סמינר מחלקתי Dr. Joseph Bloom

School of Mechanical Engineering Seminar
Wednesday, November 4, 2015 at 15:00
Wolfson Building of Mechanical Engineering, Room 206

The Eagle Has Landed

Joseph M. Bloom, Ph.D Harvard University

The presentation is about the first application of fracture mechanics in the design and fitness-for-service of a U.S.. Air Force fighter aircraft.  The F-15 fighter was developed in the late 1960’s and named in the early 1970’s, the “Eagle.”  The speaker was a significant part of a team of engineers that developed the F-15 Fracture Control Plan.

Nondestructive test (NDT) techniques were thought to be able to find flaws smaller than those which could grow to failure during the life of the aircraft.  All combat aircraft before that time were designed based on “S-N” data.  Finding flaws or defects in production parts would prevent failure of the part, or at the very least unnecessary repair. The application of fracture mechanics would point out weaknesses in the quality assurance of the new aircraft.  The speaker will present the step-by-step approaches used on the F-15 Eagle. Also, he will discuss how “state-of-the-art” fracture mechanics (1970) prediction of spectrum crack growth from constant amplitude crack growth data was used.  The concept of retardation (due to the application of peak loads) which slows crack growth will be discussed.  Now recognized and used in the aviation industry, the concept of retardation was a major break -thru at that time.

Complete algorithms were developed from scratch and then validated through limited “expensive” testing.  Eventually, this work led to the establishment of NDT requirements for the finished parts.  The fracture control plan was used as a general guideline for the final aircraft inspection requirement. Dr. Bloom left the project just after the prototype was flown in late 1972. The production model (F-15A) was completed in March 1973. In 1976 Israel bought the F-15.  Now Israel  flies  the F-15I.  The  Eagle  has now landed!    It is now the most important defense weapon in Israel’s arsenal.