FIELD OF THE INVENTION
00001. The present invention relates to a fabrication method for preparing the
composite sheets by using high strength fibres and an epoxy resin, which is
particularly useful at low temperature applications.
BACKGROUND OF THE INVENTION
2. Composites materials are replacing metal components in many
industries due to their wide-ranging properties and promising performance.
These materials are extending boundaries of designers in all engineering areas.
This family of synthesized materials has the potential to offer new solutions to
the problems for which there was difficulty in finding solution earlier. With the
recent developments, it is possible to select tougher and lighter composites with
properties that can suit a particular application.
3. Composite materials are finding its application in several fields ranging
from automobiles to aerospace. Advanced materials are used in aerospace
applications due to requirement of very light weight parts and high performance.
In cases of application where high performance under low temperature is
required, the material selection is a complex process. Several studies reported
the mechanical behaviour of fibre reinforced composites at ambient temperature
but not much about the performance of FRP (fibre reinforced plastic) composites
under low temperature. Hence, an in-depth work on selection of fibres, epoxy
resins, fabrication of samples and testing needs to be done to understand the
behaviour of composite materials for high strength and low temperature
conditions.
4. Different composite fabrics such as kevlar, graphite, carbon, glass
fibres are used for aerospace application.
5. These composites have great advantages such as low weight, variability
in matching mechanical and thermal properties etc., but they have a main

drawback of high brittleness under cryogenic conditions. Reduction in
mechanical strength especially under multi-axial load condition is observed.
Hence, these composites should maintain integrity at cryogenic temperatures for
their application under low temperatures.
00006. Patent No. US 4113684, titled “Low temperature cure epoxy-amine
adhesive compositions”: This invention describes method of high performance
adhesive preparation. A composition, which is suitable for use as an adhesive,
is made by mixing one part of an adduct reaction product consisting of a solid
epoxy resin and a stoichiometric excess of an aliphatic amine with about one
part to about six parts of a reactive solid epoxy resin powder having an average
particle size of from about 10 microns to about 420 microns, the mixture being
capable of melting at temperatures of over about 60o C, wherein the epoxy of
resin powder amine remains unreacted until melting. The material is an
unreacted mixture of reactive epoxy resin powder and adduct, which can be used
as an adhesive and is capable of melting at temperatures of above about 60°C
and forming across linked adhesive material. The type and amount of epoxy
powder was chosen so that it would react completely with the solid adduct when
they are made compatible through melt activation. The adhesive is, therefore, a
two phase material, the first phase is the epoxy-amine adduct and the second
phase is sufficient epoxy powder to react with the adduct upon melting. The
adduct is dispersed evenly throughout the epoxy powder and the system is stable
because of the separation of the two solid phases. The epoxy powder remains
unreacted until melt application. This adhesive has a long storage life and can
be cold molded into pellets, rods, or intricate shaped design configurations. This
high performance structural adhesive will find applications in the wood, glass,
plastics, fabrics, and metal joining industries. It can be applied in solid or slurry
form to bond a variety of substrates.

7. Patent No. US 4798761, titled “Epoxy resin compositions for use in low
temperature curing applications” : The present invention pertains to resinous
compositions suitable for use in low temperature curing applications including
the repair of composite articles. Compositions comprising a mixture of an epoxy
resin composition consisting essentially of at least one epoxy resin which has an
average of not more than two vicinal epoxy groups per molecule, at least one
epoxy resin which has an average of more than two vicinal epoxy groups per
molecule and at least one rubber or elastomer; and optionally, a low viscosity
reactive diluent, are useful in preparing low temperature curable compositions.
Also, low temperature curable compositions containing the above components
with at least one cycloaliphatic amine hardener and optionally, an accelerator
for component is claimed. Composite objects are employed for most outdoors
parts, they are subjected to all types of environments. In humid environments,
the composites tend to absorb moisture. The moisture in wet composites tends
to vaporize when subjected to the heat usually involved in curing the patches
during their repair, and causes blistering, disbondment and often delamination.
It would be desirable to have an adhesive and a resinous binder material for use
in the repair of the objects prepared from composites which cure below the
normal curing temperature of the epoxy resins currently employed in the repair
of composite parts or objects. The repair material would most preferably cure
below the boiling point of water and produce a polymeric system which has
thermal and mechanical properties similar to the composite part being repaired.
Low temperature curable epoxy resin systems with good thermal and mechanical
properties would find applications in electronic encapsulants, production of
electrical laminates, and structural composite parts. These materials are
especially valuable in several composite production techniques like resin transfer
molding, braiding, filament winding, pultrusion and similar methods of rapid
composite formation.
8. Patent No. US 7208228 B2, titled “Epoxy resin for fiber reinforced
composite materials”: This invention relates to epoxy resin compositions not only

