ABSTRACTS 



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PHYSICS. — Thermal expansion of alpha and of beta brass between 

 O-eOO^C. P. D. Merica and L. W. Schad. Bur. Stands. Sci. 

 Paper No. 321. Pp. 20. 1918. 



In connection with the investigation of the failure of brass by crack- 

 ing, a comparison has been made of the thermal expansions between 

 ordinary temperature and GOO^'C. of the two constituents, alpha and 

 beta, of which 60 : 40 brass is composed. The results show that whereas 

 at ordinary temperature the unit expansions of beta brass (55 per cent 

 copper) and of alpha brass (65 per cent copper) are very nearly equal, — 

 about 18 X 10~^ per degree C. — that of the beta brass becomes about 50 

 per cent greater than that of the alpha between 400* and 450°C., just 

 below the beta transformation temperature. 



This difference in expansion must result in the existence of differential 

 local or ''grain" stresses in a heterogeneous brass containing both 

 alpha and beta when quenched from temperatures higher than from 

 400 to 500°C. at such a rate of cooling that geometrical adjustment 

 cannot take place between these elements of the mass. The stress 

 distribution in such a quenched brass is very complex; an approximate 

 calculation on certain very arbitrary assumptions would indicate the 

 possibihty of the development by quenching of average tensional 

 stresses of 15,000 pounds per square inch and more in the beta 

 constituent. 



The possible effect of such stresses on the mechanical properties and 

 service behavior of brass and other materials is discussed. Experi- 

 ments showed that these stresses caused in all probability a decrease 

 of the proportional limit over that in the quenched and annealed state. 

 They have failed to show, however, that such quenched brass will 

 "corrosion-crack" in the mercurous nitrate test. 



Attention is called to the desirabiHty of studying this feature of 

 heterogeneous alloy structure more fully. P. D, M. 



573 



