bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification of System Parameters of Slab Vibrated With Vibrator by Using Wavelet Transform
Authors: Imanishi Naoto , Sone Akira , Masuda Arata
Published: August 2008

In health monitoring of slabs of a road bridge, it is suitable to carry out on the basis of their stiffness, which is evaluated by spring constants of a spring-mass system model of the slab. When the value of the spring constant is known, the rigidity of the slab and the deflection against the predetermined load can be estimated. These can be used as the basic data of maintenance management of them. The authors have been proposing the method to identify the spring constant of the slab by wavelet transform of an excitation force and acceleration responses. In this paper, the method to identify the spring constants of slabs is theoretically investigated under the noisy conditions. The method to find the specific values of constant α in an analyzing wavelet by which the most reliable value of the spring constant is given according to the graphic form showing the relation between identified mass and constant α.
Comparison of Strong and Partioned Fluid Structure Code Coupling Methods
Authors: Longatte E. , Verreman V. , Bendjeddou Z. , Souli M.
Published: August 2008

As far as flow-induced vibrations are concerned, fluid structure interactions and fluid elastic effects are involved. They may be characterized by parameters like added mass, added damping and added stiffness describing fluid and flow effects on structure motion. From a numerical point of view, identifying these parameters requires numerical simulation of coupled fluid and structure problems. To perform such a multi-physics computation, several numerical methods can be considered involving either a partitioned or a monolithic fluid structure code coupling procedure. Monolithic process is a fully implicit method ensuring the energy conservation of the coupled system. However its implementation may be difficult when specific methods are required for both fluid and structure solvers. The partitioned procedure does not feature the same disadvantage because fluid and structure computations are staggered in time. However a specific attention must be paid to the energy conservation of the full coupled system and one must choose code coupling schemes in order to avoid or to reduce as much as possible numerical dissipation polluting the results. In the present paper, several techniques for fluid structure code coupling are compared. Several configurations are considered and numerical results are discussed in terms of added mass and damping for structures vibrating in fluid at rest. These results contribute to the validation of a full fluid structure code coupling procedure with many possible applications in the fields of fluid structure interactions and flow-induced vibrations.
The Characterization of Guided Waves on Hollow Cylinder From Non-Axisymmetric End Loading
Authors: Li Longtao , He Cunfu , Wu Bin , Li Ying , Wang Xiuyan
Published: August 2008

Ultrasonic guided waves are used for the rapid testing of a steel pipe (O.D 70 mm, I.D 63 mm, 2544 mm long). The non-axisymmetric transducer ring (arc) is put on one end of the pipe to excite and receive the guided wave in the pipe. An artificial hole of 1 mm diameter can not be found by conventional axisymmetric end loading transducer. However, the non-axisymmetric transducer ring (arc), compared with the axisymmetric transducer ring, is very sensitive to the artificial hole when The middle point (MP) of the transducer arcs coincided with the center of the artificial hole on the cross section of the pipe. The results show that the non-axisymmetric end loading technology can locate the crack or defect on the pipe not only in the axial direction but also in the circumferential direction.
An Investigation of an Impact Vibration Absorber With Hysteresis Damping
Authors: Aoki Shigeru , Watanabe Takeshi
Published: August 2008

The dynamic vibration absorber is a device for reducing the vibration of many structures and mechanical equipment. It consists of a small mass which is attached to the primary vibrating system or main mass. The impact damper is one of such dynamic vibration absorbers in which motion of auxiliary mass is limited by motion-limiting stop or placed inside a container. In this paper, in order to consider energy loss for an impact represented by the coefficient of restitution and duration of collision, an analytical model with hystresis damping is introduced. Using this model, dynamic response of the system under harmonic and that under random excitations are analyzed. Some numerical results are shown.
Probabilistic Fracture Mechanics Assessment of Wall-Thinned Nuclear Piping System
Authors: Lee Sang-Min , Chang Yoon-Suk , Kim Young-Jin
Published: August 2008

The integrity of nuclear piping systems must be maintained during operation. In order to maintain the integrity, reliable assessment procedures including fracture mechanics analysis, etc, are required. Up to now, the integrity assessment has been performed using conventional deterministic approaches even though there are many uncertainties to hinder a rational evaluation. In this respect, probabilistic approach is considered as an appropriate method for piping system evaluation. The objectives of this paper are to develop a probabilistic assessment program using reliability index and simulation technique and to estimate the failure probability of wall-thinned pipes in secondary systems. The probabilistic assessment program consists of three evaluation modules that are: first order reliability method, second order reliability method and crude Monte Carlo simulation method. The developed program has been applied to evaluate failure probabilities of wall-thinned piping system subjected to internal pressure, global bending moment and combined loading. The evaluation results showed a promising applicability of the probabilistic integrity assessment program.
Development and Application of a Plugging Margin Evaluation Method Taking Into Account the Fouling of Shell-and-Tube Heat Exchangers
Authors: Hwang Kyeong Mo , Jin Tae Eun
Published: August 2008

