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Cartapip-treated pulps are evaluated for increased strength properties / Thesis (Ph.D.)--Institute of Paper Science and Technology, 1995.

A polymer-based composite reinforced with a mixture of Ni and Al powders was investigated as an example of a multifunctional structural energetic material. Micron-sized Ni powder, nano/micron-sized Al powders, and Teflon or epoxy were fabricated as bulk materials by pressing or casting. The thermally initiated reaction response of these materials was evaluated using differential thermal analysis coupled with x-ray diffraction. The analyses showed evidence of thermally initiated reactions between Ni and Al powders, as well as between Ni+Al and Teflon. Nano-sized Al powder showed a preference for reaction with Teflon over Ni, while micron-sized Al reacted strongly with Ni regardless of the presence of a binder. Teflon was shown to be very reactive with the Ni+Al/nano Al mixture, whereas epoxy was not reactive with the metallic powders, and also inhibited reaction between Ni and nano Al. The structural/mechanical behavior of these materials was evaluated using elastic and plastic property measurements via static and dynamic compression tests. Dynamic mechanical testing using reverse Taylor anvil-on-rod impact tests combined with velocity interferometry gave qualitative and quantitative information about the transient deformation and failure response of the composites. The material containing 20wt% epoxy and nano-sized Al powder showed the most superior mechanical properties in terms of elastic modulus and static and dynamic compressive strength. The addition of Ni and Al powders to the epoxy matrix increased the strength of the composites, and their tendency toward brittle fracture, as evidenced by Ni particle pullout in SEM analysis. The results illustrate that nano-sized Al particles provide significant enhancement to strength of epoxy composites, but at the expense of reactivity. The nano-Al particles get dissociated from the Ni and Al mixture and swept into the epoxy, generating a nano-Al containing epoxy matrix with embedded Ni particles. The chemical reactivity of the system is thus sacrificed as contacts between Ni and Al powders are minimized. A mixture of nano-sized Ni and Al particles may however provide the best combination of high strength and reactivity.

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In this study, a novel technique was used to produce aluminum based in situ composites from powder mixtures of Al and CeO2. This technique has combined hot working nature of friction stir processing (FSP) and exothermic reaction between Al and oxide. Billet of powder mixtures was prepared by the use of conventional pressing and sintering route. The sintered billet was then subjected to multiple passages of friction stir processing (FSP). The microstructure was characterized by the use of TEM, SEM and XRD. The reinforcing phases were identified as Al11Ce3 and £_*-Al2O3. The Al2O3 particles with an average size of ~10 nm are uniformly distributed in the aluminum matrix, which has an average grain size about 390-500 nm. The analysis of TEM indicated that these Al2O3 particles exhibit crystallographic orientation relationship with the aluminum matrix, i.e., (223)£_*-Al2O3//(111)Al and [1-10]£_*-Al2O3 roughly parallel to [1-10]Al. The precipitates of Al2O3 exhibiting crystallographic orientation relationship with the aluminum clearly indicates that they were formed from solid state precipitation. Apparently, significant supersaturation of oxygen in aluminum had been created in FSP, and nanometric Al2O3 particles were then precipitated uniformly in the aluminum matrix. This study shows that both sintering temperature and the tool traversing speed used in FSP have significant influence on the microstructure and mechanical properties of the composite. The composites produced exhibit high strength both at ambient and elevated temperatures. For example, the composite produced by 833K sintering followed by FSP with tool traversing speed of 30 mm/min possesses enhanced modulus (E = 109 GPa) and strength (UTS = 488 MPa) as well as a tensile ductility of ~3%. The major contributions to the high strength of the composite are the submicrometer grain structure of aluminum matrix and the Orowan strengthening caused by the fine dispersion of nanometer size Al2O3 particles inside aluminum grains. In addition, the composite also exhibits high strength at elevated temperatures up to 773 K. The good thermal stability and high temperature strength of the composite may be attributed to the uniform dispersion of nanometric Al2O3 particles, which are very stable at elevated temperatures.

The innovative Al/APC-2 hybrid nanocomposite fiber metal laminates (FMLs) were successfully fabricated. To overcome the usual problem of delamination, the Al alloy 2024-T3 thin sheets were treated by chromic acid anodic (CAA) method to achieve perfectly bonding with matrix PEEK eventually. It was found much better than the previously surface treatment method of CrO3-based chemical etching. A systematic study of hybrid specimens subjected to both static tensile and fatigue tests was conducted at elevated temperatures to obtain their mechanical properties, fatigue lives and failure mechanisms. From the tensile tests, the mechanical properties of Al/APC-2 hybrid cross-ply and quasi-isotropic nanocomposite FLMs at elevated temperatures were received, such as ultimate tensile strength and longitudinal stiffness. Also, the predicted stress-strain curves was proposed and in good agreement with experimental data. The average values of received notched strength were affected significantly by stress concentration and high temperature. The modified point stress criterion (PSC) was used with the varied characteristic length dependent on nature of material and specimen geometry. The predicted notched strengths by the modified PSC model were not only precisely validated, but extended to the application at elevated temperatures. The received fatigue data were plotted in S-N curves at variously elevated temperatures. The predictions of fatigue life curves were also presented and verified. The predicted S-N curves were compared with experimental data and found quite accurate.

Carbon nanotubes (CNT) are a new form of carbon with exceptional electrical and mechanical properties. This makes them attractive as inclusions in nanocomposite materials with the potential to provide improvements in electrical and mechanical properties and allows for the creation of a new range of multifunctional materials. In this study single wall carbon nanotubes (SWCNT) were dispersed in polystyrene using a solution mixing method, with the aid of a surfactant. A good dispersion was achieved and the resulting nanocomposites were characterized for electrical conductivity and mechanical properties by 3 point flexural and fracture toughness tests. Results show a significant improvement in electrical properties with electrical percolation occurring between 0.1 and 0.2 wt%. A minor improvement was observed in the flexural modulus but the strength and fracture toughness values in the nanocomposites decreased relative to the neat material. Scanning electron microscopy (SEM) was performed to characterize the morphology and fracture surface of the specimens. The results of testing and microscopy show that the presence of the nanotubes has an adverse effect on the crazing mechanism in Polystyrene (PS) resulting in a deterioration of the mechanical properties that depend on this mechanism.