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Textile reinforced concrete (TRC) is a combination of a cementitious matrix and a textile reinforcement that has good mechanical properties. This makes a highly promising composite material for a wide range of construction practices. One notable application of this innovative composite deals with the production of thin sandwich panels. Hence it is noteworthy to examine the control parameters (depth & number of layers) that affect the mechanical properties of TRC sandwich panels with chosen fibre meshes and core material.Initially, 24 different TRC panels were cast and modelled with varying depths (45 mm, 55 mm and 65 mm) and layers (3, 4, 5 and 6), incorporating two different fibre mesh reinforcements. The flexural behavior of these panels was studied both experimentally and numerically using ABAQUS software. The optimized control parameters was obtained from the results was TRC panel of 5 layers of Aramid fibre mesh having 55 mm depth.Further exploration focused on the effect of overall depth variation on the flexural behavior of TRC sandwich panels. A panel with Aramid fibre reinforcement and a calcium silicate board core, featuring a 55 mm overall depth, exhibited a remarkable 69.49 % increase in bending stress compared to a panel with a depth of 118 mm. These findings underscore the significance of optimized control parameters, showcasing the potential for enhancing the mechanical performance of TRC sandwich panels in construction practices. [Display omitted] • The flexural behavior of TRC sandwich panels with aramid fibre mesh as a reinforcement and calcium silicate board as a core was investigated both experimentally and numerically. • The impact of the type of fibre meshes, number of layers and depth (control parameters) on TRC sandwich panels was analyzed. • Optimized control parameters were identified, with a TRC panel consisting of 5 layers of Aramid fibre mesh and a depth of 55 mm showing superior performance. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and analytical study about the sound insulation of innovative sandwich panels - named EasyFloor – for the rehabilitation of degraded timber floors in old buildings. Two types of panels were developed: (i) an all-composite sandwich panel, made of glass fibre reinforced polymer (GFRP) face sheets and webs, and polyurethane (PUR) foam; (ii) and a hybrid sandwich panel, where the top face sheet comprises a thin layer of concrete. The study included the comparative analysis of the airborne sound reduction and impact sound pressure level of both types of panels based on experimental tests on full-scale specimens, including a typical floor covering. The acoustic insulation properties determined experimentally were compared with predictions from different analytical models typically applied to sandwich panels, and also with performance requirements defined in building regulation. Among the different analytical models that were assessed, Sharp's model provided the most accurate predictions when considering the natural and dilatation frequencies as the critical frequency. The comparison of the normalized airborne and impact sound indices determined experimentally with requirements set in building regulation shows that the use of GFRP-PUR panels in the rehabilitation of lightweight timber floors and in new construction, where building comfort requirements are stricter, require mitigation measures to improve sound insulation. • Acoustic behaviour of web-core all-composite and hybrid sandwich panels. • Airborne and impact sound insulation tests. • Influence of panel architecture and effects of resilient floor covering. • Assessment of different analytical models for sound reduction prediction. • Comparison with building comfort requirements. [ABSTRACT FROM AUTHOR]

• An integrated 3D printing of fiber-reinforced sandwich panels is proposed. • The epoxy resin pre-impregnated fibers are employed to print overhanging structure. • The integrated 3D printed sandwich panels excel in lightweight properties. • The Schwarz Primitive core structure has the maximum energy absorption. • FE model is developed to analyze the damage mechanism of printed samples. Sandwich panel structures have widespread applications in various components, owing to their excellent lightweight properties. However, conventional manufacturing methods involve multiple steps, which limits the exploration of innovative sandwich panel structure. In this study, an integrated 3D printing method for continuous fibers reinforced sandwich panel with Triply Periodic Minimal Surface (TPMS) core structure is proposed via Fused Deposition Modelling (FDM). A bridging layer and a continuous basalt fiber pre-impregnated by stiff thermoset epoxy resin are utilized to address the issue of overhanging printing for the upper face sheet. Two kinds of TPMS are employed as the core, as well as two kinds of honeycomb. Multi-step printed samples using a bonding process and counterpart samples without fiber were prepared for the comparison. 3-point bending tests were conducted and a finite element model which can represent the structure characteristic is proposed to investigate the mechanical properties. The results show that the integrated printed sample exhibits better performance in terms of printing quality, flexural modulus, strength and energy absorption (EA) compared with the multi-step printed sample. It has an excellent ability to avoid the catastrophic damage which is usually encountered in the multi-step printed sample due to the introduction of brittle epoxy resin, showing a notable 162.88 % augmentation in specific energy absorption (SEA). The significant improvement lies in that it uses the reinforcement of fiber and the energy absorption capacity of core to full advantage via the strong binding. In addition, as one kind of TPMS, Schwarz Primary structure exhibits the maximum flexural modulus, strength and energy absorption among the four cores. The proposed design and fabrication methodology pave the way for the creation of high-performance sandwich panels with different core structures. [Display omitted] [ABSTRACT FROM AUTHOR]

This study investigates the potential of developing corrugated panels from tea oil camellia shell (TOCS), an abundant agricultural waste in the southern provinces of China, with an annual production of approximately 4 million tons, using experimental and computational methods. Hence, various corrugated geometries were designed using AutoCAD software, and finite element analysis (FEA) was conducted using Ansys Mechanical software to optimize the panel geometry based on TOCS engineering data. Bending performance simulations revealed that a trapezoidal geometry with a 3 mm edge radius exhibited superior bending performance. Therefore, this geometry was selected to fabricate corrugated panels of different densities to assess the impact of density variation. Mechanical characterization included evaluation of bending stiffness, maximum moment, total deflection, compression strength, ultimate strength, dowel bearing strength, and face screw resistance of the panels was performed. Furthermore, specific energy absorption and failure mechanisms of mechanical tests were analyzed. The results indicate that TOCS-based sandwich panels, characterized by their lightweight and sustainable nature, not only meet, or exceed the criteria specified in APA PS 2–10 for use as structural materials but also mitigate the environmental hazards associated with landfill disposal or burning of agricultural waste. • Developing a light-weight and eco-friendly sandwich panel based on agricultural waste. • Increased surface layer density enhances mechanical properties, meeting ANSI A208. • Density variations enhance energy absorption and failure resistance. • Trapezoidal geometry is optimized for superior load-bearing and stress distribution. [ABSTRACT FROM AUTHOR]

The nonlinear stochastic behavior of soft-core sandwich panels and the evolution of uncertainty along the nonlinear path are investigated. The paper focuses on the way the geometrically nonlinear and unstable behavior is affected by uncertainty and considers, for the first time, the evolution of uncertainty along the unstable structural response. The structural modeling relies on the EHSAPT and its integration into the geometrically nonlinear stochastic regime. A tailored nonlinear FE model that is based on a variational formulation and an arc-length solution scheme are developed. The stochastic analysis adopts the Perturbation-based SFEM and its generalization for the evolution of uncertainty along the process axis. A numerical study demonstrates the stochastic methodology and explores the impact of uncertainty on the nonlinear structural behavior. The evolution of the stochastic stress resultants at the displaced end is studied along the two axes of evolution. The differences between the two representations and their physical and engineering significance are highlighted revealing significant changes to the uncertainty evolution pattern with the shift from global buckling to localized wrinkling instabilities. The representation of the stochastic results along the process axis also quantifies the level of uncertainty near critical and singular points where conventional analyses diverge. [ABSTRACT FROM AUTHOR]

