A Critical Analysis of the Conventionally Employed Creep Lifing Methods

Abstract

The deformation of structural alloys presents problems for power plants and aerospace applications due to the demand for elevated temperatures for higher efficiencies and reductions in greenhouse gas emissions. The materials used in such applications experience harsh environments which may lead to deformation and failure of critical components. To avoid such catastrophic failures and also increase efficiency, future designs must utilise novel/improved alloy systems with enhanced temperature capability. In recognising this issue, a detailed understanding of creep is essential for the success of these designs by ensuring components do not experience excessive deformation which may ultimately lead to failure. To achieve this, a variety of parametric methods have been developed to quantify creep and creep fracture in high temperature applications. This study reviews a number of well-known traditionally employed creep lifing methods with some more recent approaches also included. The first section of this paper focuses on predicting the long-term creep rupture properties which is an area of interest for the power generation sector. The second section looks at pre-defined strains and the re-production of full creep curves based on available data which is pertinent to the aerospace industry where components are replaced before failure.

A method for long-term creep–rupture strength prediction based on a small sample of experimental results, smoothed bootstrapping and time–temperature parameters

“…However, whilst the fatigue mechanism is significant under any temperature regime, the creep mechanism is especially intense as the temperature rises [7][8][9][10]. Many creep-rupture models exist, and parametric models in particular play an important role in the prediction of rupture strengths [11]. Since their introduction, first by Larson and Miller [12], Manson and Haferd [13] and later by Orr et al [14], time-temperature parameters have become a common method of describing creep-rupture data [11,15,16].…”

Use of small specimen creep data in component life management: A review

“…More detail on these methods can be found in ref [58] with regards to extrapolation and in ref [78] for an analysis on continuum damage mechanics.…”

“…where T is the temperature in Kelvin, tf is the rupture life in hours and CLM is a constant originally assigned a value of 20 for all metallic materials, has now been found to vary [58]. It is derived as a result of curve fitting to experimental data and is related to the activation energy for creep fracture.…”

“…A common extrapolation method is the Larson-Miller parameter (eq. 12) [56] (used with the small punch creep test [57]), well known in the accelerated creep extrapolation of uniaxial tests [58] = .…”

A Discussion of Non-Constant Creep Activation Energy

“…This form of creep activation energy in eqn. (3) is the most commonly used [6] and forms the backbone of most creep lifing models [7].…”