bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Study on the Mechanical Characteristics of Cracked Rockmass under Lateral Constraints
Authors: Han Li Jun , He Yong Nian
Published: March 2009

Surrounding rocks of deep underground engineering are generally cracked, between which and support exists combined effect that can be reflected by the mechanical characteristics of cracked rock mass under lateral Constraints. In this paper, the strength and deformation characteristics of the cracked rock mass under lateral Constraints are investigated with methods of physical and numerical experiments. The results show that the rock mass behaves as equivalent continuum and tends to stable after deforming and re-fracturing, and has stress hardening behavior. These characteristics are obviously different from that of shearing slippage of rock samples at the residual stage of triaxial experiment.
Numerical Simulation of Crack Development in Reinforced Concrete Structures under Eccentric Loading
Authors: Zhang Juan Xia , Liu Junjie , Tang Chun An , Chang Xu , Wang Shu Hong , Zu Wancheng , Zhao Wen
Published: March 2009

Reinforced concrete structures are generally designed to allow cracking under service loading. Accurate modeling of crack formation and propagation at lower load levels is therefore important. In this paper, a Material Failure Process Analysis code (MFPA2D) is used to model the crack initiation and propagation in reinforced concrete bridge pier subjected to eccentric loading. In our numerical model, the reinforced concrete is assumed to be a three-phase composite composed of concrete, reinforcement and interfaces between them. Numerically obtained results of cracking loads and global load-displacement response agree well with experimentally measured values. It has been found that the fracture of the concrete observed at the macroscopic level is predominated by tensile damage at the mesoscopic level.
Fracture Characteristics of Intermittent Jointed Rock Masses under Blast Loading
Authors: Yu Qi Wu Peng shao , Zhang Yong , He Yong Nian
Published: March 2009

Rock masses usually contain intermittent joints. The existence of joints not only
significantly affects the static properties of rock masses, but also their dynamic response and stability under blast waves. The present study focuses on investigating the fundamental fracture characteristics of intermittent jointed rock masses subjected to blast loading. A series of blasting tests were conducted on organic glass samples. The results are analyzed in order to obtain the characteristics of initiation, propagation and coalescence of wing cracks in rock bridges. The study indicates that the fracture behavior of intermittent jointed rock masses may be significantly affected by the preliminary static stress fields, the density and filling states of rock joints, the incident angles of blast waves relative to the joints, and the amplitudes of incident waves. From visual observation, three initiation modes and four coalescence modes of wing cracks are suggested. Finally, a comparison has been made between the fracture characteristics of intermittent jointed rock masses under single static stress field and that of under blast loading.
Risk-Based Inspection of Refinery Units: A Practical Application
Authors: Choi Song Chun , Han Sang In , Jung Hee Jun , Kim Ji Yoon
Published: March 2009

Recently, regulatory bodies quite often encourage to adopt risk-based inspection (RBI) and management programs because they can enhance safety simultaneously with deregulation in Korea. RBI is an integrated methodology that factors risk into inspection and maintenance decision making. This paper describes an example of how to use known risk assessment codes (API 580, API 581 BRD)
to address such safety analysis requirements for risk management in the refining industry. Specifically, this paper reports the methodology and the results of application to the refinery units using the KGS-RBITM program, developed by the Korea Gas Safety Corporation in reference of API Codes and ASME PC (Post Construction) with a suitable consideration of Korean situation. The results of the
risk and reliability assessment using KGS-RBITM program are useful in determining whether the detected defects are tolerable or required to be repaired. The subsequent decisions are to manage the future inspection, repair and maintenance planning in the risk reduction control.
Study on Structural Integrity of C/C Composite Using as Core Restraint Mechanism in HTGR
Authors: Tsuji Nobumasa , Shibata Taiju , Sumita Junya , Ishihara Masahiro , Iyoku Tatsuo
Published: March 2009

High temperature gas cooled reactor (HTGR) with higher outlet coolant temperature nearly 1000°C is expected for direct utilization of process heat to hydrogen production. The thermal analysis of reactor internals with 3 dimensional, flow paths coupled model was conducted to demonstrate how strictly PSR block gaps must be closed to limit core bypass flow rate ratio lest fuel temperature should exceed admissible level, and the highly heat resistant core restraint mechanism
must be developed in consequence. Potential applicability of the core restraint mechanism made of C/C composite, the attractive candidate material, was demonstrated by point design with adequate thickness and FEM stress analysis for material with orthotropic anisotropy .
A Study on the Mechanical Properties of the Honeycomb Sandwich Composites made by VARTM
Authors: Eum Soo Hyun , Kim Yun Hae , Han Joong Won , Kim Kook Jin , Shin Do Hoon , Yim Cheolmun , Murakami Riichi
Published: March 2009

To prove the suitability the honeycomb composites structure with VARTM, the mechanical properties of the skin materials and honeycomb composites structure were evaluated with the static strength tests. The mechanical properties of honeycomb composites structure made by VARTM were satisfied with the real using conditions instead of the composites structure made by autoclave process. Accordingly, the honeycomb sandwich composites made by VARTM is available for manufacturing various composites parts. VARTM was very effective method to manufacture the honeycomb sandwich composites. It was possible that the manufacturing process was changed from autoclave process to VARTM to solve the problems on the autoclave process.
Effect of Liquid-Phase-Impact Diffusion Welding Parameters on the Strength of Welded Joints of Aluminum Matrix Composite SiCp/ZL101
Authors: Niu Ji Tai , Guo Wei , Zhai Jin Fan , Wang Mu Zhen
Published: March 2009