• Stressed-skin full scale test on steel monopitch portal frame was conducted. • Comparison of test data provided clear influence of the cladding on the horizontal structure stiffness. • FE numerical model was created, validated based on the test data. • The approach for taking into account the cladding horizontal shear stiffness was derived and compared. This paper presents a study on the influence of sandwich panel roof cladding on the horizontal stiffness of load-bearing steel structures (stressed skin action). A full-scale test was carried out on a steel monopitch portal frame structure made in two stages – without (bare steel structure) and with roof sandwich panel cladding. Data obtained from both stages of the test are presented and are used to demonstrate the significant increase in horizontal stiffness caused by the cladding system. The test data were then used to validate an FE numerical model. A roof cladding made of composite panels is relatively stiff in its own plane. However, the critical detail is the connection of the panels to the sub-structure (e.g. purlins or rafters), i.e. the screw bearing capacity. Even within the serviceability limits, the internal sheet of the composite panel suffers a certain level of permanent bearing damage. Based on the test data, the results of the FE numerical model and the analytical approach for calculating the shear stiffness of the sandwich panels, the approach for taking into account the influence of the cladding on the horizontal stiffness was derived and compared. This approach is believed to be safe and simple for practical use, and it leads to load-bearing structure members with more slender cross-sections. In addition, the data and results that are obtained expand the limited amount of available data related to stressed skin action. [ABSTRACT FROM AUTHOR]

• The novel honeycomb core sandwich structures were fabricated by combinations of solid-state joining and adhesive bonding processes. • The combined friction stir spot welded, with disc inserts and adhesive bonded, demonstrated exceptional peak load-to-weight ratio and fracture energy. • The peak load of the hybrid bonding specimen with disc insert improved by 705 % and 854 % in the peel and shear test compared to the conventional adhesive bonded specimen. • The stiffness and peak load results of FEA of three-point bending were in good agreement with the experimental results for all types of adhesive-bonded specimens. In the present work, the novel sandwich structures with honeycomb core are fabricated by a solid-state joining process — friction stir spot welding (FSSW), without and with disc inserts (abbreviated as FSSW and FSSW_D) and hybrid joints without and with disc inserts (abbreviated as FSSW_AB and FSSW_D_AB). Their mechanical performance was compared with adhesive-bonded (AB) joints through the lap-shear, peel, bend, and scaled-up forming tests. Further, numerical simulations of a few FSSW strategies and AB joints are performed in Abaqus to predict the load-displacement response and Mises stress during bending. Proposing the fabrication stretegies, implementation and testing, along with numerical prediction of behavior of such joints, are the novel contributions. The peel tests showed substantial improvement in load capacity from 232 % to 705 % for FSSW, FSSW_AB, FSSW_D, and FSSW_D_AB joints, compared to AB joints. In the lap-shear tests, all joint types displayed significantly enhanced peak load over AB joints, ranging from 568 % to 1015 %. The hybrid joints, such as FSSW_AB and FSSW_D_AB, consistently outperformed the corresponding spot-welded joints, FSSW and FSSW_D, due to the sharing of load between the AB and metallurgical bonding. The FSSW_D_AB joints demonstrated exceptional peak load-to-weight ratio and fracture energy. The failure modes were consistent, with disc-inserted structures showing failure at the front-side welds for lap-shear and peel tests. During bending, the numerical modelling results were in good agreement up to the peak load. Bending panels made by FSSW_D_AB demonstrated improvement in specific stiffness and peak load by 46 % and 6.12 %, respectively, compared to the AB panel. Lastly, the scaled-up hybrid sandwich panel (FSSW_D_AB) showed significant improvement in deliverables when compared with the AB panel. [ABSTRACT FROM AUTHOR]

• Classification of the deformation modes of sandwich panels with Miura-ori cores is proposed. • An analytical meso‑scale model of panels' deformation with strong origami cores is developed. • The applicability of the homogenisation approach to the core material properties is analysed. • Experiments were conducted to validate the finite element studies and analytical models. • Comparison of the bending strengths of Miura-ori, PVC and honeycomb core panels is presented. Collapse mechanisms of sandwich panels with Miura-ori cores are analysed and classification of the deformation regimes under three-point bending is proposed. It is revealed that the homogenisation approach to the core material properties is not applicable to the deformation of panels with relatively strong origami cores due to the immediate simultaneous local deformations of the core and face sheets. To describe this deformation regime, an analytical model based on the development of new stationary hinge lines in Miura-ori cells and rigid motion rotation of the adjacent planes is proposed. The model pertains to a single degree-of-freedom model governed by the global bending angle of the panel. On the other hand, the homogenisation approach to the core material properties proved to be applicable to bending analysis of panels with relatively soft Miura-ori cores. This approach is used to analytically obtain the collapse load related to several deformation modes. Parametric FE analysis is conducted to further explore the deformation regimes of panels with different face sheet thicknesses. Experiments were conducted to validate the finite element studies and analytical models. A good agreement between the analytically predicted collapse forces and those obtained by the FE simulations is shown. Deformation mode maps are constructed based on the analytical and FE analyses in terms of the face sheet thicknesses and core strength. A brief comparison between the bending strength of sandwich panels with Miura-ori cores and panels with PVC and honeycomb cores is presented, demonstrating the superiority of the honeycomb cores loaded in the out-of-plane direction. On the other hand, the possibility of the development of high shear strains in metallic Miura-ori cores without damage gives them advantages compared to three-point bending of panels with low density PVC foam cores. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel design optimization method for functionally graded multi-morphology cores is proposed faster than topology optimization method. • Functionally graded multi-lattice cores demonstrated a 96% increase in maximum load and 174% in stiffness compared to the uniform lattice. • The central area of the structure has experienced minimal displacement and deformation under bending load, resulting in increased strength and rigidity. • The gradient change in the morphology of the core has delayed the fracture and increased the uniformity and coherence in the structure. This investigation aims to present a high-strength sandwich core with functionally graded multi-morphology lattice inner structures through vat photo-polymerization additive manufacturing (AM). The five better strut-based designs based on [1] , are considered here. All printed specimens have been fabricated from photopolymer resin to ensure manufacturability in a digital light processing (DLP) 3D printer. Firstly, the resin and structural characteristics have been examined. Simultaneously, the lattice core is divided into three regions based on the von Mises stress distribution and tensile and compression responses in finite element analysis (FEA). Based on the mechanical responses of the beam-based structures, these topologies have been applied in each region in an optimal fixed relative density distribution, considering different steps and types. This proposed technique is numerically investigated and experimentally validated using a three-point bending test. As a result, the optimized core demonstrated a 96% increase in maximum fracture force and a 174% increase in stiffness compared to the homogeneous body. Additionally, it exhibited a different deformation mode than the single morphology under similar conditions. These significant findings indicate that this approach provides a new perspective on a high-strength design involving more than three morphologies, and it is faster than computational topology optimization processes. [ABSTRACT FROM AUTHOR]

Active façade systems incorporating solar thermal collectors currently offer very promising energetic solutions. From among the available systems, a simple solution is the unglazed heat collector for potential integration in low-temperature applications. However, when adopting system definitions, the modification of some design parameters and their impact has to be fully understood. In this study, the case of an unglazed collector integrated into a sandwich panel is assessed and a specific analysis is performed for a proper assessment of the influence of key design parameters. Based on that case study of the real built system, a CFD model is developed and validated and a parametric assessment is then performed, by altering the configurations of both the panel and the hydraulic circuit. In this way, the potential of each measure to harness solar energy can be evaluated and each parameter with its different level of impact can be highlighted, to identify those of higher relevance. A characterization of the real solution completes the study, by providing the efficiency curves and the total energy collected during the experimental campaign. The maximum estimate of the efficiency of a 6 m2 façade was within a range between 0.47 and 0.34 and the heat loss factor was between 4.8 and 7.5. The case study exercises reveal the real energy efficiency and solar production patterns. There was also an opportunity to consider significant improvements to increase the output of the active façade. The main conclusions concerned the different criteria that improved the definition of the system and greater comprehension of alternative designs that may be integrated in the underlying concept. Image 1 • Quantification of key design parameters for a lightweight active façade system. • Identification of main design aspects for efficiency improvements. • Complete characterization of an active façade with an unglazed metallic collector. • Study of the interrelation between efficiency and energy output for the system. • Numerical model developed and validated with real measured data. [ABSTRACT FROM AUTHOR]

