bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Properties of Aluminum Metal Matrix Composites
Authors: Agrianidis P. , Agrianidis T. , Anthymidis K.G. , Trakali A.
Published: October 2009

Aluminum matrix composites reinforced by ceramic particles are well know for their good thermo-physical and mechanical properties. As a result, during the last years, there has been a considerable interest in using aluminum metal matrix composites (MMCs) in the automobile industry. These potential applications have greatly stimulated the tribological studies of MMCs under different operating conditions.
In this paper, TiB – particles - reinforced aluminum - tungsten matrix composites were fabricated by the cost – effective squeeze – casting technology and their microstructure characteristics and mechanical properties were investigated. The microstructure observation showed that the produced composites were dense, with no micro-holes and obvious defects. Their wear resistance was evaluated using a pin on disc type equipment under dry wear conditions and found significantly increased compared to pure Al metal.
Stress State Dependent Cohesive Zone Model for Thin Walled Structures
Authors: Rajendran M. , Schneider Ingo , Banerjee Anuradha
Published: October 2009

A new stress-state dependent cohesive zone model for thin walled structures is
proposed. The model incorporates the stress-state explicitly within the traction-separation law
using basic elasticity-plasticity equations combined with a model parameter. The numerical
implementation of the model is able to reproduce ductile fracture observed in a pre-cracked
C(T) specimen as well as a notched plate specimen of the same material.
A New Wireless Smart Sensor for Fatigue Damage Detection of a Single Steel Bar
Authors: Enoki Manabu , Fujino Yozo , Sorrivi Elisa , Takayuki S. , Viola Erasmo
Published: October 2009

In this study, a new wireless smart sensor for fatigue damage detection of a single steel bar is proposed. A modified stress intensity factor is used to introduce a master curve of fatigue crack growth. Acoustic Emission signals are also measured and incorporated in the procedure for the structural health monitoring.
Numerical Simulation on Failure Process of Concrete-Filled Rectangular Steel Tube Column
Authors: Zou Guang Ping , Xia Pei Xiu , Zhang Xue Dong
Published: October 2009

Realistic Failure Process Analysis (RFPA3D) was used to simulate the concrete-filled rectangular steel tube columns which are subjected to axial loads. The ultimate bearing capacity and the load-strain figures were presented. The Numerical simulation results were verified by experimental data of the paper [5]. Meanwhile, the development process of crack in the specimen was described. The whole failure process of rectangular steel tube columns was reproduced. The failure principles of concrete-filled rectangular steel tube column were discussed deeply.
Targeting Problems of Composite Failure
Authors: Beaumont Peter W.R.
Published: October 2009

Predicting precisely where a crack will develop in a material under stress and exactly when in time catastrophic fracture of the component will occur is one the oldest unsolved mysteries in the design and building of large-scale engineering structures. Fitness considerations for long-life implementation of aerospace composites include understanding phenomena such as fatigue, creep and stress corrosion cracking that affect reliability, life expectancy, and durability of structure. Structural integrity analysis treats the design, the materials used, and figures out how best components and parts can be joined; furthermore, SI takes into account service duty.
Cracks in Magnetoelectroelastic Solids under Impact Loading
Authors: Wünsche Michael , Sáez Andrés , García-Sánchez Felipe , Zhang Chuan Zeng
Published: October 2009

In this paper, transient dynamic crack analysis in two-dimensional, linear magnetoelectroelastic solids is presented. For this purpose, a time-domain boundary element method (BEM) is developed and the elastodynamic fundamental solutions for linear magnetoelectroelastic and anisotropic materials are derived. The spatial discretization of the boundary integral equations is performed by a Galerkin-method while a collocation method is implemented for the temporal discretization of the arising convolution integrals. An explicit time-stepping scheme is developed to compute the discrete boundary data and the generalized crack-opening-displacements. To show the effects of the coupled fields and the different dynamic loading conditions on the dynamic intensity factors, numerical examples will be presented and discussed.
Damage Detection in Piezoceramics via BEM
Authors: Rus G. , García-Sánchez Felipe , Sáez Andrés , Gallego R.
Published: October 2009

Piezoelectric ceramics have recently become one of the most used materials in all kinds of electromechanical systems. However, the presence of defects in such materials prevents them from fulfilling their function. A number of numerical, analytical and experimental works are recently being developed to understand the behaviour of piezoelectrics with presence of damage, but very few aimed at locating defects. One of the current challenges in monitoring piezoelectrics is the correct interpretation of the readings from sensors, in order to reliably recover the defect characteristics minimizing uncertainties due to noise and model. An inverse problem strategy is proposed for this reconstruction, starting from the electromechanical response measurement as input data, and incorporating a numerical model that simulates that response. This model is solved using a Boundary Element Method (BEM), whose formulation is developed for the 2D static case. The damage identification inverse problem is solved using genetic algorithms for the minimization of the discrepancy or cost functional. The effect of noise on measurements and uncertainties in the model is studied in detail through a sensitivity analysis for some simple cases of defect.
Study of the Stress Distribution Around an Orthotropic Bi-Material Notch Tip
Authors: Klusák Jan , Profant Tomáš , Kotoul Michal
Published: October 2009

