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1
Oh, Myongsook Susan. "Softening coal pyrolysis". Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/15245.
Testo completoAbstract (sommario):
Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1985.MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.
Bibliography: leaves 275-284.
by Myongsook Susan Oh.
Sc.D.
2
Vineberg, Daryl Geoffrey. "A study of lead softening /". Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=80149.
Testo completoAbstract (sommario):
Softening represents one of the stages in the pyrometallurgical refining of lead, in which oxygen is top-blown into a bath of impure bullion through a group of lances in order to preferentially oxidize arsenic, antimony and tin dissolved in the melt. The oxides of these species float to the melt surface, where they are removed as dross.It has been observed at Teck Cominco Lead Operations in Trail, BC that there is an "ignition temperature" in the range of 600°C, below which the softening reactions are reported to occur very slowly, if at all. Currently, disproportionately large efforts are made to initiate and sustain the softening process. This research was motivated by Teck Cominco's wish to have a clearer understanding of the ignition temperature phenomena, and a more robust and reliable process control.
Experimental trials were performed using a homemade thermogravimetric analyzer with a data acquisition system. The unit was constructed in such a way as to allow for simultaneous video recording of the sample surface, for future examination and reference.
3
Chugg, Kevin John. "The mechanisms of fabric softening". Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385381.
Testo completo
4
Firoozi, Sadegh. "Thermodynamics and mechanisms of lead softening". Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=100362.
Testo completoAbstract (sommario):
Visualization and quantitative oxidation kinetic experiments on 100 g samples of Pb-As at 600°C; thermal analysis and phase-equilibrium measurements of Pb-PbO-As2O3 samples under argon over the temperature range of 420°C to 875°C; computational thermodynamic solution modeling; and phase diagram and equilibrium calculations using FACTSage(TM) were performed to elaborate the poorly documented thermodynamics of the slags in the lead softening stage in the pyrometallurgical refining of lead. In the softening stage, the minor element impurities: arsenic, antimony and tin are removed from lead bullion by oxidation and are transferred to a skimmable oxide slag phase.It was found that optimizing an ionic molten oxide solution model that was conceptualized to contain Pb2+ and O2- with AsO3-4 and AsO3-3 ions, or with SbO3-4 and SbO3-3 ions in the respective PbO rich regions of the Pb-As-O and the Pb-Sb-O systems, was able to accurately reproduce the measured and published thermodynamic data. It was also found that the subsystems in the PbO-As2O 3-As2O5 and PbO-Sb2O3-Sb 2O5 systems showed small deviation from the ideal ionic solution model and small magnitude excess Gibbs energy parameters were sufficient to fit the predicted liquidus curves to the experimental measurements.
Arsenic in the +3 and +5 oxidation states was measured in the PbO rich region of the Pb-As-O liquid solution in the temperature range of 420°C to 875°C. The variability in the ratio of trivalent arsenic to the total arsenic content, as well as the complex variation of arsenic distribution between metal and oxide phases found strong interaction between the lead, arsenic and oxygen atoms at the 3PbO to 1AS2O3 molar ratio thus suggesting a short range ordering corresponding to the formation of AsO3-3 groupings, and indicating that the Pb3(AsO3) 2(l) species was likely to be present in the PbO rich region of the Pb-As-O system and contributing to an understanding of the Pb-As-O liquid oxide structure. Also, two new compounds (Pb3(AsO3) 2(s), Pb2AsO4(s)) were identified in the Pb-PbO-As 2O3 quenched samples via wavelength-dispersive spectrometry using the electron microprobe. The present work has application in commercial oxygen partial lead softening (OPLS), as uniquely practiced at Teck Cominco Ltd., British Columbia. There, pure oxygen gas is injected into the bath of impure bullion through a number of submerged lances in order to oxidize only part of the arsenic, antimony and tin into a slag phase. For such an operating practice, it was concluded from the visualization and quantitative oxidation experiments that the formation of solid oxides as the product of oxidation produced a physical barrier to the progress of oxidation and resulted in the commercially observed, highly-problematic, process initiation issues. When the product was liquid, there was much less of a barrier to rapid oxygen mass transfer to the minor element impurities and the softening reactions were easy to initiate. Such a change in the physical state of the products of oxidation was correlated to the optimized ternary Pb-As-O and Pb-Sb-O phase diagrams.
A current point of interest in partial lead softening is to increase the arsenic content of the slag phase. Arsenic distribution between lead bullion and slag calculated by the optimized solution model of the Pb-As-O system suggests that this can be achieved in a counter-current contacting of the slag and bullion.
5
Zheng, Xiao-Qin Materials Science & Engineering Faculty of Science UNSW. "Packing of particles during softening and melting process". Awarded by:University of New South Wales. School of Materials Science & Engineering, 2007. http://handle.unsw.edu.au/1959.4/31517.
Testo completoAbstract (sommario):
Softening deformation of iron ore in the form of sinter, pellet, and lump ore in the cohesive zone of an ironmaking blast furnace is an important phenomenon that has a significant effect on gas permeability and consequently blast furnace production efficiency. The macroscopic softening deformation behavior of the bed and the microscopic deformation behavior of the individual particles in the packed bed are investigated in this study using wax balls to simulate the fused layer behavior of the cohesive zone. The effects of softening temperature, load pressure, and bed composition (mono - single melting particles, including pure or blend particles vs binary ??? two different melting point particles) on softening deformation are examined. The principal findings of this study are: 1. At low softening temperatures, an increase in load pressure increases the deformation rate almost linearly. 2. At higher softening temperatures, an increase in load pressure dramatically increases the deformation rate, and after a certain time there is no more significant change in deformation rate. 3. The bed deformation rate of a mono bed is much greater than that of a binary one. 4. In a binary system, the softening deformation rate increases almost proportionally with the increase in the amount of lower melting point wax balls. 5. In a mono system with blend particles, the content of the lower melting point material has a more significant effect on overall bed deformation than the higher melting point one. 6. The macro softening deformation of the bed behaves the theory of creep deformation. 7. A mathematical model for predicting bed porosity change due to softening deformation based on creep deformation theory has been developed. 8. Increase in load pressure also reduces the peak contact face number of the distribution curves, and this is more prominent with higher porosity values. 9. The contribution of contact face number to bed porosity reduction is more pronounced in a mono system than in a binary system. 10. The porosity reduction in a binary bed is more due to the contact face area increase, presumably of the lower melting point particles. 11. The mono system has a single peak contact face number distribution pattern while the binary system exhibits a bimodal distribution pattern once the higher melting point material starts to deform. 12. In a binary system, an increase in deformation condition severity tends to reduce the contact face number of the higher melting point material without having to increase the contact face number of the lower melting point material accordingly to achieve a given porosity.
6
Aguinaldo, Jorge T. "Precipitative Softening and Ultrafiltration Treatment of Beverage Water". Scholar Commons, 2006. http://scholarcommons.usf.edu/etd/3895.
Testo completoAbstract (sommario):
Lime softening, chlorination, clarification and filtration have been long recognized
treatment processes for beverage water specifically the carbonated soft drink (CSD) because
it provides consistent water quality required for bottling plants, however these processes are
becoming uneconomical and causes more problems than the benefits they offer. These
processes require very large foot print, occupy large plant volume, and generate large
volume of sludge which causes disposal problems. Chlorination produces trihalomethanes
(THMs) and other by-products which are detrimental to health and imparts tastes to the final
products. Using the newly developed submerged spiral wound ultrafiltration membranes in
conjunction with lime softening may replace the conventional lime softening, clarification
and filtration processes.
This research was conducted to demonstrate the feasibility of integrating immersed
ultrafiltration (UF) membrane with lime softening. The objectives of this research was to
achieve the water quality required by the CSD bottlers; determine the relationships of
operating parameters such as pH and membrane flux with trans-membrane pressure (TMP),
and membrane permeability; determine the optimum dosage of lime; evaluate the operating
parameters as basis for the design and construction of the full scale plant; and predict the
membrane cleaning intervals.
A pilot unit consisting of lime reactor and UF system was designed and built for this
research. The pilot unit was operated at various pH ranging from 7.3 to 11.2 and at
membrane flux rates of 15, 30 and 45 gfd. The pilot unit was also operated at the CSD
bottler’s operating conditions which is pH 9.8 at flux of 30 gfd. The pilot unit operated for a
total of 1800 hours. The raw water source was from city water supply.
