Soft Interlayer Research Articles

Bionic Soft Multimodal Actuators for Fast, Large Deformation under Ultralow Magnetic Conditions

AbstractVery recently, magnetically driven soft actuators have prompted increasing interest due to their programmable deformation, swift response, and remote actuation. However, it is still challenging to trigger strong and fast actuating performances with an extremely weak magnetic field due to the difficult task of in situ programming of magnetic domains and the limited mechanical structures. Here, first a bionic sandwich structure is proposed for designing soft magnetic actuators with a specific threshold value. The crab‐like jointed structure of PDMS‐embedded NdFeB upper/lower layers is essential for generating the desirable threshold effect, while a flytrap‐inspired soft interlayer is further implemented to decrease the driving magnetic field. Theoretical analysis and numerical simulations are implemented to optimize the actuating performances of soft actuators (deformation rate, deformation angle) by modulating the structural parameters. Experimental results show that the biomimetic features yield a promptly switchable bistable state, a superior strong deformation rate of 1.93, and a maximum deformation angle of 25.5° under an ultralow magnetic field of 1 mT. Two demonstrative applications of soft actuators are investigated, including threshold switching and soft grippers, suggesting their broad applications in engineering fields. Remarkably, the magnetic soft grippers associated with the gecko‐inspired adhesion surface exhibit an improved and stable grasping ability. This work focuses on designing highly deformable actuators and functions in emerging areas of soft robotics.

Residual stress tuned magnetic properties of thick CoMnP/Cu multilayers

Electrodeposited hard magnetic thick films have vast applications in the microelectromechanical systems (MEMS). Yet the very large residual stresses (σr) built-up in monolayered thick magnetic films leads to cracks, dimensional changes and deteriorated magnetic properties. Here, we explored quantitatively magnetic properties of CoMnP/Cu multilayers tuned by σr, which in turn are varied by the inserted soft Cu interlayer and thickness of single CoMnP magnetic layers. The configuration of the multilayers is an alternating CoMnP/Cu on Cu-substrate. The thickness of Cu interlayer was 1.4 μm. We kept a sum of all magnetic layers in the multilayers at ∼20 μm to benchmark with a 19.4 μm monolayered CoMnP. The magnetic layers are 94 wt.% Co and possess highly textured (002) hexagonal close packed microstructures. We characterized the apparent crystallite stresses through sin2ψ method by X-ray diffractometer (XRD) and residual film stress by curvature method. The insertion of Cu interlayers effectively reduces σr by 23% through stacking with six single-layered CoMnP. The out-of-plane (OP) anisotropy is slightly reduced. While the maximum energy product in the in-plane (IP) direction can be significantly enhanced by 430% ∼ 690% with increasing the number of the CoMnP single layer in the multilayers. The magneto-elastic behaviors well explain the evolution of the total anisotropy energy of the mono- and multi-layers. By CoMnP/Cu configurations we successfully worked out a strategy to preserve prestigious OP performance while to enhance IP properties by 4 to 6 times to meet ever increasing challenges in MEMS applications.

Elastodynamic Behaviour of Laminate Structures with Soft Thin Interlayers: Theory and Experiment.

Laminate structures composed of stiff plates and thin soft interlayers are widely used in aerospace, automotive and civil engineering encouraging the development of reliable non-destructive strategies for their condition assessment. In the paper, elastodynamic behaviour of such laminate structures is investigated with emphasis on its application in ultrasonic based NDT and SHM for the identification of interlayer mechanical and interfacial contact properties. A particular attention is given to the practically important frequency range, in which the wavelength considerably exceeds the thickness of the film. Three layer model with spring-type boundary conditions employed for imperfect contact simulation is used for numerical investigation. Novel effective boundary conditions are derived via asymptotic expansion technique and used for analysis of the peculiar properties of elastic guided waves in considered laminates. It is revealed that the thin and soft film influences the behaviour of the laminate mainly via the effective stiffnesses being a combination of the elastic moduli of the film, its thickness and interface stiffnesses. To evaluate each of these parameters separately (or to figure out that the available experimental data are insufficient), a step-wise procedure employing the effective boundary conditions is proposed and tested versus the laser Doppler vibrometry data for Lamb waves in Aluminium/Polymer film/Alumunium structure. A good agreement between theoretical and experimental data is demonstrated for a certain symmetric laminate specimen. The possibility of using film-related thickness resonance frequencies to estimate the film properties and contact quality is also demonstrated. Additionally, the rich family of edge waves is also investigated, and the splitting of fundamental edge waves into pairs is revealed.