Knowledge of the stress distribution is the first and necessary step for the reliable assessment of construction with a geometrical or material discontinuity. General geometry and orthotropic material characteristics of both material components lead to singular stress distribution with general stress singularity exponents different from ½. For the final stress field determination both analytical and numerical approaches are utilised. The results of the theoretical approaches are compared to results from finite element method.
The Fatigue Reliability Analysis of Stress Criterion in Multiaxial High Cycle Fatigue
Authors: Zou Guang Ping , Xue Qi Chao , Chang Zhong Liang
Published: October 2009

The stress criterion of multiaxial high cycle fatigue is a type of non-linear equation of high-order. It is used to predict the failure of fatigue in proportional torsion and bending loads. Soon-Bok Lee presented a new design criterion for fully reversed out-of phase torsion and bending. The values are randomized in different random distributions in Lee’s criterion formula. The correlations among random variables are considered and limit state equation is also established. This paper attempts to use First Order Reliability Method (FORM) and Second Order Reliability Method (SORM) to calculate the reliability of material fatigue in torsion and bending loads. The example is calculated and it is found that the failure probability estimated by using the SORM is more reliable than those of the FORM in multiaxial high cycle fatigue.
Effects of Severe Air Blast Shot Peening on Microstructure and Residual Stress State of Al Alloys
Authors: Guagliano Mario , Bagherifard Sara , Fernàndez Parienete Ines , Ghelichi Ramin
Published: October 2009

Surface grain refinement is a relatively new process aimed to enhance mechanical material properties. In this study Al7075-T6 bars have been shot peened with parameters much different from those of conventional shot peening. Microstructure gradient has been observed by means of transmission electron microscopy (TEM), X-ray diffraction (XRD) and nano indentation tester. A fine grained layer was found on top surface of the specimens. Measurements indicate of notable improvements in cases of hardness and elastic modulus in comparison with untreated material. XRD results also show significant depth affected both in terms of residual stress and FWHM.
The results imply that using optimized shot peening parameters, it would be possible to create a fine grained layer on surface of component and consequently increase fatigue life and any other property affected by grain size.
A Hermitian Type Triangular Element only with Corner Nodes and its Application to XFEM
Authors: Kanto Yasuhiro
Published: October 2009

A new triangular element of Hermitian type, i.e., the degrees of freedom includes differentiation of value as well as value itself, is proposed and XFEM formulation is demonstrated. Some numerical examples are also shown.
Fatigue Strength Evaluation Methods Using Stress Distributions
Authors: Nakamura F. , Abe Tomoyasu , Hattori Toshio , Yamashita Minoru
Published: October 2009

The stress and displacement fields near the bonding edge, sharp notch, and contact edge show singularity behaviours, so methods of evaluating the strength of these points using maximum stresses calculated by a numerical stress analysis, such as the finite element method, are generally not valid. We have previously presented a new method of evaluating the strength of these singular points using two stress singularity parameters H and λ. In this paper we have developed a method of formularizing critical stress-singularity parameter Hth for each order of stress singularity λ by utilizing critical distance stress theories (point method and line method), which can be derived from two typical strength parameters, namely, fatigue limit σw0 and threshold stress-intensity factor range ΔKth. These estimated critical Hth (λ) value agreed well with the experimentally measured value. Using these simple critical distance stress approach we estimated the fretting-fatigue-crack initiation criteria for any contact edge angle and optimized the contact-edge geometry. Moreover, we apply this new strength criteria to general stress concentration structures.
On the Path and Area Jx1-Integral Components and their Relationship to the Out-of-Plane Constraint in Elastic Cracked Plates
Authors: Fernández Canteli A. , Giner E. , Fernández Zúñiga D. , Fernández Sáez J.
Published: October 2009

In this paper, the path and area components of the Jx1-integral, JP and JA, in three dimensional elastic cracked plates under mode-I loading are investigated aiming at relating them to the out-of-plane constraint conditions resulting from different specimen thicknesses. It is concluded that the JP and JA components of the Jx1-integral vary in the region where the out-of-plane constraint extends. Sufficiently far from the crack front, these integrals tend to stabilize, indicating that the thickness constraint vanishes and that a 2D-like stress and strain fields have been reached. A pure plane strain condition is only attained when the specimen thickness is very large when compared to the in-plane dimensions. For thin plates, it is shown that the 2D plane stress condition is impossible in the close neighbourhood of a 3D crack front under elastic behaviour so that the consideration of an equivalent Young modulus E', used to find a simple relation between the J(s)-integral and KI for different constraint levels can be misleading.
Particular Aspects Concerning Low Velocity Impact on Composite Tubes
Authors: Constantin Nicolae , Sorohan Ştefan , Găvan Mircea , Anghel Viorel
Published: October 2009

