Showing papers on "Creep published in 2008"
TL;DR: The suppression of particle coarsening during creep and the maintenance of a homogeneous distribution of M23C6 carbides near prior austenite grain boundaries are effective for preventing the long-term degradation of creep strength and for improving long- term creep strength by the addition of boron.
420 citations
TL;DR: In this article, the authors have demonstrated that long-term microstructure stability in 9-12% Cr steels under technical loading conditions is equivalent to precipitate stability and that high Cr contents of 10% and above in the steels accelerate Z-phase precipitation, which may completely dissolve fine V and Nb containing MX nitrides.
383 citations
TL;DR: A literature survey was carried out to collect data on the properties of granites at high temperatures including Young's modulus, uniaxial compressive strength, tensile strength, Poisson's ratio, coefficient of linear thermal expansion, creep behaviour and the development of micro-crack on heating using scanning electron microscope (SEM) as mentioned in this paper.
273 citations
01 Jan 2008
TL;DR: The development of creep-resistant steels has been discussed in this article, where the authors present a detailed description of the deformation and deformation mechanism map of creep deformation in steel.
Abstract: Part 1 General: Introduction The development of creep-resistant steels Specifications for creep-resistant steels: Europe Specifications for creep-resistant steels Production of creep-resistant steels for turbines. Part 2 Behaviour of creep-resistant steels: Physical and elastic behaviour of creep-resistant steels Diffusion behaviour of creep-resistant steels Fundamental aspects of creep deformation and deformation mechanism map Strengthening mechanisms in steel for creep and creep rupture Precipitation during heat treatment and service - Characterisation, simulation and strength contribution Grain boundaries in creep resistant steels Fracture mechanism map and fundamental aspects of creep fracture Mechanisms of creep deformation in steel Constitutive equations for creep curves and predicting service life Creep strain analysis in steel Creep crack growth behaviour and creep-fatigue behaviour of steels Creep strength of welded joints of ferritic steels Fracture mechanics: understanding in microdimensions Mechanisms of oxidation and corrosion and the influence of steam oxidation on service life of steam power plant components. Part 3 Applications: Alloy design philosophy of creep-resistant steels Using creep-resistant steels in turbines Using creep-resistant steels in nuclear reactors Creep damage - Industry needs and future R&D.
270 citations
TL;DR: In this paper, high-Cr ferritic model steels containing various additions of the refractory elements Nb and/or W were studied with respect to oxidation behaviour (hot) tensile properties, creep behaviour and high-temperature electrical conductivity of the surface oxide scales.
217 citations
TL;DR: A numerical simulation of crack development within APS TBC systems is presented in this article, revealing a small influence influence of both on the stress state in the thermal barrier coating system subjected to temperature loading.
Abstract: A numerical simulation of crack development within APS TBC systems is presented. The TGO thickening and creep deformation of all system constituents is modelled. Two dimensional periodic unit cell is used to examine the effect of interfacial asperity on stress distribution and subsequent delamination of APS TBC. A study of cyclic loading and of creep of the base material on the stress distribution close to the asperity at the TGO/BC interface is made, revealing a small influence influence of both on the stress state in the thermal barrier coating system subjected to temperature loading. Cohesive zone elements at the oxide/ceramic interface model the development of the interfacial micro-crack. The finite element analysis shows that the development of the interfacial crack allows for a micro-crack formation within APS TBC. Subsequent TGO growth results in a tensional zone within the oxide layer. Linking of the micro-cracks at the interface and within TBC through TGO could lead to a coating delamination in the unit cell.
210 citations
TL;DR: In this paper, a new anisotropic model for time-dependent behaviour of soft soils is presented, based on a previously developed isotropic creep model, assuming rotated Modified Cam Clay ellipses as contours of volumetric creep strain rates.
Abstract: In this paper a new anisotropic model for time-dependent behaviour of soft soils is presented. The formulation is based on a previously developed isotropic creep model, assuming rotated Modified Cam Clay ellipses as contours of volumetric creep strain rates. A rotational hardening law is adopted to account for changes in anisotropy due to viscous strains. Although this will introduce some new soil parameters, they do not need calibration as they can be expressed as functions of basic soil parameters through simple analytical expressions. To start with, the one-dimensional response of the model is discussed, making it possible to explore how the model is capable of capturing key features of viscous soft soil behaviour. Subsequently, the three-dimensional generalisation of the model is presented, followed by comparison with experimental data, showing good agreement in both triaxial undrained compression and extension. In the authors' opinion, the simple formulation of the model makes it attractive for use in engineering practice.
