Crack identification by 'arrival time' using XFEM and a genetic algorithm

A computational framework is developed in which cracks in two-dimensional structures are identified, in conjunction with non-destructive testing of specimens. As opposed to a previous study by the authors. which was based oil time-harmonic excitation with it single frequency, here the transient response of the structure to a short-duration signal is measured along part of the external boundary. Crack detection is performed using the solution of an inverse time-dependent problem. It is shown that the arrival time of the input signal to the points of measurement is a good criterion for crack identification in the time domain. The inverse problem of identification is solved using a genetic algorithm, while each forward problem is solved by the time-dependent extended finite element method (XFEM). The XFEM scheme is efficient in that it allows the use of a single regular mesh for a large number of forward time response problems with different crack geometries. Numerical examples involving a crack in a flat membrane are presented. Identification based oil 'arrival time' is shown to perform better than that based on time-harmonic response. Copyright (c) 2008 John Wiley & Sons, Ltd.