Abstract-Guided wave mode conversion phenomenon in composite materials: numerical and experimental study

Tomasz Wandowski,  Paweł Kudela,  Paweł Malinowski,  Wiesław Ostachowicz,

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10972/109720N/Guided-wave-mode-conversion-phenomenon-in-composite-materials--numerical/10.1117/12.2512682.short

In this paper results of numerical and experimental analysis of S0/A0 elastic wave mode conversion phenomenon at various discontinuities in glass fibre reinforced polymer (GFRP) panels are presented. Analysis of S0/A0 mode conversion effect at Teflon inserts simulating delamination and impact damage with energies 5 J, 10 J and 15 J is conducted. In the case of Teflon inserts circular inserts with the same diameters located at different depth and inserts with various shapes located at the same depth were investigated. Numerical analysis is based on the time domain spectral element method (SEM). SEM computational algorithm is adapted for parallel calculation using graphic processor units (GPUs). Numerical model takes also into account the influence of material damping. Numerical results are compared with experimental results based on full wavefield measurements using scanning laser Doppler vibrometry (SLDV). It is shown that based on the effects of S0/A0 mode conversion it is possible to detect the damage and determine its shape and size. In the research, auxiliary Non-Destructive Testing (NDT) method is also utilised. The aim of its application is to indicate the depth of discontinuity and to prove that delamination was created in the case of impact damage. The auxiliary method is based on terahertz spectroscopy (THz) where the analysis of propagation of electromagnetic waves in the terahertz band is conducted. The THz spectroscopy is a useful technique for damage assessment in the dielectric materials.

© (2019) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-Moisture detection in composites by terahertz spectroscopy

Paweł Malinowski1, Norbert Pałka2, Szymon Opoka1, Tomasz Wandowski1 and Wiesław Ostachowicz1,3

http://iopscience.iop.org/1742-6596/628/1/012100

The application of Glass Fibre Reinforced Polymers (GFRP) in many branches of industry has been increasing steadily. Many research works focus on damage identification for structures made out of such materials. However, not only delaminations, cracks or other damage can have a negative influence of GFRP parts performance. Previous research proved that fluid absorption influences the mechanical performance of composites. GFRP parts can be contaminated by moisture or release agent during manufacturing, while fuel, hydraulic fluid and moisture ingression into the composite can be the in-service treats. In the reported research authors focus on moisture detection. There are numerous sources of moisture such as post manufacturing NDT inspection with ultrasonics coupled by water or exposition to moisture during transportation and in service. An NDT tool used for the research is a terahertz (THz) spectrometer. The device uses an electromagnetic radiation in the terahertz range (0.1-3 THz) and allows for reflection and transmission measurements. The spectrometer is equipped with moving table that allows for XY scanning of large objects such as GFRP panels. In the conducted research refractive indices were experimentally extracted from the materials of interest (water and GFRP). Time signals as well as C-scans were analysed for samples with moisture contamination. In order to be sure that the observed effects are related to moisture contamination reference measurements were conducted. The obtained results showed that the THz NDT technique can detect moisture hidden under a GFRP with multiple layers.

Abstract-New trends in non-destructive assessment of aerospace structures

Wieslaw M. Ostachowicz ; Pawel H. Malinowski ; Tomasz Wandowski

http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=2213453

Wieslaw M. Ostachowicz, Pawel H. Malinowski, Tomasz Wandowski

The Szewalski Institute of Fluid-Flow Machinery (Poland)

Proc. SPIE 9435, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2015, 943502 (March 27, 2015); doi:10.1117/12.2178155

The scope of the paper includes non–destructive assessment of the structure's material condition, for the aerospace structures during its useful lifetime. The paper presents multidisciplinary technologies devoted to development and implementation of methods and systems that realize inspection and damage detection by non–destructive methods. The paper covers several disciplines which are based on topics such as piezoelectric transducers, elastic waves propagation phenomenon, structural vibrations analysis, electro–mechanical impedance method, terahertz technique, laser induced fluorescence and 3D laser vibrometry applications. Among various techniques available the paper presents selected numerical simulations and experimental validations of considered structures. Authors address also the problem of adhesive bonding in the case of carbon fiber reinforced polymers (CFRP). Techniques for detection of weak bonds are presented together with signal processing approaches. The reported investigations concern weak adhesive bonds caused by both manufacturing (e.g. release agent, poor curing) and in–service contaminations (e.g. moisture). Also the paper provides helpful information about dispersion, mode conversion and wave scattering from stiffeners and boundaries. It addresses the problem of optimisation of excitation signal parameters and sensor placement, as well as analysis of signals reflected from damage. It also includes a variety of techniques being related to diagnostics (damage size estimation and damage type recognition) and prognostics. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.