Structural Reliability Analysis of Corroded Landing Gear Drag Beam Considering Uncertainties in Radiographic Thickness Measurement

Abstract

This study investigated the reliability of a corroded drag beam of a helicopter landing gear. The drag beam made up of high-strength steel failed due to corrosion-initiated cracking. The fracture probability was calculated using a simple capacity and demand model. The strength distribution of the drag beam was obtained through the estimated thickness using radiography, and a model for thickness measurement was developed using a linear attenuation coefficient for both a base metal and a corrosion product. The thickness reduction by corrosion was estimated by comparing the photon intensities of the corroded region and the region of known thickness without any corrosion. Due to uncertainties in the model parameters—thickness of the good area, photon intensity with or without the corrosion product, and corrosion rate—Monte Carlo simulation was conducted. The load distribution was obtained using the flight load data from strain gauges attached to the drag beams, which mainly carried a compressive load and a much smaller torsional load. The results show that the currently operated drag beams have a sufficient margin of safety. Considering uncertainties, the inspection of the drag beam using radiography proved that it was structurally reliable.