A Frequency based Free Vibration Analysis of a Hat Stiffened Plate for Identification of the Damage

Hat section has excellent properties, in bending about its both principal axes. Due to this property, hat section is generally used to increase the strength of the parent structure. Therefore, hat stiffened structures, finds many industrial applications like in automobile, airplane, and naval ships. In all such applications, an inherent structure that finds is a hat stiffened plate. This paper has presented an analysis of diagonally hat stiffened plate structure for the detection of damage caused due to the breaking of spot weld connections. A transformed section method was used to model the structure at intact condition and solved by Euler- Bernoulli's equation to find its natural frequencies. Similarly a model for damaged hat plate structure was prepared. Using the conjugate beam method, a static deflection of lumped masses was determined, to solve the matrix equation of motion. Eigen values extracted from the solution and corresponding natural frequencies were found in the damaged condition. A finite element (FE) model of the hat plate structure was solved by ANSYS package, for both intact and damaged conditions. An experimental modal analysis (EMA) had conducted to validate the results. A good agreement found among the results from all the three approaches