Дисертації з теми "CREEP ESTIMATION"

Accurate and reliable component life prediction is crucial to ensure both the safety and economics of gas turbine operations. In the pursuit of improved accuracy and reliability, current model-based creep life estimation methods have become more and more complicated and therefore demand huge amounts of work and significant amounts of computational time. Because of the underlying problems arising from current life estimation methods, this research aims to develop an alternative performance-based creep life estimation method that is able to provide a quick solution to creep life prediction while at the same time maintaining the achieved accuracy and reliability as that of the model-based method. Using an artificial neural network, the existing creep life prediction subprocesses and secondary inputs are ‘absorbed’ into simple parallel computing units that are able to create direct mapping between various gas turbine operating and health conditions or gas path sensors and creep life. The outcome of this research is the creation of three proposed neural-based creep life prediction architectures known as the Range-Based, Functional-Based and Sensor-Based. An integrated creep life estimation model was first developed and incorporated into an in-house performance simulation and diagnostics software. Using the integrated model, the effects of several operating and health parameters on a selected turbo-shaft engine model turbine blade’s creep life was initially performed using an introduced Creep Factor approach. The outcomes of this investigation were then used to populate input-output samples to train and validate the neural-based creep life prediction architectures. To ensure that the proposed neural architectures are able to achieve generalisation and produce accurate creep life prediction for both clean and degraded engine conditions, four-stage assessments were carried out. Finally, the effects of input uncertainties on the creep life prediction were investigated to assess how sensitive the proposed architectures are to different levels of uncertainty. The results show that all of the proposed neural architectures were able to produce accurate creep life predictions for both clean and degraded engine conditions. When comparing the three proposed architectures, the Sensor-Based architecture was found to be the most accurate in both conditions. Despite the accurate creep life prediction, it was also found that all of the proposed architectures were sensitive to input uncertainties with the Functional-Based architecture being the least sensitive to the uncertainty.

The aim of this study is to develop a combined experimental and analytical framework for accelerated lifetime estimates of semi-crystalline plastic pipes which is sensitive to changes in structure, orientation, and morphology introduced by processing conditions. To accomplish this task, high-density polyethylene (HDPE) is chosen as the exemplary base material. As a new accelerated test protocol, several characterization tests were planned and conducted on as-manufactured HDPE pipe segments. Custom fixtures are designed and developed to admit uniaxial characterization tests. The yield behavior of the material was modeled using two hydrostatic pressure modified Eyring equations in parallel to describe the characterization test data collected in axial tension and compression. Subsequently, creep rupture failure of the pipes under hydrostatic pressure is predicted using the model. The model predictions are validated using the experimental creep rupture failure data collected from internal pressurization of pipes using a custom-designed, fully automatic test system. The results indicate that the method allows the prediction of pipe service lifetimes in excess of 50 years using experiments conducted over approximately 10 days instead of the traditional 13 months. The analytical model is joined with a commercial finite element package to allow simulations including different thermal-mechanical loading conditions as well as complicated geometries. The numerical model is validated using the characterization test data at different temperatures and deformation rates. The results suggest that the long-term performance of the pipe is dominated by the plastic behavior of the material and its viscoelastic response is found to play an insignificant role in this manner. Because of the potential role of residual stresses on the long-term behavior, the residual stress across the wall thickness is measured for three geometrically different HDPE pipes. As expected, the magnitude of tensile and compressive residual stresses are found to be greater in pipes with thicker walls. The effect of the residual stress on the long-term performance of the pipes is investigated by including the residual stress measurements into the numerical simulations. The residual stress slightly accelerates the failure process; however, for the pipe geometries examined, this acceleration is insignificant.
Doctor of Philosophy
The use of plastic pipes to carry liquids and gases has greatly increased in recent decades, primarily because of their moderate costs, long service lifetimes, and corrosion resistance compared with materials such as corrugated steel and ductile iron. Before these pipes can be effectively used, however, designers need the capability to quickly predict the service lifetime so that they can choose the best plastic material and pipe design for a specific application. This capability also allows manufacturers to modify materials to improve performance. The aim of this study is to develop a combination of experiments and models to quickly predict the service lifetime of plastic pipes. High-density polyethylene (HDPE) was chosen as the plastic material on which the model was developed. Several characterization tests are planned and conducted on as-manufactured HDPE pipe segments. The yielding behavior of the material is modeled and the lifetime predictions are evaluated. The predictions are validated by experimental data captured during pipe burst tests conducted in the lab. The results indicate that the method allows the accurate prediction of pipe service lifetimes in excess of 50 years using experiments conducted over approximately 10 days instead of the traditional 13 months, resulting in significant savings in time (and consequently costs) and making it possible to introduce new materials into production more rapidly.

