bluuebunny/crossref_metadata_2025 huggingface dataset:
Crack Growth in 18G2A Steels With Different Constraint
Authors: Wang Z. X. , Chao Y. J. , Lam P. S.
Published: August 2009

A constraint theory in fracture mechanics is used to analyze the test data of 18G2A steels using single edge-notched bend (SENB) specimens with various crack depth to specimen width ratios (a/W). A bending correction factor is included in the two-parameter (J-A2) asymptotic solution to improve the theoretical prediction of the stress field for deep cracks under large scale yielding condition, where J is the J-integral and A2 is the constraint parameter, which depends on the in-plane geometry of the cracked body (a/W). As a result, the valid region for a traditional J-controlled crack growth is extended, and the ASTM specimen size requirements for fracture toughness testing can be relaxed. In addition, it is shown that the functional dependence of J-R curves on A2 for 18G2A steels is established with test data; and the predicted J-R curves agree very well with the experimental curves. This ensures the transferability of laboratory test data to an actual structure provided the constraint level (A2) of the cracked structure is known or determined. This allows an appropriate J-R curve with the same constraint level to be constructed and used in flaw stability analysis of any cracked body.
Applicability of Optimal Seismic Design Methodology for Piping Systems Subjected to Seismic Waves With Various Frequency Characteristics
Authors: Ito Tomohiro , Fujita Katsuhisa , Michiue Masashi
Published: August 2009

In this study, the optimal seismic design methodology which can consider the structural integrity of both piping systems and elasto-plastic support devices are developed. This methodology employs genetic algorithm and can search the optimal conditions such as supporting locations, capacity and stiffness of supporting devices. A lead extrusion damper is treated here as a typical elasto-plastic damper. Numerical simulations are performed using a simple piping system model for the various kinds of seismic waves with different frequency characteristics. As a result, it is shown that the optimal seismic design methodology proposed here is applicable to the seismic design of piping systems supported by elasto-plastic dampers subjected to the seismic waves with various kinds of frequency characteristics.
Mechanism of Rotational Screw Thread Loosening in Bolted Joints Under Repeated Temperature Changes
Authors: Sawa Toshiyuki , Ishimura Mitsutoshi , Yamanaka Hiroshi , Fukuba Yusuke
Published: August 2009

Bolted joints have been used in mechanical structures. However, loosening accidents sometimes happen under several types of loadings. Recently, some studies have been conducted on the screw thread loosening in bolted joints. It is verified that bolted joints are loosened when transverse repeated loadings are applied. Some studies on no rotational loosening in bolted joints under thermal changes have also conducted. However, few studies on rotational screw thread loosening in bolted joints have conducted. In this study, rotational screw thread loosening in bolted joint under repeated temperature changes is examined. Effects of the linear thermal expansion coefficient of clamped parts and number of repeated temperature changes are examined by the measurements and finite element analyses. In the experiments, a bolted joint, which consist of two rectangular plates fastened at room temperature by two bolts and nuts, are put in a furnace and heated by an electric heater. Then, the bolted joint is cooled at room temperature. These thermal cycles are repeated. Bolt temperature and bolt load were measured. Loosening is evaluated from the reductions in the bolt load. Finite element analyses were carried out for clarifying the loosening mechanism. Discussion is made on the mechanism of rotational screw thread loosening in bolted joints under repeated temperature changes. The results show that loosening occurs under repeated temperature changes due to difference in the linear thermal expansion coefficients of the different clamped parts.
Mathematical Solution for Evaluating Fluid Pressure on Rigid Flat-Bottom Cylindrical Shell Tanks Due to Uplift Motion
Authors: Taniguchi Tomoyo , Ando Yoshinori
Published: August 2009

Solving the equation of continuity given by the Laplace equation on the cylindrical coordinates, the mathematical solution for evaluating fluid pressure on rigid flat-bottom cylindrical shell tanks is derived. However, since difficulty of applying asymmetric boundary conditions on the cylindrical coordinates which trace realistic uplift motion of tanks restricts application of the preceding mathematical solution to the actual case scenario, the slice model consisting of a rigid rectangular tank with unit depth on a parallel plane to the uplift motion and offsetting from a center of tanks is developed. Comparison reveals applicability of the slice model for evaluating the fluid pressure on the rigid flat-bottom cylindrical rigid shell tanks.
Earthquake-Resistant Design of RC Frame With “Dual Functions” Metallic Dampers
Authors: Li Hong-Nan , Li Gang
Published: August 2009

