Sinusoidal Core Research Articles

Effect of geometric configurations and curvature angle of corrugated sandwich structures on impact behavior

AbstractThe aim of this study is to numerically investigate the low‐velocity impact behavior of carbon fiber reinforced orthogonal woven fabric composite sandwich structures with five different geometric configurations and four different curve angles. Low velocity impact simulations were performed in LS DYNA finite element program to investigate the effects of core configuration and curve angle on peak contact force, energy absorption efficiency and damage mode. A progressive damage analysis based on the combination of the Hashin damage criterion and the Cohesive Zone Model (CZM) with bilinear traction‐separation law was performed using the MAT‐54 (ENHANCED_COMPOSITE_DAMAGE) material model. Among the five different cores, Trapezoidal core has the highest peak force average of 2.9 kN while Triangular core sandwich structure has the lowest with 1.23 kN. Absorbed energy efficiency average was highest for rectangular core with 0.95 and lowest for sinusoidal core with 0.69. The specific absorbed energy value was highest for Triangular core with 0.312 J/g and lowest for Sinusoidal core with 0.178 J/g. The damage area on the structure increased with increasing curve angle. It was determined that the core structure and curve angle is an effective parameter on peak force and energy absorption efficiency.Highlights Impact behavior of sandwich composite structures was examined. The effects of core type and curve angles on peak force, energy absorption efficiency and specific absorption energy were investigated. Specific absorption energy rates were compared with studies in the literature.

Bending behavior of 3D printed continuous fiber reinforced composite sandwich cylindrical shells

Continuous carbon fiber reinforced composite sandwich cylindrical shells (CFRCSs) have been widely used in aerospace and automotive fields due to their excellent load-bearing performance. However, traditional manufacturing methods involve complex processes and expensive molds. This study uses 3D printing technology to manufacture CFRCSs with sinusoidal, triangular, and trapezoidal core. The sample surface and inside fiber distribution is inspected by the optical microscope and X-ray microscope, respectively. It is found that the samples have the defects of uneven resin distribution, fiber breaking, and fiber waviness. The bending behaviors of CFRCSs are investigated by the three-point bending test. The results show that the CFRCSs with sinusoidal core have the maximum ultimate load of about 3094 N, while those with the triangular core structure have the minimum ultimate load of about 1774 N. The triangular and sinusoidal structures mainly undergo debonding at the junction of the core and the panel and fracture at the core because of the small contact area between the core and panel. In contrast, the trapezoidal structure is mainly brittle fracture with fiber pull-out at the bottom panel and fracture at the top panel. The core type greatly influences the bending mechanical properties of the printed CFRCSs. 3D printing technology can be used to manufacture CFRCSs with required mechanical properties by flexibly designing the core shape.

Experimental investigation of the compressive strength of hybrid composite sandwich beams with double-corrugated sinusoidal core reinforced by graphene and polyurethane foam

In this paper, the effects of some system parameters such as nanographene, core geometry, and polyurethane foam on the compressive strength of composite sandwich beams with double corrugated lattice core subjected to flatwise-compression load are investigated experimentally. The face sheets and core of the sandwich beams are made of 10-layers bidirectional carbon fibers using the vacuum infusion process. According to the results of the flatwise-compression test, it was revealed that some factors, including height and angle of the core, the weight percentage of nanographene, and polyurethane foam, can be considered as effective parameters to enhance the compressive strength of the composite sandwich beams. Scanning electron microscopy images were utilized to observe the composition and distribution of the nanoparticles. It was observed that adding nanographene particles to the composite laminates significantly affects the mechanical properties and flexural strength of the sandwich beams. In addition, experimental results showed that the shape of the core can be an effective parameter to control the elasticity and strength of the sandwich beams, and also polyurethane foam dramatically increases the compressive strength and can postpone core failure.