For any machine designed to generate power, or to fulfill its functions in general, maintenance actions will have an impact on many aspects of its overall capabilities, especially its performance and the length of its useful life. Since these are vital in order to generate maximum profit, the maintenance actions that affect them must be given serious consideration. For this reason, this research aims to propose a method that will enhance the cost saving potential with more accurately determined maintenance intervals and greater exploitation of the remaining life of the components by utilizing the capabilities of condition based monitoring. Initially, the research focuses on the description and the understanding of maintenance methods as they are performed within the aviation industry, but it also aims to investigate the state of the art Condition Based Monitoring Maintenance (CBMM) and its associated advantaged relating to the older methods. The thesis begins by describing the fundamental aviation maintenance management domains, paying particular attention to CBMM, and continues with the diagnostic and prognostic methods that are in use in order to support the condition monitoring concept. Next, a description is given of the actual implementations of the CBMM process, with the presentation of the maintenance enhancement systems, namely the Central Maintenance System and the Aircraft Condition Monitoring System. Lastly, a case study is presented of the estimation of the remaining useful life of a turbine blade, as it relates to the primary failure mode of creep. The case study endorses the use of the condition monitoring diagnostic methods discussed previously and also aims to demonstrate the predictive capabilities of the Engine Usage Diagnostics at both the design and the into-service stage. The created/simulated engine performance models concern several operating conditions of the engine while the impact of each of those on the remaining useful life of the blade is investigated. The benefit of this research is that it proposes a practical, effective, and relatively easy way to perform maintenance by predicting the need according to the usage. Additionally, the data required have already been measured, which paves the way for the creation of more intelligent engine control units. The contribution and innovation of the research is demonstrated by the fact that no similar approaches to creep life prediction have been published for the same type of engine, namely the CFM56 5B2. Last but not least, the results are presented in the most beneficial form of remaining hours before the failure.

This thesis presents how to establish a theoretical model to predict risk of thermal cracking in young concrete when cast on ground or an arbitrary construction. The crack risk in young concrete is determined in two steps: 1) calculation of temperature distribution within newly cast concrete and adjacent structure; 2) calculation of stresses caused by thermal and moisture (due to self-desiccation, if drying shrinkage not included) changes in the analyzed structure. If the stress reaches the tensile strength of the young concrete, one or several cracks will occur. The main focus of this work is how to establish a theoretical model denoted Equivalent Restraint Method model, ERM, and the correlation between ERM models and empirical experiences. A key factor in these kind of calculations is how to model the restraint from any adjacent construction part or adjoining restraining block of any type. The building of a road tunnel and a railway tunnel has been studied to collect temperature measurements and crack patterns from the first object, and temperature and thermal dilation measurements from the second object, respectively. These measurements and observed cracks were compared to the theoretical calculations to determine the level of agreement between empirical and theoretical results. Furthermore, this work describes how to obtain a set of fully tested material parameters at CompLAB (test laboratory at Luleå University of Technology, LTU) suitable to be incorporated into the calculation software used. It is of great importance that the obtained material parameters describe the thermal and mechanical properties of the young concrete accurately, in order to perform reliable crack risk calculations.  Therefore, analysis was performed that show how a variation in the evaluated laboratory tests will affect the obtained parameters and what effects it has on calculated thermal stresses.

