Effect of safety measures on reliability of aircraft structures subjected to damage growth

This paper demonstrates the effect of various safety measures used to design aircraft structures for damage tolerance. In addition, it sheds light on the effectiveness of measures like certification tests in improving structural safety. Typically, aircraft are designed with a safety factor of 2 on the service life in addition to other safety measures, such as conservative material properties. This paper demonstrates that small variation in material properties, loading and errors in modeling damage growth can produce large scatter in fatigue life, which means that quality control measures like certification tests are not very effective in reducing failure probability. However, it is shown that the use of machined cracks in certification can substantially increase the effectiveness of certification testing.