Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 56-58). Also available via the Internet.

Kinetic equation parameters for the curing reaction of a commercial glass fiber reinforced high performance epoxy prepreg composed of the tetrafunctional epoxy tetraglycidyl 4,4-diaminodiphenyl methane (TGDDM), the tetrafunctional amine curing agent 4,4'-diaminodiphenylsulfone (DDS) and an ionic initiator/accelerator, are determined by various thermal analysis techniques and the results compared. The reaction is monitored by heat generated determined by differential scanning calorimetry (DSC) and by high speed DSC when the reaction rate is high. The changes in physical properties indicating increasing conversion are followed by shifts in glass transition temperature determined by DSC, temperature-modulated DSC (TMDSC), step scan DSC and high speed DSC, thermomechanical (TMA) and dynamic mechanical (DMA) analysis and thermally stimulated depolarization (TSD). Changes in viscosity, also indicative of degree of conversion, are monitored by DMA. Thermal stability as a function of degree of cure is monitored by thermogravimetric analysis (TGA). The parameters of the general kinetic equations, including activation energy and rate constant, are explained and used to compare results of various techniques. The utilities of the kinetic descriptions are demonstrated in the construction of a useful time-temperature-transformation (TTT) diagram and a continuous heating transformation (CHT) diagram for rapid determination of processing parameters in the processing of prepregs. Shrinkage due to both resin consolidation and fiber rearrangement is measured as the linear expansion of the piston on a quartz dilatometry cell using TMA. The shrinkage of prepregs was determined to depend on the curing temperature, pressure applied and the fiber orientation. Chemical modification of an epoxy was done by mixing a fluorinated aromatic amine (aniline) with a standard aliphatic amine as a curing agent for a commercial Diglycidylether of Bisphenol-A (DGEBA) epoxy. The resulting cured network was tested for wear resistance using tribological techniques. Of the six anilines, 3-fluoroaniline and 4-fluoroaniline were determined to have lower wear than the unmodified epoxy, while the others showed much higher wear rates.

Nanomaterial composites hold improvement potential for many materials. Improvements arise through known material behaviors and unique nanoscale effects to improve performance in areas including elastic modulus and damping as well as various processes, and products. Review of research spurred development of a load-stage. The load stage could be used independently, or in conjunction with an AFM to investigate bulk and nanoscale material mechanics. The effect of MWCNT content on structural damping, elastic modulus, toughness, loss modulus, and glass transition temperature was investigated using the load stage, AMF, and DMA. Initial investigation showed elastic modulus increased 23% with 1wt.% MWCNT versus pure epoxy and in-situ imaging observed micro/nanoscale deformation. Dynamic capabilities of the load stage were investigated as a method to achieve higher stress than available through DMA. The system showed energy dissipation across all reinforce levels, with ~480% peak for the 1wt.% MWCNT material vs. the neat epoxy at 1Hz. / ND NASA EPSCoR FAR0017788 / NDSU Development Foundation FAR0017503 / National Science Foundation (NSF) Grant# HRD-0811239 to the NDSU Advance FORWARD Program

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Introduction of a composition gradient at a join between two materials of different elastic properties should reduce the stress concentrating effect of the interfacial discontinuity. A crack oriented perpendicular to this elasticity gradient will experience mode-mixity, and possible subsequent crack deflection. Explicit analytical solutions for the stress state at the tip of an angled crack in a graded material of a given finite geometry do not exist, and ongoing crack path development in such a gradient has not been characterised. An infiltration processing technique is developed which allows two materials to be joined through a region of graded composition, of tailored width and composition profile. Composition discontinuities at layer interfaces in a stepped gradient can be tolerated due to the resulting interpenetrating network structured (INS) microstructure. Firing stresses were found to be a limitation of the processing technique, overcome by limiting the steepness of the elastic gradient. Alumina and epoxy resin graded composites were produced and tested under monotonic loading, resulting in stable crack path evolution. Stress-field asymmetry at the tip of a crack oriented perpendicular to an elastic gradient was demonstrated, followed by subsequent crack deflection. Stress intensity factor and deflection angle increase with increasing gradient steepness. Rising R-curve behaviour was demonstrated for all compositions of the INS composite, with initiation and plateau toughness decreasing with increasing epoxy content. Evidence of crack bridging by intact ligaments of the epoxy phase in the crack wake explains this behaviour. Crack deflection towards the epoxy region was anticipated and demonstrated for all gradient configurations. An increase in relative crack depth was seen to increase mode-mixity at the crack-tip and subsequent crack deflection, up to a relative depth of ~0.5. No conclusive evidence was found for the influence of crack bridging on crack deflection. Toughness was shown to increase with the inclusion of a microstructural gradient. Measured toughness within graded samples was shown to be controlled by both the local composition and the volume of bridging ligaments in the crack wake. The optimum gradient should ??? extend over the widest region practical, ??? encompass the widest composition range possible, and ??? demonstrate extrinsic crack extension toughening.

Graduation date: 2004

Univ., Diss.--Göteborg, 2007. / Enth. außerdem 5 Zeitschriftenaufsätze.

Thesis--Auburn University, 2010. / Abstract. Includes bibliographic references.