The market for nonwoven fabrics has experienced extreme growth in recent years and is expected to double in size from 2010 to 2020. This remarkable growth can be attributed to its numerous applications, ease of manufacturing, and customizable properties such as fabric stiffness, extensibility, and composition. The lifetime of the fabric is extremely important to producers and depends strongly on its micro-mechanical properties. Previously published studies have investigated the bulk fabric properties and the constituent fiber properties. However, nothing has been done to determine the properties of individual thermo-mechanical bonds that connect the constituent fibers of the fabric together. These bonds provide the mechanical integrity of the nonwoven fabrics. This study is the first to examine individual bonds by measuring their mechanical properties via uniaxial tensile tests and by computing the basis weight and orientation of the fibers surrounding the bonds. The results demonstrate that there is a high correlation between the fiber structure around the bond and the bond mechanical properties. The amount and directions of fibers affect how the load is transmitted through the bond and distributed across the fabric. Namely, if there are a few fibers surrounding the bond, or the primary fiber direction is different from the loading direction, then the force sustained by the bond is significantly lower and the bond does not deform. Conversely, if there are many fibers in the loading direction then the bond can sustain a significantly large force and undergoes deformation. The fiber and bond deformation are also observed through microscopic images captured during the uniaxial tensile tests. Ultimately, this research details the results for an effective method to test and analyze the mechanical integrity of thermo-mechanically bond and the lifetime of the nonwoven fabrics. / Master of Science

The aim of this study is concentrated on the experimental investigation of wear resistance of rubber powder modified rubber blends. Styrene-Butadiene-Rubber (SBR) blends applied for conveying belt top covers have been modified by ground rubber (rubber powder) based on SBR. We theoretically described the rubber wear mechanism due to loading conditions occurring at conveyor belts in the field, to simulate wear behavior of top cover rubber materials. An own developed testing equipment based on gravimetric determination of mass loss of rubber test specimen was used investigating dynamic wear with respect to fracture properties of top cover materials. Furthermore we investigated fatigue crack growth (FCG) data over a broad range of tearing energy by Tear Analyzer to characterize crack propagation behavior of rubber powder modified rubber blends. Thus, we demonstrate the influence of rubber powder on resistance against occurrence of fracture as well as dynamic wear as a function of the rubber powder content in rubber blends applied for conveying belt top covers.

Pour répondre à la demande croissante d’allègement des véhicules automobiles, les aciéristes développent une nouvelle gamme d’aciers à Très Haute Résistance (THR), dite de troisième génération. Cette thèse, inscrite dans le projet ANR MATETPRO « MeMnAl Steels », s’intéresse plus particulièrement à deux nouvelles familles d’aciers THR Fe-C-Mn-Al, produites par ArcelorMittal et potentielles candidates pour la caisse en blanc des futurs véhicules. Elle vise à mieux cerner les paramètres microstructuraux permettant de contrôler et optimiser le comportement à rupture de ces aciers.Pour représenter les deux familles d’aciers, deux matériaux modèles ont été élaborés par laminage puis recuit intercritique, conduisant à une microstructure duplex : austénite retenue (γr, pouvant se transformer en martensite par effet TRIP) et ferrite. La microstructure du premier acier, dite UFG, est ultrafine (grains de taille inférieure au micromètre) tandis que celle du second est bimodale, mêlant gros grains de ferrite δ et régions à grains fins de ferrite α et d’austénite retenue γr.Les propriétés mécaniques de la microstructure UFG dépendent fortement de la température de recuit, en raison des variations de stabilité de l’austénite retenue. A l’inverse, la microstructure bimodale est très robuste vis-à-vis de la température de recuit mais très sensible à la température d’essai. L’endommagement en traction et en résilience est très peu développé pour ces deux familles. Il est localisé aux interfaces ferrite-martensite (formée pendant l’essai). Le lien entre les modes de rupture et la microstructure bimodale, étudié à l’aide d’essais Charpy, a montré l’existence de deux transitions distinctes de mode de rupture : une transition entre rupture ductile à grandes cupules et clivage pour les gros grains de ferrite δ et une transition entre rupture interfaciale et rupture ductile à fines cupules pour les zones à grains fins {α + γr}. La rupture de la