Curing Pressure Influence of Out-of-Autoclave Processing on Structural Composites for Commercial Aviation

Autoclaving is a process that ensures the highest quality of carbon fiber reinforced polymer (CFRP) composite structures used in aviation. During the autoclave process, consolidation of prepreg laminas through simultaneous elevated pressure and temperature results in a uniform high-end material system. This work focuses on analyzing in a fundamental way the applications of pressure and temperature separately during prepreg consolidation. A controlled pressure vessel (press-clave) has been designed that applies pressure during the curing process while the temperature is being applied locally by heat blankets. This vessel gives the ability to design manufacturing processes with different pressures while applying temperature at desired regions of the composite. The pressure role on the curing extent and its effect on the interlayer region are also tested in order to evaluate the consolidation of prepregs to a completely uniform material. Such studies may also be used to provide insight into the morphology of interlayer reinforcement concepts, which are widely used in the featherweight composites. Specimens manufactured by press-clave, which separates pressure from heat, are analytically tested and compared to autoclaved specimens in order to demonstrate the suitability of the press-clave to manufacture high-quality composites with excessively reduced cost

Kinetic viscoelasticity modeling applied to degradation during carbon–carbon composite processing

Kinetic viscoelasticity modeling has been successfully utilized to describe phenomena during cure of thermoset based carbon fiber reinforced matrices. The basic difference from classic viscoelasticity is that the fundamental material descriptors change as a result of reaction kinetics. Accordingly, we can apply the same concept for different kinetic phenomena with simultaneous curing and degradation. The application of this concept can easily be utilized in processing and manufacturing of carbon–carbon composites, where phenolic resin matrices are cured degraded and reinfused in a carbon fiber bed. This work provides a major step towards understanding complex viscoelastic phenomena that go beyond simple thermomechanical descriptors.United States. Air Force Office of Scientific ResearchNational Science Foundation (U.S.) (Joint U.S.-Greece Program

Structure development in a thermoplastic polyimide. Cold crystallization as revealed by microhardness

8 pags., 10 figs., 7 tabs.The isothermal `cold crystallization' of the thermoplastic polyimide (New TPI) has been studied using the microhardness technique to examine the property-microstructure correlation. By using wide- and small-angle X-ray diffraction and differential scanning calorimetry, the influence of the experimental parameters, i.e., treatment temperature Tc and time tc on the micromechanical properties of the `cold crystallized' samples has been examined. It is shown that both macroscopic hardness H and volume crystallinity xc increase with Tc and tc. For the samples prepared in the secondary crystallization range, it is demonstrated that H values strongly depend on the hardness of the crystalline units Hc. In this range, long spacing L, crystal thickness lc and crystallinity (both linear xCL, and derived from density xc) slightly increase with Tc. From the DSC study, it is demonstrated that the proportion of `liquid-like' and `rigid' amorphous fraction present in each sample is directly related with the crystallization conditions. Finally, from the SAXS and DSC combined study, information concerning the secondary crystallization mechanism has been obtained.The authors are indebted to DGICYT (Grant PB94-0049), Madrid (Spain). We wish also to thank NEDO's International Joint Research Programme, Japan, for the generous support of this investigation. Partial financial support was provided by the Polymeric Composites Laboratory Consortium at the University of Washington

Microhardness of carbon fiber reinforced epoxy and thermoplastic polyimide composites

5 pags. 4 figs.We have examined the micro indentation hardness of a series of carbon fiber reinforced epoxy and thermoplastic polyimide (TPI) composites. In the epoxy systems, the influence of Nylon particles was studied. The effect of crystallization of the thermoplastic polyimide upon the microhardness values of the resin was also investigated. The microstructure of the TPI‐composites was characterized by X‐ray diffraction. The results show that the addition of carbon fibers to the neat resins greatly increases the microhardness and thus the yield stress of the composite. The value of the microhardness technique is highlighted in emphasizing the heterogeneity of the CFRC. Copyright © 1995 Society of Plastics Engineer