• The development of an energy generating sandwich panel and associated management system is presented. • Numerical simulations that were used to size all the elements of the system are presented. • Thermal tests of the cladding panel are reported. • Experimental validation of all the developed elements is also presented. There is currently a global need to reduce the emission of greenhouse gases. Since buildings are the largest contributor to global warming emissions, improving their energy performance through the implementation of renewable energy technologies is a way forward to reduce energy use and thus carbon footprint. This article presents a new building envelope system that harvests solar energy through the steel skin of the façade of the building. The energy is generated by a steel sandwich panel featuring a modular design that enables full integration into the building envelope of both new constructed and refurbished buildings. The heat transfer means is a glycol and water mixture that flows inside a pipework arrangement embedded into the sandwich panel and connected to a distribution system. This distribution system deploys the energy generated into a buffer tank for further production of heating, cooling and domestic hot water through the use of a heat pump. The elements of this solar system were developed under the framework of the Building Active Steel Skin Envelope (BASSE) project funded by the Research Fund for Coal and Steel (RFCS). A detailed description of the components of the BASSE system as well as how they were developed is presented. Building on satisfactory thermal testing and the successful implementation of the system on a pilot building, the BASSE system was validated. The experimental results have shown that the coefficient of performance (COP) of the heat pump is in between 4.1–4.6. A validated simulation tool estimated that the cladding panel generates 3321.14 kWh/year which is 30.4% efficiency. Simulation results showed that a 35 BASSE panel installation on residential buildings subjected to temperate climate are Net Zero Energy Buildings (NZEB). [ABSTRACT FROM AUTHOR]

Composite structural elements can serve dual purposes of transferring the load and insulating the buildings. This paper presents and discusses the results of experimental study carried out to understand the flexural behavior of prototype precast insulated concrete sandwich panels using truss-shaped continuous shear connectors. Experimental study consisted of four prototype concrete sandwich panels tested under four-point bending simulating one-way slab action. Panel thickness and size of wire mesh used as reinforcement in concrete wythes are the major parameters considered. Test results indicate that the truss-shaped shear connectors are effective to achieve composite action of the panels until failure. Test results also indicate that the panel thickness affects the flexural load carrying capacity, and size of wire mesh affects the ductility. Experimental and analytical studies are required in this area towards developing guidelines for design of concrete sandwich panels for field applications. [ABSTRACT FROM AUTHOR]

• Two-dimensional fatigue behavior in GFRP/balsa sandwich panels was investigated. • Decreasing crack growth rates were obtained under load-control. • The hysteresis area of load-displacement loops increased with crack propagation. • The hysteresis loops showed an increase in the cyclic stiffness within each cycle. An experimental investigation of the two-dimensional (2D) debonding behavior of GFRP/balsa sandwich panels with embedded circular disbonds at the face sheet/core interface subjected to out-of-plane fatigue loads was conducted. The constant amplitude fatigue experiments were performed under load control and different R -ratios. Two face sheet configurations were investigated: a pure woven ply layup (SPA) and a combination of continuous filament mat (CFM) and woven plies (SPB). For the latter, the CFM layers (which are prone to develop fiber-bridging) were placed above and below the woven plies. In contrast to one-dimensional (1D) beam-like fatigue fracture experiments, decreasing crack growth rates and stable crack propagation were achieved under load control as a result of the 2D growth of the disbonds. The fatigue fracture performance obtained under R = 0.1 for the SPB configuration was less efficient than for the SPA configuration owing to the fiber-bridging crushing associated with high fatigue amplitudes. Under higher R -ratios, a reduced amount of fiber-bridging crushing was observed, leading to a corresponding crack arrest and much longer life. The load-displacement hysteresis loops exhibited an increase in the cyclic stiffness within each fatigue cycle throughout the experiments. This stiffening was mainly caused by in-plane stretching stresses that developed in the debonded part of the face sheets whose magnitude and evolution were evaluated based on the in-plane strains monitored during the experiments. [ABSTRACT FROM AUTHOR]

Abstract The two-dimensional (2D) debonding behavior of GFRP/balsa sandwich panels presenting embedded circular disbonds at the face sheet/core interface was experimentally investigated. The bottom of the panels was fixed and out-of-plane quasi-static tensile loads were applied to open the crack. Two different face sheet configurations were studied. The first consisted of a pure woven ply layup while in the second, layers of continuous filament mat (CFM) were placed above and below the woven plies. The inclusion of CFM layers at the face sheet/core interface resulted in an enhanced fracture behavior exhibiting improved load-bearing performance and significant crack arrest. In-plane stretching strains appeared in the deformed face sheets due to the 2D embedded nature of the crack. The magnitude of the stretching was quantified based on the in-plane strains monitored throughout the experiments. As a result of the stretching, shear mode contributions were activated, causing the initiation of secondary cracks in the pure woven configuration and crack migration in the woven/CFM configuration. The migration in the latter occurred from the face sheet/core interface to the woven/CFM interface, generating dense fiber-bridging. This intensified fiber-bridging was found to be the main cause of the already-mentioned improvement in the fracture performance of the woven/CFM configuration. [ABSTRACT FROM AUTHOR]

Highlights • FRP bridge deck that incorporates PU foam was developed for ABC and repair. • Results of testing indicated that the deck significantly exceeded the AASHTO requirements. • The decks behaved linearly-elastically throughout the full range of loading. • The experimental results were used to evaluate the applicability of existing FRP design equations. Abstract A fiber-reinforced polymer (FRP) bridge deck panel that incorporates a polyurethane foam core was developed for accelerated bridge construction and repair. This low cost panel was tested under monotonic loading and compared to applicable FRP design equations. This new prototype system consisted of two stiff facesheets of stitch bonded plain-weave woven E-glass fabric with sloping webs of E-glass woven fabric that are separated by trapezoidal-shaped, low-density polyurethane foam. The polyurethane foam was used in an attempt to reduce initial costs. The panels used in this study were manufactured using a one-step, vacuum-assisted, resin transfer molding process (VARTM) using a newly formulated, two-part, thermoset, polyurethane resin developed by Bayer MaterialScience to facilitate the infusion process. The results of the flexural and shear testing indicated that the prototype panels significantly exceeded the AASHTO Design Code Strength requirements by nearly three times. Even more importantly, the panels behaved linearly-elastically throughout the full range of loading and possessed significant post-buckling strength. In addition, the results of these full-scale panels were used to evaluate the applicability of existing FRP design equations when used for the design of the VARTM- manufactured, prototype FRP bridge deck. Results showed that the existing FRP design equations correctly predicted a flexural failure due to local buckling of the compression flange and a bearing failure due local buckling of the webs beneath the concentrated load. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Multi-criteria optimization study of sandwich panels for building floors. • There is a general proportionality between cost and carbon footprint. • Heavier and stiffer materials provide better acoustic performance, but increase panel costs. • Ribs along outer edges of panels fulfil structural requirements, but inner webs can improve acoustic behaviour. • Lower core density is generally preferable, provided that wrinkling failure of faces is prevented. Abstract Composite sandwich panels are being increasingly considered for civil engineering structural applications, offering high versatility in constituent materials and their geometrical arrangement. This translates to a high number of design variables, in addition to a potentially large number of design requirements and objectives related to the panels' functions. This paper presents an optimization study of a composite sandwich panel system for building floor rehabilitation, using the Direct MultiSearch (DMS) method. Pultruded multicellular panels with a polyurethane (PUR) foam core and carbon- or glass-fibre reinforced polymer (C/GFRPF) faces and ribs/webs are considered. The panel architecture was defined using 3 geometrical variables and 14 material related variables. In addition, 8 competing objective functions were studied, related to aspects such as structural serviceability and resistance, thermal insulation, acoustic performance, cost minimization, and environmental performance. The results are presented in the form of Pareto optimal sets, from which several conclusions are drawn regarding common design-related options. The influence of core material density, of the number of ribs/webs, or of the type of fibre reinforcement and its respective layup on the different objective functions are addressed. Optimal solutions for meeting different design purposes are presented, providing useful insights for structural designers and sandwich panel manufacturers. [ABSTRACT FROM AUTHOR]

