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Effect of Different Defects of Spot Welded Joint in Automotive Body on Fatigue Strength: Experimental and Numerical Investigation

Ganjabi, Mohammad Amin | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52345 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Farrahi, Gholamhossein; Mehmanparast, Ali; Reza Kashyzadeh, Kazem
  7. Abstract:
  8. On average there are to resistance spot welding connections per vehicle. The quality of these welding directly affects the quality of the finished product and the strength of the vehicle against various loads, including road roughness, different maneuvers and even sudden impacts from accidents. During the spot welding process, unintentional failures occur due to the wrong choice of current, force and time. The aim of this study is to investigate the fatigue strength of three-sheets welding joints in numerical and laboratory methods, considering the defects of (Undersize weld, Stick, edge of sheet metal and Edge of sheet metal-SECANT) . For this purpose, a healthy spot welding model was first developed and simulated in finite element software. Then the qualitative parameters of the spot welding including the diameter of the welding core, depth of penetration and residual stresses were extracted. Then, similarly, the spot welding process is simulated for imperfections of the (Undersize weld, Stick, edge of sheet metal and Edge of sheet metal-SECANT). The linear regression formula developed in previous research was used to obtain the parameters of force, current and quadrupole time of the welding process with low defect welding Undersize weld. Then, under predetermined boundary conditions, the tensile strength of these joints (healthy and defective resistance spot welds) is obtained as a force-displacement diagram by finite element simulation. Also in this study, considering the residual stresses of the welding process, the fatigue analysis of joints is investigated. The tensile and fatigue tests were also performed on the joint sample of three sheets of healthy resistive spot welds and compared with the simulation results. The results of this study show that the variation of weld Undersize weld has a significant effect on the tensile strength and fatigue life of the weld joints. Thus, by reducing the welding Undersize weld by %, the tensile strength and fatigue life of the joint under the same loading decreased by and %, respectively. For Stick defects, the tensile strength and fatigue life of the welding core decreased by % percent and fatigue life by and %, respectively Also, for edge of sheet metal of the weld Undersize weld , the reduction of tensile strength and fatigue life of the joint are equal to and % respectively. for the Edge of sheet metal-SECANT defect for edge corrosion of the weld core, The tensile strength and fatigue life reduction were and % respectively
  9. Keywords:
  10. Resistance Spot Welding ; Simulation ; Fatigue Test ; Shear Connection ; Automobile Body

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