Showing papers in "Thin-walled Structures in 2021"
TL;DR: Auxetic materials and structures have attracted increasing attention because of their extraordinary mechanical properties as discussed by the authors, and various types of auxetic tubular structures have been designed and studied in diverse fields, including mechanical and medical engineering.
Abstract: Auxetic materials and structures have attracted increasing attention because of their extraordinary mechanical properties. Various types of auxetic tubular structures have been designed and studied in diverse fields, including mechanical and medical engineering. In this paper, design methods and advanced manufacturing technologies of auxetic tubular structures are extensively reviewed, including various types of cellular auxetic tubes, nonporous and porous auxetic tubes, macro and micro auxetic tubes. Furthermore, auxetic behaviour, mechanical properties and potential applications of auxetic tubular structures are elaborated. Finally, the challenges and opportunities on the auxetic tubes are discussed to inspire future research work.
117 citations
TL;DR: A critical review of the state of art materials in the categories such as metals and alloys, polymers, ceramics, and biomaterials are presented along with their applications, benefits, and the problems associated with the formation of microstructures, mechanical properties, and controlling process parameters.
Abstract: Additive Manufacturing (AM) is the significantly progressing field in terms of methods, materials, and performance of fabricated parts. Periodical evaluation on the understanding of AM processes and its evolution is needed since the field is growing rapidly. To address this requirement, this paper presents a detailed review of the Additive Manufacturing (AM) methods, materials used, and challenges associated with them. A critical review of the state of art materials in the categories such as metals and alloys, polymers, ceramics, and biomaterials are presented along with their applications, benefits, and the problems associated with the formation of microstructures, mechanical properties, and controlling process parameters. The perspectives and the status of different materials on the fabrication of thin-walled structures using AM techniques have also been discussed. Additionally, the main challenges with AM techniques such as inaccuracy, surface quality, reinforcement distribution, and other common problems identified from the literature are presented. On the whole, this paper provides a comprehensive outlook on AM techniques, challenges, and future research directions.
95 citations
TL;DR: In this paper, a modified porosity-dependent power-law function is used to estimate the effective mechanical properties of PFGM micro/nano-plates with various porosity distribution patterns.
Abstract: The prime objective of the present investigation is to analyze the nonlinear buckling and postbuckling characteristics of micro/nano-plates made of a porous functionally graded material (PFGM) in the presence of nonlocality and strain gradient size dependencies. In accordance with this purpose, a modified porosity-dependent power-law function is put to use to estimate the effective mechanical properties of PFGM micro/nano-plates with various porosity distribution patterns. To solve the constructed nonlinear nonlocal strain gradient problem, the non-uniform rational B-spline (NURBS)-based isogeometric analysis is utilized as an efficient discretization technique. It is concluded that by taking the geometrical nonlinearity into account and moving to deeper part of the postbuckling regime, the significance of the both nonlocality and strain gradient size dependencies decreases. Also, by increasing the material property gradient index, an enhancement in the nonlocal and strain gradient size effects is found which is more considerable at deeper part of the postbuckling domain. In addition, it is demonstrated that for a PFGM micro/nano-plate, the value of the porosity index has a negligible influence on the significance of size dependencies, and this observation is the same for the both types of simply supported and clamped boundary conditions.
84 citations
TL;DR: In this article, the impact behavior of composite sandwich panels with different types of auxetic (negative Poisson's ratio) and non-auxetic prismatic core structures is described.
Abstract: This work describes the low-velocity impact behavior of composite sandwich panels with different types of auxetic (negative Poisson’s ratio) and non-auxetic prismatic core structures Sandwich panels have been manufactured with carbon/fiber epoxy composite face sheets, polyurethane rigid foam core or 3D printed PLA plastic cellular honeycombs head (hexagonal, re-entrant, hexachiral and arrowhead) The material properties of the constituents have been determined via tensile and compression tests The cellular core topologies have the same wall thickness and number of cells (39x4, except for the hexachiral topology) A rigid striker with a hemispherical head tip is dropped on the specimens with a speed of 26 m/s Explicit finite element (FE) models are validated by the experimental results Parametric numerical analyses using the validated FE have been carried out with different impact energies of 10, 20, 30, 40, 50, 60 and 76 J to identify the best core designs The results show that non-auxetic cores could have advantages over the auxetic ones at small deformation (impact energy is equal to 10 J) thanks to the larger contact surface and higher thickness of the cellular structure The auxetic core, however, provides greater impact resistance and energy absorption capability as the impact energy increases due to the larger densification and lower indentation during collapse The arrowhead-based panels in particular possess 25%, 13% and 11% larger crash efficiency than the other samples for impacts with 50, 60 and 76 J The hexachiral lattice provides the best performance at 10, 20 and 30 J, and also possesses advantages over the other cellular configurations (except for the arrowhead core) in the case of 40, 50, 60 and 76 J impact loading As a result, the arrowhead and hexachiral configurations are those mostly recommended for applications involving impacts under large deformations
67 citations
TL;DR: In this paper, the failure process of an electromagnetic self-piecing riveted-bonded hybrid joint could be divided into two parts: adhesive failure firstly and then rivet failure.
