Metal matrix composites have two important interfacial problems between the matrix and the reinforcement which can reduce its desirable mechanical properties. Chemical differences between the matrix and the reinforcement can lead to reactions and deterioration of the reinforcement. Secondly, structural differences between the matrix and the reinforcement lead to bonding conditions which are far from ideal. By using a reinforcement which has a similar chemistry and local atomic structure to that of the matrix, these critical problems can be reduced. A crystalline matrix reinforced with an amorphous form of the matrix is a possible solution to the problem. Composites of amorphous Fe-W alloy particles reinforcing an Fe matrix were produced using mechanical alloying. Bulk samples were produced and their properties were studied. After analyzing the results, the amorphous alloys were determined to be effective strengtheners. However, porosity in the composites led to a reduction of the strengthening imparted by the reinforcement. / Master of Science

Fish scales can be considered as a laminated composite based on collagen fibrils arranged in a cross-plywood structure. This collagen-based composite is often partially mineralized (primarily hydroxyapatite) in the scale exterior in order to resist penetration and hence to enhance protection. Together with the overlapping assembly, the fish scales offer an excellent model system for developing fiber composite materials and flexible armor systems. The primary objective of this thesis is to characterize the distribution of the mineral phase within individual scale and to investigate the corresponding mechanical consequences of the scale as a whole and its different fields through experimental and computational approaches. In this thesis, we chose the scales from the black drum (Pogonias cromis) fish as a model system. First of all, the exterior surface morphology of individual scales was systematically studied, from which several distinct structural regions are identified, including focus field (central), lateral field (dorsal and ventral), rostral field (anterior), and caudal field (posterior). In the focus field, the classic two-layer design, i.e., mineralized exterior layer and collagen-based interior layer, was observed, and nanoindentation results revealed that the high mineral exterior layer results in a much higher hardness (800 vs 450 MPa). Moreover, macroscopic tensile tests indicate that the mechanical removal of mineralized layer did not lead to reduction in strength values, whereas acid-treated demineralized scales showed reduced mechanical properties. Finally, we identified a previously unreported mineral distribution pattern in the rostral field, in which the mineral phase is segregated into long strips along the anterior-posterior direction (width, ~300 μm). In addition, towards the interior of the scale, it appears that the mineral deposition is highly correlated with the collagen orientation, resulting a unique mineralized-unmineralized collagen-based composite structure. We built finite element models to compare this unique structure to two other mineral phases in different fields at the individual scale. This unique structure demonstrates a larger deformation displacement when load was applied, indicating that it provides further flexibility in anterior end of an individual scale. The mineralized phases and structures of various fields within a single scale provide different mechanical characteristics and properties. The structural and mechanical analysis of the various regions of the fish scale can further investigate the flexibility and protective capacity of the individual scale. / Master of Science / There are many protective systems that attracted scientists' attention, and the typical examples include the nacre, crustacean exoskeletons, and teleost fish scales. Fish scales can be considered as the most common flexible bio-inspired armor system, because they consist of mostly collagen fiber and a highly mineralized hydroxyapatite external layer. Due to the need for swimming and effective protection from predators, fish scales need to have excellent flexibility and penetration resistance. In the previous studies on fish scales, researchers usually focused on the entire scale as a multilayered composite, looking at their response against tension and fracture. The primary objective of this thesis is to characterize the distribution of the mineral phase within individual scale and to investigate the corresponding mechanical consequences of the scale as a whole and its different fields through experimental and computational approaches. In this thesis, we chose the scales from the black drum (Pogonias cromis) fish as a model system. First of all, the exterior surface morphology of individual scales was systematically studied, from which several distinct structural regions were identified, including the focus field (central), lateral field (dorsal and ventral), rostral field (anterior), and caudal field (posterior). In the focus field, the classic two-layer design, i.e., mineralized exterior layer and collagen-based interior layer, was observed, and nanoindentation results revealed that the high mineral exterior layer results in a much higher hardness (800 vs 450 MPa). In addition, we identified a previously unreported unique mineralized-unmineralized collagen-based composite structure in the rostral field, in which the mineral phase is segregated into long strips along the anterior-posterior direction (width, ~300 μm). We built finite element models to compare this unique structure to two other mineral phases in different fields at the individual scale. This unique structure demonstrates a larger deformation displacement when load was applied, indicating that it provides further flexibility at the anterior end of an individual scale, implying that the flexibility is more important at the anterior end of scales where the multi-scales overlap and are covered. The structural and mechanical analysis of the various regions of the fish scale can further investigate the flexibility and protective capacity of the individual scale, and provide further design inspiration for flexible armor designs.

