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Statistical Analysis of Surface Hardness for Determination of Residual Stresses

Mousavi, Mohammad Saleh | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: English
  3. Document No: 46530 (58)
  4. University: Sharif University of Technology, International Campus, Kish Island
  5. Department: Science and Engineering
  6. Advisor(s): Hossein Farrahi, Gholam; Faghidian, Ali
  7. Abstract:
  8. Residual stresses are stress fields that exist in the absence of any external loads. All mechanical processes can cause deformation that may lead to residual stresses. It is well established that virtually no material, no component and no structure of technical importance exists free of residual stresses. However, in practice, the knowledge of the true distribution of exiting residual stress is rare. The residual stress fields are very challenging to evaluate, independent of the measurement techniques. The important aspect about the residual stress determination is that often true distribution is unknown in the engineering specimen. A simple and non-destructive method to measure residual stress is a necessity. Although determination of surface residual stress utilizing surface hardness measurement is a fast and effective method compared to other methods. In the present method, the empirical and experimental studies are performed besides the finite element analysis. The CK-45 steel is used in the present study. A fixture is designed and manufactured here for performing four point bending test. A symmetric two dimensional finite element model is used with utilizing ABAQUS finite element software to evaluate the residual stress field in specimens and then the surface hardness is experimentally measured. Afterwards, a comprehensive study is done on the hardness test data via statistical analysis. It was found that, compared to Bayesian-Cauchy reference method, the Shepard method has almost the same level of accuracy with less computational cost and could omit the outlier data while the Gaussian simple average results are affected by the outliers. Finally the mathematical relation between the experimental surface hardness data and FE-based predicted residual stresses is obtained with utilizing the linear regression analysis. It is found that the surface hardness of CK-45 steel caries linearly via the bending residual stress. An empirical linear relation between the surface hardness and residual stress is presented for CK-45 steel
  9. Keywords:
  10. Residual Stress ; Finite Element Method ; Statistical Analysis ; Surface Hardening ; Four Point Bending Test

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