Historically, the development of CC composites has focused on multidirectionally reinforced materials. Focusing was a result of material being used for basically nonstructural applications in which heat resistance was the primary material function. These components were thick; consequently, the poor shear and through-the-thickness direction properties required additional reinforcement directions.
Future CC composite applications will continue to rquire multidirectionally reinforced materials, but there is also a growing interest in thin, laminate construction, CC composites for structural applications requiring ligh weight and good high-temperature behavior.
For these thin-section CC composite materials, one asks how the properties might be predicted. The author and the MSC have investigated this area and found that standard laminated plate analysis codes are adequate for predicting the behavior of thin-section CC composites.
The code utilized for thin-section CC composite materials can be simply a standard laminate analysis code. The author has been utilizing CLASS, which is a personal computer assemblage model is built into the code so that the user can predict layer properties for a variety of fibers and matrix materials and then can construct the laminates from these layers. In addition, the code has the ability to combine particles such as needles, spheres, or platelets in matrix by using upper and lower bound solutions as well as the differential scheme approach. This code allows creating matrices with various inhibitors or short fiber reinforcements and then adding long fibers to create a layer. Also, this code permits transversely isotropic constituents, all of which are temperature dependent. All of the constituent and layers properties are stored within a small data base for later access by the code. Thus, properties can be entered once and used over again.
The basic analysis of thin CC composite material are identical to those of standard epoxy laminates. The difference is in the difficulty of defining the constituent properties and degree of sublayer cracking. As described next, if data can be obtained on one material and that material used to define the constituent properties through data correlations, then the properties of other laminated constructions can be predicted with excellent accuracy. The only caveats are that the new material must contain the same fibers and that is must be processed in a very similar fashion to that of the basic material. These limitations, however, should not be considered major drawbacks because as a material is developed, standard lay-ups are generally employed to characterize that process. Alternate lay-ups then can be employed with the optimized processing conditions. In this case, the analytical prediction of composite properties can be the most useful method to use.
Material development can take place on a basic material construction, and tests from material taken from optimized processing conditions can be used to tune the input constituent properties. The code then can be utilized to predict the properties of other constructions and to define the material pay-up best suited for the given application. Finally, the optimized construction is fabricated and tested to verify the analytical modeling assumptions.