Xiao, Jing (1997) Damage and fracture of brittle viscoelastic solids with application to ice load models. Doctoral (PhD) thesis, Memorial University of Newfoundland.
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In this work a multiaxial constitutive theory for brittle, viscoelastic materials is presented based on viscoelasticity, continuum damage theory and fracture mechanics. The microstructural nature of the material and micromechanical processes have been modelled by damage mechanics using averaging procedures with a finite collection of state variables. The change in the state variable is directly related to the individual deformation process. The constitutive model includes the effects of damage including microcracking, dynamic recrystallization and pressure melting on the reduction in elastic modulus and the enhancement in creep deformation. Damage evolution is based on Schapery's approach using the generalized J integral theory. The influence of confining pressure on damage progress is included. Volumetric deformation under compression is also investigated, which is mostly dilatation due to microstructural changes (damage). -- A triaxial test program has been carried out in the laboratory at Memorial University. A description of the test program, specimen preparation, test equipment and procedure used has been presented. The experimental observations and results have been discussed and are summarized. Triaxial tests were designed to investigate the deformation of ice and the influence of damage on the mechanical properties of ice. These tests have also served to verify the constitutive modelling. The theoretical model provides good agreement with test results. -- The role of fracture and spalling in ice-structure interaction has been investigated. Fracture analysis, using the J-integral, has been carried out in the numerical scheme, which is based on finite elements and the computer program ABAQUS. This analysis is consistent with the damage mechanics and has been carried out on the basis of plane strain assumptions and the direction of crack propagation was calculated by maximizing the strain energy release rate. The direction of maximum tensile stress was also considered. Available data for ice on the tensile and shearing modes (I and II) of crack propagation were taken into account. -- Analysis showed that localization of damage occurs if the geometry leads to stress concentration at the structure-ice interface. Calculations indicate that the load on a structure would be high if the failure in the ice was by distributed damage only. Initial analysis showed that a small crack near the interface would propagate at loads about one-half of those found using damage analysis only. The analysis included crack propagation and removal of material. These initial results are very promising for a realistic analysis of ice-structure interaction. -- Load oscillations induced by ice crushing failure against a structure have also been investigated. Evidence of pressure melting has been reported from both laboratory and medium-scale field indentation tests. Possible effects of pressure melting on ice-induced vibrations are presented. A simplified damage model using only one Maxwell unit is proposed for the highly damaged materials. Two trial test cases are carried out using the simplified damage model to simulate the extrusion of crushed ice in the laboratory and field indentation tests. Preliminary analyses have shown promising results in the light of experimental programs where load oscillations have been observed.
|Item Type:||Thesis (Doctoral (PhD))|
|Additional Information:||Bibliography: leaves 179-187|
|Department(s):||Engineering and Applied Science, Faculty of|
|Library of Congress Subject Heading:||Ice mechanics; Continuum damage mechanics; Viscoelasticity|
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