Metal Skin Research Articles

Inspection of defects in composite structures using long pulse thermography and shearography

Long pulse thermography (LPT) and shearography have been developed as primary methods for detecting debonding or delamination defects in composites due to their full-field imaging, non-contact operation, and high detection efficiency. Both methods utilize halogen lamps as the excitation source for thermal loading. However, the defects detected by the two techniques differ due to their distinct inspection mechanisms. In this study, LPT and shearography are employed to evaluate internal damage in various composite structures. The experimental results demonstrate that LPT, when combined with thermal signal processing algorithms, can clearly detect debonding defects in rubber-to-metal bonded plates, whereas excessive adhesive defects can only be identified by shearography. Flat-bottom holes in the CFRP panel can only be detected by LPT, and shearography is particularly effective for detecting composite materials with a metal skin. For the quantitative measurement of defect sizes, the average errors of the rubber-to-metal bonded plate and CFRP panel using LPT are 4.9 % and 2.2 %, respectively, whereas the average errors of the rubber-to-metal bonded plate and aluminum honeycomb panel using shearography are 15.12 % and 95.4 %, respectively. This indicates that LPT is superior to shearography in quantitatively measuring defect sizes. These two nondestructive testing methods, based on different principles, each have their own advantages and disadvantages. Employing a multi-modal inspection method can leverage their complementary advantages, preventing misdetection and leakage of internal defects in composites.

Dynamic wetting performance and resin-flow behavior of two-level selective laser-etched metal surface in resin transfer moulding process of fiber-metal laminates

ABSTRACT In selective laser etching for the interfacial strengthening of Fiber Metal Laminates (FMLs), the wettability of customized structured features significantly affects their overall mechanical properties. For two-level features, their complicated geometry makes the evaluation of wettability difficult, which introduces challenges to feature design. In this study, a sandwich FMLs comprising an AA2024-O metal skin and a plain-woven carbon-fiber fabric core is investigated. Three types of two-level feature interfaces are designed and introduced into the FMLs structure. To understand the effect of two-level features on the resin flow and dynamic wetting progress in resin transfer molding, two-phase flow Computational Fluid Dynamics numerical models coupled with porous media and level-set numerical methods are built. The feasibility of the numerical simulation in the qualitative analysis was verified by comparing the results with those of the testing porosity values from X-ray scanning. In addition, the mechanisms of pore formation and transportation are revealed. These results indicate that the deeper groove structure in the etched features plays an important role in discharging residual air and determining the transformation of pores to reduce porosity. The permeability orientations of the porous media and surface structure both have significant impacts on the flow behavior and formation of pores.

Orbital-selective metal skin induced by alkali-metal-dosing Mott-insulating Ca2RuO4

Doped Mott insulators are the starting point for interesting physics such as high temperature superconductivity and quantum spin liquids. For multi-band Mott insulators, orbital selective ground states have been envisioned. However, orbital selective metals and Mott insulators have been difficult to realize experimentally. Here we demonstrate by photoemission spectroscopy how Ca2RuO4, upon alkali-metal surface doping, develops a single-band metal skin. Our dynamical mean field theory calculations reveal that homogeneous electron doping of Ca2RuO4 results in a multi-band metal. All together, our results provide evidence for an orbital-selective Mott insulator breakdown, which is unachievable via simple electron doping. Supported by a cluster model and cluster perturbation theory calculations, we demonstrate a type of skin metal-insulator transition induced by surface dopants that orbital-selectively hybridize with the bulk Mott state and in turn produce coherent in-gap states.

Metal gel particles loaded with epidermal cell growth factor promote skin wound repair mechanism by regulating miRNA

Abstract Skin wounds are prone to fungal infections and may threaten patients’ lives in severe cases. However, conventional treatment protocols rarely promote skin wound repair by modulating microRNA (miRNA). A novel binuclear cobalt(ii) complex with the chemical formula [Co2(MBBA)2(HPT)2(H2O)2]·2H2O (1) was synthesized through the reaction of 2-(4-methylbenzoyl) benzoic acid and 3-(pyridin-2-yl)-1H-1,2,4-triazole in the presence of 3,4-pyridine dicarboxylic acid as the template reagent. With natural polysaccharide hyaluronic acid and carboxymethyl chitosan as raw material, based on the chemical synthesis of epidermal cell growth factor for the load of metal gel particles, the microstructure and skin wound healing effect were studied. Molecular docking simulation showed that neither the carboxyl nor triazole group formed binding interactions with the active sites on proteins. Instead, the carbonyl group interacted with the active sites through hydrogen bonding. This study not only provides an effective solution to promote skin wound repair by modulating miRNAs but also provides useful ideas for synthesizing organometallic ligand-based hydrogels and their applications in biomedical fields.

