Showing papers in "Mechanics of Advanced Materials and Structures in 2022"

Mechanical and microstructural properties of expanded polyethylene powder/mica filled hybrid polystyrene composites

Abstract: Abstract In this study, expanded polyethylene powder (EPE) and mica mineral were utilized in varying proportions as fillers in a solvated polystyrene-based resin (PBR) matrix. The hand-lay-up composites and resin were characterized using FTIR, SEM-EDS, and hardness tests. FTIR spectra revealed that chemical interactions exist between the filler(s) and the PBR matrix. SEM analysis showed that by increasing the concentration of mica in the matrix, the roughness of the composite’s surface increased. The hardness test showed that increasing the concentration of the mica mineral and decreasing the concentration of EPE in the resin matrix improved the hardness of the composite. GRAPHICAL ABSTRACT

Mechanical properties of carbon/glass fiber reinforced polymer plates with sandwich structure exposed to freezing-thawing environment: Effects of water immersion, bending loading and fiber hybrid mode

Abstract: Abstract In this article, two kinds of carbon/glass fiber hybrid rod with the sandwich structures were designed and developed through the pultrusion technology, including the fiber random hybrid (RH) mode with multi-layer sandwich structure and fiber core-shell hybrid (CH) mode with single-layer sandwich structure. The hybrid sandwich-structure plates were prepared from the rod and immersed in bending loading, temperature alternating and sustained water immersion as long as 360 days. The effect of fiber hybrid mode/sandwich structure on the degradation mechanism of mechanical properties was revealed through the digital image correlation and thermogravimetric analysis. Through the fiber hybrid design, the strength improvement percentages of RH plates with multi-layer sandwich structure were up to ∼50% (tensile strength), 30 ∼ 40% (flexural strength) and 18% (in-plane shear strength) compared to CH plates with single-layer sandwich structure. Higher bending loading level brought about the decrease of flexural strength and in-plane shear strength close to 18% and 19%, respectively. During the immersion, microcracks or microvoids formed and expanded in the resin tensile area under the bending loading and water diffusion, leading to the uncoordinated stress concentration for single-layer sandwich-structure CH plate. By uniformly dispersing carbon fibers into glass fibers, the uneven interface stress concentration can be effectively alleviated for multi-layer sandwich-structure RH plates. The comparison of mechanical properties with the others’ work showed the interface shear strength was more sensitive to the bending loading and immersion temperature. The long-term life prediction showed the maximum increase percentages of mechanical properties of multi-layer sandwich structure were 435.4% (tensile strength) and 149.2% (flexural strength) and 110.7–114.2% (shear strength) compared to the single-layer sandwich structure.

Differential quadrature technique for frequencies of the coupled circular arch–arch beam bridge system

Abstract: Abstract This study is appointed to discover the dynamic behavior related to one of the most applicable systems used in engineering, namely coupled beam bridge system. For this reason, the system, which is constructed by two circular arch beams and an elastic layer between them, is vibrationally investigated here. In addition, the geometrical strategy is hired to modify the essential position associated with the situation of the two beams lying on each other. Moreover, the first-order shear deformation theory (FSDT) and the cylindrical panel scheme are employed to discover the fundamental features of the relationships linked to the system. Moreover, by engaging Hamilton’s principle and part-by-part integration (or Green–Gauss theory), the governing equations related to the motion of the system are achieved. Furthermore, the robust semi-analytical technique, renowned by the generalized differential quadrature operator is executed to split up the motion equations linked to the system. Additionally, to confirm the offered configuration, some benchmarks are chosen and solved. Finally, the influence of the diverse boundary conditions, geometrical characteristics, and different values related to the elastic mid-layer stiffness on the natural frequencies of the coupled circular arch–arch beam bridge system are determined.

On vibrational-based numerical simulation of a jet engine cowl shell-like structure

Abstract: Abstract The present research proposes an applicable and impressive analytical model of Aircraft Engine Cowl (AEC) due to auspicate its frequency parameter. For the first time, the authors configured the structure of AEC by joining two well-known shapes of shell, including elliptical and conical. This procedure is implemented by obtaining the governing motion organization of differential equations affiliated with the Joined Elliptical-Conical Shells (JECS) in line with first-order shear deformation theory (FSDT) and General Shell Formulation (GSF). Moreover, Functionally Graded Materials (FGMs) with various spreading forms along the structure’s thickness are used to enhance the dynamic performance of AEC. It is worth mentioning that the recognized Rule of Mixture (RM) is engaged for achieving the equivalent mechanical characteristics of FGM. Finally, a well-known semi-analytical Generalized Differential Quadrature (GDQ) procedure is hired to extract the resulting system of motion equations to access the free vibration responses of AEC with diverse Boundary Conditions (BCs). It is worth mentioning that an applicable and interesting numerical model is done to inspect the remnants of geometric and material features on the oscillation demeanor of AEC structures. It will be verified that the projected procedure can be helpful for AEC’s vibration analysis and extendable for other types of studies to predict the AEC structure's static and dynamic treatment.

