Articles de revues : « Backstress »

1

Servatan, M., S. M. Hashemi et A. Varvani-Farahani. « Ratcheting Simulation of Additively Manufactured Aluminum 4043 Samples through Finite Element Analysis ». Applied Sciences 13, n^o 20 (22 octobre 2023) : 11553. http://dx.doi.org/10.3390/app132011553.

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This study presents a finite element-based ratcheting assessment of additively manufactured aluminum 4043 samples undergoing asymmetric loading cycles. The Chaboche material model in ANSYS was utilized and the effects of mesh and element type were examined. Different element numbers were used in a thorough convergence study to obtain independent meshing structures. The coefficients of this model were defined through stress–strain hysteresis loops determined from the strain-controlled tests. The backstress evolution and the corresponding yield surface translation in the deviatoric stress space were discussed as three different mesh elements of linear brick, quadratic tetrahedron, and quadratic brick were adopted. The magnitude of backstress was affected as different element types were employed. The first-order brick elements resulted in the highest backstress increments, while the lowest backstresses were determined when quadratic brick elements were taken. Backstress increments are positioned in an intermediate level with the use of quadratic tetrahedron elements. The choice of the element type, shape, and number influenced material ratcheting response over the loading process. The use of quadratic brick elements elevated the simulated ratcheting curves. The quadratic tetrahedron and linear brick elements, however, suppressed ratcheting level as compared with those of experimental data. The closeness of the simulated ratcheting results to those of the measured values was found to be highly dependent on these finite element variables.

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McDowell, D. L. « A Bounding Surface Theory for Cyclic Thermoplasticity ». Journal of Engineering Materials and Technology 114, n^o 3 (1 juillet 1992) : 297–303. http://dx.doi.org/10.1115/1.2904176.

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A nonisothermal, rate and time independent generalization of nonlinear kinematic hardening theory for cyclic plasticity is introduced. The model includes decomposition of backstress and of isotropic hardening between the yield surface radius and the backstress amplitude. A purely temperature dependent component of yield surface radius is assumed in addition to an isotropic hardening component. Issues of thermoplastic material stability and temperature history independence are clearly distinguished and addressed via implications of temperature rate terms. Correlations are reported for OFHC copper subjected to thermomechanical cyclic loading.

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3

Kassner, M. E., P. Geantil, L. E. Levine et B. C. Larson. « Backstress, the Bauschinger Effect and Cyclic Deformation ». Materials Science Forum 604-605 (octobre 2008) : 39–51. http://dx.doi.org/10.4028/www.scientific.net/msf.604-605.39.

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Backstresses or long range internal stresses (LRIS) in the past have been suggested by many to exist in plastically deformed crystalline materials. Elevated stresses can be present in regions of elevated dislocation density or dislocation heterogeneities in the deformed microstructures. The heterogeneities include edge dislocation dipole bundles (veins) and the edge dipole walls of persistent slip bands (PSBs) in cyclically deformed materials and cell and subgrain walls in monotonically deformed materials. The existence of long range internal stress is especially important for the understanding of cyclic deformation and also monotonic deformation. X-ray microbeam diffraction experiments performed by the authors using synchrotron x-ray microbeams determined the elastic strains within the cell interiors. The studies were performed using, oriented, monotonically deformed Cu single crystals. The results demonstrate that small long-range internal stresses are present in cell interiors. These LRIS vary substantially from cell to cell as 0 % to 50 % of the applied stress. The results are related to the Bauschinger effect, often explained in terms of LRIS.

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Borstad, C. P., E. Rignot, J. Mouginot et M. P. Schodlok. « Creep deformation and buttressing capacity of damaged ice shelves : theory and application to Larsen C ice shelf ». Cryosphere Discussions 7, n^o 4 (19 juillet 2013) : 3567–610. http://dx.doi.org/10.5194/tcd-7-3567-2013.

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Abstract. Around the perimeter of Antarctica, much of the ice sheet discharges to the ocean through floating ice shelves. The buttressing provided by ice shelves is critical for modulating the flux of ice into the ocean, and the presently observed thinning of ice shelves is believed to be reducing their buttressing capacity and contributing to the acceleration and thinning of the grounded ice sheet. However, relatively little attention has been paid to the role that fractures play in the flow and stability of ice shelves and their capacity to buttress the flow of grounded ice. Here, we develop an analytical framework for describing the role that fractures play in the creep deformation and buttressing capacity of ice shelves. We apply principles of continuum damage mechanics to derive a new analytical relation for the creep of an ice shelf as a function of ice thickness, temperature, material properties, resistive backstress and damage. By combining this analytical theory with an inverse method solution for the spatial rheology of an ice shelf, both backstress and damage can be calculated. We demonstrate the applicability of this new theory using satellite remote sensing and Operation IceBridge data for the Larsen C ice shelf, finding damage associated with known crevasses and rifts. We find that increasing thickness of mélange between rift flanks correlates with decreasing damage, with some rifts deforming coherently with the ice shelf as if completely healed. We quantify the stabilizing backstress caused by ice rises and lateral confinement, finding high backstress associated with two ice rises that likely stabilize the ice front in its current configuration. Though overall the ice shelf appears stable at present, the ice in contact with the Bawden ice rise is weakened by fractures, and additional damage or thinning in this area could portend significant change for the shelf. Using this new approach, field and remote sensing data can be utilized to monitor the structural integrity of ice shelves, their ability to buttress the flow of ice at the grounding line, and thus their indirect contribution to ice sheet mass balance and global sea level.

