On the Recovery and Fatigue Life Extension of Stainless Steel 316 Metals by Means of Recovery Heat Treatment

In this paper, we propose a methodology for enhancing the fatigue life of SS316 by performing intermittent recovery heat-treatment (RHT) in the Argon environment at different temperatures. To this end, fully-reversed fatigue bending tests are conducted on the heat-treated SS316 specimens. Damping values are obtained using the impact excitation technique to assess the damage remaining in the material after each RHT and the corresponding fatigue life. Damping is also used to distinguish the three stages of the fatigue phenomenon and the onset of crack initiation. The results show that by performing intermittent RHTs, the density of dislocation is decreased substantially and fatigue life is improved. Examination of the damping results also reveals that the material becomes more brittle after the RHT due to the decrease in the density of dislocations. The fatigue life of the specimens is governed by these two phenomena

Forced boiling of nanofluids, effects of contact angle and surface wettability

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Nanofluids are the suspension of ultra fine particles in a conventional base fluid which tremendously changes the heat transfer characteristics of the original fluid. In this paper the boiling characteristics of different nanofluids was studied numerically using a CFD approach. Dispersions of Al2O3, SiO2, and ZrO2 nanoparticles in water at different concentrations (0.1, 0.01 and 0.001% by volume) have been used. Effects of some noticeable parameters such as nanoparticle concentration and temperature profile on the critical heat flux (CHF) have been investigated. The results of CFD simulation based on two-phase models were compared with experimental data. Boiling curves and critical heat flux were measured for the base fluid and the nanofluids. Based on the simulation results, it was concluded that the using of the Zirconium oxide (0.001%) led to modest (up to 31%) increase in the CHF. The minimum enhancement belongs to the aluminum oxide (0.1%) which increases the critical heat flux up to 11%. According to the experimental results, despite of expectation, addition of the nanoparticles causes decreasing the boiling heat transfer coefficient. This reduction is related to the changing of the surface characteristic causing by depositing the nanoparticles. In the Al2O3/water and SiO2/water nanofluids, the surface contact angle increases with increase in the nanoparticle volume fraction, so the CHF decreases

Indentation-based characterization of creep and hardness behavior of magnesium carbon nanotube nanocomposites at room temperature

The time-dependent plastic deformation response of magnesium/carbon nanotube (CNT) nanocomposites containing 0.25, 0.5, and 0.75 vol% of carbon nanotubes is investigated through depth nanoindentation tests against monolithic pure magnesium in the present study. The Mg-CNT nanocomposite materials were successfully synthesized via a powder metallurgy technique coupled with microwave sintering followed by hot extrusion to produce 8-mm diameter, long solid bars. All depth-sensing indentation creep tests were conducted at ambient (room) temperature employing a diamond Berkovich pyramidal indenter. These tests are dual-stage, i.e., loading to a prescribed peak load of 50 mN, holding the peak load constant for a dwell period of 500 s, and finally unloading. Various strain rates of 0.01, 0.1, 1, and 10 s−1were performed to assess the effects of strain rate and dwell time on the ambient temperature creep response of the Mg-CNT nanocomposites. The outcomes of these tests are explained through material hardness, microstructure, the extent of CNT content in each material, and strain rate sensitivity. Upon analyzing the nanoindentation creep tests, the dominant creep mechanism at room temperature was found to be a dislocation creep mechanism. It is also found that CNTs increase the creep resistance of magnesium. Findings of this study can be used as a starting point for a high-temperature creep study on Mg-CNT nanocomposites. This paper is a continued study from our group on time-dependent plastic deformation of Mg nanocomposites (i.e., see Haghshenas et al., Journal of Composite Materials, https://doi.org/10.1177/0021998318808358). The short-term goal is to provide a compressive picture of the controlling creep mechanisms and their dependency upon, time, temperature, strain rate, volume fraction of the nanoparticles, and the type of the nanoparticles. Mg, in general, is a notorious material for high-temperature application; therefore, the long-term objective is to propose Mg nanocomposite as reliable replacements for Mg when lightweight and creep resistance are needed. However, to be able to confidently suggest such a replacement detailed understanding on the controlling phenomena, mention as short-term goals, are required

A phonetic and phonological study of the nominal piece in Standard Colloquial Persian.

This thesis presents a phonetic and phonological description of the nominal piece in Standard Colloquial Persian. The phonetic description is given in articulatory feature analysis as briefly outlined in paragraph 0.5. The phonological description is in prosodic terms. Intonation has been excluded from this thesis as it is primarily a sentence prosody.1 In order to achieve maximum congruence between the phonological and grammatical levels, the phonological statements are given within a grammatical framework outlined in parts at the beginning of the relevant chapters. The introduction gives the necessary information about the data analysed, previous analyses and some justification for the choice of the theory. A general discussion on syllable, some existing phonetic definitions, and the need for syllable is presented in Chapter 1 where a definition of syllable in Persian is suggested together with its types. The phonetic features observed in the data are described in Chapters 2 and 3 in. terms of syllable features and syllable segments. The phonetic features observed between syllables at morpheme boundaries as well as some rules for syllable division are given in Chapter 4. Chapter 5 provides further description of glottal, pre-glottal and long contoids. 1. For a description of intonation in Persian see J. Towhidi's "A Study of Intonation and Related Features of Persian ...", research for Ph.D. thesis, London University, S.O.A.S. In Chapter 6 the phonological structure of syllable is given and the syllable prosodies are stated. In Chapter 7 different phonematic systems are set up for different places in the syllable. The syllable structure of nominal words is set up in Chapter 8, and various prosodies of nominal words are described. Chapter 9 deals with the description of the nominal piece and junction prosodies which express the relation between the components of nominal piece. Chapter 10 provides a brief summary of some interesting experimental findings obtained with the help of the techniques of palatography, mingography and spectrography. Most of the descriptions based on perceptual analysis of the data are found to be supported by instrumental evidence

