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High-Performance Structural Fibers for Advanced Polymer Matrix Composites
Understand the residual stress gradients and defects that develop under specific manufacturing processes.
The first opportunity requires some significant, focused funding that involves the fiber manufacturers, resin manufacturers, composite processors, and either academia or a large neutral testing facility. A carefully designed set of experiments is needed that would alter fiber properties, fiber strength distributions, interface properties (using some of the new interfaces developed in academia), and matrix properties and then characterize the resulting interface behavior, as well as the macroscopic tensile, compressive, fatigue, creep, and toughness behavior as a function of each variable. Although a few studies have attempted a portion of this, no large-scale study has been conducted.
The second opportunity is in the area of modeling of properties. Continuum models must be linked to micromechanical models and perhaps even molecular-level models. The fiber and interphase property variations must be included and the nonlinear behavior of the matrix must not be ignored. The modeling must consider the thermal and stress gradients that develop for a given processing method, as well as the thickness and curvature of the final part. Realistic modeling of the processing defects that occur must be included.
Finally, the stochastics of the failure process and how it translates from small samples to the component level must be considered. This is a difficult task, but a great deal of progress has been made in this area recently.28
Interdisciplinary and Interinstitutional Development
A common theme in the committee’s discussions was the appropriate role of academic research in the development of the fiber and composites industry. There has often been a disconnect between academic and industrial research efforts in the composites area. For example, the academic community has studied interfaces in great detail, but often the technology developed—and the fundamentals learned—are not used by industry, either because of poor transfer of technology, poor use of the literature by companies, or the inability to scale the interfaces developed. Even when industry is aware of developments in academia, the time and resources required to redevelop the expertise in the industry are often considered too high. On the other hand, most academic facilities cannot produce fibers, interfaces, matrices, and composites and thus rely on industrial materials. Although the field is highly proprietary (making it difficult for academics to get information to study their materials properly or for industry to share), there are some precompetitive issues that would best be addressed by a collaborative, interdisciplinary or interinstitutional research program facilitated by government.
The committee did not specifically explore the form that such interinstitutional collaborations might take: it merely notes that the current paradigm of academia studying model materials—or materials that it is not allowed to completely characterize—leads to less than ideal science.
A.M. Sastry, C.W. Wang, and L. Berhan. 2001. Deformation and failure in stochastic fibrous networks: Scale, dimension and application. Key Engineering Materials, Trans Tech Publications 200:229-250.