bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure and Mechanical Properties of A 1.4%C Ultra High Carbon Steel
Authors: Liu Yong Ning , Zhu Jie Wu , Xu Yan
Published: March 2009

1.4 %C ultra high carbon steel (UHCS) was prepared in order to study the structure of martensite transformation and mechanical properties. Ultra-fine spherical carbide and ultra-fine austenite grain size were obtained. A great deal of lath martensite was observed after quenching. The phenomenon does not agree with the traditional knowledge that the lath martensite would disappear when carbon content is in excess of 0.8% in austenite. The strength, fatigue properties and fracture toughness have been measured. A good combination of strength, toughness and fatigue properties come from fine and uniform distributed carbide particles and ultra-fine austenite grain size. Fracture strength increases by 48%, yield strength increases by 15% and plasticity keep the same comparing with that of hardened and tempered 40CrNiMo. The carbon content of ultrahigh carbon steels (UHCS) is in the range of 1.0-2.1% [1, 2]. Traditional heat treatments for normal steels will cause the microstructure of UHCS to be coarse and do not produce optimal properties. With controlled rolling and special heat treatment, UHCS can be in ferrite, pearlite, bainnite or martensite structures, which all have different mechanical properties. The yield stress of a 1.8%C, 1.6%Al ferrite UHCS can reach 1500MPa, which is much higher than that of high strength and plain alloy steels [3]. The tensile strength of a 1.25%C-1.5%Cr pearlite UHCS can reach 1810Mpa and its elongation can be 18%. When it is treated into martensite, its compression strength reached to 4690Mpa and compression strain reached to 26% [1, 4], which is comparable to WC-12Co. Such good mechanical properties can be ascribed to the ultra fine grain sizes because of the undissolved carbide particles which resist growth of austenite grain during heating. Another reason could be the lath martensite structures. O.D.Sherby [4] had reported that there was a lot of lath martensite in quenched UHCS. The UHCS was considered not only as tool steels but also as good structure materials. Fracture and fatigue properties are important for structure materials. However, they have rarely been studied. The present paper is going to study the martensite structure and mechanical properties of a prepared 1.4% C UHCS.
Three-Dimensional Material Failure Process Analysis
Authors: Tang Chun An , Liang Zheng Zhao , Zhang Yong Bin , Xu Tao
Published: March 2009

This paper introduces a newly developed three-dimensional Material Failure Process
Analysis code, MFPA3D to model the failure processes of brittle materials, such as concrete, ceramics, fibrous materials, and rocks. This numerical code, based on a stress analysis method (finite element method) and a material failure constitutive law, can be taken as a tool in numerical modeling analysis to enhance our understanding of the failure mechanisms of brittle materials. Properties of material heterogeneity are taken into account. The material is discretized into numerous small elements with fixed size. Fracture behavior can be modeled by reducing the material stiffness and strength after the peak strength of the material has been reached. The evolution of the cracking process down to full fracture implies strain softening, which describes the post-peak gradual decline of stress at increasing strain. In the present study, a Mohr-Coulomb criterion envelop with a tension cut-off is used so that the element may fail either in shear or in tension. Simulated fracture or crack patterns of two examples are found quite realistic, and the results strongly depend on the heterogeneity level.
Applied Research of Fracture for Three-Points Bending to Blanking of Tool Steel
Authors: Rui Zhi Yuan , Li You Tang , Zhao Jun Tian
Published: March 2009

The application of fracture in three-points bending to blanking of tool steel was studied. Several mechanical models of stress blanking were discussed at first. And then the experiments were made in special equipment of three points bending designed by us. Several problems, such as the effect of wedge on fracture, the effect of support condition on the quality of blanking, the effect of the geometrical parameters of notch on blanking were studied with the help of experiment. The suitable parameters of three-point bending for blanking, depth and tip radius of notch, the ratio of blanking length to the diameter of the bar and suitable support in asymmetrical geometry have been proposed.
Experimental Limit Load of Forged Piping Branch Junctions and Comparison with Existing Solutions
Authors: Xuan Fu Zhen , Li Pei Ning , Wang Chen
Published: March 2009

Limit load test results from fourteen forged piping branch junctions are reported. Eight were uncracked. Three had outside, non-through wall cracks running parallel to the run pipe centerline at the flank and the others had crotch corner cracks among the selected specimens. The collapse behaviors such as bulging deformation at the side flanks of junctions with and without crack were depicted. Based on the experimental data, the relationships of limit load with structural dimension and crack size were then summarized and the existing solutions were evaluated in use of the test results.
Research on Intercritical Rolling of 0.2C-1.5Si-1.5Mn TRIP Steels by Thermo-Mechanical Simulation
Authors: Wang Zuo Cheng , Kim Sung Joon , Lee Chang Gil , Lee Tae Ho
Published: March 2009

