bluuebunny/crossref_metadata_2025 huggingface dataset:
Stress Effects on Activity of Primary Cracks Initiating at Stress Concentrator
Authors: Song Sam Hong , Kim Jin Bong
Published: July 2003

This study has been performed to investigate the stress distribution around defects that behave as stress concentrators and fracture mechanical analysis for cracks initiating at stress concentrators. The stress distribution was analyzed using Finite Element Method and non-dimensional stress intensity factor was determined by the mean stress method. This method could be applied to determine the activity of primary crack initiated at the stress concentrator in experiment. In addition, stress interaction effects around defects and cracks were compared.
Analysis of a Curved Interfacial Crack Between Viscoelastic Foam and Anisotropic Composites Under Antiplane Shear
Authors: Chun Heoung Jae , Park Sang Hyun
Published: July 2003

The analysis of curved interfacial crack between viscoelastic foam and anisotropic composites was conducted under antiplane shear loading applied at infinity. In the analysis, in order to represent viscoelastic behavior of foam, the Kelvin-Maxwell model was incorporated and Laplace transform was applied to treat the viscoelastic characteristics of foam. The curved interfacial crack problem was reduced to a Hilbert problem and a closed-form asymptotic solution was derived. The stress intensity factors in the vicinity of the interfacial crack tip were predicted by considering both anisotropic characteristics of composites and viscoelastic properties of foam. It was found from the analysis that the stress intensity factor was governed by material properties such as shear modulus and relaxation time, and increased with the increase in the curvature as well as the ratio of stiffness coefficients of composite materials. It was also observed that the effect of fiber orientation in the composite materials on the stress intensity factor decreased with the increase in the difference in stiffness coefficients between foam and composite.
Effects of Negative Stress Ratios on Crack Propagation Behavior After an Overload
Authors: Makabe C. , McEvily A. J. , Purnowidodo A. , Yamauchi A.
Published: July 2003

A study of the effect of an overload on fatigue crack propagation behavior has been carried out at baseline R-values of 0, -1, and -1.5. The usual delayed retardation event was observed at R = 0. At R = -1 the degree of retardation was reduced. At R = -1.5 the fatigue crack growth rate was observed to accelerate after the overload. These behaviors were related to the extent of crack closure, which existed following the overload. The rate of fatigue crack propagation for all loading conditions was correlated with the parameter Δ K eff - Δ K effth , where Δ K effth is the effective value of the stress intensity factor range at threshold.
A Probabilistic Integrity Assessment of Flaw in Zirconium Alloy Pressure Tube Considering Delayed Hydride Cracking
Authors: Kwak Sang Log , Lee Joon Seong , Kim Young Jin , Park Youn Won
Published: July 2003

In the CANDU nuclear reactor, pressure tubes of cold-worked Zr-2.5Nb material are used in the reactor core to contain the nuclear fuel bundles and heavy water coolant. Pressure tubes are major component of nuclear reactor, but only selected samples are periodically examined due to numerous numbers of tubes. Pressure tube material gradually pick up deuterium, as such are susceptible to a crack initiation and propagation process called delayed hydride cracking (DHC), which is the characteristic of pressure tube integrity evaluation. If cracks are not detected, such a cracking mechanism could lead to unstable rupture of the pressure tube. Up to this time, integrity evaluations are performed using conventional deterministic approaches. So it is expected that the results obtained are too conservative to perform a rational evaluation of lifetime. In this respect, a probabilistic safety assessment method is more appropriate for the assessment of overall pressure tube safety. This paper describes failure criteria for probabilistic analysis and fracture mechanics analyses of the pressure tubes in consideration of DHC. Major input parameters such as initial hydrogen concentration, the depth and aspect ratio of an initial surface crack, DHC velocity and fracture toughness are considered as probabilistic variables. Failure assessment diagram of pressure tube material is proposed and applied in the probabilistic analysis. In all the analyses, failure probabilities are calculated using the Monte Carlo simulation. As a result of analysis, conservatism of deterministic failure criteria is showed.
Corrosion Fatigue Characteristics of 12Cr Alloy Steel in Na2SO4 Solution
Authors: Bae D. H. , Cho S. Y.
Published: July 2003

In order to estimate reliability of 12Cr alloy steel using as the turbine blade material of the steam power plant, its corrosion fatigue characteristics in Na 2 SO 4 solution considering its percentage and temperature that were determined from the polarization test results were investigated, and compared with the results in air. The corrosion characteristic of 12Cr alloy steel was remarkably susceptible in 12.7wt.% (IM) Na 2 SO 4 solution, and its susceptibility increased with the solution temperature increase. The corrosion fatigue characteristics in 12.7wt.% Na 2 SO 4 solution were similar to that of in air at 25°C. The crack growth rate was however increased with the temperature of solution increase. The reasons showing such results are due to the difference of the crack growth mechanism according to the electro-chemical activity of the corrosion factors.
Corrosion - Fatigue Performance of Magnesium Alloys
Authors: Ferguson W. G. , Liu Wu , MacCulloch John
Published: July 2003

