Low cycle fatigue life prediction in shot-peened components of different geometries – Part II:life prediction

This study investigates the effects of shot peening on the low-cycle fatigue (LCF) performance of a low pressure steam turbine blade material. The finite element (FE) model incorporating shot peening effects, which has been introduced in Part I, has been used to predict the stabilised stress/strain state in shot-peened samples during fatigue loading. The application of this model has been extended to different notched geometries in this study. Based on the modelling results, both the Smith-Watson-Topper and Fatemi-Socie critical plane fatigue criteria have been used to predict the fatigue life of shot-peened samples (treated with two different peening intensities) with varying notched geometries. A good agreement between experiments and predictions was obtained. The application of a critical distance method considering the stress and strain hardening gradients near the shot-peened surface has been found to improve the life prediction results. The effects of surface defects on the accuracy of life predictions using the proposed method were also discusse

Experimental and numerical investigation of the effects of shot peening on low-cycle fatigue behaviour of notched geometries

In service, turbine components are subjected to low-cycle fatigue (LCF) during start-up and shut-down operations, especially at the fir tree root blade-disc connection which has a complex geometry and corresponding high stress concentration. Shot peening generates compressive residual stress (CRS) and strain hardening which can improve fatigue life. However, prediction of the fatigue life of shot-peened components under LCF is challenging due to the complex interaction between the shot peening induced effects and service conditions, especially in regions of high stress concentration. The current study aims to develop a validated 3-D eigenstrain-based modelling tool, which is capable of simulating the stress/strain evolution under LCF in shot-peened notched samples representative of the real turbine blade fir tree geometry. The residual stress and strain hardening profiles caused by shot peening were first evaluated by experiments and then incorporated into the finite element (FE) model separately. In addition, the Smith – Watson – Topper (SWT) method was used to predict the fatigue life of shot peened samples, based on the stress/strain data generated using the developed FE model

On the mechanism of oxidation-fatigue damage at intermediate temperatures in a single crystal Ni-based superalloy

The combined effects of environment (oxidation) and mechanical load (fatigue) that control crack propagation in a single crystal Ni-based superalloy have been investigated with particular focus on the intermediate service temperature range. Fatigue tests have been carried out at different frequencies, hold times and environments, to study the parameters influencing crack propagation at 550 °C. The direct current potential drop method was used to monitor the crack growth while STEM-EDS were used to analyse the fracture mode and crack tip regions.It was found that the micro-mechanism of fatigue crack propagation at intermediate temperatures is a complex process with several competing mechanisms acting on the crack tip simultaneously. Crystallographic slip processes by γ′ shearing are active at these temperatures while at the same time thermally activated processes that promote crack propagation through the γ channels also take place. In addition, the effects of oxidation were found to be two-fold. It was demonstrated that these temperatures are not high enough to cause macroscopic embrittlement of the crack tip but finger-like protrusions were found to penetrate the material ahead of the crack tip at the nano-scale. The kinetics of such a mechanism were accentuated by the plastic strains at the crack tip, which given enough time, can promote cleavage fracture at the γ/γ′ interface. At the same time, given that the crack driving force is lower than a transition value, oxide formation on the crack tip surfaces can bridge the opening of the crack tip and reduce the effective driving force

Application of X-Ray microtomography to evaluate complex microstructure and predict the lower bound fatigue potential of cast Al–7(0.7)Si–4Cu–3Ni–Mg alloys

The 3D architecture of intermetallics and porosity in two multicomponent cast Al–7(0.7)Si–4Cu–3Ni–Mg alloys is characterized using conventional microscopy and X-ray microtomography. The two alloys are found to contain intermetallic phases such as Al3Ni, Al3(NiCu)2, Al9FeNi, and Al5Cu2Mg8Si6 that have complex networked morphology in 3D. The results also show that HIPping does not significantly affect the volume fraction, size, and shape distribution of the intermetallic phases in both alloys. A novel technique similar to serial sectioning that circumvents quantification difficulties associated with interconnected particles is used to quantify the intermetallics. The largest particle size distribution is then correlated to fatigue performance using extreme value analysis to predict the maximum particle size in a sample of S-N fatigue specimens and subsequently, the lower bound fatigue life. The predictions are found to correlate well with fatigue data. The effect of HIPping on porosity characteristics is also characterized. Large pore clusters with complex morphology are observed in the unHIPped versions of both alloys, but more significant in the low Si (Al–0.7Si–4Cu–3Ni–Mg) alloy. However, these are significantly reduced after HIPping. The differences between 2D and 3D pore morphology and size distribution is discussed in terms of the appropriate pore size parameter for fatigue life prediction

Data for figures in "Low cycle fatigue life prediction in shot-peened components of different geometries – Part II Life prediction"

This dataset reports data for the figures published in: C. You, M. Achintha, K.A. Soady, P.A.S. Reed &quot;Low cycle fatigue life prediction in shot-peened components of different geometries &ndash; Part II Life prediction&quot; The excel files included in this dataset were named in terms of the number of figures. Each excel file refers to a figure in the paper.</span

Data supporting: Oxidation behaviour of single crystal nickel based superalloys: Intermediate temperature effects at 450-550oC

This data supports the following publication: Evangelou A., Soady K.A., Lockyer S., Gao N., Reed P.A.S.(2017), Oxidation behaviour of single crystal nickel based superalloys: Intermediate temperature effects at 450-550oC. Abstract: The oxidation behaviour of two commercially available single crystal nickel based superalloys has been investigated at the lower operating temperature range (450-550&ordm;C) of an industrial gas turbine blade. Isothermal oxidation was carried out for varying times up to 640h and the low temperature exposure resulted in a sub-micron thick oxide. The external and internal oxide kinetics were studied via high resolution image analysis and both showed sub-parabolic growth rates. Thermogravimetric tests indicated that the overall oxidation growth obeys a near quartic power law while parabolic kinetics can describe the transient oxidation period. Characterisation of the resulting oxides was carried out using field emission gun scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Results from thermodynamic modelling (Thermo-Calc) of the oxide formation are also presented to further assess the postulated mechanism of low temperature oxidation in these nickel based superalloys.</span

Data for figures in &quot;Low cycle fatigue life prediction in shot-peened components of different geometries &ndash; Part I Residual stress relaxation&quot;

This dataset reports data for the figures published in: C. You, M. Achintha, K.A. Soady, N. Smyth, M.E. Fitzpatrick, P.A.S Reed &quot;Low cycle fatigue life prediction in shot-peened components of different geometries &ndash; Part I Residual stress relaxation&quot; The excel files included in this dataset were named in terms of the number of figures. Each excel file refers to a figure in the paper.</span

Introducing research data - fourth edition

Research Data Introduction material, used with students in the University of Southampton with contributions from Archaeology, Chemistry, Medicine and Engineering.Every discipline, from the arts and humanities to physics, is increasingly using data to drive forward its goals. Medicine might use it for recording the statistics of a particular drugs trial; physicists have complex experiments---such as the Large Hadron Collider at CERN---producing massive quantities of data on an hourly basis; and archaeologists meticulously preserve digital records of excavation sites and artefacts.This guide first introduces the forms data can take by showing five ways of looking at data, then presents some case studies of data usage in several disciplines in an attempt to illustrate the types of data you might encounter in your research and give you some tips or tricks that will help you in your own discipline.The final part of the guide gives some general advice on managing and understanding data