with high modulus capable of giving composite materials higher compressive
strength and improved tube bending properties, but also with good tack capable
of excellent process ability. An epoxy resin composition for a cured material,
comprising an epoxy resin comprising an epoxy compound X, which has an
epoxy equivalent weight of at least 400. A curing agent, and a liquid rubber that
is liquid at room temperature and comprises a reactive group; wherein the epoxy
compound X has a solubility parameter value of SpX, the liquid rubber has a
solubility parameter value of Spy and the ratio of Spy/SpX could be in the range
of 0.7 to 1.3. The liquid rubber could form no visible domains by optical
microscopy or has a maximum domain size of at most 3 microns in the cured
material. The epoxy resin composition provides a fiber-reinforced material with
higher compressive modulus and strength, toughness and better handling ability
over standard epoxy resin systems. This invention is excellent for small thin
walled tube structures like fishing rods or applications that require good
compressive strength. This invention provides a high modulus, high compression
strength resin system that produces high bending strength composite tubes
where the prepreg used has good handling characteristics. This also provides a
prepreg to be prepared by impregnating reinforcing fibers with the mentioned
epoxy resin compositions. Two or more of the above fibers maybe combined into
one prepreg form. The invention further provides a fiber-reinforced composite
material comprising a cured product of the above mentioned epoxy resin
compositions and reinforcing fibers.
00009. Patent No. US 8263216 B2, titled “Epoxy resin composition for fiber
reinforced composite material, prepreg, and fiber-reinforced composite material”:
The invention relates to an epoxy resin composition for fiber reinforced composite
material (epoxy resin composition), prepreg, and fiber composite material. More
specifically, the invention relates to an epoxy resin composition useful for
producing a fiber reinforced composite material that maintains a high
mechanical strength in a severe operating environment such as at a low

temperature, and serves effectively as a structural member, and a prepreg, as
well as fiber reinforced composite material. This discloses a fiber-reinforced
composite material that is high in heat resistance and strength while being low
in the content of Volatile matter that volatilizes during curing. Also, epoxy resin
composition for production thereof, and a prepreg produced from the epoxy resin
composition. Specifically the invention provides an epoxy resin composition
comprising an epoxy resin with two or more ring structures each consisting of
four or more members, and at least one amine type or ether type glycidyl group
directly connected to the ring structures, a tri- or more-functional epoxy resin,
and a curing agent, and also provides a prepreg produced by impregnating
reinforcing fiber with the epoxy resin composition and a fiber-reinforced
composite material produced by curing the prepreg. The invention aims to
provide an epoxy resin composition useful for producing a carbon fiber reinforced
composite material that is low in content of components that volatilize during
curing, high in heat resistance and mechanical strength in a severe operating
environment, such as at a low temperature, and suitable for producing
structural members, and a prepreg, as well as carbon fiber reinforced composite
materials.
000010. In general, exposing the composites to cryogenic temperatures can
cause micro-cracks as well as delamination due to thermal residual stresses.
These micro-cracks provide a pathway for the ingress of moisture and may lead
to complete fracture of the composite. Matrix resins will have brittle nature and
do not allow relaxation of residual stresses or stress concentration to take place.
At cryogenic temperature, fibrous polymeric composites undergo inelastic
deformation and damage when subject to mechanical loading. The low
temperature operating conditions will cause the matrix to shrink. In fibre
reinforced polymer matrix composites, the coefficient of thermal expansion of the
matrix is usually an order of magnitude greater than that of the fibres.
Contraction of the matrix is resisted by relatively stiff fibres through fibre-matrix

