bluuebunny/crossref_metadata_2025 huggingface dataset:
Deterioration of FRC Plate due to Explosion and Change of Temperature
Authors: Prochazka Petr P.
Published: November 2012

Recently it was shown that the temperature plays very important role in coupling with the impact of shock wave caused by explosion in a free space. The deterioration of fiber reinforced concrete structures, FRC, at the face to which the main impact of the coupled load is directed is not easy to describe. In couple of previous papers of the author the problem was solved under condition that the structure behaves elastically. It appeared that a numerical tool known as free hexagon method, which is based on soft contact problem in combination with boundary elements, seems a powerful approach solving any disconnecting media. The soft contact is identified by nonlinear spring rules. Similar idea is used in the suggested paper for solving the coupled problem envisaged, but the mesh of free hexagons is split into the air and the structure. If the impact of explosion and the subsequent shock wave cause is viewed separately from the changes in material due to temperature a very fast changes in stresses and movements in material are observed in the first case while the changes due to temperature develop much slower. On the other hand in combination of both influences the temperature increase the activity inside of structures considerably. In the paper the theory is briefly described and selected examples illustrate the mobility of the application of the method to a problem of FRC plate.
Monitoring Fatigue Cracks and Stress Intensity Factors Based on the Distributed Dislocation Technique
Authors: Boukellif Ramdane , Ricoeur Andreas
Published: November 2012

We present a method for crack detection and stress intensity factor measurement in plate structures by using strain gauges and applying the dislocation method. The presented approach is based on the strain measured at different locations on the surface of the structure. This allows both the identification of crack position parameters, such as length, location and angles with respect to a reference coordinate system and the calculation of stress intensity factors (SIF). The method solving the direct problem is based on the idea of representing the crack by a line of point dislocations. The latter are formed by applying a constant displacement between adjacent points located at either side of the crack. Thus, the approach is based on the weighted superposition of elastic Greens functions representing the strain field due to the presence of a crack, where the weights are being identified by inverse problem solution. Since the strain fields are controlled by both external loads and the crack growth the unknown parameters are crack length, position and inclination as well as loading quantities. The particle swarm algorithm (PSO) came out to be most suitable for parameter identification in a high dimensional space.
Fatigue Properties of Solution-Treated Type 304 Stainless Steel after Nitriding
Authors: Nakamura Yuki , Nakajima Masaki , Shimizu Toshihiro , Suzuki Kentaro , Bai Yu , Uematsu Yoshihiko
Published: November 2012

The solution treatment after nitriding (STAN) was performed to stabilize the γ- phase in a metastable austenitic stainless steel, type 304, and to improve the strength of type 304 by the solid solution of nitrogen. Plasma nitriding was conducted at 500°C for 8.5h, and then solution treatment was performed at 1200°C for 1h. As a result, the static strength and the hardness were improved by the STAN. Rotary bending fatigue tests were performed on the specimens with STAN (solid solution strengthened) together with the untreated and the nitrided ones in laboratory air and in 3%NaCl solution. In laboratory air, the fatigue strength of the solid solution strengthened specimen increased compared to that of the untreated specimens, where fatigue limits were 340MPa and 290MPa for the solid solution strengthened and the untreated, respectively. However, the fatigue limit of the solid solution strengthened specimen was lower than that of the nitrided specimen, that is, 380MPa. On the other hand, in 3%NaCl solution, the fatigue strengths of the nitrided specimens and the solid solution strengthened specimens decreased significantly compared to those in laboratory air. After the fatigue tests at the stress level of fatigue limit in laboratory air, the strain-induced martensitic transformation was examined by XRD. In the solid solution strengthened specimens, the strain-induced martensitic transformation was not detected during fatigue tests until 3x107 cycles, indicating that the γ- phase was stabilized by the solid solution of nitrogen.
Fatigue Crack Growth of Alloy 7050-T7451 Plate in L-S Orientation
Authors: Bao Rui , Zhao Xiao Chen , Zhang Ting , Zhang Jian Yu
Published: November 2012

Experiments have been conducted to investigate the crack growth characteristics of 7050-T7451 aluminium plate in L-S orientation. Two loading conditions are selected, i.e. constant amplitude and constant stress intensity factor range (ΔK). The effects of ΔK-levels and stress ratios (R) on crack splitting are studied. Test data shows that crack splitting could result in the reverse of crack growth rate trend with the increasing R ratio at high ΔK-level. The appearance of crack splitting depends on both ΔK and R.
Determination of Intensity Factors for Interfacial Cracks in TIP Materials
Authors: Zhong Hong Jun , Lei Jun
Published: November 2012

An explicit extrapolating formula for a general case of the interfacial crack plane lying with an angle to the poling axis in transversely isotropic piezoelectric (TIP) materials is derived, which is very feasible to determine the intensity factors for numerical methods such as FEM or BEM. Additionally, a more concise extrapolating formula for the typical state of the interfacial crack plane lying perpendicular to the poling axis is also presented in this paper.
Failure of Composite T-Joints in Bending with Through-the-Thickness Reinforcement: Stitching Vs Z-Pinning
Authors: Cui H. , Li Yu Long
Published: November 2012

