Ali H. Nayfeh 
Introduction to Perturbation Techniques [PDF ebook] 

Algebraic Equations.
Integrals.
The Duffing Equation.
The Linear Damped Oscillator.
Self-Excited Oscillators.
Systems with Quadratic and Cubic Nonlinearities.
General Weakly Nonlinear Systems.
Forced Oscillations of the Duffing Equation.
Multifrequency Excitations.
The Mathieu Equation.
Boundary-Layer Problems.
Linear Equations with Variable Coefficients.
Differential Equations with a Large Parameter.
Solvability Conditions.
Appendices.
Bibliography.
Index.

Ali H. Nayfeh received his BS in engineering science and his MS and Ph D in aeronautics and astronautics from Stanford University. He holds honorary doctorates from Marine Technical University, Russia, Technical University of Munich, Germany, and Politechnika Szczecinska, Poland. He is currently University Distinguished Professor of Engineering at Virginia Tech. He is the Editor of the Wiley Series in Nonlinear Science and Editor in Chief of Nonlinear Dynamics and the Journal of Vibration and Control.