Arbitrary skin metallization by pencil-writing inspired solid-ink rubbing for advanced energy storage and harvesting

The development of a durable metallic coating on diverse substrates is both intriguing and challenging, particularly in the research of metal-conductive materials for applications such as batteries, soft electronics, and beyond. Herein, by learning from the pencil-writing process, a facile solid-ink rubbing technology (SIR-tech) is invented to address the above challenge. The solid-ink is exampled by rational combination of liquid metal and graphite particles. By harnessing the synergistic effects between rubbing and adhesion, controllable metallic skin is successfully formed onto metals, woods, ceramics, and plastics without limitation in size and shape. Moreover, outperforming pure liquid-metal coating, the composite metallic skin by SIR-tech is very robust due to the self-lamination of graphite nanoplate exfoliated by liquid-metal rubbing. The critical factors controlling the structures-properties of the composite metallic skin have been systematically investigated as well. For applications, the SIR-tech is demonstrated to fabricate high-performance composite current collectors for next-generation batteries without traditional metal foils. Meanwhile, advanced skin-electrodes are further demonstrated for stable triboelectricity generation even under temperature fluctuation from −196 to 120 °C. This facile and highly-flexible SIR-tech may work as a powerful platform for the studies on functional coatings by liquid metals and beyond.

A Self-Regenerable Fiber Sloughing Its Heavy Metal Skin for Ultrahigh Separation Capability

A Self-Regenerable Fiber Sloughing Its Heavy Metal Skin for Ultrahigh Separation Capability

Electromagnetic response of disordered superconducting cavities

We present the results for the resonant frequency shift and quality factor of disordered niobium (Nb) superconducting radio-frequency cavities driven out of equilibrium by the resonant microwave field. The theory is based on the non-equilibrium theory of superconductivity for the current response to the electromagnetic field at the vacuum–metal interface. We are able to accurately predict the observed frequency shifts with a precision of order fractions of kHz over the full temperature range 0 < T ≤ Tc, including the negative frequency shift anomalies that are observed very near Tc. The origin of these anomalies is shown to be the competition between the normal metal skin depth and the London penetration depth, which diverges as T→Tc−. An analytical approximation to the full current response, valid for |T − Tc|≪ Tc, accounts for the negative frequency shift near Tc. The non-monotonic dependence of the quality factor on the quasiparticle scattering rate is related to the pair-breaking effect of disorder on the superfluid fraction and, thus, the London penetration depth.

A Sweeter Solution to CT Skin Marking

ObjectiveTo investigate individually wrapped candy as an alternative to traditional metallic skin markers for computed tomography (CT) examinations. MethodsWe retrospectively reviewed 30 CT examinations where metallic ball bearings (BBs), vitamin capsules, and various candy types were used for skin marking. Hounsfield unit (HU) values and qualitative analysis including assessing for beam hardening artifact and determining the ease of visualizing and recognizing the marker type used was recorded. ResultsMetallic skin markers were easily visualized, but resulted in beam hardening artifact and were potentially confused for foreign bodies or surgical material. Vitamin capsules were easily visualized and did not result in beam hardening artifact, but were potentially confused for exophytic skin lesions. All candy types tested were easily visualized and recognized, did not result in beam hardening artifact, and allowed for an air gap due to individual packaging. ConclusionsWe propose individually wrapped candy as an effective alternative to metallic skin markers for CT examinations.

