TEST ON SPRINGS

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Aim :-To determine the Shear Modulus (or) Modulus of Rigidity of the given spring material.
Equipment:-

• Spring Testing Machine 2000kN
• vernier calipers
• Closed coil Spring

Theory:- springs are elastic member which distort under load and regain their original shape when load is removed. They are used in railway carriages, motor cars, scooters, motorcycles, rickshaws, governors etc. According to their uses the springs perform the following Functions:

1. To absorb shock or impact loading as in carriage springs.
2. To store energy as in clock springs.
3. To apply forces to and to control motions as in brakes and clutches.
4. To measure forces as in spring balances.
5. To change the variations characteristic of a member as in flexible mounting of motors. The spring is usually made of either high carbon steel (0.7 to 1.0%) or medium carbon alloy steels. Phosphor bronze, brass, 18/8 stainless steel and Monel and other metal alloys are used for corrosion resistance spring. Several types of spring are available for different application. Springs may classify as helical springs, leaf springs and flat spring depending upon their shape. They are fabricated of high shear strength materials such as high carbon alloy steels spring form elements of not only mechanical system but also structural system. In several cases it is essential to idealize complex structural systems by suitable spring.

Equation:- Modulus of rigidity of a given spring: \[ C=\frac{64WR^3n}{\delta d^4}\]

Where
${C}$ = Shear modulus (or) Modulus of rigidity
${R}$ = Mean radius of the spring (cm)
${n}$ = Number of turns in the spring
${d}$ = Mean Diameter of the spring wire(cm)
${W}$ = Load applied on the spring (kg)
${\delta}$ = Deflection of the spring (cm)

Procedure:-

1. Note the particulars of the spring such as mean diameter of the spring, mean diameter of the spring wire, number of turns.
2. Place the spring in such a way that the axis of the spring is truly vertical and exactly below the centre of the loading frame.
3. Note the initial reading of the deflection gauge and ensure the load indicates dial gauge should be zero.
4. Apply the required amount of load by manually operated hydraulic pump and note the corresponding deflection gauge reading.
5. Repeat step (4) by increasing the load on the spring. Take at least 15 sets of readings.

Observations:-

Sl. No	Applied Load ${W}$(kg)	Deflection Gauge reading $\delta$(mm)	Net Deflection $\delta$(mm)	Shear Modulus, $C$ (__X$10^5 \frac{kg}{cm^2}$)

Result:- Average shear modulus of the given spring = ____________

Precautions:-

1. Load should be applied on the spring without any eccentricity.
2. Deflection gauge needle should touch the bottom plate of the providing ring and should be vertical.
3. Gently apply the load by 'manually operated hydraulic pump. without any vibrations either in the spring or in the loading frame.

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