No description available.

Thesis (M.S.)--University of Texas at El Paso, 2009. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Thesis (MScEng (Industrial Engineering))--University of Stellenbosch, 2005. / The LOMOLD process is a new plastic moulding process being researched at the University of Stellenbosch. The process essentially combines injection moulding and compression moulding. Molten plastic is forced into the mould cavity using a plunger. This plunger then forms part of the cavity wall. The plunger face must therefore follow the geometry of the part. Rapid Tooling evolved from Rapid Prototyping. There are two categories of Rapid Tooling: indirect and direct rapid tools. Indirect rapid tools are manufactured by using a master pattern to form the mould cavity. The accuracy of the mould cavity depends heavily on the accuracy of the master pattern. The master pattern is usually produced using Rapid Prototyping technology. Direct rapid tools use Rapid Prototyping technology to build the mould through and additive, layer by layer process or a subtractive process. This research investigates the use of Rapid Tools for the LOMOLD process. Aluminium Filled Epoxy Tooling (AFET) represents the indirect technology and CNC-machined tooling the direct technology. Both of these technologies are available at the University of Stellenbosch. Parts are manufactured on these tools using an experimental LOMOLD machine. These two technologies are compared in terms of part accuracy, tool lead time, tool cost and part cost. The research concluded that the only advantage the AFET has over the CNC-machined tool is a shorter manufacturing lead-time. In terms of tool cost, tool life, part geometric accuracy, part cost and cycle time the CNC tool is superior. Therefore the application of AFET is limited to small volume, prototype or pre-production runs for tool design confirmation, part functional testing and part appearance testing. It is also demonstrated that a cooling system on the AFET tool has no significant influence on the tool performance and should therefore, especially for production runs less than 150 parts, not be included in the tool to save on tool cost. Another conclusion is that the LOMOLD process is not consistent enough for a production process. This statement could be limited to the machine used for the research but to prove this statement wrong, the machine must be improved and more investigation is required.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2009. / The objective of this project was to measure the performance of high-strength aluminium alloys as injection mould material compared against conventionally used tool steel.

No description available.

This work is concerned with the processing of pellets of polypropylene (PP) containing pregenerated microfibrils of thermotropic liquid crystal polymers (TLCPs), referred to as microcomposites. The processing methods used are injection molding, sheet extrusion, and extrusion blow molding. The TLCPs used are HX6000 and Vectra A950. The microcomposites are produced by drawing strands of PP and TLCPs generated by means of a novel mixing technique and pelletizing the strands. The work was undertaken in an effort to improve on the properties observed for in situ composites in which the TLCP fibrils are generated in elongational flow fields that occur during processing. In situ composites usually exhibit highly anisotropic mechanical properties and the properties do not reflect the full reinforcing potential of the TLCP fibers. Factors considered include the effect of in situ composite strand properties on the properties of the injection molded composite, the melt temperature used in injection molding, TLCP concentration, and the melt temperature of the TLCP. It was found in this work that microcomposites can be processed by means of injection molding, sheet extrusion, and extrusion blow molding. It was necessary to process the materials at low temperatures to maintain the TLCP fibrils. However, HX6000, the higher melting TLCP allowed higher processing temperatures than Vectra A. When the TLCP fibrils were maintained, the properties of the TLCP reinforced composites did show reduced anisotropy as compared to an in situ composite. The tensile strength of the composites produced by all three methods was about equal. The modulus of the injection molded composites was slightly higher than that of the composite sheets, but the composite sheets showed a lower degree of anisotropy. In all three processing methods the modulus of the TLCP reinforced composite was a function of the modulus of the in situ composite strand used to produce the microcomposite. Therefore, it is recommended that to improve the properties of the microcomposites the properties of the in situ composite strands should be improved. Furthermore, the mechanical properties of the composites increased with increasing TLCP composition. To provide a basis of comparison the properties of the extruded sheets and the injection molded composites were compared to both the predictions of composite theory and the properties of glass reinforced composites. It was found that the modulus of the 10 wt% composites approached the predictions of composite theory, but at higher TLCP loadings the modulus showed negative deviations from the predictions of composite theory. This is believed to be the result of a reduction of fiber aspect ratio due to poor fiber distribution and fiber breakup. The modulus of the TLCP reinforced composites was about the same as the modulus of the glass reinforced composites produced by both sheet extrusion and injection molding. The tensile strengths were slightly lower than that of the glass reinforced composites. It is expected that as the modulus and strength of the reinforcing TLCP fibrils are improved the properties of the TLCP reinforced composites should exceed those of glass reinforced composites. It was concluded that the processing of microcomposites is a viable means of producing composites based on TLCPs and thermoplastics with good mechanical properties and low degrees of mechanical anisotropy. / Ph. D.