To determine the effect of a coating on fatigue strength, three point bend fatigue tests of coated and un-coated AM50 and AZ91D magnesium high pressure die cast specimens were made and S-N curves determined. Environments used were air, tap water and natural seawater. A difference in corrosion fatigue performance has been found, between AZ91D and AM50 and for both alloys performance in air was superior to both water environments. AZ91D has better corrosion fatigue resistance in tap water than in seawater; conversely, AM50 has better corrosion fatigue resistance in seawater than tap water. The results showed that the fatigue life was not reduced in these water environments for coated specimens, as the coating usually provided protection from corrosion.
Tensile and Creep Properties of the Refractory Nb Base In-Situ Composite
Authors: Kim Jin Hak , Tabaru Tatsuo , Hirai Hisatoshi
Published: July 2003

Niobium-base in-situ composite Nb-18Si-5Mo-5Hf-2C (in mol%) was prepared and heat-treated at 2070 K for 20 hour. The uni-axile tensile tests at high temperature ranges and the constant load tensile creep tests at 1570 K were performed. The specimen tensile-tested at 1470 K exhibited the excellent UTS of 450 MPa, and the brittle to ductile transition temperature is between 1470 and 1670 K. The specimens creep tested showed good creep strength; the stress exponent is about 5. The tensile fracture surface of the in-situ composite is complex and attributed to cleavage of the Nb 5 Si 3, Nb ss / Nb 5 Si 3 interface separation, ductile rupture of the Nb ss and correlations of these. On the otherhand, the fracture surface of creep tested consists of intergranular above 150 MPa and transgranular below 120 MPa with severely deformed Nb ss .
Degradation Evaluation of HK-40 Steel Using Electrical Resistivity
Authors: Nahm Seung Hoon , Yu Kwang Min , Park Jong Seo , Nam Young Hyun , Han Sang In , Kim Jeong Min , Kim Am Kee
Published: July 2003

More effective nondestructive technology for the estimation on material properties has been sought. In this research, a new electrical resistivity method was attempted for the estimation of the creep damage of a degraded heater tube steel. HK40 steel specimens with five different periods of aging were prepared by an isothermal heat treatment at 1050°C and the electrical resistivity was determined by a standard DC four-point probe method. The electrical resistivity at room temperature monotonously decreased with the extent of degradation of the material. It was also observed that Vickers hardness was correlated with the electrical resistivity. The microstructural changes of material during aging was examined by microscope.
Elevated Temperature Behavior of Creep and Fatigue in Welded P92 Steel
Authors: Lim Byeongsoo , Kim Bumjoon , Park Moonhee , Won Sungjoon
Published: July 2003

Fatigue strength and life of weldment at high temperature is very important for high temperature materials used in power plants. In this study, creep properties of weld metal, HAZ and base metal of P92 steel were evaluated by SP (small punch) creep test method. Fatigue crack growth behaviors in weld metal, HAZ and base metal of P92 steel were investigated at high temperature. Microstructure and microhardness of the weldment were also investigated for better analysis.
Effect of Cavity Growth Rate and Cr on High Temperature Crack Growth in P92 and P122 Steels
Authors: Lim Byeongsoo , Jeong Chanseo
Published: July 2003

In this work, the velocity of crack propagation at high temperature was investigated with da / dt - C t relationship using recently developed P92 and P122 steels. Role of cavity in crack growth rate and load line displacement rate was studied by measuring the cavity size and density, which will influence crack nucleation and growth. Since temperature and stress changes are particularly important at high temperature, crack growth behavior was evaluated under various temperature and K i(initial stress intensity factor). Effect of Cr content was evaluated by measuring crack growth activation energy in thesis.
Effects of Surface Hardening and Residual Stress on the Fatigue Characteristics of Nitrided SACM 645 Steel
Authors: Hwang Byung Won , Suh Chang Min , Jang Ho Kyung
Published: July 2003

To analyze the effect of the surface hardening and residual stress on the fatigue strength and behavior of crack nucleation, fatigue test were performed on SACM 645 steels nitrided using the Nitemper method. The gas nitriding was performed for 9 hours at 540°C and 8 hours at 570°C to obtain different depths of hardening, and some of the specimens were subjected to stress relief (SR) treatment to clarify effect of residual stress on the fatigue characteristics. After nitriding, the fatigue strength of specimens was 40% higher than that of base materials. It was also found that the increment in the fatigue characteristics was due to the compressive residual stresses that formed on the surface of specimens and produced subsurface crack nucleation during fatigue.
The Comparison of Fatigue Crack Growth Behaviors for Long Term Used and Heat Treated 1Cr-0.5Mo Steel Under Various Load Frequencies and Temperature
Authors: Jang Sang Yup , Nahm Seung Hoon , Suh Chang Min , Kho Young Tai , Ha Jung Soo
Published: July 2003