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Benn, Douglas I., Adrian Luckman, Jan A. Åström, Anna J. Crawford, Stephen L. Cornford, Suzanne L. Bevan, Thomas Zwinger et al. « Rapid fragmentation of Thwaites Eastern Ice Shelf ». Cryosphere 16, n^o 6 (27 juin 2022) : 2545–64. http://dx.doi.org/10.5194/tc-16-2545-2022.

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Abstract. Ice shelves play a key role in the dynamics of marine ice sheets by buttressing grounded ice and limiting rates of ice flux to the oceans. In response to recent climatic and oceanic change, ice shelves fringing the West Antarctic Ice Sheet (WAIS) have begun to fragment and retreat, with major implications for ice-sheet stability. Here, we focus on the Thwaites Eastern Ice Shelf (TEIS), the remaining pinned floating extension of Thwaites Glacier. We show that TEIS has undergone a process of fragmentation in the last 5 years, including brittle failure along a major shear zone, formation of tensile cracks on the main body of the shelf, and a release of tabular bergs on both the eastern and western flanks. Simulations with the Helsinki Discrete Element Model (HiDEM) show that this pattern of failure is associated with high backstress from a submarine pinning point at the distal edge of the shelf. We show that a significant zone of shear, upstream of the main pinning point, developed in response to the rapid acceleration of the shelf between 2002 and 2006, seeding damage on the shelf. Subsequently, basal melting and positive feedback between damage and strain rates weakened TEIS, allowing damage to accumulate. Thus, although backstress on TEIS has likely diminished over time as the pinning point shrunk, accumulation of damage has ensured that the ice in the shear zone remained the weakest link in the system. Experiments with the BISICLES ice-sheet model indicate that additional damage to or unpinning of TEIS is unlikely to trigger significantly increased ice loss from WAIS, but the calving response to the loss of TEIS remains highly uncertain. It is widely recognised that ice-shelf fragmentation and collapse can be triggered by hydrofracturing and/or unpinning from ice-shelf margins or grounding points. Our results indicate a third mechanism, backstress triggered failure, that can occur if and when an ice shelf is no longer able to withstand stress imposed by pinning points. In most circumstances, pinning points are essential for ice-shelf stability, but as ice shelves thin and weaken, the concentration of backstress in damaged ice upstream of a pinning point may provide the seeds of their demise.

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Wolff, M., M. Böhm, M. Dalgic, G. Löwisch, N. Lysenko et J. Rath. « Parameter identification for a TRIP model with backstress ». Computational Materials Science 37, n^o 1-2 (août 2006) : 37–41. http://dx.doi.org/10.1016/j.commatsci.2005.12.007.

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7

Voyiadjis, G. Z., et P. I. Kattan. « Phenomenological evolution equations for the backstress and spin tensors ». Acta Mechanica 88, n^o 1-2 (mars 1991) : 91–111. http://dx.doi.org/10.1007/bf01170595.

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Foga, Steve, Leigh A. Stearns et C. J. van der Veen. « Application of Satellite Remote Sensing Techniques to Quantify Terminus and Ice Mélange Behavior at Helheim Glacier, East Greenland ». Marine Technology Society Journal 48, n^o 5 (1 septembre 2014) : 81–91. http://dx.doi.org/10.4031/mtsj.48.5.3.

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AbstractIceberg calving is an efficient mechanism for ice mass loss, and rapidly calving glaciers are often considered to be inherently unstable. However, the physical controls on calving are not well understood. Recent studies hypothesize that the presence of a rigid ice mélange (composed of icebergs, bergy bits, and sea ice) can reduce iceberg calving by providing “backstress” to the terminus. To test this hypothesis we use remote sensing techniques to construct a time series model of calving rate and size and composition of the adjacent ice mélange. We describe a semi-automated routine for expediting the digitization process and illustrate the methods for Helheim Glacier, East Greenland, using 2008 data. Ice velocities of the glacier terminus and ice mélange are derived with feature-tracking software applied to radar imagery, which is successfully tracked year-round. Object-based image analysis (OBIA) is used to inventory icebergs and sea ice within the ice mélange. We find that the model successfully identifies the calving rate and ice mélange response trends associated with seasonal increases in terminus retreat and advance and shows seasonal trends of ice mélange potentially providing seasonal backstress on the glacier terminus.

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9

Brahme, Abhijit P., Kaan Inal, Raja K. Mishra et S. Saimoto. « The backstress effect of evolving deformation boundaries in FCC polycrystals ». International Journal of Plasticity 27, n^o 8 (août 2011) : 1252–66. http://dx.doi.org/10.1016/j.ijplas.2011.02.006.

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10

Wierzba, Bartek, Tsutomu Mashimo et Marek Danielewski. « Competition between Chemical and Gravity Forces in Binary Alloys ». High Temperature Materials and Processes 37, n^o 3 (26 mars 2018) : 285–88. http://dx.doi.org/10.1515/htmp-2016-0194.

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AbstractWe present the first experimental results of the growth of Cu6Sn5 and Cu3Sn under an external force field – during the sedimentation process. The results are compared with the proposed model under the combined influence of the Kirkendall effect, backstress and sedimentation. It is shown that Cu3Sn consumes the preformed Cu6Sn5 phase during sedimentation under a strong gravitational field of 779,000 G at 200 °C.

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11

Novikova, Elena V., Mariia A. Trimonova, Sergey B. Turuntaev, Evgeny V. Zenchenko et Petr E. Zenchenko. « Backstress Influence on the Formation Stress Field in Hydraulic Fracturing Experiments ». Geosciences 13, n^o 6 (23 mai 2023) : 153. http://dx.doi.org/10.3390/geosciences13060153.

