bluuebunny/crossref_metadata_2025 huggingface dataset:
FRACTESUS Project: General Framework of Materials Selection and Testing Processes
Authors: Brynk Tomasz , Lambrecht Marlies , Uytdenhouwen Inge , Arffman Pentti , Altstadt Eberhard , Petit Tom
Published: October 2021

The H2020 project entitled “Fracture mechanics testing of irradiated RPV steels by means of sub-sized specimens (FRACTESUS)” started on the 1st October 2020. The aim of this project is to demonstrate the applicability of miniaturized compact tension specimens in fracture toughness testing of the reactor pressure vessel steels under hot cell conditions. Validation of this method in an industrially-relevant environment will be an important step towards achieving its acceptance by the nuclear authorities, and finally, to induce its prospective usage by the nuclear power plant operators. Successful implementation of a miniaturized specimens testing technique will result, among others, in the optimization of surveillance material usage and savings in irradiated materials testing. The general project overview showing its structure, partners involved and main deliverables was published elsewhere. Here, we focus on some technical aspects being of the utmost importance in the initial stage of the project and which will have a crucial impact on its overall progress. The general consideration on the selection of the best available materials for testing are discussed on the examples of 73W weld, A533B LUS and the WWER-440 base metal 15Kh2MFAA. Moreover, the general scheme of the testing process, which is planned within the project, is briefly presented as well as the basic assumptions about the numerical modeling task aimed for rationalizing experimental findings.
Strength Distribution Characteristics of Elbow Pipes Considering Low Cycle Fatigue Based on Analysis
Authors: Shimazu Ryuya , Sakai Michiya , Ono Yohei , Matsuura Shinichi
Published: October 2021

When designing and evaluating the strength of the piping system of a nuclear power plant, ductile rupture or plastic collapse is often assumed to be the limit state. However, previous studies have reported that the primary failure mode of piping systems is fatigue. Therefore, it is important to conduct a fragility assessment of the piping system under the assumption that the failure mode is fatigue. In this study, a method for calculating the strength distribution characteristics of elbow pipes based on material characteristics is proposed. The linear cumulative damage is considered as a damage assessment index to conduct a fragility assessment by assuming that fatigue occurs. The strain at the elbow pipes was calculated by finite element analysis, while the linear cumulative damage corresponding to the number of cycles was evaluated based on the strain using the Probabilistic ε-N curve. The failure probability of elbow pipes corresponding to the input acceleration was obtained under specific given parameters, and parts of the curves that compose the fragility curve are shown. The analysis results show that the 5% failure probability can be evaluated using the relationship between the failure probability and either the open or closed angle of the elbow pipes, without considering the thickness variations in the fragility assessment of elbow pipes.
Evaluation of an Alloy 52 / Cladded Carbon Steel Repair Weld by Cold Metal Transfer
Authors: Huotilainen Caitlin , Keinänen Heikki , Kuutti Juha , Nevasmaa Pekka , Sirén Henrik , Virkkunen Iikka
Published: October 2021

Extending the lifetime of existing nuclear power reactors is an increasingly important topic. As the existing fleet of nuclear power reactors ages and approaches the end of their design lifetimes or enters periods of lifetime extension, there is an increased probability for defect repairs due to extended exposure to the operating environment (e.g. high temperature, high pressure, corrosion environment, neutron irradiation, etc.). Concerning repair welding, should a critical need for repair arise, qualified and validated solutions must be readily available for rapid deployment. A proposed method using robotized gas metal arc welding-cold metal transfer to repair a “worst-case” scenario, linear crack like defect beneath the cladding, which extended into the reactor pressure vessel steel, was evaluated on laboratory scale in previous works (PVP2020-21233, PVP2020-21236). These previous studies demonstrated that cold metal transfer has the potential to produce high quality welds in the case of a reactor pressure repair.

In the current study, the lessons learned from the previous work were applied to repair a postulated surface crack on a thermally embrittled and cladded low alloy steel plate using a nickel base Alloy 52 filler metal. Two excavations were filled using different weld bead arrangements — a traditional pattern (92 weld beads, Q = 0.6 kJ/min) and a 45°-hatch pattern (184 weld beads, Q = 0.9 kJ/min) — by gas metal arc welding-cold metal transfer. No pre-heating or post-weld heat treatment were applied, to remain in line with what can be expected in a real pressure vessel repair situation. The 0° angle pattern acts as a reference for previous studies, while the 45°-hatch pattern, aims to minimize the residual stresses caused by repair welding. Finite element modeling was used to predict the initial (cladded, embrittled and excavated) condition of the steel plate, followed by simulating the welding using the actual welding conditions and material constants for both bead patterns as input parameters. The resulting deformation, strains and stresses created in the material due to repair welding were predicted and the welding’s effectiveness was estimated. In addition, the post-repair weld mechanical properties and microstructure, specifically focusing on the fusion boundary and heat-affected zone, were evaluated using various microscopy techniques and hardness measurements. The outcomes of the performed simulations, corresponding characterizations and lessons learned are presented in this study.
Advanced Structural Integrity Assessment Tools for Safe Long Term Operation - ATLAS+ Project: Status of the Activities of the WP3 on Modelling in 2021
Authors: Blouin Arnaud , Marie Stéphane , Nicak Tomas , Timperi Antti , Gill Peter
Published: October 2021

The main objective and mission of the ATLAS+ project is to develop advanced structural assessment tools to address the remaining technology gaps for the safe and long term operation of nuclear reactor pressure coolant boundary systems.

