Coupled effects of hygrothermal degradation and fatigue damage of sheet molding compound (SMC) composite

Industrial sheet molding compound (SMC) composite structures are susceptible to environmental degradation, primarily from moisture and temperature. Furthermore, these materials are subjected to fatigue loading. It is therefore necessary to generate Wohler curves for a range of service conditions, taking into account exposure time and temperature. Given the time-consuming nature of these preliminary characterizations, this paper presents an innovative approach to rapid fatigue life prediction using both monotonic and fatigue tests. The core concept of the proposed model is to establish an equation of state that correlates first-cycle macroscopic damage to fatigue life. By coupling this relationship with micromechanical modelling of quasi-static damage, we can rapidly determine SN curves for any considered aged state. The methodology also integrates the microstructure as an input, significantly reducing the need for extensive experimental characterization. A comparison between experimental and simulated Wöhler curves shows excellent agreement over different ageing conditions for SMC composites.