bluuebunny/crossref_metadata_2025 huggingface dataset:
Quasi-Static Simulation of Crack Growth in Elastic Materials Considering Internal Boundaries and Interfaces
Authors: Judt P. , Ricoeur Andreas
Published: November 2012

This work presents numerical methods used for predicting crack paths in technicalstructures based on the theory of linear elastic fracture mechanics. The FE-method is usedin combination with an efficient remeshing algorithm to simulate crack growth. A post pro-cessor providing loading parameters such as the J-integral and stress intensity factors (SIF) ispresented. Path-independent contour integrals are used to avoid special requirements concern-ing crack tip meshing and to enable efficient calculations for domains including interfaces andinternal boundaries. In particular, the interaction of cracks and internal boundaries and inter-faces is investigated. The simulation combines crack propagation within elastic bodies and atbi-material interfaces. The latter is based on a cohesive zone model. The presented numericalresults of crack paths are verified by experiments.
Computational Characterization of Micro-To Macroscopic Deformation Behavior of Double Network Hydrogel
Authors: Riku Isamu , Mimura Koji
Published: November 2012

To take advantage of the toughness mechanism of DN gels and explore the possibility for engineering application as the structural member, the information on the mechanical behaviour of DN gels under various loading conditions is indispensable. Therefore, in this paper, we at first constitute a model of DN gel by paralleling a slider element with a nonlinear rubber elasticity spring element based on the nonaffine molecular chain network model, where each element represents the first and the second network of DN gel respectively. The theoretical stress-strain relation of this model shows a strain softening and subsequent strain hardening response, which has been considered as an agent of the propagation of the necking during the simple tension of glassy polymer. Continuously, based on this model, we propose a constitutive equation for DN gel and a three-dimensional simple tension simulation is performed. The computational results show that the propagation of the necking together with the macroscopic mechanical response of DN gel can be reproduced by the proposed model very well.
Multilevel/Multiobjective Design of Composite Structures
Authors: Bacarreza Omar , Aliabadi M.H. , Apicella A.
Published: November 2012

A multilevel multiobjective platform for structural sizing reproducing the sequence of actions taken during design and structural sizing in industry is presented in this paper. This platform is integrated at two design levels labeled as Preliminary Design Level and Detailed Design Level. The set of design variables can be divided into a group of variables describing the main conceptual layout that affect the dimensions and architecture of the model and a second group of variables influencing the material and mechanical behavior. This kind of approach can be effective if it is possible to separate the constraints that are strongly dependent on the design variables of different design levels.
Micro-Analyses of Small Cracks in 6061-T6 Aluminium Alloy Subjected to High-Cycle Fatigue
Authors: Takahashi Yoshimasa , Shikama Takahiro , Noguchi Hiroshi
Published: November 2012

The growth of a small crack controlling the high-cycle fatigue life of a precipitation-strengthened 6061-T6 aluminium alloy was critically investigated. As the applied stress lowered, the small crack was arrested for a long period (over 106cycles) at grain boundaries before regrowth, which resulted in a significantly slow growth process. The morphological and crystallographic details of the small crack were then analyzed with focused ion beam and transmission electron microscopy. It was revealed that the small crack was formed along fine persistent slip bands (PSBs) whose structure was fairly different from that reported for other metals. The concept of PSB-limited fatigue strength may be extended to include the present material type.
Structural Design and Finite Element Analysis of Composite Wind Turbine Blade
Authors: Zhu Shi Fan , Rustamov Ibrohim
Published: November 2012

This paper presents structural studies of a medium scale composite wind turbine blade construction made of epoxy glass fiber for a 750kW rated power stall regulated horizontal axis wind turbine system. The complex geometry of the blade with a skin-spar foam sandwich structure was generated by utilizing commercial code ANSYS finite element package. Dimensions of twist, chord and thickness were developed by computer program. NREL S-series airfoils with different chord thickness are used along current blade cross-sections. The current design method uses blade element momentum (BEM) theory to complete satisfactory blade design and can be carried out using a spreadsheet, lift and drag curves for the chosen aerofoil. According to composite laminate theory and finite element method, optimal blade design was obtained. The focus is on the structural static strength of wind turbine blades loaded in flap-wise direction and methods for optimizing the blade cross-section to improve structural reliability. Moreover, the natural frequencies and modal shapes of the rotor blade were calculated for defining dynamic characteristics. Structural analysis was performed by using the finite element method in order to evaluate and confirm the blade to be sound and stable under various load conditions.
Simulation of Pylon Emergency Break-Away of Large Commercial Aircraft
Authors: Zhang Xin , Li Yu Long
Published: November 2012

