Mechanical Properties Of Sandwich Structures Research Articles

Mechanical properties of sandwich structures with different webs enhanced by filling polyurethane foam and encasing rectangular tube

In this paper, sandwich structures with different forms of webs are prepared by fused deposition modeling technology. The effect of the concave and convex shape of the web and its position on the mechanical properties of sandwich structure is explored. The different constraints are implemented on the sandwich structure by encasing thin-walled rectangular tube externally and filling polyurethane foam internally, respectively. Then, a sandwich structure with both rectangular tube and polyurethane foam, namely, rectangular tube encased foam-filled sandwich structure is proposed to synergistically enhance the sandwich structure. The encased rectangular tube strengthens the sandwich structure and avoids the failure of the whole structure under small strain. Rectangular tube encased foam-filled sandwich structure reduces the oscillation in the plateau stage of compressive curve and has the highest mechanical properties.

Impact behavior of periodic, stochastic, and anisotropic minimal surface-lattice sandwich structures

Recent advancements in 3D printing technologies have made it possible to fabricate intricate lattice architectures with high precision. These lattices can now be utilized to design lightweight sandwich structures that serve multiple functions. To enhance the impact loading performance of these structures, it is crucial to understand how the lattice's topological properties, particularly those with minimal surface attributes like periodic or stochastic Primitive and Gyroid triply periodic minimal surfaces (TPMS) and spinodal-like stochastic cellular materials, associate with the mechanical properties of sandwich structures while keeping the skin thickness fixed. Thus, this paper explores the low-velocity impact behavior of various sheet/shell-based minimal surface-latticed cores of sandwich structures with woven composite skins. The elasto-plastic-damage numerical simulations consider lattice core periodicity, randomness, and anisotropy while keeping the relative density constant. Core lattice randomness and anisotropy are designed using the Gaussian Random Field (GRF) method for spinodal-based stochastic cellular materials and stochastic TPMS. The simulation results showed that the periodic Primitive-lattice core exhibits high out-of-plane shearing strength, enabling the sandwich structure to demonstrate the highest perforation limit. GRF spinodal-based core achieved the highest peak load due to its anisotropic mechanical properties. However, the post-yielding bending of the lattice sheet limited its ability to resist perforation, and absorb and dissipated energy. Interestingly, the stochastic Gyroid TPMS topology, with its inherent densely-distributed microstructure, showed high sensitivity to loading rate, resulting in enhanced energy absorption and dissipation of the sandwich structure. These findings offer valuable insights for optimizing multifunctional sandwich structures with superior impact performance and their design for additive manufacturing.

Short beam shear performance of spread‐tow woven stitched composite with anti‐sandwich structure

AbstractSpread‐tow woven fabrics (STW) have attracted considerable attention because of their ultrathin structure and low porosity, which benefit the design and application of STW composites. Little is known about how the thickness relationship between the middle and surface layers affect the mechanical properties of sandwich structures. Therefore, this study developed an anti‐sandwich stitched composite with STW in the center and a nonwoven felt/STW hybrid on both sides. The interlayer shear behavior and damage mode transformation of STW composites with different middle‐layer thicknesses were studied using short‐beam shear tests, digital image correlation (DIC) full‐field strain nephograms and micro‐computed tomography (micro‐CT). The results showed that the anti‐sandwich structure improved the shear strength, particularly when the middle layer thickness was four times that of the surface layer. As the middle layer thickness ratio decreased, the synergistic effect of the anti‐sandwich structure was weakened, and the damage mode changed from ductile to brittle. Furthermore, the hybrid ratio of the STW/nonwoven fabric in the surface layer had little effect on the performance because of the good interfacial adhesion between the STW and nonwoven fabric. The anti‐sandwich structure that can improve the properties and stability of STW composites provides a reference for the structural design of STW composites in engineering applications.Highlights An anti‐sandwich composite was developed by spread tow woven fabrics. Nine types of anti‐sandwich composite were designed and fabricated. The thickness of the middle layer affected the synergistic mechanisms. The optimal anti‐sandwich structure has a 4.59% increase in shear strength. The specific shear strength is 14.86% higher over pure spread tow laminates.

