Objective: For assessment of the modulus of rigidity (Shear modulus) of materials for the spring

Tool and Equipment

1. Dial gauge
2. Spring Testing Machine

Description of the machine

The spring testing machine consists of two uprights connected to an inflexible foundation and additionally three cross heads. The upper and lower cross heads are firmly clasped to the uprights whereas the center one is created to shift on exceptionally finished gunmetal bearings over the top of the uprights. To the middle cross head is latched the loading cradle where tire weights for loading the spring during the process of the test are positioned. The spring for tension test is therefore retained on hooks amongst the upper and middle cross heads whereas that for compression test is positioned on collar amongst the middle and lower cross heads. Clutch mechanisms are thus given to contribute in holding the middle cross heads for fixing of the spring. Therefore, also an attachment with a fine regulatory equipment to repair the dial gauge for measuring extensions of the spring.

Sample

1. Close coiled spring
2. Open coil spring

Process

Tension Test (Test on close coil spring):

Attach the close coiled spring to the hooks amongst the upper and the middle cross heads with the process of clutch mechanism. Discharge the clutches and allow the spring to suspend freely amongst hooks. Attach the dial gauge and regulate it to mark nil on the dial. Load the spring by positioning one calibrated tire weight, on the cradle and mark down the corresponding deflection from the dial gauge. Position each one of tire weights, making down the dial gauge marking each time a weight is positioned. Carry on the observation while unpacking the spring as well.

Compression Test (Test on open coiled Spring):

Position the spring on the bearing collars amongst the middle and lower cross heads with the help of clutch mechanisms. Suspend the clutch and let the spring position without any pressure between the collars. Now regulate the dial gauge to mark nil on the dial. Once again load the spring and mark its deflection with the same method as for the tension spring.

Observations

Tabularize the record.

Graph

Plot the variation of deflection with load for both the close coiled and open coiled spring.

Load-Deflection Graph

Calculations

1. Close coiled spring

R = Mean radius of the spring

N = No. of Coils.

d = diameter of the wire.

N = Shear modulus of the spring materials.

W = Load applied.

= Deflection

1. Open coiled spring

Where, N, R, n, d, W & are as above.

E= Modulus of Elasticity of the spring Material

P=L/n = ———————-

Take E= 2×10^5 N/mm2 and complete the calculation.

Results:

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