Advanced composite materials such as carbon fiber reinforced plastics (CFRP) excel
in mechanical properties like the specific strength and the specific rigidity as compared with
metallic materials, and have excellent properties in electrical property and thermal characteristics. In recent years, CFRP have been used in many fields in addition to aerospace structures.
On the other hand, evaluating the dynamic behaviors and the strength characteristics of CFRP structures is much more complex than in a metallic material.
The transverse stiffness of composite materials is much smaller than the in-plane stiffness, and the mechanical properties of composite
structures degrade severely by external impact events. When the impact loading generated by the foreign body collision such as the tool drop
is applied to the composite structures, internal damage such as delamination, fiber breakage, and matrix crack is caused easily which is difficult to detect from the surface.
Those internal damages need to be found nondestructively in order to avoid a remarkable decrease in the rigidity and strength of the structures. Usually, the inspection
method using ultrasonic wave or X rays has been used for the detection of damages in composite materials, but the method is labor-intensive and cannot disregard the existence of a human error.
Recently, the technology that is called a structural health monitoring has been developed remarkably, and the
research activity has been done actively. The structural health monitoring is the technology that automatically observes the health state of the structure using measurement information from the sensor built into the structure.
Especially, information on the impact load that causes damage is very important for doing an effective diagnosis and an evaluation of the structure safety. If information on the maximum impact load and the impact energy is obtained in real time, the occurrence of the impact damage can be predicted. Thus, when monitoring the impact load from the sensor response becomes possible in real time, structural health can be evaluated automatically, and great improvement of the structure safety becomes possible.
The present paper discusses an experimental identification method of impact load acting an CFRP panels. Especially the present paper develops an impact load identification method under multiple loading.
edited by Takao UMINO