Earthquake can make structures damaged and crumble. The traditional approach to seismic design has been based upon providing a combination of strength and ductility to resist the imposed loads. Thus, the level of the structure security cannot be achieved, because the disadvantage of the designing method is lack of adjusting capability subjected to an uncertain earthquake. The presence of some damping (energy dissipation) in buildings has been recognized and studied by professional researchers. Passive energy-dissipated system, as a category of vibration control methods, lead the inputting energy from earthquake to special element, thereby reducing energy-dissipating demand on primary structural members and minimizing possible structural damage. One of the most effective mechanisms available for the dissipation of input energy of a structure during an earthquake is through the inelastic deformation of metallic substances. Added damping and stiffness (ADAS) elements are designed through the flexural yielding deformation of steel plates. Metallic material is a popular (and inexpensive) choice for an energy dissipation device because of its relatively high elastic stiffness, good ductility and its high potential for dissipating energy in the post-yield region. The idea of utilizing separate metallic dampers in a structure to absorb a large portion of the seismic energy began with the conceptual and experimental work by Kelly et al.. Numerous different types of energy-absorbed devices have been proposed, for example, X-shaped and triangular plate dampers by Whittaker et al. The normal metallic damper is to use the out-of-plane bending deformation of metallic plate to provide damping for structure to reduce its dynamic response to environmental loadings. Since the bending curvature produced by a force, which is perpendicular to the metallic plates of damper applied at the ends is uniform over the full height of the plate, the plate can inelastically deform well without deflection concentration. However, the inelastic deformation of the damper may occur even subjected to a relatively small disturbance (wind or earthquake) since the out-of-plane stiffness of metallic plates of damper is very small. As a result, it has to be replaced after the disturbance. How to improve the stiffness of metallic dampers is an important issue. In this paper, a new idea of designing the metallic damper is presented, i.e. the metallic damper with “dual functions”, and the quasi-static tests with the dampers are carried out. Design and fitting process of the reinforced concrete frame with dual functional metallic damper are introduced. A three-dimensional frame structure model is made with ADPL language in ANSYS program. Seismic responses of the structure with and without metallic damper are calculated and compared. The results show that the metallic dampers with the “dual functions” presented here not only provide certain stiffness in the normal application, but also are of good ability of the seismic energy dissipation.
Development of Evaluation Method of Vibrational Stress in Piping System Applying Multiple Laser Displacement Sensors
Authors: Noda Michiyasu , Maekawa Akira , Suzuki Michiaki , Shintani Masanori
Published: August 2009

Many damages of the piping system in the nuclear power plants have occurred due to the vibration fatigue induced by the mechanical vibration of pumps and so on. One of the preventive measures for the problem of vibration is the evaluation of vibrational stress, which is the methods using the strain gauge and the accelerometer. However, these evaluation methods require highly specialized skills and many man-hours, and nuclear plants are awaiting the development of vibration-measuring techniques and evaluation techniques that are easy to perform and produce accurate results promptly. The purpose of this study is the development of the method and the device measuring the vibrational stress directory using the laser displacement sensor. The proposed method evaluates the vibrational stress as follows: Three laser displacement sensors measure the displacement of the piping induced by vibrating, and the strain of the piping is calculated from the difference among the sensor-measured displacements to determine vibrational stress. The measurement equipment isn’t direct contact with the piping evaluated, can be easily reduced in size, and can realize quick and accurate measurement. This paper describes the concept of the proposed evaluation method of vibrational stress in the piping system using three laser displacement sensors, along with its theory and measurement procedure. And then, refer to the proposal of the evaluation method of torsional vibration using six laser displacement sensors. This paper also compares the stress values calculated based on the cantilever vibration identified by this method and the stress values calculated based on material mechanics, and discusses the applicability of the method in actual plants.
The Statistical Material Selection and Structural Design Maps for High Temperature Components
Authors: Fujiyama Kazunari , Shima Tomohiro , Muraoka Takashi , Mizuno Yoshishige
Published: August 2009

The concept of material selection map proposed by Ashby [1] was modified to statistical maps for reliability design of high temperature components. The proposed procedure for making maps contained following steps; (i)define a performance index such as cost, (ii)define constraint conditions such as material strength, (iii)mapping the performance index under the constraint conditions and statistical distribution of material properties. The statistical distribution of material properties were expressed as the function of normalized parameters to obtain unified regressions for wide variation of material heats. The material properties used were tensile, creep and low cycle fatigue related ones for several ferritic and austenitic heat resistant steels mostly referred to NIMS (National Institute for Materials Science) database. This proposed mapping procedure was applied to the design of pipes and flanges under creep and thermomechanical low cycle fatigue conditions. The maps could show the statistically upper and lower bounds of allowable geometrical dimensions. The maps showed the effectiveness for optimizing the dimensions from the design aspects of creep and fatigue reliability.
Comparison of Failure Modes of Piping Systems With Wall Thinning Subjected to In-Plane, Out-of-Plane and Mixed Mode Bending Under Seismic Load: Computational Approach
Authors: Tsunoi Satoshi , Mikami Akira , Nakamura Izumi , Otani Akihito , Shiratori Masaki
Published: August 2009

The authors have proposed an analytical model by which they can simulate the dynamic and failure behaviors of piping systems with local wall thinning against seismic loadings. In the previous paper [13], the authors have carried out a series of experimental investigations about dynamic and failure behaviors of the piping system with fully circumferential 50% wall thinning at an elbow or two elbows. In this paper these experiments have been simulated by using the above proposed analytical model and investigated to what extent they can catch the experimental behaviors by simulations.
Fatigue and Cyclic Plasticity Properties of a Super-Austenitic Stainless Steel
Authors: Kalnaus Sergiy , Fan Feifei , Jiang Yanyao
Published: August 2009

