Equivalent Mechanical Parameters Research Articles

CVAE-Based Inverse Design of Two-Dimensional Honeycomb Pentamode Metastructure for Acoustic Cloaking

In this work, a method for inverse design of two-dimensional honeycomb pentamode metastructures (HPM) based on the Conditional Variational Auto-Encoder (CVAE) is proposed to achieve acoustic cloaking. The parameter distribution of the perfect acoustic cloak with two-dimensional cylindrical Kohn-Shen-Vogelius-Weinstein (KSVW) mapping is first derived. The CVAE model framework is then established along with its loss function in terms of the design parameters of the HPM. The inverse design performance of the deep generative model is evaluated using a large number of random test samples based on finite element simulations, showing that the equivalent mechanical parameters obtained from inverse design are highly consistent with the target parameters of the perfect acoustic cloak. For the HPM cloak design given by the trained deep generative model, the total scattering cross section (TSCS) is significantly reduced as compared to the case without a cloak, thereby demonstrating the effectiveness of the CVAE-based inverse design of acoustic cloak.

Multiscale Analysis of Impact-Resistance in Self-Healing Poly(ethylene-co-methacrylic acid) (EMAA) Plain Woven Composites.

A study combining multiscale numerical simulation and low-velocity impact (LVI) experiments was performed to explore the comprehensive effects on the impact-resistance of EMAA filaments incorporated as thermoplastic healing agents into a plain woven composite. A multiscale micro-meso-macro modeling framework was established, sequentially propagating mechanical performance parameters among micro-meso-macro models. The equivalent mechanical parameters of the carbon fiber bundles were predicted based on the microscopic model. The mesoscopic representative volume element (RVE) model was crafted by extracting the actual architecture of the monolayer EMAA filaments encompassing the plain woven composite. Subsequently, the fiber and matrix of the mesoscopic model were transformed into a monolayer-equivalent cross-panel model containing monolayers aligned at 0° and 90° by local homogenization, which was extended into a macroscopic equivalent model to study the impact-resistance behavior. The predicted force-time curves, energy-time curves, and damage profile align closely with experimental measurements, confirming the reliability of the proposed multiscale modeling approach. The multiscale analysis reveals that the EMAA stitching network can effectively improve the impact-resistance of plain woven composite laminates. Furthermore, there exist positive correlations between EMAA content and both impact-resistance and self-healing efficiency, achieving a self-healing efficiency of up to 98.28%.

Study on the mechanical behavior of microcapsules during the mixing process of asphalt mixture

To enhance the survival rate of microcapsules during the mixing process of asphalt mixture, the mechanical behavior of microcapsules during this process was investigated through simulation. Initially, the asphalt mixture containing microcapsules was divided into mesoscopic and microscopic scales. Utilizing composite material models, the stepwise inclusion method and high-temperature tensile tests, the equivalent mechanical parameters for the microcapsules, asphalt mastic and asphalt mortar at mixing temperature were estimated. Following this, the mixing process of the asphalt mixture incorporating microcapsules was simulated employing the discrete element method (DEM) coupled with multi-body dynamics (MBD). This simulation was instrumental in identifying optimal mixing parameters and enabled the analysis of force chain transmission across the multi-scale model. Furthermore, the finite element method (FEM) was employed to develop a monomer model of the microcapsules, facilitating the assessment of their mechanical behavior under optimal mixing conditions. Finally, a detailed sensitivity analysis was performed to investigate the influence of various parameters on the mechanical behavior of microcapsules. The results indicated that, at the mixing temperature, the equivalent Young’s modulus and Poisson's ratio for urea-formaldehyde (UF) resin microcapsules, asphalt mastic, and asphalt mortar were determined to be 0.22 GPa and 0.478, 19.87 GPa and 0.4986, and 88.77 GPa and 0.468, respectively. The optimal mixing parameters for AC-16 asphalt mixture including mixing speed, filling rate and mixing duration were identified as 49 rpm, 50 % and 53 s, under which the most adverse load on the microcapsule is 80 mN. Under the most adverse load, microcapsules might rupture from the inside out, and their survival rate was not less than 68.9 %. Increasing the particle size of microcapsules and reducing the relative radius of the microcapsule core could potentially enhance the crack resistance of microcapsules during mixing.