In this paper, a new method for welding aluminum matrix composites is mainly described. It is liquid-phase-impact (LPI) diffusion welding, which has gained China National Patent. The results show that by liquid-phase-impact diffusion welding, when the certain amount of liquid phase alloy appears, with effect of certain impact speed, the interface of matrix-reinforcement and reinforcement-reinforcement are joined perfectly. Because the welding time is very short, the harmful phase is avoided in welded area and bad effect on the interface between the aluminum matrix and reinforcement hasn’t caused, and the work efficiency has improved enormously. With the technique, particle reinforcement aluminum matrix composite SiCp/ZL101 has welded successfully, and joint strength is about 75% of the strength of composite (as-casted), deformation less than 3%.
Laser Surface Cladding of Al-Si Alloy
Authors: Cai Xun , Yang Xiaoyu , Zhao Tao , Li Liuhe , Chen Qiu Long
Published: March 2009

The mixture of Ni based alloy powder and WC particles were used as a feeding material to modify the surface properties of cast Al-Si alloy using a CO2 continuous transverse flow laser beam with maximum power of 10 kW. Microstructures and chemical components of the laser surface cladding (LSC) layers were studied using SEM, XRD, TEM and EDS. It is shown that the LSC layers were composed of γ-（ Ni, Cr, Fe, W）matrix phase and many enhancing phases, such as Ni2Al3, Ni3Al, WC, W2C, Cr2B, etc.. The microstructure of the LSC layers was greatly affected by the scanning rate b V and the powder of feeding rate p m under the same laser power. With the increasing of b V and p m , the dissolution phenomenon of WC particles was improved; the length, the diameter and the amount of the acicular constituent were markedly reduced. Microhardness and wear resistance tests were also performed: the average microhardness of the LSC layers was around 5.1 to 5.9GPa, which was five times higher than that of the Al-Si substrate. The wear resistance of the layer was about 20 times as big as that of cast Al-Si alloy when P=6kW, b V =13.3mm s-1, p m =100mg s-1, L=500N. The results showed that the mechanical properties of LSC layers on cast Al-Si alloy can be markedly enhanced with proper processing parameters. However, due to the sudden change of physical and mechanical properties between laser modified layer and substrate, some defects, especially crack, actually occur in the surface modified layer and the interface zone. And finally Ni/WC surface gradient layer was obtained on cast Al-Si alloy through thrice laser scanning technique. The microhardness of the laser gradient layer gradually changed from surface to substrate, so that it can reduce stress concentration in the whole laser surface layer, especially in the interface zone.
The Effect of External Electromagnetic Force in Gas Metal Arc Welding on the Transfer Mode
Authors: Lee S.H. , Kim J.S. , Lee Bo Young , Lee Sang Yul
Published: March 2009

In Gas Metal Arc Welding (GMAW), electromagnetic force is one of the most important factors that effects the metal transfer, short-circuit rate, spatter generation rate and mechanical properties for welding metal. Shielding gas and welding current have a great influence on metal transfer mode in GMAW. In this paper different ways for external electromagnetic forces are applied by attaching a cylindrically rounded conducting wire solenoid on touch tip holding. It was conformed that the intensities of electromagnetic force and kinds of shielding gases influence on the droplet transfer mode. With the applied electromagnetic field, the arc transfer mode changes from normal mode to rotating mode. The rotating direction changes with the change of electromagnetic current direction. Applied electromagnetic field intensity varied by electromagnetic current influences on the spatter generation rate in CO2 welding. In MIG welding, the influences of electromagnetic force on the spatter generation showed different tendency as in the CO2 welding. This paper is for the purpose of discussing these factors.
On Mechanical Properties of Dissimilar Friction Welded Steel Bars
Authors: Kim Seon Jin , Kong Yu Sik , Kim Yeong Sik , Kwon Sang Woo
Published: March 2009

An experimental study of dissimilar friction welding was conducted using 15mm diameter solid bar in chrome molybdenum steel (SCM440) to carbon steel (S45C) not only to optimize the friction welding conditions, but also to investigate the fatigue performance. The main friction welding parameters were selected to endure good quality welds on the basis of visual examination, tensile tests, Vickers hardness surveys of the bond of area and HAZ, and microstructure investigations. In this study, the specimens were tested as welded. For fatigue strength, the notched specimens for the optimal conditions were rotary bending fatigue tested. The results were compared with S-N curves for the base metals.
Analysis of Spherical Void Growth and Coalescence in Metal Plastic Straining Process
Authors: Vu Cong Hoa , Seo Do Won , Lim Jae Kyoo
Published: March 2009

