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Glued Laminated Timber Beams Reinforced With Sisal Fibres

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The current appeal for sustainable building materials has expanded the use of timber in construction. However, due to timber be a raw material, natural defects are present, what reduce its strength capacity and cause, in particular, brittle failures in the tensile region of timber beams. In order to increase the mechanical properties of these beams, fibre reinforcement can be applied. In this context, natural fibres, such as Sisal fibres, already used in various fields of construction, are an alternative for reinforcement of timber structural elements, by taking into account their adequate mechanical properties and, in special, for low-mechanical resistance wood species, such as Pinu sp, a species used widely in timber construction. This paper deals with an experimental analysis glued laminated timber beams (Glulam) of Pinus sp species, reinforced by Sisal fibres. Bending tests were performed on six beams with the following dimensions, 53 mm-width by 180 mm-height by 3000 mm-length, which were prepared with eight lamellas by 8 mmthickness. These beams were reinforced with Sisal strips that were glued by Epoxy adhesive on the bottom part of these beams. In addition, comparisons of result with nonreinforced Glulam were carried out. From the analyses of the experimental results, a decrease of 20 to 30% for the normal stresses, 5 to 10% for the shear stresses and 8 to 12 % for the displacements in relation to non-reinforced beams were verified.
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Glued Laminated Timber Beams Reinforced
With Sisal Fibres
Nilson T. Mascia
University of Campinas/FEC, Campinas, Brazil
Email: nilson@fec.unicamp.br
Bruno F. Donadon
University of Campinas/FEC, Campinas, Brazil
E-mail: donadon.bf@gmail.com.
Ramon Vilela
University of Campinas/FEC, Campinas, Brazil
Email: ramonvilela@outlook.com
Abstract-The current appeal for sustainable building
materials has expanded the use of timber in construction.
However, due to timber be a raw material, natural defects
are present, what reduce its strength capacity and cause,
in particular, brittle failures in the tensile region of timber
beams. In order to increase the mechanical properties of
these beams, fibre reinforcement can be applied. In this
context, natural fibres, such as Sisal fibres, already used
in various fields of construction, are an alternative for
reinforcement of timber structural elements, by taking
into account their adequate mechanical properties and, in
special, for low-mechanical resistance wood species,
such as Pinu sp, a species used widely in timber
construction. This paper deals with an experimental
analysis glued laminated timber beams (Glulam) of Pinus
sp species, reinforced by Sisal fibres. Bending tests were
performed on six beams with the following dimensions,
53 mm-width by 180 mm-height by 3000 mm-length,
which were prepared with eight lamellas by 8 mm-
thickness. These beams were reinforced with Sisal strips
that were glued by Epoxy adhesive on the bottom part of
these beams. In addition, comparisons of result with non-
reinforced Glulam were carried out. From the analyses of
the experimental results, a decrease of 20 to 30% for the
normal stresses, 5 to 10% for the shear stresses and 8 to
12 % for the displacements in relation to non-reinforced
beams were verified.
Index TermsNatural fibres, Sisal fibres, Glulam,
Reinforcement, Bending test.
Manuscript received September 4, 2018; revised September 25,
2018; accepted September 25, 2018.
Nilson T.Mascia, corresponding author.
I. INTRODUCTION
In long duration life, structural systems are subjected
to permanent and variable loads, chemical and biological
agents´ interaction or design load variations. These
actions can affect a structure in such way that it can no
longer maintain its initial design resistance, causing the
necessity to repair or reinforce it.
According to Ref [1], there are two main methods to
rehabilitate affected timber elements, which are: (i) the
replacement of the damaged sections; (ii) the utilization
of reinforcement materials that complement the
mechanical resistance of the damaged timber structural
elements. The main issue with the first solution is that it
is sometimes restricted by various facts, such as
environmental impact, lack or incompatibility of the
required wood species and high costs. This generates the
necessity to seek other effective alternatives, as the
second method, turning the use of FRP (Fibre Reinforced
Polymers) materials into a very interesting option that
deserves to be specifically studied.
Addressing to composite materials used in
constructions, they can be divided into three major
groups: fibrous composites, laminated composites and
particulate composites, with a possible combination
among these types [2].
The laminated composites formed by the union of
lamellas can consist of the same or different materials or
also have different geometrical characteristics and
dimensions.
