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Effect of structure on the properties of an Italian Pleistocene clayCotecchia, Federica January 1996 (has links)
No description available.
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The behaviour of clayey sands under monotonic and cyclic loadingGeorgiannou, Vasiliki Nikolaou January 1988 (has links)
No description available.
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Numerical modelling of localisation in soilsShuttle, Dawn Alison January 1988 (has links)
No description available.
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The behaviour of silt under undrained and drained loadingNapitupulu, Jonner January 1990 (has links)
No description available.
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Controlled gradient consolidation of soft soils with reference to the development of Kâ†oTing, Chi Man Roger January 1990 (has links)
No description available.
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Mechanical properties and behaviour of silicate and acrylamide grouted sandHaji-Bakar, Ismail January 1990 (has links)
No description available.
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Stress-strain behaviour of rubberGough, Julia January 2000 (has links)
Several aspects of the stress-strain behaviour of rubber, important for evaluating its properties for finite element analysis and engineering applications, are investigated. Measurements of the deformation behaviour of an elastomer containing a compressible filler are used to assess theoretical equations for the compression modulus of rubber pads bonded to rigid endplates. The volume fraction of filler is estimated from a simple model. The first cycle stress-strain behaviour of filled and unfilled rubbers is characterised from uniaxial tests and by measuring both non-zero principal stresses with a novel pure shear technique. Various theoretical forms for the strain energy density function are assessed. The results support the assumption that the strain energy of filled natural rubber is a function only of the first strain invariant. Finite element modelling of the behaviour of a hyperelastic material in simple shear reveals that the proximity of the free edges in conventional simple shear testpieces strongly influences the stresses and deflections in the thickness direction. These finding are qualitatively supported by experiment. The effect of free edges on the shear modulus is also assessed. Deviations from hyperelastic behaviour are investigated through experimental studies of stress relaxation, cyclic stress softening and the superposition of a torsion on a uniaxial extension. Anisotropic deformations can result in corresponding differences in the amounts of stress relaxation or stress softening in different directions. Isotropic models cannot model these features but may be adequate for most practical applications. The relationship between the modulus and crystallinity of partially crystalline rubber is determined experimentally. The reinforcing effect of the crystals is found to be approximately independent of their morphology and of the modulus of the amorphous rubber. Studies of yielding of partially crystalline rubber show that the yield stress increases with increasing amounts of crystallization whereas the yield strain remains roughly constant.
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Micromechanical Modelling of PolyethyleneAlvarado Contreras, Jose Andres 11 1900 (has links)
The increasing use of polyethylene in diverse applications motivates the need for understanding
how its molecular properties relate to the overall behaviour of the material.
Although microstructure and mechanical properties of polymers have been the subject of
several studies, the irreversible microstructural rearrangements occurring at large deformations
are not completely understood. The purpose of this thesis is to describe how the
concepts of Continuum Damage Mechanics can be applied to modelling of polyethylene
materials under different loading conditions.
The first part of the thesis consists of the theoretical formulation and numerical
implementation of a three-dimensional micromechanical model for crystalline polyethylene.
Based on the theory of shear slip on crystallographic planes, the proposed model is
expressed in the framework of viscoplasticity coupled with degradation at large deformations.
Earlier models aid in the interpretation of the mechanical behaviour of crystalline
polyethylene under different loading conditions; however, they cannot predict the microstructural
damage caused by deformation. The model, originally due to Parks and
Ahzi (1990), was further developed in the light of the concept of Continuum Damage
Mechanics to consider the original microstructure, the particular irreversible rearrangements,
and the deformation mechanisms. Damage mechanics has been a matter of intensive
research by many authors, yet it has not been introduced to the micromodelling
of semicrystalline polymeric materials such as polyethylene. Regarding the material representation,
the microstructure is simplified as an aggregate of randomly oriented and
perfectly bonded crystals. To simulate large deformations, the new constitutive model
attempts to take into account existence of intracrystalline microcracks.