The filtrate from the pilot unit achieved alkalinity reduction to 20 to 30 mg/L
preferred by CSD bottlers, with lime dosage close to the calculated value. The filtrate
turbidity during the test was consistently within 0.4 to 0.5 NTU. The TMP values obtained
during the test ranges from 0.1 to 2.5 psi, while the permeability values ranges from 18.19 to
29.6 gfd/psi. The increase in flux results to corresponding increase in TMP, and increase in
operating pH, increases the rate of TMP. Permeability decreases with increasing operating
pH. The TOC reduction ranges from 2.6 % to 15.8% with increasing operating pH. No
scaling of the UF membranes was observed during the test. Thirty days UF membrane
cleaning interval was predicted. The results from this research can use as the basis of
designing and operating a full scale Lime Softening UF Treatment Plant.
7
Tano, Robert. "Localization modelling with inner softening band finite elements". Licentiate thesis, Luleå tekniska universitet, 1997. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-26293.
Testo completo
8
Woo, Zhong-Zheng. "Dynamic analysis for nonlinear materials including strain-softening". Diss., The University of Arizona, 1991. http://hdl.handle.net/10150/185388.
Testo completoAbstract (sommario):
The implementation of the δ₀₊ᵣ model in a finite element program is discussed. The idea of considering damage as a structural performance helps to avoid singularity. Strategies in drift correction is considered. The generalized time finite element method (GTFEM) is also discussed and implemented. It shows improved accuracy and stability with highly non-linear material properties.
9
Sande, Gunnar. "Softening Behaviour of Selected Commercially Pure Aluminium Model Alloys". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18897.
Testo completoAbstract (sommario):
A characterization of the softening behaviour of four different commercially pure aluminium alloys has been carried out. The work is related to the MOREAL project (Modelling towards value-added recycling friendly aluminium alloys), where the main goal is to quantify the effect of the elements in recyclable aluminium alloys on microstructure and mechanical properties during thermo-mechanical processing. Typical elements are iron (Fe), silicon (Si) and manganese (Mn), and the alloys studied in this work contain Fe and Si with different amount and ratio: alloy A1 with 0.15 wt% Fe and 0.05 wt% Si; alloy A2 with 0.15 wt% Fe and 0.15 wt% Si; alloy B1 with 0.5 wt% Fe and 0.05 wt% Si and alloy B2 with 0.5 wt% Fe and 0.15 wt% Si.The as-cast material of all four alloys were homogenized at 600 °C for 24 hours followed by a cooling sequence to 450 °C, implying a total dwell time of 160 hours. The alloys were then cold rolled to a strain of 2.6 and isothermally annealed at temperatures from 275 °C to 375 °C, and the physical and mechanical properties were followed with electrical conductivity and hardness measurements. The microstructure and texture has been investigated with electron backscattering diffraction (EBSD) in scanning electron microscope (SEM), optical light microscopy and orientation distribution functions (ODF) from X-ray diffraction. Alloy A1 and A2 where fully recrystallzed after 10 000 seconds when isothermally annealed at 300 °C. Alloy B1 and B2 are slightly faster to reach the fully recrystallized state than alloy A1 and A2. The decrease in mechanical properties during softening was nearly linear on a logarithmic time scale, especially for alloy B1 and B2, with the onset of recrystallization difficult to seperate from the recovery. Electrical conductivity measurements showed that there was minimal concurrent precipitation. Images of the microstructure of the samples annealed at 275 °C show a long recovery phase followed by recrystallization. Particle stimulated nucleation (PSN) sites seems to be an important nucleation mechanism as it is found that the initial grain size have little effect on the softening kinetics, indicating that nucleation on old grain boundaries is of little importance. The recrystallization texture is weak with the typical Cube orientation slightly rotated around the normal direction. The recrystallized grain size was found to be smaller in alloy B1 and B2 (16-20 μm) than in alloy A1 and A2 (21-27 μm), most likely due to more PSN sites in these alloys. The grain growth that followed after recrystallization was found to be slightly larger for alloy A1 and A2 than alloy B1 and B2, most likely due to the effect from solute drag.
10
Gumusoglu, M. Cetin. "Analysis of underground excavations in strain softening rock masses". Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/38339.
Testo completo
11
Mshana, S. J. "Rate-dependent constitutive equations of cyclic softening and hardening". Thesis, University of Ottawa (Canada), 1986. http://hdl.handle.net/10393/5422.
Testo completo
12
Stange, Roland, Kenechukwu David Nnetu e Josef A. Käs. "Cell stiffening and softening evoked by optical stress application". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-182542.
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13
Owiny, J. R. "Factors affecting softening of the ovine cervix at parturation". Thesis, University of Liverpool, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377817.
Testo completo
14
Stange, Roland, Kenechukwu David Nnetu e Josef A. Käs. "Cell stiffening and softening evoked by optical stress application". Diffusion fundamentals 20 (2013) 30, S. 1, 2013. https://ul.qucosa.de/id/qucosa%3A13596.
Testo completo
15
Хоменко, Олексій Віталійович, Алексей Витальевич Хоменко, Oleksii Vitaliiovych Khomenko, B. N. J. Persson, М. А. Khomenko e S. V. Rudenko. "Synergetic model of frictional softening of ice surface layer". Thesis, Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна Національної академії наук України, 2015. http://essuir.sumdu.edu.ua/handle/123456789/41630.
Testo completo
16
Ciacciulli, A. "FRUIT FLESH IN PEACH:CHARACTERIZATION OF THE 'SLOW SOFTENING' TEXTURE". Doctoral thesis, Università degli Studi di Milano, 2018. http://hdl.handle.net/2434/540666.
Testo completoAbstract (sommario):
The aim of this research was to deepen the knowledge about the slow softening texture in peach.
The texture is a synthesis of several parameters detected by senses, derived from the food structure. The paramount sense in the texture perception is the tactile one, principally perceived by hand and mouth. The tactile perception is a combination of four classes of mechanoreceptors, each one specialized to perceive mechanic deformation with different speed. This combined perception influences the consumer evaluation of food quality, giving the texture importance among food characteristics. The texture could also affect the taste perception through mechanical actions on food structure. The mechanical property linked to the texture is associated with the cellular organization and the cell wall strength. The main cell wall component affecting texture in fresh fruit is pectin, a polymer of galacturonic acid. The disassembly of pectin involves several enzymatic and non-enzymatic activities acting directly in pectin cleavage or indirectly disrupting non-covalent interactions. The gold standard of texture analyses is the sensorial one, however several issues make sensorial analyses inapplicable to breeding programs to select plant with improved fruit texture. Several efforts were made to achieve instrumental analyses capable of substitute humans in texture analyses. To mimic the tactile sense, a discipline studying the material response to an applied force, the rheology, is applied. The easiest instrumental measure of rheology parameters is the penetrometer test, diffused to measure the firmness, but exploitable to collect the Young’s modulus and the slope of yield stress represented respectively elasticity and fracturability.
In peach, so far at least four textures were described, melting (M), stony hard (SH), non-melting (NM) and slow softening (SS). Prior to this work, no reliable objective nor fast tool were available to phenotype and select the SS trait in peach germplasm. The only reliable approach was a sensorial assessment done by a texture-trained panel, requiring repeated and time-consuming assessment. An objective, instrumental method, was set up by processing the data of a digital penetrometer test. The penetrometer itself, as reported in paragraph 2, does not support the ability to discriminate among the different texture types, as already reported in other works. In addition, this method appears to be affected by the fruit ripening season, since the early-ripening accessions tend to show faster loss of firmness, while the late-ripening exhibit a slower firmness loss.
Using the data collected in our experiment, the texture dynamic (TD) model was developed from the observation of differences in the rheogram shape due to the elasticity and fracturability parameters. The TD model, that excludes the firmness effect on the fracturability and elasticity parameters, was thus developed, after testing it on 20 accessions in three years, allowing for reliable discrimination between SS and M phenotype. Differences in the TD were also found when comparing M vs SH and M vs NM textures. In particular, when comparing M and SS, TD value is explained for the 96% from the texture.
The developed method was then applied (together with sensorial evaluation) to genetically dissect the SS trait. Association and QTL mapping approaches were combined by analyzing a germplasm panel and a biparental progeny, and a single locus at the end of chromosome 8 was identified. RNA-seq analysis of 2 SS and 2 M accessions suggested some common features with the SH type described in literature. In both texture types a lower auxin response was found when compared to the M type. This agrees with the already known activity of auxin in the modulation of cell wall rearrangement and expansion. Therefore, slower softening could be associated to slower cell wall rearrangement. In future, comparison of auxin content in slow softening and melting type peaches might provide further insight into the validity of this hypothesis. In detail, by RNA-seq comparing M and SS a total of 64 differentially expressed genes were found in the genomic region harboring the SS locus. Out of these 64 genes, 16 are uncharacterized, while among the characterized ones, 4 are putatively involved in auxin response based on peach genome annotation. Analysis of polymorphisms in these 4 DEGs based on resequencing data of the ‘Max10’ and ‘Rebus 028’ parents of biparental population did not uncover any variants in agreement with the observed segregation. Analyzing 2kb gene models flanking regions, 16 genes were associated with polymorphisms outside the coding sequence: the possible regulatory effects of such variants require further evaluation by expression analyses.
