FATIGUE & DURABILITY

Fatigue failure—cracking of under repeated stressing—has been a concern of engineering for decades. As sources of vibration and of dynamic loading of materials have increased, fatigue failures have become more common and increasingly important in engineering design. Not surprisingly, the rapid utilization of composite materials within the aerospace industry has made fatigue behavior of composite materials an important topic of discussion. Exposure of advanced polymeric matrix composite materials (, to “real life” use and environment may result in irreversible changes in the original properties of the material. This process of change over time is loosely referred to as “aging”. Material aging may translate to structural changes in mission-critical components that can have potentially catastrophic effects.

For large transport commercial aircraft “durability” is defined as ability of the structure to retain adequate properties (strength, stiffness, and environmental resistance) throughout its service life. Damage tolerance is defined to be the ability of the structure to sustain design limit loads in the presence of damage caused by fatigue, corrosion, environmental effects, accidental events, and other sources until such damage is detected, through inspections or malfunctions and repaired. Structural damage tolerance ensures that damage will be found by maintenance practices before becoming a safety threat.