179 citations
TL;DR: In this paper, a crystal plasticity model for near-alpha hcp titanium alloys embodying a quasi-cleavage failure mechanism is presented and employed to investigate the conditions necessary in order for facet nucleation to occur in cold-dwell fatigue.
Abstract: A crystal plasticity model for near-alpha hcp titanium alloys embodying a quasi-cleavage failure mechanism is presented and employed to investigate the conditions necessary in order for facet nucleation to occur in cold-dwell fatigue. A model polycrystal is used to investigate the effects of combinations of crystallographic orientations (and in particular, a rogue grain combination), the essential role of (cold) creep during hold periods in the loading cycle and the more damaging effect of a load hold rather than a strain hold in facet nucleation. Direct comparisons of model predictions are made with dwell fatigue test results. More generally, the crystal model for faceting is found to be consistent with a range of experimental observations.
170 citations
TL;DR: A review of the current state of knowledge of the in-reactor deformation of cold-worked Zr-2.5Nb pressure tubes can be found in this article.
163 citations
TL;DR: In this article, cyclic tests with or without tensile holding periods were conducted in air at 823 K on a modified 9Cr-1Mo martensitic steel and the relationship between the number of cycles to failure of pure fatigue tests and the cyclic strain range was established.
163 citations
TL;DR: In this article, a low-temperature high-stress rheology of olivine was investigated under water-saturated conditions by large strain shear deformation experiments using the Griggs-type apparatus.
TL;DR: Porous microstructure endows hydroxyapatite with inelastic deformation properties, which are important in a material for bone substitution usage, which is similar to Rice's finding with the minimum solid area model.
TL;DR: In this article, a mesoscopic continuum model of a two-dimensional polycrystal with deformation mechanisms including grain interior plasticity, grain-boundary diffusion and grainboundary sliding is proposed to capture the transition from sliding-and diffusion-dominated creep in nanocrystals with relatively small grain sizes at low strain rates to plasticity-dominated flow in nano-crystals with larger grain sizes with higher strain rates.
TL;DR: In this article, the authors constructed constitutive equations for single-crystal nickel-based superalloys with respect to dislocation drift in the channels of the matrix phase of the face-centred cubic (fcc) type, dislocation climb at the interfaces with the reinforcing L 1 2 precipitates, and the processes leading to cutting of the interfaces by dislocation ribbons via stacking fault shear of the a 〈 1 1 2 〉 type.
TL;DR: In this article, the microstructure and microstructural stability of die-cast AE42 (Mg-4Al-2RE) alloy were investigated by transmission electron microscopy, and it was shown that the formation of Mg17Al12 after ageing at 200°C is not due to the decomposition of A111RE3 as reported in the literature, but rather is associated with the supersaturation of Al solute in the α-Mg matrix.
TL;DR: In this article, the role of grain and phase boundary sliding on rheology and fabric development has been investigated on fine-grained, two-phase aggregates of olivine and orthopyroxene, and it was shown that interface-controlled diffusion creep leads to strong crystallographic preferred orientations (CPO) of the component minerals, which develops in the near absence of dislocation activity.
Abstract: [1] Experimental deformation experiments have been conducted on fine-grained, two-phase aggregates of olivine and orthopyroxene to investigate the role of grain and phase boundary sliding on rheology and fabric development. A suite of large-strain (γ ≥ 1) general shear experiments conducted at T = 1200°C and P = 1.6 GPa on aggregates ranging from 65 to 0 vol % orthopyroxene, to characterize the evolution of fabric, were complemented by small-strain axial compression experiments at T = 1200°C and P = 0.3 GPa, to better constrain the rheology. Microstructural and rheological data suggest that deformation of these two-phase aggregates in the diffusion creep regime occurs via interface-reaction-controlled diffusion creep that is accompanied by extensive migration of olivine-orthopyroxene phase boundaries. The resulting rheologies suggest that olivine + orthopyroxene composites are weaker than the olivine end-member at the conditions tested. Physically, this behavior arises because long-range, i.e., grain-scale, diffusion of Si4+ is unnecessary in these pseudobinary two-phase aggregates. We further demonstrate that interface-controlled diffusion creep leads to strong crystallographic preferred orientations (CPO) of the component minerals, which develops in the near absence of dislocation activity. The CPO formed in these anhydrous, low-stress experiments has the olivine a axis aligned perpendicular to the flow direction (“type B” fabric) argued by some to be the unique result of deformation under conditions of high differential stress and high water fugacity. Phase boundary dynamics, thus, are argued as a significant factor in the accumulation of strain in polyphase aggregates.
