failure theory

In Simple tension test material is pulled from both the ends, the elongation of material(strain) with respect to the load is noted. From such an observation one can easily determine maximum strength of the material. For ductile material upper yield point is considered to be maximum strength of material, while for brittle material it is taken as ultimate strength of the material

On the basic of the simple tension test there are five theories are derived-

1) maximum principle stress theorem

2) maximum shear stress theorem

3) maximum strain theory 

4) maximum strain energy theorem

5) maximum distortion theorem

           maximum principle stress theorem

Failure will occur when the magnitude of the major principal stress reaches that which caused fracture in a simple tension test.

or,According to this theory when the maximum principal stress induced in a material under complex load condition exceeds the maximum normal strength in a simple tension test the material fails.                 

some material, and it lies on or outside of the envelope, we say that the material fails.   

safe zone inside the curve(max. principle stress th.)

           maximum shear stress theorem

According to this theory when the maximum shear strength in actual case exceeds maximum allowable shear stress in simple tension test the material case.Yielding will occur when the maximum shear stress reaches that which caused yielding in a simple tension test.

                                                

                     

safe zone under curve(max. shear stress theory)