The effect of temperature on TMF(HCF) crack initiation endurance

https://doi.org/10.1016/j.ijfatigue.2020.105559Get rights and content

Highlights

  • •

    For Tmax in the range 400–480 °C, superimposed HCF loading cycles with strain amplitudes up to a threshold value of ∼±0.03% appear to have no significant influence on out-of-phase TMF crack initiation endurances for vermicular GJV-450 cast irons.

  • •

    In the same Tmax range, superimposed HCF loading cycles with higher strain amplitudes become increasingly influential, with increasing temperature, over an increasing Δε range of effectiveness.

  • •

    The extent of influence of superimposed HCF loading on OP-TMF crack initiation endurance is related to an increase in the effect of oxidation on crack development with increasing temperature.

Abstract

Thermo-mechanical fatigue (TMF) testing is increasingly used as a means of bench-marking the response of critical locations in high temperature components during operation by subjecting laboratory specimens to service and cyclic loading conditions involving the simultaneous action of thermal and mechanical strains. In this paper, evidence is presented to show the effect of maximum temperature in TMF cycles without and with superimposed high frequency (HCF) loading on crack initiation endurances for GJV-450 vermicular cast irons. For TMF cycles with maximum temperatures in the range 400–480 °C, there is little influence of superimposed higher frequency HCF strain amplitudes of up to ±0.03% on crack initiation endurance, whereas the effects of higher superimposed HCF loading are more significant.

Section snippets

Background and introduction

Thermo-mechanical fatigue (TMF) testing is increasingly used as a means of bench-marking the response of critical locations in high temperature components during operation by subjecting laboratory specimens to service like loading cycles involving the simultaneous action of thermal and mechanical strain (e.g. [1], [2]). With improvements to both testing machine construction philosophy and digital control capability, it is now possible to apply even more complex service related cycle shapes

Thermo-mechanical fatigue

The TMF crack initiation endurances shown in Fig. 1b are for production cast vermicular (GJV-450) cast irons subjected to the thermo-mechanical cycles shown in Fig. 1a. Testing was conducted in accordance with [7], using a 100 kN servohydraulic testing machine with induction heating and digital control as explained in [5]. The so-called G-type out-of-phase cycle involved a thermal transient between 50 °C and Tmax, and a thermo-mechanical strain constrained by G to relate to thermal strain, i.e.Δ

High cycle fatigue

The HCF properties of GJV-450 at temperatures of (a) 400 °C and (b) 450 °C are represented by the evidence given in Fig. 3, with Rσ = 0 in each case being coincident with σm = RU. At temperatures up to 480 °C, there was only a small influence of temperature on RU and Rσ(T,σm), with the relationships for 400 and 450 °C being compared in Fig. 3b.

The limiting fatigue strengths typically determined from N(σa) test records for a specified endurance [11] are strongly dependent on mean stress, and often

Mechanical interaction

TMF tests with superimposed HCF loading were conducted in a similar way to conventional thermo-mechanical fatigue tests, but with a more complex loading cycle [5], e.g. Fig. 4. In these tests, a high frequency (10 Hz) strain amplitude was superimposed on the entire thermo-mechanical strain cycle (which essentially acted as the mean strain). The outcome was ε(σ) hysteresis loops of the type shown in Fig. 4b.

The crack initiation endurance results could be considered in two ways, i.e. either as a

Conclusions

The effect of maximum temperature (Tmax) in G-type out-of-phase (OP) TMF(HCF) cycles on crack initiation endurances has been examined for a number of vermicular (compacted graphite) GJV-450 cast irons, with the following conclusions.

  • (i)

    The temperature dependence, of the ductility- and strength-controlled regimes of OP-TMF crack initiation endurances may be represented by the so-called Manson-Coffin equation more traditionally adopted for the representation of isothermal LCF endurance data.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The contribution of Dr Valli Kalyanasundaram, in particular with respect to microstructural examination of the GJV-450 irons is gratefully acknowledged.

References (19)

There are more references available in the full text version of this article.

Cited by (0)

View full text
© 2020 Elsevier Ltd. All rights reserved.