Nowadays, radomes that are employed to protect antennas inside from physical environment are required to have dual-band or even multi-band transmission performance. In this paper, a design scheme based on the theory of small reflections is proposed for the design of dual-band and multi-band A-sandwich radomes. Subsequently, two A-sandwich composite radome walls are designed and fabricated according to the design scheme. Finally, both numerical simulations and experiments are conducted to verify the electromagnetic characteristics of the radome walls. Results indicate that one of the A-sandwich radome walls has two passbands in 4.0–11.4 GHz and 25.2–40.0 GHz, while the other one has three passbands in 4.0–8.2 GHz, 18.0–20.5 GHz, and 29.1–40.0 GHz, respectively. The proposed method is experimentally demonstrated to be an effective approach for designing dual-band and multi-band dielectric radome walls for both centimeter and millimeter wave applications.

•An in-house constructed elevated temperature indentation apparatus was developed.•High temperature indentation tests on YSZ coatings up to 1200 °C were performed.•Hardness and elastic modulus of YSZ coatings were extracted.In this paper, high temperature indentation tests in air up to 1200 °C were firstly conducted to measure hardness and elastic modulus of nanostructured 8 wt% yttria partially stabilized zirconia (YSZ) coatings. An in-house constructed elevated temperature indentation apparatus was developed. The load-displacement curves of YSZ coatings testing at 25, 1000 and 1200 °C were obtained. Hardness and elastic modulus were evaluated from the load-displacement curves. It is found that the value of hardness and elastic modulus both decrease with increasing temperature. This may be attributed to the enhanced plasticity of YSZ coatings at high temperatures. The microphotographs of residual indentation impressions also show that plastic deformation tends to occur with increasing temperature.

•A compressive load decreases the coercive field while a tensile load increases it.•The transition between butterfly and square-like magnetostriction loops is found.•The transition is due to the single domain evolution from swinging to turning clockwise. The stress-induced magnetic domain switching in FeGa thin films is studied using phase-field method. In particular, the magnetic field is applied along the [110] direction and biaxial stresses are applied along [100] and [010]. A compressive pre-stress corresponds to a smaller coercive magnetic field while a tensile pre-stress corresponded to a larger coercive field. At the same time, it is also found that the transition between butterfly and square-like magnetostriction loops occurs at the critical opposite biaxial stress state. The two different evolutions correspond to two different mechanisms: one is that the single domain swings across a fan area back and forth; the other is that the single domain turns a clockwise circle. The results can be explained by the stress tuned anisotropy energy well.

•A dual-band A-sandwich radome wall is designed for both centimeter and millimeter wave applications at high temperature.•A calibration method is proposed to eliminate the temperature-dependent errors of the microwave measurement system.•Experiments show the radome wall is feasible for the 4–10 GHz and 24–40 GHz frequency spans at temperatures up to 800 °C.•Experimental and calculation results demonstrate the effectiveness of the dual-band design method.Modern aircraft have reached higher and higher flight speed, resulting in the urgent demand of design and characterization for high-temperature airborne radomes, especially for those with dual-band or multi-band properties. In this paper, an A-sandwich radome wall structure made of quartz is designed for both centimeter and millimeter wave applications at high temperatures. Its transmission performance in the 4– 40 GHz frequency range at ambient temperature to 800 °C is characterized by a broadband free-space microwave measurement system, which is mainly composed of a vector network analyzer, spot-focusing lens horn antennas, and a furnace for heating sample. A calibration method is proposed to eliminate the temperature-dependent distortion of microwave signals by the microwave-transparent walls of the furnace, and the errors caused by the wall position variations as well. Transmission measurements show that the radome wall structure is feasible for dual-band applications in the 4– 10 GHz and 24– 40 GHz frequency spans with the transmission efficiency higher than 70% at temperatures up to 800 °C, and demonstrate the effectiveness of the design method. It can be expected that the free-space microwave measurement system in conjunction with the proposed calibration method is capable of damage detection for aerospace structures under high-temperature conditions.Download high-res image (101KB)Download full-size image

In this study the frequency dependence of harmonic hysteretic magnetoelectric (ME) effect in magnetostrictive-piezoelectric laminate was investigated. Taking into account the nonlinear magnetostrictive effect and the structural vibration, a ME dynamic model was proposed to quantitatively describe the frequency-dependent hysteretic characteristics. The model was validated by comparing the simulated ME response with experiment at both the quasi-static and high frequency conditions. As the frequency increases, the shape evolution of the ME hysteresis loop from crescent to butterfly and ellipse was observed. Moreover, the influences of the magnetic bias field, damping ratio and magnetostrictive loss factor were also investigated. It was found that the dynamic ME hysteresis was the combined result of competition between the first two orders of harmonic components and the corresponding phase shift. The former was controlled by the frequency doubling and the mechanical resonance effect, and the latter was originated from the magnetostrictive loss and mechanical damping.