Ductile fracture occurs due to micro-void nucleation, growth and finally coalescence into micro-crack. In this study a new ductile fracture condition that based on the microscopic phenomena of void nucleation, growth and coalescence was proposed. Using this condition and combining with finite element model to predict the fracture locations in bulk metal forming. The macroscopic behavior of the material is described according to the flow rules of Levy-Mises. An idealized spherical void within an finite matrix is assumed. The void volume is calculated by taking the increasing volume of the continuum, caused by plastic straining, incorporated in the yield functions. In the model there includes the strain-hardening coefficient of the Ludwik-Holomom stress-strain relationship and concentration of stress. The accumulated damage value is a phenomenon in this model. The results show that it is in close accordance with observations of some experimental specimens. However, in order to obtaining the high trustiness many experiments have to be carried out.
The Effect of Vacuum Thermal Cycling on LF6 Aluminium Alloy Welded Joints
Authors: Niu Ji Tai , Guo Wei , Guo Yong Liang , Meng Qing Chang
Published: March 2009

The investigation aimed at the invalidation mechanism analysis and reliability evaluation of aluminum alloy welded joint under space environment will provide spaceflight designing epartments and manufactures with important technology gist and data so as to greatly reduce paceflights manufactured cost and improve spaceflight working reliability. In this paper, the tensile properties and microstructures of LF6 aluminum alloy welded joint under vacuum thermal cycling
have been studied by means of vacuum thermal cycling system. The influence of vacuum thermal cycling on the tensile properties of the welded joint has investigated. Results show that the strength and the enlongation reach their maximum values at about 75 times cycling. The changes of the tensile properties are regarded as resulted from the changes of grain and the motion of dislocation.
Evaluation of Mechanical Properties for Narrow-Gap Weld Zone in Reactor Coolant Loop
Authors: Kwon Jae Do , Woo Seung Wan , Lee Choon Yeol , Kang Suk Chull , Shin Ho Sang
Published: March 2009

Conventionally, shield metal arc welding (SMAW) process was applied to join pipes of RCL, which caused lot of loss in time and cost due to excessive heat input and defects in joining section. Recently, narrow-gap welding (NGW) process was introduced to overcome the disadvantages of SMAW. However, the application of NGW to nuclear power plant is not yet common because safety of NGW process is not proven. In present paper, the welded coupons are manufactured under different welding processes in carbon steel. Then, microstructure observations and various mechanical tests are performed. It is verified that the mechanical properties of carbon steel are greatly changed after repair welding process due to applied heat flux, and that the effect of post-welding heat treatment is beneficial.
Chemical Shrinkage and Residual Stresses in Laminated Composites during Cure
Authors: Lee Soo Yong , Park Jung Sun
Published: March 2009

The residual stress that occurs in fiber-reinforced thermosetting composite materials during cure is one of the severe factors that can deteriorate the performance of composite structures. To investigate residual stresses occurring in laminated composites during cure, an incremental viscoelastic constitutive equation is derived as a function of temperature, degree of cure and chemical shrinkage. A finite element program is developed on the basis of a 3-D degenerated shell element and the first order shear deformation theory. Experiments were performed to measure the coefficients of chemical shrinkage of the Hercules AS4/3501-6 composite during cure. Residual strains were measured using strain gages during cure and compared with the results of finite element analysis. Good agreement is found between numerical and experimental results. It is found that the chemical shrinkage seriously affects the residual strains of the composite during cure.
The Cause Examination of the Crack of the End Beam for Welding Structure Type Bogie
Authors: Hong Jai Sung , Ham Young Sam , Paik Young Nam , Oh Taek Yul
Published: March 2009

Bogie is the connection device between carbody and wheel in railway vehicles. It is the core part that exert a important effect on the passenger safety and running safety. Bogie largely consists of the bogie frame, suspension, air brake system and wheel set. A static and dynamic load have acted on it complexly. When the bogie is designed, a finite element method, static load test, fatigue test, running test should be considered. A welded structure type bogie was developed for high speed freight car. But some bogie frames have the problems in end beam. There were some cracks ine end beams. The crack situation of the end beam have a bad effect on the brake system. In that case, the cars would be in danger of derailment. This report shows the cause of end beam crack, improvement method. In order to clear the crack cause, many tests were tried. The test result concludes that the crack cause of the end beam is not the brake load but the vibration at the real line running on the track. It is estimated that the improved car which end beam was reinforced was safe enough within permitted life of the car (25years). On the basis of the results, the existing end beam was improved. The safe of the improved end beam was proved by real line test on the track. The operation of freight car have no problems any more.
Smart Cure Monitoring Method of Carbon/Epoxy Laminates Using Electric Capacitance Change with Applied Alternating Current Frequency
Authors: Inada Takaomi , Todoroki Akira
Published: March 2009

Authors have developed an electric resistance change method for delamination monitoring of carbon/epoxy composite laminates. The method employs reinforcement fibers as sensors; electrodes are co-cured. Co-cured electrodes for delamination monitoring are adopted in the present study as sensors for monitoring the degree of cure. This study proposes a new method using electrical capacitance change for monitoring the degree of cure without using additional sensors. Applying
alternating current between electrodes during the cure process provides dielectric properties of carbon/epoxy composites. As with the conventional cure monitoring method using extra dielectric sensors, the degree of cure of composites is monitored by measuring the dielectric constant of composites. The dielectric constant of epoxy resin changes concomitant with change of frequency of applied alternating current (AC). Using dependency of the applied AC frequency of the dielectric constant, the degree of cure is measured directly. The proposed method is applied to single and multi-ply carbon/epoxy composite laminates. The method demonstrates excellent estimations of the degree of cure without additional sensors.
A Study of Deformation Behavior in Polymer
Authors: Shinozaki Akira , Kishimoto Kikuo , Inoue Hirotsugu
Published: March 2009

