. The dimensions of the weld regions are fixed by hardness tests. Fracture toughness tests of Al6061 laser beam welded joints were performed with the compact tension (C(T)) specimens. The Rousselier model is used and the parameters: initial void volume fraction (f0) and average void distance (lc) are identified by metallographic investigations, for the BM, the FZ and the HAZ. Numerical calibration of the Rousselier parameters is performed on notched round specimens. The same Rousselier parameters are used to predict force vs. Crack Opening Displacement (COD) of C(T) specimens.
Fatigue and Fracture Resistance of an Aircraft Landing Gear Steels V-ROL N and VIP P-ROL N Heat Treated to Lower Strength Limit
Authors: Černý Ivo , Sís Jiří
Published: September 2014

V-ROL N is an aircraft steel produced in Czech Republic at Poldi Kladno, used for many years for a manufacture of aircraft landing gears, particularly for a small passenger aircraft L 410. The V-ROL N steel, known by its very good or even excellent fatigue and fracture properties, has not been more available due to recent privatization of the company. Therefore, a substitution of materials previously used became an issue. The paper contains results of a comprehensive experimental programme aimed at comparison of the V-ROL N steel used in the past, still available for research purposes, with another steel of a similar type, VIP P-ROL N steel, manufactured in Czech Republic by another company. Fatigue resistance of both versions can be considered as good. Slightly higher scatter of fatigue results of VIP P-ROL N version can be attributed to an occurrence of impurities, although quite rare, responsible for fatigue crack initiation.
The Effect of Specimen Size on the Determination of Residual Stress in Polymer Pipe Wall
Authors: Poduška Jan , Kučera Jaroslav , Hutař Pavel , Ševčík Martin , Křivánek J. , Sadílek Jiří , Náhlík Luboš
Published: September 2014

As a result of the production process, there are axial and tangential residual stresses present in pressure pipes made of polymer materials such as polyethylene or polypropylene. The residual stress magnitude and distribution have a significant influence on the pipe lifetime. In this contribution the results from experiments focused on determining the tangential residual stress distribution in the walls of polypropylene pipes of different dimensions are compared. The experimental method used involves measuring the deformation of ring shaped specimens that were slit in the axial direction. Measured deformation of the ring specimen is a result of the tangential and axial stress superposition. However, the effect of the axial residual stress depends on the specimen axial dimension and tangential residual stress estimated basing on experimental data should be corrected according to axial dimension of the specimen used. The correction suggested in this article is determined based on three-dimensional FEM simulations of the experiment.
Description of Fatigue Crack Propagation under Mixed-Mode II+III in Terms of J-Integral
Authors: Horníková Jana , Šandera Pavel , Vojtek Tomáš , Pokluda Jaroslav
Published: September 2014

The paper is dedicated to experiments on near-threshold fatigue cracks under mixed-mode II+III in the ARMCO iron. The mixed mode crack growth was described using an equivalent factor ΔJeff,eq=(1-α)ΔJeff,eqII+αΔJeff,eqIII. The most appropriate description was found for α = 0.67 indicating that the mode III component should be more efficient than that of the mode II which is in contradiction of a ΔKeq–based analysis. This result shows that, unlike in the austenitic steel, the difference in the efficiency of modes II and III in the ARMCO iron is very small.
Hydrogen-Assisted Rolling-Contact Fatigue of Wind Turbines Bearings
Authors: Toribio Jesús , Lorenzo Miguel , Vergara Diego , Kharin Viktor
Published: September 2014

This work analyses the effects of hydrogen-assisted rolling-contact fatigue on bearings of wind turbines. To this end, the well-known ball-on-rod test to evaluate the resistance to rolling-contact fatigue was simulated by the finite element method for obtaining the stress-strain state undergone by the bearings considering their in-service conditions. Results of this paper allow a simple estimation of the hydrogen amount in potential damage zones of the specimen.
The Effect of Soil Load on Fracture Behaviour of Three-Layer Polymer Pipe for Non-Pressurised Applications
Authors: Ševčík Martin , Arbeiter Florian , Hutař Pavel , Pinter Gerald , Náhlík Luboš
Published: September 2014