Abstract: riveted–adhesive hybrid joining technique is suitable for joining dissimilar material due to excellent performance and tightness of the joint. In this paper, electromagnetic self-piecing riveted–adhesive hybrid joining method was proposed to join Al/steel structure. The mechanical properties and failure behavior of electromagnetic self-piecing riveting, adhesive and its hybrid joints were compared. The shear tests were conducted, and digital image correlation (DIC) technique was employed to analyze the strain of the sheets. The typical failure fracture was observed to reveal the failure mechanism. The results showed that the peak load of the hybrid joint was 177.3% larger than that of the riveted joint, and the energy absorption of the hybrid joint was 360.0% and 47.9% higher than that of the riveted and bonded joint respectively. The failure process of electromagnetic self-piecing riveted–bonded hybrid joint could be divided into two parts: adhesive failure firstly and then rivet failure. The rivet in hybrid joint after adhesive failure could still suffer a certain amount of load, so that suddenly complete failure was not easy to happen. This indicated that the hybrid joint had better reliability and security. In general, the combination of electromagnetic self-piecing riveting and adhesive bonding could produce beneficial coupling effect.
64 citations
TL;DR: In this paper, the authors investigated the nonlinear forced vibration of GPLRMF rectangular plates in primary, super-harmonic, and subharmonic resonances of this novel nanocomposite structure.
Abstract: Nonlinear forced vibration of graphene platelet reinforced metal foam (GPLRMF) rectangular plates is investigated. Attention is focused on the primary, superharmonic, and subharmonic resonances of this novel nanocomposite structure. Three kinds of graphene platelet (GPL) pattern and three kinds of porosity distribution are taken into account. Based on the von Karman nonlinear plate theory, governing equations and general boundary conditions of the GPLRMF plates are obtained via Hamilton’s principle. By introducing stress functions, nonlinear ordinary differential equations of the plates are obtained by using the Galerkin method. Then, frequency–response and force–response relationships of the GPLRMF plates are solved by applying the multiple scale method. A validation study is conducted to verify the present method. Results show that GPLRMF plates exhibit hardening nonlinearity in primary and superharmonic resonances. Dispersing more small-size pores or more GPLs near the middle surface will lead to the larger vibration amplitude and resonance domain of the plates in primary and superharmonic resonances. While uniformly distributed pores or uniformly distributed GPLs will result in the larger vibration amplitude in the case of subharmonic. Moreover, change of porosity coefficient or GPL weight fraction can significantly alter the nonlinear dynamic behavior of GPLRMF plates.
63 citations
TL;DR: In this paper, the forced resonance vibration analysis of curved micro-size beams made of graphene nanoplatelets (GNPs) reinforced polymer composites is presented, which is based on the Halpin-Tsai model and a modified rule of mixture.
Abstract: In this paper, the forced resonance vibration analysis of curved micro-size beams made of graphene nanoplatelets (GNPs) reinforced polymer composites is presented. The approximating of the effective material properties is on the basis of Halpin–Tsai model and a modified rule of mixture. The Timoshenko beam theory is applied to describe the displacement field for the microbeam. To incorporate small-size effects, the modified strain gradient theory, possessing three independent length scale coefficients, is employed. Hamilton principle is applied to formulate the size-dependent governing motion equations, which then is solved by Navier solution method. Ultimately, the influences of length scale coefficients, opening angle, weight fraction and the total number of layers in GNPs on composite curved microbeams corresponding to different GNPs distribution are discussed in detail through parametric studies. It is shown that, the resonance position is significantly affected by changing these parameters.
62 citations
TL;DR: In this paper, the authors predict the size-dependent dynamic stability of truncated conical microshells made of a functionally graded material (FGM) integrated with magnetostrictive facesheets.
Abstract: The objective of this investigation is to predict the size-dependent dynamic stability of truncated conical microshells made of a functionally graded material (FGM) integrated with magnetostrictive facesheets. The microshells are subjected to a combination of axial compressive load and magnetic field in the presence of the nonlocality and strain gradient size dependencies. The conical microshells are assumed to be surrounded by a two-parameter Winkler-Pasternak medium augmented via a Kelvin-Voigt viscoelastic approach taking a nonlinear cubic stiffness into account. The nonlocal strain gradient-based differential equations of motion are constructed based upon the third-order shear deformation conical shell theory including the magnetic permeability tensor together with the magnetic fluxes. The discretization process within the framework of the generalized differential quadrature technique is employed to achieve the nonlocal strain gradient-based load-frequency responses. It is found that increasing the material gradient index results in to decrease the nonlocal strain gradient frequency obtained for a specific value of the axial compression within the prebuckling regime. However, within the postbuckling domain, an increment in the value of the material gradient index plays an opposite role. Also, the gap between the load-frequency curves associated with various material gradient indexes are more prominent for the nonlocal strain gradient cases in comparison with the classical one.
