Indiana University-Purdue University Indianapolis (IUPUI) / Articular cartilage is subjected to dynamic mechanical loading during normal daily activities. This complex mechanical loading, including cell deformation and interstitial fluid flow, affects chondrocyte mechano-chemical signaling and subsequent cartilage homeostasis and remodeling. Focal adhesion kinase (FAK) and Src are known to be main mechanotransduction proteins, but little is known about the effect of mechanical loading on FAK and Src under its varying magnitudes and types. In this study, we addressed two questions using C28/I2 chondrocytes subjected to the different types and magnitudes of mechanical loading: Does a magnitude of the mechanical loading affect activities of FAK and Src? Does a type of the mechanical loading also affect their activities? Using fluorescence resonance energy transfer (FRET)-based FAK and Src biosensor in live C28/I2 chondrocytes, we monitored the effects of interstitial fluid flow and combined effects of cell deformation/interstitial fluid flow on FAK and Src activities. The results revealed that both FAK and Src activities in C28/I2 chondrocytes were dependent on the different magnitudes of the applied fluid flow. On the other hand, the type of mechanical loading differently affected FAK and Src activities. Although FAK and Src displayed similar activities in response to interstitial fluid flow only, simultaneous application of cell deformation and interstitial fluid flow induced differential FAK and Src activities possibly due to the additive effects of cell deformation and interstitial fluid flow on Src, but not on FAK. Collectively, the data suggest that the intensities and types of mechanical loading are critical in regulating FAK and Src activities in chondrocytes.

Nature develops several materials with remarkable functional properties composed of comparatively simple base substances. Biological materials are often composites, which optime the conformation to their function. On the other hand, synthetic materials are designed a priori, structuring them according to the performance to be achieved. 3D printing manufacturing is the most direct method for specific component production and earmarks the sample with material and geometry designed ad-hoc for a defined purpose, starting from a biomimetic approach to functional structures. The technique has the advantage of being quick, accurate, and with a limited waste of materials. The sample printing occurs through the deposition of material layer by layer. Furthermore, the material is often a composite, which matches the characteristics of components with different geometry and properties, achieving better mechanical and physical performances. This thesis analyses the mechanics of natural and custom-made composites: the spider body and the manufacturing of metallic and non-metallic graphene composites. The spider body is investigated in different sections of the exoskeleton and specifically the fangs. The study involves the mechanical characterization of the single components by the nanoindentation technique, with a special focus on the hardness and Young's modulus. The experimental results were mapped, purposing to present an accurate comparison of the mechanical properties of the spider body. The different stiffness of components is due to the tuning of the same basic material (the cuticle, i.e. mainly composed of chitin) for achieving different mechanical functions, which have improved the animal adaptation to specific evolutive requirements. The synthetic composites, suitable for 3D printing fabrication, are metallic and non-metallic matrices combined with carbon-based fillers. Non-metallic graphene composites are multiscale compounds. Specifically, the material is a blend of acrylonitrile-butadiene-styrene (ABS) matrix and different percentages of micro-carbon fibers (MCF). In the second step, nanoscale filler of carbon nanotubes (CNT) or graphene nanoplatelets (GNP) are added to the base mixture. The production process of composite materials followed a specific protocol for the optimal procedure and the machine parameters, as also foreseen in the literature. This method allowed the control over the percentages of the different materials to be adopted and ensured a homogeneous distribution of fillers in the plastic matrix. Multiscale compounds provide the basic materials for the extrusion of fused filaments, suitable for 3D printing of the samples. The composites were tested in the configuration of compression moulded sheets, as reference tests, and also in the corresponding 3D printed specimens. The addition of the micro-filler inside the ABS matrix caused a notable increment in stiffness and a slight increase in strength, with a significant reduction in deformation at the break. Concurrently, the addition of nanofillers was very effective in improving electrical conductivity compared to pure ABS and micro-composites, even at the lowest filler content. Composites with GNP as a nano-filler had a good impact on the stiffness of the materials, while the electrical conductivity of the composites is favoured by the presence of CNTs. Moreover, the extrusion of the filament and the print of fused filament fabrication led to the creation of voids within the structure, causing a significant loss of mechanical properties and a slight improvement in the electrical conductivity of the multiscale moulded composites. The final aim of this work is the identification of 3D-printed multiscale composites capable of the best matching of mechanical and electrical properties among the different compounds proposed. Since structures with metallic matrix and high mechanical performances are suitable for aerospace and automotive industry applications, metallic graphene composites are studied in the additive manufacturing sector. A comprehensive study of the mechanical and electrical properties of an innovative copper-graphene oxide composite (Cu-GO) was developed in collaboration with Fondazione E. Amaldi, in Rome. An extensive survey campaign on the working conditions was developed, leading to the definition of an optimal protocol of printing parameters for obtaining the samples with the highest density. The composite powders were prepared following two different routes to disperse the nanofiller into Cu matrix and, afterward, were processed by selective laser melting (SLM) technique. Analyses of the morphology, macroscopic and microscopic structure, and degree of oxidation of the printed samples were performed. Samples prepared followed the mechanical mixing procedure showed a better response to the 3D printing process in all tests. The mechanical characterization has instead provided a clear increase in the resistance of the material prepared with the ultrasonicated bath method, despite the greater porosity of specimens. The interesting comparison obtained between samples from different routes highlights the influence of powder preparation and working conditions on the printing results. We hope that the research could be useful to investigate in detail the potential applications suitable for composites in different technological fields and stimulate further comparative analysis.