In order to simplify the production routine and to save cost of hot-rolled TRIP steels, the intercritical rolling process was investigated using thermo-mechanical simulation technology. Both 0.2C-1.5Mn-1.5Si and 0.2C-1.5Mn-1.5Si-0.5Cu TRIP steels were chosen so as to study the effect of 0.5 pct Cu addition on microstructure and retained austenite volume fraction of 0.2C-1.5Mn-1.5Si TRIP steel. It is found that grain size refinement happened during intercritical deformation, and multi-phase microstructure could be achieved after isothermal treatment, so intercritical annealing
can be eliminated to avoid grain size coarse and to keep the refine grain size in intercritical-deformed TRIP steels.
Finite Element Simulation for Tensile Properties of δ-Al2O3f/Al Alloy Composites with Thermal Residual Stress Considered
Authors: Zhang Juan , Gao Qing , Kang Guo Zheng , Yang Xianjie
Published: March 2009

First, the characteristics of thermal residual stress in randomly oriented short δ-Al2O3 fiber reinforced aluminum alloy composites were analyzed by an elasto-plastic finite element method regarding the effect of the variation in short fiber orientation. Then, the effective moduli and initial tensile stress-strain curves of the composites were simulated by finite element method with the thermal residual stress taken into account. It is concluded that the simulated results obtained with thermal residual stress contained agree with corresponding experimental results better than those obtained in thermal residual stress-free cases.
Transient Dynamic Response of Delaminated Composite Twisted Cylindrical Shells Subjected to Low Velocity Impact
Authors: Karmakar Amit , Kishimoto Kikuo
Published: March 2009

In this paper a transient dynamic finite element analysis is presented to study the response of centrally impacted delaminated composite pretwisted cylindrical shells. An eight noded isoparametric plate bending element is employed in the finite element formulation. Effects of transverse shear deformation and rotary inertia are included. To satisfy the compatibility of deformation and equilibrium of resultant forces and moments at the delamination crack front a multipoint constraint algorithm is incorporated. The modified Hertzian contact law which accounts for permanent indentation is utilized to compute the contact force, and the time dependent equations
are solved by Newmark’s time integration algorithm. Parametric studies are performed in respect of relative size of delamination and angle of twist for graphite-epoxy composite cylindrical shallow shells subjected to low velocity normal impact.
Impact Analysis and Test on the Spacer Grid Assembly for PWRs
Authors: Song Kee Nam , Yoon Kyung Ho , Kang Heung Seok , Lee Kang Hee
Published: March 2009

A spacer grid assembly is one of the main structural components of the fuel assemblies of Pressurized light Water Reactors. The spacer grid assembly is structurally required to have enough buckling strength under various kinds of lateral loads acting on the fuel assembly so as to keep the fuel assembly straight. The structural performance of the spacer grid assembly is characterized in terms of
its dynamic crush strength, which is usually acquired from the test. In this study, a dynamic buckling test and a finite element analysis on the KAERI designed spacer grid assembly are carried out. The pendulum-type tester was used in the test. In the finite element analysis, we proposed an analysis methodology that could predict the dynamic failure behavior of the spacer grid assembly using a commercial finite element code ABAQUS/explicit with appropriate boundary conditions. As a result
of the comparisons, the analysis result is in good agreement with the test result to within a 10% difference range. Therefore, we could predict the dynamic behaviors of a spacer grid assembly in advance before performing the dynamic buckling test.
Prediction of Slip Displacement in Nuclear Fuel Fretting Wear
Authors: Kim Hyung Kyu , Song Ju Sun , Lee Young Ho , Jung Youn Ho , Kim Jae Hoon
Published: March 2009

Slipping characteristic on the contacts between the tubes and the supports is investigated to study the fretting wear of a vibratory tube. Tests were carried out to simulate the vibration of the fuel rods supported by the springs and dimples. A tube was forced to vibrate with 30Hz. The supporting condition was varied artificially: positive contact force or gap existence. During the tube vibration, amplitudes were measured continuously in the vicinity of the supports. Simple equations were derived to evaluate the slip displacement on the contacts. As a result, it was found that the supporting condition affected the vibration characteristic near the contacts. In the positive contact condition, the phase difference of the vibration signals at both sides of the contact was 180 degrees. It is altered in the gap condition and the higher frequency components than 30Hz appeared. The severer wear in the case of the gap existence is discussed with the evaluated slip distance per cycle.
Effect of Micro-Addition Rare Earth and Chrome on Friction and Wear Behavior of Boronized Layer
Authors: Xu Bin , Wang Shu Hua , Lu Yu Peng , Cui Jianjun , Li Mu Sen
Published: March 2009

Application of powder boronizing to mechanical industry has been restricted because of the brittleness of boronized layer, which inevitably leads to decrease of service life of boronized parts. Therefore, attention should be paid to reducing the brittleness of boronized layer without decreasing its high hardness. In the present paper, a study on the effect of micro-addition rare earth and chrome on friction and wear behavior of boronized layer was carried out using an MM-200 wear test machine. Compared with that of pure single Fe2B phase, the brittleness of the boronized layer containing minim rare earth and chrome elements, obtained by powder RE-chrome-boronizing, is reduced, which results in increasing the bearing capacity and wear resistance of the boronized layer. The friction and wear mechanism is also briefly analyzed.
Fretting Wear Characteristics of INCONEL 690 and INCONEL 600 in Water Environment
Authors: Jeong Sung Hoon , Park Chi Yong , Lee Young Ze
Published: March 2009

