Section 77 . The Plastic Limit 



As has already been pointed out, the plastic limit, in practice, is the most important charac- 

 teristic of the mechanical properties of ice. 



Actually, a knowledge of the limit of plasticity is necessary for computing the work of ice- 

 breakers , for constructing ice-crossings and aerodromes , etc . 



According to Veinberg, the average limits of plasticity of fresh ice (after they were reduced 

 to a temperature of -3°) obtained by different investigators vary as follows: 



2 

 for compression from 12. 4 to 123 kg/cm , 



, 2 

 for flexure from 1. 4 to 59. 6 kg/cm , 



/ 2 

 for breaking (average of 235 tests) 11. 1 kg/cm , 



, 2 

 for shearing (average of 111 tests) 5.8 kg/ cm , 



, 2 

 for torsion (average of 9 tests) 5. 1 kg/ cm . 



Veinberg made his reductions to a temperature of -3° according to table 60 from which it can 

 be seen that the temperature affects the strength of ice less than as is indicated by Royen's 

 formula. 



TABLE 60. COEFFICIENTS FOR REDUCING ICE RESISTANCE TO A 

 TEMPERATURE OF -3° 



As Veinberg indicates, all the values which have been presented were obtained for static 

 ag. With dynamic loi 

 fresh and low salinity ice. 



9 



loading. With dynamic loading (a blow) Nazarov obtained a limit of plasticity near 5 kg/cm for 



Table 61 gives the results of certain tests of fresh ice for flexure at different temperatures; 

 the effect of temperature can be seen very clearly from these results. 



The tests of artificially prepared ice conducted by Makarov have shown that the limits of 

 plasticity during the compression of sea ice increase with a decrease of temperature and salinity of 

 sea ice (table 62). During the voyage on the Se do win 1934, Bruns and Beriugin (the latter after his 

 winter at Cape Zhelaniia) made large scale determinations of the limit of plasticity. For example, 

 at this time as a result of 25 determinations of the limits of plasticity of fresh, transparent ice 

 (composing the upper part of an ice flow) under a load directed perpendicularly to the plane of 

 freezing proved to be, on an average, almost twice as great than under a load directed parallel to 

 the plane. For ice, even slightly saline, the ratio of the perpendicular to parallel load decreased 

 and approached unity for summer ice which was considerably wasted by melting. On an average, 

 of the many hundreds of determinations of the limit of plasticity of sea ice formed during calm 

 growth (without any sort of hummocking) this ratio proved to be 1.24 (table 63). 



188 



