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Curves and tabular data present the results of strength tests made during and after 2 1/2 years of aging on rivets and rivet wire of 3/16-inch nominal diameter. The specimens were of aluminum alloy: 24s, 17s, and a17s of the duralumin type and 53s of the magnesium-silicide type.
A method is developed whereby the fundamental mechanisms are investigated by which processing, heat treatment, and chemical composition control the properties of alloys at high temperatures. The method used metallographic examination -- both optical and electronic --studies of x-ray diffraction-line widths, intensities, and lattice parameters, and hardness surveys to evaluate fundamental structural conditions. Mechanical properties at high temperatures are then measured and correlated with these measured structural conditions. In accordance with this method, a study was made of the fundamental mechanism by which aging controlled the short-time creep and rupture properties of solution-treated low-carbon n-155 alloy at 1200 degrees F.
Rats subjected to centrifugation show a marked decrease in body temperature relating to gravity level. Several studies have indicated, that an initial response to centrifugation is followed by acclimation. To test for differences between young (Y; 2 months) and mature (M; 8 months) rats in their response in temperature, both groups were exposed to hypergravity induced by centrifugation. Thirty-six male rats were divided into four groups according to age and G-load (control (1.0G-Y and 1.0G-M), 2.0G-Y or 2.0G-M) and were housed in pairs in standard vivarium cages. During the 7-day period of centrifugation, temperature was measured every five minutes by surgically implanted telemeters. Body mass was measured daily. We found that initial body temperature in 2.0G-M was less than that of 2.0G-Y. Both hypergravity groups (2.0G-Y and 2.0G-M) showed a decrease in temperature at the onset of centrifugation, and the change in temperature (Delta = 0.5 C) remained the same between the groups. Significant differences persisted with 2.0G-Y recovering to control values in four days and 2.0G-M recovering in five days. These results indicate that the mature animals have a similar response as the younger animals, but take longer to acclimate.
Normative data are limited on autonomic function tests, especially beyond age 60 years. We therefore evaluated these tests in a total of 557 normal subjects evenly distributed by age and gender from 10 to 83 years. Heart rate (HR) response to deep breathing fell with increasing age. Valsalva ratio varied with both age and gender. QSART (quantitative sudomotor axon-reflex test) volume was consistently greater in men (approximately double) and progressively declined with age for all three lower extremity sites but not the forearm site. Orthostatic blood pressure reduction was greater with increasing age. HR at rest was significantly higher in women, and the increment with head-up tilt fell with increasing age. For no tests did we find a regression to zero, and some tests seem to level off with increasing age, indicating that diagnosis of autonomic failure was possible to over 80 years of age.
An experimental program is underway to measure the impact and high strain rate properties of triaxial braided composite materials and to quantify any degradation in properties as a result of thermal and hygroscopic aging typically encountered during service. Impact tests are being conducted on flat panels using a projectile designed to induce high rate deformation similar to that experienced in a jet engine fan case during a fan blade-out event. The tests are being conducted on as-fabricated panels and panels subjected to various numbers of aging cycles. High strain rate properties are being measured using a unique Hopkinson bar apparatus that has a larger diameter than conventional Hopkinson bars. This larger diameter is needed to measure representative material properties because of the large unit cell size of the materials examined in this work. In this paper the experimental techniques used for impact and high strain rate testing are described and some preliminary results are presented for both as-fabricated and aged composites.
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The effects of various levels of gravity force (obtained by rotation in clinostats or by centrifugation) and the near-weightlessness condition aboard orbiting spacecraft on the fertilization, embryonic development, maturation, and aging of animals are examined. Results obtained from the American and Soviet spaceborne biology experiments are presented including those on mammals, amphibians, fish, birds, invertebrates, and protozoa. Theoretical issues related to the effect of gravity on various physiological systems are discused together with the future research goals concerning human life in space. It is noted that life in space (after adaptation to near-weightlessness) might be significantly prolonged due to a reduction in metabolic rate and a concomitant decrease in oxygen radical reactions.
