HIGH-TECH LABCOURSES
HIGH-TECH
LABCOURSES
Interfacial ruptures responsible for the onset of frictional sliding
When two solids are pressed together and sheared, frictional forces resist sliding. Sliding occurs when a rupture propagates along the interface between the two solids. The rupture weakens the microcontacts that resist shear, and is the exact analogue of a shear cracks propagating in an intact material. A seismic event is the result of such a rupture propagating along a seismic fault at speed approaching that of sound.
In this lab-course, frictional ruptures will be detected as they propagate along the interface between two solid bodies in contact, based on strain measurements. The strain variations induced by the rupture will be characterised using the analytical tools of fracture mechanics.
PREREQUISITE
This lab-course is suited to students from the L3 level with a background in solid mechanics.
DESCRIPTION
In this module, two PMMA plates (a transparent plastic) are pressed together under normal stress, and one plate is translated at a constant velocity, inducing a shear force in the system. The solids undergo stick-slip dynamics, i.e. an alternation of ‘stick’ phases, during which no sliding occurs, and 'slip' phases, during which rapid sliding occurs.
One of the plate is instrumented with 20 strain gauges, which are glued to its faces along the interface, 3 mm above. These gauges allow to measure variations in the strain field induced by the passage of the interfacial rupture beneath the strain gauge. The strain measurements recording is triggered by an accelerometer that detects the occurrence of the rapid sliding event.
During this session, participants will generate ruptures. By comparing the strain variation with that predicted by fracture mechanics, they will extract interface properties such as fracture energy and determine the relationship between rupture speed and initial loading. By varying the normal stress, they will be able to assess the relationship between fracture energy and normal stress.