ATLAS+ WP3 focuses mainly on ductile tearing prediction for large defects in piping and associated components: Several approaches have been developed to accurately model the ductile tearing process and to take into account phenomena such as triaxiality effects, or the ability to predict large tearing in industrial components. These advanced models include local approach coupled models or advanced energetic approaches. Unfortunately, the application of these tools is currently rather limited to R&D expertise. However, because of the continuous progress in the performance of calculation tools and accumulated knowledge, in particular by members of the ATLAS+ consortium, these models can now be considered as relevant for application in the context of engineering assessments.

WP3 has been planned to:

• Illustrate the implementation of these models for industrial applications through the interpretation of large scale mock-ups (with cracks in weld joints for some of them),

• Make recommendations for the implementation of the advanced models in engineering assessments,

• Correct data from the conventional engineering approach by developing a methodology to produce J-Δa curve suitable case by case, based on local approach models,

• Improve the tools, guidance and procedures for undertaking leak-before-break (LBB) assessments of piping components, particularly in relation to representing structural representative fracture toughness J-Resistance curves and the influence of weld residual stresses.

To achieve these goals, WP3 is divided into 4 sub-WPs. This paper presents the progress of the work performed in each sub-WP after 48 months of activities.
Effect of Piping System Vibration (FIV, AIV, PIV) on Pipe Support Loads
Authors: Appiah Emmanuel , Wiseman Phillip
Published: October 2021

Integrity of a piping system is a prerequisite for personnel safety and operational reliability in industries where pipelines are critical means of transferring products from one process point to the other, such as power plants, refinery plants, and chemical industries. An essential aspect of designing a reliable piping system is to design supports of suitable load carrying capacity. This also depends on accurate determination of expected support loads including loads due to vibration of the system. Piping design codes such as ASME B31.3 and B31.1 provide a general framework but do not address vibration and its impact from a detailed perspective. In many situations, the potential impact of vibration is overlooked during support load determination. In recent piping system construction, the effect of vibration has increased due to increase in fluid flow rates and use of high strength thin wall materials. Common factors that contribute to vibration include: turbulent flow (flow induced vibration, FIV), relief valve operation (acoustic induced vibration, AIV), rotating and reciprocating equipment (pulsation induced vibrations, PIV). The effect of vibration depends on the strength of excitation and the flexibility of the piping system. As vibration of the piping system increases, loads transfer to the pipe supports also increase. Catastrophic failure of a piping system can occur if its natural frequency lock-in with the frequency of the excitation source. For holistic system integrity, the loads induced due to vibrations need to be accounted for in the support design. In this paper, we investigate the contributions of the various vibration loads in a piping system, the effect of neglecting the various vibration loads on the system integrity, and an empirical method to readily determine the vibration loads to reduce cost and time require in support design processes.
Measurement of Steam-Generator Tube Damping Caused by Anti-Vibration-Bar Supports
Authors: Smith Bruce A. W. , Feenstra Paul , Liu Michael
Published: October 2021

In 2013, Atomic Energy of Canada Limited (now Canadian Nuclear Laboratories) took vibration measurements to examine low-frequency damping associated with tube vibration parallel to anti-vibration bar supports. These tests were performed to better understand and control in-plane fluidelastic instability of tubes in the U-bend region of recirculating steam generators.

In the tests, the damping ratios of a single steam generator tube vibrating parallel to a single pair of anti-vibration bars were measured using both a log-decrement and a power-based method. Non-contacting excitation and position-sensing techniques were employed to improve accuracy. The tests examined the effects of fluid (water or air), natural frequency, gap width, preload, and vibration normal to the bars. Additional tests were also done using a drilled-hole support and without supports to allow validation against previously published work. Most of the tests were performed in water.

