The effect of the interphase/interface region on the static mechanical properties, creep and creep rupture behavior of thermoplastic (J2) composites was investigated. The mechanical properties of the J2 composites were altered by systematic changes in fiber surface chemistry. Four fiber systems were used including the AU4, AS4(1) & (2), and AS4CGP fibers. (AS4(1) and AS4(2) represent different batch numbers.) Surface energies and chemistry of carbon fibers were examined using the Dynamic Contact Angle (DCA) method and X-ray Photoelectron Spectroscopy (XPS), respectively. The meso indentation technique was used to measure the interfacial shear strengths (ISS) of the composites. For the same batch of the composites, the ISS ratios for AS4(2)/J2 to AU4/J2 and AS4CGP/J2 to AU4/J2 were 1.22 and 1.24, respectively. The mechanical properties of these composites in the fiber direction were insensitive to the ISS. The transverse and shear moduli of the J2 composites were also not affected by the ISS. The static strengths, in general, ordered themselves from strong to weak as follows: AS4(2)/J2> AS4CGP/J2> AU4/J2. However, the creep rupture strength revealed a different ordering: AS4CGP/J2> AS4(2)/J2> AU4/J2. This suggests that static mechanical properties may not be a good indicator for long term mechanical performance. Experimental results showed that the interphase/interface region did not affect the degradation rates of the creep rupture strength of the J2 composites. DMA creep tests were performed at elevated temperatures for J2 composites. A master curve of each composite was generated. The shift factors obeyed the Arrhenius type equation. The activation energies of composites were approximately the same. The creep response of the AU4/J2, AS4(2)/J2, and AS4CGP/J2 composites were not dependent upon the ISS. Severe delaminations were observed in the AS4(1)/Jd2 composite laminates. The ([±45/90₂]_s) laminate tensile strength of AS4(1)/J2 composite was less than that of AS4(2)/J2 and AS4CGP/J2 composite. The creep rupture strength of the AS4(1)/J2 composite laminates degraded about two times faster than that of the other three composite systems. / Ph. D.

High glass transition (eg. 360 °C) melt processable thermoplastic polyimide homopolymers and poly(imide-siloxane) segmented copolymers were prepared from a number of diamines and dianhydrides via solution imidization, polydimethylsiloxane segment incorporation and molecular weight control with non-reactive phthalimide end-groups. The adhesive bond performance of these polyimides was investigated as a function of molecular weight, siloxane incorporation, residual solvent, test temperature, and polyimide structure via single lap shear samples prepared from treated Ti-6AI-4V alloy adherends and compression molded film adhesives or scrim cloth adhesives. The adhesive bond strengths increased greatly with siloxane segment incorporation at 10, 20 and 30 weight percent, and decreased slightly with total polymer molecular weight. As the test temperature was increased, adhesive bond strength increased, decreased or showed a maximum at some temperatures depending on the polyimide structure and siloxane content. The presence of residual solvent increased adhesive bond strength at ambient temperature but decreased the strength at the elevated temperatures. The variation of adhesive bond strength with residual solvent, siloxane and test temperature was attributed to the influence of these parameters on the brittle-ductile transition behavior of the polyimide system. This conclusion was supported by stress-strain measurements which indicated that tensile strength and modulus decreased with siloxane concentration and test temperature, demonstrating that there was an optimum combination of strength and strain for maximum adhesive bond strength. A model was developed to describe this behavior. The poly(imide-30%siloxane) segmented copolymer and a miscible poly(ether-imide) also demonstrated excellent adhesive bond strength with poly(arylene ether ketone) PEEK®-graphite composites. Oxygen or ammonia gas plasma treatment was very effective in further improving adhesive bond strength of melt laminated PEEK®-graphite composites. / Ph. D.

Thesis (Ph. D.)--Ohio University, November, 2000. / Title from PDF t.p.

Thesis (M.Sc.(Chemical Engineering))--University of Pretoria, 2007. / Abstract in English. Includes bibliographical references (leaves 74-80).

Thesis (Ph. D.)--University of Alabama at Birmingham, 2007. / Additional advisors: Derrick R. Dean, Alan W. Eberhardt, Ramana G. Reddy, Uday K. Vaidya. Description based on contents viewed Feb. 13, 2009; title from PDF t.p. Includes bibliographical references.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1997. / "UMI number: 9724066"--T.p. verso. Vita. Includes bibliographical references (p. 182-189). Available electronically via Internet.

Thesis (M.S.)--Michigan State University. Dept. of Civil and Environmental Engineering, 2008. / Title from PDF t.p. (viewed on Aug. 3, 2009) Includes bibliographical references (p.129-132). Also issued in print.

No description available.

Environmental issues enforce transportation sectors to limit their carbon dioxide emissions in various ways. Automotive manufacturers attempt to reduce carbon dioxide emission by seeking various strategies, e.g., increasing aerodynamic efficiency, using more fuel-efficient engines, reducing friction and wear of transmission systems, and, most importantly, by using lightweight materials and structures. This dissertation is a contribution toward a lightweight design of structures by proposing numerical models suitable for damage prediction of thermoplastic composite materials. In this dissertation, predictive damage models for two different length scales, namely micromechanics, and mesomechanics, were proposed. Micromechanics is used to predict the nonlinear damage behavior of elementary thermoplastic composite ply, while the mesomechanics is used to predict the failure behavior of thermoplastic composite laminates (test coupon or plate scale). For the micromechanics, a representative volume element (RVE) of such materials was rigorously determined using a geometrical two-point probability function and the eigenvalue stabilization of homogenized elastic tensor obtained by Hill-Mandel kinematic homogenization. We proposed a viscoelastic viscoplastic model for the polypropylene matrix to extend the capability of the micromechanics model in predicting the damage behavior of the composite ply at higher rates. At the mesoscale, we improved the classical mesomechanics damage modeling in the off-axis direction by introducing the confinement effect. The pragmatic approach consists of separating the progressive damage into two parts, namely “diffuse damage regime” and “transverse-cracking regime”, were described by two distinct damage parameters. We also enriched the mesomechanics model by proposing a viscoelastic and viscoplastic model to account for the rate-dependent behavior of the thermoplastic composites. We showed that the predictions given by the proposed micromechanics and mesomechanics models were in excellent agreement with the experimental results in terms of the global stress-strain curves, including the linear and nonlinear portion of the response and also the failure point, making it useful virtual testing tools for the design of thermoplastic composites.

Reticulitermids were significantly more likely to discover subterranean baits connected by physical guidelines than freestanding baits under both laboratory and field conditions. In the laboratory, subterranean termites built significantly longer tunnels adjacent to cellulosic guidelines than plastic guidelines. In the field, all guideline materials were equally effective at directing tunneling activity. Reticulitermes spp. workers were tested to determine their preferred substrate temperature. The preferred range for Reticulitermes spp. workers was found to be 18 to 27 degrees C. A laboratory bioassay was performed to determine if Reticulitermes spp. aggregates within thermal shadows. Significantly more Reticulitermes spp. workers aggregated within cool thermal shadows than control areas. In a multiple choice bioassay, mean consumption was higher for paper baits treated with fructose, galactose, glucose, raffinose, sucrose, trehalose and uric acid than for control baits. In a multiple choice bioassay, mean consumption was significantly lower for baits treated with arbutin, and most amino acids than for control baits. In the no-choice bioassay, the amount of paper bait consumed did not differ significantly for any of the treated baits tested and control baits. / Ph. D.