A new methodology of polymer pipe lifetime estimation taking into account residual stresses is described in this thesis. Engineering equations derived based on numerical simulations of a hydrostatic pressure test are proposed. Residual lifetime calculations were performed for different loading conditions using experimental data of a creep crack propagation in studied material and stress distribution in the pipe wall. The effects which significantly influence lifetime estimation were quantified with special focus on residual stresses.

The Lusk Creek Watershed, located in Pope County, IL, long has been recognized as a high quality area and as biologically significant. Yet, surveys of the macroinvertebrate fauna have been limited. Thus, a survey of the benthic insect community in the upper portion of Lusk Creek was conducted from May 2003 to April 2005. Eleven sites were selected and characterized by physical properties and water chemistry. Insect distribution patterns, abundance, and diversity (richness, evenness) were examined. A total of 20,888 specimens, mostly immatures, were examined during the study and represented eight orders. The Diptera, by far, was the most common order, with 18,590 specimens, almost all of which were members of the Chironomidae and Simuliidae. The EPT (Ephemeroptera, Plecoptera, Trichoptera) combined were common with 1,550 specimens but paled in comparison to the Diptera. The Coleoptera was represented by 647 specimens, almost all of which were members of Stenelmis (n = 612). The Shannon diversity index (H') showed that the H' values for individual sites were similar to those reported for other relatively undisturbed streams. Analyses of richness suggested that as many as 37 taxa were unobserved, indicating the survey was incomplete.

O método convencional de ensaios para a obtenção das curvas de fluência de geossintéticos pode necessitar de períodos de até 10.000 horas. Entretanto, a utilização de ensaios acelerados têm se mostrado bastante eficiente, especialmente para avaliar rapidamente a qualidade do material. Estudos bem sucedidos realizados por diversos autores, utilizaram o método Stepped Isothermal Method (SIM) para acelerar a fluência nos geotêxteis. Neste trabalho, com base neste método foi estimada a fluência de dois geotêxteis com 300 g/m² do tipo não tecido de poliéster (PET) de fibra curta e contínua. Neste estudo, foi analisada a fluência causada por carregamentos de 5, 10, 20, 40 e 60% da carga que causa a ruptura do material. Com base nos resultados conclui-se que os valores de deformação por fluência obtidos são satisfatórios, pois as previsões de alcance de até 355 anos estão próximos aos valores encontrados na literatura internacional. Ainda, para o tempo de 100 anos ficou evidenciado que para o geotêxtil não tecido do tipo PET, de fibra curta ou contínua, o comportamento mecânico do geotêxtil é mais influenciado pela deformação inicial do que pela fluência.
The conventional method of tests to achieve the geosynthetic creep curves may require times of up to 10,000 hours. However, the use of accelerated tests have shown to be very effective, especially for rapidly assessing the quality of the material. Successful studies by various authors used the Stepped Isothermal Method Method (SIM) to accelerate creep in geotextiles. In this work, based on this method was estimated creep of two non-woven geotextiles of polyester with 300 g/m², short or continuous fiber. In this study, creep caused by loads of 5, 10, 20, 40 and 60% of the rupture load of the material was analyzed. Based on the results, it is concluded that the creep strain values obtained are satisfactory, because up to 355 years range forecasts are close to those found in the literature. Still, for the 100-year time, it became evident that for the nonwoven geotextile type PET with short or continuous fiber, the mechanical behavior of the geotextile is more influenced by the initial deformation than by creep.