The study had in view various aspects which can arise during the low velocity impact tests made on composite pipes/tubes. It implied numerical simulations, made by ANSYS and LS-DYNA codes, on glass fiber/epoxy composite pipes. The geometry and material characteristics were taken from real pipes, which have been experimentally tested in parallel, using a drop weight impact tower. The main parameter in view was the impact force history, which gives most information upon the impact event and, accordingly, is used by most of researchers for characterizing the damages produced on the impacted body and for assessing the impact installation.
Fracture Analysis of Semi-Infinite Interface Crack between Two Dissimilar Orthotropic Composite Materials
Authors: Li Jun Lin , Zhang Shao Qin
Published: October 2009

The problem of orthotropic bi-materials semi-infinite interfacial crack was studied, by constructing new stress functions and using composite complex functions methods of material fracture on plane. It overcame oscillation singularity of stress and existing theoretical solution. When secular equations’ discriminations are and , the theoretical solutions to the stress fields and the displacements fields of semi-infinite interface crack between two dissimilar orthotropic composite materials near the crack tip are obtained.
Tensile Fracture Characterization of Thermosetting Plastics by Infrared Thermography Technique
Authors: Kim Jeong Guk
Published: October 2009

The tensile fracture behavior of thermosetting plastic materials was investigated with the aid of a nondestructive evaluation (NDE) technique. The materials, unsaturated polyester resin (UPR), which is applicable to buffer the vibration and impact properties in rail structure, were used for this investigation. In order to explain a stress-strain behavior of plastic sample, the infrared thermography technique was applied. A high-speed infrared (IR) camera was employed for in-situ monitoring of progressive damages of UPR samples during tensile testing. In this investigation, the IR thermography technique was used to facilitate a better understanding of damage evolution, fracture mechanism, and failure mode of thermosetting plastic materials during monotonic loadings.
Multi-Particle Unit Cell Models for Particulate-Reinforced Titanium Matrix Composites
Authors: Song Wei Dong , Liu Hai Yan , Ning Jian Guo
Published: October 2009

Fixed point iteration method for multi-particle unit cell’s boundary condition is presented. On the basis of this method, the macroscopic effective material parameters can be obtained from a microscopic point of view. Multi-particle unit cell models containing some important microstructure characteristics of TP-650 titanium matrix composites are established. The real displacement constrained conditions are applied on the multi-particle unit cell using this method, and the mechanical properties and fracture behaviors of the composites under tensile loading are simulated. A good agreement was obtained between the experimental results and the numerical predictions, which verifying the rationality of the FE models based on fixed point iteration method.
Simulation of Curved Fatigue Crack Growth with Calculation of the Plastic Limit Load
Authors: Theilig Holger , Holländer Dirk , Wünsche Michael
Published: October 2009

In this paper a higher order crack path simulation algorithm for multiple interacting cracks is presented using piecewise parabolic curved increments including the consideration of the plastic limit loads. For this reason, the program PCCS-2D has been extended to analyse the crack growth and the plastic limit load for each crack propagation step in a fully automatic simulation. The proposed solution algorithm provides a powerful tool for flaw assessment with the FAD proce¬dure in combination with a numerical crack path simulation. Several numerical examples are pre¬sented to show the accuracy and the efficiency of the crack path simulation including the analysis of the plastic limit loads
J Integral Computation for Cracks in Polypropylene Pipes under Internal Pressure
Authors: Aminallah L. , Mesmacque Gerard , Serier B. , Amrouche Abdelwaheb , Benseddiq N.
Published: October 2009

In the present work, the three-dimensional finite element method is used to analyze the propagation criteria for a semi-elliptical crack in a polypropylene pipe under internal pressure. The crack propagation behavior is analyzed by J-integral calculation. The effects of the crack position in the pipe and the loading, as well as the size and configuration of the crack, are examined. The results obtained enable us to deduce that the propagation of a crack depends on several factors.
Effect of Water Absorption on Strength of the Aeronautical Composite Material Fiberdux HTA/6376
Authors: Pantelakis Spiros , Katsiropoulos C.V. , Tserpes K.I. , Felgeyrolles Therese
Published: October 2009

The effect of water absorption on tensile strength and fatigue life of the Fiberdux HTA/6376 composite laminated material was experimentally and numerically investigated. For the investigation, a quasi-isotropic and a cross-ply layup were considered. Tensile and fatigue tests were carried out with dry and wet specimens subjected to water absorption up to the water uptake saturation point. Fractographic analyses of fracture surfaces were conducted to detect the type of accumulated damage. To describe the mechanical behavior of the material a FE-based progressive damage model was developed. Material properties used in the model are those of the saturated material evaluated experimentally. Convergent results reveal an appreciable degradation in the ultimate tensile strength and fatigue life of the composite material owing to water absorption.
The Study of Microstructure and Biocompatibility for Porous Polylactic Acid Scaffolds
Authors: Xu Wen Feng , Liao Xiao Ling
Published: October 2009