Tension-compression, torsion and axial-torsion experiments were conducted on AL-6XN® alloy. The main goal was to investigate experimentally, in detail, the cyclic plasticity behavior as well as fatigue life of AL-6XN® steel. Details of cyclic stress-strain response were collected during the experiments, which can serve as a baseline for development of cyclic plasticity model for this material. Microscopic observations of cracking behavior conducted in the present study allow connecting the fracture mechanism with fatigue life prediction. It was observed, that fatigue life of this material is a function of the fracture mode (mixed or tensile). The mixed cracking was observed in the specimens tested under higher applied strain levels, while the tensile cracking was revealed in the tests under lower strain amplitudes. Strain-life curves of the specimens failed in mixed mode and of those failed in tensile mode run parallel to each other, but the specimens that exhibit mixed failure mode show lower fatigue life as compared to the tensile mode specimens. Transition between mixed and tensile cracking orientations was studied in detail. The results of the experimental work presented in this study can serve for design of fatigue models for this material in the future.
Simple Nonlinear Methods for Predicting Two-Phase Instabilities in a Helically Coiled Steam Generator
Authors: Choi Seok-Ki , Kim Seong-O , Kang Han-Ok
Published: August 2009

A simple model to analyze the non-linear density-wave instability in a sodium cooled, helically coiled steam generator is developed. The model is formulated with three regions with moving boundaries. The homogeneous equilibrium flow model is used for the two-phase region and the shell-side energy conservation is also considered for the heat flux variation in each region. The proposed model is applied to the analysis of two-phase instability in a JAEA (Japan Atomic Energy Agency) 50MWt No.2 steam generator. The steady state results show that the proposed model accurately predicts the six cases of the operating temperatures in the primary and secondary sides. The sizes of the three regions and the secondary side pressure drop according to the flow rate, and the temperature variation in the vertical direction are also predicted well. The temporal variations of the inlet flow rate according to the throttling coefficient, the boiling and superheating boundaries and the pressure drop in the two-phase and superheating regions are obtained from the unsteady analysis.
Tensile Behavior of Nb7.5Ta for Heat-Exchanger Applications
Authors: Ghosh Arindam , Kondur Venkateswarlu , Roy Ajit Kumar
Published: August 2009

Hydrogen generation using sulfur-iodine cycle involves the formation and decomposition of sulfuric acid and hydrogen iodide (HI). The decomposition of HI has been proposed to occur at a maximum temperature of 400°C. Nb7.5Ta has been identified as a candidate structural material for use in heat-exchanger during the decomposition of HI. This paper presents the results of tensile testing at temperatures ranging from ambient to 400°C. A gradual drop in tensile strength was noted with increasing temperature. Reduced failure strain was observed at temperatures up to 300°C, which is known to be associated with the occurrence of dynamic strain aging (DSA). Since the concentration of precipitate and dislocations can influence the DSA behavior of susceptible materials, efforts are in progress to characterize dislocations using transmission electron microscopy. All tested specimens exhibited ductile failures, characterized by dimples.
The Evaluation of the Cracking Susceptibility of Alloy 718 in an Acidic Solution
Authors: Venkatesh Anand , Roy Ajit K.
Published: August 2009

An austenitic iron-nickel-chromium-molybdenum steel, known as Alloy 718 (N07718), has been investigated for its corrosion resistance in an aqueous environment relevant to the sulfur-iodine (S-I) process, proposed to generate hydrogen using nuclear heat. The slow-strain-rate (SSR) testing method was used to evaluate the cracking susceptibility of this alloy at ambient and elevated temperatures. A strain rate of 3.3 × 10−6 sec−1 was used in these tests. The localized corrosion behavior of this alloy was also evaluated by the cyclic potentiodynamic polarization technique. Further, the fracture morphology of the specimens used in SSR testing was determined by scanning electron microscopy.
Evaluation of Microstructures and Creep Damages in HAZ of P91 Steel Weldment
Authors: Tabuchi Masaaki , Hongo Hiromichi , Li Yongkui , Watanabe Takashi , Takahashi Yukio
Published: August 2009

The present paper aims to clarify the Type IV creep damage process of Mod.9Cr-1Mo (Gr.91) steel weldment. Long-term creep tests for base metal and simulated fine-grained HAZ and welded joints were conducted at 550, 600 and 650 °C. Furthermore, creep tests of thick welded joint specimens were interrupted at 0.2, 0.5, 0.7, 0.8, 0.9 of rupture life, and damage distributions were measured quantitatively. It was found that creep voids initiated at the early stage of life inside the specimen thickness, and grew into cracks at the later stage of life. Experimental creep damage distributions were compared with computed ones using FEM and damage mechanics analysis. The effect of multiaxial stress condition on creep damage evolution is discussed.
Flow Induced Pulsations Caused by Corrugated Tubes
Authors: Belfroid Stefan P. C. , Shatto Donald P. , Peters Rene M. C. A. M.
Published: August 2009

