A phased array-based method for damage detection and localization in thin plates

A method for damage localization based on the phased array idea has been developed. Four arrays oftransducers are used to perform a beam-forming procedure. Each array consists of nine transducersplaced along a line, which are able to excite and register elastic waves. The A0 Lamb wave mode hasbeen chosen for the localization method. The arrays are placed in such a way that the angulardifference between them is 458 and the rotation point is the middle transducer, which is common for allthe arrays. The idea has been tested on a square aluminium plate modeled by the Spectral Element Method. Two types of damage were considered, namely distributed damage, which was modeled asstiffness reduction, and cracks, modeled as separation of nodes between selected spectral elements.The plate is excited by a wave packet. The whole array system is placed in the middle of the plate.Each linear phased array in the system acts independently and produces maps of a scanned fieldbased on the beam-forming procedure. These maps are made of time signals (transferred to spacedomain) that represent the difference between the damaged plate signals and those from the intactplate. An algorithm was developed to join all four maps. The final map is modified by proposed signal processing algorithm to indicate the damaged area of the plate more precisely. The problem fordamage localization was investigated and exemplary maps confirming the effectiveness of theproposed system were obtained. It was also shown that the response of the introduced configurationremoves the ambiguity of damage localization normally present when a linear phased array is utilized.The investigation is based exclusively on numerical data

Analysis of S0/A0 elastic wave mode conversion phenomenon in glass fibre reinforced polymers

In this paper results of experimental analysis of elastic guided wave mode conversion phenomenon in glass fibre reinforced polymers GFRP are presented. Results of research presented in this paper are strictly focused on S0/A0' mode conversion caused by discontinuities in the form of circular teflon insert simulating damage and impact damage. Experimental research is based on non-contact elastic wave sensing with utilisation of scanning laser Doppler vibrometer SLDV and full wave-field measurements. In presented research influence of location of circular teflon insert on S0/A0' mode conversion is investigated. Teflon inserts were located between layers of composite material at different depth. Moreover influence of impact damage with different energy on S0/A0' mode conversion is investigated. Analysis of influence of investigated discontinuities on S0/A0' mode conversion are based on the elastic wave mode filtration in frequency-wavenumber domain. Mode filtration process allows to remove effects of unwanted type of mode propagation in forward or backward direction. Effects of S0/A0' mode conversion are characterise by mode conversion indicator based on amplitude of new mode A0'

Analysis of Air-Coupled Transducer-Based Elastic Waves Generation in CFRP Plates

In this paper, the analysis of non-contact elastic waves generation in carbon fiber reinforced-polymer (CFRP) plate was conducted. Full non-contact elastic waves generation and sensing methods were also analyzed. Elastic waves generation was based on an air-coupled transducer (ACT) while waves sensing was based on a laser Doppler vibrometer. The excitation frequency was equal to 40 kHz. An optimal ACT slope angle for the generation of elastic waves mode was determined with the aid of dispersion curves calculated by using a semi-analytical model. Due to the stack sequence in the composite plate (unidirectional composite), ACT slope angles were different for waves generation in the direction along and across reinforcing fibers direction. Moreover, experimental verification of the optimal ACT slope angles was conducted. It was possible to generate A0 wave mode in the direction along and across the reinforcing fibers. Optimal angles determined using ACT were equal to 16° (along fibers) and 34° (across fibers). In the case of optimal angles, elastic waves amplitudes are almost two times higher than for the case of ACT oriented perpendicularly to the plate surface. Moreover, experimental results based on ACT showed that it was possible to generate the SH0 mode in the direction across the fiber for optimal angles equal to 10°. Finally, based on the A0 wave mode propagation, the process for localization of discontinuities was performed. Discontinuities in the form of additional mass simulating damage were investigated. A simple signal processing algorithm based on elastic wave energy was used for creating damage maps. Authors compared discontinuity localization for ACT oriented perpendicularly to the plate and at the optimal slope angle. The utilization of non-contact waves excitation at optimal ACT slope angles helped to focus the wave energy in the desired direction. Moreover, in this case, elastic waves with the highest amplitudes were generated

Damage assessment in wind turbine technology

The economic efficiency of wind turbines WT is strictly dependent on their availability and reliability. This problem is most important in the case of offshore wind turbines OWT. There is a search for new materials, new manufacturing process, and new rules of structural designs. The aim of it, is to achieve far tighter safety margins than previously developed wind turbine solutions. Attention of many researchers is focused on the problem of WT/OWT reliability. In this paper Structural Health Monitoring (SHM) approach for wind turbines is presented. This approach is based on such topics as piezoelectric transducers, elastic waves propagation phenomenon, fibre Bragg gratings sensors, structural vibrations analysis. The combination of mentioned techniques allows to perform efficient both local and global SHM of the OWT. Research results presented in this paper are mainly related to fibre reinforced polymer materials FRPs due to fact that they are widely utilized in wind turbine blades manufacturing. However, certain results for metallic structures (tower structure) were also presented. Considered above investigations are intended to develop future SHM techniques that include sensors, hardware, software and methodologies of WT/OWT structural assessment

Damage assessment in wind turbine technology

The economic efficiency of wind turbines WT is strictly dependent on their availability and reliability. This problem is most important in the case of offshore wind turbines OWT. There is a search for new materials, new manufacturing process, and new rules of structural designs. The aim of it, is to achieve far tighter safety margins than previously developed wind turbine solutions. Attention of many researchers is focused on the problem of WT/OWT reliability. In this paper Structural Health Monitoring (SHM) approach for wind turbines is presented. This approach is based on such topics as piezoelectric transducers, elastic waves propagation phenomenon, fibre Bragg gratings sensors, structural vibrations analysis. The combination of mentioned techniques allows to perform efficient both local and global SHM of the OWT. Research results presented in this paper are mainly related to fibre reinforced polymer materials FRPs due to fact that they are widely utilized in wind turbine blades manufacturing. However, certain results for metallic structures (tower structure) were also presented. Considered above investigations are intended to develop future SHM techniques that include sensors, hardware, software and methodologies of WT/OWT structural assessment