With the increasing use of aluminum in naval vessels and the ever-present danger of fires, it is important to have a good understanding of the behavior of aluminum at elevated temperatures. The aluminum samples 5083-H116 and 6061-T651 were examined under a variety of loading conditions and temperatures. Tensile testing was completed on both materials to measure strength properties of elastic modulus, yield strength, and ultimate strength as well as reduction of area from room temperature to 500 deg C taking measurements every 50 deg C. These tests showed how much the material weakened as temperature increases. Low temperatures had a minimal effect on strength while exposure to temperatures between 200 and 300 deg C had the most significant impact. Creep testing was also completed for these materials. These tests were completed at temperatures between 200 and 400 deg C in 50 deg C increments. Stresses for these tests were in the range of 13 to 160MPa for 5083 aluminum and between 13 to 220MPa for 6061 aluminum. These tests showed a significant relationship between stress and temperature and how changes to one can cause a very different resulting behavior. In addition to the creep testing, three creep models were examined as a means of predicting creep behavior. These models included a power law, exponential, and hyperbolic-sine versions and were able to predict creep results with decent accuracy depending on the stress used in the model. / Master of Science

Results of an experimental test program are presented to determine the bursting strength of polyethylene terephthalate film and fabric cylinders containing axial silts of various lengths. The results demonstrate that the fabric material is superior to the film material as regards residual strength in the presence of a slit. It is shown that the strength-weight ratio of the fabric cylinders is approximately twice that of the film cylinders, largely due to the strength advantage of fiber over film. The results are compared with the predicted bursting strength obtained from two different semiempirical analyses, one based on notch strength analysis and the other employing fracture mechanics concepts. The comparison demonstrates that large errors can result from the application of the notch-strength analysis yields a scatter band which is consistent with the data scatter and follows the trend of the data. / Master of Science

Experimental and analytical investigations have shown that the interphase, with properties different from either the fiber or matrix, has a considerable influence composite material strength. The greatest obstacle, however, to this work lies in identifying the specific properties present in the interphase region of a composite and knowing how specific properties affect the performance of the material given particular service conditions. In this work. the author attempts to identify specific properties of two distinct interphases developed from fiber sizings and study their effect on the static and fatigue compression performance. Two different interphases, as formed by the introduction of contrasting fiber sizings, were studied in this dissertation. The interphase produced from the amorphous thermoplastic polyvinylpyrrolidone (PVP) size showed a graded morphology very different from that formed in the presence of the unreacted epoxy size in a thermoplastic toughened epoxy matrix. However, these morphological differences were not introduced in an untoughened epoxy matrix, although many of the differences in composite performance between the two interphase materials were similar. Model studies of PVP modified epoxy showed that at low weight percent loadings of PVP failure strain and mode I toughness were increased but significantly decreased for loadings approaching 20 w%. The effect of this altered interphase zone on elastic and inelastic properties of uniaxial tests was significant. The PVP interphase increased failure strain and strength for both tension and compression. Only the inelastic properties of the off-axis tests were affected by the contrasting interphases, and were similar for both toughened and untoughened epoxy matrix systems. The PVP interphase material showed significant improvements in low cycle notched cross-ply compressive fatigue (one order of magnitude) and fatigue limit (10% of UCS) as compared to the conventional epoxy interphase. These enhancements were the result of the inherent toughness and damage tolerance of the material as influenced by the improved inelastic properties of the PVP interphase. Thus, it is the inelastic characteristics of the interphase (and not strength alone) which are dominant in the understanding of compression strength, as is made further evident by the initial postbuckling description of the fiber-binder system. Completion of the nonlinear (kinematic and constitutive) buckling problem by asymptotic approximation will lead to a fundamental description of the failure mode and strength as related to local inelastic properties and initial imperfections. / Ph. D.