This paper describes the tests including the test apparatus, test methods, and analysis techniques. A summary of the results is presented. These results show that the damping ratios measured without any supports and with a drilled-hole support are consistent with previously published data. Contrary to an existing design guideline, the anti-vibration bars resulted in no significant additional viscous or squeeze-film damping for vibration parallel to the bars. The results also showed that anti-vibration bars can introduce significant in-plane Coulomb-type damping because of friction and impacting.
Research on Characteristics of Fluid Exciting Force of Reactor Internals
Authors: Feng Zhipeng , Deng Liwen , Huang Xuan , Shen Pingchuan , Liu Shuai , Cai Fengchun
Published: October 2021

Flow-induced vibration is an important issue related to the safety and reliability of nuclear reactor, which need to be analyzed and evaluated in the design stage. In order to obtain the input loads and key parameters used in the calculation of flow-induced vibration of reactor vessel internals (RVIs) that need to satisfy the engineering requirements. The typical RVIs are selected as the research object, and the fluid exciting force characteristics are studied based on the computational fluid dynamics methods. The results show that the fluid exciting force acting on the RVIs is a wide-band stochastic process. For upper internal, the largest pressure fluctuation occurs at the guide tubes and support columns located near the outlet. Therefore, it is necessary to pay more attention to these guide tubes and support columns in response analysis. As for core barrel, the root mean square value of the pressure fluctuation changes drastically at the inlet and outlet location. For lower internal, the lower flow field of RVIs is relatively disordered, and its pressure fluctuation possesses irregular characteristics. Each component of lower internal need to be considered in analysis and evaluation.
Failure Modes for Acrylic Polymers in Section VIII Pressure Vessels
Authors: Kemper Bart , Richards Guy , Nappi Taylor , Thipparthi Veda , Escobar Ana
Published: October 2021

Section VIII of the Boiler and Pressure Vessel Code is introducing the use of acrylics as a pressure vessel material. The design method is specified in ASME PVHO-1, Safety Standard for Pressure Vessels for Human Occupancy. The current method relies upon an empirical method developed in the 1960–70’s. It does not use “allowable stress” or other mechanical properties traditionally used to calculate design dimensions, but instead uses a fixed range of dimensions for specific shapes and determines the wall thickness using a curve. Understanding the PVHO-1 design assumptions and typical failure modes is important for a non-PVHO pressure vessel designer using acrylics. An ASME Codes & Standards task group is developing a “design by analysis” method (DBA) for acrylics and other glassy polymers for pressure vessel components. The proposed DBA methodology uses Verification and Validation (V&V) techniques and Finite Element Method (FEM) as the design method framework in order to advance the use of glassy polymers as pressure vessel materials.
A Multi-Scale Failure-Probability-and-NDE-Based Fatigue Life Model for Estimating Component Co-Reliability of Uncracked and Cracked Pipes
Authors: Fong Jeffrey T. , Marcal Pedro V. , Rainsberger Robert , Heckert N. Alan , Filliben James J. , Doctor Steven R. , Finney Ned A.
Published: October 2021

The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC) Committee has recently developed a new Section XI (Nuclear Components Inspection) Division 2 Code [1] named “Reliability and Integrity Management (RIM).” RIM incorporates a new concept known as “System-Based Code (SBC)” originally due to Asada and his colleagues [2, 3], where an integrated approach from design to service inspection is introduced using three new types of statistical quantities: (1) “system reliability index,” or “system co-reliability target” for any system consisting of structures and components, (2) “structural co-reliability,” for any structure, and (3) “component co-reliability” for any component. In a recent paper published in the International Journal of Pressure Vessels and Piping, Fong, Heckert, Filliben, and Freiman [6] developed a new theory of fatigue and creep rupture life modeling for metal alloys at room and elevated temperatures such that the co-reliability of an uncracked component can be estimated from fatigue and creep rupture test data with simple loading histories. In this paper, we extend the theory to include a methodology to estimate the co-reliability of a cracked pipe from fatigue crack growth rate test data, probability of detection (POD) data, and nondestructive evaluation (NDE) of initial crack sizing data for simple loading histories. To illustrate an application of this new modeling approach, we present four numerical example case studies using (a) the fatigue failure data of six AISI 4340 steel specimens at room temperature (Dowling, N. E., 1973) for an uncracked steel pipe, and (b) the fatigue crack growth rate data of 17 specimens of 2024-T3 aluminum (von Euw, Hertzberg, and Roberts, 1972) for a cracked aluminum pipe (see discussion after Eq. (16)). The four cases are: (1) Uncracked and uninspected pipe. (2) Inspected pipe with a crack-found-location-and-size call. (3) Uncracked and inspected pipe with a no-crack-found call and a POD value. (4) Inspected pipe with a crack-found-location-and-size call and a structural health monitoring (SHM) program. Significance and limitations of this new fatigue life modeling approach to the estimation of component co-reliability of uncracked and cracked pipes are presented and discussed.
A Case for New Low Pressure Vessel (LPV) Codes for Design Pressures Below 15 psi (100 kPA)
Authors: Millet Barry , Ebrahimi Kaveh , Lu James , Spencer Donald
Published: October 2021

Today the ASME Boiler and Pressure Vessel Code Section VIII (ASME Code) covers pressure vessels for design pressure above 15 psi (100 kPa) but not for design pressures below 15 psi.

