Results 1 - 10 of 253
Results 1 - 10 of 253. Search took: 0.019 seconds
|Sort by: date | relevance|
[en] The article Statistical filtering of useful concrete creep data from imperfect laboratory tests, written by Mohammad Rasoolinejad, Saeed Rahimi-Aghdam, Zdenek P. Bazant, was originally published online without Open Access. After publication in volume 51, article ID 153 RILEM decided to grant the author to opt for open choice and to make the article an open-access publication.
[en] Highlights: • Shrinkage of concrete is measured with various temperature and humidity conditions. • The fib MC2010 shrinkage model is accurate for low RH and high T conditions. • The fib MC2010 shrinkage model slightly underestimate for other conditions. • The fib MC2010 creep model conservatively predicts creep strains. - Abstract: Creep and shrinkage of concrete is influenced by many factors including relative humidity and temperature. The combined effect of low relative humidity (<20%) and high temperature (38 °C) on creep and shrinkage of concrete is uncertain as limited tests have been conducted in this domain. Also unknown is the ability of the fib MC2010 model code in predicting the shrinkage and creep at the environment. This paper presents the results of experiments conducted in which concrete was cast and exposed to the aforementioned environmental conditions. The shrinkage and creep behaviour of the concrete was observed for 110 days, and experimental results were compared with predicted values using fib MC2010 model code.
[en] The upsetting of a composite cylinder in frictionless creep is analyzed in energy terms. Three loading programs that lead to upsetting of the cylinder by the same amount in the same time are compared. Variational analysis indicates that the kinematic loading program is best for industrial use.
[en] We have carried out measurements of domain wall dynamics in a Pt/Co/GdOx(t) wedge sample with perpendicular magnetic anisotropy. When driven by an easy-axis field Hz in the presence of an in-plane field Hx, the domain wall propagation is different along x, as expected for samples presenting Dzyaloshinskii–Moriya (DMI) interaction. In the creep regime, the sign and the value of the domain wall velocity asymmetry changes along the wedge. We show that in our samples the domain wall speed versus Hx curves in the creep regime cannot be explained simply in terms of the variation of the domain wall energy with Hx, as suggested by previous works. For this reason the strength and the sign of the DMI cannot be extracted from these measurements. To obtain reliable information on the DMI strength using magnetic field-induced domain wall dynamics, measurements have been performed with high fields, bringing the DW close to the flow regime of propagation. In this case we find large values of the DMI, consistent in magnitude and sign with those obtained from Brillouin light scattering measurements. (paper)
[en] The effect of gamma-ray irradiation on the cement mortar creep is investigated in this study. The creep investigation is accompanied by the shrinkage measurements and the compressive strength test. The measured creep and shrinkage strains are compared with the values calculated according to the existing models which showed that the creep and the shrinkage of both the control and the irradiated samples lie within the interval predicted by the models. However, creep of the irradiated samples is slightly higher. The gamma-ray irradiation also leads to the significant decrease in compressive strength (20% on average). The physics behind this process is still unclear and demands supplementary porosity and mineral composition investigation. (author).
[en] As nuclear energy systems become more advanced, the materials encompassing them need to perform at higher temperatures for longer periods of time. In this Master's thesis we experiment with an oxide dispersion strengthened (ODS) austenitic steel that has been recently developed. ODS materials have a small concentration of nano oxide particles dispersed in their matrix, and typically have higher strength and better extreme temperature creep resistance characteristics than ordinary steels. However, no ODS materials have ever been installed in a commercial power reactor to date. Being a newer research material, there are many unanswered phenomena that need to be addressed regarding the performance under irradiation. Furthermore, due to the ODS material traditionally needing to follow a powder metallurgy fabrication route, there are many processing parameters that need to be optimized before achieving a nuclear grade material specification. In this Master's thesis we explore the development of a novel ODS processing technology conducted in Beijing, China, to produce solutionized bulk ODS samples with ~97% theoretical density. This is done using relatively low temperatures and ultra high pressure (UHP) equipment, to compact the mechanically alloyed (MA) steel powder into bulk samples without any thermal phase change influence or oxide precipitation. By having solutionized bulk ODS samples, transmission electron microscopy (TEM) observation of nano oxide precipitation within the steel material can be studied by applying post heat treatments. These types of samples will be very useful to the science and engineering community, to answer questions regarding material powder compacting, oxide synthesis, and performance. Subsequent analysis performed at Queen's University included X-ray diffraction (XRD) and inductively coupled plasma optical emission spectrometry (ICP-OES). Additional TEM in-situ 1MeV Kr2+ irradiation experiments coupled with energy dispersive X-ray (EDX) techniques, were also performed on large (200nm+) non-stoichiometric oxides embedded within the austenite steel grains, in an attempt to quantify the elemental compositional changes during high temperature (520oC) heavy ion irradiation. (author)