As the operating time of a power plant approaches its design life, the characteristics of crack initiation and growth in thick-section boiler components becomes major concerns. But few data have been reported for long term served materials because it is very difficult to acquire that. In this study, the characteristics of the crack growth behavior of used 1Cr - 0.5Mo steel which was served for a boiler header for 30 years and heat-treated 1Cr - 0.5Mo steel were studied experimentally by performing fatigue crack growth tests at 538°C and room temperature under triangular and trapezoidal wave-shapes. In order to evaluate hold time effect at elevated temperature, the results of fatigue test with 10 seconds hold time (0.083 Hz) were compared with the results of fatigue test with triangular wave-shapes (0.5Hz). As frequency decreased, the fatigue-crack growth rate showed a significant increase at high temperature. In the case of fatigue test with hold time, the rates of fatigue crack propagation were faster than those in the results of fatigue test without hold time. Finally, fatigue crack growth rates of reheat-treated material were slower than those of long term served material. And the behavior could be characterized by stress intensity factor range.
Fatigue Strength Evaluation of Spot-Welded Multi-Lap Joint by the Maximum Stress Intensity Factor, Kθmax
Authors: Bae Dongho , Nam Taehun , Jung Wonseok , Sohn Ilseon
Published: July 2003

Fatigue strength and reliability of structural components in railroad commercial vehicles are usually decided by spot weld. Thus, it is very important to develop a fatigue design method for spot welded multi-lap joints in railroad commercial vehicles. The objective of this paper is to provide an integrated fatigue design criterion for spot-welded multi-lap joints used in the body of railroad commercial vehicles. Based on finite element analysis, the fatigue life data for spot-welded multi-lap joints is correlated in terms of the maximum stress intensity factor, K θ max , that is the fracture mechanical parameter. From the results, using Δ K θ max - N f relationship, a proper fatigue life design rule independent on geometric variables and material properties for components having spot welded multi-lap joints can be established.
Evaluation of Corrosion Degradation of 12Cr Alloy Steel Using an Ultrasonic Backward Radiation
Authors: Song S. J. , Kim Young H. , Bae D. H. , Jung M. H. , Kwon S. D.
Published: July 2003

The corrosion degradation characteristics of the 12Cr alloy steel, which is widely used in fossil power plants as a turbine blade material, are evaluated nondestructively by use of the backward radiation of propagating Rayleigh wave. For this purpose, an automated system for measuring the ultrasonic backward radiation has been developed, and the frequency dependency of the Rayleigh surface wave has been investigated indirectly by observing the angular dependency of the acquired signals. The velocity of Rayleigh wave decreased as the increase of aging time, which implies the increase of the effective degraded layer thickness. And the peak amplitude of the radiation increased as aging time, which relates to the increase of inter-granular corrosion. The result observed in this study demonstrates high potential of the backward radiated ultrasound as a tool for nondestructive evaluation of the corrosion degradation characteristics of aged materials.
Estimation of Stress Intensity Factors for Vertical Edge Crack Under Hertzian Contact by Geometric Function Method
Authors: Jin Songbo , Kim Seock Sam
Published: July 2003

The stress near the surface of a component due to Hertzian contact can be well fitted by a exponentially distributed stresses. Knowledge of edge crack under such stresses were used to compute the stress intensity factor for vertical edge crack in a semi-infinite body under Hertzian contact by geometric function method. Very satisfactory results were obtained comparing with previous studies and it was proved that the geometric function method employed in this paper more convenient than other methods. The current analysis may facilitate further exploration of the wear mechanism.
Strain Energy Approach for Axial and Torsional Fatigue Life Prediction in Aged NiCrMoV Steels
Authors: Song Gee Wook , Hyun Jung Seob , Ha Jeong Soo
Published: July 2003

Axial and torsional low cycle fatigue tests were performed for NiCrMoV steels serviced low-pressure turbine rotor of nuclear power plant. The results were used to evaluate multiaxial fatigue life models including Tresca, von Mises and Brown and Miller's critical plane. The fatigue life predicted by the multiaxial fatigue models didn't correspond with the experimental results in small strain range. We proposed the total strain energy density model to predict torsional fatigue life from axial fatigue data. The total strain energy density model was found to best correlate the experimental data with predictions being within a factor of 2.
Study of Thermal Fatigue of H13 Die Steel with Various Surface Treatments
Authors: Ivanov V. V. , Ferguson W. G. , Paine I. R.
Published: July 2003

Surfaces of die-casting dies are subjected to very severe conditions of cyclical thermal and mechanical load, and chemical and mechanical wear. Dies mostly fail due to a combination of heat checking, erosion, corrosion and soldering. It is conceivable that appropriate surface treatments and coatings have a favourable influence on the temperature dependant performance of the surface of the die. The objective of this study was to examine various surface treatments and coatings. including shot peening, nitriding, nitro-carburizing, laser hardening and remelting, electro-spark alloying (deposition) and plasma spraying, under thermal fatigue conditions. Thermal cycling tests were conducted by alternate dipping of treated samples in an LM24 melt and in water. Results and interpretation are presented in this paper. The best thermal fatigue resistance was shown for a double surface treatment of laser hardening plus electro-spark deposition.
Genetic Algorithm Application in Multiaxial Fatigue Criteria Computation
Authors: Kang Jae Youn , Choi Byung Ik , Lee Hak Joo , Lee Sang Rok , Kim Joo Sung , Kim Kee Joo
Published: July 2003

Both critical plane and stress invariant approaches are used to evaluate fatigue limit criteria of machine component subjected to non-proportional cyclic loading. Critical plane methods require finding the smallest circle enclosing all the tips of shear stress vectors acting on the critical plane. In stress invariant methods, the maximum amplitude of the second invariant of the stress deviator should be determined. In this paper, the previous algorithms for constructing the minimum circumscribed circle or hyper-sphere are briefly reviewed and the method using genetic algorithm is proposed.
A Fatigue Design Method of Spot-Welded Lap Joint Using Neural Network
Authors: Bae Dongho , Jung Wonseok , Sohn Ilseon
Published: July 2003