Fracture behaviour of a three-layer polymer pipe subjected to nonhomogenous distribution of external pressure induced by soil embedding is studied in this paper. Both long term and additional short term loading is considered. Such loading induces tensile stresses in the inner pipe wall which can lead to crack initiation and further slow crack propagation. The material interface between a protective layer and the base pipe can contribute to crack deceleration and can prolong the residual lifetime of the pipe. The paper presents three-dimensional numerical analysis of a commercial three-layer pipe containing an internal semi-elliptical crack. The effect of soil load on the fracture behaviour of the cracked pipe is quantified and discussed.
High-Cycle Fatigue Damage of Oxygen-Free and Deoxidized-Phosphorous Copper Processed by Equal Channel Angular Pressing
Authors: Goto Masahiro , Teshima N. , Han S.Z. , Ahn J.H. , Yakushiji T.
Published: September 2014

Two Cu samples: oxygen-free copper (99.99 wt% Cu) and deoxidized low-phosphorous copper (99.9 wt% Cu) were processed by equal channel angular pressing (ECAP). After the ECAP processing using 4 passes, equiaxed grains (~300 nm grain size) and elongated grains were formed for both samples. Fatigue strength of ultrafine grained Cu was enhanced by the addition of trace impurities. The formation behavior of surface damage and the change in surface hardness during stressing were monitored. A close relationship was observed between the change in hardness and the formation behavior of damage. The effect of trace impurities on the fatigue damage was discussed from the viewpoints of the grain coarsening and the crack initiation/growth behaviors.
Modeling Delamination Growth in Composite Panels Subjected to Fatigue Load
Authors: Riccio Aniello , Ronza F. , Sellitto Andrea , Scaramuzzino Francesco
Published: September 2014

One of the most critical aspects of composite structures is indeed associated to delamination phenomenon, especially with reference to their fatigue behavior. As a matter of facts, delaminations are strongly influenced by the fatigue induced degradation phenomena which can lead to a significant increase of delaminated area with the number of cycles, reducing the structural load carrying capability. In the present paper, an advanced numerical approach, very similar to the Paris Law formulation and based on the Energy Release Rate, is presented. The proposed formulation, in the frame of a geometrical non-linear analysis, is able to take into account the local damage accumulation along the delamination front in order to evaluate the delamination growth under fatigue loading conditions. In order to test the effectiveness of the proposed numerical approach, the fatigue behavior of a delaminated panel with a central hole has been simulated and the obtained numerical results have been compared with literature experimental results.
Intersection of Interface Crack Front with Free Edge
Authors: Møberg Alex , Budzik Michal K. , Jensen Henrik M.
Published: September 2014

Delamination in layered materials is analyzed in a fracture mechanical framework. The work deals with quasi-static propagation of crack fronts along planar interfaces between different isotropic, elastic layers. Special focus is here on local effects at the sides of the layers which are assumed to be stress free. The interface crack front meets the free sides of the specimen at an angle which depends on the elastic mismatch in the system. Finite element calculations allowing the shape of the crack front to be arbitrary are carried out for double cantilever beam type specimens. An iterative procedure is formulated which adjusts the shape of the crack front so that an interface fracture criterion is satisfied locally along the front. Apart from the overall shape of the crack front, the angle of intersection with the free sides is in particular determined numerically by this procedure. Comparisons with analytical formulations and experimental results are performed.
Design/Manufacturing System for Composite Ankle Foot Orthosis
Authors: Enoki Shinichi , Huang Chao Jung , Katayama Tsutao , Nakamura Yasunori , Matsuoka Takashi , Tanaka Kazuto
Published: September 2014

In this study, we tried Design / Manufacturing system by using optimum design and rapid manufacturing for Composite Ankle Foot Orthosis. As a result, we found that the manufacturing process is effective on the cost and the design process has possibility to be optimum shape. There are more than one billion people who have a disability in many countries. Some of the people have foot drop and clubfoot. The disabilities become difficult for the people to gait. They use AFO for supporting their gait. However existing manufacturing methods of AFO are expensive because they contain a process to manufacture negative model for manufacturing positive model needed to forming AFO. This process reduces dimension accuracy of the positive model. The time for modification of the positive model becomes long. Our manufacturing process fabricates the positive model directly by using hand-held 3D Scanner and CAD/CAM system. Therefore negative model is not needed and the cost becomes lower. Instead of the reduced manufacturing time, we submitted optimum design with scanned AFO model on flexure and with simplified model on strength.
Numerical Simulation for Mechanical Behavior of Carbon Black Filled Rubber Composites Based on Cubic Representative Volume Element
Authors: Li Qing , Yang Xiao Xiang
Published: September 2014