Tel Eritmeli İlkörnekleme (FDM) ile Üretilen Sandviç Yapıların Mekanik Davranışı Üzerinde Dolgu Parametrelerinin Etkisinin İncelenmesi

This study focuses on the investigation of infill patterns and their influence on the mechanical behavior of sandwich structures fabricated using the Fused Deposition Modeling (FDM) technique. Polylactic Acid (PLA) was chosen as the primary material, known for its favorable mechanical properties and biodegradability. Six different infill patterns, including Cubic, Line, Triangular, Trihexagonal, Octet, and Gyroid, were employed to fabricate sandwich structures with varying infill densities (20%, 30%, and 40%). The samples were subjected to edgewise compressive strength tests, and the force-displacement curves were analyzed to evaluate the performance of the structures. The results revealed that the Cubic infill pattern exhibited superior strength in all infill densities, while other patterns showed variations in performance. Moreover, the analysis of damage types indicated different failure modes, such as core shear and facesheet buckling, depending on the infill pattern and density. These findings contribute to understanding the role of infill patterns in enhancing the mechanical properties of sandwich structures fabricated via FDM.

Flexural behaviors and failure mechanisms of CFRP sandwich structures with enhanced dual-phase lattice cores

Inspired by bionic/metallurgical microstructures, novel dual-phase lattice/ Carbon Fiber Reinforced Polymer (CFRP) composite sandwich structures are proposed to improve the energy absorption (EA). The composite sandwich structures for different dual-phase strengthening strategies are designed, where the topology optimization is used to yield efficient lattice distribution configurations. The experimental samples are fabricated by 3D-printing and three-point bending tests are conducted. The flexural failure process and failure modes are observed and analyzed to reveal the failure mechanisms. Results show that DPL-1-CFRP and DPL-2-CFRP have higher peak load (+24.8 % and 18.0 %), post-peak average load (42.6 % and 20.8 %) and specific energy absorption (+7.8 % and + 21.1 %) compared to SPL-1-CFRP. It is indicated that the interactive failure mechanism of dual-phase lattice is effective in improving the mechanical properties of sandwich structure. It represents the occurrence of synergistic deformation between struts rather than a single brittle fracture. Finally, several potential failure mechanisms for the separation of the core and end faces are revealed. This novel concept and structural design greatly contribute to improve mechanical properties of sandwich structure.

Bending behavior of 3D printed sandwich structures with different core geometries and thermal aging durations

In recent years, the Fused Deposition Modeling (FDM) method has been employed in the production of small-scale structural elements with moderate loads, such as small-unmanned aerial vehicles, sports equipment, dental implant molds, and similar applications. In these cases, the FDM technique can utilize polymers like Polyamide (PA), Polylactic Acid (PLA), and Acrylonitrile Butadiene Styrene (ABS) to manufacture structural components. Lightweight sandwich structures are utilized as structural elements in various industries due to their unique characteristics, high stiffness-to-weight ratio, and energy absorption capabilities. Although the number of studies on the mechanical properties of sandwich structures manufactured with FDM has increased in recent years, experimental data on the mechanical characteristics of sandwich structures manufactured with FDM under different thermal aging durations are still insufficient. Driven by this motivation, the energy absorption capabilities of sandwich structures with different four core geometries (i.e., circular, hexagonal, square, and triangular) were experimentally investigated under different thermal aging durations. The sandwich structures were manufactured from PLA material by the FDM method. Four different thermal aging durations, 0, 15, 30 and 45 days, were considered for environmental conditions. Quasi-static three-point bending experiments were conducted to assess the energy absorption capability of lightweight sandwich structures featuring diverse core topologies. The bending test results demonstrate that the core topology significantly affects the energy absorption abilities of sandwich structures. Moreover, fractographic analysis using scanning electron microscopy (SEM) was conducted to gain deeper insights into the impact of thermal aging on aged specimens. In addition, it was concluded that the energy absorption performances of all sandwich structures with different core structure topologies were adversely affected by increasing the thermal aging time.