As the operating time of heat exchangers progresses, fouling caused by water-borne deposits and the number of plugged tubes increase and thermal performance decreases. Both fouling and tube plugging are known to interfere with normal flow characteristics and to reduce thermal efficiencies of heat exchangers. The heat exchangers of Korean nuclear power plants have been analyzed in terms of heat transfer rate and overall heat transfer coefficient as a means of heat exchanger management. Except for fouling resulting from the operation of heat exchangers, all the tubes of heat exchangers have been replaced when the number of plugged tubes exceeded the plugging criteria based on design performance sheet. This paper describes a plugging margin evaluation method taking into account the fouling of shell-and-tube heat exchangers. The method can evaluate thermal performance, estimate future fouling variation, and consider current fouling level in the calculation of plugging margin. To identify the effectiveness of the developed method, fouling and plugging margin evaluations were performed at a component cooling heat exchanger in a Korean nuclear power plant.
Evaluation of Loads on a Hypercompressor Plunger in Service Conditions
Authors: Giacomelli Enzo , Campo Nicola , Pratesi Simone , Zonfrillo Giovanni , Meneghin Andrea
Published: August 2008

The plunger is a very critical component for the operation of hyper-compressors. To achieve long packing ring life it is necessary to select very hard materials for the plunger. As a consequence of the special materials used, the plunger is very brittle. To guarantee safe operation it is necessary to have perfect alignment to avoid bending stress that could cause plunger failure. The effects of the whole system, including packing rings and supporting crossheads were analyzed using a multi-body dynamic simulation to determine the maximum loads acting on the plunger. This analysis verified the viability of this critical component during abnormal machine operating conditions.
A Mathematical Model of the Auto-Repair Welding System for the Large-Scale Pressure Vessel’s Hemispherical Head
Authors: Peng Tiegen , Wang Yinhua , Wu Tihua , Yu Zhonghai
Published: August 2008

A mathematical model of the auto-repair welding system for the pressure vessel’s hemispherical head is proposed according to the principles of the robotics. The welding system can be simplified to a four-axis linkage system and two types of models can be obtained. Using these mathematical models, we analyze the position of the welding torch and derive the velocity formulas of the four axes in the system. All these formulas can be used in the development of the auto-repair welding system. The welding of the transition section which is mainly discussed in this paper is complex in the whole repair process, and a geometry model is proposed for it. The auto-repair welding experiments have been given to illustrate the validity of this model.
Dynamic Relaxation and New Periodic Symmetry Techniques for Simulating Atomistic Dislocation Models Subjected to Two-Dimensional External Forces
Authors: Pan Li , Metzger Don , Niewczas Marek
Published: August 2008

The movement and interactions of dislocations, under the potential energy and the external driving forces, affect the performance of materials in various applications. The Dynamic Relaxation (DR) technique, the Embedded Atom method (EAM) potential function and a newly developed periodic symmetry method are combined and expanded for simulations of the relaxation of atomistic models with dislocation defects subjected to two-dimensional external forces. This paper focuses on solving two challenges in the simulation: (i) it evaluates correct internal forces and corresponding external forces with more complicated periodic boundary in the model and (ii) finds a proper way to revise the displacement field of atoms in the boundary layers to satisfy the requirements of the periodic symmetry in the direction other than the direction of dislocation line. The numerical parameters, such as the choice of damping ratios and the variation of forces in different directions, are studied. The example given, illustrated by behaviour of stress and/or displacement components, deals with and compares the relaxation of a dislocation model under biaxial external forces.
Synthesis of Al-SiCp and Al-Diamond Composites Through Dynamic Compaction Using Underwater Shock Wave
Authors: Tanaka Shigeru , Lee L. S. , Hokamoto Kazuyuki
Published: August 2008

Al-based composites are tried to be fabricated using dynamic compaction of powders compressed through underwater shock wave. Some composites, Al-SiCp, Al-diamond, are successfully recovered and fully densified without cracks, and the composites showed high hardness and other superior properties.
Development and Application of Risk-Based Inspection for Refinery Unit
Authors: Choi Song-Chun , Han Sang-In , Jung Hee J. , Kim Ji-Yoon , Song Sung-Jin
Published: August 2008

Recently, regulatory bodies quite often encourage to adopt risk-based inspection (RBI) and management programs because they can enhance safety simultaneously with deregulation in Korea. RBI is an integrated methodology that factors risk into inspection and maintenance decision making. This paper describes an example of how to use known risk assessment codes (API 580, API 581 BRD) to address such safety analysis requirements for risk management in the refining industry. Specifically, this paper reports the methodology and the results of application to the refinery units using the KGS-RBI™ program, developed by the Korea Gas Safety Corporation in reference of API Codes and ASME PC (Post Construction) with a suitable consideration of Korean situation. The results of the risk and reliability assessment using KGS-RBI™ program are useful in determining whether the detected defects are tolerable or required to be repaired. The subsequent decisions are to manage the future inspection, repair and maintenance planning in the risk reduction control.
Improvement of Static Fatigue Strength of Silicon Nitride Composite
Authors: Takahashi Koji , Ando Kotoji , Saito Shinji
Published: August 2008