Most large commercial aircraft engines are hanged below wings. When the aircraft makes an emergent landing process, at the same time, the landing gear cannot work or the centrifugal force becomes unbalanced as the fan blades fly away. In order to ensure safe landing, overall tank crack and fuel leak should be avoid at the crack area.
Access to a large number of emergent landing accidents, emergency break-away is essential. In this paper, the break-away position, which locates between the pylon and the wing, is mainly considered. We choose true size in the models of wing, pylon and engine. High strength steel is employed for the bolts which connect pylon and wing. Earth and lake are employed concrete and pure water respectively. SPH method is applied in the case that the aircraft lands on the lake. Whats more, different landing cases have been analyzed. By constantly adjusting the size of pins, a set of conclusions of the emergent landing problem are obtained in the simulation process. The locus of centroid of engine and pylon is obtained, and then the condition which may achieve safe flight and avoid the secondary damage to wings can be chosen, from which we can provide reasonable designing strength of the wing box and accordingly provide reference for the design of aircraft structure.
Dynamic Mechanical Behavior of Two Fiber-Reinforced Composites
Authors: Guo Y.Z. , Chen X. , Wang Xi Yun , Tan S.G. , Zeng Z. , Li Yu Long
Published: November 2012

The mechanical behavior of two composites, i.e., CF3031/QY8911 (CQ, hereafter in this paper) and EW100A/BA9916 (EB, hereafter in this paper), under dynamic loadings were carefully studied by using split Hopkinson pressure bar (SHPB) system. The results show that compressive strength of CQ increases with increasing strain-rates, while for EB the compressive strength at strain-rate 1500/s is lower then that at 800/s or 400/s. More interestingly, most of the stress strain curves of both of the two composites are not monotonous but exhibit double-peak shape. To identify this unusual phenominon, a high speed photographic system is introduced. The deformation as well as fracture characteristics of the composites under dynamic loadings were captured. The photoes indicate that two different failure mechanisms work during dynamic fracture process. The first one is axial splitting between the fiber and the matrix and the second one is overall shear. The interficial strength between the fiber and matrix, which is also strain rate dependent, determines the fracture modes and the shape of the stress/strain curves.
The Sensitivity of the Foam-Core Parameters under Impact Loading
Authors: Xu Fei , Duan Min Ge
Published: November 2012

This study presents the numerical investigation of the low-velocity impact for the foam-cored sandwich composites. Firstly, the proposed FEA model is validated by comparing the results between simulation and test. The user subroutine VUMAT and the crushable foam model are chosen to describe the damage of the face sheets and the characteristics of the foam material, respectively. The detailed damage process of the sheets and the foam is clearly shown. The sensitivity of seven parameters related to foam-core material are studied. It is shown that the yield strength, the fracture strain and the fracture displacement have significant effects on the impact-resistance of the foam-cored sandwich composites.
The Conservation Laws and Path-Independent Integrals for Piezo-Magnetic Media
Authors: Song Hai Yan , Zhou Jian Sheng , Liu Zong Min
Published: November 2012

Path-independent integrals have important application value in dislocation, fracture mechanics and other defects theories. Motivated by concepts of Jacobi integral and cyclic integral in analytical mechanics and energy-momentum tensor in electro-magntic field, the conservation laws and path-independent integrals for piezo-magnetic media are derived in this paper.
Study on Mode I Quasi-Static Growing Crack in a Rigid-Viscoelastic Material Interfacial Crack
Authors: Yang Yong , Yang Zai Lin , Tang Li Qiang
Published: November 2012

Under high temperature, many metals show viscoelastic properties, which are closely related to environmental factors and strain rate. Engineering practice also shows that time-dependent deformation of materials have great effects on the structural strength, rigidity and life duration. So visco-elasticity has drawn much attention in the mechanical and engineering fields.
Analysis of Interface Deformation of Steel-Concrete-Steel Sandwich Beam
Authors: Xia Pei Xiu , Zou Guang Ping , Chang Zhong Liang
Published: November 2012

The effect of the interface slip is neglected in most studies on calculating deflection of sandwich beams. By taking a simply supported sandwich beams under uniformly distributed loads as an example, simplified analytical models of the interface slip are established, and corresponding clculation formulas of interface slip between steel panels and concrete and section curvatures are derived. The formula for deflection of sandwich beams are then presented. This formula reflects the relationship of influence each other between the interface slip and deflection.
Numerical Simulation of Compressive Residual Strength for Damaged Composite Laminates
Authors: Qu Tian Jiao , Zheng Xi Tao , Zhang Di
Published: November 2012

After the low-velocity impact test of composite laminates of T800/BA9916, CAI test and compression test of laminates with a hole have been carried out. Two types of models were set up by the finite element software ABAQUS respectively. The FEA results were good agreement with the testing results. The investigation of models with a hole indicates that the appearance time of ultimate compressive load is earlier than that of fiber breakage expanding to boundary. Moreover, the diameter and the depth of blind hole significantly influence the ultimate compressive load.
A Research on Characterization for Damage Tolerance of Composite Laminates
Authors: Zhang Di , Zheng Xi Tao , Cheng Li Nan
Published: November 2012

This paper mainly presents a method that can characterize the damage tolerance capability of composite laminates based on the knee-point feature. Based on the experimental study and numerical result, the Knee-point mechanism has been investigated. A new influence coefficient, δ, was introduced, which is applied to calculating the influence of every piles damage to the residual strength of the whole laminates. Finally, a conclusion can be drawn that the damage of 0° piles can represent the damage of the whole laminates, whilst the damage area of 0° piles can be applied to characterizing the damage tolerance capability of composite laminates.
Analysis of Crack Arrest by Electromagnetic Heating in Metal with Oblique-Elliptical Embedding Crack
Authors: Fu Yu Ming , Zhou Hong Mei , Wang Jun Li , Zheng Li Juan
Published: November 2012