Corrugated tubes can produce a tonal noise when used for gas transport, for instance in the case of flexible risers. The whistling sound is generated by shear layer instability due to the boundary layer separation at each corrugation. This whistling is examined by investigating the frequency, amplitude and onset of the pulsations generated by 2" artificially corrugated tubes and cable feeds. Special attention is given to the influence of the geometry of the corrugations and to the influence of the boundary conditions of the tubes. Two distinct modes are measured. One high mode with a typical Strouhal number Sr = 0.35 and one with a Strouhal number of Sr = 0.1. The relative length scale for the corrugations to be used in the Strouhal number is a modified gap width, which is the gap width excluding the downstream edge radius. The exact Strouhal number for a corrugation is furthermore dependent on details of the corrugation, as the convective velocity of the flow disturbances is influenced by details in the geometry such as edge rounding. The amplitude of the generated pulsations scales with the acoustic pressure (ρcU) and will saturate for higher flow rates (p′/ρcU = constant). The saturation level is independent of pressure and tube length and is solely dependent on the corrugation geometry. Larger cavities will generate higher amplitude pulsations. The onset of the whistling is dependent on the tube itself and the system boundaries. Only for very long tubes is the onset insensitive to the system boundaries and will the onset be determined by corrugations. In that case the onset is determined by a critical boundary layer thickness. For smaller tubes, this critical layer thickness is still relevant, but the boundary conditions will have a large effect. A system with a high reflection coefficient will start at lower gas velocities than a system with a low reflection coefficient. Based on the current results the frequency and amplitude of the pulsations can be predicted.
Numerical Analysis of Unsteady Flow Field in the RWT for the Prediction of the Potential for Air Ingression Into the ECC Supply Lines During the SBLOCA at the KSNPs
Authors: Jo Jong Chull , Yu Seon Oh
Published: August 2009

This paper addresses the three-dimensional analysis of unsteady flow in the RWT (Refueling Water Tank) for the prediction of the potential for air ingression into the ECC (Emergency Core Cooling) pump during the SBLOCA (Small Break Loss Of Coolant Accident) at KSNPs (Korean Standard Nuclear Power plants). Upon the receipt of RAS (Recirculation Actuation Signal) by the occurrence of SBLOCA, the RWT outlet valve is designed to be isolated manually. At the nuclear power plants without the provision of automatic isolation operation of the valve on the downstream of the RWT line, the refueling water begins to discharge from the RWT, which may result in forming and developing the vortex flow in the RWT, under the condition of the minimum pressure of containment and minimum water level of containment recirculation sump during the phase of RAS. Due to the vortex flow, when the water level is below the critical height, a dip starts to develop, causing air ingression before the refueling water drains fully. Hence it can be surmised that there is a possibility of ECC pump failure due to air ingression into the ECC supply line even before the RWT is fully drained. Therefore, in this work, when the RAS is actuated followed by the SBLOCA occurrence, a quantitative evaluation for the maximum limiting allowable time for the manual closing of RWT outlet valve is carried out to eliminate the possibility of air ingression into the ECC pump from the RWT. To do this, the unsteady flow field in the RWT including the drain pit with the connected discharge piping in the process of SBLOCA is analyzed using a CFD (Computational Fluid Dynamics) code. In addition, the transient flow behavior accompanying air entrainment resulting from the dip formation due to vortex flow at the upper part of RWT is examined and the applicable limiting time of the isolation valve closing for preventing air ingression is assessed.
Progress on the National Project CARISMA: Crack Arrest Testing of Irradiated Materials
Authors: Keim Elisabeth , Schnabel Hilmar , Hein Hieronymus , Seibert Tanja
Published: August 2009

The German national project CARISMA [1] deals with testing of fracture toughness values for initiation and arrest of original RPV materials in the irradiated condition. After all basic testing, crack arrest specimens have been manufactured out of large pre-irradiated 100 mm thick fracture toughness specimens. Their dimensions are according to the crack arrest testing standard. Ferritic base material as well as ferritic weld material has been investigated. The results are evaluated and correlations to Charpy results (like the 4 kN criterion) are introduced. In addition a Master Curve like trend curve is adjusted.
Internal Pressure Fatigue Test of Cr-Mo Steel in 45MPa Hydrogen Environment
Authors: Takasawa Koichi , Wada Yoru , Ishigaki Ryoji , Tanaka Yasuhiko , Iwadate Tadao , Ohnishi Keizo
Published: August 2009

Internal pressure fatigue properties of Cr-Mo steel (JIS G 4052, SCM435H) in high-pressure hydrogen or nitrogen atmosphere were investigated by the internal pressure fatigue test using a specially designed apparatus. Internal pressure was varied in the range from 0 to 40.5MPa, and test temperature was 20°C. The cycle length of internal pressure was varied up to 1000 seconds. We obtained the following results. 1. The number of fracture cycles in 45MPa hydrogen atmosphere was much less than those of in the 45MPa nitrogen atmosphere. 2. The number of fracture cycles was not depended on the cycle length. 3. In the fracture surface region where quasi-cleavage and intergranular surfaces are coexisting, the crack growth behavior is different from that of in the quasi-cleavage region.
Research on Shockwave Propagation in Hydrogen
Authors: Murakami Masayuki , Hemuki Yosuke , Itoh Shigeru
Published: August 2009