The polylactic acids (PLA) scaffolds materials have been used to be the scaffolds materials of bone, cartilage gristle, blood vessel, nerve and skin due to its bioactivity, biocompatibility and biodegradable, today, the porous polylactic acid scaffolds had widely applied to tissue engineering. In the paper, the advance in study of microstructure and biocompatibility for this material were summarized. The lack in study of microstructure and compatibility has been pointed out and some viewpoints for further investigations are also made in this paper.
Dynamic Stress Intensity Factor of Fixed Beam with Several Notches by Infinitely Similar Element Method
Authors: Li You Tang , Yan Chang Feng , Feng Rui Cheng
Published: October 2009

The dynamics stress intensity factor of fixed specimen with several notches was analyzed by semi-analytic method. The semi-analytic formula was taken as the interpolation function near notch tip and the degrees of freedom near notch tip were transformed into a small set of generalized coordinates by means of the series expansion formulas of the displacement field. The dynamics stress intensity factor for fixed specimen with two notches or cracks under centralized loading and well-proportioned loading was obtained. The results show that the KI and KII are existed at the same time for fixed specimen with several notches under dynamics loading.
Fatigue Test on Integral Joint of the Main Truss of the Baling River Bridge
Authors: Liu Gao , Wu Wen Ming , Tang Liang , Wang Tian Liang
Published: October 2009

The Baling River Bridge is a single-span simply-supported suspension bridge with a main span of 1088 m. The steel stiffening truss is employed as its main girder and comprises the integral joints connecting the chord members. The integral joint is a key structure and determines the safety of the bridge, but it is very complex in detail and has an undefined fatigue resistance. In order to investigate its mechanical behavior and fatigue reliability, a fatigue test was performed on a 1:1.4 scale model of the integral joint of the main truss of the Bridge. With an assumption of the load spectra represented by the standard fatigue vehicle in BS 5400, the test fatigue load was derived accounting for the multiple vehicle effect and the model scale. The test result shows that no cracks were detected in the model when subjected to two million stress range cycles, and the structure has an reliable fatigue resistance satisfying the design requirement. This type of integral joint is an alternative for long-span truss bridges.
A Preliminary Approach to the Relationship between the Rockburst Proneness and the Spectrum Characteristic of Rock
Authors: Zhang Guang , Chen Jing Xi , Han Wei Min
Published: October 2009

How to judge the rockburst proneness of rocks is one of the key works to predict rockburst. A preliminary approach is made to the relationship between the rockburst proneness and the spectrum characteristic of the rocks by means of experiments in the present paper. The following conclusions are obtained. Firstly, under the condition without loading, there is not any regular relation between the rockburst proneness and the spectrum characteristic of the tested rocks. And secondly, under the condition of uniaxial loading, the spectrum curves of the tested rocks with different rockburst proneness all change with the increase of stress. These curves possess similar tendencies, but different shapes, inflexions and developing rates.
Asymptotic Stress Field for a Crack Normal to a Ceramic–Metal Interface
Authors: Marsavina Liviu , Sadowski Tomasz , Faur Nicolae
Published: October 2009

Ceramic – metal interfaces are often present in composite materials. The presence of cracks has a major impact on the reliability of advanced materials, like fiber or particle reinforced ceramic composites, ceramic interfaces, laminated ceramics. The understanding of the failure mechanisms is very important, as much as the estimation of fracture parameters at a tip of the crack approaching an interface and crack propagation path. The asymptotic solution of the stress field at the tip of a crack normal to a bi-material interface is presented. A cracked sandwich plate loaded by uniform normal stress was numerically investigated using Finite Element Analysis. The numerical results of the circumferential stress distribution were compared with the analytical solutions. The results for the non-dimensional stress intensity factors show that at lower crack lengths the influence of material mismatch is lower but this influence increases with increasing the crack length.
Study of the Effect of DCT and PVD Treatments on the Fatigue Behaviour of AISI 302 Stainless Steel
Authors: Baldissera Paolo , Cavalleri Stefano , Marcassoli Paolo , Tordini Federico
Published: October 2009

In this paper the influence of DCT (Deep Cryogenic Treatment) and a CrN arc-deposited PVD (Physical Vapor Deposition) coating on the fatigue behaviour of AISI 302 stainless steel was studied. Rotating bending tests were carried out on standard specimens to evaluate the fatigue limit at 300000 load cycles. The single and the combined effects of the two treatments were investigated by addressing untreated, PVD-coated and both PVD-coated and DC-treated specimens to the tests. All the series of specimens were also tested statically and laboratory analyses including fracture surface SEM observations and hardness measurements were performed.
Study on Simplified Test Method about Fatigue Performance of Cold Patch Asphalt Mixtures
Authors: Yang Peng , Zhang Xiao Ning , Liu Xiao Wen
Published: October 2009