Comparative Study of Surgical Site Wound Infection Rates in Patients with Dynamic Hip Screw Fixation Skin Closure with Polypropylene Suture Versus Metallic Skin Staples

Comparative Study of Surgical Site Wound Infection Rates in Patients with Dynamic Hip Screw Fixation Skin Closure with Polypropylene Suture Versus Metallic Skin Staples

Optimum alternate material selection methodology for an aircraft skin

Weight penalty has been a challenge for design engineers of aerospace vehicles. Today’s high-efficiency combat aircraft undergoes intense stress and strain during flying missions, which require stronger and stiffer materials to retain structural integrity. Though metallic materials have been successfully used for the construction of aircraft structures and components, metals still have a low strength-to-weight ratio. This paper aims to develop an alternate optimised material selection methodology to replace the metallic skin of a medium-sized military aircraft. The search for the optimum material will result in reduced aircraft weight which will be benefitted by extra payload on the aircraft. The selection methodology is comprised of finding design pressure limits on the aircraft skin, and comparison of properties (strength, elastic modulus, shear modulus, etc.) and performance (safety factor, deflection, and stress) of the existing metallic skin with alternate optimised material. The comparison was made under aerodynamic pressure, bending force, and twisting moment. Carbon Fibre Reinforced Polymer/Epoxy (CFRP) Uni-Directional (UD) prepreg (elastic modolus is 209 GPa) was selected as an alternate optimum material to replace the aluminium alloy skin of the aircraft studied. The selected alternate optimum material resulted in the reduction of aircraft skin weight by 30%.

Influence of density gradient and hybrid effect on quasi-static axial crushing behavior of lattice cylindrical structures

Uniform/gradient lattice cylindrical structures (ULCS/GLCS) and hybrid uniform/gradient lattice cylindrical structures (HULCS/HGLCS) are innovatively designed and fabricated. The axial crushing behaviors of these four-type cylindrical structures are investigated by the quasi-static axial compression experiments and numerical simulations. The influence of the density gradient and the hybrid effect (metal skin+ABS core) on the deformation mode, loading capacity, and energy absorption of the lattice cylindrical structures are elaborated systematically. The results show that the gradient design realizes the function of regulation and controllability of the structural deformation. The softer layers (with smaller relative density) in GLCS begin to deform first and then gradually extend to the harder layers (with larger relative density). And it effectively reduces the initial peak compression force (PCF), and makes the load more stable on the premise of energy absorption. However, unstably catastrophic failures are observed before the final densification in both ULCS and GLCS during the compression due to the brittleness of the ABS material and the compression–expansion​ deformation of structure. For HULCS/HGLCS, it presents progressive crushing mode and overcome the unstably catastrophic failure due to the ductility and constraint of the metal skins. The effect of “1 ＋ 1 > 2” on energy absorption from hybrid effect is achieved in HULCS/HGLCS, in which the EA of HULCS and HGLCS increases by 74.62% and 100.78% comparing the sum of all components individually compressed. Moreover, the progressive peak with increasing trend of HGLCS demonstrated that the hybrid design enhances the advantages of gradient design in sandwich structures.

Naked metallic skin for homo-epitaxial deposition in lithium metal batteries

Regulating the morphology of lithium plating is the key to extending the cycle life of lithium metal batteries. Fatal dendritic growth is closely related to out-of-plane nucleation on the lithium metal surface. Herein, we report a nearly perfect lattice match between the lithium metal foil and lithium deposits by removing the native oxide layer using simple bromine-based acid-base chemistry. The naked lithium surface induces homo-epitaxial lithium plating with columnar morphologies and lower overpotentials. Using the naked lithium foil, the lithium-lithium symmetric cell maintains stable cycling at 10 mA cm−2 for more than 10,000 cycles, and the full-cell paired with LiFePO4 with high areal capacity of 3.3 mAh cm−2 and practical N/P ratio of 2.5 exhibits 86% capacity retention after 300 cycles. This study elucidates the usefulness of controlling the initial surface state to facilitate homo-epitaxial lithium plating for sustainable cycling of lithium metal batteries.

