Effect of salt water exposure on foam-cored polyurethane sandwich composites

2018 ◽  
Vol 22 (4) ◽  
pp. 1256-1273 ◽  
Author(s):  
Z Huo ◽  
M Mohamed ◽  
JR Nicholas ◽  
S Anandan ◽  
K Chandrashekhara
Keyword(s):  
Moisture Absorption ◽  
Mechanical Performance ◽  
Salt Water ◽  
Flexural Modulus ◽  
Interfacial Fracture ◽  
Core Material ◽  
Foam Core ◽  
Sandwich Composites ◽  
Water Exposure ◽  
Polyurethane Composite

This study investigated the effect of moisture absorption on the mechanical performance of polyurethane sandwich composites. The core material was a closed cell polyurethane foam. Face sheets were made of E-glass/polyurethane composite laminates. Vacuum-assisted resin transfer molding process was used to manufacture specimens for testing. The foam core, laminates, and sandwich composites were submerged in salt water for prolonged periods of time. Mechanical property degradation due to moisture absorption for each constituent was evaluated. Compression test was performed on the foam core samples. Laminates were evaluated by three-point bending tests. The interfacial bond strength in the sandwich structure was evaluated by double cantilever beam mode-I interfacial fracture test. The testing results revealed that the effect of salt water exposure on the compressive properties of the foam core is insignificant. The flexural modulus of polyurethane laminates degraded 8.9% and flexural strength degraded 13.0% after 166 days in 50% salinity salt water at 34°C conditioning. The interfacial fracture toughness of polyurethane sandwich composites degraded 22.4% after 166 days in 50% salinity salt water at 34°C conditioning.

Design of composite lattice materials combined with fabrication approaches

2018 ◽  
Vol 53 (3) ◽  
pp. 393-404 ◽  
Author(s):  
Jun Xu ◽  
Yaobo Wu ◽  
Xiang Gao ◽  
Huaping Wu ◽  
Steven Nutt ◽  
...  
Keyword(s):  
Shear Strength ◽  
Mechanical Performance ◽  
Analytical Models ◽  
Core Material ◽  
Foam Core ◽  
Hierarchical Lattice ◽  
Bottom Up ◽  
Lattice Materials ◽  
Assembly Technique ◽  
Composite Lattice

Lattice materials can be designed through their microstructure while concurrently considering fabrication feasibility. Here, we propose two types of composite lattice materials with enhanced resistance to buckling: (a) hollow lattice materials fabricated by a newly developed bottom-up assembly technique and the previously developed thermal expansion molding technique and (b) hierarchical lattice materials with foam core sandwich trusses fabricated by interlocking assembly process. The mechanical performance of sandwich structures featuring the two types of lattice cores was tested and analyzed theoretically. For hollow lattice core material, samples from two different fabrication processes were compared and both failed by nodal rupture or debonding. In contrast, hierarchical lattice structures failed by shear buckling without interfacial failure in the sandwich struts. Calculations using established analytical models indicated that the shear strength of hollow lattice cores could be optimized by judicious selection of the thickness of patterned plates. Likewise, the shear strength of hierarchical foam core truss cores could be maximized (with minimal weight) through design of truss geometry. The bottom-up assembly technique could provide a feasible way for mass production of lattice cores, but the design about how to assembly is critical. Hierarchical lattice cores with foam sandwich trusses should be a suitable choice for future lightweight material application.

scholarly journals Moisture Absorption Effects on the Mechanical Properties of Sandwich Biocomposites with Cork Core and Flax/PLA Face Sheets

Molecules ◽  
2021 ◽  
Vol 26 (23) ◽  
pp. 7295
Author(s):  
Hom Nath Dhakal ◽  
Chulin Jiang ◽  
Moumita Sit ◽  
Zhongyi Zhang ◽  
Moussa Khalfallah ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Failure Modes ◽  
Moisture Absorption ◽  
Mechanical Performance ◽  
Core Sample ◽  
Environmental Benefits ◽  
Matrix Cracking ◽  
Core Material ◽  
Poly Lactic Acid ◽  
The Core

