This experiment will allow you to find the spring constant of the spring you are using and, if graphed correctly allow you to work out the energy transferred into the spring when it is deformed past the limit of proportionality.
Extending tape measure
Mass hangers (kilograms in 100g divisions)
Measure the length of the spring with no mass attached
Add a 0.1kg mass, measure the extension of the spring
Keep adding masses and measuring the extension until the spring stretches past the limit of proportionality (it will not return to its original length in this case)
Remove the masses one at a time until all the masses are removed.
Calculate the force applied (1kg = 9.8N of force)
Plot a graph of the results with the Extension on the x axis. Use separate colours for adding and subtracting masses so you have two lines.
The slope of the linear part of the graph is the spring constant for the spring.
The area between tho two lines represents the energy that has been transferred to the spring.