Improved output force response speed of the biological gel artificial muscle prepared from carboxylated chitosan and sodium carboxymethyl cellulose

Abstract: Abstract A high response speed biological gel artificial muscle (BGAM) with a networked pore structure is proposed. The BGAM is prepared from carboxylated chitosan and sodium carboxymethyl cellulose. For the given parameters including the driving voltage and the size of the BGAM, the response speed of the BGAM in this paper is 15 times faster than the BGAM in the existing research. The best result on the response speed of 0.115 mN/s is obtained, the porosity is 18.5%, the elastic modulus is 2.73 MPa, the specific capacitance is 0.23mF/cm2. This BGAM, prepared by cross-linking natural polymers, is biocompatible and degradable.

Dynamic response of fluid-conveying hybrid smart carbon nanotubes considering slip boundary conditions under a moving nanoparticle

Abstract: Abstract The idea of transferring vital drugs through nanotubes in the human body has attracted the attention of many researchers in the field of nanomedicine. Accordingly, the main objective of this article is to investigate the forced vibration response of two hybrid smart carbon nanotubes connected using springs and conveying a nanofluid, with each one including either a piezoelectric or electrorheological fluid layer. To this aim, a slip boundary condition along with a Knudsen number is employed to address the vibration behavior of smart hybrid sandwich nanotubes acted upon by a moving sinusoidal load, while equations are derived with the aid of the Timoshenko beam model and nonlocal strain gradient theory. The former theory is complemented with hardening and softening material effects which can greatly enhance the precision of the results. Furthermore, Hamilton’s principle is implemented to obtain the equations of motion. Regarding the time response of the structure, a combination of modal analysis and the Laplace transform is applied. The accuracy of the developed procedure is verified through a set of comparisons of static deflection (as a result of a point load) and vibration frequencies. In addition, the impact of a number of parameters ranging from nanoparticle velocity to material length scale is investigated.

Low-frequency property and vibration reduction design of chiral star-shaped compositive mechanical metamaterials

Abstract: Abstract The advantage of mechanical metamaterials is that the properties can be improved at the macro level through reasonable artificial design at the micro level. Mechanical metamaterials are applied to solve the problems of vibration and noise in engineering applications. In this paper, a creative chiral star-shaped compositive mechanical metamaterial (CSCMM) is proposed by combining the chiral lattice structure and star-shaped honeycomb. The generation mechanism of the bandgap and the impaction of structural parameters are studied to obtain the low-frequency bandgap by single-phase materials. On this basis, the influence of star angle on bandgap generation and the variation of structure vibration mode during bandgap generation are studied. In addition, the phase and group velocities of elastic waves in chiral star-shaped compositive mechanical metamaterial are studied. Finally, the frequency response function (FRF) of the elastic wave propagating in the structure is calculated, and the result is consistent with the band diagram. Therefore, the design method of compositive mechanical metamaterial can effectively realize the improvement of property and reduce the attenuation of elastic waves, and it provides a new design idea for the vibration and noise reduction design of metamaterial.

Nonlinear buckling mode transition analysis in nonlocal couple stress-based stability of FG piezoelectric nanoshells under thermo-electromechanical load

Abstract: Abstract Smart materials and structures at the nanoscale represent the main components in manufacturing plan for nano-electromechanical systems. In this research study, an unconventional shell model based upon the nonlocal couple stress (NCS) continuum mechanics accommodating the both softening and stiffening features of size dependency is formulated to analyze the buckling mode transition phenomenon in nonlinear stability characteristics of functionally graded (FG) piezoelectric nanoshells subjected to thermo-electromechanical load. To accomplish this objective, an efficient numerical strategy based upon the moving Kriging meshfree (MKM) technique is employed via different nodal distribution schemes, including Chebyshev, regular uniform and irregular ones. The established NCS-based numerical model has the capability to incorporate the buckling mode transition phenomenon as well as satisfying the function property of the Kronecker delta via imposing essential boundary conditions with no use of predefined mesh and directly at the associated nodes. It is also demonstrated that by changing the sign of electric actuation from negative to positive, the softening character of nonlocality as well as the strengthening character associated with the couple stress size dependency become a bit more significant. Furthermore, the roles of both unconventional stress tensors are more prominent in the value of the second bifurcation point in comparison with the first one.

