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Biodegradable, biocompatible polylactide (PLA) synthesized from renewable resources has attracted extensive interests over the past decades and holds great potential to replace many petroleum-derived plastics. With no loss of biodegradability and biocompatibility, we highly toughened PLA using a novel bioelastomer (BE)–synthesized from biomass diols and diacids. Although PLA and BE are immiscible, BE particles of ∼1 μm in diameter are uniformly dispersed in the matrix, and this indicates some compatibility between PLA and BE. BE significantly increased the cold crystallization ability of PLA, which was valuable for practical processing and performance. SEM micrographs of fracture surface showed a brittle-to-ductile transition owing to addition of BE. At 11.5 vol%, notched Izod impact strength improved from 2.4 to 10.3 kJ/m2, 330% increment; the increase is superior to previous toughening effect by using petroleum-based tougheners.

Few studies of blasting exist because of difficulties in obtaining reliable fragmentation data or even obtaining consistent blasting results. Many researchers have attempted to predict blast fragmentation using the Kuz-Ram model, an empirical fragmentation model suggested by Cunningham. The purpose of this study is to develop an empirical model to relate specific explosives energy (ESE) to blasting fragmentation reduction ratio (RR) and rock fracture toughness (KIC). The reduction ratio was obtained by analyzing the bench face block size distribution and the muck fragment size distribution using image analysis. The fracture toughness was determined using the Edge Notched Disk Wedge Splitting test. Blasting data from twelve (12) blasts at four (4) different quarries were analyzed. Based on this data set, an empirical relationship, ESE=11.7 RR801.202 KIC4.14 has been developed. Using this relationship, based on the predicted blasting energy input for a desired eighty-percent passing (P80) muckpile fragment size the burden and spacing may be determined. / Master of Science

It has been suggested that the use of fibre bundles rather than individual fibres can improve the toughness properties of a short-fibre composite. Previous experimental work on this topic employed materials in which bundles were impregnated prior to manufacture or materials with poorly defined fibre-bundling. This study is the first to consider the mechanical properties of a series of materials where the bundles have been impregnated during manufacture of the material, and the materials tested contained a well-defined proportion of fibres within bundles of a known size. A novel manufacturing technique has been developed that can be used to produce short carbon fibre reinforced polypropylene materials with a controlled proportion of fibres in bundles. Materials manufactured in this work contained 0 %, 25 %, 50 %, 75 % and 100 % of the fibres in bundles. The fibres had a length of 5 mm or 10 mm and the bundles contained either 1000 or 6000 fibres. An increase in the proportion of fibres within bundles results in a decrease in the tensile modulus of the short-fibre composites. This decrease was less severe for materials containing bundles with a greater aspect ratio or laminates with a greater thickness. A model for the modulus of the materials has been developed which illustrates some of the effects of fibre-bundling on the structure of a short-fibre composite. For the materials studied, tensile strength of materials containing bundles was one quarter of the tensile strength of the filamentised material. Only one combination of fibre length and bundle size resulted in a clear increase in toughness, as measured by JJ, compared to the filamentised material and this increase appears to be due to areas of unreinforced matrix in the material. Materials containing both filamentised fibres and fibre bundles had relatively low values of J, The fracture surfaces were imaged and three distinct ways in which a bundle may fail have been identified. Discussion of the fracture mechanisms active in these materials concludes that the use of fibre-bundling to improve toughness is unlikely to be effective due to the mechanism that has been proposed

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No description available.

This thesis presents research toward the development of a simple inexpensive fracture toughness tool for polymeric materials. Experiments were conducted to test the specimen configuration and the fracture toughness tool against an established ASTM standard for polymer fracture toughness, D5045, and a commonly used four-point bend method. The materials used in this study were polycarbonate and high density polyethylene. Reductions in both the production time and the variability resulting from the preparation of the specimens were addressed through the use of specially designed fixtures. The effects from the razor cut depths used in the chevron notch were compared to the fracture toughness values obtained in order to determine the effect upon the validity of the fracture toughness.