Fretting is the oscillatory motion with very small amplitudes, which usually occurs
between two solid surfaces in contact. Fretting wear is the removal of material from contacting surfaces through fretting action. Fretting wear of steam generator tubes in nuclear power plant becomes a serious problem in recent years. The materials for the tubes usually are INCONEL 690 (I-690) and INCONEL 600 (I-600). In this paper, fretting wear tests for I-690 and I-600 were performed under various applied loads in water at room temperature. Results showed that the fretting wear loss of I-690 and I-600 tubes was largely influenced by stick-slip. The fretting wear mechanisms were the abrasive wear in slip regime and the delamination wear in stick regime. Also, I-690 had somewhat better wear resistance than I-600.
Wear Characteristics of INCONEL 690 and INCONEL 600 in Elevated Temperature
Authors: Jeong Sung Hoon , Lee Young Ze
Published: March 2009

In this paper, the fretting wear characteristics of INCONEL 690 (I-690) and INCONEL 600 (I-600) was evaluated to verify the wear mechanism and the wear life. Because of the excellent corrosion-resistance of nickel-based alloy, those materials are used for steam generator tube in nuclear power plants. Sometimes the tubes are damaged due to small amplitude vibration, so called fretting wear. To verify the fretting wear mechanisms the wear experiment was carried with the crossed-cylinder wear tester, which used a cam to oscillate the specimen. The test was carried out at loads of 40N and 90N in elevated temperatures of water. The temperatures of water were 20°C, 50°C and 80°C. The increase of water temperature causes the oxidation of the contact area to be delayed, and the amount of wear on oxide layer to be reduced. The main wear mechanisms of fretting were abrasive wear and oxidation wear.
Anisotropic Deformation Effect on the Fracture of Core Components Made of Two-Dimensional C/C Composite
Authors: Sumita Junya , Shibata Taiju , Ishihara Masahiro , Iyoku Tatsuo , Tsuji Nobumasa
Published: March 2009

The carbon fiber reinforced carbon-carbon composite (C/C composite) is one of the candidates due to its excellent thermal stability as well as high strength. A two-dimensional C/C composite has great anisotropy in those properties in with- and across- fiber directions. It is, therefore, important to consider the anisotropy for the stress evaluation and for the fracture probability of the components. In the present study, FEM analyses on deformation and stress of the component were carried out taking account of the anisotropy. In addition, the fracture probability of the components was evaluated by the statistical fracture theory. It was found that anisotropy affect the thermal stress and the risk of rupture.
Evaluation of DBTT and Creep Properties of Aged Main Valve Casing by Using Small Punch Specimens
Authors: Sugimoto Takayuki , Komazaki Shinichi , Misawa Toshihei
Published: March 2009

Both the change in DBTT and the degradation of creep properties of the aged CrMoV cast steel which had been actually used as a main steam valve were evaluated from the conventional SP test and the SP creep (SP-C) test using by SP test specimens. The CVN DBTTs of the virgin and aged steels were estimated to be 280 and 369 K by the conventional SP test, respectively. This increase in DBTT after the long-term service exposure was considered to be caused by carbide-induced embrittlement due to coarse carbides. The SP-C test results revealed that the creep rupture strength of the aged steel was inferior to that of the virgin steel. The ratio, F / s , between the load of the SP-C test (F) and the stress of the uniaxial test ( s) was determined to be 2.4 for the same value of the Larson-Miller parameter in the creep rupture data. This linear relationship enables us to convert the results of the SP-C test into those corresponding to a conventional uniaxial creep test. Consequently, the SP testing method is expected to be appropriate tool for the determination of material deterioration and, in turn, the assessment of remaining-life of high-temperature components.
Bonding Strength and Microstructure of Cermet/Cu-Based Alloy Composite Brazed Coatings
Authors: Wang Xin Hong , Zou Zeng Da , Zhang Min , Song Si Li , Qu Shi Yao
Published: March 2009

WC-TiC-Co cermet and CuZnNi alloy composite coatings were produced on mild steel by a high temperature inside-furnace brazing technique. The microstructure, phase constituents and interfacial diffusion behavior of cermet and Cu-based alloy were investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron probe microanalysis (EPMA) and X-ray diffraction. The tensile strength and wear property of composite coatings were also investigated. The results show that crème particles were not decomposed severely during the inside- furnace brazing process. The microstructure of the matrix is α and β phases. Diffusion occurred at the cermet/Cu-based alloy interface. The tensile strength of the composite coatings reached 240-300MPa, which depended on the brazing temperature and was far higher than that of the flame hardfacing layers. Cermet fracture was basically a brittle fracture in nature and matrix involves ductile fracture.
Optimal Grinding Condition of ZrO2 Ferrule for Optical Fiber Connector Using the Taguchi Method
Authors: Suh Chang Min , Kim Sang Chun , Chae Jung Sik
Published: March 2009