In summary, the major results are the setup of a reliable tool to score objectively the SS texture and the detection of a major locus and his dominant mendelian inheritance. However, NGS and RNA-seq approaches are presented as a speculative data only, because they are not supported by hormones content in fruit, and the large locus detected did not allow indication of a putative variant.
These results will: a) give impetus in exploring SS genetic and physiology; b) support the design of future crosses and experiments; c) increase marker density in the locus; d) point out the possible central role of auxin (to validate the hypothesis of a similarity between SS and SH physiology); e) allow texture assessment of improved cultivars; and f) allow phenotyping of segregating progenies to develop molecular markers associated with the SS trait.
17
Lee, Si Hyung Materials Science & Engineering Faculty of Science UNSW. "Reduction and softening/melting behaviour of olivine pellet in the experimental blast furnace". Awarded By:University of New South Wales. Materials Science & Engineering, 2009. http://handle.unsw.edu.au/1959.4/40939.
Testo completoAbstract (sommario):
An in-depth study has been carried out on the reduction, softening and melting behavior of olivine based pellets in the experimental blast furnace. The aim of the project was to develop a fundamental understanding of the reduction mechanisms of olivine based pellets and to develop a correlation between the reduction rate and the softening behavior in the cohesive zone of blast furnace. The carburization characteristics of reduced iron were also investigated by examining olivine pellet and coke samples excavated and probed from an experimental blast furnace as well as the experimental investigations of pure hematite and heat treated coke. X-ray diffraction analysis was used to successfully determine the reduction degree of olivine pellets in different parts of the experimental blast furnace. These results were found to be consistent with assessments of reduction degree based on a detailed chemical analysis. The average reduction degree of iron oxide was seen to increase as the pellets descended towards lower zones of the EBF. Up to 75% reduction was completed before the pellet had reached the cohesive zone; remaining reduction was completed within the cohesive zone. Coke Lc showed a linear variation with experimental temperature above 11000C; a correlation was established to estimate furnace temperature as a function of EBF depth. The reduction degree of iron ore pellet showed a linear correlation with distance from the stock line of the EBF to the upper part of cohesive zone. But an abrupt increase in reduction rate was observed in the cohesive zone, a result observed in both EBF and experimental studies. The presence of olivine did not have much influence on the reduction degree of iron ore pellets for temperatures below 1100oC in the upper shaft zone of the EBF. However, olivine was found to increase the rate of reduction in the advanced stages of reduction in the cohesive zone for temperatures in excess of 1100oC. This effect was attributed to the formation of increased amount of molten iron oxide within the pellet. The initial melt formation and acceleration of the reduction rate in the cohesive zone of the EBF were also investigated. From the comparison between the reduction degree of excavated olivine pellets in this study and previous studies of EBF, it was found that the excavated pellets were located in the cohesive zone and increase of reduction rate in this zone could be verified by not only the change of gas composition, but also initial melt formation containing FeO phase. The chemical composition of slag phases of excavated pellet samples were located on the line between 2FeO??SiO2 and 2MgO??SiO2 in the FeO-MgO-SiO2 ternary phase diagram. This result is in good agreement with the assumption that the initial slag formation of the olivine pellets had proceeded from the fayalite and after reduction the FeO contents in the slag phase had decreased and eventually precipitated as slag with a higher melting point. From the analysis of carbon contents of the excavated pellets in cohesive zone, it was observed that the carburization of iron pellets began after the complete reduction. This study has established that the reduction rate of iron pellet is the rate controlling step for carburization irrespective of the carburization reaction by the solid carbon.
18
Barraclough, Thomas William. "Strain softening and strain localisation in irreversible deformation of snow". Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/16218.
Testo completoAbstract (sommario):
The aim of this work was to visualise heterogeneous deformation in snow under controlled laboratory conditions. Heterogeneous deformation was observed for both homogenous and heterogeneous loading conditions. Understanding deformation of snow is important in many scientific fields including vehicle traction, avalanche forecasting, and winter sports. This thesis investigates the deformation behaviour of snow on the centimetre scale under moderate strain rates (0.005 to 0.1 s-1) when subject to one-dimensional compression or to indentation. In order to allow controlled and repeatable snow deformation experiments, a new type of artificial snow was developed. This snow type was examined by low temperature scanning electron microscopy and by traditional avalanche observer’s methodology. Penetrometer experiments were conducted on the artificial snow and on natural seasonal snow in Scotland. The two snow types were found to be similar: results obtained on artificial snow are thus applicable to natural snow. A reproducible technique of manufacture and a thorough characterisation of the artificial snow are presented. One-dimensional compression experiments were conducted on the artificial snow. The experiments were in confined compression in a specially constructed apparatus, designed to provide for back-lit photography. Images were taken at 0.25 second intervals and analysed using digital image correlation, thus providing 2D strain fields. With careful control of photographic parameters, it is demonstrated that process of applying tracer substances to the snow is not necessary, thus allowing an unprecedented resolution. Spontaneously-forming strain localisations were observed for the first time, indicating strain softening behaviour. Damage was observed to propagate through the specimen as a moving front, resembling a wave. The force required to propagate the front remained nearly constant until the whole specimen was compacted, at which point a new front formed and the process repeated. The experimental method was extended to 2D indention experiments with a range of sizes and shapes of indenter. Complex deformation fields were observed, extending up to 6 times the width of the indenter on each side. Observed deformation included tensile tearing as well as compression and shear. The maximum local strain achieved in the indentation experiments was similar to that achieved by the first compaction front in one-dimensional compression. The work here presented has implications for snow deformation generally: strain localisation introduces a characteristic length, which may prevent scaling of models or results. The indentation results are particularly relevant to snow penetrometry, where indentation experiments are used to try and extract microstructural information from buried snow layers for the purpose of avalanche prediction. The common assumption that the penetrometer interacts only with snow very close to its tip may need to be reconsidered.
19
Stewart, Gregg Ryan. "Static and dynamic aging and softening in 304 stainless steel". Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=84847.
Testo completoAbstract (sommario):
Interactions between diffusing impurity atoms and dislocations can occur during or following the deformation of metals. These interactions cause dislocation pinning, leading to strain aging. At lower temperatures (<400°C), the relevant solutes are interstitial (in particular, carbon and nitrogen). At higher temperatures (>800°C), substitutional impurities are expected to be most influential. The same mechanisms that result in the yield drops, increased flow stresses and increased work hardening associated with strain aging at low temperatures should result in significant modification of recovery and recrystallization behaviour at higher temperatures.The present work involves the deformation of austenitic (304) stainless steel at high temperatures (800°C to 1280°C) in 1-hit and 2-hit high-temperature compression and multi-hit hot torsion testing. Experimental variables include the strain rate, temperature and interpass time.
Significant anomalies in the static softening kinetics are observed; under certain deformation conditions, the normal relationship between temperature and fractional softening is reversed. This effect is attributed to the non-equilibrium segregation of phosphorus during the interpass holding time. Analysis of dynamic recrystallization (DRX) in the material has revealed retardation of the initiation of recrystallization; this effect is explained in terms of the segregation of substitutional elements to the boundaries of new DRX grains.
20
Taherian, Ali Reza. "Thermal softening kinetics and textural quality of thermally processed vegetables". Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=23301.
Testo completoAbstract (sommario):
Dry Romano beans (Phaseolus vulgaris) were soaked and cooked at temperatures ranging from 70 to 100$ sp circ$C for different time intervals. The rate of texture softening associated with each temperature was found to be consistent with two simultaneous pseudo first-order kinetic mechanisms 1 and 2. Approximately 40% of the firmness of Romano beans was lost by the rapid softening mechanism 1. The remaining firmness loss was characterized by mechanism 2 which was found to be much slower ($ sim$1/50th of the former). The temperature dependence indicator (z value) of reaction rate constants were 30 and 24 C$ sp circ$, respectively for mechanisms 1 and 2 with associated activation energies of 82 kJ/mole and 103 kJ/mole, respectively.Turnip (Brassica napobbrassica) and beet roots (B. Vulgaris L.) were cooked at temperatures ranging from 70 to 100$ sp circ$C for different time intervals. Three textural properties (firmness, springiness, and stiffness) were found to follow the same trend of apparent first order kinetic theory with two substrates. Temperature dependence of softening (z value) was found to be within 27 and 35 C$ sp circ ,$ with activation energies in the range of 93 and 60 kJ/mole.