Pentaerythritol tetranitrate (PETN) is one of the most commonly used explosives for both military and mining applications. PETN is used in EBW (exploding bridge wire) and EFI (exploding foil initiator) detonator devices. Due the widespread usage of PETN, studies focusing on how the explosive changes with age, primarily its function in detonators has received particular interest. Aging studies have identified several factors that affect PETN detonator function over time, most notably the specific surface area of the explosive powder. Though small-scale studies have been performed on specific detonator systems with isolated batches of material, what is missing is a large statistically-significant study focusing on PETN aging characteristics - such as powder coarsening - and their influence on detonator performance. Herein we report the first large statistically viable PETN aging study focusing on four batches of PETN powder from the same stock of PETN using two stabilizers, polysaccharide and TriPEON. PETN was aged both as a free-flowing powder as well as in modified EBW RP-2 detonators, for one month at 75 °C. The PETN powder has been analyzed chemically using Fisher specific surface area analysis, SEM imaging and light scattering particle size analysis. Additionally the detonators were tested for performance through voltage-sweep threshold testing and function time measurements. Findings from the study indicate that aging at 75 °C for one month significantly changes the specific surface area and particle size of unstabilized PETN, leading to increases in detonator function time, but not detonator threshold values. Powders stabilized with TriPEON displayed less significant increases in function time, while powder stabilized with polysaccharide exhibited no aging effects, despite the high temperature aging.
The research consisted of two major parts, first modeling and simulation of the combined effects of aging and damage on polymer composites and secondly an experimental phase examining composite response at elevated temperatures, again activating both aging and damage. For the simulation, a damage model for polymeric composite laminates operating at elevated temperatures was developed. Viscoelastic behavior of the material is accounted for via the correspondence principle and a variational approach is adopted to compute the temporal stresses within the laminate. Also, the effect of physical aging on ply level stress and on overall laminate behavior is included. An important feature of the model is that damage evolution predictions for viscoelastic laminates can be made. This allows us to track the mechanical response of the laminate up to large load levels though within the confines of linear viscoelastic constitutive behavior. An experimental investigation of microcracking and physical aging effects in polymer matrix composites was also pursued. The goal of the study was to assess the impact of aging on damage accumulation, in ten-ns of microcracking, and the impact of damage on aging and viscoelastic behavior. The testing was performed both at room and elevated temperatures on [+/- 45/903](sub s) and [02/903](sub s) laminates, both containing a set of 90 deg plies centrally located to facilitate investigation of microcracking. Edge replication and X-ray-radiography were utilized to quantify damage. Sequenced creep tests were performed to characterize viscoelastic and aging parameters. Results indicate that while the aging times studied have limited ]Influence on damage evolution, elevated temperature and viscoelastic effects have a profound effect on the damage mode seen. Some results are counterintuitive, including the lower strain to failure for elevated temperature tests and the catastrophic failure mode observed for the [+/- 45/9O3](sub s), specimens. The fracture toughness for transverse cracks increases with increasing temperature for both systems: transverse cracking was completely absent prior to failure in [+/- 45/903](sub s), and was suppressed for [02/903](sub s). No significant effect of damage on aging or viscoelastic parameters was observed.
