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1
Fernandez, Lorences Jose O. "Crystallinity changes in PET and Nylon 11 with strain, strain rate and temperature." Thesis, Loughborough University, 1999. https://dspace.lboro.ac.uk/2134/32894.
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The mechanical properties of PET (widely used in bottles and synthetic fibres) and Nylon 11 (also used in the fabrication of synthetic fibres) were studied over several decades of strain rate at different temperatures in an effort to provide a more complete description of these materials behaviour. Processing techniques can be improved if such information is available. Tests were carried out using a conventional Hounsfield machine and two in-house-developed dropweight and a cross bow systems from 10°C to 200°C. The three systems enable true stress vs. true strain curves to be calculated.
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Larour, Patrick [Verfasser]. "Strain rate sensitivity of automotive sheet steels: influence of plastic strain, strain rate, temperature, microstructure, bake hardening and pre-strain / vorgelegt von Patrick Larour." Aachen : Shaker, 2010. http://d-nb.info/1007085649/34.
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Tanner, Albert Buck. "Modeling temperature and strain rate history effects in OFHC CU." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/17143.
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Ashton, Mark. "Behaviour of metals as a function of strain-rate and temperature." Thesis, Loughborough University, 1999. https://dspace.lboro.ac.uk/2134/10449.
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Five materials, copper (two versions), iron, and armour plate steel (two versions) have been tested at different strain-rates and temperatures. All tests were in compression. The materials were studied to provide experimental data for input into hydrocode models of armour behaviour by the Defence Research Agency, Fort Halstead. A wide selection of metals was examined so that comparisons could be drawn between modelling the behaviour of face centred and body centred cubic metals, and to carry out a broader investigation into how the results obtained were affected by the test methods. Experiments were performed at temperatures from -100°C to 20°C and mean plastic strain-rates from 10-3 to 103 S-l, using a Split Hopkinson Pressure Bar (SHPB) system for high strain-rates and a Hounsfield 50 kN machine for quasistatic conditions. The stress-strain behaviour of the materials as a function of temperature and strain-rate was then determined. The effects of interfacial friction on the measured compreSSlve properties of copper and the armour plate steels have been investigated. Since the coefficient of friction was the critical parameter, ring tests were carried out and the Avitzur analysis applied. In general, the coefficient of friction decreased with increasing strain-rate and temperature. The tested specimen's appearance indicated the same friction trends. Hydrocode modelling of the SHPB system produced corrections to the flow stress, to compensate for interfacial friction, that agree well with those predicted by the Avitzur analysis. Deformed finite element mesh plots analysed in conjunction with barrelled specimens have given a clearer insight into the mechanisms of interfacial friction. The Armstrong-Zerilli constitutive models have been applied to copper, iron and armour plate steel results corrected for thermal softening and specimen-platen interfacial friction. These models have been shown to provide a reasonable description of the materials' behaviour. The research investigation has shown that in order to obtain fundamental stressstrain behaviour of the materials, then corrections must be applied, which can be quite significant. These corrections must take into account the effects of material thermal softening and the specimen-platen interfacial friction.
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Roshanaei, Sina. "Stress-Strain data for metals in bar and sheet form : strain rate, thickness and temperature influences." Thesis, Brunel University, 2017. http://bura.brunel.ac.uk/handle/2438/15614.
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Over the past few decades various models of different formats have been developed to correctly evaluate and predict the strength of materials. However, these models are limited in certain environmental conditions in implementing the effect of material's thickness into their models. As such an there was a need to consider the basics of mechanical engineering and to try and define the trend, thickness has upon the behaviour of materials with respect to environmental conditions. The work consisted of a representation of tensile testing testing of common engineering alloys across a wide range of temperature, strain rate and thickness. Acquisition of high strain rate data and extended strain data (split-hopkinson, bulge forming and plane strain compression). A review of existing graphical techniques and limited applications using strength reduction factors, as well as applying the accepted empirical formulae, Johnson-Cook, Armstrong-Zerrili, Ramberg-Osgood and Hollomon. Later, recognising a need for a new approach as with a universal (quartic) polynomial fit to all plastic flow curves in which coefficients are T, ε̇ and t̄ dependant. Adoptation of a common numerical procedure for strain intercept ε0 and cut-off instability co-ordinates (σi, εi)- each as the solution to the roots of a quartic. Therefore, a proposal of the flow curve tables allowing interpolation and extrapolation, a numerical representation of any previous "Atlas of Curves". Subsequently, leading to reconstruction of the full stress-strain curve with the addition of elastic strain calculated from the modulus applicable to the specific test condition by further testing of these data from literature; both improving the existing and producing new empirical and simulation based models to analyse the materials, which will be subjected to dynamic loading as well as temperature and strain rates variations. The main objective of the work, was involved in creating a polynomial fit to describe the three physical conditions in terms of coefficients and to verify the findings in a FEA package, ABAQUS. A new process in reading the stress-strain data. By means of such development an instability study of strain limits based on Considére criteria was developed which illustrated the ways to prolong the instability limit. A secondary study of this work relates to creating a bridge between the micro-structure and macro-structure of the tested materials. A series of correlations and trends were developed to further signify the shift in micro-structural restructuring, whilst the material is under load. Another important aspect of the work consists, of carrying out an analytical study on Ramberg-Osgood equation. Ramberg-Osgood equation has been at the forefront of many engineering advancement. However it can yet be improved and reformatted by means of defining a set value for its variable constants. As such a fix ƞt value based on a best-fit approach was developed which was analytically tested.
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Smith, Anthony Justin. "Procedure and Results for Constitutive Equations for Advanced High Strength Steels Incorporating Strain, Strain Rate, and Temperature." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1343150464.
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Bindas, Erica Bindas. "EFFECT OF TEMPERATURE, STRAIN RATE, AND AXIAL STRAIN ON DIRECT POWDER FORGED ALUMINUM-SILICON CARBIDE METAL MATRIX COMPOSITES." Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1530871866585058.
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Zaroulis, John Spyros. "Temperature, strain rate and strain state dependence of evolution of mechanical behavior and structure of poly(ethylene-terephthalate) with finite strain deformation." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11251.
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Reedy, Michael Wayne. "An approach to low temperature high strain rate superplasticity in aluminum alloy 2090." Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/26891.
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Calmunger, Mattias. "High-Temperature Behaviour of Austenitic Alloys : Influence of Temperature and Strain Rate on Mechanical Properties and Microstructural Development." Licentiate thesis, Linköpings universitet, Konstruktionsmaterial, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-98242.
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The global increase in energy consumption and the global warming from greenhouse gas emission creates the need for more environmental friendly energy production processes. Biomass power plants with higher efficiency could generate more energy but also reduce the emission of greenhouse gases, e.g. CO2. Biomass is the largest global contributor to renewable energy and offers no net contribution of CO2 to the atmosphere. One way to increase the efficiency of the power plants is to increase temperature and pressure in the boiler parts of the power plant. The materials used for the future biomass power plants, with higher temperature and pressure, require improved properties, such as higher yield strength, creep strength and high-temperature corrosion resistance. Austenitic stainless steels and nickel-base alloys have shown good mechanical and chemical properties at the operation temperatures of today’s biomass power plants. However, the performance of austenitic stainless steels at the future elevated temperatures is not fully understood. The aim of this licentiate thesis is to increase our knowledge about the mechanical performance of austenitic stainless steels at the demanding conditions of the new generation power plants. This is done by using slow strain rate tensile deformation at elevated temperature and long term hightemperature ageing together with impact toughness testing. Microscopy is used to investigate deformation, damage and fracture behaviours during slow deformation and the long term influence of temperature on toughness in the microstructure of these austenitic alloys. Results show that the main deformation mechanisms are planar dislocation deformations, such as planar slip and slip bands. Intergranular fracture may occur due to precipitation in grain boundaries both in tensile deformed and impact toughness tested alloys. The shape and amount of σ-phase precipitates have been found to strongly influence the fracture behaviour of some of the austenitic stainless steels. In addition, ductility is affected differently by temperature depending on alloy tested and dynamic strain ageing may not always lead to a lower ductility.
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Richeton, Julien. "Modeling and validation of the finite strain response of amorphous polymers for a wide range of temperature and strain rate." Université Louis Pasteur (Strasbourg) (1971-2008), 2005. http://www.theses.fr/2005STR13159.
