Chapter-4- Types of Loads

Types of Loads:-

We will see in details study of load before going into depth of strength of materials. It is very important to understand the different type of load in strength of material (s o m), then only we well be able to calculate the stress on the body.

Type of load with respect to Time.

1.Static load

    a)Dead load

    b)Gradually applied load 

2.Dynamic load

    a)Impact load

   b)Fatigue load 

Static Load

are such type of load whose magnitude and direction remains constant for the entire periods of time. Where 

Dynamic Load 

magnitude and direction are continuously changing. Those load which increases gradually with respect to time is Gradually Applied Load (G.A.P).

Impact Load

is a load which is acting for short interval of time, they are always a function of velocity. Impact load is also known as Suddenly Applied Load or Instantaneous load.

Fatigue load 

are those load whose magnitude or direction or both magnitude and direction changes with respect to time. These load are repeatedly applied load with respect to time.

Fatigue life 

of a component is defined as number of revolution that a component can undergoes before initiation of first crack. Fatigue crack can be initiated first at stress concentration region, where the surface is irregular or having some kind of defect.

Endurance Limit

is the measure of fatigue life i.e. failure stress of a material under completely reversed fatigue load condition. It is obtained from S.N curve which is drawn using fatigue test reading. It gives relation between stress and number of revolution. 

It is defined as maximum value of completely reversed bending stress that a material can withstand for an infinite no. of cycle without initiation of crack.

Based on direction of load with respect to cross section.

Normal load 

which are acting perpendicular to the plane of cross section.

Shear load 

which are acting parallel to the plane of cross section.

Axial load 

are such type of load which are acting along the longitudinal axis. 

Eccentric axial load (ECC. Axial Load) 

act parallel to the longitudinal axis.

Transverse Axial load (TSL) 

are such type of load which are acting perpendicular to the longitudinal axis. 

 Eccentric transverse axial load (ECC. TSL) 

act parallel to the longitudinal axis

  

Summery of loads:-

Sl. No.	Type of load	Plane of Cross Section	Longitudinal Axis	Centroidal Axis
1	Axial load	Perpendicular to the plane of cross section	Along the longitudinal axis	Along the polar axis
2	ECC. Axial Load	Perpendicular to the plane of cross section	Parallel to the longitudinal axis	Parallel to the polar axis
3	Transverse Shear Load	Parallel to plane of cross section	Perpendicular to longitudinal and passing through longitudinal axis	Perpendicular to poplar axis and passes through centroid of that cross section
4	ECC. TSL	Parallel to plane of cross section	perpendicular to longitudinal but away from longitudinal axis	Perpendicular to polar axis but away from centroid axis of cross sections
5	Bending Couple	Perpendicular to the plane of cross section	Along longitudinal al axis	Acts about either horizontal or vertical to centroidal axis
6	Twisting Couple	Parallel to plane of cross section	Perpendicular to the longitudinal axis	Act about the polar axis

 

 

 

Chapter-3 - Forces

Forces:-

In physics forces can be described as push and pull which changes the object in motion, In strength of material forces can be surface forces when distributed over area of surface and body forces when distributed over volume of the body.

Surface Forces - these are distributed over the area of body e.g.- Pully

Body Forces - these are distributed over the volume of body e.g.-Shaft

Chapter-2-Factor of safety (FOF)

Factor of safety (FOF)

Factor of safety:-

Factor of safety is used to determine.
     

1. Permissible Stress 
2. Allowable Stress
3. Safe Stress
4. Working Stress 

                                          

Failure Strength:-

For Static Load ;

Yield Strength is the failure criteria for the Ductile Material
Ultimate Strength is the failure criteria for Brittle Material also Ductile Material

For Static Load;

Endurance Limit is the failure criteria.

Brittle:- 

Material will not permits any deformation and goes to fractures ultimate strength will be the failure strength.

Ductile:- 

• Case-1: When a material does not undergo permanent deformation or is under the elastic limit, yield strength will be the failure strength.

• Case-1I: When Material undergo permanent deformation, ultimate strength will be the failure strength.

Chapter-1-Introductionn to Strength of Material (SOM)

Introduction to Strength of Material (SOM)-Mechanics of Deformable body

Strength of Material :-

It is study of internal resisting force developed due to elastic deformation of a body under the action of load.
Assumption made in Strength of Material Equation:-

1. Material is assumed to be homogeneous and isotropic.
2. Component is assumed to be prismatic.
3. Load is assumed as static load
4. Effect of self weight is neglected. 

Static Load:- 

When magnitude and direction is constant with respect to time.

Prismatic:-

All dimension are constant or same throughout the structure.

Homogeneous:-

Material is said it be isotropic, when it exhibit same elastic property at a point in a given direction.

Isotropic:-

Material is said it be isotropic, when it exhibit same elastic properties in any direction at a given point.