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Experimental and Numerical Study of Multi-track Laser Cladding to Evaluate Effects of Residual Stress on Fatigue Life

Ghorashi, Mir Siavash | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 52204 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Movahhedy, Mohammad Reza; Farrahi, Gholam Hossein; Shodja Razavi, Reza
  7. Abstract:
  8. Laser cladding is a processing technique of layer-by-layer material deposition which is widely used to repair important components. However, tensile residual stresses generated in this process may result in detrimental effects such as crack, undesirable deformation and reduced fatigue life. A thermo-mechanical finite element model is developed to accurately predict residual stresses of the multiple beads laser cladding process with incorporating the cyclic plasticity into the analysis by utilizing the nonlinear kinematic hardening behavior. FE results are presented for Inconel 718, a material for which the laser cladding process is widely used. The FE results are compared with those of conducted incremental center hole drilling experiments on three specimens with different clad beads to evaluate the effect of cyclic plasticity modeling on the residual stresses. The results indicate that incorporating the nonlinear kinematic hardening model into the analysis can reduce the difference between its estimated residual stresses and the experimental results by about fifty percent comparing with the analyses without kinematic hardening. The results also indicate that the nonlinear cyclic plasticity modeling provides the opportunity to capture important phenomena of hardening and stress relaxation in the laser cladding. In order to quantitatively evaluate the destructive effect of laser cladding on the fatigue endurance, fatigue tests are first performed on the as-received and laser-cladded specimens. Then, microstructural analysis by scanning electron microscope (SEM) is carried out to identify the root causes of the drawback of laser cladding. Moreover, by employing a comprehensive laser cladding FE analysis considering cyclic plastic material modeling, the induced residual stress distribution is determined. To decrease the detrimental effects of laser cladding on the microstructure and residual stresses, the specimens are next subjected to severe shot peening treatment, and then extra set of fatigue tests are conducted on the specimens. The conducted experiments show that the laser cladding can cause the deterioration of the fatigue life of the specimens at about forty percent, and the damaged fatigue life can be almost restored by the severe shot peening. The experiments also indicate that the clad-toe zone is the weakest area concerning fatigue issues in LC specimens with or without shot peening post-process
  9. Keywords:
  10. Residual Stress ; Cladding ; Laser Clading ; Cyclic Plasticity ; Fatigue ; Shot Peening ; Inconel 718 Nickel Based Superalloy

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