This paper deals with the propagation of a shockwave in the hydrogen vessel. The aim of this research is the improvement of safety to store hydrogen. The shockwave is generated by the high explosive of the proper quantity and is controlled by a PMMA card gap. The shockwave propagation is visualized by using a high-speed camera image and movie. Shooting procedure is by a shadow graph method. We succeeded in photography of shockwave propagation and combustion phenomenon. Results are then compared with other medium.
Evaluation of Shock Wave Generation by the Metal Wire Explosion
Authors: Okamoto Naoki , Otsuka Masahiko , Itoh Shigeru
Published: August 2009

In this study, we are aimed for application of shock wave to food processing. An explosive is usually used as an energy source to generate shock wave, but there are various obstacles for use of an explosive. So, we introduce shock wave generated by the metal wire explosion using high voltage discharge. Almost foods after processing by shock wave are shown the effects of softening and improvement of osmosis. In this time, we measured pressure generated by the each devices and the value of hardness and pH of processed food to evaluate the device. As a result, when we compared shock pressure by an explosive with that of high voltage discharge, these values approximately at the same level were measured. From comparison of the result that processed food in each device, hardness and pH together are not shown big difference. Thus, it was shown that this device with the metal wire explosion had ability for enough processing.
Study on Dynamic Strength Evaluation Method of Mechanical Members Based on Energy Balance
Authors: Minagawa Keisuke , Fujita Satoshi , Kitamura Seiji , Okamura Shigeki
Published: August 2009

This paper describes the dynamic strength evaluation of piping installed in nuclear power plants from a viewpoint of energy balance. Mechanical structures installed in nuclear power plants such as piping and equipment are usually designed statically in elastic region. Although these mechanical structures have sufficient seismic safety margin, comprehending the ultimate strength is very important in order to improve the seismic safety reliability in unexpected severe earthquakes. In this study, ultimate strength of a simple single-degree-of-freedom model is investigated from a viewpoint of energy balance equation that is one of valid methods for structural calculation. The investigation is implemented by forced vibration experiment. In the experiment, colored random wave having predominant frequency that is similar to natural frequency of the experimental model is input. Stainless steel and carbon steel are selected as material of experimental model. Excitation is continued until the experimental model is damaged, and is carried out with various input levels. As a result of the experiment, it is confirmed that input energy for failure increase with an increase of time for failure. Additionally it is confirmed that input energy for failure depend on the material.
Improvement in Toughness of Transportation and Storage Cask Steel for Spent Nuclear Fuel
Authors: Kwon Hee Kyung , Kim Byoung Koo , Kim Kuk Cheol , Song Keun Ho , Kim Jeong Tae
Published: August 2009

Nuclear power plants have been operated for fifty years. Currently the managements of spent fuel are on progress vigorously. Casks for transportation and/or storage of spent nuclear fuel are usually made of SA350 low alloy steels. The wall thickness of the casks are greater than 300mm. But because leakage of nuclear fuel or radioactive material from unexpected brittle fracture is not acceptable, Nil-ductility transition temperatures of colder than −150°F are needed. The effects of chemical composition and heat treatment on low temperature impact properties of SA350 are investigated in this study. The microstructure of SA350 steel is composed of ferrite and pearlite. The variations of microstructure, low temperature impact properties and strength at room temperature with carbon, vanadium and manganese content are analyzed. To improve the low temperature impact properties, heat treatment at an temperature between quenching and tempering temperature is introduced. With the optimum combination of alloying elements and heat treatment, the impact properties can be improved down to the level of nil-ductility transition temperature −150°F.
Effect of Hydrogen Gas Pressure on the Mechanical Properties of Low Alloy Steel for Hydrogen Pressure Vessels
Authors: Wada Yoru , Ishigaki Ryoji , Tanaka Yasuhiko , Iwadate Tadao , Ohnishi Keizo
Published: August 2009

To provide engineering data useful in design, manufacture and operation of hydrogen storage vessels in hydrogen refueling stations, fatigue test machine equipped with high-pressure hydrogen autoclave was introduced. The effect of steel’s strength level, temperature effect, fracture toughness and pressure effect were evaluated in gaseous hydrogen environment. When steel’s strength level exceeds around 930MPa to 1000MPa, the elongation and notch tensile properties deleteriously degraded. The elongation reduction by the effect of hydrogen increased with lowering the temperature. The same sensitivity to temperature on crack growth behavior was observed. However, it was shown that the gaseous hydrogen environment only affect the slow stable crack growth but did not affect the critical flaw growth of the steel at low temperature, i.e. fast fracture. The pressure dependence of notch tensile strength ranging from 0.1MPa to 75MPa hydrogen pressure shows approximately 1/2 power dependence.
Effect of Surface Machining on the Fatigue Life of Low Alloy Steel for Hydrogen Pressure Vessels
Authors: Wada Yoru , Ishigaki Ryoji , Tanaka Yasuhiko , Iwadate Tadao , Ohnishi Keizo
Published: August 2009