Focusing on glued laminated timber beams, it is
important to consider the natural defects, such as knots,
or the orientation of the fibres, that can influence the
mechanical characteristics of the lamellas and in the
beam as a whole. This affects the timber mechanical
properties reducing, for example, the tensile strength and
can cause a brittle failure with a lesser load than the one
established in structural design [3]. Thus, the use of fibres
as a reinforcement of the structural elements intends to
115
avoid the brittle failure and increase the tensile strength
as well.
As found in technical literature, natural fibres have
attracted attention for presenting adequate mechanical
characteristics for such application. The use of natural
fibres, as Sisal fibres for example, associated with glued
laminated timber beams, in particular, those
manufactured with wood species from reforestation, is in
accordance with the current economic interest and
sustainable appeal [4].
The Sisal fibres are commercialized in Brazil in
several formats such as: fabric, cords, strips, wire, rolls,
etc. Table I presents the tensile strength and the modulus
of elasticity for some fibres [5].
TABLE I. MECHANICAL CHARACTERISTICS OF NATURAL
FIBRES
Fibre
Tensile Strength(MPa)
Modulus
Elasticity (GPa)
Coconut
131-175
4-13
Sisal
511-635
9,4-22
Curauá
859-1404
20-36
Juta
393-773
26,5
The failure strength and the modulus of elasticity,
besides the lengthening in rupture, depend on the amount
of cellulose and the orientation of the micro-fibres. As a
natural product, these characteristics have a wide
variation from one plant to another.
Further the mechanical characteristics of Sisal,
associated with other advantages such as, the facility to
find, extract and process the material, low cost and
biodegradability has led to a significant amount of
scientific research of unquestionable importance
regarding the use of natural fibres. Nevertheless, the Sisal
fibre utilization is only interesting when applying with
low resistance wood species.
In this context, this paper covers an experimental
analysis of glued laminated timber beams reinforced by
Sisal fibres by considering bending results of the six
tested beams.
II. FIBRES AND MATRIX
Fibres are characterized by the ratio between length
and diameter. For ratios less than 100, the fibres are
considered short and for greater than 100 the fibres are
long. Sisal fibres are an example of long fibres. In
general, the characteristics of the fibres are classified
resistance by density and rigidity by density as well [6].
In order to use fibres as a reinforcing material, they
need to be connected to the structure. The material of
union is called the matrix and has the following main
characteristics: to maintain and protect the arrangement
of fibres and to distribute stress between the substrate and
the fibre. The matrix is mainly responsible for providing
resistance to shear stress on the lamellas.
Usually the matrix has mechanical properties lesser
than that of fibres and a lower density (which provides
greater lightness in structural elements). It can be
constructed with polymers, metal, ceramic or other
materials.
The materials presented in the matrix are varied,
depending largely on the type of use of the composite as
well as the type of fibres involved in the construction.
Examples of materials in the matrices are epoxy, plastics
and polyester.
Epoxy, in general, is classified as a structural adhesive
or engineering adhesive. This high-performance adhesive
is used in the construction of aircraft, cars and many other
products where a high resistance, stiffness and low
density are required. Currently this type of adhesive can
be used with great efficiency in wood, glass, metals and
plastic.
III. SISAL FIBRES
Agave Sisalana Perrini, known worldwide, is a native
species to the Yucatan peninsula, Mexico; the plant and
also the fibres known as Sisal belong to the class of
natural hard fibres. Currently, Sisal represents a natural
fibre with great commercial applications, and is estimated
to be in more than half of the total amount of the natural
fibres used in Brazil, being the largest producer and
exporter of Sisal fibre, [7]. The Sisal fibres are found
commercially, in several formats: fabric, cords, strips,
wire, rolls (See Fig. 1), etc. and Table I previously
presented the tensile strength and the modulus of
elasticity for a number of different fibres.
Figure 1. Rolls of Sisal fibres.
The Sisal plant is a monocotyledonous, whose roots
are fibrous, emerging from the base of a pseudo stem.
The fibres of Sisal are made of elementary fibres of 4 to
12 µm diameter that are aggregated by a natural bond of
small cells of 1 to 2 µm. Such arrays are found along the
length of the plant on a regular shape, with lengths of 45
to 160 cm.
