O texto normativo NBR 7190/1997, da Associação Brasileira de Normas Técnicas (ABNT), adota três ciclos de carregamento nos ensaios para a determinação de propriedades de rigidez e resistência da madeira. A partir das recomendações de tal documento foram realizados ensaios de compressão normal às fibras, compressão paralela às fibras, flexão estática e tração paralela às fibras com corpos-de-prova de Cambará Rosa (Erisma sp), Eucalipto Grandis (Eucalyptus grandis), Envira (Xylopia sp), Champanhe (Dipteryx odorata), Pinus Caribaea (Pinus caribaea var. caribaea), Pinus Elliottii (Pinus elliottii var. elliottii) e Pinus Hondurensis (Pinus caribaea var. hondurensis). Os valores dos módulos de elasticidade (E) obtidos mostraram-se estatisticamente equivalentes no segundo e terceiro ciclos de carregamento. Esta análise sugere, então, que o terceiro ciclo de carregamento é desnecessário. Foram comparados, também, os valores dos módulos de elasticidade de trinta e quatro espécies de madeiras tropicais brasileiras, obtidos nos ensaios de compressão paralela às fibras, tração paralela às fibras e flexão estática. Concluiu-se que estes são estatisticamente equivalentes. / The NBR 7190/1997, adopted by of Brazilian Technical Standard Association (ABNT), indicates three loading cycles for tests to determine wood stiffness and strength. Based on recommendations of ABNT methods tests were carried out in compression perpendicular to grain, compression parallel to grain, static bending and tension parallel to grain, with Cambará Rosa (Erisma sp), Eucalipto Grandis (Eucalyptus grandis), Envira (Xylopia sp), Champanhe (Dipteryx odorata), Pinus Caribaea (Pinus caribaea var. caribaea), Pinus Elliottii (Pinus elliottii var. elliottii) and Pinus Hondurensis (Pinus caribaea var. hondurensis) species. Modulus of elasticity values (E) obtained were statistically equivalent in second and third loading cycles. This analysis suggests that the third loading cycle is not necessary. Modulus of elasticity values of thirty four Brazilian tropical wood species were compared in compression parallel to grain, tension parallel to grain and static bending. The analysis showed that these values are statistically equivalent.

Este trabalho tem o objetivo de avaliar a influência das propriedades elásticas da interface bloco-argamassa no comportamento elástico global de paredes de alvenaria. Por ser um material heterogêneo, as propriedades mecânicas da alvenaria são influenciadas pelas propriedades dos seus diferentes componentes, bloco e argamassa, e pela ligação entre eles. As juntas de argamassa constituem planos de fraqueza, desta forma, características como rigidez, direção e o estado de tensão podem influenciar consideravelmente o comportamento global e consequentemente os parâmetros de projeto. O trabalho foi composto por duas etapas, uma experimental e outra numérica. Na etapa experimental um extenso programa de ensaios foi realizado buscando avaliar as propriedades elásticas normais e tangenciais as juntas de argamassa. Nesta etapa também é apresentado um conjunto de procedimentos que possibilita a caracterização dos componentes da alvenaria de forma não destrutiva. Um estudo paramétrico foi realizado na parte numérica, permitindo identificar quais propriedades da interface exercem mais efeito sobre o comportamento elástico da alvenaria. Também foi avaliado como a heterogeneidade da alvenaria pode afetar a distribuição de ações horizontais ao longo de uma edificação. Os resultados obtidos indicaram que a interface bloco-argamassa exerce influência significativa sobre o comportamento elástico da alvenaria, entretanto esta relação depende da razão altura/largura da parede estudada. A distribuição das ações horizontais demonstrou ser bastante afetada pela deformação por cisalhamento, no entanto a consideração da interface não resultou em contribuição significativa. / This work aims to evaluate the influence of the elastic properties of unit - mortar interface in the global elastic behavior of masonry panels. As a heterogeneous material, the mechanical properties of masonry are influenced by the properties of its different components, unit, mortar, and the bond between them. The mortar joints are weakness planes, thus features like stiffness, direction and state of stress can greatly influence the global behavior and the design parameters. The study was composed of an experimental and numerical analysis. In experimental analysis an extensive test program was conducted with focus on normal and tangential elastic properties of the unit-mortar interface. In this part of the work a set of procedures that enable the characterization of the masonry components nondestructively is also presented. A parametric study was conducted in the numerical analysis, allowing the identification of which properties of the interface have a greater effect on the elastic behavior of masonry. The effect of the heterogeneity of the masonry in the distribution of lateral loads in a building was also evaluated. Results indicated that the block-mortar interface has a significant influence on the elastic behavior of masonry; however this relationship depends on the ratio aspect of the panel. The distribution of lateral loads was greatly affected by shear deformation; however the consideration of the interface resulted in no significant contribution.