The effect of surface machining on fatigue life in high pressure hydrogen gas was investigated. The test was conducted under the elastic range under 45MPa gaseous hydrogen environment by the ground specimen which were machined so that the surface roughness to be Rmax = 19μm(Mark: 19s), 26μm(26s) and 93μm(93s) and by the polished specimen which are prepared so that the surface roughness to be Rmax = 1μm(1s), 3.6μm(3.6s) and 10μm(10s). The hydrogen fatigue life of ground specimens was considerably reduced with increasing surface roughness as compared to the fatigue life in air at the same surface condition. On the other hand, for the annealed conditions of the ground specimen, the reduction by hydrogen effect was fairly small. The residual stress for the ground specimen at the surface rises sharply in tension while the residual stress for the annealed specimen was nearly equal to zero. We have shown that the hydrogen fatigue damage can be evaluated by obtaining the information about residual stress on surface, stress concentration by maximum surface roughness and the threshold stress intensity SH above which hydrogen fatigue damage occurs.
Force Transfer for High Order Finite Element Methods Using Intersected Meshes
Authors: Kollmannsberger Stefan , Du¨ster Alexander , Rank Ernst
Published: August 2009

High order Finite Element Methods have been shown to be an efficient approach for computing the behavior of fluids and structures alike. However the coupling of such methods in a framework for a partitioned fluid-structure interaction is still in its early stages. A difficulty hereby is a conservative transfer of the loads from the fluid to the solid and an appropriate transfer of the structural displacements back to the boundary of the fluid. This contribution describes the coupling of a high order finite element structural code to the commercial finite volume fluid solver CFX and focuses on the transfer of the loads. For this purpose, the fluid mesh and the structural mesh are intersected. The force acting on the solid is then computed by a composed integration scheme performed on the intersected mesh. The approach can be interpreted as a projection method taking into account the discretization on both sides, i.e. fluid and solid. Numerical examples will demonstrate the basic properties of this new type of data transfer.
Field Measurement of Dynamic Instability of a 50-Ton Tainter-Gate
Authors: Anami Keiko , Ishii Noriaki , Knisely Charles W. , Oku Tatsuya
Published: August 2009

The 2-degrees-of-freedom coupled-mode self-excited vibration of Tainter gate has been demonstrated in hydraulic model studies of 2D and 3D gate models. The concurrent development of a theoretical model has permitted the prediction that some full-scale Tainter-gates could be potentially susceptible to this coupled-mode self-excited vibration. However, there are many people who regard with suspicion the prediction that a massive Tainter-gate might actually undergo this type of vibrations. In response to these skeptics, this paper presents the test results from an actual operational 50-ton Tainter-gate to determine its propensity for large-amplitude self-excited vibration. Further, the previously developed theoretical analysis was applied to the tested gate to uncover an essential dynamic instability for this installation, as well as to provide a framework for the design of a retrofit and an optimized maintenance plan.
Transformation Temperatures and Welding Residual Stresses in Ferritic Steels
Authors: Francis J. A. , Stone H. J. , Kundu S. , Rogge R. B. , Bhadeshia H. K. D. H. , Withers P. J. , Karlsson L.
Published: August 2009

Residual stress in the vicinity of a weld can have a large influence on structural integrity. Here the extent to which the martensite-start temperature of the weld filler metal can be adjusted to mitigate residual stress distributions in ferritic steel welds has been investigated. Three single-pass groove welds were deposited by manual-metal-arc welding on 12mm thick steel plates using filler metals designed to have different martensite-start temperatures. Their residual stress distributions were then characterised by neutron diffraction. It was found that a lower transformation temperature leads to a potentially less harmful stress distribution in and near the fusion zone. The experimental method is reported and the results are interpreted in the context of designing better welding consumables.
Effect of Stress Intensity Factor Estimation Scheme on the Failure Probability of RPV During Pressurized Thermal Shock
Authors: Onizawa Kunio , Osakabe Kazuya
Published: August 2009

During a pressurized thermal shock (PTS) event, the overlay cladding on the inner surface of reactor pressure vessel (RPV) is subjected to high tensile stress compared to base metal because of the difference in thermal expansion coefficients between cladding and base metal. To calculate a stress intensity factor for a postulated crack considering the stress discontinuity with the plastic yielding of cladding, the scheme developed previously has been incorporated into the PASCAL code for the structural integrity analysis. Using the new scheme, conditional probabilities of crack initiation (PCI) were calculated for a typical RPV with a surface crack or under-clad crack under some PTS transients. The PCI values were quantitatively evaluated as a function of neutron fluence using the PASCAL code. It is concluded that the new scheme reduces significantly the PCI value for a surface crack as compared with the conventional method based on elastic stress analysis.
Application of Direction Optimized-Friction Pendulum System to Seismic Mitigation of Sensitive Equipment
Authors: Tsai C. S. , Chen Wen-Shin , Chiang T. C. , Lin Yung-Chang
Published: August 2009

