Solution
David answered on
Dec 21 2021
SOLUTIONS
Que. 1 (a) Study of Mechanical behavior of materials –
Structures are subjected with different types of load, structure are made with different types of construction & engineering materials.
The properties that calculate the behavior of material in a structure under different types of loading is called mechanical properties .These properties are calculated by testing of specimen of materials.
Stress- when a force is acting on a object and tends to deform the object, the materials of the object exerts an internal resistance force to oppose the changing in dimensions. This internal resistance force per unit area is called as Stress. Its unit is N/m2
Strain – it is defined as change in dimension to original dimension. It is unit less
P Area = A, change in length = ∆l
Stress = P/A and strain = ∆l/L
Stress is directly proportional to strain- according to Hooks law.
There are some basic Mechanical properties –
1. Strength – Capacity to resist force or pressure
2. Ductility – it’s material’s ability to be deformed or to be stretched under the action of tensile load.
3. Toughness- The amount of energy stored in a material per unit volume up to fracture point.
4. Hardness- Resistance of material against indentation, penetration, scratching & wear.
5. Stiffness- Ability of material to resist deformation.
6. Elastic modulus- Ratio of stress to strain.
7. Impact strength- Ability of material to withstand against impact or sudden load. It is given in the form of energy.
8. Strain hardening- Strengthen of metal by plastic deformation. Also called as work hardening.
9. Brittleness- These materials have very little deformation before fracture.
10. Poisson ratio- Ratio of lateral to longitudinal strain.
11. Malleability- ability of a material to be converted in to sheet under the action of compressive load.
Stress –strain diagram-
Point A – It is proportionality limit; up to this point hooks law will be followed.
Point B – Elastic limit, up to this point the deformation will be elastic.
Point C – Ultimate stress, it is the maximum value of stress in stress – strain diagram.
Point D- it is the fracture point, up to this point the material will have only elastic & plastic deformation ,but at this point fracture or rupture take place.
Que. 1 (b) - Basic thermal properties
There are basically three types of thermal properties.
1. Heat capacity- C= ∆Q/∆T it’s shows the ability of material to abso
thermal energy.
We can say that heat capacity is defined as the ratio of heat, added or removed from the system, to the change in temperature. Unit = J/0C
Specific heat c, C= mc
Heat capacity can be calculated in two conditions,
Heat capacity at Constant pressure, CP = (∆Q/∆T) P
Heat capacity at Constant volume, CV = (∆Q/∆T) v
2. Thermal expansion – If materials are heated then there will be expansion and if materials are cooled then there will be contraction.
∆L/Li = a ∆T, where Li is original length of bar. ∆T change in temperature ( Tf -Ti )
a is linear coefficient of thermal expansion. a= ∆L/ (Li ∆T)
3. Thermal stress- when materials are heated or cooled, there will be some changes in dimension of materials and a stress will be produced which is known as thermal stress because it is produced due to thermal action. For example,
For a rod the thermal stress is б=E a ∆T, where E is young modulus
The co-efficient of linear expansion- Let us take a rod of length Li at temperature Ti , now it is heated up to temperature Tf ,and final length of bar after heating is Lf
∆L = Lf – Li and ∆T = Tf – Ti
a= ∆L/ (Li ∆T) so we may say that the coefficient of linear expansion is defined as the change in length of unit length of bar due to change in temperature by unit degree. Unit = 0C-1 or K-1
The co-efficient of thermal conductivity-
According to Fourier law we have, q = - λ (dT/dX)
Where q is amount of heat flow per unit area per unit time
dT/dX is temperature gradient. If we think dT/dX = 1 then, q = - λ
Co-efficient of thermal conductivity is defined as amount of heat flow per unit area per unit time with unit temperature gradient.
Construction materials
Co-efficient of thermal expansion
Co-efficient of thermal conductivity (k - W/(m. K))
Concrete
12 10-6 0C-1
0.1 To 1.7
Timbe
3 to 5 x10-6 K-1
0.048
Steel
13 x 10-6 0C-1
54
Que. 1 (c) – Method of measuring hardness
(1) Brinell hardness test (2) Vickers hardness test (3) Rockwell hardness test
(4) Rockwell superficial hardness test (5) Micro hardness test (6) Mohs hardness test
Brinell hardness test method-
We use a ca
ide ball as indenter in this test. Indenter is placed over the surface of work piece & force is applied on indenter for 10 to 15 sec, this time duration is called as dwell time. Now indenter is removed from the work piece, indenter leaves a round indent over the surface of work piece .we measure the size of round indent with the help of portable microscope and by using following formula to calculate
inell hardness number ,we may aware that how much material is hard. More
inell hardness number shows that material is...