Yes / Complex biological tissues are highly viscoelastic and dynamic. Efforts to repair or replace cartilage, tendon, muscle, and vasculature using materials that facilitate repair and regeneration have been ongoing for decades. However, materials that possess the mechanical, chemical and resorption characteristics necessary to recapitulate these tissues have been difficult to mimic using synthetic resorbable biomaterials. Herein, we report a series of resorbable elastomer-like materials that are compositionally identical and possess varying ratios of cis:trans double bonds in the backbone. These features afford concomitant control over the mechanical and surface eroding degradation properties of these materials. We show the materials can be functionalized post-polymerization with bioactive species and enhance cell adhesion. Furthermore, an in vivo rat model demonstrates that degradation and resorption are dependent on succinate stoichiometry in the elastomers and the results show limited inflammation highlighting their potential for use in soft tissue regeneration and drug delivery.

No / The main aim of this study is to investigate the effects of nano-SiO2 (NS), nano-Al2O3 (NA), nano-TiO2 (NT) and nano-Fe2O3 (NF) particles in single, binary, ternary, and quaternary combinations on compressive, splitting tensile, and flexural strengths of concrete. The residual compressive strength of control and nano-added concretes are also determined at 300, 500, and 800 °C elevated temperatures. Furthermore, X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses have been conducted to examine the chemical composition and microstructure of concrete samples. The main parameters investigated were the amount and various combinations of NS, NA, NT and NF, producing thirty-one concrete batches, one control and thirty NS, NA, NT and NF added concrete mixes. The total nanoparticle amounts in the concrete mixes of 0.5%, 1%, and 1.5% by weight of cement were studied. A total of 558 concrete specimens with nanoparticles were tested at 28 days to determine compressive, splitting tensile, flexural, and residual compressive strength of concretes at ambient and elevated temperatures. It can be clearly concluded that NS and NA particles are more effective than NT and NF particles in improving the mechanical properties of concrete. The largest increase in compressive, splitting tensile, and flexural strength was obtained for 1.5% of NS and NA hybrid combination as 13.95%, 18.55%, and 21.88%, respectively. Furthermore, the residual compressive strength of single and hybrid nano-added concrete specimens significantly reduced, especially at 800 °C. Although the largest decrease in residual compressive strength of 57.65% was recorded for control concrete, the lowest reduction of 41.59% was observed for concrete with 1.5% of NS and NA hybrid combination at 800 °C.