Manufacturers of pressure vessels under 10ft (3048mm) and with design pressure under 15 psi (100 kPa) design to the ASME Code but do not stamp them. The ASME Code is explicit in not allowing this.

Manufacturers of low pressure vessels over 10 ft (3048 mm) in diameter, design and built to “good engineering practice” using Finite Element Analysis, the ASME Code, API and the AISC Manual of Steel Construction.

This paper provides an overview of these existing codes, standards with their methods for design, fabrication and testing then provides an outline of a Code with two classes of low pressure vessels (LPV). The audience for the smaller pressure vessels would be small batch chemical, pharmaceutical, food, and beverage processing facilities who require small near atmospheric pressure vessels. The audience for the larger pressure vessels would be power plants, refineries, chemical plant, steel mills and concrete plants flue gas treatment and CO2 sequestration of exhaust products.
Influence of Finite-Length Plate Proximity on Vortex-Induced Vibrations of Elastic Cable
Authors: Ivanov Oleg , Vedeneev Vasily
Published: October 2021

Vortex-induced vibrations of an elastic cylinder near a finite-length plate are experimentally investigated. A rubber cylinder of diameter D was spanned in the test section of a wind tunnel near a plate of length nearly 6D. The oscillation amplitude peak for a single cylinder was 0.3D, Reynolds number for oscillating peak-amplitude regime based on the cylinder diameter was in the range 180...260. The oscillation amplitude ratio A/D appeared to decrease with the reduction of the gap ratio G/D between the cylinder surface and the plate for the cylinder located sufficiently upstream from the plate trailing edge. However, for the cylinder location at the same level or downstream from the plate trailing edge, there are regions of essentially larger oscillation amplitude compared to the isolated cylinder case. Maximum amplitude increase by 39% was obtained.
Delayed Hydride Cracking Initiation Evaluation of Interacting Flaws in a CANDU Reactor Zr-Nb Pressure Tube
Authors: Scarth Douglas , Doddihal Preeti , Ip Monique
Published: October 2021

In-service evaluation of a flaw that is detected in a Zr-2.5Nb alloy pressure tube in a CANada Deuterium Uranium (CANDU) nuclear reactor includes an analysis to demonstrate that delayed hydride cracking will not initiate from the flaw. The flaw can be assessed either as planar or volumetric with a finite root radius. Two adjacent flaws caused by fretting due to flow-induced vibration were detected by in-service ultrasonic examination in a Zr-2.5Nb alloy pressure tube in a CANDU reactor. The flaws were replicated to obtain details of flaw geometry. The two flaws are volumetric in nature, have irregular shapes, and were determined to intersect. Although both flaws are volumetric, for pragmatic reasons one flaw was treated as planar. The other flaw was treated as blunt. The flaws were evaluated for delayed hydride cracking initiation in accordance with the Canadian Standards Association Standard N285.8. A three-dimensional finite element stress analysis was performed to quantify the interaction between the two flaws, as well as the peak stress at the root of the blunt flaw. Both flaws met the acceptance criteria for prevention of delayed hydride cracking initiation, and the pressure tube was returned to service. This paper provides a summary of the delayed hydride cracking initiation evaluation of these two flaws, and highlights the methods that need to be applied for flaws with irregular shapes and that interact.
Optimization for Nuclear Class 1 Opening Reinforcement
Authors: Reinhardt Wolf
Published: October 2021

An important element in evolving Section III of the ASME Code is the re-examination of Code rules to identify the potential for efficiencies. The present paper looks at the rules for reinforcement of openings. The present Code rules require the area of material removed to create the opening (up to the design thickness) to be added around the opening with certain limits on the distance from the opening. Past studies have suggested that the present rules may add more material than needed to maintain the strength of the vessel in some cases.

The optimum amount of reinforcement is therefore postulated to be determined by the criterion that the limit pressure should not be reduced excessively relative to the limit pressure of the vessel in the absence of the opening.

Limit analysis is performed to derive possible rules on the amount and distribution of around an opening. Options for alternative rules for reinforcement of openings, and restrictions on the present Code rules, are proposed.
Progress of EASICS Validation Experiments and Code Comparison of R5, RCC-MRX and ASME III Division V
Authors: James Peter , Coon David , Austin Colin , Underwood Nicholas , Meek Caroline , Chevalier Marc , Dean David
Published: October 2021

The “Establishing AMR Structural Integrity Codes and Standards for UK GDA” (EASICS) project was established in 2019 to help support the acceptance of Advanced Modular Reactors, or AMRs, which are typically based on high temperature Generation IV reactors. The EASICS project is aiming to provide guidance on the requirements for codes and standards for the design of AMRs for use in the UK, to ensure that state-of-the art knowledge will be brought to bear on developing the required design and assessment methodologies. The EASICS project started in July 2019 and is looking to complete by December 2021.