The second part of the work presents the theoretical formulation and numerical
implementation of a three-dimensional constitutive model for the mechanical behaviour
of semicrystalline polyethylene. The model proposed herein attempts to describe the deformation and degradation process in semicrystalline polyethylene following the approach
of damage mechanics. Structural degradation, an important phenomenon at large
deformations, has not received sufficient attention in the literature. The modifications to
the constitutive equations consist essentially of introducing the concept of Continuum
Damage Mechanics to describe the rupture of the intermolecular (van der Waals) bonds
that hold crystals as coherent structures. In order to model the mechanical behaviour,
the material morphology is simplified as a collection of inclusions comprising the crystalline
and amorphous phases with their characteristic average volume fractions. In the
spatial arrangement, each inclusion consists of crystalline material lying in a thin lamella
attached to an amorphous layer. To consider microstructural damage, two different approaches
are analyzed. The first approach assumes damage occurs only in the crystalline
phase, i.e., degradation of the amorphous phase is ignored. The second approach considers
the effect of damage on the mechanical behaviour of both the amorphous and
crystalline phases.
To illustrate the proposed constitutive formulations, the models were used to predict
the responses of crystalline and semicrystalline polyethylene under uniaxial tension
and simple shear. The numerical simulations were compared with experimental data
previously obtained by Bartczak et al. (1994), G‘Sell and Jonas (1981), G‘Sell et al. (1983),
Hillmansen et al. (2000), and Li et al. (2001). Our model’s predictions show a consistently
good agreement with the experimental results and a significant improvement with
respect to the ones obtained by Parks and Ahzi (1990), Schoenfeld et al. (1995), Yang
and Chen (2001), Lee et al. (1993b), Lee et al. (1993a), and Nikolov et al. (2006). The
newly proposed formulations demonstrate that these types of constitutive models based
on Continuum Damage Mechanics are appropriate for predicting large deformations and
failure in polyethylene materials.
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Micromechanical Modelling of PolyethyleneAlvarado Contreras, Jose Andres 11 1900 (has links)
The increasing use of polyethylene in diverse applications motivates the need for understanding
how its molecular properties relate to the overall behaviour of the material.
Although microstructure and mechanical properties of polymers have been the subject of
several studies, the irreversible microstructural rearrangements occurring at large deformations
are not completely understood. The purpose of this thesis is to describe how the
concepts of Continuum Damage Mechanics can be applied to modelling of polyethylene
materials under different loading conditions.
The first part of the thesis consists of the theoretical formulation and numerical
implementation of a three-dimensional micromechanical model for crystalline polyethylene.
Based on the theory of shear slip on crystallographic planes, the proposed model is
expressed in the framework of viscoplasticity coupled with degradation at large deformations.
Earlier models aid in the interpretation of the mechanical behaviour of crystalline
polyethylene under different loading conditions; however, they cannot predict the microstructural
damage caused by deformation. The model, originally due to Parks and
Ahzi (1990), was further developed in the light of the concept of Continuum Damage
Mechanics to consider the original microstructure, the particular irreversible rearrangements,
and the deformation mechanisms. Damage mechanics has been a matter of intensive
research by many authors, yet it has not been introduced to the micromodelling
of semicrystalline polymeric materials such as polyethylene. Regarding the material representation,
the microstructure is simplified as an aggregate of randomly oriented and
perfectly bonded crystals. To simulate large deformations, the new constitutive model
attempts to take into account existence of intracrystalline microcracks.