Investigation of the energy absorption capacity of foam-filled 3D-printed glass fiber reinforced thermoplastic auxetic honeycomb structures

Abstract: Abstract In this paper, the energy absorption capacity of continuous fiber-reinforced thermoplastic auxetic structures is examined experimentally and the results compared with both numerical and analytical methods. To this extent, a 3 D printing technology of Fused Deposition Modeling (FDM) is implemented for fabricating the auxetic honeycombs and quasi-static compression test is conducted to extract the load-displacement behavior of the structure. Both hollow and foam filled lattice structures are tested, and the results revealed that the absorbed energy increased by 20% for PLA and 70% for PA specimens, when using foam. Finite element analysis is also performed using the explicit solver. The onset of failure is determined using the maximum stress criterion and VUSDFLD subroutine and the damage growth is modeled by decreasing the mechanical properties of the elements. The obtained results are in relatively good agreement with the experimental analysis. In addition, a theoretical formulation is developed and the probabilistic analysis is performed to draw the honeycomb failure design envelope, which is a practical tool for designing of various honeycomb configurations. The failure envelope shows that decreasing the strut angle increases the honeycomb failure load, however, the auxetic property of the structure decreases.

Dynamic stability of hybrid fiber/nanocomposite-reinforced toroidal shells subjected to the periodic axial and pressure loadings

Abstract: Abstract In this article, the dynamic instability of the hybrid fiber/nanocomposite-reinforced toroidal shells is investigated. By using the approximation of Fourier series and applying the Galerkin method, a semi-analytical solution is achieved. The proposed method provides an accurate assessment of the dynamic stability of the shell with no computational costs in comparison to the numerical methods. By comparing the obtained results for some examples with those available in the present literature, the accuracy of present formulation is approved. In order to evaluate the effects of geometrical and mechanical specifications on the dynamic instability of the proposed shells, a comprehensive parametric study is performed, as well.

Investigation on the interphase effects on the energy harvesting characteristics of three phase magneto-electro-elastic cantilever beam

Abstract: Abstract In this work the influence of the interphase region in a three-phase magneto-electro-elastic composite material on the energy harvesting characteristics of a vibration based cantilever beam is studied analytically. The three-phase composite made of Barium Titanate/Terfenol-D/Cobalt Ferrite with different interphase regions have been considered for the evaluation. The mathematical expressions for the coupled governing equations are derived through a lumped parameter model in conjunction with Gauss's Law, Newton's Law and Faraday's Law. The generated electric and magnetic potential are harvested through the surface electrodes and a wound coil. The numerical results suggest that the interphase volume fraction and composition adversely affect the coupled material properties, which in turn significantly alters the output response of the energy harvester. Also, the lower values of resistance and number of turns of coil have a predominant effect on the energy harvester's performance. The results of this work demonstrate the significance of the interphase region and its effects on the coupled energy harvesting behavior in multifunctional composite materials.

Simulation of bridging mechanisms in complex laminates using a hybrid PF-CZM method

Abstract: Abstract Delamination and cracking of matrix/fiber is a common failure phenomena reported in fiber reinforced composite materials. As complex stress states develop in laminated structures, they are prone to develop fracture phenomena. Therefore, designs with large damage tolerance are currently implemented in most of the industrial sectors. This can be achieved by designing such materials with superior fracture resistance, which requires a comprehensive understanding of failure mechanisms. Cohesive Zone Models (CZM) are a popular technique to study debonding and decohesion in composite structures. Furthermore, due to the accurate simulation of complex crack paths including crack branching, the Phase Field (PF) approach has gained notable relevance in fracture studies, including the interplay between debonding and crack propagation in the matrix. In order to get a further insight into these intricate scenarios, involving bridging mechanisms in intralayer and interlayer, crack simulation coupling the phase field approach and the cohesive zone model is herein exploited for identifying crack migration through material layers. The crack paths and the related force–displacement curves of 2D multilayered material models of complex laminates are predicted and compared.