Residual stress analysis of electrodeposited thick CoMnP monolayers and CoMnP/Cu multilayers

Residual stress in electroplated hard magnetic layers is crucial to the stability and durability in end applications. We electrodeposited highly HCP (002) textured CoMnP hard magnetic layers on copper substrate. We characterized and compared the residual stresses of mono- and multi-layered configurations using sin2ψ X-ray diffraction (XRD) for the apparent crystallite stress (σXRD), and curvature measurement methods for the macro-stress (σf). Intermediate Cu layer having a fixed thickness of 1.4 μm was introduced as a stress reliever for the multilayered CoMnP/Cu through sequential electrodeposition. In multilayers, thickness of all single magnetic layers was added to around ~20 μm similar to that of a monolayer. The surface morphology, layer composition and microstructure remain the same regardless of individual CoMnP single layer thickness. XRD results of ϕ-scan and ψ-scan depict the transversely isotropic CoMnP layers are under an equi-biaxial stress status, making a simplified analytical solution of sin2ψ method. The residual stresses measured by XRD sin2ψ method have been correlated with those acquired by curvature method. Increasing the number of layers from 2, 3 to 6 in the CoMnP/Cu multilayers reduces the σXRD by 8.3%, 25%, 33%, respectively; while the σf by 7.7%, 15% and 23%, respectively, as compared to those of the CoMnP mono-layer. These reductions are attributed to the released strain energy due to soft interlayer confinement and stacking fault formation. Elaborated includes unambiguous understandings of residual stress and microstructures for the electrodeposited CoMnP layers.

Study on the Influence of a Soft Soil Interlayer on Spatially Varying Ground Motions

The existence of local soft interlayer can significantly amplify or attenuate the ground motion and thus might influence the lagged spatial coherency between spatially varying earthquake ground motions. A target site with a local soft interlayer was assumed first, and then two numerical examples were set. In example 1, linear soil behavior was considered and a large amount of quasi-stationary spatially varying earthquake ground motions were generated by combining the one-dimensional wave propagation theory and the classical spectral representation method. The influence regularity of varying shear wave velocity, buried depth, and thickness of the soft interlayer on the characteristics of lagged spatial coherency was investigated. In example 2, non-linear soil behavior was taken into account and fully non-stationary spatially varying earthquake ground motions were thus generated by using time-varying transfer function and spectral representation method. An overall evaluation was carried out to shed light on the differences of characteristics of spatial coherency between non-linear soil and linear soil cases. It showed that: (i) As the shear wave velocity of interlayer declines and as the buried depth and thickness increase, remarkable reduction of spatial coherency showed up; (ii) the reduction of lagged spatial coherency caused by varying buried depth may be more inclined to concentrate in the lower frequency range; (iii) the non-linear soil behavior can cause greater further reduction of lagged spatial coherency in comparison with linear soil behavior, especially in the higher frequency range; (iv) the troughs of lagged spatial coherency curve tend to be located in the variation range of vibration frequency of time-varying spectral ratio.

Efficacy of carbon nanotubes and polydimethylsiloxane interlayer in augmenting the impact strength of glass fiber/epoxy composites

