Sandwich Sheets Research Articles

Modeling and failure mechanism study of unidirectional GFRP corrugated sandwich sheet piles based on discrete element method

In this paper, a DEM model of a unidirectional glass fiber reinforced polymer composite sandwich sheet pile (UGFRP-CSSP) is developed to elucidate the damage mechanisms under longitudinal bending and axial compression at the mesoscale, in order to bridge the gap between existing knowledge and its potential applications as sheet pile walls. A series of four-point bending and axial compression tests are performed on UGFRP-CSSP to validate the DEM model, which is calibrated through a sensitivity analysis of the mesoscopic parameters. The failure behavior, crack progress, and initial crack formation of the UGFRP-CSSP are investigated by correlating the results from physical experiments and numerical simulations. The research reveals that the DEM model accurately depicts the failure behavior under bending and compression of unidirectional (UD) composite elements, offering a mesoscopic perspective on the failure origins. It is identified that the tensile shear strength of the resin is the weak point leading to initial failure, as it is lower than that of the glass fibers. Longitudinal bending failure typically initiates at the skin-core interface and around the central axis of core, with cracks propagating longitudinally due to compression shear failure between fibers. Axial compression failure also occurs predominantly at the skin-core interface, with similar longitudinal cracking attributed to tensile shear failure at the acute angle fiber connections in the long span side. Finally, a new viewpoint was proposed that the fiber modulus may have a decisive impact on the failure behavior of UD composite materials.

Characterization of resistance welded hybrid sandwich sheets with additively manufactured core structure

Abstract Production of additively manufactured sandwich sheets is limited to small sizes. In the new introduced process route, additively manufactured core structures are joined with rolled face sheets by resistance welding, and the formability of the hybrid sandwich sheets is investigated. The necessity of developing the humps to improve the quality of resistance welding is initially investigated. Two different core structures, namely honeycomb and hollow sphere, are selected, and electrical-thermal coupled simulations with the ABAQUS software are performed to study the temperature distribution during resistance welding without and with hump. The strength of the joints for the fabricated sandwich sheets is verified by a quasi-static shear test. It is experimentally proven that the sandwich sheets without a hump in the core structure are not fully joined, and desired temperature localization is possible only by applying the hump. This is because the hump reduces the contact area, which leads to an increase in current density at the point where the resistance ratios are changed. This leads to higher temperatures in the intended joining zone. Different hump geometries for the core structure are designed, fabricated, and joined to the face sheets under different process parameters. The spot contact yields up to 50% higher shear strength than the linear or area contact. The free air bending results show that the double weld is essential for successful subsequent bending. It is also concluded that increasing the resistance welding time by more than 120 ms does not affect the joining strength of hybrid sheets.

Prediction of peel strength of sandwich sheets made of aluminium alloys fabricated by friction stir spot welding based hybrid process using cohesive zone modeling and finite element simulations

The present work examines the fabrication and numerical modelling of honeycomb core sandwich sheets utilizing Friction Stir Spot Welding (FSSW) techniques as prospective substitutes for adhesive-bonded structures. Here, the sandwich sheet contains AA5052-H32 skins and AA3003 honeycomb core. Two strategies, FSSW with disc insert (FSSW_D) and FSSW with disc insert and adhesive bonding (FSSW_D_AB), were evaluated against traditional adhesive-bonded sandwiches using peel test performance and finite element (FE) simulation with cohesive zone modelling (CZM). In the CZM, a homogenized core with an equivalent cohesive layer was substituted for the honeycomb core and cohesive layer. The utilization of FSSW_D and FSSW_D_AB methods resulted in substantial improvements in maximum load capacity, with enhancements in the hybrid sandwich specimen ranging from 254 % to 399 % compared to adhesive-bonded connections. The maximum load of hybrid joints (FSSW_D_AB) was 15 %–23 % higher than that of ordinary spot-welded joints (FSSW_D). An approach to model the hybrid sandwich specimen using both the homogenized core and equivalent cohesive zone model accurately was proposed. FE analysis, including peel tests of adhesive-bonded, spot-welded, and hybrid joints, was performed, and the numerical predictions agreed satisfactorily with the experimental values for all the joint types.

