Experimental Development of Nonlinear Transfer Function Measurements.

Modal analysis is the primary means of analyzing structural responses to external forcing, informing decision-making or further physical testing of the structure. Nevertheless, most commercially available solutions assume the test article behaves linearly with excitation amplitude. If significant amounts of nonlinear stiffness or damping are present in the structure, large errors in linear analysis may result which could lead to improper decisions that may be costly. Therefore, it is useful to develop experimental techniques or computational models which account for nonlinearity during modal analysis. This paper describes a method of generating frequency response functions at various excitation energy levels to generate a three-dimensional transfer function surface. The resulting transfer function surface is agnostic of drive-point location, allowing excitations at different drive points to be compared directly. This result holds only if the drive point is sufficiently far from node points. The Brake-Reuss beam is used as the experimental exemplar at various levels of impact testing. Best practices learned during experimentation are included.