“…In exploring the optimality of a warranty policy, many issues are proposed, such as the renewed period of warranty (Chukova and Hayakawa, 2004; Mitra and Patankar, 1997; Thomas, 1989), the cost structure for replacement (Barlow and Hunter, 1960), repair (Tilquin and Cléroux, 1975), periodic replacement of shock (Boland and Proschan, 1982), optimal time for repair (Sheu, 1993), optimal time of repair or replacement (Jhang and Sheu, 1995), minor and catastrophic failure (Sheu, 1993), optimal maintenance (Juang and Anderson, 2004; Wang and Sheu, 2003; Bai and Pham, 2004), and association between price, quality, and warranty period (Lin and Shue, 2005; Lin et al , 2001; Kotler, 1976; Peterson, 1970). Some of these studies assume that the failure process obeys a non‐homogeneous procession process (Nakagawa and Kowada, 1983; Savits, 1988; Juang and Anderson, 2004).…”