The aim of this study was to evaluate the moisture absorption behaviour and its influence on the mechanical properties of newly developed sandwich biocomposites with flax fibre-reinforced poly-lactic acid (PLA) face sheets and soft cork as the core material. Three different types of sandwich biocomposite laminates comprised of different layup configurations, namely, non-woven flax/PLA (Sample A), non-woven flax/PLA and cork as core (Sample B) and non-woven flax/paper backing/PLA, cork as core (Sample C), were fabricated. In order to evaluate the influence of moisture ingress on the mechanical properties, the biocomposites were immersed in seawater for a period of 1200 h. The biocomposites (both dry and water immersed) were then subjected to tensile, flexural and low-velocity falling weight impact tests. It was observed from the experimental results that the moisture uptake significantly influenced the mechanical properties of the biocomposites. The presence of the cork and paper in sample C made it more susceptible to water absorption, reaching a value of 34.33%. The presence of cork in the core also has a considerable effect on the mechanical, as well as energy dissipation, behaviours. The results of sample A exhibited improved mechanical performance in both dry and wet conditions compared to samples B and C. Sample A exhibits 32.6% more tensile strength and 81.4% more flexural strength in dry conditions than that in sample C. The scanning electron microscopy (SEM) and X-ray micro-CT images revealed that the failure modes observed are a combination of matrix cracking, core crushing and face core debonding. The results from this study suggest that flax/PLA sandwich biocomposites can be used in various lightweight applications with improved environmental benefits.

Reduction of Moisture Sensitivity in Natural Fibres

2001 ◽  
Vol 702 ◽  
Author(s):  
Gerard T. Pott
Keyword(s):  
Hydrothermal Treatment ◽  
Moisture Absorption ◽  
Mechanical Performance ◽  
Flexural Modulus ◽  
Natural Fibres ◽  
Raw Material ◽  
Biological Degradation ◽  
Moisture Sensitivity ◽  
Oh Groups ◽  
Fibre Yield

ABSTRACTWhen natural fibres are applied as reinforcement in polymer composites the moisture sensitivity, causing fibre swell and ultimately rotting through fungi attack, can be a very serious problem. A number of methods have been developed dealing with this problem that change the chemical and / or physical composition of the fibre, resulting in reduced moisture sensitivity. To this category belong acetylation and hydrothermal treatment. For acetylation, acetic anhydride is used as a chemical that reacts with reactive OH-groups of the lignocellulose material, increasing hydrophobicity. In hydrothermal treatment no chemicals are used, only water and energy.The main focus of this paper is on hydrothermal treatment, the Duralin® process in particular, of bast fibres such as flax, jute and hemp. Acetylation is reviewed briefly. A survey is given of the structure and composition of bast fibres and the moisture adsorption and desorption mechanisms in these fibres.The Duralin® process involves three steps, hydrothermolysis, drying and curing. The raw material for the Duralin® process applied to flax is green rippled flax straw. This eliminates the need for the traditional dew-retting, a risky process where the freshly harvested flax stems lay on the field for about four weeks. The Duralin® process reduces moisture absorption and biological degradation, the fibre yield is higher than after dew-retting and the shives can be used as a filler material in polymers and for making a water proof particle board. The main causes for reduced water uptake after Duralin treatment will be reviewed.Duralin® fibres have equal or higher tensile strength and higher flexural modulus than fibres extracted from dew-retted flax. Compounds reinforced with these fibres have apart from decreased moisture sensitivity a better mechanical performance. Both the amount and the release rate of decomposition products resulting from compounding with polypropylene are significantly less for Duralin® fibres than for dew-retted or green fibres. Duralin® fibres are on a weight basis competitive with glass fibres.