A THERMAL BEHAVIOUR STUDY OF NATURAL FIBER-REINFORCED POLYMER COMPOSITE/HONEYCOMB CORE SANDWICH PANELS

The unique honeycomb structure has provided good modulus with a lightweight material, especially in aerospace and vehicle applications. Realizing that the thermal analysis of natural fiber honeycomb sandwiches was still lacking in observation, the research needs to investigate thermal transfer characteristics to promote engineering demand. The objective of this research was to investigate honeycomb sandwiches' thermal behaviour by implementing local natural fibers of coconut, oil palm, and sugar cane for sheet plate structure through experimental and numerical analysis. The natural fiber was varied by weight content with the ratio of composite given in a range of 0%wt. - 8%wt. The results have demonstrated that the face sheet plate was paramount part to absorb thermal flow. The study displayed the low thermal conductivity of the face sheet will counter significantly the heat transfer of the honeycomb structure. The experimental investigation found that the coconut fiber successfully performs as an insulator in a honeycomb sandwich which reached 6.78 W.m-1K-1 of thermal conductivity which was an 85.86% improvement as an insulator. While palm oil and sugar cane presented at 11.12 W.m-1K-1 and 10.59 W.m-1K-1, it was slightly higher compared to the coconut. In the numerical investigation, fiber distribution development was successfully performed in a honeycomb sandwich sheet plate composite. The thermal conductivity showed a difference from the experimental, where the higher thermal resistance was shown by palm oil and sugar cane at 8.22 W.m-1K-1 and 8.16 W.m-1K-1, respectively.

AA5052-PVC-AA5052 (Al-PVC-Al) Sandwich Sheets Forming Analysis through In-Plane Plane Stretching Tests.

Sheet metal forming is one of the key processes for the automotive sector to be considered. Sheet metal formability is being tested as received, joining them with different welding/joining processes (i.e., tailored blanks) and making them as sandwich forms to reduce the total weight of the body. These sandwich formations of sheets are an advanced method by incorporating PVC/polymer sheets in between metal sheets with a suitable binder. The present work has investigated the formability of AA5052-PVC-AA5052 (Al-PVC-Al) sandwich sheets by considering the sheet rolling direction as a parameter. The mechanical properties of base metal and sandwich sheets were evaluated by conducting the uniaxial tensile tests. For forming behaviour of Al-PVC-Al sandwich sheets, in-plane plane stretching tests were performed on the universal tensile testing machine. From the results, it has been observed that 0-degree and 90-degree rolling direction of AA5052 sheets provided almost similar forming behaviour where the 45-degree rolling direction showed less formability. The limit strains (by which the forming limit curve has been developed and the safe and failure zones are separated) are 0.043, 0.038, and 0.043 of 0°, 45°, and 90°, respectively. Considering 0°-P-90°, 90°-P-90, 0°-P-45°, 0°-P-90°, and 45°-P-45° sandwich sheets with their corresponding limit strains of 0.060, 0.058,0.057, 0.052, and 0.050, a better formability is seen in 0°-P-90° sandwich, followed by 90°-P-90, 0°-P-45°, 0°-P-90°, and 45°-P-45°. The improvement in the formability is calculated as 28.33%, 25.86%, and 24.0% in comparison with the base metal in 0-degree, 90-degree, and 45-degree rolling directions and 0°-P-90°, 90°-P-90, and 45°-P-45° sandwich sheets.

Anisotropy effects on the tensile properties of AA5052 and AA5052-PVC-AA5052 sandwich sheets

Abstract The essence on sheet metal industry innovation for making light weight bodies has been increasing day-to-day in the automotive sector. Based on the current demand and significance of sheet metals, the present work has been carried out on AA5052-PVC-AA5052 sandwich sheets to find out its tensile behaviour and hence related mechanical properties. The tensile behaviours of as received AA5052 alloy sheet of 1 mm thickness, PVC sheet of 0.5 mm thickness and AA5052-PVC-AA5052 sandwich sheet of 2.5 mm thickness were investigated. From the test results, the mechanical properties like yield strength (YS), ultimate tensile strength (UTS), uniform elongation (UE), total elongation (TE), strain hardening exponent (n) and material strength coefficient (K) were evaluated. From the experimental results, rolling direction of base metal AA5052 alloy sheet has an influence on the mechanical properties; moreover, among three rolling directions such as 0°, 45° and 90°, better mechanical properties have been observed in 90° rolling direction. Similar tendency is seen in the case of sandwich sheets of 90°-P-90° rolling direction than other sandwich sheets. From this work, one can understand the improvement of mechanical properties with different combinations and rolling directions of AA5052 alloy sheet. The manufacturing industry can use these data as it is for their inclusion to the future products.

