Edgewise Compression Research Articles

Mechanical Properties of Eco-Friendly, Lightweight Flax and Hybrid Basalt/Flax Foam Core Sandwich Panels.

Greener materials, particularly in sandwich panels, are in increasing demand in the transportation and building sectors to reduce environmental impacts. This shift is driven by strict environmental legislation and the need to reduce material costs and fuel consumption, necessitating the utilisation of more sustainable components in the transportation and construction sectors, with improved load-bearing capabilities and diminished ecological footprints. Therefore, this study aims to analyse and evaluate the structural performance of polyethylene terephthalate (PET) core and flax or basalt/flax FRP sandwich panels as an alternative to conventional synthetic materials. The novel eco-friendly sandwich panels were manufactured using the co-curing technique. Four-point bending, edgewise compression and core shear tests were performed and insights into how the skin properties affect the strength, stiffness and failure mode of specimens were provided. The stress-strain behaviour, facing modulus and strength, flexural rigidity, core shear strength and failure modes were evaluated. The flexural facing modulus of the flax and flax/basalt sandwich skins were found to be 5.1 GPa and 9.8 GPa, respectively. The flexural rigidity of the eco-friendly sandwich panel was compared with published results and demonstrated a promising structural performance. The environmental benefits and challenges were outlined and critically evaluated focusing on transportation and construction applications.

Ensemble Feature Selection for Clustering Damage Modes in Carbon Fiber‐Reinforced Polymer Sandwich Composites Using Acoustic Emission

Acoustic emission (AE) serves as a noninvasive technique for real‐time structural health monitoring, capturing the stress waves produced by the formation and growth of cracks within a material. This study presents a novel ensemble feature selection methodology to rank features highly relevant with damage modes in AE signals gathered from edgewise compression tests on honeycomb‐core carbon fiber‐reinforced polymer. Two distinct features, amplitude and peak frequency, are selected for labeling the AE signals. An ensemble‐supervised feature selection method ranks feature importance according to these labels. Using the ranking list, unsupervised clustering models are then applied to identify damage modes. The comparative results reveal a robust correlation between the damage modes and the features of counts and energy when amplitude is selected. Similarly, when peak frequency is chosen, a significant association is observed between the damage modes and the features of partial powers 1 and 2. These findings demonstrate that, in addition to the commonly used features, other features, such as partial powers, exhibit a correlation with damage modes.

Impact damage resistance and tolerance of alumina-based oxide/oxide ceramic matrix composite upon one sided thermal shock and hold

In this study, ceramic matrix composite specimens constituting Nextel™720 fibers and alumina matrix were subjected to one-sided thermal shock and subsequent 30-min hold at temperatures of 1200℃, 1350℃ and 1500℃. The plates were then subjected to low velocity impact at 5 J impact energy, followed by edgewise compression with digital image correlation. No noticeable change in mass, roughness and specimen dimensions were observed after the thermal shock and hold event at any of the temperatures for any of the specimens. External and internal damage resulting from the impact event also showed no dependence on the thermal shock temperature. The percentage compressive strength retention after low velocity impact ranged from 61 % to 68 % for all cases considered, again with no trends observed based on shock temperature. However, the compressive modulus for the impacted panels that were exposed to high temperature were higher than the pristine (non-thermal shocked) impacted panels.

Compression behavior of lightweight corrugated composite Sandwich panels with smart facesheets reinforced by shape memory alloy wires: an experimental study

AbstractThis paper presents an experimental examination of the compression demeanor of lightweight corrugated core composite (CCC) sandwich panel and corrugated core smart composites (CCSC) sandwich panels subjected to quasi‐static edgewise compression loading. The existence of shape memory alloy (SMA) wires and pre‐strain percentages of SMA are the indicators studied in this article. The fabrication procedure presented and the appraisement of the mechanical properties of the CCC and CCSC sandwich panels are expressed. The core geometry of samples is trapezoid corrugated made of aluminum. The facesheets are four layers of woven glass fiber/ epoxy laminated composite. For evaluation of the efficacy of the presence of SMA wires on mechanical specifications of sandwich panels, three SMA wires with various pre‐strain percentages (0%, 3%, and 6%) are embedded in each composite facesheet. Mechanical properties of all types of CCC and CCSC sandwich panels such as maximum force, critical damage force, specific strength, absorb energy, specific toughness, Young's modulus, and specific stiffness were evaluated. Results showed that the CCC sandwich panel has higher mechanical specifications than the CCSC sandwich panels with 0% and 3% pre‐strain. Also, increasing pre‐strained SMA wires improves all mechanical parameters of CCSC sandwich panels. CCSC sandwich panel with 6% pre‐strain has the highest compression properties than other sandwich panels. Maximum Force, Critical Damage Force, Specific Strength, Absorbed Energy, Specific Toughness, Young's Modulus, and Specific Stiffness of CCSC sandwich panel with 6% pre‐strain are 14.73 kN, 13.6 kN, 9.55 MPa/g, 26.61 kJ, 0.346 MJ/m3g, 4395 MPa and 0.61 kN/mm g, respectively.Highlights Lightweight CCC sandwich panel and CCSC sandwich panel manufactured. Compression behavior of CCC sandwich panel and CCSC sandwich panel evaluated. Pre‐strained SMA wires improves energy absorption of CCSC sandwich panels. Higher specific toughness was obtained with 6% pre‐strain SMA. Presence of SMA wires with no pre‐strain cannot improve the specific strength.

