Polyurethane network binders were synthesized using polyethylene glycol (PEG) prepolymers, cellulose acetate butyrate (CAB), curative [Desmodur N100 (N100) or Desmodur N3200 (N3200)], and catalyst [dibutyltin dilaurate (DBTDL)]. Triacetin (TA) was added as plasticizer before the reaction. Polyurethanes were prepared by varying the molar ratio of ¡VNCO/-OH, weight ratio of TA/PEG, molecular weight of PEG, the amount of catalyst, the order of adding catalyst and curative, and the stirred time. Synthesized polyurethanes were characterized by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), tensile tests, and swelling tests to study their reaction, degradation, thermal, and mechanical properties. When the ratio of ¡VNCO/-OH was between 1.2 and 1.4, polyurethane gave the best mechanical properties. Additionally, the quenched polyurethane had a lower degree of crystallinity When the weight ratio of TA and PEG was bigger than 2, crystallization of polyurethane could be minimized during the tensile testing or after quenching. In this study, it was found that PEG with molecular weight of 4000 yielded the best mechanical properties. These results indicate that better and uniform mechanical properties can be obtained by using enough stirring time via varying the amount of catalyst and adding catalyst before curing agent.

The tensile behavior of the monolithic amorphous ZrCu and crystalline Cu thin films and the ZrCu/Cu multilayered thin films, coated on polyimide (PI) substrates in different layer thicknesses has been investigated. The scanning electron microscope (SEM) morphology of the as-deposited thin film is composed of sphere domains. Between the domains, stress concentration is induced. The cracks perpendicular to the loading direction would propagate along the domains. The constituent component examined by energy dispersive X-ray spectrometer (EDS) shows that the average composition (in atomic percent) amorphous thin film is Zr46.78Cu53.22, closed to the designed Zr50Cu50 goal. The X-ray diffraction (XRD) results show that the multilayered specimens are composed of both amorphous ZrCu and nanocrystalline Cu crystal structure. As the monolayer thickness become lower, the normalized peak height and grain sizes of Cu become lower. To obtain the mechanical properties of the coated films, deducting the contribution of substrates is used in this study. The tensile Young¡¦s moduli of monolithic amorphous ZrCu and nanocrystalline Cu thin films are close to the results extracted from micro-compression. Based on the current tensile results for the moduli of multilayered thin films, the obtained mechanical data are demonstrated to be reliable and are consistent with the theoretical values predicted by Rule of Mixture. As the thickness decreases from 100 nm down to 10 nm, the tensile Young¡¦s moduli do not vary much. On the other hand, the maximum tensile stress shows strong variation, being highest for the layer thickness of 25 nm. The deformed surface morphologies characterized by scanning electron microscopy also exhibit a similar trend. The optimum tensile properties of the monolithic and multilayered thin film combinations are examined and discussed in this thesis.

Oligomers of hard and soft segments of unsaturated polyesters (UP) were synthesized. They were blended in different ratios and cured with various amounts of styrene. Based on the criteria of tensile strength and strain, hard segment/soft segment (60/40 wt %) UPs containing 35 wt % and 45 wt % of extra amount of styrene were chosen for further studies. Inorganic-organic hybrid materials were prepared by incorporating tetraethoxysilane and poly(dimethylsiloxane) into the UP resins via the sol-gel process by changing the ratios of HCl/TEOS, H2O/TEOS, TEOS/PDMS and the reaction time. The specimens of these hybrid materials after curing were characterized using the tensile tester, rheometer, scanning electron microscope (SEM), 29Si-NMR and thermogravimeter. In the condition of HCl/TEOS molar ratio 0.07, H2O/TEOS molar ratio 4, TEOS/PDMS weight ratio 90/10 and the reaction time 3 hours, the results of 29Si-NMR, SEM and silicone mapping indicate that these silica gels with 3D network were well dispersed in the UP resins. These specimens had tensile strength of 512¡Ó16 kgf/cm2 and elongation of 11¡Ó4 % which are above the criteria of inhibitors. From the erosion testing, flame retardants was added unsaturated polyester and inorganic-organic hybrid materials that can help to resist heat flame, remain of a fire on the surface had the char forming.

No description available.

