Art. 13. 



DISTRIBUTION OF STRESS. 



11 



after the outer have solidified ; the resistance of the outer parts to 

 the contraction of the inner produces initial tension in the latter. 



Initial stresses may be largely eliminated by annealing or 

 by stresses which are large enough to produce considerable 

 permanent set. 



(c) There may be undiscoverable defects, such as blowholes 



(.a) Compression 



(t>) Tension 



(C) Shear 



- a 

 (ct; Bending 



Comoress/on 



(fj Compress/on 

 and bending 



Fig. 6. 



Tension and 

 Bend/ny 



in castings, which might have the same effect as an eccentric 

 application of the load. 



(d) It is difficult to apply a force exactly in the axis of a 

 tension or compression piece so as to produce a uniform distri- 

 bution of stress. 



(e) If there is any interference with the transverse deform- 

 ation of a tension or compression piece, the longitudinal 

 deformations will be changed. If there be a hole or a 

 notch (Fig. 7) in a tension piece, the unit strength on a 

 section through the notch or hole will be greater than for 

 a plain piece ; the material outside of the notch, near it, 

 acts like a transverse force to prevent contraction of the 

 cross section. This effect disappears when the notch is 

 made long enough, but near the point of transition, from 

 the smaller to the larger sections, there will be a non- 

 uniform distribution of stress; the transition should be 

 a gradual one. 



In a block under compression, there is always friction 



) C 



7. 



on the faces to which the external forces are applied, and this 

 interferes with lateral expansion. 



