Thermomechanical Fatigue Life Prediction of Cylinder Heads in Combustion Engines

Abstract

While the deformation and damage behavior of aluminum cylinder heads under complex thermal mechanical loading has been the subject of numerous studies in the past, cast iron cylinder heads have been in the focus of thermomechanical fatigue (TMF) only to a minor extent. In this paper, a feasible procedure is presented to set up material models and estimate service life of cast iron cylinder heads under variable thermomechanical loading conditions by the use of computer-aided engineering tools. In addition, the influence of thermal load and mechanical constraints on TMF life span is shown. A specimen model is used for parameter identification in material model setup and a cylinder head model is used for correlation with cracking phenomena. Investigation of different thermomechanical load influences is conducted on the cylinder head model. The principal strain and energy based fatigue criteria are used in assessment of TMF lifetime for the cast iron family and material specific evaluation procedures are pointed out. The results highlight the importance of exact definitions of the boundary conditions and underline the sensitivity of TMF lifespan of cast iron cylinder heads with respect to the defined boundary conditions. Considering this sensitivity, an approach conforming to the engine development requirements is proposed. It is shown that both the crack location and fatigue lifetime are predicted with high accuracy.

Damage evolution in compacted graphite iron during thermomechanical fatigue testing

“…In this investigation, the cyclic mechanical strain and temperature variables differ with a 180 degrees phase shift, i.e. the maximum temperature coincides with the minimum mechanical strain, since this corresponds to the load situation normally felt in engine materials 1 . This is often referred to as out-of-phase (OP) TMF testing.…”

Thermo-mechanical and superimposed high-cycle fatigue interactions in compacted graphite iron

“…These life-limiting aspects can be alleviated by a sophisticated engine design which to a wider extent is based on computer simulations using commercial nite element (FE) software rather than on component prototype testing [1,2,3,4]. Such simulations are often divided into three uncoupled analyses, the thermal, mechanical and fatigue analysis [2], where the development of the latter is the subject of this paper.…”

Effects of Holding Time on Thermomechanical Fatigue Properties of Compacted Graphite Iron Through Tests with Notched Specimens

“…[1] Especially the valve bridges in cylinder heads, the areas between intakes and outtakes are severely subjected to so called out-of-phase (OP) loading, where a maximum tensile stress occurs at the minimum temperature level of the cycles, and vice versa. [1] According to Lo¨he et al, [2] multiple mechanisms take place during a thermomechanical out-of-phase cycle: plastic deformation, creep, oxidation, coarsening of the microstructure, and crack initiation and propagation. However, these damage mechanisms significantly depend on the material, temperature, frequency, mean stress level, and environment.…”