טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentWeisberg Elan
SubjectDuctile Fracture under Complex Loading Scenarios
DepartmentDepartment of Mechanical Engineering
Supervisor Dr. Shmuel Osovski
Full Thesis textFull thesis text - English Version


Abstract

Ductile structural alloys such as Ti6Al4 have many desirable qualities such as their large damage tolerance and Density-normalized strength. These characteristics make such materials an attractive candidate for use in the aerospace and automobile industries. Failure in such structures may lead to fatal accidents and loss of revenue as a result of the structure being out of commission. Thus, the ability to predict failure and model ductile fracture is of great essence.

Ductile fracture of structural alloys is a process involving the nucleation, growth and coalescence of micron sized voids. Although several models describing this process exist in the literature, they all share a common limitation, which is their inability to deal with fracture in low triaxialities. Several researchers have proposed a solution. In this work, the GTN model with the Nahson-Hutchinson extension accounting for shear induced damage is used to examine the path dependency of ductile fracture.

Although it is well established that plastic deformation is a path dependent process, use of a failure envelope is prevalent in many FE element codes. Use of a failure envelope does not account for the evolution of parameters such as plastic strain and stress triaxiality over deformation history but rather defines failure by their final value.

A new specimen allowing for tension and shear loading was designed in order to show the dependence of strain to failure upon loading history.

Numerical Results show that by applying shear loading followed by tensile loading (and vice versa) in different proportions, strain to failure receives a different value for each loading scenario.

By examining these complex loading scenarios for a range of material parameters, the dependence of strain to failure upon loading history alongside the examination of the predictive capabilities of the modified GTN with the NH extension damage model is shown. The influence of different material parameters on the failure process is examined in detail. It is shown that when investing shear fracture, the adequacy of the shear specimen depends on the material examined.