Investigation of mechanical properties of 3D printed sandwich structures using PLA and ABS

Sandwich structures have gained popularity in structural, automotive and aerospace applications due to their superior mechanical properties. This study aims to explore the mechanical properties of polymer sandwich structures produced using Fused Deposition Modelling (FDM). The research investigates the mechanical properties of sandwich structures made by combining two polymers, polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS). Tensile tests were conducted to obtain mechanical properties, and the results showed that sandwich structures perform better than pure ABS specimens. Out of the combinations tested, the structure with ABS as the core and PLA as the face demonstrated the best results. Furthermore, the study revealed that the sandwich structure with ABS as the face and PLA as the core has better mechanical properties compared to pure ABS. These findings provide valuable insights into the capabilities and limitations while using these polymer combinations in structural applications. The research is expected to assist in the design and engineering of FDM-based products by identifying the optimal 3-D printed polymer sandwich structure for specific structural applications.

Sound insulation performance of honeycomb core aluminum sandwich panels with flexible epoxy-based foam infill

The most distinctive features of sound insulation structures are their flexibility and porosity. Therefore, the flexible epoxy matrix material was made cellular using a suitable foaming agent. In addition, hollow glass microspheres (HGMs) were added to the epoxy matrix. Thus, the sound wave refraction was increased by obtaining cavities in the cell walls. Structures with different densities and voids were created by changing the ratios of the filling material and foaming agents used in the sandwich. An aluminum (Al) honeycomb was used to protect the insulation materials' structural integrity and ensure the homogeneous distribution of sound waves. The effect of density differences on sound insulation values was investigated. The mechanical properties of sandwich structures were determined using compression and three-point bending tests. The distribution of the filler in the matrix was visualized using SEM. TGA, DSC, thermal conductivity, dielectric, and flammability tests were also performed to determine their thermal, electrical, and flammability properties. During the formation of cells in the flexible epoxy, the HGMs were positioned in the cell wall by internal gas pressure. Low-density structures performed better at low frequencies, while high-density structures at high frequencies.

Fabrication and mechanical characterisation of composite sandwich structure having kevlar honeycomb core

ABSTRACT Composite sandwich structures are predominantly used in aerospace, civil engineering works, and automotive industries for load-bearing and lightweight structures. Recently, the core structures have been getting modified, due to the lack of strength, stiffness, and weight ratio. Very few past researches have shown research data on testing and mechanical properties of sandwich structures with commercial Kevlar honeycomb as a core. To overcome the above-said issues, an innovative composite sandwich structure is designed with carbon fibre resin-based sheets and a Kevlar honeycomb core. Carbon fibre face sheets with a thickness of 0.8 mm also an Aerospace Grade Kevlar honeycomb core with a cell size of 3.2 mm, a density of 48 kg/mm3 and a height of 12.7 mm are used to build the proposed sandwich structure. The fabricated sandwich plate was then subjected to various tests by American Standards for Testing and Materials (ASTM) standards to determine the various mechanical properties, such as stiffness, pressure, and stresses. Also, water absorption and soil degradation experiments were conducted on a sandwich plate to describe the additional properties of this sandwich structure. As a result, the specimen produced by the proposed method has low weight with high load withstanding capability as the shear is restricted with the help of carbon fibre also it has low deflection at critical load and high strength.

RETRACTED: Mechanical Properties Study on Sandwich Composites of Glass Fiber Reinforced Plastics (GFRP) Using Liquid Thermoplastic Resin, Elium®: Preliminary Experiments

Composite sandwich structures have been used in high performance applications such as wind turbine blades, due to their unique lightweight structure and superior mechanical properties. In the current study, a new liquid thermoplastic and thermoset resin were used to fabricate four different composite sandwich panels with two various foam types and densities. Composites made with epoxy resin are presented to comprehensively compare the mechanical properties of sandwich structures to elium resin. In the case of the mechanical properties and due to a new liquid thermoplastic resin, extensive comparisons of three-point bending, climbing drum peel, and flatwise tensile strength were investigated and compared with each other. The flexural and flatwise strength of sandwich composite increased by 53% and 75%, respectively, when using Elium resin. Then, the highest value was shown in the GF/PVC/ELIUM structure. The results revealed that Elium resin could be excellent in the case of mechanical properties to replace traditional resins to fabricate various composite structures and manage the challenge of recyclable composites. Elium resin can replace thermoset-based resins for the manufacturing of laminates and composites that are fully recyclable at room temperature with comparable mechanical properties.

