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Stress
Introduction
What is Stress?
Normal Stress
Units
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View Full Document Example Stress Calculations
0.1 inch
Dia. Rod
1.0 inch
Dia. Rod
Introduction to Stress  continued
• Internal forces develop within objects due to external forces and
moments applied to an object.
• These internal forces are developed due to the stretching of numerous
atomic bonds between atoms that makeup materials.
• The average intensity of these internal forces is defined as the
stress
or
force per unit area.
• The internal force or stress developed in an object depends on the
geometric characteristics of the object such as the crosssectional area.
• The type of material used to make the object also plays a role, since the
stresses acting on the object can cause it to deflect, deform, or fracture.
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View Full Document Make an imaginary cut through a bar with an applied external force,
P
,
to view the internal forces or
stress
acting within the bar.
P
P
P
• The stress,
σ
, represents the intensity of the
internal forces due to the action of the removed
part of the bar.
• The stress is continuously distributed over the
entire crosssection.
• The FBD can be used to show that the stress,
σ
,
equals the external force,
P
, divided by the
crosssectional area,
A
.
P
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View Full Document Recall from Statics that a positive force acts in the positive direction
with respect to a coordinate axis.
x
y
Sign convention for stress using bars as examples
A positive stress is due to tension and elongation due to applied forces.
A negative stress is due to compression and shortening due to applied forces.
P
P
P
P
P
External forces acting on an object cause a
distribution of forces
in the object.
Determining this
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This note was uploaded on 05/07/2011 for the course 3ME WB1114 taught by Professor I.paraschiv during the Spring '08 term at Technische Universiteit Delft.
 Spring '08
 I.PARASCHIV

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