The mechanical properties of polymers are strongly influenced by meso-scale (10-9-10-3 m) structure such as entanglement, molecular weight distribution, orientation, etc. It is well known that sunlight induces the UV degradation of polymers. The mechanical properties of polymer are strongly influenced by UV irradiation because of chemical change of meso-scale structure. However the detail
relationship between the mechanical properties and chemical change of meso-scale structure is not clear. In this study, it is aimed to clear this relationship by the simulation. Network models considered the meso-scale structure are constructed. Degradation is described to delete the chain elements in the network model. Large strain deformation of these network models is evolved via molecular dynamics analysis improved by us. It is possible to describe the degradation by this method.
A Study of the Static and Dynamic Characteristics for Automotive Rubber Mount by FEA and Experiment
Authors: Kim Wan Doo , Hur Shin , Woo Chang Su , Kim Wan Soo , Lee Seong Beom
Published: March 2009

An automotive transmission rubber mount is a device used in automotive systems to
cushion the loads transmitted from the vehicle body structure. TM (transmission) rubber mount has been used to support engine in the vertical direction. In this study, the rubber specimens of the transmission mount are tested to obtain the hyperelastic and viscoelastic properties by the static and dynamic test, respectively. Uni-axial tension test, biaxial tension test, and pure shear test are carried out and Mooney-Rivlin constants are obtained from those static tests. Also, the viscoelastic properties such as storage and loss modulus are obtained from dynamic test. Using the static and dynamic test data, the dynamic stiffness of TM rubber mount subjected to static and dynamic load are predicted with finite element analysis. Solutions allow for comparison between FEA and experimental results.
It is shown that the predictions of FEA are close to the experimental results.
Fatigue Life Evaluation of ERW Joint in the Pipe Using Monte-Carlo Simulation
Authors: Kim Choong Myeong , Kim Jung Kyu , Kim Chul Su
Published: March 2009

The optimum welding condition for the input power was experimentally determined using the ERW simulator. The optimum condition derived from the nondestructive defect inspection and impact energy was the heat input power of 250kW with normalizing treatment at 900oC. In order to evaluate the fatigue life of ERW pipes, fatigue crack growth test for base metal and weld joint with the optimum condition were performed. As stress intensity factor range ( DKS) increased, the fatigue crack propagation rate (da/dN) of the weld joint became slower than that of the base metal. The fatigue life of ERW pipe was statistically estimated using Monte-Carlo simulation with the standard deviation of material constants (C and m) of the Paris law in the specimen. The fatigue life at failure probability PF = 50% is 2.3×105 cycle. Since the fatigue test of pipe in field has a lot of difficulties due to cost, equipment and time, the life derived from the simulation was identified using the common durability simulation software.
Study on Vehicle Collision-Avoiding Radar and Intelligent Cruise Control System
Authors: Song Gui Qiu , Yang Ying , Hang Haiqiang , Wang Shu Hong
Published: March 2009

An integrated vehicle collision-avoiding radar and intelligent cruise control system is
proposed. Collision-avoiding radar measures the distance of a vehicle-to-vehicle and roadblocks automatically, and then Cruise Control System design optimal acceleration for the vehicle-to-vehicle distance control. An integrated radar and intelligent cruise control law has been proposed. Using this control law, the brake controller forces the vehicle acceleration to converge to the desired acceleration. It has been shown via the simulations with good distance control performance in both
high speed and low speed stop and good driving situations. Vehicle Collision-avoiding Radar System and Intelligent Cruise Control System have very important significance on improving vehicle active safety and reducing driver’s fatigue. Collision-avoiding Radar System and Intelligent Cruise Control System will be the necessary equipment in future vehicle.
A Study on the Contact Behaviors of Infinitely Variable Transmission System with Full Toroidal Shapes of Disks
Authors: Jang Si Youl , Choi Wan
Published: March 2009

The torque of the continuously variable transmission system with friction drive mechanism is transmitted by contacting roller with input and output disks. For the higher transmitted torque, it is necessary to apply large load in order to get higher friction force, which in turn generates severe high stress on the contact surfaces of roller and disks. The toroidal type CVT system has simple component arrays that have three contact points between roller and each input or output disk to get the torque transmitted. However, compact assembly design of the three sets of rollers contacting with input and output disks needs the roller to stay with unsymmetrical angled position with each other. Therefore, the contact shapes between roller and disk vary according to the transmission ratio and should be investigated to avoid the excessive contact stress over than ~1.8 GPa. In this study, the contact geometries of roller and disks in the toroidal type CVT system are computed during the gear ratios. The contact area of which the size depends on the material elasticity, curvatures of roller and disk, and applied load are all of elliptic shapes because of the convex and concave curvatures of roller and disk shapes, respectively. From the computed results considering the size of roller diameter, roller stroke and applied load, it is found that the shapes of contact area changes the sizes of major and minor elliptical diameters in the rolling direction during the gear ratios due to the unsymmetrical angled position of roller.
High Temperature Oxidation Behavior and Strength of Ti-Al-Nb Ternary Alloys
Authors: Ding Xiao Fei , Tan Yi , Shen Yong , Wang Fu Gang , Yang Jenn Ming
Published: March 2009

