Automotive industry faces numerous evolutions regarding environment regulations and parts reliability. Through the specific case of a cylinder head, actual and forthcoming challenges for low-cycle and thermal–mechanical fatigue design in an industrial context are presented. With a description of current design approaches and highlighting limitations, this work focuses on variable loadings, constitutive models and their interaction with the environment, fatigue criteria, and structure validations, the four major steps to meet a reliable design. The need to carry out extended experimental databases for different complexity levels is emphasized to provide a better understanding of loadings and their impact on the strength of materials and structures, as well as the production of more physically-based models that are easier to identify and lead to higher levels of reliability in the thermal–mechanical design process.

a b s t r a c tThis paper proposes two algorithms for better controlling the size of time increment in case of returnmapping integration scheme for elasto-viscoplastic constitutive models. Computation errors in terms of local stress-strain loops in Finite Element Analyses could indeed have a very strong impact on fatigue lifetime estimation protocol if time increment size are freely chosen by the FE solver. Proposed algorithm enables both to precisely describe the transition between elasticity and viscoplasticity and to avoid too important increase of time step during large viscoplasticity evolutions. The precision of the computed mechanical answer has been successfully tested for different kinds of multi-axial and anisothermal loading conditions on simple finite element and more complex meshed structures. Fatigue lifetime estimation errors have also been investigated for stabilized stress-strain cycle and common criteria and the proposed algorithm show very precise results with a limited computation time increase and without drastic limitation of the time increment size.

Abstract. Through the peculiar case of an automotive cylinder head, actual and forthcoming challenges for low-cycle and thermal-mechanical fatigue design in an industrial context are presented. A special focus is applied on variable loadings, constitutive models and their interaction with the environment, fatigue criteria and structure validations.