Cylindrical turnip, beet root pieces and Romano beans were packed in thin profile plastic containers and cylindrical metal cans and thermally processed in the static and rotational modes. Through heat penetration testing, process times were adjusted to give an equivalent lethality of 10 min for each product. Thin profile packed vegetables, in all cases, were found to have a firmer and stiffer texture. On the other hand, for rotational processing, the result showed no significant improvement in textural properties (firmness, springiness and stiffness) over the still counterparts. It was found that previously determined kinetic data could be used to estimate texture retention.
21
Balrey, Gurprett Singh. "Mechanism for reduction of fruit softening by Rab 11a silencing". Thesis, University of Nottingham, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490824.
Testo completoAbstract (sommario):
It has been shown that LeRablla antisense tomato plants exhibit a reduced softening phenotype compared to wild type fruits. Thus, the LeRabl 1 protein may be involved in trafficking of cell wall hydrolysing enzymes to the cell wall during ripening. It has since been shown that LeRablla is highly expressed in immature fruit and expression decreased as the fruit developed reaching barely detectable levels in ripening fruit. The possibility thus exists that the observed phenotype may be due to silencing of related gene(s).
22
Abdul, Aziz Sa'ardin. "Characterising the effective material softening in ultrasonic forming of metals". Thesis, University of Glasgow, 2012. http://theses.gla.ac.uk/3704/.
Testo completoAbstract (sommario):
This thesis has presented experimental and finite element (FE) analyses of the static and ultrasonic forming of two metals; aluminium 1050 and magnesium AM50. Aluminium and magnesium are considered to be soft metals and can be easily shaped by any of the main industrial metalworking processes. Frequently aluminium and magnesium have been the subject of research studies. These two metals most commonly chosen in manufacturing industry because of their cost, mechanical properties and flexibility in processing. In this research, simple compression and forming tests were designed and the effects of superimposed ultrasonic excitation on workpiece and die, which is tuned to a longitudinal mode at 20.8 kHz, were studied via stress-strain measurements. Research through experiments and finite element simulations studies in the application of ultrasonic excitation has been carried out to gain quantitative understanding of the mechanisms of improvement in ultrasonic forming characteristics, such as a reduction in material flow stress and oscillatory stress. This research study has shown these mechanisms by applying ultrasonic vibration to the tool and die in the forming test and, similarly, effects were measured and predicted in the experimental and numerical analysis. The development and application of high power ultrasonic techniques in forming processes required the use of specifically designed ultrasonic components to correctly transmit the energy from the transducer to the workpiece and die interface. The application along with the ultrasonic vibration amplitude required for the process, were considered in order to design the most suitable horn profile. In this study, a 20 kHz transducer was used to provide up to 10 µm of peak-to-peak vibration amplitude, depending on the generator setting. Therefore, the booster and horn were designed to provide a range of ultrasonic vibration amplitudes between 5 to 20 µm and also used as a tool and die in the study of ultrasonic metal forming. The horn was designed using finite element modelling (FEM), and modal frequencies and associated mode shapes were subsequently confirmed using experimental modal analysis (EMA). The ultrasonic system has been measured and calculated as having a longitudinal mode of vibration at 20.8 kHz and to provide an amplitude gain of four. In this study, a generator uses mains electricity to generate a high frequency ultrasonic signal to drive the transducer, which is tuned to a specific frequency of 20 kHz. The booster and horn were designed to meet the criteria of transducer, which is to provide a longitudinal vibration at tuned frequency of 20 kHz. However, the profile of booster and horn have been measured and calculated as having a longitudinal mode of vibration at 20.8 kHz, which is considered close to the transducer tuned frequency. The review of previous studies of superimposed ultrasonic excitation on upsetting showed that the most experimental characterisations of the volume effects mainly depended on an interpretation of measurements of the mean flow stress, and have neglected the oscillatory stress. In this study, the characteristics of oscillatory stress and the material behaviour in plastic deformation when superimposed ultrasonic excitation is applied on a static compression test under dry friction were considered. The effects were explained in terms of flow stress reduction, oscillatory stress, mean flow stress, maximum and minimum path of oscillatory stress in the stress-strain diagram. The results showed that the static flow stress of compressive deformation was lowered by the ultrasonic vibration superimposed on the static load and this phenomenon has been referred to as the material softening mechanism which is influenced by volume and surface effects. The volume effect is defined as a reduction in flow stress of the material being formed and the surface effect is defined as a reduction in frictional conditions at the interface between the vibrating device and the workpiece. Finite element models were used to investigate numerically the volume and surface effects during ultrasonically assisted compression. The finite element models were developed using material model parameters which were identified from the experimental analysis. The influence of volume and surface effects were investigated separately in the FE model and it was shown that the volume effect dominated the effective material softening results during ultrasonic excitation. The application of ultrasonic excitation on metals under plastic deformation conditions has been investigated previously. Most researchers have reported that superimposing ultrasonic excitation on metal working processes reduced the material flow stress. A further study of superimposed ultrasonic excitation on a static load during elastic deformation in metal working was not investigated, so it is not possible to determine the effect of ultrasonic excitation on the material. In this study, the investigation of oscillatory stress behaviour in the ultrasonic compression test of cylinder metal specimens during elastic deformation was carried out. In the stress-strain diagram, the ultrasonic vibration was shown to have lowered the static flow stress during elastic deformation under dry contact conditions and it was found that the reduction in static flow stress linearly increased with ultrasonic vibration amplitude. The stress reduction was influenced by volume and surface effects which occurred during the superimposed ultrasonic excitation. The results also showed that the maximum path of oscillatory stress exceeded the static flow stress, however, the mean flow stress is lower than the static flow stress at the onset of ultrasonic excitation. To investigate the influence that volume and surface effects have on material softening during experimental compression tests, a series of FE models were developed. As mentioned previously, the FE models were developed using material model parameters which were identified from the experimental analysis in Figure A1, however, the mechanism of flow stress reduction which is related to acoustic softening and friction reduction which is labelled as (i) cannot be predicted in FE models. The FE models adopted the material softening effects in order to simulate realistic stress reduction compared with experimental results. The significant stress reduction in the FE analysis was obtained by adjusting the yield stress and contact conditions parameter. It was concluded that the surface effect dominated the stress reduction during metal upsetting test in elastic deformation. The study continued to a simple forming test where samples of flat sheet metal were forced into a shaped die by a shaped plunger on a test machine. The results of this study illustrated how ultrasonically assisted metal forming resulted in a lowering of the static forming force during ultrasonic excitation of the die. As a result, the static forming force was seen to be reduced by ultrasonic excitation of the die and the path of the maximum oscillatory force was observed to be parallel to or below the path of the static forming force. Force reduction was measured in these experiments using a high power ultrasonic transducer and also by tuning the die and then the punch during the metal forming test. It was found that a good coupling between punch, specimen and die allowed ultrasonic energy to be effectively transferred into the materials during superimposed ultrasonic excitation in the static forming test. This thesis has concluded that evaluation of the benefits of ultrasonic excitation not only relied on measurements of the mean flow stress alone but also on measurement of the oscillatory stress during superimposed ultrasonic excitation on forming tests.
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Tahar, Benabdellah. "Câ†2 continuous hardening/softening elasto-plasticity model for concrete". Thesis, University of Sheffield, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323061.
Testo completo
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CARVALHO, RENATO BREDER DE. "NUMERICAL SIMULATION OF SOFTENING IN ELASTIC-PLASTIC TRUSSES WITH DAMAGE". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1993. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=33231@1.
Testo completoAbstract (sommario):
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORO presente trabalho apresenta uma técnica numérica geral para a aproximação da solução do problema de evolução quasi-estático em treliças elasto-plásticas com dano. Uma formulação geral e abstrata é apresentada e uma técnica numérica simples, baseada na técnica de decomposição do operador com um algoritmo sequencial associado, é proposta. Alguns exemplos tratando da análise de falha de treliças metálicas são usados para mostrar a efetividade do método.
This work is corcerned with a general numerical technique for approximating the solution of quase-static evolution problems in damageable elasto-plastic trusses. An abstract and general formulation of the problem is presented and a simple numerical technique based on the operator splitting technique associated with a product formula algorithm is proposed. Some examples concerning the failure analysis of metallic trusses are used to show the effectiveness of the method.
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Karypidis, Michail I. "The effect of softening agents on the wear of textiles". Thesis, University of Manchester, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602948.