Experimental results of damage development in and mechanical response of heat-treated NicaloniCAS-II laminates subjected to monotonic flexure and axial loading and to cyclic tensile loading are reported. The specimens were subjected to post-processing heat treatments at 900°, 1000°, and l100°C in air for 100 hours. Changes at the fiber/matrix interface/interphase due to post-processing heat treatments were also characterized. The combined effect of fiber debonding and transverse matrix cracking in both 90° and 0° plies plays an important role in damage development in [0/90]₄₅ Nicalon/CAS-II laminates, especially in developing the secondary damage modes such as longitudinal matrix cracking and delamination. Frictional wear effects found in cyclically loaded specimens may be responsible for the observed temperature profiles during the intermediate stage of fatigue life. It is also believed that frictional wear is critical to the failure of notch sensitive fibers. Different damage modes such as "brittle" matrix crack propagation and "quasi-brittle" matrix crack propagation were observed in heat-treated specimens. Results obtained from microanalysis using an analytical scanning transmission electron microscope equipped with an energy dispersive spectrometer, and microindentation indicated that the changes of damage and failure modes were directly related to the changes of characteristics at the fiber/matreix interface/interphase. / Ph. D.

A utilização de polímeros ligno-celulósicos combinados com polímeros artificiais na forma de materiais compostos é fruto do desenvolvimento de uma linha de pesquisa que tinha como objetivo inicial a utilização dos primeiros como enchimento de uma matriz termofixa ou termoplástica aglutinante. Com o advento da necessidade do reaproveitamento de resíduos de processos industriais, as pesquisas e a utilização de resíduos fibrosos e partículas de madeira cresceram em importância e passaram a contribuir ainda mais decisivamente no desenvolvimento de novas técnicas, processos, equipamentos e insumos que possibilitam ampla gama de aplicações dos produtos obtidos. O presente trabalho objetivou a fabricação de placas compostas de serragem de duas espécies amplamente utilizadas em serrarias combinada com polietileno de baixa densidade reciclável (PEBD). Serragem e farinha de madeira de Pinus elliottii e Eucalyptus grandis , provenientes de lenho e de casca, foram separadas, beneficiadas e misturadas com partículas de PEBD também classificadas por tamanho, na proporção de 40% de madeira e 60% de plástico. A mistura foi prensada a 150 ° C por 30 minutos à pressão de 3 MPa. Foram fabricadas 44 placas de 6 mm de espessura nominal e 40 x 50 cm de lados, em 4 repetições de 11 tratamentos. Foram produzidos corpos-de-prova de todas as placas para os ensaios físicomecânicos segundo a norma ASTM D-1037, determinando-se a massa específica, o teor de umidade, a variação da massa e da espessura ocorridas em 2 e 24 horas de imersão em água, o módulo de elasticidade e o módulo de ruptura na flexão estática, a resistência à compressão e a força máxima de arrancamento de prego e de parafuso de fenda. O lenho de Pinus de granulometria fina combinado com PEBD fino apresentou as melhores propriedades físicomecânicas. Os tratamentos com lenho de Eucalyptus obtiveram o melhor desempenho geral e naqueles em que se utilizou a casca de Pinus os resultados não foram satisfatórios. Dentre os tratamentos que utilizaram cascas, a de Eucalyptus de granulometria grossa foi superior. O lenho de Pinus , principalmente em granulometrias mais finas e homogêneas revelaram-se promissores na utilização externa e as placas obtidas de casca de Pinus revelaram um grande potencial de utilização em usos internos não estruturais, como material alternativo. / Using ligno-celullose polymers combined with artificial polymers in form of composite material is result of a developing research line which had as initial objective the use of the firsts as just filling material in an agglutinant thermoplastic matrix. Due to the necessity of reusing industrial processing residues, the research and utilization of fiber and woody particles had grown in importance and started to contribute on the development of new techniques, processes, equipment and materials that make possible creating a huge variety of products and applications. The present work had the objective of manufacturing composite boards using sawdust from two different species widely used in sawmill combined with recyclable low density polyethylene. Pinus elliotii and Eucalyptus grandis sawdust and wood flour, produced from lumber and bark had been separated, treated and mixed with PEBD particles also classified by size, in the proportion of 40% wood and 60% plastic. The mixture was pressed at 150 °C during 30 minutes under 3 MPa pressure. It were manufactured 44 boards 6 mm nominal thickness and 40 x 50 cm sides in 4 replications of 11 treatments. Samples were obtained from all boards for physicmechanical tests according to ASTM D – 1037 standard, determining specific gravity, moisture content, mass and thickness variation occurred in 2 and 24 hours in water, modulus of elasticity and modulus of rupture in the static bending, compression strength and the withdrawal load of nail and screw. The Pinus wood of thin granulosity combined with thin LDPE had presented better physic-mechanical properties. The treatments in which was used Eucalyptus wood had shown better general performance and those in which was utilized Pinus bark had not presented satisfactory performance. Amongst the treatments in which bark was used, the Eucalyptus of thick granulosity had showed better performance. Boards made of Pinus wood specially in thinner and homogeneous granulosities seems to be excellent for exterior application and those in which was used Pinus bark had shown great potential as an alternative material for non structural purposes for interior applications.