In the recent years, earthquake proof devices have been used to promote the earthquake resistant capabilities of many structures and public constructions. In addition, the high-tech industries are an important key to economic development in some earthquake prone areas, and many historical relics are also located in these areas. Therefore, how to protect the critical equipments from earthquake damage is an important issue. Among many control devices, sliding type isolators such as the FPS, MFPS and TFPS, ect. Isolators are used to lengthen the natural periods of equipment, and to isolate the seismic energy trying to impart to structures. However, the frequency and displacement capacity have been predefined when the radius of curvature of the concave surface or stiffness of base isolator is once determined. In this study, the base isolator with variable frequencies and displacement capacities has been proposed, and several shaking table tests of critical sensitive equipment with the proposed isolators have been carried out in Feng Chia University. The experimental results illustrated that the most responses of tested equipment have been reduced during earthquake.
Finite Element Formulations for Direction Optimized-Variable Curvature Friction Pendulum System
Authors: Tsai C. S. , Chiang T. C. , Chen Wen-Shin
Published: August 2009

The base isolation technology has been recognized as a very effective tool for controlling the seismic response of a structure during earthquakes. However, it is suggested from recent studies that the earthquakes with long predominant periods results in significant seismic responses of the base isolated structure. In view of this, a new base isolator called the Directional Optimized-Variable Curvature Friction Pendulum System (DO-VCFPS) has been proposed in this study. The radii of the curvature of the trench concave surface and the spherical sliding surface are lengthened with increasing the sliding displacement. Therefore, the isolation period can be shifted further away from the predominant periods of ground motions. Furthermore, by using the series connection of a trench concave surface and a spherical sliding surface, the isolation period is a function of the angle between the directions of the resultant displacement. In order to prove the efficiency of the proposed device, the finite element formulations of the DOVCFPS have been derived in this study. The numerical results show that the combination of the advantages of the Variable Curvature Friction Pendulum System (VCFPS) and the Directional Optimization Friction Pendulum System (DO-FPS) can improve the disadvantages of a base isolated structure with fixed isolation period.
On the Expected Errors in Calibration of the Beremin Cleavage Model Parameters
Authors: Beardsmore D. W. , Teng H. , Martin Michael
Published: August 2009

We present the detailed results of a series of Monte Carlo simulations of the Gao and Dodds calibration procedure that was carried out to determine the likely size in the errors in the Beremin cleavage model parameter estimates that might be expected for fracture toughness data sets of various sizes. The calibration process was carried out a large number of times using different sample sizes, and mean values and standard errors in the parameter estimates were determined. Modified boundary layer finite element models were used to represent high and low constraint conditions (as in the fracture tests) as well as the SSY condition. The “experimental” Jc values were obtained numerically by random sampling of a Beremin distribution function with known values of the true parameters. A number of cautionary remarks in the application of the calibration method are made.
Microscale Numerical Simulation on Dynamic Damage for the Deflagrated Pressure Vessels
Authors: Ye Jianjun , Yang Jian , Zheng Jinyang , Sheng Jie , Ou Guofu
Published: August 2009

The defects on the surface of the deflagrated pressure vessels leading to damage are usually in the form of pits, scratches or machine marks. A microscale numerical simulation method is presented for the dynamic damage process under the instantaneous impacted shock. The surface defects are described as the rectangle gap, the round gap and the groove. For fcc and other close-packed metals material, the embedded atom method (EAM), which has proven particularly good at modeling bulk and defect properties of metals and metal alloys, is used to describe the interactions among the metal atoms. The Molecular Dynamics (MD) code named LAMMPS is used to calculate the velocity of atoms and the pressure distribution in dynamic damage process. The results show the different damage effects of the metal material with different surface defects under the instantaneous impacted shock by the deflagration.
Proposals of Improvements of RCC-MR Creep-Fatigue Rules
Authors: Berton Marie-Noe¨l , Ancelet Olivier , Cabrillat Marie The´re`se , Chapuliot Ste´phane
Published: August 2009

The RCC-MR creep-fatigue rules were developed and written in the framework of studies for the first SFR (Sodium Fast Reactors). These reactors were characterized by low primary loads and moderately high temperatures. The rule thus has to be improved with the aim of decreasing its conservatisms in case of higher temperatures and/or higher pressures (for GEN IV Gas Cooled Reactors). Studies were realized to improve the rule on the following points: - the position of the temperature dwell time in the cycle : the current rule always considers that the dwell time is located at one of the extremes of the cycle, what can be very conservative in some cases, - the symmetrisation effect of the stabilized cycle, - the case where the primary loads vary during the cycle, - the primary and secondary stresses combination during the temperature dwell time for the evaluation of the stress relaxation. These works are based on viscoelastoplastic calculations of stabilized cycles and the new proposals are applied on different tests. The consequences on creep-fatigue damage evaluation can be very significant.
Remote Measurement of the Pipe Thickness Reduction by Microwaves
Authors: Ju Yang
Published: August 2009

A method which can inspect a pipe in a large scale and measure the thickness reduction remotely was demonstrated. A copper pipe having 17 mm inner diameter, 1 mm wall thickness, and 900 mm length was measured. The thickness reduction having the value from 10% to 80% of the wall thickness was detected significantly. By building up a resonance for the microwave signal propagated in the pipe, it is possible to determine the thickness reduction using the measured resonance frequency.
Evaluation of Strength Characteristics Considering Microscopic Heterogeneity of Structural Steels and Weld Zone by Using FEM-MD Coupling Method
Authors: Mochizuki Masahito , Higuchi Ryota , Katsuyama Jinya , Toyoda Masao
Published: August 2009