Si3N4/SiC composite ceramics were hot-pressed in order to investigate their crack-healing behavior under cyclic stress and the resultant static fatigue strength. Semi-elliptical surface cracks of 100 μm in surface length were made on each specimen. The pre-cracked specimens were crack-healed under a cyclic bending stress of 210MPa in air at 900, 1000, 1100, and 1200 °C. The bending strength and static fatigue strength of the crack-healed specimens were systematically investigated at each healing temperature. The specimens which has been crack-healed and static fatigue-tested at 900 and 1000°C showed lower static fatigue strength than those tested at 1100 and 1200 °C. Detailed investigation on the fracture surface of static fatigue-tested specimens showed that oxidation of the base material had strong effects on the static fatigue strength. It was found that if the specimens were pre-oxidized in air at 1300 °C, the surface was covered by a protective oxide layer, leading to a significant improvement of static fatigue strength at 900 and 1000 °C.
The Assessment of Residual Stress Effects on Ductile Tearing Using Continuum Damage Mechanics
Authors: Sherry Andrew H. , Wilkes Mark A. , Sharples John K. , Budden Peter J.
Published: August 2008

This paper presents the results of a numerical study undertaken to assess the influence of residual stresses on the ductile tearing behaviour of a high strength, low toughness aluminium alloy. The Gurson-Tvergaard model [1, 2] was calibrated against conventional fracture toughness data using parameters relating to void nucleation, growth and coalescence. The calibrated model was used to predict the load versus ductile tearing behaviour of a series of full-scale and quarter-scale wide-plate tests. These centre-cracked tension tests included specimens that contained a self-balancing residual stress field that was tensile in the region of the through-wall crack. Analyses of the full-scale wide-plate tests indicated that the model provides a good prediction of the load versus ductile tearing behaviour up to approximately 3 mm of stable tearing. The influence of residual stress on the load versus crack growth behaviour was accurately simulated. Predictions of the load versus crack growth behaviour of full-scale wide-plate tests for crack extensions greater than 3 mm, and of the quarter-scale tests, were low in terms of predicted load at a given amount of tearing. This was considered to result from: (i) the ‘valid’ calibration range in terms of specimen thickness and crack extension, (ii) the development of shear lips and (iii) differences in the micro-mechanism of ductile void formation under plane strain and under plane stress conditions.
Explosive Welding of Metal Sheets
Authors: Matsui Yamato , Otsuka Masahiko , Itoh Shigeru
Published: August 2008

In this work explosive line and spot welding were used for the bonding of light-weight metal sheets. Materials involved are aluminum alloys 5052-O, 6061-T6, and 7075-T6, a magnesium alloy AZ31B-O and a commercially pure titanium (TP270C). Plates of similar and dissimilar metal combinations are explosion welded over a small overlapping area. The strength of the welds was measured using shear strength tests and the metal interface was analyzed using optical microscopy. The shear strength of the welds have been tested and appeared to high shearing strength. Explosive line and spot welding show a high strength to explosive mass ratio, making it a good candidate to be scaled up and used in commercial applications.
Experimental Study on Vertical Component Seismic Isolation System With Coned Disk Spring
Authors: Kitamura S. , Okamura S. , Takahashi K.
Published: August 2008

In Japan, several kinds of three-dimensional seismic isolation system for next-generation nuclear power plant such as fast reactors have been studied in recent years. We proposed a structural concept of a vertical component isolation system, assuming a building adopting a horizontal base isolation system. In this concept, a reactor vessel and major primary components are suspended from a large common deck supported by isolation devices consisting of large coned disk springs. In order to verify the isolation performance of the vertical component isolation system, 1/8 series of shaking table tests using a scale model were conducted. The test model was composed of 4 vertical isolation devices, common deck and horizontal load suspension system. For the design earthquake, the system smoothly operated, and sufficient isolation characteristics were shown. The simulation analysis results matched well the test results, so the validity of the design technique was able to be verified. As the result, the prospect that the vertical isolation system applied to the FBR plant could technically realize was obtained.
Development of Stress Intensity Factor Coefficients Database for a Surface Crack of an RPV Considering the Stress Discontinuity Between Cladding and Base Metal
Authors: Onizawa Kunio , Shibata Katsuyuki , Suzuki Masahide
Published: August 2008

