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Multifunctional materials are highly desired for the design of compact engineering structures, such as aircraft where weight reduction, sound absorption, load carrying, and energy harvesting are key considerations. However, design challenge remains in the balance of multiple functionalities. Here, we combine the sandwich structure with the neck-embedded cavities to design a cellular metamaterial having sound-absorption, compression/impact resistance and energy harvesting functionalities. For sound absorption, an autoencoder-like neural network is constructed to generate an instant design, after which a probabilistic module is inserted to optimize it by searching solutions in a slightly expanded design space. This inverse design has been experimentally validated, showing broadband sound absorption from 400 to 650 Hz merely with nine ultra-thin resonators. Beyond serving as absorber, the resonant cavities, once installed with well-tuned piezoelectric membranes, can gather broadband acoustic energy at low frequencies. Additionally, the cellular metamaterial inherits the excellent mechanical properties of honeycomb cores, having a low density of 0.64 g/cm3 yet displaying a high yield strength (21.2 MPa) in out-of-plane compression test and a superior energy absorption capability (8.6 J/cm3) in low-velocity impact tests. This work presents an effective approach to design lightweight metamaterials of superior mechanical and acoustic functionalities highly sought-after in practical engineering.

Abstract Fiber‐reinforced composites are a popular lightweight materials used in a variety of engineering applications, such as aerospace, architecture, automotive, and marine construction, due to their attractive mechanical properties. Constructing lattice materials from fiber‐reinforced composites is an efficient approach for developing ultra‐lightweight structural systems with superior mechanical properties and multifunctional benefits. In contrast to corrugated, foam, and honeycomb core materials, composite lattice materials can be manufactured with various architectural designs, such as woven, grid, and truss cores. Moreover, lattice materials with open‐cell topology provide multifunctional advantages over conventional closed‐cell honeycomb and foam structures and are thus highly desirable for developing aerospace systems, hypersonic vehicles, long‐range rockets and missiles, ship and naval structures, and protective systems. The objective of this study is to review and analyze dynamic mechanical behavior performed by different researchers in the area of composite lattice materials and to highlight topics for future research.

The impact mechanical properties of graded hourglass lattice sandwich structures under impact compression were studied using experiments and numerical simulations. The influence of the gradient distribution on the deformation mode, peak load, and energy absorption capacity of the hourglass lattice sandwich structure under the same impact energy level, different impact masses, and different impact velocities is discussed. The results show that the difference in impact mass and velocity has a significant effect on the impact mechanical properties of the graded hourglass lattice sandwich structure under the same impact energy level. The gradient distribution mode is a factor that requires careful consideration in the design. A reasonable gradient distribution design can control the initial and compression peak loads to achieve similarly low values and improve the load consistency of the hourglass lattice sandwich structure. The total energy absorption of the hourglass lattice sandwich structures with different gradient distributions is the same; however, the energy absorption capacity is different at different deformation stages. When the moving distance is 0.005 m, the gradient hourglass lattice sandwich structures with the mass decline distribution can absorb 1 kJ/kg more energy than the gradient hourglass lattice sandwich structures with the mass increment distribution. When the moving distance is 0.037 m, the mass decline distribution gradient hourglass lattice sandwich structures absorb 1 kJ/kg less energy than the mass increment distribution gradient hourglass lattice sandwich structures.

