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1

Damage analysis of composites integrated with RFID chip used in aeronautics

Alhas H-A., Bayraktar E., Nizam C., Khalil J.

Archives of Materials Science and Engineering

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2013

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Vol. 59, nr 1

5--13

EN

Purpose: A new approach to production process by direct integration of the RFID (Radio-frequency identification) chips into the composite parts used during the manufacturing (moulding) process of the composite parts has been presented. This research aims a new application of RFID technology and measurement of the resistance of RFID chips integrated into composite parts under X-ray diffraction beams and also impact choc (crash test). This work gives the actual results of an applied research carried out in laboratory (Supmeca-Paris) scale and also in industrial scales carried out in the manufacturing department of the French aeronautic company (Eurocopter-Paris). Design/methodology/approach: Application of RFID technology in manufacturing of the composite parts is related to the continuous quality improvement of manufacturing company. Findings: RFID Chips integrated directly in the composite parts during the manufacturing process can improve the efficiency of the manufacturing process and also decrease the lead time and processing time. This application in manufacturing of the composite parts will enable to achieve success for the aeronautic companies. Research limitations/implications: In the future, Industrial companies can transform their manufacturing processes by applying RFID technology that increases manufacturing cycle time, maximize efficiency and eliminate unnecessary steps. Practical implications: Using RFID technology in production will help industrial companies and also customers reduce their time and operating costs significantly and increase employee productivity. This application can also decrease lead time and make faster progress toward their sustainability goals. Originality/value: A detail comparison was made between two approaches; conventional production system and new approach by integrating RFID in composite part. At the end of analysis, time saving in the production was calculated as 135 minutes (more than 2 hours) by following real data.

2

Elastomeric matrix composites: effect of processing conditions on the physical, mechanical and viscoelastic properties

Zaimova D, Bayraktar E., Katundi D., Dishovsky N

Journal of Achievements in Materials and Manufacturing Engineering

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2012

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Vol. 50, nr 2

81--91

EN

Purpose: The aim of this study is to investigate the influence of accelerator-vulcanizing agent system and the vulcanization temperature on the properties of vulcanizates based on Natural rubber/Polybutadiene rubber (NR/ BR) compounds. This preliminary study will allow optimizing the composition for improving the mechanical properties and understanding the damage behaviour. Design/methodology/approach: NR/BR based composites with different vulcanization temperatures and curing systems were characterized in respect of their curing characteristics (for 140°C and 160°C) and mechanical properties. The cure characteristics of the rubber compounds were studied by using the Monsanto MDR 2000 rheometer. The mechanical properties were investigated- tensile strength, elongation at break, tensile modulus at 100% (M100) and at 300% (M300) deformation. The hardness (Shore A) and molecular mass of the samples were also determined. Scanning electron microscopy was used to study the microstructure of the fracture surfaces. Findings: The processing, physical, mechanical and viscoelastic properties and chemical structure of the mixture of Natural rubber/Polybutadiene rubber (NR/BR) compounds have been evaluated in detail for the compounds of D1 and D2 (140/160). Research limitations/implications limitations/implications: Some critical point, control of the temperature during vulcanization in press, can introduce some restrictions; these measurements can play on the final vulcanizates and in the course of processing. Practical implications: In practical way, mechanical test results (tensile and shore A) give very useful information about the damage behaviour of the elastomeric matrix composites. Originality/valut: Natural rubber/Polybutadiene rubber (NR/BR) compounds were mixed by additions of some certain elements to improve physical, mechanical and viscoelastic properties and damage behaviours of these compounds produced under certain conditions.

3

Effect of laser cutting parameters on surface quality of low carbon steel (S235)

Zaied M, Bayraktar E., Katundi D., Boujelbene M., Miraoui I

Journal of Achievements in Materials and Manufacturing Engineering

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2012

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Vol. 54, nr 1

128--134

EN

Purpose: This work analysis surface roughness parameters as a function of Laser power and cutting speed. The surface roughness parameters are determined after statistical analysis (ANOVA) and propose a simple mathematical model. Design/methodology/approach: Machining were carried out by Laser cutting (CO2) of sheet metal (low carbon steel, S235) produces different surface quality. The statistical processing of the experimental results enabled development of a mathematical model to calculate the cut surface quality according to the cutting parameters used in the present work. Findings: The prediction of surface roughness values according to the mathematical model are very precisely analysis and determining of surface roughness values is a very practical tool by the experimental design method. It enables a high quality range in analysing experiments and achieving optimal exact values. A rather small experimental data are required to generate useful information and thus develop the predictive equations for surface roughness values as Ra, Rt and Rz. Depending on the surface roughness data provided by the experimental design, a first-order predicting equation has been developed in this paper. Practical implications: A simple and practical tool was proposed with the experimental design for predicting the surface roughness values as a function of variables of Laser power and cutting speed for a low carbon steel (S235). This type of analysis gives detailed information on the effect of Laser cutting parameters on the surface roughness. Originality/value: Experimental data was compared with modelling data to verify the adequacy of the model prediction. As shown in this work, the factor of cutting speed the most important influence on the surface roughness.

