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DOE OSTI2013

Geologic CO2 Input Into Groundwater and the Atmosphere, Soda Springs, ID, USA

A set of CO2 flux, geochemical, and hydrologic measurement techniques was used to characterize the source of and quantify gaseous and dissolved CO2 discharges from the area of Soda Springs, southeastern Idaho. An eddy covariance system was deployed for approximately one month near a bubbling spring and measured net CO2 fluxes from - 74 to 1147 g m- 2 d- 1. An inversion of measured eddy covariance CO2 fluxes and corresponding modeled source weight functions mapped the surface CO2 flux distribution within and quantified CO2 emission rate (24.9 t d- 1) from a 0.05 km2 area surrounding the spring. Soil CO2 fluxes (< 1 to 52,178 g m- 2 d- 1) were measured within a 0.05 km2 area of diffuse degassing using the accumulation chamber method. The estimated CO2 emission rate from this area was 49 t d- 1. A carbon mass balance approach was used to estimate dissolved CO2 discharges from contributing sources at nine springs and the Soda Springs geyser. Total dissolved inorganic carbon (as CO2) discharge for all sampled groundwater features was 57.1 t d- 1. Of this quantity, approximately 3% was derived from biogenic carbon dissolved in infiltrating groundwater, 35% was derived from carbonate mineral dissolution within the aquifer(s), and 62% was derived from deep source(s). Isotopic compositions of helium (1.74–2.37 Ra) and deeply derived carbon (d13C approximately 3‰) suggested contribution of volatiles from mantle and carbonate sources. Assuming that the deeply derived CO2 discharge estimated for sampled groundwater features (approximately 35 t d- 1) is representative of springs throughout the study area, the total rate of deeply derived CO2 input into the groundwater system within this area could be ~ 350 t d- 1, similar to CO2 emission rates from a number of quiescent volcanoes.

99 GENERAL AND MISCELLANEOUS↗

DOE OSTI2011

Experimental Studies on Dynamic Vibration Absorber using Shape Memory Alloy (NiTi) Springs

Shape memory alloy (SMA) springs have been used as actuators in many applications although their use in the vibration control area is very recent. Since shape memory alloys differ from conventional alloy materials in many ways, the traditional design approach for springs is not completely suitable for designing SMA springs. Some vibration control concepts utilizing unique characteristics of SMA's will be presented in this paper.A dynamic vibration absorber (DVA) using shape memory alloy (SMA) actuator is developed for attenuation of vibration in a cantilever beam. The design procedure of the DVA is presented. The system consists of a cantilever beam which is considered to generate the real-time vibration using shaker. A SMA spring is used with a mass attached to its end. The stiffness of the SMA spring is dynamically varied in such a way to attenuate the vibration. Both simulation and experimentation are carried out using PID controller. The experiments were carried out by interfacing the experimental setup with a computer using LabVIEW software, Data acquisition and control are implemented using a PCI data acquisition card. Standard PID controllers have been used to control the vibration of the beam. Experimental results are used to demonstrate the effectiveness of the controllers designed and the usefulness of the proposed test platform by exciting the structure at resonance. In experimental setup, an accelerometer is used to measure the vibration which is fed to computer and correspondingly the SMA spring is actuated to change its stiffness to control the vibration. The results obtained illustrate that the developed DVA using SMA actuator is very effective in reducing structural response and have great potential to be an active vibration control medium.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Observed and Simulated Spring and Summer Dryness in the United States: The Impact of the Pacific Sea Surface Temperature and Beyond

This study characterizes major modes of variability in the spring and summer U.S. dryness, as measured by the seasonal total number of dry (no-precipitation) days, and assesses the impact of the Pacific sea surface temperature. The most severe spring and summer dry conditions typically occur in the western United States. Maximum covariance analysis reveals that the Pacific Decadal Oscillation (PDO) is the primary driver of interannual variability in the U.S. dryness. El Niño–Southern Oscillation (ENSO) also contributes in part (especially during spring). Beyond the PDO and ENSO impact, interannual variations in spring dryness exhibit a meridional dipole structure, while variations during summer are related to a northwest-southeast (NW-SE) oriented dipole. The spring meridional dipole is associated with circulation anomalies resembling the West Pacific teleconnection pattern, while the summer NW-SE dipole is a downstream manifestation of a quasi-stationary wave train. A parallel analysis of Coupled Model Intercomparison Project's fifth phase models' historical simulations demonstrates that such models generally capture the relation between U.S. dryness and the PDO, albeit with varying degrees of accuracy. The models also show reasonable skill in simulating the residual meridional dipole in spring dryness variability but have difficulty representing the NW-SE oriented dipole occurring during summer. The model shortcomings isolated here largely arise from a misrepresentation of the corresponding large-scale circulation and moisture transport anomalies. These model biases suggest that great challenges exist in our ongoing pursuit of reliable projections of the U.S. hydroclimate variability.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2023