Identifying material parameters in composite plates is a necessary first step in a variety of structural applications. For example, understanding the material parameters of carbon fiber composite is important in investigating sensor and actuator placement on micro-air-vehicle wings for control and wing morphing purposes. Knowing the material parameters can also help examine the health of composite structures and detect wear or defects. Traditional testing methods for finding material parameters such as stiffness and damping require multiple types of experiments such as tensile tests and shaker tests. These tests are not without complications. Methods such as tensile testing can be destructive to the test specimens while use of strain gages and accelerometers can be inappropriate due to the lightweight nature of the structures. The proposed inverse problem testing methods using digital image correlation via high speed cameras can potentially eliminate the disadvantages of traditional methods as well as determine the required material parameters including stiffness and damping by conducting only one type of experiment. These material parameters include stiffness and damping for both isotropic and orthotropic materials, and ply angle layup specifically for carbon fiber materials. A finite element model based on the Kirchoff-Love thin plate theory is used to produce theoretical data for comparison with experimental data collected using digital image correlation. Shaker experiments are also carried out using digital image correlation to investigate the modal frequencies as validation of the results of the inverse problem. We apply these techniques first to an aluminum plate for which material parameters are known to test the performance and efficiency of the method. We then apply the method to a composite plates to determine not only these parameters, but also the layup angle. The inverse problem successfully estimates the Young's modulus and damping for the aluminum material. In addition, the vibration analysis produces consistent resonance frequencies for the first two modes for both theoretical and experimental data. However, carbon fiber plates present challenges due to limitations of the Kirchoff-Love plate theory used as the underlining theoretical model for the finite element approximation used in the inverse problem, resulting in a persistent mismatch of resonance frequencies in experimental data. / Graduation date: 2012

Favorable properties of Balsa wood make it an interesting alternative in a number of applications including thermal insulation or as a lightweight core material in sandwich composites. Increasing use in construction necessitates a better understanding of its mechanical and failure properties. In the present work, mode I and mode II fracture toughness for different types of balsa wood and a sandwich structure (balsa as core and fiber glass as skin layer) are studied experimentally by using load-displacement diagrams and visually acquired crack growth data. / Graduation date: 2013