microstructure UFG est ductile à température ambiante et interfaciale à plus basse température. Cette microstructure UFG peut être vue comme un matériau modèle représentant les régions à grains fins {α + γr} de la microstructure bimodale.Pour les deux familles d’aciers, le comportement élastoplastique comme le comportement à rupture semblent dominés par la stabilité de l’austénite retenue. / To fulfil the increasing demand on lightweighting automotive vehicles, steelmakers are developing a third generation of Advanced High Strength Steels (AHSS). This work, part of the ANR project MATETPRO “MeMnAl Steels”, addressed two new families of third generation AHSS produced by ArcelorMittal which may be used for the body in white of upcoming cars. It aimed at improving our current understanding of the microstructural features allowing controlling and optimizing the fracture behavior of this steel family.Two model materials were manufactured by hot and cold rolling followed by intercritical annealing. The resulting, so-called duplex microstructure is a mixture of ferrite and retained austenite (γr, which can transform into martensite by TRIP effect). The microstructure of the first steel was made of ultra-fine grains (UFG) of ferrite and retained austenite (grain size below one micrometer), while the second steel possessed a bimodal microstructure made of coarse δ-ferrite grains and fine-grained regions of α-ferrite and retained austenite γr.The mechanical properties of the UFG microstructure were strongly sensitive to the annealing temperature, due to variations in the stability of retained austenite. On the contrary, the bimodal microstructure was very robust regarding the annealing temperature but very sensitive to the test temperature. For these two families, damage development is scarce and mainly located at ferrite-martensite interfaces. Charpy impact tests on steels with the bimodal microstructure showed that each microstructural region presents its own fracture mechanisms and a specific ductile-to-brittle transition. A transition from brittle cleavage to large-dimpled, ductile fracture was observed for coarse δ-ferrite grains, while fined-grained regions presented a transition from interfacial fracture to fine-dimpled, ductile fracture. Fracture of the UFG microstructure was ductile at room temperature and interfacial at lower temperatures. This UFG microstructure can be interpreted as a model material embodying the behavior of the fine-grained {α + γr} regions in the bimodal microstructure.For both two steels, the constitutive and fracture behavior seem to be dominated by the stability of retained austenite.

No description available.

Concrete has established itself as the most widely used structural material. There is hardly any place where human life and concrete structure do not exist together. It's use is seen in wide variety of structures like buildings, bridges, dams, nuclear structures, floating and submerged structures and so on. Hence, in view of safety, serviceability and economy, proper understanding of the behaviour of concrete is imperative in designing these complex structures. Current reinforced concrete codes are based on strength and serviceability concepts. The tensile strength of concrete is totally neglected in the limit state method of analysis. The concrete in tension is assumed to be fully cracked and conservative method of design is adopted. The crack causes a considerable degradation of stiffness of overall structure and gives rise to regions of stress concentration, which are not accounted for, in the present design methods. Besides, it is found that the size of the structural component significantly influences the stress at failure. It has been fairly well established that large specimens fail by catastrophic crack propagation while small specimens tend to fail in a ductile manner with considerable amount of slow crack growth preceding fracture. Initial attempts to understand the cracking of concrete through the principles of fracture mechanics was made in 1960's. It was concluded that the LEFM and small scale yielding fracture mechanics which are developed for metals are inapplicable to concrete structures except for certain limiting situations such as the behaviour at extremely large sizes. The reasons for the inapplicability of LEFM principles to concrete structures are attributed to slow crack growth, formation of nonlinear fracture process zone, and softening behaviour of concrete in tension. Several analytical and numerical models have been proposed to characterize the fracture behaviour of concrete. In the present work a simple numerical method is proposed to analyse the Mode-I fracture behaviour of concrete structures, using finite element method. The stiffness matrices calculated at the beginning of the analysis are used till the end without any modification. For this reason, the method is named as Initial Stiffness Method (ISM). An