The Rate of Canopy Development Modulates the Link Between the Timing of Spring Leaf Emergence and Summer Moisture

Shifts in phenological timing have important implications for ecosystem processes, with spring leaf emergence as a dominant control of carbon, water, and energy cycling. Phenological events are predominantly determined by weather and climate, therefore dynamic in time and sensitive to climate feedbacks. Improving our understanding of how ecosystems respond to changes in phenological timing will enhance our ability to assess summer soil water availability, since the timing of spring leaf emergence may lead to soil moisture deficits later in the growing season. We leveraged data from five AmeriFlux towers in central and eastern United States to investigate the extent spring leaf emergence (i.e., start of spring, SoS ) influences rates at which forest canopies develop and how this impacts summer soil moisture ( θ JJA ) variability. Our results indicate that ecosystem processes, specifically gross primary production ( GPP ) and evapotranspiration ( ET ), exhibit compensatory responses to varying leaf emergence; with delayed spring-onset, the canopy developed more quickly, resulting in rapid GPP and ET increases, consistent across sites. Nonetheless, early SoS is a relatively good indicator for potential summer soil water deficits, particularly when it occurs together with meteorological conditions (i.e., lower-than-average precipitation, hot summer temperatures) that contribute to soil water deficits. When these meteorological conditions coincide with early SoS , θ JJA deficits are exacerbated. To the extent that these extreme conditions occur more frequently under future climate scenarios, the dynamics of spring phenology and hydroclimate may play an increasingly important role in portending the likelihood of summer water deficits, which are projected to become more severe.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2017

Weakening temperature control on the interannual variations of spring carbon uptake across northern lands

Ongoing spring warming allows the growing season to begin earlier, enhancing carbon uptake in northern ecosystems. We use 34 years of atmospheric CO 2 concentration measurements at Barrow, Alaska (BRW, 71° N) to show that the interannual relationship between spring temperature and carbon uptake has recently shifted. Here, we use two indicators: the spring zero-crossing date of atmospheric CO 2 (SZC) and the magnitude of CO 2 drawdown between May and June (SCC). The previously reported strong correlation between SZC, SCC and spring land temperature (ST) was found in the first 17 years of measurements, but disappeared in the last 17 years. As a result, the sensitivity of both SZC and SCC to warming decreased. Simulations with an atmospheric transport model coupled to a terrestrial ecosystem model suggest that the weakened interannual correlation of SZC and SCC with ST in the last 17 years is attributable to the declining temperature response of spring net primary productivity (NPP) rather than to changes in heterotrophic respiration or in atmospheric transport patterns. Reduced chilling during dormancy and emerging light limitation are possible mechanisms that may have contributed to the loss of NPP response to ST. These results thus challenge the ‘warmer spring–bigger sink’ mechanism.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2023

Increased photosynthesis during spring drought in energy-limited ecosystems

Abstract Drought is often thought to reduce ecosystem photosynthesis. However, theory suggests there is potential for increased photosynthesis during meteorological drought, especially in energy-limited ecosystems. Here, we examine the response of photosynthesis (gross primary productivity, GPP) to meteorological drought across the water-energy limitation spectrum. We find a consistent increase in eddy covariance GPP during spring drought in energy-limited ecosystems (83% of the energy-limited sites). Half of spring GPP sensitivity to precipitation was predicted solely from the wetness index (R 2 = 0.47, p < 0.001), with weaker relationships in summer and fall. Our results suggest GPP increases during spring drought for 55% of vegetated Northern Hemisphere lands ( >30° N). We then compare these results to terrestrial biosphere model outputs and remote sensing products. In contrast to trends detected in eddy covariance data, model mean GPP always declined under spring precipitation deficits after controlling for air temperature and light availability. While remote sensing products captured the observed negative spring GPP sensitivity in energy-limited ecosystems, terrestrial biosphere models proved insufficiently sensitive to spring precipitation deficits.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2014

An early look of comet C/2013 A1 (Siding Spring): Breathtaker or nightmare?

