I am assuming you are a final year mechanical engineer, but if not start by looking up welding.

http://en.wikipedia.org/wiki/Welding

Then once you have a good grasp of what welding is, move on to looking at welding of two metals together so you understand that part. Then you can start looking at different weld strengths.

The topic is too broad to try and cover everything so try picking a specific area or application of welding that would allow you to do a comparison between different types of welding of different types of materials. Perhaps welding pressure vessels made out of different materials.

The internet has plenty of information.

Jack of All Traders,

Thanks for the comment. Here's the thing. We need to look for Welding Calculations on these types of test:

(1) Brinell Test

(2) Vickers Test

(3) Rockwell Test

(4) Charpy Test

I know that these are the test for hardness and toughness, but my lecturer wants me to look for Welding Calculations involving strengths of plates welded together. Help me please

All the answers can be simply found by typing in the name of the test into an internet search engine or Wikipedia home page.

Eg - entering "Brinell Test" produced this and many more.

http://www.gordonengland.co.uk/hardness/brinell.htm

http://en.wikipedia.org/wiki/Brinell_scale