[cokhk] APPARAIUS FOR APPLYING BENDING MOMENTS 67 



where m is Poisson's ratio and this criterion results in the equation 

 M = (m— 1) M /2m + (m + 1) Js/W^f^/'Zm 



The third theory ado^Dts the view that failure occurs when the shear 

 stress reaches the limit of resistance of the material. For principal 

 stresses of p„ and p^„ it is easy to show that the maximum shear stress 

 has the value j9„ — p^„ leading to the equation 



Recent experiments^ appear to point to this last theory as the true 



one. 



' Guest. " On the strength of Ductile Materials under Combined Stress." 

 Phil. Mag., July. 1900. 