4

Effect of cutting parameters on chip formation in orthogonal cutting

Ben Salem S, Bayraktar E., Boujelbene M., Katundi D.

Journal of Achievements in Materials and Manufacturing Engineering

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2012

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Vol. 50, nr 1

7--17

EN

Purpose: of this paper is to study the chip formation to obtain the optimal cutting conditions and to observe the different chip formation mechanisms. Analysis of machining of a hardened alloy, X160CrMoV12-1 (cold work steel: AISI D2 with a ferritic and cementite matrix and coarse primary carbides), showed that there are relationships between the chip geometry, cutting conditions and the different micrographs under different metallurgical states. Design/methodology/approach: Machining of hardened alloys has some metallurgical and mechanical difficulties even if many successful processes have been increasingly developed. A lot of study has been carried out on this subject, however only with modest progress showing specific results concerning the real efficiency of chip formation. Hence, some crucial questions remain unanswered: the evolution of white layers produced during progressive tool flank wear in dry hard turning and to correlate this with the surface integrity of the machined surface. For the experimental study here, various cutting speeds and feed rates have been applied on the work material. Findings: The “saw-tooth type chips” geometry has been examined and a specific attention was given to the chip samples that were metallographically processed and observed under scanning electronic microscope (SEM) to determine if white layers are present. Research limitations/implications: This research will be followed by a detail modelling and need more experimental results for a given a good prediction of the results occurred on the damage related to the microstructure by using the cutting parameters. Practical implications: A special detail was given to the mechanism of chip formation resulting from hard machining process and behaviour of steel at different metallurgical states on the material during the case of annealing and or the case of quench operations. Originality/value: For the sake of simplicity, ANOVA (Analysis of Variance) was used to determine the influence of cutting parameters. It gives a practical and useful tool for the machining in the industrial operations.

5

Toughness of welded stainless steels sheets for automotive industry

Bayraktar E., Katundi D., Yilbas B S, Claeys J

Journal of Achievements in Materials and Manufacturing Engineering

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2011

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Vol. 44, nr 1

35--41

EN

Purpose: In the automotive industry, more and more it is compulsory to develop new grades of stainless steels, such as high resistant Martensitic Stainless Steels (MA-SS) and Ferritic Stainless Steels (FSS) in order to realise certain or many complex deep drawn pieces. For these grades, resistance spot welding (RSW) is the most widespread process used largely for many parts of the car body in the automotive industry. This paper aims to characterise mechanical behaviour (toughness) of the different steel grades under dynamic test conditions. Design/methodology/approach: A special crash test device is used in different temperatures and the simulated crash tests are performed at a constant speed of 5.52 m/s. Findings: The specimen is submitted to impact tensile test at different temperatures. According to testing temperature, fracture mode varies: At low temperatures, brittle fracture occurs: due to stress concentration, fracture always occurs in the notched section. At high temperatures, the specimen fails by ductile fracture. Toughness of the steel sheets (base metals, BM or welded parts) is well compared at different materials and test conditions. Research limitations/implications: Evaluation of welded thin sheets submitted to the dynamic loading in order to correlate in real service conditions in order to realize a useful correlation between the transition temperature and deep drawability can be used for evaluating of the welding conditions and also of the material characteristics. For detail study, this type of the test needs a standard formulation. Practical implications: This is a new conception of specimen and of the impact/crash machine. It is widely used in automotive industry for practical and economic reason to give rapid answers to designer and also steel makers for ranking the materials. Originality/value: New developed test called impact crash test for evaluating the toughness of thin welded joints (tailored blanks) / mechanical assemblies in high formability steel sheets for stamping submitted to dynamic loads such as experienced in real crash tests.

