Strength of Materials. 



331 



the bearing is out of true so that the strain comes upon one 

 i-diiv the raiTvina' pn\ver is greatly lessened. 



402. Tensile or Stretching Strength of Timber. The ten- 

 sile strength of materials is measured by the least weight 

 which will break a vertical rod one inch square firmly and 

 squarely fixed at its upper end, the load hanging from the 

 lower end. Below are given the results of experiments 

 with different varieties of wood, but the strengths vary 

 greatly with the age of the trees, with the part of the tree 

 from which the piece comes, the degree of seasoning, etc. 



Elm 6,000 Ibs. per square inch. 



American hickory 11,000 Ibs. per square inch. 



Maple 10, 000 Ibs. per square inch. 



Oak, white aud red. 10,000 Ibs. per square inch. 



Poplar 7, 000 Ibs. per square inch. 



White pine 10, 000 Ibs. per square inch. 



4C3. Tensile or Cohesive Strength of Other Materials. 



American cast iron 16,000to 28,000 Ibs. per sq. inch. 



Wrought iron wire, annealed 30, 000 to 60,000 Ibs. per sq. inch. 



Wrought iron wire, hard 50,000 to 100,000 Ibs. per sq. inch. 



Wrought iron wire ropos per sq. in. of rope 38, 000 Ibs. per sq. inch. 



Leather belts, l,f,0) to 5.0JO, good 2,000 Ibs. per sq. inch. 



Rope, manila, bot > 12,000 Ibs. per sq. inch. 



Rope, hemp, ba t 15, 000 Ibs. per sq. inch. 



404. Transverse Strength of Materials. When a board is 

 placed upon edge and fixed at one end as represented at A, 

 Fig. 144, a load acting at W puts the upper edge under a 

 stretching stress. 



5 A 



\- >1 ^ 



Fir,. 144. 



We know from experience that in case the board breaks 

 under its load when so situated the fracture will occur 



