Random Vibration Fatigue Analysis of Brackets Installed on Tracked Land Vehicle

Abstract

Fulfilling the operational static requirements may not be enough for the materials used in engineering applications. Generally, failures occur due to dynamic loadings, especially in the military environments. If these dynamic loadings are cyclic, fatigue failure is more likely to occur even if stresses are under the yield strength. Vibration induced fatigue is one of the most important phenomena that is used in the structural analysis of components. Therefore, an accurate and reliable fatigue life investigations are necessary. In this thesis, theoretical and experimental random vibration induced fatigue analysis of mounting brackets that are installed on tracked land vehicle is carried out. Fatigue life estimations are conducted considering both uniaxial and multiaxial loading cases and results are compared. Assuming the loading case as uniaxial may cause overestimation of service life. Therefore, multiaxial vibration fatigue analysis will give more accurate results since it contains cross effects of loadings to each other. However, simultaneous multiaxial shakers are not commonly available in the world, so testing of these types of loadings may be challenging. To overcome experimental difficulties, multiaxial loading is converted to the equivalent uniaxial loading that gives same damage to the critical location of the structure. The loading data is collected in the time domain with the help of the accelerometers, then, it is transformed into frequency domain. Theoretical calculations are performed using frequency domain approach by developing a numerical code in MATLAB for fatigue life estimations of the structure. Also, using commercial fatigue life estimation software, nCode DesignLife, finite element (FE) analysis is performed, and FE model is verified using the modal testing results. In addition to the theoretical stuff, experiments are conducted to compare the results and verify fatigue life estimation of the structure.