61 citations
TL;DR: In this paper, a star-circle honeycomb (SCH) was designed to improve the energy absorption capacity of the honeycomb, where double-inclined walls replacing the horizontal walls of the star-shaped honeycomb were replaced with a thin-walled circle contacting with the four concave corners of the SSH.
Abstract: In order to improve the energy absorption capacity of the honeycomb, a combined auxetic honeycomb is designed in this paper. By using the double-inclined walls replacing the horizontal walls of the star-shaped honeycomb (SSH), and introducing a thin-walled circle contacting with the four concave corners of the SSH, the star-circle honeycomb (SCH) is designed. The in-plane dynamic crushing behaviors was explored based on finite element method (FEM). There are three types of deformation modes observed with different impact velocity, including low-, medium- and high-velocity loading modes and the stress-strain curve exhibits two plateau stress stages. Based on the deformation characteristics of the representative unit, theoretical calculation models were established to estimate the plateau stress of the SCH under low- and high-velocity loading according the conservation of energy and the theoretical calculation was in keep well with the numerical simulation. A deformation modes map was summarized to investigate the effects of the impact velocity and the relative density on the deformation modes and the energy absorption capability and the dynamic Poisson's ratio were studied. The result shows that the SCH presents better energy absorption compared with SSH as well as retaining the negative Poisson's ratio property. The deformation mechanism was revealed form the structural design and plastic hinge dissipation. This work presents a different design strategy for the auxetic honeycomb, expected to guide the design of more novel auxetic with better energy absorption and mechanical property.
61 citations
TL;DR: Based on DBN prediction data, a comprehensive reliability analysis was conducted, which shows the proposed equations can predict the enhanced and reduced axial capacity of CFS channel sections with edge-Stiffened/un-stiffened web holes accurately.
Abstract: This paper proposes a framework of deep belief network (DBN) for studying the structural performance of cold-formed steel (CFS) channel sections with edge-stiffened/un-stiffened web holes, under axial compression. A total of 50,000 data points for training the DBN are generated from elasto plastic finite element analysis, which incorporates both initial geometric imperfections and residual stresses. A comparison against 23 experimental results was conducted, and it was found that the DBN predictions were conservative by 3% for columns with un-stiffened web holes, and 8% for columns with edge-stiffened web holes. When compared with Backpropagation Neural Network (a typical shallow artificial neural network) and linear regression model based on PaddlePaddle, it was found that the proposed DBN outperformed better than both the methods, using the same big training data used in this paper. When the same comparison was made for Effective Width Method and Direct Strength Method, the results from them were conservative by 5% and 12% against the experimental results, respectively for columns with un-stiffened web holes. Hole effects on the structural performance of channel sections under axial compression were also investigated. Based on the DBN output data, design recommendations of axial capacity enhancement/reduction factors were given for columns (stub, intermediate and slender) with edge-stiffened/un-stiffened web holes. Based on DBN prediction data, a comprehensive reliability analysis was conducted, which shows the proposed equations can predict the enhanced and reduced axial capacity of CFS channel sections with edge-stiffened/un-stiffened web holes accurately.
60 citations
TL;DR: In this article, the authors studied the nonlinear free and forced vibration of a cylindrical panel on visco-Pasternak foundations in thermal environment subjected to blast load and established the fundamental equations based on Reddy's higher order shear deformation shell theory.
Abstract: Recently, auxetic cellular solids in the forms of honeycombs and carbon nanotube reinforced composite (CNTRC) have great potential in a diverse range of applications. This paper studies the nonlinear free and forced vibration of sandwich cylindrical panel on visco-Pasternak foundations in thermal environment subjected to blast load The sandwich cylindrical panel consists of auxetic honeycombs core layer and two CNTRC face sheets. The Poisson’ ratio of the auxetic core is negative and the material properties of CNTRC face sheets are assumed to continuously vary in the thickness direction according to four different types of linear functions. The blast load is determined from the distance of the center of blast to center of the structure and the mass of explosive materials. The fundamental equations are established based on Reddy’s higher order shear deformation shell theory taking into account the effect of initial imperfection and visco-Pasternak foundations. The Galerkin and Runge–Kutta methods are used to obtain the nonlinear dynamic response and the natural frequency of the sandwich cylindrical panel. The numerical results show the effect of geometrical parameters, visco foundations, initial imperfection, temperature increment, nanotube volume fraction and blast load on the nonlinear vibration characteristics of the sandwich cylindrical panel. The accuracy of present approach and theoretical results is verified by some comparisons with the known data in the literature.
TL;DR: In this article, a bio-inspired fractal multi-cell circular (BFMC) tubes for energy absorption were constructed based on the fractal tree-like forms found in many biological structures such as giant water lily and dragon blood tree.