State of the art review on mechanical properties of sandwich composite structures

AbstractSandwich composite structures are widely used in various industries namely, aerospace, automotive, packaging, biomedical, civil and electronics due to their high specific strength and energy absorption capabilities. Mechanical properties of sandwich structure depend on material properties of face sheet and core, and strength of face sheet‐core interface. Most commonly used composite materials are carbon fiber reinforced plastics, glass fiber reinforced plastics, ceramic matrix composites, and metal matrix composites. Several researchers have used nano‐fillers namely, nano‐clay, carbon nanotube, and nano‐silica for improvement of mechanical properties of composite structures. In this paper, an extensive literature review has been discussed regarding influence of various material and geometrical parameters on mechanical properties of sandwich composite structure. Initially, influence of various fiber reinforcement and nano‐fillers on mechanical properties are discussed. Then, deformation behavior and mechanical properties of honeycomb core is elaborated. Further, influence of temperature variation on composite structure is discussed. Moreover, crucial insights on reviewed literature are presented and future advancements in the field of sandwich composite structure are discussed.

On the mechanical performance of honeycomb-core sandwich L-joint under bending load: an experimental-numerical study

The mechanical properties of sandwich structures have drawn much attention from research and industrial application, while sandwich structures in the form of L-joint have been rarely addressed. In this paper, L-joint sandwich structures were experimentally tested under bending load to investigate the mechanical performance during structural deformation and damage evolution. The corresponding testing process was numerically simulated using finite element (FE) modeling. Nomex® honeycomb was selected as the core material of the sandwich structure, with the outer facesheets made of thermosetting Carbon Fiber Reinforced Polymer (CFRP) prepreg. Sandwich structures in the form of thin-walled beams and L-joint were then manufactured with specially-designed molds. Quasi-static three-point bending tests up to failure were conducted on the sandwich panels. Experimental results revealed that the main failure mode of the sandwich panel was the fracture in the honeycomb wall. The stiffness and strength properties of the sandwich structure were analyzed with FE modelling results, which showed good agreement with the experimental data. The adhesively bonded and hybrid rivet-bonded sandwich L-joints were investigated under vertical crushing load, showing the main failure region located in the corner area of the L-joint. The proposed experimental-numerical method on the mechanical performance of sandwich structures can provide reliable guidance on the connection of the caravan floor and side walls in automotive industries.

Fabrication and Mechanical Properties of POSS Coated CNTs Reinforced Expancel Foam Core Sandwich Structures

Background: Sandwich structures are progressively being used in various engineering applications due to the superior bending-stiffness-to-weight ratio of these structures. We adapted a novel technique to incorporate carbon nanotubes (CNTs) and polyhedral oligomeric silsesquioxanes (POSS) into a sandwich composite structure utilizing a sonochemical and high temperature vacuum assisted resin transfer molding technique. Objective: The objective of this work was to create a sandwich composite structure comprising of a nanophased foam core and reinforced nanophased face sheets, and to examine the thermal and mechanical properties of the structure. To prepare the sandwich structure, POSS nanoparticles were sonochemically attached to CNTs and dispersed in a high temperature resin system to make the face sheet materials and also coated on expandable thermoplastic microspheres for the fabrication of foam core materials. Methods: The nanophased foam core was fabricated with POSS infused thermoplastic microspheres (Expancel) using a Tetrahedron MTP-14 programmable compression molder. The reinforced nanophased face sheet was fabricated by infusing POSS coated CNT in epoxy resin and then curing into a compression stainless steel mold. Result: Thermal analysis of POSS-infused thermoplastic microspheres foam (TMF) showed an increase in thermal stability in both nitrogen and oxygen atmospheres, 19% increase in thermal residue were observed for 4 wt% GI-POSS TMF compared to neat TMF. Quasi-static compression results indicated significant increases (73%) in compressive modulus, and an increase (5%) in compressive strength for the 1 wt% EC-POSS/CNTs resin system. The nanophased sandwich structure constructed from the above resin system and the foam core system displayed an increase (9%) in modulus over the neat sandwich structure. Conclusion: The incorporation of POSS-nanofillier in the foam core and POSS-coated nanotubes in the face sheet significantly improved the thermal and mechanical properties of sandwich structure. Furthermore, the sandwich structure that was constructed from nanophased resin system showed an increase in modulus, with buckling in the foam core but no visible cracking.

