Thermomechanical Fatigue of Lost Foam Cast Al–Si Cylinder Heads—Assessment of Crack Origin Based on the Evaluation of Pore Distribution

Abstract

In automotive cylinder heads, thermomechanical fatigue (TMF) leads to crack initiation within the critical loaded sections. This effect becomes even more relevant in lost foam cast cylinder heads since its system-dependent porosity shows a significant influence on the lifetime under TMF loading. This work covers the identification of a criterion for crack initiation in order to provide the basis for an effective quality control with improved statistical safety by nondestructive testing. Specimens extracted from lost foam cylinder heads were investigated by uniaxial TMF tests, X-ray micro computer tomography (μCT), and scanning electron microscopy (SEM). Due to pore analyses on a global and local scale, it is concluded that pore networks are crucial for crack initiation. Thus, a tool for computation of pore accumulations from μCT data containing interaction criteria by Murakami was developed in order to assess the crack origin. The consideration of pore accumulations significantly improves the predictive accuracy compared to the consideration of single pores.

Metal Plasticity and Fatigue at High Temperature

“…As a part of this Special Issue, researchers were invited to submit their innovative research papers aimed at providing a state-of-the-art knowledge on the topic of metal plasticity, creep deformation and fatigue strength of metals operating at high temperatures, with emphasis on both experimental characterization and numerical modeling of material behavior. A total of eleven research papers were published [1][2][3][4][5][6][7][8][9][10][11].…”

“…Thermo-mechanical fatigue (TMF) is studied in [5][6][7]. The paper written by Szmytka et al [5] provides an overview of a TMF design protocol through the analysis of the specific case of a cylinder head, which summarizes the studies led by the authors over the last five years.…”

“…Four typical issues in high-temperature design-loading identification, aging and constitutive models, TMF criteria, and validation tests-are addressed and critically analyzed, while some improvements are proposed. In [6], Wagner et al work on the identification of a criterion for crack initiation to provide the basis for a nondestructive quality control of TMF-loaded porous components with improved statistical safety. The paper by Ghodrat et al [7] presents an adapted version of Paris' fatigue crack-growth law where cyclic plastic strains at the crack tip are considered as the parameter that controls crack growth.…”

“…Papers in this Special Issue addressed different types of material, from stainless steel studied by [1,2,4,10], to aluminum alloys investigated by [3,6,9], Ni-based supper alloy in [8], spheroidal graphite iron by [7], and copper alloy discussed in [11].…”

“…The developed constitutive methods have, in most cases, been compared to experimental data obtained with tensile tests [3], fatigue tests [3,4,8], TMF tests [6,7], creep tests [2], and stress relaxation, aging tests presented in [9].…”