MECHANICS OF MATERIALS 



65 





compression, simple shear is distributed uniformly over the 

 cross section and may be expressed in pounds per square 

 inch. The fractures shown in the first two parts of Figure 

 91 are ex- 

 plained by 

 the fact that 

 the shearing 

 stresses 

 caused by the 

 compressive 

 forces become 

 large enough 

 to cause rup- 

 tures along 



Fig. 91. Change in materials caused by compression 



surfaces at an angle with the axis of the body. 



Complex stresses. As stresses are found in parts of struc- 

 tures and machines they seldom exist as simple stresses, but 

 are found combined with each other in many different ways. 

 Flexure. Figure 93 shows a simple beam. The stresses 



set up in it due to 

 its own weight and 

 the weight of the 

 load supported by 

 it are a tension in 

 the fibers near the 

 lower side and a 

 compression in the 

 fibers near the 

 upper side and 

 shearing stresses in 

 both vertical and 

 seY^ s j?oo/bs.pers f in horizontal planes. 



This combination 

 Fig. 92. Shear {q CSL \\ e d flexure . 



Examination of a plank which has been broken when sup- 

 ported as above will show quite plainly that the fibers near 



K 



wm*w>/M 



sffi* 



Unit stress on 