Abstract: This study proposes novel bio-inspired fractal multi-cell circular (BFMC) tubes for energy absorption. The inner structures of the proposed BFMC tubes were constructed based on the fractal tree-like forms found in many biological structures such as giant water lily and dragon blood tree. The crashworthiness performances of the proposed structures with different fractal orders and mass were numerically investigated. The numerical results indicated that the specific energy absorption (SEA) increased with the fractal order and the SEA of the 2nd-order BFMC tube was 35.43% higher than that of the conventional multi-cell circular tube. Furthermore, the complex proportional assessment (COPRAS) method was adopted to optimize the performance of the BFMC. The results demonstrated that the proposed structure with four number of tree-like branches and 2nd-order fractal provided the best performance. Finally, a theoretical derivation of the mean crushing force (MCF) was developed for the proposed tubes based on the simplified super folding element theory. The theoretical results of MCF agreed well with the numerical results. The findings of this study provide an effective guide for using the biomimetic approach with the fractal tree-like forms for the design of a multi-cell energy absorber with high energy absorption efficiency.
TL;DR: In this article, a comprehensive review on the impact characteristics of fiber metal laminates through experimental, numerical and analytical methods is provided, and some feasible methods are suggested to enhance the impact resistance of FML materials.
Abstract: Fiber metal laminates (FMLs) comprised of metal alloy and composite materials have been extensively applied in a broad range of engineering structures in virtue of their outstanding functional characteristics and cost benefits. This paper provides a comprehensive review on the state-of-the-art of the impact characteristics of fiber metal laminates through experimental, numerical and analytical methods. First, influences of various internal and external factors/parameters on the impact responses and damage mechanisms of fiber metal laminates are discussed in detail for different impact conditions. Second, a range of numerical techniques are compared to evaluate their effectiveness for modeling the impact behavior of fiber metal laminates as reported in literature. Third, analytical models and associated engineering applications of fiber metal laminated structures are also discussed. Based upon the material constituents and manufacturing techniques, some feasible methods are suggested to enhance the impact resistance of FML materials. Finally, the concluding remarks and outlooks are provided for recommending the potential future studies on novel FML materials and structures.
TL;DR: In this article, the authors presented the smart control and frequency characteristics of a graphene nanoplatelets composite (GPLRC) cylindrical shell surrounded by piezoelectric layers as sensor and actuator (PLSA).
Abstract: In this article, smart control and frequency characteristics of a graphene nanoplatelets composite (GPLRC) cylindrical shell surrounded by piezoelectric layers as sensor and actuator (PLSA) are presented. The current structure is under an external load. For the semi-numerical method, the strain-stress relations can be determined through the first-order shear deformable theory (FSDT). For access to various mass densities as well as the Poisson ratio, the rule of the mixture is applied, although the modified Halpin-Tsai theory for obtaining the module of elasticity. The external voltage is applied to the sensor layer, while a Proportional-Derivative (PD) controller has been utilized for controlling the output of the sensor. The boundary conditions are derived through governing equations of the GPLRC cylindrical shell surrounded by PLSA using an energy method known as Hamilton's principle and finally are solved using a generalized differential quadrature method (GDQM). Apart from a semi-numerical solution, a finite element model was presented using the finite element package to simulate the response of the smart GPLRC cylindrical shell. The results created from a finite element simulation illustrates a close agreement with the semi-numerical method results. The outcomes show that the PD controller, viscoelastic foundation, slenderness factor (L/R), external voltage, and GPL's weight fraction have a considerable impact on the amplitude and vibration behavior of a GPLRC smart cylindrical shell. As an applicable result in related industries, the parameter and consideration of the PD controller have a positive effect on the static and dynamic behaviors of the structure subjected to an external load.
TL;DR: In this paper, a robust Bezier-based multi-step method is extended to solve the governing fourth-order complex partial differential equation (PDE) in linear elastic fracture mechanics (LEFM) problems.
Abstract: In this study, a robust Bezier-based multi-step method is extended to accurately solve the governing fourth-order complex partial differential equation (PDE) in linear elastic fracture mechanics (LEFM) problems. The Bezier technique was first introduced by the authors to solve initial value problems in one dimension. Now, the method is further extended to simultaneously solve Boundary Value Problems (BVPs) in orthogonal directions. To examine the accuracy and performance of the present method, the first-mode normalized stress intensity factor (SIF) of a 2D epoxy resin plate having an initial edge crack and reinforced with randomly oriented graphene nanoplatelets (GnP) is determined and compared with the associated exact analytical solution using the Bayesian statistical analysis. Besides, the impact of GnP aspect ratio on the normalized crack opening displacement (COD) of the reinforced matrix is elaborated for the first time in the literature. Results of the present study suggest that GnPs with maximum aspect ratio are most effective to enhance elastic properties of the plate and potentially limit the edge crack propagation. Specifically, inclusion of 0.5 and 1.0% of needle-shaped GnPs in a notched epoxy resin plate decrease the maximum normalized COD by 33 and 50%, respectively, while for square-shaped GnPs, these reductions are limited to 20 and 37%, respectively.
TL;DR: In this paper, the impact response of the tube-reinforced honeycomb sandwich structure was investigated and the results showed that the stiffness and peak load of the honeycomb structure were increased by the metallic tube filler.