The dynamically new comet, C/2013 A1 (Siding Spring), is to make a close approach to Mars on 2014 October 19 at 18:30 UT at a distance of 40 ± 1 Martian radii. Such an extremely rare event offers a precious opportunity for the spacecrafts on Mars to closely study a dynamically new comet itself as well as the planet-comet interaction. Meanwhile, the high-speed meteoroids released from C/Siding Spring also pose a threat to physically damage the spacecrafts. Here we present our observations and modeling results of C/Siding Spring to characterize the comet and assess the risk posed to the spacecrafts on Mars. We find that the optical tail of C/Siding Spring is dominated by larger particles at the time of the observation. Synchrone simulation suggests that the comet was already active in late 2012 when it was more than 7 AU from the Sun. By parameterizing the dust activity with a semi-analytic model, we find that the ejection speed of C/Siding Spring is comparable to comets such as the target of the Rosetta mission, 67P/Churyumov-Gerasimenko. Under a nominal situation, the simulated dust cone will miss the planet by about 20 Martian radii. At the extreme ends of uncertainties, the simulated dust cone will engulf Mars, but the meteoric influx at Mars is still comparable to the nominal sporadic influx, seemly indicating that an intense and enduring meteoroid bombardment due to C/Siding Spring is unlikely. Further simulation also suggests that gravitational disruption of the dust tail may be significant enough to be observable at Earth.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

Large methane emission upon spring thaw from natural wetlands in the northern permafrost region

The permafrost carbon climate feedback is one of the major mechanisms in controlling the climate ecosystem interactions in northern high latitudes. Of this feedback, methane (CH4) emission from natural wetlands is critically important due to its high warming potential. The freeze thaw transition has been confirmed to play an important role in annual CH4 budget, yet the magnitude of this effect is uncertain. An intensive field campaign was carried out in the Sanjiang Plain, Northeast China to estimate the CH4 emission in the spring freeze thaw transition period. The observation concluded that a large CH4 source was caused by spring thaw; the maximum hourly emission rate was 48.6 g C m 2 h 1, more than three orders of the regularly observed CH4 emission rate in the growing season. In some sporadically observed 'hot spots', the spring thawing effect contributed to a large CH4 source of 31.3 10.1 g C m 2, which is approximately 80% of the previously calculated annual CH4 emission in the same study area. If our results are typical for natural wetlands in the Northern Hemisphere permafrost region, we estimate a global CH4 source strength of 0.5 1.0 Tg C (1 Tg =1012 g) caused by spring thaw in the Northern Hemisphere permafrost region in the year 2011. Combining with available satellite and flask data, a regional extrapolation reaches a temporal pattern of CH4 emission during 2003 2009 which is consistent with recently observed changes in atmospheric CH4 concentration in the high latitudes. This suggests that the CH4 emission upon spring thaw in the high latitudes might be enhanced by the projected climate warming. These findings indicate that the spring thawing effect is an important mechanism in the permafrost carbon climate feedback and needs to be incorporated in Earth system models.

Song, Changchun↗

DOE OSTI2019

Investigating the Performance of a Variable Stiffness Magnetic Spring for Resonant Ocean Power Generation

This paper presents a new type of variable stiffness magnetic spring which can have a highly linear translational force characteristic. The variable stiffness is achieved through the rotation of a central magnet. Both positive and negative spring constants can be created. Using an analytic-based field analysis modelling technique the operating principle and linearity characteristics of the adjustable magnetic spring are studied. The use of a magnetic spring with an adjustable negative spring constant could enable an ocean generator to continuously operate in a resonant state thereby greatly increasing its power generation capability. The presented variable stiffness spring could also be useful in other energy harvesting and robotic actuator applications.

