SCEC Award Number 20126 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Experimental Investigation of Multi-scale Flash Weakening
Investigator(s)
Name Organization
Frederick Chester Texas A&M University Judith Chester Texas A&M University
Other Participants Monica Barbery, Ph.D. student
Morgan Krauss, Undergraduate Student
Charles Babendreier, Undergraduate Student
SCEC Priorities 1d, 3c, 2d SCEC Groups FARM, Geology, SDOT
Report Due Date 03/15/2021 Date Report Submitted 03/28/2021
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 1) further develop numerical modeling for analysis of flash-weakening in our experiments, 2) continue experimentation to contribute mechanical and temperature data for our parametric study of the effects of sliding velocity, deceleration path, and normal stress, on friction, and 3) conduct observational studies to determine the factors leading to self-organization of mm-scale contacts during sliding that support high stress and heat-generation rates. Project accomplishments include : 1) A suite of high-speed friction experiments on granite surfaces with different multi-scale roughness, and a variety of sliding velocity paths at different constant velocity, different sliding distance, and both high and low deceleration to low velocity and arrest employing several different peak sliding-velocity and subsequent deceleration histories were conducted; 2) The local normal stress, σl, distributions determined from surface T and sliding contact history using T-dependent flash-weakening friction relations are similar for all experiments, are consistent with previous experiments, and have improved our characterization of local normal-stress distributions at low slip. During the COVID-19 extension, we will complete or work to test the efficacy of the flash-weakening model based on micrometer-scale asperity contact junctions and local (mm-sale) surface temperature, and identifying the factors leading to self-organization of the mm-scale contacts formed during sliding.
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 conducted a unique suite of high-speed sliding friction experiments on samples with different scale-dependent roughness, differ peak sliding velocity followed by both low and high deceleration. For all experiments we image the flash-heated contacts with a high-speed IR camera. These new data will permit us to further quantify of the governing parameters for flash weakening behavior, and advance constitutive relations for flash weakening friction that are useful for dynamic earthquake rupture modeling.
Broader Impacts 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 and imaging flash-heated sliding surfaces, we will be able to better quantify the governing parameters for flash weakening behavior, and document effects of multi-scale roughness on dynamic weakening behaviors.
Exemplary Figure Figure 2. Example of friction behavior for a step to high velocity for samples with two different surface geometries (RT=LT and RT=0.5LT) with various peak-velocity and post-peak deceleration, and with different magnitudes of slip at peak velocity. For all the experiments the flash-temperature of the sliding surface, upon emerging from the base of the double-direct shear sample assembly, is imaged using the high-speed IR camera as described in Barbery et al. (submitted to JGR, 2020). The data from this multi-variable parametric study of flash-weakening friction is being used to better quantify the fundamental microscopic asperity contact properties of diameter, breakdown temperature, and shear strength.