This paper discusses the usage of several creep models in combination with ANSYS MECHANICAL APDL finite element software and analytical calculations to predict creep strain in terms of axial and radial distortion for the typical gas turbine rotor disc model. Creep analysis of gas turbine disc using different creep models at offset design condition is the main consideration of this work. For many components of industrial gas turbine, the design for creep is conservative because of close control of dimensions required over the life, the maintenance of critical dimensions, such as clearance between rotating and static parts. Components operate for extensive periods of time under heavy loads in conditions of non-uniform temperature which go up to 5350C during the process. The stress-strain state also changes over time due to creep phenomena. These conditions make difficult to simulate the actual body by other means like finite element analysis; it is essential to establish creep properties over all ranges of temperatures, stresses and durations of time for the reliable prediction of creep deformation and stress rupture in gas turbine components. A typical gas turbine disc model is used in this present study to investigate the relationship between operating conditions and design parameters on the creep phenomena. Several ANSYS creep mathematical models are investigated to use for perfect fitting according to the conditions and available data. Time hardening and strain hardening creep model is further studied to analyze the creep of disk. While doing creep analysis, ambient temperature is set to standard 320C. But this standard process is not valid for every site of world so a different procedure has been set up to simulate the offset design conditions to capture site specific creep issues. Results show variations in axial and radial creep strain with respect to analysis done at constant average temperature for 160k hours. A good agreement is also found between the results obtained in this current study and the results available in the literature for strain hardening and time hardening model. It is found that stress relaxation after 160K hour using time hardening model is more than using strain hardening. Analysis with offset design condition shows that to capture the clearance correctly and more realistically, offset design condition needs to be simulated. Present work concludes that further study is required in the area of creep mathematical model and validation of simulated results with experimental data.

碩士
國立中興大學
水土保持學系
88
Due to steep topography, weak geology, heavy rainfall in the typhoon season, tremendous soil loss disaster usually occurs in Taiwan especially at the mudstone areas. Geographic Information System (GIS), Remote Sensing (RS), and Global Positioning System (GPS) coupled with Universal Soil Loss Equation (USLE) were used to estimate watershed soil loss in Erhjen Creek located at mudstone areas. Watershed topographic and hydrologic information of interest was also extracted automatically from Digital Terrain Model (DTM) in this study for the references of slopeland planning and design. There is no obvious difference between model estimation and field measured in watershed soil loss. Regression analysis shows that the amount of soil loss for 19 analyzed sub-watersheds: 6 sub-watersheds related to Rainfall Index, 11 sub-watersheds related to Soil Erosion Index and 3 sub-watersheds related to aspect factors. The amounts of soil loss for 19 analyzed sub-watersheds are all highly correlated to the slope length, slope, and cropping factors. The slope length, slope, and cropping are the key factors to reduce soil loss at the mudstone slope land.

碩士
國立成功大學
資源工程學系碩博士班
94
This study is aimed to evaluate the groundwater resources of the Chihben Creek Basin at Taitung county in southeastern Taiwan. Since the shortage of the hydrogeological parameters, then selected the non hydrologeological parameter methods: the recession-curve-displacement method and the base-flow-record estimation method, which developed by USGS, to estimate this basin’s groundwater resources. On the other hand, this study try to research the geological data of this creek basin, and by refer to the similar geological conditions to choose the initial hydrogeological parameters, to which simulating and rating by IGW. Been estimated the groundwater resources of the Chihben Creek Basin with three kinds of codes, the results showed that from 1980 to 2004 the average amount of annual groundwater recharge is approximately 2.24×108～2.87×108 m3.

