m El-Damcese - Department of Mathematics (Section of Statistics), Faculty of Science, Tanta University, ۳۱۵۲۱, Tanta, Egypt
f Abbas - Department of Mathematics, Umm Al-Qura University, ۲۰۶۴, Makka, Kingdom of Saudi Arabia
e El-Ghamry - Department of Engineering Physics and Mathematics, Faculty of Engineering, Tanta University, ۳۱۵۲۱, Tanta, Egypt

Reliability is the most important performance issue in engineering design process but in the real world problems, there are limitations for using conventional reliability. Fuzzy logic has proved to be effectivein expressing uncertainties in different fields, including engineering reliability. In this paper, for bothseries and parallel systems composed of three identical or different elements, the reliability has been analyzed using the fuzzy concepts and some characteristics such as the mean time to failure have been evaluated, taking in our account that all the operating units have increasable time varying failure rateswith fuzzy triangular membership functions. This paper includes a numerical example to illustrate the model and validate the analytical results

Reliability Analysis,Mean Time to Failure,Time-varying Fuzzy Failure Rates,Parallel System,Series System