“…Subsequent to Boland et al (1992) and Mi (1999), a large amount of research has been conducted along this line. See, for example, Valdés and Zequeira (2003), Romera, Valdés, and Zequeira (2003), Hu and Wang (2009), Li, Zhang, and Wu (2009), Li and Ding (2010, Li, Wu, and Zhang (2013) and Li, Fang, and Mi (2015). On the other hand, some authors have focused on simple coherent systems with independent component lifetimes having some specific distributions, such as exponential distributions.…”