Finite element analyses of porous dental implant designs based on 3D printing concept to evaluate biomechanical behaviors of healthy and osteoporotic bones

Abstract: Abstract Conventional dense titanium (Ti) implants cause stress shielding, aseptic loosening and implant failure. This study investigates the effects of porous dental implants (63% porous and 77% porous) with different neck angles (straight, 10° and 15°) on the healthy and osteoporotic bone under different loading conditions (axial load and buccolingual load). Simulation results showed that in cortical bone, the von Mises stresses are greater in the case of 77% porous Ti implant A (straight) as compared to implant B and C (10°, 15° angled neck). Overall, in the case of the osteoporotic bone, the strains are higher than the healthy bone.

Vibro-acoustic analysis of the sound transmission through aerospace composite structures

Abstract: Abstract An in-plane honeycomb sandwich structure used in aerospace applications has been modeled, in order to study the structural-acoustic performances of the sandwich panel using a finite element analysis software. A modal and steady state analysis were conducted to investigate the vibro-acoustic and sound transmission characteristics of the sandwich panel. Several materials used in aerospace composite structures were tested to compare their acoustic performances and to deduce which material have a good acoustic insulation property. Two different cases of structural acoustic design, were performed in this research taking into account the effect of changing material, thickness of skins and the total mass on the sound transmission characteristics of the sandwich panel through varying the effective properties without compromising the mass of the panel in case of the first design. In case of the second design, we consider the thickness of skins as constant. The results reveals that the glass fiber reinforced polymer (GFRP) cores with fiber-reinforced plastic (FRP) facing materials have a better vibro-acoustic and sound transmission characteristics comparing to all other design cases presented in this article. GFRP cores with an FRP facing can replace the aluminum materials without affecting the acoustic performances of the panel with a mass reduction of the panel.

Structure design of arc-shaped auxetic metamaterials with tunable Poisson’s ratio

Abstract: Abstract Metamaterials with negative Poisson’s ratios, showing unusual properties, are worth studying and tunability for Poisson’s ratio is still a difficult problem. In this study, a 2 D/3D arc-shaped lattice metamaterial with tunable Poisson’s ratio is designed and fabricated by additive manufacturing technology. Experimental and numerical results indicate that structures with distinct geometric features exhibit different auxetic effects, which is attributed to the deformation mode shifting from bending to stretching of the arc-shaped beams. In the bending deformation stage, the designed structure exhibits a constant negative Poisson’s ratio. In the stretching deformation, Poisson’s ratio begins to increase. The calculation formula of Poisson's ratio has been theoretically deduced for auxetic metamaterial and verified by experiments and simulations. The Poisson’s ratio of structure can be designed by adjusting the angle of the arc-shaped ligaments. Three-dimensional (3 D) auxetic structures are designed by the periodic distribution of 2D structures horizontally and vertically, and exhibit auxetic behavior perpendicular to the loading direction. The results of 2D structures also can be applied to 3 D structures. The Poisson's ratio can also be adjusted by changing geometric parameters of 3D structures. These findings can offer new insight for the design and manufacturing of metamaterials with negative Poisson’s ratio.

Electric field-induced nonlinear behavior of lead zirconate titanate piezoceramic actuators in bending mode

Abstract: Abstract In this article, analytical solutions of piezoelectric bimorph and unimorph actuator in cantilever configurations are developed using the second-order constitutive equation. Tip deflection ratio (TDR), a dimensionless parameter, is defined to analyze the effect of second-order coefficients of piezoelectric materials on the response of bimorph and unimorph actuators. Four piezoelectric unimorphs of varying geometries are fabricated and tested to verify the nonlinear response under applied electric field. Furthermore, second-order coefficients of lead zirconate titanate (PZT; APC 850) are derived by fitting the experimental data with nonlinear analytical solution. The nonlinear response of all the piezoelectric unimorphs compares well with the experimental results.

Numerical simulation of deployable ultra-thin composite shell structures for space applications and comparison with experiments

Abstract: Abstract In the present article, the geometrical nonlinear behavior of deployable booms undergoing large displacements and rotations is investigated. The triangular rollable and collapsible boom made of fiber-reinforced composite materials is considered along with a metallic tape spring. The mathematical model makes use of higher-order 1D structural theories based on the Carrera unified formulation, which allows the description of moderate nonlinearities to deep post-buckling mechanics of ultra-thin shells in a hierarchical and scalable manner. Particular attention is focused on the study of equilibrium paths of the booms subjected to coiling bending. Dedicated experimental tests reveal the validity of the proposed finite element approach, whereas the investigation of different lamination sequences offer a valuable perspective for possible future designs.

