Fiber-reinforced Sandwich Structures Research Articles

The effect of span length on the flexural properties of glass and basalt fiber reinforced sandwich structures with balsa wood core for sustainable shipbuilding

The current research aims to analyze the mechanical characterization of sandwich materials through a three-point flexural test. The sandwich structures in question composed of balsa wood as a core and four different types of fiber reinforced vinyl ester composite facesheets, namely Glass, Basalt, Glass/Carbon, and Basalt/Carbon. The sandwich panels were prepared using the vacuum infused processing method. The primary objective of this investigation is to explore the feasibility of utilizing basalt fibers for the production of structural parts in shipbuilding and replacing the already existed glass fibers. The flexural test was carried out with using three-point flexural test with varying the span length from 120 mm, 180 mm, 220 mm. Additionally, an analysis of variance (ANOVA) was then carried out to compare the mean values of properties deduced from these tests. The results showed that using basalt fibers instead of glass fiber reinforced enhanced the flexural stiffness of the sandwich structure. The flexural strength and modulus are shown to depend on span length and fiber type. The flexural modulus increases with an increase in span length. Similarly, flexural strength increases in glass fiber-based structures, while a slight reduction is observed in basalt fiber-reinforced structures the larger span length. The findings of this research suggest that basalt fibers hold potential as a replacement for glass fibers in producing structural components in shipbuilding. These results offer valuable information that can aid in the design and optimization of sandwich materials in shipbuilding.

A Comparison of Different Excitation Sources in Inspection of Fiber-Reinforced Sandwich Structures Having Light-Weighted Non-Metallic Cores with Thermography and Relative Post-Processing

A Comparison of Different Excitation Sources in Inspection of Fiber-Reinforced Sandwich Structures Having Light-Weighted Non-Metallic Cores with Thermography and Relative Post-Processing

Review of carbon fiber-reinforced sandwich structures

This paper first reviews the research progress of carbon fiber-reinforced sandwich plates with grid cores, truss cores, and foam cores, and the results can be summarized in the following four points. 1) The load-bearing capacity and energy absorption capacity of grid-core and foam-core structures under bending loads have been improved by toughening with short fibers and Z-pinned fibers. 2) The progressive buckling mode of the core layer under compressive loading can significantly improve the energy absorption capacity of a sandwich structure. 3) The compressive failure of a truss-core sandwich structure is closely related to the strength at the nodes. 4) Following a literature review, this paper discusses the existing problems in sandwich structures and the corresponding countermeasures, and the results can be summarized in the following two points. 1) After implementing the current toughening measures, the debonding is improved to a certain extent; however, this approach does not prevent debonding. 2) No method has been presented that can increase the strength of the end nodes in truss-core members. Therefore, it is encouraging that a trabeculae/honeycomb-core sandwich structure composed of fiber-reinforced proteins—mimicking the biological structure found in a beetle forewing—can effectively solve the abovementioned problems.

Extensions of the coating approach for topology optimization of composite sandwich structures

Additive manufacturing offers new design opportunities for composite sandwich structures. The work presented herein builds on the concepts of the coating approach for topology optimization of shell-infill structures by using density gradients to determine local material orientations. A generalized material property interpolation scheme is presented and the sensitivity analysis for the minimum compliance optimization problem is developed. The approach is demonstrated for an orthotropic shell using the Messerschmitt-Bölkow-Blohm benchmark problem and results approach the isotropic solution when an equivalent in-plane modulus is considered. To adapt the approach to composite sandwich structures, a methodology based on the addition of a contour finding step is presented to define separate properties in the exterior shell from interior shells. The work introduces a new approach in topology optimization to tackle composite fibre reinforced sandwich structures that would benefit from a complex core structure obtained by additive manufacturing.

Quasi-static indentation analysis on three-dimensional printed continuous-fiber sandwich composites

Fiber reinforced sandwich structures are widely used as structural elements due to their lightweight and high load-bearing capacity. In this paper, effort is taken to fabricate fiber facesheet (0°/90° orientation) and corrugated cores (trapezoidal vertical pillared, core-1 and sinusoidal vertical pillared, core-2) of the sandwich structure using fused filament fabrication and Inkjet printing techniques, respectively. Firstly, the quasi-static indentation properties of the additively manufactured facesheet, cores, and sandwich structures were investigated. In addition, acoustic emission signals were monitored during quasi-static indentation testing and the resulting hits data were correlated with quasi-static indentation test results. The quasi-static indentation test results showed that sinusoidal sandwich structures have the highest load-bearing capacity of 1.79 kN until crack initiation and a total energy-absorption capacity of 20.05 J. Acoustic emission hits recorded in the range of 1–30, 30–100, and above 100 represented crack initiation, crack propagation, and specimen failure, respectively. Lastly, micro-computed tomography analysis was performed on the sandwich structures at intermediate indentation displacements, thus leading to the identification of hard to detect failure points and damage propagation. Fracture surface morphology of the sandwich structures showed that fiber pullout and core shear were the dominant damage mechanisms.

