The purpose of this thesis is to investigate the fatigue life of two components in different hydraulic quick couplings. The crack which initiates the fatigue failure usually occurs in the bottom of one of the threads. Thus, the threads in the coupling are carefully investigated. A few different approaches for determining the fatigue life are studied for each component. CAD (Computer Aided Design) models for both components are created and analyzed with FEM (Finite Element Method). By analyzing these components with FEM the stresses and the strains are calculated. These values for stress and strain are used to determine the fatigue life for the different components. The first component is suffering from high cycle fatigue. Four different approaches for high cycle fatigue are investigated. These four are Wöhler-curve, Haigh-diagram, von Mises fatigue criterion and Mises-Sines fatigue criterion. It was found that all of them but the von Mises fatigue criterion give a good approximation of the fatigue life. von Mises fatigue criterion does not consider the midstress, which can be a reason for this. The three other approaches indicate that the component will be suffering from fatigue, but will be relatively close to infinite life. The Wöhler-curve indicates that the component will withstand about 470 000 loading cycles. Compared to the experimental tests where the component withstands about 700 000 loading cycles, it can be said that the approach is a good estimation of the fatigue life. Approximated material data are used. For further work it is essential to obtain experimental material data for better approximation of the fatigue life. The second component is suffering from low cycle fatigue, which means that different approaches are needed. The approaches are originally from Coffin-Manson and Morrow. A total of four low cycle fatigue criterion have been studied. The first one is made by CoffinManson and takes the plastic strain in to account, the second is made by Morrow and takes both the elastic and the plastic strain in to account.  The third is a modification of Morrow’s criterion, and will consider the midstresses as well. The fourth is a simplification of Morrow’s criterion where more common material parameters are used. These four have been compared and it can be seen that the CoffinManson criterion gives the best approximation of the reality. The Coffin-Manson criterion gives an approximation of 50 000 loading cycles to fatigue failure which, compared to that the experimental tests suffered from fatigue failure after about 40 000 loading cycles, is a good estimation of the fatigue life.

Detta examensarbete utfördes på Scania CV AB och behandlar delar i lastbilens avgassystem som utsätts för korrosion och nötning. Huvudmålet med detta arbete är att utveckla en provmetod för livslängdsundersökning av flexibla slangar. En serie tester utfördes för att förstå grundorsakerna till brott och en FE-analys utfördes för att verifiera resultaten till dessa prov. En stor del av den flexibla slangen blir stel på grund av höga avgastemperaturer och som leder till plastisk deformation av slangen. Men de tre första lindningarna som ligger närmast motorn behåller sin flexibilitet på grund av kontinuerliga motorvibrationer. Slutsatsen är att huvudorsaken som gör att de flexibla slangarna går av, är slitage som leder till sprickinitiering. Den sprickan sprider sig i form av lågcykelutmattning d.v.s att det tar ganska kort tid tills brott sker i den flexibla slangen. Korrosion initierar mellan de icke-flexibla delar av slangen Korrosionshastigheten ökar med tiden och det orsakar små hål på ytorna. Baserat på testresultaten är den mest lämpliga stället för livslängdsundersökningar Scanias komponentprovceller. Genom att mäta slitagedjupet under repeterbara förhållanden som rekommenderas i rapporten och med hjälp av data från kundutfall, kan en livslängd uppskattas. För att kunna förbättra livslängden för de flexibla slangarna, rekommenderas att använda rostfritt stål typ 1.4828 vid tillverkning av dessa slangar bör varmformning användas, samt att avståndet mellan lagrena respektive tjockleken ökas. Flera tester med olika teststidsintervall behöver göras för att ta reda på nötningshastigheten. / This thesis was conducted at Scania CV AB with information based on corrosion and wear. The main goal of this work is to develop a test method to investigate the stripwounded hose’s lifetime. A series of tests were performed to understand the reasons of their failure and a FE analysis was performed to verify the results obtained from these tests. It was observed that a large part of stripwounded hose becomes stiff due to high temperatures of the exhaust gas. The high temperature leads to plastic deformation of the hose. In contrast, the three first windings closest to the engine keep their flexibility due to continuously engine vibrations while there is sign of wear between the layers in these three windings more than other parts of the stripwounded hose. Hence, it is concluded that the main reason for stripwounded hose’s unpredictable failures is wear which leads to crack initiation. The crack propagation is in type of low cycle fatigue which means that it takes a short time until the stripewounded hose breaks. Corrosion is initiated between the non-flexible parts of the hose. The rate of corrosion is increased by time and causes small holes on the surfaces. According to results from the experiments the most suitable location for the lifetime investigation is Scania’s component test cells . Several tests with different time spans needs to be performed. By measuring the wear depth rate under repeatable test conditions and bycomparing with stripwounded hoses from customer trucks, a lifetime can be estimated. To improve the fatigue lifetime of the stripwounded hoses, it is recommended to use stainless steel of type 1.4828, manufactured through hot-forming with larger distance between layers and thicker layers to find out the wear rate.