bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Stress Intensity Factors of Cracked Beams for Structural Analysis
Authors: Viola Erasmo , Li Yong , Fantuzzi Nicholas
Published: September 2011

In this paper simple engineering methods for a fast and close approximation of stress intensity factors of cracked beams and bars, subjected to bending moment, normal and shear forces, as well as torque, are examined. As far as the circular cross section is concerned, comparisons are made on the base of numerical calculations. The agreement between the present results and those previously published is discussed. New formulae for calculating the stress intensity factors are proposed.
Finite Temperature Nanovoids Evolution in FCC Metals Using Quasicontinuum Method
Authors: Ponga M. , Romero Ignasio , Ortiz M. , Ariza M.P.
Published: September 2011

Tensile failure of metals often occurs through void nucleation, growth and coalescence. This work is concerned with the study of plastic nanovoid cavitation in face-centeredcubic (FCC) crystals at ﬁnite temperature. In particular, the Quasicontinuum (QC) method,suitably extended to ﬁnite temperatures, is taken as the basis for the analysis. We speciﬁcallyfocus on nanovoids in copper single crystals deforming in uniaxial and triaxial tension. Thecomplex structure of dislocations around the nanovoid and the evolution of stress, deformationand temperature of the sample is described in the present work.
Valuation of TMF Lifetime Calculation Methods and their Limitations of Usability
Authors: Köberl H. , Winter Gerhard , Eichlseder Wilfried
Published: September 2011

Cyclic loading of metallic engineering components at constant elevated or fluctuating temperature causes a complex evolution of damage which can hardly be described. At the same time the thermal expansion is restricted in some regions, due to the complex geometry of the components. Therefore, mechanical stresses occur and cyclic plastic deformation leads to thermo-mechanical fatigue (TMF) of the material. A careful analysis and comparison of the experimental results, based on a systematical variation of the relevant influence factors, allow to develop empirical models for computing the fatigue life of thermo-mechanical loaded components made of Ni alloys (IN718, Ni200/201). Different lifetime calculation methods were executed and analyzed to fulfil the requirements for the fatigue analysis of components made of these alloys. In addition, the model parameters can be optimized using these results. Based on the parameters, which define the usability of the investigated lifetime models, e.g. temperature, stress, plastic strain, the limiting combination of the parameters can be described. This graphical representation of the “border line” or limiting combination can also be used for any other materials. The results show that the main lifetime calculation models can only applied in a limited range. This limited range is mainly defined by temperature, strain constraining and their combination.
Fatigue Crack Growth Simulation in Railway Axles
Authors: De Iorio Antonio , Grasso Marzio , Penta F. , Pucillo G. P.
Published: September 2011

In order to carry out the railway axle design according to the “Damage Tolerance” philosophy, reliable crack-growth models for these kind of components are necessary. Indeed, damage tolerance principles have received more and more attention from railway technical community, thanks to its ambitious task concerning the inspection intervals prevision of railway components subjected to non-stationary loading conditions. In this paper, a simple routine is exposed that is able to calculate the characteristic parameters of the Linear Elastic Fracture Mechanics (LEFM) for a generic cracked mechanical component. Such parameters are then used in a two parameters propagation law to estimate the necessary time for a crack to become critical.
Evaluation of the Fatigue Resistance of Chromium Slurry Coating Steel Substrate Compounds by Means of an Improved Impact Testing Procedure
Authors: Anthymidis K.G. , David Kostas , Trakali A. , Tsipas D.N.
Published: September 2011

Chromium coatings have been used for the protection of gas turbine blades in power plants during the last years due to their very good resistance against steam corrosion. Microhardness, scratch, adhesion and pin-on-disk sliding tests are commonly used for rapid evaluation of the mechanical properties of these coatings [1,2]. However, very limited information exists on their fatigue resistance. In this paper we present the experimental results of the impact testing examination of the above coatings. This experimental method is capable to assess the fatigue and the impact wear resistance of coatings working under cyclic impact loading conditions. From the experimental results it was concluded that the slurry Cr, Zr coatings deposited on P91 steel showed adequate fatigue strength for the above-mentioned kind of use.
Stress Responses to Large Simple Shear Deformation in Elasticity Based on the Logarithmic Strain
Authors: Yang Li Hong , Qu Jia , He Yun Zeng
Published: September 2011

The logarithmic strain is more suitable for analyzing large strain problems because the volume invariability condition in small deformation is equivalent to volume invariability condition in large deformation when using the logarithmic strain. Large simple shear deformation has always been used in the analysis of large strain problems. In this paper, elastic large strain constitutive model was introduced based on the logarithmic strain and large simple shear deformation was analyzed by using the constitutive model given in the paper. The stress responses to large simple shear deformation were derived corresponding to four objective rates of tensors. The results show that normal stresses may maintain good monotonicity, but there exists different levels of oscillation of shear stress corresponding to various objective rates, and there was the most severe oscillation of stress when adopting Jaumann rate. The objective rate should not be the only factor bringing about oscillation of shear stress.
The Study of AE and ESSPI Technique on the CBF Composite
Authors: Chang Zhong Liang , Zou Guang Ping , Chen Si , Chen Liang
Published: September 2011

