Hold Period Research Articles

Procedures for Multiaxial Creep-Fatigue Verifications of Nuclear Components

Nuclear high heat flux components (HHFCs) experience large thermal gradients and high heat flux variations, which induce severe thermal cyclic loadings. The most critical design issue for these components is their endurance strength under the required number of thermal cycles.The aim of this work is to provide procedures to perform the multiaxial creep-fatigue life assessment of HHFCs. Since the existing design codes present limitations due to simplifying assumptions concerning procedures for the multiaxial fatigue verification considering interactive effects of creep-fatigue and local stress and temperature conditions, better accurate verification methods and rules are developed starting from the available scientific literature and experimental data. The new verification methods identify the shape of the most damaging hysteresis loop considering plasticity and creep strains in both tensile and compressive conditions.The developed procedures are used to post-process the thermomechanical results of finite element (FE) analyses. They foresee the calculation of the creep-fatigue damage in each node and for each cyclic loading of the analyzed FE model by using the fatigue curve corresponding to the shape of the local hysteresis loop. Furthermore, the most fatigued elements are bounded and the causes of damage are identified to improve the local design. The fatigue damage is evaluated considering the effects of local conditions: temperature, multiaxial stress-strain state, strain intensity range, effect of local mean stresses, material shakedown, accumulated damage for multiple cyclic loads, combined effect of creep-fatigue, hold periods, and neutron flux.The developed procedures are successfully verified by comparing the results with experimental data for different levels of mean stress.This paper presents a description of the procedures and design rules focusing on the innovative aspects. The new procedures have been developed in the framework of the activities for the design, manufacturing, and procurement of the ITER neutral beam injector, and they are applied for creep-fatigue verifications of the in-vessel HHFCs.

Verification of Selected Key Assumptions for the Analysis of Depth-Sensing Indentation Data

Methods for indentation analysis involve assumptions that may be problematic for visco-elastic materials. Three assumptions are discussed: (1) the unloading is predominantly elastic, (2) tip/sample adhesion and friction are negligible, and (3) no cracking occurs around the indent. A series of copolymers is investigated by indentation at room temperature, just below their glass transitions. Closer to the glass transition assumptions (1) and (2) were violated. Erroneous analysis due to extensive creep was identified by comparison of the creep rate at the end of the hold period with the unloading displacement rate and from the power of the fit to the unloading response. Assumption (3) was studied by scanning the indenter tip over the residual indent in polystyrene, which is known to be susceptible to stress localization.

Encapsulation of Microelectronic Components Using Open-Ended Microwave Oven

An open-ended microwave oven system is presented and characterized for the rapid encapsulation of microelectronic components. In situ real-time measurement of the temperature of the curing materials is carried out by an infrared pyrometer integrated in the microwave head of the oven. An automatic computer-controlled closed feedback loop has been used to measure the temperature in the curing material and modulate the system operating power to obtain predefined curing temperature cycles for efficient curing. Uniform curing of the encapsulant material is achieved with typical cure time of ~300s with a ramp rate of 1.66°C/s and a hold period of ~100s . Differential scanning calorimeter based measurement for the curing of the polymer dielectric indicates a near 100% degree of cure.

Thermal cycling induced δ to α phase transformation via an intermediate β phase on a δ-stabilized Pu–Ga alloy

The thermal cycling induced δ to α phase transformation in a δ-stabilised Pu–Ga alloy has been investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The alloy specimen was thermally cycled from 25°C to 180°C within the DSC furnace enabling coincident collection of phase transformation information. The cycling was carried out with varied isothermal hold periods at 25°C between each DSC run. The α phase was detected in the original well-homogenised alloy and the amount of α phase was found to increase with both thermal cycling number and isothermal hold time. Nearly 8% α phase was detected after 210 cycles, with no sign that α phase in-growth had ceased or slowed. Possible mechanisms, by which thermal cycling facilitates the nucleation and in-growth of the increasing α phase content are discussed. It is hypothesised that the δ to α phase transformation proceeds via an intermediate β phase at elevated temperature. Based on this investigation, it is also suggested that thermal cycling may be used as a novel experimental method to study the meta-stable nature of δ-stabilized Pu alloys.

