Nonlinear Material Properties Research Articles

Voxel Design of Grayscale DLP 3D-Printed Soft Robots.

Grayscale digital light processing (DLP) printing is a simple yet effective way to realize the variation of material properties by tuning the grayscale value. However, there is a lack of available design methods for grayscale DLP 3D-printed structures due to the complexities arising from the voxel-level grayscale distribution, nonlinear material properties, and intricate structures. Inspired by the dexterous motions of natural organisms, a design and fabrication framework for grayscale DLP-printed soft robots is developed by combining a grayscale-dependent hyperelastic constitutive model and a voxel-based finite-element model. The constitutive model establishes the relationship between the projected grayscale value and the nonlinear mechanical properties, while the voxel-based finite-element model enables fast and efficient calculation of the mechanical performances with arbitrarily distributed material properties. A multiphysics modeling and experimental method is developed to validate the homogenization assumption of the degree of conversion(DoC) variation in a single voxel. The design framework is used to design structures with reduced stress concentration and programmable multimodal motions. This work paves the way for integrated design and fabrication of functional structures using grayscale DLP 3Dprinting.

Nonlinear Optical Properties of 2D Materials and their Applications.

2D materials are a subject of intense research in recent years owing to their exclusive photoelectric properties. With giant nonlinear susceptibility and perfect phase matching, 2D materials have marvelous nonlinear light-matter interactions. The nonlinear optical properties of 2D materials are of great significance to the design and analysis of applied materials and functional devices. Here, the fundamental of nonlinear optics (NLO) for 2D materials is introduced, and the methods for characterizing and measuring second-order and third-order nonlinear susceptibility of 2D materials are reviewed. Furthermore, the theoretical and experimental values of second-order susceptibility χ(2) and third-order susceptibility χ(3) are tabulated. Several applications and possible future research directions of second-harmonic generation (SHG) and third-harmonic generation (THG) for 2D materials are presented.

Enhanced optical nonlinearity of epsilon-near-zero metasurface by quasi-bound state in the continuum

Bound states in the continuum (BICs) provide a powerful way to enhance the nonlinear properties of materials, epsilon-near-zero (ENZ) materials are considered as promising candidates with strong nonlinearities. However, the realization of BIC based on ENZ materials in the near-infrared (NIR) is very challenging due to the large loss in the NIR. Here, a high-quality quasi-BIC based on the ENZ metasurface is proposed for the first time, which is composed of patterned ENZ films embedded in a dielectric-metal hybrid structure, and realizes destructive interference between the Berreman mode and photonic mode to form the Friedrich-Wintergen BIC (FW-BIC). The electric field is strongly confined in the ENZ film, resulting in considerable field enhancement, and the nonlinear refractive index coefficient is 1.63 × 10−12 m2/W, which is three orders of magnitude larger than that of the ITO film. The instantaneous response time is 600 fs and extremely high modulation speed up to the THz level. Benefiting from the perfect absorption and narrow linewidth of quasi-BIC and the change in refractive index of the metasurface induced by Kerr nonlinearity, the absolute modulation is from near-zero to 92% with an extinction ratio of 23.2 dB. It provides a promising platform for the development of integrated ultrafast high-speed photonics.

Introducing Optical Nonlinearity in PDMS Using Organic Solvent Swelling

The feasibility of introducing optical nonlinearity in poly-dimethyl siloxane (PDMS) using organic solvent swelling was investigated. The third-order nonlinear refraction and absorption properties of the individual materials, as well as the PDMS/solvent compounds after swelling were characterized. The well-established Z-scan technique served as characterization method for the nonlinear properties under picosecond pulsed laser excitation at a 532 nm wavelength. These experiments included investigations on the organic solvents nitrobenzene, 2,6-lutidine, and toluene, which showed inherent optical nonlinearity. We showed that nitrobenzene, one of the most well-known nonlinear optical materials, has proven suboptimal in this context due to its limited swelling effect in PDMS and comparatively high (non)linear absorption, resulting in undesirable thermal effects and potential photo-induced damage in the composite material. Toluene and 2,6-lutidine not only exhibited lower absorption compared to nitrobenzene but also show a more pronounced swelling effect in PDMS. The incorporation of toluene caused a weight change of up to 116% of PDMS, resulting in substantial nonlinear optical effects, reflected in the nonlinear refractive index of the PDMS/toluene composite n2=3.1×10−15 cm2/W.