The CBF (continuous basalt fiber) composite as new and high mechanical property material have been widely applied in actual engineering. The composite material may inevitably occur all kinds of defects during fabrication and using, so in this paper, the AE (acoustic emission) and ESSPI (electronic shearography speckle pattern interferometry) technique are adopt to study the defects or damage of the CBF composite plate. The AE technique is adopted to detect the damage phenomenon of the CBF composit plate specimen tension experiment, and the ESSPI technique is adopt to study the defects of the CBF composite plate which its defects are made by artificial. From the experiment results it can be see that these techniques can detect the position and damage of the CBF composite plate, and these study can provide useful reference for the application of the CBF composite.
Study on Damage Parameters and its Size Effect of Concrete by Tension Test
Authors: Wang Xiang Dong , Wang Yue Feng , Wang Yan , Wu Yong Jin , Hua Xi
Published: September 2011

The carrying capacity decreases continuously as the material property deteriorates under the action of some external factors. It is important to evaluate the damage of concrete, in which the damage parameter plays an important role. An experimentation method is designed in this paper, with which we can simulate the initial damage by mixing initiator into concrete. Using the elastic modulus of axial tension experimentation, the tension initial damage D0 and tension damage Peak value Df have been gained. The Size effect of concrete tension damage parameters is verified. The curve of damage-parameters and size is gained, the trend of the tension damage parameters is obtained.
Effect of Rotational Speed on Thin-Rim Gear Bending Fatigue Crack Initiation Life
Authors: Opalić Milan , Vučković Krešimir , Žeželj Dragan
Published: September 2011

Thin-rim gears are often used in aircraft applications in order to reduce weight. The objective of this study is to investigate the effect of rotational speed (centrifugal force) on bending fatigue crack initiation life of thin-rim gear manufactured from case carburized 14NiCrMo13-4 steel. Stresses in gear are determined from two-dimensional finite element model, assuming plane stress conditions. The fact that, in actual thin-rim gear operation, a significant reversed stress occurs at the root of the tooth adjacent to the loaded tooth is considered. Material is assumed to be homogenous, isotropic and linear elastic. Elastic strains are calculated from obtained stresses and corrected using Neuber’s rule to account plasticity effects. The number of load cycles required to initiate bending fatigue crack is predicted using strain-life approach for variety of gear rotational speeds and rim thicknesses. Strain-controlled fatigue properties were approximated from material hardness, while the mean stress as well as residual stress effects are included through Morrow’s mean stress correction. The proposed approach is validated by comparison with available experimental data from literature and used for parametric studies. Predicted numbers of load cycles required to initiate potential bending fatigue crack are presented for the variety of cases studied.
Numerical Implementation of Constitutive Material Law for Simulating the Kinkband Formation in Fiber Composites
Authors: Veluri Badrinath , Jensen Henrik Myhre
Published: September 2011

Finite element models with a constitutive material behavior that represents the non-linear response of fiber composites are used to simulate the compressive failure mechanism i.e. kinkband formation. A constitutive material law in framework of micromechanical modeling containing comprehensive constitutive equations for the constituent materials is adopted to model the non-linear behavior of the unidirectional layered materials. This material law is implemented as UMAT user subroutine in ABAQUS/Standard to study kinkband formation. The methodology provides a procedure to investigate the kinkband formation due to fiber misalignment for various complex structures having voids and material discontinuities that occur normally during the manufacture of these unidirectional fiber composites.
Fatigue Crack Propagation in New Generation Aluminium Alloys
Authors: Richard Sébastien , Sarrazin-Baudoux Christine , Petit Jean
Published: September 2011

The fatigue crack propagation behaviour of a new third generation Al-Cu-Li alloy type 2050-T84 developed for aeronautical applications is studied in comparison to a new generation Al-Cu-Mg alloy type 2022-T851. The alloy resistance against crack growth is shown to depend on alloy composition, aging condition and atmosphere environment. The crack path and the growth rate at moderate DK and in the near-threshold domain are discussed in terms of the slip morphology with respect to the microstructure. The different crack propagation regimes, as identified by mean of micro-fractographic observations and EBSD analysis are discussed on the basis of a modelling framework elaborated for conventional metallic alloys.
An Effect of Shot Peening on Retardation and Growth of Short Fatigue Cracks in an Aircraft Al-Alloy
Authors: Černý Ivo
Published: September 2011