This study presents a non-explosive method for simulating blast loading on reinforced concrete (RC) slabs. The method involves using a newly developed blast simulator to apply a speedy impact load on the slab, which generates a pressure wave similar to that of an actual blast. Both experimental and numerical simulations were carried out to evaluate the effectiveness of the method. The experimental results showed that the non-explosive method can produce a pressure wave with a peak pressure and duration analogous to those of an actual blast. The numerical simulations also showed good agreement with the experimental results. Additionally, parameter studies were conducted to evaluate the effects of the rubber shape, the impact velocity, the bottom thickness, and the upper thickness on the impact loading. The results indicate that pyramidal rubber is more suitable as an impact cushion for simulating blast loading than planar rubber. The impact velocity has the widest range of regulation for peak pressure and impulse. As the velocity increases from 12.76 to 23.41 m/s, the corresponding range of values for peak pressure is 6.457 to 17.108 MPa, and for impulse, it is 8.573 to 14.151 MPa∙ms. The variation in the upper thickness of the pyramidal rubber has a more positive effect on the impact load than the bottom thickness. With the upper thickness increasing from 30 mm to 130 mm, the peak pressure decreased by 59.01%, and the impulse increased by 16.64%. Meanwhile, when the bottom part’s thickness increased from 30 mm to 130 mm, the peak pressure decreased by 44.59%, and the impulse increased by 11.01%. The proposed method provides a safe and cost-effective alternative to traditional explosive methods for simulating blast loading on RC slabs.

Current skull repair biomaterials used in clinical surgery face problems such as unmatched mechanical properties and poor biocompatibility. To overcome these problems, the multilayer micro-lattice biomaterials (MB) combining both suitable mechanical properties and biocompatibility are proposed based on skull structural characteristics. The quasi-static compressive mechanical properties of MB are studied experimentally, numerically and theoretically, which are verified by experimental results. The typical deformations, such as distinct shear zone and stress concentration of nodes, are observed. The strength and modulus of the above MB specimens are in the range of 86.72 ± 0.84 to 197.73 ± 0.74 MPa and 2.99 ± 0.13 to 7.56 ± 0.54 GPa, respectively. Simultaneously, the properties of MB with gradient design, including positive, negative and hybrid gradient are investigated by finite element (FE) simulation. The MB with hybrid gradient can better match the structural characteristics of skull. Since the designed MB has out-of-plane compression characteristics comparable to that of skull and suitable biological space for cell growth, it can be implanted into the human body to matched surrounding skull tissue well. The insight of MB combining with design constraints of biomaterials provides a novel method for designing/tuning skull repair biomaterials that might result in the optimized clinical skull surgery effect.

The global poultry industry has grown to the extent that the number of chickens now well exceeds the number of humans on Earth. Escherichia coli infections in poultry cause significant morbidity and economic losses for producers each year. We obtained 94 E. coli isolates from 12 colibacillosis outbreaks on Saskatchewan farms and screened them for antimicrobial resistance and biofilm formation. Fifty-six isolates were from broilers with confirmed colibacillosis, and 38 isolates were from healthy broilers in the same flocks (cecal E. coli). Resistance to penicillins, tetracyclines, and aminoglycosides was common in isolates from all 12 outbreaks, while cephalosporin resistance varied by outbreak. Most E. coli were able to form biofilms in at least one of three growth media (1/2 TSB, M63, and BHI broth). There was an overall trend that disease-causing E. coli had more antibiotic resistance and were more likely to form biofilms in nutrient-rich media (BHI) as compared to cecal strains. However, on an individual strain basis, there was no correlation between antimicrobial resistance and biofilm formation. The 21 strongest biofilm forming strains consisted of both disease-causing and cecal isolates that were either drug resistant or susceptible. Draft whole genome sequencing indicated that many known antimicrobial resistance genes were present on plasmids, with disease-causing E. coli having more plasmids on average than their cecal counterparts. We tested four common disinfectants for their ability to kill 12 of the best biofilm forming strains. All disinfectants killed single cells effectively, but biofilm cells were more resistant, although the difference was less pronounced for the disinfectants that have multiple modes of action. Our results indicate that there is significant diversity and complexity in E. coli poultry isolates, with different lifestyle pressures affecting disease-causing and cecal isolates.

