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This paper investigates the method for water ingress detection in an aluminum honeycomb sandwich structure by laser ultrasonics. To clarify the propagation of Scholte waves generated at the solid-liquid interface, the theoretical dispersion curves in the water-aluminum layered structure are calculated by the global matrix method. Using a laser ultrasonic visualizing inspector, the guided wave propagation in the wavefields has been visualized, which shows the mode conversion behaviors occurring in the water ingress area. The clarification of mode conversion is then investigated by the finite element method. The Scholte modes at the solid-fluid interface and the Lamb modes in the face sheet are interconverted because of the change in the waveguide structure. Wavenumber filter reconstruction and the resulting energy maps are applied to illustrate the mode conversion in the wavefields and to detect the water ingress area. Results show that the appearance of the water layer contributes to the mode conversion behaviors during the guided wave propagation in the honeycomb sandwich structure, which offers the potential for water ingress detection based on the mode conversion behaviors. [ABSTRACT FROM AUTHOR]

Detecting disbonds in honeycomb sandwich structures using ultrasonics is challenging due to the complex wave propagation. This paper investigates the method for disbond quantification in honeycomb sandwich structures using laser ultrasonics. In the experiments on an aluminum specimen, the detection frequency range was determined by the local defect resonance (LDR) in the disbond regions. The energy maps of bandpass wavefields identified the locations of disbonds. To improve the results, a frequency-wavenumber analysis of the wavefields was performed. The wavenumber spectra were reconstructed by wavenumber filtering to strengthen the outline components for quantifying disbonds. Local cross-correlation (LCC) was proposed to show the outlines of disbonds and honeycomb cells, whose results agreed well with the X-ray imaging. Moreover, LCC could also quantify a disbond in the composite honeycomb sandwich structure. Consequently, combining energy maps and LCC results can effectively detect the locations and sizes of disbonds in honeycomb sandwich structures. [ABSTRACT FROM AUTHOR]

For the development of new types of lightweight sandwich structures, the compressive properties and strengthening mechanism of the middle-trabecular beetle elytron plate were investigated for various values of η (the ratio of the trabecular radius to the honeycomb wall length). The results are as follows: (1) When η = 0.1, the increases in the compressive strength and standard energy absorption capacity of the middle-trabecular beetle elytron plate compared with the honeycomb plate exceed those of the end-trabecular beetle elytron plate; with an increase to η = 0.15, the compressive strength remains nearly the same, the energy absorption capacity undergoes a significant further increase, and the trabeculae exhibit Φ-type failure. (2) The strengthening mechanism that gives rise to the compressive properties of the middle-trabecular beetle elytron plate is proposed as follows: the trabeculae are located at the center of the honeycomb walls, where the maximum deformations would otherwise occur; they constrain the deformation of the honeycomb walls; and the number of trabeculae in the middle-trabecular beetle elytron plate also exceeds that in the end-trabecular beetle elytron plate. (3) Middle-trabecular beetle elytron plates have the advantage of facile manufacturing, which will establish a basis for promoting the application of beetle elytron plates. [ABSTRACT FROM AUTHOR]

In the present study, the edgewise compressive mechanical properties of the biomimetic fully integrated honeycomb plates manufactured from short basalt fiber reinforced polymer are studied. The findings are as follows: (1) Fully integrated honeycomb plates are primarily characterized by compression failure of the non-perforated surface when bearing an edgewise compressive load. The fully integrated honeycomb plates clearly exhibit the features of plasticity. (2) A buckling failure mode of the upper or lower laminates is not observed in the fully integrated honeycomb plates, and the fully integrated honeycomb plates possess the ideal integrity. Additionally, the fully integrated honeycomb plates produced with 9-mm-long fibers have the greater shearing modulus of elasticity and good plastic deformation ability. These results are of significance for disaster prevention and safety in quakeproof applications. (3) The failure features, mechanical property parameters, and simple calculation formula for edgewise compression of fully integrated honeycomb plates obtained in this work provide a foundation for the prediction of edgewise compression and the design of fully integrated honeycomb plates in future engineering applications. [ABSTRACT FROM AUTHOR]