In order to establish a long life fatigue design criterion of spot-welded thin sheet structures such as the automobile and the train bodies, an economical method was proposed. As a mechanical parameter to determine the fatigue design criterion of spot-welded structure, the maximum stress equation was defined by using artificial neural network. By using the maximum stress equation and the fatigue data previously obtained as the fatigue test results, the fatigue design criterion of spot-welded joint could be predicted without any additional fatigue tests. The results predicted by this method showed good agreement with actual fatigue test results.
Quantitative Measurement of Micro-Deformation of Electropolished Carbon Steel Using an Image Processing Technique
Authors: Fukuda Takayuki , Nisitani Hironobu , Kawasue Kikuhito
Published: July 2003

An automatic technique for the quantitative measurement of micro-surface deformation of a specimen using image-processing is introduced. Static tensile and torsional tests of two kinds of electropolished carbon steels are carried out. One has a banded structure and another has not. The banded structure gives a great influence on the micro-deformation depending on the type of loads. The characteristics of micro-deformations under these static loads are made clear from the results obtained by the image-processing technique.
A Study on Fatigue Fracture Mechanism of Cr-Mo Steel SCM435 in Super Long Life Range
Authors: Murakami Ri Ichi , Yonekura Daisuke , Murayama Taishi
Published: July 2003

For high strength steels, a characteristic fatigue behavior, which S-N curve comes down again in the long life region of N > 107 cycles, was reported by many researchers. Specifically, for high strength steel, the fatigue limit is temporal value because of the fish-eye fracture in the long life region over about N = 107 cycles. However, fish eye fracture does not appear for medium strength steel in super long life range. In this paper, cantilever-type rotational bending fatigue tests were carried out for quenched and tempered Cr-Mo steel (JIS: SCM435) up to 109 cycles at room temperature in air. The S-N curve showed a horizontal part in long life region over 107 cycles. In addition, fish- eye fracture was not observed and for all specimens, the crack initiation occurred from the specimen surface. The fatigue fracture behavior of SCM435 in super long life was discussed based on optical microscopy observation and scanning electron microscopy observation.
Probabilistic Life Assessment Method of Low Cycle Fatigue for Power Plant Components
Authors: Kang Myung Soo
Published: July 2003

This study focuses on the probabilistic analysis method to the determination of low cycle fatigue life for power plant components. The analysis incorporates standard life assessment modeling techniques used in the determination analysis of the low cycle fatigue. The probabilistic life assessment is developed to increase the reliability of life assessment. A probabilistic life assessment procedure can provide the engineer with the probability of structural failure as a function of operating time given the uncertainties in the input data. The probabilistic life assessment involves some uncertainties, for example, initial crack size, aspect ratio, crack initiation time, crack location, structural geometry, material properties, and loading condition, and a triangle distribution function is used for random variable generation. The resulting information provides the engineer with an assessment of the probability of structural failure. This information can form the basis of inspection planning and retirement-for-cause decisions. This study forms basis of the probabilistic life assessment technique and will be extended to other damage mechanisms.
Surface Study of Ti3Al and Ti3Al-11Nb, TiAl and TiAl-2Cr by X-Ray Photoelectron Spectroscopy
Authors: Lee J. , Gao W. , Hodgson M.
Published: July 2003

Oxide films formed on intermetallics Ti 3 Al , Ti 3 Al -11at.%Nb, TiAl and TiAl-2at.%Cr were studied by X-Ray Photoelectron Spectroscopy (XPS). An addition of 11at%Nb to Ti 3 Al increases the Ti:Al atomic ratio on the surface from 2.8:1 to 20:1. This may explain the better electrochemical corrosion resistance of Ti 3 Al -11Nb than Ti 3 Al . Meanwhile, an addition of 2at.%Cr to TiAl decreases the Ti atomic percentage from 11.8 to 9.5. The Ti:Al atomic ratio changes from 1:0.2 to 1:1.8. The Cr addition enhances the formation of an Al-enriched passive film, which may be the reason for the improved TiAl high temperature oxidation resistance. TiO 2 is the main component of the top oxide layers formed on the intermetallics of Ti 3 Al , Ti 3 Al -11Nb and TiAl. In contrast the top layer of TiAl-2Cr is mainly Al 2 O 3. XPS results show that the compositions are quite different between the bulk materials and the top oxide layer on these intermetallics.
Effects of Temperature on Mode II Fracture Toughness of Multidirectional CFRP Laminates
Authors: Kim Hyoung Soo , Wang Wen Xue , Takao Yoshihiro , Ben Goichi
Published: July 2003