Heart valve replacement is a very effective method to treat severe valvular stenosis or valvular insufficiency. The valve can be divided into the mechanical valve and biological valve according to the main materials of the valve leaflets. The former has good durability, but the patients need to take anticoagulants all their lives, otherwise, thrombosis will occur; the latter has good blood compatibility, and only 3–6 months of postoperative anticoagulation is required, but its durability is lower than the former. Compared with a traditional valve used materials, the fabric composite valve leaflets have both mechanical valve and biological valve advantages, i.e. it can have both good blood compatibility and excellent fatigue resistance. This material is comprised of the internal fabric layer and bilateral external polyurethane layers jointed with adhesive, and it can adjust the flexibility, wear-resistance and fatigue resistance of the valve leaflet through adjusting the thickness of the outer polyurethane protective layer, the weaving method, the fiber diameter and the surface density of the inner ultra-high molecular weight polyethylene (UHMWPE) fabric. In this article, we tested the long-term durability of a fabric composite with its property close to the valve leaflet made of bovine pericardium, to evaluate the material performance loss under long-term fatigue and the wear degree of this material with different polyurethane layer thicknesses. As many as two hundred million cycles of fatigue test and the hydrodynamic performance test before and after the fatigue test proved that the material could withstand a service life of at least five years without structural failure or functional degradation. According to the SEM images after the experiment, it can be predicted that this material can achieve a longer fatigue life.

This paper focuses on the effect of temperature on the out-of-plane compressive properties and failure mechanism of carbon fiber/epoxy composite pyramidal truss cores sandwich panels (CF/CPTSP). CF/CPTSP with novel reinforced frames are manufactured by the water jet cutting and interlocking assembly method in this paper. The theoretical analysis is presented to predict the out-of-plane compressive stiffness and strength of CF/CPTSP at different ambient temperatures. The tests of composite sandwich panels are performed throughout the temperature range from −90∘C to 180∘C. Good agreement is found between theoretical predictions and experimental measurements. Experimental results indicate that the low temperature increases the compressive stiffness and strength of CF/CPTSP. However, the high temperature causes the degradation of the compressive stiffness and strength. Meanwhile, the effects of temperature on the failure mode of composite sandwich panels are also observed.

The mechanical properties of Z-pins reinforced composites adhesively bonded single-lap joints (SLJs) under un-directional tension loading are investigated by experimental and numerical methods. Three kinds of joint configurations, including SLJs with three/two rows of Z-pins and "I" array of Z-pins, are investigated by tension test. The failure modes and mechanism of reinforced joints with different Z-pins numbers and alignment are analyzed, and the comparison is performed for the failure strengths of no Z-pins and Z-pins reinforced joints. According to experimental results, failure modes of three kinds of joints are all mixed failure. It turns out that the Z-pins are pulled out ultimately. The strength of joints of more Z-pins at the end of the overlap area is relatively bigger for the joint of the same Z-pins numbers. The strength of joints with Z-pins compared with non Z-pins joints is growing at 16%. Finally, the three-dimensional distribution of interfacial stress in the lap zone of three kinds of Z-pins reinforced joints is simulated, and the numerical results are in good agreement with the experimental results. It is effective that the numerical calculation of stress analysis is verified. [ABSTRACT FROM AUTHOR]

The effective biaxial modulus (Meff) of fiber-textured hexagonal, tetragonal, and orthorhombic films is estimated by using the Voigt–Reuss–Hill and Vook–Witt grain-interaction models. The orientation distribution function with Gaussian distributions of the two Euler angles θ and [lowercase_phi_synonym] is adopted to analyze the effect of texture dispersion degree on Meff. Numerical results that are based on ZnO, BaTiO3, and yttrium barium copper oxide (YBCO) materials show that the Vook–Witt average of Meff is identical to the Voigt–Reuss–Hill average of Meff for the (001) plane of ideally fiber-textured hexagonal and tetragonal films. The [lowercase_phi_synonym] distribution has no influence on Meff of the (hkl)-fiber-textured hexagonal film at any θ distribution in terms of the isotropy in the plane perpendicular to the [001] direction. Comparably, tetragonal and orthorhombic films represent considerable actions of [lowercase_phi_synonym] dispersion on Meff, and the effect of [lowercase_phi_synonym] dispersion on Meff of a (001)-fiber-textured YBCO film is smaller than that for a (001)-fiber-textured BaTiO3 film since the shear anisotropic factor in the (001) shear plane of a YBCO film more closely approaches 1. Enhanced θ and [lowercase_phi_synonym] distributions destroy the perfect fiber textures, and as a result, the films exhibit an evolution from ideal (hkl) fiber textures to random textures with varying full widths at half maximums of θ and [lowercase_phi_synonym]. [ABSTRACT FROM AUTHOR]