The Sensitivity of the Foam-Core Parameters under Impact Loading

2012 ◽  
Vol 525-526 ◽  
pp. 289-292
Author(s):  
Fei Xu ◽  
Min Ge Duan
Keyword(s):  
Impact Resistance ◽  
Low Velocity Impact ◽  
Core Material ◽  
Foam Core ◽  
Sandwich Composites ◽  
Low Velocity ◽  
Fea Model ◽  
The Face ◽  
Damage Process ◽  
The Impact

This study presents the numerical investigation of the low-velocity impact for the foam-cored sandwich composites. Firstly, the proposed FEA model is validated by comparing the results between simulation and test. The user subroutine VUMAT and the crushable foam model are chosen to describe the damage of the face sheets and the characteristics of the foam material, respectively. The detailed damage process of the sheets and the foam is clearly shown. The sensitivity of seven parameters related to foam-core material are studied. It is shown that the yield strength, the fracture strain and the fracture displacement have significant effects on the impact-resistance of the foam-cored sandwich composites.

Influence of Alkali Treatment and Nanoclay Content on the Properties of Rice Husk Filled Polyester Composites

2017 ◽  
Vol 882 ◽  
pp. 89-100 ◽  
Author(s):  
Omid Nabinejad ◽  
Sujan Debnath ◽  
Teh J. Ying ◽  
Willey Y.H. Liew ◽  
Ian J. Davies
Keyword(s):  
Water Absorption ◽  
Rice Husk ◽  
Moisture Absorption ◽  
Mechanical Performance ◽  
Alkali Treatment ◽  
Unsaturated Polyester ◽  
Flexural Modulus ◽  
Tensile Modulus ◽  
Scanning Electron Micrographs ◽  
Nanoclay Content

The effect of alkali treatment and nanoclay addition on the mechanical properties and water absorption behavior of rice husk particle (RHP) reinforced unsaturated polyester (UP) composites was investigated. Thermogravimetric analysis (TGA) indicated that the alkali treatment removed most of the hemicellulose and impurities from the RHP with the tensile strength, tensile modulus, flexural strength and flexural modulus of the resulting composites being improved by alkali treatment. The results indicated that the 5% sodium hydroxide concentration had the optimum performance on mechanical strength and water absorption resistance. Furthermore, the influence of nanoclay addition (1, 3 and 5 wt%) on the properties of optimum alkali treated RHP-UP composites was investigated with the lowest content (1 wt%) of nanoclay showing the highest mechanical performance. However, further addition of nanoclay improved the moisture absorption resistance of the composites. Good interface bonding between the filler and matrix was observed from scanning electron micrographs for the optimum RHP alkali treated and nanoclay dispersed RHP-UP composites.

Thermal stability and flammability characteristics of phenolic syntactic foam core sandwich composites

2020 ◽  
pp. 109963622092666
Author(s):  
SJ Amith Kumar ◽  
SJAjith Kumar ◽  
Bharath K Nagaraja
Keyword(s):  
Thermal Stability ◽  
Composite Structures ◽  
Syntactic Foam ◽  
Spherical Particles ◽  
Core Material ◽  
Foam Core ◽  
Sandwich Composites ◽  
Minimum Concentration ◽  
Polymeric Foam ◽  
Structural Applications

Polymeric foam core sandwich composites are the nascent materials used in marine and aerospace structural applications for its low-density characteristics. A special class of foam called syntactic foam is one of the promising core material having high specific properties. However, these polymeric foam core sandwich composite structures may encounter problems in correlation with temperature and fire. Damages that happen due to the variation in temperature and by the catch of fire are sometimes imperceptible which may lead to the deterioration of load carrying ability or catastrophic failure of these composite structures. Present investigation is focused on the possibilities of reducing the extent of damages due to variation in temperature and by the catch of fire by enhancing its thermal stability and flame resistance characteristics. This was achieved from the development of syntactic foam by embedding hollow micro-spherical particles in phenolic resin for fire containment or fire isolation. Result of the experimentation reveals that the phenolic syntactic foam core was thermally more stable than glass/epoxy face skins up to a temperature of 450°C. The minimum concentration of oxygen required for burning was found to be 30%, in which phenolic syntactic foam core helps in flame isolation, whereas E-glass/epoxy face skins contribute to flame spread in the event of burning of sandwich composites. Improved thermal stability and fire resistance characteristics of developed sandwich composites are attributed to the phenolic syntactic foam core and by its orientation.