Mechanical Behavior of a Series of Copolyester Blends near the Glass Transition: Monotonic and Load-Hold Behavior in Compression

Monotonic loading tests were conducted on five commercial blends of poly(ethylene terephthalate) (PET) and poly(1,4-cyclohexylenedimethylene terephthalate) (PCT) at temperatures of 90°C and 100°C and strain rates of 0.1/s, 0.05/s, and 0.005/s in uniaxial and plane strain compression. On comparing the mechanical behavior of the five materials, it was found that the behavior of the low-PCT content materials was different from the high-PCT content materials only at conditions that favored strain-induced crystallization, particularly in plane strain compression. Load-hold tests were also conducted on three of the blends with similar results to the monotonic tests. Material differences were only pronounced at certain conditions, and in these cases the low-PCT content materials showed increased strain hardening after the hold period while the high-PCT content material did not. Therefore, it was found that the addition of a hold period was not exclusively required to observe differences in the crystallizable materials over the noncrystallizing blends. The increased strain hardening likely associated with crystallization in PET was only observed when the following conditions were met: (i) strain rates of 0.1/s and above, (ii) temperatures of 90°C–100°C, (iii) plane strain compression, and (iv) after a certain level of deformation.

Steady state visually evoked potential (SSVEP) topography changes associated with cocoa flavanol consumption

In a randomized, double-blind placebo controlled trial, 63 middle-aged volunteers aged between 40 and 65years were administered a daily chocolate drink containing 250mg or 500mg cocoa flavanols versus a low cocoa flavanol (placebo) drink over a 30-day period. Participants were tested at baseline as well as at the end of the treatment period on a test of Spatial Working Memory. Steady State Probe Topography (SST) was used to assess neurocognitive changes associated with cocoa flavanol supplementation during the completion of the Spatial Working Memory task. SST is an electrophysiological technique which utilizes a 13Hz diffuse visual flicker in order to generate a steady state visually evoked potential (SSVEP). Changes in the amplitude and phase of the SSVEP response after 30days were compared between treatment groups. Behavioral measures of accuracy and reaction time were not found to be significantly different between treatment groups, while average SSVEP amplitude and phase differences at a number of posterior parietal and centro-frontal sites were found to be significantly different between groups during memory encoding, the working memory hold period and retrieval. In the absence of significant behavioral effects, these differences in brain activation can be interpreted as evidence of increased neural efficiency in spatial working memory function associated with chronic cocoa flavanol consumption.

Closure to “Discussion of ‘Yield Function for Solder Elastoviscoplastic Modeling’” (2005, ASME J. Electron. Packag., 127, pp. 147–156)

Closure to “Discussion of ‘Yield Function for Solder Elastoviscoplastic Modeling’” (2005, ASME J. Electron. Packag., 127, pp. 147–156)

Development and implementation of a three-choice serial reaction time task for zebrafish ( Danio rerio)

Zebrafish are an established and widely utilized developmental genetic model system, but limitations in developed behavioral assays have meant that their potential as a model in behavioral neuroscience has yet to be fully realized. Here, we describe the development of a novel operant behavioral assay to examine a variety of aspects of stimulus control in zebrafish using a 3 choice serial reaction time task (3 CSRTT). Fish were briefly exposed to three spatially distinct, but perceptually identical stimuli, presented in a random order after a fixed-time inter-trial interval (ITI). Entries to the correct response aperture either during the stimulus presentation, or within a brief limited hold period following presentation, were reinforced with illumination of the magazine light and delivery of a small food reward. Following training, premature responding was probed with a long-ITI session three times; once at baseline, once following a saline injection and once following an injection of a low dose of amphetamine (AMPH; 0.025 mg/kg). We predicted that if premature responding was related to impulsivity (as in rodents) it would be reduced following the AMPH injection. Results confirmed that zebrafish could learn to perform a complex operant task similar to tasks developed for rodents which are used to probe sustained attention and impulsivity, but the results from the AMPH trials were inconclusive. This study provides the foundations for development and further validation of this species as a model for some aspects of human attentional and impulse control disorders, such as substance abuse disorder.

