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:

- Deflection (d) =
__64 WR__^{3}N Sec__a__[ cos^{2}a / N + 2Sin^{2}a /E] N/mm^{2}

d

^{2}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

- Tan
^{ }a = pitch / 2ПR

- Pitch = (L-d) / n

Where,

d=Dia of spring wire in mm

L=Length of spring in mm

N=no of turns in spring

- 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 W

_{max }x d_{max}Where,

W

_{max}=Maximum load appliedd

_{max}=Maximum deflectionProcedure:

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 |

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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/mm ^{2} | Stiffness in N/mm | |

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Result:

Under compression test on open coil helical spring

- Rigidity Modulus (N) =
- Stiffness of spring (K)=
- Maximum energy stored =

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