SEM analysis of pop-ins manifested in layered porous geological material

Nanoindentation pop-ins in composite source shale were characterized as Type I and Type II, where the slopes on load-displacement (p-h) curves are defined as Delta p/Delta h = 0 or Delta p/Delta h > 0, respectively. Type I were associated with sudden instantaneous failure as elastic perfectly plastic Coulomb-type and sudden grain dislodging, while Type II were related to shear band progressive failure and/or grain sliding or progressive pile-up. Pop-ins were primarily observed when indenting perpendicular to the shale layers. Estimating magnitudes of pop-in energy dissipation varied widely with shale matrix phases. Meanwhile, Type III pop-ins defined by Delta p/Delta h < 0, were never observed.

Automated summary

The study investigated nanoindentation pop-ins in composite source shale and defined two types, Type I and Type II, based on the slopes of load-displacement curves as Delta p/Delta h = 0 or Delta p/Delta h > 0. Pop-ins were mainly observed when indenting perpendicular to the shale layers, with a wide variation in the estimate of pop-in energy dissipation magnitude across shale matrix phases. Type III pop-ins with Delta p/Delta h < 0 were never observed.