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Optimization of Fillet Rolling of Ductile Cast Iron Crankshaft in Order to Increase the Bending Fatigue Resistance

Eftekhari, Mohammad Reza | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 42665 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Farrahi, Gholamhossein
  7. Abstract:
  8. In order to reduce stress concentration, crankshaft is designed with a fillet radius in the corner of pin to web contact. Fatigue fracture under bending load initiated in fillet region is known as the main failure mechanism of crankshaft, so fillet rolling process is used to increase the bending fatigue resistance of the crankshaft. This process induces compressive residual stress under fillet surface in order to retard the fatigue initiation and to slow fatigue crack propagation. At first, influence of fillet rolling process on bending fatigue resistance of a ductile cast iron crankshaft is investigated. The residual stress distribution under the crankshaft fillet induced by this process and stress distribution near fillet under bending load is determined by using finite element analysis in ABAQUS software. Based on linear elastic fracture mechanics approach, an equivalent stress intensity factor on plane is obtained. By comparing this equivalent stress intensity factor with threshold stress intensity factor, possibility of failure before and after rolling process is determined. For validating the FEM results, they are compared with bending fatigue test results. For optimization of fillet rolling process, a mathematical model is extracted. Rolling load, fillet radius, rolling angle and bending moment are inputs and maximum equivalent stress intensity factor is output for this model. According to this model the optimum condition for maximum bending strength is determined. Experimental and theoretical results show that fillet rolling has improved the fatigue resistance of our specimen about 150% and fatigue fracture occurs in 35 degree plane. 6500 N rolling force, 40 degree rolling angle and 1.3 mm fillet radius are optimum parameters.
  9. Keywords:
  10. Crankshaft ; Residual Stress ; Fatigue ; Optimization ; Fillet Rolling

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