Desser Tire and Rubber Company, Inc., and its affiliate repair station, Aero Wheel and Brake Service uses state of the art Laser Shearography testing testing for advanced interferometry non-destructive testing of aircraft and motorcycle tire carcasses.

Although this NDT measurement principle is not required by the FAA or the DOT, we feel such a system significantly contributes to the safety and quality features of our retreaded aircraft tires. Michelin and Goodyear Aircraft retread tire divisions use this same method for testing on heavy turboprop and jet transport tires.

As a matter of fact....our motorcycle tires may be more thoroughly tested than a new tire. Since most new tires are not subject to Laser Shearography, we can find areas of concern that have not ever been looked for by the original manufacturer.

Shearography Measuring System

Shearography was originally designed for strain analysis and inspection and evaluation of honeycomb and bonded composites. Laser Shearography is very sensitive to slight changes in surface strain due to subsurface flaws, and it is able to detect imperfections and defects such as belt-edge separations, bead blisters, undercure, liner separation and broken cord and ply construction in aircraft tires.

Our new system accommodates aircraft tires up to 49" in diameter, incorporating the latest computer imaging analysis software, electronic Phase-Shearing-Interferometry methods, integrated laser-diode CCD camera, and adapted optic illumination image analysis in real time. The system will store the recorded test on disc for accurate traceability by work order and serial number.

The benefits of this system are:

1. Dramatically increased carcass abnormality detection
2. Immediate carcass fatigue detection
3. Immediate internal damage of carcass detection
4. 100% validation of used carcass
5. Increased detectability of carcass deterioration

Desser Tire and Rubber Company, Inc., is the only aircraft tire retreader (excluding OEM's) that has taken this action to support the safety and reliability of our retreaded aircraft tire products for our valued customers. We will continue to look for ways to improve on the quality and processes in the products we provide. We look forward to supporting the needs of corporate and commuter aircraft operators worldwide.

Below is the technical aspect of laser shearography:

Basics of Interferometry
The following are Non Destructive Testing methods typically used for the inspection of new tires and casings for retreading:

Ultra Sonics - low resolution
X-Ray - other anomalies
Interferometry - interferometry is the core technology in our applications and therefore it is declared in more detail now

Interferometric Methods
In the past:
film-based Holographic Interferometry and Shearography

Today:
film-less "Speckle-Interferometry" and "Speckle-Shearing"
- Compact sealed optical setup with an
- integrated interferometer with CCD-camera
- integrated laser laser diodes
- Standard PC with an image analysis system

Principle of Measurement
the basic effect is the interference of light waves
- fast and sensitive (~ 0,0004 mm fringe to fringe)
- safe, no radiation (machine setup is laser class1) to get this interference effect the light source has to meet the following main requirements:
- single frequency and constant over the time (coherent)
the measuring technique is based on:
- Michelson Interferometer for the Shearing-Setup
- Classic Phase-Shifting Method for Image Analysis
- Multiple Laser-Diodes
(US Patent, No. US 6,417,916 B1)

Test-Setup for tire testing:

• the measuring setup is positioned relative to the tire inside or/and outside
• the inspection of the tire is in sections of circumference
• the whole setup is within a chamber to stress the tire with a pressure differential

Measuring:
the surface is illuminated with coherent light and simultaneously observed with the shearing setup

two phase shifted images
- before and after stress load - are superposed and preprocessed

Courtesy of SDS Systemtechnik GmbH.