An experimental investigation is carried out to explore the possibility of carbon nanotubes addition and incorporation of polydimethylsiloxane soft interlayer in improving the impact strength and energy-absorbing capability of conventional glass fiber-reinforced plastics. To this end, deformation behavior of glass fiber-reinforced plastics, carbon nanotube-modified glass fiber-reinforced plastics, and glass fiber-reinforced plastics-polydimethylsiloxane sandwich coupons under high strain rate loading are compared using the split-Hopkinson pressure bar testing technique. While neat epoxy is used to process conventional glass fiber-reinforced plastics, the carbon nanotubes-modified glass fiber-reinforced plastics samples are fabricated using 0.5 wt. % carbon nanotube-modified epoxy. The split-Hopkinson pressure bar testing reveals that the addition of carbon nanotubes improves the peak stress and energy-absorbing capacity of the epoxy matrix. The improved impact response of carbon nanotube-modified epoxy translates into enhanced peak stress and energy-absorbing capability of carbon nanotubes-modified glass fiber-reinforced plastics in comparison to conventional glass fiber-reinforced plastics under impact loading. The microscopy analysis of failed composite samples reveals that while glass fiber-reinforced plastics primarily fails at the fiber/epoxy interface, the failure initiates in the epoxy matrix in carbon nanotubes-modified glass fiber-reinforced plastics samples. The impact testing of sandwich samples shows that the insertion of neat and 0.05 wt. % carbon nanotube-modified polydimethylsiloxane interlayer helps to distribute the impact load in a wider domain and thus delays the failure of glass fiber-reinforced plastics sandwich coupons. Moreover, the carbon nanotube-modified polydimethylsiloxane interlayer is better suited to increase the damage resistance and energy-absorbing ability of glass fiber-reinforced plastics. The present study provides a feasible strategy to enhance the failure strength and energy-absorbing capacity of conventional composites using carbon nanotube-modified epoxy and polydimethylsiloxane-based interlayer.

Evaluation of crack resistance of welded joints with soft interlayers

Introduction. Welded joints in large-sized metal structures (e.g., in the structures of ship hulls) subject to low-cycle fatigue are considered. The characteristic appearance of soft interlayers, which are significantly plastically deformed under working loads, was noted. Deformation of the metal structure with damage, especially in the form of cracks, reduces the strength and reliability of structural elements and joints. Pre-deformation negatively affects plasticity; therefore, much depends on the residual plasticity of the cracking material. At the same time, with a decrease in residual plasticity, such an important reliability indicator as the resistance of the material to crack propagation — the fracture toughness – decreases. The paper is devoted to the development of a model that includes analytical dependences for assessing the crack resistance of metal structures and their welded joints with soft interlayers according to the crack resistance limit for all crack sizes.Materials and Methods. The theory and methods of linear mechanics of materials destruction, structural-mechanical approach are used. The calculation results were analyzed and compared to the experimental data and other analytical solutions. The numerical experiment was performed for the ferrite-perlite steel grades of 10, 50, 22K, St3sp, etc., widely used in industry, as well as for alloy steels hardened to medium and high strength of 30KhGSA, 37KhN3A, etc. Results. Analytical dependences are obtained for calculating the relative crack resistance limit according to three main known mechanical characteristics of the state of the material of the soft interlayer of the welded joint.Discussion and Conclusions. The results obtained can be used to assess the crack resistance of pre-deformed structural elements and welded joints (including those with soft interlayers) operating under a transverse load. The results of experimental data and analytical calculations are shown in dimensionless form, which enables to obtain invariant results with respect to the fracture toughness limit.

Theoretical and experimental study on identification of the soft interlayer in coal mine roadway roof

Theoretical and experimental study on identification of the soft interlayer in coal mine roadway roof

Joint Inversion of Rayleigh and Love Dispersion Curves Extracted from Ambient Seismic Noise Based on Secular Function

Traditional multi-mode dispersion curve inversion requires correct mode discrimination. However, when the stratum contains complex structures such as low-speed soft interlayer or high-speed hard interlayer, the dispersion curve may show phenomena such as “mode kissing” and “mode jumping”, which can easily cause mode misjudgment and lead to erroneous inversion results. Based on the “secular function”, this paper constructs a new type of objective function applied to the inversion of dispersion curve. This objective function does not require prior mode discrimination, which effectively solves the “mode misjudgment” problem of multi-mode dispersion curve inversion. The joint inversion of Rayleigh and Love dispersion curves extracted from ambient seismic noise is used to improve the constraint of the inversion and avoid the inversion falling into a local minimum in the case of a large-scale search of parameters. Finally, a numerical simulation was performed to verify the feasibility of the new inversion method.

