SCEC Award Number 19228 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Experimental Investigation of Multi-Scale Flash Weakening - Continuation Project
Investigator(s)
Name Organization
Frederick Chester Texas A&M University Judith Chester Texas A&M University
Other Participants Ms. Monica Barbery
SCEC Priorities 1d, 3c, 2d SCEC Groups FARM, Geology, CXM
Report Due Date 04/30/2020 Date Report Submitted 04/29/2020
Project Abstract
 This is a continuation of a SCEC funded project to understand coseismic weakening by flash heating along fault surfaces. The purpose of the project is to conduct high-speed friction experiments on machined surfaces to document the effects of multi-scale roughness on transient and steady-state flash-weakening behavior. The ultimate goal is to develop improved constitutive relations and determine the material properties that govern transient and steady-state flash weakening. In the first year of the project we developed a novel approach of machining rock surfaces with multi-scale roughness that control the heating and cooling times of contact junctions during high-speed frictional sliding. We showed that for flash-weakening, the steady-state friction decreases with an increase in the ratio of heating to cooling times of contacts. In this continuation project, we used IR imaging to characterize the distribution of local surface temperature of contacts undergoing flash heating. We also developed a model of flash heating in the experiments, with heating and cooling time dictated by the machined surface geometry, and that incorporates a temperature-dependent friction relation for flash weakening, to determine the local normal stress distribution on the sliding surfaces from the observed temperature distributions as a function of slip. This is the first time that contact geometries, flash temperatures, and local normal stress distributions have been determined for sliding surfaces in rock at seismic slip rates. These accomplishments provide the foundation to develop a coupled, thermo-mechanical numerical model of sliding surfaces governed by flash-weakening constitutive relations that describes transient friction during earthquake slip.
Intellectual Merit This project successfully contributes new knowledge of frictional contact surfaces undergoing flash weakening, a process thought to be important in dynamic earthquake rupture. Using a one-of-a-kind friction testing apparatus, we have for the first time imaged flash-heated contacts, and by machining grooves on sliding surfaces to constrain characteristics of contact lifetimes, we have been able for the first time to determine the normal stress distribution across the sliding interface during high speed slip. These results set the stage for further quantification of the governing parameters for flash weakening behavior, and advancing constitutive relations for flash weakening friction that are useful for dynamic earthquake rupture modeling.
Broader Impacts The project involves very fundamental research into the genesis of friction behaviors that are important to predictive modeling of earthquake effects. The project supported work by Ph.D. candidate Ms. Monica Barbery.

The work reported in the Technical Report come from a manuscript authored by Ms. Monica Barbery and the co-PIs, which will be added to the SCEC Publications Database upon submission to the J. Geophys. Res. Solid Earth in the next month.
Exemplary Figure The Summary of Research Results figure in the report would serve as an exemplary figure. Caption: Absolute % area of mm-scale contact with slip by range of local normal stress as a function of displacement during high-speed sliding along granite surfaces. Results show contacts are is small and carry higher normal stress initially, but evolve to larger area with lower normal stress due to wear and gouge accumulation.

Figure 4 also may serve as an exemplary figure.The caption for Fig. 4 is in the text.