The stitched composite T-joints and Z-pinned ones subject to bending load were investigated in this paper. A simple theoretical model characterizing the failure process of through the thickness reinforcement (TTR) during mode I delamination was presented. The experimental results showed that the initial damage load and maximum load of stitched specimens are higher than that of Z-pinned ones, while the energy absorption of stitched specimens during delamination is lower than that of Z-pinned ones. The energy absorption values predicted by the present model meet the experiments reasonably well. High friction force at the interface between TTR tow and matrix, with a long pull-out displacement of the tow, helps to improve the delamination resistance.
A 3-Dimensional Model Related to Stress-Strain-Time of Rock Salts
Authors: Zhang Hua Bin , Wang Zhi Yin , Ma Ji Wei
Published: November 2012

To build a stress-strain-time relationship of salt rock with unified instantaneous law and creep law, we combine the stress-strain curve with whole process of creep curve, looking for inner relation between softening curve and creep deformation. Finally, the stress-strain-time space surface is obtained. The researching results demonstrated that time and space development law of rock salts can be well reflected by it.
Numerical Modelling of Particulate Composite with a Hyperelastic Matrix
Authors: Máša Bohuslav , Náhlík Luboš , Hutař Pavel
Published: November 2012

The main aim of the paper is an estimation of the macroscopic mechanical properties of particulate composites using numerical methods. Matrix of the considered composite was cross-linked polymethyl methacrylate - PMMA in a rubbery state, which exhibits hyperelastic behaviour. The three parameter Mooney Rivlin material model, which is based on the strain energy density function, was chosen for description of the matrix behaviour. Alumina based particles (Al2O3) were used as a filler. Numerical modelling based on the finite element method (FEM) was performed to determine stress-strain curve of the considered particulate composite. Representative volume element (RVE) model was chosen for FE analyses as a modelling approach of a composite microstructure. Various geometry arrangements of particles and various directions of loading have been considered and composite anisotropy has been investigated. A good agreement between numerical calculations with damage model and experimental data has been found and the described method may have a great potential for numerical modelling of composite behaviour and design of new particulate composite materials.
Grain-Boundary Segregation of Phosphorus and Inter-Granular Fracture Behavior under Low Tensile Stresses
Authors: Fu Yu Dong , Li Qing Fen , Sun Wei Xin
Published: November 2012

The present work is an effort to provide experimental results focusing on segregation behavior of phosphorus at grain boundary and the intergranular fracture behavio under low tensile stresses. AES (Auger electron spectroscopy) experiments and dynamic analyses on the non-equilibrium grain-boundary segregation (NGS) of phosphorus and the SEM photos of intergranular fracture in Auger specimens in 12Cr1MoV steel were carried out in this paper. The variation of phosphorus segregation level in grain boundary under different low tensile stresses and at different temperature were obtained. Results show that NGS of phosphorus occurred in the experimental steel while subjected to low tensile stresses. Maximum values of phosphorus segregation level were obtained at the critical times. SEM photos of intergranular fracture in Auger specimens of the test steel show that the intergranular fracture rate increased with increasing concentration of phosphorus. The intergranular fracture behavior is accordant with the segregation behavior of phosphorus at grain boundary.
Effect of the Neodymium Content on Mechanical Properties of the Electro-Brush Plated Nano-Al2O3/Ni Composite Coating
Authors: Jin Guo , Cui Xiu Fang , Liu Er Bao , Li Qing Fen
Published: November 2012

The effect of the neodymium content on mechanical properties of the electro-brush plated nanoAl2O3/Ni composite coating was investigated in this paper. The microstructure and phase structure were studied with scanning electron microscope (SEM) and X-ray diffraction (XRD). The hardness and abrasion properties of several coatings with different neodymium content were studied by nanoindentation test and friction / wear experiment. Results show that the coatings are much finer and more compact when the neodymium was added, and the hardness and abrasion property of the coatings with neodymium were improved obviously. Besides, the small cracks conduced by the upgrowth stress in the coatings were ameliorated when the rare earth neodymium was added. The improvement mechanism was further discussed.
Analysis of Crack Tip Field in Materials with Creep Behavior
Authors: Meng Qing Hua , Liang Wen Yan , Wang Zhen Qing
Published: November 2012

The stress and strain field near the tip of Mode I growing crack in materials under creep conditions is examined. The case of the effective stress equal to zero is considered. The asymptotic equations for the crack of the crack tip field are derived and solved numerically. It is concluded that the rates of stress and strain posses the rδ-1 singularity near the tip crack, and the stresses remain finite at the crack tip.
J-Integral and its Dual Form Based on Finite Deformation Theory
Authors: Liu Zong Min , Mao Ji Ze , Song Hai Yan
Published: November 2012