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This work presents an analysis of data obtained through unique laboratory experiments on hydraulic fracturing. In the experiments, sufficiently large artificial samples were used to model a reservoir. Thus, it was possible to simulate several wells simultaneously, given that hydraulic fracture was initiated in one of them. In addition, the setup construction provided a true triaxial stress–strain state. The setup allowed us to investigate parameters that are difficult to access in real conditions. The data processing based on six laboratory experiments on hydraulic fracturing showed discrepancies between the values of the minimum stresses calculated from the fracture closure pressure and the actual values known based on the experimental conditions. There was also a discrepancy between the theoretical values of the fracture breakdown pressure and those obtained through the experiments. This paper examines phenomena such as backstress as the main reasons for this discrepancy. Backstress is stress acting on the walls of a fracture or well and is caused by the filtered hydraulic fracturing fluid. The authors demonstrated that by taking into account this phenomenon, one can significantly reduce the differences between calculated and experimental values. Therefore, the authors call for the careful use of the standard theory when determining the stress state in real fields.

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12

Wierzba, Bartek. « Void Formation during Diffusion – Two-Dimensional Approach ». High Temperature Materials and Processes 35, n^o 6 (1 juin 2016) : 629–33. http://dx.doi.org/10.1515/htmp-2015-0049.

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AbstractThe final set of equations defining the interdiffusion process in solid state is presented. The model is supplemented by vacancy evolution equation. The competition between the Kirkendall shift, backstress effect and vacancy migration is considered. The proper diffusion flux based on the Nernst–Planck formula is proposed. As a result, the comparison of the experimental and calculated evolution of the void formation in the Fe-Pd diffusion couple is shown.

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13

Borstad, C. P., E. Rignot, J. Mouginot et M. P. Schodlok. « Creep deformation and buttressing capacity of damaged ice shelves : theory and application to Larsen C ice shelf ». Cryosphere 7, n^o 6 (18 décembre 2013) : 1931–47. http://dx.doi.org/10.5194/tc-7-1931-2013.

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Abstract. Around the perimeter of Antarctica, much of the ice sheet discharges to the ocean through floating ice shelves. The buttressing provided by ice shelves is critical for modulating the flux of ice into the ocean, and the presently observed thinning of ice shelves is believed to be reducing their buttressing capacity and contributing to the acceleration and thinning of the grounded ice sheet. However, relatively little attention has been paid to the role that fractures play in the ability of ice shelves to sustain and transmit buttressing stresses. Here, we present a new framework for quantifying the role that fractures play in the creep deformation and buttressing capacity of ice shelves. We apply principles of continuum damage mechanics to derive a new analytical relation for the creep of an ice shelf that accounts for the softening influence of fractures on longitudinal deformation using a state damage variable. We use this new analytical relation, combined with a temperature calculation for the ice, to partition an inverse method solution for ice shelf rigidity into independent solutions for softening damage and stabilizing backstress. Using this new approach, field and remote sensing data can be utilized to monitor the structural integrity of ice shelves, their ability to buttress the flow of ice at the grounding line, and thus their indirect contribution to ice sheet mass balance and global sea level. We apply this technique to the Larsen C ice shelf using remote sensing and Operation IceBridge data, finding damage in areas with known crevasses and rifts. Backstress is highest near the grounding line and upstream of ice rises, in agreement with patterns observed on other ice shelves. The ice in contact with the Bawden ice rise is weakened by fractures, and additional damage or thinning in this area could diminish the backstress transmitted upstream. We model the consequences for the ice shelf if it loses contact with this small ice rise, finding that flow speeds would increase by 25% or more over an area the size of the former Larsen B ice shelf. Such a perturbation could potentially destabilize the northern part of Larsen C along pre-existing lines of weakness, highlighting the importance of the feedback between buttressing and fracturing in an ice shelf.

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Yoshida, Fusahito, Hiroshi Hamasaki et Takeshi Uemori. « Description of Closure of Cyclic Stress-Strain Loop and Ratcheting Based on Y-U Model ». Key Engineering Materials 725 (décembre 2016) : 351–56. http://dx.doi.org/10.4028/www.scientific.net/kem.725.351.

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This paper proposes a cyclic plasticity model to describe the closure of a cyclic stress-strain hysteresis loop based on the Y-U model. In this model, the backstress moves in a cyclic memory surface following a newly proposed kinematic hardening law. For this model just the same Y-U parameters can be used, and no additional material parameters are needed. By using a supplementary rule, this model is also able to describe ratcheting.

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UEMORI, TAKESHI, YUJI MITO, SATOSHI SUMIKAWA, RYUTARO HINO, FUSAHITO YOSHIDA et TETSUO NAKA. « PLASTIC DEFORMATION BEHAVIOR OF HIGH STRENGTH STEEL SHEET UNDER NON-PROPORTIONAL LOADING AND ITS MODELING ». International Journal of Modern Physics B 22, n^o 31n32 (30 décembre 2008) : 5394–99. http://dx.doi.org/10.1142/s0217979208050553.

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This paper deals with plastic deformations of a high tensile strength steel sheet (HTSS sheet) under biaxial stress condition including strain path. Using a cruciform specimen of a HTSS sheet of 780MPa-TS, experiments under proportional and non-proportional loadings were investigated. Numerical simulations of stress-strain responses for several strain paths after biaxial stretching were conducted using a large-strain cyclic plasticity model (Yoshida-Uemori model). The results of numerical simulation agrees well the corresponding experimental results, which is attributed to the accurate modeling of the backstress evolution of the anisotropic yield function.

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Gusak, A., B. Wierzba et M. Danielewski. « Competition between Kirkendall shift and backstress in interdiffusion revisited – simple analytic model ». Philosophical Magazine 94, n^o 10 (3 mars 2014) : 1153–65. http://dx.doi.org/10.1080/14786435.2013.878053.