Soft template-directed interlayer confinement synthesis of a Fe-Co dual single-atom catalyst for Zn-air batteries

Dual single-atom catalysts (DSACs) with maximized atomic utilization efficiency largely depend on stabilization of dual-metallic single atoms on ideal supports, such as those two-dimensional (2D) atomic layers with open double-sided surfaces. However, the modulation of metal-2D support interactions is critical for enhancing the catalytic performance of DSACs, which has rarely been achieved by routine 2D atomic nanosheets. Here we report a soft template-directed interlayer confinement route for the synthesis of a Fe-Co DSAC. Fe and Co single atoms are stabilized separately on 2D carbon nanosheets via coordination with nitrogen (N) and sulfur (S) heteroatoms to form a FeN4S1/CoN4S1 configuration. The synergistic effect of Fe-Co dual metal centers can optimize the adsorption/desorption features and decrease the reaction barriers for enhanced oxygen reduction reaction (ORR) activities. The Fe-Co DSAC exhibits outstanding electrocatalytic activities of ORR with a half-wave potential of 0.86 V and Zn-air batteries with a maximum power density of 152.8 mW cm−2, outperforming the monometallic Fe and Co SACs. This work paves a new avenue for synthesis of effective DSACs for high-performance electrocatalysis.

Stability Analysis of Rock Slope with Multilayer Weak Interlayer

The existence of the weak interlayer of the rock slope changes its mechanical characteristics. To ensure the safety of the slope, it is necessary to analyze the overall stability of the slope. Taking the double-layer weak interlayer rock slope beside 318 National Road in Qiyue Mountain, Hubei Province, as an example, a slope model with a weak interlayer was established through GTS software, and the model was imported into FLAC3D for calculation, and the deformation of the slope by the double-layer soft interlayer was studied. The influence of characteristics and safety factors reveals the controlling effect of the double-layer weak interlayer on the stability of the slope and its failure mode. The potential sliding surface of the slope is determined to be the lower weak interlayer, and the weak interlayer after the anchor cable reinforcement is carried out. Numerical analysis shows that the reasonable application of anchor cables significantly improves slope stability. The research results can provide reference significance for slope stability analysis of similar projects.

Study on the Impact of Hydraulic Fracturing on Surrounding Ancillary Buildings considering SSI

Hydraulic fracturing is a key technology in the development of unconventional oil and gas reservoirs. With the continuous industrialization and large-scale development of shale gas production in China, the workload of hydraulic fracturing is also increasing rapidly, and the induced seismic events are also increasing gradually, resulting in different degrees of damage to the surrounding ancillary buildings. In order to study the impact of hydraulic fracturing on ancillary buildings, the finite element software ABAQUS was used to establish a three-dimensional model of middle and high-rise isolated structures to simulate the earthquake triggered by hydraulic fracturing. Then, considering the SSI (soil-structure interaction) effect of soil-based structure, the nonlinear dynamic response of the structure under the action of ground motion was analyzed. Through the adoption of different types of soil and the foundation depth, the influence of various parameters is discussed. The study found that in the case of not considering SSI, basal shear force, and displacement between floors of the seismic-isolation structure significantly greater than considering SSI, using hard soil layer, base shear displacement is greater than the soft soil layer and interlayer, shows that due to the effect of hydraulic fracturing, making fluid diffusion in soil, the seismic energy dissipation effect. It is also found that the period, base shear, peak displacement, and interlayer displacement of deep foundation pit are increased compared with shallow foundation pit considering SSI effect.

A non-linear direct peridynamics plate theory

In this paper a direct non-local peridynamics theory for thin plates is developed. Peridynamic points are assumed to behave like rigid bodies with independent translation and finite rotation degrees of freedom. The non-local mechanical interaction between points is characterized by force and moment vectors. The balance equations including the linear momentum, the angular momentum and the energy are presented. Peridynamic deformation states of the plate are introduced including the actual bond vector (relative translation of two points within the bond) and the relative finite rotation tensor (actual relative orientation of two points in the bond). The corresponding power-conjugate bond force and bond moment states are derived. The framework to develop constitutive equations for the plate peridynamic states is addressed. Special cases of the theory including plates with zero drilling moments, membranes, soft interlayers as well as stiff plate layers with small relative rotations are considered.

