Transcript lecture 3 deformable body - IBT LUMHS

Deformable Body Mechanics
Engr .Saeed Ahmed Maitlo
Lecturer
Institute of Biomedical Technology
LUMHS Jamshoro
Applied Mechanics
Rigid Body Mechanics
Statics
Dynamics
Kinematics
Kinetics
Deformable Body Mechanics
Elasticity
Plasticity
Viscoelasticity
Fluid Mechanmics
Liquids
Gases
Deformable Body Mechanics
The mechanics of deformable bodies is
the field that is concerned with the
deformability of objects. An elastic body is
defined as one in which all deformations
are recoverable upon removal of external
forces. this feature of some materials can
easily be visualized by observing a spring
or a rubber band.
If you stretch (deform) a spring and then
release it (remove the applied force), it
will resume its original (unreformed) size
and shape.
A plastic body ,on the other hand,
undergoes permanent (unrecoverable)
deformations.
Again use a spring apply a large force on
spring so as to stretch the spring
extensively, and then release it. the spring
will bounce back, but there may be
increase in its length.
Note that depending on the extent and
duration of applied forces, a material may
exhibit elastic or elastoplastic as in the
case of spring
Elasticity
The beam can bend to conform to the constraints of the supports.
Elasticity vs. Plasticity
Elastic: You can bend it, but it will come right back
when you remove the external force (like a spring).
Plastic: You can bend it, and it will stay where it left
off (like soldering wire).
Some materials tend to behave elastically, some
plastically, but….
Almost all materials will have both behaviors.
Small deflection – elastic.
Large deflection – plastic.
VISCOELASTICITY
First define what is known as a fluid. in
general, materials are classified as either
solid or fluid. When an external force is
applied to a solid body, the body will
deform will certain extent. the continuous
application of the same force will not
necessarily deform the solid body
continuously.
on the other hand , a continuously applied
force on a fluid body will cause a
continuous deformation (flow).viscosity is
a fluid property that is quantitative
measure of resistance to flow.
In nature there are some materials that
have both fluid and solid properties. the
term viscoelastic is used to refer to the
mechanical properties of such materials
exhibit viscoelastic properties.
Elasticity vs. Viscoelasticity
Elastic: Force is proportional to deflection (e.g. a spring).
Viscoelastic: Force is proportional deflection AND to rate of
deflection (e.g. silly putty).
Viscous: Force is proportional to deflection only (e.g. a shock
absorber or a fluid).
BASIC CONCEPTS
Engineering mechanics is based on
Newtonian mechanics in which the basic
concepts are
Length
Time
Mass
These are absolute concepts because
they are independent of each other
Length: is a concepts for describing size
quantitatively
Time is a concepts for ordering the flow of
events.
Mass is the property of all matter and is
the quantitative measure of inertia. inertia
is the resistance to the change in motion
of matter.
Newton's Second Law
Acceleration is produced when a force
acts on a mass. The greater the mass
(of the object being accelerated) the
greater the amount of force needed (to
accelerate the object).
Example
Mike's car, which weighs 1,000 kg, is out of gas.
Mike is trying to push the car to a gas station, and he
makes the car go 0.05 m/s/s. Using Newton's Second
Law, you can compute how much force Mike is
applying to the car.
F = ma;
1000*0.5=
Answer = 50 newtons
Newton's Third Law
Newton's third law states that to every
body action there is always an equal
reaction, and that the force of action
Presentation topics
laws of triangle.
Parallelogram.
Polygon forces.