Active strategies for structural health monitoring using ultrasonic guided waves mainly deal with excitation signals that are band limited in order to minimize the effect of dispersion. The underlying idea is to activate only the fundamental wave modes so that the signal complexity decreases and individual wave packets in the sensor signals can be identified separately. However, it would be advantageous to increase the temporal resolution of the signal in order to enhance the performance of the post-processing algorithms, for example, travel-time-based damage localization algorithms that need precise arrival time estimations or imaging approaches processing the deconvolved signals directly. This article suggests a new technique to deconvolve narrowband and nonstationary ultrasonic signals by means of a time-varying inverse filter. This filter is realized through the application of the matching pursuit decomposition algorithm. The properties of this methodology are quantitatively compared with several onset-time estimation approaches and evaluated with experimental pitch-catch and differential signals between the pristine and the damaged structure.

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This study presents that finite element (FE) simulations of rotary draw bending are improved by taking into account the stiffnesses of the machine axes. The results show the influence of the axis stiffnesses of the bend die, the wiper die, the pressure die and the mandrel on the formation of wrinkles at the inner tube bend. For this purpose the axis stiffnesses are varied in FE-simulations and wrinkle evaluation factors of the final components are determined and compared. Low axis stiffnesses correspond to large axial displacements when force is applied and cause greater wrinkle formation. In addition, practical tests are carried out on the machine to measure the axis displacements and associated forces. The resulting axis stiffnesses are entered into the FE simulation. The final geometry of the bending component of the FE simulation is compared with the geometry of a component produced in a practical test. The consideration of the axis stiffness in the calculation in contrast to ideally stiff axes provides wrinkle heights that are closer to the wrinkle heights in the practical test. The knowledge gained improves the prediction of the component quality and allows the evaluation of axis displacements measured on bending machines. The overall aim of the project is to react to machine-specific axis stiffnesses in the form of process control.

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