Pillar stability of salt caverns used for gas storage considering sedimentary rhythm of the interlayers

In view of the low permeability and good damage self-healing properties of rock salt, salt caverns are thought to be ideal media to hold natural gas. However, widely distributed salt formations in China were formed bedded by lacustrine sedimentation with significant sedimentary rhythm characteristics. The various interlayers in bedded salt formations may cause instability of the cavern pillar due to their uncoordinated deformation, thus threatening the safety of the whole gas storage caverns. Combining theoretical analysis and numerical simulation, the influence of different characteristics of interlayers on the stability of salt cavern pillars were detailed analyzed. Some main conclusions were summarized as follows: 1) In a sedimentary rhythm, the rock salt and the soft interlayers can be considered as one category, and the hard interlayers can be treated as another category. Compared with the hard interlayers, rock salt and the soft interlayers contributes more to the shrinkage of salt cavern; 2) With the decrease of pillar width or the increase of operating time, the principal stress curves (both σ1 and σ3) in the interlayers along the line between the centers of the two caverns generally experience the process of "Bimodal type - Saddle type - Unimodal type"; 3) The entire plastic zone expansion process in hard interlayers of the cavern pillar shows the periodic law of "interfaces - middle interlayer - interfaces - middle interlayer"; 4) As to site selection of salt caverns for gas storage, bedded salt formations with too many interlayers should be avoided. If the interlayers cannot be avoided, the salt cavern should be constructed with interlayers located far away from the cavern center.

Constructing van der waals heterostructural sulfides PbTiS3 of reversible conversion-alloying mechanism for superior electrochemical lithium storage

Metal sulfides have been universally studied as anode materials for lithium ion batteries (LIBs). Herein, we studied the lithiation storage behavior of a novel metal sulfide PbTiS3 (PTS), which is one of misfit layer compounds (MLCs) including intercalation-type TiS2 layer and conversion-alloying-type PbS layer. In-situ powder X-ray diffraction measurement reveals that the final lithiated product Li22Pb5 can be restored, indicating a reversible conversion-alloying mechanism in PTS. Theoretical calculation indicates the soft PbS interlayers of rock salt structure can hinder the distortion of TiS2 layers upon lithiation, resulting in a high structural integration of PTS anodes as well as a high concentration of intercalated Li ions. Moreover, with the assistance of the strong interfacial C–O–Pb/Ti interaction between PTS and graphene oxide (GO), PTS can be embedded in the conductive GO network which could stabilize PTS structure during long term cycling. Consequently, the fabricated LIBs anode delivers a relatively high reversible capacity (569 mA h g−1 at 2.0 A g−1 after 1000 cycles) and an outstanding high-rate capability. Besides, the assembled lithium ion full battery maintains a capacity retention of 70% after 100 cycles at 0.1 A g−1. This work provides insights into the design of MLCs as next-generation secondary batteries.

CPT-Based evaluation of sediment characteristics and effective internal friction angle in the yellow river estuary

The Yellow River Estuary is a typical constructive delta with a complex sedimentary structure. To analyze the physical, mechanical properties, and structural characteristics of the surface sediments in the delta, reveal the sedimentary environment and avoid geological hazards, cone penetration test (CPT) is used for nautical in situ testing and evaluating effective internal friction angle (φ'). Four typical areas formed by the diversion of the Yellow River Estuary in different periods are selected as the research objects to perform the in situ CPT, particle size analysis test, scanning electron microscopy, and triaxial test, building calculation model. The main conclusions are as follows: (1) The sediment given priority to are silt and silty clay, where the stratigraphic distribution difference is more significant, accompanied by soft interlayer or alternating layers of hard. (2) Hard soil in the sediments cause abrupt changes and fluctuations in the cone tip resistance and sleeve friction resistance. (3) The empirical formulas proposed by Berezantsev, Khristoforov, and Golubkov, Kulhawy and Mayne, and Mayne are used to predict φ' and the effect of inversion is good. (4) The coefficients of formulas are significantly improved, modified according to site variability.