Descending Systems Translate Transient Cortical Commands into a Sustained Muscle Activation Signal

Controlling motor actions requires online adjustments of time-varying parameters. Although numerous studies have attempted to identify the parameters coded in different motor sites, the relationships between the temporal profile of neuronal responses and the dynamics of motor behavior remain poorly understood in particular because motor parameters such as force and movement direction often change over time. We studied time-dependent coding of cortical and spinal neurons in primates performing an isometric wrist task with an active hold period, which made it possible to segregate motor behavior into its phasic and sustained components. Here, we show that cortical neurons transiently code motor-related parameters when actively acquiring a goal, whereas spinal interneurons provide persistent information regarding maintained torque level and posture. Moreover, motor cortical neurons differed substantially from spinal neurons with regard to the evolvement of parameter-specific coding over the course of a trial. These results suggest that the motor cortex and spinal cord use different control policies: Cortical neurons produce transient motor commands governing ensuing actions, whereas spinal neurons exhibit sustained coding of ongoing motor states. Hence, motor structures downstream to M1 need to integrate cortical commands to produce state-dependent spinal firing.

In vivo evaluation of a MR-guided 980nm laser interstitial thermal therapy system for ablations in porcine liver

To evaluate the use of a 980-nm diode laser for magnetic resonance-guided laser interstitial thermal therapy (MR-guided LITT) ablations in liver tissue in an in vivo porcine model. MR-guided guided LITT was performed on nine juvenile pigs placed under general anesthesia. Target ablation sites were selected in the left and right lobes of the liver. Laser applicators were placed in the liver using intermittent MR guidance. Up to four separate ablations were performed in each animal using a 15 or 30 W laser generator using one or two applicators. During the ablations, continuous MR-based temperature mapping (MR-thermal mapping), using a proton resonance frequency technique, was performed to monitor the size of the ablation in real-time. Extent of thermal tissue damage was continuously estimated based on Arrhenius model. Two-minute ablations were performed at each site. MR-thermal mapping of ablations within the posteroinferior liver were accomplished with continuous breathing at low tidal volume. In the mid right lobe of the liver, due to motion artefacts, MR-thermometry was performed intermittently during breath hold periods. In the left lobe of the liver, ablations were performed with ventilation using positive end expiratory pressure (PEEP) of 10 cm of water. Upon completion, MR imaging with gadolinium contrast was performed to assess the extent of treatment. Thermal lesions were subsequently measured using both, MR-thermal dose and MR gadolinium images, for comparison. Following the animal euthanasia, the liver was harvested and subjected to formalin fixation and paraffin embedding for histological examination. Between one and four focal liver ablations (total 24 ablations) were successfully performed in nine animals with either a 15 or 30 W laser generator. For the 15-W laser generator, the average single applicator ablation size was (2.0 ± 0.5) × (2.6 ± 0.4) cm(2) , as measured by magnetic resonance (MR) thermometry, or (1.7 ± 0.4) × (2.2 ± 0.6) cm(2) , as measured with gadolinium contrast, with the difference being not statistically significant. For the 30-W laser generator, the average single applicator ablation size was (2.4 ± 0.3) × (3.3 ± 0.5) cm(2) by MR thermometry and (2.1 ± 0.4) × (2.9 ± 0.3) cm(2) by gadolinium enhancement, with no statistically significant difference. Simultaneously activating two applicators with the 15 W generator demonstrated ablation sizes of (3.7 ± 0.9) × (3.2 ± 0.1) cm(2) using MR thermometry and (2.3 ± 0.6) × (2.4 ± 0.3) cm(2) with gadolinium contrast, while using two applicators in the 30-W laser generator, yielded (4.5 ± 0.6) × (3.9 ± 0.2) cm(2) using MR thermometry and (4.4 ± 1.1) × (3.6 ± 0.5) cm(2) with gadolinium contrast enhancement. In our experience, we found that liver ablations performed with a MR-guided 980-nm diode LITT system through the saline cooled catheter applicator could be performed throughout the liver. Additionally, liver ablations were safe and produced a clinically applicable ablation zone. These results suggest the 980-nm diode laser MR-guided LITT system could be effective in treatments of hepatic tumors.

