Acoustic Emission Testing

Aerospace Damage assessment by Acoustic Emission monitoring

Landing gear fatigue testing is the aim to provide a health monitoring system for Messier-Dowty landing gear whilst undergoing certification testing using acoustic emission (AE) testing. Objectives include creating an early warning system for any possible fatigue or corrosion failure within the structure providing estimates of the location and size of the damage without visual inspection. It is possible to identify the load case information and the critical loads that cause damage.

Sources of AE include; fatigue crack growth, crack face closure, corrosion and mechanical noise. Sensors positioned on the test specimen will collect signals from all generated sources.

Source Identification

These recorded signals will be compared with a database of signals collected during extensive fatigue trials. Those signals that show fatigue crack characteristics are accepted.

Source Location

These accepted signals will then be located. Source location is based on the measurement of time difference between the arrival of individual AE signals at different sensors.

Final Analysis

The results of source locations will be plotted on to a model of the landing gear enabling a user with no prior experience in acoustic emission monitoring to identify regions of possible fatigue cracking.  Correct sensor selection allows crack detection.

Compact Test Specimen

Compact test specimens were used to provide AE signals from fatigue crack growth. Results showed that it was possible to identify 0.67mm of crack growth.

Four-Point Bend Test

Four point bend tests allow signals from crack growth from both notches and small radii to be collected. Small radii have been identified as causes of crack initiation in landing gear.

The side stay is a major structural component of a landing gear.

Structural health monitoring is paramount in the aircraft industry, not only to ensure the safety and reliability of aircraft in flight and to ensure timely maintenance of critical components, but also increasingly to monitor structures under test for airworthiness certification of new designs.