We propose a new approach for defining mechanical properties of the brain tissue in-vivo by taking MRI or CT images of a brain response to ventriculostomy operation, i.e., the relief of the elevated pressure in the ventricular cavities. Then, based on 3-D image analysis, the displacement fields are recovered from these images. Constitutive parameters of the brain tissue are determined using inverse analysis and a numerical method allowing for computations of large strain deformations. We tested this approach in controlled laboratory experiments with silicone brain models mimicking brain geometry, mechanical properties, and boundary conditions. The ventriculostomy was simulated by inflating and deflating internal cavities that model cerebral ventricles. Subsequently, the silicone brain model was described by a hyperelastic (neo-Hookean) material. The obtained mechanical properties have been verified with direct laboratory tests. Properties of real brain tissue are more complicated, but the proposed approach requires only conventional medical images collected before and after ventriculostomy. Breast cancer is the second most prevalent cancer in women, and an operative mastectomy is frequently a part of the treatment. Women often choose to follow a mastectomy with a reconstruction surgery using a breast implant. Furthermore, there is a growing demand for breast augmentation for the sake of aesthetic improvement. In this dissertation, we also developed a quantitative large-strain 3-D mechanical model of female breast deformation. The results show that the stiffness of skin and the constitutive parameters of the breast tissue are important factors affecting breast shape. Our results also suggest that the published Mooney-Rivlin parameters of breast tissue are underestimated by at least one or two orders of magnitude. Scale analysis, representing female breast as a cantilever beam, confirms these conclusions. Subdural hematoma (tearing and bleeding between scull and brain) is one of the major complications of the ventriculostomy operations. Understanding the mechanism of subdural hematoma is critically important for development of more effective medical treatments. In this work, we developed a simple, spherically-symmetrical poroelastic model of the ventriculostomy operation and studied brain response to the pressure change in the ventricles. The observed effect of the material properties on the occurrence of subdural hematoma may be useful for making clinical decisions.

An investigation of the high-strain-rate mechanical properties, deformation mechanisms, and fracture characteristics of a Zr-based bulk metallic glass (BMG) and its composite with tungsten was conducted through the use of controlled impact experiments and constitutive modeling. The overall objective of this research was to determine the high-strain-rate deformation and failure mechanisms of a BMG and its composite as a function of stress state and strain rate, and describe the mechanical behavior over a range of loading conditions. The research involved performing controlled impact experiments on BMG composites consisting of an amorphous Zr57Nb5Cu15.4Ni12.6Al10 (LM106) with crystalline tungsten reinforcement particles. Monolithic LM106 was also examined to aid in the understanding of the composite. The mechanical behavior of the composite was investigated over a range of strain rates (10^3 s^-1 to 10^6 s^-1), stress states (compression, compression-shear, tension), and temperatures (RT to 600 C) to determine the dependence of mechanical properties and deformation and failure modes (i.e., homogeneous deformation vs. inhomogeneous shear banding) on these parameters. Mechanical testing in the quasi-static to intermediate strain rate regimes was performed using an Instron, Drop Weight Tower, and Split Hopkinson Pressure Bar, respectively. High-strain-rate mechanical properties of the BMG-matrix composite and monolithic BMG were investigated using dynamic compression (reverse Taylor) and dynamic tension (spall) impact experiments performed using a gas gun instrumented with velocity interferometry and high-speed digital photography. These experiments provided information about dynamic strength and deformation modes, and allowed for validation of constitutive models via comparison of experimental and simulated transient deformation profiles and free surface velocity traces. Hugoniot equation of state measurements were performed on the monolithic BMG to investigate the high pressure phase stability of the glass and the possible implications of a high pressure phase transformation on mechanical properties. Specimens were recovered for post-impact microstructural and thermal analysis to gain information about the mechanisms of dynamic deformation and fracture, and to examine for possible shock-induced phase transformations of the amorphous phase.

