bluuebunny/crossref_metadata_2025 huggingface dataset:
Precision Calculation Algorithm and Error Analysis of Zoom Magnification Measurement
Authors: Zeng Zheng Dong , Sun Chang Ku , Zheng Yi Zhong , Yan Ming Dong , Ng Seng Keong
Published: September 2011

The high precise measurement for magnification of optical system of microscope has been demonstrated by using special barcode design and precise barcode image processing technologies. The magnification measurement with 50ppm accuracy is obtained. According to the measurement error estimation, the accuracy for system magnification device is about 0.06%. Barcode position is possible to reach 0.5μm for low magnification and 0.1μm for high magnification.
A Combined Measurement Method with PIV and Schlieren Technology on under Expanded Supersonic Jet
Authors: Jiang Guan Lei , Wen Ming , Ye Ji Fei , Wu Wen Tang
Published: September 2011

A combined measurement method with PIV and schlieren technology is described in this article. The velocity field and the shock wave structure can be obtained simultaneously with this combined measurement method by a synchronous time controller and the post-processing. The color schlieren can capture the instantaneous image effectively and clearly, while the PIV can calculate the time average velocity field and put out with the visual image. Both of them are ripe technologies, they can setup easily and even get some commercial groupwares. In this article, this combined measurement method study the under expanded supersonic jet successfully. Not only limit in the under expanded supersonic jet, this combined measurement method also can apply in the other supersonic flow. They are complementary advantaged to the investigation of supersonic flow.
Corrosion-Fatigue of High Strength Steel Bars: Evolution of Crack Aspect Ratio
Authors: Toribio Jesús , Matos Juan Carlos , González Beatriz , Escuadra J.
Published: September 2011

Abstract. This paper shows the evolution of the surface crack front in prestressing steel wires subjected to fatigue in air and to corrosion-fatigue in Ca(OH)2+NaCl. To this end, a numerical modelling was made on the basis of a discretization of the crack front (characterized with elliptical shape), considering that the crack advance at each point is perpendicular to such a front according to a Paris-Erdogan law, and using a three-parameter stress intensity factor (SIF). Each analyzed case (a particular initial crack geometry) was characterized by the evolution of the semielliptical crack aspect ratio (relation between the semiaxes of the ellipse) with the relative crack depth and by the variation of the maximum dimensionless SIF at the crack front
Lifetime Determination of the Raceway of a Large Three-Row Roller Slewing Bearing
Authors: Göncz Peter , Potočnik Rok , Glodež Srečko
Published: September 2011

This paper deals with calculation procedure for lifetime determination of a large three-row roller slewing bearing. First, the contact force distribution between the rollers and the bearing raceway is determined both analytically and numerically. Then, the position and the magnitude of the maximum contact force are identified. In a separate numerical model finite element analyses are performed to determine the subsurface stress distribution as the result of contact between the raceway and different rollers. These stress fields serve as an input for the fatigue lifetime calculation, which is done in accordance with the stress-life approach (S-N). At the end the influence of roller geometry on the calculated fatigue life is presented.
Analysis of Combined Adhesive and Cohesive Cracking at Roughened Surfaces
Authors: van der Sluis Olaf , Noijen Sander P.M. , Bouquet J. B. , Timmermans P.H.M.
Published: September 2011

Macroscopic delamination of polymer-metal interfaces is one of the main failure modesobserved in micro-electronic components. Due to the irregularly shaped metal roughness proﬁle, thisdelamination not only consists of interface separation but also bulk cracking at the micro-scale ofthe roughness. In fact, one of the key mechanisms that results in increased adhesion toughness atroughened interfaces is the transition from adhesive to cohesive failure. A semi-analytical approachis discussed in which the competition between adhesive and cohesive cracking is analyzed by meansof the theoretical relation between interface and kinking stress intensity factors. The parameters thatdeﬁne this relation, the solution coefﬁcients, are quantiﬁed by ﬁnite element (FE) simulations. Accordingly, the crack kinking location and kinking angle into the softer polymer is readily calculated.Furthermore, the geometrical effect of roughness is evaluated by means of FE simulations in whichthe interface topology follows from measured roughness proﬁles while also including interface delamination using cohesive zone elements.
Development of Predictive Models for Fatigue Crack Growth in Rails
Authors: De Iorio Antonio , Grasso Marzio , Kotsikos George , Penta F. , Pucillo G. P.
Published: September 2011

Fatigue failures of rails often occur at the rail foot, since the geometry of this zone gives rise to stress concentrations under service loads or defects during rail manufacture and installation. In this paper, the fatigue behavior of cracks at the web/foot region of a rail is analyzed numerically. Analytical models in the literature for a semi-elliptical surface crack in a finite plate assume that the geometry of the front remains semi-elliptical during the whole propagation phase and the ellipse axes do not undergo translations or rotations. Fatigue tests show that this is not the case for such cracks in rails. A predictive model for crack growth has been developed by assuming an initial small crack at one probable initiation point between the web and foot of the rail in reference to a service condition loading. SIF values have been estimated by means of the finite element method and the plastic radius correction. The results attained were compared with crack growth experimental data.
Identification of Slant Cracks in a Cantilever Beam Using Design of Experiment and Neuro-Genetic Technique
Authors: Hajhosseini Mohammad , Nahvi H.
Published: September 2011

