Basic principles of TAP Hammer (or Coin) Testing

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Sofema Online (SOL) considers the basic principles related to effective inspection of composite materials using TAP hammer method.


The following information identifies in details the basic principles of tap hammer testing as part of Aviation Composite Inspection techniques how to ensure effective practical training how to provide oversight of the correct performance of the task

>> Tap hammer testing, also known as tap testing or coin tap testing, is a simple and effective non-destructive testing (NDT) method used in aviation for the inspection of composite materials. It is primarily used to detect delamination’s, voids, or disbonds in composite structures.

>> Composite materials have different acoustic and vibrational characteristics compared to metallic materials. When the tap hammer strikes a defect-free area, the composite structure produces a characteristic sound and vibration response. Any variations in these responses indicate the presence of defects.

Basic Principles of Tap Hammer Testing:

>> The principle behind tap testing is simple. When a composite material is tapped with a small hammer or similar tool, it produces a distinctive sound.

>> When the hammer strikes the surface, it creates a compressive wave that travels through the material. If there is a defect, the wave will reflect back, altering the sound produced.

>> This sound is different when the material is solid compared to when there is a void or delamination.

>> Thus, by listening to the sound produced by the tap, experienced technicians can often identify potential issues.

Sound and Vibrational Differences:

The basic principle behind tap testing involves understanding the differences in sound and vibrational response between healthy and damaged composite structures.

>> A healthy structure will produce a sharp, crisp sound, while a damaged or delaminated structure will emit a dull, hollow sound.

Skill and Experience:

It's important to note that tap testing is as much an art as it is a science. The ability to accurately identify defects is often dependent on the experience and training of the inspector.

The tap hammer produces an audible sound when it strikes the composite surface. An experienced inspector listens to the sound produced and determines if it is consistent with a defect-free structure or if there are anomalies that suggest the presence of defects.

>> Different defects can produce distinct sounds, allowing for identification of specific issues.

>> The tap hammer also generates vibrations that propagate through the composite material. An inspector can place their hand or a sensor on the structure to feel these vibrations.

>> Defects in the composite, such as delaminations or disbonds, can alter the vibration patterns, resulting in variations that can be detected through touch or with specialized vibration analysis tools.

Ensuring Effective Training Including Practical

>> Provide trainees with a solid theoretical background about composite materials and the science behind tap hammer testing.

>> This includes the nature of composite materials, their common defects, and the physical principles of sound and vibration.

>> Carry out demonstrations on known good and bad samples to provide a practical illustration of the sound differences.

>> Use of various tools and samples with different thicknesses and composite materials can also be beneficial.

>> Encourage plenty of hands-on practice with supervision. Trainees should practice on composite panels with known defects until they are able to reliably detect these defects.


>> The training is conducted by knowledgeable and experienced instructors who can share practical insights, troubleshoot issues, and provide expert guidance.

>> Instructors should be well-versed in tap hammer testing techniques and composite inspection standards.

>> We need to Provide trainees with opportunities to inspect actual aircraft components or composite structures that have known defects.

o   This allows them to compare their findings with the known defects, reinforcing their understanding of tap hammer testing and increasing their proficiency.

Next Steps

>> Follow this link to the SAS Library to find & Download related documents for Free

Sofema Aviation Services ( offers the following 2 day course - Composite Material TAP Testing for Aviation Inspectors

For additional questions or comments – please email [email protected]




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