Section III., 1904. [ S ] Trans. R. S. C. 



II. — The Relation of Thermal Change to Tension and Compression Stress 

 with an Account of some Experiments on Impulsive Stress. 



By E. G. CoKER, M.A., D.Sc, F.K.S.E., 



Associate Professor of Civil Engineering, 



And C. M. McKergow, M.Sc. 

 Demonstrator of Civil Engineering, both of McGill University. 



(Oommuniicated toy Prcf. H. T, Boivey, aand read June 22, 1904.) 



The thermal effects of stress upon bodies appears to have been first 

 studied by Weber/ who found that when an iron wire was suddenly 

 stretched a thermal effect was produced, and that the thermal change 

 was proportional to the stress. He further showed that metal wires 

 v/hen stretched are lowered in temperature, and when compressed the 

 temperature is raised. Lord Kelvin ^ deduced the general equations 

 of thermo-elasticity from the laws of thermo-dynamics, and proved that 

 with stresses of the most general type the thermal effect is proportional 

 tc the applied stress, provided the material remains perfectly elastic. 

 I'or simple tension and compression stress, to which this paper is limited, 

 an expression for the thermal change may be very easily deduced as 

 follows : — 



If we consider a unit mass of rod of length 1, subjected to a com- 

 pression stress of intensity p, which shortens the bar by an amount 

 dl, then if E be the initial intrinsic energy of the bar, and dH be the 

 amount of heat developed by the compression, we have 



dE 4- pdl = JdH 



= jj Kdt H- Ldp I say 



from which we obtain by an easy application of the second law of 

 thermodynamics 



J t dl t J 



\ J ' dt ~ J ^ 



v'here « is the coefficient of expansion of the l)ar for unit increase of 

 temperature. 



^ Poggendorff Annalen. Bd. XX, 1830. 



» Collected papers. Vol I, p. 293. 



