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No / Long glass fibre (LGF) composites are extensively used in manufacturing to produce components with enhanced mechanical properties. Long fibres with length 12 to 25mm are added to a thermoplastic matrix. However severe fibre breakage can occur in the injection moulding process resulting in shorter fibre length distribution (FLD). The majority of this breakage occurs due to the melt experiencing extreme shear stress during the preparation and injection stage. Care should be taken to ensure that the longer fibres make it through the injection moulding process without their length being significantly degraded. This study is based on commercial 12 mm long glass-fibre reinforced polypropylene (PP) and short glass fibre Nylon. Due to the semi-flexiable behaviour of long glass fibres, the fibre orientation distribution (FOD) will differ from the orientation distribution of short glass fibre in an injection molded part. In order to investigate the effect the change in fibre length has on the fibre orientation distribution or vice versa, FOD data was measured using the 2D section image analyser. The overall purpose of the research is to show how the orientation distribution chnages in an injection moulded centre gated disc and end gated plaque geometry and to compare this data against fibre orientation predictions obtained from Autodesk Moldflow Simulation Insight.

Yes / This paper studied the effect of different types of multi-walled carbon nanotubes (MWCNTs) on the dynamic mechanical properties of cementitious composites. Impact compression test was conducted on various specimens to obtain the dynamic stress-strain curves and dynamic compressive strength as well as deformation of cementitious composites. The dynamic impact toughness and impact dissipation energy were, then, estimated. Furthermore, the microscopic morphology of cementitious composites was identified by using the scanning electron microscope to show the reinforcing mechanisms of MWCNTs on cementitious composites. Experimental results show that all types of MWCNTs can increase the dynamic compressive strength and ultimate strain of the composite, but the dynamic peak strain of the composite presents deviations with the MWCNT incorporation. The composite with thick-short MWCNTs has a 100.8% increase in the impact toughness, and the composite with thin-long MWCNTs presents an increased dissipation energy up to 93.8%. MWCNTs with special structure or coating treatment have higher reinforcing effect to strength of the composite against untreated MWCNTs. The modifying mechanisms of MWCNTs on cementitious composite are mainly attributed to their nucleation and bridging effects, which prevent the micro-crack generation and delay the macro-crack propagation through increasing the energy consumption.

The effect of various inorganic and organic additives as possible nucleating agents on the crystallisation behaviour of P. E. T. and the suosequent influence on the morphological and mechanical properties has been examined. Various methods of mixing(: the polymer and additive were investigated and a method involving the screw-Extrusion of the polymer and the additive was ultimately adopted. Crystallisation studies were carried out using differential scanning calorimetry under dynamic and isothermal modes. The results produced under conditions of isothermal crystallisation were analysed by means of a computer. Despite differences between batches of polymer all the additives with the exception of indigo produced a nucleating effect in the polymer as indicated by an increase in the rate of crystallisation compared with that of the base polymer. Two organo-metallic substances (sodium benzoate and sodium stearate) proved to be the most effective in this respect by decreasing the degree of supercooling of the polymer by 20 [degrees]. Morphological studies were carried out on isothermally crystallised samples, after etching and replication using a transmission electron microscope. A nodular structure whose dimensions were sensitive to both the nucleating agent and the temperature of crystallisation was observed. Mechanical testing of samples direct from the D. S. C. was carried out using a compression method. The breaking loads were found to vary with both the type of nucleating agent used and the crystallisation temperature chosen. A separate study involving the exanination of the resulting fracture surfaces by scanning electron microscopy revealed that a, high breaking load was associated with a fine discontinuous structure whereas lower breaking loads were characterised by a more continuous linear appearance. This implies a higher energy of fracture due to the increased surface area of the fracture surface of the former.

