High-Performance Structural Fibers for Advanced Polymer Matrix Composites (2005) / Chapter Skim
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2 Fibers in Composites
2 Fibers in Composites
Pages 18-27
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From page 18... ...
We are only beginning to understand how fiber properties can be translated into superior properties of the overall composite. MATRIX RESINS Although the fibers play a dominant role in determining the stiffness and strength of a composite, the choice of the matrix will determine maximum service temperature, viable processing approaches, and long-term durability.
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From page 19... ...
Vacuumassisted resin transfer molding (VARTM) has been identified as an affordable process and is used to fabricate structural armor for ground vehicle hull structures containing integral ceramic FIGURE 2.1 The M829A2 sabot, which stabilizes the trajectory of the munition composites, as well as early in flight, was designed with graphite fiber-reinforced epoxy material that large-scale topside ship resulted in a 30 percent weight reduction in the sabot component.
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From page 20... ...
(c) It is critical to controlling composite properties because Matrix Matrix fiber-matrix interaction occurs through the interface.
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From page 21... ...
This variability in interface properties can originate from several sources, including how evenly the sizing or coating covers the fiber; variability in wetting of the matrix that can create poorly bonded regions; variation in surface roughness of the fiber; and matrix variability. The interface is crucial in controlling composite properties because load is transferred from the matrix to the fiber through the interface and deformation of the interface region (debonding or yielding)
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From page 22... ...
Although some work has been done in this area -- namely the use of LaRC PETI-5, a phenylethynyl-terminated imide oligomer, as well as some proprietary resins -- this is an area in need of some focus.15,16 The role of the interface in controlling properties is still not fully understood, particularly as it applies to lifetime prediction, and a better understanding is needed. The interface has a significant effect on fatigue behavior, creep, and environmental stability, yet direct inclusion of interface properties into lifetime models is still under development.17 To complicate matters further, the interface variability is also a relevant parameter and can lead, for example, to enhanced toughness.18 One opportunity for improving the cost-effectiveness of composites is tighter design criteria, and this requires -- in addition to an understanding of matrix and fiber effects -- a thorough understanding of the role of interface variability on composite properties.
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From page 23... ...
Processing The acquisition costs for a composite part are comprised of numerous factors including design aspects as well as the costs of raw materials, processing, tooling, assembly, and inspection. Manufacturing and assembly costs have traditionally been significant cost drivers and are typically greater than material costs in aircraft structures (see Figure 2.3)
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From page 24... ...
In rehabilitation applications, lowcost prepreg and hand-layup, pultrusion of reinforcing strips and secondary bonding, filament winding, and VARTM are examples of typical fabrication processes. For bridge decks, pultrusion and VARTM of polyester and vinyl ester have been demonstrated successfully using glass fiber preforms.24 Substitution of commercially available carbon fiber for glass in these stiffness-critical applications is a possibility, but the durability of the bond between the carbon fiber and the vinyl ester matrix must be improved.
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From page 25... ...
Research in automation using simulation, sensing, and control systems should be pursued to advance this process from prototype to a production-ready process. Translation of Fiber Properties to Composite Properties Precisely how the distribution of individual fiber strengths affects the reliability of a composite structure containing billions of continuous fibers is an extremely important question.
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From page 26... ...
The magnitudes of composite material and component qualification or certification efforts and costs vary widely and depend on many factors, including specific product requirements, the criticality of the application, and the degree to which human safety is involved. In military aircraft, for example, the process of design development, material qualification, process development, structural analysis, and testing can be extremely complex and costly due to mission criticality, the need for high reliability under extreme conditions, and survivability requirements.
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From page 27... ...
Lack of knowledge in this regard can lead to excessive design safety margins that result in increased weight and cost and lower system performance. A better understanding of the effect of constituent variability on composite properties is crucial to taking advantage of fibers on the market today as well as future fibers, as is the development of micromechanical and continuum-based models that include the stochastic process for the prediction of composite behavior.
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