Safe-Life Fatigue and Sensitivity Analysis: A Pathway Towards Embracing Uncertainty?

Within the aerospace industry, conservatism exists within the safe-life fatigue design process of safety critical structures. This conservatism exists due to reduction factors which are required to counteract the probabilistic nature of fatigue and results in components that have to be retired from service prematurely. Understanding the sources of uncertainty and how they propagate from design inputs to the component safe-life is the first step to challenging the conservatism currently required. Variance Based Sensitivity Analysis (VBSA) can be used to apportion the uncertainty within a process output to the uncertainty within the process inputs. This paper explores the feasibility of applying VBSA methods to the safe-life design process using a landing gear case study and the “Sensitivity Analysis For Everybody” (SAFE) toolbox. The VBSA results identified that the parameter representing the number of cycles to failure associated with the cyclic load which accumulated the most fatigue damage within the component provided the largest contribution to the uncertainty within the component safe-life value. Whilst the over-arching concept of VBSA was found to be suitable for further application, the specific implementation presented within this paper displayed limitations, which are to be rectified if VBSA methods are to be applied within future work.