Cracks present a serious threat to the performance of beam-like structures. In this paper, the flexural vibration of a cantilever beam having a slant crack is considered. The beam natural frequencies are obtained for various crack locations, depths and angles, using the finite element method. These natural frequencies and crack specifications are then used to train a neural network. The input of the neural network is the crack specifications and the output is five natural frequencies of the beam. With the trained neural network, genetic algorithm is then used to determine the beam crack specifications by minimizing the differences from the measured frequencies. Simulations are performed to evaluate performance of the neural network. Results show that the proposed scheme can detect slant cracks in cantilever beams with good accuracy.
Non-Linear Behaviour of Base-Isolated Building Supported on Flexible Soil under Damaging Earthquakes
Authors: Mahmoud Sayed , Austrell Per Erik , Jankowski Robert
Published: September 2011

Seismic isolation is a strategy to reduce damage of structures exposed to devastating earthquake excitations. Isolation systems, applied at the base of buildings, lower the fundamental frequency of the structure below the range of dominant frequencies of the ground motion as well as allow to dissipate more energy during structural vibrations. The effectiveness of the base-isolated buildings in damage reduction has been confirmed numerically for the models of structures with fixed supports. The aim of the present paper is to show the results of the non-linear analysis of the response of a base-isolated building supported on soft soil incorporating soil-structure interaction. The detailed study has been conducted for the building equipped with high damping rubber bearings used as isolation devices. The results of numerical simulations demonstrate that soil flexibility has a significant influence on the behaviour of isolated base of the structure. Considering the flexibility of soil significantly affects the rigid superstructure response lowering its potential to reduce structural damage.
Coupling Infrared Thermography and Acoustic Emission Measurement to Quantify the Shakedown State of Shape Memory Alloys
Authors: Dunand-Châtellet Clement , Moumni Ziad
Published: September 2011

This paper provides an original experimental characterization of the shakedown state of a shape memory alloy structure under cyclic pseudo-elastic loading. This analysis is performed through the observation of the dissipated energy at a macroscopic scale as well as the temperature on the surface of the sample through infrared thermography measurement. Morevover, a deeper study is led thanks to acoustic emission to quantify the shifts between microscopic evolutions at a lower scale. The main conclusion is that these 3 quantities are correlated and enable us to identify different stages the structure crosses until the shakedown state.
Experimental and Numerical Investigation of Fatigue Behaviour of Nodular Cast Iron
Authors: Čanžar Predrag , Tonković Zdenko , Bakić Ante , Kodvanj Janos
Published: September 2011

This paper presents an experimental and numerical study on two different types of the nodular cast iron EN-GJS-400-18-LT. The experimental procedure includes symmetrical and unsymmetrical strain controlled tests on the cylindrical specimens as well as crack initiation and propagation tests on the compact tension and single edged notched specimens. Different loading regimes are applied, and monitoring of the crack length during the tests is performed by an optical system. Within the framework of numerical investigations an efficient algorithm for modelling of cyclic plasticity is examined. Experimental results show that two material types have significantly different the crack behaviour.
Influence of Curing Temperature on the Mechanical Properties of Alkali-Activated Bottom Ash Geopolymer Mortar
Authors: Ryu Gum Sung , Kim Si Hwan , Koh Kyung Taek , Kang Su Tae , Lee Jang Hwa
Published: September 2011

The fabrication of Portland cement causes numerous problems accompanying the large exhaustion of gas. Even if fly ash, an industrial by-product produced in thermoelectric power plants, is recycled in concrete by partial replacing of cement, more than 50% remains still discharged in marine and ashore landfills and, continue to provoke environmental problems. Recently, active research has been dedicated to alkali-activated concrete that does not use cement as binder. This alkali-activated concrete as a cement zero concrete activated by alkali solution using bottom ash rich in Si and Al instead of cement is effective in reducing gas exhaustion. This study is a basic research for the fabrication of concrete without cement and using 100% of bottom ash among the industrial by-products. Therefore, the purposes are to develop cement zero concrete by evaluating the mechanical properties by age according to the change of the molar concentration and ratio (SH/SS) of the alkali-activator and the curing temperature, and to investigate the reaction mechanism. From the test results, the compressive strength increased with larger molar concentration and the optimal curing temperature was 60°C. In addition, the measurement of the leaching according to the molar concentration of fly ash having similar chemical composition showed that the leaching of Si4+ and Al3+ increased. Compared to 6M, the leached quantities of Si4+ and Al3+ were twice larger for 9M and 12M. The formation of gel at the surface of fly ash indicated that fly ash was more activated in higher alkaline environment.
A Study on the Fracture Test in Railroad Truck
Authors: Yoon Sung Cheol , Kim Jeong Guk , Baik Kwang Sun , Goo Byeong Choon , Choe Kang Youn
Published: September 2011

