Considerations Related to Aircraft Composite Inspection BVD & NVD

Sofema Online (SOL) www.sofemaonline.com considers the challenges related to the following damage of composite material

>> Barely Visible Damage (BVD)
>> and Externally Non-Visible Damage (NVD).

Introduction

Composite materials typically do not don’t show damage in the same way metals do. Additionally, composites are susceptible to hidden cracks and defects that may occur during manufacturing or service.

Impact damage that would cause visible dents in traditional aluminium airframes will instead cause sub-surface delamination that may not have any surface-breaking feature.

>> This phenomenon, known as Barely Visible Damage (BVD) or barely visible Impact Damage (BVID) creates new challenges to maintaining the highest level of serviceability

How to best address Barely Visible Damage (BVD) during aircraft composite inspection consider best practice techniques

>> Barely Visible Damage (BVD) in aircraft composite inspection refers to minor flaws that are difficult to detect using traditional inspection methods.
>> BVDs often include delamination, inclusions, voids, or micro-cracks which could compromise the structural integrity of an aircraft if left untreated.

Addressing Externally Non-Visible Damage (NVD) during Aircraft Composite Inspection

Addressing NVD in aircraft composite inspection requires a combination of knowledge, experience, and ongoing training.

>> Conduct thorough visual inspections:

o Visual inspections remain an important part of detecting NVD.
o Train inspectors to carefully examine composite surfaces for any signs of

>> abnormalities, including discoloured areas,
>> depressions,
>> cracks, or
>> delaminations.

o Inspectors should use appropriate lighting and inspection aids, such as magnifying lenses or borescopes, to enhance their ability to detect subtle damage.

General Comments

>> Consider the importance of meticulous visual inspection techniques for detecting BVD.
>> Train inspectors to look for subtle changes in surface finish, texture, or colour that could indicate damage.
>> Encourage the use of proper lighting conditions, magnifying tools, and inspection aids to enhance visibility.

Visual Inspection & Tap Testing

The main methods used by aerospace industries to inspect damage are visual inspection and tapping.

Visual inspection, which is quick and low-cost, is an obvious approach to assessing surface damage.

A tap test is one of the simplest non-destructive inspection methods which serves as a first line of defence when looking for flaws in composite structures.

Tap test works well for thin laminates, honeycomb structures and other sandwich panels, but it is not so effective on thicker parts.

When testing thick composite structures, deeply buried defects are inaudible to the human ear.

Tap test only requires a Tap Hammer or coin and a good sense of hearing. As the surface is impacted it emits a sound which is dependent upon the local stiffness.

When a tap occurs over a damaged area, where the local stiffness is lower, the sound is dampened, producing a “dead” tone compared to a tap over an undamaged region which produces a higher tone.

With this simple method, operators are able to quickly identify major flaws requiring further inspection of the structure.

Next Steps

Sofema Aviation Services (www.sassofia.com) offers the following 2-day course: Composite Material Introduction & TAP Testing for Aviation Inspectors – 2 Days

Visit the website or contact team@sassofia.com for more details.