Aluminum matrix composites perform a major role in developing novelty materials with improved mechanical performance for applications in the automotive, electronics, construction, and aerospace industries. However, the most common materials utilized as reinforcement in these composites present difficulties of dispersion at high volume fractions, structural damage, and undesirable reactions with the aluminum matrix. In addition, aluminum composites can also exhibit a reduction in plastic deformation and an increase in density compared to the base matrix, which has limited their massive implementation. This has opened the search for alternative reinforcement materials. Carbon allotropes present a high potential to overcome the limitations of aluminum matrix composites owing to their structural, mechanical, and electrical properties as well as chemical and thermal stability. In this research, we aimed to evaluate the influence of small fractions of carbon allotropes (activated nanocarbon and graphene nanoplatelets) on the structures and properties of three different aluminum matrices (pure aluminum, 6061 alloy, and 2024 alloy). First, the characteristics, manufacturing methods, and state of the art of metal matrix composites and carbon allotropes are reviewed. Then, the experimental investigation for the aluminum composites reinforced with graphene nanoplatelets and activated nanocarbon obtained through powder metallurgy, induction casting, and heat treatment is presented. The microstructural study showed the degree of uniform distribution of the carbon nanoparticles in the metal matrix, which revealed the morphology of the particulate fillers, the changes in the matrices, and the characteristics at the interface of the composites during several stages of the manufacturing processes. The mechanical characterization presented enhancements of yield strength, ultimate strength, and hardness after the introduction of activated nanocarbon and graphene nanoplatelets as a function of the volume fractions. The materials followed different paths of strengthening mechanisms depending on the matrix and manufacturing techniques. Similarly, the materials showed variable plastic deformation before failure and damping behavior, which were highly influenced by the manufacturing method, aluminum matrix, heat treatment, and temperature. Therefore, this work demonstrates the potential of graphene nanoplatelets and activated nanocarbon to be considered ideal reinforcements for aluminum matrix composites compared to common ceramic materials. The carbonaceous materials exhibited excellent distribution and interface, leading to a general improvement of the properties of the composites for both solid and liquid manufacturing methods. It also provides a better understanding of the influence of a small volume fraction of carbon nanoparticle reinforcements, different aluminum matrices, and manufacturing techniques on the performance of aluminum matrix composites. The findings of this study can be tailored to obtain aluminum matrix composites for specific engineering applications that require higher specific strength and improved damping behavior.

Spider silks are biological materials that have inspired the humankind since its beginning. From raising the interest of ancient philosophers to the practical outcomes in the societies, spider silks have always been part of our culture and, thus, of our scientific development. They are protein-based materials with exceptional mechanical and biological properties that from liquid solutions passes to the solid fibres once extruded from the body of the spiders. Spider silks have deeply been investigated in these decades for their possible outcomes in biomedical technology as a supporting material for drugs delivery or tissues regeneration. Furthermore, spiders build webs with the support of different types of silks to create mechanically efficient structures, which are currently under investigation as models for metamaterials and fabrics with superior mechanical properties. This diversity in materials and structures makes spider silks scientific outcomes potentially infinite. In this work, we present some of the outputs of these three years of PhD. We explored the properties of the native material across different aspects (different species and glands) and trying to find possible derived applications (tissue engineering). Then we explored the mechanical behaviour of the natural structures (such as orb webs or attachment discs) coupled with their biological functions. In order to develop to an industrial level this material, we tried to understand and improve the physical properties of artificial spider silk, which helps also in understanding the ones of the native materials.

The current understanding of the mechanical properties and deformation behavior of some individual phases in titanium alloys is limited due to the fine scale at which these phases precipitate within the β-phase matrix. The α and ω phases represent the most widely observed phases in titanium alloys depending on the alloy composition and also the heat treatment procedure adopted during processing. The possibility of precipitating ω-phase depends on the content of the β-stabilizers within the system. Although a significant compositional partitioning occurs within ω-phase upon aging treatment, the knowledge of ω-phase mechanical properties as a function of composition is very limited. The initial part of the current work focuses on the effect of common β-stabilizers elements on the phase stability and mechanical properties of the ω-phase using first-principles calculations. A relation between the bonding nature, the phase stability, and elastic properties was proposed. Thereafter αʺ martensitic phase was investigated in Ti-Nb and Ti-Nb-O alloys. The phase stability and martensitic start temperature of αʺ-phase was studied as a function of Nb and oxygen content. Also, the effect of the lattice shear distortion induced by oxygen atom on stabilizing β-phase was investigated. Subsequently the effect of the β-stabilizers' elements on stacking faults energy and ductility in α-Ti alloys was studied. Both prismatic and basal slip system were investigated with different concentration of β-stabilizers at the slip plane. Lastly, while the Tadmor and Bernstein model was employed to predict the partial dislocation emission and twinning propensity, the Rice criterion was used to estimate the effect of different β-stabilizers on the ductility of α-Ti alloys.