Based on the connection between macroscopic and microscopic characteristics of carbon black filled rubber composites, Representative Volume Element (RVE) containing one single particle has been proposed, and three dimensional cubic RVE has been established to study and analyze the macroscopic mechanical properties of the carbon black filled rubber composites by the micromechanical finite element method. The research shows that the stiffness of the composite is increased with the increase of the volume fraction of carbon black filler particles. By comparison, it is shown that the results of the predictions on the stress-strain behavior of the rubber composite made with the cubic RVE numerical models containing one spherical particle are in good agreement with the experimental results for seven and fifteen percent carbon black filler content, but there is some discrepancy between them for twenty-five percent carbon black filler content. The results of the predictions on the stress-strain behavior of the rubber composite made with the cubic RVE numerical models containing one cubical particle are higher than the experimental results, and the higher the carbon black filler content, the greater is the discrepancy between them.
Numerical Analysis of Three-Dimensional Semi-Elliptical Interfacial Cracks Subjected to Indentation Load
Authors: Kurihara N. , Arai Masayuki
Published: September 2014

The aim of this study is to show elastic J-integral needed to evaluate the interfacial fracture toughness of bi-material in indentation test. Three dimensional J-integrals along the crack front tip in semi-elliptical crack lying on the interface were analyzed using domain integral technique installed in commercialized finite element code MARC. The J-integral was calculated under several kind of aspect ratio of semi-elliptical cracks. In order to have to evaluate the interfacial fracture toughness from interfacial crack length and indentation load obtained in indentation tests, the analytical formula for two dimensional interfacial crack J-integral under plane stress, which had been introduced by J. R. Rice and G. C. Sih, was modified in reflecting upon the three dimensional effect. Finally, the indentation test was conducted for Aluminum alloy/ PMMA combination sample, and the associated fracture toughness was evaluated.Fig.1 Schematic illustration of indentation testFig.2 Schematic illustration of analysis mode
Comparison of Artificial Neural Networks and the Transfer Function Method for Force Reconstruction in Curved Composite Plates
Authors: Thiene Marco , Sharif-Khodaei Z. , Aliabadi M.H.
Published: September 2014

This paper presents two of the most recent approaches for impact force reconstruction, applied to a curved composite panel. The first one is based on the development of an artificial neural network, while the other on the evaluation of transfer functions in the frequency domain. Both methods provide advantages and disadvantages so that a detailed study should be conducted in order to determine which one can be considered more suitable for impact identification purposes. The aim of this paper is to present a comparison between these two methods, in particular when impacts on different surfaces of the plate are present. The main contribution is the application of the two approaches on a curved composite panel. The radius of curvature plays an important role in the contact force due to impacts on the inner or outer surface of the panel, introducing one more parameter in the reconstruction problem.
Fatigue Crack Growth Rates and Tensile Strength of Titanium Produced by Means of Selective Laser Melting
Authors: Brynk Tomasz , Romelczyk-Baishya Barbara , Pakiela Zbigniew , Kurzynowski Tomasz , Chlebus Edward
Published: September 2014

Mini-samples technique was utilized to determine mechanical properties of technically pure titanium produced by means of selective laser melting (SLM). Full-field digital image correlation (DIC) measurements and inverse method were applied for crack tip position and stress intensity factors calculations in the case of fatigue crack growth rate tests. DIC was also used for strain measurement during tensile tests on sub sized samples. There was studied the influence of samples orientation on the mechanical properties of mini-samples. Samples were cut out from rectangular cubes and were oriented with 0°, 45° or 90° angle to the direction of laser beam travel. There were also tested samples directly produced via SLM. Additionally microstructure observations were performed to verify the quality of SLM processed materials and explain mechanical properties variations.
Microindentation Test Modelling in the Silicon Nitride Ceramics by Application of the Cohesive Zone Approach
Authors: Kozák Vladislav , Chlup Zdeněk
Published: September 2014

