Anistropy is an important feature of the materials that needs to be kept in view for processing. The strength of materials may depend on the Anisotropic behavior of the material.

1. DIRECTIONAL PROPERTIESDIRECTIONAL PROPERTIES
OF MATERIALSOF MATERIALS
andand
APPLICATION OFAPPLICATION OF
CONTROLLED ANISTROPYCONTROLLED ANISTROPY
By: Rub Nawaz Ansari

2. DIRECTIONAL PROPERTIESDIRECTIONAL PROPERTIES
OF MATERIALSOF MATERIALS
Substances in which measured properties
are independent of the direction of
measurement are isotropic
The physical properties of single crystals of
some substances depend on the
crystallographic direction in which
measurements are taken; this directionality
of properties is termed as anisotropy
Common examples of anisotropic materials
are wood and composites.

3. an amorphous solid is isotropic.
In contrast, crystalline materials are
generally anisotropic, so the magnitude of
many physical properties depends on
direction in the crystal.

4. CrystallineCrystalline AmorphousAmorphous

5. The dependence of the physical
properties (mechanical, thermal,
electrical, magnetic, and optical) of a
substance on direction (as opposed to
isotropy, the independence of properties
from direction).
However, not all the properties of
crystals are Directional. The density and
specific heat capacity of all crystals are
independent of direction.

6. Daily Life Examples of DirectionalDaily Life Examples of Directional
PropertiesProperties
Examples of anisotropy are:
mica plates split easily into thin leaves
only along a certain plane (parallel to this
plane the cohesive forces between the
mica particles are very small)
meat is more easily cut along the fibers
cotton material is torn easily along a
thread (the strength of the material is the
lowest in these directions).

7. When a sphere made of an isotropic
substance is heated, it expands uniformly
in all directions, that is, it remains a
sphere. A crystalline sphere changes its
shape when heated, turning into an
ellipsoid, (Figure a)
It may happen that a sphere upon heating
will expand in change in shape of a
crystalline sphere (dashed circles) upon
heating one direction and contract in
another (perpendicular to the former
Figure b).

8. FigureFigure

9. Mechanical anisotropyMechanical anisotropy
Mechanical anisotropy is the variation of
mechanical properties—strength, solidity,
viscosity, and elasticity—in various
directions.
Polycrystalline materials (metals and
alloys), consisting of an aggregation of
randomly oriented crystal grains
(crystallites), are in general isotropic or
nearly isotropic.

10. The anisotropic properties of
polycrystalline materials become manifest
if as a result of processing (annealing,
rolling, and so on) a preferred orientation
of the individual crystals is developed in
some direction (structure).
Thus, during the rolling of steel plate the
grains of the metal are oriented in the
direction of the rolling, and anisotropy
occurs as a result (chiefly in the
mechanical properties)

11. for example, in rolled steels the yield
limit, and the ultimate elongation along
and across the direction of rolling differ
by 15 to 20 percent (up to 65 percent).

12. TEXTURETEXTURE
 Sometimes the grains in polycrystalline materials have a
preferential crystallographic orientation, in which case
the material is said to have a “texture.”
 The magnitude of a measured property represents
some average of the directional values. In material
science, texture is the distribution of crystallographic
orientations of a polycrystalline sample.
 A sample in which these orientations are fully random
is said to have no texture. If the crystallographic
orientations are not random, but have some preferred
orientation, then the sample has a weak, moderate or
strong texture.

13. Anisotropy in polycrystalline materials can
also be due to certain texture patterns often
produced during manufacturing of the
material.
In the case of rolling, "stringers" of texture
are produced in the direction of rolling,
which can lead to vastly different properties
in the rolling and transverse directions.
Some materials, such as wood and fiber-
reinforced composites are very anisotropic,
being much stronger along the grain/fiber
than across it.

14. Directionally dependent physical
properties of anisotropic materials are
significant due to the affects it has on
how the material behaves.
For example, in the case of fracture
mechanics, the way the microstructure of
the material is oriented will affect the
strength and stiffness of the material in
various directions therefore affecting
direction of crack growth.

15. Mechanical analogy ofMechanical analogy of
anisotropic responseanisotropic response
This can be demonstrated with a simple
mechanical model, consisting of a mass
supported by two springs.
This can be demonstrated with a simple
mechanical model, consisting of a mass
supported by two springs.

16. The following photographs show the
response of the model under the
application of various forces.
 Model with no force applied Model with horizontal force
producing horizontal displacement
(parallel response) 90o

17. Model with vertical force producing Model with 45º displacement from
vertical displacement non-45º force (non-parallel
(parallel response) 0o
anisotropic response) 45º
Note that the displacement of the mass is only
parallel to the force when the force acts parallel
or perpendicular to the springs. These are the
directions of the principal axes.

18. When heating the section cut
perpendicularly to the c-axis, the
observed shape is a circle, showing
that the thermal conductivity is the
same in all directions in this plane.
However, when using the section
cut parallel to the c-axis, the shape
seen is an ellipse, which shows that
the thermal conductivity in this plane
is direction-dependent.

19. Images of heat flow patterns

20. Applications of ControlledApplications of Controlled
AnistropyAnistropy
Anisotropy may be induced in a material
during the manufacturing through processes
like rolling or forging or Aneealing.
This induced anisotropy gives rise to the
concept of orientation-dependent material
properties such as yield strength, ductility,
strain hardening, fracture strength, or fatigue
resistance. Inclusion of the effects of
anisotropy is essential in correctly predicting
the deformation behavior of a material.

21. ALUMINIUMALUMINIUM
Annealing may change the anisotropy of
tensile properties.
In the as-rolled condition Aluminium, the
transverse direction is the strongest and
45 degrees to the rolling direction is the
weakest.
On annealing at 280 and 300 °C the
anisotropy is unchanged but annealing at
340 °C affects anisotropy.

22. Aluminum alloy castings can display the
tensile properties of most forgings,
extrusions and rolled plate.
Because wrought products are normally
characterized by finely recrystallized grain
structures with specific anisotropy and
highly textured microstructural features,
ductility in longitudinal directions is
typically greater than in castings that
contain coarser grain structures.

23. Anisotropic behavior in a rolled aluminum-lithium sheet material usedAnisotropic behavior in a rolled aluminum-lithium sheet material used
in aerospace applications. The sketch relates the position of tensilein aerospace applications. The sketch relates the position of tensile
bars to the mechanical properties that are obtainedbars to the mechanical properties that are obtained

24. A number of fan blades for cooling
automotive and truck engines,
manufactured through stamping
blades from cold-rolled steel sheet.
All produced at the same time, have
failed by the initiation and
propagation of a fatigue crack
transverse to the axis of the blade
All other fan blades perform
satisfactorily.

26. Cast IronCast Iron
Cast iron, is composed of anisotropic
graphite inclusions in a metal matrix. One
application of cast iron can be found in
truck engine cylinder heads.

27. A problem present in cylinder heads
is thermo-mechanical fatigue (TMF).
TMF is related to the thermal
stresses developed due to the start
up-shut down thermal cycling, which
leads to valve bridge cracking and
ultimately to TMF failure.

28. TMF cracks at valve bridges

29. Types of Graphite FlakesTypes of Graphite Flakes

30. Thank You
Very Much