The objective of this investigation was to develop a test methodology to assess the fatigue performance of cold patch asphalt mixtures, potentially usable in the field as a quality control method.The methodology was developed by identifying the relationships between the parameters from a Laboratory Fatigue Test (IDT,according to ASTM D4123 ), and the penetration rate (NPR) from a lighter version of the Dynamic Cone Penetrometer (DCP) at various densification levels. Multiple linear regression analysis (MLRA) was used to develop equations to estimate number of load cycles to fatigue, and critical tensile strain. The fatigue equations were satisfactorily validated after comparing the measure stability parameters from two mixtures not used in the regression analysis. Cross-validation using SPSS procedure was also implemented.
Investigate of Performance of Asphalt Concrete with Gneiss
Authors: Pang Ling , Wu Shao Peng , Xie Jun , Hu De Ming
Published: October 2009

The use of gneiss as aggregates might help meet the pavement constructing demands. However, the study of the pavement performances of gneiss asphalt mixture is few. In this paper, the microstructure of gneiss aggregate was studied by Scanning Electron Microscopy (SEM). And the pavement performances of gneiss asphalt mixture with different improving measure were characterized by means of Indirect Tensile Strength Test and Four-Point Bending Fatigue Test. Gneiss is flaky, surface texture rougher and imporosity characteristic in microstructure, resulting to its adhesion and processing property are poor. Experiment results indicate that the use of hydrated lime replacing limestone power partly in filler can improve pavement properties of the gneiss asphalt mixtures distinctly.
Stresses Developed within Thermally Grown Oxides on a Coated Superalloy Substrate
Authors: Hilson Gabrielle , Flewitt Peter E.J.
Published: October 2009

Residual macro-stresses have to be evaluated using trial samples that comprise a CMSX4 superalloy coated with either a RT22 or a CN91 bond-coat. The samples were exposed in air to a matrix of temperatures, in the range 850°C to 1050°C, and times extending upto 4000hrs to produce thermally grown oxide. This oxide is essentially Al2O3 which allows stresses to be measured by photoluminescence spectroscopy. In addition, Raman spectroscopy and X-ray diffraction have been used to characterise the oxides formed. The results are discussed with respect to confidence in the measurements, changes in stress with temperature and exposure time and the potential for photoluminescence spectroscopy to be used to measure stresses for service components.
Vapor Pressure Modeling for Fire Damage Assessment of HPC
Authors: Zhao Jie , Guo Zhan Qi , Peng Gai Fei
Published: October 2009

High-performance concrete will undergo severe damage under fire conditions. It is well known that vapor pressure induced by high temperatures plays an important role in the damaging process. This paper presents a method of vapor pressure modeling, called equivalent expansion method, which can be implemented in FEM analysis. The modeling procedure consists of two parts, i.e. vapor pressure determination and vapor pressure modeling incorporated in FEM analysis. In order to make analysis more accurate, steam table is employed instead of ideal gas equation.
Inelastic Damage-Involved Response of Colliding Buildings during Earthquakes
Authors: Mahmoud Sayed , Jankowski Robert
Published: October 2009

Interactions between adjacent, insufficiently separated buildings have been repeatedly observed during major earthquakes. This phenomenon, known as the earthquake-induced structural pounding, may be the reason of local damage at the contact points as well as may lead to the extensive damage at the base of the colliding structure or even initiate its total collapse. In this paper, we examine the importance of inelastic modelling of structural behaviour as the result of damage due to earthquake excitation and structural pounding. The study concerns two adjacent four-storey buildings with different dynamic properties. In the numerical simulations, the nonlinear viscoelastic model is used to model the pounding force during collisions at different storey levels of the structures. The model allows us to take into consideration the dissipation of energy due to damage taking place at the time of collision. Three different ground motion records with different peak ground acceleration levels are used in the study. The comparison between elastic and inelastic damage-involved structural behaviour is investigated. The results of the study show significant changes in the dynamic responses of the inelastic systems as compared to those of elastic ones. The results clearly indicate that modelling the colliding buildings to behave inelastically is really essential in order to obtain accurate damage-involved structural response under earthquake excitation.
Defects vs. Small Notches Competition in Fatigue Failure Initiation of Cast Steel
Authors: Cova Matteo , Livieri Paolo , Susmel Luca , Tovo Roberto
Published: October 2009

In the field of cast metals, fatigue strength assessment necessarily deals with the strength reduction caused by randomly distributed small-sized defects. When components are taken into account, stress raisers due to component geometry are possible crack initiation sites as well as defects. For the investigation of the overall performance, an appropriate model considering notch sensitivity of parent material and defect behavior shall be used. Unfortunately, several mechanical models of material sensitivity to notches and defects require the knowledge of the un-defected material strength, which is not obtainable in this case. In this contribution, experimental fatigue tests have been carried out on plane and notched specimens, considering small size notches as well. An appropriate analysis of the generated results allowed the evaluation of the material behavior and its notch sensitivity according to critical distances theories. The obtained results have been confirmed also direct inspection of broken samples.
Material Parameter Identification of Interpenetrating Metal-Ceramic Composites
Authors: Piat Romana , Roy Siddharta , Wanner Alexander
Published: October 2009