The leaves of Sisal are an example of natural
composite with lignocellulosic material presenting in 75
to 80% of the total weight of the leaves, reinforced by
helical micro fibres of cellulose, which represent about 9
to 12% of the total weight. The composition of Sisal fibre
is cellulose, lignin and hemicelluloses, [6].
116
Fig. 2 shows Sisal plants and Fig. 3 presents an image
of Sisal fibre bundles from a scanning electron
microscope, produced by the authors of this paper.
Figure 2. Sisal plant.
According to Ref [6], the failure strength and the
modulus of elasticity, besides the lengthening of rupture,
depend on the amount of cellulose and the orientation of
the micro-fibres. As a natural product, these
characteristics have a wide variation from one plant to
another.
Figure 3. Microscope electronic image of Sisal fibre bundles- scale
bar 200 µm.
Another issue to take into account is related to the
chemical treatment of the Sisal fibres, [8] and [9]. The
chemical treatment has the function of removing from the
surface fibres waxes and lubricants of the handling and
manufacturing process, and also remove the lignin
present on the surface as shown in Fig. 4 and Fig. 5 (both
produced by the authors of this paper). This helps to
improve the interaction between the fibres and the matrix
because the lignin in the fibres prevent direct contact of
cellulose (which is resistant fibre material) with the
matrix, creating a good bonding between the two
products. With the removal of lignin, the roughness of the
fibre surface increases the adherence with the matrix.
This procedure, on the other hand, reduces the tensile
strength of Sisal fibres when compared to fibres that do
not receive chemical treatment.
The treatment alkali for the preparation of fibres in
a 2% NaOH solution at 25 ° C for 1 hour was used.
Figure 4. Microscope electronic image of Sisal fibre bundles- scale
bar 20 µm without treatment.
Figure 5. Microscope electronic image of Sisal fibre bundles- scale
bar 20 µm after treatment.
IV. MATERIALS AND METHODS
A. Tensile test for Sisal strips
To evaluate the mechanical properties of the Sisal
fibres, 32 strips were obtained from rolls of raw material.
The dimensions of the strips were 2 mm depth by 50mm
width by 3000 mm length. The Sisal density was 1,588
g/m3 and its grammage 1,393 g/m2. Fig. 6 shows the
strips of Sisal used to evaluate their elastic and strength
properties.
117
Figure 6: Strips of Sisal fibres.
For evaluating its tensile strength and the modulus of
elasticity, the universal testing machine, WDW 100e, was
used, which an electronic universal is testing machine
produced by TIME-Shijin Group. Fig. 7 illustrates the
tensile test set up used for Sisal based on the ASTM
D3379 [10] whereas Fig. 8 the load-extension results
obtained in the tests.
Figure 7. Details of the Sisal strip in tensile test.
The average properties obtained in the experimental
tensile tests are: for strips of Sisal fibres: modulus of
elasticity Ex = 15,2 GPa, tensile strength Polyurethane
adhesive,PU. It is important to note that the yarn
mechanical properties for Sisal are much greater than for
the strips [11].
B. Bending tests for beams
Six beams of glued laminated timber (as shown in Fig.
8) were used in the bending tests. These beams were
manufactured with 8 layers of Pinus elliotti pieces, 22.5
mm of thickness, 53 mm of width and 3000 mm of length
glued by Polyurethane adhesive, PU.
The final dimensions of the beams were 53 mm
thick, 180 mm height and 3000 mm length.
Figure 8. Scheme of the cross section (dimension in mm) and the
layers to manufacture the beams.
The mechanical properties of Pinus elliotti obtained by
compressive tests according to the Brazilian code [12],
and the average values were for the longitudinal modulus
of elasticity (axis x) Ex = 11.9 GPa, and for the tensile
strength ft = 31 MPa. This species is considered a low-
resistance class according the Brazilian code.
In order to evaluate the mechanical performance of the
reinforced laminated timber beams, the mechanical
classification through non-destructive bending test was
carried out, thus obtaining the mechanical properties of
stiffness and elasticity of the beams before the fibre
reinforcement application.
The bending classification test was performed up to the
load corresponding to 50% of the reference mean
ultimate load.
After the classification stage, reinforcements of strips
of Sisal fibres were applied at the bottom region of the
laminated timber beams using epoxy resin Sikadur 32.