Testo completoAbstract (sommario):
The application of softeners to textile is known to enhance the fabric handle. In this study the potential for novel softeners, commonly used in the cosmetic industries, has been investigated with a view to improving the textile handle and also imparting a protective effect against wear abrasion. To assess Cotton and Tencel fabric handle and wear strength objectively, the Kawabata Evaluation System for Fabrics (KES-F) and the Martindale Flat Abrasion instrument have been utilised. In addition a novel Y am-on-Y am abrasion system has been developed to assess dry and wet abrasion. Both beneficial and detrimental effects have been demonstrated on the cellulosic substrates by the application of softeners and the performance behaviour has been discussed. As part of the project an experimental rinse conditioner formulation for domestic laundering was evaluated and its effectiveness in comparison to a standard formulation studied. However, little benefit was observed in terms of fabric handle and the ineffective behaviour investigated using the surface sensitive analytical technique, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). ToF-SIMS was able to characterise a range of softeners demonstrate their substantivity to the cellulosic substrate and the preferential adsorption of a cationic imidazoline softener at the fibre surface. The Y am-on-Y am abrasion system has been used successfully to probe the wet fibrillation of reneel yams and has the appropriate sensitivity and reproducibility to differentiate between fibre erosslinking regions and non-crosslinking reagents. The influence of reactive dyes, crease resist finishes and novel colourless cross linking has been investigated and the behaviour related to the level of fibre crosslinking. The affect of softeners on abrasion performance has also been evaluated and their affects on wet and dry yam abrasion established.
26
Ungsuwarungsri, Tawach Knauss Wolfgang Gustav. "The effect of strain-softening cohesive material on crack stability /". Diss., Pasadena, Calif. : California Institute of Technology, 1986. http://resolver.caltech.edu/CaltechETD:etd-02242004-152909.
Testo completo
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Bob, Mustafa M. "Enhanced removal of natural organic matter during lime-soda softening". Connect to this title online, 2003. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1047486107.
Testo completoAbstract (sommario):
Thesis (Ph. D)--Ohio State University, 2002.Title from first page of PDF file. Document formatted into pages; contains xxii, 119 p.: ill. Includes abstract and vita. Advisor: Harold W. Walker, Civil Engineering Program. Includes bibliographical references (p. 115-119).
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Nasreldin, Gaisoni Abdin. "Adaptive mesh refinement for localisation problems involving strain-softening geomaterials". Thesis, University of Manchester, 2009. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.499950.
Testo completo
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Downs, Susan L. "Cell wall degrading enzymes in mango fruit cultivars". Thesis, University of Nottingham, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267670.
Testo completo
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Qi, Baoxiu. "A study of the effects of heating on banana and plantain fruit". Thesis, University of Bath, 1997. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390304.
Testo completo
31
Sjølstad, Knut. "Deformation and Softening behaviour of commercial AlMn-alloys : Experiments and Modelling". Doctoral thesis, Norwegian University of Science and Technology, Department of Materials Technology, 2003. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-143.
Testo completoAbstract (sommario):
A comprehensive study of the softening behaviour of two different non-heat treatable AlMn-alloys has been carried out. These alloys were a laboratory processed and an industrially processed AA3103-alloy. The primary objective of the laboratory processed alloy has been directed towards the relationship between the amount of manganese in supersaturated solid solution and the material behaviour during deformation and annealing. The focus for the industrially processed alloy was a detailed material characterisation during hot and cold rolling as well as to follow the softening behaviour of the alloy.
The cold rolled microstructures were characterised with respect to subgrain size, misorientation across the subgrain boundaries, particle break-up and global texture. As far as it concerns the cold deformed microstructure it was found that the different homogenisation treatments, resulting in different amount of Mn in supersaturation, had little effect on the deformed microstructure.
Detailed experimental work on the softening behaviour after cold deformation and the interaction between recrystallisation and precipitation, i.e. concurrent precipitation, has been carried out. Hardness and yield stress measurements, which defines the strength of the material, revealed that the softening behaviour was significantly slowed down in case of concurrent precipitation. It was further found that the precipitation reaction in this case occurred on the subgrain boundaries. Thus the precipitates considerably retarded the recrystallisation reaction as compared to the case when no precipitation occurred.
TTT-diagrams have been constructed on the basis of hardness and conductivity measurements. From these diagrams a characteristic temperature, Tc , for the different material conditions are identified. It was found that as the annealing was carried above this temperature the microstructure consisted of a fine grained equiaxed microstructure. Below Tc the grains become elongated in the rolling direction and the average grain size became much coarser.
With respect to recrystallisation texture, a very strong P-texture and in addition some ND-rotated cube texture was found in case of concurrent precipitation. This viistrong P-texture was investigated in detail, and it can be concluded that particle stimulated nucleation of recrystallisation (PSN) plays a significant role in the nucleation of these components. It was found that these texture components had a growth advantage in the early stage of annealing and that they are most probably a result of microgrowth selection, which often are related to a nucleation effect. When precipitation did not interact with recovery and recrystallisation the recrystallisation texture was either random or consisted of a weak cube texture.
The softening behaviour of the different materials has been modelled by a physically based softening model, which involves both the recovery and recrystallisation reactions. Both for the AlMn-alloys and for an additional commercially pure Al-alloy, relatively good model predictions were obtained for the softening behaviour when recrystallisation occurred prior to precipitation. However, when the softening reactions were retarded by heavy precipitation of dispersoids the model, in its original form, was not capable to predict the softening behaviour. In this case an additional retarding drag, which reduces the total number of viable recrystallisation nuclei, was added. With the addition of this drag relatively good model predictions were also obtained in case of concurrent precipitation. However, the model was not capable to predict the softening behaviour of the industrially processed AlMn-alloy particularly well.
32
Vahedi, Arman. "Predicting the Settling Velocity of Lime Softening Flocs using Fractal Geometry". Elsevier, 2010. http://hdl.handle.net/1993/4953.
Testo completoAbstract (sommario):
Stokes’ law that is traditionally used for modeling the sedimentation of flocs, incorrectly assumes that the floc is solid and spherical. Consequently the settling rates of flocs cannot be estimated using the Stokes law.
The application of fractal dimensions to study the internal structure and settling of flocs formed in lime softening process was investigated. An optical microscope with motorized stage was used to measure the fractal dimensions of lime softening flocs directly on their images in 2 and 3D space. The fractal dimensions of the lime softening flocs were 1.15-1.27 for floc boundary, 1.49-1.90 for cross-sectional area and 2.55-2.99 for floc volume. Free settling tests were used for indirect determination of 3D fractal dimension. The measured settling velocity of flocs ranged from 0.1 to 7.1 mm/s (average: 2.37 mm/s) for the flocs with equivalent diameters from 10µm to 260µm (average: 124 µm).
Floc settling model incorporating variable floc fractal dimensions as well as variable primary particle size was found to describe the settling velocity of large (>60 µm) lime softening flocs better than Stokes’ law. Settling velocities of smaller flocs (<60 µm) could still be quite well predicted by the Stokes’ law. The variation of fractal dimensions with lime floc size in this study indicated that two mechanisms are involved in the formation of these flocs: cluster-cluster aggregation for small flocs (>60 µm) and diffusion-limited aggregation for large flocs (<60 µm). Therefore, the relationship between the floc fractal dimension and floc size appears to be determined by floc aggregation mechanisms.
The settling velocity of lime softening flocs was also modeled by a general model that assumes multiple normally distributed fractal dimensions for each floc size. The settling velocities were in the range of 0-10mm/s and in good agreement with measured settling velocities (0.1-7.1mm/s). The Stokes’ law overestimates the settling velocity of lime flocs. It seems that the settling velocity of flocs is mainly controlled by aggregation mechanisms and forming large floc does not guarantee improved sedimentation.
The multifractal analysis of lime softening flocs showed that these aggregates are multifractal and a spectrum of fractal dimensions is required to describe the structure of an individual floc.
33
Anya, Chinasa Chukwuemeka. "The strengthening and "softening" of low-carbon structural steels by silicon". Thesis, University of Strathclyde, 1989. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21217.