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Sammonds, Peter Robert. "Triaxial deformation experiments on natural sea ice as a function of temperature and strain rate." Thesis, University College London (University of London), 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241922.
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Khan, Amnah Sehar. "Electromechanical response of bulk PZT 95/5 and associated polymers across temperature and strain rate." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/48495.
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Piezoelectricity is the ability of certain, non-conductive, materials to generate an electrical charge when pressure is applied to them. The voltage produced is directly proportional to the applied stress. The amount of charge generated can depend on, for example, the applied strain rate or the temperature. Due to this ability, piezoceramics, such as PZT ceramics, find use in many different applications, primarily as sensors or actuators. Sensors work by detecting pressure, mechanically deforming and thus producing a voltage. Actuators, on the other hand, mechanically deform upon application of an electric field. To develop a better understanding of the piezoelectric ceramic lead zirconate titanate (PZT) 95/5, a range of studies including varying temperatures, porosities, and strain rates have been conducted. The effects on the voltage output and failure of poled PZT samples of different porosities have been investigated using different compressive strain rates (10^-4 – 10^4 s^-1), reached with quasi-static loading equipment, drop-weight towers, and Split Hopkinson Pressure Bars (SHPBs). The main cylindrical specimens were of 4.4 mm diameter, thickness 0.8 - 4.4 mm, and density 7.3 - 8.3 g cm^-3. The temperature range of -20°C to +80°C was achieved using purpose-built environmental chambers. The resulting stress-strain relationships are compared; all the samples ultimately displaying a brittle response at failure [1]. To support this work, ideal geometric specimen sizes were identified for the different types of loading experiment, by carrying out a range of strain-rate compression experiments on well-studied materials such as aluminium and copper. In addition, different experimental platforms were successfully developed in order to reach non-ambient temperatures in the Split Hopkinson Pressure Bar experiments. Finally, as piezoceramics, when used in real world applications, are often coated in protective layers of polymer, several different types of industrial polymer have been characterised across the full range of strain rates and temperatures.
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Gockel, Brian T. "Constitutive Response of a Near-Alpha Titanium Alloy as a Function of Temperature and Strain Rate." Research Showcase @ CMU, 2016. http://repository.cmu.edu/dissertations/762.
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Dupaix, Rebecca B. (Rebecca Brown) 1976. "Temperature and rate dependent finite strain behavior of poly(ethylene terephthalate) and poly(ethylene terephthalate)-glycol above the glass transition temperature." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/7972.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003.Includes bibliographical references (p. 333-348).
Poly(ethylene terephthalate) is widely used for consumer products such as drawn fibers, stretched films, and soda bottles. Much of its commercial success lies in the fact that it crystallizes at large strains during warm deformation processing. The imparted crystallinity increases its stiffness and strength, improves its dimensional stability, and increases its density. The crystallization process and the stress-strain behavior above the glass transition depend strongly on temperature, strain rate, strain magnitude, and strain state. A robust constitutive model to accurately account for this stress-strain behavior in the processing regime is highly desirable in order to predict and computationally design warm deformation processes to achieve desired end product geometries and properties. This thesis aims to better understand the material behavior above the glass transition temperature in the processing regime. It examines the strain rate, strain state, and temperature dependent mechanical behavior of two polymers: PET and PETG, an amorphous non-crystallizing copolymer of PET, in order to isolate the effects of crystallization on the stress-strain behavior. Experiments over a wide range of temperatures and strain rates were performed in uniaxial and plane strain compression. A constitutive model of the observed rate and temperature dependent stress-strain behavior was then developed. The model represents the material's resistance to deformation with two parallel elements: an intermolecular resistance to flow and a resistance due to molecular network interactions.
(cont.) The model predicts the temperature and rate dependence of many stress-strain features of PET and PETG very well, including the initial modulus, flow stress, initial hardening modulus, and dramatic strain hardening. The modeling results indicate that the large strain hardening behavior of both materials can only be captured by including a critical orientation parameter to halt the molecular relaxation process once the network achieves a specific level of molecular orientation. This suggests that much of the strain hardening in PET is due to molecular orientation and not to strain-induced crystallization. An example blow molding process is simulated to demonstrate the industrial applicability of the proposed model.
by Rebecca B. Dupaix.
Ph.D.
16
Wan, Margaret. "Assessment of occupational heat strain." [Tampa, Fla] : University of South Florida, 2006. http://purl.fcla.edu/usf/dc/et/SFE0001661.
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Caccialupi, Alessandro. "Systems development for high temperature, high strain rate material testing of hard steels for plasticity behavior modeling." Thesis, Available online, Georgia Institute of Technology, 2004:, 2003. http://etd.gatech.edu/theses/available/etd-04082004-180051/unrestricted/caccialupi%5Falessandro%5F200312%5Fms.pdf.
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Mouille, Hervé. "Influence of strain rate and temperature upon the mechanical and fracture behavior of a simulated solid propellant /." This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-07212009-040252/.
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Bonfils, Laure. "Characterisation of the high strain rate deformation behaviour of α-β titanium alloys at near-transus temperature." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:e2507c22-6478-4461-be57-347382a5ee0c.
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The aim of this thesis is to provide microstructural and mechanical characterisation of α-β titanium alloys exposed to a range of thermo-mechanical conditions, in particular under-going high rate deformation at elevated temperatures, representative of the Linear Friction Welding (LFW) manufacturing process. Three α-β titanium alloys provided by Rolls-Royce are studied: Ti-64 blade, disc and Ti-6246 disc. Ti-64 and Ti-6246 show complex deformation behaviour with strain, strain rate and temperature, especially near the transus temperature, where the low temperature α phase is transformed into the high temperature β phase. The microstructure and mechanical properties evolve in an interconnected fashion, and understanding this mutual influence is necessary to better predict the behaviour of these alloys. Characterisation of the mechanical properties was performed through uniaxial compression tests at strain rates from 0.001 to 3000 s-1, using an Instron screw-driven machine at quasi-static rates, a servo-hydraulic machine at medium rates and a Split-Hopkinson Pressure Bar and a drop-weight tower at high strain rates. The tests were performed over a range of temperatures from room temperature to 1300 °C. The main focus was on high strain rate and high temperature tests, with the development of a gravity driven direct impact Hopkinson bar, referred as a drop-weight system, which is intended to evaluate the mechanical response of metals to high strain rate loading at temperatures up to c. 1300 °C. The design and principles of operation of the system are presented, along with calibration and validation data. Preliminary tests were performed on stock Ti-64, heated at two rates: 1 and 20 °C s-1. The evolution of the mechanical properties was analysed, focussing on the strain rate, temperature and phases dependencies. Characterisation of the microstructure was realised by performing interrupted compression tests, first at room temperature, three plastic strains, 4%, 10% and 20%, and two different strain rates, 0.001 and 2000 s-1; then at 4% plastic strain, a strain rate of 2000 s-1 and three elevated temperatures, 700, 900 and 1100 °C. A better understanding of the microstructure evolution with strain, strain rates and temperature, including the macrotexture and microtexture of the specimens, was obtained using Electron Backscatter Diffraction (EBSD) to characterise the texture of the undeformed and deformed materials. The better understanding of the flow stress and microstructural evolution of both Ti-64 and its individual α and β phases with various strain rates and temperatures is intended to be used in the development of more accurate models representing the behaviour of these alloys. Predicting the microstructure evolution and then the mechanical properties of a material is essential to optimise the final mechanical properties of the alloys when welded by manufacturing processes such as the LFW process.
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Mouille, Hervé. "Influence of strain rate and temperature upon the mechanical and fracture behavior of a simulated solid propellant." Thesis, Virginia Tech, 1992. http://hdl.handle.net/10919/43774.
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Papo, Jones Malesela. "The effect of alloy chemistry and strain rate on the Md30 temperature of metastable austenitic stainless steels." Master's thesis, University of Cape Town, 1994. http://hdl.handle.net/11427/14045.
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Includes bibliographical references.The work covered in this thesis provides a comprehensive discussion of the transformation behaviour of Type 304 metastable stainless steels with small' variations in alloy composition. The study focuses mainly on the austenite stability with respect to alloy composition, rate of deformation and temperature. To achieve these objectives, uniaxial tensile tests at 0.3 true strain were performed at low and high strain rates (10-3s-1 and 3 x 10-2s-1 respectively), in the temperature range of -60 to 55°C under isothermal testing conditions.