Failure analysis of 3D woven spacer sandwich composites with woven cross-links and face sheet thickening under compressive and flexural loading

The effect of face sheet thickening on the mechanical properties of sandwich structures reinforced with 3 D woven spacer fabrics having woven cross-links has been presented in this work. Spacer fabrics forming cells of rectangular (RECT), trapezoidal (TPZ) and triangular (TR) shapes were used as reinforcement of sandwich structures with non-thickened face sheets. While for thickened face sheet structures, additional layers of 2 D fabric were integrally woven with the top and bottom face sheets of spacer fabrics, having almost similar cell geometrical parameters as that of the former structures, in a single step of weaving. Composites manufactured from these structures were characterized for their out-of-plane compressive and flexural properties. The specific compressive load was observed to be lower for thickened face sheet structures. The flexural load was higher for thickened face sheet structures; but the specific bending load decreased for the same. Flexural stress was also found to decrease with thickening of the face sheets. The results obtained could be helpful in designing sandwich composites connected woven fabric cross-links with enhanced mechanical properties.

Bendable metal-based composite sheets with a truncated dome core made of carbon fibre reinforced thermoplastics

Bendable metal-based composite sheets with a truncated dome core made of CFRTP (carbon fibre reinforced thermoplastics) were developed to expand the range of applications and improve the mechanical properties of sandwich structures. The newly proposed truncated dome core structure was composed of a periodic array of domes which were introduced into an initially flat CFRTP sheet through stamping. Theoretical analyses were conducted to determine the conditions required for successfully forming sandwich sheets into curved shapes. The flexural properties and formability of sandwich sheets were tested experimentally. The numerical simulation shows that the optimal relative density of the truncated dome core is 0.22. Experimental results of formability tests agree well with the theoretical predictions, which demonstrates the validity of the theoretical models. Sandwich sheets with both A2017P and SUS304 face sheets of a thickness of 0.5 mm can be bent without any failure at a bending radius of 60 mm.

Lightweight Potential of 3D Endless Fiber Reinforcement of Polyurethane Foam Cores with Spacer Fabrics in Hybrid Sandwich Structures with Fiber Reinforced Thermoplastic Facings

Sandwich structures consisting of fibre-reinforced plastic (FRP) facings and core are ideally suited as substitution materials for reducing component masses. The endless fibre reinforcement has the greatest performance potential. Both thermoset and thermoplastics are already being processed into endless fibre-reinforced sandwich facings according to the state of the art. The 3D endless fibre reinforcement of cores is a current research topic. This paper describes the development of a hybrid sandwich consisting of thermoplastic composite facings and an innovative core composite. This is made of polyurethane (PUR) rigid or flexible foam, which is reinforced with spacer fabric. The sandwich manufacturing in Reaction Injection Moulding (RIM) includes the original forming of the core and the simultaneous bonding of the facings. This efficient process offers the potential for the production of such complex structures in medium or large series. The sandwich structures and their individual components were characterised in the standardised compression and bending test. The lightweight potential of spacer fabric reinforcement is demonstrated by comparing the specific mechanical properties of sandwich structures with and without core reinforcement. In comparison to reinforced and unreinforced foams, the effect of sandwich design is also shown.