attempt has also been made to modify the lattice model existing in literature. The contents of the thesis are organised in six chapters. In chapter 1, a brief introduction to basic principles of fracture mechanics theory is presented. This is included mainly for the completeness of the thesis. In chapter 2, a brief review of literature regarding the application of principles of fracture mechanics to concrete structures is presented. The need for the introduction of fracture mechanics to concrete is presented. Early work, applying LEFM principles to concrete structures is discussed. The reasons for the inapplicability of linear elastic fracture mechanics principles to concrete structures are discussed. Necessities for nonlinear fracture mechanics principles are pointed out. Attention is focused on the influence of the factors like slow crack growth, formation of nonlinear fracture process zone and softening behaviour of concrete in tension on the fracture behaviour. Besides a possible use of fracture energy as an alternative fracture criterion for concrete is contemplated. Several analytical and numerical models (assuming concrete as homogeneous continuum), proposed so far to characterize the fracture behaviour of concrete, are presented and discussed in detail. Different heterogeneous models presented so far are also discussed. In chapter 3, a simple numerical method to analyse the fracture of concrete (strain softening material) in Mode-I, using FEM is proposed. The stiffness matrices are generated only once and are used till the end of the analysis. This feature makes the model simple and computationally efficient. A new parameter namely, strain softening parameter α has been introduced. It is found that this strain softening parameter ‘α’ is a structural property. The results obtained from the present method are found to converge with increasing number of elements thus making the method mesh independent, and thus objective. The method was validated by analysing the beams tested and reported by various researchers. The predicted values of maximum load by the present method are found to agree well with the experimental values. Initially, all the beams are analysed using uniform meshes and load-deflection diagrams are plotted. All the beams are again analysed using graded meshes. The load-deflection, load-CMOD diagrams are plotted from the results obtained from the analysis using graded meshes. In chapter 4, the results obtained in chapter 3 are analysed for size effect. Literature regarding size effect of concrete structures has been reviewed. In addition to the size effect on nominal stress at failure which exists in literature, two new parameters namely, post peak slope and softening slope parameter α have been used to confirm the size effect. This does not exist in the literature. In chapter 5, an attempt is made to modify the lattice model existing in literature. This is done with a view to model concrete as a heterogeneous medium, which would be nearer to reality. The softening property of concrete has been incorporated. The model was validated against some of the experimental results existing in literature. The results are found to be encouraging. The results from this model show the post peak softening similar to the experimentally observed ones. The effects of different probabilistic distributions to the properties of mortar on the maximum load of the beam are studied. It is found that normal distribution of properties to mortar gives the best results. A study is made regarding the sensitivity of various properties of mortar on the maximum load of the beam. It is concluded that load carrying capacity of the beam can be increased by using a mortar of higher tensile strength. Finally in chapter 6, general conclusions and suggestions for further investigations are discussed.

The aim of this study is concentrated on the experimental investigation of wear resistance of rubber powder modified rubber blends. Styrene-Butadiene-Rubber (SBR) blends applied for conveying belt top covers have been modified by ground rubber (rubber powder) based on SBR. We theoretically described the rubber wear mechanism due to loading conditions occurring at conveyor belts in the field, to simulate wear behavior of top cover rubber materials. An own developed testing equipment based on gravimetric determination of mass loss of rubber test specimen was used investigating dynamic wear with respect to fracture properties of top cover materials. Furthermore we investigated fatigue crack growth (FCG) data over a broad range of tearing energy by Tear Analyzer to characterize crack propagation behavior of rubber powder modified rubber blends. Thus, we demonstrate the influence of rubber powder on resistance against occurrence of fracture as well as dynamic wear as a function of the rubber powder content in rubber blends applied for conveying belt top covers.

No description available.