Sinusoidal-Core Long Period Fiber Grating for Refractive Index Measurement

Optic fiber sensors for refractive index (RI) measurement have brought about widespread attention in an extensive range owing to their unique properties. In this paper, we theoretically analyzed and experimentally verified a brand-new type of long period fiber grating with two resonant peaks. This structure is obtained by side-polishing method and melting tapered method. Firstly, a single-mode fiber (SMF) is produced into staggered V-shaped grooves on symmetrical sides by high-frequency CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser. It is then heated and stretched by optic fiber melting tapered system for bending the core towards two-sides grooves. The sinusoidal core is closer to external environment and exhibits a stronger refractive index modulation, which prompts this structure more sensitive to RI. The structure possesses two resonant peaks of 1382.6 nm (dip-1) and 1473.4 nm (dip-2), which can be used to measure temperature and RI simultaneously. The experimental results present that the maximum RI sensitivity of the proposed sensor exhibits 620 nm/RIU (RI unit) in dip-2. Furthermore, compact sensing area, low cost and strong mechanical property of the proposed sensor make itself more suitable for high-accuracy RI measurement.

Crashworthiness analysis and multiobjective optimization of bio-inspired sandwich structure under impact load

A novel bio-inspired sandwich structure with sinusoidal cores (hereinafter referred to as BS) was developed based on the dactyl club microstructure of Odontodactylus scyllarus (O. scyllarus), including two different configurations of the core section (abbreviated as BSS and BSD). The crashworthiness of BSS and BSD with different height–length ratios η (the ratio between height A and length λ of the sinusoidal core unit, and η ranges from 0.4 to 1.6.) were comprehensively investigated under low-velocity impact condition, taking initial peak crush force (Fp), specific energy absorption (SEA) and crush force efficiency (CFE) as evaluation criteria. The crashworthiness between BSSs with λ=20mm and BSSs with A=20mm under the same η condition was discussed. Simulation results showed that the crashworthiness of BSSs with λ=20mm is better than that of BSSs with A=20mm. The BSDs have superior crashworthiness when the difference between η1 and η2 is the smaller. The BSDs demonstrate better crashworthiness when η1 and η2 exceed 0.8 compared with other cases. A metamodel-based multiobjective optimization method based on a polynomial regression (PR) metamodel and a multiobjective particle optimization (MOPSO) algorithm were employed to optimize the dimensions of BSS and BSD under four designed cases, where the wall thickness t and η were regarded as the design variables. The optimal solutions for the multiobjective optimization of BSS and BSD were obtained for different cases. The multiobjective optimization results showed that the BSS is advantageous in terms of the optimal criteria under Case-I and Case-II compared with BSD, whereas the differences between BSS and BSD under Case-III and Case-IV are insignificant. Further research pertaining to the crashworthiness of bio-inspired sandwich structures with multi-layer sinusoidal cores should be conducted.

Crushing responses and optimization of novel sandwich columns

The paper proposes a design method of the sandwich column with the corrugated sinusoidal core and develops the triangular corrugated sandwich column (TCSC), quadrangular corrugated sandwich column (QCSC) and hexagonal corrugated sandwich column (HCSC). The experimental tests of the TCSC and QCSC with A = 8 and N = 1 are conducted to estimate the crushing responses and the reliability of the numerical model of the sandwich column. The crushing responses are numerically investigated of the TCSC, QCSC and HCSC with different geometrical characteristics and the same mass under the axial impacting load. The results show that the energy absorption of the sandwich column is significantly affected by the geometric parameters A and N of the sinusoidal core tube, and the sandwich design has the large advantage of the energy absorption over corresponding members. Furthermore, the theoretical model of the mean crushing force is derived using the simplified super folding element theory, and the comparisons on experimental result and the finite element analysis demonstrate high prediction accuracy of the theoretical model. Lastly, a numerical optimization is proposed by combining orthogonal experimental design and discrete optimization to obtain the optimal crashworthiness of the sandwich column. Optimization results show that the discrete optimization method can be fast convergence and obtain the optimal design parameters. The energy absorption of the optimal sandwich column is about 10% higher than the initial design. Furthermore, the HCSC has the highest specific energy absorption under the same mass and design constraints.

