Resin matrices properties

Preliminary design, which will be performed according the corresponding procedures for adhesively bonded joints. Matrix resin properties are used instead of adhesive properties. The adhesive layer thickness is evaluated by assuming a particular value. 

Polyimides (PI) were among the eadiest candidates in the field of thermally stable polymers. In addition to high temperature property retention, these materials also exhibit chemical resistance and relative ease of synthesis and use. This has led to numerous innovations in the chemistry of synthesis and cure mechanisms, stmcture variations, and ultimately products and appHcations. Polyimides (qv) are available as films, fibers, enamels or varnishes, adhesives, matrix resins for composites, and mol ding powders. They are used in numerous commercial and military aircraft as stmctural composites, eg, over a ton of polyimide film is presently used on the NASA shuttle orbiter. Work continues on these materials, including the more recent electronic apphcations. 

Table 2. Structure and Properties of Aromatic Diamines and Acid Anhydrides Used in Epoxy-Matrix Resins...

Let s address the issue of nonlinear material behavior, i.e., nonlinear stress-strain behavior. Where does this nonlinear material behavior come from Generally, any of the matrix-dominated properties will exhibit some degree of material nonlinearity because a matrix material is generally a plastic material, such as a resin or even a metal in a metal-matrix composite. For example, in a boron-aluminum composite material, recognize that the aluminum matrix is a metal with an inherently nonlinear stress-strain curve. Thus, the matrix-dominated properties, 3 and Gj2i generally have some level of nonlinear stress-strain curve. 

In addition to the amount of filler content, the shape, size and size distribution, surface wettability, interface bonding, and compatibility with the matrix resin of the filler can all influence electrical conductivity, mechanical properties, and other performance characteristics of the composite plates. As mentioned previously, to achieve higher electrical conductivity, the conductive graphite or carbon fillers must form an interconnected or percolated network in the dielectrical matrix like that in GrafTech plates. The interface bonding and compatibility between... 

One of the most important properties which control the damage tolerance under impact loading and the CAI is the failure strain of the matrix resin (see Fig. 8.8). The matrix failure strain influences the critical transverse strain level at which transverse cracks initiate in shear mode under impact loading, and the resistance to further delamination in predominantly opening mode under subsequent compressive loading (Hirschbuehler, 1987 Evans and Masters, 1987 Masters, 1987a, b Recker et al., 1990). The CAI of near quasi-isotropic composite laminates which are reinforced with AS-4 carbon fibers of volume fractions in the range of 65-69% has... 

Cured Bisbenzocyclobutene (BCB) terminated resin systems exhibit good mechanical properties with 70Z to 85X retention of properties at 260 C and high thermal stability. The Materials Laboratory has studied these materials for use as high temperature structural matrix resins in composites. They are well suited for this use since they do not require the use of catalysts and cure without the evolution of volatiles. 

Composite In polymer technology a combination of a polymeric matrix and a reinforcing fiber with properties that the component materials do not have. The most common matrix resins are unsaturated thermosetting polyesters and epoxies, and reinforcing fibers are glass, carbon, and aramid fibers. The reinforcing fibers may be continuous or discontinuous. Some matrix resins are thermoplastics. 

As before, the homopolymer forming reaction involved the generation of an o-quinoidimethane from benzocyclobutene which in turn reacted with the double bond of a maleimide functionality on a second monomer to give chain extended AB material via a Diels-Alder pathway. The polymers prepared to date using this type of approach have been shown to have excellent thermal and mechanical properties and have been considered as potential candidates for use as matrix resins for advanced composites. This area has been investigated by the researchers at both the Air Force Wright Laboratories and the Dow Chemical Co. 

Table 22. Properties of graphite fibre composite using poly as a matrix resin...

As can be seen from the results, the composite formed from monomer/-polymer 114a with Celion G30-500 8HS fabric exhibited excellent mechanical properties [28], To a first approximation it would appear that the inherent fracture toughness of the matrix resin has been carried over to the composite panels. The CAI (compressive strength after impact) and OHC (open hole compression) tests are a direct measurements of the toughness of the composite part, the value of 332 MPa for the CAI compares very favorably to the value of 300 MPa typical for the thermoplastic composites. The OHC values under hot-wet test conditions would seem to indicate that the composite has very good retention of its mechanical properties at both 177°C and 203 °C. 

The idea of synthesizing imide oligomers which carry acetylenic terminations appeared attractive because homopolymerization through acetylenic endgroups occurs without any volatile evolution and provides materials with good properties. Landis et. al (8,9) published the synthesis of such acetylene terminated imide oligomers from benzophenone tetracarboxylic anhydride, aromatic diamine and 3-ethynylaniline via the classical route. As usual, the amide acid is formed as an intermediate which, after chemical cyclodehydration, provides the polymide. Since ethynyl-terminated polyimide is used as a matrix resin for fiber composites, processing is possible via the amide acid, which is soluble in acetone, or via the fully imidized prepolymer, which is soluble in NMP. The chemical structure of the fully imidized ethynyl-terminated polyimide is provided in Fig. 44. 

Throughout this chapter the chemical concepts employed to synthesize and cure addition poly(imides) have been discussed and their use as matrix resins for fiber composites has frequently been mentioned. The most important property of the imide backbone structure is the inherent thermal stability. The target of achieving the temperature performance of linear poly(imide) has not been reached, because of the aliphatic nature of the reactive endgroups, and because of the low molecular weight of the imide backbone required for processing. Future developments of addition polyimides will, as in the past, focus on the requirement of high thermal and thermal oxidative stability of the crosslinked... 

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