Fabrication and mechanical properties of thermoplastic corrugated sandwich panel with enhanced face‐core interface

AbstractThermoplastic sandwich structures are widely utilized in engineering fields due to their high specific strength and stiffness, recyclability, and impact toughness. The face‐core interface strength is crucial to maximize the performance benefits of sandwich structures. Two sizes of corrugated sandwich panels with hot‐melt bonding and resistance welding connection methods were fabricated. The mechanical properties of sandwich panels were compared using a combination of experimental, numerical, and analytical investigation. Edgewise compression (EC) and 3‐point bending (3 PB) tests were conducted to obtain load–displacement curves and investigate different failure modes of sandwich panels. The peak edge compression and bending loads of the resistance welded structures were 42% and 92% higher, respectively, and the face‐core interface was always well‐connected compared to those of the hot‐melt bonding. The results indicate that the resistance welding method can be utilized as a core bonding technique for thermoplastic composite sandwich structures and has great potential for aerospace application.Highlights A method that includes hot‐melt bonding and resistance welding are develop to produce thermoplastic composite corrugated sandwich panels (TPC‐CSPs). The TPC‐CSPs fabricated by resistance welding exhibit superior interface connection performance compared to hot‐melt bonding and this method enhance the structural load bearing capacity. The numerical and analytical method were presented to investigate the failure model, which was consistent with the experimental results.

Mechanical Behaviour of Glass Fibre-Reinforced Polymer/Polyvinyl Chloride Foam Cored Sandwich Structures

This study focuses on the fabrication and analysis of the mechanical behaviour of unidirectional (UD) glass fibre-reinforced polymer (GFRP) facesheet and polyvinyl chloride (PVC) foam core sandwich structures fabricated by a vacuum-assisted resin infusion method (VARIM). These sandwich structures are commonly used in marine and wind turbine blade applications. To date, relatively little knowledge about the functional behaviour of UD GFRP compared to composites reinforced with bidirectional mats is available for day-to-day applications. The effects of the facesheet orientation, facesheet thickness, and core thickness on the mechanical behaviour of the specimens were examined. The UD fibres were oriented in cross-ply (0/90), angle-ply (+45/−45), and quasi-isotropic orientations. Various mechanical properties such as tensile, flexural, flatwise compression, and edgewise compression tests were examined. Characterization of the tensile properties of the facesheet showed that the cross-ply orientation had a higher strength than the angle-ply and quasi-isotropic orientations. The flexural load-carrying capacity of the cross-ply facesheet orientation was superior to the other orientations. The increase in the core thickness changed the flexural failure mode from face yield and core shear to core indentation. Flatwise compression (FWC) was tested to determine the core characteristics of the sandwich structure, and the peak loads of 4.90, 1.81, and 3.90 kN were obtained for 10-, 15-, and 20 mm core thicknesses, respectively. Edgewise compression (EWC) exhibited stable end crushing for thinner facesheet, whereas thicker facesheet showed core crushing and buckling. When the facesheet thickness was increased from 1.5 mm to 3 mm in the EWC, the buckling load increase ranged from 2.53% to 44.83% for core thicknesses 10-, 15-, and 20 mm, respectively.

Edgewise compression mechanisms in sandwich panels with foam-core and jute/glass hybrid composite faces

Natural fibers may represent an economical and sustainable alternative to produce sandwich panels. This study investigates the influence of the slenderness ratio on the buckling load of sandwich panels with jute, glass, and hybrid faces and a polyethylene terephthalate foam core. Failure and damage of the panel face with natural fibers are studied, also evaluating the suitability of failure criteria, especially considering the limited literature on that. Numerical analyses of the panels were performed using implicit and dynamic explicit solvers with Hashin’s failure criteria. The hybrid faces showed a higher buckling load, being the most suitable option.