6

State of cure evaluation by different experimental methods in thick rubber parts

Zaimova D, Bayraktar E., Dishovsky N

Journal of Achievements in Materials and Manufacturing Engineering

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2011

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Vol. 44, nr 2

161--167

EN

Purpose: The aims of this paper is to quantify the state of cure by different techniques (physico-chemical; mechanical; thermal; spectroscopic) on the thick elastomeric composites (rubber parts). An optimization is aimed from the experimental results. For this purpose, a detailed comparison is carried out with simulation for industrial applications. Design/methodology/approach: Comparison among the used experimental methods for measuring curing phenomenon is made by choosing the following criteria: destructivity, need of specific sample geometry, reversion detection, error and timing; validation the numerical simulation with experimental results; As a first step, test sheets were obtained from the rubber-based compound. Different methods (DSC, NMR, mass swelling, tensile test, compression set test, relaxation, hardness, shear stress etc.) were used to quantify the state of cure experimentally. The same techniques were applied for evaluating the state of cure in a thick part obtained from the tested compound. Then the results for the thick part were correlated with the results for the test sheets obtained by rheometer. Finally, a comparison was carried out among the used methods by several criteria. Also numerical data obtained for evolution of state of cure in the thick parts is compared by means of special software with the experimental data. Finding Applications of different methods have given very successful results for measuring the state of cure in the test sheets. However, the present results showed that some of the mechanical methods (shear stress, stress-strain, compression set and relaxation) are not suitable for measuring the state of cure in thick parts but NMR, DSC, mass swelling and hardness are very suitable. Research limitations/implications Certain test such as shear stress and Dynamic Scanning Calorimetry (DSC) give high values of error and don’t detect reversion. Additionally, a specific geometry of the specimen is needed for relaxation and tensile tests. Practical implications: Certain tests such as mass swelling, tensile and hardness test give very practical and reliable results for measuring the state of cure in rubber parts in industrial applications. Originality/value A good correlation has been found between numerical and experimental results which give the possibility to make a reliable prediction on the distribution of state of cure in thick parts. Mass swelling method has been adapted to this research conditions and this modified test gave better results than other used methods.

7

Prediction of surface roughness by experimental design methodology in Electrical Discharge Machining (EDM)

Ben Salem S., Tebni W., Bayraktar E.

Journal of Achievements in Materials and Manufacturing Engineering

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2011

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Vol. 49, nr 2

150--157

EN

Purpose: This work models the Ra parameter as a function of current intensity (I), the electrode material and the work material. The surface is directly related to the average intensity (I) during machining. If the intensity is increased to 25 A, the roughness of the room rises dramatically to 15 microns. Design/methodology/approach: Machining with a copper tool produces a better surface than can be achieved by a graphite tool. Copper tool machining has been performed in an efficient way, eliminating the necessity of a large number of experiments. The statistical processing of the results enabled development of a mathematical model to calculate the machined surface quality according to the parameters of the cut used. Findings: The mathematical model, which precisely determines surface roughness, is a tool for cutting parameters and has been obtained by the experimental design method. It enables a high quality range in analysing experiments and achieving optimal exact values. A relatively small number of designed experiments are required to generate useful information and thus develop the predictive equations for surface roughness. Depending on the surface roughness data provided by the experimental design, a first-order predicting equation has been developed. Practical implications: The experimental design was proposed for predicting the relative importance of various factors (composition of the steels and electrical discharge machining (EDM) processing conditions) to obtain efficient pieces. This model gives detailed information on the effect of parameters of cut on the surface roughness. Originality/value: Experimental data was compared with modelling data to verify the adequacy of the model prediction. As shown in this work, the factor of intensity has the most important influence on the surface roughness.

8

Parametric Finite Element Analysis for a square cup deep drawing process

Ayari F., Bayraktar E.