[pt] O uso de todos os tipos de amianto na construção civil tem diminuído drasticamente devido a problemas sérios de saúde associados a sua manipulação. De fato é previsto banir totalmente o seu uso, dentro de um curto espaço de tempo, nos países desenvolvidos bem como nos em desenvolvimento. Na necessidade de se encontrar um substituto adequado para o amianto, tem-se pesquisado compósitos de argamassa reforçada com fibras vegetais e polpas celulósicas. Devido ao processo de polpação, que remove as impurezas não celulósicas, como a lignina e a hemicelulose, diminuindo o ataque às fibras, sem a necessidade de recorrer a modificações na matriz cimentícia, as polpas celulósicas podem ser o substituto ideal para o amianto. Assim sendo, o principal objetivo desta dissertação é determinar experimentalmente as características mecânicas e os parâmetros de fratura de compósitos de matriz cimentícia reforçada por polpa de bambu refinada e sem refino. As polpas celulósicas foram utilizadas nas porcentagens de 8 e 14 por cento em relação à massa do cimento, porcentagens estas que, conforme a literatura, são associadas à otimização da energia absorvida no ensaio de flexão. A avaliação do comportamento mecânico dos compósitos considerados neste trabalho foi realizada através de ensaios de compressão e impacto, bem como de flexão em três pontos em espécimes não entalhados e em outros contendo entalhes de raios de curvatura diferentes. Propriedades mecânicas, tais como módulo de elasticidade, resistência à compressão, ao impacto e à flexão, bem como integral J na carga máxima, são apresentadas e discutidas em termos de aspectos microestruturais e fractográficos dos corpos de prova ensaiados. / [en] As handling and manipulation of asbestos pose grave health hazards, its use in civil construction has been drastically dwindling and will in fact be completely prohibited, in a few years, in developed countries. With the need arising to find an adequate substitute, vegetable fibers and cellulosic pulps have been considered to be viable alternatives. Taking into account the fact that the process for pulp production entails the removal of impurities, such as lignin and hemicellulose, cellulosic pulps seem to be the ideal substitute to asbestos, as their use does not necessitate modifications in the cementitious matrix. Accordingly, the purpose of this work is to experimentally determine basic mechanical characteristics and pertinent fracture parameters of bamboo pulp reinforced cement. Refined and non-refined pulps were used in the proportions of 8 and 14 percent of the weight of dry cement. These percentages were adopted as they imply, according to literature, in optimizing the energy absorbed by the composite in bend loading. Evaluation of the mechanical behavior of the composites considered in this work was realized by means of compression and impact testing. Three point bend tests were also carried out using unnotched as well as notched specimens of different notch root radii. Mechanical properties such as modulus of elasticity, compressive, impact and bend strengths, and J integral at maximum load are presented and discussed in terms of pertinent microstructural and fractographic aspects of test specimens.

Auf der Basis der Bemessungsgrundlagen (DAfStb-Richtlinie „Stahlfaserbeton“, DBV-Merkblatt „Stahlfaserbeton“ und DIN 1045-1) wurden ausgewählte Bauteilversuche mit entsprechenden rechnerischen Überprüfungen der experimentell ermittelten Ergebnisse durchgeführt. Die Untersuchungen konzentrierten sich auf die Ermittlung der Effizienz von ausgewählten Stahlfasern in Betonen mit und ohne Betonstahlbewehrung in durch Biegung ohne Längskraft belasteten Versuchskörpern unter Betrachtung der Grenzzustände der Gebrauchstauglichkeit (GZG) und Tragfähigkeit (GZT). Das Versuchsprogramms umfasste neben der Prüfung ausgewählter Frischbetoneigenschaften die Bestimmung von Festbetonparametern an standardisierten Probekörpern. Des Weiteren wurden 4-Punkt-Biegezugversuche an Balken mit den Abmessungen l/h/b = 70/15/15 cm aus reinem Stahlfaserbeton sowie stahlfaserbewehrtem Stahlbeton, in Anlehnung an das DBV-Merkblatt „Stahlfaserbeton“ und die Richtlinie „Stahlfaserbeton“ vom DAfStb, durchgeführt. Aufbauend auf den Erkenntnissen aus den Materialversuchen im Labormaßstab wurden anschließend Untersuchungen an großformatigen Biegebalken (l/h/b = 420/40/20 cm) durchgeführt. Im Weiteren erfolgten Prüfungen und Auswertungen von Einzelfaserausziehversuchen mit ausgewählten Stahldrahtfasern in Verbindung mit Betonen unterschiedlicher Druckfestigkeit unter Berücksichtigung des Einflusses der Einbindelänge sowie des Einbindewinkels. Im Rahmen des Versuchsprogramms wurden die auf der Grundlage der 4-Punkt-Biegezugversuche ermittelten Ergebnisse