Methods of processing polypropylene (PP)/ liquid crystalline polymer blends to obtain high mechanical properties from injection molded samples were investigated in this dissertation. Three liquid crystalline polymers (LCPs), two liquid crystalline (LC) copolyesters and one LC poly(ester-amide), were used. The PP/LCP blends were compatibilized with a maleic anhydride grafted polypropylene (MAP) to enhance the mechanical properties. The effect of increasing MAP content on the mechanical properties, morphology, and interfacial tension of injection molded tensile bars and plaques made from blends with 30 wt% LCP was investigated. It was determined that MAP enhances both the tensile strength and modulus, but the tensile strength is increased to a greater degree than the tensile modulus. For the LC copolyesters, the tensile strength appeared to reach a maximum while for the LC poly(ester-amide) the tensile strength increased without limit in the range of MAP contents studied. Simultaneously, a finer dispersion was created as the MAP content was increased. Calculation of the interfacial tension from contact angle measurements indicated that the interfacial tension decreased as MAP was added to the PP matrix. Analysis of the MAP concentration after blending indicated that MAP did not react with the LCP, but enhanced tensile properties resulted from physical interaction such as hydrogen bonding. This mechanism is consistent with the greater property improvements found in the LC poly(ester-amide) blends where the amide group is expected to undergo stronger hydrogen bonding than the ester group. Analysis of the injection molding of these blends found that heat transfer and solidification significantly affected the flexural modulus of these blends. Injection molding conditions such as fill time, mold thickness, mold temperature and melt temperature were investigated in three molds of different thicknesses. Different processing relationships were found between the LC copolyesters and the LC poly(ester-amide). For the former LCP blends, the highest moduli were obtained from the thinnest mold in a manner parallel to that of the moduli of neat LCPs. For the latter LCP blends, the highest moduli were obtained in the intermediate thickness mold. The differences between the copolyester and LC poly(ester-amide)s processing / property relationships were related to the melt rheology of the LCPs. For the LC copolyesters, maximum mechanical properties were obtained when the melt temperature was selected so that the storage and loss moduli of the LCP were nearly equal. This equality of storage and loss moduli could not be achieved with the LC poly(ester-amide). In addition, upon cooling, the storage and loss moduli of the LC poly(ester-amide) indicated that rapid solidification occurred while a much lower rate of solidification was indicated for the LC copolyesters. In addition the mechanical properties were sensitive to the rate of cooling as indicated by the Graetz number. It was speculated that attainment of the highest mechanical properties was related to the LCP being deformed during the filling stage followed by rapid solidification of the LCP morphology upon cessation of flow. / Ph. D.

This research project is partnership project involving industrial, university and government collaborators. The overall objective is to develop and enhance tools for use in Resin Transfer Moulding (RTM) design technology in order to re-design existing metallic parts using composite materials. / The specific objective of this work is to present preliminary research findings of the development of an optimized design of a leading edge slat (horizontal stabilizer component) from the Bell Model 407 Helicopter. The results presented here focus on the static stress analysis and the structure design aspects. The findings will serve as a basis for future design optimization as well as further developments in the use of RTM technology in re-designing metallic aeronautic components and can be considered to be "semi-optimized". / This research is based on extensive finite element analysis (FEA) of several composite material configurations, with a comparison made with the original metallic design. Different key criteria of the part design such as ply lay-up, bracket geometry, angle and configuration are tested using FEA technology with the objective of selecting the design which is minimizing stress concentrations. The influence of the modification of model-related parameters was also studied. / Preliminary comparative studies show that the slat configuration with half brackets opened towards the inside with an angle of 70 degrees (angle between the top of the airfoil and the side of the bracket) is the best option according to minimum stress concentration and structural flexibility. This choice is confirmed by other factors such as material savings and ease of processing.

I have used computer simulations to investigate the behavior of polymeric materials at the molecular level. The simulations were performed using the molecular dynamics method with Lennard-Jones potentials defining the interactions between particles in the system. Significant effort was put into the creation of realistic materials on the computer. For this purpose, an algorithm was developed based on the step-wise polymerization process. The resulting computer-generated materials (CGMs) exhibit several features of real materials, such as molecular weight distribution and presence of chain entanglements. The effect of the addition of a liquid crystalline (LC) phase to the flexible matrix was also studied. The concentration and distribution of the second phase (2P) were found to influence the mechanical and tribological properties of the CGMs. The size of the 2P agglomerates was found to have negligible influence on the properties within the studied range. Moreover, although the 2P reinforcement increases the modulus, it favors crack formation and propagation. Regions of high LC concentration exhibit high probability of becoming part of the crack propagation path. Simulations of the tensile deformation under a uniaxial force have shown that the molecular deformation mechanisms developing in the material depend on several variables, such as the magnitude of the force, the force increase rate, and the level of orientation of the chains. Three-dimensional (3D) graphical visualization tools were developed for representation and analysis of the simulation results. These also present interesting educational possibilities. Computer simulations provide us information which is inaccessible experimentally. From the concomitant use of simulations and experiments, a better understanding of the molecular phenomena that take place during deformation of polymers has been established.

Study developed during the Master's degree studies of Mechanical Engineering deals with the use of recycled plastic in the injection molding and its influence on the mechanical properties of the mold. Examined product is used in the automotive industry as a connector body. The housing is manufactured from a plastic material, polyamide. The annual production volume of 3 000 000 pieces. According to tests specified in standard USCAR2 regrind influence on mechanical properties and dimensions was evaluated. After the technical evaluation of the project, research was also judged from economic point of view. In this task, savings with the different content of the recycled material during production was calculated. The final chapters justify change of properties and they are proposing the use of recycled materials in practice.