Journal of Achievements in Materials and Manufacturing Engineering

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2011

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Vol. 48, nr 1

64--86

EN

Purpose: This manuscript deals with the FEA of the sheet metal forming process that involves various nonlinearities. Our objective is to develop a parametric study that can leads mainly to predict accurately the final geometry of the sheet blank and the distribution of strains and stresses and also to control various forming defects, such as thinning as well as parameters affecting strongly the final form of the sheet after forming process. Design/methodology/approach: The main approach of the current paper is to conduct a validation study of the FEM model. In fact, a 3D parametric FEA model is build using Abaqus /Explicit standard code. Numerous available test data was compared to theoretical predictions via our model. Here, several elastic plastic materials low was used in the FEA model and then, they were validated via experimental results. Findings: Several 2D and 3D plots, which can be used to predict incipient thinning strengths for sheets with flat initial configuration, have been presented for the various loading conditions. Unfortunately, most professionals in the forming process, lack this expertise, which is an obstacle to fully exploit the potential of optimization process of metal forming structures. In this study optimization approach is used to improve the final quality of a deep drawn product d by determining the optimal values of geometric tools parameters. Research limitations/implications: This paper is a first part study of a numerical parametric investigation that is dealing with the most influent parameters in a forming process to simulate the deep drawing of square cup (such as geometric, material parameters and coefficient of frictions). In the future it will be possible to get a large amount of information about typical sheet forming process with various material and geometric parameters and to control them in order to get the most accurate final form under particular loading, material and geometric cases. Originality/value: This model is used with conjunction with optimisation tool to classify geometric parameters that are participating to failure criterion. A mono objective function has been developed within this study to optimise this forming process as a very practical user friend manual.

9

Damage analysis of the ceramic reinforced steel matrix composites sheets: experimental and numerical study

Bayraktar E., Ayari F., Katundi D., Chevalier J.-P., Bonnet F.

Journal of Achievements in Materials and Manufacturing Engineering

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2011

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Vol. 49, nr 1

53--61

EN

Purpose: of this paper reports damage analysis of TiB2 (ceramic particles) reinforced steel matrix composite sheets. This new steel composite receives much attention as potential structural materials due to their high specific strength and stiffness. The goal of the research described in this paper is to study the usage of this new steel family in the manufacture of light structures. Design/methodology/approach: therefore in this study is focused to the titanium diboride TiB2 reinforced steel matrix composite sheets that they were characterized by optical and scanning electron microscopes after the mechanical tests carried out on the base metal and welded specimens under dynamic and static test conditions. Findings: The non homogeneity of the structure in this type of composites makes deeply complexity of their numerical and analytical modelling to predict their damage during the loading. For example, the interfaces essentially play a key role in determining mechanical and physical properties. For this reason, a Finite Element (FEM) analysis is used for modelling to simulate the macroscopic behaviour of this material, taking into account the relevant microscopic scales. Practical implications: defined in this research is based on the impact dynamic behaviour of this steel sheets by using a special impact tensile test developed formerly that all details were published in this journal. This type of test gives more comprehensible information about special steel sheets (welded or base metal) in case of dynamic crash conditions. Originality/value: The present research gives detail information on the new steel matrix composite sheets reinforced TiB2 ceramic particles. This new composite was developed by ARCELOR research group and impact dynamic behaviour and weldability of the welded parts and base metals from this composite steel are discussed here in order to give practical and useful solution for industrial applications.

10

A mathematical model to choose effective cutting parameters in electroerosion, EDM

Medfai A., Boujelbene M., Bayraktar E.

Journal of Achievements in Materials and Manufacturing Engineering

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2011

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Vol. 47, nr 1

97--102

EN

Purpose: Machining by electroerosion is a process of removal of material by fusion, vaporization and erosion, reserved essentially for conductor and semiconductor materials. It can be used to machine metals and alloys, the tempered steels, different type of ceramic alloys, other metallic carbides and even for harder materials such as polycrystalline diamond etc. The aim of this paper is to develop a mathematical model for the effect of cutting parameters on the machining by electro discharge machining used widely in industrial applications. Design/methodology/approach: It is about a study and detail analyzes effect of the cutting conditions in machining by electroerosion of steel 42CD4-42CrMo4 on the surface quality of the parts. The statistical method of the analysis of variance “ANOVA” makes it possible to release the considerable effects of the parameters of cut on the criteria of performance of machining by electroerosion, EDM. Findings: The result of the study shows that the nature of the electrode used and the different grades of the materials machined by Electro Discharge Machining, EDM, influence considerably the volume of the removal of material and the surface quality of the produced parts. However, more the resistivity of the electrode increases, more relative wear of the electrode will be important and more the volume of removal of material decreases. Research limitations/implications: This study needs more experimental results for evaluation of the cutting parameters in detail and introduce in the model developed here. Practical implications: This model developed based on the experimental study gives very simple choice of cutting parameters depending on the materials. Originality/value: A very simple model has been develop here after a comprehensive study and this model contains an experimental design, and application ANOVA analysis as a function of experimental results and allows to obtain a smooth surface and high quality machined pieces and can decrease at cost price of the pieces in the manufacturing engineering.

11

Fretting wear damage-I: numerical study of composite steel sheets reinforced with TiB2

Ayari F., Bayraktar E.

