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Showing papers on "Creep published in 2005"


Book
11 Feb 2005
TL;DR: In this article, a detailed analysis of continuoustime damage mechanics is presented, including failure of brittle and quasi-brittle materials, low cycle fatigue, and high cycle fatigue.
Abstract: Background on Continuum Damage Mechanics.- Numerical Analysis of Damage.- Ductile Failures.- Low Cycle Fatigue.- Creep, Creep-Fatigue, and Dynamic Failures.- High Cycle Fatigue.- Failure of Brittle and Quasi-Brittle Materials.

952 citations


Journal ArticleDOI
TL;DR: In this article, a set of material property data is established based on published physical, mechanical, and thermal properties of alumina specimens that conform to the constraints of the material specification.
Abstract: Results of a data evaluation exercise are presented for a particular specification of sintered alpha-alumina (mass fraction of Al2O3, ≥0995; relative density (rho/rhotheoretical), ≥098; and nominal grain size, 5 μm) A comprehensive set of material property data is established based on published physical, mechanical, and thermal properties of alumina specimens that conform to the constraints of the material specification The criteria imposed on the properties are that the values should be derived from independent experimental studies, that the values for physically related properties should be mutually self-consistent, and that the sets of values should be compatible with established material property relations The properties assessed in this manner include crystallography, thermal expansion, density, sound velocity, elastic modulus, shear modulus, Poisson's ratio, bulk modulus, compressive strength, flexural strength, Weibull characteristic strength, Weibull modulus, tensile strength, hardness, fracture toughness, creep rate, creep rate stress exponent, creep activation energy, friction coefficient, wear coefficient, melting point, specific heat, thermal conductivity, and thermal diffusivity

669 citations


Journal ArticleDOI
Oldrich Polach1
01 Mar 2005-Wear
TL;DR: In this article, the authors present a method to simulate various real wheel-rail contact conditions using one parameter set, which can be identified from measurements or the recommended parameters for modelling of typical wheel rail contact conditions in engineering applications.

425 citations


Journal ArticleDOI
TL;DR: In this paper, the authors showed that adding 1.2 × 2 Zn to this alloy significantly enhanced the age hardening response and the creep strength and the remarkable improvement in strength and creep resistance is associated with a uniform and dense distribution of basal precipitate plates that are not observed in the Zn-free alloy.

412 citations


Journal ArticleDOI
18 Mar 2005-Science
TL;DR: Results from use of a previously unknown method for characterizing the rheological response of nanometer-thick polymer films show that the material exhibits previously unobserved stiffening in the rubbery response regime.
Abstract: Measurement of the thermoviscoelastic behavior of glass-forming liquids in the nanometer size range offers the possibility of increased understanding of the fundamental nature of the glass-transition phenomenon itself. We present results from use of a previously unknown method for characterizing the rheological response of nanometer-thick polymer films. The method relies on the imaging capabilities of the atomic force microscope and the reduction in size of the classical bubble inflation method of measuring the biaxial creep response of ultrathin polymer films. Creep compliance as a function of time and temperature was measured in the linear viscoelastic regime for films of poly(vinyl acetate) at a thickness of 27.5 nanometers. Although little evidence for a change in the glass temperature is found, the material exhibits previously unobserved stiffening in the rubbery response regime.

284 citations


Journal ArticleDOI
TL;DR: In this paper, the development of dislocation configurations in two single-crystal superalloys during high-temperature low-stress creep was investigated with the use of transmission electron microscopy.

268 citations


Journal ArticleDOI
TL;DR: In this article, a new method has been developed and optimized employing a simple device, a special specimen geometry, and corrections for friction and off-axis loading for measuring hardening under reversed uniaxial loading.

248 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the deformation properties of the superalloy Rene 88 DT alloys with small-strain (0.2-0.5%) creep at 650°C using conventional and high-resolution transmission electron microscopy.