End notched flexure (ENF) tests were performed to investigate the effects of temperature and fiber orientation on Mode II interlaminar fracture behavior, GIIC (GII at the crack initiation), of carbon fiber-reinforced epoxy composites, T800H/#3631. The values of GIIC for three kinds of laminates, [012//012], [22.5/-22.5/08/-22.5/22.5//-22.5/22.5/08/22.5/-22.5] and [45/-45/08/-45/45//-45/45/08/45/-45], with a pre-cracked interface, that is // in each laminate, were obtained at three temperatures, i.e. -100°C, 25°C and 150°C. It is shown that GIIC is obviously affected by the temperature and fiber orientation. The scanning electron microscope (SEM) observation was also carried out to investigate the fracture surface. SEM analysis suggested that the decreased Mode II interlaminar fracture toughness for all kinds of specimens at high temperature could be attributed to temperature-induced matrix property change or fiber-matrix interfacial weakening.
Computational Simulation of Fracture Behavior Due to Mechanical and Constituent Properties of CFCCs
Authors: Kwon Oh Heon , Yun Yu Seong
Published: July 2003

Continuous fiber reinforced ceramic matrix composites (CFCCs) are recently a subject of a lot of research interest due to advantages which are high specific stiffness and strength, high toughness and nonbrittle failure as compared to monolithic ceramics. The basic purpose of the present study is to describe graphically the fracture behavior of CFCCs according to a dependence on constituent properties. In CFCCs, following matrix cracking, intact fibers bridge effects impose closure tractions behind the crack tip that reduce the driving force for further cracking. Thus matrix cracking stress and bridging stress are important. Then the change of fiber volume fraction is given for the matrix cracking stress by the numerical simulation. Numerical simulation are carried out by using a finite element analysis code ANSYS. The double mesh concept is applied to account for fiber and matrix material properties.
Fatigue Crack Growth in Aluminum Borate Whisker Reinforced AC4CH Alloy Matrix Composite Fabricated by Squeeze Casing
Authors: Park Won Jo , Choi Yong Bum , Huh Sun Chul , Yoon Han Ki
Published: July 2003

Al 18 B 4 O 33 w / AC4CH composite was fabricated using squeeze-casting method in which the molten aluminum was infiltrated into the whisker preform mounted on the mould. The aluminum borate whisker is very effective in the improvement of the mechanical properties of the AC4CH alloy. This paper is focused on fatigue crack growth behavior of the composite under different stress ratios R = 0.1 and R = 0.05. The effects of stress ratio on fatigue crack growth behavior of Al 18 B 4 O 33 w / AC4CH have also been investigated. In addition, the fracture of the fatigue crack growth was also investigated using scanning electro microscopy (SEM). As the results of an investigation, the whisker reinforcement phases in the AC4CH alloy matrix are irregularly shaped and randomly dispersed. The fatigue crack growth behavior at equivalent stress intensity factor in Al 18 B 4 O 33 w / AC4CH was faster than that of AC4CH alloy and the curves are very steep compared to the traditional metallic alloy. The region of stable crack growth in AC4CH was shown that the characteristic of surface has rough shape. It was appeared a kind of dimple type on the surface. But in case of Al 18 B 4 O 33 w / AC4CH , the characteristic of surface was gross brittle failure.
Chraracteristics of Crack Growth of Alumina Ceramics Under Cyclic Loads
Authors: Huh Yong Hak , Cho Seong Jae , Song Jiho
Published: July 2003

Characteristics of crack growth under cyclic loading for alumina ceramics have been investigated. Three alumina ceramics with different grain size were fabricated by hot-pressing. Cyclic fatigue tests were carried out using four-point bend specimen. From examination of crack path and microstructural behavior from the tested specimens, grain bridging along the crack interface and intergranular fracture mode at the fracture surface were observed. The crack growth rate curve presented by using the cyclic parameter, [Formula: see text], could be divided into three regions. These regions were closely related to the fraction of intergranular fracture area. Crack closure influencing the cyclic parameter was evaluated as a function of stress ratio.
Active Vibration Control of Epoxy Matrix Composite Beams with Embedded Shape Memory Alloy TiNi Fibers
Authors: Aoki T. , Shimamoto A.
Published: July 2003

In this paper, epoxy matrix composite beams with embedded TiNi (SMA: Shape Memory Alloy) fiber are applied to enhance the strength and fracture toughness of the machinery components. It is also well known that SMA shows the remarkable changes of stiffness and damping ratio between martensite at lower temperature and austenite at high temperature. A shape recovery force is associated with inverse phase transformation of SMA. The effects of heating with current and pre-strain in TiNi fiber of SMA on vibration characteristics are experimentally investigated. The active vibration control is achieved by controlling the current and pre-strain.
Measurement of Deformation of Epoxy Resin Plates with an Embedded SMA Wire Using Digital Image Correlation
Authors: Umezaki Eisaku , Ichikawa Tadashi
Published: July 2003

The deformation of the surface of epoxy resin plates with an embedded linear shape-memory alloy (SMA) wire as an actuator in smart structure members is measured as a function of the duration of the supply of electric current to the SMA wire, using a digital image correlation technique. Results show that the two-dimensional deformation of the plate surface can be measured, and that the maximum deformation of the plate surface can be obtained on both sides of a crack and increases with the duration of the current supply. Therefore, the deformation of the plate surface measured using the digital image correlation technique suggests the possibility of its application in the prediction of crack closure in epoxy resin plates with embedded SMA wires heated by supplying electric current.
Ultrasonic Nondestructive Evaluation of Carbon/Carbon Composites
Authors: Im Kwang Hee , Hsu David K. , Cho Young Tae
Published: July 2003