碩士
國立中興大學
水土保持學系所
106
Taiwan is located at the junction of the Eurasian Plate and the Philippine Sea Plate. Due to frequent earthquakes, steep mountain terrain, fragile geological formation and the influence of extreme weather, Taiwan has usually been suffering serious landslides in the mountainous watershed, and resulting in derived disasters, which in turn affected the ecological environment and further jeopardized the safety of downstream protected objects. Watershed of A-bang Creek, a tributary of the Dajia River, was selected as a research area. Digital elevation model and multi-phase Landsat satellite imageries of the pre- and/or post- Chi-chi earthquake were used for extracting the normalized differential vegetation index to derive location and vegetation recovery rate of the landslides. Sites of primary disasters could be classified into areas of collapse and deposition using K-means cluster analysis; and the amount of deposition volume could be as the factor of hazard and the topographic wetness index as vulnerability indicator to assess the risk of watershed landslide derived disaster. Results show that the debris of earthquake induced landslide is initially deposited at the sites of lower and/or the toe of the slope land; and then will be transported downwardly to the protected objects depicting an obvious aftermath disaster through the following rainfall events. This study is focusing on establishing a method of assessing derived disaster using related environmental indicators. Topology relations of the protected objects and the primary disasters are discussed to determine the priority selection of the hotspots for the references of related authorities on conservation treatment and management of landslide derived disasters in the watershed.

The WET-Temp (Watershed Evaluation Tool Temperature) model is designed to take advantage of spatially explicit datasets to predict stream temperature distribution. Datasets describing vegetation cover, stream network locations, elevation and stream discharge are utilized by WET-Temp to quantify geometric relationships between the sun, stream channel and riparian areas. These relationships are used to estimate the energy gained or lost by the stream via various heat flux processes (solar and longwave radiation, evaporation, convection and advection). The sum of these processes is expressed as a differential energy balance equation applied at discrete locations across the stream network. The model describes diurnal temperature dynamics at each of these locations and thus temperature distribution across the entire network. WET-Temp is calibrated to a tributary of the South Santiam River in western Oregon, McDowell Creek. The mean differences between measured and modeled values in McDowell Creek were 0.6��C for daily maximum temperature and 1.3��C for daily minimum temperature. The model was then used to predict maximum and minimum temperatures in an adjacent tributary, Hamilton Creek. The mean differences between modeled and measured values in this paired basin were 1.8��C for daily maximum temperatures and 1.4��C for daily minimum temperatures. Influences of model parameters on modeled temperature distributions are explored in a sensitivity analysis. The ability of WET-Temp to utilize spatially explicit datasets in estimating temperature distributions across stream networks advances the state of the art in modeling stream temperature.
Graduation date: 2003