Ellipse crack tip can be passivated when pulse current is perpendicular to crack surface of metal structure which can achieve the purpose of crack. In practice, it is hard that the loading current direction perpendicular to the crack surface because of the crack existence of different position and orientation. Theory and numerical simulation analyze the effect of crack arrest by electromagnetic heating based on metal structure with oblique-elliptical embedding crack. And current density and temperature distribution of crack tip are derived. The result shows that due to heat concentration around the oblique-elliptical embedding crack tip, the crack tip temperature exceeds the melting point of materials and small welded joints are formed by metal melting. Thermal compressive stress which is generated near the crack tip can prevent the crack propagation effectively. Thus, electromagnetic heating is proved to be an effective method of preventing general crack propagation.
Effects of Surface Roughness on the Fatigue Life of Alloy Steel
Authors: Xiao W.L. , Chen H.B. , Yin Yan
Published: November 2012

Surface roughness characterizes the micro-geometric appearance variation and significantly affects the fatigue properties of machined specimen. Low cycle fatigue (LCF) tests of alloy steel specimens with different surface roughness were carried out in this paper to investigate the effect of roughness on fatigue life. The dumbbell plate specimens were tested in uniaxial stress-controlled mode on the hydraulic servo machine at room temperature. Obviously discrepant lifetime results corresponding to different surface roughness implied that the greater the roughness was, the lower the fatigue life was. An approximate power function relationship between the roughness and the fatigue life was established through the fitting of the experimental data.
Experimental Research on Fracture Toughness of High Grade Line Pipe
Authors: Xiong Qing Ren , Zhang Jian Xun , Feng Yao Rong , Wang Hai Tao , Ma Qiu Rong , Xu Zhen Zhen
Published: November 2012

Crack tip opening displacement (CTOD) tests were carried out on different positions of X70, X80 and X100 pipe by three-point bend testing method. The results show that the crack propagation resistance and the tear modulus of base metal, heat affected zone (HAZ), and weld of X70 and X80 pipe are larger than that of X100 pipe. At the same time,The initial CTOD values and the CTOD values withmaximum load of X70 and X80 pipe are larger than that of X100 pipe.The test results suggest that the fracture toughness, crack initiation and propagation resistance of theX70 and X80 pipe are greater than that of X100 pipe, and the mechanismis analyzed finally.
The Research on Wood Fiber/Stainless Steel Net Electromagnetic Shielding Composite Board
Authors: Su Chu Wang , Yuan Quan Ping , Gan Wei Xing , Huang Jing Da , Huang Yuan Yi
Published: November 2012

In this paper, the electromagnetic shielding function composite fiberboards were made by filling with stainless steel nets dipped with urea-formaldehyde resin adhesive (UF) and the influence of different mesh and layers of nets on its electromagnetic shielding performance, static bending strength (MOR), modulus of elasticity (MOE) and internal bonding strength (IB) were studied. The results showed that: when the mechanical strength was enough and the frequency was in range of 50MHz to 1GHz, of all the composite fiberboards filled with one-layer stainless steel net, the one filled with 60 mesh was best and the minimum shielding effectiveness (SE) was 36.22 dB; when filled with two-layers nets, the one filled with 80 mesh was best and the minimum SE was 42.54dB; when filled with three-layers nets, the one filled with 60 mesh was best and the minimum SE was 50.77dB.
An Evaluation on the Restrained Shrinkage of Ultra-High Performance Concrete
Authors: Park Jung Jun , Yoo Doo Yeol , Kim Sung Wook , Yoon Young Soo
Published: November 2012

Since ultra-high performance concrete (UHPC) is subject to large occurrence of shrinkage at early age due to its low water-to-cement ratio, the mixing of large quantities of powdered admixtures and the absence of coarse aggregates, UHPC presents large risks of shrinkage cracking caused by the restraints provided by the form and reinforcing bars. Accordingly, this study intends to evaluate the shrinkage behavior of UHPC under restrained state by performing restrained shrinkage test using ring-test. The test results reveal that increasing thickness of the inner ring increases the tensile creep at early age leading to the reduction of the average strain and residual stress of the inner ring.
Size Effect of PHE Prototype on High-Temperature Structural Integrity
Authors: Song Kee Nam
Published: November 2012

PHE (Process Heat Exchanger) is a key component for transferring the high-temperature heat generated from a VHTR (Very High Temperature Reactor) to a chemical reaction for massive production of hydrogen. Recently, Korea Atomic Energy Research Institute (KAERI) has manufactured a small-scale and a medium-scale PHE prototype made of Hastelloy-X of high-temperature alloy and a performance test on the PHE prototype is scheduled in a small-scale nitrogen gas loop established at KAERI. In this study, in order to compare the high-temperature structural integrity of the PHE prototypes under the normal test condition of the gas loop, high-temperature structural analyses on the PHE prototypes were carried out and the analyses results were compared to each other. As a result of comparisons, the high-temperature structural integrity of the medium-scale PHE prototype gets worse due to higher thermal expansion by a size effect.
Characterization of Ductile Failure Behavior of the Ferritic Steel Using Damage Mechanics Modeling Approach
Authors: Kucharczyk Pawel , Münstermann Sebastian
Published: November 2012

