Deformable Body MechanicsDeformable Body Mechanics

Engr .Saeed Ahmed MaitloEngr .Saeed Ahmed Maitlo

LecturerLecturer

Institute of Biomedical Technology Institute of Biomedical Technology LUMHS JamshoroLUMHS Jamshoro

Applied MechanicsApplied MechanicsRigid Body MechanicsRigid Body Mechanics

StaticsStaticsDynamicsDynamics

KinematicsKinematicsKineticsKinetics

Deformable Body MechanicsDeformable Body MechanicsElasticityElasticityPlasticityPlasticityViscoelasticityViscoelasticity

Fluid MechanmicsFluid MechanmicsLiquidsLiquidsGasesGases

Deformable Body MechanicsDeformable Body Mechanics

The mechanics of deformable bodies is the The mechanics of deformable bodies is the field that is concerned with the deformability field that is concerned with the deformability of objects. An elastic body is defined as one of objects. An elastic body is defined as one in which all deformations are recoverable in which all deformations are recoverable upon removal of external forces. this feature upon removal of external forces. this feature of some materials can easily be visualized of some materials can easily be visualized by observing a spring or a rubber band.by observing a spring or a rubber band.If you stretch (deform) a spring and then If you stretch (deform) a spring and then release it (remove the applied force), it will release it (remove the applied force), it will resume its original (unreformed) size and resume its original (unreformed) size and shape.shape.

A plastic body ,on the other hand, undergoes A plastic body ,on the other hand, undergoes permanent (unrecoverable) deformations.permanent (unrecoverable) deformations.Again use a spring apply a large force on Again use a spring apply a large force on spring so as to stretch the spring spring so as to stretch the spring extensively, and then release it. the spring extensively, and then release it. the spring will bounce back, but there may be increase will bounce back, but there may be increase in its length. in its length. Note that depending on the extent and Note that depending on the extent and duration of applied forces, a material may duration of applied forces, a material may exhibit elastic or elastoplastic as in the case exhibit elastic or elastoplastic as in the case of springof spring

ElasticityElasticity

The beam can bend to conform to the constraints of the supports.

Elasticity vs. PlasticityElasticity 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.

VISCOELASTICITYVISCOELASTICITY

First define what is known as a fluid. in First define what is known as a fluid. in general, materials are classified as either general, materials are classified as either solid or fluid. When an external force is solid or fluid. When an external force is applied to a solid body, the body will applied to a solid body, the body will deform will certain extent. the continuous deform will certain extent. the continuous application of the same force will not application of the same force will not necessarily deform the solid body necessarily deform the solid body continuously.continuously.

on the other hand , a continuously applied on the other hand , a continuously applied force on a fluid body will cause a force on a fluid body will cause a continuous deformation (flow).viscosity is continuous deformation (flow).viscosity is a fluid property that is quantitative a fluid property that is quantitative measure of resistance to flow.measure of resistance to flow.In nature there are some materials that In nature there are some materials that have both fluid and solid properties. the have both fluid and solid properties. the term viscoelastic is used to refer to the term viscoelastic is used to refer to the mechanical properties of such materials mechanical properties of such materials exhibit viscoelastic properties. exhibit viscoelastic properties.

Elasticity vs. ViscoelasticityElasticity 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 CONCEPTSBASIC CONCEPTS

Engineering mechanics is based on Engineering mechanics is based on Newtonian mechanics in which the basic Newtonian mechanics in which the basic concepts areconcepts areLengthLengthTime Time MassMassThese are absolute concepts because These are absolute concepts because they are independent of each otherthey are independent of each otherLength: is a concepts for describing size Length: is a concepts for describing size quantitativelyquantitatively

Time is a concepts for ordering the flow of Time is a concepts for ordering the flow of events.events.Mass is the property of all matter and is Mass is the property of all matter and is the quantitative measure of inertia. inertia the quantitative measure of inertia. inertia is the resistance to the change in motion is the resistance to the change in motion of matter.of matter.

Newton's Second LawNewton's Second Law

Acceleration is produced when a force Acceleration is produced when a force acts on a mass. The greater the mass acts on a mass. The greater the mass (of the object being accelerated) the (of the object being accelerated) the greater the amount of force needed (to greater the amount of force needed (to accelerate the object).accelerate the object).

ExampleExampleMike's car, which weighs 1,000 kg, is out of gas. Mike is 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 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 car go 0.05 m/s/s. Using Newton's Second Law, you can compute how much force Mike is applying to the car.compute how much force Mike is applying to the car.

F = ma; 1000*0.5=F = ma; 1000*0.5=

Answer = 50 newtonsAnswer = 50 newtons

Newton's Third LawNewton's Third Law

Newton's third law states that to every Newton's third law states that to every body action there is always an equal body action there is always an equal reaction, and that the force of action reaction, and that the force of action

Presentation topicsPresentation topics

laws of triangle.laws of triangle.

Parallelogram.Parallelogram.

Polygon forces.Polygon forces.