Archives of Materials Science and Engineering

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2011

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Vol. 51, nr 1

48-54

EN

Purpose: of this paper is based on the damage analysis by fretting wearing occurred on the composite steel sheets reinforced with TiB2 ceramic particles. There is a real lack to find a reliable data and detail research in literature that makes the purpose of this manuscript. Design/methodology/approach: Fretting is a surface degradation process in which removal of material is induced by small amplitude oscillatory movement between contacting components, such as flexible coupling joint structures etc. The main parameters affecting fretting wear are reported to be normal load, slip amplitude, frequency of the oscillatory movement, contact geometry, surface roughness and material properties. In this study, a finite element-based method is presented for simulating the contact of a rigid cylinder on flat fretting wear for the composite steel sheets reinforced with TiB2 ceramic particles. Findings: The general purpose commercial code ABAQUS was employed; this model can be used to facilitate generalization of the present approach to more complex applications. In this study a particular mesh technique was used to optimize the computation time, especially when dynamic analysis is used. In fact, two-dimensional, four-node, plane strain (linear) elements are employed throughout. The mesh (element size) in the contact area is very fine to capture the complicated variation of the surface and subsurface stresses and relative slip. The contact surface is constituted with a rigid hard steel cylinder material and a flat plate of composite steel sheets reinforced with TiB2 ceramic particles. Practical implications: This manuscript concerns a typical contact with the cylindrical plan geometry as it models the major problems and also stress distribution due to the contact was well defined. Our assembly is then, composed with a cylindrical contact with a plan substrate. An elastic - plastic analysis of fretting stress using a finite element ABAQUS is enhanced. The cylindrical pad is made of a rigid material and a flat plate the composite steel sheets reinforced with TiB2 ceramic particles. A bilinear elastic - plastic isotropic hardening model with a von Mises yield surface is employed to characterize the material behaviour of these composite steel sheets reinforced with TiB2 ceramic particles.This manuscript give a real and practical usage as a friendship notice concerning this subject. Originality/value: is very well shown that this model is firstly verified through comparison with an analytical elastic solution. Various parameters, such as friction coefficient, the normal force applied on the top of the pad, tangential force applied to the left side of the pad, and bulk tension applied on the right edge of the substrate are adopted to study the influences of these parameters on fretting stresses to understand the implication and importance of elastic-plastic analysis in fretting fatigue experiments. Keywords: Fretting wear; Slip; Contact; FEM; Mesh refinement; Composite steel sheets; Reinforcement of TIB2

12

Development of a new aluminium matrix composite reinforced with iron oxide (Fe3O4)

Bayraktar E., Katundi D.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 38, nr 1

7-14

EN

Purpose: of this paper is to develop new aluminium matrix (intermetallic) composites reinforced with iron oxide (Fe3O4) that will be used in aeronautical engineering or in electronic industry. Different parameters such as sintering time and temperature, reinforcement, compact pressure were evaluated. The final purpose of this project is going on to improve conductivity and magnetic permeability of this new composite. Design/methodology/approach: In this paper, a new alternative materials “aluminium–iron oxide (Fe3O4, naturally as the mineral magnetite) powder composite” has been developed by using a microwave (in the laboratory scale) sintering programme with various aspect ratios, that iron oxide (Fe3O4) particle sizes and aluminium powders together were prepared. This paper contains partially preliminary results of our going-on research project. Findings: Green density increased regularly depending on the compact pressure and percentage of the iron oxide (Fe3O4). Micro and macro porosity was not found due to very clean microwave sintering. Density after microwave sintering was higher than that of traditional sintering in an electrical oven. Research limitations/implications: This project is going on and magnetic permeability and conductivity of this composite will be improved. Practical implications: This composite is new and clean and thanks to the new microwave sintering basically will be used in aeronautical engineering. Microwave heating results in lower energy costs and decreased processing times for many industrial processes. Originality/value: Originality of this paper is to use a new reinforcement in the aluminium matrix composite; Fe3O4-iron oxide. A new method - microwave sintering- has been carried out on this composite.