16 TIDAL AND WAVE POWER↗

DOE OSTI2019

Contrasting spring and summer large-scale environments associated with mesoscale convective systems over the U.S. Great Plains

Mesoscale convective systems (MCSs) are frequently observed over the U.S. Great Plains during boreal spring and summer. Here, four types of synoptically-favorable environments for spring MCSs and two types of synoptically- favorable and unfavorable environments for summer MCSs are identified using self-organizing maps (SOM) with the inputs of observational data. During spring, frontal systems providing a lifting mechanism and an enhanced Great Plains low-level jet (GPLLJ) providing anomalous moisture are important features identified by SOM analysis as they create favorable dynamical and thermodynamic environments for MCS development. During summer, the composite MCS environment shows small positive convective available potential energy (CAPE) and convective inhibition (CIN) anomalies, which are in stark contrast with the large positive CAPE and negative CIN anomalies in spring. This contrast suggests that convection may occur even within weak dynamical and thermodynamic perturbations in summer so that MCSs may be inherently less predictable in summer. The two synoptically-favorable environments identified in summer have frontal characteristics and an enhanced GPLLJ, but both shift north compared to spring. The two synoptically-unfavorable environments feature enhanced upper-level ridges, but differ in the strength of the GPLLJ. In both seasons, MCS precipitation amount, area and rate are much larger in the frontal-related MCSs than non-frontal MCSs. A large-scale index constructed using the pattern correlation between the large-scale environment and the synoptically-favorable SOM types is found to be skillful for predicting MCS number, precipitation rate and area in spring, but its explanatory power decreases significantly in summer. The low predictability of summer MCSs deserves further investigation in the future.

Song, Fengfei↗

DOE OSTI2024

Tropical Interbasin Interaction as Effective Predictors of Late-Spring Precipitation Variability in the Southern Great Plains

Abstract The southern Great Plains experience fluctuating precipitation extremes that significantly impact agriculture and water management. Despite ongoing efforts to enhance forecast accuracy, the underlying causes of these climatic phenomena remain inadequately understood. This study elucidates the relative influence of the tropical Pacific and Atlantic basins on April–May–June precipitation variability in this region. Our partial ocean assimilation experiments using the Community Earth System Model unveil the prominent role of interbasin interaction, with the Pacific and Atlantic contributing approximately 70% and 30%, respectively, to these interbasin contrasts. Our statistical analyses suggest that these tropical interbasin contrasts could serve as a more reliable indicator for late-spring precipitation anomalies than El Niño–Southern Oscillation. The conclusions are reinforced by analyses of seven climate forecasting systems within the North American Multi-Model Ensemble, offering an optimistic outlook for enhancing real-time forecasting of late-spring precipitation in the southern plains. However, the current predictive skills of the interbasin contrasts across the prediction systems are hindered by the lower predictability of the tropical Atlantic Ocean, pointing to the need for future research to refine climate prediction models further. Significance Statement Agriculture and infrastructure in the southern plains face challenges from severe late-spring precipitation extremes. Traditional predictors like El Niño–Southern Oscillation (ENSO) lose effectiveness during the critical spring-to-summer transition, creating a forecasting gap. This study introduces the concept of tropical interbasin interactions, known to enhance seasonal predictability for late-spring precipitation in the southern plains. Novel climate model experiments highlight contributions from the tropical Pacific and Atlantic, offering a promising predictability that potentially surpasses the limitations of ENSO-based predictions. These outcomes hold the potential for developing operational forecasts of late-spring precipitation anomalies in the southern plains, enabling proactive risk management.

Chikamoto, Yoshimitsu↗

DOE OSTI2012

Fish Bioaccumulation Studies Associated with the Kingston Fly Ash Spill, Spring 2009 – Fall 2010