In general, there are large strains and displacements on the crack tip. So it is necessary to study-integral and its dual form based on finite deformation theory. Base forces theory is a new theory for describing finite deformation. -integral and its dual form based on base forces theory are presented in the paper. This work provides theoretical foundation for studying crack propagation.
Pressureless Sintering and Properties of Boron Carbide-Titanium Diboride Composites by In Situ Reaction
Authors: Liu Ai Dong , Qiao Ying Jie , Liu Ying Ying
Published: November 2012

Pressureless sintering to obtain high density boron carbide-titanium diboride composites by in-situ reaction was studied. Pressureless sintering behavior of this material was investigated between 1800-2150 .The effects of composition, sintering temperature and tine were examined. Density up to 98.5% T.D. was reached at 2150. Maximum values of flexural strength (502 MPa), hardness (33 Gpa) and fracture toughnes (4.6 MPa·m1/2) were observed in the specimens containing 15 vol.% TiB2.
Modelling of Discontinuous Environment
Authors: Boštík Jiří , Weiglová Kamila
Published: November 2012

Deformation process and strength of rock environment is significantly influenced by a presence of discontinuity planes. The paper deals with experimental modeling of underground structures in such a rock environment. Parametric analysis presents results from twin circular tunnels simulated in a scale model. The cases with and without zone of dislocations in between the tunnels were observed. Another variable factor studied was the distance between tunnels. The relation between model surface displacement and excavated length of the tunnel, which was monitored during the simulations, was used for mutual comparison of individual cases.
Fatigue Assessment of Trimaran Structure Based on Simplified Procedure
Authors: Ren Hui Long , Khurram Shehzad , Zhen Chun Bo , Asifa Khurram
Published: November 2012

In recent years, Trimaran platform design has got the attention of naval architects owing to its superior seagoing performance. Trimaran structure experiences severe loads due to its unique configuration and high speed, causing stress concentration, especially in cross deck region and accelerate fatigue damage. This paper presents fatigue strength assessment of Trimaran structure by simplified procedure. A methodology is proposed to evaluate fatigue loads and loading conditions by load combinations of direct calculation procedure of Lloyds Register Rules for Classification of Trimaran (LR Rules). Global FE analysis, in ANSYS, is performed to investigate the stress response. The stress range is computed by hot-spot stress approach, and its long term distribution is specified by Weibull distribution. Fatigue damage of selected critical details is calculated using mathematical formulation of simplified fatigue assessment procedure of Common Structure Rules (CSR).
A Comparative Study between Steel Grillage and SPS Stiffening Plate Based on FEA Eigen Value Analysis
Authors: Xue Qi Chao , Zou Guang Ping , Wu Ye , Li Jia , Shang Lei
Published: November 2012

Sandwich plate system (SPS) with polyurethane elastomer is more and more used on ship buildings as grillage. A Comparative Study on critical buckling loads between steel grillage and SPS stiffening plate are carried out in this paper. Plate elements and beam elements are used in numerical simulation and a rectangular model is taken as a calculating example. By using of FEA software ANSYS, ultimate buckling loads are calculated with different influential factors between steel grillage and SPS stiffening plate, including the number of stiffening ribs, inertia moment of stiffening ribs, and the thickness of plates. the analysis results of comparison shows that SPS stiffening plates have better performance than steel grillage under in plane compressive loadings.
Yield Criterion and Crack Tip Plastic Zone of Nickel-Based Single Crystal
Authors: Yang Li Hong , Zou Guang Ping , Qu Jia
Published: November 2012

A modified Hill yield criterion considering tension-shear stress coupling was given and material parameters of nickel-based single crystal in this criterion was determined by the Least Square Method. Crack tip plastic zones of nickel-based single crystal plate were analyzed by using this modified yield criterion and the plastic zones corresponding to mixed mode I, II crack, were derived. The crack tip plastic zones of nickel-based single crystal were compared to that of isotropic material. The influences of tension-shear stress coupling, compound ratio of mixed mode I, II crack and temperature on crack tip plastic zones were discussed. The results obtained in this paper indicate that the increasing rate of crack tip plastic zones with compound ratio in the plane stress condition is greater than that in the plane strain condition for nickel-based single crystal and the temperature has greater influence on the size of crack tip plastic zones.
Influence of Welding Conditions on Residual Stresses of Multi-Pass Tube Sheet Welds
Authors: Li Hong , Zheng Yong , Li Li
Published: November 2012

Residual stresses and residual plastic strains of the welded structures are the products of nonlinear behaviors during welding. The residual stresses will cause errors during the assembly of the structure and injure the beauty of appearance of the structure. Based on an elastic-plastic-model, finite element numerical simulation of a representative tube sheet penetration assembly with loop welding line joined by multi-pass welding is carried out and the influence of welding conditions on residual stresses of the tube sheet welds is studied in this paper. Nonlinear three dimensional transient temperature fields and real-time dynamic stresses field are analyzed by FEM. The heat source is modeled as a moving heat flux following a double ellipsoid distribution and the temperature-dependent properties of materials are considered. The method of birth and death of element in finite element analysis is applied to simulate the gradual growth of weld pass metal. It is shown that welding sequence, size of groove welding and weld toes dressing will obviously change the magnitude of the residual stresses of tube sheet welds.
Reliability Analysis for Stiffened Plate on the Maximum Entropy Method
Authors: He Jian , Chen Xiao Yan
Published: November 2012