Analytical and finite element investigations of the cross-arranged trapezoidal- and sinusoidal-corrugated-cores panels

This article intends to study the performance of sandwich panels consisting of four isotropic flat plates and three trapezoidal or sinusoidal cores. The sandwich panels, subjected to the uniform loading resting on simply supported edges, are analyzed by an analytical method based on the classical plate theory and commercially available software. The homogenization method is used for the analytical method to replace the core by a flat plate with an equivalent stiffness. Results show that the deflected shape of the equivalent sandwich plate with the flat core is similar to that of the original corrugated plate measured by using shell elements in ABAQUS. The effects of geometric characteristics on the deflection and Von-Mises’s stress are also studied by the finite element method analysis. Results show that the trapezoidal-core panel has better performance as compared to the sinusoidal-core one. Moreover, results show that the corrugation thickness and amplitude have considerable effects on the performance of the panel. A wide validity range is also obtained for the thickness of the sinusoidal-core panel as compared to the trapezoidal-core panel.

Mathematical models for predicting the quasi-static stress characteristics of corrugated paperboard with sinusoidal core along the longitudinal compression

This paper presents two mathematical models to predict the initial peak stress and the plateau stress of five-layered and seven-layered corrugated paperboards respectively, which are simplified and regarded as the orthotropic panels under longitudinal compression. The resultant stress-strain curve exhibits an initial stiffening stage with the initial peak stress determining the edgewise crush resistance of paperboard, and a long plateau stage with which most impact energy can be absorbed. By analyzing the elastic buckling of board walls, the model for prediction of the initial peak stress is obtained, while the plateau stress model is developed based on the gradual process of compression and energy conservation principle. And then, experiments are conducted to validate the presented models by comparing the predicted values with those by experiments, showing overall good agreement. It can be concluded that the proposed models are suitable for design of multi-layered corrugated box and cushioning packaging.

Effect of Rate Sensitivity on Structural Sandwich Plates with Sinusoidal Corrugated Cores

A plane strain elastic–viscoplastic‐based finite element model is developed to simulate a composite system with sinusoidal corrugated cores under tensile loading conditions. Numerical study shows that the rate sensitivity in the reinforced core provides a positive impact on loading capacity, the necking strain retardation, and improvement in the ductility of a composite. By carefully selecting the reinforced sinusoidal core geometric parameters, extra margin can be gained in improving the uniform elongation without comprising the loading capacity of a composite system. For a given volume fraction of reinforced core, an optimized reinforcement arrangement is found to achieve an improved ductility for a plate with sinusoidal corrugated core.

Free vibration analysis of fiber-reinforced polymer honeycomb sandwich beams with a refined sandwich beam theory

Free vibration of a fiber-reinforced polymer honeycomb sandwich beam with sinusoidal core configuration is studied based on a refined sandwich beam theory. Using a micro/macromechanics approach for face laminates and a mechanics of material approach for honeycomb core, the equivalent elastic properties of face laminates and honeycomb core are obtained. A free vibration model based on the refined sandwich beam theory is formulated using the Hamilton's variational principle. Analytical solutions for a cantilevered sandwich beam are obtained by the Ritz method. Experimental results conducted on the fiber-reinforced polymer honeycomb sandwich beams with different lengths are applied to validate the proposed analytical solutions. As a comparison and further verification, the analytical solutions based on the Timoshenko beam theory and high-order beam theory are also presented. The analytical solutions in term of natural frequencies are compared with the numerical simulation results as well. Good agreements among various comparisons demonstrate the accuracy and capability of the refined sandwich beam theory and its potentials in design applications and health monitoring of fiber-reinforced polymer honeycomb sandwich beams.