The strength properties of structural steels or their weld zone are influenced by the microscopic heterogeneity. It is important to investigate the stress distribution for clarification of the mechanism of fracture and the material design by considering a grain boundary or its neighborhood because either can be a zone where the stress concentration is likely to occur due to a mismatch of the displacement. For this purpose, FEM-MD coupling method is one of the useful methods because it can treat the mismatch of the displacement caused by the microscopic heterogeneity. In this study, FEM-MD coupling method is proposed and the influence of the microscopic heterogeneity of steels is investigated by using FEM-MD coupling method.
Investigation of a Shell and Tube Exchanger in Liquefied Natural Gas Vaporization Service
Authors: Porter M. A. , Miller D. D. , Martens D. H. , McGuffie S. M.
Published: August 2009

Liquefied natural gas (LNG) is commonly converted from liquid to vapor for gas distribution. One of the methods for vaporizing LNG is to use a shell and tube heat exchanger. Water is used on the shell side to provide the heat source and LNG is then vaporized through the tube side passages of the exchanger. In many of these applications, the LNG is at a high pressure on the tube side while the water is at a lower pressure than the LNG as it flows through the shell side. The industry consensus document API 521 [1] “Guide to Pressure Relieving and Depressuring Systems,” Fourth Edition, paragraph 3.18 “Heat Transfer Equipment Failure” states that a complete tube rupture is to be considered for the possible overpressure of the equipment. The typical shell and tube exchanger application described above has rupture discs on the shell body to protect the shell from being over-pressured due to a tube rupture scenario. The possible freezing of the water in the shell due to mixing with cryogenic LNG is a concern. The issue to consider is whether freezing will occur before the rupture discs can safely relieve a possible over-pressure condition of the shell. A numerical analysis of the condition was performed using Computational Fluid Dynamics (CFD) software. The exchanger service, the analysis procedure and the conclusions found are detailed in this paper.
3-D Non-Linear Finite Element Analysis of a Non-Gasketed Flange Joint Under Combined Internal Pressure and Axial Loading
Authors: Abid Muhammad , Awan Abdul W.
Published: August 2009

A number of analytical and experimental studies have been conducted to study ‘strength’ and ‘sealing capability’ of bolted flange joint only under internal pressure loading. Due to the ignorance of the external i.e. axial loading, the optimized performance of the bolted flange joint can not be achieved. A very limited work is found in literature under combined internal pressure and axial loading. In addition, the present design codes do not address the effects of axial loading on the structural integrity and sealing ability of the flange joints. From previous studies, non-gasketed joint is claimed to have better performance as compared to conventional gasketed joint. To investigate non-gasketed joint’s performance i.e. joint strength and sealing capability under combined internal pressure and any applied external loading, an extensive 3D nonlinear finite element analysis is carried out and overall joint performance and behavior is discussed.
A Rational Approach to Evaluate a Steam Turbine Rotor Grabbing and Locking Event
Authors: Neto Miguel Mattar , Lueska Carlos
Published: August 2009

In the paper, an unique event of a steam turbine rotor grabbing and locking will be described and evaluated. The turbine power is 21,740 kW and it is used in a pulp and paper production plant. The turbine is a high speed machine, 8,300 rpm, reaction multi-stage type, coupled by a reduction gear to a 4-pole electric generator, with 1,800 rpm. The steam turbine rotor grabbing and locking event evaluation is based on a proposed rational approach, i. e., based on the connection of the failure mechanisms observed and the identification of possible causes of these mechanisms. It is important to notice that the failure mechanisms and their causes are not the same. The failure mechanisms are the damages observed such as wear, fracture, severe deformation, etc. that impair or limit the safe and economical operation of a mechanical component. The causes, on the other hand, are the operational characteristics, the aging factors, the loads, etc. that introduce conditions to the failure mechanisms development. Using the proposed rational approach, the failure mechanisms causes that induce this unique event of steam turbine grabbing and locking are identified. Also, corrective and improvement actions based on the proposed rational approach are addressed to evaluate similar events and to avoid such a type of event in similar components.
Experimental Evaluation of J Resistance Curves for Ductile Steels Using SE(T) Fracture Specimens
Authors: Cravero Sebastian , Ruggieri Claudio , Piovatto Roberto , Bose Waldek W. , Spinelli Dirceu
Published: August 2009

This work presents an investigation of the ductile tearing properties for an API 5L X60 pipeline steel using experimentally measured crack growth resistance curves (J-R curves). Use of these materials are motivated by the increasing demand in the number of applications for manufacturing high strength pipes for the Brazilian oil and gas industry including marine applications and steel catenary risers. Testing of the pipeline steels employed side-grooved SE(T) specimen with varying crack size to determine the J-R curves based upon the unloading compliance method using a single specimen technique. Recent developed compliance functions and eta-factors applicable for SE(T) fracture specimens are introduced to determine crack growth resistance data from laboratory measurements of load-displacement records. This experimental characterization provides additional toughness data which serve to evaluate crack growth resistance properties of pipeline steels using SE(T) specimens with varying geometries.