Interface bonding, setting up residual stresses within the material
microstructure. These residual stresses may cause micro-cracking with in the
matrix and matrix-fibre interfaces. Also, temperature change is an
accompanying change in matrix strength and stiffness. Most resins become
stronger and stiffer as they are cooled. Composite material damage usually
begins with the formation of microscopic cracks in the matrix or at the matrix-
fibre interface. When these cracks develop to a certain density and size, they
coalesce to form macroscopic matrix cracks. Transverse matrix cracking in
composite laminates has been shown to affect laminate stiffness, strength,
dimensional stability (thermal expansion), and fatigue resistance.
11. Hence, it is of utmost importance to provide a composite sheets
through different composite materials.
12. The selection of composite material for application under low
temperature and high strength conditions is a complex process. This requires a
lot of testing with variety of fibre-epoxy combinations. Increase in use of
composite materials in many areas has been observed in the past few decades.
The properties of fibre reinforced composites like high strength to weight ratio,
high stiffness to weight ratio, flexibility in design, ease of fabrication and
economical as compared to metals, make it an excellent choice for various range
of products.

13. In the present invention, the constituents of the composite materials
can be judiciously chosen so that one or more of the advantages like high specific
strength, specific modulus, material damping capacity etc as desired could be
obtained.
14. The present invention aims to exploit the advantage of composite
materials and its application under high strength and cryogenic temperature
conditions.

OBJECTS OF THE INVENTION
000015. It is therefore the primary object of the present invention to provide a
fabrication method for preparing composite sheets by using high strength fibres
and epoxy resin, which are suitable in low temperature application or more
particularly in cryogenic temperature.
16. Another object of the present invention is to provide a fabrication
method for preparing composite sheets, which exhibits high tensile strength,
high elasticity and dimensional stability.
17. Yet another object of the present invention is to provide a fabrication
method for preparing composite sheets, which provides flex performance and
relatively easy processing.
18. Further object of the present invention is to provide a fabrication
method for preparing composite sheets, which provides substantially high tensile
strength, under liquid nitrogen temperature i. e. 77K at a test speed of
5mm/min.
19. Another object of the present invention is to provide a fabrication
method for preparing composite sheets, which is simple, rapid yet effective.
SUMMARY OF THE INVENTION
000020. One or more drawbacks of conventional systems and process for a
method of preparing composite sheets are overcome, and additional advantages
are provided through the composition as claimed in the present disclosure.
Additional features and advantages are realized through the technicalities of the
present disclosure. Other embodiments and aspects of the disclosure are
described in details herein and are considered to be part of the claimed
disclosure.

000021. A method for preparing of composite sheets comprises the steps of :
i) mixing of the epoxy resin with the curing agent in the ratio of 4:1;
ii) fabrication of kevlar-49 and Epoxy/S-glass (EG-S) sheets through multiple
composite layers;
iii) coating of epoxy resin on the successive composite layer before placing of
one layer of fabric on the other;
iv) pouring of liquid epoxy resin produced from bisphenol-A and epichlorohydrin
with liquid aromatic amine based curing agent and uniformly spreading with
help of a brush;
v) moving of a roller for removal of fair trapping; and
vi) compression pressing of the laminates at a temperature and pressure of
50°C and 10.3 MPa respectively with a cure line of 8 hours.
characterized in that the composite sheets provides high tensile strength at
yield under liquid nitrogen temperature of 77k.
000022. Various objects, features, aspects, and advantages of the inventive
subject matter will become more apparent from the following detailed description
of preferred embodiments, along with the accompanying drawing figures.
000023. It is to be understood that the aspects and embodiments of the
disclosure described above may be used in any combination with each other.
Several of the aspects and embodiments may be combined to form a further
embodiment of the disclosure.
000024. The foregoing summary is illustrative only and is not intended to be in
any way limiting. In addition to the illustrative aspects, embodiments, and