There is an impetus in the UK to move away from empirical pavement foundation design and the current method specification, towards an analytical design approach. For an analytical design approach to be adopted, the required performance properties of stiffness and resistance to permanent deformation of the foundation materials (sub grade and capping) need to be measured, both in the laboratory for design and in the field in order to ensure compliance. This thesis studies the influence of the sub grade on the constructability and performance of a series of full-scale pavement foundations. This has been achieved by measuring the performance parameters of several sub grade materials in the laboratory, using repeated load triaxial testing. These data have been compared to comparable data collected in situ using dynamic stiffness measuring devices during the construction of trial pavement foundations. The performance of the trial foundations has been measured during the placement and compaction of the different foundation materials, and again after their subsequent trafficking. The testing demonstrates the stress dependency of the foundation materials. The laboratory testing shows that the sub grade permanent deformation under cyclic loading (used to simulate construction operations) becomes unstable at a deviator stress of half the deviator stress at failure (0.5qmax)· The stiffness at this applied stress and above is shown to be approaching a consistent value. This indicates that large changes in the stiffness of inversely stress dependent fine grained soils occur below the deviator stress at which the permanent deformation becomes unstable. Significant variability of data has been found in the performance parameters measured (both in the laboratory and in the field) for samples of subgrade collected from small areas of the same site. However comparable patterns of stress dependency have been observed between measured laboratory and field performance using the different apparatus. The resistance to permanent deformation is shown to be a more critical design load case for construction than the need for adequate stiffness of support required to compact the foundation layers. The performance of a composite road foundation is shown to be material and site specific, and this will have important implications for design and site compliance testing.

Les films polyélectrolytes ont émergé comme un outil polyvalent dans le domaine desbiomatériaux et de l’ingénierie tissulaire. Dans cette étude, nous avons conçu des films à base debiopolymère, dont la rigidité peut être modulée par photo-réticulation. L’adhésion de bactéries etde cellules mammifères sur ces films a été étudiée. Une telle manipulation de rigidité superficielleconduit à une réponse différentielle des bactéries et des cellules mammifères. Les bactéries àGram négatif présentent une meilleure croissance sur des films nous alors que les cellulesmammifères préféraient les films plus rigides. Ces films ont été spatialement structurés à l’aided’un photomasque, permettant de créer des zones adjacentes de rigidité variable et de formecontrôlée. Les motifs photostructurés ont conduit les cellules à s’organiser préférentiellement surles zones les plus rigides. Une étude comparative a été réalisée avec des micropatronsbiochimiques. Les résultats ont montré des réponses similaires pour trois types cellulairesdifférents. Ces films offrent des perspectives intéressantes pour l’ingénierie tissulaire et pour letest de médicaments. / Polyelectrolyte multilayers have emerged as a versatile tool in the field of biomaterials and tissueengineering. In this study, photocrosslinkable polyelectrolyte films based on biopolymers whosestiffness can be easily tuned by UV irradiation were prepared. Then, they were tested againstbacteria and mammalian cells to address the influence of the film stiffness on cell behavior. Suchsuperficial stiffness manipulation resulted in differential response of bacteria and mammaliancells. Gram negative bacteria evidenced better growth on softer films while various mammaliancells preferred stiffer films. Stiffness patterns of various geometries and sizes were generated byexposing the films to the UV light through a photomask incorporated in transparent substrates.The patterned films composed of stiff motifs distributed in a soft background induced apreferential spatial organization, which depended on pattern shape and size. A comparative studywith commercial biochemical patterns revealed similar pattern fidelity for three differentmammalian cell types. Such mechanical patterns on a 2D film appear promising for futureapplications in tissue engineering or for drug screening.