Comparative study of the mechanical properties of glass and Kevlar fiber-reinforced honeycomb composite

Honeycomb sandwich structures have wide range of applications in the aircraft, automobile, and satellite sectors due to their superior properties such as high specific strength, stiffness, energy absorption, and high impact strength. In this study, mechanical characteristics such as compression, three-point bending, and in-plane impact properties of 3D woven honeycomb composites produced from Kevlar and glass fiber were investigated. The focus of this research is to compare the mechanical performance of woven honeycomb composites developed from these two fibers with similar cell structures. The results revealed that Kevlar fiber honeycomb composite shows higher peak load and energy absorption for flatwise and edgewise compression while in three-point bending and in-plane impact, glass fiber honeycomb composite shows higher peak load, and impact energy absorption. The deformations shown in all the mechanical properties give the ductile behavior for Kevlar fiber and brittle behavior for glass fiber composite. The findings of the study suggest that the failure modes are mostly determined by the nature of the material itself.

Mechanical performance of stitched foam-filled honeycomb sandwich panels

Foam-filled Honeycomb Sandwich panels (FHS) are widely used in various industrial applications due to their superior multifunctional properties. However, these sandwich panels fail in some extreme conditions due to interfacial failure between the face sheet and core. To overcome this issue, novel stitched foam-filled honeycomb sandwich panels (SFHS) were fabricated by integrating the top face sheet and bottom face sheet by the stitching technique. Stitching through the face sheet and core is to improve the interfacial strength and increases the mechanical properties of the sandwich panel. FHS and SFHS were prepared by the Vacuum Assisted Resin Transfer molding (VARTM). Flexural, flatwise, and edgewise compression analysis values for SFHS panels are 2.02, 1.28, and 1.25 times higher than for FHS panels. SFHS panel weight increased slightly but had superior mechanical properties than FHS. These innovative SFHS panels can be broadly used for applications including structural, flooring, and body panels.

Development and evaluation of the sandwich edgewise compression after impact test

A compression after impact test method has been developed to assess the damage tolerance of sandwich structures under edgewise compressive loading. This test method, recently standardized as ASTM D8287, was designed to test specimens that have been impact damaged per ASTM D7766. The fixture design utilizes end loading with top and bottom edge supports to prevent end-brooming and out-of-plane rotation. Additionally, knife edge side supports provide out-of-plane restraint to buckling, similar to the existing laminate edgewise compression after impact test fixture. The sandwich configurations investigated were constructed from glass/epoxy and carbon/epoxy facesheets with a Nomex honeycomb core. Mechanical testing was conducted to evaluate the proposed specimen design, fixturing, and test procedure. Finite element analysis was used to verify the strain gage placement and damage size limits.

Load bearing investigations on novel Acrylonitrile butadiene styrene‐carbon quantum dots 3D printed core/bamboo fiber polyester sandwich composite for structural applications

AbstractIn this research, a novel 3D printed core and natural fiber polyester composite skin based thick sandwich panel was developed as structural material for domestic and commercial infrastructure applications. The main objective of this research was to analyze how the carbon quantum dots (C‐dots) from agriculture waste strengthen the softer thermoplastic acrylonitrile butadiene styrene (ABS) core and overall sandwich panel's load bearing properties. The core of sandwich was prepared using additive manufacturing method whereas the skin was developed by hand layup method. According to the results the C‐dots of 20 phr into the ABS improved the compression properties of core in both flatwise and edgewise directions. A highest tensile and flexural strength of skin was observed to be 114 and 146 MPa respectively. The addition of C‐dots improved the load bearing effect and also restricts the deformation against load. This performance improved novel 3D printed core and bamboo fiber skin sandwich could be used as an alternative construction and building material where the commercial plywood and other forms of powder wood face damages via weather and termite issues.Highlights Higher filler volume of up to 20 phr of carbon quantum dots in acrylonitrile butadiene styrene (ABS) were developed Novel 3D printed thin walled core of 1 mm diameter was developed using carbon quantum dots and ABS. Bamboo fiber‐polyester skin with highest tensile strength of 114 MPa was developed. Improved flatwise compression and tensile strength were achieved for ABS core with 20 phr of Carbon quantum dots Flexural strength and edgewise compression properties were improved with 20 phr of Carbon quantum dots in ABS

Structural response of steel sandwich panels with PUR foam core subjected to edgewise compression: Experimental, numerical, and analytical considerations

