| The fault of mechanical main parts usually result in production breaking and waster, the sever fault even do harm to person. Plate and beam is the element of over head traveling crane. Crack damage of plates and beams is the main fault forms of structure. With more and more large structure appearing in our lives, if the crack were not diagnosis in time, the expanding crack would damage the whole structure in the end. Once the accidence occurred, it cannot be recovered. To avoid accident in advance, fault of both structure and equipment is necessary. In order to measure the position and degree of damage in time , the domestic and international scholar has done a large amount of work, presenting a series of method of discerning structure damage, but the law based on mode parameter damage discern is still the most generally most basic method. Crack diagnosis to beam is more perfect than of plate. Crack diagnosis to plate will be emphasized in this dissertation. The diagnosis to crack is based on vibration without considering the stress influence from the crack tip.FEM numerical simulation to cracks with different location, different length and different angle is taken with ANSYS. Mode tangent angle variance ration (Δtg a ) of the cantilever plate in two directions is gotten from the the beam the mode slope variance ratio.Over head traveling crane is a complex structure with random load and actuator. It is necessary to make a good choice with appropriate diagnosis index. Two diagnosis indexes are used in this dissertation. Influence both to natural frequency and Atga by different cracks is analyzed. Closer to the clasped edge, longer crack and lagle crack can all bring bigger influence to the dynamic features.Modal experiment of cracked cantileveer is carried out. A database of the relation between intact and cracked plate and mode and natural frequency is established. Compared the experiment with FEM numerical simulation, and evaluate errors in experiment data.
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