In Situ Scanning Electron Microscope (SEM) Observations of Damage and Crack Growth of Shale

To better understand the formation and evolution of hierarchical crack networks in shales, observations of microscopic damage, and crack growth were conducted using an in situ tensile apparatus inside a scanning electron microscope. An arched specimen with an artificial notch incised into the curved...

Full description

Saved in:
Bibliographic Details
Published in:Microscopy and microanalysis 2018-04, Vol.24 (2), p.107-115
Main Authors: Cui, Zhendong, Han, Weige
Format: Article
Language:English
Subjects:
Anisotropy
Bedding
Brittle fracture
Brittleness
Coalescence
Coalescing
Compressive properties
Crack initiation
Crack propagation
Crack tips
Damage
Elastic recovery
Fracture mechanics
Fractures
Fracturing
Hydraulic fracturing
Investigations
Kinking
Laboratories
Materials Science Applications
Mechanics
Porosity
Scanning electron microscopy
Shale
Shales
Stress concentration
Tensile stress
Tips
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:To better understand the formation and evolution of hierarchical crack networks in shales, observations of microscopic damage, and crack growth were conducted using an in situ tensile apparatus inside a scanning electron microscope. An arched specimen with an artificial notch incised into the curved edge was shown to afford effective observation of the damage and crack growth process that occurs during the brittle fracturing of shale. Because this arched specimen design can induce a squeezing effect, reducing the tensile stress concentration at the crack tip, and preventing the brittle shale from unstable fracturing to some extent. Both induced and natural pores and cracks were observed at different scales around the main crack path or on fractured surfaces. Observations indicate that the crack initiation zone develops around the crack tip where tensile stresses are concentrated and micro/nanoscale cracks nucleate. Crack advancement generally occurs by the continuous generation and coalescence of damage zones having intermittent en echelon microscopic cracks located ahead of the crack tips. Mineral anisotropy and pressure build-up around crack tips causes crack kinking, deflection, and branching. Crack growth is often accompanied by the cessation or closure of former branch cracks due to elastic recovery and induced compressive stress. The branching and interactions of cracks form a three-dimensional hierarchical network that includes induced branch cracks having similar paths, as well as natural structures such as nanopores, bedding planes, and microscopic cracks.
ISSN:1431-9276
1435-8115
DOI:10.1017/S1431927618000211