Finite-Element Analysis of Fatigue Lifetime in Pavements

A computational model was developed to predict fatigue life of pavements under repeated loading and implemented into the three-dimensional finite-element code DYNA3D and the two-dimensional finite-element code NIKE2D. The model simulates the cracking response of flexible or rigid pavements under fatigue. An equation for fatigue crack growth was developed, which grows cracks under single cycles of loading at stresses well below yield. The cracks are incorporated into the material response and result in anisotropic behavior and decreased stiffness for cracked pavements. A procedure for estimating fatigue lifetimes by performing a limited series of calculations was developed. For each calculation, crack growth rate for a single loading cycle is calculated, crack extension is extrapolated to many cycles, and the cracking in the pavement is updated. The next cycle is calculated for the damaged pavement. The procedure is repeated until full damage is reached. Well-controlled laboratory bending fatigue test results generated at the University of California at Berkeley (UCB) for asphalt pavement were used to verify that the model assumptions are appropriate for modeling fatigue damage growth in asphalt pavement. The UCB bending fatigue tests were simulated using the repeat loading algorithm in DYNA3D. Calculations of crack growth for a given load cycle were compared in the NIKE2D and DYNA3D implementations.