The impedance matrix method is applied to study the scattering of flexural waves propagating in an infinite thin plate containing an N-beam resonator. The resonator consists of a circular hole containing a smaller plate connected to the background plate by a number N of rectangular beams. After representing the boundary conditions in a modal multipole expansion form, a compact expression is obtained for the T-matrix, which relates the incident and the scattered transverse (out-of-plane) waves. The analysis of the scattering cross-section reveals interesting scattering features, like resonances and anisotropy, associated to this type of resonators. Numerical experiments performed within the framework of the finite element method support the accuracy of the model here developed. [ABSTRACT FROM AUTHOR]

Recently, the ray tracing method has been used to derive the non-singular cylindrical invisibility cloaks for out-of-plane shear waves, which is impossible via the transformation method directly owing to the singular push-forward mapping. In this paper, the method is adopted to design a kind of non-singular acoustic cloak. Based on Hamilton's equations of motion, eikonal equation and pre-designed ray equations, we derive several constraint equations for bulk modulus and density tensor. On the premise that the perfect matching conditions are satisfied, a series of non-singular physical profiles can be obtained by arranging the singular terms reasonably. The physical profiles derived by the ray tracing method will degenerate to the transformation-based solutions when taking the transport equation into consideration. This illuminates the essence of the newly designed cloaks that they are actually the so-called eikonal cloaks that can accurately control the paths of energy flux but with small disturbance in energy distribution along the paths. The near-perfect invisible performance has been demonstrated by the numerical ray tracing results and the pressure distribution snapshots. Finally, a kind of reduced cloak is conceived, and the good invisible performance has been measured quantitatively by the normalized scattering width. [ABSTRACT FROM AUTHOR]

When heat flux flows in a given medium, its path will solely he determined. This implies that material parameters determined by the predesigned path of heat flux will guide heat to flow along the designed path. Based on this idea, we develop a new method for the design of the cylindrical thermal cloak which can make heat flux detour the cloaked object. For the inhomogeneous anisotropic medium, we derive the relation between the path trajectory of heat flux and material parameters and obtain two differential equations and one boundaiy condition which are used to determine material parameters in the cylindrical cloak. The transient behavior on the flow of heat flux is simulated by Comsol Multiphysics and the transient thermal protection of the cylindrical cloak for the cloaked object is examined. The effect of the product of density and specific heat on the dynamic diffusion process of heat flux is analyzed. Since one can flexibly design the path of heat flux in the cloak, it has the large degree of freedom to construct thermal cloaks with the specific distributions of material parameters. The present method provides a new blue print for the transient thermal protection of a specific target. [ABSTRACT FROM AUTHOR]

The previously reported magical thermal devices, such as the thermal invisible cloak and the thermal concentrator, are generalized into one general case named here thermal illusion device. The thermal illusion device is displayed by the design of a thermal reshaper which can reshape an arbitrary thermal object into another one with arbitrary cross section. General expressions of the material parameters for the thermal reshaper are derived unambiguously to greatly facilitate the design of general thermal illusion device. We believe that this work will broaden the current research and pave a path to the thermal invisibility. Numerical simulations show good agreement with the analytical results of the thermal illusion device. [ABSTRACT FROM AUTHOR]

