Finite element simulation of semi-finishing turning of Electron Beam Melted Ti6Al4V under dry and cryogenic cooling

open6noIn the last few years, important step forwards have been made on Finite Element Simulation of machining operations. Wrought Ti6Al4V alloy has been deeply investigated both numerically and experimentally due to its wide application in the industry. Recently, Additive Manufacturing technologies as the Electron Beam Melting and the Direct Melting Laser Sintering are more and more employed in the production of biomedical and aeronautical components made of Ti6Al4V alloy. Fine acicular microstructures are generated by the application of additive manufacturing technologies, affecting the mechanical properties and the machinability. By the consequence, this peculiarity has to be considered in modelling the material behaviour. In this work, a numerical analysis of cylindrical external turning on Electron Beam Melted (EBM) Ti6Al4V alloy is presented. A Johnson-Cook constitutive equation was implemented as a flow stress model and adapted with respect to the wrought Ti6Al4V alloy. The model was calibrated and validated through the cutting forces and temperatures measurements acquired under dry and cryogenic lubricating conditions.openBordin, A; Imbrogno, S.; Rotella, G.; Bruschi, S.; Ghiotti, A.; Umbrello, D.Bordin, Alberto; Imbrogno, S.; Rotella, G.; Bruschi, Stefania; Ghiotti, Andrea; Umbrello, D

Using Occupancy Surveys to Assess Summer Resource Selection of Sympatric Bighorn Sheep and Mountain Goats in Northern Yellowstone

Both bighorn sheep and mountain goats are generalist herbivores that overlap extensively in broad food and habitat requirements, but there have been few studies examining the potential for competition between sympatric populations. One area in which native bighorn sheep are living in sympatry with non-native mountain goats is the southern Gallatin Mountain range within and adjacent to the northwest boundary of Yellowstone National Park. Existing data of bighorn sheep and mountain goat observations for the area vary in spatial precision and records of areas where observers looked for but did not detect animals are not available. To gain a better understanding of the relationship between bighorn sheep and mountain goats and their habitat, it is necessary to understand resource selection and the extent of overlap in resource use among sympatric populations on fine spatial and temporal scales. In order to meet this need we designed and implemented formal, ground-based occupancy surveys during the summer of 2011. A crew of four spent 113 observer days in the field and hiked approximately 210 miles recording presence-absence data for both mountain ungulates. A total of 6,932 sample units were surveyed, with 68 bighorn sheep and 95 mountain goat groups detected. Detection probabilities for bighorn sheep and mountain goats were 66.9% and 54.5% respectively. We summarize the objectives and field design of the project and report on our efforts to develop enhanced habitat models which will provide managers with additional ecological insights

Montana’s New State-Wide Bighorn Sheep Research Initiative

Bighorn sheep (Ovis canadensis) conservation and management in Montana has been, and continues to be, a challenge. The majority of Montana’s bighorn sheep populations are patchily distributed across the state and are relatively small, with many populations static or periodically experiencing dramatic declines despite the fact that adequate habitat seems to be abundant. Wildlife managers and biologists are routinely making decisions on bighorn sheep population augmentation and restoration, harvest, habitat management, disease prevention and response, and other conservation actions without adequate knowledge of the drivers of demographic processes that inform management of many of Montana’s more successfully restored ungulate species. Field studies of bighorn sheep in Montana have been limited primarily to short-term, master’s thesis projects focused on a specific herd. A 6-yr research program has been designed and funded on the premise that research insights that are broadly applicable for management and conservation are best obtained by addressing the same questions in multiple populations representing differing demographic characteristics, ecological settings, and management histories that capture the range of variation realized by the species of interest. The research program will involve field studies of seven bighorn sheep herds in Montana, with data on each herd collected over a 5-yr period. Herds were selected to capture a wide range of variability in disease outbreak history, habitat types, and herd attributes in an effort to maximize our ability to partition and quantify the potential relative effects of these factors on lamb and adult survival, recruitment, and population dynamics

Assessing Maternal Energetic Allocation During Lactation for the Weddell Seal Using Photogrammetric Techniques

