Non-Destructive Testing (NDT) Aviation Tooling

Sofema Online (SOL) considers current tooling and best practices related to aviation & aerospace NDT Inspections

Introduction

The need to ensure high standards of quality and safety during manufacturing, assembly and while in-service is paramount and has led to the development of NDT standards and specifications.

The use of Non-Destructive Testing (NDT) within aviation maintenance and aerospace, in general, continues to increase with the advent of new techniques as well as the increase in data handling and analysis.

NDT can generally be split into two areas: surface techniques and sub-surface techniques and whilst NDT Tooling is increasing in complexity, traditional techniques such as tap tests or liquid penetration tests will always see a place in the hierarchy of available tooling.

Within the testing environment, we have a range of established tools, from tap testing through to advanced technologies, such as 3D computed tomography.

Visual inspections are the oldest and simplest method of non-destructive testing, seeking evidence of cracks, corrosion, and damages or other apparent defects for example misalignment.

Visual Inspection Tooling

Various equipment is used for visual inspections, including magnifying glasses, mirrors as well as video borescopes and remote viewing systems.

Liquid “dye” penetrant testing is a simple and quick method widely used in aviation to detect surface defects and structural damage in non-porous materials.

The item to be tested is coated with a highly viscous dye, the object is then wiped  leaving the dye which has penetrated the cracks to reveal any cracks and flaws.

Tap Testing (Acoustic Emission Testing) is the application of an abrupt force to the test object, a ‘tap test’ and the analysis of the results either audibly or using sensors to record the resulting stress waves and small deformations that occur.

Leak Testing

Involves pressurizing and immersing the test object in liquid to trace and record leaks.

Radiography

Radiography in aerospace applications typically uses X-rays for thin materials and gamma rays for thicker materials Images are typically captured digitally.

CT Scanning

3D computed tomography (CT) scanning, captures multiple X-rays of a test object to build up a cross-section view of the object on a computer.

Ultrasound

Ultrasonic testing is a common sub-surface technique which uses high-frequency sound waves to locate defects within a component or material. It is commonly used to detect defects in welds, fittings, joints, and adhesive bond quality. The technique records and analyses the reflection of sound waves.

Typical testing techniques include straight beam inspection, immersion testing and phased array inspections.

All of the techniques use an ultrasonic transducer, called a probe, which is used to send and receive soundwaves, the results being displayed as a graph on a screen.

Magnetic Particle

By inducing a magnetic field in the test object and applying magnetic particles to it either in dry form or suspended in a liquid, (may be coloured or fluorescent) it is possible to then examine the object for any evidence of defects.

This technique specifically is used to detect discontinuities in ferromagnetic materials.

Eddy Current

Eddy current testing is widely used in aircraft maintenance to detect cracks caused by fatigue or corrosion. The principle provides for an induced electromagnetic field within a conductive test object and measures the secondary magnetic field generated around the electric current to determine where flaws are.

Vibration Analysis

Monitors the vibration signatures generated (typically) by rotating machinery and interprets them to detect when something out of the ordinary occurs. Sensors, which use eddy currents, velocity sensors or accelerometers attached to the machinery, can be used for the monitoring.

Thermal - Infrared

Works by detecting anomalies in the heat flow in a material or component and involves the  mapping of the surface temperatures of an object and can be used to detect damage such as corrosion, delamination, voids and disbonds.

Laser Techniques

Most useful for detecting small flaws which may be only a few micrometers in size and includes techniques such as Shearography, holography and profilometry use laser light in different ways to detect deformation on the surface of objects and computer processing to compare stressed and unstressed conditions.

Further Guidance

Sofema Aviation Services (SAS) and Sofema Online (SOL) provide training for aircraft inspectors delivered as classroom, webinar & online. For details please email:  office@sassofia.com or online@sassofia.com