In this paper, the effects of chamfering conditions on the surface roughness of ZrO2 ferrule applied to an optical fiber connector were investigated. The mesh number of the diamond wheel, the grinding speed of the spindle, the feed rate, and the initial cutting depth during grinding chamfer were regarded as the main parameters that have an effect on the surface roughness. Among these parameters, optimal combinations for chamfering conditions were obtained by using the Taguchi method. In addition, analytic values for maximum surface roughness (Rmax) estimated by the theoretical equations which were derived from the formative model of surface roughness on the grinding chamfer were compared with those of the experiments.
Effect of Microstructure on Fatigue Crack Growth Resistance of Magnesium Alloy under Biaxial Stress
Authors: Ito Yasumi , Shimamoto Akira
Published: March 2009

Fatigue crack propagation tests are conducted on magnesium alloy, cruciform specimens under biaxial and uniaxial loadings by using the biaxial fatigue tester which was developed by the authors. We investigate the effect of microstructures of specimens on fatigue crack growth resistance under biaxial stresses. From electron-microscope observations of a fatigue fracture and microstructure observations, it becomes clear that the mechanical properties of a magnesium-alloy, AZ31B, are greatly influenced by the diameter of crystal grains. We find that static tensile strength falls by heat-treating in the high temperature region where the diameter of crystal grains of an X-Y plane becomes large. We also find that the crack progress velocity under equal biaxial stresses gets faster by heat-treating in the high temperature region where the diameter of crystal grain of a Z-X plane becomes large.
A Study on the Fracture Behavior of Magnesium and Aluminium Alloy under Dynamic Biaxial Stress
Authors: Hwang Do Yeon , Shimamoto Akira , Kubota Ryo
Published: March 2009

In this study, the dynamic behaviors of cracks under dynamic biaxial stress are investigated. We conduct dynamic loading fracture experiments on the aluminum (2024-T3) and the magnesium alloy (AZ31B-O) under equitable biaxial stress with a hydraulic high-speed biaxial experimental machine. The processed specimens are cruciform with a crack. Different kinds of cracks are defined by their crack angles. We analyze the results by the caustic method. We obtained the stress
intensity factor and the fracture toughness value in the neighborhood of the crack tip under dynamic biaxial stress. We analyzed the obtained data, and then, we compared results.
Mode II Fatigue Crack Behavior in Compact Tension Shear Specimen
Authors: Song Sam Hong , Lee Jeong Moo
Published: March 2009

The need for research on fatigue behavior of mechanical element under mixed-mode
loading has been increasing as the user environment today becomes more and more complicated. However there haven’t been enough investigations on behavior in shear loads comparing to those under tensile loading conditions. So, for this paper, we investigated the characteristics and properties of initiation and propagation behavior for fatigue crack observed for different shapes of the initial crack and magnitudes of load in the modified compact tension shear (CTS) specimen subjected to mode II load. In the low-load condition, the secondary fatigue crack was created in the notch root due to friction on the pre-crack surface grew to a main crack. In the high-load condition meanwhile, fatigue crack under shear loading propagated branching from the pre-crack tip. Influenced by the shear loading condition, fatigue crack propagation was retarded in the initial propagation region due to the decrease in crack driving force and friction on the crack surface. In both cases, however, fatigue cracks grew in tensile mode. The propagation direction of fatigue crack under mode II loading was approximately at a 70 degree angle from the initial crack, regardless of its shape and load magnitude.
Effect of Stress State on Mode II Stable Crack Extension
Authors: Mourad Abdel Hamid I.
Published: March 2009

The effect of assumption of plane state of stress on the predictability of experimental
results observed during the mode II stable crack growth (SCG) through 8 mm thick compact tension specimens (CTS) of a workhardening aluminum alloy (D16AT) has been studied. Experimental results include load-sliding displacement diagram, extent of SCG, crack front geometry and fracture surface fractographs. The experimental results show that the crack extends in its own plane, the fracture surface is flat, smooth and free of any shear lip. The crack front geometry, which is straight initially, remains mostly so throughout the SCG. Theoretical investigations have been done using an elastic-plastic finite element scheme and the COA/COD criterion as the criterion governing the growth. Finite element results, assuming plane stress and plane strain conditions separately, on the load-sliding displacement diagrams, J-resistance curve, plastic zones and variation of equivalent stress and strain along the crack-line ahead of the crack tip are also presented. The resistance curve is a straight-line and the magnitudes of equivalent stress and strain increases as the crack extension proceeds. In general, the predictions based on the assumption of plane state of stress are closer to the experimental results.
Mechanical Properties of LaB6-ZrB2 Composites
Authors: Min Guang Hui , Gao Ruilan , Yu Hua Shun , Han Jiande
Published: March 2009

The polycrystallined LaB6-ZrB2 composites with different content of ZrB2 were fabricated by vacuum hot-pressed sintering technique in this paper. The effects of ZrB2 content on the microstructure and mechanical properties were investigated. For the eutectic LaB6-ZrB2 (21wt%) composite, the hardness, flexural strength and fracture toughness is of 93.0 (HRA), 330.0MPa and 3.70MPa·m1/2, respectively. The results showed the hardness and flexural strength of LaB6-ZrB2 polycrystalline have been enhanced with the increasing of ZrB2 content, but the fracture toughness increases first then arrives at peak value, which is corresponding to the ZrB2 content of 21wt%. The microstructure observation revealed an improved densification due to addition of ZrB2. The fracture morphology showed a tendency of the fracturing from intergranular to transgranular manner with increasing the ZrB2 content. The fracture behavior of the composites was analyzed in the paper
Bottom-Mounted Nozzle Failure Modes of a Nuclear Reactor Pressure Vessel under Severe Accident Conditions
Authors: Lee Tae Hyun , Oh Young Jin , Hwang Il Soon
Published: March 2009