The truck that is used as running equipment for freight car support is a core structural part that supports the load of the car body and that greatly influences the safety of freights and vehicles, as well as their running performance. The running equipment is composed of truck frames, wheels and wheel axles, independent suspensions, and brakes. Among these components, the truck frame supporting the load of the vehicles and freights may be the most important one. This study was carried out to analyze the structure of truck frames and to determine whether they are safe when the maximum vertical load, breaking load, and front and rear loads are applied to them. This was done by subjecting the truck frames to stress tests and then measuring the stress on each of their parts. Before the load test, a structural-analysis program was used for the stress distribution analysis of the truck frame. To measure the stresses based on the results of the structural analysis, strain gages were attached to the surfaces of truck frames. The results of the stress tests showed that truck frames have a safe vehicle load design.
Fracture Behavior and Mechanical Properties of Bamboo Fiber Reinforced Concrete
Authors: Terai Masakazu , Minami Koichi
Published: September 2011

Fiber reinforced concrete is superior to plain concrete in toughness, which is the energy absorption at fracture. This study is intended to use fibers extracted from bamboo for tensile reinforcement of concrete. Some experiments were carried out to explore the possibility of bamboo fiber reinforced concrete. As a result, the compressive strength of concrete with 1-2% bamboo fiber is little different from the case without reinforcement. On the other, the splitting tensile and the flexural strength significantly increased with an increased volume fraction of fibers. The strength of bamboo fiber reinforced concrete increased with increasing fiber content as a result of fiber bridging.
The Scattering of SH-Wave Caused by Subsurface Circular Cavities in a Layered Half-Space
Authors: Chen Dong Ni , Qi Hui , Shi Yong
Published: September 2011

The scattering of SH-wave caused by the subsurface circular cavities in an elastic half-space covered with an elastic layer was discussed, which was based on the complex function method ,wave functions expansion method and big circular arc postulation method in which the circular boundary of large radius was used to approximate straight boundary of surface elastic layer. By the theory of Helmholtz, the general solution of the Biot’s wave function was achieved. Utilizing the complex series expansion technology and the boundary conditions, we could transform the present problem into the problem in which we needed to solve the infinite linear algebraic equations with unknown coefficients in wave functions. Finally, the dynamic stress concentration factors around the circular cavities were discussed in numerical examples.
Effect of Hydrogen on Mechanical Properties of Type 310S Stainless Steel
Authors: Takano Noriyuki , Kaidu Yutaka
Published: September 2011

It is known that type 310S stainless steel is insensitive to hydrogen embrittlement. Then, the effect of hydrogen on the mechanical properties has not been studied in detail. In the present work, SSRT was carried out under hydrogen cathodic charging condition. Elongation increased by hydrogen charging, while reduction of area decreased. A lot of micro-cracks were observed on the side surface of fractured specimens into which hydrogen was charged, while no cracks were observed on the side surface of fractured specimens without hydrogen charging. Micro-cracks were also observed on the surface of unloaded specimens that were annealed after hydrogen charging. Therefore, it is considered that cracks occur from the defects induced by hydrogen charging.
Study on Gradient-Dependent Nonlocal Damage Constitutive Models of Concrete under Freeze-Thaw Action
Authors: Liu Zong Min , Mao Ji Ze , Song Hai Yan , Chen Xue Dong
Published: September 2011

Concrete materials with a large number of micro-cracks were defined as inhomogeneous materials. And the mechanical properties of inhomogeneous materials were regarded as high-order deformation gradient dependent. Starting from the nonlocal thermodynamics theory and the hypothesis of total energy equivalence, the gradient-dependent nonlocal damage constitutive models of concrete under freeze-thaw action would be established in this paper.
Numerical Simulation of Series Experiments of Concrete Fracture
Authors: Deng Ai Min , Wang Xiang Dong , Xu Dao Yuan
Published: September 2011

With progress of the computer technology and numerical simulation method, the numerical simulation of the fracture process of concrete materials has become possible. In this paper, the numerical simulation models of the two types of samples were carried out with the SOLID65 concrete element based on the ANSYS software platform. According to the results, the non-linear characteristic of the concrete material exhibited in the loading process is reflected by the phenomenon that the slope of the later stage shows some reduction in the simulated load - loading point displacement curve. That is to say, the behavior of the appearance and development of cracks can be simulated with SOLID65 concrete element in ANSYS.
Potential of Shape Memory Complex Materials SMC as Welfare Equipment Actuator
Authors: Aoki Teruko , Fukunaga Keigo , Shimamoto Akira
Published: September 2011

Intelligent materials have been studied in various fields. In this study, Shape Memory Composite (SMC) is produced as one of those intelligent materials. SMC consists of Shape Memory Polymer (SMP) and Shape Memory Alloy (SMA). These two materials possess different characteristics in temperature changes. Therefore, we investigated the possibility of the SMC’s actuator function as an intelligent material. The actuator function is achieved by applying a current to SMA fiber of SMC to grab and release objects. As a result of this investigation, meaningful data for actuator to design SMC is obtained.
High Cycle Fatigue Parameters of High Chromium Steel
Authors: Drobne Matej , Göncz Peter , Glodež Srečko
Published: September 2011

