"The Institute has completed a multi-year research effort to develop a computational fracture mechanics capability for the U.S. Air Force Research Laboratory. The theory and appropriate algorithms were developed and implemented into an advanced computer program that calculates whether or not a crack will propagate, and, if it does propagate, the direction and speed of propagation"
Your link is interesting, but they seem to avoid answering the question raised -- how likely is it that a crack will form.
From washington.edu . . .
"The year 1979 was the planned launch year for the first shuttle prototype vehicle, Columbia. During that year, the vehicle shed some 40% of its "critical" ceramic thermal insulation in a flight riding piggy-back on a Boeing 747 from California to Cape Kennedy."
Link: Learning to Take the Heat: Insulation for the Space Shuttle
AEDC Performs Shuttle Materials Test for NASA/Lockheed Martin
ARNOLD AFB, Tenn.
-Arnold Engineering Development Center is assisting the National Aeronautics Space Administration with improvements in existing Space Shuttle materials. According to NASA, during several previous Space Shuttle flights, including the shuttle launched Nov. 29, 1998, the shuttle external tank experienced a significant loss of foam from the intertank. The material lost caused damage to the thermal protection high-temperature tiles on the lower surface of the shuttle orbiter.
The loss of external tank foam material and subsequent damage to reentry tiles is a concern because it causes tile replacement costs to significantly increase,,u. however, it is not a flight safety issue. As a result, NASA-Marshall Space Flight Center selected AEDC to perform flight hardware materials tests on the shuttle's external tank panels in the center's von Karman Facility Supersonic Tunnel A.
The purpose was to establish the cause of failure for the tank thermal protection materials at specified simulated flight conditions. "NASA chose AEDC due to its technical expertise and historical program successes," Steve Holmes, a NASA-MSFC technical coordinator, said
(These are two different articles)
A review of the records of the STS-86 records revealed that a change to the type of foam was used on the external tank.
This event is significant because the pattern of damage on this flight was similar to STS-87 but to a much lesser degree. The reason for the change in the type of foam is due to the desire of NASA to use "environmentally friendly" materials in the space program.
Freon was used in the production of the previous foam. This method was eliminated in favor of foam that did not require freon for its production. MSFC is investigating the consideration that some characteristics of the new foam may not be known for the ascent environment."
http://www.freerepublic.com/focus/news/834139/posts?page=54#54