In December 2008, an ash dike at the Tennessee Valley Authority (TVA) Kingston Fossil Plant ruptured, releasing over one billion gallons of coal fly ash into the Emory and Clinch Rivers. Coal fly ash may contain several contaminants of concern, but of these selenium (Se) and arsenic (As) have been highlighted because of their toxicity and tendency to bioaccumulate in aquatic food chains. To assess the potential impact of the spilled fly ash on humans and the environment, a comprehensive biological and environmental monitoring program was established, for which resident aquatic organisms (among other sample media) are collected to determine contaminant exposure and evaluate the risk to humans and wildlife. Studies on bioaccumulation and fish health are major components of the TVA Biological Monitoring Program for the Kingston fly ash project. These studies were initiated in early Spring 2009 for the purposes of: (1) documenting the levels of fly ash-associated metals in various tissues of representative sentinel fish species in the area of the fly ash spill, (2) determining if exposure to fly ash-associated metals causes short, intermediate, or long-term health effects on these sentinel fish species, (3) assessing if there are causal relationships between exposure (to metals) and effects on fish, (4) evaluating, along with information regarding other ecological and physicochemical studies, the nature and route of contaminant transfer though food chains into higher level consumers, (5) providing important information for the Ecological Risk Assessment (ERA) for the Kingston fly ash project, and (6) serving as an important technology transfer or model study focused on how to best evaluate the environmental effects of fly ash, not only at the Kingston site, but also at sites on other aquatic systems where coal-fired generating stations are located. This report summarizes the bioaccumulation results from the first two years of study after the fly ash spill, including four seasonal collections: Spring 2009, Fall 2009, Spring 2010, and Fall 2010. Both the Spring and Fall studies have focused on 3-4 sentinel fish species that represent different feeding habits, behaviors, and home ranges. In addition to bioaccumulation studies, the Spring investigations also included evaluation of fish health and reproductive integrity on the same fish used for bioaccumulation. Two associated reports present the fish health (Adams et al 2012) and reproductive studies (Greeley et al 2012) conducted in 2009 and 2010. The fish health study conducted in conjunction with the bioaccumulation and reproductive study is critical for assessing and evaluating possible causal relationships between contaminant exposure (bioaccumulation) and the response of fish to exposure as reflected by the various measurements of fish health. This report emphasizes evaluation of arsenic and selenium bioaccumulation in fish and consists of four related studies (Sections 2-5) including, (1) bioaccumulation in liver and ovaries, (2) bioaccumulation in whole body gizzard shad (Dorosoma cepedianum), (3) bioaccumulation in muscle tissue or fillets, and (4) a reconstruction analysis which establishes the relationship between selenium in muscle tissue and that of the whole body of bluegill (Lepomis machrochirus). Metals other than arsenic and selenium are evaluated separately in Section 6. This report focuses on selenium and arsenic for the following reasons: (1) based on baseline studies conducted in early 2009 in the Emory and Clinch River, only two potentially fly-ash related metals, selenium and arsenic, appeared to be elevated above background or reference levels, (2) selenium and arsenic are two of the metals in coal ash that are known to bioaccumulate and cause toxicity in wildlife, and (3) based on bioaccumulation studies of bluegill and carp (Cyprinus carpio) in the Stilling Pond during Spring 2009, which would represent a worst case situation for metal bioaccumulation, selenium and arsenic were the only two metals consistently elevated above background levels in fish. Each of the four selenium and arsenic evaluations presented in this report include an approach section, a results section which addresses primarily spatial and temporal patterns in bioaccumulation, an interpretation and discussion section, and a synthesis section which provides the main summary points of each study. Other metals in fish from near the spill site are evaluated by comparison with reference sites and evaluation of spatial and temporal trends. Statistical approaches to data analysis will be conducted after the third year of bioaccumulation monitoring when there is a larger n size available for analysis, there has been sufficient time for food-chain driven bioaccumulation (2009 data was likely closer to pre-spill exposures), and data correction factors for selenium and mercury (because of poor analytical recoveries for some samples) have been fully codified by the study team.

01 COAL, LIGNITE, AND PEAT↗

DOE OSTI2021

Investigating the Performance of a New Type of Preloaded Linear Stroke Length Magnetic Spring

This paper presents the analytic analysis, and proof-of-principle prototyping of a new type of magnetic spring with preload and a linear stroke length. An analytic based magnetic charge modeling approach is utilized to investigate the magnetic spring's energy density, stiffness characteristics and linearity. Here, it is shown that whilst the proposed magnetic spring has a lower mass and energy density than a mechanical spring, the magnetic spring offers several unique characteristics, such as contact-free operation, inherent preload as well as over-force failure protection. In addition, the operating principle of the presented magnetic spring can be extended to realize both positive and negative variable stiffness adjustment characteristics.

16 TIDAL AND WAVE POWER↗

DOE OSTI2024

Bonneville basin critical zones: Spring chemistry and gastropod ecology in playa-margin wetlands

Playa margin wetlands in the Bonneville basin are sustained by groundwater-fed brackish springs, which transport salts and other solutes into the playa basin. These wetlands are sensitive to changing water availability and quality, which are impacted by changing climate and land use, and whose sediments also provide important records of changing environmental conditions. Gastropods building their shells in these springs provide important recorders of water chemistry and may reflect changing aqueous conditions. In this paper, we analyze spring water chemistry, gastropod ecology and gastropod shell chemistry of Blue Lake (BL) and Horseshoe Springs (HRS), two groundwater-fed wetlands in the Great Salt Lake watershed. Here, we report the physical parameters including pH, temperature, and specific conductivity across the spring pond at Horseshoe springs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Maximizing Wave Energy Converter Power Extraction by Utilizing a Variable Negative Stiffness Magnetic Spring