Local failure modes associated with bottom-mounted penetration nozzles are examined as a part of research on sever accident management. Conventional creep rupture studies on reactor vessel lower head during a meltdown accident were based on an excessively simplified shear deformation model. In the present study, the mode of nozzle failures is investigated using data and nozzle materials from Sandia National Laboratory’s Lower Head Failure Experiment (SNL-LHF). Crack-like separations were revealed at the nozzle weld metal to RPV interfaces indicating the importance of normal stress component rather than the shear stress in the creep rupture. Creep rupture tests were conducted for nozzle and weld metal materials, respectively, at various temperature and stress levels. Stress distribution in the nozzle region is calculated using elastic-viscoplastic finite element analysis (FEA) using the measured properties. Calculation results are compared with earlier results based on the pure shear model of TMI-2 VIP. It has been concluded from both LHF-4 nozzle examination and FEA that normal stress at the nozzle/lower head interface is the dominant driving force for the local failure with its likelihood significantly greater than previously assumed.
Critical Temperatures for Initiating and Arresting Delayed Hydride Cracking in a Zr-2.5Nb Pressure Tube
Authors: Kim Young Suk , Im Kyung Soo , Cheong Yong Moo
Published: March 2009

The hydrogen concentration limit and critical temperatures for a delayed hydride cracking (DHC) in zirconium alloys have been reanalyzed using Kim’s DHC model that a driving force for DHC is not the stress gradient but the supersaturated hydrogen concentration or ∆C arising from a hysteresis of the terminal solid solubility on a heating and on a cooling. The DHC initiation occurs generally at the temperatures corresponding to the terminal solid solubility for precipititation (TSSP), demonstrating that the supercooling from the terminal solid solubility for dissolution (TSSD) is required to initiate the DHC. The DHC arrest temperatures correspond to the temperatures where the ∆C is reduced to zero. Therefore, we conclude that the ∆C is the driving force for the DHC and that the Kim’s DHC model is feasible.
Annealing Effect of Thermal Conductivity on Thermal Stress Induced Fracture of Nuclear Graphite
Authors: Sumita Junya , Shibata Taiju , Ishihara Masahiro , Iyoku Tatsuo , Tsuji Nobumasa
Published: March 2009

Graphite materials are used for structural components in the core of high temperature gas-cooled reactors (HTGRs) because of their excellent thermo/mechanical properties. When the core temperature is raised at an accident, the thermal stress of the components is induced, and it enhances the fracture probability of them. In general, the thermal conductivity of graphite is decreased by neutron irradiation due to irradiation-induced defects preventing heat conduction by
phonon. It is hence expected that decreased thermal conductivity is recovered to some extent by thermal annealing at the accident. Therefore, the consideration of the thermal annealing effect is placed as much important subject in the fracture/strength evaluation of the graphite components at the accident. In the present study, the thermal stress and the fracture probability of graphite components
influenced by the thermal annealing were investigated by a finite element method (FEM) analysis. It was shown that the annealing effect decreases the thermal stress and a certain level of the fracture probability.
Plastic Limit Load Solutions for Surface Crack in the Steam Generator Tubes
Authors: Lee Ouk Sub , Kim Hyun Su , Kim Jong Sung , Jin Tae Eun , Kim Hong Deok , Chung Han Sub
Published: March 2009

Operating experience of steam generators has shown that cracks of various morphologies frequently occur in the steam generator tubes. These cracked tubes can stay in service if it is proved that the tubes have sufficient safety margin to preclude the risk of burst and leak. Therefore, integrity assessment using exact limit load solutions is very important for safe operation of the steam generators. This paper provides global and local limit load solutions for surface cracks in the steam
generator tubes. Such solutions are developed based on three-dimensional (3-D) finite element analyses assuming elastic-perfectly plastic material behavior. For the crack location, both axial and circumferential surface cracks, and for each case, both external and internal cracks are considered. The resulting global and local limit load solutions are given in polynomial forms, and thus can be simply used in practical integrity assessment of the steam generator tubes, because the comparison between experimental data and FE solutions shows good agreement.
Dynamic Deformation Behavior of Rubber (NR/NBR) under High Strain Rate Compressive Loading
Authors: Lee Ouk Sub , Lee Jong Won , Kim Sung Hyun
Published: March 2009

This paper presents a modified Split Hopkinson Pressure Bar (SHPB) technique to obtain compressive stress-strain data for rubber materials. An experimental technique that modifies the conventional SHPB has been developed for measuring the dynamic compressive stress-strain responses of rubber materials with low mechanical impedance and low compressive strengths. This paper introduces an all-polymeric pressure bar set-up which achieves a closer impedance match between the pressure bar and the specimen materials. In addition, a pulse shaper is utilized to lengthen the rising time of the incident wave which helps the stress equilibrium and homogeneous deformation of rubber materials. It is found that the modified technique can determine the dynamic deformation behavior of NR and NBR rubber more accurately than those from the conventional SHPB technique.
A Methodology for Damage Strength Evaluation of a Single Biomimetic Microcapsule
Authors: Ju Bing Feng , Ju Yang , Saka Masumi
Published: March 2009