The paper contains the main results of an investigation of an effect of shot peening on residual fatigue life of specimens made of an aircraft V-95 Al-alloy (equivalent to 7075 alloy) containing physically short fatigue cracks. In the first part, an adaptation and verification of direct current potential drop method for detection and measurement of short crack growth is described and discussed. The specific properties of the material and quite large dimensions of flat specimens with side necking with a low stress concentration factor had to be considered when the position of electrodes was specified. The specimen type and dimensions were proposed considering the investigation of shot peening effects. Physically short fatigue cracks of the length from 0.2 mm to more than 3 mm, most of them between 0.8 – 1.5 mm, were prepared under high cycle fatigue loading of the constant nominal stress amplitude ±160 MPa. Specimens with existing short fatigue cracks were shot peened using two different groups of parameters. Crack growth characteristics after shot peening were measured and compared with crack growth in specimens without shot peening. Retardation of crack growth was significant particularly for cracks shorter than 2 mm. Results are also discussed form the viewpoint of fracture mechanics approach. For the specific stress amplitude, evaluated results enable to estimate threshold length of defects, which after the application of shot peening will be reliably arrested.
On Effective Properties of Layers in Damaged Composite Laminates
Authors: Varna Janis
Published: September 2011

Methodology is suggested for calculation of effective elastic constants of layer containing intralaminar cracks. Trends are presented for layers with low and medium high crack densities, where the interaction between cracks can be neglected. The effective properties of the damaged layer are determined by back- calculation using previously developed GLOB-LOC model for thermo-mechanical properties of damaged laminate [1]. It is shown that the effective transverse modulus and shear modulus of a layer decrease linearly with increasing crack density, whereas longitudinal modulus and major Poisson’s ratio do not change at all. Experimental data for multiple cracking are analyzed showing that linear approximation of crack density versus applied strain may have sufficient accuracy. These two linear trends are used to calculate the effective elastic properties of a layer as a function of strain.
Fatigue Focused Optimization of Treatment Parameters – A Case Study about Deep Cryogenic Treatment
Authors: Baldissera Paolo , Delprete Cristiana
Published: September 2011

The problem of treatment parameter optimization focused on the fatigue resistance is analysed through a case study about Deep Cryogenic Treatment (DCT) of AISI 302 steel. In particular, the possibility to integrate fatigue data fittings through the Maximum Likelihood Estimation (MLE) method in the optimization process is evaluated. Two levels of two parameters (soaking time and temperature) are considered and then expanded to three by proper scaling of their values in order to include the untreated case as a “zero” level. Fatigue focused optimization is then achieved by standard Response Surface Method (RSM) and by MLE with two models for comparison purposes.
Effect of Shot Peening on the Fatigue Behavior of some Sintered Steels
Authors: Baragetti Sergio , Gerosa Riccardo , Silva Giuseppe , Rivolta Barbara
Published: September 2011

Shot peening is a mechanical treatment usually performed on metals for improving the mechanical properties of the surface layers. The application of such treatment to sintered steels causes a local surface densification and the birth of residual compression stresses. In this paper, the effect of different shot peening cycles, selected after a preliminary optimization, has been investigated focusing especially on the fatigue resistance measured by bending tests and on the surface residual stresses measured by XRD technique. Two high performances PM steels were considered: the former was sintered starting from a diffusion bonded powder, whereas the latter is based on a pre-alloyed powder. Two different nominal densities were considered, 6.9g/cm3 and 7.1g/cm3.
Effect of Heat Treatment on Fracture during Bending in AA6016 Aluminium Alloy Sheets
Authors: Davidkov Aleksandar , Petrov Roumen H. , De Smet Peter , Kestens Leo A.I.
Published: September 2011

The bending properties of high strength precipitation-hardening AA6016-type Al alloy thin sheets in pre-aged T4P temper state were studied in this work. Microstructural features like grain boundary particles distribution and volume fraction of the matrix strengthening phases were considered as factors controlling the mechanical properties and the fracture of this grade. Remarkable decrease in ductility, accompanied by severe deterioration of bendability occurred when coarse precipitates were found into the grain boundaries. The in-situ fracture sequence investigations as well as the post-failure surfaces observations indicated that grain boundary ductile fracture mechanisms were involved in the propagation of the cracks during bending. Heat treatment simulations were carried out and the results showed that the precise control of the technological parameters during production of these sheets is the key factor responsible for obtaining an appropriate combination of strength and bendability. Only by providing both, homogeneous distribution of the matrix strengthening phases and a favourable grain boundary structure, the severe and often contradictory requirements for the functional properties of these alloys can be successfully satisfied.
Probabilistic Fracture Resistance of a Forged Quality Medium Carbon Alloy Steel
Authors: Ray Kalyan Kumar , Jha R.N.
Published: September 2011

Impact and fracture toughness of a large number of medium carbon alloy steel specimens have been ascertained using standard ASTM procedures, apart from examining their chemistry, microstructure, cleanliness, tensile behaviour and fracture surfaces. The results indicate that the scatter associated with ductility, impact and fracture toughness is considerable unlike that for strength or hardness. Analyses of the role of undesirable elements on toughness properties indicate that the scatter associated with fracture resistance of the steel primarily originates from the amount of tramp elements.
An Experimental and Numerical Investigation of the Mixed-Mode Fracture Toughness and Lap Shear Strength of Aerospace Grade Composite Joints
Authors: Mohan J. , Karač A. , Murphy Neal , Ivanković Alojz
Published: September 2011

