Flatwise Compressive Strength Research Articles

Analyzing the influences of fabrication methods on the mechanical properties of Sumberejo kenaf/epoxy sandwich composites with polyurethane foam core

Natural fiber composite sandwich structures have developed significantly to create building materials that are strong and lightweight. The purpose of this study is to compare the cold press and vacuum assisted resin infusion (VARI) methods to investigate the mechanical properties of sandwich composites made of Sumberejo kenaf fiber (KF) reinforced epoxy (EP) as the skin and polyurethane (PU) foam as the core. The kenaf fibers were alkalized by NaOH solution. The results show that manufacturing KF/EP-PU foam sandwich composites using cold press has flatwise tensile strengths that are around (0.220 ± 0.031) MPa higher than VARI, which is only about (0.170 ± 0.057) MPa. This implies that cold press creates an enhanced composite structure. The core shear strength of cold press sample was 17% higher than VARI, with a value of (0.603 ± 0.052) MPa and (0.499 ± 0.016) MPa, respectively. Also, the skin bending stress of cold press sample was (6.106 ± 1.203) MPa while VARI sample had a value of (5.405 ± 0.687) MPa. However, the VARI method exhibited higher flatwise compressive strength with a value (0.393 ± 0.004) MPa and cold press method was (0.331 ± 0.032) MPa. In conclusion, the manufacturing method substantially impacts the mechanical properties of KF/EP-PU foam sandwich composites in this study. This study is a valuable reference for natural fiber sandwich composites as a building material.

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

Karakteristik komposit sandwich dengan inti (core) open cell foam bambu berlubang

The sandwich composite employed in this study is made of bamboo open-cell foam with plywood skin. The fibre volume percentage in the bamboo foam core was 15%, and PVAc glue was used. The open-cell foam core has a square-shaped hollow in the centre with spacings of 30mm, 40mm, and 60mm. The goal of this study is to describe sandwich composites made using hollow bamboo open-cell foam cores. Density testing (ASTM C271), flatwise compression testing (ASTM C365-05), flexural testing (ASTM C393), and water absorption testing (ASTM C272) were among the tests performed. Sandwich composites with core-opened cell foam with holes had lower average density, specific flatwise compressive strength, and specific bending strength than sandwich composites without holes, according to the study's findings. The average density of the sandwich composite with core-opened cell foam with holes dropped by 6-13% as compared to the sandwich composite without holes. The average-specific flatwise compressive strength of the sandwich composite with a hollow core decreased by 2-20%. The sandwich composite's average specific bending strength was reduced by 40-50% when the core-opened cell foam with holes was used. The percentage of water absorption in the sandwich composite is the inverse. With this feature, it is believed that hollow bamboo open-cell foam would become more widely used.

Structure genome based machine learning method for woven lattice structures

As a type of lightweight composite material, three-dimensional (3D) woven lattice structure (WLS) has been extensively applied in various fields. It is extremely significant to investigate its mechanical properties. Complex structure parameters make property prediction a great challenge. In this research, structure genome (SG) of 3D WLSs was defined with four SG characteristics, including the panel thickness, the meridional and zonal angles of fiber pillars and the mass fraction of the resin. A SG-based deep neural network method was conducted to predict the fundamental mechanical properties, including the flatwise compression strength and the out-of-plane elastic modulus. The effectiveness of the proposed method was verified by comparing the experimental data with the predictions. The results show that the prediction accuracy is more than 90% for most parts of the testing set. Through sensitivity analysis, the panel thickness and the mass fraction of the resin were identified as the most dominant parameter characteristics, which determine the overall performance. The method provides guidance for structure design of 3D WLSs.