Development of facesheet for honeycomb FRP sandwich panels

Honeycomb fiber-reinforced polymer sandwich panels with sinusoidal core geometry have shown to be successful both for new construction and rehabilitation of existing bridge decks. This investigation is aimed to study the strength properties of the facesheet and to develop an optimized facesheet configuration. A progressive failure model is developed using finite element method to predict the behavior of laminated composite plates up to failure, where the failure criteria are introduced through prescribed user-defined subroutines. The accuracy of the model is verified through correlations between finite element results and existing experimental data. This model is then applied to carry out a parametric study on facesheet. Three variables are included: material properties, including bidirectional stitched fabrics, unidirectional layer of fiber roving, and chopped strand mat; layer thickness; and layer sequences. The quality of each alternative is evaluated based on stiffness and strength performance. In order to further investigate the behavior of facesheet experimentally, coupon samples on selected configurations to evaluate compressive, bending, and shear strengths were tested. The test results are also used to validate the progress failure model developed in this study. Through this combined experimental and numerical study, the strength properties of facesheet are obtained, which permit the optimization of facesheet design.

Strength evaluations of sinusoidal core for FRP sandwich bridge deck panels

Abstract Fiber-reinforced polymer (FRP) sandwich deck panels with sinusoidal core geometry have shown to be successful both in new construction and the rehabilitation of existing bridge decks. This paper is focused on an experimental study of the strength evaluations of a honeycomb sandwich core under out-of-plane compression and transverse shear. The sinusoidal core is made of E-glass Chopped Strand Mat (ChSM) and Polyester resin. The compressive, tensile and shear strengths were first obtained from coupon tests. The out-of-plane compression tests were performed on representative single-cell volume elements of sandwich panels, and the tests included “stabilized” samples to induce compression failure, and “bare” samples to induce local buckling of the core. Finally, four-point bending tests were conducted to study the structural strength behavior under transverse shear. Two types of beam samples were manufactured by orienting the sinusoidal wave either along the length (longitudinal) or along the width (transverse). Both typical shear failure mode of the core material and delamination at the core–facesheet bonding interface were observed for longitudinal samples. The failure for transverse samples was caused by core panel separation. For both single-cell and beam-type specimen tests, the number of bonding layers, i.e., the amount of ChSM contact layer and resin used to embed the core into the facesheet, and the core thickness are varied to study their influence. The experimental results described herein can be subsequently used to develop design guidelines.

RETRACTION: Homogenization and Optimization of Sinusoidal Honeycomb Cores for Transverse Shear Stiffness

Fiber-reinforced polymer (FRP) composite sandwich panels with a core of sinusoidal geometry have been recently used in highway bridge and aquaculture tank applications. The selection of geometric shape and size of sinusoidal cores to meet given design requirements is critical in efficient applications of sandwich structures, and their effective transverse shear stiffness properties are important material properties in analysis and design. Based on a combined homogenization and multi-objective optimization technique, the effective transverse shear stiffness properties of sinusoidal cores are studied and optimized. An analytical approach using two-scale homogenization technique is used to predict the effective transverse shear stiffness properties of thin-walled sinusoidal honeycomb cores. The optimization problem is then solved using a sequential quadratic programming algorithm. Two types of optimization problems are presented: the maximization of effective transverse shear stiffness of honeycomb core with...

Homogenization and Optimization of Sinusoidal Honeycomb Cores for Transverse Shear Stiffness

Fiber-reinforced polymer (FRP) composite sandwich panels with a core of sinusoidal geometry have been recently used in highway bridge and aquaculture tank applications. The selection of geometric shape and size of sinusoidal cores to meet given design requirements is critical in efficient applications of sandwich structures, and their effective transverse shear stiffness properties are important material properties in analysis and design. Based on a combined homogenization and multi-objective optimization technique, the effective transverse shear stiffness properties of sinusoidal cores are studied and optimized. An analytical approach using two-scale homogenization technique is used to predict the effective transverse shear stiffness properties of thin-walled sinusoidal honeycomb cores. The optimization problem is then solved using a sequential quadratic programming algorithm. Two types of optimization problems are presented: the maximization of effective transverse shear stiffness of honeycomb core with a given composite solid volume fraction and the minimization of composite solid volume with prescribed effective transverse shear stiffness. The geometric effects and weighting factors on the optimal design of sinusoidal cores are discussed. An optimization procedure using a response surface method and finite element analysis is also conducted to verify the proposed approach. The present combined homogenization and multi-objective optimization approach can be used to obtain favorable material performance behaviors and meet desired design requirements for honeycomb core structures.

