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Dynamics and evolution of friction and shear surface deformation of rough surfaces: Experiments and numerical modelling with direct application to earthquake dynamics


   Faculty of Environment

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  Dr S Piazolo, Dr Ali Ghanbarzadeh, Dr L Gregory  No more applications being accepted  Competition Funded PhD Project (Students Worldwide)

About the Project

Summary

This exciting project aims to shed light on the long standing problem of how friction of rough surfaces evolves through time. This project will develop an in-depth, quantitative understanding of the frictional behaviour of sliding surfaces with direct application to earthquake dynamics capitalizing on the knowledge and experimental capabilities of the cross-disciplinary research team. High impact outcomes in both fundamental and applied science are expected. Outcomes promise to be of high impact in both fundamental and applied science.


Background

The evolution of friction on rough surfaces is fundamental to the time-dependent deformation behaviour of complex surfaces. In-depth understanding of such behaviour is crucial for industrial applications in the high value manufacturing and transport industry; for example hip replacement durability is highly dependent on frictional effects. In the natural environment, understanding of the evolution of friction of slip surfaces is essential for improved earthquake assessments.

At a time of increased urbanisation, earthquakes are one of the most devastating natural hazards that cause loss of life and livelihood. Earthquakes occur as the stress built up in the Earths’ crust is released catastrophically causing slip along surfaces of movement. When a fault fails, its threshold value, the fault strength, is reached. Frictional properties of the fault surface at any one time strongly affects the process and timing of stress build up to generate subsequent earthquakes. Static/dynamic friction is a key aspect of earthquake physics. Observations show that rupture parameters such as slip and slip rate may rapidly evolve at the scale of a second but also thousands of years. This evolution may be in the presence of fluids circulating within the slip zone. Furthermore, after a major earthquake the slip (fault) plane is subject to material aging including fluid-rock interaction, which is predicted to impact the slip surface properties and therefore the period until further rupture.

In particular, processes and parameters that we need to understand include:

-  How do rough surfaces evolve through time – both surfaces and near surface materials?

-  In what way is the surface evolution dependent on rate of deformation and variation of the major and trace element chemistry of the material?

-  How important is the duration and character of aging of surfaces after rapid shear?

-  How does the composition of the fluid residing on a slip surface influence its frictional behaviour?

-  What are the underlying processes that govern fiction evolution in crystalline materials?


Aims and Objectives

Three main areas will­ be addressed:

1)    Processes and Rates: What physiochemical processes occur at different conditions? How do these physical and chemical processes interact with each other? What are their rates?

2)    Effect: How do these processes affect the frictional behaviour of a natural rock, as well as its rheology such as resistance to later re-slipping/re-fracturing?

3)    Prediction: Based on the resolution of the two questions above, what are our possibilities to predict material behaviour to allow for assessment of natural hazard posed by faults (slip surfaces).

Project plan and methods

In this project, the student will work with leading scientists in their fields at Leeds (Piazolo, Ghanbarzadeh & Gregory) in collaboration Lars Hansen (University of Minesota, USA).

The three main work packages in this projects are:

1.          Experiments using novel experimental designs (e.g. modified Universal Material Tester-UMT) allowing for direct shear experiments with high frequency cycles that can directly measure tangential loads and frictional behaviour in-situ while varying the normal force.  Here, starting material with different material properties (e.g. porosity, chemical composition) will be subject to direct shear.  

2.          Analysis of experimental samples before and after experiments using high-end microscopy including an unique Focussed Ion Beam Scanning Electron Microscope with time of flight spectrometer and Electron backscatter diffraction detectors). Analysis will be from the nanometer-scale, to the micron and to mm scale. Analytical results from experiments will be compared to natural rocks from geological faults provided by the supervisor and/or collected by the student.

3.          Numerical modelling of ongoing processes: we will build upon the numerical models using combined microscale and dislocation plasticity models existing in the engineering community (Ghanbarzadeh et al. 2020) and combine this with the microdynamic numerical platform Elle (Piazolo et al. 2019; Koehn et al. 2021). Here, results from analyses will be used to benchmark and develop the new multiscale numerical approach for friction dynamics. While many of the features needed for the modelling of friction are available in principle, the student will need to incorporate some extra parameters. The multi-scale numerical modelling system to be developed will not only be directly applicable to natural fault surface dynamics but also to industrial applications e.g. hip replacement durability is highly dependent on frictional effects.

Depending on the student’s interest additional techniques may be employed, these may include:

-     chemical isotopic tracing of reaction progression using oxygen isotopes

-       Field work and sampling to characterize materials in naturally occurring faults

Student profile

The student should be keen to perform novel experimental work, do high-end microscopy to derive both chemical and structural properties of the rocks and any changes occurring due to frictional sliding and combining this with numerical simulations. The student should have the desire to undertake a study crossing the disciplinary boundaries between materials science of manufactured and natural materials (e.g. rocks). A strong background in a quantitative science concerned with material properties and optimization (earth sciences, physics, materials science, surface chemistry) is essential.

Student Training

The successful PhD student will have access to a broad spectrum of training workshops put on by the Faculty at University of Leeds that include an extensive range from scientific computing through to managing your degree, to preparing for your viva (http://www.emeskillstraining.leeds.ac.uk/). The student will be trained in the different experimental designs to be used for this research, trained in high-end electron microscopy within the Leeds Electron Microscopy and Spectroscopy Centre (LEMAS, https://www.rms.org.uk/network-collaborate/facilities-database/facilities-database-submission-form.html?slug=lemas). The student will also have the opportunity to engage with a wider range of scientists within the Elle community (Elle = community numerical platform; http://www.microstructure.info/ ).



Funding Notes

This 3.5 years EPSRC DTP award will provide full tuition fees, a stipend at the UK research council rate (UK Sterling 15,840 for 2022/23), and a research training and support grant.

References

References
D Koehn, S Piazolo et al. 2021. Relative rates of fluid advection, elemental diffusion and replacement govern reaction front patterns. Earth and Planetary Science Letters 565, 116950
Ghanbarzadeh et al 2020. Deterministic normal contact of rough surfaces with adhesion using a surface integral method. Proceedings of the Royal Society A, 476(2242), 20200281.
Piazolo et al 2019. A review of numerical modelling of the dynamics of microstructural development in rocks and ice: Past, present and future. Journal of Structural Geology. 125, pp. 111-123

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