•The temperature-dependent strengths of CVD ZnS were obtained.•The thermal shock behavior of infrared window was studied by finite element method.•Rapid heating thermal shock tests were conducted to validate the numerical results.The thermal shock failure has been recognized as one of key failure modes of chemical vapor deposited zinc sulfide (CVD ZnS) infrared window. In this paper, the thermal shock behavior of CVD ZnS infrared window was investigated by the finite element analysis and rapid heating thermal shock experiments. To introduce the temperature-dependent strengths into the analysis of thermal shock failure, the ring-on-ring flexural tests were conducted at different temperatures. Based on the finite element simulation results, the thermal shock failure tended to occur with increasing the temperature difference, and the critical failure temperature difference was measured as 375 °C. At last, a simple rapid heating thermal shock test facility was developed, and thermal shock experiments were conducted to validate the simulation results. The thermal shock failure occurred at tested temperatures above 300 °C. This was consistent with the previous finite element simulation results.

•A magneto-mechanical coupling finite element based phase field model is proposed.•Changing the symmetry of loading situation controls the vortex charity of a nanoring.•The multi-stable magnetization states can be realized by geometrical regulation.•The demagnetizing factor is easily calculated with the phase field model.This paper proposes a real-space phase field model solved by finite element method for giant magnetostrictive materials. The model is based on the thermodynamic theory of ferromagnetic materials and employs the time-dependent Ginzburg-Laudau (TDGL) equation to predict the domain evolution process. We have derived the corresponding finite element formulation which takes the mechanical displacement, the magnetic potential, and the magnetization vector as the field variables, according to variational principle. A multi-field coupling finite element has been developed through the ABAQUS user element subroutine module to simulate the coupling between mechanical and magnetic characteristics for microstructures with arbitrary geometries and boundary conditions. The simulation results of a general magnetic nanoring coincide well with the reports in literature, which confirms the validity of the phase field method developed. The magnetization processes have also been investigated for nanorings with different geometries. The results suggest that the vortex chirality and multi-stable magnetization states can be controlled by changing both the symmetry of loading situation and the geometrical configuration. The phase field model solved by finite element method is expected to be a useful tool for the design of high density magnetic random access memories.

•An in-house constructed elevated temperature erosion test facility was developed.•The electrical properties of as-sprayed and eroded specimens were measured by impedance spectroscopy.•The erosion mechanism is dominated by the spalling of the sprayed splats caused by the propagation of microcracks.In this paper, an in-house constructed elevated temperature erosion test facility was developed to conduct the particle erosion tests of nanostructured 7YSZ coating with particles of different mass. The electrical properties of as-sprayed and eroded specimens were evaluated by impedance spectroscopy. The constant phase element parameter nc and Ac corresponding to the microcracks decreased and increased with increasing particle mass, respectively. This is due to the fact that the nucleation, propagation and coalescence of microcracks along the overlapped splat interfaces between lamellae decrease the homogeneity of the coating. The development of microcracks results in the spalling of the sprayed splats, which accounts for the material removal during the erosion process.

A new theoretical model considering the bending effect for the thick films (the ratio η of thickness to radius was larger than 1/80) using the bulge test method was established based on the energy method. The experiments of Ti films and PVDF films of different ratio η had validated the feasibility of the new theory. The universal applicability of the new theoretical model for different mechanical parameters (E and υ) was verified by FEM. The new expression of pressure-height could well predict the deformation of bulge test for the films with different thickness. As the ratio η increased, the competitive mechanism of bending energy gradually replacing stretching energy in the films was revealed. The modulus and the stress distribution of cross-section could be characterized correctly by the new theory for thick films using the bulge test technique. It will provide a powerful research tool to study the deformation mechanism of thick films in the bulge test.