Under a transient loading like pressurized thermal shock (PTS), the stress discontinuity near the interface between cladding and base metal of a reactor pressure vessel (RPV) is caused by the difference in their thermal expansion coefficients. So the stress intensity factor (SIF) of a surface crack close to the interface should be calculated taking account of the stress discontinuity. Many SIF calculations have to be performed many times in Monte Carlo simulation of the probabilistic fracture mechanics (PFM) analysis. To avoid the time consuming process from the SIF calculation in the PFM analysis, the influence coefficients were developed to calculate the SIF easily and accurately corresponding to the stress distributions in the cladding and base metal. Stress distributions in cladding and base metal are modeled to linear and third-order polynomial expressions, respectively. The non-dimensional SIF coefficients were obtained from FEM analyses. The SIF value at the surface was determined by linear extrapolation of SIF value near the surface. Using the SIF coefficients, the SIF values at the crack tips at both surface and deepest points of a surface crack are evaluated accurately and in a reasonable time.
Kevlar and Carbon Composite Body Armor: Analysis and Testing
Authors: Berg Vanessa S. , Preece Dale S. , Stofleth Jerome H. , Risenmay Mathew A.
Published: August 2008

Kevlar materials make excellent body armor due to their fabric-like flexibility and ultra-high tensile strength. Carbon composites are made up from many layers of carbon AS-4 material impregnated with epoxy. Fiber orientation is bidirectional, orientated at 0° and 90°. They also have ultra-high tensile strength but can be made into relatively hard armor pieces. Once many layers are cut and assembled they can be ergonomicically shaped in a mold during the heated curing process. Kevlar and carbon composites can be used together to produce light and effective body armor. This paper will focus on computer analysis and laboratory testing of a Kevlar/carbon composite cross-section proposed for body armor development. The carbon composite is inserted between layers of Kevlar. The computer analysis was performed with a Lagrangian transversely isotropic material model for both the Kevlar and Carbon Composite. The computer code employed is AUTODYN. Both the computer analysis and laboratory testing utilized different fragments sizes of hardened steel impacting on the armor cross-section. The steel fragments are right-circular cylinders. Laboratory testing was undertaken by firing various sizes of hardened steel fragments at square test coupons of Kevlar layers and heat cured carbon composites. The V50 velocity for the various fragment sizes was determined from the testing. This V50 data can be used to compare the body armor design with other previously designed armor systems. AUTODYN [1] computer simulations of the fragment impacts were compared to the experimental results and used to evaluate and guide the overall design process. This paper will include the detailed transversely isotropic computer simulations of the Kevlar/carbon composite cross-section as well as the experimental results and a comparison between the two. Conclusions will be drawn about the design process and the validity of current computer modeling methods for Kevlar and carbon composites.
On Evaluation of Lamb’s Integrals for Seismic Waves in a Three-Dimension Elastic Half-Space
Authors: Liao Wen-I , Teng Tsung-Jen
Published: August 2008

The analytical method such as the boundary integral (element) method or the series expansion method is usually used to solve the wave scattering problem. In these methods, the singular Green’s function should be determined firstly; the main difficulty of the use of the Lamb’s singular solutions in integral form to represent the diffracted fields is the numerical implementation for the evaluation of those improper integrals. The integrands of these integrals are highly irregular and oscillatory. In this paper, a technique is proposed to calculate the integral in wave-number domain based on the method of steepest descent. After replacing the original integration path by steepest decent path, the wave-number integral results in a Gauss-Hermite type quadrature, so the oscillating characteristics of the original integrand can be removed and results a non-oscillating integrand, it is very helpful in computing efficiency.
Fatigue Strength of Socket Welds Repaired by Structural Weld Overlay: Reference ASME Section XI Code Case N-666
Authors: McCracken Steve
Published: August 2008

ASME Code Case N-666 provides alternative rules for repair of a cracked and leaking small bore socket weld by installation of a structural weld overlay [1]. The crack is not removed but is encapsulated and sealed under the weld overlay. Vibration fatigue testing reported by the Electric Power Research Institute (EPRI) demonstrates that socket welds repaired by the method specified in ASME Code Case N-666 have equivalent or better fatigue strength compared to standard socket welds. This paper investigates fatigue test data and fracture mechanics analyses for standard socket welds and compares this to the vibration fatigue strength exhibited by overlay repaired socket welds. A relationship based on fatigue testing of a standard socket weld with root defects was proposed by Japanese researchers to correlate the reduction in fatigue strength with increasing root defect size. This relationship is compared to an EPRI finite element model that was developed to evaluate the stress intensity factor at the root of a standard socket weld. A correction factor is proposed for estimation of the stress intensity factor at the crack tip of a socket weld repaired by weld overlay. The correction factor is derived from a three-dimensional solution for straight pipe with an inside surface circumferential crack and from the finite element model for standard sized socket welds. Finally, weld residual stress analyses reported by Japanese researchers for standard socket welds are compared to weld residual stress data from recent thermal-mechanical finite element analyses for overlay repaired socket welds. The threshold for fatigue crack propagation and the influence of weld residual stress is presented to explain the high vibration fatigue strength exhibited by socket welds repaired by the method of Code Case N-666.
Spectral Response to Harmonic Excitation of Rods in a Confined Nuclear Fuel Mini-Bundle
Authors: Pomiˆrleanu Radu O.
Published: August 2008