Testo completoAbstract (sommario):
The variation of tensile properties and grain sizes, on adding silicon, up to 1.03 wt% in five grades of low carbon structural steel was studied. The reduced sensitivity of the lower yield stress, [σy], at sub-zero test temperatures, otherwise called "softening", of these steels with reduced grain sizes, brought about by the silicon additions was also investigated. Optical and transmission electron microscopes were used to characterize the ferrite-pearlite structures, decarburized layers, random interlamellar spacings in the pearlite constituent, slip line, twin and dislocation structures. The precipitates observed were studied qualitatively with the transmission electron microscope, and microanalysis was carried out by using the dispersed energy of the X-rays (EDAX). Dilatometric studies were done to establish the critical temperatures of the steel grades. Uniaxial tensile tests were carried out at between 77 and 350 K, with strain rates of 1.7x10⁻⁴, 3.3x10⁻⁴s and 0.33 s⁻¹. The data from these tests were analyzed in terms of the contribution silicon and nitrogen make to the tensile properties, and were used to determine the thermal activation parameters, hence "softening". It was found that silicon additions beyond 0.31 wt% in these steels inhibit grain growth, due to the effect of silicon on the grain nucleation kinetics. In conformity to previous reports, the Hall-Patch slope, Ky was reduced to a limit, on the initial additions of silicon, but further to this observation, it was found that low silicon steels, below 14 μm possess higher strength than high silicon steels, within 0.31 to 0.78 wt% Si. In contrast with previous reports, in which SiN precipitates were identified in similar. steel grades, under aged conditions, low temperature (∞) Si₃N₄ precipitates were observed in both the annealed and the aged samples of the steels in the present study. It was also found that reduced grain sizes increase the "softening" tendency of these steels. These results we correlated with those from limited reports found in the literature, regarding the effect of silicon (above 0.7 wt%) on the impact behaviour of these grades of steel. From the correlation, it is suggested that a new theory should be sought to explain how the initial additions of silicon, with reduced grain sizes, improve the impact behaviour. Hypotheses are advanced linking the improvement of impact behaviour with the "softening" phenomenon. It is also suggested that a higher silicon to manganese ratio, with silicon not exceeding 1 wt%, may improve not only the strength and the impact behaviour, but also-the cost indices of these grades of steel.
34
Phan, Thanh Danh. "Trafficking of hydrolases to fruit cell walls and role in softening". Thesis, University of Nottingham, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440294.
Testo completo
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MariÌn-RodriÌguez, MariÌa Celia. "Investigation of the role of pectate lyase in banana fruit softening". Thesis, University of Greenwich, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399345.
Testo completo
36
Bakar, Abu. "Adaptive and fixed mesh investigaiton of localisation in strain-softening geomaterials". Thesis, University of Manchester, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.521355.
Testo completoAbstract (sommario):
The influence of localisation in strain-softening soils has been investigated using classical continuum theory, and both fixed mesh and adaptive mesh refinement (AMR) finite element approaches. For this purpose, a non-associated cohesion-softening Mohr-Coulomb soil model has been developed and, for the adaptive mesh study. an existing AMR algorithm has been upgraded by implementing the superconvergent patch recovery smoothing technique. Both fixed mesh and adaptive mesh approaches have been used to analyse the problem of passive earth pressure failure, with the computed results for limit load and failure plane orientation being compared with analytical solutions available in the literature. Parametric studies have been included to consider the influence of degree of softening and material dilation angle. The fixed mesh results highlight the findings of previous investigators who showed that, in the presence of strain-softening, the solution is non-unique: in particular. as the mesh density increases, so the post-peak load-displacement response becomes steeper, without there being any sign of convergence. However, this mesh dependency is shown to be less significant for a rough retaining wall (i.e. as compared to a smooth wall), due to the increased influence of progressive failure. The adaptive mesh results show that, in the absence of an internal length scale facility, shear band width reduces without limit as the minimum element size gets smaller. However- for both smooth and rough walls, load-displacement response converges to a unique solution, suggesting that adaptivity may be an alternative solution to non-standard continuum theories in countering mesh dependency in strain-softening computations. A major advantage of the adaptive mesh algorithm is its ability to update meshes during an analysis, to account for new and changing regions of strain concentration. Stress and strain contours show that this gives a better definition of developing failure mechanisms, compared to the fixed mesh approach. Using AMR, the solutions are relatively free from mesh alignment effects, with mesh configurations following strain concentrations, rather than vice versa. Furthermore, the efficient use of elements means that mesh adaptivity has an important role to play in the solution of much larger geotechnical problems.
37
Wang, Gongbing 1944. "Size effect on damage in progressive softening process for simulated rock". Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276886.
Testo completoAbstract (sommario):
In the hierarchical approach of constitutive modelling, the damage accumulation and resulting strain-softening behavior of geologic materials can be modelled by introducing a concept of damage evaluation. The damage accumulation and softening behavior are affected by the size of specimens. A series of uniaxial tests on cylindrical specimens of a simulated rock were performed. The effect of specimen size on the parameters of the damage model were investigated by using the test results. The empirical results show that the damage parameters can be related to a characteristic dimension, which was expressed in terms of length and diameter of the specimen.
38
Stapleton-Hart, Nicole Colette 1965. "Dynamic response of structures with geometrically softening components including foundation interaction". Thesis, The University of Arizona, 1990. http://hdl.handle.net/10150/277871.
Testo completoAbstract (sommario):
The effects of material nonlinearity and geometric instabilities of a bracing system of a dynamically loaded steel frame, as well as nonlinear soil-structure interaction are studied in this thesis. To investigate the response of a frame subjected to severe dynamic loads, a model of the force-displacement relationship of the bracing system is developed to account for the inelastic, post-buckling behavior of a brace subjected to strong compressive loads. This thesis also develops a model of the force-deformation relationship of the foundation-soil interface, confining the study only to the slide mode of failure. From these models, a softening behavior for the bracing system and a hyperbolic load-deformation behavior of the interface are proposed. It is shown that the structural response of a frame is significantly affected when the analysis includes both the effects of softening of the bracing system and soil-structure interaction.
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Reichard, Brett David. "Uniaxial tensile testing technique to obtain softening response of ultra-high performance concrete under confining pressures". Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53866.
Testo completoAbstract (sommario):
The focus of this thesis is to research and develop a uniaxial tensile testing technique and methodology to attain the post-peak softening response for ultra-high performance concrete under confining pressure. This particular multi-axial behavior is valuable in improving current material models in finite element simulations for US Army applications into hardened target structures.
40
Zobeiry, Navid. "Extracting the strain-softening response of composites using full-field displacement measurement". Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/26239.
Testo completoAbstract (sommario):
From both numerical and experimental standpoints, it is very desirable to develop a general methodology that can be used to determine the strain-softening response and characteristic damage properties (e.g. fracture energy, damage height) of quasi-brittle materials. In the absence of a direct methodology, one has to conduct multiple experiments combined with trial-and-error procedures and/or simplifying assumptions regarding the damaging behaviour of the material in order to construct a strain-softening curve.
In this study, a new methodology is developed that directly identifies the damaging constitutive response of composite materials using full-field measurements of kinematic variables. Using this methodology, the damage related properties can be extracted and the strain-softening response of composite materials under mode I loading can be obtained directly. Compared to other available indirect approaches, this method invokes fewer assumptions about the behaviour of the material and does not require any prior assumption regarding the shape of the constitutive response, as is required in other approaches.
A series of compact compression and over-height compact tension tests are conducted on IM7/8552 quasi-isotropic laminates. Using the digital image correlation technique, full-field displacement vectors of the specimen surface are measured in each test. Based on the acquired data and using the basic principles of mechanics (equilibrium and compatibility), a family of approximate stress-strain curves are obtained. These approximate curves are then used in an iterative process to determine the optimized strain-softening response of the laminate.
To validate the capability of the method to capture the local damaging behaviour of the composite laminate, a series of destructive tests such as deplying and sectioning are performed on the damaged specimens. The tested laminates are also simulated using finite element analyses of the specimens that employ the extracted strain-softening curve as input to a damage mechanics based material model. The proposed methodology provides insight into the details of damage propagation in composite materials and is a promising tool for characterizing the strain-softening behaviour of composite laminates in a relatively easy and direct manner.
41
Greb, Andrea (Andrea L. ). "A study of the stretch-induced softening behavior of particle filled elastomers/". Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45843.
Testo completoAbstract (sommario):
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (leaf 61).
Elastomers are able to undergo relatively large deformations in an elastic manner, which makes them the material of choice for a wide range of applications. In some cases, filler particles, such as carbon black, are added to the elastomer to alter the mechanical behavior when subjected to different loading conditions. When subjected to cyclic loading conditions, elastomers undergo stress-induced softening, known as the Mullins effect, and this softening behavior is influenced by the amount of filler particle present. The softening is considered to be an evolution of the soft and hard domain microstructure of the material, with the effective soft domain increasing with stretch. In this study, finite element analysis will be used to understand the softening behavior of particle reinforced elastomers. The softening behavior of the parent elastomer will be modeled using a constitutive model proposed by Qi and Boyce (2004). Nonlinear finite element analysis using the ABAQUS code was used to model elastomers with various volume fractions of filler particles, and the stress-strain behavior of the composite and evolution of the soft domain within the matrix is computed. The addition of filler particles was found to increase the overall stiffness of the elastomer, but also to increase the stretch-induced softening, and to alter the distribution of soft domains within the material. The presence of occluded regions of matrix material was also found to have a significant effect on softening behavior.
by Andrea Greb.