analysiert und mit dem derzeit gültigen Bemessungsmodell nach DAfStb-Richtlinie „Stahlfaserbeton“ rechnerisch überprüft. Auf der Basis dieser Ergebnisse erfolgte die Entwicklung eines Ansatzes zur Optimierung der bestehenden Bemessungsansätze. Gegenstand dieser Forschungsarbeit war ebenfalls die Entwicklung eines Fasermodells, mit dem man auf der Grundlage des eingesetzten Fasergehaltes und der Faserart Rückschlüsse auf die Faseranzahl in einer rechteckigen Bruchfläche ziehen kann. Hierbei wurde ein Modell für Rechteckquerschnitte entwickelt, welches es ermöglicht, die durchschnittliche Faseranzahl in einer Bruchfläche, auf der Basis vereinfachter Annahmen, abzuschätzen. Die Verifizierung des Modells erfolgte durch den Vergleich der errechneten Faseranzahl mit zahlreichen experimentellen Versuchsergebnissen. Im letzten Abschnitt dieser Arbeit wurde die Herleitung bzw. Generierung von Bemessungshilfsmitteln zur Biegebemessung von Stahlfaserbeton mit und ohne Betonstahlbewehrung behandelt. Die Ausführungen beziehen sich dabei auf dimensionslose Bemessungstafeln und Interaktionsdiagrammen für Rechteckquerschnitte.

Rammed earth is a monolithic construction formed by compacting processed soil in progressive layers. Rammed earth is used for the construction of load bearing walls, floors, sub base material in roadways, airport runways, taxiways, aprons, foundations and earthen bunds. Soil, sand, cement and water are the ingredients used for the preparation of cement stabilized rammed earth (CSRE) specimens. The cracking in a rammed earth structure is due to the development of tensile stresses. The tensile stresses are generated due to various causes like unequal settlement of foundation, eccentric loading and / or lateral loading such as wind pressure and earthquake on an earth structure. The cracking in a rammed earth structure causes the failure of its intended function. For example formation of crack may lead to the instability of an embankment slope. And earthen dam can be destroyed gradually by erosion of soil at the crack surface (Harison et al. 1994). Hence, it becomes important to understand the fracture behaviour of cement-stabilized rammed earth structures. Well focused studies in understanding the fracture behaviour of CSRE structures are scanty. The present work attempts to address some issues on the fracture behaviour of CSRE including size effect. Through an experimental programme material properties viz. compressive strength, tensile strength and stress-strain relationships are generated for two chosen densities, 17 and 18.5 kN/m3 of CSRE both in dry and saturated condition. Soil composition, density, cement content and moisture content of the specimen during testing influence the characteristics of CSRE. In the present investigation keeping the cement at 10%, the density is varied choosing a soil-sand mixture having optimum grading limits. The basic raw materials used are soil, sand, cement and water in the ratio of 1 : 1.5 : 0.25 : 0.34 by weight. The strength properties studied alone are inadequate to predict the mechanics of fracture due to the presence of microscopic flaws, cracks, voids and other discontinuities. Therefore, some linear elastic fracture parameters such as mode I fracture toughness (KIc), critical energy release rate (GIc), net section strength (f net) and notch sensitivity are calculated, presuming that CSRE is still a brittle material because it is yet to be confirmed that CSRE is a quasibrittle material. In fact, in the present work, it is shown that CSRE has significant amount of softening. A comprehensive experimental work has been undertaken to test CSRE beam specimens for two densities, three sizes of beam and three notch to depth ratios under three point bending (TPB) in a closed loop servo-controlled machine with crack mouth opening displacement control. Results indicate that the CSRE in dry condition exhibits a greater resistance to fracture than the saturated specimen. The variation of net section strength with the notch depth is not significant. Therefore the CSRE material is notch insensitive, implying that it is less brittle. An experimental program was undertaken to determine the nonlinear fracture parameters of beam specimens both in dry and saturated condition. The influence of moisture content, density, size of the specimen as well as notch to depth ratio of the specimen on RILEM fracture energy (G F ) are presented. The GF values increase with increase in density and size of the specimen, while they decrease with increase in notch to depth ratio. Results clearly show that the total energy absorbed by the beams (W OF ) and RILEM fracture energy (G F ) for all specimens tested in dry state are higher compared to the specimens tested in saturated state, indicating