Design and development of a self-supported polymer electrolyte fuel cell system with anodic dead-end operation

Design and operational details for a self-supported polymer electrolyte fuel cell (PEFC) system with anodic dead-end fuel supply and internally humidified cathodic oxidant flow are described. During the PEFC operation, nitrogen and water back diffuse across the Nafion membrane from the cathode to the anode and accumulate in the anode flow channels affecting stack performance. The accumulated inert species are flushed from the stack by purging the fuel cell stack with a timer-activated purge valve to address the aforesaid problem. To minimize the system complexity, stack is designed in such a way that all the inert species accumulate in only one cell called the purge cell. A pulsed purge sequence comprises opening the valve for purge duration followed by purge-valve closing for the hold period and repeating the sequence in cycles. Since self-humidification is inadequate to keep the membrane wet, the anodic dead-end-operated PEFC stack with composite membrane comprising perflourosulphonic acid (Nafion) and silica is employed for keeping the membrane humidified even while operating the stack with dry hydrogen and internally humidified air.

Plastic deformation in multilayered thin films during indentation unloading: a modeling analysis incorporating viscoplastic response

The indentation behavior of metal/ceramic multilayered thin films is studied numerically using the finite element method. The axisymmetric model consists of alternating aluminum (Al) and silicon carbide (SiC) layers above a silicon (Si) substrate, with the rate-dependent viscoplastic response of Al accounted for. Different unloading rates, with and without a hold period at the peak indentation load, are considered. Attention is devoted to plastic deformation in the Al layers during the unloading phase of indentation. It is found that the hold period stabilizes the deformation so the unloading response becomes insensitive to the unloading rate. However, significant parts of the Al layers under indentation still experience plastic deformation during unloading, due to the mechanical constraint imposed by the hard SiC layers. Consequently unloading is no longer an elastic event in this heterogeneous material system. The unloading induced plasticity is further analyzed by tracking the stress and strain histories inside the material throughout the course of indentation.

Wavelet transformation based multi-time scale crystal plasticity FEM for cyclic deformation in titanium alloys under dwell load

Titanium alloys are used in high end applications due to their desirable properties. However under dwell fatigue loading, these alloys exhibit premature crack initiation and failure when compared to normal cyclic loading. This early crack initiation can be attributed to the inhomogenous plastic deformation occurring in these alloys during the hold period of dwell cyclic loading and is strongly influenced by the underlying micro-structure. This necessitates the consideration of micro-structural features and their influence on the response, for accurate life prediction in these alloys. Crystal plasticity based finite element simulations capture the micro-structural influence on the response and can prove effective for accurate prediction of crack initiation in these alloys. However 70–80% of total life in Ti-alloys based components is spent in crack initiation and this may involve crystal plasticity based finite element simulations for large number of cycles. Such simulations using conventional single scale time integration schemes can be computationally intractable. A multi-time scale method using wavelet based decomposition is thus developed in this work for accurate and computationally efficient dwell fatigue simulations of these alloys for large number of cycles.