Steady State Electromagnetic Force Analysis of Hyperloop Tube Considering Nonlinear Material Properties by FEM

Steady State Electromagnetic Force Analysis of Hyperloop Tube Considering Nonlinear Material Properties by FEM

Mechanical performance of CRTS II slab tracks in reinforced-unreinforced transition zone in extreme heat events

Anchors have been widely utilized to reinforce the CRTS II slab tracks. The mechanical performance of the tracks in the reinforced-unreinforced transition zone exposed to extreme heat waves can be very complex due to the difference in mechanical properties between the two kinds of track segments. This paper investigates the damage behavior of the tracks in the reinforced-unreinforced transition zone in extreme heat events. A finite element model of the CRTS II slab track in the transition zone has been established and validated, in which the nonlinear mechanical properties of track materials and interfaces are considered by applying the Concrete Damaged Plasticity model and the Cohesive Zone Model respectively. The nonlinear temperature field in the track structure in extreme heat events is applied to the model. Structural damage of the track, including slab-end arching and interfacial failure, in the transition zone under extreme heat is thoroughly investigated. In particular, the effects of joint use of post-installed reinforcement anchors and other track maintenance measures like interface adhesives and concrete joint restoration are studied. The following conclusions are drawn: (1) The more reinforced track-slabs in the transition zone, the milder the track diseases including slab-end arching and interfacial gapping. (2) Joint use of anchor installation and other maintenance measures such as interface adhesives and concrete joint restoration shows a better effect on mitigating track damage than using post-installed reinforcement anchors solely. (3) Concrete joint restoration overweighs interface adhesives in terms of reducing slab-end arching and interfacial damage when they are jointly used with post-installed reinforcement anchors. (4) In the transition zone, track damage surges when the air temperature increases from 42 ℃ to 47 ℃, which is the temperature range for an extreme heat wave. Monitoring of track state in the transition zones is necessary during extreme heat waves. The novel findings are expected to provide some insights into the mechanical performance of slab tracks and help to prevent potential damage to the tracks in the transition zone, which is a common and practical issue in railway engineering.

Model-Free Intelligent Control for Space Soft Robotic Manipulators

Given the advantages of softness, lightness, low cost, and interaction safety, inverse kinematic modeling and control of soft actuators has caused a research boom. However, in realizing dexterous manipulation of space large soft manipulators, it is much more difficult to achieve precise control not only because of the greater accumulation of errors in the multiple degrees of freedom and nonlinear properties of soft materials at large scales but also because of the inability of directly solving the inverse kinematics in the cases of singular pure elongation. In this work, a model-free intelligent kinematic control strategy is proposed for these problems that exhibit a mapping relationship between the output end-effector position and the input pressure. For multiple-degree-of-freedom robots, especially pneumatic soft manipulators, traditional inverse kinematic modeling methods are complex and inverse Jacobian matrix solution often encounters geometric singularities. To address this issue, this paper proposes an inverse kinematics–multilayer perceptron (IK-MLP) method for soft manipulators. In this strategy, the trained intelligent controller can be applied to control pneumatic manipulators without establishing a traditional inverse kinematic model. The control algorithm is experimentally tested based on the ground experiment system of the space soft manipulator. Simulations and experiments are carried out to validate the given model-free intelligent controller, proving that the IK-MLP method can effectively solve the singularity of inverse kinematics.

The comparison between effects of heterogeneous and homogeneous half-spaces underlying homogeneous layer on solitary Love waves

Abstract A comparative analysis is performed on the effects of heterogeneity in both linear and non-linear material characteristics of half-space on the propagation of bright and dark solitary Love waves in a non-linear layered half-space. The layer is assumed to be homogeneous, non-linear and elastic, while the half-space is vertically heterogeneous. The problem is formulated for two types of elastic materials, incompressible and generalized neo-Hookean materials, and the differences caused by the two materials in the formulation are revealed. For the media composed of generalized neo-Hookean materials, a non-linear Schrödinger equation describing the self interaction of Love waves is obtained using multiple scales method. The differences in the effects of linear and non-linear material properties of the half-space on both the existence and non-linear evolution of bright and dark solitary Love waves are compared graphically.

