Advanced composite materials represented by carbon fiber reinforced plastic (CFRP) have a feature of lightweight, high-specific strength and high-specific stiffness as compared with existing metallic materials. Therefore, CFRP has been widely used in many fields including aerospace field in recent years.
On the other hand, evaluation of the dynamic behaviors and the strength characteristics of CFRP structures is much more complex compared with that in metallic structures. Thus, effective evaluation of the structural integrity is very important during a long structural service period. It is well-known that mechanical properties of composite structure are remarkably decreased by external impact events since the interlaminar fracture toughness of composite materials is low. Due to transverse impacts caused by tool drops, bird strike or hail strike on composite structures, internal damages, such as delamination, fiber breakage, and matrix crack which are difficult to be detected by naked-eyes from the surface, are easily induced. Therefore, it is necessary to examine those internal damages by the nondestructive inspections such as X-ray or ultrasonic wave. These methods are expensive and time-consuming, which cannot be implemented in real-time, and may erroneously judge the damage existence due to human faults or errors.
Structural Health Monitoring (SHM) has actively been studied in recent years. SHM is able to automatically monitor the integrity of structures using responses from the sensors built into the structures. If the maximum impact load and the impact energy are obtained in real-time, we can estimate the damage occurrence caused by the impact load. In addition, inspection cost is able to be considerably decreased if impact load position is obtained. In this way, it is possible to greatly improve structural reliability and safety through SHM technology.
The present thesis discusses an experimental identification method of impact loading using Lamb wave. Especially, the present paper develops a rapid method for impact force identification on plate structures.
edited by Shun KUNO