232 citations


Journal ArticleDOI
TL;DR: The use of instrumented indentation to characterize the mechanical response of polymeric materials was studied in this article, where a model based on contact between a rigid probe and a linear viscoelastic material was used to calculate values for the creep compliance and stress relaxation modulus for two glassy polymeric material, epoxy and poly(methyl methacrylate), and two poly(dimethyl siloxane) (PDMS) elastomers.
Abstract: The use of instrumented indentation to characterize the mechanical response of polymeric materials was studied. A model based on contact between a rigid probe and a linear viscoelastic material was used to calculate values for the creep compliance and stress relaxation modulus for two glassy polymeric materials, epoxy and poly(methyl methacrylate), and two poly(dimethyl siloxane) (PDMS) elastomers. Results from bulk rheometry studies were used for comparison with the indentation stress relaxation results. For the two glassy polymers, the use of sharp pyramidal tips produced responses that were considerably more compliant (less stiff) than the rheometry values. Additional study of the deformation remaining in epoxy after indentation creep testing as a function of the creep hold time revealed that a large portion of the creep displacement measured was due to postyield flow. Indentation creep measurements of the epoxy with a rounded conical tip also produced nonlinear responses, but the creep compliance values appeared to approach linear viscoelastic values with decreasing creep force. Responses measured for the unfilled PDMS were mainly linear elastic, with the filled PDMS exhibiting some time-dependent and slight nonlinear responses in both rheometry and indentation measurements. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1794–1811, 2005

232 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used Boltzmann integral operators to generate displacement-time solutions for spherical indentation testing of viscoelastic materials, and used a multiple ramp-and-hold protocol for the measurement of creep responses at several loads and depths.
Abstract: Elastic-viscoelastic correspondence, utilizing Boltzmann integral operators, was used to generate displacement–time solutions for spherical indentation testing of viscoelastic materials. Solutions were found for creep following loading at a constant loading rate and compared with step-loading solutions. Experimental creep tests were performed with different loading rate–peak load level combinations on glassy and rubbery polymeric materials. The experimental data were fit to the spherical indentation ramp–creep solutions to obtain values of shear modulus and time-constants; good agreement was found between the experimental results and known modulus values. A multiple ramp-and-hold protocol was examined for the measurement of creep responses at several loads (and depths) within the same test. Emphasis is given to the use of multiple experiments (or multiple levels within a single experiment) to test a priori assumptions made in the correspondence solutions regarding linear viscoelastic material behavior and the creep function.

214 citations


Journal ArticleDOI
TL;DR: In this paper, the tensile creep behavior of two rare-earth dopant systems, lanthanum- and yttrium-doped alumina, are compared and contrasted in order to better understand the role of oversized, isovalent cation dopants in determining creep behavior.
Abstract: The tensile creep behavior of two rare-earth dopant systems, lanthanum- and yttrium-doped alumina, are compared and contrasted in order to better understand the role of oversized, isovalent cation dopants in determining creep behavior. It was found that, despite some microstructural differences, these systems displayed qualitatively a similar improvement in creep resistance, supporting the hypothesis that creep is strongly influenced by segregation. Differences in primary creep behavior and activation energy for steady-state creep were, however, observed for these systems. Given these results, it is expected that creep behavior can be further optimized by adjusting the dopant level and by controlling the microstructure.

Journal ArticleDOI
TL;DR: In this article, a detailed analysis of all elements which had an influence on the failure initiation was carried out, namely, loss of aluminium from coating due to oxidation and coating phases changing; decreasing of alloy ductility and toughness due to carbides precipitation in grain boundaries; degradation of the alloy gamma prime (γ′) phase (aging and coarsening); blade airfoil stress level; evidence of intergranular creep crack propagation.

Journal ArticleDOI
TL;DR: The creep viscosity of chemical-precursor-derived silicon carbonitride (SiCN), which is known to remain predominantly amorphous at temperatures below 1400°C, was measured in the temperature range 1090-1280°C.
Abstract: The creep viscosity of chemical-precursor-derived silicon carbonitride (SiCN), which is known to remain predominantly amorphous at temperatures below 1400°C, was measured in the temperature range 1090-1280°C. Experiments were done in uniaxial compression at constant loads in pure nitrogen atmosphere. The creep behavior exhibited three stages. In stage I the strain rate decreased rapidly with time and deformation was accompanied by densification. In stage II the samples exhibited a steady-state creep rate. In stage III, which commenced after long-term deformation, creep gradually declined to rates that were below the sensitivity of our apparatus. The relative density of the specimens during stage II and stage III remained constant at ≅2.3 g/cm3. The shear viscosity in stage II was nearly Newtonian and was measured to be 1.3 × 1013-5.0 1013 Pa·s at 1280°C, which is approximately 103 times the value for fused silica. The creep-hardened as well as uncrept specimens contained silicon nitride crystallites. The volume fraction of these crystals was variable but always less than 5%. Such a small volume fraction of crystals does not explain the dramatic creep-hardening behavior in stage III, even if it is assumed that the crystals formed during creep deformation in stage II.

