Detection and Characterization of Debonding Defects in Aeronautical Honeycomb Sandwich Composites Using Noncontact Air-Coupled Ultrasonic Testing Technique

Debonding growth evaluation in CFRP-reinforced steel structures based on correlation analysis using guided waves

Externally bonded carbon fibre reinforced polymer (CFRP) reinforcement is becoming increasingly popular in the field of structural retrofitting due to its considerable efficiency. However, debonding failure occurs sometimes at the interface between CFRP and steel substrate, which is found to be fatal for the CFRP-reinforced structures. Thus, the bonding condition between two materials should be closely monitored to ensure structural serviceability. A linear guided wave based method employing the correlation analysis is adopted in this paper to monitor the growth of debonding failure generated by fatigue in a CFRP-strengthened steel structure from a relatively small scale (smaller than 20 mm in diameter). The correlation coefficients (CC) between the benchmark signals and the signals after certain cycles of loading are calculated individually. Subsequently, the damage index (DI) is extracted on the basis of CC to illustrate the extent of debonding. Finally, the possible debonding position in the structure is predicted by a probability based imaging method.

Investigating the Effect of Dimension Parameters on Sound Transmission Losses in Nomex Honeycomb Sandwich

In this study, an impedance tube test was performed to explore the influence of various dimension parameters of Nomex honeycomb sandwich core material on sound transmission loss (STL). The parameters investigated included the size of the honeycomb cells and thickness of the face sheets and honeycomb cores, and the effects of single- and double-layered sandwich structures were also explored. The boundary element and finite element methods were used to simulate test results. The results show that the size of the honeycomb cells has an insignificant effect on STL. Increasing the thickness of face sheets can move the STL valley point of the material at high frequency (around 5 kHz) in the low-frequency direction and increase the STL in parts of the high frequency band. Increasing the thickness of the honeycomb core can improve STL, on the whole, but the magnitude of the improvement effect becomes weakened after the thickness of the core reaches 30 mm. The STL of double-layered structures was found to be superior to that of the single-layered structures. The simulations reveal that the trends in the STL curves of the honeycomb sandwich panels are influenced by the structural mode of the panels, and are related to the resonance of the materials. The results and relevant conclusions obtained through the above research verify that the law of influence of the structure dimension parameters on the STL measured by the impedance tube is similar to that of the large panel. This can provide a reference for the application of the impedance tube test method in structural noise reduction design.

Sandwich Panels Bond with Advanced Adhesive Films

Sandwich structures present several advantages, being used in many industries such as the aeronautical industry. In this study, an automated laminating line is employed to manufacture sandwich panels for boards. This work focus on an innovative solution, employing an advanced adhesive film to increase the bonding strength of sandwich structures used for this application. This was used to bond ceramic steel sheets to honeycomb‐cored structures, creating an innovative solution for the board industry. Bending tests were carried to evaluate the performance of the new sandwich solutions and to compare it against a typical one available on the market.

Guided Wave Propagation in Detection of Partial Circumferential Debonding in Concrete Structures

The following article presents results of investigating the damage detection in reinforced concrete beams with artificially introduced debonding between the rod and cover, using a non-destructive method based on elastic waves propagation. The primary aim of the research was to analyze the possible use of guided waves in partial circumferential debonding detection. Guided waves were excited and registered in reinforced concrete specimens with varying extents of debonding damage by piezoelectric sensors attached at both ends of the beams. Experimental results in the form of time-domain signals registered for variable extent of debonding were compared, and the relationships relating to the damage size and time of flight and average wave velocity were proposed. The experimental results were compared with theoretical predictions based on dispersion curves traced for the free rod of circular cross-section and rectangular reinforced concrete cross-section. The high agreement of theoretical and experimental data proved that the proposed method, taking advantage of average wave velocity, can be efficiently used for assessing debonding size in reinforced concrete structures. It was shown that the development of damage size in circumferential direction has a completely different impact on wave velocity than development of debonding length. The article contains a continuation of work previously conducted on the detection of delamination in concrete structures. The proposed relationship is the next essential step for developing a diagnostics method for detecting debondings of any size and orientation.