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Romain Beydon
Abstract
Adhesion and thermomechanical stresses of plasma sprayed metallic coatings on thermosetting matrix composite materials
Romain Beydon - 1 december 2000.
The use of carbon fibers reinforced plastics, as aeronautical structure materials, can require the adjunction of a coating to make them electrically conductor. A plasma-sprayed copper coating can ensure this function.
The bibliographic study has shown that the standard adhesion tests can not be used for thin deposits with a low Young modulus. For that reason, two tests have been specifically developed to characterize the mechanical adhesion of copper coatings on composite materials. The first is a static three point bending test. The second is a dynamic mode I crack propagation test. The use of both tests has allowed the study of the influence of the deposit thickness on the adhesion, bringing to the fore the existence of a critical thickness above which the adhesion decreases. A residual stress evaluation using an X ray diffraction technique has shown an increase of the stress level with the deposit thickness and a correlation has been done with the loss of adhesion previously demonstrated.
A 2D numerical simulation giving access to the temperature distribution and to the stress level in the sample during the deposit has been developed. It is based on the use of two original techniques to simulate the mobile heat source and the growth of the deposit. The incoming heat flux on the sample is determined with an experimental device that allows the measurement of the temperature inside the sample during spraying. The heat flux distribution as a function of the distance between the gun axis and the sample is obtained using an inverse methodology. After the validation of the simulation by comparison with some results from the literature, the levels of stresses calculated are compared to those obtained by X ray diffraction and discussed.
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