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Friday, February 4, 2011

CE1263 STRENGTH OF MATERIALS LAB COMPRESSION TEST ON OPEN COIL HELICAL SPRING Anna university lab manual download


COMPRESSIONTEST ON OPEN COIL HELICAL SPRING

Ex.No:05
Date:

Aim:
            To determine the stiffness of spring, modulus of rigidity of the spring wire and maximum strain energy stored.
Equipments Required:
1.      Spring testing machine
2.      A open coil spring
3.      Vernier caliper
Formulae:
  1. Deflection (d) = 64 WR3N Sec a [ cos2a / N + 2Sin2a /E]      N/mm2
                                           d2



Where,
            W=Load applied in Newton
            R=Mean radius of spring coil = (D-d)  / 2
            N= Bynver if tyrbs ub sorubg
            a=Helix angle of spring
            N=Modulus of rigidity of spring Material
            E=Youngs modulus of the spring material

  1. Tan a = pitch / 2ПR

  1. Pitch = (L-d) / n
Where,
d=Dia of spring wire in mm
L=Length of spring in mm
N=no of turns in spring
  1. Stiffness of spring (K)=w / d
Where,
d=Deflection of spring in mm
W=Load applied in Newtons

5. Maximum energy stores = 0.5 x Wmax x dmax
Where,
Wmax=Maximum load applied
dmax=Maximum deflection

Procedure:
1.      By using vernier caliper measure the diameter of the wire of the spring and also the diameter of spring coil.
2.      Count the number of turns.
3.      Insert the spring in the spring testing machine and load the spring by a suitable weight and note the corresponding axial deflection in compression.
4.      Increase the load and take the corresponding axial deflection readings.
5.      Plot a curve between load and deflection.  The shape fo the curve gives the stiffness of the spring











Observation:
TO determine the wire diameter, and coil diameter of spring ( each 3 readings)
Least count of vernier=

Sl.No
MainScale Reading (MSR) in mm
Vernier scale reading (VSR)
VSR x LC in mm
Total reading = MSR=(VSRxLC) in mm
















Diameter of spring coil (D)=
Diameter of spring wire(d)=
Number of turns in spring

Tabulation: To determine the load versus deflection ( min 12 readings)
Sl.No
Load in Kgf
Scale readings in mm
Deflection in mm
Rigidity modulus in N/mm2
Stiffness in N/mm

































































Result:
Under compression test on open coil helical spring
    1. Rigidity Modulus (N) =
    2. Stiffness of spring (K)=
    3. Maximum energy stored =

CE1263 STRENGTH OF MATERIALS LAB Impact Modulus Test – IZOD Method Anna university lab manual download


Ex. No. 4  Impact Modulus Test – IZOD Method

Aim : To determine the impact modulus of the given specimen by izod test.

Equipments Required:

  1. Impact Testing Machine with IZOD arrangement.
  2. Specimen
  3. Vernier caliper.

Description;

            Many machines or machine components are subjected to a suddenly applied load, which is called as impact blow. For determining the suitability of  a material to resist the impact blow. For determining the suitability of a material to resist the impact, IZod and charpy test are aried out.

CE1263 STRENGTH OF MATERIALS LAB Brinell Hardness Test Anna university lab manual download

Ex. No. 3 Brinell Hardness Test

Aim : To find the Brinell Hardness number for the given metal specimen.

Equipments Required :
  1. Brinell Hardness Testing Machine
  2. Metal Specimens
  3. Brinell Microscope.

Formulae:

            Brinell Hardness Number ( BHN) = 2P / { p D [ D - Ö ( D 2 – d 2 ) ] }

                        Where,
                                                P = Load applied in Kgf.
                                                D = Diameter of the indenter in mm.
                                                D = Diameter of the indentation in mm.

Description:

            It consists of pressing a hardened steel ball into a test specimen. In this usually a steel ball of Diameter D under a load ‘P’ is forced in to the test piece and the mean diameter ‘d ’ of the indentation left in the surface after removal of load is measured. According to ASTM specifications a 10 mm diameter ball is used for the purpose. Lower loads are used for measuring hardness of soft materials and vice versa. The Brinell hardness is obtained by dividing the test load ‘P’ by curved surface area of indentation. This curved surface is assumed to be portion of the sphere of diameter ‘ D’.

Test Requirements:
  1. Usual ball size is 10 mm  + 0.0045 mm. Some times 5 mm steel ball is also used. It shall be hardened and tempered with a hardness of at least 850 VPN. ( Vicker Pyramid Number) . It shall be polished and free from surface defects.
  2. Specimen should be smooth and free from oxide film. Thickness of the piece to be tested shall not be less than 8 times from the depth of indentation.
  3. Diameter of the indentation will be measured n two directions normal to each other with an accuracy of  + 0.25% of diameter of ball under microscope provided with cross tables and calibrated measuring screws.

Precautions:
  1. Brinell test should be performed on smooth, flat specimens from which dirt and scale have been cleaned.
  2. The test should not be made on specimens so thin that the impression shows  through the metal , nor  should impressions be made too close to the edge of the specimen.

