The tailorability of composites for specific applications has been one of its greatest attractions, and simultaneously one of its most perplexing challenges. The wide choice of materials combinations, processing methods and shapes possible, present bewildering problems of selection. In the isotropic world of traditional materials it was possible to use tables, charts, and simple formulae to check the validity of a concept, thereby relegating the need for specialists to the final stages before prototyping. This is not possible in composites, where specialists in different disciplines are needed almost routinely, even at the stages of concept generation. Concurrent engineering thus is an ideal tool for composites product development, to the extent that were it not established in other fields, it would have been invented for composites out of necessity (Wilkins and Karbhari 1991). The economics related with the traditional iterative norm of product development makes it necessary to promote an integrated approach that enables a more direct form of development. Every decision made during the product development process is intricately related to the three interacting decision areas: materials, configuration, and process plan, as shown in Figure 7.1. The concept of linking the attributes of performance, properties, microstructure, and processing has recently been developed as an extension to the notion of the necessity of recognizing design interactions.
Each of the elements in Figure 7.1 presents a spectrum of choices. The configuration of a composite is unique in that it includes both shape and microstructure, any or both of which could be varied to attain a specific attribute. Unlike manufacturing methods for metals, the processes related to the fabrication/manufacture of composites have limitations based on shape, microstructure, and materials. Theoretically any combination of two or more phases, one being a matrix and the other serving as the reinforcement, can be used as the constituents of a composite. For composites, this has often been regarded as the greatest advantage and simultaneously the most difficult challenge of materials selection. The development of composites is a complex process and requires the simultaneous consideration of various parameters such as component geometry, production volume, reinforcement and matrix types and relative volumes, tooling requirements, and process and market economics. With the increase in complexity of streams of concurrent processes, there is an increased probability of losing control of the key characteristics necessary to add value, hold down costs, and meet customer expectations. The myriad choices available make it imperative that the functions of economics, design, and manufacturing be integrated during the development process.
Figure 7.1. Interacting Decision Areas
Our ability to efficiently and competitively manufacture composites depends not only on our embracing new management techniques, but also on our developing a unifying concept of materials-by-design, wherein computer modeling is combined with theory, experiments, and heuristics. In the past, practical remedial actions in the composites test-fix loop have primarily been adapted from the metals paradigm and are often ill-suited to the task. While there remains a need to improve the traditional sequential build-test-fix design methodology for product development, emphasis must shift away from developing remedial actions and towards improving conceptual planning which can enhance responsiveness and realism at earlier stages in the process. Taken to the extreme, prior proper planning should eliminate the need for remedial measures. In any technology, the decisions made early in the product conception stage have deep implications for the subsequent stages in the development cycle. Insofar as the successful development of composites (and the associated structures) are concerned, the facilitation of the efficient selection of aspects from each of the three areas of constituent materials, configuration, and processing, takes on an added dimension of importance, as decisions related to these are locked-in very early in the product design process. The motivation for tools to aid in facilitating the decision-making process is primarily one of economic leveraging, as seen in Figure 7.2.
As is apparent from the figure, the opportunities for development-process-related cost reductions decrease as the design moves along the product realization process (PRP) time-line. Up to 70% of the total life-cycle costs are normally committed at the end of the conceptualization (or preliminary design review) stage. Due to exigencies of economy associated with product development of advanced materials, such as high initial scrap rates, high material costs, and limited reworkability, early decisions are critical and have a major impact on further development. The memory of the high cost of past materials selection errors in the prototyping of composite products has often proved to be a deterrent to their conceptual selection in new programs, especially when in competition with a familiar metals paradigm, which trades off potential customer satisfaction for lower risk. This situation commonly occurs with emergent technologies in fields where the customer-perception derived market forces have remained relatively constant (leading to conservatism), and in which current product paradigms must be displaced to gain market share. In all such cases it is essential that activities critical to the success of the PRP not be omitted during the product development cycle. Recent studies have shown that a minimum number of specified product design management activities must be performed in order to achieve a high success rate with new products or technologies (Cooper and Kleinschmidt 1986; Hise et al. 1989). Obviously, the greater the number of these activities conducted, the higher the probability of success.
Figure 7.2. Opportunities in Early Design (after Ashton 1991)