Journal ArticleDOI
TL;DR: In this article, the tensile properties and high temperature properties of die cast Mg-Sn-Al-Si (TAS831) alloy have been investigated and it has been shown that TAS-831 alloy has better combinations of tensile property at room and elevated temperatures than die cast AZ91 alloy.
Abstract: A study has been made on the tensile properties and high temperature properties of die cast Mg–Sn–Al–Si (TAS831) alloy. The microstructure of TAS831 alloy is characterized by the presence of thermally stable Mg2Sn particles within matrix and along grain boundaries. It also contains a small volume fraction of thermally stable Mg2Si particles. It has been shown that TAS831 alloy has better combinations of tensile properties at room and elevated temperatures than die cast AZ91 alloy. Creep properties of TAS831 alloy are also superior to those of AZ91 alloy. Analyses of creep behavior and load-relaxation behavior at elevated temperatures in the context of internal variable theory indicate that the presence of thermally stable dispersoids in TAS831 alloy increases the resistance to dislocation movement, thereby improving creep properties over those of AZ91 alloy. © 2005 Elsevier B.V. All rights reserved.

Journal ArticleDOI
TL;DR: In this paper, a model of grain boundary fluid flow mechanism of growth of Sn whiskers is presented, and the agreement with experimental observation is discussed. But the model is limited to a very limited temperature range, from room temperature to 60 °C.
Abstract: Spontaneous whisker growth on beta-Sn is a creep phenomenon near a surface, driven by compressive force. The compressive force is self-generated and the sample responses by growing stress-free whiskers. While a whisker grows out of a surface, it requires an oxidized surface and the oxide has to be protective. An oxide-free metal under compression in ultra-high vacuum will not grow whiskers. Due to a very limited temperature range, from room temperature to 60 °C, of spontaneous growth of Sn whiskers, a systematic study of the growth is difficult because if the temperature is lower, there is insufficient atomic diffusion and if the temperature is higher, there is no driving force because of stress relief. In this paper we review briefly the creep behavior of whisker growth on beta-Sn surfaces. We present a model of grain boundary fluid flow mechanism of growth of Sn whiskers. The agreement with experimental observation is discussed.

Journal ArticleDOI
TL;DR: In this article, a compilation of existing data shows that an increase in the volume fraction of the α-Mo phase increases the room-temperature fracture toughness at the expense of the oxidation resistance and the creep strength.
Abstract: Mo-Si-B intermetallics consisting of the phases Mo3Si and Mo5SiB2, and a molybdenum solid solution (“α-Mo”), have melting points on the order of 2000 °C. These alloys have potential as oxidation-resistant ultra-high-temperature structural materials. They can be designed with microstructures containing either individual α-Mo particles or a continuous α-Mo phase. A compilation of existing data shows that an increase in the volume fraction of the α-Mo phase increases the room-temperature fracture toughness at the expense of the oxidation resistance and the creep strength. If the α-Mo phase could be further ductilized, less α-Mo would be needed to achieve an adequate value of the fracture toughness, and the oxidation resistance would be improved. It is shown that microalloying of Mo-Si-B intermetallics with Zr and the addition of MgAl2O4 spinel particles to Mo both hold promise in this regard.

Journal ArticleDOI
TL;DR: In this article, a hydro-mechanical model, accounting for the full coupling of drying, shrinkage, creep and cracking is presented, and a new basic creep constitutive law based on microscopic considerations of the role of water is elaborated.

Journal ArticleDOI
TL;DR: In this article, the authors used the modified viscoplasticity theory based on overstress (VBO) to model the deformation behavior of polyphenylene oxide (PPO).

Journal ArticleDOI
TL;DR: In this paper, the transition from steady-state creep at low stress to deformation-induced softening at high stress was observed in the case of Pd41Ni10Cu29P20 glass.
Abstract: Bulk samples of Pd41Ni10Cu29P20 glass were tested at constant true stress (20–636MPa) in compression at 550, 555, and 565K to study the transition from steady-state creep at low stress to deformation-induced softening at high stress. In the high-stress regime strongly accelerating creep was observed. All deformation was homogeneous. The activation volume was 106A3. The isoconfigurational activation energy was 9.03±0.64eV. The disordering rate is proportional to the applied power density (stress×strain rate). The disordering process is inefficient in energy and in the production of free volume.

