Transcript Perspectives of Japan - University of Colorado Boulder

Introduction
to Brittle
Deformation
Outline
•
Principal stresses
•
Stress ellipse and stress ellipsoid
•
Fundamental fracture modes
•
Crack propagation
•
Extensional joints
•
Interpretation Problem
Principal Stresses
•
s1 - greatest principal stress
•
s2 - intermediate principal stress
•
s3 - minimum principal stress
•
Stress is a force/area
•
Principal stress directions are mutually perpendicular
Principle Stresses
•
Principal stresses are normal stresses only
Stress Ellipse
In 2-D, s1 and s3 are mutually perpendicular and form
the axes of a stress ellipse
•
s3
s1
Stress Ellipsoid
In 3-D, s1, s2 , and s3 are
mutually perpendicular and
form the axes of a stress
ellipsoid
•
The length of an axis is
related to the magnitude of the
stress
•
The stress ellipsoid to the
right might represent the stress
at a point in the shallow
subsurface
•
Stress Ellipsoid
This stress ellipsoid could represent the stress at a point
located in the suture of a collision zone between two continents
•
Fracture Modes
Direction
crack tip propagates relative to sense of slip
defines Mode type
Mode I
Mode II
Mode III
Opening
Sliding
Scissoring
How to Stop a Propagating Crack…
Extremely high stress
concentration
How to Stop a Propagating Crack…
Extremely high
stress concentration
Drill a hole and
increase the area of
the crack tip
Lower stress
Extensional Joints
•
Joint surface oriented perpendicular to s3
• Mode
I fracture - opening, no shear, no scissoring
Opening direction
s3
Growth of Joints
Growth direction
Joints in Sedimentary Rocks
Joints in Igneous Rocks