Abstract In this paper, an innovative Foam-filled Lattice Composite Bumper System (FLCBS) with fiber-reinforced polymer (FRP) skins and a foam-web core is proposed as protective structures for bridge piers against ship collision. FLCBS consists of FRP face sheets, FRP lattice webs and polyurethane (PU) foam cores, which can be manufactured at the same time by vacuum assisted resin infusion process (VARIP). FLCBS exhibits good energy-absorbing and highly designable properties. The design, performance evaluation, manufacture and installation of FLCBS for a real prestressed concrete continuous girder bridge were introduced. A detailed numerical model for performance evaluation was developed with the explicit finite element (FE) software package ANSYS/LS-DYNA. An experimental study of two foam-filled lattice composite panels under low-velocity impact was conducted to verify the numerical model for FLCBS. The corresponding FE models of the composite panels generally showed good agreement, compared to the impact load history and mid-span deflection history of experimental results. Based on the validated numerical model, both head-on collision cases and lateral collision cases with and without FLCBS were investigated. Simulation of different impact angles, velocities and locations were carried out. Numerical results indicate the obvious advantages of FLCBS by comparing peak impact force and impact duration. Significantly decrement of the peak impact force and effectively prolonged impact process indicate the superior performance of FLCBS. The modular fabrication and replacement, easy and time-efficient installation and highly designable structure make FLCBS very attractive as bridge protection in ship collisions. [ABSTRACT FROM AUTHOR]

Highlights • Establish the model to calculate critical energy release rate of sandwich panels. • Derive the equation to calculate critical energy release rate. • Calculate G IC and G IIC for facesheet/core delamination of sandwich panels. • Validate the results by comparing with previous work. Abstract Critical energy release rate is one of the basic material parameters to evaluate interfacial performance. This paper presents a method to calculate the critical energy release rate for interfacial delamination of sandwich panels. This method can be applied to the calculation of the critical energy release rate of the interface between different materials. Double Cantilever Beam (DCB) test and Cracked Sandwich Beam (CSB) test have been studied in this paper. Carbon fiber/Nomex honeycomb sandwich panels and aluminum/foam sandwich panels are used for DCB tests to determine G IC. Glass fiber/balsa sandwich panels are used for CSB tests to determine G IIC. The comparison between this paper and previous work has verified the validity of the proposed method. [ABSTRACT FROM AUTHOR]

Concrete sandwich panels (CSPs) are oftentimes subjected to extreme exterior temperatures, causing thermal gradients between inner and outer surfaces, and eventually bowing. In addition, the composite degree (k p) of CSPs has been conventionally estimated using methods that require costly and time-consuming experimental tests or rigorous numerical models. The lack of research and understanding on the effects of k p and bowing oftentimes result in overly conservative and uneconomic design, particularly for partially composite (PC) panels. This study develops simple design equations for thermal bowing and k p in CSPs based on a comprehensive parametric study using a transient thermal-structural coupled finite element (FE) model developed earlier by the authors. Key parameters considered are span (L); connector configuration, material, and reinforcement ratio; wythe and insulation thicknesses; concrete strength and thermal differential (ΔT) on both sides. In panels with L larger than 13 m, particularly those featuring steel and CFRP truss connectors and subjected to temperature gradients (ΔT) higher than 30 °C, bowing was larger than the deflection serviceability limit of L /360. Cracking in concrete wythes and yielding of steel connectors were also observed and were mainly dependent on ΔT and k p. Two existing theoretical models were evaluated using results of the parametric analysis and were found to overestimate thermal bow, particularly for panels with low k p. A proposed bowing model is presented which incorporates the effects of composite degree and yields much better predictions than these from literature. • Evaluation of thermal bowing (Δ) and composite degree (k p) in concrete sandwich panels (CSPs). • Parametric study conducted using transient thermal-mechanical FE model. • Parameters are span; connector configuration, material, and reinforcement ratio, wythe and insulation thicknesses; concrete strength; and thermal differential (ΔT). • Temperature can cause cracking and serviceability issues for CSPs, mainly when ΔT ≥ 30o. • Two models were developed, for Δ and k p , from regression analysis and can be used for design purposes. [ABSTRACT FROM AUTHOR]

3D strut-based lattices consisting of periodic representative volume elements (RVE) have gained more importance over the last few years since they provide outstanding mechanical performance and an efficient design in lightweight engineering. In sandwich panels, strut-based lattices may replace the established honeycomb cores. In this study, an analytical model is introduced to investigate 3D strut-based lattice cores of sandwich panels. Body-centered cubic and face-centered cubic RVEs reinforced by vertical struts (BCCZ and F2CCZ) are considered as sandwich cores. Since the core stiffness is generally low in comparison with the face sheet stiffness, the derived model considers through the thickness stresses in the core caused by transverse concentrated loads, which are not obtained by the common sandwich theories. Furthermore, stress concentrations near the support points are sufficiently captured thanks to higher-order displacement representations. The analysis of the core behavior is based on the homogenization and dehomogenization of the lattice core methods. Compared with the finite element analysis, the stresses in the lattice struts are determined by the proposed model with ten times less computational effort and adequate accuracy, particularly in the highly loaded vertical struts. • Determination of core strut stresses by homogenization and dehomogenization methods. • Derived model applies to strut-based lattices, e.g., BCCZ and F2CCZ unit cells. • Reduction of the computational effort by a factor of 10 compared to FE modeling. • Capturing of stress concentrations and core indentation caused by localized loads. [ABSTRACT FROM AUTHOR]

This work focuses on the general nonlinear dynamic formulation of sandwich panels based on the Extended High-order Sandwich Panel Theory. The faces and the core are both considered undergoing large deformation with moderate rotation. In the literature, when it comes to nonlinear dynamic response, various simplifying assumptions are adopted in the nonlinear kinematic relations. A critical assessment of these simplifications, as well as a comprehensive investigation of the geometric nonlinearity effects on the dynamic response of sandwich beams/wide panels is presented. The Extended High-order Sandwich Panel Theory (EHSAPT)-based finite element is used to formulate the equations of motion, and the time response is obtained by the central difference method. The transient response of a sandwich panel subjected to a distributed blast loading is studied as a numerical example. By neglecting the nonlinear terms, the nonlinear dynamic analysis is reduced to the linear dynamic small deformation analysis, for which a closed-form elasticity solution exists. This, the linear response is first compared with the closed-form linear dynamic elasticity solution. It is shown that the linear EHSAPT yields an identical response to the dynamic elasticity analysis. Subsequently, the dynamic response is evaluated by considering the geometric nonlinearities. Several simplified nonlinear models with partial nonlinear terms included are considered. These models reflect the assumptions commonly adopted in the literature. Numerical results are presented to investigate the effects of geometric nonlinearities on the displacements and stresses. It is shown that the geometric nonlinearities have a significant effect on the dynamic response of sandwich panels and, in particular, the nonlinear terms in the core kinematic equations are especially important. [ABSTRACT FROM AUTHOR]