Three types of Ti-Al-Nb ternary alloys are obtained by arc-melting and heat treatment, which are γ-TiAl single phase alloy, γ-TiAl + α2-Ti3Al duplex phase alloy, and γ-TiAl +α2-Ti3Al +Nb2Al multiple phase alloy. The phase stability is studied using optical microscope, X-ray diffractometer and electron probe microanalyzer. The oxidation behavior of three Ti-Al-Nb ternary alloys with different microstructures was investigated at 1273K using interrupted oxidation test in air. The compression test was carried out at 298K-1373K. The oxidation resistance of Ti-Al-Nb ternary
alloy at high temperature was found to be better than that of the binary Ti-Al alloy. Among the three Ti-Al-Nb ternary alloys, the two-phase alloy with γ+α2 has the best oxidation resistance and mechanical properties. The existence of α2 could enhance the oxidation resistance of the alloy at high temperature. On the contrary, the presence of Nb-enriched phase such as Nb2Al would decrease the oxidation resistance at elevated temperature due to the formation of Nb2O5, which would accelerate the exfoliation of oxide.
Irradiation and Operating Temperature Effects on the Tensile Characteristics of CANDU Pressure Tube Material
Authors: Ahn Sang Bok , Kim Do Sik , Kim Young Suk , Oh Dong Joon , Kim Jung Kyu
Published: March 2009

To investigate the degradation of mechanical properties induced mainly by neutron irradiation and operating temperatures, tensile tests were conducted from room temperature to 300°C using irradiated and unirradiated Zr-2.5Nb pressure tube materials. The irradiated longitudinal and transverse specimens collected from the coolant inlet, middle and outlet parts of the tube which had been operated in the CANDU reactor and showed different operating temperatures and irradiation fluence.
The different tensile behavior was characterized by the tensile loading direction in the unirradiated tube. The transverse specimen showed higher strength and lower elongation than those of the longitudinal one. The increased strength hardening and the decreased elongation embrittlement of the irradiated material were compared to those of the unirradiated one. While the tensile strength of the inlet was higher than that of the outlet, the elongation of the inlet was lower than that of outlet. Considering the operation condition, it was proposed that the operating temperature could be a more effective parameter than the irradiation fluence for long-time life. Through TEM observation, it was also found that while the a-type dislocation density was increased, the c-type dislocation was not changed in the irradiated material. The fact that the higher dislocation density was sequentially distributed over the inlet to the outlet parts was consistent with the distribution of the tensile strength.
Creep Crack Growth in P92 and P122 Alloy Steel Weldment
Authors: Jeong C.S. , Bae Si Yon , Lim Byeong Soo
Published: March 2009

The structures connected by welding are fractured often in Heat Affected Zone (HAZ) when cracks grow under high-temperature and high-pressure conditions. In this study, the creep crack growth tests of P92 and P122 steels were performed and the creep fracture characteristics were evaluated. Degradation rate by cavities was investigated and the influence of degradation rate on crack growth rate was evaluated. Crack growth rate of new material was compared with that of the degraded material to confirm the influence of the degradation rate by cavities on the crack growth rate. From these results, the crack growth rates in welded joints were determined. The crack growth rate of the step test specimen was much faster than that of new material under the same test conditions of step temperature, while it was slower than that of new material under the same step loading conditions. It implies that crack growth rate of the welded specimen is faster when degradation rate by cavities is high even under the same temperature and stress conditions. HAZ and weld metal have faster cavity nucleation and growth rates than base metal. Therefore, the HAZ and weld metal specimens showed shorter crack initiation time and the initial crack growth rate (da/dt)c of the HAZ and weld metal was faster than the base metal. If (da/dt)c is fast, fracture life will be reduced.
High Temperature Crack Growth Behavior of 304 Stainless Steel under Creep and Fatigue Loading
Authors: Baik Y.M. , Kim K.S.
Published: March 2009

The crack growth behavior in a 304 stainless steel has been investigated at 538°C in air environment. Compact tension specimens were subjected to fatigue, creep and creep-fatigue loading. The combined effects on crack growth rates of load level and hold time have been examined. Stress intensity factors are found to correlate crack growth rates reasonably well for fatigue crack growth. Creep crack growth rates are found to correlate with stress intensity factor and C*(t). Crack growth
rates under hold time cycles are successfully correlated with C*(t)avg under various load levels and hold times. Crack growth under creep-fatigue loading has been simulated by elastic-plastic-steady state creep finite element analyses. The results of analysis show that fatigue loading interrupts stress relaxation around the crack tip during hold time and causes stress reinstatement, thereby giving rise to
accelerated crack growth compared with crack growth under static loading. Analysis of hold time crack growth based on the cyclic stress-strain response yields crack closure during unloading, and creep deformation during hold time tends to lower the closure load.
Effects of Heat Treatment Condition on the Microstructure Evolution of Inconel 690
Authors: Lee Jung A. , Lee Joon Hyung , Kim Jeong Joo , Chai Young Suck
Published: March 2009

