Hello friends, Today we are going to talk about types of
hardness testing methods and impact testing.
Hardness tests are used to determine the hardness of any materials and impact testing is used for determining toughness.
Before knowing the types of hardness testing methods and impact testing first of all we have to know what is hardness and toughness?
Hardness and toughness both are the mechanical properties of materials which I have already discussed in our previous article.
The simple method of hardness testing of steel is the trial and
error method using a file, which is often referred to as
a file test.
According to modern science, many modern methods are adopted by which the
hardness of a metal can be tested with precision which is discussed below in
detail.
So, without wasting time let's know the types of hardness testing methods.
What is Hardness?
Hardness in steel can be defined as a property that resists penetration and deformation.The harder the steel, the more resistant it is to penetration and deformation.
Types of Hardness Testing Methods
There are the following types of hardness testing methods are used to determine the hardness of materials.- Rockwell Hardness Test
- Brinell Hardness Test
- Vickers Hardness Test
- Shore Scleroscope Hardness Test
- Knoop Hardness Test
- Mohs Hardness Test
- Barcol Hardness Test
 |
| Hardness Testing Methods |
Rockwell Hardness Test
Show in the figure some different Rockwell hardness scales for different materials.
 |
| Rockwell Hardness Scale |
Brinell Hardness Test
In these types of hardness tests, a round ball is used which is forced on the work surface.The ball is made up of hardened steel, and ball diameter is used up to 10mm.
In this test, a load of 3,000 kg is applied to test iron alloys and other similarly hard alloys.
If brass or similar soft metals are to be tested, then a load of 500 kg is applied.
The loading time is taken 10 seconds to 30 seconds maximum.
The diameter of the mark or impression is measured with a special microscope.
And then the value of brinell hardness number is calculated by the following formula:
BHN = Load/Area of Impression or Indentation
BHN = 2P/πD(D−√D^2 − d^2)
Where,
P = Load (Kgf)
D = Diameter of ball (mm)
d = Diameter of indentation (mm)
BHN = Brinell hardness number
The higher the Brinell number, the harder the metal.
These types of hardness tester are mostly applicable for material that is made up of mild steel, aluminum, low carbon steel, and copper.
Vickers Hardness Test
Vickers hardness can be calculated using the following formula:
Vickers hardness value = 18544XP /d^2
Where,
d = average hypotenuse of a mark in mm
These types of hardness testers are mostly applicable for that material which is made up of high carbon steel, silicon carbide, tungsten, carbide, etc.
Shore Scleroscope Hardness Test
These types of hardness testing methods are performed with a diamond-tipped hammer that is dropped from a given height on metal.Conversely, the degree of return reveals the degree of
hardness.
Knoop Hardness Test
These types of hardness tester are mostly used for very brittle and small thin metal and also used for micro size materials like memory cards, sim cards.These types of hardness tests also used the diamond pyramid as an Indentor tool.
The load is applied up to 25g to 5kg.
Knoop hardness tester can be calculated by using this formula,
HK = 14.2XP/d
Where,
Where P = load in kgf
d = average hypotenuse of a mark in mm
Mohs Hardness Test
It's a qualitative hardness test is also known as a scratch test.It measures hardness by applying scratch on the specimen without any quantitative number.
These types of tests are applied to that material that can't be tested by other hardness testers.
Barcol Hardness Test
These types of hardness tests are used for the hard polymer, thermosetting polymer.After discussing types of hardness testing methods, now we will know the types of impact testing that are used to find the toughness of any material.
What is Toughness?
Toughness is the mechanical properties of materials that are capable to resist impact loads.Impact Testing
In production, impact load is applied on locomotive wheels, connecting roads, etc.The value of this load is very high, and it acts on the metal components for a short time.
So the ability of the material to bear the impact load is
checked by the impact test.
For testing of toughness, a specimen is used in an impact testing
machine.
The surface of these types of specimens is made smoothly by machining and grinding.
In this specimen, a notch is cut by a milling machine through a milling cutter.
Then this test piece is broken with a blow in one stroke by holding the test piece to the impact test machine.
Impact testing is used to measure the relative
shock and impact resistance of a test specimen.
Types of Impact Testing
Generally, two types of impact testing are used.
- Charpy Impact Testing
- Izod Impact Testing
 |
| Types of Impact Testing |
Charpy Impact Testing
A specimen is used in this test.It has a specimen (10x10x55mm) cut and has a V notch up to 2 mm deep at 45°.
In this, the specimen is placed on the support like a simply supported beam.
During charpy Impact testing, the pendulum hammer position keeps up to 140°.
Now, the pendulum hammer strikes in the specimen opposite direction to the V notch.
In this way, energy is used to break the specimen which is shown in the digital dial of a machine in a joule which is the capability of that material to resist impact load.
Izod Impact Testing
It has a specimen (10x10x75mm) cut and alsoa has a V notch up to 2 mm deep at 45°.This test piece is broken with the pendulum hammer which is attached to the machine.
During Izod Impact testing the pendulum hammer position kept up to 90°.
Now, the pendulum hammer strikes the specimen in the same direction as the V notch.
In this way, energy is used to break the test piece which is shown in a digital dial of the machine in a joule.
So, here I discussed types of hardness testing methods and impact testing.
I hope you all like these posts.
Thank You.
1 Comments
For this kind of job.