Predicting Airfield Pavement Fatigue Life Using Dynamic Coupling Models

Abstract

Aviation infrastructure is vital to the functioning of the airfields and requires the use of rigid airfield pavements, which are exposed to strong and repetitive cyclic loads and have to be extremely low-maintenance and durable. The traditional pavement models use the simple Winkler spring foundation, which does not consider the transfer of shear stress between neighboring soil layers. In addition, many pre-existing dynamic analysis tools simplify the moving aeronautical forces to static or lower degrees of freedom (one-DOF to four-DOF) configurations, which leaves a significant research gap as to how “true” multidimensional aircraft suspension dynamics and runway surface irregularities interact to influence cycle-by-cycle fatigue life. This study aims to fill this gap with the development of a comprehensive 3D vehicle-pavement interaction (VPI) simulation model. The purpose of the model is to deliver a realistic prediction of the cumulative damage index and remaining service life of a rigid airfield runway following realistic, variable amplitude aeronautical stressors and operational parameters. A modified and computationally-efficient finite element framework for aircraft-pavement interaction was created using MATLAB, which included a 3-D, six-DOF aircraft model with realistic multiwheel landing gear and suspension characteristics, and a 1D FE pavement model. The pavement subgrade is mathematically represented using a two-parameter model of a Pasternak foundation to adequately model localized shear layer deformations. The time domain simulations of pavement surface roughness are generated by a technique called power spectral density (PSD) functions. The dynamic equations of motion solution is used to solve the dynamic equations of motion in order to generate high-fidelity pavement stress histories using the Newmark-β integration scheme. Lastly, these dynamic stress fluctuations pass through a Rainflow cycle counting algorithm and are compared to Miner's linear damage rule to determine the cumulative fatigue life. Parametric evaluation indicates that there are two major design drivers: pavement slab thickness and subgrade modulus. In particular, the simulated fatigue life increases by almost 90% (from 28.83 to 54.78 years) with a thickness increase from 0.1 to 0.7 m of the slab. Likewise, the subgrade modulus can be increased to yield up to a 54.9% improvement in durability. Using normal concrete and high-grade concrete mix design (M30 to M50) extends the life by 31.4%. On the other hand, adverse operating conditions have a dramatic effect on structural integrity—a rough surface on the runway increases damage and reduces pavement life by as much as 71.9%, aircraft mass reduces it by 14.7%, and asymmetric gear load distribution reduces service life by as much as 21%. This work offers a very comprehensive and efficient prediction model that is capable of building a complex 3D landing gear dynamic model and successfully incorporating two-parameter soil-structure interaction principles. The results highlight the importance of the subgrade quality and the thickness of the pavement layers in order to optimize the rigid airfield runway. Finally, the study recommends that strict control of the surface roughness during design and stringent control of the operation (aircraft speed, acceleration, gear alignment, etc.) are required when designing for a high-load aeronautical application to prevent premature fatigue failure.