A ductile failure is characterized by pronounced plastic deformations which involve significant plastic strains. The modeling of this failure behavior requires a precise description of the material plasticity starting from the crack initiation, its propagation through the material to the final fracture. The classical theory of metal plasticity based on the von Mises or Tresca formulations assumes that the effect of hydrostatic pressure on the flow potential is insignificant. Furthermore, it postulates that the flow stress is independent of the third stress invariant of the deviatoric stress tensor. The scientific findings from last few years show, however, that these both quantities should be considered for the precise description of plasticity, especially, of the real materials [1-4].
Thermal and Static Analysis of an Insulation Block from Recycled Polymer HDPE for Solution of Thermal Bridges in Wall-Footing Detail
Authors: Pěnčík Jan , Matějka Libor , Matejka Lukas
Published: November 2012

With the sustainable construction the emphasis is placed on saving energy, reducing of consumption of natural resources, extending the life cycle of recycling, etc. One of the important groups of materials that can be reused are polymers. Polymers and waste polymers can be used as a base material for products used in civil engineering. One of these products, which were developed, is an insulation block from modified recycled polymer HDPE for direct solution of thermal bridges in wall footing detail. Design of the insulation block has been done using the MAP method together with long-time experimental testing of specimens and in a testing wall in scale 1:1. In the mathematic modeling the installation block was assessed in terms of statics and thermal technology. Static assessment was performed using Standard Solid rheological model, which represents the most accurate approximation of long-time behaviour.
Numerical Analysis of a Steel Frame Building with Soft-Storey Failure under Ground Motion Excitation
Authors: Migda Wojciech , Jankowski Robert
Published: November 2012

t has been observed during earthquakes that the soft-storey failure of an upper floor of a building results in large impact load acting on structural members of the lower storeys. It may further lead to progressive collapse of the whole structure substantially intensifying human losses and material damages. The aim of this paper is to show the results of a numerical analysis focused on the behaviour of multi-storey steel frame building that suffers from a soft-storey failure under ground motion excitation. A numerical model of the structure was created in FEM computer software and was exposed to an impact that would have been generated after a soft-storey failure due to falling of the upper floors. During the analysis, the whole structure was exposed to ground motion excitation and different moments have been chosen for the impact so as to estimate the most critical moment for the structure. The results of the study show that not only the value of the impact force is crucial but also the moment when the impact occurs. This is due to the fact that horizontal deflection of the supporting members (steel columns) varies during the time of the excitation. It has been observed that the most critical moment for the building for being subjected to a vertical impact is when the horizontal deflection is close to its peak.
Relation between Structural Size and the Discretization Density of Brittle Homogeneous Lattice Models
Authors: Vořechovský Miroslav , Eliáš Jan
Published: November 2012

This paper contains the results of an investigation into the effect of the discretization of lattice models. The study is performed with homogeneous models where all elements share the same strength. Elemental constitutive law is linearly-brittle, meaning that elements behave linearly but are completely removed from the structure as soon as they reach the limit of their strength. The relation between structural size and discretization density is studied with unnotched beams loaded in three point bending (modulus of rupture test). We report the results for regular discretization and irregular networks obtained via Voronoi tessellation. This is carried out for two types of models: these being with and without rotational springs (normal and shear springs are always present). The numerically obtained dependence of strength on discretization density is compared to the analytical size effect formula.
Formability Evaluation of Non-Crimp Carbon Fabric by Non-Contact 3D Deformation Measurement System
Authors: Tanaka Kazuto , Kanazawa Kazuya , Enoki Shinichi , Katayama Tsutao
Published: November 2012

Non-Crimp Carbon Fabric (NCF) consists of unidirectional plies which are kept together by stitching yarns arranged in a number of different orientations relative to the fabric production direction. It is reported that NCF possesses excellent drape performance compared to woven fabrics. However there is not a clear criterion of a drape evaluation on the drape characteristic of the NCF. In addition, it is not clarify that stitch pattern and stitch tension influence on the drape characteristic of the NCF. Moreover, in existing bias extension test, measurement of shear angle is based on the pin-jointed net (PJN) approximation. The PJN approximation doesnt takes into consideration the fiber sliding and the effect of the stitched parameters of the NCF. In this study, the bias extension test based on the measurement of shear angle by non-contact 3D deformation measurement system was conducted to evaluate the drape performance of the NCF. We made a proposal of the formability evaluation index based on the measurement results. Moreover, the 3D draping tests were conducted onto hemisphere geometry and regular tetrahedron, in order to verify availability of the formability evaluation index. The availability of the formability evaluation index was verified.
Comparisons of High-Temperature Structural Analysis Results on the Medium-Scale PHE Prototype under the Steady-State and Trip Conditions of a Small-Scale Gas Loop
Authors: Song Kee Nam , Hong S.D. , Park H.Y.
Published: November 2012

