26 BROOMALL: stress AND STRAIN. 



plying this ratio by the coefficient of rigidity, obtaining 



1/2 X 1/2 X 2/1000 X 12,000,000 

 =^ 2000 lbs. / sq. in., as 



the unit shearing stress. 



These approximations show that the lateral stresses in the 

 plane of the cross section are too small to be dangerous. 

 Their consideration, however, is none the less interesting, 

 since they constitute a factor in the theory of internal stress. 



A mental picture of the stresses in a beam under flexure is 

 not difficult to carry in mind, and in Figure 12 an attempt is 

 made to indicate the nature of the deformations, together with 

 the kind of stresses and the general direction of their maxima. 

 After what has preceded, little explanation of the figure is 

 needed. The solid lines are maximum direct stresses, while 

 the dotted lines are maximum shears. The adjacent arrows 

 indicate the direction of the stresses. 



In the foregoing notes attention has been directed only to 

 flexure in beams of rectangular cross section, and no attempt 

 is made to treat the subject other than qualitatively. It is 

 hoped that some of the points suggested may be of interest. 

 In a future article it is the intention to take up the subject of 

 flexure in I beams, channels and unsymmetrical sections. 