The concept of the electromagnetic wave transparency is introduced into the thermal field. The conditions of the thermal transparency for a multilayered sphere with isotropic coatings, a coated spheroid with an isotropic coating, and a coated sphere with a radial anisotropic core or a radial anisotropic coat are deduced with the help of the idea of the neutral inclusion. The thermal transparency can be achieved by making the effective thermal conductivity of the composite inclusion equal to the thermal conductivity of the surrounding matrix. The validity of the theoretical analysis is checked by the corresponding simulated results, which indicate that the designed neutral inclusion can be transparent perfectly. A specific case of interest of the thermal transparency is its application to cancel the thermal stress concentration resulting from the existence of the inclusions in the particle (even the thermal-insulated particle) -reinforced composites. [ABSTRACT FROM AUTHOR]

A new interaction integral formulation is derived for obtaining mixed-mode stress intensity factors (SIFs) of an inteiface crack with the tip close to complicated material interfaces. The method is a conservation integral that relies on two admissible mechanical states (actual and auxiliary fields). By a suitable selection of the auxiliary fields, the domain formulation does not contain any integral related !o the material interfaces, which makes it quite convenient to deal with complicated interface problems. The numerical implenientation of the derived expression is combined with the extended finite element method (XFEM). According to the numerical calculations, the interaction integral shows good accuracy for straight and curved inteiface crack problems and exhibits domain-independence for material interfaces. Finally, an interfacial fracture problem is investigated for the representative centrosymmetric structure formed by two constituent materials. [ABSTRACT FROM AUTHOR]

n energy dissipation rate concept is employed in conjunction with the J-integral to calculate crack growth resistance of elastic-plastic fracture. Different from Rice's J-integral, the free energy density is employed in place of the stress working density to define an energy-momentum tensor, which yields that the slightly changed J-integral is path dependent regardless of incremental plasticity and deformational plasticity. The J-integral over the remote contour is split into the plastic influence term and the J-integral over the fracture process zone which is an appropriate estimate of the separation work of fracture. Finite element simulations are carried out to predict the plane strain mode I crack growth behavior by an embedded fracture process zone. It can be concluded that J-integral characterization is in essence a stress intensity-based fracture resistance similar to the K criterion of linear elastic fracture, and energy dissipation rate fracture resistance can be taken as an extension of the Griffith criterion to the elastic-plastic fracture. [ABSTRACT FROM AUTHOR]

Aimed at a fresh look onto the defect mechanics of electroelastic medium, the configurational force approach is developed for these materials. The notion of working is defined in a more general framework by introducing the conjugates of configurational force and the evolution velocity of migrating control volume. The balance of configurational forces is established through the invariance condition of working under the change of material observer. Eshelby relation is identified by using the invariance requirement of configurational working under reparameterization of the motion of the boundary of migrating control volume. Energy dissipation concentrated at crack tip is evaluated through the generalized mechanical version of the second law of thermodynamics applicable to migrating control volume. Theoretical investigation shows that the negative projection of the internal configurational force concentrated at the crack tip along the direction of crack propagation plays the role of energy release rate which depends on constitutive response of materials and is independent of the energy of free electric field. [ABSTRACT FROM AUTHOR]

The uniaxial tensile test and hydraulic bulging test of AZ31 magnesium alloy sheets were applied to study the influence of temperature on the material properties and obtain the forming limit curves at different temperatures. Numerical simulations of warm hydro mechanical deep drawing were carried out to investigate the effect of hydraulic pressure on the formability of a cylindrical cup, and the simplified hydraulic pressure profiles were used to simulate the loading procedure of hydraulic pressure. The optimal hydraulic pressure at different temperatures were given and verified by experimental studies at temperature 100°C and 170V. [ABSTRACT FROM AUTHOR]