The modulus of elasticity and the tensile strength for the
epoxy resin were adopted as: Ex equal to 2 GPa and ft of
50 MPa.
According to Ref [1], the usual percentage of synthetic
fibres that can be used to reinforce laminated timber
beams 3.3% of the beam section, since from this point the
resistance and stiffness gain becomes no longer
significant. For the beams used in this experimental
procedure it was used 4.4% considering both the natural
fibre thickness be greater and the mechanical properties
be smaller than synthetic fibres.
These reinforced beams were subjected to the
destructive bending test, taking the beam to failure, in
order to acquire the stiffness property and the ultimate
load to verify the failure modes.
The bending test adopted for the beams was the three-
point load system with load applied at the mid- span of
the beam. The span was 2800mm.
The static scheme of the laminated timber beam used
in the present analysis is shown in Fig. 9 and Fig. 10
shows the bending test of a laminated timber beam.
118
Figure 9. Static scheme of laminated timber beam for bending test
(dimension in mm).
Figure 10. Glued laminated timber beam for bending test.
Kyowa KFG-5-120-C1-5 (Kyowa Electronic
Instruments Co., Ltd.) strain gauges with gauge factor 2.1
± 1% and electrical resistance 119.8 ± 0.2Ω were used to
measure strains on the beams.
The strain gauges were positioned near the mid-span of
the beam (see Fig. 11), in order to obtain the strains in
some points of the cross section height and at the top and
the bottom surface as well to consequently, evaluate the
normal and shear stresses acting on that section. The
location of the strain gauges was at 20 cm from the mid-
span of the beam to avoid the region of non-uniform
stresses.
Figure 11. Central region of the beam positioned for testing with
strain gauges positioned in its section.
C. Transformed cross-section method
The calculation of the trend stress lines and the
displacement curves were based on the transformed
cross-section method, [3]. Summarily this method
consists of transforming a straight section, which contains
more than one material, into an equivalent cross section
formed by a unique material. Usually the outer lamella is
used as a reference, which is denoted by R, for the
process, determining a modular ratio between the
modulus of elasticity, ER and the other lamellas Ei and
multiplying the width hi , where i indicates each lamella,
by this relation. In the calculations presented in the
results, the reference adopted was the Sisal fibre.
In general, the cross section is symmetric, and as a
consequence the neutral line is in the middle of the
central lamella. The width of a generic lamella and the
modulus of elasticity are adjusted using the following
modular ratio as shown by (1):
(1)
The normal (σ) and shear (τ) real stresses in each
lamella depend on the modular ratio and the stresses
acting in cross section constituted by a unique material
and can be written respectively by (2) and (3):
(2)
(3)
Finally, by using the transformed section the
displacement of the laminated beam can be calculated
using the beam width (h), and the properties of each
lumber lamella: its modulus of elasticity (Exi), thickness
(bi) and distance from the centre of each lamella to the
neutral axis (zi) of the cross section as (4):
(4)
The stiffness (ExI) shown in (4) for the laminated
beams, with and without reinforcement, was calculated
via Ref. [12], as indicated in (5).
(5)
Where: ExI is the beam stiffness; ΔP is the applied
load; L is the span and Δδ is the measured vertical
displacements.
119
V. RESULTS AND DISCUSSION
A. Bending results
In order to verify the improvement in structural
performance from the use of Sisal fibres as a
reinforcement in the laminated timber beam the following
results are presented by the following figures and a table,
which were based on the analytical [3], numerical [13]
and experimental results. The analytical and numerical
results converged and only the numerical one is
presented.
These results are related to the critical position of the
section beam for both the non-reinforced and the
reinforced beams with fibres on the tensile region
considering a load of 7 kN, according to Fig. 12. This
load corresponds to 40% of the failure load level
considered to bending strength, according to the
procedures of the Brazilian code for timber structures
[12] for the design purposes, i.e, addressed to the elastic
regime.
Figure 12. Load versus deflection of laminated timber beam.
Fig. 13, Fig.14 and Fig.15 show the typical
experimental results for the normal and shear stresses and
for the displacements.
Figure. 13. Normal stresses of the laminated timber beam at the
critical cross section.
Figure 14. Shear stresses of the laminated timber beam at the critical
cross section.
Figure 15. Displacements of the laminate timber beam.
These results are taken at the critical position of the
beams and took into consideration the load of 7,000N,
according Fig.12, Table II lists a summary of the
comparison between numerical and experimental values
for reinforced and non-reinforced demonstrating the
greater difference for the maximum tensile normal stress.