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 texturing of ultra-high temperature ceramics (UHTCs) using weak magnetic fields is studied and developed for the first time. Textured UHTCs were prepared by magnetically assisted slip casting (MASC) in weak magnetic field (B ~ 0.5 T). Analytical calculations describing the balance of torques acting on the suspended particles suggested that texture would form at such low magnetic fields. The calculations include a novel contribution of Stokes drag arising from the inhomogeneous velocity profile of the fluid during slip casting. Experimental proof-of-concept of the theoretical calculations was successfully demonstrated. Calculations of Lotgering orientation factor (LOF) based on the intensities of the (00l) family of peaks measures by XRD revealed strong c-axis crystalline texture in TiB2 (LOF = 0.88) and ZrB2 (LOF = 0.79) along the direction of the magnetic field. Less texture was achieved in HfB2 (LOF = 0.39). In all cases, the density of the textured materials was less than that of control untextured materials, indicating that texturing hindered the densification. The findings from this work confirm the potential for more cost-effective, simple, and flexible processes to develop crystalline texture in UHTCs and other advanced ceramics and give new insight into the mechanisms of magnetic alignment of UHTCs under low magnetic fields. The microstructural evolution during slip casting and pressureless sintering is investigated. The interplay between magnetic alignment and particle packing was investigated using XRD and SEM. During MASC, the suspended particles rotate into their aligned configuration. Particles that deposit at the bottom of the mold near the plaster of Paris substrate have their alignment slightly disrupted over a ~220 μm-thick region. The aligned suspended particles lock into an aligned configuration as they consolidate, leading to a uniform degree of texturing across the entire sample height of several millimeters upon full consolidation of the particle network. If the magnetic field is removed before the particles fully consolidate, the suspended particles re-randomize their orientation. Grain size measurements done using the ASTM E112 line counting method on SEM images revealed anisotropic microstructures in green and sintered textured ZrB2 materials. Smaller effective grain sizes were observed in the direction of c-axis texture than the directions perpendicular to the texture. Grain aspect ratios of 1.20 and 1.13 were observed in materials where the c-axis texture directions were parallel (PAR) and perpendicular (PERP) to the slip casting direction, respectively. Constraint of the preferred a-axis grain growth direction in the textured materials inhibited their densification compared to the untextured material. The PERP material with the preferred grain growth direction constrained along the casting direction had smaller average grain sizes than the PAR material which contained the preferred grain growth directions in the circular plane normal to the casting direction. Compression testing suggests a trend towards higher strength and stiffness in materials with higher density. Classical catastrophic brittle failure was observed in the untextured materials, but in the textured materials some samples exhibited a multiple failure mode. The PERP material tended to exhibit superior strength and stiffness to the PAR material in the classical brittle failure mode due to the orientation of the stiffer a-axis along the loading direction and smaller average grain size in the plane normal to the loading direction in the PERP condition. In the multiple failure mode, the PAR material tended to reach higher strength values after the initial failure and reach slightly higher strains before ultimate failure due to the orientation of the compliant c-axis along the loading direction and ability of the grains elongated in the plane normal to the loading direction to rearrange themselves after initial failure(s). Regardless of density or texture condition, all ZrB2 samples survived thermal shock resistance (TSR) testing. Samples were heated to 1500°C in air, held for 30 minutes, then quenched in room temperature air. After TSR testing, oxide layers formed on the surface of the materials. The specific mass gain and oxide layer thickness tended to increase with increasing porosity and were dramatically increased when open porosity was dominant as in the CTRL 1900 condition. After TSR testing, the compressive strength and strain at failure were both higher compared to the as-sintered materials. The increases in the average compressive strength were 20%, 76%, and 57% in the CTRL, PAR, and PERP conditions, respectively. The combination of the presence of the oxide layer shifting the onset of macroscale damage to higher strain values, the dissipation of load in the more porous region near the oxide layer, and the constraining effect of the oxide layer acting against the expansion of the material contributed to reinforcement of the samples after TSR testing. The CTRL material outperformed the textured materials on average in terms of strength and stiffness due to the higher density. The