QUIZ
What
types of FAD analyses are covered by Signal FFS?
(scroll down for answer)
QUIZ ANSWER:
Known
flaw assessment, limiting flaw assessment, limiting load assessment and fatigue
crack growth assessments.



The Failure Assessment Diagram Explained

The Failure Assessment Diagram
(FAD) is the most commonly used method for determining the acceptability of
cracklike flaws in structures. The FAD extends the crack stability assessment
to structures experiencing both brittle and ductile fracture. It is a plot
with a limiting curve and points representing the structure of interest.
The
figure below shows a sample FAD. The xaxis of the plot is the load ratio (Lr), which is the ratio between the reference stress and
the material yield strength. The reference stress is proportional to the
farfield stress and is computed based on the loading condition, the component
geometry and the crack configuration. The yaxis
of the plot is the toughness ratio (Kr)
which is the ratio of the stress intensity factor (KI) computed for the primary and secondary loads (residual
stresses) and the fracture toughness of the material (KIC). The throughthickness stress profile is
incorporated in the computation of Lr
 Kr. The computed LrKr point
illustrates the stability of the examined flaw. Signal FFS automates analyses
using the FAD with a few simple steps.