Modification of hexachiral unit cell to enhance auxetic stent performance

Abstract: Abstract Stents possess disadvantages such as foreshortening and dogboning. Material selection alongside topological modifications are two main approaches to overcome these issues. Stents with negative Poisson’s ratio, also known as auxetic property, can lead to promising performance improvement. Therefore, in this study, three stents were designed by improving a hexachiral unit cell and underwent numerical and experimental investigations using CoCr 605 L and SS 316 L alloys. The modified auxetic stents presented higher auxeticity and NPR of −0.64 and −0.69. Higher radial expansion, stress tolerance and yield strain of these modified stents help them overcome drawbacks of non-auxetic stents.

Forced vibration analysis of multi-degree-of-freedom nonlinear systems with the extended Galerkin method

Abstract: Abstract In this study, the dynamic response behavior of a generalized nonlinear dynamic system is investigated using a newly proposed extended Galerkin method. The algebraic equations of vibration amplitudes are obtained through an integration of the weighted functions. The new method is equivalent to the harmonic balance method but with a much simpler calculation procedure and a higher efficiency. This is the first time to use the method for the analysis of nonlinear systems with high number of modes, manifesting that the method is applicable to forced vibrations of nonlinear behavior. The method is further validated by the numerical Runge-Kutta method.

Study on theoretical modeling and mechanical performance of a spinning porous graphene nanoplatelet reinforced beam attached with double blades

Abstract: Abstract In this article, theoretical modeling and vibration characteristics of a spinning double-blade beam assembly restricted by elastic supports are studied. Graphene nanoplatelet (GPL) reinforcement and porous foamed metal matrix are adopted to make up the assembly structure. Due to the nonuniformity of the porosity and graphene nanofillers, the material properties of the attached blades and beam are considered to change along the blade thickness and beam radius, respectively. They are obtained via the rule of mixture, the open-cell scheme and the Halpin-Tsai micromechanics model. These attached blades and beam are modeled in accordance with the Euler-Bernoulli beam theory and the Rayleigh beam theory, respectively. Via employing the Lagrange’s equation, the equations of motion of the double-blade beam are derived. Then, the natural frequencies of the spinning nanocomposite double-blade beam are calculated by the substructure modal synthesis method and the assumed modes method. A detailed parameter analysis is performed to study the influences of dimension, distribution pattern and weight fraction of GPLs, distribution and coefficient of porosity, length and location of the blades, stiffness and location of supports, and spinning speed on the mechanical behaviors of the double-blade beam assembly.

Numerical prediction of various defects and their formation mechanism during friction stir welding using coupled Eulerian-Lagrangian technique

Abstract: Abstract Defective weld significantly hampers the quality of the weld and selection of optimum process parameter which produces defect-free weld is an experimental tedious task. A robust numerical model capable of predicting various types of defects is required to save cost and time. In the current work, a numerical model is developed based on coupled Eulerian-Lagrangian method and the concept of Volume of Fluid is incorporated to predict defects. It is the first attempt to numerically predict and analyze various types of defects such as tunnel, void, cavity, and root defects associated with friction stir welding. Defect formation is studied by varying tool rotation speed from 600 to 1500 rpm, welding speed from 30 to 180 mm/min, and tilt angle from 0 to 3°. The tilt angle of zero degree resulted in tunnel defect and one degree resulted in void and cavity. Tilt angle of two degree produced a defect-free weld. Also, parameters with a three-degree tilt angle yielded defective welds. The defect formation mechanism is correlated with temperature history, material flow, and axial force. A process parameter window is developed indicating the defective and non-defective weld conditions.

Thermoelastic stability of CNT patterned conical shells under thermal loading in the framework of shear deformation theory

Abstract: Abstract This study presents the thermoelastic stability of carbon nanotube (CNT) patterned composite conical shells in the framework of shear deformation theory (ST). The study includes two different boundary value problems. As the material properties are independent of temperature, the truncated conical shell is assumed to be under thermal load, and when the material properties are temperature dependent, the conical shell is assumed to be under axial compressive load. The modified Donnell-type shell theory is used to derive the basic equations for CNT patterned truncated conical shells. The Galerkin method is applied to the basic equations to find the critical temperature and critical axial load expressions of CNT patterned composite truncated conical shells in the framework of ST. The effect of changes in CNT patterns, volume fraction, radius-to-thickness and length-to-thickness ratios, as well as the half-peak angle on critical parameters within the ST, are estimated by comparison with classical shell theory (CT).

