Development and analysis of three-dimensionally reinforced cellular matrix composites

The objective of this research was to develop a new class of lightweight three-dimensional textile reinforced cellular matrix composite (3-D CMC) materials using a high-pressure foaming method. The scope of the research includes fabrication, experimental evaluation and mathematical modeling of the new composite materials.; Principles of thermodynamics and transport phenomena involved in the cell nucleation and bubble growth in plastics using gas blowing agents were reviewed. The determinative factors for the foaming process were the foaming pressure, surface tension, viscous and inertial resistance forces. Foaming of epoxy resins by pressure quenching were carried out using a high-pressure vessel with a digital temperature controller and nitrogen gas as the blowing agent, at 100°C and 28–110.5 bar. The cure time was 2–2.5 hr., well before the time of gel point, 293 min., determined by means of dynamic mechanical spectroscopy. It was found that the foam density decreased monotonously and the average bubble radius slightly decreased, while the cell density increased, with the increasing foaming pressure. Cure time of 2 and 2.5 hours have no influence on the foam density, but have opposite influences on the bubble radius and cell density.; Samples of 3-D woven carbon CMC materials were fabricated using the high-pressure foaming apparatus at a foaming pressure of 60 bar as the epoxy resin cured for 1.5–2 hr. at 100°C. Photomicrographs of cross-sections of the samples revealed that the epoxy resins in the epoxy pockets of the 3-D CMC samples were removed during foaming. Average density was found 1.009 g/cm 3 for TM samples and 1.076 g/cm3 for TS samples, corresponding to weight reduction of 36.92% and 28.37%, respectively, as compared with the 3-D RMC material, where TM and TS samples used 3-D woven carbon preforms of different weaving parameters.; Tensile test, 3-point bending and high velocity projectile impact test were conducted to evaluate the mechanical performance of the 3-D CMC material. Compared with RMC materials, CMC materials demonstrated similar ultimate tensile strength and elastic modulus, lower flexure strength in bending but higher tangent modulus, and similar impact energy absorption ability at the relatively lower impact velocity. Different fracture mechanisms of the CMC materials from those of the RMC materials in 3-point bending and impact test were observed. Empty pockets and voids in the CMC structure resulted in the large deformation during impact, the slow-down of crack velocity and the multistage fracture during bending. In addition, owing to their significant weight reduction, the specific strength and specific modulus of the CMC materials were overwhelmingly better than those of the RMC.; Elasticity constants of both 3-D CMC and RMC materials were predicted using stiffness and compliance averaging methods. The measured stiffness lay between the predicted values by these two methods, with the stiffness averaging method overestimating while the compliance averaging method underestimating the constants.