The effect of heat treatment on the morphologies of precipitates and grain boundaries of Inconel 690 alloy was studied. When the specimens were slowly cooled from the solutionizing temperature, typical discontinuous coarsening of Cr-rich carbides in grain boundaries was observed. As the cooling rate decreased, Cr-rich carbides grew and wider Cr depletion zone was created between the carbide precipitates, which resulted in wavy grain boundaries. The driving force of the wavy grain boundary was explained by the coherent strain energy.
Development of Corroded Gas Pipeline Assessment Program Based on Limit Load Solution
Authors: Kim Jong Choon , Shim Do Jun , Yoon Kang Ok , Choi Jae Boong , Chang Yoon Suk , Kim Young Jin , Choi Song Chun , Kim Woo Sik
Published: March 2009

Pipelines have the highest capacity and are the safest and the least environmentally
disruptive means for transmitting gas or oil. Recently, failures due to corrosion defects have become a major concern in maintaining pipeline integrity. A number of solutions have been developed for the assessment of remaining strength of corroded pipelines. In this paper, a Fitness-For-Purpose (FFP)type limit load solution for corroded city gas pipelines is proposed. For this purpose, a series of burst tests with various types of machined defects were performed. Finite element simulations were carried out to derive an appropriate failure criterion. Based on such solution along with existing solutions, an integrity evaluation program for corroded city gas pipeline, COPAP-CITY, has been developed.
Effect of Processing Parameters on Properties and Microstructures of Warm-Rolled Interstitial-Free (IF) Steel Sheets
Authors: Wang Zuo Cheng , Jing Cai Nian , Li Yun , Han Fu Tao
Published: March 2009

In order to simplify production processes and to lower production cost of thicker coldrolled IF steel sheets for deep drawing applications, a new warm-rolled IF steel sheet was developed in our lab through hot-rolling in high-temperature ferrite range. In this paper, effect of processing parameters on properties, microstructures and precipitate morphology of warm-rolled IF steel sheets was investigated. It is found that firstly, good deep drawing properties and favorable textures were achieved as steels were warm-rolled in good lubricant condition. Secondly, most precipitates in steels were TiS, TiC, TiN and Ti4C2S2.
Strength Analysis of MEMS Micromirror Devices - Effects of Loading Mode and Etching Damage
Authors: Izumi Satoshi , Ping Chan Wee , Yamaguchi Makoto , Sakai Shinsuke , Suzuki Atsushi , Ueda Yuzuru
Published: March 2009

Strength evaluation method for MEMS micromirror has been proposed. Pure bending and combined loading tests have been performed and torsion strength has been estimated from those results. Two-parameter Weibull distribution was used to evaluate the fractured stresses estimated from FEM model. There exists the difference in strength between pure bending and combined loading. From the load factor analysis, it is found that both geometry and stress distribution have to be considered to estimate the strength of MEMS since flaw population is non-uniformly distributed. It is also found torsional strength can be estimated on the safe side by using the result of combined loading test. From the comparison between two kinds of specimen fabricated by different etching conditions, it is found that the fracture strength is greatly affected by the amount of etching damage (notching).
New Structures and Techniques for Easy Axial Loading Test of Static and Fatigue Properties of MEMS Materials
Authors: Park Jun Hyub , Kim Chung Youb , Choa Sung Hoon , Lee Chang Seung , Che Woo Seong , Song Ji Ho
Published: March 2009

Mechanical property evaluation of micrometer-sized structures is necessary to help design reliable microelectromechanical systems (MEMS) devices. Most material properties are known to exhibit dependence on specimen size and such properties of microscale structures are not well characterized. This paper describes techniques developed for tensile testing of materials used in MEMS. Epi-polycrystalline silicon is currently the most widely used material, and its tensile strength has been measured as 1.52GPa. We have developed an axial testing machine for testing microscale specimen using electro-magnetic actuator. The field magnet and the moving coil taken from an audio-speaker were utilized as the components of the actuator. Structure of specimen was designed and manufactured for easy handling and alignment. In addition to the static tensile tests, new techniques and procedures for measuring strength are described.
XRD Tensile Test Technique to Measure Mechanical Properties of Micron-Thick Si and TiN Films
Authors: Namazu Takahiro , Inoue Shozo , Ano Daisuke , Koterazawa Keiji
Published: March 2009

This paper focuses on investigating mechanical properties of micron-thick polycrystalline titanium nitride (TiN) films. We propose a new technique that can directly measure lateral strain of microscale crystalline specimen by X-ray diffraction (XRD) during tensile test. The XRD tensile test can provide not only Young’s modulus but also Poisson’s ratio of TiN films. Micron-thick TiN films were deposited onto both surfaces of single crystal silicon (Si) specimen by r.f. reactive magnetron sputtering. Young’s modulus and Poisson’s ratio of Si specimen obtained by XRD tensile tests were in good agreement with analytical values. TiN films deposited at Ar partial pressure of 0.7Pa had the average values of 290GPa and 0.36 for Young’s modulus and Poisson’s ratio. The elastic mechanical properties of TiN films gradually decreased down to 220GPa and 0.29 with increasing Ar partial pressure up to 1.0Pa, regardless of film thickness. The change in the film properties with Ar partial pressure would be attributed to the change in the film density.
Equivalent Modeling for Shape Design of IPMC (Ionic Polymer-Metal Composite) as Flapping Actuator
Authors: Park Hoon Cheol , Lee Sang Ki , Kim Kwang Jin
Published: March 2009