An online optimization escape entrapment strategy for planetary rovers based on Bayesian optimization

AbstractPlanetary rovers may become stuck due to the soft terrain on Mars and other planetary surface. The escape entrapment control strategy is of great significance for planetary rover traversing loosely consolidated granular terrain. After analyzing the performance of the published quadrupedal rotary sequence gait, a “sweeping‐spinning” gait was proposed to improve escape entrapment capability. And the forward distance of planetary rovers with “sweeping‐spinning” gait was modeled as a function of six control parameters. An online optimization escape entrapment strategy for planetary rover was proposed based on the Bayesian Optimization algorithm. Single‐factor experiments were conducted to investigate the effect of each control parameter on forward distance, and determine the parameter ranges. The average forward distance with randomly selected control parameters is 89.64 cm, while that is 136.93 cm with Bayesian optimized control parameters, which verifies the effectiveness of the escape entrapment strategy. Moreover, compared with the trajectory of a planetary rover prototype with the published quadrupedal rotary sequence gait, the trajectory of a planetary rover prototype with “sweeping‐spinning” gait is more accurate. Furthermore, the online estimated equivalent terrain mechanical parameters can be used to determine the running state of the planetary rover prototype, which was verified using experiments.

Nonlinear resonant responses and chaotic dynamics of three-dimensional braided composite cylindrical shell

The advanced three-dimensional braided composite structure has excellent integrity, which can effectively avoid the problems of interlayer stress jump and interface debonding that may occur in traditional composite laminated structures. However, most of the existing references on the three-dimensional braided composite structure are fragmented, and there is little research on their vibrations. Taking the cylindrical shell of a rocket as the object and considering the complex flight environment, a general framework for the vibration problems of the three-dimensional braided composite shell is proposed for the first time. The equivalent mechanical parameters of the three-dimensional braided composite material are calculated based on the volume averaging method. Then, the nonlinear dynamic model of the three-dimensional braided composite cylindrical shell is established, and the natural vibration characteristics are analyzed. Under the case of 1:1 internal resonance, the pseudo-arc length continuation method is used to solve the nonlinear resonant responses of this nonlinear system. Finally, we apply the fourth-order Runge-Kutta algorithm to study the chaotic dynamics of the three-dimensional braided composite cylindrical shell model. This framework presented in this paper can be extended to the study of nonlinear vibrations and chaotic dynamics of other three-dimensional braided composite structures.

Gradient honeycomb metastructure with broadband microwave absorption and effective mechanical resistance

Multifunctional metastructure integrated broadband microwave absorption and effective mechanical resistance has attracted much attention. However, multifunctional performance is limited by the lack of theoretical approaches to integrated design. Herein, a multi-layer impedance gradient honeycomb (MIGH) was designed through theoretical analysis and simulation calculation, and fabricated using 3D printing technique. A theoretical calculation strategy for impedance gradient structure was established based on the electromagnetic parameter equivalent method and the multi-layer finite iterative method. The impedance of MIGH was analyzed by the theoretical calculation strategy to resolve the broadband absorption. Intrinsic loss mechanism of matrix materials and distributions of electric fields, magnetic fields and power loss were analyzed to investigate the absorption mechanism. Experimental results indicated that a 15 ​mm thick designed metastructure can achieve the absorption more than 88.9% in the frequency range of 2-18 ​GHz. Moreover, equivalent mechanical parameters of MIGH was calculated by integral method according to the Y-shaped model. Finite Element analysis of stress distributions were carried out to predict the deformation behavior. Mechanical tests demonstrate that MIGH achieved the compression modulus of 22.89 ​MPa and flexure modulus of 17.05 ​MPa. The integration of broadband electromagnetic absorption and effective mechanical resistance was achieved by the proposed design principle and fabrication methodology.

