Leander Claes

Bio: Leander Claes is an academic researcher from University of Paderborn. The author has contributed to research in topics: Ultrasonic sensor & Acoustic wave. The author has an hindex of 6, co-authored 35 publications receiving 101 citations.

Determination of the material properties of polymers using laser-generated broadband ultrasound

Abstract: . In the non-destructive determination of material properties, the utilization of ultrasound has proven to be a viable tool. In the presented paper, a laser is used to create broadband acoustic waves in plate-shaped specimens by applying the photoacoustic effect. The waves are detected using a purpose-built ultrasonic transducer that is based on piezoceramics instead of the commonly used piezoelectric polymer films. This new transducer concept allows for detection of ultrasonic waves up to 10 MHz with high sensitivity, thereby allowing the characterization of highly damping materials such as polymers. The recorded data are analysed using different methods to obtain information on the propagation modes transmitted along the specimen. In an inverse procedure, the gained results are compared to simulations, yielding approximations for the specimen's material properties.

Characterization of continuous-fiber reinforced thermoplastics using thermoacoustically excited ultrasonic Lamb waves

Abstract: Ultrasonic measurement techniques are widely used for non-destructive detection of material defects. However, material properties, such as Young's modulus, are still mostly determined destructively, especially for materials with high damping or strong anisotropy. One method for non-destructive material characterization creates and detects ultrasonic waves in plate-shaped specimens, so that the material's influence on wave propagation can be evaluated. In this contribution, we demonstrate the application of this method for fiber-reinforced plastics, identifying effective parameters for a homogeneous, orthotropic material model.

Acoustic absorption measurement for the determination of the volume viscosity of pure fluids / Messverfahren für die akustischen Absorption zur Bestimmung der Volumenviskosität reiner Fluide

Abstract: Abstract A realistic description of fluid mechanical and acoustic processes requires the volume viscosity of the medium to be known. This work describes how the volume viscosity of pure fluids can be determined by measuring acoustic absorption with the pulse-echo method. The challenge in realizing such a measurement method lies in the separation of the different dissipative effects that superimpose on absorption. Diffraction effects ultimately cause a dissipation of acoustic energy and acoustic reflector surfaces have a small, but finite transmission coefficient. Further, influences of the transducer (in particular its frequency response), as well as the system’s electrical components have to be taken into account. In contrast to the classical approach relying on the amplitude ratio, the absorption is determined by the moments of the amplitude spectrum. The measurement system applied is originally designed for precision measurements of the sound velocity by means of the propagation time difference of two acoustic signals.

Ultrasonic transmission measurements in the characterization of viscoelasticity utilizing polymeric waveguides

Abstract: For the numerical simulation of acoustic wave propagation in (measurement) systems and their design, the use of reliable material models and material parameters is a central issue. Especially in polymers, acoustic material parameters cannot be evaluated based on quasistatically measured parameters, as are specified in data sheets by the manufacturers. In this work, a measurement method is presented which quantifies, for a given polymeric material sample, a complex-valued and frequency-dependent material model. A novel three-dimensional approach for modeling viscoelasticity is introduced. The material samples are designed as hollow cylindrical waveguides to account for the high damping characteristics of the polymers under test and to provide an axisymmetric structure for good performance of waveguide modeling and reproducible coupling conditions arising from the smaller coupling area in the experiment. Ultrasonic transmission measurements are carried out between the parallel faces of the sample. To account for the frequency dependency of the material properties, five different transducer pairs with ascending central frequency from 750 kHz to 2.5 MHz are used. After passing through the sample, each of the five received signals contains information on the material parameters which are determined in an inverse procedure. The solution of the inverse problem is carried out by iterative comparison of an innovative forward SBFEM-based simulations of the entire measurement system with the experimentally determined measurement data. For a given solution of the inverse problem, an estimate of the measurement uncertainty of each identified material parameter is calculated. Moreover, a second measurement setup, based on laser-acoustic excitation of Lamb modes in plate-shaped specimens, is presented. Using this setup, the identified material properties can be verified on samples with a varied geometry, but made from the same material.

