Lifetime assessment of cylinder heads for efficient heavy duty engines Part II: Component-level application of advanced models for thermomechanical fatigue life prediction of lamellar graphite cast iron GJL250 and vermicular graphite cast iron GJV450 cylinder heads

Paper #:
  • 2017-01-0346

  • 2017-03-28
Increasing the efficiency of heavy duty internal combustion engines is directly related to increasing specific power and, thus, increasing combustion pressure and temperature. One key component of the engine is the cylinder head which must withstand these higher temperatures and higher pressures. The path of increasing loads intensifies design conflicts, as e.g. associated with the fire deck of cylinder heads: the deck should be as thin as possible to avoid critical thermal stresses during the low frequency thermal transients but sufficiently thick to avoid failures due to the high frequency combustion pressure. A superficial solution of the design conflict is the usage of superior cast iron materials. Vermicular graphite cast iron show higher strength and fatigue resistance than the classically used lamellar graphite cast iron. However, due to their lower thermal conductivity, higher thermal stresses will arise. In this paper (Part II), the advanced model for fatigue life prediction of lamellar graphite cast iron GJL250 and the vermicular graphite cast iron GJV450 of Part I is formulated for three-dimensional stress states, so that it can be applied in a post-processing step of a finite-element calculation. To obtain reliable stresses and (time dependent plastic) strains in the finite-element calculation, a time and temperature dependent plasticity model is applied which takes non-linear kinematic hardening into account and allows the description of the tension-compression asymmetry observed for cast iron materials. The material properties of the plasticity model are identified from the results of the uniaxial test. The plasticity model and the model for fatigue life prediction are applied to asses the lifetime of heavy duty cylinder heads.
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