In this work several ultrasonic techniques were applied to carbon/carbon (C/C) composites for the evaluation. In a large carbon/carbon composite manufactured by chemical vapor infiltration (CVI) method, the spatial variation of ultrasonic velocity was measured and found to be consistent with the densification behavior in CVI process. Low frequency through-transmission scans based on both amplitude and time-of-flight of the ultrasonic pulse were used for mapping out the material property inhomogeneity. These results were compared with that obtained by dry-coupling ultrasonics. Pulse-echo C-scans was used to image near-surface material property anomalies such as the placement of spacers between disks during CVI. Also, optical micrograph had been examined on the surface of C/C composites using a destructive way.
Monitoring of Failure Mechanisms in Fiber Reinforced Composites During Cryogenic Cooling by Acoustic Emission
Authors: Choi Nak Sam , Woo Sung Choong , Kim Tae Won , Rhee Kyong Y.
Published: July 2003

Microfractures in composite laminates during cryogenic cooling were monitored employing thermo-acoustic emission(AE). During the initial stage of cryogenic cooling, very strong AE signals with low and high frequency bands were dominantly detected showing a development of large cracks accompanying fiber breakages. After that, weak emissions with low frequency bands became prevalent indicating the propagation of microfractures in the matrix and/or fiber-matrix interface. It was concluded that the breakage of bridged-fibers hindering the macroscopic cracking in the initial stage might be the representative cryogenic damage of composite laminates.
Oxidation Behaviour of SiC and TiC Particulate Reinforced Ti3Al Intermetallic Matrix Composites
Authors: Li Zhengwei , Gao Wei , Liang Jing , Zhang Deliang
Published: July 2003

Oxidation behaviours of SiC and TiC particulate reinforced Ti 3 Al intermetallic matrix composites at 700-800°C have been studied. The results showed that composites had lower oxidation rates than the cast Ti 3 Al . The most encouraging improvement is that they all possess excellent scale spallation resistance, no spallation could be observed from the composite specimens during all tests. Based on SEM and XRD results, the mechanisms of oxidation and spallation for these composites were discussed briefly.
Joining of Carbon Fibre Reinforced SiC (Cf/SiC) to Ni-Based Superalloy with Multiple Interlayers
Authors: Li Shujie , Zhang Jianjun , Liang Xiaobo , Duan Huiping , Zhang Yan
Published: July 2003

Welding of C f / SiC to Ni-based superalloy has been realized using Cu/W/Cu/W/Cu multiple interlayers. The bending strength of the joints has been improved by using the active metallic filler contacted with C f / SiC . The strength of the joints is remarkably affected by the welding temperature. The maximum value 102.1 MPa has been obtained at 970°C (dwell time: 10 min., welding pressure: 34.3 MPa). Microstructural studies were also conducted.
Effect of Anisotropic Characteristics of Composite Skins on the Electromagnetic Wave Propagation in the Foam Core Sandwich Structures
Authors: Chun Heoung Jae , Shin Hyun Su
Published: July 2003

The propagation of electromagnetic waves in the foam core sandwich structures is highly affected by anisotropic permittivity and loss tangent of composite skins. Even though many investigations were focused on the propagation of electromagnetic waves in the composite materials in last several decades, little investigations were carried out to understand adequately the propagation of the electromagnetic waves in the foam core sandwich structures. In this study, the transmittance of the arbitrary linearly polarized incident TEM waves through the solid composite laminate with various stacking sequences and foam core sandwich structures with composite skins was calculated as functions of fiber orientation of composites and incident angle of the wave by the analytical model.
Effect of Circular Hole Notch Size on Strength Characteristics of CFRP/AL7075 Hybrid Composites
Authors: Yoon Han Ki , Park Joon Soo , Lee Sang Pill , Park Yi Hyun , Kong Yu Sik , Park Won Jo
Published: July 2003

As for the properties on both the aluminum and the CFRP which are used to make CFRP/AL7075 hybrid composites, CARALL (carbon reinforced aluminum laminate). In the CARALL specimen for rule of mixture, we were analyzed notched strength by finite element method. The results obtained from FEM notched strength analysis and experimental are as follows; In the unnotch CARALL specimen, the stresses imposed CFRP, epoxy, A17075 obtained by finite element method strength solution for A/C9991, when strain 0.48%, are 392 Mpa, 26 Mpa and 321 Mpa, respectively. The slope of the stress-strain curve by FEM increase in keeping with the hole size and the yield strain decrease to 36% and 55% for A/C9993 and A/C9991 respectively. And an agreement is found between the experimental results and the FEM analytical prediction results.
Variation of Boride Layer Characteristeics by Heating Conditions and Materials
Authors: Suh Chang Min , Kim Sung Ho , Lee Jin Ho , Hwang Nam Seong
Published: July 2003

