INDiANA

Since decades, due to environmental considerations and cost reduction objectives, automotive manufacturers conduct a downsizing strategy, particularly for engine parts as cylinder blocks or cylinder heads. In the later case, aluminum alloys were first chosen to replace cast-iron and, since a few years, Lost Foam Casting (LFC) is introduced in order to replace Die Casting (DC) process as a matter of geometry optimization, cost reduction and consumption control. One of the consequences of this downsizing strategy is an increase of the engine specific power and of the combustion fluxes received by the different components. The cylinder head becomes therefore one of the most critical part of the automotive engine, submitted to high thermomechanical loadings during the start-stop operation. A major specificity of LFC process is the fact that the cooling rate is relatively slow compared to DC process, which creates a coarser microstructure when measured in terms of Dendrite Arm Spacing (DAS). Besides, the number of voids and inclusions (intermetallics, oxides) increase and form clusters. Recently, it has been demonstrated by some of the partners of the present project that Low Cycle Thermomechanical Fatigue (LCF/TMF) damage of LFC components results from a competition between porosity, intermetallic and eutectic phases which can reduce drastically, in some cases, lifetimes and, consequently, components reliability. The main objective of INDiANA project is a fine understanding of the thermomechanical fatigue process of such alloys in order to improve fatigue criteria through a multiscale modeling approach and, consequently, the target reliability of the engine components. This requires 3D metallurgical investigation, isothermal and non isothermal fatigue testing with 2D and 3D state-of-the-art full-field measurements, microstructure computations and non-linear homogenization techniques that will bridge the gap between the current phenomenological LCF modeling and the full-field micromechanical simulations. The main steps of this proposal are thus (i) to obtain a sound casting of a fatigue specimen representative of the component microstructure with controlled defects both in location and size and to characterize this cast specimen in 3D in order to validate the casting process and to obtain 3D data for numerical models, (ii) to understand the low cycle (thermo)mechanical fatigue micromechanisms by using both in-situ tests under X-ray microtomography and conventional LCF/TMF tests with coupled periodic Digital Image/Volume Correlation, (iii) to propose a predictive fatigue model for heterogeneous and defective materials based on numerical and analytical non-linear homogenization techniques and micromechanical analysis and (iv) to integrate these results in an industrial probabilistic based fatigue design strategy. This industrial integration may lead to the careful adaptation of the laboratory methods to propose a macroscopic design protocol from physical microscopic observations and mechanisms. Success of INDiANA relies upon the combination of the existing expertise of the different partners in X-ray microtomography, fatigue micromechanisms analyses, full-field measurements, casting process, numerical models and micromechanics. In addition, a major strength of the proposed consortium is the acquisition of a strong industrial expertise of components fatigue design over several years of active collaboration via common PhD thesis, postdoctoral and internships supervisions. This research project has also a potential medium-term impact upon environmental aspects by the process optimization of structural reliability and weight reduction.