Evaluation of the properties of components prepared and stored after holding of whole blood units for 8 and 24 hours at ambient temperature

The capability of holding whole blood (WB) units at ambient temperature, overnight, should help in platelet (PLT) concentrate preparation logistics. We summarize the results of a study conducted in the early 1990s that compared, in particular, PLT and red blood cell (RBC) in vivo viability properties following storage after preparation after 8- and 24-hour WB hold periods. Individuals donated units of WB on two occasions. Centrifugation at 20 to 24°C to separate PLTs and additive system RBC placement at 1 to 6°C was completed 8 hours after phlebotomy or after 24 hours in randomized order. Components were not leukoreduced. Studies including in vitro biochemical and hematologic analyses and autologous in vivo RBC and PLT evaluations were conducted at two sites. RBC 24-hour in vivo (mean ± SD) recoveries (single-label approach), after 35 days of storage, were 79.2 ± 4.3 and 79.4 ± 3.9% (n = 9; p > 0.05), with WB holding periods of 8 and 24 hours, respectively. With 42 days of storage, recovery after a 24-hour hold was slightly less than with an 8-hour hold (72.9 ± 6.5% vs. 76.0 ± 5.4%; n = 17; p < 0.05). RBC 2,3-diphosphoglycerate acid levels were substantially less after the 24-hour hold compared to after the 8-hour hold (n = 18; p < 0.05). PLT recovery after 5 days of storage with 8- and 24-hour hold periods were similar, 51.1 ± 14.9 and 50.6 ± 17.7%, respectively (n = 18; p > 0.05). The PLT survival variable and in vitro properties reflecting storage quality also showed no significant difference. RBC and PLT in vivo variables, and most in vitro variables, were not significantly different after storage with WB holding times of 8 and 24 hours except for a slight diminution of RBC recovery with the 24-hour hold after 42 days of storage.

Condition monitoring of exchange towers of heavy water plant during hydrotesting by acoustic emission technique

This paper presents results of acoustic emission (AE) testing carried out during hydrotesting of cold and hot exchange towers of a heavy water plant. Point type defect indications were observed in certain locations during ultrasonic inspection of the exchange towers. Acoustic emission monitoring during hydrotesting was carried out to determine the nature of these defects, ie whether these defects are growing or not. The cold and the hot towers were pressurised to a maximum pressure of 26.5 kg/cm 2 and 27.8 kg/cm 2 , respectively, with holds at different pressures. Acoustic emissions were picked up using sensors placed selectively at areas of interest where ultrasonic testing showed defect-like indications and at some critical areas. AE events were observed during the first pressurisation of both the towers and were attributed to micro yielding. No significant acoustic emissions were detected from either tower during the hold periods or the repressurisation. This confirmed that there is no extraneous noise and there are no severe defects in the regions monitored by the sensor arrays and nearby regions monitored by individual sensors. The combined results from AE and ultrasonic techniques confirmed the structural integrity of different regions of the towers and supported returning the towers to service for continued operation.

OS0705 ガスタービン動翼用Ni基DS超合金の多軸熱疲労寿命(OS7-1 高温・寿命,OS-7 多軸応力下における疲労損傷および疲労き裂進展1)

In this study, biaxial thermo-mechanical fatigue (TMF) tests simulating actual blade loading condition have been carried out using a directionally solidified super alloy which is typically used in 1300C class gas turbine blades. Fatigue lives under biaxial TMF life could not be correlated with Mises equivalent strain range. An equivalent shear strain range for the Ni based DS superalloy was derived based on Γ-plane theory, and the biaxial TMF life was well correlated with the equivalent shear strain range. It was found that fatigue life was reduced to 1/5 by introducing 6 minutes strain hold time at the maximum temperature. This life reduction may be occurred due to increasing of tensile stress during strain hold period.

Load Testing and Interpretation of Instrumented Augered Cast-in-Place Piles

AbstractGiven that piles are composed of different materials and installed using a variety of methods, ASTM D 1143/D 1143M-07 Standard Test Methods for Deep Foundations Under Static Axial Compression is justifiably general so that it has as many applications as reasonably possible. There are aspects of the test setup, the test procedures, and data interpretation for instrumented piles (some of which are specific to augered cast-in-place piles) that are either not discussed in detail in this ASTM standard or are not addressed at all. Specifically, the use of variable time hold times can obscure the shape of the conventional load-deflection curve, as well as, influence the interpretation of the ultimate pile capacity. Unload-reload cycles induce additional non-uniform internal axial loads within the pile which complicate interpretation of the strain gage data and increase the potential for errors. Attempts to maintain a constant top load during the hold period can lead to operational difficulties in taking ...