PHE (Process Heat Exchanger) is a key component for transferring the high-temperature heat generated from a VHTR (Very High Temperature Reactor) to a chemical reaction for massive production of hydrogen. Recently, Korea Atomic Energy Research Institute (KAERI) has manufactured a medium-scale PHE prototype made of Hastelloy-X of high-temperature alloy and a performance test on the PHE prototype is scheduled in a small-scale nitrogen gas loop established at KAERI. In this study, in order to evaluate the high-temperature structural integrity of the PHE prototype under the steady-state and trip conditions of the gas loop before the performance test on the PHE prototype, elastic and elastic-plastic structural analyses on the PHE prototype were carried out and the analyses results were compared each other.
Inelastic Seismic Behavior without and with Over-Resistance Effects of 10-Story Building RC Damaged due to the 1985 Earthquakes in Mexico City
Authors: Avila Jorge A.
Published: November 2012

The observed damage level in field, due to the 1985 earthquakes, is compared in a 10-story RC building in Mexico City with the analytical predicted behavior without and with the available over-resistance effects. The results were compared to those obtained from the conventional seismic analysis and to the observed damage behavior after the earthquake. Facing the observed behavior in many buildings, the necessity of studying in detail the available over-resistance effects merged, in order to widely explain the seismic-resistance behavior participation of such structures. The over-resistance effects are included: slab steel, deformation hardening period of reinforcement steel, average real stresses of concrete and steel, compression slab participation and concrete confinement. Lineal and non-lineal step-by-step dynamic analysis are made. The soil-structure interaction and the P-Δ effects are included in the analysis. The analytical periods are compared to those experimentally obtained. A very good congruency between the analytically predicted behavior and the observed damage level after the earthquake is obtained. The direction and the stories with maximum damages match with the direction and stories with maximum deformations obtained from the analysis. It is noticed that the structure has a superior lateral resistance capacity regarding to the given in the conventional design.
Accurate Description of Near-Crack-Tip Fields for the Estimation of Inelastic Zone Extent in Quasi-Brittle Materials
Authors: Veselý Václav , Sobek Jakub , Šestáková Lucie , Seitl Stanislav
Published: November 2012

A description of stress and displacement fields by means of the Williams power series using also higher-order terms is the focus of this paper. Coefficients of this series are determined via the over-deterministic method from the results of conventional finite element (FE) analysis. A study is conducted into the selection of the FE node set whose results are processed in this regression technique. Coefficients up to the twelfth term were determined with high precision. The effect of the position of the FE node set on the accuracy of the values of the higher-order term coefficients is reported.
Micromechanics Damage Analysis in Fiber-Reinforced Composite Material Using Finite Element Method
Authors: Kimyong Cha Yun , Aimmanee Sontipee , Uthaisangsuk Vitoon , Wechsatol Wishsanuruk
Published: November 2012

Fiber-reinforced composite materials (FRC) are used in a wide range of applications, since FRC exhibits higher strength-to-density ratio in comparison to traditional materials due to long fibers embedded in a matrix material. Failures occurred in FRC components are complicated because of the interaction of the constituents. The aim of this study is to investigate damage behavior in a unidirectional glass fiber-reinforced epoxy on both macro-and micro-levels by using finite element method. The Hashins criterion was applied to define the onset of macroscopic damage. The progression of the macroscopic damage was described using the Matzenmiller-Lubliner-Taylor model that was based on fracture energy dissipation of material. To examine the microscopic failure FE representative volume elements consisting of the glass fibers surrounded by epoxy matrix with defined volume fraction was considered. Elastic-brittle isotropic behaviour and the Coulomb-Mohr criterion were applied for both fiber and epoxy. The results of the macroscopic and microscopic analyses were correlated. As a result, damage initiation and damage development for the investigated FRC could be predicted.
A Local Compression Tests of UHPC Anchor Blocks for Post-Tensioning Tendons
Authors: Choi Eun Suk , Lee Jung Woo , Joh Chang , Kwark Jong Won , Kim Jee Sang , Choi Yoon Seok
Published: November 2012

In the application of Ultra High Performance Concrete (UHPC) to PSC girders by using the post-tensioning system, the high strength and ductility of UHPC in tension can be exploited to substitute the confined reinforcing bars which control the rupture around the anchorage device. The exploitation of such properties is expected to simplify the reinforcing details around the anchorage zone. Taking advantage of UHPC can downsize a cross section with the attributes of high compression and tensile strength. This paper reports the local behavior of UHPC anchor block under compression. Test specimens were made based on mix proportion of K-UHPC (KICT-Ultra High Performance Concrete) developed by the Korea Institute of Construction Technology (KICT). The performance of the anchor block was evaluated according to ETAG-013 (European Technical Agreement Guide No.13) of EOTA (European Organization for Technical Approvals). As the results of the experiment, it is found that the details and reinforcement of UHPC anchorage zone can be simplified with the interconnection effect and the high intensity of the matrix itself.
Monitoring Analysis of Tunnel Construction in a New Subway Line Down-Through an Existed Line
Authors: Dong Fei , Dong Jun , Cui Yu Ping , Sun Wei Ze , Li Dong Yong
Published: November 2012

