Biaxial Creep-Fatigue Failure Characteristics in Two FCC Materials

Abstract

This paper describes the failure mode observed in two types of FCC structural materials: waspaloy and type 316 stainless steel as a result of biaxial low cycle fatigue at elevated temperatures. Torsional cycling was applied at high as well as low strain ranges. Creep effect was assessed by introducing hold periods of 90 seconds in the waspaloy tests and 30 minutes in the stainless steel tests. Data obtained from fatigue and creep-fatigue tests have shown that the failure process in the two materials was controlled by two failure mechanisms which depended, to different degrees, on the state of stress, dwell time, and temperature. The failure mechanisms were assessed by observing crack growth in each material under strain level and temperature. In the waspaloy, the mode of crack growth was more temperature than stress dependent, while in the stainless steel, it was stress dependent. The microstructure analysis showed that each type of crack growth was caused by variations in slip band formation, stages of crack initiation and propagation, secondary cracking and cracking of grain boundaries. Creep showed more interaction with fatigue in the stainless steel material than in the waspaloy.

Isothermal and thermo-mechanical fatigue behavior of the nickel base superalloy Waspaloy™ under uniaxial and biaxial-planar loading

“…16 with various literature data from uniaxial tests [45,53,[67][68][69] as well as torsional tests [70][71][72]. On the basis of these literature data a fit curve as well as a corresponding scatter band for the factor two were approximated and included in Fig.…”

“…Due to the low cycle fatigue tests with constant frequencies f of 0.05 Hz according to Clavel and Pineau [53] and 0.3 Hz carried out by Cowles et al [45], different strain rates for all strain amplitudes are compared. Zamrik et al [70][71][72] No further details about the testing parameters were given by Clavel and Pineau [53].…”

High-temperature flaw assessment procedure: A state-of-the-art survey

“…An increase in crack growth rate with temperature was observed in both air and vacuum and was attributed to temperature dependence of the elastic modulus. Zamrik and Zahiri 42 concluded that temperature had a strong effect on the failure modes of the waspaloy material at 649°C -precipitation of carbide particles caused formation of embrittled regions. Huthmann and Gossmann, 43 however, studied fatigue and creep crack growth behavior of the X6CrNil8 steel (type 304 stainless steel) in air and flowing sodium at 823°K and reported no significant influence of the environment.…”