13° 



Table 74 

 MECHANICAL PROPERTIES 



Eubber and Leather 



(a) Rubber, Sheet* 



The specific gravity of rubber averages from 0.95 to 1.25, corresponding to an average weight 

 of 60 to 80 lb/ft 3 . 



Four-ply rubber belts show an average ultimate tensile strength of 0.63 to 0.65 kg/mm 2 or 

 890 to 930 lb/in 2 (Benjamin), and a working tensile stress of 0.07 to 0.11 kg/mm 2 or 100 to 

 150 lb/in 2 is recommended (Bach). 



(b) Leather, Belting 

 Oak tanned leather from the center or back of the hide : 



Minimum tensile strengths of belts f single 2.8 kg/mm 2 or 4000 lb/in 2 



(Marks, p. 622) 



\ double 2.5 kg/mm 2 or 3600 lb/in 2 



Maximum elongation for one hour application of f single 13.5 per cent 

 1.6 kg/mm 2 or 2250 lb/in 2 stress \ double 12.5 per cent 



Modulus of elasticity of leather varies from an average value of 12.5 kg/mm 2 or 17,800 

 lb/in 2 (new) to 22.5 kg/mm 2 or 32,000 lb/in 2 (old). 



Chrome leather has a tensile strength of 6.0 to 9.1 kg/mm 2 or 8500 to 12,900 lb/in 2 . 



The specific gravity of leather varies from 0.86 to 1.02, corresponding to a weight of 53.6 

 to 63.6 lb./ft 3 . 



Smithsonian Tables. 