Surface treatment is commonly used as the most efficient and cost down method of producing high hardness materials for machine parts. Currently, high hardness materials are being created from boronized materials through diffusion of Boron. This research investigated the improvement of mechanical properties as a result of boronizing, according to the variation of heating conditions and materials. Boronizing was performed at four kinds of steels SS41, S4SC, SKD61 and SUS304. All experiments were performed under equal conditions to allow for the comparison of results. Three kinds of boronizing time periods, 2hr, 3hr and 5hr were used at 900°C, and a reheated cycle was also used in this test. The results indicated that all specimens produced borides, and the X-ray deflection method demonstrated that the boride layers consisted of FeB or Fe2B.
Damage Theory for Discontinuously-Reinforced Composites Including Cracked Inhomogeneity
Authors: Cho Young Tae , Yoon Duck Young , Im Kwang Hee
Published: July 2003

In particle or short-fiber reinforced composites, cracking of the reinforcements is a significant damage mode because the cracked reinforcements lose load carrying capacity. This paper deals with an incremental damage theory of particle or short-fiber reinforced composites. The composite undergoing damage process contains intact and broken reinforcements in a matrix. To describe the load carrying capacity of the cracked reinforcement, the average stress of a cracked ellipsoidal inhomogeneity in infinite body, which was proposed in the previous paper is introduced. An incremental constitutive relation of particle or short-fiber reinforced composites including the progressive cracking damage of the reinforcements have been developed based on the Eshelby's equivalent inclusion method and Mori and Tanaka's mean field concept. Influence of the cracking damage on the stress-strain response of the composites is demonstrated.
Measurement and Prediction of Effective Thermal Conductivity for Woven Fabric Composites
Authors: Goo Nam Seo , Woo Kyeongsik
Published: July 2003

The current paper deals with the measurement and prediction of thermal conductivities for plain weave fabric composites. An experimental apparatus was setup to measure the temperature gradients from which the thermal conductivities were obtained. The thermal conductivities were also calculated using finite element analyses for plain weave unit cell models and then compared with experimental results. In addition, the effect of a phase shift and the fiber volume fraction in the tow on the thermal conductivities was addressed.
An Analysis for Arrest Toughness of Impact-Induced Delamination in Carbon/Epoxy Laminates
Authors: Kang Ki Weon , Kim Jung Kyu , Cheong Seong Kyun , Kim Yong Soo
Published: July 2003

A model is proposed to identify an arrest toughness, which governs a delamination in laminates. Also, a statistical analysis is conducted to identify a variation of arrest toughness due to material nonhomogeneity. To these ends, impact and 3-point bending tests are performed on the Carbon/Epoxy laminates with various thickness. The fracture behavior can be described by a crack arrest concept. The arrest toughness can be evaluated by an elastic work factor. Also, the Weibull distribution is suitable to predict a failure probability for the arrest toughness. Moreover, the variation of toughness increase gradually with the increase of the specimen thickness. This behavior may be attributed to a change of material nonhomogeneity with the specimen thickness.
Internal Stress Analysis of Long Fiber Reinforced Materials
Authors: Nishida Masayuki , Hanabusa Takao , Ikeuchi Yasukazu
Published: July 2003

The criterion of biaxial or triaxial analysis was examined with regard to the distribution of micro-stress in fiber reinforced materials using the finite element method (FEM). The weighted average strain <ε> and the weighted average stress <σ> were estimated taking into consideration X-ray ab-sorption by FEM. The criterion of the biaxial and the triaxial stress measurement was discussed from the weighted average stress <σ> and the calculated stress using the sin 2ψ method in the fiber phase. Finally, the experimental measurements of X-ray diffraction and Neutron diffraction were used and the results of FEM analysis were qualitatively consistent with the experimental results.
Characterization of Fracture Toughness of Hybrid MMCs the Short Fiber Reinforced Metal Matrix Composites
Authors: Han Moon Sik , Song Jung Il
Published: July 2003

Evaluation of fracture toughness of short fiber reinforced metal matrix composites (MMCs) becomes important for the application as structural materials. Therefore, in this study static and dynamic fracture toughness of MMCs manufactured by squeeze casting process were investigated. A number of MMCs have been tested with various matrix alloys, volume fractions, and specifically types of reinforcements. It was found that static and dynamic fracture toughness of metal matrix composites was remarkably decreased by the addition of ceramic reinforcements. Dynamic fracture toughness slightly decreased compared with static fracture toughness because of the effect of dynamic velocity under impact loading. The toughness of ceramic reinforced MMCs is controlled by a complexity interaction between the matrix alloy and reinforcement. Important properties which influence toughness include the type of reinforcement (its physical form, size), volume fraction and combination of reinforcement, and the matrix alloy. And notch fracture toughness of MMCs for simple evaluation was also discussed.
Processing and Properties of SIC and SIC/SIC Composite Materials by Melt Infiltration Process
Authors: Lee Sang Pill , Yoon Han Ki , Park Joon Soo , Katoh Yutai , Kohyama Akira
Published: July 2003

This paper dealt with the microstructures and the mechanical properties of monolithic SiC and SiC/SiC composite materials fabricated by the melt infiltration process. The characterization of melt infiltrated SiC and SiC/SiC composite materials with different sizes of starting SiC particles was investigated by means of electron microscopies, three point bending tests and single-fiber push-out tests. Based on the mechanical property-microstructure correlation, process optimization methodology also was discussed. The flexural strength of melt infiltrated SiC material strongly depended on the content of residual silicon, which associated with the preparation route of C/SiC matrix slurry such as the composition ratio of C and SiC particles and the size of raw SiC particles. MI-SiC/SiC composites represented good flexural strength, even if the instability of matrix morphology and the interfacial debonding were occurred.
A Study for the Characteristic Changes Under the Repeated Thermal Exposure in the Process of Repairing Aircraft Sandwich Structures
Authors: Kim Yun Hae , Han Joong Won , Kim Don Won , Choi Byung Keun , Murakami R.
Published: July 2003