An ultra-precision instrument with concomitant micromanipulation techniques is designed and set up to measure the damage strength of a single biomimetic microcapsule. It can provide the capability of simultaneously measuring the applied force and resultant displacement of a single microcapsule, with maximum force range of 5mN, resolution of 0.1µN and ultimate traveling distance up to 12mm, resolution of 1nm, respectively. By armed high magnification side-view system, it can offer extra and withal valuable information for the supervened analyzing. The bursting force of urea-formaldehyde biomimetic microcapsules of diameter 65µm in glucose solution was measured by this technique. The microcapsule was burst when the deformation reached a value of 56.2% of its diameter and the corresponding resonant force is about 1700µN. The technique provides an effective means to characterize elastic properties of micro biomimetic capsules and compare
mechanical strength of microcapsules made of different ingredients.
Chemical Modification of Diamond Films on Pure Titanium Deposited by MPCVD Method
Authors: Yim Cheolmun , Shin Do Hoon , Kim Yun Hae , Moriguchi Yasunobu , Murakami Riichi
Published: March 2009

Diamond film was deposited on the pure titanium substrate by CH4-H2 gas mixture using MPCVD method. In order to carboxylate the surface of the diamond film, it was chemically treated in H2SO4:HNO3 (9:1, case 1) stirred at room temperature or in H2SO4:HNO3 (3:1, case 2) stirred at reflux. The oxidized diamond film was successively treated with 0.1M NaOH for 2hours and 0.1M HCl at 363K for 2hours, and then washed by distilled water. The surface of diamond film was observed by scanning electron microscopy (SEM). The diamond film was characterized using Raman spectroscopy and X-ray diffraction (XRD). Carboxylated diamond film was evaluated by Fourier transform infrared spectrometer (FT-IR), Mini secondary ion mass spectrometer (Mini SIMS) and X-ray photoelectron spectroscopy (XPS). In the FT-IR spectrum, the peak at 1640cm -1 was assigned with C=O stretching vibration of carboxylic acid. In the Mini SIMS profile, the peak intensities of mass number 16 (-O-) and 17 (-OH) were increased after the chemical treatment. The XPS results indicated COO- group and C=O group on the surface of diamond film.
An Evaluation of Appropriate Probabilistic ­S-­N Curve for the Turbine Blade Steel in the Low Pressure Steam
Authors: Kim Chul Su , Kim Jung Kyu , Kim Tae Seong
Published: March 2009

In order to evaluate the variation of fatigue data of turbine blade steel in low pressure (LP) steam, it is important to estimate probabilistic stress-life (P-S-N) curve to accurately define the probability distribution. In this study, a new procedure was introduced to determine the expression of P-S-N curves. For this purpose, 3-parameter Weibull distribution was found to be the most appropriate among assumed distributions when the probability distributions of the fatigue life were examined by a comparative analysis. Furthermore, the parameter of P-S-N curve was evaluated using various optimization techniques to maximize the correlation coefficient. As a result, the sequential linear program method is used for estimation of P-S-N curve.
A New Stochastic Model for Prediction of Fatigue Crack Propagation
Authors: Farhangdoost Khalil , Pooladi B. E.
Published: March 2009

Fatigue damage plays a significant role in fatigue life of structures and mechanical parts. Characterizing crack length as a random process in fatigue life, is a matter of controversy which is the first step of this new stochastic model for prediction of fatigue crack propagation. Minimum uncertainties and capability of using closure load are the model advantages. Generating series of a nonstationary process, effects of load history in immediate last step of crack propagation using Total Probability Theory (TPT) are some assumptions of this model. The model results have been compared with actual test results of Ti-6Al-4V CT specimens.
Reliability Evaluation of Interfacial Shear Strength on Single Carbon-Fiber/Rubber-Modified Epoxy Resin System
Authors: Lee Deok Bo , Kim Tae Won , Chung Uoo Chang
Published: March 2009

Rubber-modified epoxy resins are used as a matrix material for glass and carbon-fiber composites. Mechanical properties of fiber reinforced composites depend on the interfacial shear strength between the reinforced fiber and the matrix resin. This study is focused on the interfacial shear strength in the reinforced carbon fiber and rubber-modified epoxy resin system. To evaluate interfacial shear strength between the fiber and the resin, pull-out test is performed using a microdroplet method. Based on experimental results, numerical analysis was also simulated. It is concluded that the interfacial shear strength of carbon fiber/unmodified epoxy resin system was
higher than that of carbon fiber/modified epoxy resin system. The reason for decreased the interfacial shear strength of rubber-modified system is that contractive forces in neat epoxy resin acting on carbon fiber were less than those in rubber-modified epoxy resin system.
Reliability Estimation of Solder Joint Utilizing Thermal Fatigue Models
Authors: Lee Ouk Sub , Myoung No Hoon , Kim Dong Hyeok
Published: March 2009