The non-linear response of a sandwich panel with the core that consists of a functionally graded material (FGM) undergoing in-plane loading is investigated. The panel consists of two face sheets, metallic or composite laminated, and an FGM core that is a medium whose mechanical properties change through the depth facilitating a desirable response of the structure. The effect of the FGM core is introduced through the constitutive relations that affect conventional and high-order stress resultants and stress couples in the panel. The formulation employs the Extended High-Order Sandwich Panel Theory (EHSAPT) to assess the effect of the FGM material of the core. A variational approach is adopted to derive the linear and non-linear governing equations with a prescribed FGM distribution through the depth of the core. The wrinkling study of FGM panels includes two loading scenarios where in-plane loads are applied through a rigid edge beam connected to the core only and where the loads are applied through a rigid edge structure attached to both the face sheets and core causing uniform end shortening. The post-wrinkling behavior is also considered to prove that the initial pattern of wrinkles is not affected. [ABSTRACT FROM AUTHOR]

In this paper, the effect of salt-fog exposition on the mechanical behavior of sandwich panels having cork agglomerate core was investigated. In particular, the aim of this research work is to assess the shield function of unidirectional basalt and E-glass reinforced polymer on the aging and failure mechanism of the core when such class of material are destined to operate in hostile environments (e.g., marine environment). To do this, the manufactured sandwich panels were exposed up to 60 days to salt-fog environment, according to ASTM B 117 standard. Unaged and aged specimens were analyzed through three point bending tests after aging time of 10, 25 and 60 days. Digital Image Correlation (DIC) was carried out to perform a strain field analysis of the longitudinal cross-sections. The differences in the mechanical behavior of the synergistic cooperation of the cork core with basalt and glass fiber were highlighted thorough this technique. Moreover, the failure mechanisms related to each combinations for different aging times were described. The experimental results showed that, the intrinsic conditions of the composites (e.g., presence of defects, poor fiber-matrix adhesion), that are strictly linked to the fiber-matrix compatibility and to the impregnation quality, may induce to differences in the local mechanical behavior of the sandwich panels and to a faster aging process of the cork core in the case of basalt fiber skinned sandwich, especially in the first phases of the exposition. [ABSTRACT FROM AUTHOR]

Three-dimensional carbon fiber reinforced polymer (CFRP) cores are high performance ultra-lightweight materials that can reduce the structural mass of vehicles used in the transportation and aerospace industry, increasing capabilities and performance, and reducing fuel consumption. In this work, three different carbon fiber cores are obtained using an interlocking method from flat composite laminates with different geometries. The density of the cores is maintained less than 48 kg m −3 . Sandwich panels are manufactured using these cores and carbon fiber reinforced epoxy skins. Compressive properties of the sandwich panels are evaluated and the failure modes are studied. Experimental results are compared to those predicted by analytical modeling and finite element method analysis (FEM). [ABSTRACT FROM AUTHOR]

In this study, a new core design is introduced for sandwich composite structures. Its strength and failure behavior are investigated via three-point bending tests. E-glass-fiber-reinforced epoxy resin is selected as the material for both the core and the face sheets. The core has an egg-crate shape. Acoustic emission (AE) method is used to detect the progression of damage. Signals due to elastic waves caused by activated damage mechanisms are investigated in order to identify the corresponding failure modes. A finite element model of the sandwich structure is developed to predict the failure behavior of the specimens under the loading conditions in the tests. A promising agreement between the results of the finite element model and the experiments is observed. The force-deflection-relation, the failure load as well as the region where damage initiates are accurately predicted. [ABSTRACT FROM AUTHOR]

Sandwich panel strips with prismatic cores are modelled using the modified couple stress theory and their elastic size-dependent bending behaviour investigated. Compatibility between the discrete sandwich and continuum beam kinematics is first discussed. A micromechanics-based framework to estimate effective mechanical properties is provided and unit cell models constructed with elementary beam elements to determine the stiffness parameters of various prismatic cores. Numerical studies show that the modified couple stress Timoshenko beam enhances the static deflection predictions of the classical Timoshenko model. A sensitivity measure based on structural ratios is proposed to estimate the influence of size effects in the global beam-level response. The parameters governing size effects in elastic sandwich beams are identified: Face-to-core thickness ratio, core density and topology, vertical corrugation order and set of load and boundary conditions. Size effects are shown more pronounced in low-density cores that rely on corrugation bending as shear-carrying mechanism. Based on the external load, boundary conditions and sensitivity factor, one can assess whether size effects are non-negligible in a given engineering structure. [ABSTRACT FROM AUTHOR]

Composite sandwich structures with lattice truss cores have both lightweight characteristics and multifunctional potential, which attract a large number of studies on topological optimization, manufacture process and performance evaluation in recent years. However, reliability study on the joint is an inevitable research subject for engineering application, and few studies on inserts within sandwich panels with lattice truss cores are published. In this paper, composite pyramidal truss core sandwich panels with lightweight metallic quadrangular-prism inserts are designed and fabricated. Pull-out and shear tests are carried out to investigate their load capability and failure behaviors, respectively. It is observed that, compared to the honeycomb panels, the present sandwich panels with quadrangular-prism inserts normally can obtain a similar level of pull-out strength but a higher level of shear load capabilities. [ABSTRACT FROM AUTHOR]

We analytically investigate infinitesimal cylindrical bending deformations of two-layered triangular corrugated and webcore linearly elastic sandwich panels by using the mechanics of materials approach and the classical plate theory. The model is validated by comparing its predictions with the solution by the finite element method of the linear elasticity equations for plane strain deformations. The model can accurately capture the secondary bending of the facesheets, manifested as changes in their curvature between the webs and the resulting changes in the axial stresses, from being tensile to possibly compressive, that the commonly-employed homogenization schemes fail to capture. Subsequently, the model is used to analyze several problems with the sandwich panel having a pinned support at the left edge and a roller support at the right edge, and a uniformly distributed load applied on the top facesheet of the panel. It is found that the core plates mostly deform in compression and bending, respectively, for corrugated and web core panels. Furthermore, a significant fraction of the work done by the external load on the structure is absorbed as strain energy of deformations of the core plates near the supports. For four hybrid combinations of corrugated and webcore configurations in two-layered panels, the combination with the upper corrugated core set-up has the least maximum face sheet deflection and axial stress. The analytical technique can be easily extended to multi-layered hybrid configurations and provides quick means of finding efficient strain-energy absorbing hybrid designs. [ABSTRACT FROM AUTHOR]