To support this aim, the work presented in this paper provides an overview of two interacting aspects of the programme. The first is to perform validation tests for high temperature creep-fatigue assessments of a plant relevant component. The second aspect is to use these results, to provide a comparison of internationally recognised approaches for the assessment of high temperature (creep regime) components. This approach will be repeated for two other case scenarios deemed to be plant relevant components. This paper builds upon the initial overview paper presented at the 2020 conference providing an update on progress.

One of the cases presented herein, described as the Thin Walled Welded Pipe Test uses specialist testing of a plant relevant component under high temperature loading conditions is underway with some initial results available. The validation testing includes both fatigue tests and creep-fatigue tests on 316H welded thin section tubes. The tubes have been subjected to strain-controlled tension/compression (R-ratio of −1), with some including a displacement controlled dwell. The tests are being conducted at 525°C. An update to the progress of these tests is included herein.

To help enhance interaction with the code bodies, and to understand the impact of differences in the approaches, comparative assessments have been performed when adopting R5, ASME Section III Div 5 and RCC-MRx. One comparison will be based around the tests detailed above (tube test). A further assessment comparison will consider the Evasion mock-up tests provided by CEA (sodium based thermal shock tests). The third assessment case is loosely based around a plant relevant assessment within one of the UK Advanced Gas Reactors (AGRs). This paper provides an overview of the results from all these cases using R5, ASME Section III Div 5 and RCC-MRx.

The subsequent discussions covers results, differences and potential impact to the codes which will all help to inform a guidance document to support assessing AMRs within a UK regulatory framework.
High Temperature Hydrogen Attack (HTHA) Models for the Petrochemical Industry
Authors: Swindeman Michael , Pavlina Erik J. , Perdomo Jorge
Published: October 2021

Establishing safe operating limits for equipment operating in hydrogen service remains a concern for the petrochemical industry. A methodology to prioritize equipment, inform future inspections, and guide inspection discovery path forward decisions has been in development for the past several years. The approach is multi-tiered and considers the process conditions that lead to risk of damage, the potential extent of damage, and the effect of applied and residual stresses on the rate of damage growth. The key metric for Fe-C steels and Fe-C-0.5Mo steels is the damage index, which is calculated from a damage rate equation that has been calibrated to select laboratory test data and reported HTHA incidents documented in API 941. The damage rate and significance of damage is handled by considering damage as both diffuse (continuum assessment) and localized (crack/flaw assessment). This approach was originally intended as a means for prioritizing inspection. However, once margins are established to account for uncertainties in operating conditions and material variation, so-called time-dependent Nelson curves can be generated for use in design. This paper provides an overview of the HTHA damage modeling technique and results of recent experimental work, including component-level testing used for validation of the model.
Simplified HTHA Evaluation Using Larson Miller Parameter Concepts
Authors: Krishnamurthy Sujay , Hantz Benjamin F.
Published: October 2021

Researchers have been developing mechanistic approaches describing High Temperature Hydrogen Attack (HTHA) damage for quite some time. Although there are a variety of approaches, all of them make use of describing HTHA as a time and temperature dependent phenomena that is sensitive to methane pressure. HTHA research shows the damage process is a phenomenon that is very similar to creep damage which has an exponential relationship to the applied stress and temperature. Based on these observations, the authors propose an HTHA damage assessment procedure that uses the familiar Larson Miller Parameter (LMP) approach and employs the well-known Linear Life Fraction Rule for evaluating operating condition variations in hydrogen partial pressure and temperature.
Thermal Analysis of a 9977 Package During a KAC Fire Accident
Authors: Tamburello David , Kesterson Matthew , Escobar Andrew
Published: October 2021

The 9977 is a US Department of Energy (DOE) shipping package used to store and transport plutonium bearing materials. The shipping package utilizes a single 6-inch diameter containment vessel with the radioactive material within SAVY-4000 containers, 3013 food-pack containers, or other sealed storage containers separated by spacers. The 6-inch containment vessel is surrounded by load distribution fixtures and a foam insulation overpack to protect against fire and impact events. A storage facility fire, which is longer and hotter than the regulatory transportation fire, is evaluated to ensure radioactive material containment is maintained. A sensitivity analysis of foam insulation reduction is considered with foam eliminated either along the inside wall of the drum body (Inner Foam) or eliminated from the outer walls of the inner chamber where the 6-inch containment vessel is located (Outer Foam). These options were considered to conservatively simulate the potential foam reduction possibilities due to aging during storage. Note that the foam insulation thermal properties were limited to their beginning of life or “as built” property values. A minimum foam thickness needed to maintain containment during the hypothetical facility fire is determined for both the Inner and Outer Foam configurations as well as for both the SAVY-4000 and 3013 food-pack container configurations.
Torsional Fatigue Test Applicable to Helical Spring Material Used in Candu Fuel Channel Spacers
Authors: Gagnon Andre , Kashyap Tejasvi , Metzger Don
Published: October 2021