A new class of metal/ceramic composites has recently been developed. A porous ceramic preform, the pore structure of which is created via a freeze-casting technique, is melt-infiltrated with metallic alloy via sqzeeze-casting. The microstructure of the composite has lamellar-like domains with geometrical characteristics which are dependent on the manufacturing parameters. The aim of our study is to find a good micromechanical model in order to deduce the mechanical properties of the single domains and of the whole material as a function of the microstructural geometry and the material parameters of the ceramics (alumina) and the alloy (Al-Si eutectic). Firstly, the statistical analysis of polarized light microscopic micrographs of the cross section of the specimen was performed. Domains with the same orientation of lamellae, so-called single domains were detected, selected and measured. The material modeling was performed by a two-step homogenisation procedure using a combination of different micromechanical models. Predicted material properties were compared with ultrasonic measurements for a single domain and for the whole microstructure.
A Probabilistic Strength Prediction Method for Adhesively Bonded Joints Composed of Wooden Adherends
Authors: Hehl Simon , Vallée Till , Tannert Thomas , Bai Yu
Published: October 2009

Joining timber structural elements using mechanical fasteners goes against the anisotropic and fibrous nature of the material. Adhesive bonding is by far better adapted, since it permits a smoother load transfer. However, the strength prediction of adhesively bonded wooden joints is difficult brittle nature of the adherends, the complex stress distribution as well as the uncertainties regarding the associated material resistance. As a contribution to help close this research gap, the authors have carried out experimental and analytical investigations on adhesively bonded double lap joints composed of timber. This paper describes the experimental and numerical results and suggests a probabilistic method for the strength prediction of joints composed of brittle adherends and adhesives. The method considers the scale sensitivity of material strength modelled using a Weibull statistical function, and considers both the statistical variation and the size effect in the strength of the material. The probabilistic method presents a mechanical explanation for the increased resistance of local zones subjected to high strain or stress peaks.
Heating Steady Thermal Stress in a Composite EFBF Plate Made of Ceramic/FGM/Metal Considered Temperature Dependency
Authors: Xu Yang Jian , Tu Dai Hui
Published: October 2009

A NFE model is constructed to analyze the heating steady thermal stress in a ceramic/FGM/metal composite EFBF plate considered temperature dependency. From numerical calculation, when T0=Ta=300K and Tb=1 000K, the stress distributions in the plate were obtained. The results are as follows. With the increase of the FGM thickness, the stress distribution is more reasonable, and the largest tensile stress reduces by 45.64%. With the increase of M, the stress change increases obviously, and the compressive stress on the surface of ceramics reduces by 56.0%. Compared with A=0, the compressive stress of A=3.99 on the surface of metal increases by 94.2%, and the stress on the surface of ceramics changes from compressive stress to tensile stress. When T0=300K, Ta=700K, compared with Tb=1 050K, when Tb=1 800K, the compressive stress on the surface of metal increases 13.62 times, and the maximum compressive stress on the surface of ceramics increases 5.22 times. Compared with the two-layered ceramic/metal composite plate, the stress of ceramic/FGM/metal composite EFBF plate is very gentle, and the maximum tensile stress reduces by 44.2%. Compared with constant material properties, the maximum compressive stress on the surface of metal considered temperature dependency reduces by 59.1%. The results provide the foundations of theoretical calculation for the design and application of the composite plate.
Repairing of Degraded Hot Section Parts of Gas Turbines by Cold Spraying
Authors: Ogawa Kazuhiro , Niki Takahiro
Published: October 2009

Hot section parts of combined cycle gas turbines are susceptible to degradation due to high temperature creep, crack formation by thermal stress, and high temperature oxidation, etc. Thus, regularly repairing or replacing the hot section parts such as gas turbine blades is inevitable. For this purpose, revolutionary and advanced repair technologies for gas turbines have been developed to enhance reliability of the repaired parts and reduce the maintenance cost of the gas turbines. The cold spraying process, which has been studied as not only a new coating technology but also as a process for obtaining a thick deposition layer, is proposed as a potential repairing solution. The process results in little or no oxidation of the spray materials, so the surfaces stay clean, which in turn enables superior bonding. Since the operating temperature is relatively low, the particles do not melt and the shrinkage on cooling is very low. In this study, the cold spraying conditions were optimized by taking into account the particle kinetic energy and the rebound energy for application in repairing gas turbine blades. A high quality cold-sprayed layer is that which has lowest porosity; thus the spraying parameters were optimized to achieve low-porosity layer, which was verified by scanning electron microscopy (SEM).
Effect of Fiber-Matrix Integration on the Fracture Behavior of Aluminosilicate Fiber Reinforced Clay-Kaolin Matrix Composites
Authors: Özkal Burak , Uçar Tugba
Published: October 2009