Integral forming of continuous CFRP sandwich sheet by additive manufacturing

Sandwich sheets comprising continuous carbon fiber reinforced plastics (CFRP) are applied mainly in the aerospace industry due to their light weight and high rigidity. However, sandwich sheets require separate formation and bonding of the face sheets and core, resulting in high labor costs and early fracture due to delamination of the adhesive layer. The purpose of this study is to overcome these problems by integrating sandwich sheet using additive manufacturing. The mechanical properties of the integrally formed sandwich sheets were compared with those of adhesively formed sandwich sheets using a three-point bending test. The strain distribution was captured by digital image correlation (DIC) during the test. Additionally, the geometric design parameters of a core with superior mechanical properties were investigated. The test results showed that the integrally formed specimens exhibited superior properties compared to those of the adhesively formed specimens. It was also observed that the larger the width angle of the corrugated core, the better the mechanical properties.

Large sandwich sheets enabled by joining rolled sheets and additively manufactured core structures for forming

To overcome the size limitations of conventional laser-powderbed fusion (L-PBF) machines, a new methodology to manufacture large sandwich sheets by joining rolled sheets with additively manufactured core structures is developed, which potentially can be used as parts with a high amount of functional integration for heat exchanger systems or battery housings. Different joining mechanisms are directly applied to the core structure and tested for their strength in shear- and bending-experiments. Design guidelines for L-PBF are especially important to guarantee good geometrical accuracy of the joining mechanisms. The joint strength exceeds the face sheet material strength with certain geometric parameters. A process window is developed showing that bending of the joined sandwich sheets is possible up to a bending radius R to sandwich sheet height H ratio of R/H = 3.33. The global axial compliance of the buckling-joining mechanism leads to an increased overlap of the joining mechanism and the face sheet, thus a high bonding strength is achieved.

Evaluation of forming limit diagram and bending stiffness of SS316L/polyurethane/SS316L sandwich sheets

Abstract In this study, SS316L/polyurethane/SS316L was produced by warm roll bonding and direct adhesion without using any adhesive. By changing the polymer core thickness in the sandwich sheet, its mechanical properties, such as tensile behavior and flexural bending strength, were investigated. Also, by performing the Erichsen test and getting the experimental forming limit diagram, the forming behavior of the sandwich sheets in various thicknesses was investigated and compared with that of the monolithic steel sheet. The experimental results showed that by increasing the thickness of the sandwich sheets with polymeric core thickness of 2 mm to 2.5 and 3 mm, the bending stiffness was raised by 111% and 288%; also, the displacement in the second region of the bending test diagram, indicating the bending ability without delamination, was increased from 100% to 109%. Forming limit diagrams of the sandwich sheets were higher than those of the steel sheet, which indicates that the forming behavior of them are higher than that of the monolithic steel sheet.

Improving the formability of sandwich sheets by the hydrostatic effect of encapsulated media

Improving the formability of sandwich sheets by the hydrostatic effect of encapsulated media

Optimization Design of the Bending-Vibration Resistance of Magnetorheological Elastomer Carbon Fibre Reinforced Polymer Sandwich Sheets