In a particular nuclear application, separation between structural components is maintained by a helical spring such that the separating load bears across the diameter of the spring coils. Relative motion between the structural components due to changing load and temperature is accommodated by rolling of the spring. This rolling motion while under radial load results in cyclic loading of the spring material. Fatigue analysis of the cyclic loading must take into consideration the material degradation due to the unique operating environment, so testing of ex-service material is required. Standard fatigue test specimens are not possible due to the small dimensions of the spring component. Cyclic stress may be applied to the material via a reciprocating rolling motion as per the operating conditions but this approach has practical limitations with respect to cycle frequency and uncertainty in stress response. A fatigue test system has been developed in which cyclic stress is achieved by applying torsional load with respect to the axis of the helical spring. This load translates into a pure bending state of stress in the cross-section of the coils. The relationship between applied load and stress is achieved analytically through curved beam analysis. Some practical considerations in the test setup are discussed along with supporting analysis, and results obtained with specimens taken from pre-service components are presented. The outcome of the tests is compared to applicable data and it is concluded that the test method is effective in producing valid fatigue data.
Machine Learning Modeling of Dynamic Strength of Resistance Spot Welds in High Strength Steels
Authors: Zhu Jesse B. , Zhu Xian-Kui , Zhang Wei
Published: October 2021

Electric resistance spot welding technology has been extensively applied to join sheet metal parts in the automobile industry to decrease vehicle weight and increase its integrity. Due to the dynamic nature of motor vehicles, it is necessary to measure the dynamic strength of spot welds. Both the traditional regression approach and the state-of-the-art machine learning method are utilized in this paper to quantify the dynamic strength of spot welds based on a large database for different steels, where the dynamic strength is nominally defined as a peak load normalized by specimen thickness and weld nugget size at a specific loading rate.

Experimental results showed that the dynamic strength of spot welds is a function of the loading rate, specimen thickness, spot weld nugget size, specimen type and steel grade. To formulate the dynamic strength, the traditional regression needs to simplify the strength as a function of loading rate only, and then determine it using the best curve-fitting approach. In contrast, the machine learning method, based on an artificial neural network with built-in learning functions and algorithms, can determine a multi-variable function of dynamic strength to describe the effect of the loading rate, specimen thickness, and spot weld nugget size. To demonstrate the capability of the machine learning technology, a simple and a more complex neural network architecture are adopted to predict the dynamic strength of spot welds. The final machine learning results, advantages and disadvantages are evaluated in comparison with the regression approach.
Experimental Investigation of Jet Cross-Flow Induced Vibration of a Rod Bundle
Authors: Gad-el-Hak Ibrahim , Mureithi Njuki , Karazis Kostas , Williams Gary
Published: October 2021

Flow-induced vibration (FIV) is a constant concern in nuclear power plants. Demand for better thermal performance challenges the mechanical and flow characteristics of fuel designs. In the hypothetical case of a loss of coolant (LOCA) event in a reactor, the hydrodynamic pressure would increase significantly across the baffle plates. PWRs include safety features such as Loss-of-Coolant-Accident (LOCA) holes and slots in the core periphery baffles surrounding the fuel assemblies to release the pressure build up during a LOCA event. Accordingly, these fuel assemblies are subjected to combined axial and jet cross-flow at certain axial locations along their spans due to their proximity to the LOCA holes.

The jet flow could induce vibrations for fuel assemblies located near LOCA holes, which might lead to grid-to-rod fretting and thus potential fuel failure. Research on circular jet induced vibrations of rod bundles is limited. Thus, it is required to investigate the dynamical behavior of rod bundle subjected to jet flow to define the critical velocity at which the fuel rods may undergo instability.

This article presents an experimental study of jet flow induced vibrations for a 6 × 6 closely packed normal square rod bundle with a pitch-to-diameter ratio of 1.32 simulating the actual PWR fuel rod dimensions. A specialized test apparatus was designed to investigate the stability effect of jet centerline offset from array centerline (jet eccentricity). From the test results the instability threshold of the rod bundle subjected to jet cross-flow is determined. The results show that the rod array vibration is affected by the jet eccentricity. Two excitation mechanisms are identified. The first is an apparent lock-in type mechanism that maybe related to shear layer or jet oscillation. The second, more important excitation, is an apparent fluidelastic instability induced by the jet flow.
A Smart Wing Based on Vacuum-Packed Particles
Authors: Brigido-González J. D. , Burrow S. G. , Woods B. K. S. , Bartkowski P.
Published: October 2021

The FishBAC is a morphing aerostructure that is currently both stiffer than desired in terms of actuation energy and softer than desired for aeroelastic effects. The research aims to remove those compromises by introducing a novel material that can actively change its stiffness. The novel approach is to fill aircraft wings with particles, which can be squeezed together under vacuum pressure to make a stiff aircraft wing. When the vacuum is turned off, the grains unlock, and the wing becomes soft enough to be deformed into a new shape. This allows the wing to immediately adapt its shape to changing operating conditions — reducing noise, drag and, therefore, fuel burned.