The determination of monotonic mechanical properties and high cycle fatigue parameters of high chromium steel (HCS) is presented. The monotonic mechanical properties (ultimate compressive and ultimate tensile strength) are determined using standardized testing procedures according to DIN 50125 standard. The high cycle fatigue parameters are determined using uniaxial fatigue test where the tests specimens are loaded with pure pulsating compression load (load ratio R=0 in compression) at different load levels. Therefore, a typical S-N curve and appropriate fatigue parameters (fatigue strength coefficient sf’ and fatigue strength exponent b) are determined. The experimental results determined in this study can serve as a basis for the determination of service life of rolls using stress-life approach. However, a few guidelines for the further research work considering increased temperatures and multiaxial fatigue are given in the conclusions of this study.
Influence of Al-Si Diffusion Coating on Low Cycle Fatigue Properties of Cast Superalloy Inconel 738LC at 800 °C
Authors: Juliš Martin , Obrtlík Karel , Hutařová Simona , Podrábský Tomáš , Polák Jaroslav
Published: September 2011

High temperature low cycle fatigue behaviour of cast nickel-based superalloy Inconel 738LC in as-received condition and coated with an Al-Si diffusion layer was studied. The Al-Si protective layer was deposited on the gauge section of cylindrical specimens using the slurry technique. Fatigue tests were performed on cylindrical specimens under total strain control in symmetrical cycle at 800 °C in air. The coating has a beneficial effect on fatigue life in the low amplitude domain. The stress response of the coated material is higher for high amplitudes in comparison with the uncoated one. Fracture surfaces and sections parallel to the specimen axis have been examined to study fatigue damage mechanisms.
Effect of Friction Stir Welding Condition on Fatigue Limit of Welded Non-Combustible Mg Alloy
Authors: Hayashi Komei , Hamada Shigeru , Shigematsu Ichinori , Sakamoto Michiru , Noguchi Hiroshi
Published: September 2011

The atigue strength of Friction Stir Welding is affected by the structure and the welding defect size. The welding defect sizes have a scatter. Therfore, the effect of Friction Stir Welding condition on fatigue limit of welded noncombustible Mg alloy was investigated with the specimen which has a controlled defect size. As a result, the good correlation between the fatigue limit and the hardness of the welding area was clarified.
Residual Stresses in As-Welded Joints: Finite Element Modeling and Neutron Difraction Stress Measurements
Authors: Acevedo Claire , Drezet Jean Marie , Lefebvre J. P. , D'Alvise Laurent , Nussbaumer A.
Published: September 2011

This paper describes the numerical analysis method used to estimate welding induced residual stresses in K-shape tubular bridge joints. The knowledge of residual stress distribution is required to design the geometry of K-joints loaded under fatigue stresses. Numerical simulations are focused on the arc welding MAG process, generally used to weld joints in bridge construction. Thermo-mechanical analyses are performed in 3D using two finite element codes:ABAQUS® and MORFEO® . ABAQUS has the advantage to offer large analysis capabilities(nonlinear, transient, dynamic, etc.) whereas MORFEO is more dedicated to welding processes and offers the possibility to analyze crack propagation under fatigue loads. Computed residual stresses in the region surrounding the weld are compared with measured residual stresses in order to estimate the ability of the codes to reproduce these stresses. Position, orientation and magnitude of the highest residual stress components are discussed.
Application of the Θ-Method to 3D BEM Analysis of Cracks in Piezoelectric Components
Authors: Wippler Karsten , Kuna Meinhard
Published: September 2011

A general purpose direct BEM code has been developed for three-dimensional crack problems in piezoelectric structures. Special 3D non-continuous crack tip elements and several techniques for determining crack tip parameters were implemented. To calculate the electromechanical energy release rate for a virtual crack extension, the θ-method is employed, which was originally suggested by BONNET for linear elastic materials. The paper presents the generalization and numerical realization of the θ-method to 3D piezoelectric cracks. The great advantage of the θ-method is the direct computation of energy release rate, whereas the way via K-factors and the IRWIN matrix is more complicated. The efficiency and accuracy of the technique are shown for various example problems by comparing with analytical solutions.
The Influence of the Weld Width on Fracture Behaviour of the Heterogeneous Welded Joint
Authors: Konjatić Pejo , Kozak Dražan , Gubeljak Nenad
Published: September 2011

Since welded constructions are widely used in engineering, a certain flaws in welded joints may occur either in process of welding or in exploitation period. Easiest way to prolong working life of such welded construction is to repair welded joint to eliminate possibility of construction failure. Process of repair welding usually gives heterogeneous welded joints because during process of repair additional material is introduced into welded joint, resulting in heterogeneity from the presence of materials in welded joint point of view. Such difference in materials usually results in yield strength difference between materials, represented with mismatch ratio, and it is commonly present in welds where high strength low-alloyed (HSLA) steels were welded. Since I butt welded joints are very common in welding, a systematic investigation of such welds is performed and presented in this paper. Therefore in this investigation the influence of present material in heterogeneous weld and geometry of weld is investigated in context of fracture resistance of welded joint represented as yield load solutions in the first place. A flaw in form of crack was implemented in such heterogeneous weld and using finite element method yield load solutions for different combinations of weld geometry and material strength are obtained and presented in form of diagrams.
Flexural Wave Scattering by Double Elliptic Holes in an Infinite Thin Plate
Authors: Li Hong Liang , Guo Jing , Shao Xiao Hua
Published: September 2011