This research proposes the development of an innovative structural panels based on the use of thin outer layers of Sisal Fiber-Cement Composites (SiFCC) together with a core layer of Polypropylene Fiber-Reinforced Lightweight Concrete (PFRLC). The influence of sisal fibers was studied in two different ways, short sisal fibers (50 mm) randomly distributed in the matrix, and long unidirectional aligned sisal fibers (700 mm) applied by a cast hand layup technique. Lightweight aggregates and polypropylene fibers were used in the concrete layer forming the panel's core in order to reduce its density and improve its post-cracking tensile strength and energy absorption capacity. The behavior of the sandwich panels in four-point bending test is described, and the various failure mechanisms are reported. Mechanical properties of both SiFCC and PFRLC were obtained, which were also used in the numerical simulations. Pull-off tests were performed to evaluate the bond strength between the outer SiFCC layers and the core PFRLC. The results revealed that the long sisal fibers were more effective in terms of providing to the panel higher flexural capacity than when using short sisal fibers, long fibers ensured the development of a deflection hardening behavior followed by the formation of multiple cracks, while short sisal fibers promoted a softening response after cracking. [ABSTRACT FROM AUTHOR]

The present study establishes a numerical strategy for describing the textile/concrete bond behaviour in textile-reinforced concrete (TRC) composites that separates the cohesive and coulomb friction contributions. The textile-concrete bond approach, validated on an existing pull out test in the literature, has been used to calibrate the textile-concrete bond slip law of an existing TRC tested in tension by an innovative inverse approach thanks to its pull-out mode of failure. The calibrated bond slip law has been used as an input parameter to produce an enhanced TRC multiscale numerical model that is based on the nonlinear behaviour of its constitutive components (concrete, textile, and textile-concrete bond slip law) and takes into account all the damage mechanisms of TRC, which are mainly characterized by matrix cracking and yarn pull-out. The model has been validated on the basis of the previous TRC experimental tensile test. Two approaches have been used to account for the mechanical behaviour of a textile-reinforced concrete sandwich panel under a four-point bending test: a macroscopic 3D finite element approach, which considers the composite TRC with its macro tri-linear stress – strain relation under tensile solicitation, and the proposed TRC multiscale 3D finite element approach which, involves definition of the textile-concrete interaction bond slip law. More accurate results have been achieved with the multiscale approach; furthermore, the experimental mode of failure of the sandwich panel has been captured. [ABSTRACT FROM AUTHOR]

A failure mechanism-based progressive damage growth model is developed, applied and validated for modeling woven polymer-based foam-core sandwich panels under compression-after-impact. A Schapery theory based constitutive model, which takes account of intra-ply shear inelasticity and fiber kinking and resulting fracture is developed for the impacted plain weave fabric laminated face-sheets under compression loading. Each ply of the face-sheets is modeled as an orthotropic nonlinear elastic lamina degrading as characterized through laboratory experiments. The behavior of woven plies in the warp and fill directions is elastic until the attainment of local instability in compression. The phenomenon of fiber micro-buckling leading to kink banding, which was observed to be the mechanism controlling failure of the impacted face-sheets and hence the sandwich panels, is explicitly accounted for by allowing the fiber rotation at a material point. In the shear direction, plasticity is also considered to represent the elastic-plastic in-plane shear behavior of woven fabric plies. The constitutive model is numerically implemented using the commercially available finite element package ABAQUS through a user defined material subroutine (UMAT). The previous 3D damaged FE model which was proven to accurately capture the low–velocity impact damages is imported and subjected to a compression loading modeling. The numerical results in terms of deformation, failure mode and residual strength show a remarkable agreement with experimentally measured ones, allowing the model to be validated. [ABSTRACT FROM AUTHOR]

Sandwich structures have been widely used in marine applications due to their properties such as high weight/strength ratio. In contrast, the failure mechanism of these structures has a significant effect on the local and global dynamic responses. In the present study, sandwich panels with polymeric skins and PVC foam cores subjected to slamming impact are investigated experimentally and numerically. A high speed shock machine is used to keep approximately a constant velocity during the impact event. The dynamic resistance was analysed in terms of hydrodynamic loads, dynamic deformation and failure mechanisms for different impact velocities. On the other hand, the slamming model was implemented in Abaqus/Explicit software based on Coupled Eulerian Lagrangian model approach. In addition, different damage modes are incorporated in the numerical model, including the intralaminar, debonding in skin/core interface, and core shear to cover all possible damage modes throughout structures. Two failure criteria (Hashin criteria for the laminate composite and Christensen criteria for the core in sandwich structure) are defined and integrated into VUMAT sub-routine. In addition, the cohesive zone model is used to predict the debonding skin/core. A good agreement in both hydrodynamic loads and damage prediction were found between numerical and experimental results. [ABSTRACT FROM AUTHOR]

In this paper the shallow sandwich panels are considered to be made of the nanocomposite enriched face-sheets and the auxetic honeycomb core so that its Poisson's ratio is negative. In order to evaluate the geometrical nonlinear dynamic behavior of such sandwich panels, various periodic and impulsive loadings are considered. For the sake of solving the governing nonlinear differential equations system, an analytical approach on the basis of the Galerkin method is conducted which yields a closed form differential equation of motion which is numerically solved by the fourth-order Runge–Kutta method concept. The precision of the proposed analytical method is approved using comparison of the results related to some special examples and the relevant ones achieved by the other analytical and numerical methods in the references. The results of verification examples showed that the proposed method yields to the results with errors of less than 2% comparing to the results of previously published papers. The influences of different geometrical and mechanical parameters on the dynamic nonlinear responses of the proposed sandwich panels undergoing the various impulsive and periodic pressures are also evaluated in the framework of wide range of numerical study. The numerical studies revealed that by using the proposed method, performing the nonlinear dynamic analysis of the proposed panels without time-consuming computations is possible. [ABSTRACT FROM AUTHOR]

This paper discusses the thermal buckling analysis of composite plates and sandwich panels by means of a Ritz-based variable-kinematic formulation. Main feature of the proposed formulation consists in the representation of the structure by means of sublaminates, i.e. arbitrary groups of plies composing the panel. Each sublaminate is associated with an independent, arbitrary kinematic description, so that the use of refined, high-order theories can be restricted to specific regions, such as the core of sandwich panels. Monolithic plates can be studied as a special case where the structure is modeled using only one sublaminate. Presented are the critical temperatures, with and without accounting for the nonlinear pre-buckling effects, for a set of monolithic and sandwich configurations. When pre-buckling effects are neglected, the problem is solved as a standard eigenvalue problem. On the other hand, the introduction of pre-buckling effects leads to a nonlinear eigenvalue problem, which is solved with an iterative procedure. The results are validated against 3D solutions, and highlight the importance of accounting for pre-buckling deformations, especially in the case of sandwich panels. As demonstrated, high-fidelity predictions are obtained while keeping at minimum the amount of degrees of freedom. [ABSTRACT FROM AUTHOR]

In this paper, the adhesively bonded corrugated core sandwich panel is introduced and its elastic properties are discussed. Due to the relative displacement and rotation between face and core plates in adhesive joints caused by adhesive layer distortion, traditional elastic constants with considering both face and core plates to be fastened to each other are no longer fit for adhesively bonded sandwich panels. Therefore, its elastic constants with effect of adhesive layer distortion have been derived and presented in this paper. By submitting these elastic constants into closed-form solution, the response of simply supported sandwich panel under uniform load with small deflection is calculated which agrees well with 3D FEM analysis. Lastly, with the elastic constants, the effects of adhesive layer thickness and its elastic modules on both transverse shear stiffnesses with different shapes and dimensions are further studied and discussed. [ABSTRACT FROM AUTHOR]