With the objective of leading to innovative lightweight structural components in the construction sector using sandwich panels with polyurethane foam and steel face sheets, different studies were conducted on such structures, including experimental, numerical, and analytical campaigns. The experimental campaign includes the mechanical characterisation of the constituent materials and the edgewise compressive test of small-scale sandwich panels. The test protocols are detailed, and their influence on the results is assessed. Through the use of digital image correlation recordings, deformation patterns and failure mechanisms in the constituent materials and the composite structure are identified. Material constitutive models are calibrated based on the experimentally obtained results. The accuracy of such models is first evaluated against the stress–strain curves recorded during the experiments. In the second stage, the response of the sandwich panels subjected to edgewise compressive loading is simulated. A parametric analysis on the sensitivity of the numerical models to the initial geometrical imperfections is shown to be fundamental to capturing the behaviour of the sandwich panels. Furthermore, the experimental and numerical results are compared to analytical solutions of the problem of the edgewise compression of sandwich panels. Finally, a thorough discussion of the obtained experimental, numerical and analytical results is presented, along with comparisons to results available in the literature.

Determining mechanical and acoustical behaviors of all-recycled PP sandwich structures with bi-directional sinusoidal corrugated core

By recycling the waste polymer material and using it in weight reduction studies of electric vehicles, a double-sided gain is achieved against environmental pollution. Sandwich structures with prismatic cores obtained by recycling waste polymers can be used in structural applications of light and heavy commercial vehicles and public transportation vehicles that carry cargo and passengers. These sandwich vehicle parts could help to increase the max. range and load-carrying capacity of electric vehicles. In this study, sandwich plates with prismatic egg-box cores were produced with waste Polypropylene. Since the materials are collected from different waste sources, the physical properties (additive ratio, secondary substance determination, density) of the recycled material were measured. Thereafter, hardness, quasi-static flatwise and edgewise compression, and 3-point bending tests were done to determine the mechanical properties of the structure. After that, dynamic compression and 3-point bending tests were performed to determine the strength and impact energy absorption capacity of the structure in collision situations. Finally, impedance tube tests were carried out for the acoustic characterization, which is one of the important parameters affecting interior cabin comfort, and Sound Transmission Loss (STL) and Sound Absorption Coefficient (SAC) values of the structure were determined.

Performance evaluation of composite sandwich structures with additively manufactured aluminum honeycomb cores with increased bonding surface area

AbstractModern aerostructures, including wings and fuselages, increasingly feature sandwich structures due to their high‐energy absorption, low weight, and high flexural stiffness. The face sheet of these sandwich structures are typically thin composite laminates with interior honeycombs made of Nomex or aluminum. Standard cores are structurally efficient, but their design cannot be varied throughout the structure. With additive manufacturing (AM) technology, these core geometries can be altered to meet the design requirements that are not met in standard honeycomb cores. This study used a modified aluminum honeycomb core, with increased surface area on the top and bottom, as the core material in sandwich panels. The modified honeycomb core was produced through the laser powder bed fusion method. The behavior of the modified sandwich composite panels was evaluated through three‐point bend, edgewise compression, and impact tests, and their performance was compared to that of a conventional honeycomb core sandwich panel. The three‐point bend test results indicated that the sandwich structure's ultimate shear strength improved by 12.6% with the modified honeycomb core. Additionally, the displacement at the failure of the structure increased by 11%. The edgewise compression tests showed that the ultimate edgewise compressive strength improved by 19.1% when using the modified core. The impact test results revealed that the peak force increased by 8% and the energy‐absorbing capacity of the sandwich structure increased by 20% with the use of the modified honeycomb core.

Edgewise Compression and Three-Point Bending Analyses of Repaired Composite Sandwich Panels.

In this work, the fracture behaviour of repaired honeycomb/carbon-epoxy sandwich panels under edgewise compression and three-point bending loading was analysed. Assuming the occurrence of damage resulting from a complete perforation leading to an open hole, the followed repair strategy consists of plug filling the core hole and considering two scarf patches with an angle of 10° in order to repair the damaged skins. Experimental tests were performed on undamaged and repaired situations in order to address the alteration in the failure modes and assess the repair efficiency. It was observed that repair recovers a large part of the mechanical properties of the corresponding undamaged case. Additionally, a three-dimensional finite element analysis incorporating a mixed-mode I + II + III cohesive zone model was performed for the repaired cases. Cohesive elements were considered in the several critical regions prone to damage development. The failure modes and the resultant load-displacement curves obtained numerically were compared with the experimental ones. It was concluded that the numerical model is suitable for estimating the fracture behaviour of sandwich panel repairs.