Journal ArticleDOI
TL;DR: In this paper, the coarsening kinetics of Ag 3 Sn particles in SnAg-based solder are studied, and the results are correlated with impression creep data from individual microelectronic solder balls subjected to thermal aging treatments.
Abstract: The creep response of solder joints in a microelectronic package, which are subjected to aggressive thermo-mechanical cycling (TMC) during service, often limits the reliability of the entire package. Furthermore, during TMC, the microstructures of the new lead-free solders (Sn–Ag and Sn–Ag–Cu) can undergo significant in situ strain-enhanced coarsening, resulting in in-service evolution of the creep behavior. In this paper, the coarsening kinetics of Ag 3 Sn particles in SnAg-based solder are studied, and the results are correlated with impression creep data from individual microelectronic solder balls subjected to thermal aging treatments. Coarsening influences creep behavior in two ways. At low stresses, the creep rate increases proportionately with precipitate size. At high stresses, precipitate coarsening influences creep response by altering the threshold stress for particle-limited creep. Based on these observations, a microstructurally adaptive creep model for solder interconnects undergoing in situ coarsening is presented.

Journal ArticleDOI
TL;DR: In this paper, a fracture mechanics approach is developed, by means of which cracks are modeled in the critical areas of the TBC system and assessed using the modified crack closure integral method for determining the mode-dependent crack loading.

Journal ArticleDOI
TL;DR: In this article, the power-law relationship between strain rate and stress was observed at most of the temperatures at which pure tin, Sn-3.5Ag and Sn-5Sb electronic solder alloys, have been studied at various temperatures between ambient and 473 K (homologous temperature 0.58 to 0.85).
Abstract: Creep deformation characteristics of pure tin, and Sn-3.5Ag and Sn-5Sb electronic solder alloys, have been studied at various temperatures between ambient and 473 K (homologous temperature 0.58 to 0.85). Power-law relationships between strain rate and stress were observed at most of the temperatures. The stress exponent (n=7.6, 5.0, and 5.0) and activation energy (Q c =60.3, 60.7, and 44.7 kJ/mol) values were obtained in the case of tin, Sn-3.5Ag, and Sn-5Sb respectively. Based on n and Q c values, it is suggested that the rate controlling creep-deformation mechanism is dislocation climb controlled by lattice diffusion in pure tin and Sn-3.5Ag alloy, and viscous glide controlled by pipe diffusion in Sn-5Sb alloy. The results on Sn-3.5Ag bulk material are compared with the initial results on solder bump arrays.

Journal ArticleDOI
TL;DR: In this paper, a method for simultaneous compensation of the hysteresis and creep of piezoelectric actuator based on an inverse control in open-loop operation is described.
Abstract: Piezoelectric actuators are frequently used nowadays in a wide variety of positioning devices. However, a major deficiency of piezoelectric actuators is that their open-loop control accuracy is seriously limited by hysteresis and creep effects. This paper describes a method for simultaneous compensation of the hysteresis and creep of piezoelectric actuator based on an inverse control in open-loop operation. The basis of the inverse control is formed by a hysteresis mathematical model and a creep model, which can describe precisely two phenomena. The method of solving inverse models of hysteresis and creep is described detailedly. Finally, a tracking control experiment of piezoelectric actuators for a desired trajectory is performed according to the proposed method and the experimental results demonstrate that the positioning precision is noticeably improved in open-loop operation compared to the conventional open-loop control without any compensation.

Journal ArticleDOI
TL;DR: In this paper, the microstructural evolution during tensile deformation of an AZ31 alloy with grain size ranging from 17 to 40 µm, at intermediate temperatures, has been studied using electron backscattered diffraction (EBSD) and optical microscopy (OM) as the main characterization tools.
Abstract: The microstructural evolution during tensile deformation of an AZ31 alloy with grain size ranging from 17 to 40 µm, at intermediate temperatures, has been studied using electron backscattered diffraction (EBSD) and optical microscopy (OM) as the main characterization tools. Two deformation regimes could be distinguished. In the high-strain-rate regime, the stress exponent was found to be about 6, and the activation energy is close to that for Mg self-diffusion. These values are indicative of climb-controlled creep. In the lower strain rate range, elongations higher than 300 pct were measured. In this range, significant dynamic grain growth takes place during the test, and thus, the predominant deformation mechanisms have been investigated by means of strain-rate-change tests. It was found that the stress exponent varied during the test between 1.7 and 2.5, while the activation energy remains close to that for grain-boundary diffusion. The EBSD analysis revealed, additionally, the appearance of low to moderately misoriented boundaries that tend to lay perpendicular to the tensile axis. The enhanced ductility of this AZ31 alloy in this regime is attributed to the operation of a sequence of deformation mechanisms. Initially, grain-boundary sliding governs deformation; once dynamic grain growth occurs, dislocation slip becomes gradually more important. Dislocation interaction gives rise to the appearance of new interfaces by continuous dynamic recrystallization (CDRX).

