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Creep Deformation (creep + deformation)
Selected AbstractsThe importance of multiaxial stress in creep deformation and ruptureFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 4 2004I. W. GOODALL ABSTRACT This paper investigates the importance of multiaxial stress states by considering several distinct testing techniques used in assessing both creep deformation and creep damage accumulation. The requirements of testing programmes to determine the necessary data are discussed in respect of sensitivity and interdependence of the principal and hydrostatic stress ratios. [source] Numerical modeling of creep and creep damage in thin plates of arbitrary shape from materials with different behavior in tension and compression under plane stress conditionsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2009A. Zolochevsky Abstract A constitutive model for describing the creep and creep damage in initially isotropic materials with characteristics dependent on the loading type, such as tension, compression and shear, has been applied to the numerical modeling of creep deformation and creep damage growth in thin plates under plane stress conditions. The variational approach of establishing the basic equations of the plane stress problem under consideration has been introduced. For the solution of two-dimensional creep problems, the fourth-order Runge,Kutta,Merson's method of time integration, combined with the Ritz method and R-functions theory, has been used. Numerical solutions to various problems have been obtained, and the processes of creep deformation and creep damage growth in thin plates of arbitrary shape have been investigated. The influence of tension,compression asymmetry on the stress,strain state and damage evolution, with time, in thin plates of arbitrary shape, has been discussed. Copyright © 2009 John Wiley & Sons, Ltd. [source] THIS ARTICLE HAS BEEN RETRACTED Effect of Silica Sol on the Properties of Alumina-Based Duplex Ceramic CoresINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2008Yexia Qin A series of alumina-based ceramic cores sintered at 1300°C, 1400°C, and 1500°C for 5 h were prepared, and the phases and microstructures were characterized by X-ray diffraction and scanning electron microscopy. The effect of colloidal silica sols on the properties of ceramic core was discussed. The properties of these materials were determined. The results indicated that the microstructure of the core is characterized by the presence of substantially unreacted Al2O3 particles having a polycrystalline composition consisting essentially of in situ synthesized 3Al2O3·2SiO2 on the surface of the Al2O3 particles. The colloidal silica sol contents do not have an appreciable effect on the densification and shrinkage of the alumina ceramic core. The ceramic cores of 5 wt% colloidal silica sol contents sintered at 1500°C for 5 h showed the smallest creep deformation in the present research. [source] Superplasticity of a Fine-Grained TZ3Y Material Involving Dynamic Grain Growth and Dislocation MotionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2010Guillaume Bernard-Granger Superplastic deformation of a fully dense TZ3Y material, having a starting grain size around 135,145 nm and depleted of any amorphous phase at grain boundaries, has been investigated using compressive creep tests in air in the temperature range of 1100°,1300°C and the real stress range of 50,100 MPa. The key parameters of the creep law have been determined by performing temperature changes at a fixed stress and stress jumps at a fixed temperature. From such experiments, an average value for the apparent stress exponent of around 3 is obtained when the applied stress varied from 50 to 100 MPa and the temperature was kept constant in the range of 1100°,1300°C. The apparent activation energy of the mechanism controlling the creep deformation is evaluated at 577±75 kJ/mol in the temperature range of 1200°,1300°C, for a real stress of 70 MPa. The values of the apparent grain size exponent can be calculated from the initial grain size in the as-sintered samples and the grain size in the crept samples. In all cases, it was determined to be around 2. Observation of the microstructure of the crept samples, using scanning electron microscopy, reveals grain growth but does not show any significant elongation of the elemental grains. Transmission electron microscopy of a sample crept under 100 MPa at 1300°C reveals clear intragranular dislocation activity. This dislocation activity seems to be mainly confined in folds emitted at triple points. Because the creep parameters (experimental and calculated using a simple geometric model) and the microstructure observed are in good agreement, we propose that the creep mechanism involved is grain boundary sliding accommodated by dynamic grain growth and the formation of triple-point folds. [source] Creep Resistant Polymer Nanocomposites Reinforced with Multiwalled Carbon NanotubesMACROMOLECULAR RAPID COMMUNICATIONS, Issue 8 2007Jinglei Yang Abstract Poly(propylene) (PP) nanocomposites filled with shorter- and longer-aspect-ratio multiwalled carbon nanotubes (MWNTs) were compounded using a twin-screw extruder and an injection moulding machine. It is shown that with only 1 vol.-% of MWNTs, creep resistance of PP can be significantly improved with reduced creep deformation and creep rate at a long-term loading period. Additionally, the creep lifetime of the nanocomposites has been considerably extended by 1,000% compared to that of a neat PP. Three possible mechanisms of load transfer were considered that could contribute to the observed enhancement of creep resistance, which are: (1) fairly good interfacial strength between MWNTs and polymer matrix, (2) increasing immobility of amorphous regions due to nanotubes acting as restriction sites, and (3) high aspect ratio of MWNTs. DSC results showing crystallinity changes in the specimens before and after creep deformation present evidence to confirm these mechanisms. Our results should lead to improved grades of creep resistant polymer nanocomposites for engineering applications. [source] Moisture-induced effects on stacking strength of moulded-fibre packaging in varying environmental conditionsPACKAGING TECHNOLOGY AND SCIENCE, Issue 5 2004Gitte Sørensen Abstract Stacking strength of moulded-fibre trays was investigated as both compressional creep and static