Stiffened plate is widely used in vessel structure because of its high bearing capacity and low weight so the research of failure probability for stiffened plate under explosion load has important engineering meaning. Stiffened plate under near-field explosion is taken as research subject, dynamite density and yield stress of plate are selected as random variables, the original values of one hundred groups of random variables are gotten through the random number generation program, and the moments of random variables are obtained. Based on failure criterion of displacement ductility, the performance function of structure is established, probability density function of performance function is fitted using maximum entropy method then the failure probability of stiffened plate structure is obtained. So as to solve the problem of calculate failure probability when the sample size is small and the probability density function is unknown.
An Enhanced Time-Reversal Method for Impact Damage Monitoring on Plate-Like Structures
Authors: Chen Chun Lin , Li Yu Long , Yuan Fuh Gwo
Published: November 2012

Based on the self-focusing property of time-reversal (T-R) concept, a time focusing parameter was suggested to improve the impact source identification method developed in authors previous work. This paper presents a further study on monitoring relatively high energy impact events which caused induced damage on structures. Numerical verifications for a finite isotropic plate and a composite plate under low velocity impacts are performed to demonstrate the versatility of T-R method for impact location detection with induced plastic deformation and delamination damage on metallic and composite structures respectively. The focusing property of T-R concept was adequately utilized to detect impact/damage location. The results show that impact events with various features can be localized using T-R method by introducing the time focusing parameter. It is suited to monitor serious impact events on plate like structures in practice in future.
Influence of Finite Element Modeling Choices in the Assessment of Stress Concentrations at Fatigue Prone Locations in Orthotropic Bridge Decks
Authors: de Corte Wouter , Jansseune Arne
Published: November 2012

In orthotropic bridge decks, the rib to floorbeam connection is a major source of fatigue problems. Commonly, the trapezoidal ribs cross the floorbeam continuously necessitating clearance holes in its web, and frequently additional web cutouts are foreseen to relieve the ribs lower edges. This solution is favorable for rib cracking but will generate stress concentrations in the web itself. The shape of the additional cutout has a major influence on the sizes of the concentrations rendering differences of a factor 2 or 3 for corresponding overall geometries and loading schemes. Various authors have studied cutout shapes through full scale testing or by computation by finite element modeling. This paper presents such a study, but focuses on the influence of the finite element modeling itself. It is shown that the mesh density, the element type, the choice between shell and volume elements. This is an important finding and should not be overlooked when comparing finite element based results to coded values or measured results. In order to do so, the results of the numerical work are compared to strain results from full scale tests.
Effect of Characteristic Parameters of Exponential Cohesive Zone Model on Mode I Fracture of Laminated Composites
Authors: Zhu Guo Wei , Jia Yu Xi , Qu Peng , Nie Jia Qi , Guo Yun Li
Published: November 2012

Delamination is a particularly dangerous damage mode of high performance laminated composites. In order to describe the composites ductile cracking and its progressive evolution accurately, the adjusted exponential cohesive zone model (CZM) is adopted, which correlates the tensile traction with the corresponding interfacial separation along the fracturing interfacial zone. At first the adjusted exponential CZM is used to simulate the mode I delamination of the standard double cantilever beam (DCB). The simulated results are in good agreement with the corrected beam theory and the corresponding experimental results. Then in order to research how the interfacial properties influence the mode I fracture, the interfacial strength and the critical energy release rate are studied. The main results are obtained as follows. The interfacial strength plays a crucial role in the laminated composites delamination onset, and it affects the peak load significantly if there is not a pre-crack. Once the delamination propagation begins to occur in the laminated composites, the responses of the load-displacement plots are relatively insensitive to the interfacial strength, and only the critical energy release rate is of critical importance. Furthermore, the peak load increases with the increase of the critical energy release rate and interfacial strength.
Damage Detection for Structural Health Monitoring Using Ultrasonic Guided Waves
Authors: Li Hong Yuan , Xu Hong
Published: November 2012

The use of ultrasonic guided waves for damage detection suffers from the multi-modes and dispersion. Much attention has been paid to transducer design and excitation frequency chosen to suppress the multiple modes and dispersion. However, little attention has been paid to complex signal processing. In this paper, the dispersive propagation of the guided waves are firstly reviewed. And then the matching pursuit method is introduced as a feature extraction algorithm. In order to present well the characteristic of the guided waves signal, a dispersive dictionary is designed based on the guided waves propagation. A two-stage pursuit method consisted of coarse and fine matching is used. At last, the proposed method is verified by finite element simulation and successfully extracted damage related dispersive pulses from measured noisy signal.
Low Cycle Fatigue Behaviors of TI-6AL-4V Alloy Controlled by Strain and Stress
Authors: Wang Rui Feng , Li You Tang , An Hu Ping
Published: November 2012