Calculation and Measurement of Dielectric Parameters of Ceramic and Ferroelectric Materials in the Microwave Range

Introduction. Determination of the electrophysical parameters of linear and nonlinear dielectric materials for use in microwave technology represents an important direction. Linear dielectrics are used as a basis for the substrates of microwave circuits, as well as volumetric elements for the construction of frequency selective or resonant structures that operate across a wide temperature range. Therefore, the issue of stabilizing the electrical parameters of such structures from temperature influences appears relevant. A possible solution lies in the use of a multilayer combination of dielectrics, both with linear and nonlinear properties. Due to their nonlinear properties, ferroelectrics find application in functional units with an electrical rearrangement of frequency and phase characteristics. Therefore, it is important to determine not only the relative permittivity of the material, but also the control coefficient in the RF– microwave wavelength ranges.Aim. Construction of computational mathematical models for layered bulk and film structures to determine the relative permittivity of linear and nonlinear dielectrics in the ultrahigh frequency range.Materials and methods. The construction of computational mathematical models for the analysis of complex layered structures was carried out on the basis of Maxwell’s equations and the Galerkin method using boundary conditions for electromagnetic field components.Results. An electrodynamic analysis of a two-layer volumetric disk resonator was performed, and numerical results of calculating the resonant frequency were obtained. A numerical analysis of a multielectrode half-wave resonator with a ferroelectric film (FEF) was carried out.Conclusion. The mathematical models created and the experiment performed made it possible to numerically evaluate the properties of linear and nonlinear dielectric bulk and film materials in the microwave range.

Probability distribution functions for the ultimate strength of X-joints with collar plates in compressive load at room and fire conditions

In this paper, the results of performing finite element (FE) analysis on 360 tubular X-joints reinforced with collar plates have been used to propose a probability distribution model for ultimate strength at ambient and fire conditions. As far as the authors know, no study has been conducted on the probability distribution of the ultimate strength in X-joints with collar plates. Consequently, according to the reinforced X-joints, a total of ultimate capacity data sets was generated. The FE models were validated and compared with 35 experimental tests and numerical models. Also, in the present FE models, the welds connecting the plates to the chord member were created. Moreover, the contacts between the outer surfaces of the chord member and the inner surfaces of the reinforcing plates were modeled. In addition, nonlinear material and geometry properties were applied. In the following step, twelve theoretical probability density functions (PDFs) were fitted to relative frequency histograms of five databases. The maximum likelihood method was applied to determine the parameters of each distribution. Investigating the goodness-of-fit according to the Kolmogorov-Smirnov, Anderson Darling, and Chi-square tests showed that the Generalized Petro distribution is the best for the ultimate capacity values in collar plate retrofitted X-joints at ambient and different fire conditions. In the following step, six fully defined theoretical PDFs and cumulative distribution functions (CDFs) were established. Also, probability-probability graphs indicated that the proposed theoretical probability distributions are near the given data sets.

Nonlinear behaviour of epoxy and epoxy-based nanocomposites: an integrated experimental and computational analysis

The focus of this study is on the nonlinear mechanical properties of epoxy and epoxy-based nanocomposites, exploring frequency and strain amplitude dependency. Nanocomposite samples of epoxy are reinforced with fumed silica (FS), halloysite nanotubes (HNT) and Albipox 1000 rubber (Evonik) nanoparticles. Considering these particles have different geometries and stiffnesses, they are expected to have significantly different influences on the mechanics of the resulting composite. To enhance the reliability of the results and to reveal the impact of nanofillers on the mechanics of the material more distinctly, the manufacturing process is designed to be the same for all the specimens within the same material groups to eliminate the effects of the manufacturing process. The comprehensive characterization process consists of Fourier-Transform InfraRed Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Dynamic Mechanical Analysis (DMA). The DMA tests are designed so that the material properties are measured depending on the vibration frequency and strain amplitude. Finally, the characterized nonlinear dynamic properties of these nanocomposites are used as the input material properties into a numerical model. In this simulation, a cantilever beam with representative nonlinear material properties, for these nanocomposites, is created, as example and its forced response is plotted under the same levels of excitation in the frequency domain. Key effects of the different nanofillers are identified using the resonance behavior, primarily focusing on the stiffness and damping of the epoxy-based nanocomposites. These experimental and numerical procedures followed show the significant impact of the nanoparticle reinforcements on the nonlinear nature of these epoxy-based composites.