An optimization design of the bending-vibration resistance of magnetorheological elastomer carbon fibre reinforced polymer sandwich sheets (MECFRPSSs) was studied in this paper. Initially, by adopting the classical laminate theory, the Reddy's high-order shear deformation theory, the Rayleigh-Ritz method, etc., an analytical model of the MECFRPSSs was established to predict both bending and vibration parameters, with the three-point bending forces and a pulse load being considered separately. After the validation of the model was completed, the optimization design work of the MECFRPSSs was conducted based on an optimization model developed, in which the thickness, modulus, and density ratios of magnetorheological elastomer core to carbon fibre reinforced polymer were taken as design variables, and static bending stiffness, the averaged damping, and dynamic stiffness parameters were chosen as objective functions. Subsequently, an artificial bee colony algorithm was adopted to execute single-objective, dual-objective, and multi-objective optimizations to obtain the optimal design parameters of such structures, with the convergence effectiveness being examined in a validation example. It was found that it was hard to improve the bending, damping, and dynamic stiffness behaviours of the structure simultaneously as the values of design variables increased. Some compromised results of design parameters need to be determined, which are based on Pareto-optimal solutions. In further engineering application of the MECFRPSSs, it is suggested to use the corresponding design parameters related to a turning point to better exert their bending-vibration resistance.

Recent Trend in Joining of Metal to Polymer- A Review

The metal-polymer hybrid system is widely used in automobile and aviation sector due to its lightweight characteristics. Besides, it has many advantages such as noise reduction and damping. Inclusion of these system improve the fuel economy, which eventually results in dramatic reduction of carbon footprint. One of the important metal-polymer hybrid system is sandwich panels. These are used as structural members by the transportation industries. Joining of polymers to metals is always a challenge because of their large property difference. Traditional joining methods are not recommended practice in sandwich sheet joining. Till now, many attempts are made to join polymers to metals. This paper highlights various difficulties and defects in joining of polymer to metals. Moreover, effect of process variables is also discussed in detail. The main objective of this review is to find out an efficient process for joining of metal-polymer composite and to establish a systematic approach of improving the quality of joints in sandwich sheets. Key Words: Metal-polymer hybrids, Sandwich sheets, Joining, Welding.

Enhancement of mechanical property and formability of CFRP core sandwich sheets by additive manufacturing process-induced material and structural anisotropies

The additive manufacturing (AM) of fiber reinforced plastics has gained much interests in the design of lightweight structures with superior mechanical performance. Strong anisotropy can be induced during the extrusion process owing to the preferentially orientated fiber reinforced plastics with high aspect ratio. To make better use of AM-induced material anisotropy, an integrated material-structure-performance design strategy for AM-produced carbon fiber reinforced plastic (CFRP) structures was proposed, in which the microscopic material and mesoscopic structural anisotropies were integrated to achieve enhanced macroscopic mechanical performance of CFRP core structures and sandwich sheets. The effects of AM process parameters including the layer thickness and build orientation on microscopic material anisotropy of the AM produced CFRP were firstly investigated and the strong relationship between material anisotropy and AM process parameters was confirmed by extensive mechanical tests and microscopic observations. A new core structure possessing the arbitrary bending anisotropy was proposed and the relationship between structural anisotropy ratio and bending stiffness was clarified. In addition, the mechanical properties of core structures were tested and superior mechanical performance can be achieved by tailoring the combination of material and structural anisotropies. The effects of structural anisotropies on mechanical properties and face buckling behaviors of sandwich sheets were investigated and found that face buckling is the dominant failure behavior. The new finding that the integration of microscopic material anisotropy and mesoscopic structural anisotropy induced by AM could enhance the mechanical property and formability of CFRP core sandwich sheets is of great significance in the design of lightweight structures. • An integrated material-structure-performance design strategy for additive manufacturing (AM) produced fiber reinforced plastic structures • The effects of AM process parameters including layer thickness and build orientation on microscopic material anisotropy of CFRP are clarified • Structure that can achieve an arbitrary bending anisotropy is proposed • The relationship between structural anisotropy ratio and bending stiffness is investigated • Better mechanical performance can be achieved by the integration of material and structural anisotropies

Design and Performance Evaluation of Flame Retardant and Thermally Insulated Material-Integrated Multi-Functional Thermoplastic Corrugated Sandwich Panels

Multifunctional composite panels for flame retardant and thermal insulation have not yet been studied. In the current study, we prepared sandwich sheets by using continuous glass fiber flame retardant polypropylene prepreg tape and compared the thermal insulation properties of different fillings. Corrugated sandwich panels, featuring a corrugated space filled with different materials, were prepared and their thermal and mechanical properties are tested and verified. Determining the two structural parameters that have the greatest influence on the heat transfer performance of corrugated sandwich panels has important guiding significance for the structural design of corrugated panels.