In mechanical engineering and aerospace engineering, thin plate structure is used widely. For the sake of fixing bolt, it often design open holes in the plate. Sometimes elliptic holes should be used inevitably. When the plate is overloaded or the load is changed regularly, flexural wave is propagating in the plate. Because there are holes, it can cause stress concentration. Stress concentration could decrease the bearing capacity of structure, and reduce the service life of structure. The problem of flexural wave scattering by holes in the plate is one of the important and interesting questions in aerospace engineering for the latest decades. There are lots of materials obtained by theoretical research and experimental investigation. The problem is complicated, because there are many factors influenced. It is hard to obtain analytic solutions except for several simple conditions. In this paper, based on the theory of elastic thin plate, by using wave function expansion method and multi local complex coordinates, scattering of flexural wave and dynamic stress concentration by double elliptic holes in the thin plate are investigated. In the complex plane, the displacement field aroused by incident wave and the scattering displacement field impacted by double elliptic holes comprised of Fourier-Bessel series with undetermined coefficients are constructed. Through applying the method of multi local complex coordinates, the equations with unknown coefficients can be obtained by using the stress-free condition of the double elliptic holes in the radial direction. According to orthogonality condition for trigonometric function, these equations can be reduced to a series of algebraic equations. Then the value of the unknown coefficients can be obtained by solving these algebraic equations. So the analytical solution of this problem is obtained. By using the displacement and stress expressions, an example is provided to show the effect of the change of relative location of the elliptic holes.
Effect of an Internal Open Crack on Pipes Wave Propagation
Authors: Marzani Alessandro , Miniaci Marco , Viola Erasmo
Published: September 2011

Stress guided waves in the sonic and ultrasonic regime are acknowledged as a powerful too lto inspect pipes in a non-invasive manner.A key point of the inspection procedure is related to the dispersive behavior of guided waves, that for agiven pipe is deﬁned by the so-called dispersion curves. Such behavior, is generally predicted bymeans ofanalytical formulations. However, when the geometry of the pipe cross-section is not axially symmetric,such as in the presence of an open internal crack running along the pipe length, analytical formulations fail. Here, the computation of the guided waves properties for such a scenario is addressed via a SemiAnalytical Finite Element (SAFE) formulation in which the open crack is modeled at the mesh level.Different crack depths are considered and their effect on the waves dispersion curves are highlighted.The results could be of interest in pipeline inspection and monitoring.
Cracks Interaction Effect on the Dynamic Stability of Beams under Conservative and Nonconservative Forces
Authors: Viola Erasmo , Fantuzzi Nicholas , Marzani Alessandro
Published: September 2011

This study is an extension of the paper by E. Viola and A. Marzani [1] where the eigenfrequencies and critical loads of a single cracked beam subjected to conservative and nonconservative forceshave been investigated. Here the aim is to analyze the dynamic stability of T cross section beams withmultiple cracks. A doubly cracked Euler-Bernoulli beam subjected to triangularly distributed subtangential forces, which are the combination of axial and tangential forces, is considered. The governingequation of the system is derived via the extended Hamilton’s principle in which the kinetic energy, theelastic potential energy, the conservative work and the nonconservative work are taken into account. Thelocal ﬂexibility matrix for a beam with T cross-section is used to model the cracked section. The resultsshow that for given boundary conditions cracked beams become unstable in the form of either ﬂutter ordivergence depending on the crack parameters, the nonconservativeness of the applied load as well as theinteraction of the two cracks.
Comparison of Solutions of Stress Field Based on Hertzian and Combined Numerical-Crystallographic Approaches Beneath Nanoindenter
Authors: Horníková Jana , Šandera Pavel , Pokluda Jaroslav
Published: September 2011

Nanoindentation is considered to be a very promising experimental approach to measuring the ideal shear strength since the stressed volume beneath the sharp indenter may be defect-free. The local shear component of the stress reaches its maximum value at some close distance from the indenter in the bulk. The value of the stress can reach the ideal shear strength and, consequently become high enough to nucleate dislocations. This process might be detected as a pop-in on the nanoindentation load-displacement curve. To model the nanoindentation test for that purpose, three different approaches have been used in this works. The first approach is based on the analytical Hertzian solution of the stress field beneath the nanoindenter where only a continuum mechanics is taken into account. The second concept is based on the numerical solution without crystallographic considerations and the third one respects the fact that the dislocation generation in the substrate is subjected to crystallographic rules. The aim of this article is to compare all these concepts by their application to the nanoindentation process performed on selected bcc and fcc metallic substrates.
Advanced Finite Element Analysis to Predict Off-Axis Crushing Behaviour of Composite Aero-Structures
Authors: Ghafari-Namini N. , Ghasemnejad H. , Limbachiya M.
Published: September 2011

