Abstract
Original language  English 

Qualification  Doctor Degree 
Awarding Institution 

Supervisors/Advisors 

Award date  19 Apr 1990 
Place of Publication  Espoo 
Publisher  
Print ISBNs  9513836177 
Publication status  Published  1990 
MoE publication type  G4 Doctoral dissertation (monograph) 
Fingerprint
Keywords
 ice
 deformation
 mechanical properties
 mechanics
 microstructure
 mathematical models
 fractures (materials)
 cracking (fracturing)
Cite this
}
Mathematical modelling of deformation mechanisms in ice : Dissertation. / Santaoja, Kari.
Espoo : VTT Technical Research Centre of Finland, 1990. 236 p.Research output: Thesis › Dissertation › Monograph
TY  THES
T1  Mathematical modelling of deformation mechanisms in ice
T2  Dissertation
AU  Santaoja, Kari
PY  1990
Y1  1990
N2  Mathematical modelling of deformation mechanisms in polycrystalline isotropic ice over wide temperature and strain rate ranges was investigated in this thesis. The proposed 3dimensional constitutive equations describe both timedependent ductile deformation mechanisms and microcracking associated with Hookean deformation showing a brittle nature. A model to describe the high strain rates operative mechanisms, which form the microcrack nucleus, was introduced. It was assumed that the required four independent deformation systems were: basal glide (2 systems) and twinning (2 systems). At very high strain rates, when the dislocation motion on the basal plane is not fast enough, the total permanent response of the icebody causing microcracking may be resulting from twinning. The prominent microcracking (damage) at high strain rates is described by a fourthorder tensor. The damage evolution law is based on the potential energy theorem. The observed micromechanisms in ice are modelled for both the condition for microcrack formation and the effects of microcracks on the mechanical properties of ice. The proposed approach connects continuum damage mechanics with fracture mechanics. The proposed theory reveals the HallPetch type of relation, although the frictional stress vanishes. Computed examples satisfactorily gave the measured compressive strength of ice and predicted the ratio of the peak compressive stress to the peak tensile stress as 1.85: 1, which is much lower than the measured one  8.6 : 1. At elevated temperatures when the strain rate is low, the ductile response of ice is dominant. The following mechanisms are modelled: Hookean deformation, delayed elasticity associated with grain boundary sliding and viscoplaticity associated with dislocation movement. The uniaxial material model is based on the equation proposed by Sinha. However, a more effective approximate time integration method was applied in computing the delayed elastic strain. This work gives a micromechanical representation for the (viscoclastic) delayed elasticity. This was applied during the derivation of the 3dimensional constitutive SADSequation, which coincides in uniaxial tension with the Ashby and Duval modification of Sinha's model. A Schapery's nonlinear viscoelasticity theory based time integration method, which is a modification to the procedure applied in the uniaxial case, was proposed for the SADSequation. Although this method gives realistic predictions during loading it does not allow the material to relax correctly.
AB  Mathematical modelling of deformation mechanisms in polycrystalline isotropic ice over wide temperature and strain rate ranges was investigated in this thesis. The proposed 3dimensional constitutive equations describe both timedependent ductile deformation mechanisms and microcracking associated with Hookean deformation showing a brittle nature. A model to describe the high strain rates operative mechanisms, which form the microcrack nucleus, was introduced. It was assumed that the required four independent deformation systems were: basal glide (2 systems) and twinning (2 systems). At very high strain rates, when the dislocation motion on the basal plane is not fast enough, the total permanent response of the icebody causing microcracking may be resulting from twinning. The prominent microcracking (damage) at high strain rates is described by a fourthorder tensor. The damage evolution law is based on the potential energy theorem. The observed micromechanisms in ice are modelled for both the condition for microcrack formation and the effects of microcracks on the mechanical properties of ice. The proposed approach connects continuum damage mechanics with fracture mechanics. The proposed theory reveals the HallPetch type of relation, although the frictional stress vanishes. Computed examples satisfactorily gave the measured compressive strength of ice and predicted the ratio of the peak compressive stress to the peak tensile stress as 1.85: 1, which is much lower than the measured one  8.6 : 1. At elevated temperatures when the strain rate is low, the ductile response of ice is dominant. The following mechanisms are modelled: Hookean deformation, delayed elasticity associated with grain boundary sliding and viscoplaticity associated with dislocation movement. The uniaxial material model is based on the equation proposed by Sinha. However, a more effective approximate time integration method was applied in computing the delayed elastic strain. This work gives a micromechanical representation for the (viscoclastic) delayed elasticity. This was applied during the derivation of the 3dimensional constitutive SADSequation, which coincides in uniaxial tension with the Ashby and Duval modification of Sinha's model. A Schapery's nonlinear viscoelasticity theory based time integration method, which is a modification to the procedure applied in the uniaxial case, was proposed for the SADSequation. Although this method gives realistic predictions during loading it does not allow the material to relax correctly.
KW  ice
KW  deformation
KW  mechanical properties
KW  mechanics
KW  microstructure
KW  mathematical models
KW  fractures (materials)
KW  cracking (fracturing)
M3  Dissertation
SN  9513836177
T3  Valtion teknillinen tutkimuskeskus. Tutkimuksia  Research Reports
PB  VTT Technical Research Centre of Finland
CY  Espoo
ER 