Sharif Digital Repository

Damage identification in uniform structures using Lamb waves has been studied by the researchers; however, as most of the industrial structures are not uniform, it is necessary to study more complex structures. In this thesis, a method of identifying notch specifications as damage in a symmetric stepped beam with arbitrary number of steps using Lamb wave propagation is presented. Initially, the study will examine and compare the Lamb wave propagation in uniform, symmetric stepped and asymmetric stepped beams. In the first stage, a method for detection of damage location in symmetric stepped beam is presented. This method is based on mode conversion phenomenon of Lamb wave modes. Moreover,... 

In recent years world countries faced with the ageing aircraft fleet problem which increased the repair and maintenance costs of these aircrafts. The non-destructive inspection methods are common inspection methods of old aircrafts. To do this, the aircraft must test with a certain time scheduled inspection programme in a hangar. This method not only increased the repair and maintenance costs but also affects the flight schedule. To overcome this problem, the structural health monitoring can use to online monitoring the structure and when it needs for repair, the aircraft send to hanger. So, repair and maintenance costs minimize while the flight schedule less affected. One of the structural... 

This study presents the best layout with optimal number of sensors for an arbitrary monitoring area based on reference free damage detection and localization. In recent years, damage detection approaches with the concept of instantaneous baseline measurements in Structural Health Monitoring (SHM) with lamb wave propagation are being developed. An array of spars transducers is obligatory in SHM with lamb wave propagation, so that designing the best one is a concern for many researchers. To obtain the best sensors layout, damage localization process should be done for all definable sensors layouts in many different crack positions. Obviously, doing this seems not practical as wave propagation...