strength of material problem

Dear Youssouf:

Start here:

And you can find plenty more if you spell it correctly ("mohr's circle").

David A. Smith

it is a shortcut used to determine how energy that applied in different planes and different modes combines, used to then predict how a material will respond to input energies combined in those different ways. If you did not have the energy basis for the concepts of force and stress before doing force and stress design courses, it is not quite so clear. Basically, mohr's cirlce is a glorified kind of old-fashioned pythagorean chart that combines math equations graphically - nothing fancy, mohr just borrowed a graph method from an old greek.

To master it, you have to accept it as easier than the standard equations way, and practice it, like you would kicking a ball - use it as an apprentice would, simple things first, and in time you will get the skill necessary to do the more complex.

It is not for understanding stress itself any more than a calculator is for understanding calculus - it can show you how to get there, but not why it is. It is a tool that can show you things - and what you see depends on how well you master the use fo the tool. (Old experienced engineers often replace mohrs circle with the appropriate safety factor - "it's not about whether the engineer's calculation is right, it's about whether it works" )

The best part is when you finally can work it, and you are cruising, and you get far enough along in your studies that the exceptions in its application start showing up - brittle failures in ductile material under triaxial stress, shear ratio brittle failure, that extra calculation in aluminum after the stress is found, etc.

But you can't get to oz if you don't follow the yellow brick road first.

Hi, sorry to tell that mohr's circle is very simple in my mind, please explain your problem

mohr's circle in a tau-sigma plane (axis y and x) is a graphical method to compute principal stress. You can use several other graphical method to show limits of your material (failure theory, normal stress, maximum shear stress (Tresca criteria), energetic theory, Von mises, etc.....an for brittle material .....Coulomb-Mohr criteria, Fairhurst criteria, etc...I worked 3 years in fea analysis of crack)

if you have a sigma x (tension, compression or flexural stress normal to x plane) , a sigma y an a tau xy (shear stress in xy plane) you can compute the following component

sigma 1 = principal stress 1

sigma 2 = second principal stress

and maximum shear stress

you need to compute the center of mohr circle by the mean between sigma x and sigma y

after that you have to compute the radius of the circle.

please look at the following link to have more explanation

and after that if you speak french... (I think so) feel free to e-mail to me, as I said earlier in this e-mail, I had worked for several years with mohr circle in research team and as an professional engineer, I will be easier for me to explain in french (sorry for other member of this forum)

Yves Rossignol ing. Département de mécanique industriel GCS, Chicoutimi, Québec, Canada

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