On the tensile and compressive behavior of a sandwich panel made of flax fiber and agglomerated cork

Sandwich panels are used in buildings because of their light weight, thermal insulation, sound absorption, and better mechanical properties. Material scientists have been trying their best to replace synthetic materials as these are non-biodegradable. Stringent environmental policies, need for eco-friendly products, and problems in end-of-life disposal have made natural materials in sandwich panels the need of the hour. This research work attempts to replace the synthetic sandwich panels with natural sandwich panels without sacrificing the performance. The natural sandwich panels used in this work had agglomerated cork as the core and flax fiber as skin reinforcement. A vacuum-bagging technique was used to manufacture these panels with three core densities and three skin reinforcements. The performance of these panels was confirmed by conducting flatwise tensile, flatwise compressive, and edgewise compressive tests as per the American Society for Testing and Materials standards and the results are discussed in this article. The specific flatwise tensile strength of natural sandwich panels was 14–21% higher and the specific flatwise compressive strength was 2–10% higher than the synthetic sandwich panels. The edgewise compressive strength was found to be 32–34% lower than synthetic sandwich panels. The results suggest that natural sandwich panel could be a better alternative material for building applications.

Flatwise compression behavior of composite Nomex® honeycomb sandwich structure

In this paper, the mechanical properties of Nomex® paper coated with resin and composite Nomex® honeycomb sandwich structures (CNHSS) were obtained by tensile tests and flatwise tests respectively. The fundamental mechanical properties of the Nomex® paper were used as input materials parameters of finite element model generated at meso-scale level for the CNHSS, and the mechanical properties of CNHSSs were used to validate the numerical results. Based on the test and numerical results, the theoretical equations were modified to predict the flatwise compressive buckling strength and modulus of the CNHSS. The numerical and theoretical results clearly revealed that the CNHSS had two flatwise compressive elastic moduli. However, the flatwise test can only capture the second flatwise compressive elastic modulus due to manufacturing geometric defects of the cell walls. The numerical and test results showed that the manufacturing geometric defects of the cell walls showed little influence on the ultimate flatwise compressive strength. And the modified equation can predict the flatwise compressive buckling strength and modulus of the CNHSS with sufficient accuracy.

Mechanical Properties Of Sandwich Composites Used For Aerofoil Shell Structures Of Wind Turbine Blade

The grid-scored foams contribute significantly to the overall mechanical properties of the sandwich structures, such as aerofoil shell structure of wind turbine blades which are subjected to different loads under operating conditions. The goal of the present paper is to examine the four-point bending, flatwise and edgewise compression and in-plane shear behaviour of sandwich panels composed of composite face sheets of E-glass/ bisphenol-A epoxy resin and plain and grid-scored PVC foams. The four-point bending failure load of the grid-scored foamed sandwich beams increased by 28.1% compared to the plain foamed ones. The flatwise compression strength of samples with grid-scored foam increased by 546% compared to plain foamed samples. The resin grids contributed to an increase in the flat-wise compression stress inducing the core crushing. Under the edgewise compression load, using the grid-scored foam increased the maximum load values by only about 2.9% relative to the plain foam. The reason for this small difference can be addressed as the facings are more effective in carrying the edgewise loadings. With the use of the grid-scored foam, an increase of 38.2% was obtained in-plane shear strength compared to plain foamed sandwich beams. The resin grids improved bonding between the facings and PVC foam.

Experimental and numerical study of composite sandwich panels for lightweight structural design

Composite sandwich panels are commonly considered as lightweight materials for structural design in many applications including automotive, aerospace and defence systems. These panels must be developed and validated for its mechanical strength characteristics under different loading conditions before deploying them for the practical application. Hence, the present paper deals with the experimental and numerical studies on composite sandwich panels subjected to quasi-static edgewise and flatwise compression loads. The composite face sheet was developed using 2 × 2 bi-directional 200GSM twill carbon fibre with hot cure benzoxazine resin. Sandwich panels were made using the developed composite face sheets with aluminium honeycomb core. The developed composite face sheets were tested for tensile and flexural conditions and the sandwich panels for edgewise and flatwise compression loads. Three samples for each of these tests were conducted in Shimadzu UTM with 50 kN capacity machine. A consistent load-displacement profile and the failure pattern were observed for all the samples tested in each test category. It is noted from these tests that the composite face sheets exhibited an ultimate tensile strength of 444 MPa and a flexural strength of 842 MPa which is pretty to close to the epoxy based composites used in the aerospace applications; sandwich panels showed an edgewise compressive strength of 610 MPa and flatwise compressive strength of 3.5 MPa. Tensile test coupons initially had undergone certain delamination before failure and failed close to the specimen holding end. Flexural test specimens were shown delamination of only one layer at the loading face. However, the specimen was well intact together even after failure. Bending mode of failure was noted during edgewise compression test of the sandwich; severe delamination was seen in the tension side of the sandwich whereas a line-folding crack with failure was exhibited at the mid-plane of the specimen. In case of flatwise compression, no evident of damage was observed in the sandwich structure. The second part of the paper describes the numerical simulations of these test cases including tensile, flexural, edgewise compression and flatwise compression using an explicit finite element solver viz. LS-DYNA. Material type 22 and 26 was selected to define the material behaviour of composites and honeycomb respectively. The delamination was modelled using *CONTACT_AUTOMATIC_SURFACE_SURFACE_TIEBREAK card with option 9 that works under B-K linear fracture mechanics law to define the normal and shear failure of cracks. The numerical results were found to match well with experimental observations for the individual coupons as well as the sandwich samples. Therefore, it is concluded from this study that the developed LS-DYNA simulation methodology can be used as a tool for composite sandwich panels based lightweight structural design.

