Introduction

The aerospace industry is aiming for a cleaner means of transport. One way to achieve this is by making transportation lighter, thus directly improving fuel efficiency and reducing environmental impact. A further aim, of the industry, is to reduce maintenance time to lessen operating costs, which can result in a reduction of air transport costs, benefitting both passenger and freight services. Current developments to support these aims include using advanced materials, with the current generation of aerospace structures being 50% composite materials. These materials offer a weight reduction whilst maintaining adequate stiffness; however, their damage mechanics are very complex and less deterministic than those of metals. This results in an overall reduced benefit. Structures are manufactured thicker using additional material to accommodate unknown or unpredictable failure modes, which cannot be easily detected during maintenance. A way to overcome these issues is the adoption of a structural health monitoring (SHM) inspection system. Structural health monitoring (SHM) is understood to be the continuous or periodic and automated method for determining and monitoring the condition of a monitored object within condition monitoring (according to DIN ISO 17359). This is conducted through measurements with permanently installed or integrated transducers and the analysis of the measurement data. Its purpose is to detect damage, for example, cracks or deformations, at an early stage to initiate countermeasures. [...

Conclusions

The state of the art of structural health monitoring damage detection systems reviewed in this book shows that it is a promising area of technologies. SHM damage detection systems in civil aviation are still mostly limited to lab applications because there are still issues, which need to be solved for such systems to be integrated in an aircraft structure. Therefore, further research is needed to solve the current drawbacks/limitations of the existing SHM approaches such that this technology can be used in aircrafts. Despite the current limitations, SHM application for damage detection in aircrafts would make the flying safer and the structure lifetime longer and reduce the maintenance time and costs considering that the maintenance could be performed not at the predetermined intervals, but upon the need based on the condition that would be determined by the SHM systems used. We conclude some of the important differences and the common challenges to the methods reviewed in this book and provide an outlook on the next steps to a successful implementation

Žmogaus odos tyrimas taikant ultragarsinį impulso atspindžio metodą: apžvalga ir kūrimas

Application of ultrasonic techniques provides non-invasive investigation of a lesion and the possibility to analyze certain aspects of the skin that are inaccessible to the eye of dermatologist. For diagnostic purposes, ultrasound examination makes it possible to recognize lesions causing morphological changes in structure of skin, to localize lesions and their extent, and to measure their thickness and density. During the literature review it was defined, that an ultrasonic transducer with at least 20 MHz should be applied for effective early stage diagnosis of melanoma. The structure of the skin imaging system including the high frequency ultrasonic data acquisition unit combined with the excitation/reception circuit, mechanics for linear scanning, focused transducer, electronics for scanning control and electronics for estimation of spatial positions has been proposed

Comparison of Ultrasonic Non-Contact Air-Coupled Techniques for Characterization of Impact-Type Defects in Pultruded GFRP Composites

This article compares different air-coupled ultrasonic testing methods to characterize impact-type defects in a pultruded quasi-isotropic glass fiber-reinforced plastic (GFRP) composite plate. Using the air-coupled transducers, comparisons among three methods were performed, namely, bulk-wave through transmission, single-side access using guided waves, and ultrasonic-guided wave tomography. The air coupled through transmission technique can determine the size and shape of impact-type defects with a higher resolution, but with the consequence of time consumption and, more importantly, the necessity of access to both sides of the sample. The guided wave technique on the other hand, allows a single-side inspection and is relatively fast. It can be used to determine the size of the defect using ultrasonic B-scan, but the exact shape of the defect will be compromised. Thus, in this article, to determine the shape of the defect, application of the parallel beam tomographic reconstruction technique using guided Lamb waves is demonstrated. Furthermore, a numerical finite element simulation was performed to study the effects of guided wave propagation in the composite sample and interaction with the internal defect. Lastly, the results from the experiments of different techniques were compared according to possibilities of defect sizing and determination of its shape

Air-Coupled, Contact, and Immersion Ultrasonic Non-Destructive Testing: Comparison for Bonding Quality Evaluation

The objective of this study is to compare the performance of different ultrasonic non-destructive testing (NDT) techniques for bonding quality evaluation. Aluminium-epoxy-aluminium single lap joints containing debonding in the form of release film inclusions have been investigated using three types of ultrasonic NDT methods: contact testing, immersion testing, and air-coupled testing. Apart from the traditional bulk wave ultrasound, guided wave testing was also performed using air coupled and contact transducers for the excitation of guided waves. Guided wave propagation within adhesive bond was numerically simulated. A wide range of inspection frequencies causing different ultrasonic wavelengths has been investigated. Average errors in defect sizing per ultrasonic wavelength have been used as a feature to determine the performance of each ultrasonic NDT technique. The best performance is observed with bulk wave investigations. Particularly, the higher frequencies (10–50 MHz) in the immersion testing performed significantly better than air-coupled testing (300 kHz); however, air coupled investigations have other advantages as contactless inspection. Whereas guided wave inspections show relatively lower accuracy in defect sizing, they are good enough to detect the presence of the debonding and enable to inspect long range. Even though each technique has its advantages and limitations, guided wave techniques can be practical for the preliminary in-situ inspection of adhesively bonded specimens

Evaluation of bonding quality with advanced nondestructive testing (NDT) and data fusion

This work aims to compare quantitatively different nondestructive testing (NDT) techniques and data fusion features for the evaluation of adhesive bonding quality. Adhesively bonded composite-epoxy single-lap joints have been investigated with advanced ultrasonic nondestructive testing and induction thermography. Bonded structures with artificial debonding defects in three different case studies have been investigated: debonding with release film inclusion, debonding with brass film-large, debonding with brass film-small. After completing preprocessing of the data for data fusion, the feature matrices, depending on the interface reflection peak-to-peak amplitude and the principal component analysis, have been extracted from ultrasonic and thermography inspection results, respectively. The obtained feature matrices have been used as the source in basic (average, difference, weighted average, Hadamard product) and statistical (Dempster–Shafer rule of combination) data fusion algorithms. The defect detection performances of advanced nondestructive testing techniques, in addition to data fusion algorithms have been evaluated quantitatively by receiver operating characteristics. In conclusion, it is shown that data fusion can increase the detectability of artificial debonding in single-lap joints