Compression testing of additively manufactured continuous carbon fiber-reinforced sandwich structures

Abstract The novel, additive manufacturing technique, continuous lattice fabrication, combines the advantages of continuous fiber-reinforcement with those of additive manufacturing. This enables the generation of fiber-reinforcement within a single layer and especially along an out-of-plane load path inside all spatial dimensions. This study is a test-related evaluation of sandwich panels with lattice core structures modifying a compression test. The specimens were manufactured differentially via plug and bond and automatically using continuous lattice fabrication. Additionally, the spatial arrangement of the rods within the lattice core structure varied in terms of base area. The ultra-lightweight sandwich panels have lattice core structures with core densities < 10 mg × cm−3. The material testing was performed by a modified compression test at room temperature. The damage analysis of the single rods shows current deficits and future potentials for optimization of lattice core structures. It could be shown that sandwich panels exhibit a compression strength of up to 0.30 MPa at a core density of 6.57 mg × cm−3. Using a dimensionless lightweight index demonstrates a mechanical performance on a level comparable with that of selected core materials.

Modelling the Bending Behaviour of Novel Fibre-Reinforced Sandwich Structures with Polyurethane Foam Core

In contrast to conventional manufacturing methods for sandwich structures, in this paper a foamable polyurethane system is used to impregnate textile layers and to create the sandwich foam core in one single process step. Given this simultaneous process, a high adaptability of the resulting mechanical properties can be achieved by varying the textile reinforcement of the sandwich top layers, the foam core density and the sandwich thickness, respectively. Within this paper, a design of experiment approach is implemented by using statistical analysis of variance (ANOVA) to investigate the influence of selected geometrical and material parameters on the resulting bending properties of these novel sandwich structures. A partial factorial design helps to identify the sensitivity of individual parameters and their interaction, as well as the correlation between sandwich morphology and bending performance. Based on the gained results, statistical models will help to identify parameters with statistical significance. Therefore, optimized sandwich structures according to stress-related requirements and geometrical constraints can be designed.

Fiber-Reinforced Sandwich Structures Based on Selective Laser Sintering: A Technological View

Fiber-Reinforced Sandwich Structures Based on Selective Laser Sintering: A Technological View

Hybrid Additive Design of FRP Components – Fiber-Reinforced Sandwich Structures Based on Selective Laser Sintering Technology

With the demand for an increasing diversification of the product spectrum along with the decreasing unit quantities of each production lot, the upcoming innovative production concepts of a flexible and digitized production (“fourth industrial revolution”) tend to substitute more and more the traditional product development and production processes, which are already reaching their limits or fail to address these trends. At the same time, new technologies like additive manufacturing basically create new opportunities regarding extensive potentials in product development and manufacturing, but mostly with just insufficient strength regarding structural components.Therefore, this contribution presents an innovative technological and procedural conception of a hybrid additive manufacturing process – fiber-reinforced sandwich structures based on selective laser sintering technology. In this way, the concept supports the design of complex lightweight components, in particular through the application of a “hybrid additive lightweight engineering” (HALE) methodology.

New Materials for Sports Equipment Made of Anisotropic Fiber-reinforced Plastics with Stiffness Related Coupling Effect