features described above, further aspects, embodiments, and features will
become apparent by reference to the drawings and the following detailed
description.
25. The illustrated embodiments of the subject matter will be best
understood by reference to the drawings, wherein like parts are designated by
like numerals throughout. The following description is intended only by way of
example, and simply illustrates certain selected embodiments of devices,
systems, and processes that are consistent with the subject matter as claimed
herein, wherein:
26. Figure 1 illustrates, the sample dimension in mm (250x25x2.5).
27. The figures depict embodiments of the disclosure for purposes of
illustration only. One skilled in the art will readily recognize from the following
description that alternative embodiments of the methods illustrated herein may
be employed without departing from the principles of the disclosure described
herein.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
000028. While the embodiments of the disclosure are subject to various
modifications and alternative forms, specific embodiment thereof have been
shown by way the figures and will be described below. It should be understood,
however, that it is not intended to limit the disclosure to the particular forms
disclosed, but on the contrary, the disclosure is to cover all modifications,
equivalents and alternative falling within the scope of the disclosure.
000029. It is to be noted that a person skilled in the art would be motivated
from the present disclosure to arrive at a method for preparing composite sheets
for low temperature applications. Such a method for evaluating the same may
vary based on configuration of one

or more workpieces. However, such modifications should be construed within
the scope of the disclosure. Accordingly, the drawings illustrate only those
specific details that are pertinent to understand the embodiments of the present
disclosure, so as not to obscure the disclosure with details that will be clear to
those of ordinary skill in the art having benefit of the description herein.
30. As used in the description herein and throughout the claims that
follow, the meaning of “a”, “an”, and “the” includes plural reference unless the
context clearly dictates otherwise. Also, as used in the description herein, the
meaning of “in” includes “in” and “on” unless the context clearly dictates
otherwise.
31. The terms “comprises”, “comprising”, or any other variations thereof
used in the disclosure, are intended to cover a non-exclusive inclusion, such that
a method, sheets, fibre, composite that comprises a list of components does not
include only those components but may include other components not expressly
listed or inherent to such method, or assembly, or device. In other words, one or
more elements in a system or device proceeded by “comprises…..a “does not,
without more constraints, preclude the existence of other elements or additional
elements in the system, apparatus or device.
32. The present subject matter relates to a fabrication method for
preparing composite sheets by using high strength fibres and a suitable epoxy
resin, which has wide application at low temperature or more particularly under
cryogenic temperature up to 77K.
33. This advanced composites exhibit desirable physical and chemical
properties that include very light weight coupled with high elasticity and
strength, dimensional stability, temperature and chemical resistance, flex
performance and relatively easy processing.
34. Composite material selection is an intricate process in cases of
application where high performance under low temperature is required. An

elaborate study on selection of fibres, suitable epoxy resins, processing of
materials and extensive testing needs to be done to understand the behaviour of
composite materials for high strength and low temperature conditions. The
present invention aims to exploit the high performance capabilities with desirable
properties that composite materials offer. To predict the behaviour of composites
under low temperature, composite samples are prepared using S-glass and
Kevlar-49 fibre with suitable resin.
35. The composite sheets in accordance with the present invention
comprises two different type of high performance fibres such as high strength
aramid fibre or kevlar fibre (Kevlar-49) and high strength silica based fibre or
Epoxy/S-glass (EG-S) sheets.
36. Apart from these fibres, about 75-80% by weight of liquid epoxy resin
produced from bisphenol-A and epichlorohydrin along with about 20-25% by
weight of liquid aromatic amine based curing agent are also incorporated in the
composite sheets.
37. Kevlar fibre is an aromatic polyamide offering good mechanical
properties at a low density with the added advantage of toughness or
damage/impact resistance. They are characterized as having reasonably high
tensile strength, a good modulus, and a very low density comparatively. Kevlar
fibres are insulators of both electricity and heat. They are resistant to organic
solvents, fuels and lubricants. Kevlar fibre composites exhibit a high mechanical
strength, damping capability and the high strength and relatively low thermal
conductivity make it an interesting choice for thermal supports in cryogenic
environments, particularly in applications in which a very low heat leak and low
weight are required. S-glass fibre composite has higher tensile strength, and
higher modulus compared to other glass fibres. This high strength glass fibre is
used where increased performance is required. These fibres are lower in density
producing a lighter laminate with higher stiffness. S-glass produces enhanced
mechanical properties compared to other glass fibres and aramid fibres.