Torsion of honeycomb FRP sandwich beams with a sinusoidal core configuration

A combined analytical, numerical and experimental investigation of honeycomb fiber-reinforced polymer (HFRP) sandwich beam samples subjected to torsion loads is conducted. The sandwich panel considered in this study has unique sinusoidal core geometry in the plane extending vertically between face laminates, and it has been used primarily as decking systems in highway bridges. Using a homogenization process and mechanics of materials approach, the equivalent core material properties for the honeycomb core geometry are found, and the material properties of face sheets are obtained by micro/macromechanics. Equivalent material properties of the core and face sheets are then used to evaluate effective torsional stiffness properties of HFRP panels. The torsional analysis includes the evaluation of core equivalent in-plane and out-of plane shear properties and panel apparent torsional stiffness properties. Finite element models using layered shell elements are used to correlate with the analytical and experimental results for HFRP beams samples in torsion. Two types of models are presented in the finite element simulation: an actual geometry model, where the core and face sheet geometry are defined by layer shell elements, and an equivalent plate model, for which the equivalent material properties of the core and face sheets are utilized. In order to verify the accuracy of the analytical and numerical predictions, several honeycomb sandwich beam samples with sinusoidal core waves oriented along the longitudinal or transverse or vertical directions and with different face sheet configurations are experimentally tested in torsion. The present analysis and characterization procedures can be used in design applications and optimization of honeycomb structures, and they can also be employed to verify or refine in-plane and out-of-plane shear equivalent material properties for the present and other honeycomb FRP panels.

Transverse Shear Including Skin Effect for Composite Sandwich with Honeycomb Sinusoidal Core

Honeycomb fiber-reinforced polymer (HFRP) sandwich panels with sinusoidal core geometry have been used extensively for new construction and replacement of bridge decks. The core geometry used consists of large cavities and represents a new type of core configuration. This study is concerned with the behavior of HFRP panels under transverse shear considering skin effect, and addresses the two contributing factors due to shear warping and bending warping. Shear warping corresponds to the assumption of having a hinge connection between facesheet and core, and bending warping is induced for the assumption of a rigid connection. All previous studies have been focused mainly on shear warping, neglecting for the most part bending warping. A closed-form solution based on proper description of displacement field at the interface is derived considering shear warping. The accuracy of this solution is verified by finite-element (FE) results. The FE model is then applied to study bending warping effect, and also the core-facesheet constraint or interface bonding effect. The equivalent shear stiffness and the stress distributions subject to skin effect are defined, and suggestions for future design considerations are given.

Impact analysis of fiber reinforced polymer honeycomb composite sandwich beams

Large scale fiber reinforced polymer (FRP) composite structures have been used in highway bridge and building construction. Recent applications have demonstrated that FRP honeycomb sandwich panels can be effectively and economically applied for both new construction and rehabilitation and replacement of existing structures. This paper is concerned with impact analysis of an as-manufactured FRP honeycomb sandwich system with sinusoidal core geometry in the plane and extending vertically between face laminates. The analyses of the honeycomb structure and components including: (1) constituent materials and ply properties, (2) face laminates and core wall engineering properties, and (3) equivalent core material properties, are first introduced, and these properties for the face laminates and equivalent core are later used in dynamic analysis of sandwich beams. A higher-order impact sandwich beam theory by the authors [Yang MJ, Qiao P. Higher-order impact modeling of sandwich beams with flexible core. Int J Solids Struct 2005;42(20):5460–90] is adopted to carry out the free vibration and impact analyses of the FRP honeycomb sandwich system, from which the full elastic field (e.g., deformation and stress) under impact is predicted. The higher order vibration analysis of the FRP sandwich beams is conducted, and its accuracy is validated with the finite element Eigenvalue analysis using ABAQUS; while the predicted impact responses (e.g., contact force and central deflection) are compared with the finite element simulations by LS-DYNA. A parametric study with respect to projectile mass and velocity is performed, and the similar prediction trends with the linear solution are observed. Furthermore, the predicted stress fields are compared with the available strength data to predict the impact damage in the FRP sandwich system. The present impact analysis demonstrates the accuracy and capability of the higher order impact sandwich beam theory, and it can be used effectively in analysis, design applications and optimization of efficient FRP honeycomb composite sandwich structures for impact protection and mitigation.