In this work, flapping wings actuated by IPMCs are designed and simulated to mimick
birds wing. In order for the wing to generate lift and thrust during flapping motion, the wing must be able to flap and twist at the same time. For design of such wings, shape of the IPMC actuator need to be designed such that the actuator can create bending and twisting motions during wing strokes. To determine the shape of the IPMC actuator, an equivalent bimorph beam model has been proposed based on the measured force-displacement data of an IPMC. The equivalent model and thermal analogy are used for numerical simulation of IPMC actuated wings to determine suitable shape of the IPMC actuator. In this way, we could select a best performing wing that can create the largest twist motion during flapping of the wing.
Electrostatically Driven Soft Polymer Actuator Based on Dielectric Elastomer
Authors: Choi Hyouk Ryeol , Jung Kwang Mok , Koo Ja Choon , Nam Jae Do , Lee Young Kwan , Cho Mi Suk
Published: March 2009

ElectroActive Polymers (EAPs) are emerging as new actuating means replacing the existing technologies such as piezoelectric, electrostatic, SMA etc. The dielectric elastomer actuator is regarded as the one of the most practically applicable actuators in the near future among the EAPs. In this paper, we introduce a new material capable of being employed as the dielectric elastomer actuator. The proposed material, which is a kind of the synthetic rubber, produces larger deformation as well as higher enegy efficiency, since it has a much higher dielectric constant compared to the previous ones. Beginning with the method of material synthesis, we give the description of its basic material properties by comparing with those of the existing materials for the dielectric elastomers. Also, the advantages of the proposed material as the actuating means are discussed with the several results of the experiments.
Sub-Structure Pseudo-Dynamic Response Test of a Pseudo-Elastic Bracing System Made of Shape Memory Alloy
Authors: Ohi Kenichi , Choi Jae Hyouk
Published: March 2009

This paper deals with shape memory alloy. As a first step to assess the applicability of this kind of alloy in a structural system, a tension bar made of this kind of alloy that exhibits pseudo-elasticity at room temperature is used herein as a passive bracing system. This paper describes sub-structure pseudo-dynamic tests on pseudo-elastic bracing system with hysteretic damper. A pseudo-elastic bracing system is better to be used with other hysteretic elements such as a hysteretic damper. A damper provides energy dissipation within small displacement levels, and a pseudo-elastic bracing system works in turn as a back-up/fail-safe system when an accidental failure of damper or damper interface occurs, and also it helps to pull back the structure to the original position by uninstalling the damper after earthquake.
The Hybrid Simulation of a Steel Frame Strengthened by Fully Mechanical Braces
Authors: Choi Jae Hyouk , Ohi Kenichi
Published: March 2009

Effectiveness of steel bracing system installed with fully mechanical interfaces is
experimentally demonstrated through a series of monotonic and cyclic loading tests. Also, substructuring pseudo-dynamic earthquake response tests are performed on a possible situation of a two-story braced frame upgraded by the proposed bracing system. An earthquake record and theoretical impulses are adopted as input excitations. The results show that an impulsive excitation acts more stringently on the occurrence of brace breaking.
Tensile and Compressive Behaviors of Smart Electrorheological Materials
Authors: Choi Seung Bok , Kim Kyung Su
Published: March 2009

This paper presents experimental results of tensile and compressive behaviors of smart electrorheological (ER) materials. Two different ER materials ; chemically treated starch particles and polymethylaniline particles are synthesized followed by devising a sqreeze mode type apparatus associated with motion controller and data acquisition system. The field intensity, electrode velocity and initial gap are chosen as important test parameters that influence on the tensile and compressive characteristics. The maximum tensile stresses are evaluated at each condition and compared between two ER materials.
Application of Electric Resistance Change Method to Damage Detection of CFRP Bolted Joints
Authors: Shimamura Yoshinobu , Oda Keiko , Todoroki Akira , Kobayashi Hideo , Inada Takaomi
Published: March 2009

Bolted joints are widely used for composite structures. As is well known, excessive bearing load gives rise to bearing failure at hole boundaries. Detecting bearing failure is important for assuring integrity of composite structures. Conventional nondestructive inspection methods are expensive, cumbersome, time-consuming, and not suitable for health monitoring, and a simple, low-cost inspection method for bearing failure must be developed. Authors have experimentally demonstrated detection bearing failure by an electrical resistance change method. In this study,
detectablity of remote damage, which includes bearing failure, using an electric resistance change method is investigated analytically. The results show that fiber breaking and delamination induce permanent increase in the electric resistance of the bolted composite joints, and that the proposed method, which involves measuring electric resistance, is effective for detecting bearing failure.
A Study on the Relationship between Fatigue Crack Opening Behavior and Reversed Plastic Zone Size
Authors: Choi Hyeon Chang
Published: March 2009