The second part of the work presents the theoretical formulation and numerical
implementation of a three-dimensional constitutive model for the mechanical behaviour
of semicrystalline polyethylene. The model proposed herein attempts to describe the deformation and degradation process in semicrystalline polyethylene following the approach
of damage mechanics. Structural degradation, an important phenomenon at large
deformations, has not received sufficient attention in the literature. The modifications to
the constitutive equations consist essentially of introducing the concept of Continuum
Damage Mechanics to describe the rupture of the intermolecular (van der Waals) bonds
that hold crystals as coherent structures. In order to model the mechanical behaviour,
the material morphology is simplified as a collection of inclusions comprising the crystalline
and amorphous phases with their characteristic average volume fractions. In the
spatial arrangement, each inclusion consists of crystalline material lying in a thin lamella
attached to an amorphous layer. To consider microstructural damage, two different approaches
are analyzed. The first approach assumes damage occurs only in the crystalline
phase, i.e., degradation of the amorphous phase is ignored. The second approach considers
the effect of damage on the mechanical behaviour of both the amorphous and
crystalline phases.
To illustrate the proposed constitutive formulations, the models were used to predict
the responses of crystalline and semicrystalline polyethylene under uniaxial tension
and simple shear. The numerical simulations were compared with experimental data
previously obtained by Bartczak et al. (1994), G‘Sell and Jonas (1981), G‘Sell et al. (1983),
Hillmansen et al. (2000), and Li et al. (2001). Our model’s predictions show a consistently
good agreement with the experimental results and a significant improvement with
respect to the ones obtained by Parks and Ahzi (1990), Schoenfeld et al. (1995), Yang
and Chen (2001), Lee et al. (1993b), Lee et al. (1993a), and Nikolov et al. (2006). The
newly proposed formulations demonstrate that these types of constitutive models based
on Continuum Damage Mechanics are appropriate for predicting large deformations and
failure in polyethylene materials.
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Versuchstechnische Ermittlung und mathematische Beschreibung der mehraxialen Festigkeit von ultra-hochfestem Beton (UHPC) - Zweiaxiale Druckfestigkeit; Im Rahmen des Schwerpunktprogramms 1182 Nachhaltiges Bauen mit Ultra-Hochfestem Beton (UHPC) / Experimental Investigation and Mathematical Analysis of Multiaxial Strength of Ultra High Performance Concrete (UHPC) - Biaxial Compressive StrengthCurbach, Manfred, Speck, Kerstin 18 September 2007 (has links) (PDF)
Der vorliegende Bericht beschreibt das Verhalten von ultrahochfestem Beton unter zweiaxialer Druckbeanspruchung. Bisher wurden ein Feinkornbeton und zwei Grobkornbetone mit unterschiedlichen Faserzusätzen untersucht. Die Zylinderdruckfestigkeiten nach 28 Tagen betragen rund 150, 160 und 170 N/mm². Besonders bei dem Feinkornbeton wurde eine überwiegend horizontale Ausrichtung der Stahlfasern festgestellt, die zu einer Anisotropie im Materialverhalten führte. Zusammenfassend muss festgestellt werden, dass die zweiaxiale Druckfestigkeit von UHPC nur geringfügig größer ist als die einaxiale. Für die Mischungen mit 2,5 Vol.-% Fasergehalt übersteigt die Festigkeit bei einem Spannungsverhältnis von Spannung 1 zu Spannung 2 gleich Eins die einaxiale Festigkeit um 7 bzw. 10 %. Bei dem Beton mit 0,9 Vol.-% Fasergehalt lag diese zweiaxiale Festigkeit sogar geringfügig unter der einaxialen. Bei der Bemessung von UHPC dürfen somit die vom Normalbeton bekannten Festigkeitssteigerungen unter mehraxialer Druckbelastung, wie sie z.B. bei reinen Druckknoten von Stabwerkmodellen angesetzt werden, nicht verwendet werden! Für die Beschreibung der Bruchkurve kann nach jetzigem Erkenntnisstand das Bruchkriterium nach OTTOSEN als eine gute Näherung empfohlen werden. Die Versuche haben gezeigt, dass sich UHPC in vielen, zum Teil sicherheitsrelevanten Bereichen anders verhält als Normalbeton. Für eine umfassende Beschreibung des Tragverhaltens sind weitere Versuche unter dreiaxiale Druckbelastung und kombinierter Druck-Zug-Belastung notwendig.
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