Applying a novel slime mould algorithm- based artificial neural network to predict the settlement of a single footing on a soft soil reinforced by rigid inclusions

Abstract: Settlements are one of the most important performance indicators for designing footings over soft soils reinforced by rigid inclusions (RI). Although traditional numerical approaches can effectively calculate settlements, the necessary time calculation is important as this problem is a three dimensional one. In this investigation, 369 numerical simulations based on a finite difference (FD) approach were completed to build a database. The collected data include a variation of the footing loading (L), thickness of the load transfer platform (TH), load eccentricity (LE), Young's modulus (E), cohesion (C) and friction angle (F) of the load transfer platform granular material and the compression ratio (CR) of soft soils are input variables. and the settlements are considered as the output variables. Extreme learning machine (ELM), Elman neural network (ENN), generalized regression neural network (GRNN), support vector regression (SVR), Artificial neural network (ANN) and a hybrid model of Slime Mold algorithm- based artificial neural network (SMA-ANN) were used to predict the settlements of a single footing on soft soil reinforced by rigid inclusions. Six performance indicators including the root mean square error (RMSE), the determination coefficient (R2), the mean absolute error (MAE), the prediction accuracy (U1), the prediction quality (U2) and the variance accounted for (VAF) are proposed to compare the performance of all the proposed models. The results show that the SMA-ANN was the best model for predicting the settlement of a single footing on a soft soil reinforced by rigid inclusions. The most important input parameters are the friction angle, cohesion and young modulus of the load transfer platform.

New auxetic materials with stretch-dominant architecture using simple trusses

Abstract: Abstract Cellular auxetic materials, as a group of metamaterials, have received much interest due to their promising mechanical properties in various applications. The main shortcomings of cellular auxetic materials are their low stiffness and strength, due to a bending-dominant architecture. Here, a novel concept to design auxetic stretch-dominated structures is presented. Three example structures are analyzed in detail, to demonstrate the tunability and extensive range of positive and negative Poisson’s ratio for these structures. Results show that the relative stiffnesses of the three test structures are several times higher than those of previously reported auxetic structures, for example, reentrant models.

Crashing performance and multi-objective optimization of honeycomb-filled thin-walled energy absorber with axisymmetric thickness

Abstract: Abstract Improving the crashing performance of energy-absorbing structure is of vital significance for the safety of subways. To this end, a new type of honeycomb-filled thin-walled energy absorber with axisymmetric thickness (HTEA-AT) was proposed. Unlike the honeycomb-filled thin-walled energy absorber with uniform thickness (HTEA-UT), the thicknesses of adjacent tube walls of HTEA-AT were defined as independent variables, while the thicknesses of the opposite walls remained identical. Numerical, theoretical and experimental methods were adopted to systematically investigate the crushing mechanics of the honeycomb-filled thin-walled energy absorber (HTEA). To improve the crashworthiness of HTEA-AT and HTEA-UT, a multi-objective optimization design (MOD) was carried out. The results revealed that HTEA-AT has a lower peak force and higher energy absorption than HTEA-UT, achieving superior crashworthiness performance. In addition, a multi-criteria decision-making method combining integrated entropy and gray relational analysis (GRA) was introduced to seek the ideal balance between the energy absorption (EA) and initial peak crushing force (IPCF) in the Pareto front. The optimized results indicated that the gray correlation was the largest at optimal point C, where EA and IPCF reached a balance (EA = 177.82 kJ, IPCF = 430.03 kN). This means that the optimized configuration can provide insightful information for the crashworthiness design of the energy-absorbing structure at the end of subways.

Comparison and identification of efficient nanoparticles to improve the impact resistance of glass/epoxy laminates: Experimental and numerical approaches

Abstract: Abstract This research has studied the low-velocity impact (LVI) response of glass-epoxy composite laminates reinforced with different percentage of carbon nanotube (CNT) and nanoclay particles. The obtained results facilitate industrialists’ decision-making on selection of high-performance and cost-effective nanoparticles. Through quasi-static indentation (QSI) tests, the optimal percentages of nanoclay, and CNT were identified, and the impact test was performed on them at wide range of energies. Three key indexes were presented to evaluate the composite resistance against impact loads. The results indicate that both types of nanoparticles have contributed to an improvement in impact resistance. Moreover, a finite element analysis was performed using Abaqus/Explicit package, in which the results were in good agreement with experimental values.

