About Bursting Principle

Try this for a starter: http://www.pveng.com/FEA/FEANotes/NutsBoltsStress/NutsBoltsStress.php

lt is really very useful, thank you all!

I'd go here: How to Search the Internet - Hannon Library and learn the basics of gathering information from reliable sources, not anonymous forums whose members might have little or no actual knowledge of the subject about which you want to be enlightened.

I'd find technical publications, scientific journals, mechanical engineering courses and papers on the subject of stress and from those develop a sound, factual understanding of the different types of stress.

Or, ask your son to search with you. Maybe that will give you two some quality time together.