Both the basic model (NDPROP) and the degraded properties model (DCAP) have been shown to be capable of accurately predicting carbon-carbon composite material properties. DCAP, in particular, has been demonstrated to have the ability to model various CC materials with enough accuracy to permit reliable engineering studies of material performance with little or no experimental data.
When developing analytical models for CC composites, the philosophy should be to choose an appropriate approach for each of the specific subproblems at hand. It must be emphasized that the objective of analytical modeling is to provide a cost-effective procedure for enhancing the efficiency of the materials development process. Analytical guidance of innovative material concepts will require extensive analytical screening of potential materials. Thus, the material model must be an engineering tool that treats many complex material problems in a manner that recognizes the primary objective.
In the course of developing these models, various methods have been used, including composite cylinder assemblages, variational methods, and approximate solutions suited to the problem. The name materials engineering has been coined to describe this engineering approach. The materials engineering approach to the development of a material model for quantitative material synthesis utilizes a modular concept that provides a convenient capability to upgrade the quality of predictions without substantial overhaul of the total material model. Also, during the developmental stage when certain modules of the code are approximate or preliminary in nature, the code may be used for comparative rather than for quantitative predictions and/or for data enhancement.
The DCAP model has been used to demonstrate the feasibility of the concept of pre- and post-processor interaction with material performance codes. The DCAP code have been written so that it can interact with such thermostructural finite-element codes. The interaction between codes is effective; yet, the interface with the DCAP code remains accessible such that the program can be made to interface with other performance codes.
Material models of these types should prove valuable to the materials manufacturer in developing current and future material systems for advanced applications. Also, the models will provide the structural analysis community with an effective material property prediction tool to be used as a preprocessor to aerospace structural analysis codes.
Carbon-carbon materials are complex and posses substantial variability in properties. This complexity coupled with variability should not be looked upon as an impossible task for analytical modeling. Rather, the analysis models should be viewed as tools that can help explain the trends found in data and guide the material development process so that the next batch of material will posses those characteristics that are desirable for the structure being designed.
Once material properties for a given material construction are available, whether through testing, prediction, or a combination of both, the design analysis proceeds in a normal fashion. The only uniqueness of CC composite in the regard is its severe planes of weakness when matrix dominated properties control the failure modes. The designer needs to be aware of these planes of weakness so that those stress components are examined carefully and so that proof tests are designed that will demonstrate the failure mode.