Bismuth vanadate photoanodes for water splitting deposited by radio frequency plasma reactive co-sputtering

Photoactive bismuth vanadate (BiVO4) thin coatings were deposited on fluorine-doped tin oxide glass by plasma reactive sputtering from Bi2O3 and vanadium (V) radio frequency (RF) powered targets. The films were characterized by x-ray diffraction, scanning electron microscopy, energy dispersion spectroscopy, and UV-vis spectroscopy. The effects that the power density supplied to the Bi2O3 target, the post-annealing treatment, and the film thickness have on the structural features and on the photoelectrochemical (PEC) performances of the so obtained BiVO4 film-based photoelectrodes were investigated. Their PEC performance in water splitting was evaluated in a three-electrode cell by both incident photon to current efficiency (IPCE) and linear sweep voltammetry measurements under AM 1.5 G simulated solar light irradiation. A monoclinic phase of BiVO4, which is more photoactive than the tetragonal BiVO4 phase, was obtained by optimizing the power density supplied to the Bi2O3 target, i.e., by tuning the Bi:V:O atomic ratio. The best PEC performance was obtained for a stoichiometric 1:1 Bi:V atomic ratio, attained with 20 W power supplied at the Bi2O3 target and 300 W power supplied at the vanadium target, and an optimal 200 nm thickness of the BiVO4 film, with a 0.65 mA/cm2 photocurrent density attained at 1.23 V vs. standard calomel electrode, under simulated solar light. These results show the suitability of plasma reactive sputtering with two RF powered electrodes for the deposition of BiVO4 photoanodes for water splitting

Lattice Boltzmann Numerical Investigation of Inner Cylindrical Pin-fins Configuration on Nanofluid Natural Convective Heat Transfer in Porous Enclosure

Concerning the geometrical effect of inner cylindrical hot pins, the natural convective heat transfer of nanofluid in a homogenous porous medium in a squared enclosure is numerically studied, using lattice Boltzmann method (LBM). In order to investigate the arrangement of inner cylinders for better heat transfer performance, five different configurations (including one, three, and four pins) were compared, while the total heat transfer area of inner pins were held fixed. Squared cavity walls and inner cylinder’s surfaces were constantly held at cold and warm temperatures, respectively. In our simulation, Brinkman and Forchheimer-extended Darcy models were utilized for isothermal incompressible flow in porous media. The flow and temperature fields were simulated using coupled flow and temperature distribution functions. The effect of porous media was added as a source term in flow distribution functions. The results were validated using previous creditable data, showing relatively good agreements. After brief study of copper nano-particles volume fraction effects, five cases of interest were compared for different values of porosity and Rayleigh number by means of averaged Nusselt number of hot and cold walls; and also local Nusselt number of enclosure walls. Comparison of different cases shows the geometrical dependence of overall heat transfer performance via the average Nusselt number of hot pins strongly depending on their position. The four pin case with diamond arrangement shows the best performance in the light of enclosure walls’ average Nusselt number (heat transfer to cold walls). However, the case with three pins and downward triangular arrangement surprisingly gives promising heat transfer performance. In addition, the results show that natural convective heat transfer and flow field is intensified with increasing Rayleigh number, Darcy number, and porosity

Estimation of topographical effects at Narni ridge (Central Italy): comparisons between experimental results and numerical modelling

In the present work the seismic site response of Narni ridge (central Italy) is evaluated by comparing experimental results and numerical simulations. The inhabited village of Narni is located in the central Italian Apennines at the top of a steep massive limestone ridge. From March to September 2009 the site was instrumented with 10 weak-motion stations, 3 of which located at the base of the ridge and 7 at the top. The velocimetric network recorded 642 events of ML up to 5.3 and hypocentral distance up to about 100 km. The great amount of data are related to the April 2009 L’Aquila sequence. The site response was analyzed using both reference (SSR, Standard Spectral Ratio) and non reference spectral techniques (HVSR, Horizontal to Vertical Spectral Ratio). Moreover directional analyses were performed in order to evaluate the influence of the ridge orientation with respect to the selected source-site paths. In general the experimental results show amplification factors for frequencies between 4 and 5 Hz for almost all stations installed along the crest. The SSR technique provides amplification factors up to 4.5 detected considering directions perpendicular to the main elongation of the ridge. The results obtained from the monitoring activity were used as a target for bidimensional and tridimensional numerical simulations, performed using a hybrid finite-boundary element method for 2D and a boundary element method for 3D analyses respectively. In general, the results obtained through numerical simulation fit well the experimental data in terms of range of amplified frequencies, but they underestimate by a factor of about 2 the related amplification factors with respect to the observations