Aluminum alloy honeycomb structures were designed based on origami technology, and the specimens were fabricated by a new fabrication technology (i.e. a press and folding process). In folding process, a new folding device was successfully developed to achieve automatic fabrication of honeycomb structure. To prove the practicability of developed device, the honeycomb cores with claws were fabricated by this device, which were used to compare the mechanical properties with that bonded by common adhesive. The deformation behaviors and mechanical properties of honeycomb structures were investigated by the flatwise compressive test and three-point bending test. The load–displacement curve obtained at the room temperature showed that the load increased to a peak value and then tended rapidly to a constant. Besides, the deformation process approximately categorized into three zones, namely linear-elastic zone, plastic-plateau zone, and densification zone. The experimental results suggested that regardless of specimen type, the bending stiffness and compressive strengths were approximately 0.32 KN·m2and 0.39 MPa, respectively; revealing the bonded method by aluminum claws did not dramatically affect the mechanical properties of honeycomb structure. Moreover, the elastic deformation of honeycomb structure was numerically studied by the finite element analysis. [ABSTRACT FROM AUTHOR]

In this research, optical fiber sensors and shape memory alloys (SMA) were incorporated into sandwich panels for development of a smart honeycomb sandwich structure with damage detection and shape recovery functions. First, small-diameter fiber Bragg grating (FBG) sensors were embedded in the adhesive layer between a CFRP face-sheet and an aluminum honeycomb core. From the change in the reflection spectrum of the FBG sensors, the debonding between the face-sheet and the core and the deformation of the face-sheet due to impact loading could be well detected. Then, the authors developed the SMA honeycomb core and bonded CFRP face-sheets to the core. When an impact load was applied to the panel, the cell walls of the core were buckled and the face-sheet was bent. However, after the panel was heated over the reverse transformation finish temperature of the SMA, the core buckling disappeared and the deflection of the face-sheet was relieved. Hence the bending stiffness of the panel could be recovered. [ABSTRACT FROM AUTHOR]

The authors have developed a novel technique to detect debonding in honeycomb sandwich structures using small-diameter fiber Bragg grating (FBG) sensors. A small-diameter FBG sensor is embedded in the adhesive layer between the core and the facesheet during the curing process of the adhesive layer. After the curing process, the reflection spectrum from the small-diameter FBG sensor is distorted because the formation of fillets induces a non-uniform strain distribution in the adhesive layer. However, after debonding, the core with the fillets peels off the facesheet, and, as a result, the reflection spectrum recovers its original shape due to the release of the non-uniform strain. Debonding can thus be detected with high sensitivity in real time from the recovery in the shape of the reflection spectrum. In addition, a more reliable debonding detection technique using a small-diameter chirped FBG sensor is proposed, in which two indicators in the reflection spectrum have been successfully used for a more reliable judgment of debonding. [ABSTRACT FROM AUTHOR]

For the development of lightweight biomimetic functional-structural materials, the compressive deformation mode of beetle elytron plates (BEPs) and their strengthening mechanism of high energy absorption were investigated, with the following results: compared with honeycomb plates, the compressive strength and the energy absorption properties of BEPs are significantly increased. This is because in a BEP, the hollow trabeculae with high torsional stiffness cause the deformation behavior to be dominated by compression, generating a convex curve with three half-waves, which is consistent with the deformation of the honeycomb walls. This study reveals not only the compressive deformation mode and the mechanism of high energy absorption in BEPs but also the relationship between the biological prototype of a BEP and its function. The findings show that BEPs represent a significant improvement over honeycomb plates and show potential for widespread application as novel energy-absorbing sandwich structures. [ABSTRACT FROM AUTHOR]