Fatigue life prediction of nonlinear plates under random excitations

An efficient method is presented for estimating the high cycle fatigue life of nonlinear structures under random excitations. The procedure is based on an application of the method of equivalent linearization for constructing the response of the stress of the structure in time domain. Fatigue estimates are obtained by processing the time domain signal using the Rain-Flow cycle counting scheme in conjunction with the linear accumulative damage theory. The estimated average fatigue life of a nonlinear plate under random excitations by the present method is compared with the result obtained by direct Monte Carlo .simulations of the original nonlinear modal equations. The agreement is excellent for a wide range of levels of nonlinearity. The present method has the advantage of being much more computationally efficient than direct numerical simulations of nonlinear systems. The computational effort required of the present method for a nonlinear .system is nearly the same as that for a linear system and is not affected much by the type and level of nonlinearity in the structure. The present method offers a practical means for predicting high cycle fatigue lives of complex nonlinear structures.