Fiber-reinforced plastics (FRP) are often used in sporting goods to increase their lightweight degree. Symmetric laminate are mostly used because of the complex deformation effects of asymmetric multi-layer Structures (MLS), which are also hard to handle in the complete production process. In the board sports industry almost all products are made out of symmetric biaxial or triaxial glass fiber fabrics to increase the stiffness and strength of the sandwich composites. Carbon fiber-reinforced plastics (CFRP) are used to reduce the high performance products’ weight. FRP are also well suited to integrate additional functions. An uncommon way for such integration is the use of the material intrinsic anisotropic coupling effects of asymmetric MLS. Based on these deformation effects of FRP an all-new snowboard with the so-called anisotropic layer design technology (A.L.D.-tech) was developed at the Institute for Structure Lightweight, Technische Universität Chemnitz. In this product the anisotropic coupling effects are used for implementing a riding specific deformation of the snowboard to increase the customer value. At present, the spin-off silbaerg TM Snowboards uses three different levels of the A.L.D.-tech for the worldwide first serial products with such coupling effects; snowboards made of glass and carbon fiber reinforced sandwich structures. By varying the fabric material and the lay-up of the A.L.D.-tech MLS, different characteristics of the riding specific deformation are adjustable. For developing and computing this all-new type of board sport product the researchers used a numerical approach using a Finite Element Method (FEM) software solution provided by ANSYS. The model based on the Classical Laminate Theory (CLT) and focuses also the failure assessment by using Cuntze's failure criteria [1]. The ABD-Matrix of the CLT provides a good tool to visualize the different deformation effects of asymmetric MLS, which depends on the disc-plate problem. Due to this an A.L.D.-tech MLS with an unusual bending-curvature or bending-torsion coupling was developed, verified and launched into the market. This paper contains the description of different fabric material and lay-up combinations to adjust the grade of the anisotropic coupling of the snowboard as well as the integration of stitched sensors to measure the deformation while riding the snowboard. The comparison between numerical solution and experimental verification tests confirm the accuracy of the numerical model.

Absorption properties of natural fiber-reinforced sandwich structures based on the fabric structures

Sound absorption properties of natural fiber-reinforced sandwich structures based on the structure of the fabrics were investigated in this work. The sound absorption coefficients of the sandwich structures were measured by the impedance tubes with the aid of the transfer function. Effects of yarn sizes, fiber diameters and hybrid stacking of different fibers on the sound absorption properties were studied. The flow resistance and characteristic impedance of the reinforcing fabrics which were correlated with the fabric structures were calculated and compared. It was concluded that the thicker the fabric yarn and the bigger the fiber diameter were, the better the sound absorption properties were for natural fiber-reinforced sandwich structures.

Analysis of factors influencing deflection in sandwich panels subjected to low-velocity impact

Fiber reinforced sandwich structures typically respond very poorly to transverse impact events. This paper is an attempt to investigate the impact response of sandwich panels subjected to low-velocity impact. Experimental investigations were carried out on the influence of three design factors: height of fall, core thickness, and impactor mass, which are the most relevant parameters to be considered for deflection. The study of behavior of the mentioned response was done by using Design of Experiments tool. Response surface methodology (RSM), a sequential experimentation strategy for model building, is used to model the response in order to determine the most significant factor among the influential factors. In this case, full factorial face-centered central composite design was chosen due to the number of factors and their levels in the study. The specimen consisted of face sheets made up of bi-woven glass fiber cloth with polyurethane foam as core material. The parametric analysis reveals that deflection increases steadily with an increase in the height of fall when compared with the impactor mass and the core thickness. The reason for this study is imperative for the next generation aircraft, marine, road, and rail vehicles with improved lightweight stiff materials that can absorb higher impact energy with higher resistance to deflection.

The Influence of Water Immersion on Skin-Core Debonding in GFRP-Balsa Sandwich Structures

A new test technique has been developed in order to characterise the skincore interfacial properties of a series of fibre reinforced sandwich structures similar to those presently being used in the marine industry. The technique involves peeling the lower surface skin away from the core in a controlled fashion. Four different glass fibre reinforced epoxy/balsa structures have been tested and the effect of incorporating various skin-core interlayers assessed. Tests were also undertaken on specimens that had been immersed in seawater for a period of forty-five days. The results indicate that the fracture energies associated with skin-core debonding are relatively high, typically 1000 J/m2. It has also been shown that neither a pre-treatment of the balsa core nor the incorporation of a layer of CSM fibres resulted in an improvement in the fracture energy of the interfacial region. Immersion in seawater for forty-five days resulted in a significant increase in the fracture toughness of this region. A subsequent examination of the fracture surfaces showed that fibre bridging between the GFRP skin and the balsa core was more extensive in the soaked samples.

A study of skin-core adhesion in glass fibre reinforced sandwich materials

A test technique for measuring skin-core adhesion in fibre reinforced sandwich structures has been developed and applied. The test enables the interfacial fracture energy to be measured for most standard sandwich constructions. The technique has been subsequently employed to investigate skin-core adhesion in a number of sandwich structures similar to those currently used in the marine industry. It has been shown that the interfacial fracture toughness of a GFRP-crosslinked PVC sandwich structure can be as high as 2700 J/m2; however, sandwich constructions based on balsa cores offered considerably lower values of interfacial fracture energy. Here it was found that pre-treating the balsa core prior to bonding of the composite skins has a deleterious effect on the measured fracture toughness. Finally, the results of these tests have been correlated with data obtained from conventional climbing drum and short beam shear tests.