Mechanics of Materials ISKMM 1113

INTRODUCTION TO STRESSLecture 01-03

Instructor:Dr Muhammad Adil Khattak

(PhD,ME,MBA,BE)

017-8272871muhdadil@utm.my

Important!

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• Title: SKMM1113 - SOLID MECHANICS I – Feb,May 2014

Mechanics of Materials

Equilibrium of a Deformable Body

Reactions

Equations of Equilibrium

Equilibrium of a Deformable Body

EXAMPLE 1

Free Body Diagram (FBD)

Solving FBD

Example 2

Lets have a clear look!

Lets build its FBD

Another Look…

Start Solving step by step…

Finally got the solution!

Example 3

A closer & Bigger look!

To the point…

Finally….

Stress

Stress

Average Normal Stress in an Axially Loaded Bar

Average Normal Stress in an Axially Loaded Bar

Example 1

Using our previous knowledge…

Example 2

Problem easily done!

Average Shear Stress

Single Shear

Single Shear

Double Shear

Double Shear

Example 1

Looking for the answers!

Example 2

Lets have a closer look!

Solving the un-solved!

Finally….

FoS (Based on yield strength)

Application

1.25 – 1.5

Material properties known in detailOperating conditions known in detailLoad and the resulting stresses and strains are

known to a high degree of accuracyLow weight is important

2 – 3

For less tried materials orBrittle materials under average conditions of

environment, load and stress

3 – 4

For untried materials under average conditions of environment, load and stress

Better known materials under uncertain environment or uncertain stresses

Factor of Safety (Safety Factor)

Allowable Stress

load)(Actualcomponent on the Load

load)(Maxcomponent theofStrength FoS

Factor of Safety (Safety Factor)

In the calculations,Material strengths,

Manufacturing process

Is used to provide a design margin over the theoretical design

capacity to allow for uncertainty in the design process.

Eg: If a component needs to withstand a load of 100 N and a FoS of 3 is selected then it is designed with strength to support 300 N.

SELECTION OF FACTOR OF SAFETY (FS)

Example 1

FBD

Solution

Example 2

FBD

Solution

Solution

Example 3

FBD

Solution

Solution

Solution