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DAMAGE TOLERANCE AND FATIGUE DESIGN METHODOLOGY FOR PRIMARY COMPOSITE STRUCTURES.

Objective

1.To determine the surface reactivity of silicon nitride matrices and corresponding silicon nitride-silicon carbide composites in environments representative of fossil fuel conversion systems.
2.To determine how the presence of impurities such as sulphur vapour, sulphur dioxide and chlorine within the corrosion environment affects the surface reactivity of silicon nitride and silicon nitride-silicon carbide composites.
3.To elucidate the mechanisms of high temperature chemical degradation in corrosive environments, which contain either oxygen or sulphur or chlorine.
4.To optimise the composition of composites in terms of additive and silicon carbide content for use in aggressive situations.
The main results obtained from the work performed are summarized as follows:

a. A qualitative rating of the structure damage tolerance behaviour can be established based on the rating of materials obtained at the coupon level. Therefore a linking line between the basic properties of the composites matrices and the damage tolerance properties of detailed specimens was developed (CASA, LBF, Uni. of Leoben).

b. Several new testing techniques were developed and implemented during the work:

- Mixed Mode bending (Mode I/Mode II) for coupon testing (Univ. of Leoben).

- Microscopy method for determining delamination growth under fatigue (CASA, Un. of Leoben).

- Method to correlate the delamination growth and the change of compliance to derive the crack propagation growth and the crack propagation growth (LBF).

c. A computer program called IMPACT was developed. The program allows to calculation of the number of cycles needed for a fixed growth of the determination, or the reached size of a delamination after a fixed number of cycles in a laminate (LBF, CASA). This prediction method is applicable if there is sublaminate buckling. CASA and LBF are trying to introduce empirical factors that can allow the use of the use of the program for structures.
This model will use the laminate plate theory, the stability theory and fracture mechanics method, and needs an iterative process. The necessary input data would be obtained from standard compression after impact test samples.

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Coordinator

Construcciones Aeronauticas SA
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Avd John Lennon s/n
28906 GETAFE
Spain

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Participants (2)