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Allred, Jacob D. "An Investigation into the Mechanisms of Formation of the Hard Zone in FSW X65." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3806.
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Friction stir welding (FSW) of HSLA steel commonly produces a hard zone (HZ) on the advancing side (AS) of the weld. Despite its detrimental effects on weld toughness, the mechanisms of its formation have not been thoroughly investigated and are not well understood. This paper investigates the various mechanisms in FSW believed to affect the weld HZ, namely: strain, strain-rate, peak temperature and cooling rate. Gleeble tests indicate that strain and strain rate have negligible effects on weld HZ with cooling rate and peak temperature as dominant effects. Jominy tests resulted in cooling rate having 270% greater influence than peak temperature on the formation of lath ferrite microstructures similar to what is observed in the HZ of FSW X65. Comparing weld HZ microstructures to Jominy tests, it is estimated that cooling rates on the AS of the weld are at least 150°C/s higher than the retreating side. Reducing the cooling rate on the AS will likely lead to an improved microstructure at the weld HZ.
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Poxon, Sara. "The mechanical response of low to high density Rohacell foams." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:94065572-8e3c-4e68-8e40-12f148093717.
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The main aim of this thesis is to generate a deeper understanding of the mechanical behaviour of cellular materials, specifically for their use in aerospace applications. A closed-cell polymer foam material (Rohacell) of various foam densities was chosen for this investigation, and a comprehensive experimental study was conducted which generated significant findings that hitherto have not been reported in the literature. The research presented in this study revealed the following: The quasistatic response of Rohacell foam displays a compression/tension asymmetry in moduli and strength. In-situ experiments revealed that different macroscopic collapse mechanisms at different foam densities drove this behaviour. Improved experimental methods were developed to characterise the material response at various loading rates. Under compressive loading, as the relative density and loading rate increased, a transition in material behaviour from a ductile to brittle response at very high rates (~5x10^3 s^-1) was found, and tests conducted at different temperatures were used to validate and provide a better understanding of the causes for the observed rate dependency. The compression and tension properties of pre-crushed Rohacell foam loaded in different directions were measured, and with the use of three-point-bend tests it was shown that when the foams’ tension/compression asymmetry, or the changes in stiffness and strength due to pre-crushing (i.e. strain-induced anisotropy), are neglected, this leads to incorrect predictions of the foams’ structural response. Finally, a review of some existing Finite Element foam material models was conducted, and their ability to predict the foam response under complex loading was identified. The new data and understanding generated from this thesis will allow engineers and researchers, who are developing constitutive models for predicting the response of foam materials, specifically in aerospace applications, to account for more aspects of the mechanical behaviours in their Finite Element models.
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Umberger, Pierce David. "Modeling the High Strain Rate Tensile Response and Shear Failure of Thermoplastic Composites." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/23846.
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The high strain rate fiber direction tensile response of Ultra High Molecular Weight Polyethylene (UHMWPE) composites is of interest in applications where impact damage may occur. This response varies substantially with strain rate. However, physical testing of these composites is difficult at strain rates above 10^-1/s. A Monte Carlo simulation of composite tensile strength is constructed to estimate the tensile behavior of these composites. Load redistribution in the vicinity of fiber breaks varies according to fiber and matrix properties, which are in turn strain rate dependent. The distribution of fiber strengths is obtained from single fiber tests at strain rates ranging from 10^-4/s to 10^-1/s and shifted using the time-Temperature Superposition Principle (tTSP) to strain rates of 10^-4/s to 10^6/s. Other fiber properties are obtained from the same tests, but are assumed to be deterministic. Matrix properties are also assumed to be deterministic and are obtained from mechanical testing of neat matrix material samples. Simulation results are compared to experimental data for unidirectional lamina at strain rates up to 10^-1/s.
Above 10^-1/s, simulation results are compared to experimental data shifted using tTSP. Similarly, through-thickness shear response of UHMWPE composites is of interest to support computational modeling of impact damage. In this study, punch shear testing of UHMWPE composites is conducted to determine shear properties. Two test fixtures, one allowing, and one preventing backplane curvature are used in conjunction with finite element modeling to investigate the stress state under punch shear loading and the resulting shear strength of the composite.Ph. D.
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Kuykendall, Katherine Lynn. "An Evaluation of Constitutive Laws and their Ability to Predict Flow Stress over Large Variations in Temperature, Strain, and Strain Rate Characteristic of Friction Stir Welding." BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/2768.
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Constitutive laws commonly used to model friction stir welding have been evaluated, both qualitatively and quantitatively, and a new application of a constitutive law which can be extended to materials commonly used in FSW is presented. Existing constitutive laws have been classified as path-dependent or path-independent. Path-independent laws have been further classified according to the physical phenomena they capture: strain hardening, strain rate hardening, and/or thermal softening. Path-dependent laws can track gradients in temperature and strain rate characteristic to friction stir welding; however, path-independent laws cannot. None of the path-independent constitutive laws evaluated has been validated over the full range of strain, strain rate, and temperature in friction stir welding. Holding all parameters other than constitutive law constant in a friction stir weld model resulted in temperature differences of up to 21%. Varying locations for maximum temperature difference indicate that the constitutive laws resulted in different temperature profiles. The Sheppard and Wright law is capable of capturing saturation but incapable of capturing strain hardening with errors as large as 57% near yield. The Johnson-Cook law is capable of capturing strain hardening; however, its inability to capture saturation causes over-predictions of stress at large strains with errors as large as 37% near saturation. The Kocks and Mecking model is capable of capturing strain hardening and saturation with errors less than 5% over the entire range of plastic strain. The Sheppard and Wright and Johnson-Cook laws are incapable of capturing transients characteristic of material behavior under interrupted temperature or strain rate. The use of a state variable in the Kocks and Mecking law allows it to predict such transients. Constants for the Kocks and Mecking model for AA 5083, AA 3004, and Inconel 600 were determined from Atlas of Formability data. Constants for AA 5083 and AA 3004 were determined with the traditional Kocks and Mecking model; however, constants for Inconel 600 could not be determined without modification to the model. The temperature and strain rate combinations for Inconel 600 fell into two hardening domains: low temperatures and high strain rates exhibited twinning while high temperatures and low strain rates exhibited slip. An additional master curve was added to the Kocks and Mecking model to account for two hardening mechanisms. The errors for the Kocks and Mecking model predictions are generally within 10% for all materials analyzed.
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Deibler, Lisa Anne. "Effects of Temperature, Stress State, and Strain Rate on Flow and Fracture of Mg Metallic Glass and Viscous Fluids." Cleveland, Ohio : Case Western Reserve University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1238707832.
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Torabiandehkordi, Noushin. "High and very high cycle fatigue behavior of DP600 dual-phase steel : correlation between temperature, strain rate, and deformation mechanisms." Thesis, Paris, ENSAM, 2017. http://www.theses.fr/2017ENAM0020/document.