The low cycle fatigue behaviors of TI-6AL-4V alloy controlled by strain were investigated by experiment. The fatigue tests were performed at room temperature, and cyclic strain and stress ratio are 0.1 with triangle load wave. The results show that TI-6AL-4V alloy is soften rapidly under the cyclic tensile stresses and it is harden rapidly under the cyclic compressive stresses during the initial-stage of strain controlled fatigue, and the rates of cyclic soften and cyclic harden are decreased with the fatigue progress. The soften rate is related to the cyclic strain but little to the cyclic stress during the overall fatigue progress. The change of cyclic stress is related to the macro friction stresses. The results of experiment show that obvious cyclic creep occurs under the stress controlled low cycle fatigue conditions, and the magnitude of cyclic creep strain is related to the maximum cyclic stress. The softening of tensile friction stresses is the main factor of cyclic creep.
Analysis of Stress Singularity near the Tip of Artificial Crack
Authors: Li You Tang , Li Huai Qing
Published: November 2012

A generalized expression of the stress-singularity function at the tip of artificial crack is proposed, and a formula to calculate the stress intensity factor of artificial crack is obtained in the paper. The solutions of stress singularity of a cracked bi-materials beam under uniform tension and bending were computed. The results show that the degree of stress-singularity is determined by the exponent λ at the tip of artificial crack, and the exponent λ is, not only determined by materials parameter of artificial crack but also by angle. Key words: artificial crack; bi-material; stress singularity; eigen value; stress extrapolation method
Structural Strength Evaluation of a Stainless Railroad Car
Authors: Yoon Sung Cheol , Kim Jeong Guk , Choi Don Bum , Koo Dong Hoe , Park Geun Soo
Published: November 2012

This study is an experimental research on using stainless steel car body structure for urban railway vehicles. The car body used in the experiment was made of stainless steel. To evaluate the structural characteristics and safety of the stainless car body, static load test was carried out by means of "Performance Test Standard for Electrical Multiple Unit" with the reference code JIS E 7105. The structural safety of the car body was evaluated by implementing vertical load, horizontal compressive load, twist load, and 3-point support tests. Test results verified that the structural safety of a car body was very stable and safe under design load conditions.
Study of the Characteristic of Composite Sandwich Panel with Cut-Out under Compression Load
Authors: Lee Jong Woong , Kong Cheol Won , Jang Young Soon , Lee Young Shin
Published: November 2012

A sandwich construction is applied to wing skins and fuselages, along with many other structures in aeronautical applications, due to its increased stiffness and reduced weight. In this paper, a face-sheet composed of plain-woven composite laminate that uses prepregs (HPW193/RS3232) and a core material of aluminum honeycomb (Al5052/F40-0.0025) is used. Launch vehicle structures have cut-out areas to check the status of the payload and electric equipment. Cut-out areas reduce the structural stiffness of the launch vehicle structure. Changes in the shape of cut-outs can cause a difference in load support ability of the structure. Compression tests and FEM analysis were performed on composite sandwich panels with various types of cut-out, but with the same overall area.
Matching Asymptotic Method in Propagation of Cracks with Dugdale Model
Authors: Tuyet Dang Thi Bach , Marigo Jean Jacques , Halpern Laurence
Published: November 2012

The goal of this work is to apply the matching asymptotic method combined with a variationalapproach to study the initiation and the propagation of a cohesive crack from the tip of a preexistingnotch following the Dugdale cohesive force model when the characteristic length of the material (includedin the Dugdale model) is small by comparison with the characteristic length of the body.
Modelling Micro-Damage in Granular Solids
Authors: Buonsanti Michele , Leonardi Giovanni , Scoppelliti Francesco
Published: November 2012

The prediction of the spacing and opening of cracks in asphalt or concrete pavements, and particularly in airports (runway, taxiway and apron) is important for the durability assessment. A basic problem is the spacing of parallel planar cracks from a half space surface, approached and solved by numerous authors by means of macro-scale computational models. The calculated values of crack spacing are in relatively good agreement with the values reported in observations on asphalt concrete pavements. The constituents of granular solids are, fundamentally, made of grain in contact and, these materials are highly discontinuous and non-homogeneous with two or three phases (solid, voids with air or water), and finally binding among solid parts. The aim of this paper is to suggest a micromechanical approach in granular material solids, focusing the attention on a simple RVE (representative volume element) based on two rigid particles linked through an adhesive material (bitumen). Our final aim is to propose a micro-damageability parameter (interface loss) supposing the adhesion decreasing under the action of prescribed tangential and normal relative displacement. The reduction is attributed by progressive damage and comes with energy dissipation and moreover we assume unilateral contact conditions for normal displacement and Coulomb friction for the tangential displacement.
Modeling Delamination of Interfacial Corner Cracks in Multilayered Structures
Authors: Veluri Badrinath , Jensen Henrik Myhre
Published: November 2012