The Influence of Slip Character on the Creep and Fatigue Fracture of an α Ti-Al Alloy

The mechanical performance of engineering titanium alloys has long been known to be sensitive to the nature of applied load waveform. Sustained load hold periods imposed during the fatigue loading of two-phase α + β alloys are detrimental to material performance. A number of factors, particularly material texture, phase morphologies, and slip behavior, are thought to affect the dwell fatigue responses of these materials. This study examines the roles of slip character and applied load waveform on an alloy with a simpler microstructure than the two-phase alloys studied previously. It is found that planar slip has significant influence over the dwell, fatigue, and fracture behaviors of equiaxed-grained, single-phase α Ti-7 wt pct Al.

Structural integrity assessment of weldments at high temperature: A proposed new approach for R5

The R5 procedures provide a comprehensive methodology for the assessment of structures operating within the high temperature creep regime. This includes advice on the modifications required to the basic procedure to account for weldments in creep–fatigue crack initiation assessments. The current approach is based on the use of a Fatigue Strength Reduction Factor (FSRF) which has a value according to the particular class of welded joint. The FSRF affects the calculation of creep and fatigue damage. However, the current approach can be excessively conservative for as-welded weldments which are the main type of weldments in plant. The new approach separates the FSRF into two components which are as follows: • the geometric strain enhancement due to the material mismatch effect between parent material and weld metal and the overall weldment geometry (if applicable), which is called the Weld Strain Enhancement Factor (WSEF), and; • the fatigue endurance 1 1 The term ‘endurance’ refers to the number of cycles to crack initiation. reduction effect due to the presence of small imperfections (e.g. inclusions, porosity, etc.) in the weldment constituent materials, which is called the Weld Endurance Reduction (WER). The WSEF is used to determine the stress at the start of a dwell or hold period and, because it has a lower value than the FSRF (due to the removal of the WER), results in less conservative calculations of creep damage compared to the current procedure, which uses the full FSRF. For fatigue damage predictions, the modified route is broadly similar to the current route, since the combination of the WER and the WSEF in the modified route corresponds to the FSRF used in the current route. This paper also includes some details of the validation analysis to demonstrate improved life predictions, plus sensitivity analyses examining the influence of salient material properties on the life predictions.

Pulmonary Targeting of Nanoparticle Drug Matrices

Nanoparticle drug matrices using lipids or liposomes, with diameters of 40-300 nm, have recently been developed to encapsulate drugs like Insulin, Budesonide, and Rifampicin for pulmonary delivery raising interest in their regional lung deposition. Lung deposition has so far been modeled using a one-dimensional transport equation, with or without moving airway boundaries, and a lumped deposition term for particle diffusion, sedimentation, and impaction. Here, a two-dimensional transport model has been developed with an explicit treatment of radial diffusion, the primary mechanism for nanoparticle deposition. Regional lung deposition was calculated using Weibel's whole lung model geometry during normal breathing and medical inhalation cycles. Model predictions agree well with measurements of total and pulmonary lung deposition for particles of 10 nm to 10 μm, with earlier models incorporating moving boundaries and aerosol dynamics, and with the reported regional lung deposition of inhaled dry powder insulin. To simulate medical inhalation, the model was run with inhalation times from 2-6 sec and breath hold from 0-10 sec. A high and relatively invariant pulmonary deposition fraction between 70 and 95% was predicted for a broad nanoparticle size range (50-200 nm) for inhalation cycles with breathing rate between 500 and 2000 cm(3) sec(-1) and breath hold of 5-10 sec. Thus, nanoparticles may be able to deliver consistent lung doses, over modest breath hold periods, even with intrapatient variability in breathing rate. A linearized nomogram was provided as a heuristic for design of nanoparticle drug matrices to target the pulmonary lung.