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Uemori, Takeshi, T. Kuramitsu, Ryutaro Hino, Tetsuo Naka et Fusahito Yoshida. « Plastic Deformation Behavior of High Strength Steel Sheet under Non-Proportional Loading and its Modeling ». Key Engineering Materials 340-341 (juin 2007) : 895–900. http://dx.doi.org/10.4028/www.scientific.net/kem.340-341.895.

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This paper deals with experimental observations and modeling of plastic deformations of a high strength steel sheet (HSS sheet) under biaxial stress conditions. Using a cruciform specimen of a HSS sheet of 980MPa-TS, experiments of proportional and non-proportional loadings were performed. Numerical simulations for the biaxial stress-strain responses were conducted using a constitutive model of large-strain cyclic plasticity (Yoshida-Uemori model), and the results were compared to the experimental data. The results of numerical simulation show a good agreement with the experimental results, which is attributed to accurate modeling of the backstress evolution of the anisotropic yield surface.

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MAYAMA, Tsuyoshi, Katsuhiko SASAKI et Hiromasa ISHIKAWA. « Simulation of Biaxial Ratchetting Using the Unified Constitutive Model Considering Memorization of Backstress. » Transactions of the Japan Society of Mechanical Engineers Series A 68, n^o 675 (2002) : 1582–87. http://dx.doi.org/10.1299/kikaia.68.1582.

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Holzweissig, M. J., D. Canadinc et H. J. Maier. « In situ characterization of backstress effects on the austenite-to-bainite phase transformation ». Scripta Materialia 67, n^o 4 (août 2012) : 368–71. http://dx.doi.org/10.1016/j.scriptamat.2012.05.027.

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Liu, Lu, Yao Yao, Tao Zeng et Leon M. Keer. « A micromechanical model considering dislocation density based intra-granular backstress under cyclic loading ». Mechanics of Materials 129 (janvier 2019) : 41–49. http://dx.doi.org/10.1016/j.mechmat.2018.10.011.

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Voyiadjis, G. « Thermodynamic based model for the evolution equation of the backstress in cyclic plasticity ». International Journal of Plasticity 19, n^o 12 (décembre 2003) : 2121–47. http://dx.doi.org/10.1016/s0749-6419(03)00062-7.

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Stubstad, J. M., et G. J. Simitses. « Creep Analysis of Beams and Arches Based on a Hereditary Visco-Elastic-Plastic Constitutive Law ». Journal of Engineering Materials and Technology 112, n^o 2 (1 avril 1990) : 210–17. http://dx.doi.org/10.1115/1.2903309.

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An analytic study of planar beams and arches subjected to significant thermal cycling from ambient temperatures up to 800°C is presented. The study employs a recently unified nonlinear hereditary type of viscoelastoplastic constitutive law to characterize the time- and temperature-dependent properties of Hastelloy X, a typical aerospace alloy. The results demonstrate a strong interaction between the backstress variable of the constitutive law and the time-dependent stress distribution produced by the deformation. This interaction tends to control, in a highly nonlinear manner, the creep ratchetting response of the beam or arch. Moreover, temperature gradients in the thickness direction tend to exert an important influence during thermal cycling.

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Keller, Clement, Gael Marnier, Wilson Veloz et Lakhdar Taleb. « Influence of the stacking fault energy and temperature on the prestrain memory effect of face centered cubic metal submitted to cyclic loadings ». MATEC Web of Conferences 165 (2018) : 06008. http://dx.doi.org/10.1051/matecconf/201816506008.

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In this paper, the effect of a monotonic prehardening in tension on the subsequent cyclic stress strain curves is investigated as a function of the deformation mechanisms. To this aim, three materials are employed, copper for wavy dislocation slip, Ni20Cr alloy for planar slip and AISI 316L for intermediate deformation mechanisms. Samples were first prestrained in tension and then submitted to incremental strain cyclic tests at room temperature, and also 200°C for the 316L. Based on the analysis of the flow stress components (backstress and effective stress), the results show that all materials are sensitive to a prehardening depending on the prestrain level and cyclic test characteristics (amplitude and temperature).

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Li, Ling, Lu Ming Shen et Gwénaëlle Proust. « Crystal Plasticity Simulation of the Bauschinger Effect of Polycrystalline AA7075 through a Texture-Based Representative Volume Element Model ». Applied Mechanics and Materials 553 (mai 2014) : 22–27. http://dx.doi.org/10.4028/www.scientific.net/amm.553.22.

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A texture-based representative volume element (TBRVE) model is developed for the three-dimensional crystal plasticity (CP) finite element simulations of the Bauschinger effect (BE) of polycrystalline aluminium alloy 7075 (AA7075). In the simulations, the grain morphology is created using the Voronoi tessellation method with the material texture systematically discretised from experiment. A modified CP constitutive model, which takes into account the backstress, is used to simulate the BE during cyclic loading. The model parameters are calibrated using the first cycle stress-strain curve and used to predict the mechanical response to the cyclic saturation of AA7075. The results indicate that the proposed TBRVE CP finite element model can effectively capture the BE at the grain level.

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Aktaa, J. « Unified modelling of time dependent damage taking into account an explicit dependency on backstress ». International Journal of Fatigue 19, n^o 3 (mars 1997) : 195–200. http://dx.doi.org/10.1016/s0142-1123(97)83266-5.

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Yao, Hong, et Jian Cao. « Prediction of forming limit curves using an anisotropic yield function with prestrain induced backstress ». International Journal of Plasticity 18, n^o 8 (août 2002) : 1013–38. http://dx.doi.org/10.1016/s0749-6419(01)00022-5.

