A computational approach to thermomechanical fatigue

Abstract

This paper presents a computational approach for the lifetime assessment of structures under thermomechanical loading. One of the main features of the work is the search for simplicity and robustness in all steps of the modeling, in order to match the proposed method with industrial constraints. Among the peculiarities of the engineering environment are the imposed commercial computer programs and the short time delays for manufacturing. The proposed method is composed of a fluid flow, a thermal and a mechanical finite element computation, as well as a final fatigue analysis. The efficiency of the approach is proved by comparison with experimental results on prototype manifolds. The numerical results match both the localization of the damage zone and the lifetime

Impact of microstructure, temperature and strain ratio on energy-based low-cycle fatigue life prediction models for TiAl alloys

“…This slight hardening is not observed for the specimens tested with a negative strain ratio at 750°C. Contrary to Constantinescu et al [9] or Moumni et al [10], we noticed that fatigue criterion coefficients, α et β, are strongly dependent on microstructure, temperature or strain ratio (see Figure 5). …”

A study on the damage evolution of P91 steel under cyclic loading at high temperature

“…Finally, the rate of reduction of the stress level increases rapidly leading to failure (Nf). The Nsta and Ntan correspond to the beginning of the constant rate evolution of the peak stress level and the beginning of the stress drop in the third stage, respectively, as suggested by Constantinescu, Charkaluk [17]. The number of cycles to failure, Nf, is defined, according to the BS7270:2006 standard, as the cycle number at which the maximum stress has decreased by a prescribed percentage from that predicted by extrapolation of the second stage stabilisation curve.…”

Probabilistic thermal-mechanical fatigue criterion for lost foam casting aluminium alloys based on 2D/3D porosities distribution

“…2D analyses also tend to sometime overestimate the presence of very small pores that usually lead to bad description of the probability of failure for large number of cycles. The porosities distributions are then introduced in the computational approach used to design engine parts against TMF [3]. Under a basic assumption of growth equation of pores from an initial size a 0 to a final size a f at N f characterizing a macroscopic crack initiation, we develop a fatigue criterion under a probabilistic form as proposed by [4].…”

“…Lifetime distributions obtained by the present method and by [3] and [4] are compared. The direct prediction results show a small improvement when compared with the usage of a standard fatigue criterion in [3] but the main benefit of the proposed criterion is, as in [4], the estimation of a probability density function both as a simple relation between microstructure distribution and macroscopic lifetime observations and as a complement to a statistical distribution of tests which is generally very expensive. The proposed criterion tends to show more realistic lifetime distribution than in [3] and provide satisfying results for A319 and A356 LFC aluminium alloys.…”