The following research includes a new detailed mechanical modelling for morphing structures that are able to switch stiffness using vacuum-packed particles. The model is based on Euler-Bernoulli and Mohr-Coulomb analysis to capture the stiffness response of the particles at different vacuum levels. This model is computationally fast and is able to predict the variation of the stiffness accurately. The experimental and the model results agree with a relative error of less than 5%.
Excitation of Ultrasonic Natural Vibrations by Multi-Excitation Using Decentralized Control for Failure Monitoring
Authors: Tanaka Takashi , Tamura Takato , Oura Yasunori
Published: October 2021

The failure, e.g. fatigue crack, weld crack, and bolt loosening, of infra-structure is one of the causes of serious accidents. To prevent these accidents, structural health monitoring systems have been proposed. Among them, the evaluation methods by measurement of natural vibrations are useful for various structures because of ease in introducing a monitoring system. Currently, the natural vibrations at low-frequency range are usually used because of the difficulty of exciting natural vibrations at high-frequency range. In this paper, the excitation method of natural vibrations by multi excitation using decentralized control is developed. Firstly, the difficulty of excitation of ultrasonic natural vibrations is confirmed. Secondly, the basic performance of the multi-excitation using decentralized control is investigated by the experiment using a simple beam structure. The excitation of an ultrasonic natural vibration in the case of multi-excitation using decentralized control with the self-excitation automatically is examined. From the phase differences between each measurement signal, it is clarified that mutual synchronization is realized. Thus, it is confirmed by the measurement of vibration mode shape that an ultrasonic natural vibration is excited. Finally, it is tried to excite another natural vibration by forced entrainment.
Flexoelectric Polarization of Piezoelectric PVDF-Films Above the Curie Temperature
Authors: Seyfert Lars , ben Ammar Hassen , Schwesinger Norbert
Published: October 2021

A new field of research is the flexoelectric effect of solids. This quit new electromechanical energy conversion mechanism has not yet been sufficiently investigated till now.

Flexoelectricity defines the change of electrical polarization induced by changing of strain gradients in dielectric materials. In contradiction to the piezoelectric effect, all dielectric materials show a flexoelectric behavior. Flexoelectric conversion is not limited to defined temperature ranges. The effect is still present above the Curie temperature of piezoelectric materials. This interesting behavior could lead to new applications in different branches. This paper describes investigations on flexoelectricity at temperatures above the Curie temperature in piezoelectric polyvinylidene difluoride (PVDF) polymer films.

Changes of the mechanical strain gradient in the polymer film lead to a change of polarization. Furthermore, this leads to a charge separation on aluminum electrodes deposited on both sides of the polymer film. Finally, the charge transport to the electrodes in an external circuit can be measured. To analyze the flexoelectric polarization alone and in combination with other effects measurements were carried out at room temperature and above the Curie temperature. At temperatures of 130°C, i.e. far above the Curie temperature an unexpected strong polarization was found. It ranges between 50% and 80 % of the polarization values at room temperature.
Realization of Uniform Bending Strain in Piezoelectric Energy Harvesters by Gamma-Shaped Structures
Authors: Jeong Sinwoo , Lee Soobum , Yoo Hong Hee
Published: October 2021

Cantilever is one of the most popular structures employed for vibration-based piezoelectric energy (PE) harvesters due to its simplicity in mathematical modeling and manufacturing. However, the cantilever-shaped PE harvester (CPEH) has a nonuniform bending strain which is inefficient for piezoelectric energy harvesting. In this study, a new structure, named Γ-shaped PE harvester (ΓPEH), is proposed to achieve a uniform bending strain of the PE harvester by connecting another beam at the end of the harvester beam in 90 degree. A comparison study based on analytical solutions is made to show how the ΓPEH can outperform the CPEH and tapered PE harvester (TPEH). For a more detailed and fair comparison, the numerical models for the PE harvesters are developed using the generalized classical Ritz method, and the shape optimization is conducted under the same material volume, mass, and stress constraints. The comparison results show that the ΓPEH has higher power output than the CPEH and TPEH.
Localization of Multiple Contact-Type Failures Using Structural Intensity of Low-Frequency Vibration Caused by Frequency Down-Conversion
Authors: Tanaka Takashi , Asano Junnosuke , Oura Yasunori
Published: October 2021