Crashworthiness analysis and optimization of lotus-inspired bionic multi-cell circular tubes

Abstract: In this paper, inspired by the structural characteristics of lotus, a lotus-inspired bionic multi-cell tube (LBMT) is proposed. The theoretical model of is devised to predict the mean crushing force of LBMT. Moreover, finite element model is established and validated with experimental test. The results indicate that LBMT exhibit superior energy absorption behavior than that of traditional multi-cell tubes. Furthermore, the effect of geometric parameters μ on crashworthiness behavior has been investigated. Finally, a multi-objective optimization is conduct to obtain the Pareto front. The findings of this investigation offer a novel route of designing energy-absorbing device with excellent crashworthiness behavior.

Intelligent monitoring and residual analysis of tunnel point cloud data based on free-form approximation

Abstract: Abstract With the rapid development of urban rail transit and the aging of transportation infrastructure, the demand for shield tunnel disaster detection is about to break out. Most of the traditional monitoring methods require considerable manpower and time costs, which cannot satisfy the increasing requirements of tunnel operation and maintenance. Free-form model construction and deviation mechanism analysis are investigated in this paper to monitor the geometric deformation information of shield tunnels quickly and accurately. A method for identifying geometric features of tunnel sections based on the free-form B-spline approximation is proposed. The innovation of this paper lies in the intelligent recognition of common interference targets by the residual classification method. Furthermore, various Root Mean Squared Error (RMSE) distributions are investigated, which successfully realizes and verifies the clustering analysis of certain point cloud features.

Thermal-vibration aging of fiber-reinforced polymer cylindrical shells with polyurea coating: Theoretical and experimental studies

Abstract: Abstract Polyurea coating (PC) is a promising surface treatment technology for improving structural static and dynamic mechanical properties in a thermal environment. However, rare studies have been reported on thermal-vibration aging issues of composite shell structures treated with polyurea coating. In this paper, the thermal-vibration aging behaviors of fiber-reinforced polymer (FRP) cylindrical shells with PC are investigated both experimentally and theoretically. Initially, thermal-vibration aging experiments are performed on the four FRP cylindrical shell specimens with or without polyurea coating. The natural frequency and dynamic stiffness values of the specimens are achieved to estimate their aging behaviors, from which the dynamic aging resistance of PC is quantitatively determined. Then, an aging model for PC- FRP cylindrical shells subjected to impulse excitations in a uniform thermal environment is proposed on the basis of the first-order shear deformation theory, the multi-segment partition technique, and the virtual spring technology. The dynamic elastic moduli of FRP and PC materials are assumed to be functions of temperature change and aging time simultaneously, and the equations of motion involving thermal aging effect are derived for predicting the natural frequencies and dynamic stiffness functions. After the iterative identification principle of fitting coefficients of FRP and polyurea materials is clarified based on the artificial bee colony algorithm, the present model is verified against the experimental results when investigating the thermal-vibration aging behaviors of two new specimens. Finally, by employing the validated model, the influences of critical geometric and material parameters of the PC-FRP cylindrical shell structures on dynamic aging behavior are discussed to reveal their aging mechanism and to improve the thermal-vibration aging resistance.

Analysis of metallic and functionally graded beams using isogeometric approach and Carrera Unified Formulation

Abstract: Abstract This paper investigates the bending and vibration characteristics of metallic and functionally graded (FG) beam structures. The weak form of governing equations and boundary conditions are derived using Carrera unified formulation (CUF). The isogeometric analysis (IGA) is employed to solve the static and free vibration problems. NURBS basis functions approximate the displacement field unknowns and material gradations in cross-section. In contrast, the axial displacements are evaluated by either NURBS or Lagrange basis functions. In this framework, the equations are extracted in the form of a fundamental nucleus, which allows the study of different beam theories in a constant formulation. Several numerical examples are presented and compared with results available in the literature to address the accuracy and effectiveness of the current approach. It is found that the present results are validated for different aspect ratios, boundary conditions, and material distribution with more accuracy and low computational cost.