[en] The effects of nitrogen on the nanomechanical property and localized plasticity of nitrogen alloyed 316 series austenitic steels were investigated by using nanoindentation. Slip steps around indentations have been imaged and have indicated that nitrogen increases slip planarity greatly. The load versus displacement curves show that the addition of nitrogen increases the first excursion load and the probability of occurrence of the second excursion, which is attributed to slip planarity caused by nitrogen and the local work softening on the operative slip plane. Additionally, nitrogen increases hardness and elastic modulus, while it promotes nanoindentation creep. Planar slip caused by nitrogen inhabits the formation of strain-induced α′ martensite and then promotes the creep deformation. (paper)
[en] The scope of this work is to show the effects of multiple applications of a rejuvenation treatment studied for IN-738 on both the microstructure and the mechanical properties of the creep-damaged superalloy and to check the recovery obtained after one and two rejuvenation cycles through creep and tensile tests, whose results will be compared with the performance of the virgin material. This work will show that this rejuvenation treatment is able to recover the microstructure of creep-damaged specimens after one and two applications and that the mechanical properties of the rejuvenated alloy are very similar to the virgin material even after two rejuvenation cycles.
[en] Viscoelastic materials undergo creep due to elasticity and viscosity, two intrinsic material characteristics, and a representative rheological model can be constructed for creep behavior analysis. Based on the viscoelasticity theory, this model simulates creep by formalizing elastic and viscous deformations in spring and dash-pot elements, respectively. However, most materials have internal gaps caused by the generation process, changes in the internal or external stress, etc. In this paper, a rheological model is proposed in which a gap is introduced; hence, the phenomenological behaviors are formalized using spring, dash-pot, and gap elements. The gap element has strain, but no material property. The opening or closing of the gap according to time history influences the structural changes in the model. Owing to the gap element, the energy due to external forces is dissipated before the gap is closed. After the gap is closed, it is converted and stored as internal strain energy in the spring element, which causes creep recovery. The proposed rheological model has two types, which depend on the element combination. Further, a generalized model is obtained by constructing n models on the basis of the element material properties. To validate the proposed rheological model for various stress conditions, the results predicted by three creep models (the proposed model, Burgers model, and the step-by-step method) are compared with the previously experimental results of concrete specimens because there is a large difference between the evaluations of internally stored strain energy by the creep prediction models. Analysis of a stepwise loading case and an unloading case reveal the following characteristics and mechanism of the model. When additional stress is applied, the principle of superposition is not applied to the proposed model. Instead, the model predicts creep by considering the linearity and structural change of each element. In addition, the proposed model simulates creep recovery and permanent strain more precisely compared to other creep models, which occur due to stress removal, by considering the structural change caused by the gap.
[en] Active faults commonly repeat cycles of sudden rupture and subsequent silence of hundreds to tens of thousands of years, but some parts of mature faults exhibit continuous creep accompanied by many small earthquakes. Discovery and detailed examination of creeping faults on land have been in a rapid progress with the advent of space-borne synthetic aperture radar interferometry. In this study, we measured the spatial variation of the creep rate along the Philippine fault on Leyte Island using ALOS/PALSAR data acquired between October 2006 and January 2011. Prominent creep of mm/year was estimated in northern and central parts of the island except for a locked portion around latitude 11.08–11.20 N. We compared the creep rate distribution along the fault with the slip distribution of the 2017 6.5 Ormoc earthquake which occurred in northern Leyte, estimated from the displacements mapped by ALOS-2/PALSAR-2 interferometric data. The estimated slip of the 2017 earthquake amounted up to 2.5 m and to moment magnitude of 6.49, with the dominant rupture area coinciding with the locked portion identified from the interseismic coupling analysis. Teleseismic waveforms of the 2017 earthquake and another event that occurred in 1947 ( 6.9) exhibit close resemblance, indicating two ruptures of rather similar locations and magnitudes with a time interval of 70 years. .