Numerical Investigation of Hot Roll Bonding of Multilayer Sheet Metal

The roll bonding process of the sandwich sheet is a preferable production method to manufacture multilayer sheets and it needs clear investigation because some industrial parts cannot fulfill all of the requirements by single-layer material. In this study, a theoretical model of roll bonding has been reviewed and hot sandwich rolling processes with different plate thickness and flow stress were numerically investigated. The contact pressure-dependent bonding properties in the deformation zone were defined. Then, the liner thickness and reduction ratio are important parameters to determine the total deformation zone. When the thickness of the liner becomes large, unbonded length of deformation can be a serious problem and at the same time, the good bonding strength can be found at a higher reduction ratio of the thinner liner.

Investigation of Forming Behaviour of Metal-Polymer Sandwich Composite through Limit Dome Height Test Simulations

Metal-polymer-metal (MPM) sandwich composites are in the class of proficient engineering materials which give outstanding strength-to-weight ratios because of their comparatively low density. These materials are vital constituents within the automobile, aerospace, marine, and civil construction industries as substitutes for sheet metals that considerably reduce weight while not compromising functionality. Moreover, these materials have supplementary qualities like sound dampening and thermal insulation capabilities. For these materials to be utilized within the aforesaid industries, they need to bear numerous forming processes that are essential in product manufacturing. This paper investigated formability analysis of metal-polymer sandwich composites made of “AW 6082-PVC-AW 6082 (APA)” and “galvanized steel-PVC-galvanized steel (GPG)” sandwich sheets, considering epoxy structural adhesives as the binding agent, via FEA simulation. All the FEA simulations were performed using Altair HyperWorks software. For evaluating the formability, the actual limit dome height (LDH)—biaxial strain path—tests were simulated using FEM software. The results analyzed are forming limit diagram (FLD), punch force distribution, and a dome height at diverse conditions of punch velocity and friction. A comparison is made to represent the best combinations for formability of the sandwich composites. Maximum formability and dome height are attained at low friction conditions and forming speed. It has also been observed that LDH simulations are very sensitive to friction, and it has a substantial impact on the test outputs. Maximum thinning (or fracture) generally moves away from the apex of the dome towards the die corner radius as the friction increases from zero upwards.

Design of bendable sandwich sheets with 3D printed CFRP cores via multi-stage topology optimization

The applications of sandwich structures are mainly limited to flat panel types due to their poor bendability. To develop bendable sandwich sheets, a new design strategy was proposed in this study, in which the density-based topology optimization was integrated with the multi-stage genetic algorithm (GA) to optimize the material layout so that the sandwich topologies can withstand potential failures including core shear failure, core-face sheet delamination and face buckling at given bending conditions. The topology optimization problem was mathematically formulated based on theoretically deduced failure constraints on core shear failure, face buckling and core-face sheet delamination. The adaptive multi-stage GA was adopted to solve the topology optimization problem with massive design variables and generate optimized topologies with sufficient resolutions to be additively manufacturable. The optimal topologies at given volume fraction constraints were additively manufactured using carbon fibre reinforced nylon (Onyx) and bending tests were conducted to check the bendability. Results indicate that topologically optimized SUS304/Onyx/SUS304 sandwich sheets can be bent without failure, which demonstrates the validity of the proposed topology optimization strategy. The proposed method is potentially capable of designing bendable sandwich sheets with arbitrary material combinations and is expected to expand the application envelope of lightweight sandwich structures.

