**PERFORMANCE TEST ON COIL SPRING**

**Ex.No. 7**

**Date :**

**AIM :**

To determine the following properties of a coil spring.

- Stiffness of the given coil spring.
- Modulus of rigidity.

**APPARATUS REQUIRED :**

Spring testing machine, coil spring, vernier caliper.

**PROCEDURE :**

1. The spring is placed centrally over the lower plate slowly rotate the plate handle.

2. Measure the thickness of spring and calculate the number of turns.

3. Measure the outer diameter and inner diameter of spring using vernier caliber.

4. Keep the spring in such a way that top and bottom plate just touches the spring.

5. Adjust the pointer on the dial to read zero loads.

6. Note the deflections reading on the gauge apply the load on the spring and note the deflection reading.

7. Note the deflection while unloading and also get the average deflection.

8. Plot the graph between load and deflection.

9. The deflection of a spring is obtained from the help of the graph.

**CALCULATION :**

Formula,

Modulus of rigidity G= [(64nWR

^{3})/ (δd^{4})] N/mm^{2} where,

W - Load applied in N

δ – Deflection in mm

R – Mean coil radius of given spring in mm

d – Diameter of the spring wire in mm

n – Number of turns in the given spring

Stiffness of the spring k = (W/δ) N/mm

Mean radius R = [(d

_{o}-t)/2] mm d

_{o }– outer diameter t – Thickness

**RESULT :**

Modulus of rigidity of spring = N/mm

^{2} Stiffness of spring = N/mm

**TABULATION :**

Sl. No | Load | Deflection (mm) | Mean deflection (mm) | ||

Kg | N | Loading | Unloading | ||

**Mean radius of spring:**

MSR (mm) | VSC (mm) | TR = MSR+ VSC*LC | |

Outer diameter (d_{o})Thickness (t) |

**DIAGRAM:**

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