Multilayered electronic components, typically of heterogeneous materials, delaminate under thermal and mechanical loading. A phenomenological model focused on modeling the shape of such interface cracks close to corners in layered interconnect structures for calculating the critical stress for steady-state propagation has been developed. The crack propagation is investigated by estimating the fracture mechanics parameters that include the strain energy release rate, crack front profiles and the three-dimensional mode-mixity along the crack front. The developed numerical approach for the calculation of fracture mechanical properties has been validated with three-dimensional models for varying crack front shapes. A custom quantitative approach was formulated based on the finite element method with iterative adjustment of the crack front to estimate the critical delamination stress as a function of the fracture criterion and corner angles.
Numerical Simulation of Crack Tip Behavior under Fatigue Loading
Authors: Xu Y.G. , Tiu W. , Xu Y.Z.
Published: November 2012

Fatigue damage is a localized phenomenon controlled by the near-tip crack behavior. This paper presents an application of a dislocation distribution technique to the simulation of crack tip behavior under fatigue loading. A centre-cracked tension specimen under uni-axial fatigue loading is used in the study. Crack opening and plastic deformation around the crack tip are simulated by distributions of dislocation dipoles in crack plane and four inclined planes ahead of the crack tip. Climb dislocation dipole is used to model the opening and closing of the crack while glide dislocation dipole is used to simulate the backward and forward slip in the inclined planes during loading and unloading of the fatigue cycle. Stress field around the crack tip is obtained by the superposition of the contributions of the applied external load and the distributed dislocation dipoles. Correct boundary conditions of the model are achieved by employing a quadratic programming technique to minimize a properly constructed non-negative object function. It is found that the simulated crack closure variations under the constant amplitude fatigue load agree well with the result of a previously developed modified strip yield model with an appropriate constraint factor.
Delamination Threshold Load of Composite Laminates under Low-Velocity Impact
Authors: Xu Y.G. , Shen Z. , Tiu W. , Xu Y.Z. , Chen Yong K. , Haritos G.
Published: November 2012

A key factor affecting the use of carbon fibre reinforced composite laminates is the low velocity impact damage which may be introduced accidentally during manufacture, operation or maintenance of the component. Among the several barely visible impact damages, interlaminar delamination is the dominant failure mode and may reduce the post-impact compressive strength of the component significantly. This paper focuses on the study of the delamination threshold load (DTL) above which significant increase of delamination and thus large reduction of the residual compressive strength of the component may occur. Instrumented drop weight tests were carried out under various impact energy levels to determine the delamination threshold load. Efforts are directed to the study of the laminate thickness effect on the reliability of the detection of the DTL. The validity of the concept of DTL has been investigated and possible implications on the measurement of the DTL has been discussed. It is demonstrated that DTL exists but its detection requires proper testing conditions.
On the Direction of a Crack Initiated from an Orthotropic Bi-Material Notch Composed of Materials with Non-Uniform Fracture Mechanics Properties
Authors: Profant Tomáš , Klusák Jan , Ševeček Oldřich , Kotoul Michal
Published: November 2012

The assessment of conditions of crack initiation in a tip of a bi-material notch composed of two orthotropic materials is dealt. The assessment of the bi-material orthotropic notch stability criteria based on standard linear elastic fracture mechanics can lead to incorrect results due to a change of fracture mechanics properties. The change of the fracture mechanics properties are taken into account in the discussed stability criterion. It is shown that the criterion of this kind can qualitatively and quantitatively influence the results, and it contributes to more reliable assessment of components with geometrical and/or material discontinuity.
Fracture Behaviour of Thin Sheet Stainless Steel
Authors: Gubeljak Nenad , Jagarinec Darko , Predan Jožef , Landes John
Published: November 2012

The differences in fracture behavior between the compact tension C(T) and the middle tensile M(T) specimens make structure integrity assessment uncertain. Two different types of specimens C(T) and M(T) specimens made from stainless steel have been used for fracture toughness testing at the room temperature by the principles of the ASTM 1820-05 standard procedure. Stable crack initiation and crack propagation occurred for the C(T) specimens at lower values of crack driving force than for the M(T) specimens. Crack tip opening displacement-CTOD has been directly measured on the surface of specimens by using a stereo-optical grading method. The critical crack tip opening displacement at crack initiation CTODi has been measured as a plastic Stretch Zone Width (SZW) during a post test fractographic inspection. Comparison between the CTOD-R curves of both types of specimens shows some difference between the C(T) and the M(T) specimens, but a more significant difference appeared in the crack driving force, as consequence of different constraint (triaxiality) of the C(T) versus the M(T) specimens. Therefore, the result obtained by test on laboratory C(T) specimens cannot be directly used as fracture toughness material properties in a structure integrity assessment, except as a conservative lower bound estimate.
Estimation of Shear Behavior of Ultra High Performance Concrete I Girder without Shear Stirrups
Authors: Lee Jung Woo , Joh Chang , Choi E.S. , Kwak I.J. , Kim Byung Suk
Published: November 2012