In this paper, the effect of the confinement on the vibration of rods within nuclear fuel bundle is analyzed and discussed. Differential added damping of the rods depending on their position within the bundle adds to the classical development of modal and spectral analysis. This is accomplished by coupling the classical modeling of the variable-mass, Euler-Bernoulli beam on elastic supports with the two-dimensional computational fluid dynamics (CFD) estimation of motion-dependent effects, with the viscous effects integrally modeled. A 5×5 reduced-scale (shortened) rod bundle subject to room-temperature single-phase nominally axial flow within a square confinement is used to illustrate the response to a harmonically varying excitation. The harmonic analysis showed that there are significant differences in the response of the rods, depending on their position within the bundle.
Stresses in a Cylinder Subjected to an Internal Shock
Authors: Leishear Robert A.
Published: August 2008

Hoop stresses due to a moving shock front in a gas filled, thick walled cylinder can be approximated, using vibration theory. The equation of motion can be combined with hoop stress equations to describe the dynamic changes in hoop stress to provide insight into the phenomenon of flexural resonance, which depends on a critical velocity of the shock in the cylinder. At shock velocities below critical, the maximum hoop stress equals one times the static stress, which would be obtained in the pipe wall if the stress was slowly applied. Above the critical velocity, the maximum hoop stress is less than twice the static hoop stress. Near the critical velocity, the hoop stress approximately triples the static stress, as shown in existing experimental data in the literature. The inclusion of structural and fluid damping in the vibration equations describes the stresses, which were experimentally observed. In short, a comprehensive vibration equation is presented in this paper and is compared to available experimental work.
Vibration Characteristics of High Natural Frequency Mechanical Structures
Authors: Minagawa Keisuke , Fujita Satoshi , Endo Rokuro
Published: August 2008

Recently, it has been reported that a rupture of the piping in an earthquake is produced not by a momentary large load but by cumulative fatigue damage. Then it is expected that the rupture of equipment and piping that have high natural frequency is also caused by cumulative fatigue damage. Therefore it is very important to grasp this effect accurately. In this study, vibration characteristics at high frequency band are investigated. At first numerical analyses are carried out. In the analysis, elasto-plastic model that gives the system elasto-plastic behavior by differential equation is adopted. Then fundamental experiments by using simple single-degree-of-freedom model are carried out to investigate property of experiment model and vibration characteristic. The experiments consist of static experiments, free vibration experiments, and forced vibration experiments.
Residual Stress Measurements in Martensitic Stainless Steel
Authors: Bandyopadhyay Subhra , Budugur Suresh Silpa
Published: August 2008

Residual stresses may be generated in target structural material used in accelerator-driven transmutation. Calibration curves were developed for transmutation target structural materials using positron annihilation spectroscopic (PAS) method. These calibration curves consisted of different line shape parameters (S, T & W) determined by the PAS method on martensitic stainless steel as a function of tensile stress/strain imparted to cylindrical specimens. This paper presents a comparative analysis of residual stresses in these specimens as a function of (S, T & W) determined by the PAS technique. The resultant data showed a consistent pattern in these parameters versus applied stresses ranging between the Yield and the Ultimate tensile strength.
Comparison of FEA Results and TEMA Code in Tubular Heat Exchanger Design
Authors: Jin Weiya , Gao Zengliang , Sun Weiming , Zhang Kangda
Published: August 2008

Finite element method is applied to calculate the stress distribution and the maximum stress location of the tubesheets, tubes and other parts of a tubular heat exchanger in a petrochemical plant. Comparison between FE results and TEMA results is discussed. The temperature and stress distribution of tubesheets and other important parts can be accurately calculated by FE method, also the safety margin of the parts in the heat exchanger can be clearly given by FE method. For multi-pass heat exchanger, FE method is more useful. By analyzing FE results, it is easily to know whether the stresses in exchangers are over the allowable value. Therefore, FE method is a good measure to aid heat exchanger design when standard of TEMA is used.
Developments in Cyclic Analysis and High Temperature Design
Authors: Carter Peter , Marriott Douglas L.
Published: August 2008

Design for cyclic loading is emerging as a key question for next generation power systems. Recent developments in techniques for cyclic stress analysis have significant implications for high temperature design. In the same way that limit load analysis is now being used to overcome the difficulties and guesswork of stress classification for steady primary loads, so shakedown and ratcheting analysis can eliminate the more difficult problems of stress classification for cyclic loads. The paper shows how reference stresses defined for shakedown and ratcheting provide rapid and conservative information for design against rupture and creep damage, deformation and strain accumulation, and ratcheting. These techniques will provide additional insights to designers and are likely to augment rather than replace, existing options. These ideas have existed in the research literature for some time, but have now become more accessible by the general industry with a new analysis technique in a commercial finite element code. Examples are given which demonstrate the methodology for nozzles having non-thermal secondary stresses, and prediction of long-term distortion in thermal shock problems.
Effect of Non-Parallel Underhead Contact of a Tightened Fastener on Clamp Load and Optically Measured Deformation Field
Authors: Nassar S. A. , Zuo Y. P.
Published: August 2008