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Ce travail vise à améliorer notre compréhension du comportement en fatigue à grand et très grand nombre de cycles d’un acier ferrito-martensitique dual phase, notamment les effets de la température et de la vitesse de déformation résultant de chargements cycliques à haute fréquence. L'effet de la fréquence sur la réponse en fatigue de l'acier DP600 a été étudié en effectuant des essais de fatigue sur une machine ultrasonique travaillant à 20 kHz et sur une machine conventionnelle travaillant à des fréquences inférieures à 100 Hz. Des études de fractographie et des observations microscopiques à la surface des échantillons ont été effectuées pour étudier les mécanismes de déformation et de rupture. De plus, la thermographie infrarouge in situ a été utilisée pour étudier la réponse thermique et les mécanismes dissipatifs du matériau lors des essais de fatigue. Les courbes S-N ont été déterminées à partir de chargements de fatigue ultrasoniques à 20 kHz et d’essais conventionnels à 30 Hz. La durée de vie pour une amplitude de contrainte donnée est plus élevée dans le cas de la fatigue ultrasonique bien que la limite de fatigue soit identique dans les deux cas. L’augmentation inévitable de la température en fatigue ultrasonique à fortes amplitudes de contraintes, ainsi que le comportement dépendant de la vitesse de déformation de la ferrite, en tant que structure CC, ont été trouvés comme les paramètres clés expliquant le comportement observé en fatigue, et la réponse thermique sous les fréquences faibles et ultrasoniques. Les écarts observés entre l’essai de fatigue conventionnel et celui ultrasonique ont été évalués à travers les mécanismes de mobilité des dislocations vis dans la phase ferritique de structure cubique centrée (CC). La durée de vie plus élevée et l’amorçage de la fissure principale sur une inclusion observés en fatigue ultrasonique ont été attribués au vieillissement dynamique résultant du fort auto-échauffement du matériau aux fortes amplitudes de contraintes. L'existence d'une transition du régime thermiquement activé au régime athermique avec l’augmentation de l'amplitude de contrainte a été mise en évidence. Au-dessous de la limite de fatigue, la déformation a lieu dans un régime thermiquement activé alors qu'elle est dans un régime athermique au-dessus de la limite de fatigue. En fatigue conventionnelle, la déformation est athermique pour toutes les amplitudes de contrainte. Une carte de transition a été produite en utilisant les résultats expérimentaux pour l'acier DP600 ainsi que les données disponibles dans la littérature pour d'autres aciers à base de ferrite, montrant ainsi la corrélation entre le mouvement des dislocations vis thermiquement activé et l'absence de rupture en fatigue à très grand nombre de cycleThis work is an attempt towards a better understanding of the high cycle and very high cycle fatigue behaviors of a ferritic-martensitic dual-phase steel, with a regard to temperature and strain rate effects, resulting from accelerated fatigue loading frequencies. The influence of frequency on fatigue response of DP600 steel was investigated by conducting ultrasonic and conventional low frequency fatigue tests. Fractography studies and microscopic observations on the surface of specimens were carried out to study the deformation and fracture mechanisms under low and ultrasonic frequencies. Moreover, in situ infrared thermography was carried out to investigate the thermal response and dissipative mechanisms of the material under fatigue tests. The S-N curves were determined from ultrasonic 20-kHz fatigue loadings and conventional tests at 30 Hz. Fatigue life for a given stress amplitude was found to be higher in the case of ultrasonic fatigue whereas the fatigue limit was the same for both cases. Moreover, crack initiation was always inclusion-induced under ultrasonic loading while under conventional tests it occurred at slip bands or defects on the surface. The inevitable temperature increase under ultrasonic fatigue at high stress amplitudes along with the rate dependent deformation behavior of ferrite, as a body centered cubic (BCC) structure, were found as the key parameters explaining the observed fatigue behavior and thermal response under low and ultrasonic frequencies. The discrepancies observed between conventional and ultrasonic fatigue tests were assessed through the mechanisms of screw dislocation mobility in the ferrite phase as a BCC structure. The higher fatigue life and inclusion-induced crack initiations in the case of ultrasonic loading were attributed to the dynamic strain aging, which resulted from the high temperature increases at high stress amplitudes. The existence of a transition in deformation regime from thermally-activated to athermal regime under ultrasonic fatigue loading by increasing the stress amplitude was confirmed. Below the fatigue limit, deformation occurred in thermally-activated regime while it was in athermal regime above the fatigue limit. Under conventional loading deformation occurred in athermal regime for all stress amplitudes. From the analysis of the experimental data gathered in this work, guidelines were given regarding the comparison and interpretation of S-N curves obtained from conventional and ultrasonic fatigue testing. A transition map was produced using the experimental results for DP600 steel as well as data available in the literature for other ferrite based steels, showing the correlation between thermally-activated screw dislocation movement and the absence of failure in very high cycle fatigue
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Gur, S., S. K. Mishra, and G. N. Frantziskonis. "Thermo-mechanical strain rate-dependent behavior of shape memory alloys as vibration dampers and comparison to conventional dampers." SAGE PUBLICATIONS LTD, 2015. http://hdl.handle.net/10150/615541.
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A study on shape memory alloy materials as vibration dampers is reported. An important component is the strain rate-dependent and temperature-dependent constitutive behavior of shape memory alloy, which can significantly change its energy dissipation capacity under cyclic loading. The constitutive model used accounts for the thermo-mechanical strain rate-dependent behavior and phase transformation. With increasing structural flexibility, the hysteretic loop size of shape memory alloy dampers increases due to increasing strain rates, thus further decreasing the response of the structure to cyclic excitation. The structure examined is a beam, and its behavior with shape memory alloy dampers is compared to the same beam with conventional dampers. Parametric studies reveal the superior performance of the shape memory alloy over the conventional dampers even at the resonance frequency of the beam-damper system. An important behavior of the shape memory alloy dampers is discovered, in that they absorb energy from the fundamental and higher vibration modes. In contrast, the conventional dampers transfer energy to higher modes. For the same beam control, the stiffness requirement for the shape memory alloy dampers is significantly less than that of the conventional dampers. Response quantities of interest show improved performance of the shape memory alloy over the conventional dampers under varying excitation intensity, frequency, temperature, and strain rate.
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Nanjappa, Jagdish. "Web-based dynamic material modeling." Ohio University / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1174918633.
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池田, 光芳, Mitsuyoshi IKEDA, 黛青 趙, Daiqing ZHAO, 博史 山下, and Hiroshi YAMASHITA. "酸素富化空気を用いた対向流火炎の火炎構造およびNOx生成に関する数値解析 (速度こう配がNOx生成の抑制に与える影響)." 日本機械学会, 2004. http://hdl.handle.net/2237/8988.
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Adharapurapu, Raghavendra R. "Phase transformations in nickel-rich nickel-titanium alloys influence of strain-rate, temperature, thermomechanical treatment and nickel composition on the shape memory and superelastic characteristics /." Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2007. http://wwwlib.umi.com/cr/ucsd/fullcit?p3262183.
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Thesis (Ph. D.)--University of California, San Diego, 2007.Title from first page of PDF file (viewed July 10, 2007). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.
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Rajasekaran, Nepolean. "A Nonlinear Constitutive Model for High Density Polyethylene at High Temperature." University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1298041213.
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Vautrot, Mathieu. "Étude du comportement mécanique des matériaux dans des conditions étendues de vitesses et de températures : application à l'acier C68 dans le cas d'une opération de formage incrémental." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00795973.
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L'objectif de ce travail de thèse est la caractérisation et la modélisation du comportement thermo-mécanique d'un acier à haut taux de carbone dans des conditions de chargement identiques à celles d'un procédé de formage incrémental à 720°C. Le regain d'intérêt des industriels pour ce type de procédé provient du fait qu'ils sont moins énergivores et permettent un ratio matière valorisée sur matière brute intéressant pour des propriétés mécaniques améliorées de la pièce formée. Le recours à l'outil numérique devient aujourd'hui une solution intéressante pour optimiser au mieux la mise au point du procédé. Son application demande, entre autres, une description fine du comportement du matériau dans les conditions de sollicitations de celui-ci, c'est-à-dire sur une large plage de vitesses de déformation et de températures. Pour cela, une caractérisation du matériau est nécessaire dans ces conditions. Le comportement mécanique d'un acier à haut taux de carbone a été étudié au travers d'essais de traction quasi-statiques et dynamiques afin de déterminer la sensibilité du matériau à la température et à la vitesse de déformation. Cette caractérisation repose sur la combinaison novatrice d'un système de chauffage par induction contrôlé par pyrométrie et d'un système d'acquisition d'images numériques. Ce dernier est utilisé pour la détermination des déformations à partir des champs de déplacement obtenus par corrélation d'images. En particulier, les effets de la température sur le module d'élasticité, l'anisotropie et l'écrouissage isotrope ont été étudiés. Les résultats de ces essais ont ensuite constitué une base de données expérimentales pour l'identification des paramètres de divers modèles de comportement thermo-élasto-visco-plastique. Ces derniers sont plus ou moins complets selon le nombre de paramètres utilisés pour décrire le comportement du matériau sur l'ensemble du domaine étudié. Cela permet d'identifier le modèle avec le meilleur ratio qualité/coût-délai pour une application donnée. Chacun des modèles étudiés dispose donc d'un domaine de définition propre.
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Piao, Kun. "An Elevated-Temperature Tension-Compression Test and Its Application to Mg AZ31B." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1316096630.
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Chu, XingRong. "Caractérisation expérimentale et prédiction de la formabilité d'un alliage d'aluminium en fonction de la température et de la vitesse de déformation." Phd thesis, INSA de Rennes, 2013. http://tel.archives-ouvertes.fr/tel-00910093.