The differences of coefficient of thermal expansion (CTE) of component and FR-4 board connected by solder joint generally cause the dissimilarity in shear strain and failure in solder joint when they are heated. The first order Taylor series expansion of the limit state function (LSF) incorporating with thermal fatigue models is used in order to estimate the failure probability of solder joints under heated condition. Various thermal fatigue models, classified into five categories:
categories four such as plastic strain-based, creep strain-based, energy-based, and damage-based except stress-based, are utilized in this study. The effects of random variables such as CTE, distance of the solder joint from neutral point (DNP), temperature variation and height of solder on the failure probability of the solder joint are systematically investigated by using a failure probability model with
the first order reliability method (FORM) and thermal fatigue models.
Penetration Fracture Characteristics of CFRP Curved Laminates
Authors: Kim Young Nam , Cho Young Jea , Lee Kil Sung , Im Kwang Hee , Kim Koung Suk , Yang In Young
Published: March 2009

CFRP composite materials widely used as structural materials for airplanes, ships and aero space vehicles because of their high strength and stiffness. This study aims to investigate the effects of curvature and stacking sequence on the penetration characteristics of CFRP laminated shell. They are stacked to [02/902]S, [03/903]S and [02/903/0]S, [0/902/0]S, and their interlaminar numbers are two and
four. We are manufactured to composite laminated shells with curvature radii of 100, 150, 200mm and ∞ (flat-plate), respectively. They were cure to the appropriate hardening temperature (130°C) at the vacuum bag of an autoclave. Composite laminated shells of dimensions 100㎜×140㎜ were prepared. The velocity of the steel ball that transversely impacts a specimen was measured both before and after impact by determining the time for the ball to pass two ballistic-screen sensors located at a known distance apart. In general, the kinetic energy after impact-kinetic energy before impact increased in all specimens. Absorbed energy increased as the curvature increased [03/903]S and [02/902]S which is small interlaminar number, was higher than four interlaminar specimen.
Proposal of New Biaxial Fatigue Life Prediction Parameter by Using the Effective Shear Stress for CF8M Stainless Steels
Authors: Park Joong Cheul , Kwon Jae Do
Published: March 2009

A combined axial-torsional low cycle fatigue test was carried out to predict the fatigue life under in-phase and out-out-phase loading conditions for CF8M cast stainless steels. The Fatemi-Socie (FS) parameter which is based on the critical plane approach is not only one of the many methods but also the best method that can predict the fatigue life under a biaxial loading condition. But the result showed that, a biaxial fatigue life prediction by using the FS parameter with several different parameters for the CF8M cast stainless steels is not conservative enough but at the same time it was the best result so far. So in this present research, we proposed a new fatigue life prediction parameter (Park-Kwon parameter) by considering effective the shear stress instead of the FS parameter which considers the maximum normal stress acting on the maximum shear strain and its effectiveness was verified.
Very Long Life Fatigue Behavior of Bearing Steel AISI 52100
Authors: Wang Q.Y. , Zhang Hong Yan , Sriraman M.R. , Li Shou Xin
Published: March 2009

For many applications, the understanding of very long life fatigue in materials becomes extremely important. In this study, the fatigue behavior of bearing steel GCr15 (conforming to AISI 52100) at very high number of cycles has been examined. Experiments on hourglass specimens were conducted in air at room temperature, for fully reversed loading condition (R=-1), using a piezoelectric
fatigue testing machine operating at a frequency of 20kHz. The results indicate that the S-N data does not reach a horizontal asymptote (signifying the fatigue limit) at 107 cycles, as conventionally believed, and that the material can fracture up to 109 cycles. Therefore, to quote a fatigue limit at 107 cycles may not hold good for the material studied. The influence of defects (such as inclusions) on the crack initiation and fracture was analyzed by scanning electron microscopy.
Failure Analysis of Heterogeneous Microstructures in Ti-6Al-4V Alloy Using Probability Functions
Authors: Kim Tae Won
Published: March 2009

A stochastic approach has been presented for superplastic deformation of Ti-6Al-4V alloy, and probability functions are used to model the heterogeneous phase distributions. Experimentally observed spatial correlation functions are developed, and microstructural evolutions together with superplastic deformation behavior have been investigated by means of the probability functions. The strain-rate dependent failure strain can be correctly predicted by the model. As shown by the results
the probability varies approximately linearly with separation distance, and significant deformation enhanced probability changes occur during the process. Since an initial microstructure is the most crucial factor that determines the properties of final microstructure, Monte Carlo simulation has been used coupled with the probability functions for the reconstruction of microstructures. By imposing the precisely optimized distributions of phase on the test specimens, therefore finite element implementation shows better agreement with experimental data of the failure strain.
Creep Life Evaluation by Micro-Cavities
Authors: Jeong C.S. , Lim Byeong Soo
Published: March 2009