To harness the potential of laser powder bed fusion (LPBF) 316H stainless steel (SS) for use in advanced nuclear reactors, extensive research efforts are needed to develop optimal laser processing parameters and appropriate heat treatments, taking into account various manufacturing platforms and locations. Furthermore, it is crucial to assess the material properties in environments relevant to reactor operating conditions. In collaboration with Oak Ridge National Laboratory (ORNL) and Los Alamos National Laboratory (LANL), Argonne National Laboratory (ANL) is dedicated to gaining insights into how the manufacturing process and post-build treatments impact the performance of LPBF 316H SS. This report provides an overview of ANL's research findings for FY23, focusing on LPBF 316H SS produced using a Renishaw AM400 laser system. Specifically, our research has concentrated on three key areas: 1) Optimum laser processing parameters: Leveraging the high-throughput printing technology, we systematically varied the laser power, exposure time and point distance within the same build. By measuring the as-printed porosity, we identified an optimum printing parameter window that produced materials with near-complete density; 2) Post-built treatment development: Materials printed with the optimum laser parameters underwent treatments including stress relief, solution annealing, and hot isostatic pressing. Subsequently, we fabricated tension, creep, and fatigue specimens from materials subjected to these different conditions. Over the next year, a series of scoping tests will be conducted to facilitate the selection of the most suitable post-build treatment condition; 3) Thermal aging effects on microstructure and properties: thermal aging at 550°C, 650°C and 750°C was conducted on LPBF 316H SS specimens up to 2500 h. Microstructural characterization was performed with electron microscopy, and the evolution of the dislocation cell structures and secondary phases was studied. Microhardness tests and tension tests were conducted to quantify changes in mechanical properties. The results revealed that the aged LPBF 316H SS exhibited a high density of Cr-rich and Mo-rich fine precipitates within grains due to the presence of a high density of dislocations and the globally distributed dislocation cell structures, which served as heterogeneous nucleation sites for secondary phases. Along grain boundaries, a Mo-Cr-rich phase, observed in 750°C-aged conditions, displayed significant thermal coarsening. Throughout the aging process, various mechanisms, including stress relaxation, dislocation cell structure recovery, solution hardening, and precipitation hardening, competed to influence materials strength. These results contribute towards establishing the technical basis for qualifying LPBF 316H SS for advanced nuclear reactor applications.
The HSCT plane, envisioned to have a lifetime of over 60,000 flight hours and to travel at speeds in excess of Mach 2, is the source of intensive study at NASA. In particular, polymer matrix composites are being strongly considered for use in primary and secondary structures due to their high strength to weight ratio and the options of property tailoring. However, an added difficulty in the use of polymer based materials is that their properties change significantly over time, especially at the elevated temperatures that will be experienced during flight, and prediction of properties based on irregular thermal and mechanical loading is extremely difficult. This study focused on one aspect of long-term polymer composite behavior: physical aging. When a polymer is cooled to below its glass transition temperature, the material is not in thermodynamic equilibrium and the free volume and enthalpy evolve over time to approach their equilibrium values. During this time, the mechanical properties change significantly and this change is termed physical aging. This work begins with a review of the concepts of physical aging on a pure polymer system. The effective time theory, which can be used to predict long term behavior based on short term data, is mathematically formalized. The effects of aging to equilibrium are proven and discussed. The theory developed for polymers is then applied first to a unidirectional composite, then to a general laminate. Comparison to experimental data is excellent. It is shown that the effects of aging on the long-term properties of composites can be counter-intuitive, stressing the importance of the development and use of a predictive theory to analyze structures.
This study aimed to develop a microstructure-based mechanistic approach to address the long-term thermal aging effect on yield stress and ultimate tensile strength and to provide a physical basis for developing thermal aging factors for G91 for a design life of 60 years. Several heats of G91 steel were examined. Controlled aging experiments were conducted on two heats at temperatures of 550, 600, and 650 °C for times up to ~64,000 h. Specimens were also taken from archived creep-tested specimens of G91 and from a tube removed from the Kingston coal-fired power plant to obtain data that cover a wide range of temperatures and for aging times up to 155,000 h. Thermal aging caused significant subgrain recovery, coarsening of M 23 C 6 carbides at subgrain boundaries and MX carbonitrides within subgrains. The intermetallic Laves phase forms during aging and grows rapidly. The growth rate of the subgrain width and MX mean size during thermal aging were described by kinetic models. Thermal aging results in the reductions in the yield stress and the ultimate tensile strength of G91. The effects of thermal aging on the reductions in yield stress and ultimate tensile strength were well described by the microstructure-strength model that considers three superimposed strengthening mechanisms, namely, sub-boundary strengthening, MX precipitation hardening, and Mo solid solution strengthening. Furthermore, the model was independently validated by the ASME Code values and is being used by the ASME to develop the aging-induced strength reduction factors for G91 steel for a design life of 60 years.