The paper presents a set of newly developed exact analytical solutions for triple- equal-span arrangements of panels with fully profiled faces in flexure. Their derivation was based on a set of general fundamental equations retrieved from the governing differential equations for sandwich beams. Specifically designed tests of single- and triple-span fully profiled panels with steel faces (outer fully profiled and inner lightly profiled) and polyisocyanurate cores were conducted to investigate the response with regards to stiffness and initial failure, which are critical for serviceability limit states. Good agreement between test and theory was demonstrated, with safe results in all cases. The new design method permits the elimination of a significant amount of conservatism compared to current methods. [ABSTRACT FROM AUTHOR]

Sandwich panels with triple layered graded honeycomb cores were tested under blast loading. The structural response was analyzed by using finite element software LS-DYNA after validation against the experiments. The structural deformation modes were classified into three types and the core layer deformation was divided into three regions. For the same value of impulse, a localized impulse led to severely localized deformation mode. A relatively evenly distributed impulse resulted in largely global bending deformation. Under the same loading, graded panels with the core of the largest relative density placed near the impact face suffered a smaller deflection than the panels with uniform core. Furthermore, for the same deformation mode the normalized back face sheet deflection increased linearly with impulse. [ABSTRACT FROM AUTHOR]

The paper describes the experimental and numerical investigation of the stabilization of cold formed thin-walled Z -beams by sandwich panels. The scope of the laboratory tests included sandwich panels freely placed on Z -beams and sandwich panels mechanically fastened to Z -beams by a diverse number of fasteners. It has been shown in laboratory experiments that the sandwich panels provide lateral stabilization of the thin-walled Z -beams. Moreover, the capacity of the thin-walled beam is determined by the number of fasteners along its length. The static and low cyclic loads were investigated. The FE model defined and presented in the paper allows for the accurate determination of the kinematical and mechanical elastic response of the thin-walled Z -beam stabilized by the sandwich panels, provided the specific bow imperfection of both the beams and the specific material parameters of the beams and the sandwich panel layers. [ABSTRACT FROM AUTHOR]

This paper presented an innovative integrated Thermal Protection System (ITPS) with both thermal insulation and load bearing capabilities. Thermal short and thermal expansion mismatch effects are the key design challenges of an ITPS. The objective of this paper is to establish a topology optimization method against these two effects. The thermal-mechanical analysis model of an ITPS is presented first. Then, the limits of size optimization method in solving these two effects are studied through design of experiments. A topology optimization model of the web is established using loads and boundary conditions extracted from the global ITPS model. Optimizations were carried out under different load cases. Comparisons of structural responses, including thermal structural stress, were made between the original, optimized ITPS, and ITPSs with the same maximum back face temperature. The results showed that a reduction of 12.05% in maximum bottom temperature and a decrease of 11.2% in overall maximum structural stress had been achieved. The proposed method can effectively mitigate the thermal short and thermal expansion mismatch effects of the ITPS simultaneously. [ABSTRACT FROM AUTHOR]

The present work proposes a modeling strategy based on a two-scale approach to deal with the flexural vibroacoustic behavior of sandwich panels notably in the low-mid frequency range. The vibroacoustic indicators of interest here are primarily the sound transmission loss and the bending-shear transition frequency of the sandwich panels. The stated indicators depend mainly on the geometrical and mechanical parameters of the studied cases. The parametric analyses, therefore, bring out the effects of the different meso-scale parameters on the macro-scale responses of the sandwich panels by performing three-dimensional model of a representative elementary cell. The two-scale approach is mainly based on a numerical method known as the wave finite element method. In the developed approach, an expression of the sound transmission loss was derived wherein the shear core effect of sandwich panels has been included. The obtained results were compared with two models and experimental data to check the accuracy of the prediction and showed a good agreement. [ABSTRACT FROM AUTHOR]

Nowadays, sandwich panels are recognized for their importance in various technical fields especially in aeronautics, automotive, and structural engineering. Light-weight composite material can be used in sandwich panels due to having high stiffness-to-weight ratio. In this study, a numerical model has been conducted to study the effectiveness of fiber reinforced polymer (FRP) sandwich panels under blast effect. Results of numerical model are validated with experimental field tests in the literature. A new inner core configuration is proposed. In the experimental field test, inner core configurations were honeycomb shaped and sand was used as filling material. Newly proposed core configuration is formed of a combination of woven and honeycomb shapes and sand is used as a filling material. The two performance parameters considered in this study are the amount of energy absorbed by panels and their peak deformation. In order to track the enhancement of the panels’ performance, a parametric study has been conducted. Moreover, the effect of changing the filling materials has been investigated. A good agreement between the numerical results and the experimental measurements has been realized. Finally, the analyses have revealed that using the new core configuration noticeably enhances FRP panels’ behavior under blast loads. [ABSTRACT FROM AUTHOR]

Laser stake-welded steel sandwich panels are widely used in engineering due to their high stiffness-to-weight ratios. The welds are thinner than the plates they join so that there are two crack-like notches on each side of a weld. As a consequence, the welded joints are susceptible to fatigue. In this study, as a remedy to the fatigue problem, low-density H80-grade Divinycell polyvinylchloride foam is bonded adhesively to the voids of stake-welded web-core sandwich beams. The foam reduces shear-induced stresses in the stake-welds. The choice of Divinycell H80 is founded on earlier J -integral-based finite element fatigue assessments of sandwich panels. Empty and the H80-filled sandwich beams are tested in three-point-bending for stiffness, ultimate strength and fatigue (load ratio R = 0.05). The failure modes in the weld joint region are studied using scanning electron microscopy. The experimental results show that the filling increases the stiffness of the sandwich beams by a factor of three while the weight is increased only by 6%. The ultimate strength is increased by 2.7 times. As for the fatigue behavior, the slope increases from m = 4.508 of empty panels to m = 7.321 of filled panels while the load level at 2 million cycles increases by a factor of 8.5. [ABSTRACT FROM AUTHOR]

In this paper, high velocity impact responses of newly designed sandwich panels with aluminium (AL) foam core and metal fibre laminate (FML) skins, which are comprised of aluminium sheets and plain woven E glass fibre composite plies are investigated. Gas gun impact tests were conducted to investigate the high velocity impact response of the panels subjected to the impact from a steel ball bearing at an impact velocity of around 210 m/s. The effect of the thickness of the foam core and FML skin on the impact resistance of the panels is also investigated via experimental study. A finite element model is developed for effective numerical modelling of the impact behaviour of the sandwich panels using the commercially finite element software ANSYS LS-DYNA for more extensive study of the impact response of the sandwich panels. The simplified Johnson Cook material model, the composite damage material model based on the Chang-Chang criteria, and the crushable foam material model are used to model the aluminium sheets, composite plies and the AL foam respectively. Three types of contact algorithms, i.e. the erosion contact type, the tie-break contact type and the general 3D contact type are employed to define the various contacts during the impact and to model the delamination between the FML layers and debonding between the FML skin and the AL foam. The finite element model is validated by comparing the simulated impact behaviour to that from experimental for a sandwich panel subjected to high speed impact and demonstrated to be effective and accurate. The effect of the shape of projectile and impact angle on the impact behaviour of the sandwich panels is studied using the developed finite element model. The research findings are summarized and concluded finally. [ABSTRACT FROM AUTHOR]