Thinner and lighter members can be designed by utilizing the high stiffness and toughness, and high compressive strength of Ultra High Performance Concrete (UHPC), which reaches up to 180MPa. This high strength and ductile tensile behavior of UHPC makes it possible to design the web of the UHPC I Girder without conventional shear stirrups, which makes the UHPC I girder slender, light and economical. However, establishing shear design procedure for UHPC I girders without stirrups requires additional theoretical and experimental studies. This paper investigated shear behavior of UHPC I girder without shear stirrups. The test results show, in spite of no shear stirrups, test specimens have high ductility due to the bridging action of steel fibers against crack opening. UHPC I girders without shear stirrups tested show gradual increase of strength after initial cracking instead of brittle loss of strength as expected from the ordinary reinforced concrete I girders without stirrups. The decrease of the shear span-depth ratio increase the shear strength of the UHPC I girder without stirrups.
Electro-Mechanical Impedance Technique for Structural Health Monitoring of Composite Panels
Authors: Schwankl Martin , Sharif-Khodaei Z. , Aliabadi M.H. , Weimer Christian
Published: November 2012

Numerical modelling of EMI for damage detection has been presented in this paper. The PZT model is validated against the published experimental result for free disk and tied to the structure. The numerical modelling of the PZT patch will result in the admittance measure of the structure. The imaginary part of the admittance measure is used for developing a self-diagnostic sensor system. The real part of the admittance measure was used to develop a damage detection algorithm. Damage detection using EMI method was successfully applied to a simple composite disk and a stiffened panel. The EMI method is suitable for short range damage detection in structural parts with limited or no access.
Micromechanical Characterisation of Microstructure in Weld Heat Affected Zone of Structural Steel
Authors: Shimada Yusuke , Kayamori Yoichi , Nishida Shohei , Matsuda Mitsuhiro , Takashima Kazuki
Published: November 2012

Microstructures in the weld heat affected zone (HAZ) can cause a decrease in fracture toughness, and evaluating the effect of microstructures on fracture toughness is helpful in understanding the cause of the fracture toughness decrease. In this study, micro-sized tensile specimens were sampled from base metal and HAZ, and the mechanical properties and fracture behaviours of different steel microstructures were directly investigated by micro-sized mechanical testing.
The Applicability Study on the FRP-Concrete Composite Bridge Deck for Cable-Stayed Bridges
Authors: Kim Sung Tae , Park Sung Yong , Cho Keun Hee , Cho Jeong Rae , Kim Byung Suk
Published: November 2012

This study is related to the FRP-concrete composite bridge deck for cable-stayed bridges developed by the Korea Institute of Construction Technology since 2007. This deck disposes a FRP panel at the bottom and is orthotropic owing to its fabrication through pultrusion process. In the cable-stayed bridge applying precast deck, support conditions occur at the cross beam and edge girder. Therefore, need is to verify the performances in the longitudinal and transverse directions when applying the orthotropic deck to cable-stayed bridges. Accordingly, specimens enabling to verify the performance in each direction are fabricated and subject to structural performance test. Based on the test results, the serviceability and applicability of the FRP-concrete composite deck to cable-stayed bridges are evaluated.
Improvement of Fatigue Crack Growth Behavior in the Case of the Cracked Specimen with Relatively Narrow Width
Authors: Ferdous Md. Shafiul , Makabe Chobin , Miyazaki Tatsujiro
Published: November 2012

The improvement of acceleration behavior of crack growth was investigated with constant stress amplitude under negative stress ratio R=-1. Then a technical method to detect the fatigue crack growth was discussed. For example, when the stress amplitude exceeds a critical value, crack growth rate of overloaded specimen became higher than that of baseline which was obtained by crack growth test without applying overload. In some experimental cases, the acceleration of crack growth was observed and that could be happened on practical cases. Stop-holes were drilled at crack tips or in the vicinity of crack tips to remove the plastic zone and the effect of that on crack growth behavior were investigated. Also, steel pins were inserted into the stop-holes and its effect was discussed. Finite element method (FEM) was used to analyze the stress concentration at the edge of stop-holes. Positions of center of the stop-holes were varied at different distance from the crack tips to investigate the effect of stop-holes on fatigue crack growth. Also, stress intensity of base and stop-holed specimen was calculated. Then, the effect of stop-hole was discussed by both the experimental and analytical results. Specially, it was discussed whether the crack growth behavior was improved or not in the case of relatively smaller width specimen.
Investigation of Damping Characteristics of Metals by the Use of Inverted Torsion Pendulum Method
Authors: Asahina Toshikatsu , Shioya Tadashi , Toguri Takahiro , Sekine Masanao
Published: November 2012

Damping characteristics of metals are measured by the use of inversed torsion pendulum method. As the materials, aluminum alloys, magnesium alloys, Inconel etc are used with the temperature and frequency parameters. Mild steel is employed as a reference material for calibrating the apparatus. The measured damping coefficient of magnesium alloys is larger than that of aluminum alloys indicating that the HCP crystal structure has more damping effect than the FCC structure. The damping of these metals increases with temperature. The manner of increment of damping is investigated to analyses the microscopic mechanism of damping.
Relationship between Crack Extension Behavior and Fatigue Life of C/C Composites
Authors: Setyabudi Sofyan A. , Makabe Chobin , Fujikawa Masaki
Published: November 2012

