Arvid Martens

Characterization of visco-elastic material parameters by means of the ultrasonic polar scan method

The Ultrasonic Polar Scan (UPS) is a non-destructive technique which insonifies a material spot on a sample using ultrasonic pulses from as many oblique incidence angles ψ(φ,θ) as possible. Mapping the transmitted time-of-flight (TOF) and/or amplitudes as function of the incidence angle ψ(φ,θ) in a polar representation yields a UPS image with intriguing patterns that represent a fingerprint of the local visco-elastic properties. The present paper reports on recent advances in the revival of the UPS technique, involving the construction of an automated high-precision UPS scanner, the implementation of advanced simulation models as well as the development of efficient inversion routines. On the experimental level, unprecedented high quality TOF and amplitude UPS landscapes for a range of orthotropic (fiber reinforced) materials have been obtained. Using numerical simulation models, it can be readily demonstrated that the TOF UPS landscapes are directly connected to the elastic properties of the material, wh...

Simulation of a Circular Phased Array for a Portable Ultrasonic Polar Scan

The development of new composite materials, often anisotropic in nature, requires intricate approaches to characterize these materials and to detect internal defects. The Ultrasonic Polar Scan (UPS) is able to achieve both goals. During an UPS experiment, a material spot is insonified at several angles Psi(theta,phi), after which the reflected or transmitted signal is recorded. While excellent results have been obtained using an in-house developed 5-axis scanner, UPS measurements with the current set-up are too lengthy and cumbersome for in-situ industrial application. Therefore, we propose to replace the complex mechanical steering of the transducers by a hemispherical phased array consisting of small PZT elements. This allows to create a compact and portable setup without compromising the current data quality. By successively activating a specific set of elements of the array and choosing appropriate inter-element time delays, the beam can be electronically steered from any angle to a fixed position on the targeted sample. Consequently, UPS reflection measurements can be performed at this position from a wide range of angles in a timeframe of seconds. Additionally, by using apodization windows, it is possible to efficiently reduce the intensity of unwanted side lobes and to create a phase profile which closely resembles that of a bounded plane wave, leading to an easier interpretation of the recorded data. The appropriate time delays and apodization parameters can be found though a multi-objective inverse problem in which both the phase profile and the side lobe reduction are optimized. This approach enables the creation of an effective beam profile to be used during UPS experiments for the characterization and inspection of composite materials. Our simulation approach is a crucial step towards a next-generation UPS device for industrial applications and in-field measurements.

Recent advances in the ultrasonic polar scan method for characterizing (degraded) fiber reinforced plastics

The ultrasonic polar scan (UPS) technique originated in the 1980s as a sophisticated method for inspecting composites. However, it is only in recent times that the true capabilities and strengths of the UPS methodology have been evidenced through experiment and simulation. Nowadays, the UPS method exists in different versions which led to several novel applications in the field of material inspection and characterization. This contribution gives an overview of our recent advances. doi: 10.12783/SHM2015/323