Failure analysis of a broken support strut of an aircraft landing gear

Abstract

This study contains the analysis of a nose landing gear support strut of an aircraft that failed during landing within 2 s after nose wheel touchdown. Visual inspection revealed that threaded portion of an eye-end bolt of the support strut was fractured. Furthermore, on the upper portion of the strut, one of the two retaining pins connecting it with aircraft structure was found dislodged from housing inflicting damage to the adjacent brackets. During detailed fractography, no indication of progressive failure was observed; on the contrary, clear signatures of overload failure were found. Compositional analysis revealed the fractured eye-end bolt to be AISI 4130 steel. Metallography revealed no nonconformities in the microstructure whereas the hardness was found to be as per desired values. Finite element method was used to find the (overload failure) stress in the eye-end bolt during landing. The landing impact forces were calculated using multibody dynamic tool MSC ADAMS® and subsequently applied to the support strut model in ANSYS®. Numerical stress simulations were performed for different cases and the stresses at the eye-end were analysed. The stress at the fractured region was within yield limit for all cases of normal operation. However, the stress rose to well beyond UTS when one pin connection was dislodged from the housing, owing to a likely improper installation.