Different amounts of fiber added samples were prepared by standard ceramic processing routes and sintered at different temperatures. Although powder packing characteristics of the matrix material were negatively affected with increasing fiber content; certain improvements were observed for the density, MOR and water absorption values both for green and sintered states. Fracture surfaces of the samples after three-point bending test were investigated via detailed SEM observations and phase analyses were performed by XRD measurements. It is found that phase transformation controlled fiber-matrix integration starts with increasing sintering temperature and degree of bonding between fiber/matrix interfaces can be arranged by selecting optimum sintering temperature. Aluminosilicate fiber addition was found efficient for improving mechanical properties of clay-kaolin matrix and the mechanism of the improvement can be grouped into two categories i.e. (1) brittle fiber – brittle matrix interactions via well known pulled-out, crack deflection and bridging mechanisms prior to fiber-matrix integration (2) further densification via phase transformation controlled fiber-matrix integration after high sintering temperatures.
Energy-Based Study of Structures under Accidental Damage
Authors: Masoero Enrico , Vallini Paolo , Fantilli Alessandro P. , Chiaia Bernardino
Published: October 2009

An energy-based criterion is introduced in order to investigate the nonlinear dynamic
response of RC beams subject to rapid and unexpected damages. Since only static pushover analysis
is necessary, the structural behavior of the damaged members can be evaluated with a new
simplified procedure. It is firstly applied to the case of elastic–perfectly plastic continuous beam,
when one of the supports is quickly removed. In such a situation, the proposed procedure gives
satisfactory results if compared to those of a more rigorous dynamic analysis. By means of a
nonlinear static analysis, which encompasses also the post-peak response, the energy-based
approach is also applied to concrete beams. More specifically, it is used to predict the bearing
capacities of reinforced concrete beams, having different steel rebars, when they suddenly lose a
single support.
Influence of Friction on Stress and Strain Distributions in Small Punch Creep Test Models
Authors: Dymáček Petr , Seitl Stanislav , Milička Karel , Dobeš Ferdinand
Published: October 2009

The FEM modeling of small punch tests on miniaturized thin discs (SPT) of two heat resistant steels was performed. The FE models did represent the creep SPT, i.e. tests with constant acting force. It was shown that different values of the surface friction coefficient used in the calculations have significant impact on the calculated stress and strain state and consequently on the deformed shape of the disc. Thus, the surface friction coefficient should be considered one of the key factors for any correct correlation of SPT and uniaxial creep test results. Proper attention must be paid to the friction conditions during the long term creep deformation. An attempt to define simple approach how to relate the SPT with uniaxial tests is suggested. Some of the calculated results are compared with experiment.
Mechanical Characterization of Hydroxiapatite Micro/Macro-Porous Ceramics Obtained by Means of Innovative Gel-Casting Process
Authors: Marcassoli Paolo , Cabrini Marina , Tirillò Jacopo , Bartuli Cecilia , Palmero Paola , Montanaro Laura
Published: October 2009

An innovative gel-casting process was developed in order to obtain macro porous ceramics scaffolds of hydroxyapatite to be used in regenerative medicine for bone tissue reconstruction. Mechanical investigation was carried out on different formulations of dense hydroxyapatite samples in order to evaluate the effect of the gel casting process parameters on the density, the elastic modulus, the tensile and the compressive strength. The fracture critical stress intensity factor (KIC) was also evaluated by means of microhardness measurements. The correlations between KIC and tensile and compressive strength were examined taking into account the average and maximum size of porosity. The mechanical properties of macro and micro-porous HA are in agreement with the model of Gibson and Ashby.
Strain Localisation during a Tensile Test of Metallic Plates: Experimental and Numerical Results
Authors: Cendón D.A. , Atienza Jose M. , Elices Calafat Manuel
Published: October 2009

The stress-strain curve of a material is usually obtained from the load-displacement curve measured in a tensile test, assuming no strain localisation up to maximum load. However, strain localisation and fracture phenomena are far from being completely understood. Failure and strain localisation on plane tensile specimens has been studied in this work. A deeply instrumented experimental benchmark on steel specimens has been developed. Surface strain fields have been recorded throughout the tests, using an optical extensometer. This allowed characterisation of the strain localisation and failure processes. Tests have been numerically modelled for a more detailed analysis. Preliminary results show a substantial influence of geometrical specimen defects on the strain localisation phenomena that may be critical on the stress-strain curves obtained and in the failure mechanisms.
Influence of Small Surface Defects on Fatigue Limit of Nitrided and Shot Peening Steel
Authors: Pariente Ines Fernández , Bagherifard Sara , Ghelichi Ramin , Guagliano Mario
Published: October 2009

Effects of surface defect size and the method used to obtain the defect itself on bending fatigue behaviour of nitrided and shot peened steel was studied. Two different series of 15 sandglass specimens with a microhole in the minimum section generated after nitriding and shot peening treatments were considered. In one series the microholes were obtained by controlled electro-erosion. In the other series microholes were obtained by indentation, much more invasive that electro-erosion, simulating a damage due to a mechanical impact or scratch on the surface material, common on real components during the life span. In both cases the microholes act as a pre-existent crack. The results show that defects obtained by indentation lead to a minor fatigue limit with respect of larger defects obtained by electro-erosion. This was interpreted as the modification of the residual stress field due to the mechanical indentation. On the basis of the results some consideration is formulated about generating micro-holes with one of the discussed ways.
Fatigue Behavior of Ferritic-Pearlitic-Bainitic Steel – Effect of Positive Mean Stress
Authors: Polák Jaroslav , Petrenec Martin
Published: October 2009