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Kuroda, Mitsutoshi. « Interfacial microscopic boundary conditions associated with backstress-based higher-order gradient crystal plasticity theory ». Journal of Mechanics of Materials and Structures 12, n^o 2 (1 janvier 2017) : 193–218. http://dx.doi.org/10.2140/jomms.2017.12.193.

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Luo, Yan. « A Cyclic Softening Plastic Model of Carbon Steel 45 under Uniaxial Cyclic Straining ». Advanced Materials Research 343-344 (septembre 2011) : 85–91. http://dx.doi.org/10.4028/www.scientific.net/amr.343-344.85.

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Based on the characteristic of cyclic softening of the quenched and tempered Carbon steel 45, a cyclic plastic constitutive model was proposed to describe the cyclic behavior under symmetrical and unsymmetrical strain cycling with different strain amplitudes. In this model, the phenomenon of the decrease of the up yield limit stress with the increase of strain in the initial 1/4 cycle was taken into account. The proposed evolution equations of the yield size and backstress can simulate the cycling softening under symmetrical and unsymmetrical strain cycling well. The results indicated that either the simulated shape of the cyclic softening hysteresis loops or the evolution of stress amplitude with the increase of the cyclic number during the low cycle fatigue coincides with the experimental ones very well.

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Venteris, E. R., I. M. Whillans et C. J. Van der Veen. « Effect of extension rate on terminus position, Columbia Glacier, Alaska, U.S.A. » Annals of Glaciology 24 (1997) : 49–53. http://dx.doi.org/10.3189/s0260305500011927.

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The relations between seasonal changes in ice speed, longitudinal extension rate and terminus position are investigated for Columbia Glacier, Alaska, over the period 1977–87. The lower reach of the glacier is studied using repeat aerial photography, which extends from the terminus to the base of an icefall about 14 km up-glacier. There are regular seasonal cycles in speed and stretching rate. These cycles continue after the glacier retreats off the shoal at the end of the fjord (in about 1983), indicating that factors other than backstress, such as seasonal changes in subglacial water, control the speed of the glacier. Terminus position appears to be linked with thinning induced by longitudinal extension, as predicted by the calving model proposed by Van der Veen (1996).

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Venteris, E. R., I. M. Whillans et C. J. Van der Veen. « Effect of extension rate on terminus position, Columbia Glacier, Alaska, U.S.A. » Annals of Glaciology 24 (1997) : 49–53. http://dx.doi.org/10.1017/s0260305500011927.

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The relations between seasonal changes in ice speed, longitudinal extension rate and terminus position are investigated for Columbia Glacier, Alaska, over the period 1977–87. The lower reach of the glacier is studied using repeat aerial photography, which extends from the terminus to the base of an icefall about 14 km up-glacier. There are regular seasonal cycles in speed and stretching rate. These cycles continue after the glacier retreats off the shoal at the end of the fjord (in about 1983), indicating that factors other than backstress, such as seasonal changes in subglacial water, control the speed of the glacier. Terminus position appears to be linked with thinning induced by longitudinal extension, as predicted by the calving model proposed by Van der Veen (1996).

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Paolo, Fernando S., Alex S. Gardner, Chad A. Greene, Johan Nilsson, Michael P. Schodlok, Nicole-Jeanne Schlegel et Helen A. Fricker. « Widespread slowdown in thinning rates of West Antarctic ice shelves ». Cryosphere 17, n^o 8 (23 août 2023) : 3409–33. http://dx.doi.org/10.5194/tc-17-3409-2023.

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Abstract. Antarctica's floating ice shelves modulate discharge of grounded ice into the ocean by providing a backstress. Ice shelf thinning and grounding line retreat have reduced this backstress, driving rapid drawdown of key unstable areas of the Antarctic Ice Sheet, leading to sea-level rise. If ice shelf loss continues, it may initiate irreversible glacier retreat through the marine ice sheet instability. Identification of areas undergoing significant change requires knowledge of spatial and temporal patterns in recent ice shelf loss. We used 26 years (1992–2017) of satellite-derived Antarctic ice shelf thickness, flow, and basal melt rates to construct a time-dependent dataset of ice shelf thickness and basal melt on a 3 km grid every 3 months. We used a novel data fusion approach, state-of-the-art satellite-derived velocities, and a new surface mass balance model. Our data revealed an overall pattern of thinning all around Antarctica, with a thinning slowdown starting around 2008 widespread across the Amundsen, Bellingshausen, and Wilkes sectors. We attribute this slowdown partly to modulation in external ocean forcing, altered in West Antarctica by negative feedbacks between ice shelf thinning rates and grounded ice flow, and sub-ice-shelf cavity geometry and basal melting. In agreement with earlier studies, the highest rates of ice shelf thinning are found for those ice shelves located in the Amundsen and Bellingshausen sectors. Our study reveals that over the 1992–2017 observational period the Amundsen and Bellingshausen ice shelves experienced a slight reduction in rates of basal melting, suggesting that high rates of thinning are largely a response to changes in ocean conditions that predate our satellite altimetry record, with shorter-term variability only resulting in small deviations from the long-term trend. Our work demonstrates that causal inference drawn from ice shelf thinning and basal melt rates must take into account complex feedbacks between thinning and ice advection and between ice shelf draft and basal melt rates.

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Gusak, Andriy, Nadiya Storozhuk et King Ning Tu. « Models of Interdiffusion in a Polycrystalline Alloy : Kirkendall Effect versus Non-Equilibrium Vacancies and Backstress ». Defect and Diffusion Forum 309-310 (mars 2011) : 135–42. http://dx.doi.org/10.4028/www.scientific.net/ddf.309-310.135.

