Damage detection on a plate based on proper orthogonal decomposition

Monitoring the structural health of engineering systems in a nondestructive way is becoming increasingly important, both for safety and economy reasons. Aircraft structures are highly vulnerable to damage which may be caused over the long-term, e.g. localized corrosion, or over the very short term, e.g. damage through impact. In the aerospace industry, safety is paramount and successful detection of structural damage is vital in an age in which the boundaries of materials applications are constantly being widened. Damage detection has always been a well researched area with new techniques being continuously developed. Many NDT methods are usually used locally for the detection of defects concentrated in small portions of the structure. Therefore, the examination of the whole structure may require several applications of the nondestructive techniques. It is desirable to have global NDT methods to reveal, quickly and cheaply, the presence of damage in a zone of the structure to which a local technique would then be effectively applied for a more accurate assessment. In general the vibration properties, determined from the response of a structure, are mainly the natural frequencies and the corresponding mode shapes and damping factors. Modal shape changes seem to be more effective than natural frequency changes as damage indicators and they do not need always a mathematical model of the structure to locate damage. This paper presents the numerical verification on a plate of a new vibration method that was originally proposed in Ref. [1]. The vibration properties chosen to characterize the dynamics of the structure are derived from the theory of the proper orthogonal decomposition (POD)Ref. [2], which is emerging as a powerful experimental tool in structural dynamics. POD provides the most efficient way of capturing the dominant components of an infinite-dimensional process with only a finite number of modes. This paper will present the numerical results based on the use of acceleration values, for various damage conditions of a plate.