A relationship between fatigue crack opening behavior and the reversed plastic zone size is studied. An elastic-plastic finite element analysis (FEA) is performed to examine the opening behavior of fatigue crack. The contact elements in this analysis are adopted in the mesh of the crack tip area. The smaller element size than reversed plastic zone size is used for evaluating the distribution of reversed plastic zone. In the author’s previous results, the FEA could predict the crack
opening level, which the size of crack tip elements was in proportion to the theoretical reversed plastic zone size. It is found that the calculated reversed plastic zone size is related to the theoretical reversed plastic zone size and crack opening level. The calculated reversed plastic zone sizes are almost equal
to the reversed plastic zone size considering crack opening level obtained by experimental results. It is possible to predict the crack opening level from the reversed plastic zone size calculated by the FEA. We find that the experimental crack opening levels correspond with the opening values of crack tip contact nodes on the calculated reversed plastic zone.
Characterization of Electro-Active Paper Composite
Authors: Kim Jae Hwan , Kang Yu Keun , Yun Sung Ryul
Published: March 2009

This paper presents the characterization of Electro-active paper (EAPap). EAPap is a paper that produces large displacement with small force under electrical excitation. EAPap is made with a cellulose paper by constructing thin electrodes on both sides of the paper. When electrical voltage is applied to the electrodes the EAPap produces bending displacement. To be able to apply EAPap in many applications, characterization of EAPap is essential to understand and improve EAPap actuators. The characterization is done in terms of mechanical, electrical and physical tests. Mechanical strain and strength are investigated in sheet level and thermo-mechanical analysis is performed. Electrical resistance and admittance are analyzed to investigate the actuation mechanism. The actuation principle associated with piezoelectric effect is explained. EAPap has merits in terms of lightweight, dry condition, large displacement output, low actuation voltage and low power consumption. The most attractive characteristics of EAPap materials is their application potential for the development of biomimetic systems that are ultra-lightweight, low power, flexible, damage tolerant, noiseless, and agile.
Cure Monitoring and Stress-Strain Sensing of Single-Carbon Fiber Composites by the Measurement of Electrical Resistance
Authors: Lee Sang Il , Yoon Dong-Jin , Lee Seung Seok , Park Joung Man
Published: March 2009

Cure monitoring and stress-strain sensing of single-carbon fiber composites were
nondestructively evaluated by the measurement of electrical resistance. The difference of electrical resistance before and after curing increased highest when gauge length of the specimen was the smallest. As curing temperature increased, the electrical behavior of steel fiber was different from that of semi-conductive carbon and SiC fibers. Residual stress built in the fiber was the highest at the fiber axis direction. Whereas residual stress built in the matrix was relatively high at the fiber circumference and radius directions. Residual stress calculated from the experiment was consistent with the results from the finite element analysis (FEA). The strain at low curing temperature was larger than that of higher temperature until the load reached maximum value. The apparent modulus of the electrodeposited composites was higher than that of the untreated composites due to the improved interfacial shear strength (IFSS). The electrical resistance was responded quantitatively with stress-strain behavior during the test. Electrical resistance measurement can be feasible nondestructive techniques to evaluate cure monitoring and stress-strain sensing in the conductive fiber composites.
Finite Element Analysis and Integrity Assessment of Y-Branch
Authors: Gao Zeng Liang , Sun Wei Ming , Zheng Jinsong , Jin Wei Ya , Zhang Kangda
Published: March 2009

Y-branch is often used in connection between a main pipe and two branch pipes, for
example, in furnace, quench boiler, nuclear parts and so on. The stress distribution in the Y-branch is very complicated because of complicated shape and complex loads on it. The stresses in the Y-branches cannot be determined by theoretical equations. Finite element method is used to analyze the stresses in the Y-branches. As an example, a Y-branch used in a high temperature furnace is calculated with ANSYS software. The temperature distribution and elastic and elastic-plastic stress
fields in the Y-branch under mechanical and thermal loads are calculated. Strength, creep and fatigue of the Y-branch are evaluated based on T-1300, T-1400 of ASME Boiler and Pressure Vessel code Sec Ⅲ Div 1 Subsection NH.
Crack Opening/Sliding Morphology and Stress Intensity Factor of Slant Fatigue Crack
Authors: Shimizu Kenichi , Torii Tashiyuki , Ma YouLi
Published: March 2009

For an actual crack growth in structures subjected to the applied stress from the various directions, it is important to study about the fatigue crack propagation behavior under mixed-mode condition. In particular under the condition, crack surfaces tend to contact when the load is applied because of the compressive residual stress distributed near the crack and the zigzag crack surface morphology. In this study, using slant cracks with compressive residual stress induced in mode I fatigue crack propagation under the stress ratio of R= –1 and 0, stress intensity factors (KI)est and (KII)est were evaluated from the measured crack opening and sliding displacements. As a result, the stress intensity factor (KII)est for the crack made under the stress ratio of R= –1 with the slant angle of
45 deg. was decreased owing to the crack surface contact, while (KI)est showed relatively large values in spite of compressive residual stress.