The book included six chapters .the first chapter presents the Introduction and Literature Review, and the second chapter, which inclusive of the basic principles of the fatigue failure and the factors influencing on this failure, the the third chapter includes a modeling and numerical simulation by ANSYS program to assess some parameters effect on the fatigue behavior such as a noch on the materials.fourth chapter icludes cases studies of composite materials prepared from fibers of carbon and glass with polyether ether ketone and which have been tested under fatigue loads after evaluating thier mechanical and structural characteristics. Also, .chapter five includes a discussion the results of practical and theoretical study and the role of the fiber on the fatique behavior . last part of book contain the most important conclusions and recomandations.book is important for gratuate and post gratuate students in the field of materials engineering. As well as for engineers are interested in the transportation industry.