Complex conjugate impedance matching is a key concept for wave energy converter design. Matching the impedance of the power take-off (PTO) system to the complex conjugate of the wave energy converter's (WEC) impedance ensures efficient transfer of energy from the WEC body motion to electrical power. In low frequency waves, impedance matching often requires a negative PTO stiffness. In this paper, an adjustable stiffness magnetic torsion spring will be presented and modeled to understand its potential to improve WEC performance. The spring has the ability to provide a negative stiffness, allowing the PTO impedance to more closely match the complex conjugate of the WEC impedance at low frequencies. The spring also supports an adjustable stiffness value, meaning it can be tuned according to the incoming wave conditions. The spring's tunability may put less stress on the rest of the PTO system in wave conditions outside its normal operation zone without sacrificing electrical power output. The adjustable magnetic spring's effects are modeled and explored in this paper by examining the resultant average annual electrical power and capacity factor. The study suggests that the tunable magnetic spring has the potential to significantly improve capacity factor while maintaining a high average electrical power.

16 TIDAL AND WAVE POWER↗

DOE OSTI2024

Variable stiffness magnetic spring

This disclosure presents a new type of variable stiffness magnetic spring, which can have a highly linear translational force characteristic. The variable stiffness is achieved through the rotation of a central magnet. Both positive and negative spring constants can be created. Using an analytic-based field analysis modelling technique, the operating principle and linearity characteristics of the adjustable magnetic spring are studied. The use of a magnetic spring with an adjustable negative spring constant could enable an ocean generator to continuously operate in a resonant state, thereby greatly increasing its power generation capability. The described variable stiffness spring could also be useful in other energy harvesting applications, robotic actuator applications, and/or other applications.

Bird, Jonathan↗

DOE OSTI2018

Initial assessment of recharge areas for large karst springs: a case study from the central Zagros Mountains, Iran

Sousan Spring emerges from the Keyno Anticline, Zagros Mountains (Iran), and the mean annual discharge is ~24 m{sup 3}/s. Geological and hydrochemical evaluations suggest that the spring recharge is from the limestone Ilam-Sarvak Formation (Cretaceous) but the Mafaroon Fault, a major thrust feature, influences the regional groundwater flow path by juxtaposing other strata. Geological, geochemical, stable isotope and water balance studies were employed to interpret this behavior. Using the isotope data, the sources and elevations of the recharge area were found. Temporal variations of the isotopic data were compared with variations of electrical conductivity (EC). Unexpectedly, high EC was associated with a relative increase of discharge and depletion of δ{sup 18}O. Several hypotheses were investigated and approximate water balance studies employed for validation. It was found that an elongated catchment on the Keyno Anticline plus a lesser catchment on a pair of parallel anticlines recharge the aquifer. While the long groundwater flow path along the Keyno Anticline plus guidance by Mafaroon Fault and the adjacent Garou shaly strata lead to increased EC in the Sousan Spring at the end of the dry season, a flow pulse from two adjoining anticlines (Mahalbakh and Shirgoon) arrives at the same time to increase the discharge and deplete the δ{sup 18}O signal. Apparently the spring did not experience true base flow conditions during the recorded hydrological year. Although the spring response to specific precipitation events was similar to typical karst aquifers, standard interpretation of recession curves and related coefficients will not be practical at Sousan.

58 GEOSCIENCES↗

DOE OSTI2019

Influence of Deep Cryogenic Treatment on the Mechanical Properties of Spring Steels

Leaf springs are mechanical elements responsible for supporting the vertical load on heavy duty vehicles. For this critical structural component, the required mechanical performance depends mainly on chemical composition and heat treatment. SAE 5160 and SAE 6140 steels are widely used as springs, because after heat treatments, the strength requirements of impact and fatigue are obtained. 51CrV4-ACF steel is another spring steel option which also exhibits excellent mechanical properties. The objective of this work was to study the influence of conventional heat treatments and cryogenic treatment on properties involving fatigue and impact resistance of spring steels. Furthermore, fracture toughness was measured for these materials, and the fracture surfaces were analyzed. The results showed that the cryogenic cycles used did not provide positive effects on spring steel performance. On the other hand, the chemical composition and the application of cleanliness technology promoted higher mechanical strength: Fracture toughness of 51CrV4-ACF was 100% higher than SAE 5160 steel.

36 MATERIALS SCIENCE↗