Delamination can be observed in the sound areas during and/or after a couple times exposure to the elevated curing temperature due to the repeated repair condition. This study was conducted for checking the degree of degradation of properties of the cured parts and delamination between skin prepreg and honeycomb core. Specimens with glass honeycomb sandwich construction and glass/epoxy prepreg were prepared. The specimens were cured 1 to 5 times at 260°F in an autoclave and each additionally exposed 50, 100 and 150 hours in the 260°F oven. Each specimen was tested for tensile strength, compressive strength, flatwise tensile strength and interlaminar shear strength. To monitor the characteristics of the resin itself, the cured resin was tested using DMA and DSC. As a results, the decrease of Tg value were observed in the specific specimen which is exposed over 50 hrs at 260°F. This means the change or degradative of resin properties is also related to the decrease of flatwise tensile properties. Accordingly, minimal exposure on the curing temperature is recommended for parts in order to prevent the delation and maintain the better condition.
A Study on the Friction Characteristics of Automotive Composite Brake Pads Using Taguchi Method
Authors: Kim Yun Hae , Lee Jung Ju , Nisitani H.
Published: July 2003

It has many variables and factors to design the friction materials for automotive brake pads. The purpose of this study is to develop the proper method to design at low-cost and to find friction characteristics of each raw materials. For the purpose of examining the effect of each major raw materials, we used the Taguchi L 9(34) orthogonal matrix and 1/5 scale dynamo machine for evaluation of the friction characteristics of composite brake pads. Using Taguchi method, it is easy to investigate the influence of each component in complicated composites friction materials. After analyzing the testing results by the Taguchi method, the effect of factors and levels influenced friction behavior was studied.
Complex 3-D Behaviors of Composite Cylinders with 3-D Shape Memory Alloy Actuators
Authors: Kim Cheol , Lee Sung Hwan
Published: July 2003

Shape memory alloys (SMAs) are often used in smart materials and structures as the active components. Their ability to provide a high force and large displacement has been useful in many applications, including devices for damage control, active structural acoustic control, dynamic tuning, and shape control. In this paper, the radial displacement control of an externally pressurized elliptic composite cylinder where the SMA strip actuators are bonded on its in and outer surface is investigated numerically. The elliptic composite cylinder with SMAs was designed and analyzed to determine the feasibility of such a system for the removal of stiffeners from externally pressurized stiffened composite stuctures. SMAs start to transform from the martensitic into the austenitic state upon actuation through resistive heating, simultaneously recover the prestrain, and thus cause the composite cylinder to expand in the radial direction. The externally pressurized composite cylinder with the SMA actuators was analyzed using the 3-D finite element method.
Fem Analysis of Micro-Stage with Duralumin Material
Authors: Kwac Lee Ku , Kim Chang Hyun , Kim Jae Yeol
Published: July 2003

In after the industrial revolution in the 21st century, the world is preparing for new revolution that is society with knowledge for a basis such as IT (Information Technology), NT (Nano Technology) and BT (Bio Technology). Recently, NT is applied to various fields that are composed of science, industry, media and semiconductor-micro technology. It has need of IT that is ultra-precision positioning technology with strokes of many hundreds mm and maintenance of nm precision in fields of ultra micro processes, ultra precision measurements, photo communication parts and photo magnetic memories. For optimal design of micro-stage, we measured the displacement of piezoelectric transducer that was based on voltage value. And the micro-stage was analyzed using FEM with displacement data including voltage value of piezoelectric transducer. For verification of analysis results, the displacements were measured by using Laser interferometer. And researchers confirmed to propriety on design of micro-stage with FEM, we obtained 3.5% error rate between measurement results and analyzing results.
Non-Conforming Solid Elements for the Analyses of Bending Deformation of Isotropic/Orthotropic Materials with the Smallest D.O.F.
Authors: Kwon Y. D. , Goo N. S. , Yun T. H.
Published: July 2003

This paper proposes both a 3-D 10-node equivalent solid element and a 2-D 5-node equivalent solid element. These proposed elements have the smallest number of degree of freedom among 3-D/2-D solid elements, taking into consideration bending deformation as well as extensional and shear deformations of solids. The proposed elements exhibit greater bending stiffness than the conventional 2-D/3-D solid elements, due to the reduction of degrees of freedom. This phenomenon of greater stiffness was corrected by using a modification of Gauss sampling points. The quantity of modification is expressed as a function of material properties. Adopting this kind of modification, we can show that even the conventional 4-node elements can be applied to the analysis of bending problem successfully in proper fine mesh. The proposed elements pass the patch test and have no spurious zero energy modes. The effectiveness of MQ10 element (Q10 with the modification) is tested in several examples. The results of static and free vibration analyses of isotropic/orthotropic plates using MQ10 elements show good agreements with those using 20-node element. In addition, damped/undamped forced motion analyses using MQ10 elements were carried out, and compared with those of a 20-node element.