Research on the dynamic mechanical properties of polymethacrylimide foam sandwich structure

Polymethacrylimide foam is fully closed-cell isotropic foam which possesses high stiffness and strength to weight ratios. The paper reports the findings of an experimental study developing to investigate the quasi-static and dynamic response of sandwich panels based on polymethacrylimide foam using compression tests and Split Hopkinson Pressure Bar, respectively. The effect of thickness of aluminum face sheet, thickness and density of the polymethacrylimide core on the mechanical properties of the sandwich structures are studied respectively. It is shown that core density has the greatest effect on compressive strength of sandwich structure. The elasticity modulus and compressive strength of sandwich decreased by 40% under quasi-static compressive when the density of the core reduced by 28%. Secondly, dynamic compressive experiment results show that when the density of the core reduced by 28%, at the strain rate of 150 s−1, compressive strength decreased by 45%; strain rate 310 s−1, compressive strength reduced by 42%. When the strain rate increased from 7.6 × 10−4 s−1 to 150 s−1, compressive strength increased by 26%; strain rate increases from 7.6 × 10−4 s−1 to 310 s−1, compressive strength increased by 43%. The dynamic mechanical properties of polymethacrylimide foam sandwich panels accompanied with the increase of strain rate. Finally, dynamic constitutive relation of Cowper-Symonds function is fitted.

Influences of dispersion types and area densities of chopped fiber‐based interfacial reinforcements on mechanical properties of sandwich structures

Chopped carbon fibers with different dispersion types (colony type and uniform type) and area densities were inserted at sandwich beams, consisting of a PVC foam core covered with two glass fiber/epoxy composite face sheets. The effects of this reinforcement on the interfacial bonding between PVC foam core and glass fiber face sheets were evaluated. Their mechanical properties were measured by three‐point‐bending and Charpy impact tests. Their structures after mechanical failure were observed by scanning electron microscopy. Compared with the beam without interfacial reinforcement, the bending strength, energy absorption, and impact strength after interfacial reinforcement using 20 g/m2 uniform chopped fibers increased by up to 109%, 184%, and 47%, respectively, surpassing those of other chopped fiber mats. The weight percentage of carbon fibers/sandwich structure was less than 1%, so the chopped carbon fiber interleave had both cost effectiveness and outstanding structural performance. The improvement of interlayer toughness can mainly be attributed to the fiber bridging structure and the interlayer strength. POLYM. COMPOS., 40:E449–E455, 2019. © 2018 Society of Plastics Engineers

Mechanical Properties and Fatigue Performances on Sandwich Structures with CFRP Skin and Nomex Honeycomb Core

Composite sandwich structures with Nomex honeycomb core are commonly used in industrial applications. This paper was focused on the study of the mechanical properties of sandwich structures with CFRP (carbon fibre reinforced polymer) skin and a phenolic resin-impregnated aramid paper core, known as Nomex. The paper analyzes behaviour and determines the mechanical properties of the CFRP-Nomex specimens to different types of tests, such as: three - point bending, compression, impact. The exceptional fatigue resistance of the composite structures is responsible for their success in a variety of industrial applications. For this reason, in this paper were implemented accelerated testing techniques for CFRP-Nomex sandwich structures, resulting in a significant reduction of the test time (of 13.9 times). The main indicator that was determined using the accelerated testing methodology was the mean life that has value of 268554 cycles.

Evaluation of mechanical properties of sandwich structures with polyethylene terephthalate and polyvinyl chloride core

Sandwich structures are comprised of two external faces/skins (usually made of synthetic fiber/resin) and a core, being lightweight and with high stiffness. These structures when based on a foam core are commonly processed using liquid molding techniques. In this study, the light resin transfer molding process is used to inject the polymeric resin (vinyl ester) into the porous cavity between the impermeable core and the mold walls. The main goal of the present work is to study the effect of different types of cores (polyvinyl chloride (PVC) and polyethylene terephthalate) and faces (glass fiber cloths or mats) on the mechanical characteristics of the sandwich structures. Specimens were subjected to flexural, flatwise and edgewise compression, and Shore-D hardness testing. General comparison between the different core materials indicated higher flatwise compressive, flatwise tensile and shear strength of the PVC. However, the effect of the core on the properties of the sandwich structure, e.g. flatwise compressive and edgewise compressive strength, was much less evident.