One of the most important areas of the application of industrial microwave technology for materials processing is curing polymers and polymer based composites, and this is currently in a state of considerable flux. Curing of thermosetting composites in multi-mode applicators and joining of a range of thermoplastics in ridged waveguides have been some of the major achievements in the field. This research extends the applications horizon of microwaves in the area of random fibre reinforced thermoplastic composites joining and places emphasis on the development of facilities and methodologies aiming at maximising bond quality. It discusses the fixed frequency microwave equipment used, including a 0.8 kW variable control power generator operating at 2.45 GHz, waveguide and a tuning piston designed for obtaining a standing wave at the seam of the butted and lapped test pieces. The effect of power input and cycle time is detailed together with the underlying principles of test piece material interactions with the electromagnetic field. The process of heterogenous joining, with filler material, or primer, of 33% by weight of random glass fibre reinforced nylon 66, polystyrene (PS) and low density polyethylene (LDPE), thermoplastic composites is mentioned together with the process of autogenous joining of 33% by weight of random carbon fibre reinforced polystyrene (PS) and low density polyethylene (LDPE). The weldability dependence on the dielectric constant, dielectric loss, and hence loss tangent of these materials is also described and investigated. Measurements of the dielectric properties were carried out using the waveguide transmission, probe kit and resonant cavity techniques. X-ray photoelectron spectroscopy for surface analysis was carried out to assess if the filler material had diffused into the parent thermoplastic composite materials. Bond strength measurements of the welded thermoplastic composites were obtained using tensile shear tests. A variable frequency microwave (VFM) facility was also used to join the thermoplastic composites and bond strength results obtained were compared with those procured by the fixed frequency microwave configuration. From the measured data of LDPE/GF (33%), PS/GF (33%) and nylon 66/GF (33%), it was found that at relatively high temperatures and frequencies, these materials became less reflective and permitted more microwave energy to be absorbed. At the same time, their dielectric loss factor increased with temperature and frequency and enabled more of the absorbed energy to be converted to heat. Therefore, within limits, higher temperatures and higher frequencies were more suitable for microwave-assisted joining of the three materials tested. As to the primer/filler, only liquid rapid Araldite was found to be the most favourable in microwave-assisted joining of fibre reinforced thermoplastic (FRTP) composites because of its considerably high value of loss tangent. Another important finding was that the dielectric probe method was found to be the recommended technique to use for measurements of �ՄS and tan �� in microwave joining of materials out of all the methods applied. However, for low loss materials, the values of tan �� need to be acquired through the resonance cavity method.

It is well established that the extended range V(I) transition behavior in filamentary superconducting composites depends strongly on the processing conditions of the composite. Based on previous work, a model proposed by Warnes et al predicts that the second derivative of the V(I) transition is related to a more fundamental property the critical current distribution in the composite. The present work consolidates the said model by showing that in spite of the V(I) transition being dependent on the matrix resistance, the second derivative is relatively independent. Also, the second derivative V(I) curve has been correlated to the critical current distributions and area distributions in monofilament and multifilamentary superconductors, using image analysis techniques. The work provides a better understanding of the critical current distributions in composite superconductors and can be an effective tool for measuring conductor quality more precisely. In addition to this, image analysis techniques have been used to study the effect of processing on the structure of wires - and have been related to the predictions of a model of inplane stresses in composites. / Graduation date: 1996

Stress analysis was performed to determine the maximum stress acting on a railcar coal support-bed, using COSMOS finite element and WFM micromechanics models. The fracture strength of polyurethane impregnated Kevlar 29 fabric, proposed for integration with the railcar structure, was determined experimentally by loading the impregnated coupons in a microcomputer controlled Instron 4505. Procedures to improve the wettability of a Kevlar 29 orthogonal-weave fabric were investigated. Unimpregnated and impregnated coupons of increasing gage lengths were statically tested for tensile strength to check for gage length effect behavior. Fatigue tests were conducted to predict the stress level (endurance limit) below which the impregnated fabric bed can perform without failure for ten years of the service life. The fracture strength of the polyurethane impregnated fabric, after immersion in aqueous solutions of different pH values for seventy-five hours and in ten percent concentrated sulfuric acid solution at 212��F for ten hours, was measured. / Graduation date: 1994

