טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentMerigan Lior
SubjectEstimation of Uncertainty in Fracture Toughness
Parameter - J ic Testing
DepartmentDepartment of Quality Assurance and Reliability
Supervisor Professor Yitzhak Segal
Full Thesis textFull thesis text - English Version


Abstract

In order to create uniform access in uncertainty estimation of different tests, the ISO GUM standard was published in the year 1993, for estimation and expression of the uncertainty in measurements. At present, the ISO GUM standard  for expression of uncertainty measurement (and the  American Nation Standard Institution ANSI) provide the  most acceptable method in the world for evaluation the uncertainty in the measurement.  

Organizations and different bodies that deal in the field of measurement have published several interpretations of this standard.  In addition, there are different organizations that clarify the ISO-GUM document in different methods of several different fields.

One of the mechanical tests that exists nowadays is the test for the determination of  fracture toughness of material. The parameter we get from this measurement is Jic (material property). This property characterizes the toughness of the material near the onset of crack extension from any pre-existing fatigue crack.

Therefore, this material property is very important and when reporting this value, we must give quantitative indication of the quality of the measurement with its uncertainty .

This study covers the evaluation of uncertainty in the determination of elastic-plastic Fracture Toughness (Jic) of metallic material according to the testing Standard-ASTM E-813:87." Standard Test for Jic, A Measure of Fracture Toughness". This Standard gives a method for determining elastic-plastic fracture toughness values (Jic).

The aim of this work is to develop a general model of estimation of the uncertainty in the Fracture Toughness Parameter Testing ( in the metallic materials )according to the Iso Gum standard , and to evaluate the uncertainty of the fracture toughness value according to the model developed.

This study was carried out at the Metallurgical Laboratory of the Israel Institute of Metals.As yet, there is no available  published approach on the evaluating of uncertainty in fracture toughness parameter  Jic testing, according to ISO-GUM requirements.

After analyzing  the results we found that  the major components that contribute to the total uncertainty are: firstly the method of the standatd and secondly, the inherent material scatter (material properties variations).

The approach developed, shows how to identiy and classify all sources of uncertainty in the test, estimating the standard uncertainty for each source  and finally evaluating the expanded uncertainty (calculated under confidence level of 95% ).

All calculations described in this study are based on data that was taken during work  with the specific materials.