results suggest that reinforcement was more effective in the PAR condition than the PERP, which may be caused by the formation of a homogenous oxide layer on the PAR while the PERP formed an anisotropic layer. The work presented in this dissertation lays the foundation for affordable, energy efficient preparation of UHTCs and other ceramic materials. Equipment costs are reduced by 3 orders of magnitude, and the operating costs and energy consumption are greatly reduced. Facilitation of the preparation of textured materials opens the door to renewed investigations into their processing and performance. This work describes in detail for the first time the relationships between processing, microstructure, and properties of a textured UHTC part, providing a model for future research. Finally, the findings in this work can be used to guide process optimization, exploration of complex shapes and microstructures, and design of manufacturing schemes to create specialty textured parts for demanding structural and functional applications. / Doctor of Philosophy / Textured ultra-high temperature ceramics (UHTCs), special materials with melting temperatures above 3000°C and potential for use in thermal protection of Mach 5+ aircraft and spacecraft, were prepared by magnetically assisted slip casting (MASC) in a weak magnetic field for the first time. The magnetic field was supplied by commercially available permanent magnets which was applied to a liquid-like slurry with UHTC particles floating in it to orient the UHTC particles with their c-crystal axis along the magnetic field direction. Calculations which described the balance of rotational forces acting to align or misalign the suspended particles suggested that the UHTC particles would align in the weak magnetic field. This prediction was realized. After the liquid in the slurry was removed during MASC to leave behind an aligned particle network, the samples were densified by heating in the absence of air to 2100°C for one hour. In titanium diboride (TiB2) and zirconium diboride (ZrB2), two of the most relevant UHTC materials, strong texture was achieved; 88% and 79% of the crystals in the material were aligned along the original magnetic field direction. This is the first time that this has been reported in the scientific literature. In hafnium diboride (HfB2), only 39% of the grains were aligned. The textured materials all had lower density than the untextured materials prepared alongside them using conventional slip casting. The relationship between magnetic alignment and particle packing was investigated by observing the microstructure. During MASC, the suspended particles rotate into their aligned configuration. Particles that deposit at the bottom of the mold near the plaster of Paris substrate have their alignment slightly disrupted over a ~220 μm-thick region. The aligned suspended particles lock into an aligned configuration as they consolidate, leading to a uniform degree of texturing over across the entire sample height of several millimeters upon full consolidation of the particle network. If the magnetic field is removed before the particles fully consolidate, the suspended particles re-randomize their orientation. The findings from this work confirm the potential for more cost-effective, simple, and flexible processes to develop crystalline texture in UHTCs and other advanced ceramics and give new insight into the mechanisms of magnetic alignment of UHTCs under low magnetic fields. Because of the magnetic alignment of the particles, it is expected that the microstructure would show some difference along and across the direction that the alignment formed along the applied magnetic field. In order to determine that, the size of the grains (particles joined to each other during densification) in the materials are measured along different directions in the sample chosen for their orientational relationship to the magnetic field and casting directions. Smaller effective grain sizes were observed along the direction of magnetically aligned crystalline texture than the directions perpendicular to the texture. Because of how the crystal axes of the particles are aligned, there are differences in how the particles join each other during densification, and that results in an anisotropic microstructure where different grain sizes as a function of the magnetic field direction and the texture direction. Compression testing conducted by squeezing the samples at a fixed rate suggests a trend that indicates the samples are stronger and stiffer when the density is higher, as expected. Untextured samples abruptly failed after reaching their maximum strength value in a manner typical of brittle ceramics. Some textured samples failed in this way, but some failed at low strength values then climbed back up in strength repeatedly until they eventually gave out completely, in a crumbly mode. In the classical brittle failure mode, the PERP material with c-axis texture aligned along the sample diameter, perpendicular to the loading direction, tended to exhibit superior strength and stiffness to the PAR material with c-axis texture oriented along the height and loading directions of the sample because