Stability analysis of jointed rock mass in large underground caverns based on multi-scale analysis method

Random defects at different scales are the crucial cause of damage evolution and cascade transfer in rocks. For a large-scale underground cavern, the rock mesoscopic heterogeneity and macroscopic random joints are inevitable factors of rock stability, which needs to be further studied. In this study, a multi-scale analysis method for the stability of jointed rock mass in large underground caverns is proposed. The statistical damage theory is used to describe the mesoscopic heterogeneous rock damage. Monte Carlo simulation and measured joint geometric information are combined to reconstruct the macroscopic random joint network of rock mass. The integrated analysis of mesoscopic heterogeneity of rock and the macroscopic response of random jointed rock mass is performed by Rock Failure Process Analysis (RFPA) system. The research shows that the existence of joint affects the failure mode of rock mass and strengthens the heterogeneity. The representative elementary volume (REV) of jointed rock mass and its equivalent mechanical parameters are determined and used in the stability analysis of a large-scale underground cavern project. Results show a good agreement with the in-situ monitoring deformation of surrounding rock mass, which verifies the effectiveness of the rock mass multi-scale analysis method.

Design and analysis of thermal protection and load-bearing integrated structure of the telescopic wing

A novel three-layer integrated structure was designed to meet the thermal-insulation and load-bearing requirements of high-speed telescopic wing aircraft. The structure consists of heat shield layer, load-bearing skeleton, and pyramid lattice structure filled with aerogel to achieve the insulation function. Sensitivity analysis of the design parameters and optimal design of the integrated structure was carried out, and the structure was optimized by using response surface method. Compared to the initial structure, the optimized structure has an equivalent thermal conductivity of 0.0276, reduced by 40%, and a relative density of [Formula: see text], reduced by 3.7%. And it has a thermal conductivity that is over 20% lower than that of ceramic insulating tiles. Then, the integrated structure was regarded as a homogeneous plate, and the equivalent mechanical and thermal parameters were determined and verified by simulation and experimental results. The equivalence error was controlled within 10%. Finally, a simulation model of the telescopic wing was established. The result shows that the maximum deformation under 20 kPa surface pressure is 3.96 mm. The temperature resistance of the structure surface is up to 1500°C, and the wing internal temperature is controlled within 200°C after 1200 s of thermal loading. The results verified that the integrated structure meets the requirement of a high-speed telescopic wing.

Research on dynamic characteristics of large deformation shearer cable based on absolute node coordinate formulation method.

The development of intelligent and unmanned coal mining has put forward higher requirements on the service life and dynamic reliability of shearer cables. However, it is difficult to comprehensively consider the complexity of hosting conditions of coal mining working face and the dynamic characteristics of cables in different towing systems in the design and development of cables. The cables are periodized by pitch and have the same cross-sectional structure and properties. Based on the homogenization theory and volume average principle, the cable was assumed to be an orthotropic elastomer, and the tensile experimental method and finite element method were combined to calibrate the cable equivalent mechanical parameters. Based on the Absolute Node Coordinate Formulation (ANCF) method, the rigid-flexible coupled virtual prototype co-simulation model of shearer cable towing system was constructed to obtain the kinetic and kinematic parameters of each node of the cable and study the dynamic gradual change characteristics of the cable in different working areas. This research method has an important theoretical significance and engineering application value for the acquisition of dynamic characteristic parameters of shearer cables and the optimal design and dynamic reliability of cables.

Equivalent mechanical model of resin-coated aramid paper of Nomex honeycomb

Nomex honeycomb, as the core part of sandwich structure, has been widely used in the aviation and aerospace industries. Ultrasonic cutting, as a technology that can reduce machining defects, has been highlighted in recent years, but some problems in the cutting process still need to be investigated significantly. Finite element method (FEM) offers an alternative way of in-depth understanding of the problems. However, the multi-layer structure of the Nomex honeycomb cell wall, which is the resin-coated aramid paper, makes it difficult to establish a detailed multi-layered finite element (FE) model at a macro-scale level. Therefore, a novel segmented material mechanical model, which is applicable to the equivalent single-layer model, is proposed based on the analysis of the mechanical behaviour of the multi-layer structure of the resin-coated aramid paper. Moreover, the calculating method of equivalent mechanical parameters of the multi-layer structure are proposed theoretically. The proposed method is first verified by FE models at a micro-scale level in both single-layer and multi-layer approaches. Additionally, simulations and experiments are performed to verify that the proposed method performs well in the simulation of ultrasonic cutting for Nomex honeycomb, and the difficulty of modelling and CPU time of simulation are reduced significantly.