TL;DR: The tensile creep of the acid form of Nafion N1110 was examined under controlled environmental conditions of temperature, 25 ≤ T ≤ 110 °C, and water activity, 0 ≤ aw ≤ 0.95 as mentioned in this paper.
Abstract: The tensile creep of the acid form of Nafion N1110 was examined under controlled environmental conditions of temperature, 25 ≤ T ≤ 110 °C, and water activity, 0 ≤ aw ≤ 0.95. Water plasticizes Nafion at 25 °C; creep strain after 1 h increases and the elastic modulus decreases with increasing water activity. At temperatures ≥40 °C the elastic modulus of Nafion goes through a maximum as a function of water activity; the elastic modulus of Nafion increases as aw increases from 0 to 0.01 and then decreases with increasing water activity for aw > 0.1. Under dry conditions (aw = 0), Nafion undergoes a transition between 60 and 80 °C where its creep rate increases rapidly and its elastic modulus decreases with increasing temperature. Above this transition temperature a small water activity, aw < 0.1, dramatically reduces the creep rate and increases the elastic modulus of Nafion—at elevated temperature water stiffens Nafion. At intermediate temperatures (40−80 °C) the elastic and viscous components of creep recov...
TL;DR: In this article, the microstructures and creep properties of the oxide-dispersion-strengthened alloy 14YWT have been evaluated as a function of annealing at 1000 °C for 1 hour up to 32 days.
27 May 2008
TL;DR: In this paper, the effects of aging on mechanical behavior of lead free solders have been examined by performing creep tests on four different SAC alloys (SAC105, SAC205, SC305, SC405) that were aged for various durations (0-4 months) at room temperature (25degC), and several elevated temperatures (75, 100, and 125 degC).
Abstract: The effects of aging on mechanical behavior of lead free solders have been examined by performing creep tests on four different SAC alloys (SAC105, SAC205, SAC305, SAC405) that were aged for various durations (0-4 months) at room temperature (25degC), and several elevated temperatures (75, 100, and 125 degC). Analogous tests were performed with 63Sn-37Pb eutectic solder samples for comparison purposes. Variations of the creep properties were observed and modeled as a function of aging time and aging temperature. In addition, the chosen selection of SAC alloys has allowed us to explore the effects of silver content on aging behavior.
TL;DR: In this paper, a numerical model has been developed to predict early-age cracking for massive concrete structures, taking into account creep at early age is essential if one wants to predict quantitatively the induced stresses.
TL;DR: In this article, the effect of temperature on the hardness and the creep behavior of the 80Au/20Sn solder alloy at temperatures ranging from 25°C to 200°C was studied.
15 Jun 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a review of the presently proposed mechanisms for creep of strengthened Ni-base superalloys that are typically used for disk applications is presented, including dislocation-coupled antiphase-boundary shearing, shearing configurations involving superlattice stacking faults, Orowan looping, climb bypass and microtwinning.
Abstract: This paper reviews the presently proposed mechanisms for creep of {\gamma^{\prime}} strengthened Ni-base superalloys that are typically used for disk applications. Distinct creep strength controlling modes, such as dislocation-coupled antiphase-boundary shearing, shearing configurations involving superlattice stacking faults, Orowan looping, climb by-pass, and microtwinning have been observed. These are strongly influenced by the scale of the {\gamma^{\prime}} precipitating phase and are operative within specific ranges of temperature and stress. Insight from more recent experimental findings concerning microtwinning and extending stacking fault mechanisms suggest important similarities between these deformation modes. It is suggested that local atomic reordering in the wake of Shockley partials is responsible for the temperature dependence exhibited in this regime.