13

Corrosion behaviour of the welded steel sheets used in automotive industry

Katundi D., Tosun-Bayraktar A., Bayraktar E., Toueix D.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 38, nr 2

146-153

EN

Purpose: of this paper is to characterise the corrosion resistance in the steel sheets (Hot dip galvanizing of steel sheets) used in automotive industry. In fact, corrosion of automotive components by road salt is a widely known problem. The different parts under the car body and the interior surface of body panels suffer easily from the corrosive products deposited on roads and used mainly to melt snow. A comparison in a chemical investigation of the corrosion rate for base metals (without welding) and welded steel is required. Therefore, conformity will be accomplished between the corrosion phenomena in simulated corrosion tests and those in actual cars. Design/methodology/approach: Simulated corrosion tests, wet/humidity test and hot dust/dry cycle talk test carried on in laboratory conditions was investigated quantitatively. Dynamic behaviour of the corroded specimens have been tested dynamically to simulate under the crash test conditions. Findings: Studies carried out on the vast corroded samples have shown that the pitting corrosion damage and crack initiation sites have began and propagated generally in the HAZ in the welded steel sheets (Tailored welded blanks - TWB). Research limitations/implications: This paper contains partially results of a common research project. Some limitations exist in application of hot dust/dry cycle talk to the real open air test conditions. All of these results were carried out in the laboratory conditions. Practical implications: The problem is of extreme importance to all academic, scientific, manufacturing, maintenance and industrial societies. The outcome of the proposed study will contribute to the industrial application of ARCELOR-MITTAL. The proposed study will be benefit not only for the car industry and steel makers, but also important for the other industrial applications. The proposed research can be employed in a broad range of applications in oil and natural gas industries. This project will promote multidisciplinary research and cooperation between university and industry. Originality/value: An effective corrosion test proposed by Volvo was applied to the welded sheets (TWB) in an enclosed climatic chamber. This test is a practical and inexpensive test. Impact tensile-crash test makes it possible to analyse the corrosion damage of sheet metals under the dynamic rupture.

14

Torsional fatigue behaviour and damage mechanisms in the very high cycle regime

Bayraktar E., Xue H., Ayari F., Bathias C.

Archives of Materials Science and Engineering

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2010

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Vol. 43, nr 2

77-86

EN

Purpose: of this paper: Many engineering components operate under combined torsion and axial cyclic loading conditions, which can result in fatigue fracture after a very long life regime of fatigue. This fatigue regime were carried out beyond 109 loading cycles called very high cycle fatigue (VHCF) to understand the fatigue properties and damage mechanisms of materials. Design/methodology/approach: Torsional fatigue tests were conducted using a 20 kHz frequency ultrasonic fatigue testing device. The results obtained were compared to those of the conventional torsional fatigue test machine operated at 35 Hz to observe any discrepancy in results due to frequency effects between two experiments. Findings: All the fatigue tests were done up to 1010 cycles at room temperature. Damage mechanisms in torsional fatigues such as crack initiation and propagation in different modes were studied by imaging the samples in a Scanning Electron Microscope (SEM). The results of the two kinds of material show that the stress vs. number of cycle curves (S-N curves) display a considerable decrease in fatigue strength beyond 107 cycles. Research limitations/implications: Each test, the strain of specimen in the gage length must be calibrated with a strain gage bonded to the gage section. This is a critical point of this study. The results are very sensitive to the calibration system. Control of the displacement and the output of the power supply are made continuously by computer and recorded the magnitude of the strain in the specimen.

15

Spray drying as a method of producing silk sericin powders

Genç G., Narin G., Bayraktar E.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 37, nr 1

78-86

EN

Purpose: The purpose of paper is to analyse Spray drying as a method of producing silk sericin powders. Design/methodology/approach: Aqueous sericin solutions were used as raw material for the production of dry powders using a lab-scale spray dryer. A linear regression analysis of agglomeration was employed, in addition to experimental designs at two levels with three factors for the analysis of three responses: moisture content, particle type and agglomeration degree. The process factors were the drying air temperature (120şC and 160şC), the feed rate (1.25 × 10-7 and 2.5 × 10-7 mł/s), and the concentration of sericin solutions of 10% and 30% (w/w) fed to the spray dryer. Findings: The three responses were analyzed statistically to determine the effective parameters and it was concluded that moisture content depended on three factors--drying air temperature being the dominant parameter. Particle size and shape depended mainly on feed rate and agglomeration depended on the moisture content of the product. Practical implications: As a result of the growing interest in drug delivery through a pulmonary route for local and systemic effects, the crucial physical characteristics of the spray-dried sericin influencing the dispersion and deposition behaviour including particle size, morphology, moisture content and agglomeration degree were examined for formulation and spray drying variables. Originality/value: The most effective parameters on particle size and morphology were found to be the feed solution concentration and feed rate, while the temperature was an insignificant variable.