The fatigue and fracture mechanism of C/C composites material was investigated in notched and smooth specimen. Also, the initiation and growth behaviors of cracks were continuously observed. Specially, the phenomenon of fracture constraint in notched specimen was discussed. This phenomenon was related to the crack growth behavior and shear damage in the matrix. In the present study, fatigue limit was defined by the critical stress level that the specimen was not broken even after applied 1x106 stress cycles. When the fatigue life was longer than 1x106 stress cycles, the initiated crack was stopped to growth after reaching some critical length. Also, the density of crack initiation was low. When the fatigue life became shorter than that, the cracks extended rapidly and coalescences of cracks were observed. The crack growth behavior was strongly related to the fatigue limit and unstable fracture conditions. Also it is found that the compliance or elastic modulus of the specimen was related to residual fatigue life. Now, an observation of crack in C/C composites was performed effectively in the present study.
Evaluation of Setting Time in Ultra High Performance Concrete
Authors: Kim Sung Wook , Park Jung Jun , Yoo Doo Youl , Yoon Young Soo
Published: November 2012

Ultra high performance concrete (UHPC), characterized by a high strength and high ductility, is also subjected to large shrinkage due to its low water-to-binder ratio and its large content in high fineness materials. The large amount of autogenous shrinkage of UHPC can induce crack on structural member when it was restrained with reinforcement and form. However, shrinkage of UHPC in plastic state is not generating confining stress, which is the main cause of initial crack. Normally, the setting time in concrete is an index to distinguish shrinkage which occur confining stress or not. An estimation of setting time is conducted in compliance with ASTM C 403 till now however, that test standard reveals error of results due to discordance of test condition as following with concrete type. This study therefore evaluated setting time of UHPC through the modified test method which was proposed by KICT. Test results and analyses proved a discrepancy of setting time between ASTM and proposed method. The proposed method put faith in evaluation of setting time in accordance with UHPC.
Fracture and Damage Characterization of Natural Fiber Composites
Authors: Takagi Hitoshi , Hagiwara Yuji , Nakagaito Antonio Norio
Published: November 2012

This paper reports the microscopic fracture behavior of natural fiber-reinforced green composites. The acoustic emission (AE) method of nondestructive and real-time testing was applied to detect small-scale energy release phenomena during tensile deformation of the green composites. The unidirectional abaca fiber was embedded in a starch-based biodegradable resin matrix. Two kinds of pre-damaged abaca fibers as well as as-received (i.e. undamaged) fiber were used to examine the effect of the pre-damaged abaca fiber on the overall fracture behavior of the unidirectional green composites. In the case of the green composites reinforced with as-received abaca fiber, both of the tensile strength and fracture strain were relatively high. In the case of the green composites reinforced with pre-damaged abaca fiber, however, showed relatively smaller tensile strength and fracture strain. In addition, a wide range of amplitude AE events were measured during the tensile deformation. This tendency was enhanced in the composites reinforced with heavily damaged abaca fiber. The experimental results showed that the AE activity in the early deformation stage was associated with such the microscopic fracture of pre-damaged abaca fibers.
Characterization of Metal Magnetic Memory of Thermal Damage Correlated with Initial Cumulative Fatigue Damage for Laser Cladding Remanufacturing Technology
Authors: Zeng C. , Tian W. , Hua L.
Published: November 2012

Laser cladding act as a remanufacturing technology used more and more but the study of the fatigue properties of such products falls relatively behind. To work out the influence fatigue damage and thermal damage have on the fatigue life of laser cladding remanufactured products, this paper deals with the study of the characteristic of metal magnetic memory (MMM) signals of components experienced with fatigue test and a succeeding laser surface burning. The MMM signals was acquired for three times, that is before fatigue test, after fatigue and after laser treatment, respectively. Statistic investigation of the experiment result showed that the magnetic signal was closely related to the state of fatigue damage and thermal damage of the specimen. Based on such result, it is expected to quantify the study by statistical analysis of large samples so as to find a correlationship with the last fatigue life.
SEM In Situ Study on Pre-Corrosion and Fatigue Cracking Behavior of LY12CZ Aluminum Alloy
Authors: Li Xu Dong , Mu Zhi Tao , Liu Zhi Guo
Published: November 2012

Corrosion fatigue is a form of degradation subjected to combined damage of mechanical stress and corrosive medium, which is an issue in aircraft industry. Experimental investigations on prior corrosion fatigue cracking behavior of LY12CZ were conducted with scanning electron microscope (SEM). Results indicate corrosion damage is important for the fatigue small cracking behavior of LY12CZ aluminum alloy. The effect of corrosion pit on fatigue crack can be characterized by the depth of corrosion pit. Based on small crack, another way to evaluate crack growth rate for AALY12CZ is proposed.