The present Note presents simulations of moisture concentration and stress fields promoted by cyclical hygrothermal conditions as a result of supersonic flight in carbon-epoxy composite plates. Calculations are based on very straight hypotheses, the moisture concentration fields are obtained by employing the unidimensional Fick's diffusion law, and internal stresses are calculated by adapting the classical lamination plate theory to transient conditions. Concentration and stress fields are in a transient then permanent regime over interior regions of the plate, whereas fluctuating then periodic conditions prevail over a zone close to the lateral surfaces and of thickness e_0. The value of e_0 depends on material properties and cycle characteristics and is constant with the number of cycles. For the case under study e_0 is around 0.5 mm. As the supersonic cycles promote drying from initial humid conditions, stresses evolve toward an "after-manufacturing" condition, with progressive resurgence of residual curing stresses. The mean of all fluctuations increases with increasing cycles: in particular, zones close to the external surfaces are exposed to aggressive mixed thermal-hygroscopic stress fluctuations of amplitude as high as 40 MPa. The present Note represents a first effort toward a rational understanding of degradation and damage caused by hygrothermal cycling. Future developments include enriching the model with damage laws and, most of all, providing experimental evidence of hygrothermal fatigue. Interaction between the enriched model and experimental results is foreseen and will be the object of future publications.
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