compression strength at constant and varying humidity conditions. The compressional creep behaviour resembled that of other paper and board containers and was accelerated at humidity cycling between 33% and 94% relative humidity (r.h.) for 18 days compared to constant humidity conditions 91% and 94% r.h. Although the moulded-fibre trays did not experience failure, secondary creep rate was accelerated by a factor of 10,20 and total creep strain by a factor of 1.3,1.6. Compressional creep was thus affected by mechanosorption, whereas static compression was found not to respond to cycling of environmental humidity. Static compression strength was merely determined by the moisture content of the moulded-fibre material. The effect of varying temperature on tray moisture content was examined by transfer of the moulded-fibre tray from preconditioning at cold storage (5°C, 59% r.h.) to ambient conditions (25°C, 54%). When a food simulant [agar gel, water activity (aw) ,1] was sealed inside the moulded-fibre tray, moisture condensed on the tray outer surface (moisture gain 1.4,g/100,g dry fibre) within 40,min of transfer, contrary to when empty moulded-fibre trays were exposed to same conditions. Condensation could thus potentially induce a large initial creep deformation of the moulded-fibre tray. Copyright © 2004 John Wiley & Sons, Ltd. [source] Effects of loading rate on viscoplastic properties of polymer geosynthetics and its constitutive modelingPOLYMER ENGINEERING & SCIENCE, Issue 3 2010Fang-Le Peng On the basis of the special tensile test results under various loading histories, the rate-dependent behaviors of three polymer geosynthetics due to their viscous properties have been investigated. All the investigated polymer geosynthetics show significant loading rate effects, creep deformation, and stress relaxation. Except for the polyester geogrid showing the combined viscosity, all the investigated polymer geosynthetics exhibit the isotach viscosity. An elasto-viscoplastic constitutive model described in a nonlinear three-component model framework is developed to simulate the rate-dependent behaviors of polymer geosynthetics. The developed constitutive model is verified by comparing its simulated results with the experimental data of polymer geosynthetics presented in this study and those available from the literature. The comparison indicates that the developed model can reasonably interpret the rate-dependent behaviors of polymer geosynthetics under arbitrary loading histories, including the step-changed strain rate loading, creep, and stress relaxation applied during otherwise monotonic loading (ML). POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers [source] Study on the creep behavior of polypropylenePOLYMER ENGINEERING & SCIENCE, Issue 7 2009Xiaolin Liu The creep behavior and creep failure law of polypropylene (PP) were investigated by using a multifunctional stress-aging testing machine under different aging environmental conditions (temperature, UV, and stress). Photoinduced changes in samples were studied using gel permeation chromatography and X-ray photoelectron spectrometer. Surface morphologies were also observed by scanning electron microscopy. It was found that there is a critical failure strain (,crit) for PP during the creep course. Once the creep deformation exceeds the ,crit, creep failure of PP takes place very rapidly. The value of ,crit is independent of the tensile stress and UV irradiation, whereas it is only affected by the temperature and the nature of the PP, such as molecular weight and molecular structure. With increasing temperature, the value of ,crit increases gradually. In addition, the creep rate of PP increases rapidly with increasing tensile stress and temperature as well as under irradiation with UV light. This study may provide a new way to predict the service lifetime of PP. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] Untersuchungen zum Werkstoffverhalten des Feinkornbaustahls S 460 unter erhöhten TemperaturenBAUTECHNIK, Issue 10 2007Jörg Lange Prof. Dr.-Ing. Die Bestimmung der Tragfähigkeit von Bauteilen aus S 460 im Brandfall auf der Grundlage vereinfachter oder allgemeiner Berechnungsverfahren entsprechend EN 1993-1-2 [1] erfordert die Kenntnis der mechanischen Eigenschaften des hochfesten Feinkornbaustahls unter erhöhten Temperaturen. Hierzu wurden Untersuchungen an Probestäben aus einem normalisierend gewalzten S 460 N und einem thermomechanisch gewalzten S 460 M durchgeführt. Beide Stahlsorten unterscheiden sich sowohl in ihrer chemischen Zusammensetzung als auch in der Temperaturführung beim Walzen. Auf der Grundlage instationärer Warmkriechversuche wurden Werkstoffgesetze für den Temperaturbereich von 20 bis 900 °C hergeleitet. Die Untersuchungen zeigen eine im Vergleich zu S 460 N erhöhte Festigkeit des S 460 M bei hohen Temperaturen. Diese ist zurückzuführen auf die durch das thermomechanische Walzen verursachte Verfestigung und die Verringerung der Kriechgeschwindigkeit durch Niob- und Titanausscheidungen. Beim Vergleich der Ergebnisse mit den in EN 1993-1-2 [1] für S 460 angegebenen Werkstoffgesetzen erkennt man, dass diese sowohl die Festigkeit als auch die Steifigkeit des untersuchten S 460 N überschätzen. Examination of the mechanical properties of the microalloyed grain refined steel S 460 at elevated temperatures. To establish a basis for calculating the load-bearing capacity of steel members made of S 460 in fire, corresponding to EN 1993-1-2 [1], the mechanical properties of the microalloyed grain refined steel S 460 under high temperatures have been examined. Two different kinds of steel have been considered: a normalised rolled S 460 N and a thermomechanically rolled S 460 M, that differ in their chemical composition and the temperature control during the hot-rolling process. On the basis of transient state tensile tests, material laws have been derived for the temperature range from 20 to 900 °C. The test results show an increased strength of S 460 M at elevated temperatures in comparison to S 460 N. This is a result of the strain hardening caused by the thermomechanical deformation and the precipitates formed by niobium and titanium that constrain creep deformations. The data derived from the tests show that the stress-strain relationships given in EN 1993-1-2 [1] for S 460 overestimate both the strength and the stiffness of the examined S 460 N. [source] | |||||||||||||||||||||||||