|The Iby and
Faculty of Engineering
|Research Group and Consultation|
The Eda and Jaime Dreszer Fracture Mechanics Laboratory
Department of Solid Mechanics, Materials and Systems
The Iby and Aladar Fleischman Faculty of Engineering
Tel-Aviv University, Ramat Aviv 69978, Israel
The field of fracture mechanics deals with the prediction of crack propagation in structures. All structures have defects such as materials imperfections or manufacturing flaws, which in service become cracks. These cracks may be unimportant to the continued functioning of the structure or may run catastrophically causing great damage to property and life. Typical large structures in which this may occur include bridges, submarines, airplanes and aerospace vehicles, to name a few.
The mechanics of fracture changes from being a scientific curiosity to an engineering discipline, primarily because of the failures of the Liberty ships during World War II. The Liberty ship program functioned successfully until 1943 when one vessel broke completely in two while sailing between Siberia and Alaska. Of about 2700 Liberty ships built during the war, approximately 400 sustained fractures, of which 90 were considered serious. In 20 ships, the failure was total and half of them broken in two. A group of researchers was formed in Washington, which studied the problem in detail and fracture mechanics, as we know in today, was born.
Today aircraft are designed and built taking fracture mechanics precepts into consideration. Inspections are made of all airplanes. In fact, periodically, for airplanes that are on the ground, a 'walk around inspection' is carried out to determine if any cracks may be visually detected. Of course, there are more serious inspections, which include eddy current, ultra-sound and x-ray techniques. Many airplanes fly with cracks. The discipline of fracture mechanics aids in establishing criteria, which enable airlines to provide flight safety.
The science continues to develop, as new materials such as composites are investigated to understand their failure mechanisms and prevent catastrophic failure. Other problem, such as the debonding of joined materials and the delamination of composite materials are studied to improve the performance of structures employing such materials. As an example of debonding, many ceramic tiles bonded to the U.S. space shuttle for protection against the high temperatures upon reentry into the earth's atmosphere, fell of during flight. Solutions have been found to this problem, although greater understanding of the fracture processes of debonding is required.