In the present study, the mixed-mode fracture toughness of an adhesively bonded composite joint system was examined using a variety of linear elastic fracture mechanics (LEFM) based tests. These tests include the mode I double cantilever beam (DCB), mixed-mode asymmetrical DCB (ADCB) and mode II end load split (ELS) test. The joint system was also evaluated using the wide area lap shear (WALS) test that is often employed by the aerospace industry. While lap shear type tests are relatively simple to perform and post-process compared to their LEFM counterparts, the results can often be misleading and are greatly dependent on the overlap length, thickness of substrate and type of fillet. The experimental tests were also simulated using OpenFOAM, a finite volume based software package. Through this combined experimental-numerical approach, a greater understanding of the influence of the peel ply surface treatment and scrim cloth on the behaviour of the WALS test was achieved.
On the Evaluation of the R-Curve Including the Self-Weight Contribution: Mortar
Authors: Dourado N. , Morel S.
Published: September 2011

In fracture tests involving the Single-Edge-Notched beam loaded in Three or Four-Point-Bending as well as in other specimen shapes, the specimen weight contributes to the overall loading of the system. Unless special methods are put into practice, the contribution of the specimen weight is not compensated, leading to misevaluations of fracture parameters obtained in the experiments. In this work a method taking into account the exact contribution of the specimen self-weight is proposed to evaluate the Resistance-curve of mortar. Cohesive crack modeling accounting for the structure self-weight is used to generate the necessary load-displacement response to perform the validation of the proposed method.
A Microstructural Sensitivity Study of 316H Austenitic Stainless Steel to Inter-Granular Creep Fracture
Authors: Chen B. , Flewitt Peter E.J. , Smith David John , Younes C.M.
Published: September 2011

A preliminary sensitivity examination of the ductility exhaustion based creep damage prediction model, currently used in the R5 high temperature assessment procedure, showed that material property inputs had significant effects on damage prediction. In the present work, the link between the microstructural factors and the susceptibility to inter-granular high temperature creep failure is considered. The latter was judged to be associated with the low creep ductility. Here, the longitudinal section of a creep specimen and the fracture surface were examined. Auger electron spectroscopy was used to investigate the grain boundary composition in this specimen, which failed after a creep test of 1038h at 550°C under a triaxial stress state. The present results demonstrate that there is a possibility to correlate the susceptibility to high temperature inter-granular fracture from the low temperature fracture investigations. Finally, the susceptibility of the pre-treated 316H stainless steel to inter-granular high temperature failure and the contribution to the creep damage model are briefly discussed.
Tensile Properties of Random Distribution Short SMA Fiber Reinforced Composites
Authors: Lei Hong Shuai , Zhou Bo , Wang Zhen Qing , Wang Xiao Qiang
Published: September 2011

Shape memory alloy (SMA) reinforced composites have been widely used in aerospace engineering fields. In this paper, four basic assumptions were presented to simply the research model based on the Eshelby’s equivalent inclusion method and Mori-Tanaka scheme. Based on the three-phase equivalent system and two-step equivalent process, the effective elastic modulus and thermal expansion coefficient of unidirectional random distribution short SMA fiber reinforced composites were derived. The tensile mechanical properties of composites with fiber volume fraction (15%), size (L=3, D=1; L=5, D=1), and number (N= 30, 50), were simulated using software ANSYS12.0, and discussed the failure mode of the composites.
Study on Static and Dynamic Mechanical Property of Sandwich Plate with Aluminum Foam Core under Confining Pressure
Authors: Zou Guang Ping , Chang Zhong Liang , Wang Rui Rui
Published: September 2011

In this paper, the sandwich structure which is consist by the aluminum foam core and CBF(continuous basalt fiber) composite plate is tested by the static and dynamic mechanical property under confining pressure, and the confining pressure experiment is done through add cylindrical tube to the sandwich structure circular specimens. The static mechanical property is tested by WDW3100 electronic universal testing machine, and its dynamic mechanical property is tested by the SHPB(Spilt Hopkinson Press Bar) device, Besides, the strain rate effect of this sandwich structure under confining pressure is tested too, From the experiment results we can see the static and dynamic mechanical properties of confining and no confining results is very different, and this study will provide references for further numerical simulation and damage studying of this kind of sandwich structure.
Numerical Stress Intensity Factors Determination for Fabrication Defects in Coronary Stents
Authors: Nes Cristian Sorin , Enkelhardt Angelica , Faur Nicolae , Birlan Adrian
Published: September 2011