Measurement of the copper to superconductor ratio (Cu/SC) in composite superconducting wires is necessary for process control, quality assurance, and characterization of the final wire properties. A comparison has been made of three techniques for measuring the Cu/SC ratio on a set of commercial wires produced for the Superconducting SuperCollider (SSC) Laboratory. The simplest and most straightforward technique, chemical etching, was found to display the best reproducibility, while the electrical resistivity technique shows the most variation and sensitivity to measurement errors, as well as being the most difficult to perform. The image analysis technique is fast and fairly reproducible, and is capable of providing much more information on the wire parameters than either of the other techniques. / Graduation date: 1993

No description available.

No description available.

In this study the energy dissipation performance of machine augmented composite (MAC) materials is investigated. MAC materials are formed by inserting simple machines into a matrix material. In this work the machines take the form of fluid filled tubes, and the tube cross-sectional geometry induces fluid flow when it is deformed in its plane. This flow dissipates mechanical energy, and thus provides the composite material with attractive damping properties. The objective of this study is to gain insight into the geometry, the material property combinations, and the boundary conditions that are effective in producing high damping MAC materials. Particular attention is given to tube geometry and to dimensionless parameters that govern the energy dissipation efficiency of a MAC lamina. An important dimensionless parameter is the ratio of solid elastic moduli to the product of the driving frequency and the fluid dynamic viscosity. This is a measure of the ratio of elastic forces in the solid material to the viscous forces in the fluid material that makes up a MAC lamina. Governing equations and simulation methods are discussed. Simplified equations are derived to predict the pressure generated when a tube/matrix cell is squeezed with zero pressure end conditions. Transient, three dimensional finite element models are also used to predict the performance of the damping MAC materials with zero pressure at the ends of the tubes. For the geometry and material properties considered, the highest energy dissipation efficiency predicted by these models is approximately 0.8 out of a maximum of 1.0.

The objective of this research was to determine the effect of thermal cycling combined with mechanical loading on the development of microcracks in M40J/PMR-II- 50, the second generation aerospace application material. The objective was pursued by finding the critical controlling parameters for microcrack formation from mechanical stress-thermal cycling test. Three different in-plane strains (0%, 0.175~0.350%, and 0.325~0.650%) were applied to the composites by clamping composite specimens (M40J/PMR-II-50, [0,90]s, a unitape cross-ply) on the radial sides of half cylinders having two different radii (78.74mm and 37.96mm). Three different thermal loading experiments, 1) 23oC to –196oC to 250oC, 2) 23oC to 250oC, and 3) 23oC to -196oC, were performed as a function of mechanical inplane strain levels, heating rates, and number of thermal cycles. The apparatus generated cracks related to the in-plane stresses (or strains) on plies. The design and analysis concept of the synergistic stress-thermal cycling experiment was simplified to obtain main and interaction factors by applying 2k factorial design from the various factors affecting microcrack density of M40J/PMR-II-50. Observations indicate that the higher temperature portion of the cycle under load causes fiber/matrix interface failure. Subsequent exposure to higher stresses in the cryogenic temperature region results in composite matrix microcracking due to the additional stresses associated with the fiber-matrix thermal expansion mismatch.

Th. doct.--Université de technologie de Troyes, 2003. / Bibliogr. p. 149-158. Résumé en français et en anglais. L'ouvrage porte par erreur : ISSN 0078-3780.

Thèse de doctorat : Mécanique : Metz : 1999. / Thèse soutenue sur ensemble de travaux. Bibliogr. p.157-[166]. Annexes.