S.B.
42
Sivathanu, Vivek. "Disrupting dynamic f-actin enhances skeletal muscle contraction due to mechanical softening". Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/115667.
Testo completoAbstract (sommario):
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 128-135).
Skeletal muscle wasting disorders such as sarcopenia affect the daily mobility of millions of aging people globally due to decreased muscle mass and decreased muscle efficiency. In this study we discover a novel target to improve the efficiency of skeletal muscle by targeting the dynamic f-actin cytoskeleton. Using two model systems, an ex-vivo mouse muscle model and a novel in vitro optogenetic skeletal muscle micro-tissue model, we show that disruption of the dynamic f-actin cytoskeleton using small molecule actin dynamics inhibitors leads to a persistent 2-fold improvement in muscle active contractility. We explored possible drawbacks of f-actin disruption, including loss of mechanical integrity, cell death, and intracellular organelle damage. None of these downsides actually present themselves with f-actin disruption. Muscle fatigue resistance however does seem to be slightly affected. We performed a detailed characterization of the cytoskeletal modifications that occur during f-actin disruption using dose-response-recovery studies, live f-actin imaging, fluorescence recovery after photobleaching and more targeted f-actin disruption. Using these studies we conclude that treatments which shorten f-actin filaments seem to improve contraction. We also uncovered previously unidentified roles of branched and tropomyosin stabilized f-actin in force transmission. Biomechanical testing at the cell level using AFM and at the tissue level using a micro-tensile test shows a drop in mechanical stiffness that correlates well with a corresponding improvement in muscle force. We ruled out a range of alternate hypotheses involving changes to sarcomeric proteins and energetic activity, that could explain the force improvement, concluding that the force improvement due to f-actin disruption is due to mechanical softening of the cells which pose to a lower resistance to their own contraction. As a potential application, we show that a weak 3D printed muscle powered biological robot starts walking with f-actin disruption. This target has significant therapeutic potential in muscle disorders due to its disease non-specificity. We conclude by discussing possible future experiments that could reveal the best therapeutic applications. Key words: Muscle strength, f-actin, cytoskeleton, Skeletal Muscle Tissue Engineering, Muscle Disorders.
by Vivek Sivathanu.
Ph. D.
43
Boman, Andreas, e Jakob Selvin. "Softening Efficacy of Various Solvents on Gutta-percha and Root Canal Sealer". Thesis, Umeå universitet, Institutionen för odontologi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-129389.
Testo completoAbstract (sommario):
Solvents have been used in endodontic retreatment for a long time and the dissolving effect is well proven. Latterly chloroform has come in a bad light due to its possible carcinogenicity. Despite the negative health effect it is still used in dental environment. Other more biocompatible solvents have now reached the market and tests should be performed to evaluate the softening efficacy. The purpose of this in-vitro study was to evaluate the softening efficacy of four different solvents used in endodontics; chloroform, eucalyptol, tetrachloroethylene, orange-oil and a control group. 100 simulated canals filled with gutta-percha, epoxy amine resin based sealer, zinc oxide eugenol based sealer and non eugenolcalcium hydroxide based sealer were tested with hardness measurement before and after two minutes exposure time of medicament. Non-eugenol calcium hydroxide failed to set and was excluded from the test. A Shore A durometer was used to evaluate the hardness of the materials and all data was first analyzed with Kruskal-Wallis test and then Mann-Whitney test to compare with control group. With a digital camera connected to a microscope we also took pictures to compare the impressions with the different medicaments. The result showed that chloroform and tetrachloroethylene is significant better to soften gutta-percha than control group (p < 0.05) but only chloroform significant better than control group to soften epoxy amine resin based sealer and zinc oxide eugenol based sealer (p < 0.05). Even if the result was significant, we cannot draw any conclusions due to small sample size.
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Bessa, Raquel de Andrade. "Synthesis and characterization of composite magnetic zeolites using kaolin for softening water". Universidade Federal do CearÃ, 2016. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=17007.
Testo completoAbstract (sommario):
CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel SuperiorThe present work deals about the synthesis and characterization of magnetic zeolites obtained by hydrothermal route using kaolin from Brazilian Northeast as silicon and aluminum source. By means of the X-ray diffraction technique it was possible to identify zeolite LTA and zeolite P1 as major crystalline phases for each synthesis, with low intensity peaks referent to unreacted quartz present in the kaolin used, which is in accordance to the. FTIR spectra; the nanoparticles were identified as magnetite, with low intensity peaks referent to goethite. In scanning electron microscopy, however, it was not possible to morphologically identify these minor components, while the zeolites showed well defined morphologies, presenting unchanged morphology when in the composites form, but with nanoparticles dispersed over their surface, as expected. From transmission electron microscopy it was observed that the nanoparticles were of ca. 50 nm. Magnetic measurements indicated magnetite presence with superior diameter to critical diameter to superparamagnetic particles and remanent magnetization. Thermogravimetric analyses showed for the composites, lower mass loss than compared to the pure zeolites what may be associated to the improvement of its thermal stability. Granulometric distribution indicated nanoparticles agglomeration in variable sizes, while zeolites formed agglomerates of ca. 10 Âm. Water softening was accomplished by using both zeolites, with high efficiency on Ca2+ removal and similar behavior between the zeolite and its respective composite, being the best result observed for zeolite A, with efficiency of 97,95%, reaching equilibrium in the first contact minutes. The dependence on mass studies also showed that zeolite A and its composite presented the best efficiency, whereas zeolite P achieved the same removal levels using corresponding zeolite masses (45 mg). This way, the proposed method for zeolites synthesis proved to be efficient, so that the use of a magnet is capable to attract them, leading their excellent separation from the aqueous medium with its ionic exchange capacity unaffected.
O presente trabalho trata da sÃntese e caracterizaÃÃo de zeÃlitas magnÃticas obtidas por impregnaÃÃo de nanopartÃculas de magnetita a zeÃlitas A e P, sintetizadas por mÃtodo hidrotÃrmico utilizando caulim branco do Nordeste brasileiro como fonte de silÃcio e alumÃnio. Por meio da tÃcnica de difraÃÃo de raios-X foi possÃvel identificar como fases cristalinas majoritÃrias a zeÃlita LTA e P1 para cada sÃntese, com picos de baixa intensidade referentes a quartzo, resistente ao processo tÃrmico de tratamento prÃvio do caulim, bem como nos espectros de infravermelho; as nanopartÃculas foram identificadas como magnetita, havendo ainda indÃcios da presenÃa de goethita em pequena quantidade. Nas anÃlises de microscopia eletrÃnica de varredura, entretanto, nÃo foi possÃvel identificar esses componentes minoritÃrios morfologicamente; enquanto que a morfologia das zeÃlitas mostrou-se bem definida, sem alteraÃÃes apÃs a formaÃÃo dos compÃsitos, apenas com nanopartÃculas espalhadas em sua superfÃcie, como desejado. A partir da microscopia eletrÃnica de transmissÃo, pÃde-se observar melhor a variaÃÃo de tamanho das nanopartÃculas, em mÃdia de 50 nm. Medidas magnÃticas das amostras com essa propriedade indicaram a presenÃa de magnetita com diÃmetro superior ao diÃmetro crÃtico para partÃculas superparamagnÃticas e magnetizaÃÃo remanente. As anÃlises termogravimÃtricas mostraram que a adiÃÃo das nanopartÃculas Ãs zeÃlitas diminuiu sua perda de massa diante do aumento de temperatura e as anÃlises de distribuiÃÃo granulomÃtrica indicaram a aglomeraÃÃo das nanopartÃculas em tamanhos variÃveis, enquanto que as zeÃlitas formaram aglomerados de aproximadamente 10 Âm. Os ensaios de abrandamento de Ãguas mostraram alta eficiÃncia das zeÃlitas em remover Ca2+, com comportamento similar entre a zeÃlita e o seu respectivo compÃsito, encontrando para a zeÃlita A o maior percentual de remoÃÃo, de 97,95 %, atingindo equilÃbrio nos primeiros minutos de aplicaÃÃo. Os estudos de massa tambÃm mostraram a eficiÃncia da zeÃlita A e de seu compÃsito, tendo a zeÃlita P se aproximado dos mesmos nÃveis de remoÃÃo em massas referentes a 45 mg de zeÃlita. Assim, o mÃtodo proposto para sÃntese das zeÃlitas magnÃticas mostrou-se eficiente, de modo que a utilizaÃÃo de um Ãmà à capaz de atraÃ-las facilitando a separaÃÃo do meio apÃs a aplicaÃÃo em meio aquoso e sua capacidade de troca iÃnica nÃo foi afetada.