Objectives: Numerical stress intensity factors (SIFs) computation for several fabrication defect geometries in coronary stents. XFEM crack initiation and propagation was also performed. Methods: The model represents a self-expandable coronary stent, made from a shape memory alloy (L-605). Several flaw shapes are considered. The analysis was performed using the ABAQUS code. The loads and boundary conditions simulate the interaction between the blood vessels and stents, immediately after the angioplasty was performed. The mesh contains 3d stress hexahedral elements. For global stress and strain distributions, the model of a complete stent was used. For crack propagation analysis and SIF determination, the model represented a single segment of the stent. The stress intensity factors were computed using the contour integral method. Results and conclusions: The stress and strain fields highlight the negative effects of crack initiation and propagation on the residual life of the stent. Furthermore, by compromising the structural integrity of the stent, large strains may occur, thus increasing the risk of restenosis and further stenosis-related complications. The stress intensity factors indicate the most dangerous locations for the flaws (cracks), as well as the most dangerous geometries.
Residual Fracture Toughness of Concrete Subject to Elevated Temperatures
Authors: Yu Jiang Tao , Yu Ke Quan , Lu Zhou Dao
Published: September 2011

This paper presents an experimental investigation on the variation of residual fracture toughness of concrete after being exposed to elevated temperatures. A total of 60 specimens, with a uniform size of 200x200x230mm and precast notches of 80mm in height, were heated to constant temperatures of 65°C, 120°C, 200°C, 300°C, 350°C, 400°C, 450°C, 500°C and 600°C respectively. After cooling, standard wedge splitting tests, according to the corresponding Chinese Specification, were employed. The results indicate that the elevated temperature has significant influence on the residual fracture toughness of concrete. The magnitude of fracture toughness decreases drastically with increasing temperature. Additionally the relationship between residual fracture toughness and weight loss of specimens with respect to temperatures is also investigated.
Semi-Permeable Cracks in Magnetoelectroelastic Solids under Impact Loading
Authors: Wünsche Michael , Sáez Andrés , Zhang Chuan Zeng , García-Sánchez Felipe
Published: September 2011

In this paper, transient dynamic crack analysis in two-dimensional, linear magnetoelectroelastic solids by considering different electrical and magnetical crack-face boundary conditions is presented. For this purpose, a time-domain boundary element method (TDBEM) using dynamic fundamental solutions is developed. The spatial discretization of the boundary integral equations is performed by a Galerkin-method while a collocation method is implemented for the temporal discretization of the arising convolution integrals. An explicit time-stepping scheme is applied to compute the discrete boundary data and the generalized crack-opening-displacements. Iterative algorithms are implemented to deal with the non-linear electrical and magnetical semi-permeable crack-face boundary conditions.
A Novel Methodology for Fatigue Delamination Growth Analysis of Composites
Authors: Bacarreza Omar , M.H.Aliabadi Ferri
Published: September 2011

A novel methodology for analysis of fatigue delamination growth, capable of dealing with complex delamination shapes and mixed-modes in a computationally efficient way, is proposed. It combines the VCCT to find the energy release rates and the XFEM to update the geometry during the progressive failure, thus making it very robust and computationally efficient. The methodology is demonstrated at coupon level.
Notched Specimens Fracture Prediction with an Advanced GTN Model
Authors: Fansi Joseph , Bettaieb Mohammed , Balan Tudor , Lemoine Xavier , Habraken Anne Marie
Published: September 2011

This present contribution consists of implementing an advanced GTN damage model as a "User Material subroutine" in the Abaqus FE code. This damage model is based on specific nucleation and growth laws in order to predict the void coalescence properties of the material. When applied, this implementation predicts the damage evolution and the stress state of notched specimens made from dual phase steel. By comparing numerical predictions with experimental results, the numerical approach was improved and then validated.
Damage Mechanics in G/E Tubes under Tension-Torsion Cyclic Loading
Authors: Carraro P.A. , Quaresimin Marino
Published: September 2011

In this work, multiaxial fatigue tests results on [0F/90U,3/0F] glass/epoxy tubes are discussed. Specimens are subjected to combined tension-torsion loadings, resulting in the stress components σ2 andτ12 in the 90° layers of the tubes. The effect of shear stress on damage mechanics has been investigated and a strong influence on both damage onset and propagation has been observed. SEM investigation of fracture surfaces shows the dependence of damage modes, at the microscopic scale, on the multiaxiality condition. Comparison with previous results on tubes with different lay-ups ([904], [0F/90U,3]) shows the strong influence of the constraining 0° fabric layers on the damage onset and propagation.
Comparison between 3D FEM and Standard ISO Tooth Root Stresses
Authors: Marunić Gordana , Gregov Goran , Glažar Vladimir
Published: September 2011

The paper deals with the discussion how nominal spur tooth root stress of thin-rimmed gear determined in accordance with the standard ISO 6336-3:2006, method B, agrees with the results of the 3D FEM stress analysis. The procedure proposed by standard ISO for the tooth root stress calculation doesn’t identify the stress behaviour related to mutual affects of characteristic thin-rimmed gear geometrical parameters. Therefore, the 3D FEM analysis of tooth root stress has been performed for gear structures with middle and offset web with various rim and web thickness. The rim thickness has covered and slightly overcome the backup ratio defined by ISO procedure, while the web thickness has covered the range of practical interest.
Cyclic Mixed-Mode Crack Propagation due to Time-Dependent Multiaxial Loading in Jet Engines
Authors: Dhondt Guido
Published: September 2011

