# Strength of Material Important Definitions – For Engineering Exams – Free Study Material

Define Hooke’s law?

Within the elastic limit, when a body is loaded, then stress induced is proportional to the strain. This is called as Hook’s law.

What is linear strain?

The ratio of increase or decrease in length to the original length is called as linear strain.

What is lateral strain?

The ratio of increase or decrease in lateral dimensions to the original lateral dimensions is called as lateral strain.

What are the types of elastic constants?

Modulus of elasticity or Young’s
modulus
Modulus of rigidity or shear modulus
Bulk modulus

What is poison’s ratio?

When a member is stressed with in elastic limit, the ratio of lateral strain to its corresponding linear strain remains constant throughout the loading. This constant is called as poison’s ratio. It is the ratio of lateral strain to longitudinal or linear strain.

What is the inter relationship between the three constants?

E=2G (1+ µ) = 3K( 1 – 2µ) =9KG/(3K+G)

Where, E = Young’s modulus in N/mm2
K = Bulk modulus in N/mm2
G = Modulus of rigidity in N/mm2. µ Poisson’s ratio

Define bulk modulus?

When a body is stressed the ratio of direct stress to the corresponding volumetric strain is constant with in elastic limit. This constant is called as bulk modulus. Bulk modulus is the ratio of direct stress to volumetric strain.

Define modulus of elasticity?

Modulus of elasticity is the ratio of stress to strain.

Define factor of safety?

Factor of safety is defined as the ratio of ultimate stress to the working stress (permissible stress).

What is elasticity?

The deformation produced due to the application of external load disappears completely with the removal of the load.This property of the material is called as elasticity.

What is elastic limit?

Elastic limit is the limiting value of the load up to which the material returns back to its original position. Beyond this load, the material will not return back to its original position.

What are thermal stresses and strain?

Whenever there is increase or decrease in the temperature of the body, the body tends to expand or contract. If this deformation is
prevented, some stresses are induced in the body, these stresses
are called as thermal stresses or temperature stresses. The
corresponding strains are thermal strain or temperature strains.

Thermal stress is σt =α T E where α is co-efficient of linear expansion, T is rise in temperature E is young’s modulus

Temperature stain or thermal strain =
Extension prevented/ original length

Extension prevented = α T L
So thermal strain is et = α T

If the values of E and µ for an alloy body is 150 GPa and 0.25
respectively, find out the value of bulk modulus for the alloy?

Bulk modulus, K = (mE) / [3(m-2)] = 100 × 10 ^3
N / mm^2

What is a compound or composite bar?

A bar made of two or more different materials, joined together is called a compound or composite bar.

Write the Compatibility equation for solving compound bar problems

The extension or contraction in each bar is equal. Hence deformation per unit length
i.e. strain in each bar is equal.
δℓ = δℓ1= δℓ2= δℓ3
δℓ = Pl/ AE