25 Mar 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a series of martensitic/ferritic model steels with 12.5%Cr were studied to achieve an increased creep resistance through additional alloying with various elements for controlled precipitation of M23C6 carbides, MX carbonitrides and intermetallic Laves phase.
Abstract: In view of developing novel heat-resisting steels for applications in conventional power plants with service temperatures of 650 °C, a series of martensitic/ferritic model steels with 12 wt.%Cr were studied to achieve an increased creep resistance through additional alloying with various elements for controlled precipitation of M23C6 carbides, MX carbonitrides and intermetallic Laves phase. The alloy design relied on thermodynamic simulation calculations using Thermo-Calc and DICTRA. The mechanical testing concentrated on creep at 650 °C for up to 8000 h. The alloy optimization resulted in creep rupture strengths above those of the martensitic/ferritic P92 steel. The work was part of a cooperative project within the German MARCKO program.
TL;DR: Sun et al. as discussed by the authors extended the VBO model to account for crystallinity ratio on mechanical behavior of semicrystalline polymers, where amorphous and crystalline phase resistances acting in parallel were considered in the model, and the uniaxial loading and unloading behaviors can be simulated well with the modified VBO.
TL;DR: In this article, the authors reviewed the approaches commonly used to quantify creep and fracture behaviour and pointed out the limitations of these approaches, as well as their limitations when applied to comprehensive long-term data sets.
Abstract: The approaches commonly used to quantify creep and creep fracture behaviour are critically reviewed. Their limitations are illustrated by reference to information openly available for three martensitic steels, namely, grades 91, 92 and 122. Adopting traditional procedures, the creep design strengths of these 9–12% chromium steels have been reduced substantially as continuing experimental programmes have increased the maximum test durations from ∼30 000 towards 100 000 h. Moreover, even when applied to comprehensive long-term data sets, the estimated 100 000 h strengths vary considerably, depending on the detailed method selected to perform the calculations. In contrast, by normalising the applied stress through the appropriate ultimate tensile strength (UTS) value, new relationships allow the multi-batch stress rupture properties at various creep temperatures to be superimposed onto sigmoidal 'master curves' using the activation energy for lattice diffusion in the alloy steel matrixes (300 kJ mol−...
TL;DR: In this paper, the oxide dispersion strengthened (ODS) ferritic steel PM2000 was homogeneously implanted with α-particles under uniaxial tensile stresses ranging from 20 to 250 MPa, causing irradiation creep.
TL;DR: In this article, the authors studied the viability of Fe-rich austenitic stainless alloys strengthened by intermetallic phases and found that the addition of Si helped to refine and stabilize the size of particles, resulting in finer and denser Fe{sub 2}Nb dispersion than that in the base alloy.
TL;DR: In this article, structural relaxation of Mg-Cu-Y metallic glasses occurs at room-temperature (∼0.7 Tg) and induces an abrupt embrittlement after periods of time that depend on the relative proportions of Cu and Mg.
TL;DR: In this paper, a microbubble inflation method was used to determine the creep compliance of poly(vinyl acetate) and polystyrene ultra-thin films (13-300 nm thick) at temperatures from below to above the glass temperature.
Abstract: A novel microbubble inflation method has been used to determine the creep compliance of poly(vinyl acetate) and polystyrene ultra-thin films (13–300 nm thick) at temperatures from below to above the glass temperature. We present results that suggest that time-temperature and time-thickness superposition hold in the glassy relaxation regime. Although time-temperature superposition is found for the entire response curve for each thickness, we also find that time-thickness superposition fails as the long-time compliance is approached. This effect occurs because of a strong stiffening as the film thickness decreases. We also show first evidence of stiffening in the glassy regime of free standing films of polystyrene. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1952–1965, 2008
TL;DR: The epoxy polymers used as adhesives and as the matrices of composite materials are amorphous and highly-crosslinked (thermosetting) materials, which results in many useful properties, such as a high modulus and failure strength, low creep, and good performance at elevated temperatures as mentioned in this paper.
Abstract: The epoxy polymers used as adhesives and as the matrices of composite materials are amorphous and highly-crosslinked (thermosetting) materials. This microstructure results in many useful properties, such as a high modulus and failure strength, low creep, and good performance at elevated temperatures. However, this microstructure also leads to one highly undesirable property in that they are relatively brittle materials, with a poor resistance to crack initiation and growth.