Analysis of the industrial application of electronic speckle pattern shearing interferometry

Dunlop Aerospace Braking Systems Plc. (DABS) is an international leading aircraft wheel and brake manufacturer. DABS had two wheel units, which were causing qualification problems in terms of fatigue cracking. Loughborough University (LU) proposed a novel robust non-contact, and non-destructive optical Shearographic Sensor System (SSS) for measuring and studying aircraft wheel deformation and behaviour when subjected to large static structural loading, with the aim to: i) Develop a novel robust optical sensor system for routine industrial use. ii) Demonstrate the novel and routine implementation for large scale structural loading/testing. iii) Identify high deformation concentration areas on aircraft wheel structures. iv) Provide routine quantitative data to DABS. v) Develop the novel understanding of error propagation, resolution and repeatability of the interferometer design. A series of laboratory experiments were conducted to demonstrate the functionality, repeatability, and reliability of the instrument to produce valid deformation data in a controlled environment in the optical metrology laboratory at LU. The SSS produced valid high quality deformation data using a Square Clamped Plate (SCP). The data was calibrated and correlated using a Linear Variable Differential Transducer (LVDT) system. The repeatability and reliability tests showed a high repeatability range of the SSS in the controlled environment of (5.95x10-8m) in the case of 10mm Horizontal lateral shear with Collimated laser illumination (10HC) and (1.22x10-7m) in the case of 10mm Vertical lateral shear with Collimated laser illumination (10VC). This accelerated the transfer of the SSS into the industrial environment at DABS, where heavy testing machineries operate routinely, which generated additional error and variation sources to the data produced by the SSS. A series of deflation/ inflation pressure and static structural load tests were completed on Boeing757 and BAe 146 wheel. The results showed that the data quality was sufficiently good to allow DABS to validate the FE model of the wheel, in spite of the surrounding uncontrolled and disturbing environment. Further repeatability and reliability tests were completed on the BAel46 wheel. This was to identify and discuss the engineering reality of the repeatability, reproducibility, and accuracy of the SSS, The results showed that the SSS achieved a better repeatability range in the laboratory in comparison to the industrial workplace at DABS, whichwas (1.60xl0-5m) and (1.08xl0-5m) forthe same shearing directions. As a result, DABS was provided with large amount of numerical data from the Boeing757 and the BAe142 wheels, in partial derivative and displacement format, ready for FE model validation. Commercial exploitation of the SSS into other industrial sectors and for various applications was completed via Laser Optical Engineering Ltd.