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In order to study evolution of the concentration profiles and markers velocities in various time and space scales quasi-one-dimensional model of interdiffusion in a polycrystalline alloy is proposed considering non-equilibrium vacancies and the Kirkendall effect. Sinks/sources of vacancies are assumed to be concentrated mainly at the moving grain boundaries. This model simultaneously takes into account the movement of grains and changes of grain sizes.

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Gusak, A., B. Wierzba et M. Danielewski. « Electromigration revisited : competition between Kirkendall shift and backstress in pure metals and two-phase alloys ». Philosophical Magazine 95, n^o 10 (13 mars 2015) : 1093–104. http://dx.doi.org/10.1080/14786435.2015.1020352.

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Fischlschweiger, Michael, Georges Cailletaud et Thomas Antretter. « A mean-field model for transformation induced plasticity including backstress effects for non-proportional loadings ». International Journal of Plasticity 37 (octobre 2012) : 53–71. http://dx.doi.org/10.1016/j.ijplas.2012.04.001.

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Altenbach, Holm, Dmitry Breslavsky, Konstantin Naumenko et Oksana Tatarinova. « Two-time-scales and time-averaging approaches for the analysis of cyclic creep based on Armstrong–Frederick type constitutive model ». Proceedings of the Institution of Mechanical Engineers, Part C : Journal of Mechanical Engineering Science 233, n^o 5 (27 avril 2018) : 1690–700. http://dx.doi.org/10.1177/0954406218772609.

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The aim of this paper is the analysis of inelastic behavior under periodic cyclic loading regimes for materials showing recovery effects. Starting with the Armstrong–Frederick type model and applying the two-time-scale asymptotic technique, the constitutive equation for the mean inelastic strain rate and the evolution equation for the mean backstress variable are derived. The advantage of the presented technique is the closed analytical form of the solutions such that the influence of the loading profiles on the resulting slow cycle-by-cycle strain accumulation can be analyzed explicitly. To validate the derived equations, the original constitutive model is integrated numerically by applying the time-step procedure for various cyclic loading profiles. Numerical examples are presented to illustrate cyclic creep behavior of X20CrMoV12-1 heat resistant steel.

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Hatami, Faezeh, et Ahmad Varvani-Farahani. « Accumulation of Plastic Strain at Notch Root of Steel Specimens Undergoing Asymmetric Fatigue Cycles : Analysis and Simulation ». Materials 16, n^o 6 (7 mars 2023) : 2153. http://dx.doi.org/10.3390/ma16062153.

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The present study evaluates the ratcheting response at notch roots of 1045 steel specimens experiencing uniaxial asymmetric fatigue cycles. Local stress and strain components at the notch root were analytically evaluated through the use of Neuber, Glinka, and Hoffman-Seeger (H-S) rules coupled with the Ahmadzadeh-Varvani (A-V) kinematic hardening model. Backstress promotion through coupled kinematic hardening model with the Hoffman-Seeger, Neuber, and Glinka rules was studied. Relaxation in local stresses on the notched samples as hysteresis loops moved forward with plastic strain accumulation during asymmetric loading cycles was observed. Local ratcheting results were simulated through FE analysis, where the Chaboche model was employed as the materials hardening rule. A consistent response of the ratcheting values was evidenced as predicted, and simulated results were compared with the measured ratcheting data.

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Hsu, Jen-Che, et Kwang-Lung Lin. « Effect of internal stress on elemental diffusion and crystallization of electroless Ni–Cu–P deposit on Al ». Journal of Materials Research 18, n^o 9 (septembre 2003) : 2221–27. http://dx.doi.org/10.1557/jmr.2003.0310.

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The type and magnitude of stress in electroless Ni–Cu–P deposits on Al were manipulated by controlling the concentration of saccharin in the plating solution. Tensile, zero, and compressive stress of the electroless Ni–Cu–P deposits was obtained with 0, 8, and 10 g/l saccharin for studying the effect of stress on the diffusion and crystallization behavior of the deposit. The effect of stress on the diffusion behavior of Cu, Ni, and Al elements during annealing was investigated. Interdiffusion between Al and Ni in an amorphous Ni–Cu–P/crystal Al diffusion couple is abated by the effects of amorphous structure, atomic affinity, and backstress. Therefore, the effect of stress on diffusion is manifested by Cu elemental diffusion. The tensile stress promotes the formation of Ni3P and the diffusion of Cu into the substrate.

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Jiang, Maoyuan, et Benoit Devincre. « Uncovering the existence of anti-backstress associated with dislocations accumulated at grain boundaries during plastic deformation ». Computational Materials Science 208 (juin 2022) : 111328. http://dx.doi.org/10.1016/j.commatsci.2022.111328.

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Koo, Sungyong, Jungmoo Han, Karuppasamy Pandian Marimuthu et Hyungyil Lee. « Determination of Chaboche combined hardening parameters with dual backstress for ratcheting evaluation of AISI 52100 bearing steel ». International Journal of Fatigue 122 (mai 2019) : 152–63. http://dx.doi.org/10.1016/j.ijfatigue.2019.01.009.

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Li, Ling, Lu Ming Shen et Gwénaëlle Proust. « Crystal Plasticity Finite Element Simulations of Polycrystalline Aluminium Alloy under Cyclic Loading ». Advanced Materials Research 891-892 (mars 2014) : 1609–14. http://dx.doi.org/10.4028/www.scientific.net/amr.891-892.1609.