the stiffer crystal axis was oriented along the loading direction and the average grain size seen by the load head was smaller. In the crumbly mode, the PAR material tended to reach higher strength values after initial failure and ultimately fail later in a crumblier mode because the more compliant crystal axis was oriented along the loading direction and the grains elongated in the plane perpendicular to the loading direction could rearrange themselves better after initial failure(s) to bear more load. Regardless of density or texture condition, all ZrB2 samples survived thermal shock resistance (TSR) testing, meaning that the samples remained fully intact after experiencing a big difference in temperature in very short time. Samples were heated in a furnace to 1500°C in air, held for 30 minutes, removed from the furnace, and cooled in air. After TSR testing, the samples developed an oxide layer on the outside, in a similar manner to rust forming on a piece of metal. How much it oxidized per unit area and how thick that oxide layer was increased with increasing porosity. These quantities increased dramatically when the pores connected the interior of the sample to the outside, as in the CTRL 1900 condition. After TSR testing, the samples were stronger by 20%, 76%, and 57% in the CTRL, PAR, and PERP conditions, respectively, indicating that the oxide layer was responsible for an enhancement in strength. The results suggest that increase of strength of the oxide layer was more effective in the PAR condition than the PERP, which is believed to be caused by the formation of a homogenous oxide layer on the PAR while the PERP formed an anisotropic layer. The work presented in this dissertation reduces the start-up equipment costs associated with magnetic alignment processes by 1000 times and lays the foundation for affordable, energy efficient preparation of UHTCs and other ceramic materials. The simplicity of this technique makes it easier for future researchers to study textured materials. This work describes in detail for the first time the relationships between processing, microstructure, and properties of a textured UHTC part, providing a model for future research. Finally, the findings in this work can be used to guide process optimization, exploration of complex shapes and microstructures, and design of manufacturing schemes to create specialty textured parts for demanding applications.

OBJECTIVES: This in vitro study aims to compare and evaluate the mechanical properties of different 3D-printed resin materials. Determine the impact of 3D printer type on the mechanical properties. Investigate the filler percentage by weight for each resin material. MATERIALS AND METHODS: Eight resin materials were tested for flexural strength, flexural modulus, microhardness, fracture toughness, and wear resistance. Resin materials: Rodin Sculpture (RS), BEGO VarseoSmile Crown Plus (BVS), Desktop Health Flexcera Smile Ultra Plus (DHF), SprintRay Crown (SRC), SprintRay Ceramic Crown (SCC), Saremco Crowntec (SC), Myerson Trusana (MT), PacDent Ceramic Nanohybrid (PAC). 3D printer Asiga Max and Ackuretta SOL were used to print 12 specimens from each material to compare three-point flexural strength in bar-shape, biaxial flexural strength in disc-shape, fracture toughness in single edge V-notched beam, wear resistance in pin-shape. Three discs shape specimens from each material were used to compare the Vickers microhardness. The filler percentage by weight of each material is determined by Ash burning and Solvent extraction. The microstructure of a polished disc from each material was examined under a scanning electron microscope (SEM), and the elemental composition was investigated by Energy Dispersive Spectrometry (EDS). Results were analyzed using ANOVA, regression of least square means (α = 0.05), Tukey HSD test, Pearson correlation coefficient, and Student’s t-test. RESULTS: The flexural strength test results, utilizing the three-point method, reveal significant differences among the materials tested. The highest average was recorded in SCC at 160 MPa, while the lowest was found in SRC at 84.4 MPa. The flexural modulus also exhibited significant differences, with the highest average observed in SCC, BVS, RS, SRC, DHF, SC, and MT, measuring 7.8, 6.2, 6.0, 5.8, 4.9, 4.5, and 3.0 GPa, respectively. The resin materials with the highest biaxial flexural strength were DHF 217 MPa and MT 200 MPa, with no significant distinction between them and different from the remaining materials. SCC demonstrated a notably higher average value in Vickers microhardness 44 HVN, while DHF exhibited a significantly lower value of 15.58. The Fracture toughness test presented no significant differences between DHF, MT, and SCC, with values of 2.28, 2.27, and 2.11 MPa.m0.5, respectively, exceeding the remaining materials. In the wear test, DHF and MT had a significantly higher weight loss rate of 29.25 and 27.18 mg/million cycle, respectively. In contrast, MT's height loss rate of 2.02 mm/million cycle was the only significantly higher difference from other materials. The data indicates that the printer type does not significantly affect biaxial flexural strength. At