Modeling loss of fatigue life in aircraft landing gear due to residual stresses from hard landings

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When loads imparted to aircraft upon landing exceed 10% of designed limit loads, operators assume that**localized plastic deformation will occur in landing gear components. This results in persistent residual stresses**left in the gear, which are expected to negatively impact the fatigue life of the components. In cases when the**overloading is considered to be significant, landing gear must be taken out of service, heat-treated and**quarantined for long periods of time - an obviously expensive procedure for aircraft operators. Procedures and**inspections used to determine the need for removal from service depend on stress and fatigue analyses that**may, if they could be refined and validated, permit a less conservative approach. This could substantially**reduce operating costs without any compromise in safety.**In this initial engagement with the company, we propose to study a fundamental aspect of landing gear fatigue**analysis. Specifically, we will examine how to accurately incorporate the effect of residual stresses within the**fatigue life model. The common assumption is that a residual stress can be treated as equivalent to a constant**mean load superimposed on the cyclic loading expected in service. We can test this assumption through a**combination of FE analysis and experiments on test coupons with simplified geometries under low-cycle**fatigue. By the end of the 6-month project, we hope to be able to offer a preliminary assessment of the**mean-stress assumption. It is anticipated that this will guide further research into refinements of the modeling**of residual stress effects and improvements to the constitutive models used to predict fatigue life.