Behaviour of a large-diameter shield tunnel through multi-layered strata

In engineering practice, a large-diameter shield tunnel frequently extends through multi-layered strata. The behaviour of tunnels is more complex in multi-layered strata, but many designs are still constructed with the assumption that the soil is uniform. In this study, centrifuge tests and FEM analysis are conducted to investigate the mechanical behaviour of a large-diameter shield tunnel through multi-layered strata in terms of tunnel inner force and convergence. Two-layer strata and three-layer strata with different positions, inclinations, and thicknesses of the soft interlayer are considered, along with the relative stiffness of different layers. Both centrifuge tests and numerical simulation indicate that the relative stiffness of different layers and the position of the soft interlayer are the main factors affecting the behaviour of the tunnel in multi-layered strata. An increase in the relative stiffness leads to a significant reduction in the bending moment at the crown and springline. The maximum bending moment tends to appear in the soft layer. The distribution of inner force and convergence are asymmetrical owing to the inclination of the soil interface. Based on the results, some design suggestions are presented for large-diameter shield tunnels in multi-layered strata. Segment joints are discouraged near the soil interface and the ground around the tunnel can be considered to be soft soil when the interface is below the springline. In addition, the bending moment should be concerned carefully when the tunnel extends through the soft interlayer.

Nonlinear analytical study of structural laminated glass under hard body impact in the pre-crack stage

Emerging glass structures, which frequently use laminated glass (LG) as load bearing elements, see a significant rise in recent decade. Existing analytical solutions for LG under impact present limitation when introduced into structural LG products, as structural LG having more glass plies and soft polymeric interlayers requires more accurate nonlinear analytical model. In this study, a nonlinear analytical model was proposed for the simply supported square structural LG subjected to hard body impact. The motion equations were established based on a third order shear deformation theory and von Kármán nonlinear strain–displacement relationship. Based on a two-step perturbation method, the solutions of the motion equations were obtained. The fourth-order Runge–Kutta method was used to capture the impact force variation. Drop weight impact tests with increasing impact velocity, were conducted to record the impact force of LG panels before breakage. Eighteen LG panels with PVB or SG interlayers were tested. Through analysing the fracture initiation from high speed photos as well as the impact force variation in the impact attempt causing fracture, certain feature of the experimental impact force response was determined to be validated with analytical prediction. The validation results show that the proposed model can well reproduce the examined feature and achieve satisfactory impact force response. Case study was then designed to investigate the influence due to the safety windows film on reducing the pre-crack impact response. The effective thickness of LG based on the equivalence of indentation was also proposed for the hard body impact.

Long-term shear strength weakening of soft interlayers due to low-permeability

Soft interlayers are distiuctive geological units that serve as semi-permeable layers that regulate water flow and chemical transport in the subsurface. However, their hydrogeolocial characteristics are still poorly understood due to its unique sedimentary features. Duo to the low-permeability of Permian Maokou soft interlayers, water contents remain invariable and cause continuous weakening effect to its shear strength. Series of ring-shear creep tests are conducted to study the effect of water contents on ring-shear rheological properties. According to the experimental results, the instantaneous shear strain modulus is closely affected by water content, normal stress, and duration of test. Besides, the long-term shear strength and residual shear strength are close to each other when the normal stress is relatively small. But the strength reduction factor from the residual shear strength to the long-term shear strength should be considered under high normal stresses. Furthermore, the long-term cohesion and friction angle are obtained by fitting the long-term shear strength values under different normal stresses. An exponential function relation exists between the two long-term shear strength parameters and water contents. Finally, based on the analysis of the SEM (scanning electron microscope) results, it can be concluded that the effect of water content on rheology properties is mainly caused by lubrication, expansion of particles of samples in water. Micro-holes and cracks on failure surfaces also exhibit ductile failure characteristics.

Influence of Cyclic Wetting–Drying on the Shear Strength of Limestone with a Soft Interlayer

Influence of Cyclic Wetting–Drying on the Shear Strength of Limestone with a Soft Interlayer