For a practical engineering in which the tunnel of Subway Line No.7 between Guangqumen outside Station and Shuangjing station is down through Shuangjing Station of existed Subway Line No.10, numerical simulations of construction process of the tunnel have been investigated by FLAC 3D software and compared with site monitoring data. The sedimentation curves of the earth's surface along the cross-sectional and longitudinal direction are obtained, which show that all results including numerical simulation and site monitoring are accord with the data from the Peck formula. At the same time according to numerical computation, some relations between width and depth of excavating a tunnel are discussed. All these have important significant to theoretical research and engineer practice of subway construction.
Two Scale-Based Continuum Damage Model for Brittle Materials under Thermomechanical Loading
Authors: Ricoeur Andreas , Henneberg Dimitri
Published: November 2012

Ceramic refractory materials initially contain a multitude of defects such as voids, microcracks, grain boundaries etc. Particularly being exposed to high temperatures above 1000 °C the macroscopic properties such as effective compliance, strength and lifetime are essentially determined by microscopic features of the material. The deformation process and failure mechanisms are going along with the creation of new microdefects as well as the growth and coalescence of cracks. A brittle material damage model for dynamic thermomechanical loading conditions is presented in this paper. Representative volume elements (RVE) include microcrack initiation and growth. The material laws are formulated on the continuum level using appropriate homogenisation methods. To demonstrate the potential of the numerical tools, two examples are presented which are taken from applications. Based on experiments, cyclic thermal shock tests at refractory plates are simulated by FEM. To quantify the thermal shock resistance of ceramics, experiments suggested by Hasselman are simulated numerically supplying a critical temperature slope.
Modeling of Damage and Failure of Dual Phase Steel in Nakajima Test
Authors: Lian Jun He , Liu Peng Fei , Münstermann Sebastian
Published: November 2012

For modern high strength steels, instead of metal instability, ductile damage triggered by the formation of microvoids or microcracks resulting from the complex material microstructure, has become the key factor responsible for the final failure in the forming process of such steels. The target of this study is to describe the initiation and evolution of damage in a dual-phase (DP) steel (DP600). By applying a newly proposed approach that is able to indicate the onset of damage in an engineering sense and quantify the subsequent damage evolution, to predict the forming limits for DP600 are predicted by simulating Nakajima test. Accordingly, two forming limit curves (FLC) are numerically computed to characterize two moments: when damage becomes pronounced and when the final failure is triggered by the accumulation of damage. Comparing with the conventional experimentally calibrated FLC at necking, the limit at crack initiation predicted by modeling gives a lower but defect-free forming boundary. The forming limit at final fracture is well captured by allowing the subsequent damage evolution to a critical value.
Micromechanical Modeling for the Evaluation of Elastic Moduli of Woven Composites
Authors: Abe Daisei , Bacarreza Omar , Aliabadi M.H.
Published: November 2012

Textile composites have increasingly been used as a structural material because of their balanced properties, higher impact resistance, and easier handling and fabrication compared with unidirectional composites. However, the complex architecture of textile composites leads to difficulties in predicting the response in spite of the fact that there is the need to determine mechanical properties in product design. Micromechanical analysis, using the Finite Element Method, was conducted in order to evaluate the effective mechanical properties of plain woven and 3D woven composites. In this study, numerical models of unit cells were used and it is shown that the predicted values of homogenized mechanical properties using the developed procedure were in good agreement with experimental results.
Analysis of Stress Intensity Factor for Cracked Flattened Brazilian Disk: Part I – Analysis Method and Pure Mode I Crack
Authors: Dong Shi Ming , Wang Qing Yuan
Published: November 2012

In order to solve the problem how to calculate the stress intensity factor for a cracked flattened Brazilian disk under mode I loading, the finite element method was employed to analyze the stress intensity factor for the cracked flattened Brazilian disk under mode I loading, based on the closed-form expression of the stress intensity factor for a cracked Brazilian disk subjected to pressure. The analyzed result shows that within the certain range of the load distribution angle, the formula of the stress intensity factor for the cracked Brazilian disk can be directly used to calculate the stress intensity factor for the cracked flattened Brazilian disk under mode I loading.
Peculiarities of Fatigue Fracture of Steel Hardened by Various Surface Treatments
Authors: Ciuplys Antanas , Kvedaras Valdas
Published: November 2012

