Manufacturing processes are based on sets of activities that transform a given set of raw materials into a final state through a chain of activities known as the materials transformation process (Figure 6.8).
Figure 6.8. The Materials Transformation Process
The most critical frontier in advanced materials today is the gap between the ability to make and the fundamental understanding of the process needed for its rapid and reliable commercialization. Following Hahn (1991), an overview of process modeling is depicted in Figure 6.9.
Figure 6.9. The Principles of Process Modeling
The prime consideration in all composites processes is the evaluation of cure kinetics and degree of cure through equations such as:
Viscosity and gel as well as other properties are a function of degree of cure and temperature:
Generically, process modeling involves the solution of equations of balance of mass, energy, and linear momentum in addition to those listed above. Table 6.3 lists a number of models and investigators for specific process model sections related to autoclave cure, filament winding, pultrusion, and RTM.
In the recent past, processing models have been developed in a variety of areas and could very well be the subject of an in-depth review, not within the scope of this section. However, to do some justice to the topic, a brief review of modeling activity in the area of autoclave compression molding, RTM and compression molding is given herein (Table 6.4), suggesting the state of modeling in each area.
The interested reader is referred to the excellent reviews of Loos and Springer (1986) and Tucker (1987), Bruschke (1992), and Advani (1989), respectively for the three processes outlined in the table above. In addition, the activity of filament winding is fairly well characterized from the simulation of fiber path to the resolution of cure and compaction on residual stresses. There is increasing activity in the area of pultrusion to develop models for powder impregnation, and an increasing use of micromechanics models at the unit-cell level to predict permeability and to study micro-flow of resins through fabric bundles in RTM. It is of interest to note that although there is work being conducted in these areas in Japan, most of the simulations being used are based on the ones mentioned above. As an example, it could be mentioned that Mitsubishi Kasei routinely used the LIMS software (developed at the Center for Composite Materials, University of Delaware) to simulate flow and resin infusion during the development of an electric scooter body, fabricated by using structural reaction injection molding (SRIM). The model as used has been modified somewhat to integrate specifics related to materials and process details as used by the company. In other cases, companies using simulations for filament winding based their codes on the algorithms developed by Springer et al. at Stanford University. Other codes being used at companies such as JAMCO, KHI, etc. were those given to them as part of subcontracts or joint ventures with U.S. primes in the aerospace arena. However, this should in no way be taken to indicate that there is no development of codes and process models in Japan, and a few examples are given in the next paragraph.
State-of-the-Art Modeling in Some Important Composite Processes
State of Modeling in Various Areas of Composites Processing
Mitsui Toatsu Chemicals, Inc. uses state-of-the-art simulations for the development of new thermoplastic polyimides and novel carbon-fiber-reinforced thermoplastic composites with high heat resistance levels. The work would seem to rival that conducted at any research facility in the U.S. or across the world. At the Research Institute of Polymers and Textiles (RIPT), there is considerable work being conducted in the areas of injection molding, polymer-metal cluster composites, reaction control, synthesis, and functionalization of self-organizing polymers, and silicon-based polymers. The area of rheology of filled polymeric systems (as related to injection molding) is being studied by Mitsui Toatsu as well as RIPT, with basic studies being conducted to identify the critical mix for thermoplastic composite development. Mitsubishi Kasei is currently developing an artificial-intelligence-based organic-synthesis design aid in which the chemical structure of the target molecule is input on a graphic terminal, and alternate synthesis routes are processed and evaluated through computer simulation, rather than through experimentation.