Bending properties of sandwich sheets with metallic face sheets and additively manufactured 3D CFRP lattice cores

• Sandwich sheets with representative shell-lattice, truss-lattice and plate-lattice cores are proposed. • Effects of core topologies on mechanical properties and bendability of sandwich sheets are clarified. • Theoretical predictions of failure modes during bending of sandwich sheets with 3D lattice cores. • Bendable sandwich sheets with 3D lattice cores are successfully designed and produced. • Bendable sandwich sheets with multifunctional application potentials. To improve structural performance, bendability and potential functionality of metal-based sandwich sheets, the 3D lattice cores were sandwiched between thin metallic face sheets. The bending properties of sandwich sheets with 3D printed carbon fiber reinforced plastic (CFRP) lattice cores originating from basic topologies of spherical shell, tetrahedral truss and tetrahedral plate were systematically investigated. The effects of core topologies, core relative densities, core heights, face sheet thicknesses on structural properties were clarified. The common failure modes during bending of sandwich sheets, such as face buckling and shear failure of core, were deeply investigated by theoretical models and experimental tests. At a prescribed radius of 60 mm, the sandwich sheets with the bilayered dome, octet truss and plate lattice cores of relative density of 50 %, height of 6 mm and face sheet thickness of 0.5 mm are bendable. This study demonstrates the feasibility of design and production of bendable sandwich sheets with 3D lattice cores based on the theoretical and experimental validations. The designed bendable sandwich sheets can be adopted to replace conventional heavy monolithic metal sheets in various engineering applications, which is anticipated to fulfill the high demand for lightweight functional materials.

Density-based topology optimization integrated with genetic algorithm for optimizing formability and bending stiffness of 3D printed CFRP core sandwich sheets

To expand the application ranges of sandwich sheets from conventional 2D flat panel types to 3D complex shapes and simultaneously improve the specific bending stiffness , a novel topology optimization strategy that can optimize the bending stiffness while maintaining good formability was proposed. In the proposed approach, the density-based topology optimization was integrated with the multi-stage genetic algorithm (GA) to optimize the repeatable unit cell of the core structure of sandwich sheets. Two optimization schemes were adopted, in which one optimizes the formability and the other one optimizes the bending stiffness while fulfilling potential failure constraints. The failure constraints on core shear failure and face buckling were theoretically deduced to mathematically formulate the topology optimization problem, which was solved by the adaptive multi-stage GA to increase the possibility of generating physically meaningful and additively manufacturable topologies. For the experimental evaluations of mechanical properties and formability, the final optimal topologies under volume fraction constraints of 50% and 62.5% were additively manufactured using carbon fibre reinforced nylon. Comparing the sandwich topologies obtained by two optimization schemes, the bending stiffness of sandwich topologies with the core density of 50% and 62.5% are improved by 41.58% and 41.49%, while the energy absorption capabilities are improved by 13.60% and 29.40% respectively. L-bending and draw-bending tests indicate the improved formability of topologically optimized sandwich sheets. The proposed approach is capable of designing formable sandwich sheets with improved bending stiffness, which is expected to expand the application envelope of sandwich sheets with better mechanical properties. • Topology optimization of sandwich sheets that can not only be bent without failure but also have optimal bending stiffness. • Integration of density-based topology optimization with multi-stage genetic algorithm. • Theoretical core shear failure and face buckling constraints on sandwich sheets during bending. • Improved bending stiffness and formability of topologically optimized sandwich sheets with 3D printed CFRP cores.

Influence of Adhesion Properties on the Crash Behavior of Steel/Polymer/Steel Sandwich Crashboxes: An Experimental Study

The energy absorption behavior of crashboxes made of steel/polymer/steel (SPS) sandwich sheets can be influenced by numerous parameters, such as the materials used, their thicknesses and stacking, and the adhesion properties between their layers. Therefore, in the present study, the impact of steel/polymer adhesion quality on the occurring failure modes of the crashboxes and the resulting energy absorptions are experimentally analyzed. For this purpose, axial crushing and three-point bending tests on double-hat and top-hat crash boxes were performed, respectively. Three levels of adhesion quality are investigated: none, weak, and strong adhesion strengths. Additionally, the structural crash properties, such as energy absorption and maximal intrusion, are determined and analyzed at both of the quasi-static and highly dynamic loading rates. The results of these investigations show that the adhesion strengths chosen here significantly influence both the failure modes and the energy absorption values. In particular, the structural parameters, in the case of no adhesion, are at most half of those in the case of strong adhesion. However, it is also shown that, in the case of weak adhesion, the structural characteristics are slightly reduced. Based on these results, the possibility to adjust the adhesion strength—globally and/or locally—could be used in future activities to purposefully tailor the failure behavior of hybrid crashboxes.