Development of true-stress creep model through analysis of constant-load creep data with application to finite element methods

The creep behaviour of the nickel-superalloy RR1000 is studied through a number of constant-load creep tests. It is often assumed that creep data generated by constant-load testing are unsuitable for building a generalised creep model due to the non-constant stresses incurred. Analysis of existing models shows that significant errors may occur in many approaches, which attempt to recreate the strain evolution with time. A model is presented which is not reliant on time as a parameter and is therefore able to utilise constant-load creep data without enforcing the assumption of a constant stress. This model is demonstrated through numerical analyses to replicate the creep behaviour across a large range of stresses accurately. The proposed model is then adapted as an Abaqus™ user-subroutine to demonstrate capability within finite element analysis

Crack Growth of a Polycrystalline Nickel Alloy under TMF Loading

Thermo-mechanical fatigue (TMF) is an important factor for consideration when designing aero engine components due to recent gas turbine development, thus understanding failure mechanisms through crack growth testing is imperative. In the current work, a TMF crack growth testing method has been developed utilising induction heating and direct current potential drop techniques for polycrystalline nickel-based superalloys, such as RR1000. Results have shown that in-phase (IP) testing produces accelerated crack growth rates compared with out-of-phase (OOP) due to increased temperature at peak stress and therefore increased time dependent crack growth. The ordering of the crack growth rates is supported by detailed fractographic analysis which shows intergranular crack growth in IP test specimens, and transgranular crack growth in 90° OOP and 180°OOP tests. Isothermal tests have also been carried out for comparison of crack growth rates at the point of peak stress in the TMF cycles

QICS work package 1: migration and trapping of CO2 from a reservoir to the seabed or land surface

Natural CO2 seeps can be used as analogues for studies into surface flux and impact resulting from leaking engineered geological CO2 reservoirs. However their long-lived nature often means that the local environment has either adapted or evolvedaround the seepage site. The ‘Quantifying Impact of carbon storage’ (QICS) experiment provides the solution to this issue by releasing CO2 into an environment previously untouched by CO2. Work Package 1 (WP1) of the QICS project is primarily concerned with the migration of CO2 in the subsurface and how to relate the results of the relatively shallow experiment to a full storage scale setting in the UK North Sea. The main objectives of WP1 are to investigate potential leakage pathways from the reservoir to the surface, determine possible leakage rates and assess the potential volumes of leaked CO2 that can reach the surface environment

Evolution of Wilshire equations for creep life prediction

In the past decade, a new approach to predictive creep lifing has been developed, known as the Wilshire equations. Having been applied to a range of power generation and aerospace materials, the understanding of material behaviour associated with the equations has developed significantly. With the equations based around the dominance of diffusion controlled dislocation movement for creep deformation under typical engineering stresses and behaviours, the predictions made are related to microstructural phenomena, such as the onset of yield. The current paper seeks to review the application and development of the Wilshire equations, with suggestions for future research in the area