what is impact test ? how to perform in lab?

IMPACT TEST:  -  

In  a  impact  test a  specially prepared notched specimen  is fractured  by a  single  blow from a heavy hammer and energy required being a measure of resistance to  impact.  Impact  load is produced  by a  swinging  of an impact weight W (hammer) from a  height h. Release of the weight from the height h swings the weight through the arc of a circle, which strikes the specimen to fracture at the notch (fig..  Kinetic energy of the hammer at the time of impact is mv 2 /2, which is equal to the  relative  potential energy of  the  hammer before  its release. (mgh),where m is the  mass of  the  hammer  and v = 2gh  is its tangential velocity at  impact, g  is gravitational acceleration (9.806 m/s2 ) and h is the height through which hammer  falls. Impact velocity will be 5.126 m/s or slightly less.  Here it is interesting to note that height through which hammer drops determines the velocity and height and mass of a hammer combined determine the energy.



LAB WORK:

Title         Impact test 


Aim     To determine the Impact toughness (strain energy) through  Izod test and Charpy test.


Theory

 In  a  impact  test a  specially prepared notched specimen  is fractured  by a  single  blow from a heavy hammer and energy required being a measure of resistance to  impact.  Impact  load is produced  by a  swinging  of an impact weight W (hammer) from a  height h. Release of the weight from the height h swings the weight through the arc of a circle, which strikes the specimen to fracture at the notch (fig..  Kinetic energy of the hammer at the time of impact is mv 2 /2, which is equal to the  relative  potential energy of  the  hammer before  its release. (mgh),where m is the  mass of  the  hammer  and v = 2gh  is its tangential velocity at  impact, g  is gravitational acceleration (9.806 m/s2 ) and h is the height through which hammer  falls. Impact velocity will be 5.126 m/s or slightly less.  Here it is interesting to note that height through which hammer drops determines the velocity and height and mass of a hammer combined determine the energy.  Energy used  can be  measured from the  scale  given. The difference  between  potential energies is the fracture energy.  In test machine this value indicated by the pointer on  the  scale.  If  the scale  is calibrated  in energy units, marks  on  the  scale should be drawn keeping in view angle of fall () and angle of rise (. Height h1  and h2 equals,  h1= R (1­cos q) and h2= (1­cos q).  With the  increase  or  decrease in  values,  gap between  marks on scale  showing  energy also increase or decrease. This can be seen from the attached scale with  any impact machine.  Energy used in fracturing the specimen can be obtained approximately as Wh1­Wh2  This energy value  called impact toughness or  impact  value, which  will be  measured, per unit area at the notch.  Izod introduced Izod test in 1903. Test is as per the IS: 1598 Charpy introduced Charpy test in 1909. Test is as per the IS: 1499.

      


                                        

                                                                    a. Izod test


Specimen and equipment:  1.  Impact testing machine.(fig.3) 

 2.  Specimen and v notch is shown in the fig.4. Size of the specimen is 10mm  X 10mm X 75mm 


Mounting of the specimen: 

 Specimen is clamped to act as vertical cantilever with the notch on tension side. Direction of blow of hammer is shown in fig. (). Direction of blow is shown in fig Figure. 3.a 


Procedure 

1.  Measure the dimensions of a specimen. Also, measure the dimensions of  The notch.

  2.  Raise the hammer and note down initial reading from the dial, which will be  energy to be used to fracture the specimen. 

 3.  Place the specimen for test and see that it is placed center with respect to hammer. Check the position of notch. 

 4.  Release the hammer and note the final reading. Difference between the initial and final reading will give the actual energy required to fracture the Specimen.

  5.  Repeat the test for specimens of other materials.

  6.  Compute the energy of rupture of each specimen.


 Observation: 

Initial and final reading of the dial. Result Strain energy of given specimen is ­­­­­­­­­........



                                                      

                                                             b. Charpy test 

Specimen and equipment: 

 1.  Impact testing machine. (Fig.6)

 2.  U notch is cut across the middle of one face as shown in (fig.5).


Mounting of specimen:

Specimen is tested as a beam supported at each end (fig.7). Hammer is allowed to  hit then specimen at the opposite face behind the notch.




Procedure 

1.  Measure the dimensions of a specimen. Also, measure the dimensions of  The notch.

2.  Raise the hammer and note down initial reading from the dial, which will be  energy to be used to fracture the specimen.

 3.  Place the specimen for test and see that it is placed center with respect to hammer. Check the position of notch. 

 4.  Release the hammer and note the final reading. Difference between the initial and final reading will give the actual energy required to fracture the  Specimen.

  5.  Repeat the test for specimens of other materials.

  6.  Compute the energy of rupture of each specimen. 

Observation

Initial and final reading of the dial.

 Result   Strain energy of given specimen is......





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