碩士
國立臺灣科技大學
營建工程系
105
As global warming has been getting from bad to worse, the 《Paris Agreement》 under the 《United Nations Framework Convention on Climate Change》, known as UNFCCC or FCCC, was formally signed by 154 ratified Parties, of 197 Parties to the Convention, to be adopted as the basis for a global response to tackle the challenge posed by climate change and to stabilize greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous human interference with the climate system before 2020. The Paris Agreement's central aim is to strengthen the global response to the threat of climate change by keeping a global temperature rise this century well below 2 degrees Celsius above pre-industrial levels and to pursue efforts to limit the temperature increase even further to 1.5 degrees Celsius, which trigger nations concerned to formulate related policies on reducing greenhouse gas emissions in an active manner. However, when it comes to the reduction of greenhouse gas emissions, the government in Taiwan does not sit on the sidelines and to tell the truth, the Construction industry was accounted for nearly 30% of all carbon emissions produced in Taiwan. Moreover, including the fact that construction industry holds a large portion of producing greenhouse gas all over the world, to set an ultimate goal for reaching Carbon Neutral by supervising, regulating and reducing the greenhouse gas emissions produced by the industry is extremely important. We can manage greenhouse gas emissions by following the same rule as managing carbon emissions using the reference of Carbon Disclosure Project, which is to follow the process of tracking Carbon Inventory, Carbon Footprint and finally lead to the goal of Carbon Neutral. The purpose of this study is to apply Carbon Management process as the basis to calculate the carbon emissions produced by engineering constructions and to understand the amount of Carbon Footprint by formulating Construction Carbon Emissions calculate Model to further collocate the policy of Carbon Reduction and Carbon Neutral. The main subject of this study is the carbon emissions produced by civil engineering projects under public constructions. Furthermore, on the grounds that there are a large number of studies based on calculating carbon emissions among different types of construction projects especially in Taiwan, we therefore speculate the estimation model based on how public authorities estimate the carbon dioxide emissions produced from civil engineering projects. In view of this, the Construction Carbon Emissions Estimate Model of this study was established through the combination of budget cost structure from Public Construction Cost Estimate System, known as PCCES, and the concept of calculating carbon emissions to build up a new model for estimating carbon emissions. For PCCES has been adopted to carry out construction cost estimate, especially for public constructions, for such a long time in Taiwan, we therefore utilize this model to be the structure of estimating the carbon emissions produced by engineering projects to better facilitate the usage for users in the future. This study will work through the engineering calculation for Classification and Identification Principle of Carbon Emissions by applying engineering encoding method in PCCES, which indicates that carbon emission contains ‘the use of equipment’, ‘material production’ and ‘the process of transportation’, and construct information table to calculate various types of carbon emissions. The study results will use two creek engineering cases to be as example to conduct the estimate of carbon emissions. Through the presence of Estimation Model of Carbon Dioxide (CO2) Emissions for Public Construction, decision makers and reviewers can clearly identify the main item that produces carbon emissions during engineering projects and the estimate of carbon emissions. Furthermore, the study results can give assistance to authorities concerned when pushing ahead with Carbon Management system, and it can help for acquiring full information of carbon emissions produced by engineering projects and therefore reaching the goal of Carbon Management and Carbon Reduction.