Components in jet engines are subject to time-dependent multiaxial loading. This creates a time-varying mixed-mode stress state at the crack tip. Mixed-mode loading leads to out-of-plane crack propagation and has been treated in previous articles [1,2]. This paper concentrates on coping with the time-dependent character. Key issues are the crack propagation rate and the crack propagation direction in three-dimensional space. In order to determine the prevalent crack propagation direction the dominant loading case is determined based on its crack propagation rate. Then, a mixed-mode equivalent K-factor is calculated for all other loading cases based on the closeness of their associated crack propagation direction with the dominant one. Subsequently, a cycle extraction is performed on the crack propagation rate for all loading cases. The extracted cycles are processed based on their mimimum and maximum equivalent K-factor and the maximum temperature. The mission crack propagation rate consists of the sum of the rate of all extracted cycles.
Modelling the Contact between the Rolling Elements and the Raceways of Bulky Slewing Bearings
Authors: Krynke Marek , Kania Ludwik , Mazanek Eugeniusz
Published: September 2011

In slewing bearings, a great number of contact pairs are present on the contact surfaces between the rolling elements and raceways of the bearing. Computations to determine the load of the individual rolling elements, taking into account the flexibility of the bearing ring, are most often carried out using the finite element method. Construction of a FEM full model of the bearing, taking into account the shape of the rolling elements and the determination of the contact problem for every rolling element, leads to a singularity of stiffness matrix, which in turn makes the problem impossible to solve. In FEM models the rolling elements are replaced by one-dimensional finite elements (linear elements) to simplify the computation procedure and to obtain an optimal time for computations. The methods of modelling the rolling elements in the slewing bearing, in which balls have been replaced by truss elements with a material non-linear characteristic located between the raceway centres of the curvatures in their axial section, are presented in the paper.
Multicaterpillar Track Chassis of Big Machines - Identification of Loads
Authors: Smolnicki Tadeusz , Maślak Paweł
Published: September 2011

Multicaterpillar track chassis are used in the biggest machines. This kind of chassis is commonly used in open cast mines for mobile transfer conveyor or for bucket wheel excavators. In each machine the chassis consist of 6 to 12 caterpillar tracks, which some are steered. Existing models used for analytical calculations are based on simplified relations taken from quasistatic equations of stability and geometrical connections. The complex research was conducted on mobile transfer conveyor, which is used in open cast mine. The aim of measurements was to identify the value of force that acts on elements of chassis during the steering and driving the machine. The measurements were taken during the drive in different directions, with different positions of center of gravity. The strain gauges were used to measure the deformation on each caterpillar track, trusses and drawbar.
New Satellite Pumps
Authors: Sliwinski Paweł
Published: September 2011

Stosowanie Maszyn company from Katowice was initiator and originator of newest original high pressure satellite pumps series of types PSM. Construction solution, research and development of these pumps have been conducted by Team of Hydraulics and Pneumatics of Gdansk University of Technology in cooperation with this company within the confines of research project nr R0300103 (source of funds: Ministry of Science and Higher Education). Prof. A. Balawender was the manager of this project. Working medium for these pumps may be oil, emulsion HFA-E and water. Results of laboratory research of the pump would be presented in the article. Results of research contain: volumetric losses, hydraulic-mechanical losses, efficiencies of those pump and their characteristics of noise. For all types of pumps from PSM series characteristics are similar.
Numerical and Experimental Analysis of Stress and Strains in Flat Ends of High-Pressure Vessels
Authors: Szybiński Bogdan , Romanowicz Paweł , Zieliński Andrzej P.
Published: September 2011

Application of flat welded ends with stress relief grooves in high-pressure vessels is a common alternative to use of dished vessel ends. It is well established and follows calculation rules given in codes: EN-12952-3 [1], EN-13445-3 [2], or in ASME code [3]. However the calculation rules do not give any definite answer what should be the choice of parameters defining a circular stress relief groove, for example, position of the groove and its radius. Usually the choice of them relies on engineering practice. The present paper clearly shows the influence of this choice on stress concentration in the cylinder-endplate junction area. The results of numerical study are verified in experimental investigations performed for a cylindrical high-pressure vessel.
Measurement of Normal Force in Magnetorheological and Ferrofluid Lubricated Bearings
Authors: Salwiński Józef , Horak Wojciech
Published: September 2011

Preliminary analysis of magnetorheological fluid usability in fluid lubricated bearings has been described in the present study. Results of the study aimed at rheological properties of chosen fluids, which possess magnetic properties (both ferrofluids and magnetorheological fluids) with respect to their application in slide bearings have been presented Preliminary analysis of potential advantages related with the magnetic fluid bearing construction was carried out. Results of measurements of normal force developed within magnetorheological fluid and ferrofluid in result of magnetic field action at various shear rate values have been presented.
Wear of Ultra-Thin DLC or Tungsten-Modified DLC Coatings under Reciprocating Sliding
Authors: Druet Krzysztof , Lubinski Jacek Igor
Published: September 2011