This experimental investigation examines the effect of non-parallel contact of tightened fasteners on the resulting clamp load and on the optically measured deformation field using Electronic Speckle Pattern Interferometry (ESPI). A simple model of a single-bolt joint is used. In the model, tapered plates with two different wedge angles are used in order to simulate non-parallel contact under the fastener head. For the same level of tightening torque, the resulting clamp load, deformation field, and strain field are measured for two levels of wedge angle, and compared with those of a perfectly parallel contact. The tapered plates that were used in this study provide 5° and 10° wedge angles. The possibility of using optics to control the tightening process of threaded fastener, by monitoring the deformation and strain fields in real-time during fastener tightening, promises to significantly enhance the reliability of bolted assemblies. This is due to that the optical control would bypass the friction uncertainties that frequently make the torque control methods unreliable for critical assemblies. As a first step towards this long-term goal of developing and implementing an optical control method, this study investigates the deformation field that results from a known tightening torque for various scenarios of non-parallel contact under the fastener head. The deformation and strain fields are optically measured using an optical sensor that uses Electronic Speckle Pattern Interferometry (ESPI), and provides a 3D displacement field with high precision. A Special software is used in order to convert the deformation to a strain field. The sensor is mounted on the joint surface in order to eliminate the effect of rigid body motion. Measured clamp loads, deformation, and strain fields are investigated for 5° and 10° wedge angles and are compared with the results of perfectly parallel contact under the fastener head.
Bed Shear Stress of a Flowing Meandering Fluid-Structure Interaction
Authors: Yilmaz L.
Published: August 2008

An analytical model is developed for free-surface flow over an erodible bed and is used to investigate the stability of the fluid-bed interface and the characteristics of the bed features by measuring the shear stress distribution with hot-film sensors. The model is based on the potential flow over a two-dimensional, moving, wavy bed with a sinusoidal profile of varying amplitude, and a sediment transport relation in which the transported rate is proportional to the power of the fluid velocity at the level of the meandering bed. Consideration is given to the factors involved in determining the shear stress distribution at the flow boundary layer. The experimental results are presented in two parts. Experimental observations of meander evolution described qualitatively. The most important parameter is the shear stress distribution, because of the inhomogeneous distribution of boundary layer meander features. At the wavy boundary layer, the shear stress distribution, measured with WTG-50 hot-film-anemometer is given graphically and theoretically.
Post-Buckling Analyses of Elastic Circular Cylindrical Shells Under Axial Compression
Authors: Kobayashi Takaya , Ogasawara Tomotaka
Published: August 2008

In the design of a modern lightweight structure, it is of technical importance to assure its safety against the buckling under the applied loading conditions. For this issue, the determination of the critical load in an ideal condition is not sufficient, but it is further required to clarify the post-buckling behavior, that is, the behavior of the structure after passing through the critical load. One of the reasons is to estimate the effect of practically unavoidable imperfections on the critical load and the second is to evaluate the ultimate strength to exploit the load-carrying capacity of the structure. For the buckling problem of circular cylindrical shells under axial compression, a number of experimental and theoretical studies have been made by many researchers. In the case of the very thin shell that exhibits elastic buckling, experimental results show that after the primary buckling, secondary buckling takes place accompanying successive reductions in the number of the circumferential waves in each mode change on one-by-one step. In this paper we traced this successive buckling of circular cylindrical shells using some of the general purpose implicit FEM codes currently available. For geometrically nonlinear static problems including buckling and post-buckling, we carried out our studies with two approaches; one is to use the arc length method (the modified Riks method), and the other is stabilizing with the aid of (artificial) damping especially for the local instability. Our analysis procedure consists of the following 2 steps. Before reaching the point exhibiting the comparatively stable state after the primary buckling, the arc length method is applied. After that point, the artificial damping is applied. The results simulate unstable successive buckling and show good agreement with experiments.
Modelling the TMF-Life of a Salt Bath Experiment With Viscoplastic Constitutive Equations
Authors: Mohrmann Ralf , Seifert Thomas , Ho¨ll Harald
Published: August 2008