16

Influence of workpiece inclination angle on the surface roughness in ball end milling of the titanium alloy Ti-6Al-4V

Daymi A., Boujelbene M., Linares J. M., Bayraktar E., Ben Amara A.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 35, nr 1

79-86

EN

Purpose: The aim of this work is to provide an in-depth understanding of the surface texture produced by various workpiece inclination angles using high speed finish ball end-milling of the titanium alloy Ti-6Al-4V. Design/methodology/approach: This paper presents an approach to develop a mathematical model of surface roughness in end-milling by the experimental design methodology. Machining variables such as cutting speed, feed and radial depth of cut, which are easily controllable, are considered in building the model. The influence of the workpiece inclination angle on the surface roughness of the machined workpiece was also investigated. Findings: According to the mathematical model, an increase in either the feed or the radial depth of cut increases the surface roughness, whilst an increase in cutting speed decreases it. The radial depth of cut ae is the most significant parameter in the model. Results analysis of the 2D/3D surface roughness parameters of the machined parts shows the improvement of the surface roughness quality when it is machined with a workpiece inclination angle of 25°. Research limitations/implications: As perspectives of this work, we can study the influence of the different machining strategies on the surface integrity of this titanium alloy, including the study of the residual stress. Practical implications: We propose to study the improvement of the surface quality of the orthopedic prostheses, which is an influencing parameter in their lifetime, by implementing the high speed cutting technique. The mathematical model of the surface roughness is a very important result of this work. In fact, it allows selecting the best cutting conditions to obtain a better workpiece surface quality. Originality/value: In this work, three dimensional surface roughness parameters were studied: the 3D surface topographies were obtained using a 3D measurement station and the mathematical model of Sa. The arithmetic mean deviation of the surface was established in order to minimize the experimental works and to have an idea about the surface roughness evolution as a function of cutting parameters.

17

Experimental and numerical study of damage initiation mechanism in elastomeric composites

Silva Botelho T. D., Bayraktar E.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 36, nr 1

65-70

EN

Purpose: Experimental and Finite Element Analysis (FEA) of the damage initiation mechanisms in elastomeric composites were carried out under static loading at room temperature. Double Cantilever Beam (DCB) specimens from natural rubber (NR) vulcanised and reinforced with other materials such as carbon black, silica, fibres and textiles or metals (rubber composites). Design/methodology/approach: Very huge experimental results were compared with that of the Finite Element Analysis (FEA). Damage mechanism has been described with a threshold criterion to identify damage. The damage was evaluated just at the beginning of the tearing by assuming large strain. A typical type of specimen geometry of Double Cantilever Beam (DCB) specimens was considered under static tensile tests conducted on the notched specimens with variable depths. Findings: In this stage of this research, a finite element analysis (FEA) has been applied under the same conditions of this part in order to obtain the agreement between experimental and FEA results. The numerical modelling is a representation of a previous experimental study. The specimen is stretched more than once its initial size, so that large strains occur. A hyper elastic Moonley-Rivlin law and a Griffith criterion are chosen. The finite elements analysis was performed with ABAQUS code (V.6.4.4). Practical implications: A damage criterion was suggested in the case of simple tension conditions by assuming large strain levels. an effective finite elements model has been developed to evaluate notch size effects on the load-displacement elastic response of 3D-DCB type specimen. Originality/value: This study proposes a threshold criterion for the damage just at the beginning of the tearing for Double Cantilever Beam (DCB) specimens from rubber composites and gives a detail discussion for explaining the damage mechanisms. Comparison of FEA results with those of experimental studies gives many facilities for the sake of simplicity in industrial applications.

18

Influence of machining parameters on the surface integrity in electrical discharge machining

Boujelbene M., Bayraktar E., Tebni W., Ben Salem S.

