Coin tapping with a small hammer has been traditionally used to inspect honeycomb structures in aircraft. Personal skills that take a long time to acquire are indispensable to keep accurate detection for coin tapping method, which depends on the difference in tapping sound between normal and debonded area. Since coin tapping method depends on human senses, it makes difficult to conduct inspection in a noisy environment and it is almost impossible to sequentially obtain accuracy over a long period. In addition, the most fundamental issue in coin tapping method is that it is not quantitative.
Mitsui has developed the Woodpecker to solve these issues. Woodpecker has made it possible automatic tapping by adopting a solenoid driven hammer. It employs a CPU to comparatively evaluate the output of a force sensor attached to the hammer. The quantified results are indicated by LEDs and digital values. Its compact body and lightweight allows single handed operation, resulting in a handy detector with excellent cost performance.



Impulse Wave on Debond



Advantages of Tapping Method

When inspecting honeycomb or similar structures, tapping method has advantages over methods using an ultrasonic in the following respects. The skin becomes debonded from the core and comes up loose, or it remains attached to the core even if debonded. The former debond can be detected with ultrasonic method, but the latter cannot, because the debonded skin and core would transmit the sound waves as if they are still boneded together.