Selection of materials for repairing punctures of metal skin of semi-monocoque structures using composite patches

For repairing punctures of skin of semi-monocoque structures under field conditions, simple methods are sought to guarantee the reliability of the repaired structure. Therefore, adhesive joints and composite materials are being increasingly used in repairs. During repairs using adhesion, an important aspect that affects the quality of the joint is the selection of the adhesive and the quality of surface preparation of the parts to be joined. This is necessary to get the right bond strength and durability of the joint in working environments characterized by extreme temperatures and exposure to chemicals and moisture. The purpose of the study was to select an adhesive with good strength properties for bonding AW2024T3 aluminum sheets to carbon and glass composites, and to analyze the effect of metal surface preparation on the strength of adhesive joints (grinding, sandblasting and chemical surface preparation). The tests were carried out on overlap (metal-composite) specimens. For selected adhesives, strength tests were also carried out on specimens replicating the repaired damage with a diameter of 20 mm of metal skin repaired by different methods, including composite patches and adhesive joints. The specimens were loaded in tension and loss of stability. The tests made it possible to determine the requirements for composite patches used for repairing upper and lower airframe wing skins.

Buckling behaviour of auxetic domes under external pressure

In view of ongoing great interest in novel materials exhibiting Negative Poisson Ratio (NPR), the current study examines its influence on buckling behaviour of externally pressurized​ torispherical pressure vessel closures. Failure pressures are computed for the range of Poisson’s ratio: −1.0 ≤ν < 0.5. The following wall constructions are considered: (i) single auxetic layer, (ii) outer metallic skin supported on inside by an auxetic layer, and (iii) sandwich with auxetic core. Both metallic and auxetic layers are assumed to be isotropic, and exhibit elastic, perfectly plastic behaviour.Results of this numerical study show that the inclusion of auxetic can lead to 89% gain in failure pressures above auxetic-free configuration of the wall. The range of analysed diameter-to-wall thickness ratio varied between 666 and 2000. Two layer wall construction (metallic skin supported by auxetic layer), was found to exhibit better performance than the equivalent sandwich configuration.

Electrohydrodynamic Direct‐Writing Fabrication of Microstructure‐Enhanced Microelectrode Arrays for Customized and Curved Physiological Electronics

AbstractMetal‐based patterned conductors have a key role in flexible and curved micro/nanodevices. However, the fabrication of micro/nanoscale metal‐based electrodes with excellent electrical conductivities and well‐organized flexible/curved polymeric substrates remains a major challenge associated with a posttreatment. In this study, a maskless and direct‐writing method of electrohydrodynamic jet (e‐jet) printing combined with the conventional wet etching process is developed for fabrication of microscale conductive features of microstructure‐enhanced patterned electrodes without high‐temperature treatment. Customized metal‐patterned electrodes and various metal‐patterned electrode arrays are fabricated on a flexible/curved polyethylene terephthalate substrate. In addition, ultraviolet‐curable hierarchical micro/nanostructures can be fabricated by stable cone‐jet and electrospray modes. The results of electrocardiography (ECG) and electromyography signal measurements show that the added microstructures can increase the contact between the metal microelectrodes and skin surface, which yield lower disturbance and baseline drift and enable a stable ECG signal acquisition. Overall, e‐jet printing is a promising mask‐free approach for fabrication of conductive metal patterns for flexible and stretchable devices.

Solution of the optimization problem for the purpose of designing a lattice polymer composite structure with the outer skin

In recent years, the urgency of the problem of launch vehicles load-bearing elements optimal design has continued to grow. One of the widespread structural designs is an anisogrid lattice structure made of polymer composite materials. Such structures are mass-produced and used as load-bearing bodies of space vehicles or fuselage compartments of atmospheric aircraft of advanced structural design. Until now, the weight and parameters of the skins used in products of rocket and space equipment have not been considered when solving optimal design problems, and the design problem has been reduced to optimizing lattice structures without skin. At the same time, the very use of skins for both atmospheric aircraft and load-bearing elements for space applications is a fairly common practice. However, not considering the availability of skin when designing a lattice load-bearing shell can lead to a significant increase in the mass of the structure with skin when applicable. The paper presents a method for the optimal design of lattice structures without ring ribs, but with the metal skin available, which can significantly reduce the weight of such structures, increasing the mass efficiency of products made of polymer composite materials used in aircraft. A confirmation of the results obtained with the help of an analytical solution and the results of a numerical experiment, obtained by modeling using the finite element method, is given. It is expected that the use of the proposed approach by considering the contribution of the skin response can lead to mass saving of the shell anisogrid structure up to 30 % compared with the methods of optimal design of lattice anisogrid structures currently used without considering the availability of skin in the design of the product.

