砕氷船船首部に作用する氷圧力に関する研究 : その1,海氷の三軸圧縮強度特性

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In order to estimate ice loads acting on ice-breakers for the design of hull structures as well as an estimation of ship performance, it is essential to grasp the mechanical characteristics of sea ice, especially under multi-axial stress conditions. However, the mechanical behavior of sea ice is more complicated as compared with that of metals, where the effect of hydrostatic pressure and anisotropy of the material are distinctive. In this study, triaxial compression tests were conducted systematically by using laboratory grown saline ice specimens, where the salinity of specimen and the strain rate were taken as prime testing parameters. Before conducting the triaxial compression tests, several series of uniaxial compression tests were also carried out. As a result of the uniaxial compression tests, it was concluded that saline ice employed in this test program could represent the mechanical behavior of sea ice in terms of the uniaxial compressive strength under the test conditions used in the study. 24 series of triaxial compression tests were conducted in order to investigate the effect of the salinity of specimen, the strain rate at a test and the specimen type on triaxial compressive strengths. It was found that the triaxial compressive strengths of saline ice could be expressed by the Drucker-Prager failure criteria when the salinity of specimen as well as the strain rate at a test and the specimen type were specified. Using the coefficients of the said criteria obtained in a series of the triaxial compression tests, the effects of salinity of speciment and strain rate at a test on the triaxial compressive strengths were clarified. It was also found that the extent of anisotropy can be estimated by the coefficients of the said criteria. From the coefficients of the Drucker-Prager failure criteria obtained in the present study, an empirical formula was suggested to estimate the triaxial compressive strength for an arbitrary salinity, strain rate and specimen type (being limited within those values used) . However, it was realized that more work should be needed to round the equations out, especially on coefficient k of the said criteia. It was also realized that an anisotropic failure criteria such as the Pariseau failure criteria would be more realistic when it comes to express strength characteristics of saline ice (sea ice) rather than using the Drucker-Prager failure criteria. Establishment of an experimental technique to define the coefficients of the anisotropic failure criteria will be needed for better understanding the mechanical behavior of sea ice.

砕氷船船首部に作用する氷圧力に関する研究 : その1,海氷の三軸圧縮強度特性

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