Abstract: To improve the load carrying capacity, structural stiffness, and impact resistance of a honeycomb sandwich structure, the honeycomb holes are filled with metallic tubes. Experimentally and numerically studies were carried out on the drop weight impact response of the tube-reinforced honeycomb sandwich structure. The results show that the stiffness and peak load of the honeycomb sandwich structure were increased by the metallic tube filler. The addition of tube filler made the Mises stress and deformation distribution of the front and back face-sheets more uniform. In addition, the tube-reinforced structure absorbed the impact energy more quickly than the empty honeycomb sandwich structure and the front face-sheet deformation was markedly reduced by tube reinforcement. The peak load and contact energy (the energy absorbed by the local deformation of sandwich structures) were predicted theoretically for both empty honeycomb sandwich structure and tube-reinforced honeycomb sandwich structure. The finite element parametric study shown that, compared with the empty honeycomb sandwich structure, the maximum deflections of the front and back face-sheets of the globally filled tube-reinforced honeycomb sandwich structure were reduced by 18.6% and 36.4% respectively. The tube-reinforced honeycomb sandwich structure is a promising structure for weight sensitive applications owing to its improved load carrying capacity and impact resistance.
TL;DR: In this paper, a novel bi-graded honeycomb was proposed by introducing both in-plane and out-of-plane thickness gradients into a regular honeycomb, which could improve energy absorption capacity and decrease the peak crushing force in the Pareto frontier manner.
Abstract: A novel bi-graded honeycomb was proposed by introducing both in-plane and out-of-plane thickness gradients into a regular honeycomb. The graded honeycombs were additively manufactured by fused deposition modeling (FDM) with polylactic acid (PLA) and then tested for axial crushing. Numerical simulation models were constructed through LS-DYNA and validated using experiment results. Based on the super folding element (SFE) method, theoretical models of the proposed bi-graded honeycombs were derived and the accuracy for crushing response was validated against the numerical results. Finally, an active learning based multi-objective optimization algorithm was used to seek the optimal design. The results showed that the bi-graded design for honeycomb structures could improve energy absorption capacity and decrease the peak crushing force in the Pareto frontier manner. The specific energy absorption of the optimal bi-graded honeycomb could be 45.6% higher than that of the regular honeycomb while the peak crushing force was controlled at the same level.
TL;DR: In this paper, a tubular structure with auxeticity in the wall thickness as well as in the radial direction has been proposed, which exhibits good stability under axial compression, and its inner diameter and outer diameter have opposite deformation directions.
Abstract: A novel type of tubular structure has been proposed in this paper, which is the first tubular structure with auxeticity in the wall thickness as well as in the radial direction. This tubular structure exhibits good stability under axial compression. The most innovative feature is that its inner diameter and outer diameter have opposite deformation directions. When axially compressed (stretched), its outer diameter will become smaller (larger) while its inner diameter will become larger (smaller). Besides, its closed surfaces of tube wall can broaden its applications in the fields of civil engineering and mechanical engineering. The accuracy of the finite element model was verified by comparison between experiments and numerical analysis. Deformation characteristics of tubular models generated by offset method and rotation method were studied. The influence of cell layers, PSF (Pattern Scale Factor) value and t/R (the ratio of wall thickness t to diameter R) value was also studied by parametric analysis.
TL;DR: In this paper, the behavior of cold-formed steel lipped channel beams affected by local-distortional (L-D) interaction under non-uniform bending was investigated.
Abstract: This paper reports an experimental investigation, carried out at The University of Hong Kong, on the behaviour of cold-formed steel lipped channel beams affected by local-distortional (L-D) interaction under non-uniform bending – to the authors’ best knowledge, these are the first tests specifically devoted to this topic. This investigation consists of 16 non-conventional four-point simply supported bending tests involving twin lipped channel beams arranged in a “back-to-back” configuration and laterally restrained at the loading points. The 32 lipped channel specimens were brake-pressed from high-strength zinc-coated G450 grade structural steel sheets. Tensile coupon tests were performed to obtain the specimen material properties and initial geometrical imperfections were measured prior to testing. The beam geometries were carefully selected to enable testing beams that are prone to “true L-D interaction” (close critical distortional-to-local buckling moments) when acted by trapezoidal bending moment diagrams with four distinct gradients – all the tested specimens exhibited the sought L-D interactive nature. The output of the experimental investigation consists of (i) applied moment vs. displacement equilibrium paths, (ii) photos showing beam deformed configurations along those paths (including the failure modes) and (iii) the failure moment data. Lastly, the experimental failure moments obtained are compared with their predictions provided by the (i) current local and distortional Direct Strength Method (DSM) strength curves and (ii) available DSM-based approaches against L-D interactive failures, which were developed and calibrated exclusively in the context of beams subjected to uniform bending.
TL;DR: The comparative results indicated that the ANN model was more stable and accurate than the existing relationships and can be used for the design of new CFST columns, retrofit the existing ones, and risk assessment in fires.