Mechanical performances of polyvinyl chloride (PVC) foam sandwich composites with glass cloth face-sheet

The mechanical performances of polyvinyl chloride (PVC) foam sandwich panels with different types of cores prepared by vacuum-assisted resin infusion process (VARI) were investigated. The flatwise, edge-wise compression, flexural and impact properties of three types of PVC sandwich panels of the prepared panels were performed. The results show that the mechanical performances of the foam sandwich composites can be enhanced due to the presence of polymer pins, and the impact properties appear slightly different at different stages. Due to the existence of pins, the energy absorption and impact properties of the sandwich panels are slightly reduced during the impact rebound phase, while the impact properties of the three sandwich panels do not change much during the impact penetrated phase. The contact surface and the cross-section through the damaged area were observed to analyze the failure modes of sandwich composites.

Flexural Characterisation of Sandwich Panel with Corrugated Glass Reinforced Polymer

The corrugated foam core sandwich construction is used in variety of structural applications. These structures are subjected to flexural, impact, edgewise compression and shear loads. Traditional process for manufacturing of sandwich panel is not suitable for making corrugated core sandwich panel. In this work a novel methodology has been developed for construction of corrugated foam core sandwich panel. The present study focuses on the flexural behaviour of sandwich panel by varying the foam densities and corrugated cell. Two types of densities with one cell and two cells are used. The sandwich employs a Glass Reinforced Polymer (GRP) orthotropic material for both the two outer skins and the inner core web. In particular, the core is designed to have uneven topology to cooperate with GRP skins in membrane and flexural properties by adding a corrugated foam core. At first, a comparison has been performed between different density foams. Initially, 40 kg/m3 with 1 unit cell and 32 kg/m3 with 1 unit cell are compared, and then the same densities are compared with 2 cells. Among all, 40 kg/m3 with two cells shows highest flexural strength compared to the other specimens. Also, the sandwich panel with an empty core has been tested to understand the strength of the face sheet and corrugated core.

Comparative analysis of the mechanical performance of 3D woven honeycomb composites produced in warp and weft directions

This research work focuses on the design and manufacturing of 3D woven honeycomb fabrics and their composites in both warp and weft directions. An experimental investigation of the mechanical properties of these two composite materials was carried out. For this purpose, at first, a 3D woven honeycomb in both directions was fabricated on a customized multi-beam 3D weaving machine using E-glass fibers. The composites were created by VARIM (Vacuum assisted resin infusion method) process using epoxy resin and Aradur hardener. The mechanical characteristics such as compression, three-point bending, and in-plane impact of composite samples were investigated keeping cell parameters constant. There will be a change in composite properties as tension in warp and weft is different. Crimp and modulus will also be different. The comparison of mechanical properties of these two honeycomb composite samples revealed that warp way honeycomb shows better properties in edgewise compression and three-point bending test while weft way honeycomb shows higher energy absorption under flatwise compression and in-plane impact test. The direction of cell channels gives the direction of loading to the threads, which affects the mechanical properties.

Comparative analysis of aluminium core honeycomb with 3D woven Kevlar honeycomb composite

Sandwich structures have a high capacity for stiffness, strength, and energy absorption, and are frequently used as lightweight composite components in shipbuilding and aeronautical engineering. In this work, mechanical characterisation of aluminium honeycomb and 3D-woven Kevlar honeycomb composite sandwich panels with respect to their flatwise, edgewise compression, and three-point bending tests was carried out. The experimental results show that the 3D-woven Kevlar honeycomb is better than the aluminium honeycomb for flatwise and three-point bending behaviour. In the case of edgewise compression, aluminium honeycomb shows significant results. Aluminium honeycomb cores show the plastic collapse mechanism, while Kevlar honeycomb indicates the occurrence of buckling before failure.

Numerical modeling of flatwise energy absorption behavior of 3D woven honeycomb composites with different cell structures

Numerical simulation along with experimental validation are used to investigate the flatwise compression behavior in the out-of-plane direction of several 3D woven honeycomb composites with varied cell geometry such as hexagonal (HX), triangular, and rectangular structures. For all the structures, the perimeter of the unit cell was kept constant. Edgewise compression and three-point bending behavior were compared experimentally for all three configurations. The flatwise compression behavior of honeycomb structures has been predicted using FEM on the LS-DYNA platform, and the results have been validated using experimental data. The predicted values are found to be in good agreement with the experimental results. Hexagonal honeycomb shows better results as compared to other cell structures as revealed by both experimental and numerical analysis.