Cascade amplification of optical absorption on III–V semiconductors via plasmon-coupled graphene

Plasmons in graphene (Gr) show many fascinating characteristics, such as dynamic tunability, strong field confinement of light-matter interaction, and highly responsive, which has been widely exploited for a number of applications, including photodetectors, optical modulators, and sensors. In this paper, graphene plasmons (GPs) were motivated by implanting Au nanoparticles (Au NPs) into Ta2O5 thin layers adjacent to the Gr film, and the strong localized surface plasmon resonance (LSPR) effect has been proposed and demonstrated by placing the GPs structure on a III–V semiconductor quantum well saturable absorber (SA). It has been substantiated that the heightened interaction between light and Gr via LSPR predominantly occurs through the mechanisms of resonant energy transfer and local electromagnetic field enhancement, rather than direct electron transfer. Significant improvement on the nonlinear characteristics of the GPs modulated III–V semiconductor SA has been observed with a 17.1% large modulation depth and obviously improved working stability. A 1550 nm passive mode-locked laser has been successfully constructed with a pulse width down to 523 fs by integrating the SA into the laser cavity. This work lays the foundation for the development of high-performance mode-locked lasers and also demonstrates the substantial enhancement of nonlinear optical properties of various materials not limited to III–V semiconductors provided by this GPs' modulated structure; hence, these findings offer extensive prospects for applications in various photonics and optoelectronic devices.

Ultrafast laser pulse repetition rate dependent switching of nonlinearity in water

Tailoring the nonlinear optical properties of materials through extrinsic parameter controls is advantageous for many applications. In this article, ultrafast laser pulse repetition rate induced switching of reverse saturable absorption to saturable absorption of water is reported. For the investigations, a conventional open aperture z-scan measurement system equipped with a variable repetition rate ultrafast laser source operating at the wavelength of 1030 nm was employed. A combination of weak saturable absorption and strong reverse saturable absorption induced by three-photon absorption is observed at low and moderate repetition rates. At repetition rates above 5 kHz, there is a significant variation in nonlinear absorption, where the reverse saturable absorption starts to diminish and saturable absorption increases. For repetition rates beyond 100 kHz, the nonlinearity gets reversed, where water tends to behave more like a saturable absorber with a weak three-photon absorption component.

Fast construction of cluster interaction matrix for data-driven cluster-based reduced-order model and prediction of elastoplastic stress-strain curves and yield surface

The data-driven cluster-based reduced-order model (CROM) methods[47–50] are very effective for predicting the nonlinear effective properties of heterogeneous materials. The Cluster Interaction Matrix (CIM) in these methods can be regarded as a clustered discrete Green's function and is the critical part of CROM methods, which more and more scholars have realized. However, the explicit expression of Green's function is available only for homogeneous material. The CIM for heterogeneous materials needs to be calculated through numerical approaches, which face the challenge of computational efficiency. Therefore, this paper proposes an efficient method to construct the CIM of heterogeneous materials. By deriving the Green's function in Fourier space under the governing equation of FCA, the CIM of homogeneous materials that can provide the self-equilibrium stress field is calculated efficiently. Then, to avoid the effects of stress averaging on clusters, we augment the proposed cluster-element interaction matrix with the self-equilibrium stress basis vector of heterogeneous material without introducing additional computational cost. Based on the augmented cluster-element interaction matrix, the self-equilibrium stress space is improved, and the CIM of highly heterogeneous materials is calculated using the minimum complementary energy principle. The proposed algorithm significantly improves the offline computational accuracy of FCA, enabling efficient prediction of nonlinear effective properties and yield surface under complex load paths. Numerical examples demonstrate the efficiency and accuracy of the proposed method. In addition, we provide the relationship between the CIMs of a homogeneous material of FCA and SCA. Based on the proposed algorithm in this paper, it can be helpful for other CROM methods.

Phase field modeling on fracture behaviors of elastomers considering deformation-dependent and damage-dependent material viscosity

Elastomers have attracted great research interests owing to their high compliance and large deformation capacity. However, with inevitable flaws, elastomers are susceptible to rupture, leading to reduction in stretchability and loss of functionality. Though phase field model (PFM) provides a feasible tool in fracture simulation on brittle elastic materials, numerical study on the fracture of elastomers is still at a tentative stage with challenges stemming from the extremely large deformation and the nonlinear material properties. In addition, recent experimental observations on the insensitivity of the onset of rupture to loading rates suggest another knowledge gap in revealing the role of the rate-dependent viscoelasticity in fracture. To capture such phenomenon and fill the research gap, this work will propose a finite element (FE) framework by incorporating the polymer dynamics into the PFM. For the first time, the driving force to the fracture of viscoelastic elastomers is identified and the micro-mechanism of the material viscosity is further elucidated with the consideration of polymer chain breakage. The disentanglement of polymer chains in the fracture process is considered in the model to release the constraints on polymer chain reptation from nearby chains, capturing the inherent damage-dependent as well as the deformation-dependent material viscosity. The simulation results demonstrate good agreement with existing experimental data in both loading rate sensitivity tests and geometry sensitivity tests. With the variation of loading rates, obvious differences in stress responses are observed, while the critical fracture stretches almost keep constant. This work provides a deeper understanding on the fracture mechanisms of viscoelastic materials and is expected to provide guidance for the better design and full potential applications of elastomer-based devices.

