Mechanical components have limited life which is strongly related to the usage rate and operational conditions. Two parts could appear similar but actually not have the similar performances, because they had different usage rate, age, applied force and etc. during their life cycles. In this thesis, a new method that help to define the failure risk of mechanical components after customer utilization. The coding of Running Quality Index was performed in MATLAB program. The developed index summarizes all performance history of mechanical component/or part into a single number. A shaft test rig was designed to simulate force and number of cycle effects on the quality index. Tensile tests were conducted on St-37 steel samples exposed to varying forces, number of cycles and heat treatment to calculate Running Quality Index. The experimental results showed that increasing total number of cycles or repeated forces decreased the remaining life of samples. The developed quality index resulted in more risk penalty points for increasing number of cycles and repeated forces.