Strength of materials Basic concepts

First of all latest talk about some good books which we should follow while preparing a strength of materials for gate and Engineering services exams.

Mechanics of materials by timoshenko and Giri

Strength of materials by singer

Strength of materials by ramamrutham, Dhanpat Rai Publication

Weight age of Strength of Materials and machine design in GATE
In GATE exam the weightage of Strength of Materials and machine design is of 15 marks all together in which 10 to 12 marks are asked from strength of materials while 3-4 marks questions are asked from machine design.

Comparison of Engineering mechanics and strength of material
Engineering Mechanics - In engineering mechanics, we study about the external forces and its effect on the rigid body. Since the bodies rigid so there will not be any type of stress or strain in such bodies and so we never come across is strain and stress in engineering mechanics subject.

Strength of materials - In strength of material, we study about internal resisting forces occurring due to external forces applied on deformable bodies. Since the bodies are deformable so there will be a stress and strain produced in the body because of deformation.

Aim of strength of material and machine design
The aim of strength of material is to derive expression for different is stress and strain which are developed under different loading conditions by using experimentally obtained elastic properties while the aim of machine design is to develop a drawing a plan i.e. selection of an appropriate material, selection of appropriate shape and calculation of dimensions by using the strength of material equations, selection of manufacturing process etc, in such a way that the resulting machine component performs its functionality satisfactorily without failure.

Homogeneous and isotropic material
A material is it to be homogeneous when it exhibits same elastic properties at any point in a given direction i.e. the elastic properties are independent of point in homogeneous material.

A material is said to be isotropic when it exhibits same elastic properties in any direction at a given point i.e. elastic properties are independent of direction in isotropic materials.
Please note that every homogeneous material need not to be isotropic and vice versa.

A material is said to be both homogeneous and isotropic when it exhibits same elastic properties in any direction and at any point i.e. elastic properties are independent of both point and direction in such materials.

Anisotropic - a material is said to be an isotropic when it exhibits direction dependent elastic properties at a given point.


Load - it is defined as an external force or a couple to which a component is subjected during its functionality.

Dynamic loads

Impact loads - these are those loads which are acting for a short interval of time. Example IC engine piston and connecting rod during power stroke, components used in forging, punching etc.

Fatigue loads - these are those loads whose magnitude or direction or both changes with respect to time and are repeatedly applied.

Gradually applied load - these are those loads whose magnitude and direction both are constant with time and act for a very long time and slowly.

Completely reversed fatigue load - these are those fatigue loads whose only direction changes but not the magnitude. Note that this is worst type of loading condition in which the components suffers the most.

Fluctuating fatigue load - only magnitude of load changes and not the direction. Example of such a loading condition is belt in belt and Pulley drive.

Alternating fatigue load - both direction and magnitude of load changes in such loading conditions.