The application of various coatings on traditional material substrata (e.g. metal alloys) is a well established technology used to modify surface characteristics/performances of various components in technical systems exposed to adverse conditions, e.g. corrosive environment, high temperature, erosion and/or wear, etc. [1… 10]. Coatings can also provide a desired (mostly low) friction coefficient between solids forming various tribological systems. In recent years there has been a particular increase in interest in carbon-based coatings, either crystaline (diamond or graphite) or amorphous. This applies especially to amorphous carbon with high content of sp3 bonds characteristic of the diamond - known as DLC (diamond-like carbon). This coating can be "pure" form of DLC, if it contains only sp3 bonded carbon, but may also contain other elements and crystalline structures; Hydrogen, carbon with the "graphite" sp2 bonds, metals and/or other modifiers, which can provide the required specific properties of the coating and reduce the cost of production.
Aluminium Extrusion Weld Formation and Metal Flow Analysis in Hollow Profile Extrusions of Different Section Thickness
Authors: Khan Yawar Abbas , Valberg Henry Sigvart
Published: September 2011

Hollow and semi-hollow profiles are commonly produced by extrusion using porthole dies. The main characteristics of such dies are the presence of a mandrel (core) to shape the inner contour of hollow profile and bridges or legs to carry the mandrel. The bridges split the billet material into multiple metal streams that flow through the porthole channels and meet in the welding chamber behind the bridge where they are joined by pressure welding. When hollow profiles with different wall thickness are made the size of two adjacent portholes may be different. The material then flows through the two portholes with different flow velocity so that there is more feed through the bigger porthole into the weld chamber behind the bridge. Experiments have been performed and are reported here in which a grid pattern technique was used to characterize the metal flow through a 2D-die with porthole channels of unequal size. The design of the laboratory die has been modified in relation to the symmetric case to get different sizes of the two portholes. Since the metal flow through such a die is asymmetric the grid pattern technique was also modified to characterize the experimental flow. The results of an experimental metal flow study performed for a short billet was presented in a previous article [1]. Corresponding experiments performed with longer billets are now reported; so that two stages of the extrusion process is analysed here. The grid pattern technique has successfully mapped the non-symmetric material flow as in industrial extrusion when using different wall thickness over the section. The lateral movement of metal during extrusion is obtained from one set of experiments; the vertical movement from the other set. Finite element analysis of the extrusion process has been performed using Deform 3D. The encountering of the two metal streams behind the die bridge and the deformation characteristics within the welding chamber has been studied this way. Extrusion weld formation and deformations around the die bridge are considered here with the help of experimental results and simulation models. The nature of the metal flow achieved from the FE-model is compared with the experimental results. As regards the short billet some results are presented in [1], however improvement to the previous model gives a more perfect match. The model also provides information about the boundary conditions in real extrusion.
Experimental and Numerical Analysis of the Friction Condition in the Die Bearing during Aluminum Extrusion
Authors: Müller Sören , Muehlhause Jerome , Maier J. , Hora Pavel
Published: September 2011

Of the various boundary conditions that are relevant for the correct modeling of the extrusion process the realistic representation of the friction in the die is important since it has a significant influence on the profile temperature, the strain and strain rate distribution in the die. In order to investigate the influence of the die geometry, respectively the geometry of the die bearing, a four-hole die with exchangeable inserts was designed. Thereby each of the four inserts was equipped with a thermocouple to record the profile temperature at the die bearing. Through the combination of different die bearing geometries (cylindrical, 0.5° closing, 1° closing, 0.5° opening) in the same die the influence on the extrusion speed and profile temperature could be evaluated with the exact same extrusion conditions. The observed differences in the temperature and speed in respect to the geometry of the die bearing where evaluated and implemented in a FEM simulation in order to validate the underlying friction model.
Modeling of Friction Phenomena in Extrusion Processes by Using a New Torsion-Friction Test
Authors: Hora Pavel , Gorji Maysam , Berisha Bekim
Published: September 2011

During the extrusion processes very complex adhesion and friction effects between the die surface and the extruded material occur. If they can not be controlled, the process can not be controlled either. In the framework of this study, a recently developed experiment for the investigation of the frictional phenomena under extrusion conditions will be presented. Based on the so called Torsion-Tribo-Test, low and high pressure load cases are considered. The experimental layout, the evaluation method as well as some measurements will be presented.
Experimental and Numerical Investigations on Metal Flow during Direct Extrusion of EN AW-6082
Authors: Kammler Matthias , Hadifi T. , Nowak M. , Bouguecha A.
Published: September 2011

