טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentHanina Erez
SubjectThe Influence of Hydrostatic Pressure on Adiabatic Shear
Failure of Metals
DepartmentDepartment of Mechanical Engineering
Supervisors Professor Daniel Rittel
Dr. Zvi Rosenberg


Abstract

Adiabatic Shear Banding is a well known thermo-mechanical instability phenomenon that may occur during dynamic loading of materials. Yet, little is known about the influence of hydrostatic pressure on ASB development and failure, as reported experimental results are quite scarce.  Osakada showed that the failure strain due to ASB increases significantly with the hydrostatic pressure.

This research involve both quasi-static and dynamic tests that were carried out. The experiments consisted of uniaxial compression of AM50 and Ti6Al4V specimens that were encased in metallic sleeves. Cylindrical adapters were used to apply the load the specimen while avoiding loading of the sleeve.

All the specimens failed due to ASB formation. As expected, the axial stress measured was shifted by the radial confining stress (q), as compared with tests without confinement.

For practical purposes, we defined and identified throughout this work the failure point as that for which the equivalent stress is 80% from the peak stress. With this definition of the failure point, we found that, for AM50, the failure strain increases slightly with the radial confining stress (from 20.8% without confinement, to 23.9%, 25.6%, 26.9% with q=0.045GPa, q=0.1GPa, q=0.14GPa respectively). For the Ti6Al4V under the same assumptions, we observed a more pronounced influence of the radial confining stress (from 22.7% q=0 to 26.1% with q=0.2GPa and 29.5% with q=0.31GPa).

As expected the radial confinement or the hydrostatic pressure have no influence on the homogenous plastic deformation phase.

The formation of the ASB or the instability onset (near the peak stress) is not influenced by radial confinement for the AM50, but is quite significantly delayed for Ti6Al4V.

Is seems that the failure process is influenced by the radial confinement. With a unified definition of the failure stress, we found that the strain increases with the increase of the radial confinement or hydrostatic pressure. These conclusions meet the existing knowledge regarding failure postponement due to hydrostatic pressure.