Effect of Fibre Architecture on the Falling Weight Impact Properties of Hemp/Epoxy Composites (original) (raw)
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Effect of fibre architecture on falling weight impact properties of hemp/epoxy fibre laminates
The aim of this work is studying the falling weight impact properties of three different types of hemp/epoxy composites, two of which were realised using loose hemp fibres disposed either unidirectionally (LU laminate) or in a 0/90° (LC laminate), while the third one has been obtained using hemp mat (M laminate). The maximum fibre volume which was possibly introduced using hand layup was 55 vol.% for LU, 52 vol.% for LC and only 43 vol.% for M laminate. In practice, the aim of this investigation would be evaluating whether disposing loose hemp fibres in a mat, an operation which results in the reduction of the volume of reinforcement introduced, would yield lower falling impact properties or not. Quasi-static tests results show that the best performance, but also the largest scattering in properties is obtained from the unidirectional composites (LU): this suggests the fundamental role played by fibre orientation in these materials. In contrast, the study of impact hysteresis cycles suggest that, despite the limitations owed to the presence of through thickness fibres and the lower amount of fibres introduced, hemp mat laminates (M) are superior in terms of impact properties. In particular, impact hysteresis cycles involve, in the case of M laminates, a higher stiffness in the linear-elastic phase of impact, followed by a hardly detectable load drop, and a very large rebound energy, released at quasi-constant rate after penetration. As a result, a larger amount of energy is absorbed during impact on hemp mat laminates than on the loose hemp laminates.
A Comparative Study on Falling Weight Impact Properties of Jute/Epoxy and Hemp/Epoxy Laminates.
2009
One of the principal reasons for limited use of plant fibre composites is their sensitivity to impact loading and the difficulty in characterising and assessing the criticality of impact damage. In this study, a comparison between two composite architectures has been carried out, namely a hemp/epoxy random mat and a jute/epoxy plain weave laminate, both with 45±2% vol. of reinforcement fibres. Work carried out concentrated on comparing and discussing the falling weight impact performance of the two laminates with different fibre architecture, by studying their impact hysteresis cycles and investigating their respective modes of damage. This was done in view of a possible application of a hybrid of the two laminates for impact resistance purposes. The results allowed quantifying the superiority of hemp/epoxy on jute/epoxy laminates under falling impact loading: however, the latter laminates appear to show more consistent impact properties and a more predictable mode of damage, which was attributed to an improved a better fibre-matrix impregnation.
Low-velocity impact behaviour of hemp fibre reinforced bio-based epoxy laminates
Composites Part B: Engineering, 2016
This work addresses the damage resistance and post-impact damage tolerance of hemp fabric reinforced bio-based epoxy composites subjected to low-velocity impact at energies ranging from the barely visible impact damage (BVID) threshold up to perforation. A comparison is also reported with similar composites in terms of thickness and fibre volume fraction but based on a traditional epoxy matrix. The results confirmed the significant toughness of laminates based on a bio-based epoxy matrix and their superior damage tolerance compared to standard hemp-epoxy laminates, thus highlighting their potential use in semi-structural applications due to an improved interfacial adhesion with hemp fibres.
The low velocity impact response of non-woven hemp fibre reinforced unsaturated polyester composites
Composite Structures, 2007
Hemp fibre reinforced unsaturated polyester composites (HFRUPE) were subjected to low velocity impact tests in order to study the effects of non-woven hemp fibre reinforcement on their impact properties. HFRUPE composites specimens containing 0, 0.06, 0.10, 0.15, 0.21 and 0.26 fibre volume fractions (V f) were prepared and their impact response compared with samples containing an equivalent fibre volume fraction of chopped strand mat E-glass fibre reinforcement. Post-impact damage was assessed using scanning electron microscopy (SEM). A significant improvement in load bearing capability and impact energy absorption was found following the introduction hemp fibre as reinforcement. The results indicate a clear correlation between fibre volume fractions, stiffness of the composite laminate, impact load and total absorbed energy. Unreinforced unsaturated polyester control specimens exhibited brittle fracture behaviour with a lower peak load, lower impact energy and less time to fail than hemp reinforced unsaturated polyester composites. The impact test results show that the total energy absorbed by 0.21 fibre volume fraction (four layers) of hemp reinforced specimens is comparable to the energy absorbed by the equivalent fibre volume fraction of chopped strand mat E-glass fibre reinforced unsaturated polyester composite specimens.