the same time, Asiga exhibited significantly higher values in three-point flexural strength, flexural modulus and hardness tests. In contrast, the SOL printer demonstrated higher values in fracture toughness than Asiga. The ash and solvent extraction methods revealed that SCC had the highest filler percentage by weight, while MT had the lowest. SEM imaging showed the existence of filler particles in all materials, with PAC containing the largest particles and MT containing the smallest. DHF was the only resin material that contained exclusively spherical shape filler particles. EDS analysis disclosed the elemental composition of each material with a higher percentage in Silica, Oxygen, Barium, Titanium, and Ytterbium. CONCLUSION: The results demonstrate significant differences in the tested materials' flexural strength, flexural modulus, biaxial flexural strength, Vickers microhardness, fracture toughness, and wear rates. Even though there are significant differences in some of the mechanical properties of the printer type, it is small and might not have an effect clinically. A strong correlation exists between filler percentage with flexural modulus r = 0.83, biaxial flexural strength r = 0.60, microhardness r = 0.73, and wear resistance r= 0.82. There is a low correlation between filler percentage with fracture toughness r= 0.41, with no correlation with flexural strength in the three-point test. Filler particle percentage highly affects the mechanical properties of 3D printed resin materials. These findings could be valuable in selecting appropriate materials for specific applications.

This study aimed to evaluate the physical and mechanical properties of red oak (Quercus spp.), white oak (Quercus spp.), hard maple (Acer saccharum) and yellow-poplar (Liriodendron tulipifera) and compare them to values from past publications. Mechanical testing was conducted on small, clear, defectree specimens from red oak, white oak, hard maple and yellow-poplar following the standard ASTM D143. Percentage of latewood, moisture content, specific gravity, modulus of elasticity (MOE), modulus of rupture (MOR), compression parallel and perpendicular to the grain and Janka hardness were determined. Results indicated that mechanical properties for red oak, white oak, hard maple and yellow poplar have not changed substantially because the average values remain in a range that is very close to the ones published in past studies. Thus, values from the Wood Handbook can still be used for engineering purposes.

Structural elements comprised of high strength concrete (HSCs) have gained popularity due to their high compressive strength, increased tensile strength, and low permeability that can be achieved with smaller placements relative to what would be needed with traditional ready mixed concretes. HSCs are also gaining interest for mass placements that are very large. Determining in-place properties of any of these structures is critical to the overall success of a project and elusive to determine prior to placement. In this dissertation, a laboratory based thermo-mechanical framework is outlined to predict in-place properties of modest to mass sized HSC structures using mostly existing and common laboratory testing methods with a few additional items on the same scale as existing equipment. Various curing protocols were evaluated in this study to determine a recommended set of protocols to reproduce thermal profiles of modest and mass sized structures on laboratory scale specimens. These specimens can then be tested following standard testing protocols to reasonably estimate in-place mechanical properties. This framework is envisioned to be a foundational piece of a standard test method in the future. Approximately 600 concrete specimens were tested for compressive strength, 300 specimens for elastic modulus, 100 for splitting tensile strength as well as 100 cement paste specimens for compressive strength. Additionally, approximately 400 time-temperature curves were recorded for both cement paste and HSC specimens.

A new methodology has been developed to model the viscoelastic behavior of solids using a general spectrum function. Not all materials can be modeled using simple Kelvin-Voigt (K-V) or Maxwell elements where the viscoelastic parameters are constants. There is a need for a general spectrum function that can be used to model the Lame' functions which constitute all properties of interest. Thus far, there is no method like the one presented in this study that can determine the moduli of viscoelastic materials. This study develops a methodology by which the time dependent properties of homogeneous and non-homogeneous materials may be modeled. Once the Lame' functions are determined, the Principle of Correspondence is applied to the elastic equations to determine the necessary properties. In uniaxial tension the time dependent strain, modulus, Poisson's ratio, and compliance are determined. The time dependent deflection is determined for beams in flexure. Where applicable, parameters determined from the analytical model are compared to the available experimental data. Good agreements are found between the analytical and experimental data sets.