Procedure:
  1. Specimen is placed on the anvil. The hand wheel is rotated so that the specimen along with the anvil moves up and contact with the ball.
  2. The desired load is applied mechanically ( by gear driven screw) and the ball presses into the specimen.
  3. The diameter of the indentation made in the specimen by the pressed ball is measured by the use of a micrometer microscope, having transparent engraved scale in the field of view.
  4. The indentation diameter is measured at two places at right angles to each other, and the average of two readings is taken.
  5. The Brinell Hardness Number ( BHN) which is the pressure per unit surface area of the indentation is noted down.

Observation.

Sl.No.
Material
Load in Kgf
Diameter
Of the Indenter in mm
Diameter of the indentation in
mm
Brinell
Hardness
Number(BHN)




1
2
3


















Result:

Thus the Brinell Hardness of the Given Specimen are

  1. Mild Steel = ------ BHN
  2. EN 20      = ------- BHN.







CE1263 STRENGTH OF MATERIALS LAB Rockwell Hardness Test Anna university lab manual download


Ex. No.2              Rockwell Hardness Test.

Aim : To determine the Rockwell hardness for the given metal specimen.

Equipments Required:
1.      Rockwell Hardness Testing Machine.
2.      Metal Specimen.
Description:
            Hardness may be defined as resistance of metal to plastic deformation usually by indentation. However the term may also refer to stiffness or temper or resistance to scratch, abrasion or cutting. There are three  general types of  hardness measurements depending upon the manner in which the test is conducted.

1.      Scratch hardness measurement.
2.      Rebound hardness measurement.
3.      Indentation Hardness measurement.
In scratch hardness method the materials are rated on their ability to scratch one another and mineralogists use it.In rebound hardness measurement, a standard body is usually dropped on to the material surface and the hardness is measured in terms of the height of its rebound.The general means of judging the hardness is the resistance of a material to indentation.
Indentation hardness may be measured by various hardness test such as Brinell, Rockwell, etc. Rockwell hardness testing differs from Brinell testing. In Rockwell testing, the indenters and loads are smaller and therefore the resulting indentation on the specimen is smaller and shallower.
Rockwell testing is suitable for materials having hardness beyond the scope of Brinell testing. Rockwell testing is faster as compared to Brinell testing , because the diameter of the indentation need not be measured. The Rockwell machine gives arbitrary direct reading, Unlike Brinell testing, Rockwell testing needs no surface preparation (Polishing) of the specimen whose hardness is to be measured.
There are two scales on Rockwell testing specimen. i.e  B scale and C scale. B scale uses a steel ball indenter where as a diamond cone penetrate is employed for measuring Hardness on C scale.B scale is for testing materials of medium hardness such as low and medium carbon steels in the annealed condition. The working range of this scale is from 0 to 100. C scale is used for testing materials harder than B-100. C scale is commonly used for testing the hardness of alloy cast irons.
In Rockwell hardness testing, the minor load for all cases is 10 Kg. Where as major loads for scales C and B are 150 Kg and respectively, including minor load.

Test requirements:
  1. The test should be carried out in an ambient temperature of 20 +20 C in temperate climate and 27 +20 C in tropical climates.
  2. The testing machine shall be protected through out the test from shock and vibrations.
  3. The test piece shall be placed on a rigid support. The contact surfaces shall be clean and free from foreign matter. ( such as oil and dust)
  4. The thickness of the test piece shall be at least 8 times the permanent indentation of depth. No deformation shall be visible at the back of the test piece after the test.
  5. The distance between the centres of the two adjacent indentations shall be at least 4 times the diameters of the indentation and the distance from the centre of any indentation to the edge of the test piece shall be at least  2.5 times the diameter of the indentation unless agreed otherwise.
Precautions:
  1. Successive impressions should not be superimposed on another nor be made too close together when making hardness determinations.
  2. Nor should a measurement be made too close to the edge , or on a specimen so thin that the impression comes through the other side.
  3. Small irregularities, dirt, and scale should be avoided because of the great sensibility of the Rockwell test.
Procedure:
  1. Test piece is placed upon the machine. The dial may be showing any reading.
  2. Hand wheel is turned , thereby raising the test piece up against the steel ball indenter till the needle of the small dial is against the red mark. This applies minor load.
  3. Major load is applied by pressing the crank provided on the right hand side of the machine. Time is given as 30 sec so as to make the load reach specimen fully.
  4. When the penetration is completed, the crank is turned in the reverse direction thereby with drawing the minor load but the leaving the major load applied.
  5. The pointer moves further and becomes stand still. This reading is taken as Rockwell Hardness Number – C scale.( HRC)
  6. Hand wheel is rotated and the test piece is lowered.

Tabulation
Sl.No.
Material
Load in KgF
Indenter
Scale
Trial Number
Rockwell
Hardness
Number(HRC)




1
2
3

















Result:
            Rockwell Hardness number of the specimen was found for the given material as follows:
  1. Copper                        =  ----------- HRC
  2. Brass               =  ----------- HRC
  3. Aluminium      = ------------ HRC.