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geology
F2 surface and internal processes of the rock cycle
stress and strain
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Isa B-T
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Cards (10)
Competent rock stays the same
thickness
when
deformed
and reacts by
fracturing.
They are
brittle
e.g.
igneous
rocks,
limestone.
Incompetent rock varies in
thickness
when deformed, they behave
plasticly
and do not
fracture.
E.g.
mudstone
,
shale
and
clay.
A stress is a
force
that is
applied
to a
rock.
A strain is the change in
shape
or
volume
to the
applied
force.
S
t
r
a
i
n
=
Strain =
St
r
ain
=
△
i
n
l
e
n
g
t
h
o
f
l
i
n
e
/
o
r
i
g
i
n
a
l
l
e
n
g
t
h
o
f
l
i
n
e
.
△ in length of line / original length of line.
△
in
l
e
n
g
t
h
o
f
l
in
e
/
or
i
g
ina
ll
e
n
g
t
h
o
f
l
in
e
.
competent rock
A)
fracture point
B)
elastic
2
incompetent rock
A)
elastic limit
B)
plastic
C)
elastic
3
Higher
temperature causes rock to act mor
plastically
, so rocks
fold
and don’t fault/
fracture
at
high
temperature.
Cold
rock fractures
Strength of rock
increases
with confining pressure, deeper rocks are harder to
deform.
Short periods of stress mean
brittle
behaviour, a longer periods of stress cause rock to be more
plastic.