We investigate here heat transfer across interfaces consisting of single- and few-layer graphene sheets between silicon carbides by performing nonequilibrium molecular dynamics simulations. The interfacial thermal conducitivity κI is calculated by considering graphene layers as an interfacial phase. The results indicate that κI decreases with its thickness and heat flux but increases with the environmental temperature. Interface engineering of κI is explored by intercalating molecules between graphene layers. These guest molecules decouple electronic states across the interface, but tune κI slightly, leading to a thermally transparent but electronically insulating interface. These results provide a fundamental understanding in thermal transport across weakly bound interfaces, and design recipes for multifunctional thermal interface materials, composites and thermal management in graphene-based devices.Keywords: graphene; interface engineering; interfacial thermal transfer; thermal interface materials;

A magneto-mechanical-thermal model based on a domain rotation mechanism is developed in this paper. An energy distribution parameter related to prestress and temperature is induced, which can be determined by simple experiments. Magnetization and magnetostriction of Terfenol-D at different temperatures and prestresses are calculated and estimated, which are consistent with experiments. The model can be applied to estimate prestress effects to magnetization. The results show that compressive prestress can increase to maximum using temperature of giant magnetostrictive materials.

High-temperature oxidation of metals induces residual stresses both in the metals and in the growing oxide scales. In this work, considering the case of asymmetric oxidation, a new analysis model to elucidate the residual stress evolutions in an oxide scale/metal substrate system during an isothermal oxidation process is developed. Elastic and creep deformations in both oxide and metal phases are considered in this work. The oxidation growth strain generated in oxide scale is also taken into account and is described by the Clarke model, that is, the growth strain rate increases linearly with the oxide thickening rate during isothermal oxidation. A comprehensive numerical study is carried out by the present approach. Results reveal that the proposed model can lead to an excellent agreement with the published experimental results and thus well validate the present model. Effects of the growth parameter, creep constants, Young’s modulus, and substrate thickness on the residual stress evolutions in the oxide scale/metal substrate system have also been discussed.

Honeycomb sandwich structures are susceptible to liquid ingress, which causes a serious degradation of performance. Herein, a near-field microwave nondestructive detection technique was proposed to detect, identify, and quantitatively evaluate liquid ingress in honeycomb sandwich structures. Based on the microwave reflection spectrums, liquids of different polarity properties were identified. The amplitude of reflection microwaves was found nearly linear with respect to the height of the intruding liquids in the near field of the coaxial adapter probe. A simple characteristic peak method (CPM) based on line scans was presented and applied to quantify the size of liquid ingress region, and it turned out to be quite accurate with relative errors less than 0.5%. In summary, the near-field microwave testing technique proposed in this study is effective to detect, identify, and quantify liquid ingress in honeycomb sandwich structures.

The unexpected thermal distortions and failures in engineering raise the big concern about thermal expansion controlling. Thus, design of tailorable coefficient of thermal expansion (CTE) is urgently needed for the materials used in large temperature variation circumstance. Here, inspired by multi-fold rotational symmetry in crystallography, we have devised six kinds of periodic planar lattices, which incorporate tailorable CTE and high specific biaxial stiffness. Fabrication process, which overcame shortcomings of welding or adhesion connection, was developed for the dual-material planar lattices. The analytical predictions agreed well with the CTE measurements. It is shown that the planar lattices fabricated from positive CTE constituents, can give large positive, near zero and even negative CTEs. Furthermore, a generalized stationary node method was proposed for aperiodic lattices and even arbitrary structures with desirable thermal expansion. As an example, aperiodic quasicrystal lattices were designed and exhibited zero thermal expansion property. The proposed method for the lattices of lightweight, robust stiffness, strength and tailorable thermal expansion is useful in the engineering applications.

This paper addresses the development of a magneto-elastic coupling dynamic loss hysteresis model for giant magnetostrictive materials (GMMs). Considering the eddy current loss and anomalous loss, a dynamic constitutive model is proposed to predict the dynamic hysteresis behavior of GMMs. The model is validated by comparing the predicted results with experiments. At first, the frequency effect and anisotropy effect on the domain distribution can be obtained. Moreover, the magnetostriction cannot return to the initial value near the coercive field as the magnetization does with the increasing frequency. It can be explained that the domain distribution changes with the increasing energy loss. The model is benefit for the design and control of GMMs actuators.

An indentation method is proposed to characterize the properties of oxidation film on a SiC ceramic substrate. In this method, a series of indentation tests on the oxidation film with different maximum indentation depths were performed. The relationship between the inverse of contact depth and the inverse of reduced modulus was fitted by an exponential function. The moduli of the oxidation film and substrate as well as the thickness of the oxidation film were estimated by analyzing the fitting parameters. In order to validate the method, indentation tests were conducted on SiC substrate to determine the reference modulus of the substrate. Microstructure observation was conducted to measure the reference thickness of the oxidation film. The estimated values agreed well with the reference values. Finite element analysis was also employed to simulate the indentation tests on the oxidation film. The simulation results agreed well with the experimental results.