The reprocessing of used nuclear fuel would release volatile radionuclides into the off-gas streams of a processing plant, including ¹²⁹I. The dissolver off-gas and more dilute vessel off-gas streams (VOG) must both be targeted when mitigating ¹²⁹I environmental release because each contains some amount of iodine. Iodine-129 will likely be found as elemental iodine (I₂) and methyl iodide (CH₃I) in these off-gas streams. Reduced silver-exchanged mordenite (AgZ or Ag⁰Z) has been investigated as a potential sorbent for iodine abatement and is studied here under prototypic VOG conditions. Because of the relatively low iodine abundance and high flow rates of the VOG, total iodine concentrations are expected to be in the parts per billion range. Thus, VOG experiments need to run for extended durations at low concentrations to reach sorbent saturation. Because the sorbent will be exposed to oxidizing gas streams for extended periods of time, aging effects and sorbent degradation need to be considered when designing a sorbent-based abatement system. Three sets of experiments were performed with the aim of determining how the adsorption of iodine by AgZ is affected by differing test durations and gas compositions. The first tested the capacity of sorbent aged for 8 months under a humid air stream. The second tested differences in sorbent capacity and mass transfer zone (MTZ) length during high-concentration (1200 ppb v ) CH₃I loading in a humid nitrogen gas (N₂) stream and a humid air gas stream over 28 days. The third tested sorbent capacity and MTZ length during low concentration (< 200 ppb v ) CH₃I and I₂ loading in a humid air stream over 9 months. The results of these tests suggest that AgZ capacity drops by ~50% after 1 month of aging, by ~60% after 2 months of aging, and then does not continue to decrease significantly at up to 8 months of aging. One-month aging tests that compared N₂ and air as the gas stream diluent resulted in similar maximum loading capacities and overall loading curves, indicating that the effects of aging cannot be mitigated by avoiding air as the balance gas. The 9-month extended VOG tests did not result in clear sorbent saturation at the inlet, but it can be inferred using an assumption of a maximum capacity of 45 mg I/g AgZ. Applying this assumption, then the MTZ of CH₃I is 12.8 cm, and the MTZ of I₂ is 12.4 cm. These results are similar to previous tests. Comparisons to tests completed at Idaho National Laboratory suggest that the CH₃I MTZ may be dependent on concentration. Future work should re-evaluate the design of the VOG iodine capture system with this updated data and should seek to understand fundamental characteristics of CH₃I adsorption by AgZ, such as the effect of concentration, gas velocity, and gas composition.
Quantifying aging effects in lithium-ion cells with chemistries that have a flat open circuit potential is challenging. We implement a physics-based electrochemical model to track changes in the electrochemical impedance response of lithium titanate-based cells. Frequency domain equations of a pseudo two-dimensional model are made dimensionless, and the corresponding non-dimensional parameters are estimated using a Levenberg-Marquardt routine. The model weighs the relative contributions of changes in diffusion, ionic conduction within the electrolyte phase against solid phase electronic conduction towards cell aging. Solid-phase diffusion, charge transfer resistance and double layer capacitance at the solid-liquid interface are accounted for in the particle impedance. The estimation routine tracks dimensionless parameters using accelerated cycling data from full cells over 1000 cycles. The model can be deployed within a short time for state estimation using physics-based models without requiring prior knowledge of the battery chemistry, format, or capacity.