TABLE II. DIFFERENCE BETWEEN NUMERICAL AND
EXPERIMENTAL RESULTS FOR P = 7,000N
Comparisons
Reinforced Glulam (%)
Glulam (%)
Max. compressive
Stress Normal
4.65
19.62
Max Tensile .
Normal Stress
30.07
19.93
Max. Shear Stress
7.67
8.82
Displacement at
midspan
0.11
0.07
Specifically, the results for the six reinforced beams
demonstrated a decrease in the range of 20 to 30% for the
normal, 5 to 10% for the shear stresses and 8 to 12 % for
the displacements in relation to non-reinforced beams.
120
Ref. [14] found similar results in studies for natural fibres
(Curauá and Sisal fibres).
In addition, the tests indicated that reinforcement
led to an increase of 11 to 22 % for the ultimate load and
a reduction in these load variations as well. The ultimate
load variation reduces of 35% for non-reinforced
laminated beams to 10% for reinforced beams.
B. Failure modes
Failure must be considered one of the most significant
mechanical properties. Much of material engineering is
based on establishing economic design without failure.
The absence of failure is a necessity of safety as well as
for other fundamental considerations. Bending results in
longitudinal tension and compression stresses distributed
over the height of the cross section. The unreinforced
beam failed within the elastic region due to a tension
failure of the bottom laminations. Splintering tension
occur and this failure consists of a considerable number
of slight tension failures, producing a splintery break on
the surface of the beam. Because of the timber’s brittle
nature when exposed to tension, the beam failed in a
brittle way without visible failures before reaching
ultimate load.
The ultimate load verified in tests was 26.5 kN, in
average, the compressive stress 61 MPa, the tensile stress
in timber 60 MPa and in Sisal 62 MPa. The compressive
and tensile strain values measured around the ultimate
load were around 6,000 x 10-6.
Experimental test carried out on reinforced beams
demonstrated in this research that the most frequent
failure mechanism is the one in which tension failure
occurs, with or without partial plasticization of the
compression zone. The adhesion between timber and
composite material failed only after timber failure. The
following types of failure mechanisms prevailed for the
beams: the timber fracture at the end of the bonded
reinforced composites, timber longitudinal splitting (a
combination of tension and shear as also observed by
Ref. [15] and Ref. [16], and compressive failure was
observed in one of the specimens. The glulam beams
reinforced with Sisal especially revealed a ductile
behavior. The amount of ductile behaviour in the
reinforced beams mostly depends on the quality of the
bottom timber laminations. The fibre-adhesive-timber
composites act like connectors over the timber defects
and make the structural member section more ductile.
Fig. 16 and Fig. 17 show some details of the Sisal
strip on the beam and the failure of the tensile lamella in
bending test.
Figure 16. Region of the mid-span of the beam and the failures of the
lamellas and Sisal fibres in bending test.
Figure 17. Compressive region of the beam and the failure of the
upper lamellas in bending test.
Research findings [17], based on the theoretical
approach of Ref. [18], and stated that the reinforcement
layer absorbs a great portion of the acting stresses, which
results in a reduction of the maximum tensile stress
acting in the timber portion of the composite. Another
issue to be considered is related to the high concentration
of compressive stresses that were close to the point where
the load was applied, resulting in a crushing area. In
addition, Ref. [19] highlight these high compressive
stresses for FRP reinforcements. Fig. 18 and Fig. 19 show
this stress distribution according studies of Ref. [20]
using a numerical procedure [13] to obtain this result.
Figure 18. Stress distribution in the reinforced laminated timber
beam (in MPa).
121
Figure 19. Details of Stress distribution in the reinforced laminated
timber beam at the applied load region (in MPa).
It is also to be noted that the tests showed that
reinforcement leads to an increase of 11 to 22 % for the
ultimate load and a reduction in these load variations as
well. The ultimate load variation reduces of 35% for non-
reinforced laminated timber beams to 10% when
reinforced beams are tested. In other words, the use of
reinforced laminated beam produces a material with
greater quality control.
VI. CONCLUSIONS
An experimental study of timber laminated beams
reinforced by Sisal fibres was developed in this study.