The salt bath experiment was chosen because of the load characteristics. It is simple enough to allow treatment at moderate cost while containing a geometrical concentration of stress subject to cyclic loading under displacement control (equivalent to thermal control) and leading to a typical situation of creep and localized plasticity with realistic levels of stress and temperature. The specimen (see 1) employed is known as a ‘Type 2 Salt-Bath Specimen’. It is an ax symmetric hollow piece of Type 316 stainless steel as shown in the illustration. The righthand side, in particular the region around the 5 mm radius curve, represents a typical geometrical feature of a tube-tubeplate junction. The left hand-side is a removable plug, allowing periodic inspection of the interior surface, and it is not of structural significance. Specimens are subjected to a purely thermal loading cycle. The cycle is attained by automatically moving specimens back and forth between two baths of a molten salt, at 250 and 600 °C. The total cycle time of the cycle is 16 hours. Viscoplastic constitutive equations with two back-stress variables were used to model the non-isothermal elastic-plastic material behavior. The model parameters were adjusted to tensile, creep and cyclic data for temperatures between 200 and 600 °C. The behavior of the salt bath specimen was calculated with the finite-element program ABAQUS using the UMAT-interface. Two initial states were considered: new material and fully hardened material. For the state ‘new material’ 100 cycles were calculated in order to investigate the local cyclic hardening of the specimen. For the prediction of the lifetime under thermo-mechanical fatigue conditions a damage parameter for TMF-conditions (DTMF) was used. This parameter was calibrated to lifetime data of a similar austenitic material. The location of crack initiation and the number of cycles until crack initiation corresponds reasonably well to the experimental findings.
Fluid Models in LS-DYNA and Their Interaction With a Structure in Dynamic Simulations
Authors: Vesenjak Matej , Matthaei Stephan , Mu¨llerscho¨n Heiner , Ren Zoran
Published: August 2008

The paper outlines different approaches to fluid-structure interaction modelling in LS-DYNA. Different formulations (Lagrange, Euler, ALE and SPH) are evaluated and compared with experimental observations of a fluid sloshing problem in a simple container box. Computational simulations have shown that the motion of the fluid can be best described also with the ALE and SPH methods in LS-DYNA. Additionally, such methods are very economical and suitable for analyses of large and more complex models.
Deformation Mechanism of Metal Plate on Explosive Forming
Authors: Iyama Hirofumi , Hinata Takeshi , Itoh Shigeru
Published: August 2008

The explosive forming is one of the forming methods of a metal plate performed since the 1950s. This method is different from usual static press forming. The metal plate is accelerated by underwater shock wave, which is generated by underwater explosion of an explosive. In order to deform a metal plate in predetermined form with sufficient accuracy using this forming method, it is important to grasp the mechanism. At first, it is necessary to grasp that an underwater shock wave spreads and it collides with the metal plate. And it is also necessary to show clearly what deformation of the metal plate with high-speed. Then, we investigated about the mechanism in the numerical simulation. In this research, LS-DYNA, which is the software for shock analysis was used. Moreover, the experiment was also conducted in order to confirm whether this numerical simulation is exact.
Influence of PWR Primary Coolant Environment on Corrosion Fatigue Crack Growth of Austenitic Stainless Steel
Authors: Tice David , Platts Norman , Rigby Keith , Stairmand John , Swan David
Published: August 2008

The rate of growth of flaws in reactor circuit components by fatigue is usually determined using the reference crack growth curves in Section XI of the ASME Boiler and Pressure Vessel Code. These curves describe the rate of crack propagation per cycle (da/dN) as a function of the applied stress intensity factor range (ΔK). No reference curves for water-wetted defects in austenitic stainless steels are currently available. This paper describes the results of testing of Type 304L stainless steel in simulated PWR primary coolant over a range of temperatures and mechanical loading conditions. The data on wrought stainless steel presented in this paper demonstrate that crack growth rates can be significantly enhanced by the PWR primary environment at temperatures between 150°C and 300°C. The degree of enhancement increases significantly with reducing loading frequency and decreases with decreasing water temperature. The environmental influence on fatigue is also smaller at very high R ratio (≥0.85). At long rise times the maximum enhancement of crack growth rate over inert crack growth rates was between 1 and 2 orders of magnitude at 250–300°C. However there is evidence that at very long rise times the environmental effect starts to decrease again. The conditions under which this occurs are influenced by temperature and water flowrate, with turbulent flow conditions appearing to have a limited beneficial effect. Due to the strong time dependence of crack growth rate, the data are best rationalized using a time domain (a˙e–a˙i) approach.
Creep Crack Initiation in a Weld Steel: Effects of Residual Stress
Authors: O’Dowd Noel P. , Nikbin Kamran M. , Biglari Farid R.
Published: August 2008

In this paper, the effect of residual stress on the initiation of a crack at high temperature in a Type 347 austenitic steel weld is examined using the finite element method. Both two and three dimensional analyses have been carried out. Residual stresses have been introduced by prior mechanical deformation, using a previously developed notched compact tension specimen. It has been found that for the 347 weld material, peak stresses in the vicinity of the notch are approximately three times the yield strength at room temperature and the level of stress triaxiality (ratio between hydrostatic and equivalent stress) is approximately 1 (considerably higher than that for a uniaxial test). The finite element analysis includes the effects of stress redistribution and damage accumulation under creep conditions. For the case examined the analysis predicts that crack initiation will occur under conditions of stress relaxation if the uniaxial creep ductility of the material is less than 2.5%. Furthermore, the predicted life of the component under constant load (creep conditions) is significantly reduced due to the presence of the residual stress field.
Phase Transformation Effects on Weld Distortion and Residual Stress Predictions
Authors: Oh J. , Brust F. W.
Published: August 2008