In extrusion processes metal flow has an important influence on the microstructure and the mechanical properties of the extrudates. Thus, a deep knowledge about the metal flow during the forming process is required as basis for further computations of the microstructure evolution. In this study experimental and numerical investigations on the influence of friction on the metal flow in extrusion processes were carried out using visioplastic methods and finite element method (FEA). The objective was to determine the influence of ram speed, ram displacement and billet temperature on the material flow during extrusion of the aluminum alloy AlMgSi1 (EN AW-6082). For this purpose the forming stroke was varied at constant temperature so that a butt length of 100 mm and 150 mm could be produced. Further the influence of different ram speeds at 4.22 mm/s, 6.33 mm/s and 8.44 mm/s was investigated. In order to identify the metal flow and in special the shear zone as well as the dead metal zone, the billets of 250 mm length and a diameter of 140 mm were prepared with round aluminum indicator pins with a diameter of 4 mm which were placed in the plane of symmetry of the billet. For the experimental investigations a compact direct extrusion press with a nominal force of 10 MN (SMS Eumuco) was used. The numerical simulations were carried out using the commercial FEA system simufact.forming 8.1. After extrusion the billets were cut in the plane containing the indicator pins and the surface was polished and etched. The visioplastically determined flow lines and calculated strains were compared with computed flow lines in order to verify the results and to parameterize the simulation. Tresca’s friction model was used in the simulations to describe the frictional conditions between the billet and the tool components. The results of the experimentally and numerically determined strains of the billet at the container wall show a good similarity. With respect to the rigid modeling of the tool components and the fact that Tresca’s friction model considers relative speeds only indirectly the computed ram force curves show also quite good agreement with measured curves. However, the simulation results demonstrates that in further numerical studies advanced plastic flow criteria and flow rules should be used that take into account the anisotropy and inhomogeneity due to the changing grain size and microstructure of the workpiece material.
Experimental Analysis of Velocity Fields in Hot Extrusion of Aluminium Alloy 6351
Authors: Martins Marcelo , Button Sérgio Tonini , Bressan José Divo
Published: September 2011

Hot extrusion is a metal forming process with a huge importance in the manufacturing of long metallic bars with complex shapes, and because of this, academics and industries are especially interested in better understanding how metal flows during the process. In order to have a reliable computational tool that can help to solve and to obtain material internal flow, experimental tests and numerical simulation with the finite element method were carried out to obtain results of the velocity fields generated in hot direct extrusion of aluminum billets (aluminum alloy 6351). The experimental results of the velocity field will be used to validate a computational code based on the finite volume method.
3D FEM-NEM Material Joining Simulation in Porthole Die Extrusion
Authors: Gagliardi Francesco , Alfaro I. , Filice Luigino , Cueto Elías
Published: September 2011

The conventional tube extrusion process has been substituted by porthole die extrusion due to relevant advantages in terms of productivity and quality. However, the porthole die has a complex geometry to be effectively designed; consequently, several studies can be found out in the technical literature based on experimental and finite element analyses of the process. From this point of view, while the experimental investigations entail cost and time increasing, due to the die building complexity, finite element techniques present some drawbacks such as the difficulty to simulate material joining and the loss of accuracy due to the heavy mesh distortion and related remeshing. Therefore, the introduction of new numerical techniques for the analyses of this process could have positive effects. In this paper, the Natural Element Method (NEM) together to the alpha shapes and some extra numerical procedures are used in the simulation of tube extrusion, focusing the attention on the simulation of the welding line in a fully 3D analysis. The obtained results are compared with the finite element and experimental ones, measuring the accuracy of the proposed methodology.
Finite Element Modelling of the Charge Welds Evolution in a Porthole Die
Authors: Reggiani Barbara , Segatori Antonio , Donati Lorenzo , Tomesani Luca
Published: September 2011

Although the extrusion process is regarded as a continuous process, in practice billets are discretely loaded into the press. The joining of two consecutive billets is guaranteed by the high hydrostatic pressure of the process. Nevertheless, mechanical proprieties of the profile in the welded region are lower than those of the adjacent area thus leading to the discarding of the welded segment. Extension of the segment is mainly affected by the interaction of seam and charge welding phenomena and, nowadays, its prediction is still a tricky task involving rough empirical relations or labour intensive analyses. Aim of this work was to identify the starting and exhausting points of the charge welds evolution inside an industrial multi-profiles die, in order to determine the exact position and the minimal length to be scraped. The extrusion of four AA6060 hollow profiles through a multi-hole die were preliminary monitored in an industrial press by accurate recording of the process loads, temperatures and speeds during the process. The four profiles were sectioned starting from the ‘stop mark’ then grinded and etched in order to investigate the location and the dimension of the zone to be ridded. While the experimental activity is detailed elsewhere, this paper is focused on the finite element modelling of the process. The numerical simulation was performed by means of the Altair HyperXtrude code and predictions compared to experimental data with a particular focus on the computation of the charge evolution. It was found a good agreement both in terms of general trend and prediction of the exhausting points so thus proving the code to be a reliable tool for an accurate determination of the scraps.