Dynamic Characteristics and Effective Stiffness Properties of Honeycomb Composite Sandwich Structures for Highway Bridge Applications

In this paper, a combined analytical and experimental study of dynamic characteristics of honeycomb composite sandwich structures in bridge systems is presented, and a relatively simple and reliable dynamic experimental procedure to estimate the beam bending and transverse shear stiffness is proposed. This procedure is especially practicable for estimating the beam transverse shear stiffness, which is primarily contributed by the core and is usually difficult to measure. The composite sandwich beams are made of E-glass fiber and polyester resins, and the core consists of the corrugated cells in a sinusoidal configuration. Based on the modeling of equivalent properties for the face laminates and core elements, analytical predictions of effective flexural and transverse shear stiffness properties of sandwich beams along the longitudinal and transverse to the sinusoidal core wave directions are first obtained. Using piezoelectric sensors, the dynamic response data are collected, and the dynamic characteristics of the sandwich structures are analyzed, from which the flexural and transverse shear stiffness properties are reduced. The experimental stiffness results are then compared to the analytical stiffness properties, and relatively good correlations are obtained. The proposed dynamic tests using piezoelectric sensors can be used effectively to evaluate the dynamic characteristics and stiffness properties of large sandwich structures suitable for highway bridge applications.

Buckling Behavior of Honeycomb FRP Core with Partially Restrained Loaded Edges under Out-of-plane Compression

Fiber-reinforced polymer (FRP) sandwich deck panels with sinusoidal honeycomb core geometry have shown to be efficient in both new construction and rehabilitation of highway bridge decks. The sandwich panel consists of top and bottom laminated face sheets bonded to the honeycomb core, which extends vertically between face sheets. This paper is focused on the study of the buckling capacities of the core components under out-of-plane compression. The facesheet and core are attached by contact molding and are, therefore, not rigidly connected. Thus, this problem can be described as the instability of an FRP core panel with two rotationally restrained loaded edges. An elastic restraint coefficient is introduced to quantify the bonding layer effect between the facesheet and core, and a simple and relatively accurate test method is proposed to obtain the restraint coefficient experimentally. A combined analytical and experimental study of compression is presented. By solving a transcendental equation, the critical compression buckling stresses are obtained, and a simplified expression to predict buckling strength is formulated in terms of the elastic restraint coefficient. The analytical solution is verified by finite element (FE) analysis. Compression tests are carried out to evaluate the effect of the bonding layer thickness, and the experimental results correlate closely with analytical and FE predictions. A parametric study is conducted to study the core aspect ratio effect on the buckling load. The method described in this paper can be further extended to determine local buckling capacities of other structural shapes with elastic restraints along the loaded edges.

Mechanics of Composite Sinusoidal Honeycomb Cores

Lightweight and heavy-duty fiber-reinforced polymer (FRP) composite honeycomb sandwich structures have been increasingly used in civil infrastructure. Unique cellular core configurations, such as sinusoidal core, have been applied in sandwich construction. Due to specific core geometry, the solutions for core effective stiffness properties are not readily available. This paper presents a mechanics of materials approach to evaluate the effective stiffness properties of sinusoidal cores. In particular, the internal forces of a curved wall in a unit cell are expressed in terms of resultant forces, and based on the energy method and principle of equivalence analysis, the in-plane stiffness properties of sinusoidal cores are derived. Both finite-element modeling and experimental testing are carried out to verify the accuracy of the proposed analytical formulation. To illustrate the present analytical approach as an efficient tool in optimal analysis and size selection of sinusoidal cores, several design plots are provided and discussed. The simplified analysis and formulation presented for sinusoidal cores can be used in design application of FRP honeycomb sandwich and optimization of efficient cellular core structures.