As the operation time of a power plant increases, the degradation and the cracks inside of the structure exposed to high temperature will increase gradually. Therefore, degradation rate, crack growth rate and fracture life of the structure can be evaluated according to the level of degradation and the growth of crack length. We performed creep rupture test and crack growth test with stress and temperature changes to evaluate the degradation rate, crack growth rate and fracture life. Degradation rate was evaluated using micro-cavities. The area fraction of the cavities increased with the increasing temperature and life fraction (t/tf). da/dt, the crack growth rate against Ct estimated from the relationship between load line displacement rate and cavity increase rate, was in good agreement with the result of da/dt vs Ct acquired from the test. It shows that the creep crack growth rate can be
evaluated by the increase of cavity area fraction. It was also found that the predicted life calculated with the cavity growth rate was in good agreement with experimental results.
The Random Effects of the Seepage Field on the Slope Reliability
Authors: Zhang Guang , Chen Jing Xi , Tang Guang Hua
Published: March 2009

Proposed in this paper is an analyzing model for the slope reliability taking the random effects of the seepage field of groundwater and the dependent factors into consideration. Taking the Circle Slice Method as its base of mechanical analyses for the stability of a slope, the model can analyze the movement of groundwater by using BEM and calculate the slope reliability index, β ,and probability of failure, P, by means of Monte Carlo Method (FOSM). The way sampling on the failure surface adopted in the paper incorporates the strong points of Monte Carlo Method and First Order Second Moment Method, and its calculating efficiency is remarkably higher than that of traditional Monte Carlo Method. Employing the model proposed, the reliability indexes and probabilities of failure of a real slope are estimated. The tendencies and extents of influence of rainfall supply and the uncertainty of anisotropic character of media in permeability on the slope reliability are studied for the first time.
Safety Diagnosis of Collided Subway Electric Multiple Units (EMUs)
Authors: Chung Jong Duk , Kim Jeong Guk , Bae Dae Sung
Published: March 2009

Engineering safety diagnosis of collided subway electric multiple units (EMUs) was conducted for safety assessment. Several advanced engineering analysis techniques including nondestructive evaluation (NDE) techniques and stress and structural analyses programs, were performed for better understandings and exploration of failure analysis and safety concerns. NDE techniques such as ultrasonic testing and magnetic particle testing, were used to detect manufactureinduced and/or in-service defects and collision-induced flaws, and measure the dimensions of deformed and non-deformed parts on damaged EMUs due to a rear-end collision. Moreover, stress and structural analyses using commercial I-DEAS software provided important information on stress distribution and load transfer mechanisms as well as the amount of damages during the crash. A good agreement has been found between structural analysis results and the results of actual damages in EMUs during crash. In this investigation, various advanced engineering analysis techniques for the safety analysis of subway EMUs have been introduced and the analysis results have been used to rovide the critical information for the safety assessment of collided EMUs.
Barrier Function Method in Reliability Based Design Optimization
Authors: Lee Tae Hee , Yoo Jung Hun
Published: March 2009

In practical design applications, most design variables such as thickness, diameter and material properties are not deterministic but stochastic numbers that can be represented by their mean values with variances because of various uncertainties. When the uncertainties related with design variables and manufacturing process are considered in engineering design, the specified reliability of the design can be achieved by using the so-called reliability based design optimization. Reliability based design optimization takes into account the uncertainties in the design in order to meet the user requirement of the specified reliability while seeking optimal solution. Reliability based design optimization of a real system becomes now an emerging technique to achieve reliability, robustness and safety of the design. It is, however, well known that reliability based design optimization can often have so multiple local optima that it cannot converge into the specified reliability. To overcome this difficulty, barrier function approach in reliability based design optimization is proposed in this research and feasible solution with specified reliability index is always provided if a feasible solution is available. To illustrate the proposed formulation, reliability based design optimization of a bracket design is performed. Advanced mean value method and first order reliability method are employed for reliability analysis and their optimization results are compared with reliability index approach based on the accuracy and efficiency.
Experimental Investigation of Interlaminar Fracture Toughness of CFRP Composites with Different Stitching Patterns
Authors: Zhao Hong Ping , Li Robert Kwok Yiu , Feng Xi Qiao
Published: March 2009

Through-thickness stitching is one of the most effective techniques to improve the
delamination resistance of composite laminates. The effects of two different stitching patterns on the mode-I interlaminar fracture toughness of unidirectional carbon fiber reinforced plastics (CFRP) are examined experimentally in the present paper by using the double cantilever beam (DCB) test method. It is found that the zigzag stitching pattern results in a better toughening effect than the straight line pattern, and that the stitching density also has a considerable influence on the mode-I fracture toughness.
Failure Analysis on Rubber-Modified Epoxy Resin under Various Loading Speed Conditions
Authors: Lee Deok Bo , Kim Joo Hyung
Published: March 2009

A rubber-modified epoxy resin is widely used as adhesive and matrix materials for fiber composite material. The structural reliability of composite material depends on the fracture toughness of the matrix resin. In this study, the fracture toughness and the damage zone around a crack tip in rubber-modified epoxy resin were investigated. The volume fractures of rubber (CTBN1300×8) in the rubber-modified epoxy resin were 0%, 5% and 15% under several loading speeds. The fracture toughness(KIC) and the fracture energy(GIC) were measured by using 3-point bending specimens. The 4-point bending specimens were also used to observe damage zones at the vicinity of a crack tip in modified resins. The results show that the values of the fracture toughness and the sizes of damage zones at 5% and 15% rubber content decrease with increase in loading speed.