Łukasz Pieczonka

Investigation of Nonlinear Vibro-Acoustic Wave Modulation Mechanisms in Composite Laminates

This paper investigates the effect of low-frequency vibration and the related temperature field on nonlinear vibro-acoustic wave modulations. Experimental modal analysis was used to find natural frequencies and mode shapes of a composite laminate plate with seeded delamination. Temperature distribution was analyzed with a thermographic camera in the vicinity of damage for the identified vibration modes. These frequencies of these vibration modes were then used for low-frequency excitation in nonlinear acoustic tests. The correlation between the thermal field and the observed wave modulations was analyzed.

Study of the Effect of Process Induced Uncertainties on the Performance of a Micro-Comb Resonator

This paper presents a modeling technique based on the integration in the classic deterministic simulation methods of probabilistic computational techniques such as uncertainty analysis and sensitivity analysis. As study case, it is presented a micro-comb resonator that is actuated electrostatically to vibrate in the plane parallel to the substrate. A deterministic Finite Element coupled electromechanical analysis is performed to evaluate the mode shapes and the corresponding eigenfrequencies of the mobile mass and afterwards a Monte Carlo simulation is used to determine the dispersion of the eigenfrequency of the mode shape of interest in function of the variations of the input parameters. The scatter of the results is analyzed and then it is presented a sensitivity analysis for establishing which of the input parameters have more influence on the variability of the microresonators performance.

Analysis of Vibro-Acoustic Modulations in Nonlinear Acoustics Used for Impact Damage Detection - Numerical and Experimental Study

The paper investigates experimentally the effect of low-frequency vibration on nonlinear vibro-acoustic wave modulations applied to the detection of Barely Visible Impact Damage (BVID) in a composite plate. Finite Element (FE) modeling was used in a pretest stage to identify different motion scenarios of delaminated surfaces and relate them to natural frequencies of the damaged plate. In particular the opening-closing and frictional sliding actions of the defected interfaces have been considered. Subsequently, the identified frequencies have been used for low frequency excitation in nonlinear acoustic experiments on a composite plate with impact damage.

Vibrothermographic Testing of Structures

The paper investigates practical aspects of vibrothermographic testing of structures. Two application cases of vibrothermography are presented and discussed. The examples are weld test specimens and a military aircraft skin. Measurements have been performed with use of an in-house vibrothermographic testing system. In case of welded specimens a series of carbon steel test samples with different flaw types have been investigated. In case of aircraft testing, field measurements have been performed on a wing and fuselage sections in order to assess their structural integrity. The paper presents thermal image processing technique that allows to increase the quality and readability of the results coming from field measurements with poor ultrasonic excitation and with low thermal response from the structure. The paper is concluded with the discussion on applications of vibrothermographic testing in Structural Health Monitoring.

Investigation of the Effectiveness of Different Thermographic Testing Modalities in Damage Detection

The paper deals with practical aspects of Thermographic Nondestructive Testing (TNDT). A comparative study of burst vibrothermography (VT) and pulsed thermography (PT) measurements is presented and discussed. The authors have developed a diagnostic system for thermographic testing of structures that was used to perform experiments. Supported test modalities include burst vibrothermography and pulsed thermography, among other techniques. The system comprises both hardware and software components facilitating TNDT inspections. Experimental testing has been performed, on a composite plate, using the developed diagnostic system and two of the supported test modalities. The goal of these investigations was to compare the performance of both TNDT methods in revealing Barely Visible Impact Damage (BVID) in a composite plate.

Laser Spot Thermography of Ceramic Materials

The paper presents an application of laser spot thermography for damage detection in ceramic materials. The measurement technique is based on an external heat delivery to a test sample by means of a laser pulse and signal acquisition by an infrared camera. Damage detection is based on the analysis of surface temperature distribution near the exciting laser spot. The technique is nondestructive, noncontact and allows for full-field measurements. This paper presents an application of laser spot thermography to a ceramic sample with surface breaking crack. This type of damage is very common in case of ceramic materials as it often arises due to the manufacturing process or during the service period. This paper briefly discusses theoretical background of laser spot thermography, describes the experimental test rig and signal processing methods involved. Damage detection results obtained with laser spot thermography are compared with reference measurements obtained with vibrothermography. This is a different modality of active thermography, that have been previously proven effective for this type of damage. We demonstrate that both measurement techniques can be effectively used for damage detection and quality control applications of ceramic materials.

Experimental Investigation of Crack-Wave Interactions for Structural Damage Detection

The paper discusses experimental verification of a damage detection method based on nonlinear crack-wave interactions in aluminum beam with fatigue crack. The method under consideration is based on a low-frequency vibration excitation, used to perturb damage, combined with high-frequency interrogating waves, used to detect damage-related nonlinearities. The proposed method can detect and localize both damage-related and intrinsic nonlinearities, allowing for reliable damage detection. The method does not require baseline measurements representing an undamaged condition and it is not sensitive to temperature variations. Damage localization is obtained through proper synchronization of the low-frequency vibration with the interrogating high-frequency wave packets. This paper aims at experimental verification of the opening–closing action of a fatigue crack being the source of nonlinearity in the analyzed case. A developed vision system composed of a high-speed digital camera with microscopic optics and vision-based tracking algorithms is used to analyze crack motion during the experiment. Quantitative analysis of the crack opening–closing action is performed to better understand the process of nonlinear wave modulations.