Based on the analysis of the experimental results from the
bending tests the following conclusions are drawn:
The use of the Sisal fibres for low-mechanical
resistance wood species demonstrated to be an efficient
method for reinforcement, as it increased the values of
stiffness properties, modified the brittle mode for a more
ductile failure. In addition, the variation of the overall
stiffness properties of the laminated timber beam is
reduced, presenting an easy workability and can be
applied both locally and in the process of beam
manufacturing.
Specifically, the results for six reinforced beams
demonstrated a decrease in the range of 20 to 30% for the
normal, 5 to 10% for the shear stresses and 8 to 12 % for
the displacements in relation to non-reinforced beams.
In addition, the tests indicated that reinforcement led to
an increase of 11 to 22 % for the ultimate load and a
reduction in these load variations as well. The ultimate
load variation reduces of 35% for non-reinforced
laminated timber beams to 10% for reinforced beams.
In general, the use of the Sisal fibres as a reinforcing
material in timber laminate beams is feasible. The Sisal
fibres contribute towards preventing brittle failure on
critical tensile areas of the beams as well as being more
effective for timber beams constituted by elements with
the modulus of elasticity at least equals to these fibres.
ACKNOWLEDGEMENT
The authors thank the following Brazilian government
agency: CNPq (n. 232565/2014-7 and 303473/2016-9)
for the financial support given for the development of this
research.
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The necessity to restore the design specifications of a determined structure, combined with cost, weight and environmental impact reduction makes the use of high performance composite systems, involving, either synthetic or natural materials, interesting. By applying a layer of fiber reinforcement bonded with the glued laminated timber beam (Glulam) with an appropriate adhesive, a high performance composite system is obtained, resulting on a significant increase of strength and bending stiffness of the structural element that each isolated material did not have before. This paper carried out an analysis of the feasibility of use synthetic and natural fibers as alternative to structural reinforcement to laminated timber beams, made of the reforestation wood species Pinus caribea and Eucalyptus grandis that represent respectively two resistance classes of monocotyledon and dicotyledonous, exposing, through an analytical model. The numerical results obtained from the analysis of the Glulam beams reinforced with glass, carbon, Vectran® and natural fibers such as sisal fibers, are compared among each other considering cost, weight and gain of resistance and stiffness. It is observed that for small lengths (and therefore, small cross sections), the use of Vectran® fiber is not the best option, since an equivalent resistance gain can be obtained by applying a thicker layer of glass fiber, once it possesses a lower cost and a non-significant impact on the final structure's weight. For all the other considered cases, the choice of the Vectran® fiber is very interesting, since on these situations a thicker layer of glass fiber does not provide much cost reduction and is not enough to achieve the desired strength without increasing the structure's weight significantly. Regarding the sisal fiber, it is a material that is easy to find and with a low cost in Brazil, its utilization is interesting when working with low resistance wood species. Although the gain of resistance provided by this fiber as a reinforcement material is fairly low, the desired result can be obtained by increasing the thickness of the reinforcement layer, which still keeps the cost and weight of the reinforced element much smaller than those resulting from the implementation of a thinner layer of glass fiber.
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This work evaluates the potential of co-products from sisal fiber extraction and of plant residues at the end of the productive life cycle and their upgrading into bioproducts and biofuels, focus on Brazil, and, specifically on the Sisal Identity Territory in the state of Bahia. Sisal co-products and residues are identified and quantified; Environmental and socioeconomic indicators are applied. Energy potential and bioproducts from sisal in Brazil have been studied in universities and research centers, but not sufficiently quantified, so the scientific bases for this purpose are still limited. Considering an annual sisal fiber production in Brazil at 100,000 MT, and a 4% yield from the fiber extraction process, an estimated 2.4 million metric tons of products are thus generated by the defibering process, consisting of pulp, sisal tow, and juice. Furthermore, an estimated 900,000 metric tons per year of residual biomass from the stems at the end of the 10-year productive cycle is produced and presently left to rot in the field.
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The glued-laminated lumber (glulam) technique is an efficient process for making rational use of wood. Fiber-Reinforced Polymers (FRPs) associated with glulam beams provide significant gains in terms of strength and stiffness, and also alter the mode of rupture of these structural elements. In this context, this paper presents a theoretical model for designing reinforced glulam beams. The model allows for the calculation of the bending moment, the hypothetical distribution of linear strains along the height of the beam, and considers the wood has a linear elastic fragile behavior in tension parallel to the fibers and bilinear in compression parallel to the fibers, initially elastic and subsequently inelastic, with a negative decline in the stress-strain diagram. The stiffness was calculated by the transformed section method. Twelve non-reinforced and fiberglass reinforced glulam beams were evaluated experimentally to validate the proposed theoretical model. The results obtained indicate good congruence between the experimental and theoretical values.
