High temperature low cycle fatigue

Abstract

Fatigue at high temperature is a complex phenomenon as it is influenced by a number of time-dependent processes which become important at elevated temperatures. These processes include creep, oxidation, phase instabilities and dynamic strain ageing (DSA), acting either independently or synergistically influence fatigue behaviour, often lowering the fatigue life. Current design approaches employ linear summation of fatigue and creep damage with suitable factors on permissible damage to take care of uncertainties in interaction between cyclic and time-dependent processes. It is, therefore, important to develop a deeper understanding of the processes that occur during high temperature fatigue so that realistic life predictions could be made. Results on the high temperature fatigue behaviour of austenitic stainless steels, ferritic steels and nickel base alloys are presented here. The important mechanisms of interaction of high temperature time-dependent processes with fatigue under various conditions are discussed in detail. Emphasis is placed on cyclic stress response, fatigue life, deformation substructure and fract~'re behaviour. This is followed by a review of important life prediction techniques under combined creep-fatigue loading conditions. Life prediction techniques considered here include linear damage summation, strain range partitioning, ductility exhaustion approach, frequency modified and frequency separation methods, techniques based on hysteresis energy and damage rate models, and methods based on crack-cavitation interation models.

Fatigue behaviour of 16Mo3 steel at elevated temperatures under uniaxial as well as biaxial‐planar loading

“…This difference is caused by the significantly lower yield strength values at 500 °C and the associated higher plastic strain fraction on the total strain amplitude. Further reasons for the reduction of the fatigue lives are the influence of the creep–fatigue interaction and the more intensive corrosion in air atmosphere . As a result, the crack propagation is changed by oxidation from a zig‐zag crack path at 200 °C into a mainly straight crack path with oxidized crack surfaces at 500 °C …”

“…Further reasons for the reduction of the fatigue lives are the influence of the creep-fatigue interaction and the more intensive corrosion in air atmosphere. 11,17,[48][49][50] As a result, the crack propagation is changed by oxidation from a zig-zag crack path at 200°C into a mainly straight crack path with oxidized crack surfaces at 500°C. 11,17 Also for the 500°C data, the lifetime description according to Basquin and Manson-Coffin gives a very good correlation for uniaxial and biaxial loading for both manufacturing processes of 16Mo3, and fatigue lives fall within the scatter band of two.…”

Microstructural model for the time‐dependent thermomechanical analysis of cast irons

“…where τ y (T ) is the yield stress, which here depends on the temperature only, since hardening is alredy accounted for in (18). The Zener parameter is defined as [41]:…”

“…where (26a) is obtained by substituting equations (7), (8b), (15) and (8c) in equation (13), with D th given by (11a), and using expression (18) forγ vp .…”

“…This is reflected in thermal softening and higher creep or stress relaxations rates [2,[10][11][12][13][14][15][16][17][18][19][20][21]. This is reflected in thermal softening and higher creep or stress relaxations rates [2,[10][11][12][13][14][15][16][17][18][19][20][21].…”