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Les procédés de mise en forme de tôles minces sont très largement répandus dans l'industrie. Néanmoins, l'utilisation de ces procédés est limitée par le niveau de formabilité du matériau formé, notamment dans le cas des alliages d'aluminium. Afin d'améliorer ces limites de formabilité, des procédés de mise en forme à chaud peuvent être envisagés. L'objectif de cette thèse est d'étudier à l'aide d'approches expérimentale et numérique l'effet de la température et de la vitesse de déformation sur la formabilité des tôles en alliage d'aluminium AA5086 et de proposer une modélisation capable de prédire ces effets. Une campagne d'essais a été réalisée sur ce matériau à partir d'un essai d'emboutissage de type Marciniak. Des courbes limites de formage (CLF) ont été établies sur une plage de température allant de l'ambiant jusqu'à 200°C et pour des vitesses de déformation allant du quasi-statique à 2s-1. Des effets, positif de la température et négatif de la vitesse de déformation sur la formabilité ont été mis en évidence. La prise en compte des effets de la température et de la vitesse de déformation dans les modèles prédictifs des CLF, qu'ils soient analytiques ou numériques, est à ce jour très limitée. Dans ce travail, un modèle numérique prédictif basé sur la simulation par éléments finis du modèle géométrique de Marciniak et Kuczynski (M-K) est proposé. Les déformations limites obtenues avec de ce modèle sont très sensibles à la description du comportement thermo-viscoplastique du matériau et à la calibration du défaut géométrique pilotant l'apparition de la striction dans le modèle M-K. Des essais de traction uniaxiale réalisés dans les mêmes conditions opératoires que les essais de mise en forme de Marciniak ont permis d'identifier des lois d'écrouissage de nature très différentes (rigidifiante, saturante ou mixte). Ces lois conduisent à des prédictions très différentes de la formabilité du matériau pour une valeur donnée du défaut géométrique du modèle EF M-K. Différentes stratégies de calibration de la taille de ce défaut initial ont été envisagées. L'utilisation du point expérimental de la CLF correspondant à des conditions de déformation plane permet de calibrer de manière satisfaisante la valeur de ce défaut. Cette procédure de calibration a été appliquée pour l'ensemble des lois identifiées. Les lois de nature rigidifiante de type Ludwick se sont montrées les plus effficaces alors que les lois saturante de type Voce se sont avérées incapables de prédire la formabilité du matériau pour certaines conditions opératoires. Finalement, il est démontré qu'une valeur constante du défaut géométrique ne peut être retenue pour l'ensemble des conditions opératoires étudiées même si le modèle M-K s'est avéré assez efficace pour représenter l'effet de la température plutôt que celui de la vitesse de déformation.
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Simon, Pierre. "Modélisation du comportement mécanique et de la rupture en conditions dynamiques d’aciers de structure et à blindage." Thesis, Université de Lorraine, 2019. http://www.theses.fr/2019LORR0042/document.
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Cette étude s’intéresse à la modélisation du comportement thermoviscoplastique ainsi qu’à la rupture d’un acier de construction « S355NL » et d’un acier à blindage naval. Une campagne expérimentale a permis d’observer la réponse mécanique de ces matériaux sur une large gamme de condition de sollicitation, notamment leurs sensibilités à la vitesse de déformation ( de 〖10〗^(-3) à ~〖10〗^4 s^(-1)) et à la température (de -100 à 200 °C). Ces résultats ont été exploités lors de l’identification de lois de comportement permettant de représenter précisément le comportement mécanique de ces matériaux. Afin d’améliorer la description de la sensibilité à la vitesse de déformation, un nouvelle approche a également été développée. Une fois ces lois déterminées, elles ont été utilisées dans des simulations numériques modélisant l’impact d’un projectile sur ces aciers. Les résultats obtenus ont été comparés avec les essais expérimentaux correspondant afin d’estimer la fiabilité des données et des hypothèses utilisées lors des simulationsThe present study deals with the modelling of the thermo-viscoplastic behaviour and the failure of a structural steel “S355NL” and a naval armour steel. An experimental campaign have been performed to observe the mechanical response of these material over a wide range of conditions, especially their sensitivities to the strain rate (from 〖10〗^(-3) to ~〖10〗^4 s^(-1)) and to the temperature (from -100 to 200 °C). The obtained results have been used to identify the parameters of several constitutive relations. A new approach have been developed to improve the description of the strain rate sensitivity. These relations have been implemented in numerical simulation to model the impact of a projectile on these steels. The obtained results have been compared with corresponding experimental tests in order to assess the reliability of the data and the hypothesis used in the simulations
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Zhao, Yong. "Morphology and electrical trees in semi-crystalline polymers." Thesis, University of Reading, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314355.
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Dorléans, Vincent. "Caractérisation et modélisation du comportement et de la rupture de thermoplastiques pour une large gamme de vitesse de déformation et de température." Thesis, Valenciennes, Université Polytechnique Hauts-de-France, 2020. http://www.theses.fr/2020UPHF0031.
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De nos jours les matériaux polymères sont omniprésents dans l’habitacle d’un véhicule. C’est le cas notamment pour les composants comme la planche de bord ou les panneaux de portes. Ces éléments sont soumis à des cahiers des charges imposés par les réglementations internationales pour minimiser les blessures occasionnées à l’occupant en cas d’accident. Il est donc indispensable de caractériser les propriétés mécaniques de ces matériaux par des essais physiques impliquant différents cas de chargement sur de larges gammes de vitesse de sollicitation et de température. Les données recueillies permettent ainsi d’alimenter des modèles de comportement numériques censés reproduire avec fidélité le comportement complet d’un polymère, si possible jusqu’à rupture, en prenant en compte toutes ses spécificités. En effet, dans un souci d’optimisation des coûts de développement, la simulation numérique est aujourd’hui un outil incontournable dans la conception et le dimensionnement de composants. Ainsi dans le cadre de ces travaux, il est proposé de caractériser le comportement complet d’un polymère semi-cristallin jusqu’à la rupture pour une gamme étendue de vitesse de déformation et de température. Dans un premier temps, des DMA et des essais de traction sont réalisés pour caractériser les propriétés viscoélastiques-viscoplastiques du matériau. Puis la notion de principe d’équivalence temps/température est introduite et vérifiée expérimentalement dans les deux domaines. Un modèle basé sur les équations constitutives développées par Balieu et al. et enrichi grâce à ce principe est alors identifié puis implémenté dans le code de calcul Ls Dyna. Il est validé par comparaison à divers résultats expérimentaux. Dans un second temps, les travaux portent sur la caractérisation expérimentale et la modélisation de la rupture. Après avoir défini des géométries d’éprouvettes permettant d’atteindre des taux de triaxialité variés, des essais à rupture sont réalisés à différentes vitesses de déformation pour deux températures +23 et -30°C. Une surface de comportement à rupture est ainsi identifiée et introduite dans le modèle de rupture GISSMO. Le modèle complet, i.e. associant les lois de comportement et de rupture, et ensuite validé en comparaison à des résultats expérimentaux sur éprouvettes, mais également sur démonstrateur industrielNowadays, polymers are used for the interior parts of vehicles. It is particularly the case for components such as dashboards and door panels. These elements are submitted to requirements imposed by international regulations in order to minimize the injuries of the passengers in case of a car crash. It is therefore essential to characterize the mechanical properties of those polymeric materials for several load cases on a wide range of strain-rate and temperature. The collected data can be used to fill numerical behavior models supposed to accurately predict the whole behavior of a polymer, if possible up the failure, taking all polymer behavior specificities into account. Indeed, aiming at optimizing development costs, numerical simulation is currently a key tool in the design of engineering components. Thus, in this thesis work, it is proposed to characterize the complete whole behavior of a semi-crystalline polymer in a wide range of strain-rate and temperature until failure. First, some DMA and tensile tests are carried out in order to characterize the viscoelastic and viscoplastic properties of the material. Then, time-temperature-superposition principle is introduced and validated in the two domains. A model based on the constitutive equations developed by Balieu and al. and enriched thanks to this principle is identified and implemented in the Ls Dyna code. It is validated by comparison with experimental results. Secondly, the work focusses on the experimental characterization and the modelling of failure. Several specimen geometries are designed to reach some specific triaxiality ratios and are tested at different strain-rates and two temperatures +23 and -30°C. A failure behavior surface is thus identified and introduced in the GISSMO failure model. The complete model of behavior, i.e. constituted of behavior laws and failure criterion, is then validated based on comparison with experimental data extracted from tests on specimens, but also on an industrial demonstrator
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Jia, Bin. "Caractérisation expérimentale et modélisation du comportement de l'acier inoxydable 304 sous différentes vitesses de déformation et températures." Thesis, Paris, ENSAM, 2019. http://www.theses.fr/2019ENAM0056.
