Analysis of Crack Induced Structure Response Using Nonlinear Output Frequency Response Functions

Nonlinear Output Frequency Response Functions (NOFRF's) are a new concept recently developed for the analysis of nonlinear systems in the frequency domain. Based on this concept, the output frequency behaviours of nonlinear systems can be expressed using a number of one- dimensional functions similar to the approach used in the traditional frequency response analysis of linear systems. In this paper the NOFRF's are employed to analyse a cracked beam described by a SODF bilinear model. The results show that the NOFRF's are highly dependent upon the ratio of stiffness of the cracked and crack free situations and can thus be used as crack damage indicators. In addition, the higher order NOFRF terms are significantly sensitive to crack size and hence can be used to distinguish different situations of crack. This research study confirms the conclusion that the increasing crack size will make the structure behaviour more nonlinear and establish an important basis for the use of the NOFRF concept to detect and estimate cracks in mechanical structures.