Objectifs : Évaluer l’incidence de la macrosomie fœtale en fonction des différentes définitions (poids de naissance >4000g, >4500g, ≥90ième percentile de Kramer) en vigueur et comparer la prévalence de la morbidité maternelle et périnatale associée à la macrosomie entre les populations Cris et les populations du Québec. Des courbes postnatales spécifiques aux Cris de l’Est de la Baie-James seront proposées. Devis : Comparaison de deux cohortes prospectives Cris et Québec. La cohorte des populations Cris de l’Est de la Baie-James, comporte 2546 femmes recrutées de 2000-2010, au cours de l’étude sur la macrosomie fœtale chez les Cris de l’Est de la Baie James. La cohorte du Québec est composée de 97475 femmes et provient de l’essai clinique randomisé multicentrique QUARISMA, 2008-2010, cette étude promulguant la réduction du taux d’accouchement par  césarienne. Méthodes : Les risques de macrosomie fœtale et de la morbidité maternelle et périnatale sont évalués par des modèles de régression logistique d’équations d'estimation généralisées (EEG) ajustés et comparés selon l’ethnicité, Cris et Québec. GEE. Le groupe de référence étant les femmes du Québec. Les courbes de croissance spécifiques aux Cris sont construites par régression quantile. Résultats : Plus du tiers, soit 36,76%, des Cris et 9,329% des nouveau-nés du Québec, ont un poids de naissance >4000g. Les résultats attestent montrent que 10,92% des Cris de l’Est de la Baie-James ont un poids de naissance de plus de 4500g, ce taux est de 1,23% au Québec. La définition de la macrosomie fœtale, par un poids néonatal ≥90ième percentile de Kramer, identifie 40,02% des bébés Cris, pour 8,83% des nourrissons du  Québec, comme macrosomes. Les Cris sont plus à risque de macrosomie fœtale, comparativement à la population générale du Québec, ces associations sont statistiquement significatives : RC=5,22; 95% IC (4,66-6,05,98), pour un poids de naissance >4000g, RC=8,10; 95% IC (6,22-10,77), pour un poids de naissance >4500g et RC=6,22; 95% IC (5,77-6,72), pour un poids de naissance ≥90ième percentile de Kramer. Le risque de la morbidité périnatale majeure, de la macrosomie fœtale, est généralement moins important pour les Cris que pour la population générale du Québec : 0,76; 95% IC 0,62-0,94. La macrosomie fœtale devrait être décrite par un poids de naissance≥95ième percentile de Kramer, pour les Cris, mais préférablement au 90ième percentile des courbes postnatales spécifiques aux Cris de l’Est de la Baie-James. Les poids de naissance diagnostique spécifiques aux Cris de l’Est de la Baie-James, au 90ième percentile de la 40ième semaine d’aménorrhée, sont de 4 417g pour les filles et 4 488g pour les garçons. Conclusions : Les courbes de Kramer diagnostiquent systématiquement plus de macrosomes chez les Cris que dans la population du Québec. Par contre, le risque de morbidité périnatale majeure est inférieur pour ces communautés autochtones, aux différents seuils décrivant la macrosomie fœtale, ce qui suggère l’utilisation de courbes spécifiques aux Cris et permettrait de diminuer les interventions obstétricales non nécessaires chez les gros bébés Cris, donc non-macrosomes.
Objective: Assess the impact of fetal macrosomia based on definitions (birth weight> 4000 g,> 4500g, ≥90ième percentile Kramer) currently used in Quebec and compare the prevalence of maternal and perinatal morbidity associated with macrosomia between the Cree populations of Eastern James Bay and the general population of Quebec. Specific postnatal curves for the Cree will be constructed. Design: Comparison of two prospective cohort Cree and Quebec. Cohort of Cree populations of eastern James Bay, has recruited 2546 women from 2000 to 2010, during the study of fetal macrosomia in the Cree of eastern James Bay. Quebec cohort consisted of 97,475 women and comes from the multicenter randomized clinical trial QUARISMA 2008-2010, this study promulgates the reduction of caesarean delivery rate. Methods: The risk of fetal macrosomia, maternal and perinatal morbidity, by ethnicity, Cree and Quebec, are evaluated by generalized estimating equations models (GEE). GEE models were adjusted to control for potentially confounding factors. The reference group is Quebec women. The specific growth curves of the Cree are built by quantile regression. Results: More than a third, 36.8%, of Cree populations of Eastern James Bay and 9.3% of newborns in Quebec have a birth weight> 4000g. For a birth weight> 4500g, the results show that 10.9% of the Cree, have a birth weight of more than 4500g, the rate is 1.2% in Quebec. The definition of fetal macrosomia by neonatal birth weight≥90th percentile of Kramer identifies 40.02% Cree’s for 8.8% of infants of Quebec as macrosomic. The Cree population are more at risk of fetal macrosomia, compared to the general population of Quebec, these associations were statistically significant: OR = 5.2; 95% CI (4.6 to 6.0) for birth weight> 4000g, OR = 8.1; 95% CI (6.2 to 10.7) for birth weight> 4500g and OR = 6.2; 95% CI (5.7 to 6.7) for birth weight percentile ≥90th Kramer. The risk of major perinatal morbidity associated with fetal macrosomia, is generally less important for the Cree than for the general population of Quebec: 0.76; 95% CI 0.62-0.94. Fetal macrosomia should be described by birth weight ≥95th percentile of Kramer, for the Cree, but preferably at the 90th percentile of the specific postnatal curves of Cree populations of Eastern James Bay. The specific Cree birth weight thresholds for diagnosing fetal macrosomia, at the 90th percentile of the 40th week of gestation, are 4 417g for the girls and 4 488g for the boys. Conclusion: Kramer’s curves diagnose systematically too much macrosomic Cree babies compare to the general population of Quebec. Futhermore, the risk of major maternal and perinatal morbidity is lower for these indigenous communities, at the different definitions of fetal macrosomia, suggesting the use of specific curves for the Cree, to reduce obstetrics interventions not required in large, but non macrosomic, Cree babies.