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L’acier inox austénitique 304 est utilisé pour de nombreuses applications industrielles, notamment à cause de l’effet TRIP qui lui confère des propriétés particulières. Au cours de son élaboration ou lorsqu’il est utilisé en service, il peut être soumis à différentes vitesses de déformation et températures. Le travail présenté ici vise à étudier le comportement de cet acier sous différents trajets de chargement. Tout d’abord, un système de refroidissement a été ajouté aux barres de Hopkinson pour étudier le comportement de cet acier en compression avec des vitesses de déformation comprises entre 0.001 s-1 et 3000 s-1 et des températures entre -163°C et 172°C. Le modèle de Rusinek-Klepaczko, qui prend en compte le phénomène de transformation martensitique, a été utilisé en parallèle pour simuler son comportement thermo-viscoplastique. Pour les vitesses de déformation au-delà de 3000 s-1, un nouveau design d’éprouvette de cisaillement a ensuite été proposé et validé et l’effet de la vitesse de déformation entre 3000 s-1 et 39000 s-1 a été étudié. Enfin, un autre système de refroidissement a été développé pour les essais d’impact et de perforation à différentes vitesses (entre 80 et 180 m.s-1) et températures (entre -163°C et 200°C) et les lois de comportement ont été validées en comparant expériences et simulations numériquesDue to the unique Transformation Induced Plasticity (TRIP) effect, 304 austenitic stainless steel (ASS) is widely used in many engineering areas. During working and manufacturing process or in service, it may undergo deformation over a wide range of strain rates and temperatures. The current work presents a systematic deformation behavior study of 304 ASS by both experiments and numerical simulations. With an original cooling device coupled to the split Hopkinson pressure bar system, the compression behavior at strain rates between 0.001 s-1 and 3000 s-1 and temperatures between -163°C and 172°C was investigated. An extension of the Rusinek-Klepaczko (RK) model considering strain-induced martensitic transformation (SIMT) phenomenon was also used to simulate the thermo-viscoplastic behavior of this steel. To study the deformation behavior at extremely high strain rates exceeding 3000 s-1, a new single shear zone (SSS) specimen has been proposed and validated. Then, the effects of strain rate between 3000 s-1 and 39000 s-1 was analyzed. Finally, with a specially designed cooling device, the ballistic impact behavior under initial projectile velocities between 80 and 180 m.s-1 and temperatures between -163°C and 200°C was studied. By comparison between experiments and numerical simulations for perforation, the previously obtained constitutive relations were validated
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Cook, Frederick Philip. "Characterization of UHMWPE Laminates for High Strain Rate Applications." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/30849.
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The research presented in this thesis represents an effort to characterize the properties of ultra-high molecular weight polyethylene (UHMWPE). As a composite of polymers, the properties of UHMWPE are time-dependent. It is desired by research sponsors to know the properties of the material at high strain rates, in order to simulate the use of these materials in computer models. Properties believed to be significant which are investigated in this research are the tensile properties of lamina and laminates, and the interlaminar shear properties of laminates. The efficacy of using time-temperature superposition to shift tensile properties of the composite is investigated, and a novel apparent shear strength test is proposed and demonstrated. The effects of processing the material at various temperatures and pressures are also investigated.Master of Science
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Kaddouri, Zayad. "Impact de la température et de la succion sur le fluage d’une argile compactée." Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0194/document.
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Les argiles compactées sont utilisées dans de nombreuses applications, notamment en géotechnique et en géotechnique de l’environnement, en raison de leur faible perméabilité, et de leurs propriétés de rétention notamment. Cependant, une fois en place, ces matériaux pourraient être exposés à des sollicitations thermiques et/ou hydriques, à long et très long terme. L’objectif principal de ce travail est de quantifier expérimentalement l’impact de ces sollicitations sur la compressibilité d’une argile compactée, et plus particulièrement son fluage. Avec cet objectif, des cellules œdométriques à température contrôlée entre 5 et 70°C ont été développées. Deux types d’œdomètre à succion contrôlée par les méthodes osmotique et solutions salines ont été employés dans une gamme de succion comprise entre 0 et 20,8 MPa, et à une température constante de 20°C. Ces dispositifs ont permis d’étudier le fluage jusqu’à une contrainte verticale de 3600 kPa. L’étude s’est concentrée sur le comportement d’une argile moyennement gonflante compactée. Les résultats obtenus ont tout d’abord montré que la contrainte de préconsolidation apparente σ’p diminue à mesure que la température augmente. Le coefficient de fluage Cαe augmente avec la température, cet effet étant plus particulièrement marqué à des contraintes plus élevées. Une relation linéaire entre le coefficient de fluage Cαe et l’indice de compression incrémental C*c a été observée dans la plage de contraintes considérée et le rapport (Cαe /C*c) dépend de la température. Ensuite, deux approches expérimentales complémentaires (essais de fluage par paliers ou à vitesse de déformation contrôlée) ont mis en évidence la dépendance des caractéristiques de fluage vis-à-vis de la succion du sol. Par ailleurs, la contrainte de préconsolidation apparente σ’p augmente avec l’augmentation de la vitesse de déformation έv et de la succion. En revanche, l’indice de compression Cc et le coefficient de fluage Cαe varient d’une manière non monotone avec une valeur maximale sous une succion de 3,5 et de 2 MPa, respectivement. L’évolution de ces paramètres apparaît fortement liée à la structure interne du sol. L’analyse de la variation de σ’p avec έv et de Cαe avec Cc a montré que la relation Δlog σ’p /Δlog έv = Cαe/Cc est également valable pour le sol argileux compacté étudié dans les cas saturés et non saturésCompacted clays are used in many applications, including geotechnical and environmental geotechnical applications, due to their low permeability and retention properties. However, once in place, these materials could be exposed to thermal and/or water variations in the long and very long term. The main objective of this work is to experimentally quantify the impact of these variations on the compressibility of a compacted clay, and in particular its creep. With this objective, oedometric cells with controlled temperatures between 5 and 70°C were developed. Two types of oedometers with suction controlled by osmotic and saline methods were used in a suction range of 0 to 20.8 MPa, and at a constant temperature of 20°C. These devices were used to study creep up to a vertical stress of 3600 kPa. The study focused on the behavior of a moderately swelling compacted clay. The obtained results first showed that the yield stress σ’p decreases as the temperature increases. The creep coefficient Cαe increases with temperature, this effect being particularly marked at higher stresses. A linear relationship between the creep coefficient Cαe and the incremental compression index C*c was observed within the stress range considered and the ratio (Cαe /C*c) is temperature dependent. Then, two complementary experimental approaches (creep tests by steps or at controlled strain rate) highlighted the dependence of creep characteristics on soil suction. In addition, the yield stress σ’p increases with increasing strain rate έv and suction. In contrast, the compression index Cc and the creep coefficient Cαe vary in a non-monotonic manner with a maximum value under suction of 3.5 and 2 MPa, respectively. The evolution of these parameters appears to be strongly related to the internal structure of the soil. Analysis of the variation of σ’p with έv and Cαe with Cc showed that the relationship Δlog σ’p /Δlog έv =Cαe/Cc is also valid for the studied compacted clayey soil in saturated and unsaturated states. In conclusion, the results of this work allowed information to be gathered for better understanding the compressibility and creep behavior of compacted clayey soils as a function of temperature and suction
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Forsyth, David I. "Fibre optic sensors based on fluorescence techniques for temperature and strain measurement." Thesis, City University London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269363.
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Wilson, Dwayne. "Ability of Physiological Strain Index to Discriminate Between Sustainable and Unsustainable Heat Stress." Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/6981.
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Introduction: Assessment of heat strain is an alternative approach to assessing heat stress exposures. Two common measures of heat strain are body core temperature (TC) and heart rate (HR). In this study TC was assessed by rectal temperature (Tre). Physiological Strain Index (PSI) was developed to combine both Tre and HR into one metric. Data collected from progressive heat stress trials were used to (1) demonstrate that PSI can distinguish between Sustainable and Unsustainable heat stress; (2) suggest values for PSI that demonstrate a sustainable level of heat stress; and (3) determine if clothing or metabolic rate were effect modifiers.