Honeycomb Carbon Sandwich Composite Panel Under Compressive Load Flat-wise: Experimental Analysis

This article is an experimental study of honeycomb core carbon skin sandwich composite panel using American Standards for Testing Materials, ASTM Standards C365/C365M-11a for honeycomb structure flatwise compressive strength. The objective of this article is to describe the process of validation done in the specimens prepared in the research are, to have consistency in terms of the strength and other mechanical properties and to ensure the materials prepared in the lab and can be applied for aviation application (aircraft control surface) later. The samples were prepared in accordance with aviation industry standards using the aviation industry materials at the approved facility (Malaysian Airlines Composite workshop in Subang). The experiment was conducted using the Instron 8802 UTM by following the ASTM Standards at the Faculty of Mechanical Engineering, University Teknologi MARA. From the experiment in accordance with the test standard, the results of the experiment showed the consistency in terms of strength of the specimen. The ultimate strength was found at the average 5.88 kN.

High Temperature Mechanical Properties of a Vented Ti-6Al-4V Honeycomb Sandwich Panel.

For aerospace applications, honeycomb sandwich panels may have small perforations on the cell walls of the honeycomb core to equilibrate the internal core pressure with external gas pressure, which prevent face-sheet/core debonding due to pressure build-up at high temperature. We propose a new form of perforation on the cell walls of honeycomb sandwich panels to reduce the influence of the perforations on the cell walls on the mechanical properties. In this paper, the high temperature mechanical properties of a new vented Ti-6Al-4V honeycomb sandwich panel were investigated. A vented Ti-6AL-4V honeycomb sandwich panel with 35Ti-35Zr-15Cu-15Ni as the filler alloy was manufactured by high-temperature brazing. The element distribution of the brazed joints was examined by means of SEM (scanning electron microscopy) and EDS (energy-dispersive spectroscopy) analyses. Compared to the interaction between the face-sheets and the brazing filler, the diffusion and reaction between the honeycomb core and the brazing filler were stronger. The flatwise compression and flexural mechanical properties of the vented honeycomb sandwich panels were investigated at 20, 160, 300, and 440 °C, respectively. The flatwise compression strength, elastic modulus, and the flexural strength of the vented honeycomb sandwich panels decreased with the increase of temperature. Moreover, the flexural strength of the L-direction sandwich panels was larger than that of the W-direction sandwich panels at the same temperature. More importantly, the vented honeycomb sandwich panels exhibited good compression performance similar to the unvented honeycomb sandwich panels, and the open holes on the cell walls have no negative effect on the compression performance of the honeycomb sandwich panels in these conditions. The damage morphology observed by SEM revealed that the face-sheets and the brazing zone show ductile and brittle fracture behaviors, respectively.