Fatigue strength is one of the most important mechanical properties. Durability and reliability of car parts is often defined by their fatigue strength, since most of them are loaded with dynamic, repeating or variable loads and the main type of failure is metal fatigue. Fatigue crack usually starts on the metal surface. The interrelationship of the surface layer together with the characteristics of internal metal volume determine the value of fatigue limit and the coefficient level of stresses’ intensity, which is required for the start of fatigue crack. Various hardening methods of surface have a huge impact on fatigue strength of structural materials. The choice of surface processing method is determined by properties and microstructure of a material, as well as the purpose and working conditions of part’s material. Very often the optimum processing is a combination of several methods, which enables to obtain the required properties (high fatigue strength, wear, etc.). Hardening with high-frequency electric current (HfEC) is widely used process for the surface hardening of steel. The components are heated by means of an alternating magnetic field to a temperature within or above the transformation range followed by immediate quenching. The core of the component remains unaffected by the treatment and its physical properties are those of the bar from which it was machined. Investigation of specific fatigue fracture properties enables to determine the kinetic of processes, related with fatigue crack initiation and propagation. Analysing fractures of machine parts and comparing them with the most specific “mode” fractures it is possible to determine the nature of affecting loads and the reason of part failure. The impact of several combined surfaces processing on the fatigue strength and fractures of carbon steel samples is investigated in the work. The surface was hardened using different processing combinations: by hardening with high frequency electricity currents, rolling by rollers, heating and cooling under different temperatures. Experimentally it was proved that thermal treatment of plastically deformed carbon steel significantly increases fatigue strength. After surface hardening with the given regimes, the microstructure and residual stresses are formed in such way that fatigue crack begins to grow under the hardened sample surface. Samples, in which the fatigue crack initiates inside the sample, have higher fatigue strength than the samples, the fatigue crack of which initiates on the surface.
Thermal Stability of PECS-Compacted Cu-Composites
Authors: Ritasalo Riina , Kanerva Ulla , Hannula Simo Pekka
Published: November 2012

In this paper pulsed electric current sintering (PECS) is applied for submicron-sized copper (sm-Cu) based composite-powders aiming to produce MMC’s with higher strength and better temperature stability than reference sm-Cu. Incorporation of cuprite (Cu2O), alumina (Al2O3), titaniumdiboride (TiB2) and nano- and submicronsized diamonds (ND’s and SMD’s) improved noticeably the room temperature mechanical properties and the high-temperature stability of copper the effects becoming more noticeable with smaller dispersion size and higher amount of reinforcement. The hardness increment was at highest, when using ND’s or Al2O3. E.g., the microhardness for the reference sm-Cu sample and Cu with 3 vol.% ND’s, 6 vol.% ND’s and 2.5 vol.% Al2O3 were 1.02, 1.43, 1.77 and 1.58 GPa, respectively. Similar trend was noted also in the case of thermal stability and CTE. The study shows that Cu-ND, Cu-SMD and Cu-Cu2O are suitable for use at moderate temperatures around 623 - 673 K, whereas Cu-Al2O3 and Cu-TiB2 are suitable above 1023 K. In conclusion, PECS is suitable method to produce high quality Cu-composites having superior thermal and mechanical properties compared to those of sm-Cu.
Surface Fatigue of Al-Metal Matrix Composites at Impact Loading
Authors: Saarna Mart , Sergejev Fjodor , Gomon Jaana Kateriina , Kollo Lauri , Leparoux Marc
Published: November 2012

Aluminium 6061 has proven to be a suitable alloy as a basis for producing metal matrix composites (MMC). These MMCs have a low specific weight combined with a relatively good specific stiffness and high specific strength. The hardness and compressive strength of Al composites can be increased by reinforcing bulk material with nano particles. However the ductility of such alloys is relatively low, therefore one of the applications for such light alloys could be wear applications. In many wear conditions such as erosive or abrasive wear at normal impact angles the surface wear resistance plays a significant role. The surface fatigue properties have not been widely studied for such nanoparticle reinforced aluminium composites. The nano-reinforced composite materials were produced by means of high-energy milling (HEM) of nano-sized reinforcement particles together with a metallic matrix powder, followed by hot pressing. By utilizing up to 6 wt% multiwalled carbon nanotubes (MWCNT) as reinforcement the hardness of Al6061 MMC has been increased from 45 HV10 up to 317 HV10, compressive yield strength from 58 MPa up to 660 MPa and indentation modulus from 60 GPa up to 90 GPa compared to hot pressed Al6061. Surface fatigue tests were conducted at impact (dynamic) loading conditions using a hardened steel sphere as indenter. The Wöhler-like curves are plotted to estimate the surface fatigue. The surface fatigue indents were photographed by the aid of light optical microscopy (LOM) and analysed by image analysis software and optical profilometry (OP).
Investigation of Residual Stresses and some Elastic Properties of Brush-Plated Gold and Silver Galvanic Coatings
Authors: Lille Harri , Kõo Jakub , Ryabchikov Alexander , Reitsnik Renno , Veinthal Renno , Mikli Valdek , Sergejev Fjodor
Published: November 2012

Nickel-hardened gold and silver coatings were brush-plated from a commercial SIFCO Dalic Solution (Gold Hard Alloy), Code SPS 5370, and Silver Hard Heavy Build, Code SPS 3080, on unclosed thin-walled copper ring substrates. To determine residual stresses, the conventional curvature method (common among the electrodeposition methods) was applied, where the substrate was coated with certain thickness and then the slit increment (bending deflection) of the substrate was measured as an experimental parameter. Residual stresses on gold coatings were also determined by X-ray diffraction (XRD) based on the sin2 method. The values of residual stresses determined by the curvature method and by the XRD technique were comparable. Relaxation of residual stresses was observed. An equation for approximation of the change of residual stresses was applied assuming that the dependence of residual stresses on relaxation time is linear-fractional. The surface morphology and microstructure of the coatings was studied by means of scanning electron microscopy (SEM). The magnitudes of the modulus of elasticity and of the nanohardness of the coatings were obtained by instrumented indentation.
Effect of New Superhard Phases Formation on Properties of Composite Processed by SHS
Authors: Kommel Lembit , Tamm Toomas , Metsvahi Raido
Published: November 2012