Biomaterials have evolved over the years from the passive role of mere biocompatibility to an increasingly active role of presenting instructive cues to elicit precise responses at the molecular and cellular levels. Various characteristics common to synthetic biomaterials in vitro and extracellular matrices in vivo, such as immobilized functional or peptide groups, mechanical stiffness, bulk physical properties and topographical features, are key players that regulate cell response. The dynamics in the cell microenvironment and at the cell adhesive interface trigger a web of cell-material and cell-cell information exchanges that have a profound impact in directing the ultimate cell fate decision. Therefore, comprehension of cell substrate interactions is crucial to propel forward the evolution of new instructive biomaterials. Combinatorial biomaterials that encompass a wide range of properties can help to recapitulate the complexity of a cell microenvironment. The objective of this research was to fabricate combinatorial biomaterials with properties that span wide ranges in both surface chemistries and mechanical moduli. These materials were based on polydimethyl siloxane (PDMS), an elastomeric silicone biomaterial with physiologically relevant stiffness. After developing these mechano-chemical gradient biomaterials, we conducted high throughput screening of cell responses on them to elucidate cell substrate interactions and material directed behaviors. Our central hypothesis was that materials encompassing monotonic gradients in mechanical elastic modulus and orthogonal surface chemistry gradients could be engineered using the soft biomaterial, polydimethyl siloxane (PDMS) and that these gradient biomaterials would evoke a varied cell response. Furthermore, we expected high throughput screening of cell-material interactions using these materials would elucidate patterns and thresholds of synergy or antagonism in the overall cell response to the increased complexity presented by combinatorial materials. First, reproducible gradients in surface chemistry were generated on PDMS through surface modification techniques. Cell response to PDMS surface chemistry gradients was then screened in a rapid high throughput manner. Additionally, characteristics of the adhesive interface were probed to understand its role in cell response. Finally, a 2D combinatorial gradient with a gradient in mechanical elastic modulus and an orthogonal gradient in surface chemistry was fabricated with PDMS. High throughput screening of the synergistic influence of the varied mechanical and biochemical extracellular signals presented by the combinatorial biomaterial on cell response was conducted in a systematic manner. This research demonstrates the fabrication of combinatorial biomaterials with a wide range of mechanochemical properties for rapid screening of cell response; a technique that will facilitate the development of biomaterial design criteria for numerous biomedical engineering applications including in vitro cell culture platforms and tissue engineering.

Additive manufacturing offers a manufacturing technique to produce complex geometry prototypes at a rapid pace and low cost. These advantages advocate additive manufacturing for the design and production of cellular structures. Cellular structures are interesting because they contain a large amount of porosity (void space of air) to manifest a lightweight structure. Designs of cellular structures generate a periodic pattern; often of complex geometry, called a lattice. There has been a significant amount of research to maximize specific stiffness of lattice structures but little to evaluate low-stiffness lattices. Low-stiffness structures benefit energy absorbance through bending of the lattice. This research seeks to assess diamond lattices as low stiffness, bending structures. The research involves PA2200 (Nylon 12) laser sintered diamond lattices with experimental compression testing and direct FEA model comparison. A correction factor is applied for a design offset of laser sintered lattices. Once applied, the experimental and FEA data agree in validating the diamond lattice as a bending-dominated structure. Diamond lattices show a 4th order relationship between stiffness and parameters of thickness and unit cell length. For density, stiffness maintains a 2nd order relationship, as predicted by bending dominated structures. The resulting stiffness can be tuned over a stiffness range of four orders of magnitude. Further research shows the results for modifying the diamond lattice and scaling stiffness and density using other materials (like metals) to expand the range of stiffness and compare diamond lattices on material property charts. Lastly, the effective Poisson’s ratio varies from 0.5 to 0.4 depending on the (t/L) ratio.