A comprehensive investigation on bending stiffness of composite grid-stiffened and functional foams sandwich beam

This paper investigates the bending stiffness of composite grid-reinforced sandwich beams with functional foam cores by a combination of analysis, simulation, and experiment. First, the sandwich layer composed of stiffeners and foam cores is homogenized, and the equivalent mechanical parameters of the sandwich layer are proposed. Then, based on the first-order shear deformation theory, the three-point bending deflection of the beam is derived and verified by tests and simulations. Finally, the factors affecting the bending stiffness are investigated, such as the elastic modulus of the foam cores, the thickness of the stiffeners, the longitudinal and transverse spacing of the stiffeners, and the fiber lay-up angle of the stiffeners. The results of this paper are of great significance to the stiffness design and parameter optimization of composite grid-stiffened sandwich structures with foams for underwater vibration and noise reduction.

Design and study of a new broadband RCS carbon-glass fiber hybrid metamaterial

In this paper, a plain-woven metamaterial consisting of a ribbon-like blend of carbon fiber-glass fiber strips is proposed. The structure of the proposed hybrid material has a broadband filtering function of electromagnetic wave, can form beam reconstruction and selective wave transmission, and reduce radar scattering cross section (RCS) in the 9 GHz - 25 GHz frequency band. The macroscopic equivalent mechanical parameters are estimated by constructing the micro fine structure model and combining the periodic boundary conditions. The Hasin failure criterion is used to predict the progressive damage evolution of the proposed hybrid material under tensile loading. In addition, the plain-woven metamaterial has the advantages of simple structure and easy fabrication, which provides a new design idea for the metamaterial radome and important engineering guidance for its fabrication process.

Determination of Landslide Displacement Warning Thresholds by Applying DBA-LSTM and Numerical Simulation Algorithms

Numerical simulation has emerged as a powerful technique for landslide failure mechanism analysis and accurate stability assessment. However, due to the bias of simplified numerical models and the uncertainty of geomechanical parameters, simulation results often differ greatly from the actual situation. Therefore, in order to ensure the accuracy and rationality of numerical simulation results, and to improve landslide hazard warning capability, techniques and methods such as displacement back-analysis, machine learning, and numerical simulation are combined to create a novel landslide warning method based on DBA-LSTM (displacement back-analysis based on long short-term memory networks), and a numerical simulation algorithm is proposed, i.e., the DBA-LSTM algorithm is used to invert the equivalent physical and mechanical parameters of the numerical model, and the modified numerical model is used for stability analysis and failure simulation. Taking the Shangtan landslide as an example, the deformation mechanism of the landslide was analyzed based on the field monitoring data, and subsequently, the superiority of the DBA-LSTM algorithm was verified by comparing it with DBA-BPNN (displacement back-analysis based on back-propagation neural network); finally, the stability of the landslide was analyzed and evaluated a posteriori using the warning threshold calculated by the proposed method. The analytical results show that the displacement back-analysis based on the machine learning (DBA-ML) algorithm can achieve more than 95% accuracy, and the deep learning algorithm exemplified by LSTM had higher accuracy compared to the classical BPNN algorithm, meaning that it can be used to further improve the existing intelligent inversion theory and method. The proposed method calculates the landslide’s factor of safety (FOS) before the accelerated deformation to be 1.38 and predicts that the landslide is in a metastable state after accelerated deformation rather than in failure. Compared to traditional empirical warning models, our method can avoid false warnings and can provide a new reference for research on landslide hazard warnings.

