Lab Manual | study of Impact Testing m/c and Perform charpy impact test

AIM:- To study the Impact Testing m/c and Perform charpy impact test.

APPARATUS :- Impact testing m/c, charpy test specimens of mild steel, Aluminium, Vernier caliper, specimen setting fixture.

THEORY :- In manufacturing locomotive wheels, coins, connecting rods etc. the components are subjected to impact (shock) loads. These loads are applied suddenly. The stress induced in these components are many times more than the stress produced by gradual loading. Therefore, impact tests are performed to asses shock absorbing capacity of materials subjected to suddenly applied loads. These capabilities are expressed as (i) Rupture energy (ii) Modulus of rupture and (iii) Notch impact strength.

Two types of notch impact tests are commonly-

3. Charpy test

4. Izod test

In charpy test, the specimen is placed as ‘cantilever beam’. The specimens have V-shaped notch of 45°. U-shaped notch is also common. The notch is located on tension side of specimen during impact loading. Depth of notch is generally taken as t.5 to t/3 where ‘t’ is thickness of the specimen.

SPECIFICATION OF M/C AND SPECIMEN DETAILS : Its specifications along-with their typical values are as follows:

· Impact capacity = 300joule

· Least count of capacity (dial) scale = 2joule

· Weight of striking hammer = 18.7 kg.

· Swing diameter of hammer = 1600mm.

· Angle of hammer before striking = 160°

· Distance between supports = 40mm.

· Striking velocity of hammer = 5.6m/sec.

· Specimen size = 55x10x10 mm.

• Type of notch = V-notch

· Angle of notch = 45°

· Depth of notch = 2 mm.

PROCEDURE :-

1. Lift the hammer to an appropriate knife edge position and notch the energy stored in the hammer. For the standard charpy test the energy stored should be 164j.

2. Locate the test specimen on the m/c supports.

3. Release the hammer. The hammer will break the piece and shoot up the other side of the specimen.

4. Note the residual energy indicated on the scale by the hammer.

5. Impact strength of the test specimen is the difference of the initial energy stored in hammer and the residual energy.

OBSERVATION :-

S.No.	Initial Energy (E1) in joule	Residual joule	Energy	(E2)	in	Absorb Energy (E1-E2)

CALCULATION :-

· Modulus of rupture = Rupture / Effective volume of specimen

· Notch impact strength = Absorb energy / Effective cross section area

PRECAUTIONS :-

6. The specimen should be prepared in proper dimensions.

7. Take reading more frequently.

8. Make the loose pointer in contact with the fixed pointer after setting the pendulum.

9. Do not stand in front of swinging hammer or releasing hammer.

10. Place the specimen proper position.

RESULT :- The impact strength of given specimen = joule/mm2

CONCLUSION :-

VIVA-QUESTIONS :-

· In what way the values of impact energy will be influenced if the impact tests are conducted on two specimens, one having smooth surface and the other having scratches on the surface ?

· What is the effect of temp. on the values of rupture energy and notch impact strength ?

· What is resilience? How is it different from proof resilience and toughness?

· What is the necessity of making a notch in impact test specimen ?

· If the sharpness of V-notch is more in one specimen than the other, what will be its effect on the test result ?