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A three-dimensional crystal plasticity (CP) finite element model is developed to reproduce the grain level stress concentration and deformation of polycrystalline aluminium alloy 7075 (AA7075) during fatigue experiments. The grains contained in the model possess the same size and crystallographic orientations obtained from electron back-scatter diffraction experiments. A modified CP constitutive model, which considers the backstress evolution, is employed to describe the mechanical behaviour of AA7075 under cyclic loading. A round-notched specimen from a fatigue test is simulated using the proposed CP model. Convergence studies in terms of mesh density and plastic deformation zone size are carried out to determine the appropriate conditions for the simulation. The simulation results are compared with those obtained using the elasto-plastic model and the CP model without grain morphology. The comparison indicates that with the embedded grain morphology, the proposed model can capture very well the local response induced by the microstructure features, which is vital to the accurate fatigue life prediction of aluminium alloys.

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ÇAYLAK, Melih, Toros Arda AKŞEN et Mehmet FIRAT. « Evaluating the effectiveness of combined hardening models to determine the behavior of a plate with a hole under combined loadings ». European Mechanical Science 6, n^o 2 (26 juin 2022) : 97–104. http://dx.doi.org/10.26701/ems.1051057.

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Geometrical discontinuities in a material such as holes and notches on machine elements are called as critical regions due to the stress concentrations. They are the potential failure initiation locations Therefore, researchers put significant effort on the prediction of the material response in these discontinuities under repetitive loadings. Cyclic plasticity is concerned with the nonlinear material response under cyclic loadings. In this study, numerical cyclic stress – strain response of a plate with a hole was evaluated under the combined loadings which are cyclic bending and tensile loadings. Oxygen Free High Thermal Conductivity (OFHC) Copper alloy was considered as material, and finite element simulations were performed in Marc software. A user defined material subroutine known as Hypela2 was utilized in order to define the material response. The plasticity model used in the present study comprises J2 plasticity along with combined isotropic – kinematic hardening model. Evolution of the backstress was introduced by Armstrong – Frederic type kinematic hardening model. The results were compared with the literature study, and it was seen that presented hardening model provides accurate results in small cyclic strain range.

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ROYSTON, SAM, et G. HILMAR GUDMUNDSSON. « Changes in ice-shelf buttressing following the collapse of Larsen A Ice Shelf, Antarctica, and the resulting impact on tributaries ». Journal of Glaciology 62, n^o 235 (21 juillet 2016) : 905–11. http://dx.doi.org/10.1017/jog.2016.77.

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ABSTRACTThe dominant mass-loss process on the Antarctic Peninsula has been ice-shelf collapse, including the Larsen A Ice Shelf in early 1995. Following this collapse, there was rapid speed up and thinning of its tributary glaciers. We model the impact of this ice-shelf collapse on upstream tributaries, and compare with observations using new datasets of surface velocity and ice thickness. Using a two-horizontal-dimension shallow shelf approximation model, we are able to replicate the observed large increase in surface velocity that occurred within Drygalski Glacier, Antarctic Peninsula. The model results show an instantaneous twofold increase in flux across the grounding line, caused solely from the reduction in backstress through ice shelf removal. This demonstrates the importance of ice-shelf buttressing for flow upstream of the grounding line and highlights the need to explicitly include lateral stresses when modelling real-world settings. We hypothesise that further increases in velocity and flux observed since the ice-shelf collapse result from transient mass redistribution effects. Reproducing these effects poses the next, more stringent test of glacier and ice-sheet modelling studies.

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Schouwenaars, R., V. H. Jacobo et A. Ortiz. « Multiple dislocation pile-ups in small grains at small strains : implications for the Hall-Petch relationship and backstress screening ». IOP Conference Series : Materials Science and Engineering 63 (8 août 2014) : 012132. http://dx.doi.org/10.1088/1757-899x/63/1/012132.

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Bandyopadhyay, Ritwik, Sven E. Gustafson, Kartik Kapoor, Diwakar Naragani, Darren C. Pagan et Michael D. Sangid. « Comparative assessment of backstress models using high-energy X-ray diffraction microscopy experiments and crystal plasticity finite element simulations ». International Journal of Plasticity 136 (janvier 2021) : 102887. http://dx.doi.org/10.1016/j.ijplas.2020.102887.

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Wolff, M., M. Böhm, M. Dalgic, G. Löwisch et J. Rath. « Validation of a TP model with backstress for the pearlitic transformation of the steel 100Cr6 under step-wise loads ». Computational Materials Science 39, n^o 1 (mars 2007) : 49–54. http://dx.doi.org/10.1016/j.commatsci.2006.01.025.

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Cook, S., I. C. Rutt, T. Murray, A. Luckman, T. Zwinger, N. Selmes, A. Goldsack et T. D. James. « Modelling environmental influences on calving at Helheim Glacier in eastern Greenland ». Cryosphere 8, n^o 3 (6 mai 2014) : 827–41. http://dx.doi.org/10.5194/tc-8-827-2014.

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Abstract. Calving is an important mass-loss process for many glaciers worldwide, and has been assumed to respond to a variety of environmental influences. We present a grounded, flowline tidewater glacier model using a physically-based calving mechanism, applied to Helheim Glacier, eastern Greenland. By qualitatively examining both modelled size and frequency of calving events, and the subsequent dynamic response, the model is found to realistically reproduce key aspects of observed calving behaviour. Experiments explore four environmental variables which have been suggested to affect calving rates: water depth in crevasses, basal water pressure, undercutting of the calving face by submarine melt and backstress from ice mélange. Of the four variables, only crevasse water depth and basal water pressure were found to have a significant effect on terminus behaviour when applied at a realistic magnitude. These results are in contrast to previous modelling studies, which have suggested that ocean temperatures could strongly influence the calving front. The results raise the possibility that Greenland outlet glaciers could respond to the recent trend of increased surface melt observed in Greenland more strongly than previously thought, as surface ablation can strongly affect water depth in crevasses and water pressure at the glacier bed.