Composite Structures, 2012
In this study, the influence of varying impactor geometries on the impact damage characteristics of hemp fibre reinforced unsaturated polyester composites were subjected to a low-velocity impact loading using an instrumented falling weight impact test setup. The three varying tup geometries: hemispherical, 30°a nd 90°, at four different impact velocity levels: 2.52 m/s, 2.71 m/s, 2.89 m/s and 2.97 m/s were assessed. The experimental results to investigate the influence of impactor geometry suggest that HFRUP composites were able to withstand higher loads when tested with hemispherical impactor and also absorbed more energy than that for 90°and 30°shaped tup geometry. The post impact damage patterns and failure mechanisms of impacted samples were further characterised by ultrasonic (UT) inspection. Impact induced damage characterised by scanning electron microscope (SEM) suggests that damage induced by the impact included a typical failure mechanisms showing matrix cracking, fibre breakage and fibre pullout. As the impact velocity increases the damage to back face of the laminate increased for laminates tested with a hemispherical impactor while it decreased to certain extent for laminates tested with 90°a nd 30°impactor geometries.
Post-impact static and cyclic flexural characterisation of hemp fibre reinforced laminates
2011
The suitability for use of plant fibre composites after an impact event is still an open issue in literature. In this work, hemp fibre reinforced laminates have been subjected to cyclic flexural tests following falling weight impact at 12, 16 and 20J. At these energies, still quite far from penetration, which was at about 40J, damage starts to be increasingly apparent on both laminate surfaces. Post-impact flexural tests have been monitored using acoustic emission.
Impact Load Behaviour of Resin Transfer Moulding (RTM) Hemp Fibre Composite Laminates
Journal of Biobased Materials and Bioenergy, 2009
Aim of this work is to determine experimentally some important mechanical characteristics of RTM hemp plain weave fabric/epoxy laminates. Equipment and test methods are described and critically discussed. Main subjects of this work are: RTM process improvement, preliminary tensile and f1exural tests and impact performance. The latter is analyzed with particular attention, also comparing data with other experimental results. Attention is devoted both to the process, which strongly influences the mechanical performance of natural long fibres reinforced composites and to the low-velocity impact behaviour. This is a very important requirement for future aeronautical applications, in that composite structures should retain sufficient residual compression properties (CAI: Compression After Impact) after a Barely Visible Impact Damage (B.V.I.D).
Impact Properties of the Chemically Treated Hemp Fibre Reinforced Polyester Composites
Fibers and Polymers, 2020
Plant based hemp fibre properties were found to be highly influenced by changes in the amounts of cellulose, hemicellulose and lignin constituents within the fibre. These fibre constituents play a major role for effective interfacial adhesion between the fibre and the matrix. Chemical treatments such as alkali (NaOH), acetyl (acetic acid & acetic anhydride) and silane (siloxane) treatments have the potential to react with constituent contents by varying their amounts. In this study, hemp fibre was treated with alkali (0-10 % NaOH), acetyl and silane chemicals. Treated fibres were mixed with polyester matrix to produce composites. The effects of chemical treatments on hemp fibres and the resulted polyester matrix composite were analysed through impact testing of the composite samples. Alkali treatments on hemp fibres enhanced the impact resistance properties (around 43 % lower absorbed energy and 40 % higher rebounded energy) of its composites compared to the untreated cases. Lower absorption energy and higher rebounded energy indicates strong interfacial bonding between the fibre and matrix. Improvements are governed by the removal of hemicellulose and lignin from the fibre, which provides a platform for better chemical reactions between fibres and matrix. On the other hand, acetyl treatments on the higher concentrations of NaOH pre-treated fibres reduced the fibres' ability to support impact loadings (22 % higher rebounded energy compared to the untreated cases). In the two treatment conditions, fibre lessen their strength due to excessive removal of hemicellulose and lignin constituents, and composites exhibited lower impact properties compared to the NaOH treated samples. Similar impact properties were also recorded for alkali pre-treated silanised composites. As alkali pre-treatment removed the hydroxyl groups from the fibre, further silane treatment could not develop silanols to create strong interface bonding. As a result, composites failed under lower impact resistance compared to the NaOH treated samples.
EXPERIMENTAL INVESTIGATION OF TENSILE AND IMPACT BEHAVIOUR OF HEMP FLAX HYBRID COMPOSITE
Developments in Engineering and Technology urging the need to identify and improve a wide variety of materials using the natural fiber. Composite plays a vital role in manufacturing and defense industries. In this work, Natural fiber, namely Hemp and flax are used as reinforcement along with epoxy resins to enhance Mechanical properties. These fibers are used because of easy extraction methods and more economical. In this research work, hemp and flax composites are prepared using hand lay-up method as mono, and hybrid composites. Various mechanical tests have been carried out to determine the mechanical characteristic of the composite laminate and the results are compared.