Measuring fracture Toughness

Question 1

Conditions for a valid measurement

Answer 1

Crack must be Sharp
Crack length must be large when compared to the plastic zone size
Crack tip material must be in plane strain condition

Question 2

Standard

Answer 2

a,b >_ 2.5(Kc/Yield stress)^2

Question 3

Iterative measurement technique

Answer 3

1) make the measurement and calculate a candidate value for Kc
2) Check against the inequality
3) if the inequality is valid, then the measurement is valid, if the inequality isn’t valid, the re-do the experiment with e a bigger sample.

Question 4

Typical test piece

Answer 4

One typical example of a test piece is a SEN. This is a test specimen with a single edge notch crack. DIAGRAM. You apply an increasing cyclic load until failure, with the crack opening displacement being measured by a strain gauge.