000038. The viscosity of the used epoxy resin is 12-14 Pa.s at 25°C and density
is 1.16 Kg/l at 25°C. The viscosity of said curing agent is 9-14 Pa.s at 25°C and
density is 1.13 Kg/l at 25°C. The pot life of the curing resin is more than 4 hours
at 25°C. Plain Kevlar-49 and S-Glass fabrics are used for preparation of samples.
000039. The method for preparing the composite sheet comprises the steps of:
i) mixing of the epoxy resin with the curing agent in the ratio of 4:1;
ii) fabrication of aramid fibre or kevlar fibre and high strength silica based fibre
through multiple composite layers;
iii) coating of epoxy resin on the successive composite layer before placing of
one layer of fabric on the other;
iv) pouring of epoxy resin with liquid aromatic amine based curing agent and
uniformly spreading with help of a brush;
v) moving of a roller for removal of fair trapping; and
vi) compression pressing of the laminates at a temperature and pressure of
50°C and 10.3 MPa respectively with a cure line of 8 hours.
40. The tensile strength of the composite sheets is performed according to
the standard ASTM D 3039 with a cross head speed of 5 mm/min.
41. Fig.1 shows the rectangular cross sectional view of the composite
sample fabricated for tensile strength test. The test is conducted as per ASTM D
3039. This standard is used to measure the force required to break the composite
specimen and the extent to which the specimen stretches or elongates to that
breaking point. As per this, the dimensions of test samples shall be 250mm x
25mm x 2.5mm. The test is performed under liquid nitrogen environment at a
temperature of 77K. The test is conducted using Universal tensile tester with a
cross head speed of 5 mm/min. A liquid nitrogen chamber is installed on the
Universal test machine to maintain low temperature. Standard test fixtures are

installed inside the chamber and testing is conducted inside the controlled
environment.
42. The present invention aims to exploit the advantage of high
performance fibres, Kevlar-49 and S-glass and their application under low
temperatures. The tests performed helps in understanding the behaviour of the
chosen composites under cryogenic environment. Since the properties of many
materials vary depending on temperature, it is appropriate to test materials at
temperatures that simulate the intended end use environment.
43. The tensile strength at yield of S-glass composite under liquid nitrogen
temperature (77K) at a test speed of 5mm/min is about 111.44 MPa.
44. The tensile strength at yield of Kevlar-49 composite under liquid
nitrogen temperature (77K) at a test speed of 5mm/min is about 48.84 MPa.
45. Each of the appended claims defines a separate invention, which for
infringement purposes is recognized as including equivalents to the various
elements or limitations specified in the claims. Depending on the context, all
references below to the “invention” may in some cases refer to certain specific
embodiments only. In other cases, it will be recognized that references to the
“invention” will refer to subject matter recited in one or more, but not necessarily
all, of the claims.
46. Groupings of alternative elements or embodiments of the invention
disclosed herein are not to be construed as limitations. Each group member can
be referred to and claimed individually or in any combination with other
members of the group or other elements found herein. One or more members of
a group can be included in, or deleted from, a group for reasons of convenience
and/or patentability. When any such inclusion or deletion occurs, the
specification is herein deemed to contain the group as modified thus fulfilling
the written description of all groups used in the appended claims.
47. The present disclosure provides a method of preparing composite
sheets.