The purpose of this work is to identify the parameters of scaffold's mechanical properties by observing/monitoring their response to defined external mechanical strain. The first part of the work is summarizing the knowledge about the required properties of scaffolds, their production and the factors influencing production. The practical part of the work concerns itself with measurement, analysis and evaluation of data based on proprietary methodology. Based on the results at this stage of the research, we can confirm, that scaffolds have viscoelastic, or viscoplastic character and its response depends on the magnitude of deformation, state of hydration, ratio of solutions and period of networking. Keywords: scaffod, tensile test, rheologic model

This dissertation primarily documents the quantification of the interfacial behavior of carbon based nanomaterials, which includes two categories, one is the nanofriction properties evaluation of aligned carbon nanotube carpets, few-layer graphene as well as three types of functionalized graphene nanoribbons, the second is the mechanical characterization of individual functionalized carbon nanofibers and the interfacial fracture toughness quantification in carbon nanotube/polymer derived ceramics nanocomposite. The aligned carbon nanotube carpets have a highly anisotropic friction behavior, which means the friction force are lower for transversely aligned CNTs side than for vertically aligned CNTs surface. We can also tune the friction properties of graphene ribbons by grafting different functional groups. In addition, two narrow angular regions with high friction, separated by a wide angular interval with low friction, were identified between graphene and highly oriented pyrolytic graphite. The distance between the two friction peaks is 61◦, which corresponds well with the 60◦ symmetry of individual atomic layers in the graphite lattice. The technique that involves the usage of mcirodevices and nanoidenter was used to conduct tensile tests on pristine, fluorinated and amino-functionalized carbon nanofibers, which were found to exhibit varied load-bearing abilities and unique fracture modes. The technique was also used to perform single fiber pullout experiments to study carbon nanotube/polymer derived ceramic interface.

The work aims to manufacture AS-4/PEEK APC-2 nano-composite laminates first. We used the prepreg form of AS-4 Graphite/PEEK laminae to make APC-2 laminates of 2 mm thick with two lay-ups of cross-ply and quasi-isotropic totally 16 plies by a hot press via the modified diaphragm curing. The nano-particles SiO2 with the average diameter of 15¡Ó5 nm were uniformly spread in the specific interfaces of laminate. From mechanical testing it is found that the nanocomposite specimens of spreading 10 plies nanoparticles (3% by wt. of matrix) possesses the highest mechanical properties. we see that in cross-ply specimens the ultimate strength increases 10.91 % and stiffness 6.7 %; while in quasi-isotropic specimens the ultimate strength increases 12.48 % and stiffness 19.93 %. Second, repeat the tensile tests at 50, 75, 100, 125, 150¢J to receive respective stress-strain curve , strength and stiffness. At elevated temperatures the ultimate strength decreases slightly below 75¢J and the elastic modulus reduces slightly below 125¢J, however, both properties degrade highly at 150¢J ( Tg) for two layups generally. Finally, the constant stress amplitude tension-tension cyclic testing was conducted. It is found that both the stress-cycles (S-N) curves are very close below 104 cycles for cross-ply laminates w/wo nanoparticles, and the S-N curve of nano-laminate slightly bent down after 105 cycles. Whilst in quasi-isotropic laminates, the S-N curve of nano-laminate is always slightly below that of APC-2 laminate through the life.

TiNi shape memory alloys (SMAs) have been extensively used in various applications. The great interest in TiNi alloys is due to its unique shape memory and superelasticity effects, along with its superior wear and dent resistance. Shape memory and superelastic effects are due to a reversible martensitic transformation that can be induced either thermally or mechanically. In this study, indentation tests at different temperatures, loads and strain rates have been performed on superelastic TiNi alloy. Deformation characteristics of superelastic TiNi under indentation have been compared to AISI 304 steel as a conventional material. Also, in-situ optical microscopy tests with interrupted heating have been employed in order to gain an insight into the coupled deformation and reversible martensitic transformation behaviour of TiNi SMAs under tensile loads. An understanding of the impacts of strain rate and temperature on the deformation behaviour of TiNi SMAs under localized compressive loads has been proposed.

No description available.

As a candidate for dynamic electric contacts, Nano-twinned copper has intrinsic conductivity and enhanced fretting resistance. To better understand its general mechanical behavior, we conduct molecular dynamics simulation studies to investigate responses of nano-twinned copper to stress and to one-directional and two-directional sliding processes, in comparison with single crystal and nano-grained model systems. Obtained results suggest that the twin boundary blocks dislocation movement more effectively and the degree of emitting dislocations under stress is considerably lower than that of grain boundary. The inverse H-P relation only occurring in nano-grained materials does not necessarily result from grain boundary sliding. Under sliding conditions, dislocations are easier to be generated in the single crystal system. During the two-directional sliding process, Bauschinger effect is observed in the single crystal and nano-twinned systems, while the situation is opposite for the nano-grained system. The nano-twinned Cu shows the least dislocation accumulation during two-directional sliding. / Materials Engineering