Design method and infeasibility criteria for honeycomb pentamode cloak

Transformation acoustics cloaks can be realized using microstructured pentamode materials, but systematic design method and criteria are still missing. Based on the analytical formula of equivalent mechanical parameters, this paper presents a design method of honeycomb pentamode circular cloak for linear mapping. The finite element analysis is adopted to verify this method. The results show that under the condition of long wavelength homogenization, the stealth performance of the designed pentamode cloak is close to that of the ideal cloak, which proves the effectiveness of the design method. Three inequalities based on extreme values are also proposed as infeasibility criteria. For any linearly mapped honeycomb PM circular cloak design, it cannot be achieved when either inequality holds, which helps to quickly rule out impossible options.

Impact of the vibration measurement points geometric coordinates uncertainties on two-dimensional k-space identification: Application to a sandwich plate with honeycomb core

The purpose of the present paper is to investigate the wave propagation features in a sandwich plate with honeycomb core over a large frequency domain. Robust experiment-based identification processes are proposed to estimate propagation direction-dependent and frequency-dependent wavenumber-space (k-space) characteristics in presence of parametric uncertainties. These processes combine structural identification and uncertainty propagation methods. A special emphasis is put on wave correlation methods compared to two-dimensional Discrete Fourier Transform. The Variant of the Inhomogeneous Wave Correlation method is extended here to two-dimensional identification problems. The vibration field is experimentally measured at points which geometric coordinates are supposed to vary randomly. Statistical investigations are then carried out to quantify the impact of the measurement points geometric coordinates’ variability on the identified parameters and evaluate the robustness of the proposed identification processes against uncertainties. Valuable insights into k-space profiles, damping loss factor and equivalent mechanical parameters, regarding the structural orthotropic behavior, are highlighted. The obtained results show the large variability of the identified parameters and reveal a significant identification sensitivity to the measurement points geometric coordinates’ uncertainties. The use of the generalized Polynomial Chaos method allows robust identification with an interesting computing time reduction regarding the Latin Hypercube Sampling.

Study of equivalent mechanical properties on pyramidal lattice materials

The equivalent mechanical properties of pyramidal lattice materials were established by theoretical analysis and numerical simulation. According to the deformation of pyramidal unit cells and multi-layered pyramidal materials under the action of vertical, horizontal, and shear forces, the equivalent elastic modulus, equivalent shear modulus, and equivalent Poisson’s ratios of pyramidal lattice materials in three main directions were derived. The influence of the unit cell parameters on the equivalent elastic modulus, shear modulus, and Poisson’s ratios were analyzed at constant relative density of the material. With the increase of the inclination angle of the strut, the equivalent elastic modulus in the z-direction(Ez ) increases, and the equivalent elastic modulus in the x-direction(Ex ) and y-direction(Ey ) first increases and then decreases; the equivalent shear modulus in the x-y plane (Gxy ) decreases, while the equivalent shear modulus in the x-z plane (Gxz ) and y-z plane (Gyz ) first increases and then decreases; the equivalent Poisson’s ratios νzx , νzy increases, while νxy , νyx , νxz , νyz decreases. The size of the unit cell did not affect the equivalent elastic properties of the material, and the axial and flexural deformations of the struts are considered in displacement calculation. The solutions of analytical and numerical of the equivalent mechanical parameters were very close, and the results of the equivalent model agree well with the exact numerical model results, which proves the rationality of the homogenized equivalent method and can realize the cross-scale characterization and analysis of the pyramidal lattice materials. Highlights The equivalent mechanical expression of multi-layered pyramidal lattice material Relationship between equivalent mechanical parameter and struts inclination angle Solution of the equivalent stiffness matrix of multi-layered pyramidal materials Numerical calculation of the exact finite element and the equivalent models

Numerical Study on Anisotropy of the Representative Elementary Volume of Strength and Deformability of Jointed Rock Masses

