Introduction of composites for aircraft fabrication has given the opportunity to all researchers and original equipment manufacturers to design a lightweight structure that will reduce both fuel consumption and harmful emissions. Reliability and cost of implementing structural health monitoring (SHM) systems are two critical parameters for the utilization of composite materials in the aviation industry. SHM of composite material components in the aviation industry not only lessens the downtime of aircraft but also enhances the possibility of damage detection in order to avoid severe failure. This article presents a case study of SHM systems that has been developed from research and implemented for the inspection and safety of recent aircraft structures. Compulsory components required for proper working of an SHM system and the basis and classification of defects in composite material components of aircraft are thoroughly explained in this article. Furthermore, characterization of SHM techniques (on the basis of functioning, advantages, and limitations) for crack detection and challenges of SHM systems are also part of this case study. An experimental work and its results have been well expressed regarding guided wave inspection using two different types of fiber-optic sensors for quasi-isotropic carbon fiber–reinforced plastic laminate. The ultimate goal of this article is to highlight the current challenges of SHM and promote the concept that SHM has great potential for research in the aviation industry.

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The baseline signal in structural inspection based on guided waves is difficult to be obtained under varying environmental conditions. To guarantee the precision of damage identification, developing baseline-free damage detection methods is significant in practical structural monitoring work. Conventional instantaneous baseline measurement needs a large number of PZT transducers. In this paper, a novel damage identification method for plate-like structures based on distance compensation is proposed to overcome this shortage. Combining with the concept of instantaneous baseline measurement, pitch-catch pairs of different propagation distance can be compared together to reveal the health information of the measured paths. This method overcomes the drawback of instantaneous measurement, which can only monitor the paths of identical wave travelling distance. Both simulations and experiments are conducted to validate the proposed method. Using this method, the influence of damage size and classification on amplitude variation is discussed. Finally, a baseline-free damage imaging technique is developed based on amplitude loss ratio of the first arriving wave package. The result shows a good agreement of the predicted result and the real damage location.

This research objective is to optimize the surface roughness of Nylon-6 (PA-6) and Acrylonitrile Butadiene Styrene (ABS) by analyzing the parametric effects of the Fused Filament Fabrication (FFF) technique of Three-Dimensional Printing (3DP) parameters. This article discusses how to optimize the surface roughness using Taguchi analysis by the S/N ratio, ANOVA, and modeling methods. The effects of ABS parameters (initial line thickness, raster width, bed temperature, build pattern, extrusion temperature, print speed, and layer thickness) and PA-6 parameters (layer thickness, print speed, extrusion temperature, and build pattern) were investigated with the average surface roughness (Ra) and root-mean-square average surface roughness (Rq) as response parameters. Validation tests revealed that Ra and Rq decreased significantly. After the optimization, the Ra-ABS and Rq-PA-6 for the fabricated optimized values were 1.75 µm and 21.37 µm, respectively. Taguchi optimization of Ra-ABS, Rq-ABS, Ra-PA-6, and Rq-PA-6 was performed to make one step forward to use them in further research and prototypes.

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