Life history theory predicts that allocation of resources to reproduction varies across an individual’s life as one’s reproductive value changes with age. As individuals reach late life and residual reproductive value declines, they should increase the proportion of energy allocated to reproduction at a cost to future survival or reproduction, this is referred to as terminal investment. Characteristics of Weddell seal life history make this marine-mammal a model organism for investigating terminal investment. Previous research from this population has indicated that pups of older females exhibit a higher growth rate from birth to weaning compared to pups from mothers of prime and young ages. We offer three competing hypotheses that may explain observed increased growth rates of pups born to older mothers and hypothesize that this finding may be a result of terminal allocation. Maternal volume measurements obtained with photogrammetric techniques will be used to explore variation in maternal energetic allocation during lactation. A simple linear regression of maternal volume against maternal measured mass was used to obtain the prediction regression equation. We found a very strong relationship between measured masses and those estimated from our predictive equation (Adjusted R2:0.8958, n=31). Estimated mass loss of mothers and apparent mass conversion efficiency from mother to pup over the course of lactation will be used to assess support for competing hypotheses. Results from this study may improve our understanding of life history theory and highlight sources of variation in population vital rates

The Mountain Ungulate Research Initiative: A Collaborative Effort To Advance Understanding Of Bighorn Sheep And Mountain Goat Ecology

Bighorn sheep (Ovis canadensis) and mountain goats (Oreamnos americanus) are important components of the faunal assemblage of Montana’s mountainous ecosystems representing high-profile large mammals that garner substantial public interest. While population restoration, augmentation, and introductions have traditionally been the predominant conservation activities associated with these species in Montana, basic ecological research has been limited. A new research initiative has been developed and funded to study bighorn sheep and mountain goat spatial and population ecology in a number of ecological settings within the Greater Yellowstone Ecosystem. The aspiration of the collaborators is to develop a long-term research program that could expand to other populations of these species in Montana if we are successful. Primary objectives of the studies include 1) understanding the ecological interactions between sympatric populations, 2) developing and refining habitat suitability models, 3) documenting spatial dynamics within and among populations and identifying important movement corridors, 4) collecting vital rate data to better understand population dynamics, and 5) investigating potential responses of bighorn sheep and mountain goats to gradual changes in the regional climate. The presentation will describe the collaboration and ongoing efforts to consolidate all available data on bighorn sheep and mountain goats in the GYE. These data are used to describe mountain goat range expansion within the GYE over the past half century and to conduct initial habitat modeling efforts. We will also describe our plans for initiating field studies in the near future

Finite element modeling of microstructural changes in hard machining of SAE 8620

Surface and subsurface microstructural characterization after machining operations is a topic of great interest for both academic and industrial research activities. This paper presents a newly developed finite element (FE) model able to describe microstructural evolution and dynamic recrystallization (DRX) during orthogonal hard machining of SAE 8620 steel. In particular, it predicts grain size and hardness variation by implementing a user subroutine involving a hardness-based flow stress and empirical models. The model is validated by comparing its output with the experimental results available in literature at varying the cutting speed, inser0000-0001-6268-6720t geometry and flank wear. The results show a good ability of the customized model to predict the thermo-mechanical and microstructural phenomena taking place during the selected processes

Telemetry Studies of Mountain Ungulates in the Greater Yellowstone Area: A Progress Report

We report on the progress that has been made on initiating long-term telemetry studies of mountain goats (Oreamnos americanus) and bighorn sheep (Ovis Canadensis) in the GYA to better understand spatial ecology, demography, potential competition, and disease ecology. Six study areas representing a variety of ecological settings have been established throughout the GYA that include areas where bighorn sheep and mountain goats are sympatric as well as where each species exists in the absence of the other. We are employing a novel dual radio collar strategy and have successfully evaluated the use of drop net systems to capture groups of bighorn attracted to bait as an economical alternative to standard helicopter-based single animal capture techniques. Chemical immobilization of bighorn using BAM as an alternative to carfentanil was also tested and evaluated. A break-down Clover trap was designed for ease of transportation via horse for backcountry trapping and summer salt baiting for bighorn sheep and mountain goats was evaluated. We have initiated the first systematic disease sampling of mountain goats in the GYA using the standard protocols employed for bighorn sheep health assessments to evaluate the potential for mountain goats to influence the disease ecology of bighorn sheep in areas where they are sympatric. The research goals, strategies, and methodologies developed, tested, and employed on the collaborative GYA mountain ungulate research program are similar to those proposed for a long-term bighorn sheep research program in Montana