Ni42Cu5Ti20Zr21.5Al8Si3.5 bulk metallic glasses rods with diameters of 1 mm and 3 mm, were prepared by arc melting of composing elements in a Ti-gettered argon atmosphere. The compressive deformation and fracture behavior of the amorphous alloy samples with different size were investigated by testing machine and scanning electron microscope. The compressive stress-strain curves of 1 mm and 3 mm samples exhibited 4.5% and 0% plastic strain, while the compressive fracture strength for 1 mm and 3 mm rod is 4691 MPa and 2631 MPa, respectively. The compressive fracture surface of different size sample consisted of shear zone and non-shear one. Typical vein patterns with some melting drops can be seen on the shear region of 1 mm rod, while fish-bone shape patterns can be observed on 3 mm specimen surface. Some interesting different spacing periodic ripples existed on the non-shear zone of 1 and 3 mm rods. On the side surface of 1 mm sample, high density of shear bands was observed. The skip of shear bands can be seen on 1 mm sample surface. The mechanisms of the effect of sample size on fracture strength and plasticity of the Ni-based amorphous alloy are discussed. [ABSTRACT FROM AUTHOR]

A laminated mechanical model has been developed that can predict the mechanical properties of 3D braided composites with internal transverse crack. By using the principle of minimum complementary energy, the stress components are obtained in closed-form expressions in terms of a perturbation function, which is governed by two fourth-order inhomogeneous ordinary differential equations. The effective Young’s modulus and Poisson’s ratio of 3D braided composites with internal crack are calculated using the homogenization theorem. To demonstrate the solution, some examples are analyzed. Good agreement is obtained between the presented results and the values predicted by the modified finite element method. [ABSTRACT FROM AUTHOR]

A thermodynamic model is presented to describe the dielectric response of ferroelectric bilayers and multilayers with different orientations. Numerical analyses for PbTiO3/SrTiO3 epitaxially heteroepitaxial bilayer films on thick substrates show that complete polarization suppression and gigantic dielectric response occur at approximately 46%, 50%, and 63% of SrTiO3 fraction in the bilayer structures with (111), (110), and (001) orientations, respectively. Our study indicates that the ferroelectric and dielectric performances of ferroelectric bilayers and multilayers can be modified by changing the thicknesses and orientations of component layers, which is an effective approach for the optimization of microwave devices. [ABSTRACT FROM AUTHOR]

This paper presents a novel tri-directional negative stiffness (NS) mechanical metamaterial, consisting of disk structure elements arranged in three-dimensions. The NS behavior was achieved through the elastic instability of the disk structure. Through the combination of numerical simulations and experiments, the NS property, the deformation mechanisms, and the basic mechanical performance of the disk structure and the novel NS mechanical metamaterial were systematically investigated. The influence of the geometric parameters on the snap-through behaviors of the NS metamaterial was investigated through the experimentally verified numerical method, and further designs were conducted on the disk structure to tailor its mechanical responses. Also based on the instability of the disk structure, several novel multidirectional NS structures, which can achieve NS behavior along five and seven loading directions, were firstly proposed. This innovation improves the homogeneity of the NS metamaterials, and is expected to expand the application scope of such metamaterial, considering that the previous reported NS metamaterial can exhibit NS behavior along three-dimensions at most. Moreover, the mechanical performance of the proposed NS metamaterial is tunable, benefited from the special structure form of itself. To our knowledge, this work is first to design NS metamaterial using the disk structures, and report the multidirectional (more than tri-directions) NS metamaterials. [ABSTRACT FROM AUTHOR]

Since the concept of invisible cloak was proposed by Pendry and Leonhardt in 2006, many researchers have applied the theory of coordinate transformation to thermodynamics and overcome the complexity of inhomogeneous and anisotropic of material parameters. However, only two-dimensional (2D) thermal illusion devices are researched recently. According to this situation, our study focuses on three-dimensional (3D) thermal illusion devices including shrinker (or invisible cloak), concentrator, amplifier, reshaper, and rotator with arbitrary shape in a general way. In this paper, the corresponding material parameters of thermal illusion devices mentioned above are derived based on the theory of transformation thermodynamics and the simulated results agree well with the theoretical derivations. In addition, the conventional invisible cloak just controls the temperature gradient rather than the temperature value which is more concerned in physical applications. Here, we find that the temperature value of the cloaked object can be controlled by adjusting the location of the original point of the coordinate system. [ABSTRACT FROM AUTHOR]