Extensive da mage to ice occ urs during ice-structure interac ti o n by microc racking, recrystalli zati o n a nd melting, Th e obj ecti ve of this wo rk was to investigate this da m a ge process unde r confin ed-stress conditi o ns beli eved to bc assoc ia ted with impact zo nes th a t occ ur durin g ice-structure inte r ac ti on, "Da m age" refers to mi c ros truc tura l mod ifi cati o n th at causes d e teriorati on o f the m ee ha nica l prope rti es, Prior exp erimental work h as shown that a sm a ll a mo unt of defo rm a ti on causes pe rm a nent da mage in ice, leading to e nh a nced creep ra tes during subsequc nt load ing, To investigate thi s soft ening, fr es hwater g ra nul a r ice was defo rmed under m od era te confineme nt (20 :'IiPa ) a t -10°C, a t two rates which brac ket duc ti le a nd brittl e beh avio r (10 2 s I a nd 10 + s I). Sa mples were deform ed to different level s of ax ial strain up to 28,8% , Thin sec tio ns we re exam i ned to assess the prog ressive cha nges in microstructure, Bo th g ra in-bound a ry a nd intra-g ra nul a r c rac king began a t strains co rrespond ing to th e peak stress (1-2% ) fo r tests at both stra in ra tes. The peak stresses we re 23.4 MPa for the tests a t 10 2 S I a nd 9.8 MPa for th e tes ts a t 10 + s I, At strains of > 1-2%, d e n se elusters of intra-g ra nul a r crac ks b ega n to develop in th e samples tes ted a t the highe r ra te, At th e lower ra te, d yna mic rec rys ta lli zati on was a ppa rently the do min a nt defo rm a ti o n m eeha nism b eyo nd the pea k stress. The a\' C rage g r a in-size decreased stro ngly during th e fi rst few per ce nt stra in a nd then m a intained a rela tivel y stabl e va lue.

This work investigates the deformation of ice under deviatoric stresses and confining pressures expected during ice–structure interaction. Granular ice was tested under a range of confining pressures (5–60 MPa) and deviatoric stresses (up to 25 MPa), with sample temperatures between –8° and –10°C. Samples were deformed to increasing end-levels of axial strain, and were thin-sectioned and photographed immediately following testing.At all confinement levels, the original texture of the sample is completely transformed within the first 10–15% strain, to a fine-grained matrix with a few larger, isolated grains. At low confinements, grain-size reduction is associated with extensive microcracking. At high confinements, few cracks are observed. Observations suggest that microcracking, melting and recrystallization are active at all levels of confinement, though the relative importance of each depends on the confinement, stress and accumulated strain.Deviatoric stress is a strong factor in controlling the creep, reflected in both the time required for the sample to reach accelerated creep and the tertiary creep rate itself. Two exceptions to this pattern were noted. First, some samples experienced strain localization and eventual rupture. These specimens tended to have higher creep rates even in the initial stages of strain. Second, prior damage resulted in rapid softening compared with the behavior of undamaged specimens. However, when strain rates are compared among all samples at a given level of cumulative axial strain, the creep behavior obeys a power law over the whole range of strain levels tested. Effective viscosity decreased from 107.8 to l06.4 MPa−n s within the first 10% strain, during which the most substantial microstructural changes occurred, and then stayed relatively stable. The stress exponent, n, remained within the range 4.0–4.6.The dominant deformation mechanism appears to depend strongly on confining pressure (cracking at low pressure and dynamic recrystallization at high pressure). Creep rates at high confinement appear to increase relative to those at intermediate confinement, but the influence of temperature must be addressed further.

This work investigates the deformation of ice under deviatoric stresses and confining pressures expected during ice–structure interaction. Granular ice was tested under a range of confining pressures (5–60 MPa) and deviatoric stresses (up to 25 MPa), with sample temperatures between –8° and –10°C. Samples were deformed to increasing end-levels of axial strain, and were thin-sectioned and photographed immediately following testing.At all confinement levels, the original texture of the sample is completely transformed within the first 10–15% strain, to a fine-grained matrix with a few larger, isolated grains. At low confinements, grain-size reduction is associated with extensive microcracking. At high confinements, few cracks are observed. Observations suggest that microcracking, melting and recrystallization are active at all levels of confinement, though the relative importance of each depends on the confinement, stress and accumulated strain.Deviatoric stress is a strong factor in controlling the creep, reflected in both the time required for the sample to reach accelerated creep and the tertiary creep rate itself. Two exceptions to this pattern were noted. First, some samples experienced strain localization and eventual rupture. These specimens tended to have higher creep ratesevenin the initial stages of strain. Second, prior damage resulted in rapid softening compared with the behavior of undamaged specimens. However, when strain rates are compared among all samples at a given level of cumulative axial strain, the creep behavior obeys a power law over the whole range of strain levels tested. Effective viscosity decreased from 107.8to l06.4MPa−ns within the first 10% strain, during which the most substantial microstructural changes occurred, and then stayed relatively stable. The stress exponent,n, remained within the range 4.0–4.6.The dominant deformation mechanism appears to depend strongly on confining pressure (cracking at low pressure and dynamic recrystallization at high pressure). Creep rates at high confinement appear to increase relative to those at intermediate confinement, but the influence of temperature must be addressed further.

Extensive damage to ice occurs during ice structure interaction by microcracking, recrystallization and melting. The objective of this work was to investigate this damage process under confined-stress conditions believed to be associated with impact zones that occur during ice–structure interaction. “Damage” refers to microstructural modification that causes deterioration of the mechanical properties. Prior experimental work has shown that a small amount of deformation causes permanent damage in ice, leading to enhanced creep rates during subsequent loading. To investigate this softening, freshwater granular ice was deformed under moderate confinement (20 MPa) at –10°C, at two rates which bracket ductile and brittle behavior (10−2 s−1 and 10−4 s−1). Samples were deformed to different levels of axial strain up to 28.8%. Thin sections were examined to assess the progressive changes in microstructure.Both grain-boundary and intra-granular cracking began at strains corresponding to the peak stress (1–2%) for tests at both strain rates. The peak stresses were 23.4 MPa for the tests at 10−2 s−1 and 9.8 MPa for the tests at 10−4 s−1. At strains of > 1–2%, dense clusters of intra-granular cracks began to develop in the samples tested at the higher rate. At the lower rate, dynamic recrystallization was apparently the dominant deformation mechanism beyond the peak stress. The average grain-size decreased strongly during the first few per cent strain and then maintained a relatively stable value.