Advanced finite element analysis (FEA) is carried out to simulate the off-axis crushing process of glass/epoxy twill/weave composite box structures. The FE results were compared to relevant experimental result and it was shown that the applied model is capable to predict the damage behaviour and energy absorption of composite box aero-structures under off-axis loading condition.
Effect on the Alkali-Activator Mixing Ratio of Geopolymer Mortar Using Bottom Ash
Authors: Kim Si Hwan , Ryu Gum Sung , Koh Kyung Taek , Kang Su Tae , Lee Jang Hwa
Published: September 2011

This Study purposed to review on the strength of geopolymer mortar and the change in liquidity depending on the mixing ratio of alkali-activator in developing the geopolymer mortar using bottom ash as binder. Alkali-activator was used through mixing 9M-Sodium hydroxide (SH) and 3 kinds of Sodium sillicate(SS) and its strength was measured by material age after curing for 48 hours at 60°C. As a result, the pressure strength was shown as 40MP when the mass ratios of 9M-Sodium hydroxide and 3 kinds of Sodium sillicate were35 vs. 65 and 50 vs. 50, but the solution of the mass ratio of 50 vs. 50 showed the rapid solid phenomenon in the process of mortar manufacturing, thereby disadvantage in construction. In addition, in case of storing the mixed solution in room temperature, as the mix ratio of 9M-Sodium hydroxide increases, the solution solidified. Accordingly, when considering on strength, liquidity and storage, it’s most preferable to fix the mass ratio of 9M-Sodium hydroxide and 3 kinds of Sodium sillicate at 35 vs. 65.
Research on Acoustic Emission Test Method for Metal Fatigue Fracture Based on Wavelet Packets Feature Extraction
Authors: Wang Qi , Chen Yin Sheng , Song Kai
Published: September 2011

The appearance and growth of the microcracks in the structure is an important factor that influences the structure safety and its service life. Thus it is very important to detect the crack and monitor its growth at the beginning of the crack. Aiming at the main style of failures in metal structure - fatigue fracture, this paper research acoustic emission waveforms analysis that base on wavelet packets feature extraction, through processing acoustic emission signal to test metal fatigue fracture. First, this paper analyses the reason of metal fatigue fracture and introduces the theory of acoustic emission. Based on that, we establish the time domain module of acoustic emission signal and extract the feature of acoustic emission signal using wavelet packets. According to the experimental results bending specimen, acoustic emission techniques monitoring fatigue crack propagation is certificated not only to resemble variable rule of fatigue crack propagation but also to catch generation of fatigue crack in real time. Compared with the method of parameter extraction, this method can not only realize real-time and dynamic monitoring, but also get the result that is similar with fatigue crack expanding rate curve.
Numerical Simulation of Multiple Fatigue Crack Growth with Additional Crack Initiation
Authors: Holländer Dirk , Wünsche Michael , Henkel S. , Theilig Holger
Published: September 2011

In this paper, advanced numerical simulations of curved crack growth in the case of mul­tiple crack systems in combination with the analysis of the plastic limit load by the lower bound theorem of plasticity are presented. In order to take additionally initiated cracks during the crack growth process into account, the numerical simulation algorithm has been extended by using the Smith-Watson-Topper (SWT) parameter in combination with a linear fatigue damage accumula­tion.
Elastic-Viscoplastic Field at the Mixed-Mode Crack-Tip under Compression and Shear
Authors: Liang Wen Yan , Wang Zhen Qing , Liu Fang
Published: September 2011

In the present paper, the mechanical model of dynamic propagation interface crack of the compression-shear mixed mode is proposed by using the elastic-viscoplastic constitutive model. Then the governing equations of propagation crack interface at crack tip are given. The numerical analysis is accomplished for the interface crack of compression-shear mixed mode by introducing a displacement potential function and some boundary conditions at interface crack tip. The distributed regularities of stress-strain fields of interface crack tip are discussed with several special parameters. The numerical results show that the viscosity effect is a main factor of interface propagating at crack-tip field, and the interface crack-tip is a viscoplastic field that is governed by viscosity coefficient、Mach number and singularity exponent.
Investigation on Damage Tolerance of Carbon/Epoxy Laminate for Aircraft Structural Design
Authors: Park Hyun Bum , Kong Chang Duk , Lee Kyung Sun
Published: September 2011

In Korea, the KC-100, which is a small scale piston propeller general aviation aircraft, has been developed to establish a domestic certificate infrastructure and system through the BASA(Bilateral Aviation Safety Agreement) program by KAI(Korea Aerospace Industries, Ltd.). This aircraft adopted the whole composite structure concept for an environmental friendly aircraft through low fuel consumption due to structure weight reduction. However the carbon/epoxy composite structure, which is mainly used for this aircraft, is very weak against foreign object damage. Therefore the purpose of the damage tolerance design philosophy is to ensure that the aircraft can operate safely for a period of time with damage present within the airframe. This study is to investigate the residual compressive strength of the carbon/epoxy UD and fabric laminate due to impact damages. Through investigation on compressive strength, design allowable of carbon/epoxy laminate is determined by the experiment to address design criteria of the composite structure.
Damage Analysis of Concrete Subjected to Freeze-Thaw Cycles and Chloride Ion Erosion
Authors: Mao Ji Ze , Zhang Zhi Yuan , Liu Zong Min , Sun Chao
Published: September 2011