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Chopped sisal fibers and finely powdered high-density polyethylene were surface functionalized using dichlorosilane (DS) under radio frequency (RF)-plasma conditions and characterized by electron spectroscopy for chemical analysis (ESCA) and fluorescence labeling techniques. A high-capacity (10 L), rotating, 13.56 MHz, electrodeless plasma installation, specially designed to allow the uniform surface modification of powdery and particulate matter of irregular shape, was used. A three-factor fractional experimental design was employed to evaluate the effect of RF-power, pressure, and reaction time on the ESCA-based relative atomic composition of plasma-treated samples. It was demonstrated that SiHxCly functionalities are present on plasma-exposed surfaces and these functionalization reactions can be controlled by selecting proper plasma parameters. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2145–2154, 2002
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The increasing preoccupation with the environment and use of natural products has strongly contributed in the use of material derived from biomass, and in particular vegetal fibers. Within this context curaua fiber, originating from the Brazilian Amazon, has become prominent for its mechanical performance in relation to other vegetal fibers. This work is part of a wide research about the development of hybrid composites with curaua fibers. Its main objective is to present a brief description and characterization of the curaua fiber, still little known in the scientific community, compared to other vegetal fibers traditionally employed in polymeric composites. The characterization consists of tensile test, morphological analysis, and thermogravimetric analysis.
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The glued- laminated lumber (glulam) technique is an efficient process for the rational use of wood. Fiber-reinforced polymer (FRPs) associated with glulam beams provide significant improvements in strength and stiffness and alter the failure mode of these structural elements. In this context, this paper presents guidance for glulam beam production, an experimental analysis of glulam beams made of Pinus caribea var. hondurensis species without and with externally-bonded FRP and theoretical models to evaluate reinforced glulam beams (bending strength and stiffness). Concerning the bending strength of the beams, this paper aims only to analyze the limit state of ultimate strength in compression and tension. A specific disposal was used in order to avoid lateral buckling, once the tested beams have a higher ratio height-to-width. The results indicate the need of production control so as to guarantee a higher efficiency of the glulam beams. The FRP introduced in the tensile section of glulam beams resulted in improvements on their bending strength and stiffness due to the reinforcement thickness increase. During the beams testing, two failure stages were observed. The first was a tensile failure on the sheet positioned under the reinforcement layer, while the second occurred as a result of a preliminary compression yielding on the upper side of the lumber, followed by both a shear failure on the fiber-lumber interface and a tensile failure in wood. The model shows a good correlation between the experimental and estimated results. KeywordsGlulam–FRP–Reinforcement
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The present paper investigates the effect of fiber treatment on the mechanical properties of unidirectional sisal-reinforced epoxy composites. Treatments including alkalization, acetylation, cyanoethylation, the use of silane coupling agent, and heating were carried out to modify the fiber surface and its internal structure. As indicated by infrared spectroscopy, X-ray diffraction and tensile tests, variations in composition, structure, dimensions, morphology and mechanical properties of the sisal fibers can be induced by means of different modification methods. When the treated fibers were incorporated into an epoxy matrix, mechanical characterization of the laminates revealed the importance of two types of interface: one between fiber bundles and the matrix and the other between the ultimate cells. In general, fiber treatments can significantly improve adhesion at the former interface and also lead to ingress of the matrix resin into the fibers, obstructing pull-out of the cells. As a result, the dependence of laminate mechanical properties on treatment methods becomes complicated. On the basis of a detailed analysis, the relationship between optimized fiber treatment and performance improvement of sisal composites was proposed.
Polyurethane resin composite derived from castor oil and vegetable fibres
  • R V Silva
R.V., Silva, "Polyurethane resin composite derived from castor oil and vegetable fibres",(in portuguese). São Carlos, PhD. Ph.D. Dissertation -Escola de Engenharia de São Carlos,USP,Brazil 2003.
Fibres and composites for reinforced timber beams
  • N T Mascia
N. T. Mascia, "Fibres and composites for reinforced timber beams", ( in Portuguese) Report,Cnpq-IVALSA. Florence, Italy, 2016.