Representative elementary volume (REV) is a significant parameter in analyzing the size effect and the continuous media theory of natural jointed rock masses. Generalized RVEs, which include the REV of jointed rock masses (RREV) and the REV of mechanical parameters of jointed rock masses (PREV), were introduced and investigated based on the anisotropy of natural jointed rock masses. A two-dimensional model was developed based on the available geology, material heterogeneity and Monte Carlo simulation of joint network. The size effect and anisotropy of the elastic modulus and the uniaxial compressive strength (UCS) of jointed rock masses were investigated, and then, the PREV was determined. Numerical results showed that the PREVs for both the elastic modulus and UCS exhibited strong anisotropy. The RREV dimension was determined as 14 × 14 m based on the PREV of different rotational directions. The equivalent mechanical parameters of the elastic modulus and UCS were determined for different rotational directions. It is suggested that the anisotropy of the PREV should be considered when the RREV and corresponding equivalent mechanical parameters are assessed.

Simulation Research on Defect Detection of Plate Weld Based on Sensitivity Analysis

In order to improve the efficiency of traditional local non-destructive testing method in detecting the defects of large plate welds and obtain the equivalent mechanical parameters of weld defects, a method for detecting plate weld defects based on local vibration area sensitivity analysis is proposed. This method does not need to pay attention to the specific form of the weld defect, and it regards the defect as a reduction in the local Young’s modulus. A plate welding model was established in ABAQUS finite element software to simulate the detection process of different defect positions and different defect levels. The results show that the sensitivity matrix constructed with the elastic modulus of 5% change can be applied to the detection of defects with a degree of 3% to 20%. It shows that the proposed method can be used to locate and quantify weld defects with sufficient accuracy.

Vibration Analysis of Composite Multilayer Floor of High‐Speed Train

Mechanical properties of floor prototypes made for high‐speed trains from composite multilayer floor structures of different materials and thicknesses were tested. Based on the test results, the equivalent mechanical parameters of different layers of the panels, core materials, etc., were calculated, and the multilayer mixed finite element model of the floor was built and verified. The multilayer mixed floor model was introduced into the car body of a high‐speed train, and the test signals of the high‐speed train were used as inputs to calculate the vibration response of composite floor structure. Vibration spectra of the high‐speed train composite floor made of different materials and structures were compared and analyzed. The results show that the calculation of the floor vibration response of the vehicle car body within the framework of the equivalent model of the multilayer structure based on the mechanical performance test is an effective method to evaluate vibration characteristics. The vibration isolation performance of the stainless steel panel floor is better than that of the aluminum alloy panel, but its large mass is not favorable in lightweight body design. The vibration energy of birch core material floor is significantly smaller than the alder core material of the same size. The vibration isolation performance of the floor enhanced with the increase in the thickness of the outer metal panel, but when the outer metal panel thickness exceeds 0.8 mm, the influence becomes small. Therefore, the stainless steel‐birch core composite floor with a large panel thickness has the best vibration isolation performance and can be used for the floor above the bogie and the suspended excitation source. Then, an optimal analysis considering mass and vibration characteristics was carried out, and the results show that there exists an optimal solution for the high‐speed train. Regarding the overall design basis of the vehicle, the aluminum alloy panel lightweight structure can be used in combination with other general parts.

Equivalent Modeling Method and Experimental Verification of Honeycomb Sandwich Panels

In this paper, the sandwich panel theory of honeycomb sandwich panel is applied to the finite element model of solar wing veneer. The equivalent mechanical parameters are extracted by its equivalent calculation equation, and then the model of solar wing veneer is completed by applying specific boundary conditions. The dynamic analysis of the solar wing veneer structure is carried out, and the first 5 order modal frequencies and their vibration nephogram are obtained. The modal frequency and mode shape of the test are obtained by modal test of the solar wing veneer. Comparing the simulation results with the experimental results, it is found that the first five-order modal frequency error is less than 11 %, and the simulation results are in good agreement with the experimental results. The results show that the equivalent accuracy of sandwich panel theory is very high, and the design and analysis time can be saved in the allowable calculation error range, which provides important support and reference for the honeycomb structure design of solar wing.