Welding distortion and residual stress has remained one of the major challenges in manufacturing. Extensive experimental efforts have been made throughout the history of manufacturing to understand and control the welding distortion and residual stresses. Extensive work has also been reported in the past couple decades in using analytical and computational methods to predict and quantify the effect of distortion and residual stress during the welding process. Examples of industrial welding applications using computational methods which highlight the challenges and benefits of using analysis and simulation tools to improve the quality and reduce the time and cost of the welding process development and problem resolution are discussed in [1–3]. One issue with regard to computational weld modeling needing addressed is with regard to material modeling. Since material melts and re-solidifies during welding, the use of a proper ‘weld’ constitutive model is critical. In particular, one issue regarding weld constitutive models is the phase transformations which can be important in some materials during weld solidification. This paper addresses this issue and shows some examples where the phase transformation effect is of second order importance and discusses when it must be properly considered.
Advanced Cyclic Plasticity Models in Simulating Ratcheting Responses of Straight and Elbow Piping Components, and Notched Plates
Authors: Rahman Syed M. , Hassan Tasnim
Published: August 2008

Ratcheting is defined as the accumulation of strain or deformation in structures under cyclic loading. Damage accumulation due to ratcheting can cause failure of structures through fatigue cracks or plastic collapse. Ratcheting damage accumulation in structures may occur under repeated reversals of loading induced by earthquakes, extreme weather conditions, and mechanical and thermal operating conditions. A major challenge in structural and solid mechanics is the prediction of ratcheting responses of structures under any or combination of these loading conditions. Accurate prediction of ratcheting-fatigue and ratcheting-collapse is imperative in order to incorporate the ratcheting related failures into the ASME design Code in a rational manner. This would require predictions of both local (stress-strain) and global (load-deflection) responses simultaneously. In progressing towards this direction, a set of experimental ratcheting responses for straight and elbow piping components and notched plates is developed. Advanced cyclic plasticity models, such as, modified Chaboche, Ohno-Wang, and AbdelKarim-Ohno models, are implemented in ANSYS for simulation of these experimental responses. Various integration schemes for implementing the constitutive models into the structural analysis code ANSYS are studied. Results from the experimental and analytical studies are presented and discussed in order to demonstrate the current state of simulation modeling of structural ratcheting.
Flow Induced Vibration Piping Monitoring Program Implementation at Nuclear Plants as a Result of Extended Power Uprates
Authors: Bhavani Dilip
Published: August 2008

This paper defines the requirements and objectives for performing Flow Induced Vibration (FIV) Monitoring and Analysis program on selected piping systems that have a potential to experience high vibration levels at nuclear plants. The contributing factor is the implementation of extended power uprates that increase flows in the critical systems. The work windows for the implementation of the testing are during the startup of the plant refueling outage and the subsequent startup following the implementation of the power uprates. The work includes procurement of instrumentation, software and hardware packages, design / fabrication of instrumentation mounting devices, and installation of instrumentation on piping. The work also includes technical services such as engineering, on-site testing support, documentation, quality control, quality assurance and analyses required to verify that the flow induced vibratory levels of the selected piping systems are within acceptable limits for those operating conditions anticipated during service. This paper outlines design and installation limitations experienced during the limited outage windows when this program is initiated during the plant’s outage. The paper further outlines the scope required to successfully implement the required Design Change Package (DCP) to install the instrumentation, cable, plant hardware, and other supporting equipment to measure vibration levels and ensure acceptability.
Evaluation of Short- and Long-Term Creep Rupture Properties for Grade 91 Materials
Authors: Cohn Marvin J.
Published: August 2008

Recent literature indicates that there is a concern regarding the short-term vs. long-term creep rupture base metal properties for Grade 91 material. Evaluations of recent creep rupture data suggest that the material properties degrade more severely than expected and extrapolated creep rupture properties may be very optimistic. One of the approaches to evaluate creep rupture data is with a parameterized master curve such as the Larson-Miller parameter. Evaluations of creep rupture data indicate that the effects of material degradation can be considered with appropriate stress, time and temperature relationships. Using the Larson-Miller parameter methodology, the selected heats of Grade 91 creep rupture data indicate a reasonable relationship that does not appear to degrade rapidly for the longer term data. If even longer term creep rupture data suggest severe aging degradation as compared to current extrapolations, a transition of the Larson-Miller parameter constant from 31 to 20 does not appear to be a good method to calculate the degraded life estimates. As longer term creep rupture data become available, resulting oxide thicknesses should be measured and reported. The adverse effect of oxidation at longer times, resulting in loss of material and effectively higher stress, should be evaluated.