Three dimensionalization techniques for epipolar views, and design process reconstruction.

Lead Research Organisation: University of Bristol
Department Name: Mechanical Engineering

Abstract

Fatigue and cracking damage in many metal systems is magnified when it occurs in oxidising or corrosive environments. The mechanisms involved are frequently complicated since there can be multiple regime changes reflecting both the mechanics of the material and the chemistry of the environment. Several industries are affected by such problems and it is becoming increasing clear that existing assumptions when dealing with the early stages of environmental damage are insufficient for making useful predictive models of lifetime during design or safety assessments.

Several recent advances suggest there is scope for considerable advancement in our understanding of environmentally-influenced damage.
- Crystal plasticity methods for micromechanical models provide data on how complex microstructures interact to generate intergrain and interphase stresses.
- Atomic force microscopy (AFM) can now make real time measurements. This will provide accurate, small-scale data on microcracking and surface damage.
- Synchrotron X-ray methods for high-speed, high-resolution imaging and grain-scale strain mapping are now mature enough to be used on real systems. These methods are also phase selective and so generate maps of parent and product phases.

The combination of these techniques with a properly developed suite of micro-testing rigs will permit more accurate predictions of the effect of environment on crack initiation. Critically, this work is highly interdisciplinary and will need to combine inorganic chemistry with a knowledge of fracture and microstructure damage.

Publications

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De Francisco U (2020) Hydrogen environmentally assisted cracking during static loading of AA7075 and AA7449 in Materials Science and Engineering: A

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509619/1 01/10/2016 30/09/2021
1940939 Studentship EP/N509619/1 18/09/2017 30/09/2021 Unai De Francisco
 
Description Recently, the European Aviation Safety Agency (EASA) reported that a new generation of high strength aluminium alloys used in aircraft components have been found to crack in moist environments. This phenomenon is called hydrogen environmentally assisted cracking (HEAC). Despite the importance of this issue in aircraft, the understanding of HEAC is very limited and it is not well understood why these novel alloys are more susceptible than older ones.
In the first part of this PhD, we have focused in experimentally comparing the HEAC behaviour of novel and older aluminium alloys to compare the kinetics of HEAC and characterise the HEAC behaviour relative to the microstructure of the alloys. The investigation was focused on the behaviour at a microstructural scale, to encompass the influence of crack nucleation, which has been typically neglected in previous investigations. This was performed successfully and the data has been published in our first publication (https://doi.org/10.1016/j.msea.2019.138662).
Exploitation Route This new understanding of the HEAC behaviour of aluminium alloys may be helpful for the prognosis and developement of aircraft component materials. The HEAC kinetics data may be used to asses the influence of different loads on aircraft components and estimate the component lifetime. Additionally, the characterisation of the HEAC behaviour relative to the microstructure, may be used to mitigate cracking by developing alloys with less microstructural features which may induce crack nucleation and rapid crack growth.
Sectors Aerospace, Defence and Marine

 
Description Tomography experiment at PETRA III, Hamburg 
Organisation Deutsches Electronen-Synchrotron (DESY)
Country Germany 
Sector Academic/University 
PI Contribution We have performed an experiment at the PETRA III facility in Hamburg. We successfully performed an in-Situ tomography experiment to characterise the 3D growth of hydrogen environmentally assisted cracking (HEAC) in aircraft high strength aluminium alloys. This data is currently being analysed and will give insight into the crack growth behaviour. For this experiment I designed the rig necessary to expose the aluminium alloys to a load in a warm moist environment for in-Situ imaging. Additionally, we travelled to Hamburg to perform the experiment at the facility with the support of the local scientists. Finally, we are currently analysing the data and hope to find significant findings.
Collaborator Contribution Our partners at Petra III (beamline scientists Dr. Felix Beckmann and Dr. Julian Moosmann) helped us throughout the experiment at PETRA III by preparing and fine-tuning the X-ray beam and guiding us about the use of the equipment.
Impact The data is currently being analysed but we should have some key findings soon
Start Year 2019