Investigating what Effects Aviation Fluids Have on the Flatwise Compressive Strength of Nomex® Honeycomb Core Material

Investigating what Effects Aviation Fluids Have on the Flatwise Compressive Strength of Nomex® Honeycomb Core Material

Investigating the effects aviation fluids have on the flatwise compressive strength of Nomex® honeycomb core material

Composite honeycomb sandwich structure is widely used for aircraft structures such as control surfaces, radomes, engine cowls, and aircraft interior structure because of its lightweight and high strength characteristics. One of the disadvantages of honeycomb sandwich structure is that they are prone to fluid intrusion. The purpose of this study is to determine if the structural properties of honeycomb core are affected by contact with a fluid. The test specimens were manufactured of fiberglass prepreg for the facesheets and Nomex® honeycomb core for the core material in accordance with ASTM C-365/365M. Test specimens were soaked in several different kinds of fluids, such as aircraft fuel, turbine engine oil, hydraulic fluid, and water for a period of 60 days. Some of specimens were tested right after soaking period ended, and some of them were dried before they were tested. A flatwise compressive test was performed, and the test results were analyzed to determine how the contact with aircraft fluids affected the compressive strength of the Nomex® honeycomb core and how the strength was recovered when the specimens were dry. In addition, the investigation of de-bonding between facesheet and core material after soaking was performed to support the study.

The energy absorption and bearing capacity of light-weight bio-inspired structures produced by selective laser melting

Sandwich structures are widely used in aviation and aerospace fields because they can absorb vast energy due to their excellent continuous compression behaviors. And in this work, the light-weight bio-inspired sandwich structure of titanium alloy was designed based on cybister elytra and produced by selective laser melting (SLM). The results show that bio-inspired structures can realize the light-weight effectively by increasing the core height. The specific and ultimate flatwise compressive strengths first increase and then decrease when core height increases. The load-displacement curves of bio-inspired structures during flatwise compression consists of elastic deformation, buffer and compaction zone. Comparatively, the edgewise compression lacks buffer zone. And the bio-inspired structure has an excellent flatwise comprehensive performance when its core height is 6 mm, whose peak flatwise compressive strength and specific volume energy absorption are 84.30 MPa, 101.30 MJ/m3, respectively. The specific ultimate strength of bio-inspired structures is optimized at the core height of 4 mm on the edgewise compression tests. And the fracture of the side arc damaged area shows an obviously ductile fracture and the panel and core of the middle area are brittle fracture in the flatwise compressive tests. Finally, The ANSYS simulation results are consistent with experimental results during the whole compressions, which will provide an accurate guidance in next researches

Assessment on the ageing of sandwich composites with vinylester-based composite faces and PVC foam core in various harsh environments

The behaviour of moisture absorption and evolution of various mechanical properties for the sandwich composites immersed into two humid conditions: seawater with 30 °C (SWL) and purewater with 80 °C (PWH) have been examined by Ding et al. (2018). In this paper, three relatively harsh environmental conditions: salt-fog spray ageing (SFS), hygrothermal atmosphere alternating high low temperature (HHL) and solar radiation in combination with water vapour (SRW) are determined. Further studies on the ageing behaviour of previously selected sandwich composites constituted of thick ECR glass fibre reinforced vinylester composite faces bonded to closed-cell PVC were carried out under aggression of newly added three artificial environmental conditions. To this end, the specimens were prepared by VIMP and then exposed to the new three conditions for 1008 h. The moisture uptake before desiccation and after desiccation as well as various mechanical properties, including flatwise tension strength, flatwise compressive strength, in-plane shear strength, shear strength using short beam bending and edgewise compressive strength, were measured and compared with previous data from SWL and PWH. The weight change indicates that the specimens exposed to newly added environmental conditions absorb much less moisture and chemically bound water, meanwhile the mechanical characterization reveals that specimens exposed to the SRW deteriorate significantly in the faces-core interfacial properties.