This report is a part of the research project "A New Model for Deformation of Carton Board Packages by Manual Handling". This project is a collaboration between Örebro University and two companies engaged in carton board packages. This report describes whether Syntouch's BioTac is an appropriate tool, compared with a consumer study when investigating the grip stiffness of consumer packaging. Syntouch's BioTac is an artificial sensor designed to imitate the force of a human fingertip. The concept of grip stiffness is used in the packaging industry to describe the packaging’s properties to withstand clamping pressure when handling by the user. That is, the robustness of the packaging. The carton board packaging should perceive as stiff, firm to grip and not deform during handling. The purpose is to perform laboratory tests with the BioTac sensor, to see if the sensor can be used as a measurement method for grip stiffness of card board materials. / Denna rapport som ingår i forskningsprojektet ”A New Model for Deformation of Carton Board Packages by Manual Handling”. Detta projekt är ett samarbete mellan Örebro Universitet och två företag som arbetar med förpackningar. I denna rapport beskrivs och analyseras om Syntouch’s BioTac är ett lämpligt verktyg, i jämförelse med en konsumentstudie vid undersökning av en förpacknings greppstyvhet. Syntouch’s BioTac är en konstgjord sensor som är utformad för att imitera kraften som en mänsklig fingertopp har. Greppstyvhet är ett begrepp som används i förpackningsindustrin och beskriver förpackningens egenskaper att kunna motstå klämtryck vid hantering. Det vill säga förpackningens robusthet. Förpackningen skall uppfattas som styv, greppvänlig och skall ej deformeras vid hantering. Syftet med det här arbetet är att utföra laborativa tester med sensorn BioTac, för att se om sensorn kan användas som en objektiv mätmetod för greppstyvhet för olika förpackningsmaterial.

La scoliose infantile est une déformation rachidienne évolutive survenant chez l'enfant de moins de 3 ans. La technique de correction la plus répandue actuellement est celle des « tiges de croissance ». Cependant, la rigidité du matériel provoque la dégénérescence des disques intervertébraux, ce qui di-minue l'efficacité du traitement. Des études récentes ont montré l'effet bénéfique d'implants flexibles sur les disques. Notre équipe a donc développé le concept d'une suspension implantable qui permet de garder la mobilité axiale des segments instrumentés, associé à un nouveau système de fixation rotulée. Cepen-dant, quelle valeur de raideur permet de préserver les disques tout en corrigeant efficacement la sco-liose ? Cette thèse a donc pour objectifs de démontrer l'intérêt d'une suspension pour les disques inter-vertébraux et d'obtenir des informations quantifiables sur la valeur optimale de raideur. Pour cela des prototypes de suspension avec fixation rotulée, implantables chez le mammifère quadrupède et l'Homme, ont été développés afin d'étudier in vivo et in silico plusieurs gammes de flexibilité. Une étude in vivo sur chèvres adultes saines a été menée pour tester ces prototypes pour 2 raideurs différentes. L'état des disques intervertébraux après 6 mois a été évalué par IRM et par coupes histologiques. En parallèle la biomécanique d'un rachis humain sain puis scoliotique, instrumenté avec différents disposi-tifs (tiges classiques, suspensions, avec ou sans rotules), a été étudiée avec un modèle numérique mul-ti-corps rigides, préalablement validé par comparaison avec des données in vitro de la littérature. Les résultats de l'étude in vivo n'ont pas montré de différence significative entre les différentes instrumentations testées. Un temps d'essai plus long semble nécessaire pour voir apparaître la dégéné-rescence discale. Les simulations numériques ont montré une nette amélioration de la mobilité des segments ins-trumentés avec une suspension rotulée. La majorité de la mobilité est cependant assuré par le nouveau système de fixation et non par la présence d'une plus grande souplesse axiale. La suspension permet néanmoins un gain supplémentaire pour certains mouvements du rachis. Aucune différence significative n'a été constatée entre les 2 valeurs de raideurs étudiées. La présence de fixations rotulée diminue par contre fortement la correction obtenue lors des simulations de chirurgie de distraction. La suspension seule présente un intérêt certain lors de la correc-tion en diminuant les efforts transmis au matériel. Les développements futurs s'orienteraient donc vers une suspension combinée à des fixations rotulées présentant également des raideurs en rotation pour conserver correction et mobilité / Infantile scoliosis is a progressive spinal deformity occurring in children under 3 years-old. The most common currently correction technic is the "growing rods" one. However, the implant rigidity causes intervertebral discs degeneration, which decreases the treatment efficiency. Recent studies have shown the benefic effect of flexible implants on discs. Our team has developed the concept of an implantable suspension that keeps the axial mobility of the instrumented segments, associated with a new fastening ball joint system. However, which is the stiffness value that preserves discs while correcting scoliosis? This thesis goal is to demonstrate the effectiveness of a suspension device for preserving inter-vertebral discs health and obtain quantifiable information on the optimum stiffness value. Prototype suspensions with ball joint fastenings, implantable in quadruped mammals and humans, have been de-veloped to study several ranges of stiffness values in vivo and in silico. An in vivo study on healthy adult goats was conducted to test these prototypes for two different stiffness values. The intervertebral discs health after 6 months was evaluated by MRI and histological sections. In parallel the biomechanics of a human spine was studied with a rigid multi-body numerical model previously validated against in vitro literature data. Healthy and scoliosis subjects instrumented with different devices (traditional rods, sus-pensions, with or without the ball) were modeled. The results of the in vivo study showed no significant difference between the several instrumen-tations. A longer test time seems necessary to observe the onset of disc degeneration. Numerical simulations have shown a marked mobility improvement for the segments in the in-strumented area with a suspension device associated with a ball joint system. However, the majority of the mobility is provided by the new fixing system and not by a greater axial flexibility. The suspension still allows additional gain for certain spine movements. No significant differences were found between the two studied stiffness values. The presence of a ball joint fastening decreases strongly the correction obtained during surgery distraction simulations. The suspension has an interest during correction by reducing the forces trans-mitted to the material when used alone. Future developments thus would lead to a suspension device associated with ball joint fasten-ings that also have rotational stiffness to keep both good scoliosis correction and segments mobility