Methods: Two previous progressive heat stress studies included 494 trials with 988 pairs of Sustainable and Unsustainable exposures over a range of relative humidity (rh), metabolic rates (M) and clothing using 29 participants. To assess the discrimination ability of PSI, conditional logistic regression and logistic regression were used. The accuracy of PSI was assessed using Receiver Operating Characteristic curves (ROC).
Results: The present study found that primary (Tre, HR, and Tsk) and derived (PSI and ΔTre-sk) HSMs can accurately predict Unsustainable heat stress exposures based on AUCs that ranged from 0.73 to 0.86. Skin temperature had the highest AUC (0.86) with PSI in the mid-range (0.79).
The values of the HSMs associated with a predicted probability of 0.25 were considered as screening values (PSI < 2.6, ΔTre-sk > 1.9 °C, Tre < 37.5, HR < 109, and Tsk < 35.8). The value of using any one of these individual indicators is that they act as a screening tool to decide if an exposure assessment is needed.
Metabolic rate was found to be a confounder for all the HSMs except for RTsk. It was not statistically significant for HSMs derived models (PSI and ΔTre-sk). And its effect modification was not significant in any model.
Conclusions: Based on the ROC curve, PSI can accurately predict Unsustainable heat stress exposures (AUC 0.79). HR alone has a similar capacity to distinguish Unsustainable exposures (AUC 0.78) under relatively constant exposure (metabolic rate and environment) for an hour or so. Screening limits with high sensitivity, however, have low thresholds. This limits the utility of these heat strain metrics. To the extent that the observed strain is low, there is good evidence that the exposure is Sustainable.
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Šlais, Miroslav. "Studium vlivu rychlostních a teplotních parametrů na tvařitelnost Ti slitin." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2012. http://www.nusl.cz/ntk/nusl-234028.
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The PhD thesis deals with the influence of temperature and strain rate on the mechanical behaviour of the Ti-6Al-4V titanium alloy. After verification tests under static loading conditions, the samples were deformed at high strain rates and elevated temperatures, using device for Hopkinson pressure bar test. The result is dependence of stress and strain rate on strain in the temperature range of 20 to 500°C. The deformed shape of specimen from the Taylor anvil test is compared with the results of the simulation in the Ansys – LS Dyna software. The parameters of Johnson-Cook equation were determined from these experiments. Also, the influence of loading conditions on the microstructure was studied. Both optical and scanning electron microscopes were used for the observations. During the research, some adjustments to the experimental devices were made in order to suppress the high-frequency components and noise in the recorded pulses. A functional tensile test adapter for the Hopkinson test was developed; it is registered under No. 2007/008 at the Technology Transfer Office of BUT.
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Liu, Shibo. "Numerical and experimental study on residual stresses in laser beam welding of dual phase DP600 steel plates." Thesis, Rennes, INSA, 2017. http://www.theses.fr/2017ISAR0003/document.
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Le procédé de soudage laser est largement utilisé dans les travaux d'assemblage, en particulier, dans ledomaine de l'industrie automobile. L'acier dual phase DP600 est un acier à haute résistance qui permet deréduire le poids de l'automobile dans le cadre de l'allègement des structures. Notre travail s' estessentiellement basé sur l'évaluation des contraintes résiduelles générées dans l'acier DP600 lors du soudagepar laser. Deux approches ont été réalisées. L'approche expérimentale a été réalisée à l'aide de méthodes derayon X et par neutrons pour calculer les contraintes résiduelles. L'approche de simulation a été réalisée parcouplage de différentes formulations numériques.Numériquement, le formalisme de la mécanique continue a été utilisé par des simulations par éléments finis(FEM) pour analyser et évaluer les contraintes résiduelles. Sur la base de tests de traction expérimentaux, lemodèle constitutif élasto-thermo-plastique de l'acier DP600 a été identifié. L'écrouissage du matériau a étéétudié par la loi de Ludwik et de Voce. A partir de résultats experimentaux, un modèle a été proposé et lesrésultats analysés en utilisant une loi de mélange martensite (écrouissage Ludwik) et ferrite (adoucissementde Voce). De même, nous avons étudié la sensibilité à la température en utilisant plusieurs modèles :Johnson-Cook, Khan, Chen. A partir de cette étude, nous avons proposé un modèle de sensibilité à tatempérature. Enfin, un modèle de sensibilité à la déformation plastique, à la vitesse de déformation issu destravaux d'A.Gavrus et un modèle d'anisotropie planaire définit par la théorie de Hill ont été ajoutés.Une méthode d'automate cellulaire (CA) 2D a été programmée pour simuler l'évolution de la microstructurelors de la solification liée au processus de soudage laser. Dans ce modèle, les phénomènes de nucléationavec prise en compte de l'orientation de la croissance, de la concentration et de la vitesse de croissance àl'interface solide/liquide, l'anisotropie de la tension de surface, de la diffusion, ainsi que la fraction desphases en présence ont été pris en compte. De plus, les équations de conservation ont été étudiées en détail etanalysés. Les résultats ainsi que le champ de température issu du modèle FEM ont été importés dans lemodèle CA. En comparant la simulation et les résultats expérimentaux, de bonnes concordances ont ététrouvées.Par la suite, nous avons réalisés un couplage des deux modèles CA et FEM. Concernant le procédé laser, lesrésultats du modèle par éléments finis ont été analysés. La géométrie de l'échantillon, la source de chaleur,les conditions aux limites, le comportement thermo-mécanique de l'acier dual phase DP600 telles que laconductivité, la densité, la chaleur spécifique, l'expansion, l'élasticité et la plasticité sont introduites. Lesmodèles d'analyse du terme d'écrouissage, de la sensibilité à la vitesse de déformation, de la sensibilité à latempérature, de l'anisotropie plastique et de l'anisotropie élastique ont été simulés. Les fractions volumiquesconcernant ta nature des deux phases en présence ont été également étudiées.Les résultats numériques finaux tes contraintes résiduelles ont été étudiées. Les comparaisons avec desmesures experimentales ont montré à la fois quels phénomènes étudiés sont prépondérants et tes effets moinsinfluents sur l'évaluation des contraintes résiduelles. Les résultats tes plus probants ont montré des bonnesconvergences entre l'approche numérique et expérimentale. Ces résultats confortent la robustesse du modèlenumérique developpéLaser welding process is widely used in assembly work of automobi le industry. DP600 dual phase steeis a high strength steel to reduce automobile weight. Residual stresses are produced during laser weldingDP600. Continuum mechanics is used for analyzing res idual stresses by finite element simulation.Based on experimental tensile tests, the DP600 steel constitutive model are identified. The hardening termaccording to Ludwik law, Voce law and a proposed synthesis model are studied. The temperature sensitivityof Johnson-Cook, Khan, Chen and a proposed temperature sensitivity model are investigated. The strain ratesensitivity model proposed by A. Gavrus and planar anisotropy defined by Hi ll theory are also used.Cellul ar Automaton (CA) 20 method are programed for the simulation of solidification microstructureevolution during laser welding process. The temperature field of CA are imported from finite element analysimodel. The analysis function of nucleation, solid fraction, interface concentration, surface tension an isotropy,diffusion, interface growth ve locity and conservation equations are presented in detail. By comparing thesimulation and experimental results, good accordances are found.Modelling by a finite element method of laser welding process are presented. Geometry of specimen, heatsource, boundary conditions, DP600 dual phase steel material properties such as conductivity, density, specifiheat, expansion, elasticity and plasticity are introduced. Models analyzing hardening term, strain ratesensitivity, temperature sensitivity, plastic an isotropy and elastic an isotropy are simulated.The numerical results of laser welding DP600 steel process are presented. The influence of hardening term,strain rate sensitivity, temperature sensitivity and anisotropy on residual stresses are analyzed. Comparisonwith experimental data show good numerical accuracy.Keywords: Laser Welding, DP600, Residual Stress, Cellular Automaton, Hardening, Temperature sensitivity,Strain Rate Sensitivity, Anisotropy, Mixture dual phase law
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Konieczny, Mark J. "Full-Field Strain and Temperature Measurement of Epoxy Resin PR-520 Subjected to Tensile, Compressive, and Torsional Loading at Various Strain Rates." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1556880386878411.