Towards real-time assessment of anisotropic plate properties using elastic guided waves

Abstract: A method to recover the elastic properties, thickness, or orientation of the principal symmetry axes of anisotropic plates is presented. This method relies on the measurements of multimode guided waves, which are launched and detected in arbitrary directions along the plate using a multi-element linear transducer array driven by a programmable electronic device. A model-based inverse problem solution is proposed to optimally recover the properties of interest. The main contribution consists in defining an objective function built from the dispersion equation, which allows accounting for higher-order modes without the need to pair each experimental data point to a specific guided mode. This avoids the numerical calculation of the dispersion curves and errors in the mode identification. Compared to standard root-finding algorithms, the computational gain of the procedure is estimated to be on the order of 200. The objective function is optimized using genetic algorithms, which allow identifying from a singl...

Determination of elastic constants of additive manufactured Inconel 625 specimens using an ultrasonic technique

Abstract: The nature of additive manufacturing (AM) processes prescribes direction-dependent properties of the final parts. The degree of material anisotropy is highly dependent on the process parameters and the machine setup which complicates the design of AM parts. A basic problem in the design and quality control of parts and components manufactured by the AM processes is the evaluation of the resulting elastic properties, specifically along the principal directions. In a destructive testing approach, many specimens in the principal directions are normally required to determine the elastic properties of a material. However, an alternative low-cost method based on the ultrasonic wave propagation velocities can also be used for this purpose. In this article, an ultrasonic-based method for the determination of the elastic constants of the Inconel 625 (IN625) material as manufactured via the laser powder-bed fusion process (L-PBF) is presented. Several specimens are fabricated with various process parameters such as laser power, scan speed, and hatch spacing, and nondestructively tested. The material elastic constants are then determined by measuring the ultrasonic wave velocities within the specimen. The results are verified qualitatively with the published results and destructive tensile tests. The obtained results showed a good correlation indicating the effectiveness of the proposed method for the determination of elastic constants of additively manufactured IN625 material.

Determination of the material properties of polymers using laser-generated broadband ultrasound

Abstract: . In the non-destructive determination of material properties, the utilization of ultrasound has proven to be a viable tool. In the presented paper, a laser is used to create broadband acoustic waves in plate-shaped specimens by applying the photoacoustic effect. The waves are detected using a purpose-built ultrasonic transducer that is based on piezoceramics instead of the commonly used piezoelectric polymer films. This new transducer concept allows for detection of ultrasonic waves up to 10 MHz with high sensitivity, thereby allowing the characterization of highly damping materials such as polymers. The recorded data are analysed using different methods to obtain information on the propagation modes transmitted along the specimen. In an inverse procedure, the gained results are compared to simulations, yielding approximations for the specimen's material properties.

Inhomogeneous mechanical properties in additively manufactured parts characterized by nondestructive laser ultrasound technique

Abstract: Additive manufacturing (AM) or Three dimensional (3D) printing has become a promising manufacturing technique in architecture, aerospace, biomedical and automotive industries. However, additively manufactured parts need to demonstrate their stable mechanical properties like elastic modulus and strength. In this study, four various thickness of 3D printing samples were prepared to measure the elastic modulus by tensile testing and laser ultrasound technique (LUT). Besides, an inversion technique is followed to extract the elastic modulus from the 3D printed parts through LUT measured dispersion curve. Results indicate that significant differences in Young's modulus were observed between the various thickness of the tensile specimens. All the elastic modulus inverted values were well agreed with experimental measurements with the controlled error percentage of 0.02–1.35%. Further, individual layer modulus was calculated from the inversed averaged modulus and fitted with parabolic equation. Form the obtained outcomes, to print a sample with 40-layers, the first (top) layer modulus was 3254 MPa while bottom layer shows 4706 MPa which indicates a difference of 45% with inhomogeneous across the printed layers. While printing a new layer, the ultraviolet (UV) light can be exposed to previously printed layers and this more irradiation of UV light could stimulate to additional polymerization of remaining unreacted monomers and increased the modulus in the bottom layer.