displacement

I am hoping someone has some historical knowledge of some
interesting mechanics, or just an interest to discuss it. A superposition principle is widely used to solve crack problems, with illustrations like these:

http://ars.sciencedirect.com/content/image/1-s2.0-S0142112308002211-gr1.jpg

http://ars.els-cdn.com/content/image/1-s2.0-S0142112399000778-gr2.gif

Hi all, 

[Warning: The writing is long, as is usually the case with my posts :)]

It all began with a paper that I proposed for an upcoming conference in India. The extended abstract got accepted, of course, but my work is still in progress, and today I am not sure if I can meet the deadline. So, I may perhaps withdraw it, and then submit a longer version of it to a journal, later.

What is stress? Who has ever seen stress? Is stress a physical quantity?

Professor Yi-Heng Chen, Xi’an Jiaotong University, 710049, P.R.China

e-mail: yhchen2@mail.xjtu.edu.cn

In fact, this question has been bothering the present author for more than 15 years.