Development of hall coefficient method for residual stress measurement
Chng, Kah Hoe
Date of Issue2017
School of Mechanical and Aerospace Engineering
Residual stresses play an important role in the aerospace industry, because they enable the prediction of the remaining life of crucial aero engine components. The evaluation of the residual stresses is usually done using non-destructive techniques, such as ultrasonic and eddy current conductivity techniques. Due to the non-invasive nature of evaluation, non-destructive techniques allow frequent routine assessments of the expensive components. However, these non-destructive techniques are currently unreliable because they lack selectivity to the measurements of residual stresses, and measurement results are affected by disturbance factors such as cold-work, microstructural changes, material anisotropy and hardness. Therefore, this prompts a need for the development of a non-destructive technique with a higher selectivity to residual stresses than the disturbance factors. In this project, a Hall-effect based non-destructive technique is used to characterise residual stresses with the Hall coefficient, which is largely affected by the concentration density of the free charge carriers and less sensitive to disturbance factors. Four experiments were conducted on the four fixture designs proposed in this project. The experiment using fixture 3 showed that Hall coefficients on both copper and IN100 specimens converged to a value that corresponds to that in literature, with the results from copper specimens achieving a 0.0067% accuracy after approximately 400 measurement cycles. In addition, experiment results using fixture 4 successfully showed a clear trend of an increase in the Hall coefficient values with the increase of tensile stress on IN100 specimens, using spot welded electrodes.
Final Year Project (FYP)
Nanyang Technological University