Non-destructive inspection of composite materials

Testing carbon fiber reinforced material for damage, wear, and useful life


Intentionally introduced damage

Conductive composite materials, such as carbon fiber reinforced composite materials, are rapidly gaining widespread use for a variety of applications in aircraft, spacecraft, and civil infrastructure. Characteristics such as strength-to-weight and malleability combined with decreasing costs are making it a go-to material for component designers and manufacturers.

But even with excellent strength and service life of these composites, it is necessary to monitor the structural condition of the material to ensure the ongoing health and safety of the overall structure in many applications.

Electrical resistance measurements have shown some promise in detecting damage in the fiber composites, particularly in those systems where embedded sensors or electrical networks are used. In these cases, electrical connections are attached to the structural component, and electrical resistance is measured. Since a fracture of carbon fibers increases the overall electrical resistance, increased electrical resistance is indicative of damage. While this method is effective for identifying certain types of damage in the material, other types of damage and or deterioration of the composite component may occur with little or no change in measured electrical resistance. Consequently, the composite may suffer serious structural damage or deterioration without warning.

Army researchers have greatly improved upon the above method of inspecting components made from conductive composite materials by measuring the impedance of the material through different pathways of the component. An impedance measurement of the component is made and compared to the measurement of a known blank which is structurally sound. Variations from the known are not only indicative of damage but given the multidimensional measurement derived from impedance data, the magnitude, and type of damage can be ascertained. The type of damage could include fracture of carbon fibers or carbon nanotubes, delamination, and the like.

This technology could be ideal for structural health monitoring of wind turbine blades.

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