Doctor of Philosophy / The drastic improvements in stiffness and strength even with the addition of small percentage of clay to a polymer are commonly traded-off with significant reductions in fracture toughness. It is believed that the presence of a stiff nano-filler will restrict the mobility of the surrounding matrix chains, and thus limit its ability to undergo plastic deformation, thereby decreasing their fracture toughness. To understand the role of rigid nano-fillers, like clay and their constraint effect on the surrounding polymer matrix, the effects of preferentially organized polyamide 6 lamellae in the vicinity of organoclay layers on the toughening processes are studied and compared with polyamide 6 filled with an elastomeric additive (POE-g-MA). It is suggested that to impart high toughness to polymer/organoclay nanocomposites, full debonding at the polymer-organoclay interface is necessary so that shear yielding of large volumes of matrix material can be enhanced. However, due to the strong tethering junctions between the individual organoclay layers and the matrix, full-scale debonding at the polymer-organoclay interface is rarely observed under stress conditions indicating that the constraint on the polymer adjacent to the clay is not relieved. Therefore, this has led to the development of ternary nanocomposites by adding a soft elastomeric dispersed phase to polymer/clay systems to obtain well-balanced mechanical properties. Polyamide 66/SEBS-g-MA/organoclay nanocomposites are prepared with four different blending protocols to understand the effect of blending protocol on the microstructure, mechanical properties and fracture mechanisms of the ternary nanocomposites so as to obtain new insights for producing better toughened polymer nanocomposites. In general, it is found that the level of enhancement of fracture toughness of ternary nanocomposites depends on: (i) the location and extent of dispersion of organoclay and (ii) the internal cavitation of rubber particles leading to effective relief of crack-tip tri-axial constraint and thus activating the matrix plastic deformation. Based on the wear/scratch damage studies on different polymer nanocomposite systems, it is suggested that elastic modulus and toughness of polymer nanocomposites are not the predominant factors controlling the material removal or friction coefficient and cannot be the sole indicators to compare and rank candidate materials. It is also found that nano-fillers by themselves, even if uniformly dispersed with good interfacial interaction with the matrix, do not irrevocably improve the wear (and friction) properties. Although it is important to consider these factors, it is necessary to thoroughly understand all microstructural parameters and their response to wear/scratch damage. Other important factors that should be considered are the formation of a uniform and stable transfer film on the counterface slider and the role of excessive organic surfactants or other modifiers added to disperse nanoparticles in a polymer matrix. It is also emphasized that the mechanisms of removal of materials during the wearing/scratching process should be studied meticulously with the use of high resolution microscopic and other analytical tools as this knowledge is critical to understand the surface integrity of polymer nanocomposites.

Wafer bonding is a process by which two or more mirror-polished flat surfaces are joined together. This process is increasingly used in microelectronics and microsystems industries as a key fabrication technique for various applications: production of SOI wafers, pressure sensors, accelerometers and all sorts of advanced MEMS. Unfortunately, the lack of reliability of these systems does not allow them to enter the production market. This lack of reliability is often related to the lack of understanding and control of the thermo-mechanical properties of materials used for the fabrication of MEMS (indeed, at this small scale, properties of materials are sometimes quite different than at large scale) but it is also due to the limited knowledge of the different phenomena occurring during the working of these devices, the most detrimental of them being fracture. Among all of these fracture processes, the integrity of the interfaces and, particularly, the interfaces created by wafer bonding is a generic problem with significant technological relevance. In order to understand the bonding behavior of silicon wafers, the interface chemistry occurring during the different steps of the bonding process has been detailed. The formation of strong covalent bonds across the two surfaces is responsible of the high fracture resistance of gwafer bondingh interfaces after appropriate surface treatments and annealing. The bonding process (surface treatments and annealing step) has been optimized toward reaching the best combination of interface toughness and bonding uniformity. The fracture resistance of gwafer bondingh interfaces or interface toughness has been determined using a steady-state method developed in the framework of this thesis. The high sensitivity to geometrical and environmental factors of gwafer bondingh interfaces has been quantified and related to the interface chemistry. A new technique involving the insertion of a dissipative ductile interlayer between the silicon substrate and the top silicon oxide has been proposed in order to increase the overall fracture resistance. A multiscale modeling strategy which involves the description of the interface fracture at the atomic scale, of the plasticity in the thin interlayer at the microscopic scale, and of the macroscopic structure of specimen has been used to guide the optimization of this technique. Numerical simulations have shown the influence of the ductile interlayer parameters (yield strength, workhardening exponent and thickness) and the critical strength of the interface on the overall toughness of such assemblies. A first set of experimental data has allowed increasing the interface toughness by 70%. The critical strength of the interface is finally determined by inverse identification and turns out to be in the expected range of theoretical strength. The knowledge of the strength and the fracture toughness of gwafer bondingh interfaces is of practical importance because these two values can be used in a simple fracture model (e.g. cohesive-zone model) in order to observe the behavior of such interfaces under complex loading using finite element simulations.

The design methodology and realization of nanocomposite films aiming for mechanical (superhardness, toughness) and functional (optical, microelectronic) properties were discussed in this paper. Superhard TiCrCN and nc-TiN/a-SiNx films and super-tough nc-TiC/a-C(Al) films were prepared through co-sputtering method by optimal design of microstructure. The nanocrystalline silicon (nc-Si) passivated with a matrix of thermally grown silicon dioxide were prepared using implantation of Si into SiO₂ film, and showed improved photoluminescence and optical properties. Also discussed is the nano-composite design of thin film resistor with optimized temperature coefficient of resistivity. / Singapore-MIT Alliance (SMA)