Abstract: Search for enhancing the efficiency has led to composite structures such as concrete-filled steel tubes (CFST) with increasing applications across the world. The fire performance of CFST columns needs to be understood comprehensively. In this paper, the effectiveness of the most important parameters on fire resistance rating (FRR) and residual strength index (RSI) was evaluated using artificial neural network (ANN). Relationships were derived from the developed ANN model for predicting the FRR and RSI of CFST columns. Near 300 experimental data points were extracted from the literature and were used for training, validating, and testing the ANN models. The correlation coefficient (R) of the network for FRR and RSI is 0.967 and 0.97, respectively. The derived relationships from the ANN model have the R coefficient of 0.61 and 0.74 for FRR and RSI, respectively. Also, the limitations of existing empirical relationships were compared with the derived relationships. The comparative results indicated that the ANN model was more stable and accurate than the existing relationships. Moreover, a graphical user interface was developed to predict the FRR and RSI of CFST columns. The derived relationships can be used for the design of new CFST columns, retrofit the existing ones, and risk assessment in fires.
TL;DR: In this article, the design of cold-formed steel semi-oval hollow non-slender sections under combined compression and major axis bending in positive direction is studied, and a non-linear finite element model is developed to simulate the beam-column tests.
Abstract: The design of cold-formed steel semi-oval hollow non-slender sections under combined compression and major axis bending in positive direction is studied in this paper. A non-linear finite element model was developed to simulate the beam-column tests. The model was validated against the available experimental results. An extensive parametric study on 140 short and long beam-columns loaded at different eccentricities as well as the corresponding 28 concentric loaded column counterparts was conducted covering a wide range of cross-section geometries, different member slenderness and loading eccentricities. The numerical results obtained in this study together with the available experimental results were compared with the design strengths predicted by the American Specification, Australian Standard as well as European Code and North American Specification. Reliability analysis was conducted to assess the reliability of different design rules. It is shown that the existing design rules provide reliable but quite conservative design strength predictions. Existing design rules are modified such that the accuracy of the design strength predictions is improved. Among the modified design methods, it is recommended to adopt the modified ANSI/AISC360 design method for cold-formed steel semi-oval non-slender sections subjected to combined compression and major axis bending in positive direction since it provides the most accurate design predictions.
TL;DR: In this article, the impact analysis of a nanocomposite truncated conical shells (NSTCS) was investigated using higher-order shear deformation theory (HSDT) and Mindlin theory (FSDT).
Abstract: The present paper concerns low-velocity impact for nanocomposite sandwich truncated conical shells (NSTCS). Graphene platelets (GPLs)-reinforced as core layer is covered through magnetostrictive layers as face sheets. The supposed impacts are applied over the above face layer and further, the interaction among impactors as well as NSTCS is assumed utilizing novel equivalent three-degree-of-freedom (TDOF) with spring–mass–damper (SMD) model. For modeling the core layer and face sheets mathematically, higher-order shear deformation theory (HSDT) besides first-order shear deformation or Mindlin theory (FSDT) is utilized, respectively. To presume this sandwich structure much more realistic, the Kelvin–Voigt model will be used. According to Hamilton’s principle concerning continuity boundary conditions, the governing equations are obtained. Utilizing differential cubature (DC) as well as Bolotin procedures, the governing equations will be solved. In this work, different variables covering various boundary edges, Controller, cone’s semi vertex angle, damping, feedback gain, the proportion of core to face sheets thickness, dispersion kinds of GPLs and their volume percent, and their effects on low-velocity impact analysis of the sandwich structure will be investigated. To indicate the accuracy of applied theories as well as methods. the results are collated with another paper. It is found that increment of GPLs volume percent leads to rise the deflection as well as maximum contact force whereas contact duration is reduced.
TL;DR: In this article, the first order shear deformation theory of shells is used to investigate the effects of shear strains and rotary inertia on the vibration frequencies of a conical-spherical functionally graded material (FGM) shell.
Abstract: Natural frequencies of a conical–spherical functionally graded material (FGM) shell are obtained in this study. It is assumed that the conical and spherical shell components have identical thickness. The system of joined shell is made from FGMs, where properties of the shell are graded through the thickness direction. The first order shear deformation theory of shells is used to investigate the effects of shear strains and rotary inertia. The Donnel type of kinematic assumptions are adopted to establish the general equations of motion and the associated boundary and continuity conditions with the aid of Hamilton’s principle. The resulting system of equations are discretized using the semi-analytical generalized differential quadrature (GDQ) method. Considering various types of boundary conditions for the shell ends and intersection continuity conditions, an eigenvalue problem is established to examine the vibration frequencies. After proving the efficiency and validity of the present method for the case of thin isotropic homogeneous joined shells with the data of conventional finite element software, parametric studies are carried out for the system of combined moderately thick conical–spherical joined shells made of FGMs and various types of end supports.
TL;DR: These optimal front rails are applied to the full frontal barrier impact analysis of a sport utility vehicle (SUV) model, and the crashworthiness of this model is improved significantly.
