Life assessment of a landing gear component based on non-linear analyses

Advanced aircraft trainers often require repair, modification, and inspection programs to meet the requirements of their structural life extension programs (SLEP). Presented as a real world example of this is a complex analysis effort designed to capture the effects of rework to nose landing gear (NLG) steering collars, which in some cases through years of fielded service have developed corrosion that penetrates the plating finishes and into the base metal.  Rework of these components generally involves machining that can extend beyond blueprint drawing tolerances, thus requiring analyses to substantiate a return to service with adequate remaining static strength and service life.

To validate the repair’s material removal limits, a detailed three-dimensional hp-finite element model (FEM) was generated using nearly 7.5M degrees-of-freedom (DOF). This model includes adjacent structural components which interface with the steering collar, as linear contact and standard clearances are considered in the analyses.

Due to the non-linear nature of the model, primarily due to contact interactions, typical linear superposition of external loads and stress transfer functions used in airframe level models are not appropriate. Using an external loads usage spectrum, analysts grouped discrete timestep loading events into dozens of similar load-type events. Representative loadcases were chosen for each of these load-types and FEM simulations were completed. Fatigue critical locations (FCL) were identified by peak stress values in each loadcase and the nodal data was extracted. A numerical routine was written to select the appropriate load-type, loadcase, and scaling factor to assign a stress value for each entry in the time-stepped spectrum. Industry standard spectrum filtering and cycle counting routines were used to generate spectra for each FCL and then perform crack initiation (fatigue) and crack growth (damage tolerance) analyses.

The results of the structural life analyses showed that the repaired component maintained ample life beyond the design service goal (DSG) and salvage of nearly all decommissioned parts.

Presenter Information
Mr. Matthew Hammond
Senior Stress Engineer
Andromeda Systems Incorporated

James Mattson, US Navy
Thomas Scarpinato, US Navy
Nicholas Hatcher, Andromeda Systems Incorporated
Jason Cisneros, Andromeda Systems Incorporated
Candido “Ray” Huertas, Andromeda Systems Incorporated