Allowing for the Nonlinear Elastic Properties of Composite Materials in Designing Shell Elements with Holes of Rockets

Allowing for the Nonlinear Elastic Properties of Composite Materials in Designing Shell Elements with Holes of Rockets

Nonlinear Finite Element Simulation and Analysis of Steel Frame Structures Considering Nonlinear Behavior

This paper focuses on investigating the nonlinear behavior of steel frame structures in practical engineering applications. Utilizing finite element analysis, the study simulates the response of structures under extreme loads such as strong earthquakes. By incorporating nonlinear material properties and contact effects, the numerical simulation and analysis explore phenomena such as plastic deformation, yield, and instability in frame structures. The research outcomes contribute to a deeper understanding of the energy dissipation and safety performance of these structures.

Nonlinear Optical Properties of Zn(II) Porphyrin, Graphene Nanoplates, and Ferrocene Hybrid Materials.

Following some previous work by some of us on the second order nonlinear optical (NLO) properties of Zn(II) meso-tetraphenylporphyrin (ZnP), fullerene, and ferrocene (Fc) diads and triads, in the present research, we explore the NLO response of some new hybrids with two-dimensional graphene nanoplates (GNP) instead of a zero-dimensional fullerene moiety as the acceptor unit. The experimental data, collected by Electric Field Induced Second Harmonic generation (EFISH) technique in CH2Cl2 solution with a 1907 nm incident wavelength, combined with Coupled-Perturbed (CP) and Finite Field (FF) Density Functional Theory (DFT) calculations, show a strongly enhanced contribution of the cubic electronic term γ(-2ω; ω, ω, 0), due to the extended π-conjugation of the carbonaceous acceptor moiety.

Liquid‐Core Optical Fibers—A Dynamic Platform for Nonlinear Photonics

AbstractSoftphotonics has emerged as a new discipline that utilizes soft matter (i.e., liquids, gels, bio‐materials) as waveguide materials with versatile functionalities. The flexible properties of soft matter show great potential for further exploiting nonlinear in‐fiber phenomena to gain more insights into their fundamental dynamics and to inspire a new generation of broadband optical light sources and signal processors that are adaptable, reconfigurable, and biocompatible. In particular, incorporating solvents with extraordinary temperature sensitivity, miscibility, and nonlinearity into optical fibers has spawned a series of inventions and fundamental scientific findings over the last decades. This review highlights the current state of development of nonlinear photonics in liquid‐filled fibers. The current state of knowledge in the linear and nonlinear material properties of the most prominent solvents (CS2, CCl4, C2Cl4, benzene and its derivatives) are revisited, and recent advances in nonlinear liquid‐core fiber optics, including a special highlight on phenomena that are unique to liquids, such as modified solitary states and local dispersion control are summarized. Finally, the leading scientific challenges for advancing the field, which highlights liquid‐core fibers as a rich platform for science and technology, are discussed.

Experimental and analytical investigation of notched steel plate as a novel shear connector

To ensure durability and save time in construction, steel–concrete composite slabs are widely used in aging bridge replacement. This paper proposes a novel type of shear connector named notched steel plate (NSP). The shear properties of four types of NSP shear connectors with heights of 50 mm and 75 mm and thickness values of 9 mm and 12 mm were evaluated by conducting push-out tests. Concrete cracks occurred firstly during the loading. After removing the concrete block, fracture of NSP shear connectors at the welding zone between NSP and steel plate was observed. A finite-element (FE) analysis was conducted considering the nonlinear properties of materials and interface between the NSP and concrete block. The shear stiffness, shear capacity and failure pattern obtained using the FE model matched with the test data. The verified FE model was used to investigate the failure mechanism of NSP and to clarify the effect of the constraint force, concrete compressive strength and steel strength on the NSP shear capacity. The experimental shear capacity values were compared with the values calculated by the specifications for channel and angle shear connectors. The results of the NSP shear capacity were similar to those obtained based on the American Institute of Steel Construction (AISC) specifications and Eurocode 4.