The change in the mechanical characteristics of the membranes is correlated to the level and number of RH operating cycles applied to PEMFC. This was examined in the experimental work of [233] where an increase of both parameters resulted in a significant reduction of the MEA ductility. The average strain-to-failure was reduced by around 40% (from 1.32 to 0.58) after 100 cycles in the 30-80% RH range. Also, the elastic modulus of the membrane was reduced from w480 to 280 MPa when RH increased from 25 to 75%. These results which were validated using a finite element model, revealed the formation and growth of mechanical defects such as crack and crazing in the membrane and MEAs. Kusoglu et al. [236] were also able to simulate the trend of the in-plane stresses across the membrane during five humidity loading cycles (95e30% RH).