Journal ArticleDOI
TL;DR: In this paper, a correction formula for the general power-law viscoelastic situation using a Maxwell material model was proved for the amorphous selenium at ambient and elevated temperatures and was found to be effective in correcting for creep effects.

Journal ArticleDOI
TL;DR: In this paper, a mechanical model is presented, in which viscoelastic response is described by the action of time-dependent latch elements, and the model represents visco-elastic changes occurring through incremental jumps as opposed to continuous motion.
Abstract: A mechanical model is presented, in which viscoelastic response is described by the action of time-dependent latch elements. The model represents viscoelastic changes occurring through incremental jumps as opposed to continuous motion. This is supported by the observation that polymeric creep, recovery and stress relaxation can be correlated with stretched exponential functions, i.e. Weibull and Kohlrausch-Williams-Watts, since (i) the former is also used in reliability engineering to represent the failure of discrete elements and (ii) there is evidence of the latter being an approximation to the Eyring potential energy barrier relationship, which describes motion in terms of molecular jumps.

Journal ArticleDOI
TL;DR: In this article, the authors report the development of creep resistant Mg-Ca-Zn based alloys that can be strengthened via age hardening, which shows tensile and creep properties superior to magnesium alloy AZ91.

Journal ArticleDOI
TL;DR: In this article, the authors applied the time-temperature superposition principle to the viscoelastic properties of a kenaf-fiber/high-density polyethylene (HDPE) composite, and its validity was tested.
Abstract: The time–temperature superposition principle was applied to the viscoelastic properties of a kenaf-fiber/high-density polyethylene (HDPE) composite, and its validity was tested. With a composite of 50% kenaf fibers, 48% HDPE, and 2% compatibilizer, frequency scans from a dynamic mechanical analyzer were performed in the range of 0.1–10 Hz at five different temperatures. Twelve-minute creep tests were also performed at the same temperatures. Creep data were modeled with a simple two-parameter power-law model. Frequency isotherms were shifted horizontally and vertically along the frequency axis, and master curves were constructed. The resulting master curves were compared with an extrapolated creep model and a 24-h creep test. The results indicated that the composite material was thermorheologically complex, and a single horizontal shift was not adequate to predict the long-term performance of the material. This information will be useful for the eventual development of an engineering methodology for creep necessary for the design of structural building products from these composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1995–2004, 2005

Journal ArticleDOI
TL;DR: In this article, a range of mechanical compression tests were conducted on frozen soil samples at temperatures close to the melting point of ice to determine both the creep and the strength properties under triaxial stress conditions.
Abstract: A range of mechanical compression tests were conducted on frozen soil samples at temperatures close to the melting point of ice to determine both the creep and the strength properties under triaxial stress conditions. The samples were obtained from two rock glaciers in the Swiss Alps. For comparison, additional samples were prepared artificially for testing. The results showed that the minimum creep strain rate increases exponentially with increasing temperature and applied deviatoric stress. The applied strain rate is the main parameter influencing resistance. However, test results show that the micromechanical behaviour is similar for all tests and independent of the applied loading condition. Measurements of the volumetric strain showed that the sample composition has a major influence, so samples with high air void ratios resulted in continuous contraction (i.e., reduction of the sample volume), whereas samples with low volumetric air and ice contents demonstrated dilatant behaviour.Key words: permafr...

Journal ArticleDOI
TL;DR: In this paper, the deformation of a neck between two spherical particles of the same size by coupled grain-boundary and surface diffusion has been simulated numerically through the finite-difference method.
Abstract: The deformation of a neck between two spherical particles of the same size by coupled grain-boundary and surface diffusion has been simulated numerically through the finite-difference method. In the case of pure sintering where there is no applied stress, the results agree quite well with simple analytical models. When a force is applied, it is found that they do not deform as truncated spheres, even when surface diffusion is much faster than grain-boundary diffusion. Expressions are given representing the rate of approach of the particles and the rate of growth of the neck as a function of the current neck radius and the applied stress.