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Suchocki, Cyprian. « On finite element implementation of cyclic elastoplasticity : theory, coding, and exemplary problems ». Acta Mechanica 233, n^o 1 (7 décembre 2021) : 83–120. http://dx.doi.org/10.1007/s00707-021-03069-3.

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AbstractIn this work the finite element (FE) implementation of the small strain cyclic plasticity is discussed. The family of elastoplastic constitutive models is considered which uses the mixed, kinematic-isotropic hardening rule. It is assumed that the kinematic hardening is governed by the Armstrong–Frederick law. The radial return mapping algorithm is utilized to discretize the general form of the constitutive equation. A relation for the consistent elastoplastic tangent operator is derived. To the best of the author’s knowledge, this formula has not been presented in the literature yet. The obtained set of equations can be used to implement the cyclic plasticity models into numerous commercial or non-commercial FE packages. A user subroutine UMAT (User’s MATerial) has been developed in order to implement the cyclic plasticity model by Yoshida into the open-source FE program CalculiX. The coding is included in the Appendix. It can be easily modified to implement any isotropic hardening rule for which the yield stress is a function of the effective plastic strain. The number of the utilized backstress variables can be easily increased as well. Several validation tests which have been performed in order to verify the code’s performance are discussed.

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Cook, S., I. C. Rutt, T. Murray, A. Luckman, N. Selmes, A. Goldsack et T. Zwinger. « Modelling environmental influences on calving at Helheim Glacier, East Greenland ». Cryosphere Discussions 7, n^o 5 (4 septembre 2013) : 4407–42. http://dx.doi.org/10.5194/tcd-7-4407-2013.

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Abstract. Calving is an important mass-loss process for many glaciers worldwide, and has been assumed to respond to a variety of environmental influences. We present a grounded, flowline tidewater glacier model, using a physically realistic calving mechanism, which is applied to Helheim Glacier, East Greenland. By qualitatively examining both modelled size and frequency of calving events, and the subsequent dynamic response, the model is found to produce a realistic representation of calving behaviour. Experiments use four environmental variables which have been suggested to affect calving rates: water depth in crevasses, basal water pressure, undercutting of the calving face by submarine melt and backstress from ice mélange. Of the four variables, only crevasse water depth and basal water pressure were found to have a significant effect on terminus behaviour when applied at a realistic magnitude. These results are in contrast to previous modelling studies, which have suggested that ocean temperatures could strongly influence the calving front. The results raise the possibility that Greenland outlet glaciers could respond more strongly than previously thought to the recent trend of increased surface melt observed in Greenland, as surface ablation can strongly affect water depth in crevasses and water pressure at the glacier bed.

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Natesan, Elanghovan, Stefan Eriksson, Johan Ahlström et Christer Persson. « Effect of Temperature on Deformation and Fatigue Behaviour of A356–T7 Cast Aluminium Alloys Used in High Specific Power IC Engine Cylinder Heads ». Materials 13, n^o 5 (7 mars 2020) : 1202. http://dx.doi.org/10.3390/ma13051202.

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Aggressive downsizing of the internal combustion engines used as part of electrified powertrains in recent years have resulted in increasing thermal loads on the cylinder heads and consequently, the susceptibility to premature thermo-mechanical fatigue failures. To enable a reliable computer aided engineering (CAE) prediction of the component lives, we need more reliable material deformation and fatigue performance data. Material for testing was extracted from the highly loaded valve bridge area of specially cast cylinder heads to study the monotonic and cyclic deformation behaviour of the A356–T7 + 0.5% Cu alloy at various temperatures. Monotonic tensile tests performed at different temperatures indicate decreasing strength from 211 MPa at room temperature to 73 MPa at 300 °C and a corresponding increase in ductility. Completely reversed, strain controlled, uniaxial fatigue tests were carried out at 150, 200 and 250 °C. A dilatometric study carried out to study the thermal expansion behaviour of the alloy in the temperature range 25–360 °C shows a thermal expansion coefficient of (25–30) × 10−6 °C−1. Under cyclic loading, increasing plastic strains are observed with increasing temperatures for similar load levels. The experimental data of the cyclic deformation behaviour are calibrated against a nonlinear combined kinematic–isotropic hardening model with both a linear and non-linear backstress.

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James, G. H., P. K. Imbrie, P. S. Hill, D. H. Allen et W. E. Haisler. « An Experimental Comparison of Several Current Viscoplastic Constitutive Models at Elevated Temperature ». Journal of Engineering Materials and Technology 109, n^o 2 (1 avril 1987) : 130–39. http://dx.doi.org/10.1115/1.3225952.

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Four current viscoplastic models are compared experimentally for Inconel 718 at 593°C. This material system responds with apparent negative strain rate sensitivity, undergoes cyclic work softening, and is susceptible to low cycle fatigue. The models used include Bodner’s anisotropic model, Krieg, Swearengen, and Rhode’s model, Schmidt and Miller’s model, and Walker’s exponential model. Schmidt and Miller’s model and Walker’s model correct for negative strain rate sensitivity response. A correction similar to Schmidt’s is applied to the models of Bodner and Krieg et al. A series of tests has been performed to create a sufficient data base from which to evaluate material constants. A method to evaluate the constants is developed which draws on common assumptions for this type of material, recent advances by other researchers, and iterative techniques. A complex history test, not used in calculating the constants, is then used to compare the predictive capabilities of the models. The combination of exponentially based inelastic strain rate equations and dynamic recovery is shown to model this material system with the greatest success. The method of constant calculation developed in this work was successfully applied to the complex material response encountered. Backstress measuring tests were found to be invaluable and warrant further development.

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