Archives of Materials Science and Engineering

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2009

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Vol. 37, nr 2

110-116

EN

Purpose: The aim of this research is to make a study of the influence of machining parameters on the surface integrity in electrical discharge machining. The material used for this study is the X200Cr15 and 50CrV4 steel for dies and moulds, dies castings, forging dies etc. Design/methodology/approach: The methodology consists of the analysis and determination of the white layer thickness WLT, the material removal rate MRR, the electrode wear ratio EWR and the micro hardness of each pulse discharge energy and parameters of electrical discharge machining. Findings: The Results of the tests undertaken in this study show that increasing energy discharge increase instability and therefore, the quality of the workpiece surface becomes rougher and the white layer thickness increases. This is due to more melting and recasting of material.With the increase of the discharge energy, the amount of particles in the gap becomes too large and can form electrically conducting paths between the tool electrode and the workpiece, causing unwanted discharges, which become electric arcs (arcing). these electric arcs damage the electrodes surfaces (tool and workpiece surfaces) and can occur microcracks. Research limitations/implications: A possible future work would be the development of a general the phenomenal of the residual stress of the wire electrical discharge machining in titanium alloys. The behavior is of the residual stress studies are planed in the future. Practical implications: The relationship found between the total energy of discharge pulses, composition of the steels and the type of machining on the surface integrity (the surface texture, the metallurgical surface aspect, the microhardness in the heat affected zone, HAZ) of different workpiece materials has an important practical implication since it allows selecting the best cutting condition combination from the points of view both the security and the economy for the established requirements in each case. Results are of great importance for aerospace and automotive industry. Originality/value: The paper is original since the bibliographical review has allowed testing that, although works about these themes exist, none approaches the problem like it has been made in this work. The paper could be an interesting source of information for engineers and researchers who work with machining dies and also significant complex parts in aeronautics.

19

Theoretical analysis of plastic zone of a circle crack under gigacycle fatigue regime

Wu T., Mo T., Chen W., Bayraktar E.

Archives of Computational Materials Science and Surface Engineering

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2009

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Vol. 1, nr 4

245-251

EN

Purpose: Different kinds of alloys used in industry for structures and engine components are subjected to very high cycle fatigue (gigacycle regime) damage under the service conditions. In this study, fatigue damage evolution of some metallic-industrial alloys was investigated on very high cycle fatigue regime and calculation of the stress intensity factor (SIF) using finite element method (FEM) was realized under the ultrasonic vibration conditions. A formula of SIF vs. Cracks size and position of the crack has been developed. In fact, calculation of the SIF under ultrasonic vibrating fatigue has to be a function of amplitude instead of nominal stress as frequently used in traditional fatigue from Woehler. Design/methodology/approach: The specimens are tested at ultrasonic fatigue frequency of 20 kHz with a stress ratio of R=-1 (tension-compression) under load control. In order to control the displacement amplitude at the end of the amplifier was calibrated by optical sensor before each fatigue test. Failure mechanisms have been studied by means of the scanning electron microscope (SEM). The fracture origin and/or inclusions were identified by use of energy disperse analysis. Findings: An analytical approach was validated to calculate the stress intensity factor, KI, for the specimen specially designed for Gigacycle fatigue test. Practical implications: This heat source will be useful to position and size the small crack inside the specimen according to surface temperature variation with further heat transfer analysis. The relation between energy power and stress intensity factor helps to determine crack size and position from the temperature field on the specimen surface. Originality/value: Based on the SIF calculation and from classical fracture mechanics, dissipated energy of the plastic zone of the crack is derived and considered as heat source when the crack initiates.

20

Parametric Finite Element Analysis of square cup deep drawing

Ayari F., Lazghab T., Bayraktar E.

Archives of Computational Materials Science and Surface Engineering

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2009

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Vol. 1, nr 2

106-111

EN

Purpose: This paper deals with the FEA of the sheet metal forming process that involves various nonlinearities. Our objective is to develop a parametric study that can leads mainly to predict accurately the final geometry of the sheet blank and the distribution of strains and stresses and also to control various forming defects, such as thinning as well as parameters affecting strongly the final form of the sheet after forming process. Design/methodology/approach: In cold forming (deep drawing) operation, sheet metal is subject to large strains in order to obtain the final desired shape. However, under severe forming conditions the sheet metal may experience some thinning and even some tearing during the process. Parameters of the deep forming process that may contribute to such conditions include, aspect ratio, blank initial thickness, forming temperature, shoulder radii of the die and punch, contact conditions between the blank and the die, holder and punch, punch displacement rate, etc. The work presented in the current paper is a first part study of numerical parametric investigation that is dealing with the most influent parameters in a forming process to simulate the deep drawing of square cup (such as geometric parameters and coefficient of friction). The purpose of the current paper is to conduct a validation study of the FEM model that is used to conduct the study described above. In fact, a 3D parametric FEA model is built using ABAQUS/Explicit standard code. Findings: A methodology to develop this kind of theoretic resolution is pointed out and has been illustrated for a set of variables. Several 2D and 3D plots, which can be used to predict incipient thinning strengths for sheets with flat initial configuration, have been presented for the various loading conditions. Research limitations/implications: As it was mentioned above, this paper is the first part of a study of the numerical parametric investigation that is dealing with the most influent parameters in a forming process to simulate the deep drawing of square cup (such as geometric, material parameters and coefficient of frictions).