Dwell fatigue effects at low temperatures in a range of titanium alloys have been well documented since the 1970s. However, attempts to model dwell fatigue phenomena are limited. The time dependent effects have been shown to be due to the inherent strain accumulation behaviour at ambient or low temperatures, loosely termed ‘cold creep’ in alloys such as Ti-6Al-4V. Periods of dwell in a fatigue cycle or the application of a high mean stress not only cause stress relaxation, but can lead to premature failures characterised by quasi-cleavage facets under certain conditions. The conditions under which these facets form are not fully understood.
This paper introduces a method for predicting cold creep in Ti-6Al-4V by attempting to quantify time dependent deformation and rupture caused by the formation of quasi-cleavage facets observed in this titanium alloy. A logarithmic creep method has been used to describe low temperature creep curves. However this method fails to predict the curve shape at higher stresses. An additional term is used to quantify creep rates at all conditions. A finite element model has been developed, based on this method, which accurately predicts stress relaxation at ambient temperature and quantifies time dependent failure in a notched specimen under cyclic loading
W. Harrison, M.T. Whittaker, R.J. Lancaster
Materials Science and Engineering: A Volume 574, 1 July 2013, Pages 130–136