The contact-type failure, e.g. fatigue crack in early stage, delamination of composite material and adhesive failure, leads to the serious accidents. When the object with the contact-type failure vibrates due to ultrasonic vibrations of different frequencies, the interaction of the contact interfaces of failure occurs. As the result of this interaction, the low-frequency vibration, of which frequency is the difference frequency of ultrasonic vibrations, generates (Frequency down-conversion). The detection, evaluation and localization by measurement of structural intensity of low-frequency vibration caused by frequency down-conversion has been proposed. In this paper, the performance of the proposed method in the case of multiple contact-type failures is investigated. Firstly, the detection method of contact-type failure based on frequency down-conversion of elastic vibrations is introduced. Overview of frequency down-conversion and the example of detection of contact-type failure is shown. Secondly, the proposed method for single failure is explained. By the measurement result of structural intensity of the low-frequency vibration caused by frequency down-conversion, it is confirmed that the contact-type failure can localize as the excitation point of low-frequency vibration. Finally, the influence of other failures on the localization accuracy is investigated. From these results, it is clarified that the contact-type failure, of which the excitation force of low-frequency vibration is the largest, only localizes.
Reliability Study on Spring Interconnections for Piezo-Jet Printed Electronics Under Environmental Stress
Authors: Erben Andreas , Matvieieva Nataliia , Frauendorf Moritz , Bucht André , Drossel Welf-Guntram
Published: October 2021

In the current paper the reliability of spring interconnections for the use in automotive applications was investigated. A commercially available connector was used for contacting a piezo-jet printed silver pad on polycarbonate. The structures were tested using vibration tests at three different temperatures (−25°C, 25°C and 85°C) and measured using four-point probe measurement system and white light spectrometry. The obtained results showed the reliability of the printed structure and the contact, despite of the contact resistance change. The reasons of this change and experimental results are discussed in the paper. The investigations described in the paper provide an initial approach to the development of spring interconnections for printed electronics.
Design of Pennate Topology Fluidic Artificial Muscle Bundles Under Spatial Constraints
Authors: Duan Emily , Bryant Matthew
Published: October 2021

In this paper, we investigate the design of pennate topology fluidic artificial muscle bundles under spatial and operating constraints. Soft fluidic actuators are of great interest to roboticists and engineers due to their potential for inherent compliance and safe human-robot interaction. McKibben fluidic artificial muscles (FAMs) are soft fluidic actuators that are especially attractive due to their high force-to-weight ratio, inherent flexibility, relatively inexpensive construction, and muscle-like force-contraction behavior. Observations of natural muscles of equivalent cross-sectional area have indicated that muscles with a pennate fiber configuration can achieve higher output forces as compared to the parallel configuration due to larger physiological cross-sectional area (PCSA). However, this is not universally true because the contraction and rotation behavior of individual actuator units (fibers) are both key factors contributing to situations where bipennate muscle configurations are advantageous as compared to parallel muscle configurations. This paper analytically explores a design case for pennate topology artificial muscle bundles that maximize fiber radius. The findings can provide insights on optimizing artificial muscle topologies under spatial constraints. Furthermore, the study can be extended to evaluate muscle topology implications on work capacity and efficiency for tracking a desired dynamic motion.
Design and Structural Integration of a Semi-Active Tuned Mass Damper for Improved Vibration Control on Airframe Structures
Authors: Chatziathanasiou Grigorios M. , Dimitriou Dimitris K. , Chrysochoidis Nikolaos A. , Saravanos Dimitris A.
Published: October 2021

Aircraft vibrations induced by low-frequency unsteady aerodynamic loads affect the comfort of passengers and reduce the airframe fatigue life. In order to attain high and broadband vibration attenuation levels, a Semi-Active Tuned Mass Damper (SATMD) is developed, that exhibits robust vibration control capabilities and requires minimal structural interference. The SATMD consists of a piezoelectric device, connected to an external Resistive-Inductive electrical circuit, and a small auxiliary mass. Simulations and testing of this damper have shown high sensitivity of its performance to: (1) the location of its structural integration and (2) its electromechanical characteristics. The current paper investigates the tailoring of these design parameters on a lab-scale airframe model, aiming at simultaneous control of 3 modes. The numerical results reveal a favorable strategy to tailor the electromechanical properties. The proposed SATMD leads to more than 10dB simultaneous reduction to all targeted modes, highlighting the robustness of the proposed damping device and the importance of the tailoring process.
Experimental Verification of Stiffness-Variability of an Active Tensegrity With Nylon Actuators
Authors: Yoshizumi Tomoya , Masuda Arata , Miura Nanako
Published: October 2021

A tensegrity is a pin-jointed structure composed of isolated compressive members supported by an interconnected network of tensile members, which respectively bear compressive and tensile prestress. This study focuses on its unique feature of stiffness variability induced by the change of the member length, in which the overall structural behavior to an external force varies from a hard and elastic phase to a soft and compliant phase. In this paper, a small-sized tensegrity structure in the form of a truncated octahedron consisting of 12 compressive members and 36 tensile members was designed and fabricated, in which coiled nylon strings were installed as heat-induced contractive actuators replacing four of its tensile members to demonstrate the significant variability of the structural stiffness. Morphing under gravity due to the contraction of the actuators was observed, and the static behavior of the tensegrity under an applied external force was experimentally quantified to verify the large variability of the structural stiffness.