DefinePK

Abstract

Due to limited fatigue strength, the fatigue cracks ours in the material under service conditions. Cracks are also found inside the material due to poor manufacturing processes. Single sided cracks are produced in the material as a result of fluctuating loads. Crack generally may be of two types, transverse cracks and oblique cracks. The magnitude and orientation of the manufacturing defect decides the origin of either transverse cracks or oblique cracks in the beam. Hence it is very essential to study the effect of top side and bottom side oblique cracks on the beam. Out of two cracks i.e. top side or bottom side cracks, one crack will be comparatively more critical, hence it requires much attention. Crack get propagated in the material due to the action of fatigue load and at the end, it gives catastrophic failure. Understanding the dynamics of the cracked beam is of most importance because various vibration parameters like natural frequency, resonant amplitude of uncracked and cracked cases of a beam used as a basic criteria in the crack detection by vibration methods. In this study, most practical spring steel material (EN 47) is considered for the cantilever beam. ANSYS software used to find the natural frequency and zero frequency deflection of cracked cases of beams. Stiffness of defective beams is calculated by a conventional formula (Load / deflection). In this study, it is found that the value of stiffness and natural frequencies for top side cracked cases are comparatively on lower side than bottom side cracked cases when crack angle equal to 200. It is also found that up to 100 crack angle, the algebraic sum of stiffness of top side cracked cases is equal to the algebraic sum of stiffness of bottom side cracked cases. This condition is true also for natural frequency. It is also observed that, when crack angle is 200, then presence of top side crack and bottom side crack of the same configuration in the cantilever beam is a function of natural frequency, when cantilever beam is of a square cross section.