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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