In the previous tutorial, we have discussed the list of Material Testing Methods, in this tutorial we are going to discuss how to conduct the tensile test.
Tensile testing is used to find the behaviour of the material when it is subjected to a slowly applied tensile load up to when the material gets a fracture.
This test will be conducted on the universal testing machine. Also, know as UTM.
Universal Testing Machine
The main parts of the Universal testing machine are
- Upper cross Head
- Movable cross Head
- Load Indicator
- Speed control
- Space for tensile specimen
- Space for Compressive Specimen
Construction of Universal Testing Machine
The universal testing machine has two vertical threaded shafts where the movable crosshead will slide on these vertical Bars. the Cross head will be constant. If it is a tensile test then the specimen will be placed in between the Cross head and the movable head jaws, if it is a compressive test The specimen will be placed in between the movable head and the table. With the help of the loading dial indicator, we can observe how much load is applied to the specimen during the test.
We can do both the Tensile test and the compressive test on this universal testing machine.
Back to the subject Tensile testing, We have to place the specimen in between the upper crosshead and the movable crosshead for tensile tesing.
Now we have to apply the load gradually so that the movable crosshead will move downwards.
We have to slowly increase the load until the specimen get a fracture or break completely.
Stress-strain diagram for the Tensile testing
- A = Proportional limit
- B= Elastic limit
- C = Yield Point
- D = Ultimate Tensile Strength
- E = Fracture
- O-B = Elastic region
- B-E = Plastic Region
Read more about the Stress-strain diagram here!
You can see that the specimen will be able to elongate and can come back to its original shape when the load is removed up till the point B since it is the elastic limit.
After the applied load crosses elastic limit the specimen cannot regain its original shape even after removal of the load but still, it will elongate till the Point D. The point D is called Ultimate tensile strength.
After the load reaching the point D, the specimen starts necking (Reduction in the cross section) due to the local extension.
Due to the necking, the load will be reduced for the final fracture. you can observe the drop in the graph from point D to the point E.
Stress-strain diagram for the different materials
Stress-strain diagram for the different materials is shown below
a) Stress-strain diagram for Brittle material vs the Ductile material
b) Stress-strain diagram for Carbon steels, cast iron, plastic
This is how we will conduct the tensile test and observation of the fracture for the different materials. If you have any thought please let us know in the comments sections.