strength of materials ch 1 unfinished
DESCRIPTION
stess and strainTRANSCRIPT
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STRENGTH OF MATERIALS
MOHAMMAD AIZRULSHAH BIN KAMARUDDINPPPTDH42M PRODUCT DESIGN
DEPARTMENT OF MECHANICAL ENGINEERINGPOLITEKNIK MUADZAM SHAH
BY
JJ310
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CHAPTERFORCES ONM TERI LS
JJ310
This topics will analyses the effect of forces onmaterials, HOOKEs LAWS, Shear stress and Shear
and Shear strain
Objectives Explain the effect of forces on materials
Differentiate between tensional , compression and shear forces
Define stress, strain and YOUNGS MODULUS
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OUTLINE
Fundamental concept
Dynamics
Statics
Impact
Fatigue and Alternating loads
Type of forces
Tensional
compression
shear
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Effects forces on materials
Force
Force is a quantitative description of the interaction between two
physical bodies, such as an object and its environment. Force is
proportional to acceleration. In calculus terms, force is the derivative
of momentumwith respect to time. Unit in N or kgm/s2
=
Where
=
=
http://physics.about.com/od/glossary/g/acceleration.htmhttp://physics.about.com/od/glossary/g/momentum.htmhttp://physics.about.com/od/glossary/g/momentum.htmhttp://physics.about.com/od/glossary/g/acceleration.htm -
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Effects forces on materials
Dynamics
The rigid body in analysis is in motion.
Statics
The rigid body in analysis is in stationary state.Impact
is a high forceor shockapplied over a short timeperiod when two or more bodies collide
http://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Shock_(mechanics)http://en.wikipedia.org/wiki/Shock_(mechanics)http://en.wikipedia.org/wiki/Force -
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Effects forces on materials
Fatigue
weakening of a material caused by repeatedlyapplied loads( alternating loads)
Alternating loads
Load that is applied, removed and applied again, always acting onthe same direction
Alternating load that reverse direction during every cycle of loading.
Fluctuating load that varies about an average value.
commonly associated with machinery, engines, turbines, generators,shafts, propellers, airplane parts, automobile parts..
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TYPE OF FORCES
Tensile
Tensile is a force that
tends to stretch a
material.
increase the length
Example?
Compressive
Compressive is a force that
tends to squeeze or crusha
material.
Example?
Shear
Shear is a force that
tends to slideone face of
the material over an
adjacent face.
bend, slide or twist.
Example?
decrease the length
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Problem 1
Figure (a) represents a crane and Figure (b) a
transmission joint. State the types of forcesacting, labeled A to F.
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STRESS & STRAIN
STRESS
The intensity forces acting on a material innormal direction that cause deformation orchange of dimension.
Ratio of applied force Fcross sectional areaAofthe material
Tensile stress
Compressive stress
1 Pa = 1N/m2
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Example 1
Figure 1. Shows a steel block with cross area of15000mm2subjected to loading shown.Determine the normal stress
M=500KG =
=500 9.81 /2
15000106 2
= 327000 2
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Example 2
Figure 2 shows a steel cable used to lift a mass
of 600kg. The cable cross section area is A =
2000mm2
i. Calculate the stress in the cable
ii. What will happen if the cable cross section area is reduce to
1000mm2
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Tensile stress
Force that act within a body that tends to change the
length measurement of a body.
Example 3
Example 4
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Compressive Stress
???????
Example 5
Example 6