Silicon nitride based ceramics have received considerable attention during the last decades due to their very good room and high-temperature properties. Ceramics such as silicon nitride (Si3N4) are acknowledged as first choice for modern bearing applications. The influence of grain bridging on the strength and toughness was found. The prediction of crack propagation through interface elements based on the fracture mechanics approach and cohesive zone model is investigated from amount damage models. Using cohesive models the behaviour of materials is realized by two types of elements. The former is the element for classical continuum and the latter is the connecting cohesive element. Within the standard finite element package Abaqus the new finite element has been developed; it is written via the UEL procedure. The shape of the traction separation law for experimental materials is estimated from macroscopic tests, J–R curve is predicted and stability of the bridging law is tested. The shape of the bridging law is verified using the microindentation test, where the maximum crack length not exceeded 150 μm. The scope of the bridging effect is verified using the standard XFEM elements implemented in Abaqus.
An Integrated Creep-Fatigue Theory for Material Damage Modeling
Authors: Wu Xi Jia
Published: September 2014

This paper presents an integrated creep-fatigue (ICF) theory to describe the non-linear creep-fatigue interaction during thermomechanical loading. The ICF theory recognizes the damage evolution as a holistic process consisting of nucleation and propagation of surface or subsurface cracks in coalescence with internally distributed damage, leading to final fracture. In a polycrystalline material under combined cyclic and dwell loading, crack nucleation and propagation occurs by fatigue or oxidation mechanisms, whereas internally distributed damage often occurs in the form of grain boundary cavities or microcracks due to creep or dwell effects, particularly at high temperatures. Based on the above mechanism, a damage evolution equation is mathematically derived, and the generality of the above physical mechanisms warrants the applicability of the ICF theory over a wide range of stresses and temperatures. This paper uses Mar-M 509, a cobalt base superalloy, as an example to illustrate how the ICF theory describes creep and low cycle fatigue (LCF).
Continuum Approach to Computational Multi-Scale Modeling of Fracture
Authors: Oliver Javier , Caicedo M. , Roubin E. , Huespe A.E.
Published: September 2014

This paper presents a FE2 multi-scale framework for numerical modeling of the structural failure of heterogeneous quasi-brittle materials. The model is assessed by application to cementitious materials. Using the Continuum Strong Discontinuity Approach (CSD), innovative numerical tools, such as strain injection and crack path field techniques, provide a robust, and mesh-size, mesh-bias and RVE-size objective, procedure to model crack onset and propagation at the macro-scale.
Correlation of Dent Depth to Maximum Contact Force and Damage of Composite Laminates
Authors: Shen Z. , Xu Y.G. , Chrysanthou Andreas
Published: September 2014

A major concern affecting the efficient use of carbon fibre reinforced composite laminates in the aerospace industry is the low velocity impact damage which may be introduced accidentally during manufacture, operation or maintenance of the composite structures. It is widely reported that the contact behavior of composite laminates under low-velocity impact can be obtained under quasi-static loading conditions. This paper focuses on the study of the correlation of the dent depth to the maximum contact force and damage of composite laminates under quasi-static loading. Analytical and finite element simulation approaches were employed to investigate relations between the contact force and the dent depth. Experimental investigations on the correlation between dent depth, maximum contact force and damage include quasi-static indentation testing, optical and scanning electron microscopic examination of the damage under different loading levels. The effect of damage initiation and growth on the contact behaviour has been discussed. Results show that consistent correlations between the dent depth, maximum contact force and damage exist and can be predicted with the analytical and numerical approaches. Dent depth can be used as an engineering parameter in assessing the severity of damage for composite structures that are subjected to low-velocity impact. This may lead to the development of a cost-effective technique for the inspection and maintenance of composite structures in aerospace applications.
Deformation-Induced Dynamic Precipitation during Creep in Magnesium-Tin Alloys
Authors: Huang Yuan Ding , Dieringa Hajo , Kainer Karl Ulrich , Hort Norbert
Published: September 2014

The oversaturated solutes in the alloy matrix, which are caused by nonequilibrium phase transformation during casting or T4 treatment, can precipitate in the subsequent annealing treatments or during service at high temperatures. Under deformation the precipitation could be enhanced in comparison to conventional isothermal ageing. The present work investigates the dynamic precipitation of oversaturated Mg-Sn alloys during creep. The influence of this dynamic precipitation on creep properties is discussed. It is found that the distribution of deformation-induced precipitates is inhomogeneous. These precipitates are first formed at grain boundaries and then at deformation bands which are kinetically and thermodynamically favourable. The dynamic precipitation accompanies the volume change of phases, which influences the subsequent formation and growth of voids. Consequently, the creep behaviour also changes due to different precipitation under deformation.