Abstract: Front rail is a key assembly for the frontal impact of vehicle. In this work, based on the key information of benchmark vehicles and high-strength steels, front rails are designed to improve the crash performance of vehicle and reduce its structural mass (SM). First, the finite element analysis (FEA) of the front rail is carried out, and dynamic drop testings are performed to verify the accuracy of finite element model. Then, the sectional dimensions, materials and thicknesses of ten benchmark models are studied, and the crashworthiness of these models is obtained by FEA. Next, based on these benchmark models, three front rails with representative sectional sizes are obtained through mesh deformation. By experimental design and FEA, the response surface models (RSMs) of these three front rails are constructed. Based on multi-objective artificial tree (MOAT) algorithm, these three front rails are optimized with the goals of minimize SM and maximize mean crushing force (MCF). The optimal design schemes of these models are obtained. These optimal front rails are applied to the full frontal barrier impact analysis of a sport utility vehicle (SUV) model, and the crashworthiness of this model is improved significantly. Since the selection of materials, thicknesses and sectional dimensions bases on engineering practice and benchmark cases, these optimal schemes in this work can be directly applied to actual vehicle model. In brief, this work has significant practical value.
TL;DR: In this paper, a dynamic buckling analysis for a rotationally restrained functionally graded (FG) graphene nanoplatelets reinforced composite (FG-GPLRC) porous arch under a uniform step load where GPL nanofillers are uniformly dispersed while the porosity coefficient varies along the thickness direction of the arch is presented.
Abstract: This paper presents a dynamic buckling analysis for a rotationally restrained functionally graded (FG) graphene nanoplatelets (GPLs) reinforced composite (FG-GPLRC) porous arch under a uniform step load where GPL nanofillers are uniformly dispersed while the porosity coefficient varies along the thickness direction of the arch. The effective material properties of the FG-GPLRC porous arch are determined by the volume fraction distribution of materials. Analytical solutions for the symmetric limit point dynamic buckling and anti-symmetric bifurcation dynamic buckling loads of rotationally restrained FG-GPLRC porous arches are derived by using an energy-based approach. Critical geometric parameters that determine the dynamic buckling mode switching behavior are also identified and discussed. Depending on the geometric parameters and the rotational restraint stiffness, the FG-GPLRC porous arch can buckle in either a symmetric limit point mode or an anti-symmetric bifurcation mode dynamically. It is also found that the dynamic buckling load of the arch can be considerably improved by adding a small amount of GPLs as reinforcing nanofillers. The influences of the porosity coefficients, GPL weight fractions, arch dimensions and geometries on the dynamic buckling behavior of rotationally restrained FG-GPLRC porous arches are comprehensively investigated through extensive parametric studies.
TL;DR: In this article, a phase field approximation of fracture for functionally graded materials (FGM) using a diffusive crack approach incorporating the characteristic length scale as a material parameter is proposed, where a rule of mixture is employed to estimate the material properties, according to the volume fractions of the constituent materials, which have been varied according to given grading profiles.
Abstract: A phase field (PF) approximation of fracture for functionally graded materials (FGM) using a diffusive crack approach incorporating the characteristic length scale as a material parameter is herein proposed. A rule of mixture is employed to estimate the material properties, according to the volume fractions of the constituent materials, which have been varied according to given grading profiles. In addition to the previous aspects, the current formulation includes the internal length scale of the phase field approach variable from point to point, to model a spatial variation of the material strength. Based on the ideas stemming from the study of size-scale effects, Γ -convergence for the proposed model is proved when the internal length scale is either constant or a bounded function. In a comprehensive sensitivity analysis, the effects of various model parameters for different grading profiles are analyzed. We first prove that the fracture energy and the elastic energy of FGM is bounded by their homogeneous constituents. Constitutive examples of boundary value problems solved using the BFGS solver are provided to bolster this claim. Finally, crack propagation events in conjunction with the differences with respect to their homogeneous surrogates are discussed through several representative applications, providing equivalence relationships for size-scale effects and demonstrating the applicability of the current model for structural analysis of FGMs.
TL;DR: In this paper, the effect of hybridization design and filler types on the energy dissipation mechanism under axial compression was investigated, and the experimental results revealed that the hollow composite tubes collapsed in progressive and the impact energy was absorbed by the generation of cracks, fiber fracture and friction.
Abstract: Carbon fiber reinforced plastic (CFRP) and glass fiber reinforced plastic (GFRP) have shown great promise in the design of light-weight thin-walled energy absorbers. Herein, circular CFRP/GFRP hybrid tubes and tubes, reinforced with internal composite skeletons (XS and OS), were fabricated to further enhance the energy absorption capacities. The crashworthiness and failure pattern of reinforced structures were compared with the hollow and aluminum foam-filled composite tubes. Moreover, low-velocity drop-weight impact tests were carried out to investigate the effect of hybridization design and filler types on the energy dissipation mechanism under axial compression. The experimental results revealed that the hollow composite tubes collapsed in progressive and the impact energy was absorbed by the generation of cracks, fiber fracture and friction. Also, the GFRP tubes exhibited better crashworthiness than CFRP tubes under low velocity impact, which was different from the quasi-static compression conditions. In contrast to hollow counterparts, the mean crushing force (MCF) of foam-filled tubes was improved by approximately 40%, whereas the specific energy absorption (SEA) was reduced by 30% due to the low weight efficiency of the aluminum foam. The filling of XS-skeleton divided the tube into four cells and improved the MCF by more than 10%. However, it reduced the SEA by around 8% due to unstable and inefficient deformation of XS-skeleton during crushing. By contrast, the OS-skeleton divided the hollow tube into more cells and collapsed progressively, resulting in superior energy absorption characteristics. Herein, the OS-filled GFRP tube was found to be the most crashworthy structure that improved the crushing force efficiency (CFE) and SEA by 50% and 7%, respectively.
