A B S T R A C T In this paper thermomechanical fatigue assessment in the automotive industry is discussed.The design strategy is based upon a consistent approach of the thermomechanical loading, the mechanical constitutive law of the material, the damage parameters and the fatigue strength criteria. The good understanding of these different steps allows one to perform predictive calculations of automotive parts subjected to thermomechanical loading. The main hypotheses and modelling choices are presented and results are illustrated by a series of computations on real 3D structures. Cracked area and lifetime prediction are described in the case of aluminium alloy cylinder heads subjected to transient thermal loadings.Development in numerical simulation over the past 20 years have led to increased performance of numerical tools and the development of new algorithms. Today this enables ever-quicker calculations of loads and displacements in structures. Nevertheless, whilst academic work is quite active few studies have been performed on structures subjected to multiaxial thermomechanical loading. Only a small number of components in automotive technology experience thermomechanical loading cycles of a severity capable of producing low-cycle fatigue. Most of these parts are related to the engine: cylinderheads, exhaust manifolds, crankcases, . . . . It is important to note that the low-cycle fatigue problems in such engine components are related to the start-operate-stop cycles and not to the combustion cycles. Therefore they involve large temperature changes. A previous study was dedicated to cast-iron exhaust manifolds. 1 This work showed an original comprehensive approach, which resulted in a reliable prediction of damage location and of lifetime in spite of basic assumptions like the separation of the damage and the mechanical constitutive behaviour. The paper presents an overview of this approach and the specific details of the applications in the case of the cylinder head in aluminium. The results are illustrated by a series of computations on real 3D structures. The words comprehensive approach shall denote the following series of items:Correspondence: Jean-Jacques Thomas. r thermal analysis, r elasto-viscoplastic mechanical analysis and r fatigue analysis.These three aspects are linked together; the thermal loading and the material behaviour determine the mechanical response of the structure and from that the fatigue strength of the structure can be estimated through a damage indicator and a pertinent fatigue criterion.For a design strategy, one should not concentrate separately on these four aspects of the problem. It should be a comprehensive approach to obtain an important robustness and to allow its integration in a development process 2 by the ability to answer the asked question in the appropriate time. That is to say in our case: is the fatigue strength of the component guaranteed or not before the production of tooling for a prototype? The cylinder head is made of an aluminium alloy (in this case an A...
In this work a numerical method for the design of components submitted to severe cyclic thermomechanical loading is developed. This tool is based on a Finite Element (FE) analysis. In a first part the temperature distribution is obtained and used in the second part for the mechanical computation. The analyses use the description of the geometry of the part, a precise information of the thermal properties, an appropriate behavior of the material at low and high temperature and a good assessment of the boundary conditions (heat transfer coefficients, contact, ...). This method is applied to asses the low cycle fatigue design of a diesel turbo-charged exhaust manifold in cast iron. These calculations, failure location and lifetime estimation, obtained on two versions of this component, are compared to experimental data. The results show a good agreement in terms of critical zones location and of lifetime comparison in both versions and permit thus to classify the versions.
The optimal design of parts submitted to thermomechanical loadings is a key issue for the safety and quality assessments of structures. In this context, the present paper discusses the choice of a behavior model and the determination of its parameters. For cast iron and aluminum alloy applications, two constitutive laws are compared : one is based on a classical unified viscoplastic model and the other is based on a two layer plastic-viscous rheological model. The following discussion shows that the use of anisothermal experiments is very important for the identification of material parameters and that simple models can be successfully applied for the predictive lifetime assessments of large 3D structures.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.