Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Patent
1995-10-17
1998-11-24
Lusignan, Michael
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
4273855, 427386, 428368, 428375, 428394, 428395, B32B 900
Patent
active
058404244
DESCRIPTION:
BRIEF SUMMARY
This invention relates to curable composite materials.
Continuous-fibre reinforced thermoset resin composite materials have been used for many applications, especially in the aerospace industry in which strength-to-weight ratios are particularly important. Some of these applications involve significant thermal cycling of the parts made from the composite materials. For example, the composite materials have been used in the manufacture of jet engine components wherein the parts are subjected to thermal cycling between ambient temperatures and the relatively high continuous use temperature ("CUT") experienced by the engine components in flight. Currently, carbon fibre/epoxy resin composite materials, which typically have a CUT of 130.degree. C. -150.degree. C., are used for parts subjected to relatively low CUT regimes in the engine.
However, efforts are now being made to develop such composite materials for higher CUT regimes. Thermosetting polyimide resins offer significant improvement in CUTs. NASA has developed such a thermosetting polyimide resin with a CUT of up to 316.degree. C. in atmospheric air. This resin is commercially available under the designation PMR-15. Developments of the PMR-15 resin have resulted in resins which have even higher CUTs. PMR-15, and its developments, have been widely reviewed in the literature, for example T T Serafini, Proceedings of 5th International Conference on Composite Materials, 1007-1023, Metal Soc 1985, AIME, D Wilson, British Polymer Journal, 20(5), 405-416, 1988 and D A Scola and J H Vontell, Chemtech 112-121, February 1989.
However, in applications such as jet engines, PMR composite materials do exhibit some problems. For example, one problem is their poor resistance to microcracking resulting from thermal cycling; see for example M Simpson, P M Jacobs and F R Jones, Composites, 22(2), 89-98, 99-104 and 105-112, 1991, F Jones and Z Xiang, "Aspects of the Thermal Degradation of PMR-15 Based Composites" presented at Third European Conference on Composite Materials, March 1989 and D Wilson, J K Wells, J N Hay, D Lind, G A Owens and F Johnson, SAMPE Journal, 35-42, May/June 1987.
The microcracking arises from thermal strains which develop within the composite material on cooling from the cure temperatures (typically 300.degree. C. -330.degree. C. for PMR resins). The strains originate in unidirectional laminates owing to the mismatch between the coefficients of thermal expansion of the fibres and the matrix resin. In angle ply laminates, this effect is compounded by the anisotropy of the various plies with respect to thermal expansion. Thus, it can be appreciated that, for (0,90) laminates, ie as in woven fabrics which constitute a significant proportion of continuous-fibre reinforced composite materials, the thermal stresses, and hence the potential for microcracking, are at their greatest. The subsequent thermal cycling experienced by the composite materials as, for example, a jet engine component, results in the thermal strains repeatedly being applied to the component and hence promotes microcracking in the component. Owing to the characteristic brittleness of thermoset resins, the microcracking will, at best, compromise component mechanical performance and, at worst, may lead to catastrophic component failure.
Various proposals to alleviate the problem of microcracking in such composite materials have been made. For example, in the Wilson et al reference above (SAMPE Journal, 35-42, May/June 1987), the effects of cure temperatures for PMR-15/(0,90) carbon fibre fabric laminates have been investigated. The laminates were subjected to thermal cycling from -196.degree. C. to 280.degree. C. for 20 cycles. It was concluded that curing at 280.degree. C. -290.degree. C. substantially reduced microcracking without unduly affecting mechanical properties of the composite material. However, the thermal oxidative stability ("TOS") of the composite materials appeared to be slightly lowered despite being studied at only 300.degree. C., well below the normal CUT for the comp
REFERENCES:
patent: Re35081 (1995-11-01), Quigley
patent: 3881977 (1975-05-01), Dauksys
patent: 4894012 (1990-01-01), Goldberg et al.
Jenkins Stephen Derek
McGrail Patrick Terence
Fiberite Inc.
Lusignan Michael
LandOfFree
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