TL;DR: In this article, the vibrational behavior of composite coupled conical-conical shell structures is predicted by using a modified generalized differential quadrature method (GDQM) to solve the system of differential equations, an efficient and modified GDQM is employed.
Abstract: This article is dedicated to predict the vibrational behavior of composite coupled conical-conical shell structures. The structural material is composed of two phases, including polymer epoxy matrix and Carbon NanoTube (CNT) fibers. To improve the vibrational structural behavior, the distributions of CNTs throughout the thickness of shells are assumed to be Functionally Graded. In order to enhance the research, five different patterns are considered for distribution of the CNT fibers within the matrix. The governing equations of motion associated with conical shells are obtained by using Donnell's theory and Hamilton method. In addition, the five-parameter shell theory is utilized in this article. As a result, five differential equations are achieved by using variation calculation. To solve the system of differential equations, an efficient and modified Generalized Differential Quadrature Method (GDQM) is employed. All the natural frequencies of shell structures are found for different states. By considering continuity conditions, the required modification is applied to GDQM. To validate the proposed formulation, some well-known benchmarks are solved. Moreover, several numerical examples and parametric studies are implemented to show the high accuracy and capability of the authors' scheme for analyzing coupled shells. To obtain accurate responses, 15 grid points are required for using in GDQM. Besides, it is observed that the minimum and maximum dimensionless frequency parameters are obtained by the patterns F G − O and F G − X , respectively.
TL;DR: In this article, a 3D-printing technique, experiments, theoretical formulation and numerical simulation are combined to investigate a novel class of lightweight sandwich structures with TPMS cores, and a numerical model is developed to analyse the behaviours of the sandwich structures under bending loading.
Abstract: Triply periodic minimal surface (TPMS) based cellular structures have drawn increasingly attention due to their mathematically controlled topologies and promising mechanical properties. Here, we combine 3D-printing technique, experiments, theoretical formulation and numerical simulation to investigate a novel class of lightweight sandwich structures with TPMS cores. Sandwich structures with Primitive, Neovius and IWP core topologies are designed and fabricated using a 3D-printing technique. The bending properties, failure mechanism as well as energy absorption capacity of these TPMS sandwich structures are evaluated via a three-point bending test. A numerical model is developed to analyse the behaviours of the sandwich structures under bending loading. Theoretical formulation is employed to compare with the experimental data and numerical simulation. A good agreement is achieved between the attendant experimental data, theoretical formulation, and numerical simulation. In addition, a comprehensive parametric study is conducted to understand the effect of core topologies, relative density of the TPMS core, and geometrical parameters on the bending properties and energy absorption capacity of the sandwich structures based on the numerical model proposed. Both the relative density of the core and the geometrical designs of the TPMS sandwich structures exhibit a significant effect on the bending properties and energy absorption capacity. In contrast, the topologies of the TPMS cores have a limited effect on the bending properties at low relative density for designs with a thick face-panel. The sandwich structures with a Neovius core have better performance compared to other core topologies for designs with a thin face-panel. Overall, this study indicates that sandwich structures with TPMS cores could be designed to deliver desirable bending properties and energy absorption capacity, and the findings of this study provide insights into future designs of novel sandwich structures for various engineering applications.
TL;DR: In this article, a non-polynomial framework for bending responses of three-phase multi-scale hybrid laminated nanocomposite reinforced circular/annular plates (MHLNCRCP/ MHLNCRAP) based upon the threedimensional theory of elasticity for various sets of boundary conditions is presented.
Abstract: This survey addresses the non-polynomial framework for bending responses of three-phase multi-scale hybrid laminated nanocomposite (MHLNC) reinforced circular/annular plates (MHLNCRCP/ MHLNCRAP) based upon the three-dimensional theory of elasticity for various sets of boundary conditions. The sandwich structure with two, three, five, and seven layers is modeled using compatibility conditions. The state-space based differential quadrature method (SS-DQM) is presented to examine the bending behavior of MHLNCRCP/ MHLNCRAP by considering various boundary conditions. Halpin–Tsai equations and fiber micromechanics are used in the hierarchy to predict the bulk material properties of the multi-scale composite. Singular point is investigated for modeling the annular disk. The carbon nanotubes (CNTs) are supposed to be randomly oriented and uniformly distributed through an epoxy resin matrix. Afterward, a parametric study is done to present the effects of various symmetric cross-ply laminated layers, various types of sandwich circular/annular plates, and various types of pressure on the bending characteristics of the MHLNCRCP/ MHLNCRAP. Numerical results reveal that sinusoidal load is the best pressure for improving the nanocomposite circular/annular plates’ deformation resistance and stress.