With the development of damage mechanics, many researchers have used it to analyze the constitutive equation of concrete. Since the special environment in the cold marine regions, the offshore structures are common to subject to the comprehensive effects of freeze-thaw action and chloride erosion. This might cause concrete materials degradation and reduce the mechanical performance of concrete seriously. In this paper, based on the analysis and mechanical experiments of concrete materials under the comprehensive effects of freeze-thaw action and chloride ion erosion, the damage evolution equation of concrete elastic modulus along with the freeze-thaw cycles and chloride ion contents was established. The effects of chloride ion were investigated during the process of concrete degradation. According to the damage evolution equation, a new constitutive equation of concrete under freeze-thaw action and chloride erosion was established. And then, by means of the element simulation analysis of concrete beams when subjected to the comprehensive actions, the feasibility and applicability of the equation was examined and discussed. In this equation, both the freeze-thaw action and chloride ion erosion were considered together. It will be more suitable for analyzing the durability of concrete structures in the real cold marine regions. It will also provide some references for concrete constitutive theory.
The Effect of Nonlinear Matrix on Crack Propagation in the Particulate Composite
Authors: Majer Zdeněk , Hutař Pavel
Published: September 2011

In this paper polymer particulate composite was studied. The composite was modeled as a three-phase continuum – soft matrix, interphase and rigid particles. On the basis of fracture mechanics methodology the interaction of micro-crack propagation in the soft matrix filled by rigid particles (covered by the interphase) was analyzed. The properties of soft matrix (elasto-plastic material) were determined from the experiment and they were used for estimations of the crack behavior.
Lamb-Wave Based Technique for Impact Damage Detection in Composite Stiffened Panels
Authors: Sharif-Khodaei Z. , Rojas-Diaz Ramon , M.H.Aliabadi Ferri
Published: September 2011

The propagation characteristic of Lamb waves activated by Piezoelectric actuators and collected by sensors in a stiffened panel has been investigated. A network of actuators is used to scan the structure before and after the presence of damage. A diagnostic imaging algorithm has been developed based on the probability of damage at each point of the structure measured by the signal reading of sensors in the benchmark and damaged structure. A damage localization image is then reconstructed by superimposing the image obtained from each sensor-actuator path. Three-dimensional finite element model with a transducer network is modeled. Damage is introduced as a small softening area in the stiffened panel. Applying the imaging algorithm, the damage location was predicted with good accuracy. This method proves to be suitable for stiffened panels, where the complicated geometry and boundary reflections make the signal processing more complicated.
Fatigue Behaviour of Notched Ti-6Al-4V in Inert Environment
Authors: Baragetti Sergio , Cavalleri Stefano , Tordini Federico
Published: September 2011

This work focuses on the fatigue behaviour of notched Ti-6Al-4V titanium alloy in inert environment. V-notched flat samples were cycled under axial fatigue (R = 0.1) under inert conditions by immersion in paraffin oil. A step-loading technique was used to determine the fatigue limit at the complete fracture for a constant fatigue life of 2×105 load cycles. The results were compared with previous data obtained with tests carried out in air and 3.5 wt.% NaCl solution. Fracture surfaces were examined under stereoscopic microscope.
A Comprehensive Study of the Performances of PVD WC/C-Coated Racing Gears
Authors: Baragetti Sergio , Cavalleri Stefano , Tordini Federico
Published: September 2011

In this work a preliminary data set including experimental results from fatigue tests on smooth and foreign object damaged (FOD) aluminium samples coated with WC/C deposited with PVD (physical vapour deposition) technique was considered before testing WC/C-coated spur gears for racing motorcycles under rolling contact fatigue (RCF). The fatigue behaviour of the samples was correlated with the results obtained with the RCF tests on the coated gears. A special device mounted on a universal testing machine was used to carry out the RCF tests.
Fracture Analysis of Cube- and Cylinder-Shaped WST Specimens Made of Cementitious Composites with Various Characteristic Length
Authors: Řoutil Ladislav , Veselý Václav , Seitl Stanislav
Published: September 2011

The paper is focused on finding reasonable proportions for both cube-shaped and cylinder-shaped silicate-based composite specimens subjected to wedge-splitting tests. The analysis is conducted using finite element method code with an implemented cohesive crack model. The aspect of the material’s brittleness, related to the heterogeneity of the material and described by what is termed as the characteristic length of quasi-brittle material, is accented. The results yield some recommendations for the determination of parameters of nonlinear fracture models for cementitious composites by means of wedge splitting tests of laboratory specimens of the two standard shapes.
Dynamic Behavior of Granular Mixture Solids
Authors: Buonsanti Michele , Leonardi Giovanni , Scoppelliti Francesco , Cirianni F.
Published: September 2011