scholarly journals Effects of Water and Chemical Solutions Ageing on the Physical, Mechanical, Thermal and Flammability Properties of Natural Fibre-Reinforced Thermoplastic Composites

Molecules ◽  
2021 ◽  
Vol 26 (15) ◽  
pp. 4581
Author(s):  
Baljinder K. Kandola ◽  
S. Ilker Mistik ◽  
Wiwat Pornwannachai ◽  
A. Richard Horrocks
Keyword(s):  
Salt Water ◽  
Flexural Modulus ◽  
Moisture Sorption ◽  
Natural Fibre ◽  
Thermoplastic Composites ◽  
Wool Fibre ◽  
Poly Lactic Acid ◽  
Natural Polymers ◽  
Chemical Solutions ◽  
Pp Composites

Biocomposites comprising a combination of natural fibres and bio-based polymers are good alternatives to those produced from synthetic components in terms of sustainability and environmental issues. However, it is well known that water or aqueous chemical solutions affect natural polymers/fibres more than the respective synthetic components. In this study the effects of water, salt water, acidic and alkali solutions ageing on water uptake, mechanical properties and flammability of natural fibre-reinforced polypropylene (PP) and poly(lactic acid) (PLA) composites were compared. Jute, sisal and wool fibre- reinforced PP and PLA composites were prepared using a novel, patented nonwoven technology followed by the hot press method. The prepared composites were aged in water and chemical solutions for up to 3 week periods. Water absorption, flexural properties and the thermal and flammability performances of the composites were investigated before and after ageing each process. The effect of post-ageing drying on the retention of mechanical and flammability properties has also been studied. A linear relationship between irreversible flexural modulus reduction and water adsorption/desorption was observed. The aqueous chemical solutions caused further but minor effects in terms of moisture sorption and flexural modulus changes. PLA composites were affected more than the respective PP composites, because of their hydrolytic sensitivity. From thermal analytical results, these changes in PP composites could be attributed to ageing effects on fibres, whereas in PLA composite changes related to both those of fibres present and of the polymer. Ageing however, had no adverse effect on the flammability of the composites.

scholarly journals Long-fibre reinforced polymer composites by 3D printing: influence of nature of reinforcement and processing parameters on mechanical performance

2020 ◽  
Vol 1 (1) ◽  
Author(s):  
Francis Dantas ◽  
Kevin Couling ◽  
Gregory J. Gibbons
Keyword(s):  
Carbon Fibre ◽  
Polymer Composites ◽  
Mechanical Performance ◽  
Flexural Modulus ◽  
Matrix Material ◽  
Processing Parameters ◽  
Fibre Reinforcement ◽  
Reinforced Polymer ◽  
Unreinforced Material ◽  
Fibre Reinforced Polymer

Abstract The aim of this study was to identify the effect of material type (matrix and reinforcement) and process parameters, on the mechanical properties of 3D Printed long-fibre reinforced polymer composites manufactured using a commercial 3D Printer (Mark Two). The effect of matrix material (Onyx or polyamide), reinforcement type (Carbon, Kevlar®, and HSHT glass), volume of reinforcement, and reinforcement lay-up orientation on both Ultimate Tensile Strength (UTS) and Flexural Modulus were investigated. For Onyx, carbon fibre reinforcement offered the largest increase in both UTS and Flexural Modulus over unreinforced material (1228 ± 19% and 1114 ± 6% respectively). Kevlar® and HSHT also provided improvements but these were less significant. Similarly, for Nylon, the UTS and Flexural Modulus were increased by 1431 ± 56% and 1924 ± 5% by the addition of carbon fibre reinforcement. Statistical analysis indicated that changing the number of layers of reinforcement had the largest impact on both UTS and Flexural Strength, and all parameters were statistically significant.

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