The fatigue properties of ferritic-pearlitic-bainitic steel using specimens produced from massive forging were measured in stress controlled regime with positive mean stress. The cyclic creep curves and cyclic hardening/softening curves were evaluated. The fatigue life was plotted in dependence on the mean stress and on the plastic strain amplitude. The principal contribution to the drop of the fatigue life with the mean stress is due to the increase of the plastic strain amplitude in cycling with mean stress.
Evaluation of Flexural Performance in UHPC(Ultra High Performance Concrete) According to Placement Methods
Authors: Ryu Gum Sung , Kang Su Tae , Park Jung Jun , Koh Gyung Taek
Published: October 2009

Apart from its high compressive, tensile and flexural strengths reaching approximately 200MPa, 15MPa and 35MPa, respectively, Ultra High Performance Concrete (UHPC) is characterized by its high resistance against degrading factors that can delay their penetration and diffusion speeds down to 1/20 to maximum 1/10,000 compared to ordinary concrete. UHPC also exhibits self-compaction properties with a slump flow of about 220mm. Furthermore, the most remarkable feature of UHPC is the improvement of its flexural strength and toughness through the admixing of steel fiber. Accordingly, this study evaluates the effects of the placement method on the flexural performance of UHPC. As a result, the flexural strength of UHPC appears to be extremely dependent on the placement method with variation of the maximum flexural strength up to 2 to 3 times while poor influence is observed on the initial crack strength.
Comparison of Fatigue Behavior of FS (Friction Stir) and TIG Welded Al 6N01 Alloy
Authors: Yoon K.H. , Kwun S.I. , Yeon Yun Mo
Published: October 2009

The fatigue properties of friction stir (FS) and TIG welded Al 6N01-T5 alloys were compared in the present study. The low cycle fatigue (LCF) test was performed under total strain amplitudes in the range of ± 0.6 ~ ± 1.5% and with a strain rate of 3 x 10-3/s. During low cycle fatigue, the base metal showed little cyclic hardening or softening, whereas both the FS and TIG welded zones showed a large amount of cyclic hardening until fracture, although the fatigue life of the TIG welded zone was much shorter than that of the FS welded zone. The fatigue crack growth rate (FCGR) was retarded in the heat affected zone (HAZ) on the advancing side of the FS welded zone, due to the compressive residual stress in this region. The differences in the fatigue properties in these two welded zones were discussed in terms of the microstructural changes during fatigue.
Residual Stress on Inconel 718 Turbine Components after Machining
Authors: Lavella Mario , Berruti Teresa
Published: October 2009

Results of residual stress measurements on Inconel 718 turbine components after machining are here presented. The work is focused on the experimental detection of the residual stress state produced after turning (orthogonal cutting and standard) and milling. The aim of the experimental activity was to supply an experimental data base of proved reliability for milling and turning model validation. This activity was performed inside the EU STREP project VERDI. The residual stresses were detected by means of X-ray diffraction technique. The experimental plan of measurements was performed on components worked with different working parameters (cutting velocity and feed rate) and by means of new and worn tool. The trends of residual stress versus depth are presented.
Analysis of the Dynamics and Vibrations of Structures Subjected to Unsteady Aerodynamic Loads for Crack Detection
Authors: Mateescu Dan , Han Yong , Misra Arun
Published: October 2009

This paper is devoted to the analysis of the dynamics and vibrations of wing-like structures with bonded piezoelectric strips and subjected to unsteady aerodynamic loads for crack detection. Pairs of piezoelectric strips, acting as strain sensors, are bonded at the same locations on the opposite sides of a thin structure executing flexural oscillations. In this crack detection strategy, the measured voltage outputs of the two piezoelectric sensors forming a pair are conveniently subtracted in order to eliminate the voltage corresponding to the same level of strain on both sides. This differential voltage output is used to indicate the presence of a crack in the structure. The nonlinear mechanical behavior of the crack in the compression and extension phases of the oscillatory cycle increases substantially the sensitivity of this detection procedure. Furthermore, this crack detection method can take advantage of the aeroelastic oscillations of the wing structures, which are always present during normal flight evolutions of an aircraft. The numerical analysis of the dynamics of structure subjected to unsteady aerodynamic loads uses a finite element formulation for the structure and the piezoelectric strips and a panel method is used to compute the unsteady aerodynamic loads acting on the oscillating wing structure. Numerical simulation results are presented in the paper to explore the feasibility of this crack detection strategy by using the aeroelastic oscillations of the wing-like structures with bonded piezoelectric strips.