My work has been focused on compliant mechanisms, origami engineering, and rapid prototyping. Two of the projects that I worked on were focused on compliant mechanisms and origami engineering. The similar goal of both of those projects was to create an origami membrane whose kinematics mimic that of an existing mechanism. The first project created an origami membrane to mimic the kinematics of a planar shape-changing mechanism. This mechanism was a square shaped unit-cell which could shear, compress, and expand in its own plane. In addition to waterproofing the mechanism, the first project also sought to optimize the dimensions of the mechanism in order to reduce internal stresses during actuation. The results of the optimization portion of this project were a reduction of internal stresses by more than 22%. The results of the origami synthesis portion of the project was the creation of a membrane with an origami pattern whose kinematics mimic that of the shape-shifting surface. The origami membrane is capable of being folded into each of the various positions that the shape-shifting surface is able to fold into. The second project sought to create a similar type of origami fold pattern, but for a Shape Morphing Space Frame (SMSF). This project created an origami membrane designed to mimic the kinematics of a mechanism that had been developed in a different previous project. The mechanism consisted of a series of Linear Bistable Elements (LBEs) which were assembled to form a cylinder. When the LBEs were actuated the cylinder would deform to a hyperboloid. This project created an origami membrane whose kinematics mimic that of the shape-morphing space frame and was able to change side length by more than 30%. The origami membrane was able to fold to each of the SMSF’s states. This project also developed a method for synthesizing an origami fold pattern with shape-morphing triangles. Both of the first two projects that comprise this dissertation sought to develop an origami fold pattern whose kinematics mimic that of an existing mechanism. In each of these projects one of the future goals for the project was to create a prototype where the mechanism and the origami are fabricated together as one integrated prototype. Possible methods of accomplishing this goal include rapid prototyping. Thus, the mechanics of rapid prototyping are of concern for future work on these projects. The third project developed a part which could be printed from a Fused Deposition Modeling (FDM) machine to test certain material properties (yield strength and elastic modulus) after it had been processed through the FDM. This would allow the material properties to be tested without the use of expensive test equipment. This project developed eight parts which could be used to bracket certain material properties of rapid prototyped parts after processing. The parts developed in this project were capable of bracketing the material properties of the materials in question, and were able to do so when tested across multiple FDM machines. The results of this work were stress-strain data which indicates the behavior of the part under load, and a method for inexpensively testing the material properties of rapid prototyped parts after processing.

Please read the abstract in the section 00front of this document / Thesis (PhD)--University of Pretoria, 2009. / Civil Engineering / unrestricted