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Kraxner, Julia [Verfasser]. "Vimentin Intermediate Filament Softening - Recovery Behavior and Post-Translational Modifications / Julia Kraxner". Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2021. http://nbn-resolving.de/urn:nbn:de:gbv:7-21.11130/00-1735-0000-0008-590D-7-0.
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Rebouah, Marie. "Anisotropic stress softening and viscoelasticity in rubber like materials and architectured materials". Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENI104.
Testo completoAbstract (sommario):
Ce travail de thèse présente une étude du comportement mécanique des matériaux mous soumis à de grandes déformations. Dans ce cadre deux types de matériaux ont été considérés : des matériaux de type élastomères et des matériaux architecturés mimant des matériaux du vivant. Dans un premier temps, cette étude se focalise sur des matériaux de type élastomères pour une meilleure compréhension des phénomènes, notamment grâce à une large étude expérimentale qui n'aurait pas pu être menée sur des tissus du vivant. La caractérisation mécanique des élastomères permet de mettre en évidence différents phénomènes tel que : l'adoucissement de contrainte (aussi connu sous le nom d'effet Mullins), l'anisotropie induite, la déformation résiduelle et la viscoélasticité. Dans le but de créer un modèle capable de prendre en compte tous ces effets dans le cadre des grandes déformations, différents élastomères ont été utilisés pour mettre en évidence chacun de ces phénomènes. Ainsi, chaque matériau a permis d'isoler un phénomène afin de développer et de valider une nouvelle partie du modèle. Par la suite, des matériaux architecturés de type élastomères ont été fabriqués et utilisés pour induire une anisotropie initiale. Le modèle proposé précédemment est alors étendu à la prise en compte de cette anisotropie initiale. Une extension à la modélisation des tissus du vivant (qui sont pour la plupart initialement anisotropes) devient ainsi possible. Chaque modèle a été implanté numériquement dans un code de calcul par éléments finis (excepté pour la viscoélasticité), et la robustesse du modèle a été validée grâce à des essais expérimentaux complexes (bulge test) ou sur des structures complexes (plaque trouée)This thesis work presents a study of the mechanical behavior of soft materials submitted to large deformations. In this context two types of materials were considered: rubber like materials and architectured materials to mimic soft tissues. As a first step, this study focuses on rubber like materials for a better understanding of the phenomena, especially through an large experimental study that could not be lead on soft tissues.The mechanical characterization of the rubber like materials allows highlighting several phenomena such as: the stress softening (also known as Mullins effect), induced anisotropy, permanent set and viscoelasticity. With the aim to create a model able to take into account all these effect in the framework of large deformations, several rubber like materials were used to highlight each one of these phenomena. In this way, each material permits to isolate one phenomenon to develop and validate a new part of the model.Thereafter, architectured materials made of rubber like materials were used to induce an initial anisotropy. The model proposed previously is adapted to take into account this initial anisotropy. An extension to modeling soft tissues (most of them are initially anisotropic) becomes possible.Each model was numerically implemented in a finite element code (except for the viscoelasticity), and the robustness of the model was validated by means of complex experimental tests (bulge test) or on complex structures (holey plate)
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Giroux, Pierre-François. "Experimental study and simulation of cyclic softening of tempered martensite ferritic steels". Paris, ENMP, 2011. http://www.theses.fr/2011ENMP0087.
Testo completoAbstract (sommario):
Inscrit au sein d'un grand projet aboutissant à la mise en œuvre des réacteurs nucléaires de génération IV, ce travail de thèse porte sur l'étude des aciers martensitiques revenus à 9 % de chrome. Actuellement utilisés pour des applications à haute température, notamment dans les centrales thermiques, ils présentent en fatigue et en fatigue-fluage un phénomène d'adoucissement mécanique et des évolutions microstructurales particulièrement prononcées : disparition de nombreux joints de sous-grains, baisse de la densité de dislocations, apparition et/ou grossissement de précipités et de nouvelles phases. Les objectifs principaux de cette thèse sont (i) d'établir expérimentalement une corrélation entre l'adoucissement mécanique des aciers à 9 % de chrome constaté en fatigue à 550 °C et l'évolution de leur microstructure au cours de ce type de sollicitation et (ii) de modéliser les mécanismes physiques de déformation afin de prédire le comportement mécanique de ces aciers sous chargement cyclique. Une étude des propriétés mécaniques en traction monotone et sous sollicitations cycliques à 550 °C a été conduite sur un acier de Grade 92 (9Cr-0,5Mo-1,8W-V-Nb). L'expertise des éprouvettes de traction suggère que l'adoucissement du matériau est principalement lié à une augmentation de la taille moyenne des sous-grains de plus de 15 % par rapport à l'état initial. L'étude de l'évolution de la contrainte macroscopique durant les essais cycliques montre que l'adoucissement du matériau est dû à la diminution de l'écrouissage cinématique. Les observations effectuées au MET montrent une augmentation de la taille moyenne des sous-grains comprise entre 65 et 95 % et une diminution de la densité de dislocations de plus de 50 % dans le matériau après les essais de fatigue, par rapport à l'état initial. Un modèle auto-cohérent à champs moyens fondé sur l'élastoviscoplasticité polycristalline, prédisant le comportement mécanique macroscopique du matériau et l'évolution microstructurale au cours de la déformation est proposé. En décrivant les mécanismes de déformation à partir d'observations microstructurales, le modèle utilise seulement deux paramètres ajustables (énergie et volume d'activation) liés aux mécanismes de déformation viscoplastique. Les valeurs de l'ensemble des autres paramètres sont fixées grâce à des mesures expérimentales ou des calculs issus de la littérature. Le modèle prédit correctement l'adoucissement macroscopique et donne une bonne tendance des évolutions microstructurales au cours de la déformation. L'étude paramétrique montre une bonne stabilité des prédictions dès lors que les paramètres expérimentaux varient dans un intervalle de mesure physiquement acceptable. Enfin, quelques perspectives d'amélioration du modèle sont testées et des essais de torsion cyclique avec et sans contrainte moyenne sont simulésThe present work focuses on the high temperature mechanical behaviour of 9%Cr tempered martensite steels, considered as potential candidates for structural components in future Generation IV nuclear power plants. Already used for energy production in fossil power plants, they are sensitive to softening during high-temperature cycling and creep-fatigue. This phenomenon is coupled to a pronounced microstructural degradation: vanishing of subgrain boundaries, decrease in dislocation density, nucleation and/or growth of precipitates and new phases. This study aims at (i) linking the macroscopic cyclic softening of 9%Cr steels and their microstructural evolution during cycling and (ii) proposing a physically-based modelling of deformation mechanisms in order to predict the macroscopic mechanical behaviour of these steels during cycling. Mechanical study including uniaxial tensile tests and cycling at 550 °C was performed on a Grade 92 steel (9Cr-0,5Mo-1,8W-V-Nb). Examination of tensile specimens suggested that the physical mechanism responsible for softening is mainly the evolution of mean subgrain size, which increases by more than 15 % compared to the as-received state. The evolution of macroscopic stress during cycling shows that cyclic softening is due to the decrease in kinematic hardening. TEM observations highlighted that the mean subgrain size increases by 65 to 95 % while the dislocation density decreases by more than 50 % during cycling, compared to the as-received state. A self-consistent homogenization model based on polycrystalline elastoviscoplasticity, predicting the mechanical behaviour of the material and its microstructural evolution during deformation is proposed. This model takes the physical deformation mechanisms into account and only two adjustable parameters (activation energy and activation volume) linked to the viscoplastic deformation mechanisms are used. The value of other parameters were either experimentally measured or deduced from computations available in literature. The model correctly predicts the macroscopic softening behaviour and gives a good trend of the microstructural evolution during cycling. The parametrical study shows that the predictions of the model are rather stable with respect to the variation of the physically-based parameters. Finally, some hypotheses which permit us to improve the model are presented and torsion tests (with or without constant superimposed tensile stress) are modeled
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Dounias, George Theodoros. "Progressive failure in embankment dams". Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/8350.
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Tibbits, C. William. "Studies on the pectin network of the tomato fruit cell wall". Thesis, University of East Anglia, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327392.
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Muyibi, Suleyman Aremu. "Factors affecting coagulation of turbid water and softening hardwater with Moringa oleifera seed extracts". Thesis, University of Newcastle Upon Tyne, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308368.
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