A flapper valve is made from a hardened and tempered high strength strip steel which opens and shuts as it is subjected to very high cyclic loads. Steel strip of which flapper valves are made from can   encounter a surface defect which are anticipated to influence fatigue life negatively. In this study, the influence of surface scratches on fatigue life of flapper valve strip was investigated. The analysis was carried out by using thirty samples that were blanked out of eight different steel strips in the transverse direction. Of these samples, fifteen of them had scratches on the surface and fifteen did not, all these samples were fatigue tested by constant amplitude method. An S-N curve was plotted based upon the values and results from the fatigue test, considering the curve as the nerve center in relation with fractrographic studies using the Scanning electron microscope. Therefore this master thesis work aims to explain the influence of scratches on fatigue life of flapper valve strip and suggest future improvements based on the findings.

This thesis deals with the design of a sporttester, which is a device capable of calculating the cadence of the taken steps and monitoring the impact force of foot on the ground while running. Exposure to long-term strong impacts while running can cause serious fatigue fractures of the hip, calf bone or the foot area. The purpose of the sporttester is to monitor and signal strong impacts to the runner, thus helping to prevent fatigue fractures. The aforementioned features are evaluated based on the change in acceleration measured by the accelerometer. The calculated values of step cadence, running speed and impact force are sent via Bluetooth Low Energy to a compatible mobile application.