Sandwich panels with cellular cores are being widely used as blast mitigation materials, due to their light weight and good energy absorption properties. In the present study, the behaviour of sandwich panels against different shock loadings is evaluated using piston driven shock tube. The sandwich panels are fabricated using aluminium(Al) foam core and E-glass/epoxy composite face sheets of different thicknesses. Different shock loads were generated by varying the driven gas pressures. The foams and sandwich panels were subjected to peak shock reflected pressures ranging from 50 bars to 150 bars and the corresponding transmitted pressure pulses were recorded. The behaviour of the foams and sandwich panels under shock wave loading was evaluated by post test visual damage assessment. The effect of face sheet thickness on failure mechanisms of sandwich panel is also studied. The failure mechanisms of foams at higher shock pressures were observed to be core crushing and core fracture, whereas sandwich panels exhibited face sheet deflection, core crushing, fibre breakage at back face sheet and back face delamination. [ABSTRACT FROM AUTHOR]

• Innovative multilayer sandwich panels were produced using Aleppo wood veneer and agglomerate or expanded corkboards. • The cork-based multilayer sandwich panels can be used in interior applications. • The thermal conductivity of different cork-based sandwich panels was evaluated. • Increasing the density and the number of cork layers increase the density and the thermal conductivity of the sandwich panels. Six different types of cork-based sandwich panels were produced, using Aleppo pine as the face or inner sheets and a cork (agglomerate or expanded) as the core, with a view to applications in building insulation. The physical properties of these sandwich panels were evaluated by scanning electron microscopy, measurements of density, moisture absorption, and moisture desorption. The thermal conductivity of the sandwich panels was evaluated by three different methods: the guarded-hot-plate, thermal conductivity meter, and heat-flow meter (CTMF) methods. The overall results suggest that eco-friendly cork-based sandwich panels are efficient thermal insulators and may be used to reduce energy consumption in buildings. [ABSTRACT FROM AUTHOR]

• Sandwich panels with aluminum face-sheets and aluminum foam core was studied. • Ballistic limit velocity of the panels was obtained experimentally and numerically. • The effect of aluminum foam density and thickness of the panel were investigated. • Panels with maximum ballistic limit velocity were obtained with the equal weight. Sandwich panels have been widely used in various industries due to their high strength and energy absorption capacity. In this study, the ballistic behavior of a sandwich panel comprised of two aluminum face-sheets and an aluminum foam as the sandwich core is studied. The panels are constructed and subjected to the blunt-nosed projectile. The experimental test consists of a sandwich panel with three different ranges of foam densities and two thicknesses for the panels beside hardened steel projectiles. Then, numerical simulations of the projectile perforation in the panels are conducted that are in good agreement with the experiments. The failure mechanism of the sandwich panels is investigated and the role of foam core is discussed. Failure mechanism and the amount of plug depends on foam density and projectile velocity, such that different failure mechanisms such as plugging, petaling, and dishing occurred for the face-sheets. After that, the ballistic limit velocity (V BL) of sandwich panels was calculated via experiments and finite element simulations. The experiments and simulations showed that increasing the density and thickness of the foam core generally leads to an increase in V BL. Finally, we study the panels with the constant mass and (or) constant height with different foam densities and the effect of foam density is investigated in these cases. [ABSTRACT FROM AUTHOR]

The diagonal-enhanced square grid configuration inspired by glass sponge has great potential in mechanics, with geometries serving as honeycomb cores for sandwich panels, which can improve the structure's energy absorption capabilities. Modeling the hexagonal honeycomb core (HHC) sandwich panels, a finite element numerical model for low-speed impact of sandwich panels with high accuracy is proposed, and low-speed impact response of bio-inspired diagonal-enhanced square honeycomb core (BSHC) sandwich panels is studied. The impact response of BSHC sandwich panels, Hexagonal honeycomb core (HHC) sandwich panels and ordinary square honeycomb core (OSHC) sandwich panels were studied with the same relative densities and the same face-sheets. BSHC can lead to significantly enhanced the peak loads and stiffness of the sandwich panels. BSHC sandwich panels not only have excellent energy absorption performance, but also outperform HHC sandwich panels in terms of resistance to impact deformation. BSHC can transfer dynamic loads from the front face-sheet to the back face-sheet efficiently without stress concentration in the core itself. A theoretical analysis of the energy absorption capacity of the BSHCs and HHC were performed to illustrate the energy absorption mechanism. In addition, the peak load and contact energy of BSHC sandwich panels and HHC sandwich panels were theoretically predicted under low-speed impact. • The BSHC lead to significant peak load and higher stiffness of sandwich panels, increasing impact resistance. • The BSHC sandwich panels have excellent energy absorption performance. • The BSHC can effectively reduce the stress and deformation of sandwich panels. [ABSTRACT FROM AUTHOR]

• Incorporation of novel solutions of hemp fabrics to the FRCM composites as wythes of sandwich panels. • Bending and compression behavior of full-scale sandwich panels with hemp-FRCM. • Development of ductile sandwich panel with effective composite action of hemp-FRCM. • Simplified analytical approach validated from experimental results. Sandwich panels composed of fabric-reinforced cementitious matrix (FRCM) and extruded polystyrene foam (EPS) represent a light and insulating solution compared with other types of enclosure walls, such as steel-reinforced concrete (RC) panels. To improve the sustainability and lightness of FRCM sandwich panels used for building enclosures, this study proposes the use of hemp fabrics in contrast to glass fabrics. Modal analysis and bending and compression tests were conducted on full-scale panels with hemp- and glass-FRCMs. The results obtained from these tests indicate that the use of hemp fabrics with greater equivalent thickness and deformation capacity than glass fabrics make the production of ductile and strength (35 % more than glass-FRCM) sandwich panels possible. Nevertheless, glass-FRCMs allow the production of more stiffened panels. In addition, this study presents a simplified analytical model of sandwich FRCM panels based on the definition of cracked section strength, which is useful in the case of full composite action in the sandwich solution. [ABSTRACT FROM AUTHOR]

This paper presents a novel numerical tool for the bending analysis of thin and thick composite plates, including monolithic and sandwich structures. The formulation is developed within a displacement-based approach, where the Principle of Virtual Displacements (PVD) and the method of Ritz are adopted to derive the governing equations. The approach relies upon the Sublaminate Generalized Unified Formulation (S-GUF) as underlying kinematic theory describing the behavior across the plate thickness. Main idea of the S-GUF is to group the plies into a number of smaller units called sublaminates, each of them characterized by an independent, variable-kinematic theory. Continuity conditions between the sublaminates are enforced in strong form during the assembly procedure of the governing equations. The S-GUF appears particularly useful when theories of different order are needed to approximate the displacement field of different portions of the structure, such as in the case of sandwich panels. A number of test cases from the literature is discussed, and results are validated against exact 3D solutions. The results demonstrate the ability of the approach to obtain accurate results, both in terms of deformed shapes, and intra- and inter-laminar stress distributions. A set of novel results is also presented for future benchmarking purposes. [ABSTRACT FROM AUTHOR]

A series of experimental tests carried out on a composite prototype to be used as a floor module of an emergency house is presented in this paper. The prototype comprises a frame structure formed by GFRP pultruded profiles, and two sandwich panels constituted by GFRP skins and a polyurethane foam core that configures the floor slab. The present work is part of the project “ClickHouse – Development of a prefabricated emergency house prototype made of composites materials” and investigates the feasibility of the assemblage process of the prototype and performance to support load conditions typical of residential houses. Furthermore, sandwich panels are also independently tested, analysing their flexural response, failure mechanisms and creep behaviour. Obtained results confirm the good performance of the prototype to be used as floor module of an emergency housing, with a good mechanical behaviour and the capacity of being transported to the disaster areas in the form of various low weight segments, and rapidly installed. Additionally, finite element simulations were carried out to assess the stress distributions in the prototype components and to evaluate the global behaviour and load transfer mechanism of the connections. [ABSTRACT FROM AUTHOR]