Numerical and experimental analysis of free vibrations and static bending of a sandwich beam with a hyperelastic core

In the present paper, the hyperelastic behavior of a sandwich beam and isotropic beam is numerically and experimentally analyzed. To this end, the sandwich beam has a natural rubber-made core, and metal skin is made of aluminum; the isotropic beam is built of natural rubber. Free vibrations and quasi-static bending are investigated for both sandwich and homogeneous beams. Also, an axial tensile test is conducted based on ASTM D412 standard to obtain the natural rubber's mechanical properties. In the experimental bending test, the displacement and strain contour are extracted by the Digital image correlation method.

CFD Model of Turboprop Engine Nacelle Airflow for Ground Idle Condition

Research in this paper is concerned on bay cooling of the new type of turboprop engine. The considered engine integration substantially increases the temperature inside the front nacelle compartment. In order to achieve the optimal temperature conditions for engine parts inside the nacelle for all operating regimes and engine/nacelle regime after aircraft landing at heat soak-back, a new bay cooling system is proposed. Proposed cooling system consists of standard NACA inlets at the front of the nacelle, two additional groups of gills on rear part of front nacelle compartment, Zone1, and standard nacelle gaps (around exhausts), plus spinner gap. The sizing approach in the given multicriteria task is based on given temperature ratings of the engine accessories. Moreover, for structural reasons, metal skin and stiffeners in the front part of the nacelle should be maintained below the defined temperature limits. Using a 3D CFD model of the front nacelle compartment, this compartment is analysed, utilizing the software ANSYS. The benchmark testing of the considered turboprop engine of ATP type, performed by manufacturer, is used for defining the all necessary boundary conditions in this research.

Thermal–Structural Coupling Analysis for Multiple Honeycomb Plates Connected by Hinges

The dynamical model of multiple honeycomb plates connected by hinges, including the thermal–structural coupling effect, is investigated in this paper. Under the assumption of small deformations and strains, the classical plate theory is used to establish the dynamical model of the honeycomb plate. The Chebyshev polynomial is adopted to describe the deformation of the plate and the linear torsional spring to represent the elastic hinge. Using the Rayleigh–Ritz method, the characteristic equation of the honeycomb sandwich structure is derived, from which the natural frequencies are obtained. Considering the thermal effect of the plate, the thermal–structural coupling dynamical equation is obtained. The thermal conduction in the thickness direction is calculated by the finite difference method. The present model is validated by comparing with the result generated by an equivalent orthotropic plate model established by the finite element (FE) software MSC Patran. The response analysis reveals the important effect of the metal skin and the hinge stiffness on the dynamic characteristics of the honeycomb sandwich structure. Numerical simulations reveal thermal–structural coupling features for the multi-honeycomb-plate structure from the perspective of the change in dynamic characteristics and the distribution of the temperature gradient. The thermal–structural coupling calculation method adopted herein can be used to solve the thermal conduction of the plate. It serves as the theoretical method for analyzing the dynamical behavior of the solar panel subjected to the solar heat.

Application of a dynamic thermoelastic coupled model for an aerospace aluminium composite panel

An analytical-numerical coupled model has been derived to predict the effects of dynamic thermo-mechanical loading on aluminium composite panels specifically in the form of metallic skin sandwich structures, for the purposes of enhanced design of spacecraft structures where the environmental conditions comprise combined mechanical and thermal loading. The mechanical loading can arise as a consequence of localised structural dynamics, and the thermal loading is attributable principally to the effects of solar irradiation and eclipse during a satellite’s orbit, and together they have the potential to influence de-point adversely, in particular. On this basis a combined physics model is required to deal with the generalised thermoelastic problem and this paper reports on the theoretical work done to achieve that. The research has considered the literature in detail and a refined model has been proposed for an aerospace application which results in an analytical-numerical solution for the thermoelastic problem in aluminium composite panels. The model is explored for a panel under a range of centrally located static mechanical loads, in conjunction with thermal loading provided in the form of various controlled and elevated environmental temperature functions, all for prescribed physical boundary conditions. Both forms of loading are shown to influence the displacement of the panel significantly, thereby confirming the importance of a combined physics model for analysing structures in this context.