טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentAbraham Ofer
SubjectThe Influence of Hydrostatic Pressure on Metals Behavior
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Emeritus Jehuda Tirosh


Abstract

The behavior of materials under hydrostatic pressure is an old but still mysterious phenomenon. Namely, the material is enforced to shift its behavior from brittle-like failure (unnoticeable deformation before fracture) to ductile-like failure (fracture which is proceeded with large deformation with a necking appearance). The goal of this work is to find a physical explanation to such phenomenon.


The basic assumption is that micro-cracks (though with minute amount) are always exists in actuality in all materials. The question is what effect these cracks have on the material response to hydrostatic pressure, which surrounded the material in addition to a tensile load.


If the cracks are considered to be in a geometrical shape of an ellipse, then all configurations of cracks can be described by changing the parameter of the eccentricity of the ellipse: from a slit (m=1) to a circular void (m=0). Under such simplification of the geometries of all cracks it is shown that the motion of the cracks during the loading program (unidirectional tension and confining hydrostatic pressure at different ratios) can be traced in an analytic form. Consequently, changes in the orientation, shape and volume of the cracks, inevitably leads to some changes in the material behavior.


 The suggested solution is compared to experiments found in the literature, of tensile tests of brittle materials (Tungsten, Molybdenum, cast iron, etc.) under high hydrostatic fluid pressures. The conformity is very well.