Meeting Number 1 1

ES 13 MECHANICS OF DEFORMABLE BODIES I

DEFINITIONS

Mechanics - science describing the behavior of bodies under the action of forces.

Three Fundamental Areas of Engineering Mechanics

1. Statics (ES 11) 2. Dynamics (ES 12)

3. Strength of Materials

/ Mechanics of Deformable Bodies I (ES 13 and 14) External Effects of a Force Internal Effects of a Force

Rigid Body - a body that does not deform under the action of forces.

Non-Rigid Body - a body that deforms under application of

loads.

Indention Bulging

Friction

Force

Devoted primarily to the study of the external effects of forces on rigid

bodies

Deals with the relations between externally applied loads and their internal effects on bodies

Deformation Development of internal stresses

Development of forces at surfaces of contact between bodies

Change in state of motion of the body

Meeting Number 1 2

LOAD CLASSIFICATION

A. According to Time

1. Static Load - gradual application of loads for which equilibrium is achieved at a very short time.

2. Sustained Load - load that is constant over a long period

of time

3. Impact Load - impulsive and rapid application of loads

4. Repeated Load - successive application and removal of loads

B. According to Distribution

1. Concentrated Load - point load 2. Distributed Load - a load distributed along a line or a

surface.

C. According to Location and Method of Application

1. Centric Load - load that pass through the centroid of the resisting section.

2. Torsional Load - load that twists a member 3. Flexural / Bending Load - load that is applied transversely

to the longitudinal axis of the member. 4. Combined Loading - any combination of the first 3 above.

Concentrated

Load

Distributed

Load

Meeting Number 1 3

REACTIONS and INTERNAL FORCES

Reactions - surface forces that develop at the supports or points of contact between bodies.

Equations of Equilibrium

General Force System

0

0

0

Fz

Fy

Fx

0

0

0

Mz

My

Mx

Coplanar Force System

0

0

0

Mp

Fy

Fx

Concurrent Force System

0

0

Fy

Fx

Internal forces - forces developed within the body of a member due to application of external loads.

T

Rx

R

Ry

Ry

Rx M

Cable

Roller

Hinge

Fixed

Meeting Number 1 4

CONCEPT of STRESS

Stress - intensity of load/force per unit area (P/A) Units: MPa, kPa, Pa, psi, ksi

Normal Stress, = N/A - stresses acting perpendicular to the surface of a cross section.

Shear Stress, = V/A - stresses acting parallel or tangent to the surface of a cross section

Consider two bars of equal length, supporting maximum axial

loads, Which bar is stronger?

Bar 1 A = 10 mm2

Bar 2 A = 1000 mm2

500 N 5000 N

= P/A (Assumed to be uniform if load is centric)

A

P

V

N Area, A

a

a