Equivalents:
48. With respect to the use of substantially any plural and/or singular
terms herein, those having skill in the art can translate from the plural to the
singular and/or from the singular to the plural as is appropriate to the context
and/or application. The various singular/plural permutations may be expressly
set forth herein for sake of clarity.
49. It will be understood by those within the art that, in general, terms
used herein, and especially in the appended claims (e.g., bodies of the appended
claims) are generally intended as “open” terms (e.g., the term “including” should
be interpreted as “including but not limited to”, the term “having” should be
interpreted as “having at least”, the term “includes” should be interpreted as
“includes but is not limited to”, etc.). It will be further understood by those within
the art that if a specific number of an introduced claim recitation is intended,
such an intent will be explicitly recited in the claim, and in the absence of such
recitation no such intent is present. For example, as an aid to understanding,
the following appended claims may contain usage of the introductory phrases
“at least one” and “one or more” to introduce claim recitations. However, the use
of such phrases should not be construed to imply that the introduction of a claim
recitation by the indefinite articles “a” or “an” limits any particular claim
containing such introduced claim recitation to inventions containing only one
such recitation, even when the same claim includes the introductory phrases
“one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a”
and/or “an” should typically be interpreted to mean “at least one” or “one or
more”); the same holds true for the use of definite articles used to introduce claim
recitations. In addition, eve it a specific number of an introduced claim recitation
is explicitly recited, those skilled in the art will recognize that such recitation
should typically be interpreted to mean at least the recited number (e.g., the bare
recitation of “two recitations”, without other modifiers, typically means at least
two recitations, or two or more recitations).

000050. The terminology used herein is for the purpose of describing particular
embodiments only and is not intended to be limiting of the present disclosure. It

will be appreciated that several of the above-disclosed and other features and
functions, or alternatives thereof, may be combined into other systems or
applications. Various presently unforeseen or unanticipated alternatives,
modifications, variations, or improvements therein may subsequently be made
by those skilled in the art without departing from the scope of the present
disclosure as encompassed by the following claims.
000051. The claims, as originally presented and as they may be amended,
encompass variations, alternatives, modifications, improvements, equivalents,
and substantial equivalents of the embodiments and teachings disclosed herein,
including those that are presently unforeseen or unappreciated, and that, for
example, may arise from applicants/patentees and others.
000052. While various aspects and embodiments have been disclosed herein,
other aspects and embodiments will be apparent to those skilled in the art. The
various aspects and embodiments disclosed herein are for purposes of
illustration and are not intended to be limiting, with the true scope and spirit
being indicated by the following claims.

WE CLAIM :
1. A method for preparing of composite sheets comprises the steps of :
i) mixing of the epoxy resin with the curing agent in the ratio of 4:1;
ii) fabrication of aramid fibre or kevlar fibre (kevlar-49) and high strength silica
based fibre through multiple composite layers;
iii) coating of epoxy resin on the successive composite layer before placing of
one layer of fabric on the other;
iv) pouring of epoxy resin liquid aromatic amine based curing agent and
uniformly spreading with help of a brush;
v) moving of a roller for removal of fair trapping; and
vi) compression pressing of the laminates at a temperature and pressure of
50°C and 10.3 MPa respectively with a cure line of 8 hours.
characterized in that the composite sheets provides high tensile strength at
yield under liquid nitrogen temperature of 77k.
2. The method for preparing of composite sheets as claimed in claim 1, wherein
the epoxy resin and curing agent is mixed in a ratio of 1:4.
3. The method for preparing of composite sheets as claimed in claim 1, wherein
the laminates are subjected to compression pressed at a temperature and
pressure of 50°C and 10.3 MPa respectively.
4. The method for preparing of composite sheets as claimed in claim 1, wherein
the curing of the laminates occur for a duration of 8 hours.
5. The method for preparing of composite sheets as claimed in claim 1, wherein
the viscosity and density of epoxy resin are 12-14 Pa.s at 25°C and 1.16Kg/1 at
25°C.

6. The method for preparing of composite sheets as claimed in claim 1, wherein
the viscosity and density of curing agent are 9-14 Pa.s at 25°C and 1.13Kg/1 at
25°C.
7. The composite sheet prepared by process as claimed in claim 1 comprises:
high performance fibres such as aramid fibre or kevlar fibre (kevlar-49) and silica
based fibre, liquid epoxy resin produced from bisphenol-A and epichlorohydrin
and liquid aromatic amine based curing agent.