that the dry specimen offers higher resistance to the crack propagation. The RILEM fracture energy GF , determined from TPB tests, is said to be size dependent. The assumption made in the work of fracture is that the total strain energy is utilized for the fracture of the specimen. The fracture energy is proportional to the size of the fracture process zone (FPZ), which also implies that size of FPZ increases with increase in the un-cracked ligament (d - a) of beam. This also means that FPZ is proportional to the depth d for a given notch to depth ratio, because for a given notch/depth, (d - a) which is also is proportional to d because is a constant. This corroborates the fact that fracture energy increases with size. Interestingly, the same conclusion has been drawn by Karihaloo et al. (2006). They have plotted a curve relating fracture process zone length and overall depth the beam. In the present study a new method namely Fracture energy release rate method proposed by Muralidhara et al. (2013) is used. In the new method the plot of GF /(d - a) versus (d - a) is obtained from a set of experimental results. The plot is found to follow power law and showed almost constant value of GF /(d - a) at larger ligament lengths. This means the fracture energy reaches a constant value at large ligament lengths reaffirming that the fracture energy from very large specimen is size-independent. This Fracture energy release rate method is used to determine size-independent fracture energy GRf , based on the relationship between RILEM fracture energy and the un-cracked ligament length. The experimental results from the present work agree well with the proposed new method. Similarly, the method is extended to determine nominal shear strength τv for large size beam. Results show that for both densities GRf decrease in saturated condition, while in dry condition as the density is increased from 17 to 18.5 kN/m3 the GRf decrease by 7.58%, indicating that the brittleness increases with higher density. The τv for large size beam increases with density both in dry and saturated condition. The size effect method for evaluating material fracture properties proposed by Bazant (1984) is applied to cement stabilised rammed earth. By measuring the peak loads of 2D geometrically similar notched beam specimens of different sizes, nonlinear fracture parameters such as fracture energy (Gf ), fracture toughness (KIc), effective length of the fracture process zone (Cf ), brittleness number (β), characteristic length (l 0) and the critical crack tip opening displacement (CT ODc) are determined for both dry and saturated conditions. The crack growth resistance curves (R-curve) are also developed for dry and saturated specimens. In the size effect method, for both densities 18.5 and 17 kN/m3 the values of nonlinear fracture properties, namely G f , Cf , KIc, CT ODc and l 0 are lower for the saturated specimen compared to those of the dry specimen. In dry condition as the density is increased from 17 to 18.5 kN/m3 the Gf decreases to 13.54%, indicating that the brittleness increase with higher density. The areas under the load-displacement and load-CMOD curves are a measure of the fracture energy and these areas are low for saturated specimens. The crack growth resistance curves (R-curve) plotted using the size-effect law from peak loads are the measure of resistance against crack growth R. The value of R is high for dry specimen compared to that of the saturated specimens. During aggregate pullout or the opening of crack, the interlock or friction between the crack surfaces may cause the energy dissipation through friction and bridging across the crack. Therefore the wet friction in case of saturated specimen must be smaller resulting in more brittleness compared to the larger dry friction for dry specimen. In the present investigation the Digital Image Correlation (DIC) technique is used to study the FPZ properties in cement stabilised rammed earth. The MATLAB package written by Eberl et al. (2006) is suitably modified and used for image correlation to suit our requirements. CMOD measured using DIC technique is validated by comparison with the CMOD measured using clip gauge. The FPZ properties such as the development of FPZ and crack opening displacements at different loading points as well as the influence of notch/depth ratio on FPZ length (lFPZ ) are evaluated for both dry and saturated conditions. At peak load the lFPZ are about 0.315 and 0.137 times the un-cracked ligament length respectively for specimens tested under dry and saturated conditions. In dry and saturated states the FPZ length decreases as the ratio increases. Lower values of lFPZ in saturated specimen indicates that it is relatively more brittle compared to dry specimen.