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Surand, Martin. "Étude du comportement viscoplastique en traction et en fluage de l’alliage TA6V de 20 à 600 degrés Celsius." Thesis, Toulouse, INPT, 2013. http://www.theses.fr/2013INPT0096/document.
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Les durées de vie classiques des pièces en aéronautique sont de plusieurs dizaines d’années. Cependant, certaines applications en marge impliquent des durées de vie bien plus courtes, sans réparation ou récupération des pièces. Les modèles de conception classiques doivent être adaptés et la démarche du choix matériau se faire « au juste besoin », autorisant l’utilisation des matériaux aux conditions limites de leur intégrité. Afin d’estimer ces limites, la caractérisation à plus hautes températures d’alliages existants est entreprise. C’est dans cette optique que se placent les travaux de thèse présentés dans ce manuscrit. L’alliage étudié est le Ti-6Al-4V (TA6V) forgé qui possède à l’issu du traitement thermomécanique une microstructure duplex. Il est actuellement l’alliage de titane le plus couramment utilisé en aéronautique et son utilisation est généralement limitée aux environs de 350°C pour des durées de vie classiques. Dans le but d’utiliser cet alliage pendant une dizaine d’heure, l’étude menée consiste à caractériser le TA6V de 20°C à 600°C. La caractérisation se centre, dans un premier temps, sur l’état métallurgique de la matière initiale issue du galet forgé et sur sa stabilité en température. Ensuite, le comportement mécanique du TA6V est étudié de 20°C à 600°C en traction, mettant en évidence une sensibilité de la contrainte d’écoulement à la vitesse de déformation dépendant de la température. Ce comportement est mis en lien avec le phénomène de vieillissement dynamique. La caractérisation du comportement mécanique est poursuivie par une campagne étendue de fluage de 20°C à 600°C pour différents niveaux de contraintes (de 0,3 à 1 fois la limite d’élasticité en traction). Ces essais montrent différents comportements en fonction de la température. La matière déformée en traction et en fluage est analysée en microscopie électronique en transmission afin d’apporter des informations sur les mécanismes de déformation gouvernant les différents comportements de l’alliage. Les campagnes de caractérisation en traction et en fluage ont permis d’établir un modèle de comportement viscoplastique du TA6V de 20°C à 600°C validé par l’ajustement des résultats obtenus à l’issue d’essais thermomécaniques complexes avec la simulation de ces essais par éléments finis. La corrélation des résultats en traction et en fluage et la détermination des mécanismes de déformation conduit à une discussion sur le comportement viscoplastique du TA6V, pour finalement aboutir à une proposition de modélisation du fluage du TA6V de 20°C à 600°C. Le modèle permet de reproduire qualitativement des courbes de fluage à partir de la sensibilité à la vitesse de déformation mesurée au cours d’essais de tractionClassical life time of aeronautic parts lasts several decades. However, for some special applications with short life time and without repairs or recovery of parts, material design is tailored “close to real needs”. This justifies characterization at higher temperatures of well-known alloys and not developing new alloys. The study presented in this manuscript is included within this frame of short life applications. Forged Ti-6Al-4V (Ti-64) alloy with a bimodal microstructure is the most common titanium alloy in aeronautic and is usually limited below 350°C applications during classical life time. In order to use this alloy during a ten hour application, this thesis consists in characterizing Ti-64 from 20°C to 600°C. In a first time, characterization is focused on initial metallurgical state coming from a forged billet and on its thermal stability. Then, mechanical behavior of Ti-64 is studied by tensile testing from 20°C to 600°C, highlighting strain rate sensitivity (SRS) of flow stress. SRS is depending on temperature. This dependency is usually due to dynamic strain ageing phenomenon. Mechanical behavior characterization continues with creep testing from 20°C to 600°C for several stress levels (from 0.3 to 1 time yield stress values). Different behaviors versus temperature are revealed. Deformed samples by tensile testing and creep testing are analyzed by transmission electronic microscopy to bring information about deformation mechanisms controlling the different behaviors of the alloy. Thanks to tensile and creep testing, a viscoplastic modeling of Ti-64 from 20°C to 600°C has been performed and validated by fitting results from complex thermo mechanical tests with finite elements simulations. Comparison of mechanical behavior with deformation mechanisms leads to a discussion about viscoplasticity of Ti-64, and finally results in a proposal modeling creep behavior of Ti-64 from 20°C to 600°C. The model is able to estimate qualitatively creep curves using strain rate sensitivity measured during tensile tests
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Hasni, Abdellatif. "Etude des principales proprietes chimiques des solutions eau-chlorure de magnesium : application a la comprehension des phenomenes de corrosion sous contrainte de l'acier inoxydable austenitique 17-12-mo." Paris 6, 1988. http://www.theses.fr/1988PA066287.
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Etude du ph d'equilibre et du domaine d'acidite des solutions aqueuses de mgcl::(2) et de leur dependance vis-a-vis de la concentration et de la temperature des solutions. Analyse du comportement en corrosion sous tension de l'acier 17cr-12ni-2mo dans les solutions aqueuses de mgcl::(2) en fonction des differents parametres (concentration, temperature)
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ZHOU, XIAO-WEI. "Contribution au comportement dynamique des materiaux metalliques : etude experimentale de l'alliage al-li en torsion et en compression, simulation numerique du processus de penetration a grande vitesse." Nantes, 1988. http://www.theses.fr/1988NANT2014.
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Etude experimentale sur les alliages al-li soumis a des essais de traction et de compression pour des vitesses de deformation comprises entre 10**(-4) et 310**(3) s**(-1) et de 10**(-3) a 210**(3) s**(-1) respectivement. Auparavant ces alliages ont ete traites thermiquement. Analyse de la sensibilite a la vitesse de deformation. Influence du mecanisme d'activation thermique sur le processus de deformation. Determination du mode de rupture. Analyse des facies de rupture pour les echantillons deformes en traction et de la formation des cellules de dislocation dans ceux deformes en compression. Simulation numerique du processus de penetration a grande vitesse d'une cible mince par un projectile circulaire en utilisant un modele de fluide elasto-plastique. Comparaison avec des resultats experimentaux
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Castres, Magali. "Modélisation dynamique avancée des composites à matrice organique (CMO) pour l’étude de la vulnérabilité des structures aéronautiques." Thesis, Ecole centrale de Lille, 2018. http://www.theses.fr/2018ECLI0006/document.
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Les matériaux composites à matrice organique sont largement utilisés dans l'industrie des transports et notamment dans le domaine aéronautique. Pour permettre un dimensionnement optimal des structures, il est nécessaire d'étudier le comportement des matériaux CMO sur une large gamme de vitesses et de températures.L'objectif de cette thèse est de proposer un modèle de comportement et de rupture permettant de prédire la réponse des CMO sur une large gamme de vitesses de sollicitation et de températures. Les recherches se sont intéressées dans un premier temps à la caractérisation de la transition entre les régimes de comportement linéaire et non linéaire du matériau unidirectionnel T700GC/M21 (renforts de fibres de carbone, résine époxy), ainsi qu'à la dépendance de cette transition à la vitesse de sollicitation et à la température. Les travaux se sont ensuite focalisés sur l'étude expérimentale du régime de comportement non linéaire endommageable du T700GC/M21. Enfin, au terme de ces deux étapes, une version améliorée du modèle disponible à l'ONERA pour les composites stratifiés (OPFM) a été proposée, version intégrant un critère de transition linéaire/non linéaire de comportement, et une prise en compte de l'influence de la vitesse de sollicitation et de la température sur la réponse du matériauNowadays, organic matrix composite materials are widely used in the transportation industry, and particularly in the aeronautical industry. To provide an optimal dimensioning of the structures, it is necessary to study the mechanical behavior of OMC on a large range of strain rates and temperatures. The aim of this PhD thesis is to propose a behavior and a rupture model to predict the mechanical response of OMC for a large range of strain rates and temperatures. The research was initially focused on the characterization of the transition between the linear and nonlinear behavior of the material T700GC/M21, a carbon / epoxy unidirectional laminate as well as the strain rate and temperature dependencies of this transition. The work was then focused on the experimental study of the nonlinear damaged behavior of the T700GC/M21. Finally, completing these first two steps, an updated version of the behavior model available at ONERA (OPFM) was proposed which includes the transition between linear and nonlinear behavior and the influence of strain rate and temperature on the mechanical response of the material