Carbon nanotubes are molecular-scale tubes of graphitic carbon that possess many unique properties. They have high tensile strength and elastic modulus, are thermally and electrically conductive, and can be structurally modified using well established carbon chemistries. There is global interest in taking advantage of their unique combination of properties and using these interesting materials as components in nanoscale devices and composite materials. The goal of this research was the correlation of the mechanical properties of coiled carbon nanotubes with their chemical structure. Individual nanocoils, grown by chemical vapor deposition, were attached to scanning probe tip using the arc discharge method. Using a scanning probe microscope the nanocoils are repeatedly brought into and out of contact with a chemically-modified substrate. Precise control over the length (or area) of contact with the substrate is achievable through simultaneous monitoring the cantilever deflection resonance, and correlating these with scanner movement. The mechanical response of nanocoils depended upon the extent of their compression. Nonlinear response of the nanocoil was observed consistent with compression, buckling, and slip-stick motion of the nanocoil. The chemical structure of the nanocoil and its orientation on the tip was determined using scanning and transmission electron microscopy. The mechanical stiffness of eighteen different nanocoils was determined in three ways. In the first, the spring constant of each nanocoil was computed from the slope of the linear response region of the force-distance curve. The assumptions upon which this calculation is based are: 1) under compression, the cantilever-nanocoil system can be modeled as two-springs in series, and 2) the nanocoil behaves as an ideal spring as the load from the cantilever is applied. Nanocoil spring constants determined in this fashion ranged from 6.5x10-3 to 5.16 TPa for the CCNTs understudy. In the second, the spring constant of the nanocoil was computed from measuring the critical force required to buckle the nanocoil. The critical force method measured the force at the point where the nanocoil-cantilever system diverges from a linear region in the force curve. Nanocoil spring constants determined in this fashion ranged from 1.3x10-5 to 10.4 TPa for the CCNTs understudy. In the third, the spring constant of each nanocoil was computed from the thermal resonance of the cantilever-nanocoil system. Prior to contact of the nanocoil with the substrate, the effective spring constant of the system is essentially that of the cantilever. At the point of contact and prior to buckling or slip-stick motion, the effective spring constant of the system is modeled as two springs in parallel. Nanocoil spring constants determined in this fashion ranged from 2.7x10-3 to 0.03 TPa for the CCNTs understudy. Using the thermal resonance of the cantilever system a trend was observed relating nanocoil structure to the calculated modulus. Hollow, tube-like nanostructures had a higher measured modulus than solid or fibrous structures by several orders of magnitude. One can conclude that the structure of carbon nanocoils can be determined from using their mechanical properties. This correlation should significantly contribute to the knowledge of the scientific and engineering community. It will enable the integration of carbon nanocoils in microelectromechanical (MEMS) or nanoelectromechanical systems (NEMS) as resonators, vibration dampers, or any other application in which springs are used within complex devices.

Global and regional mechanics of the cardiac ventricles were investigated using an anatomicallyaccurate computational model formulated from concise mathematical descriptions ofthe left and right ventricular wall geometries and the non-homogeneous laminar microstructureof cardiac muscle. The finite element method for finite deformation elasticity was developedfor the analysis and included specialised coordinate systems, interpolation schemesand parallel processing techniques for greater computational efficiency.The ventricular mechanics model incorporated the fully orthotropic pole-zero constitutivelaw, based on the three-dimensional architecture of myocardium, to account for the nonlinearmaterial response of resting cardiac muscle, relative to the three anatomically relevant axes.A fibre distribution model was introduced to reconcile some of the pole-zero constitutiveparameters with direct mechanical properties of the tissue (such as the limiting strainsestimated from detailed physiological observations of the collagen helices that surroundmyofibres), whilst other parameters were estimated from in-vitro biaxial tension tests onthin sections of myocardium. A non-invasive approach to in-vivo myocardial materialparameter estimation was also developed, based on a magnetic resonance imaging techniqueto effectively tag ventricular wall tissue.The spatially non-homogeneous distribution of myocardial residual strain was accounted forin the ventricular mechanics model using a specialised growth tensor. A simple model of fluidshift was formulated to account for the changes in local tissue volume due to movement ofintramyocardial blood. Contractile properties of ventricular myofibres were approximatedusing a quasi-static relationship between the fibre extension ratio, intracellular calciumconcentration and active fibre stress, and the framework has been developed to include amore realistic model of active myocardial mechanics, which could be coupled to a realisticdescription of the time-varying spread of electrical excitation throughout the ventricularwalls. Simple volumetric cavity models were incorporated to investigate the effects of arterialimpedance on systolic wall mechanics.Ventricular mechanics model predictions of the cavity pressure versus volume relationships,longitudinal dimension changes, torsional wall deformations and regional distributions ofmyocardial strain during the diastolic filling, isovolumic contraction and ejection phasesof the cardiac cycle showed good overall agreement with reported observations derivedfrom experimental studies of isolated and in-vivo canine hearts. Predictions of the spatialdistributions of mechanical stress at end-diastole and end-systole are illustrated.