'Spectral Analysis Bond Inspection' (SABI)

This proof of concept project aims to demonstrate the potential of an innovative new
ultrasound probe, electronics and analytical software to detect damage to, and flaws in,
complex composite materials and components. Advanced composite materials, particularly
Carbon Fibre Reinforced Plastics (CFRP), are being increasingly used for critical structures
and components in both civilian and military aircraft. Their mechanical stiffness and
toughness, coupled with reduced weight and immunity to corrosion, make them highly
desirable when compared to traditional metal alloys. However, their weakness is their
vulnerability to impact damage.
A particular problem is low-energy impact damage that does not leave any visible superficial
damage but can result in potentially catastrophic, invisible, damage within the composite. In
particular situations, such as control surfaces and engine cowlings, the composite structure is
more complex, generally including a honeycomb structure bonded within the CFRP to
provide greater stiffness. Conventional high frequency (2-10 MHz) ultrasonic Non Destructive
Testing (NDT) can detect flaws (e.g. de-lamination) in CFRP/GRP material but because high
frequency ultrasound is rapidly attenuated in air they cannot detect bonding failures or core
damage in honeycomb and foam cored materials.
Baugh and Weedon (B&W) is proposing a novel low frequency ultrasound probe that will be
able to detect bonding or other structural failures in the latest multi-layer composites used in
advanced aerospace designs. Unlike current approaches the intended design will be capable of
being incorporated into a sensor array, to provide large area coverage and be “swept” over an
area to ensure a high probability of defect detection. The deliverable from the Project will be a
proof of concept demonstrator capable of detecting known flaws in a sample and presenting
the results in the form of a simple to understand “plan” view of the structure under test.