In this paper a theoretical and numerical study of impulsive loads over a granular medium free surface has been developed. We will model a real case, as a high deformable solid impacting a less deformable surface, and consequently subject to micro and macro medium failure. Developing a macroscopic approach we resolve the macro-stress in the homogenized two-dimensional medium and subsequently apply a representative volume element (RVE) analysis modeling to the micro-scale. The problem is developed by energetic approach on an elasto-plastic element using an energy functional containing bulk and surface contributions. Finally, a numerical application is presented.
Load Sequence Effect on Fatigue Damage
Authors: Xu Y.G. , Wang L. , Chen Y. , Tiu W.
Published: September 2011

Reliable damage tolerant design of airframe structures relies on the accurate life prediction of fatigue cracks propagating from a detectable size to the critical size, which is challenging due to the complex load sequence effect under spectrum loading. This paper aims at gaining a further understanding of the complex influence of the loading history on fatigue damage through a detailed numerical simulation of the near-tip crack behaviour using the crack closure concept. The spectrum loading is broken down into a number of simple yet representative loading scenarios with overload/underload superimposed onto the baseline constant amplitude fatigue loading. Detailed finite element (FE) simulation of the plasticity-induced crack closure (PICC) has been carried out to catch the transient behaviour of PICC and link it to the fatigue damage. The load interaction effect has been analysed with the aim to identify the possible dominant loading cycle which could simplify the fatigue life prediction process in the industry. It is concluded that more reliable damage tolerant design can be achieved if the load sequence effect on fatigue damage can be taken into account more accurately for a structure under spectrum loadings.
Energy Absorption Capabilities of a Square Tube System
Authors: Caputo Francesco , Lamanna Giuseppe , Soprano Alessandro
Published: September 2011

In the present paper the authors refer about a series of experimental tests, where an aluminium alloy square tube, filled with an aluminium foam, was crushed by a longitudinal load at a speed of 10 m/s. The test apparatus consisted of a sled installed on a very stiff frame moving on appropriate guides, as the specimen was set on a home-made fixture. Two arrangements of square tubes were considered as specimens: a “standard” one and an “optimized” one. Both crushing behaviours and energy absorption capabilities were analyzed experimentally and numerically simulated by means of the explicit FE code LS-DYNA®; the complete numerical model consisted of the striker, the assemblage of square tubes and the base. A high-speed video recording system was used to capture the images from the physical test. The results from the numerical analyses were compared to those obtained from the experiments: those results showed that the force–deﬂection response had been overestimated by the numerical model. The authors attempted to justify this inconsistency by considering the influence of the strain rate parameters of the considered Cowper-Symonds analytical model on the results. It was shown that the “optimized” energy absorber exhibited a more desirable force–deﬂection response than the standard one due to some easy design changes, which involved the insertion of aluminium foam dampers.
The Influence of Short Glass and Polypropylene Fibers on First Crack Formation and Toughness of Cement Based Composites after their Exposure to Fire Conditions
Authors: Pandermarakis Zacharias G. , Sotiropoulou Anastasia B. , Nikoloutsopoulos Nikolaos D.
Published: September 2011

The influence of glass and polypropylene short fiber addition on fracture response of cement based composites after their exposure to high temperatures up to 900°C and for time intervals up to 2 hours was investigated during this study. These conditions simulate adequately closed those of a common real fire exposure. Measurements of their bending and compressive strength and also of ultrasonic wave propagation before and after their burning were carried out. Three distinct response zones are appeared that arise mainly by the incoming chemo-physical changes of constituents due to the attainment of remarked temperature levels. These changes involve the evaporation of physically bounded water in pores and paste in the region of 100°C, the de-hydration of calcium hydroxide of cement paste in the region of 400°C and the decomposition of calcium carbonate of limestone aggregates in the region of 900°C. The fiber addition at common level volume percentage of about 0.3 %, improve only slightly their fracture features –as first crack formation, energy absorption, even their strength– up to 300 - 400°C after of which this addition appears to have opposite effects. The essential changes seem to concern the improved cohesive features of cement based composites and the desired benefits arise mainly by ensuring better conditions for their durability and the restriction of their fragmentation and brittleness leading to a tougher future response.
Characterisation of the Fracture Energy and Toughening Mechanisms of a Nano-Toughened Epoxy Adhesive
Authors: Mc Auliffe D. , Karač A. , Murphy Neal , Ivanković Alojz
Published: September 2011

In this study the adhesive joint fracture behaviour of a nano-toughened epoxy adhesive was investigated. Two experimental test methods were used; (i) the standard tapered double cantilever beam (TDCB) test to measure the mode I adhesive joint fracture energy, GIC, as a function of bond gap thickness and (ii) a circumferentially deep notched tensile test to determine the cohesive strength of the adhesive for a range of constraint levels. It was found that the fracture energy of the adhesive followed the well-known bond gap thickness dependency [1]. SEM analysis of the TDCB fracture surfaces revealed significant plastic void growth. Finally, numerical modelling of the experimental tests suggested that most of the fracture energy was dissipated via highly localised plasticity in the fracture process zone ahead of the crack tip.