(a1), (a2), and (a3): non-corroded specimen  under the different constant stress levels; (b1), (b2), and (b3): 24 h pre-corroded specimen under the  different constant stress levels; (c1), (c2), and (c3): 48 h pre-corroded specimen under the different  constant stress levels; and (d1), (d2), and (d3): 96 h pre-corroded specimen under the different  constant stress levels.