Hygroscopic ageing of nonstandard size sandwich composites with vinylester-based composite faces and PVC foam core

Abstract This paper aims to assess the hygroscopic behaviour of nonstandard size sandwich composites constituted of thick Electronical-Chemical Resistance (ECR) glass fibre reinforced vinylester composite faces bonded to closed-cell Polyvinyl Chloride (PVC) foam core in the service environment as a reference and basis for materials selection. In order to exhibit the change of sandwich composites properties in realistic environment, the specimens fabricated by Vacuum Infusion Moulding Processing (VIMP) were immersed in two humid conditions: seawater with 30 °C (SWL) and purewater with 80 °C (PWH) for 1680 h. The moisture uptake and various mechanical properties of specimens, including the flatwise tension strength, flatwise compressive strength, in-plane shear strength, shear strength using short beam bending and edgewise compressive strength were tracked periodically. The results from water absorption measurement indicate that the specimens immersed in two humid conditions reach saturation levels after immersion of 1008 h, and non-Fickian and Fickian diffusion occur simultaneously. The characterization on mechanical properties was mainly placed on the variation of PVC foam core and faces-core interface properties, and corresponding results reveal that the moisture absorption has insignificant effects on the PVC foam core properties but appreciably affects the composite faces and face-core interface properties, especially for the specimens immersed in PWH.

The Comparison on Mechanical Bonding Properties of Untreated Coconut Fiber towards Synthetic Fiber for Fiberglass Boat Building

The development of high performance materials made from natural resources is increasing worldwide. The interest in natural fiber reinforced polymer composite materials is rapidly growing both in terms of their industrial applications and fundamental research. They are renewable, cheap, completely or partially recyclable, and biodegradable. The coconut fiber can be a potential candidate to replace the industrial core and foam which its application are worldwide and it is used to increase the thickness of the fiberglass boat. In this research, three types of testing panel are constructed by using 10 mm of Coconut Fiber, 3D Core Foam and Infusion Grooved PVC Foam as the sandwich core. The resin infusion method which is produce quality final products have been used. The findings be obtained by conducting two testing methods, for the Flatwise Tensile Strength testing, the specimens taken from Coconut Fiber product yielded a higher value of strength which is 3.005 MPa compared to the specimens taken from Infusion Grooved PVC Foam and 3D Core Foam which is 2.963 MPa and 1.264 MPa respectively. For the Flatwise Compressive Strength testing, the specimens taken from the Coconut Fiber product had higher value of compressive stress compared to the value of specimens taken from Infusion Grooved PVC Foam and 3D Core Foam which is 29.66 MPa, 2.58 MPa and 4.68 MPa respectively. This research has proved that the Coconut Fiber is quite suitable to become as one of the laminating schedule for the construction of the fiberglass boat hull.

Flatwise Compression Strength and Energy Absorption of Polyurethane Foam-Filled Lattice Core Sandwich Panels

In the present study, the effect of the polyurethane foam-filled lattice core sandwich panel on the energy absorption and the compression strength was investigated. In the compression tests, it was found that the foam-filled sandwich panels have a greater load-carrying capacity compared to the sum of the unfilled specimens and the filled polyurethane block. Moreover, the energy absorption efficiency of foam-filled sandwich panels with higher relative density (5.1 and 5.7%) lattice cores was lower than that of the unfilled specimen when the compressive strain was small, whereas it was superior when the compressive strain reached about 0.1, and this superiority became more pronounced with the strain increase. Moreover, the energy absorption of foam-filled sandwich panels with lower relative density (4.43%) lattice cores was superior to that of the unfilled specimen.

Evaluation of Flatwise Compression Strength of Stitched Foam Sandwich Panel

Evaluation of Flatwise Compression Strength of Stitched Foam Sandwich Panel

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.

Moisture absorption and mechanical degradation studies of polyurethane foam cored E-glass-reinforced vinyl-ester sandwich composites

The present paper explores the experimental observations and result of hygrothermic aging of polyurethane foam cored E-glass reinforced vinyl-ester sandwich composites for a long duration of time under salt fog exposure. Four types of sandwich specimens were used for the study. Polyurethane foam cored E-glass mat (woven roving, chopped strand mat, chopped strand stitched mat and stitch bond mat) type reinforcement in vinyl-ester sandwich composites were prepared by manual hand layup method using compression technique. The prepared specimens were tested for moisture up-take behavior and the resulting property degradation in terms of flexural strength, flatwise and edgewise compression strength. The mechanical properties under the salt fog exposure with 95% RH using artificial sea water fogging were monitored for 180 days. The specimens showed reduced strength in terms of core shear and facing bending strength, edgewise and flatwise compressive strength. Scanning electron micrograph of the fracture specimens show face sheet/core debonding.