Stress is the internal resistance of a material against an applied load or force. There are different types of stress that rocks can experience, including lithostatic stress from the weight of overlying rocks, and differential stress from tectonic forces like tension, compression, and shearing. Rocks deform in response to stress in different ways depending on factors like pressure, temperature, and composition. At low stresses rocks deform elastically and return to their original shape when unloaded. At higher stresses near the surface, rocks deform brittlely and fracture. Deeper underground, higher temperatures cause ductile deformation where rocks flow plastically. The stress-strain behavior of rocks is important for understanding their mechanical properties and failure under stress

1. STRESS
BY
ANKUR SAHAY
REG NO:-16MT001278

2. INTRODUCTION
• STRESS
It is the internal resistance of the metal/rock /soil
specimen offered against loading or deformation.
• UNIT
N/mm2 or Mpa
• STRENGTH
Maximum value of stress at which material fails.

3. DIFFERENT KINDS OF STRESS ON ROCK
Lithostatic stress:Rock beneath the Earth's surface
experiences equal pressure exerted on it from all directions
because of the weight of the overlying rock. It is like the
hydrostatic stress (water pressure) that a person feels pressing
all around their body when diving down deep in water
Differential (deviatoric) stress: In many cases,
rock may experience an additional,unequal stress due to tectonic
forces. There are three basic kinds.
tensional stress (stretching)
compressional stress (squeezing)
shearing stress (side to side shearing)

4. Strain - Rock Deformation in Response to Stress:-
Rock responds to stress differently depending on the pressure and
temperature (depth in Earth) and mineralogic composition of the rock.
Elastic deformation: For small differential stresses, less than the yield
strength, rock deforms like a spring. It changes shape by a very small
amount in response to the stress, but the deformation is not
permanent. If the stress could be reversed the rock would return to its
original shape.

5. Brittle deformation: Near the Earth's surface rock behaves in its familiar
brittle fashion. If a differential stress is applied that is greater than the rock's
yield strength, the rock fractures, it breaks. Note: the part of the rock that
didn't break springs back to its original shape. This elastic rebound is what
causes earthquakes.
Ductile deformation: Deeper than 10-20 km the enormous litho static stress
makes it nearly impossible to produce a fracture (crack - with space between
masses of rock) but the high temperature makes rock softer, less brittle, more
malleable. Rock undergoes plastic deformation when a differential stress is
applied that is stronger than its yield strength. It flows. This occurs in the
lower continental crust and in the mantle

6. STRESS STRAIN CURVE FOR
DUCTILE MATERIAL

7. YOUNG’S MODULUS
A measure of elasticity, equal to the ratio of the stress acting on a substance to the strain
produced.
ELASTIC LIMIT
The maximum extent to which a solid may be stretched without permanent alteration of
size or shape.
PLASTIC REGION
If a material is forced beyond the elastic region, it experiences plastic deformation.
ULTIMATE STRENGTH
It is the capacity of a material or structure to withstand loads tending to elongate, as
opposed to compressive strength, which withstands loads tending to reduce size.
RESILIENCE is the ability of a material to absorb energy when it is deformed elastically,
and release that energy upon unloading.
PROOF RESILIENCE is defined as the maximum energy that can be absorbed within the
elastic limit, without creating a permanent distortion.
TOUGHNESS
It is the maximum strain energy which can be stored in material before fracture.

8. DUCTILITY is a solid material's ability to deform under tensile stress; this is often
characterized by the material's ability to be stretched into a wire.
BRITTLENESS A material is brittle if, when subjected to stress, it breaks without significant
deformation.
Malleability is the quality of something that can be shaped into something else without
breaking, like the malleability of clay.
CREEP –It is a plastic deformation which is permanent in nature and it occurs with time at
constant loading.
Fatigue is the weakening of a material caused by repeatedly applied loads. It is the
progressive and localised structural damage that occurs when a material is subjected to
cyclic loading.

9. 3-D STRESS ELEMENT
Stress is a tensor quantity means it is bidirectional.
In 3-D stress element, there are 9 stress component can be
expressed in the form of matrix.
In 2-D loading there will be only 4 stress elements.

11. ELASTIC CONSTANT
1. MODULUS OF ELASTICITY OR YOUNG’S MODULUS
Ratio of stress to strain within the elastic limit is a constant which is
defined by Hooke as the Modulus of elasticity or Young’s modulus (E).
2. SHEAR MODULUS OR MODULUS OF RIGIDITY
Denoted by G, or sometimes S , is defined as the ratio of shear
stress to the shear strain.
3. BULK MODULUS(K)
It is defined as the ratio of direct stress and volumetric strain.
4. POISSON’S RATIO
Defined as the ratio of lateral strain and longitudinal strain.

12. INTER RELATIONSHIP B/W
ELASTIC CONSTANTS

13. UNCONFINED COMPRESSIVE
STRENGTH OF ROCK SAMPLE

16. SHEAR STRENGTH OF ROCK
The compressive strength of rock is a function of the confining
pressure. As the confining pressure increases so does the strength.
The variation of peak stress with confining pressure is referred as
rock criterion of failure.
The simplest and the best known method is Mohr Coulomb
criterion : the linear approximation of variation of peak stress with
confining pressure.

17. MOHR CIRCLE
• Graphical construction that visualize the
relationship between the principal stresses
and tractions on a boundary (like a fault).

20. COULOMB LAW OF FAILURE
t
c
sn
Coulomb equation
tc = c + tan f sn
Where,
tc = critical shear stress required for
faulting (shear strength)
c = cohesive strength
tan f = coefficient of internal
friction = m
f

21. MOHR-COLOUMB FAILURE CRITERION

22. MOHR STRESS DIAGRAM
a) Mohr circle radius = ½(s1 – s3] that is
centered on ½(s1 + s3] from the origin.
b) The Mohr circle radius, ½(s1 - s2] is the
maximum shear stress ss max.
c) The stress difference (s1 – s3), called
differential stress is indicated by sd

23. BYERLEE'S LAW
Byerlee's law, also known as Byerlee's friction law concerns the shear
stress (τ) required to slide one rock over another.
For a given experiment and at normal stresses (σn) below about 200
MPa the shear stress increases approximately linearly with the normal stress (τ =
0.85 σn) and is highly dependent on rock type and the character (roughness) of
the surfaces . Byerlee's law states that with increased normal stress the required
shear stress continues to increase, but the rate of increase decreases (τ = 0.5 + 0.6
σn), and becomes nearly independent of rock type.
The law describes an important property of crustal rock, and can be used
to determine when slip along a geological fault takes place.

26. THANK YOU