Illite and Illite-Smectite clays are reportedly the Caney Shale's most prevalent clay minerals. The swelling and fines migration of clays may occur when water-based fluids contact the clay minerals. This may result in the reduction of pore space and permeability, and wettability alteration. Therefore, we quantified the swelling potentials, fines migration and wettability alteration of Illite and Illite-Smectite clays upon exposure to model brines and a produced water, and a model oil and a crude oil. We measured density, viscosity, pH, TDS, and interfacial tension as they are important in multiphase flow and displacement characteristics. Geomaterial microfluidics is recently being used to study physicochemical interactions of solid-fluid systems. It facilitates visualizing the surface behavior upon exposure to various fluids. This study includes preparation and characterization of Illite-Smectite clay-coated glass capillary tubes. Illite and Illite-Smectite clay-coated geomaterial microfluidic surfaces were prepared to investigate the effects of first contact fluid, brine salinity, and aging on wettability. In this work, advancing and receding contact angles of model brine-air, model oil-air, produced water-air, crude oil-air, model brine-model oil systems, and produced water-crude oil systems have been measured in the untreated, and clay-coated microfluidic channels of 1000 µm width and 50 µm depth. The aging effect was studied by retaining the non-aqueous and aqueous solutions in the corresponding microfluidic channels for approximately 24 h in the case of channels first contacted by aqueous and non-aqueous solutions, respectively. The advancing and receding contact angles of Caney shale-crude oil-produced water systems were also measured. The experimental findings indicate the swelling potential, fines migration, and wettability alteration of Illite and Illite-Smectite clays. The results signify the influence of first contact fluid, brine salinity, and aging on wettability of the untreated and clay-coated microfluidic surfaces. The experiments also demonstrate the wetting nature of the Caney shale samples from reservoir and non-reservoir zones.
Water in deep aquifers in arid regions is often considered to be "fossil" when modern recharge rates are negligible relative to the reservoir capacity. Over the past five decades, the Nubian Sandstone Aquifer (NSA) in the arid region of the Sinai Peninsula (Egypt) and the Negev Desert (Israel) has been considered to contain fossil water based on 14 C dating, which revealed 14 C ages of about 30 kyr over most of the aquifer. However, this relatively homogeneous age distribution contradicts the expected increase in groundwater age in the direction of decreasing piezometric head along the flow trajectories. Here, dating results with the longer-lived 81 Kr radioisotope (t 1/2 = 229 ± 11 kyr) are presented, highlighting a wide age range of 40 kyr to 630 kyr in the confined sections of the aquifer, all with very low 14 C activity (<1 pmC). Elevated 81Kr and 14 C activities were only observed within or close to the system's recharge areas. These findings support a new perception of groundwater replenishment during different epochs from the early mid- Pleistocene to the Holocene. By tracking the downstream age evolution, rejuvenation was identified in places where the confinement had been breached. At other locations, the existence of an older groundwater body contributing to the aquifer was detected by means of strongly depleted 81 Kr activity. High spatial heterogeneity in groundwater ages close to the discharge zone of the system is attributed to pronounced age stratification with depth. Calculated ages in the more isolated sections of the system were used to assess regional flow velocity, hydraulic conductivity, and their agreement with present recharge rates. We conclude that regional aquifers in which low 14 C activity suggests homogeneous ancient groundwater age should be reevaluated with 81Kr. With an effective age range beyond one million years, this may enable the restoration of recharge history and provide crucial information for the management of groundwater resources.
Small amounts of high-capacity silicon-based materials are already used in the anode of commercial Li-ion batteries, helping increase their energy density. Despite their remarkable storage capability, silicon continu-ously reacts with the electrolyte, accelerating time-dependent cell performance fade. Nevertheless, very limited information is available on the specific consequences of this reactivity for the calendar aging of Li-ion cells. Here, we analyze aging effects on 450 mAh pouch cells containing 15 wt% of Si (and 73 wt% graphite) after storage at 21 °C for four years. We show that severe losses of Si capacity occurred due to particle isolation when cells were stored at high states of charge (SOC), but not when cells were fully discharged prior to storage. Impedance rise was also significantly higher when cells were kept at high SOCs and was mostly due to phenomena taking place at the cathode; the continuous electrolyte reduction at the anode did not lead to a major increase in bulk electrode resistance. A series of post-test characterization provided additional information on the effects of time and SOC on the calendar aging of Si-containing cells. In conclusion, our study highlights the many challenges posed by Si during calendar aging and can inform future studies in the field.