Correlates of Recruitment in Montana Bighorn Sheep Populations: An Initiative to Synthesize Montana Bighorn Sheep Recruitment Data and Gain Biological Insight

Bighorn sheep (Ovis Canadensis) populations in Montana have been strongly affectedby disease outbreaks in recent years, resulting in the death of approximately 1500 bighorns as well as depressed recruitment rates in some affected herds. The ecology of these disease outbreaks is not well understood and there have been several proposals for a state-wide research project addressing disease ecology of bighorns in Montana. Such a project is a large investment and any extra knowledge of the bighorn populations that can be gained from existing data would improve study design and enhance the success of any future research effort. Last year we used management data to index bighorn recruitment rates of 23 bighorn herds in the Greater Yellowstone Area (GYA) and found strong correlations between recruitment and both annual and regional climate patterns. This year we have received funding from Montana Fish, Wildlife and Parks to conduct a similar analysis of bighorn recruitment rates across Montana. The planned analysis will investigate potential correlations between bighorn recruitment and climate covariates, similar to the GYA effort, but will also explore additional covariates to capture differences in management strategies, genetics, disease history, migration patterns, and population connectivity among the state’s bighorn sheep populations. The presentation will focus on the goals of our work as well as the advantages of conducting preliminary data analysis prior to implementing large scale research projects

Temporary Emigration Of Female Weddell Seals Prior To First Reproduction

Temporary emigration (TE) from a breeding site is common in some colonial-breeding species, but implications are poorly understood because TE is difficult to quantify. We used capture-mark-recapture models and a dataset of 5450 female Weddell seals (Leptonychotes weddellii) born in Erebus Bay, Antarctica to investigate sources of variation in TE rates and evaluate possible implications for recruitment. Temporary emigration rates and recruitment rates were state- and age-dependent and annually variable. For seals that attended reproductive colonies the previous year, mean TE rates decreased from 0.98 (sd = 0.02) at age 1 to 0.15 (sd = 0.16) at age 8, whereas mean recruitment rates increased from 0.06 (sd = 0.03) at age 5 to 0.52 (sd= 0.16) at age 10. Seals that did not attend reproductive colonies the previous year had greater TE rates and lower recruitment rates than seals that did attend colonies, but the confidence interval for the effect of TE on recruitment included zero. Our results suggest that 1) motivation to emigrate varies temporally depending on environmental conditions, 2) as seals grow older they have increased motivation to attend reproductive colonies even before they are ready to recruit, and 3) some seals appear to always be more likely than others to emigrate. We suspect that TE may allow seals to buffer variability in survival rates

Variation in Birth Mass and Mass Gain During Lactation for a Long-Lived Mammal: A Case Study Using the Weddell Seal

Reproduction in mammals is costly, with implications for trade-offs between current reproduction and survival.  Life history theory suggests the amount of energy allocated to reproduction should change as a function of increasing maternal age, and empirical work supports both within-individual decreases (consistent with senescence) and increases (consistent with constraint and restraint).  The Weddell seal (Leptonychotes weddellii) is an ideal organism with which to study patterns of maternal energy allocation due to the life history.  Here, we used a long-term mark-recapture database of individually marked mothers and pups in Erebus Bay, Antarctica, to develop a stratified sample of masses from pups and known-age females across maternal ages in 11 different years.  Hierarchical modeling of potential sources of variation in:  1) pup masses at parturition, 2) pup mass gains from parturition to mid-lactation (~20 days), and 3) pup mass gains from mid-lactation to late-lactation (~20-days to ~35-days) was used to 1) evaluate the relative support for increases/decreases in reproductive allocation as a function of maternal age, 2) assess how patterns of reproductive allocation may reflect pre-parturition resource acquisition and/or post-parturition resource allocation, and 3) estimate the magnitude of individual heterogeneity in maternal effects after accounting for maternal and offspring characteristics. Our results provide strong evidence that reproductive investment at parturition and pup mass gains from parturition through late-lactation vary with maternal age and breeding history and result in important differences in late-lactation pup masses.   Such variation may have consequences for the early-life success of offspring, and thus implications at the population level