A composite was produced from initial powder mixture of B4C (70 wt.%) and Al (30 wt. %) with WC-Co additives introduced during ball-milling and acting as catalysts by self-propagating high-temperature synthesis and followed by heat treatment of raw samples under gaseous nitrogen flow at 650, 800, 1000, 1150 and 1450 °C, respectively. Formation of different new superhard phases was detected via XRD investigation and analysis of microstructures. Micromechanical properties were tested by nanoindentation. The tribological behavior in dry sliding conditions of the composite was investigated using the ball-on-disk technique against alumina balls. The friction coefficient of the composite increased and wear rate decreased with formation of c-BC2N, c-BN, B13C2, W2B5, Al3BC, AlN, etc. contents during heat treatment at increased temperatures.
Characterization of Mechanical Milling Cermet Powders Produced by Disintegrator Technology
Authors: Käerdi Helmo , Goljandin Dmitri , Kulu Priit , Sarjas Heikki , Mikli Valdek
Published: November 2012

The current paper deals with characterization of TiC−NiMo cermet powders produced by mechanical milling technology. TiC-based cermets scrap was processed by semi-industrial and laboratory disintegrator milling system. Chemical composition, shape and size of produced powders were analyzed. To estimate the properties of recycled cermet powders the sieving analysis, and angularity studies were conducted. The grindability was estimated using specific energy parameter (Es). Considering that viewpoint, the study is focused on angularity studies as the shape of spray powder has considerable influence on spraying efficiency, the quality and reliability of the coating. To describe the angularity of milled powders, spike parameter – quadratic fit (SPQ) was used and experiments for determination of SPQ sensitivity and precision to characterize particles angularity were performed. Uncertainty of measurements demonstrated trustworthiness of results. The standard deviation of SPQ regardless of milling cycles is the same. For use of produced powders as reinforcements in sprayed coatings the technological parameters of powders were studied. Perspective future use of powders as reinforcements in composite coatings as well as abrasives in tooling were demonstrated.
Investigation of TiO2 Ceramic Surface Conductivity Using Conductive Atomic Force Microscopy
Authors: Rubenis Kristaps , Kundzins Karlis , Locs Janis , Ozolins Jurijs
Published: November 2012

Dense TiO2 (rutile) ceramic samples were prepared by sintering compacts of titanium dioxide anatase powder at 1500 °C for 5h. Sintered samples were polished and annealed in vacuum at 1000 °C for 1h. Structural properties of the samples were studied by X-ray diffraction, polarized light and scanning electron microscopy. The surface topography and local electrical conductivity of the samples were investigated by atomic force microscopy technique under atmospheric conditions. Enhanced electrical conductivity was observed at grain boundaries while the polished, vacuum annealed grains surface showed non-homogeneous conductivity.
Tribological Parameters of Copper-Alumina Composite
Authors: Hvizdoš Pavol , Kulu Priit , Besterci Michal
Published: November 2012

Basic mechanical and wear properties of a commercial copper based composite Glidcop were studied. A Glidcop AL-60 grade (with 1.1 wt.% Al2O3) was used as the initial material. It was further treated by the Equal Channel Angular Pressing (ECAP) process in order to induce massive plastic deformation and to achieve very fine grained microstructure. Both, as-received and ECAP-ed materials were then characterized and the results compared. Hardness and elasticity modulus of the experimental materials were measured by instrumented indentation. Tribological properties were studied by pin-on-disk technique in dry sliding against a steel ball at a various temperatures from room temperature up to 600 °C. For all systems the coefficient of friction and specific wear rates were evaluated. Worn surfaces were studied by scanning electron microscopy and level of oxidation was measured using EDX spectrometry. It was found that above 200 °C the coefficient of friction decreased by about 50 %. The wear resistance with increasing temperature increased due to formation of harder oxide rich surface layer. Damage mechanisms were identified and their relationship with structural characteristics was inferred.
Development and Testing of Materials with Reduced Wear by Fixed Abrasive
Authors: Jankauskas Vytenis , Skirkus Remigijus
Published: November 2012

Abrasive wear into embedded abrasive (Al2O3) of Fe–C–Si–Mn–Cr–B layers welded by an electric arc has been studied. The amounts of carbon (0.45–2.92%), chromium (1.1–18.7%) and hardness (73–82 HRA) of welded layers have no impact on wear. Due to great differences in hardness of welded layers and abrasive, the metal surfaces are intensively wearing due to microcutting. It is determined that the harder the layers, the greater their resistance to wear. Alloying of a medium content carbon layer (0.45% C) with boron of 0.51% reduces the wear up to 27%. Minimal amounts of carbon 0.45%, chromium 1.1%, boron 0.5% guarantee stable and high resistance of welded layers to wear.