82 



BELL SYSTEM TECHNICAL JOU R^AL 



into the compo7ients 7„, , Ty,, , T,., , which are oppositely directed to 

 those of the second face. The remaining stress components on the other 

 four faces have the designation 



Face OABE 

 CFGD 

 OADG 



bcfp: 



r. 



n 



n 



(2) 



Fig. 1. — Cube showing method for specifying stresses. 



The resultant force in the X direction is obtained by summing all the forces 

 with components in the X direction or 



F\ = (n., - r„J dydz + {T^y, - T.y,) dxdz + (n„ - T^,) dxdy. (3) 

 But 



Tzxt — ~~Txx^ 4" —^ — dx; iiyj — J xyj 



+ 'I^'.,r. r„.= -r„,+^v. 



(4) 



and equation (3) can be written in the form 



/dTxx , dTxv 1 dT; 



J'' 



l-^' + --j^^ + ''-±^^dxdydz. 

 \ dx dy dz ) 



(5) 



Similarlv the resultant forces in the other directions are 





(6) 



