FORM 2
The Patent Act 1970
(39 of 1970)
&
The Patent Rules  2005

COMPLETE SPECIFICATION
(SEE SECTION 10 AND RULE 13)

TITLE OF THE INVENTION

“NON SYMMETRIC QUASI-ISOTROPIC COMPOSITE LAMINATES WITHOUT IN-PLANE AND OUT OF PLANE COUPLING EFFECT”

APPLICANTS:

Name : HCL Technologies Limited

Nationality : Indian

Address : HCL Technologies Ltd.  50-53 Greams Road 
Chennai – 600006  Tamil Nadu  India

The following Specification particularly describes and ascertains the nature of this invention and the manner in which it is to be performed:
FIELD OF INVENTION
[001] The embodiments herein relate to composite materials  and more particularly but not exclusively to a non-symmetric layup sequence for composite laminates and the use of such non-symmetric composite laminates for building structural parts without in-plane and out of plane coupling effect.

BACKGROUND OF INVENTION
[002] In the field of structural engineering  and more importantly in the field of aero structures  lightweight materials such as aluminium and magnesium alloys have been used for the production of structural parts. Further  for the manufacture of structural parts that require high strength  materials such as steel and titanium alloys are used. The weight of the structural parts is significant as it affects the functioning of the member or device in which the structural parts are used. For example  in aircraft industries  weight of the aircraft (determined based on the weight of structural parts such as panels  frames  stringers  skins  hulls and so on) is an important factor as it affects the operating expense and functioning of the aircraft. Aircraft with lighter weight consumes less fuel and may be able to travel for longer distance as compared to the aircraft with greater weight. Similarly  functioning of the aircraft such as speed  rate of climb and so on are more prominent in the aircraft having lighter weight compared to the aircraft having more weight. Although  the usage of lightweight materials for the production of structural parts results in the structural part having lesser weight  it should be noted that the lightweight structural parts manufactured using the lightweight materials are subjected to fatigue failure which makes the lightweight materials partially inefficient for the usage. On the other hand  although  the usage of heavyweight materials for the production of structural parts results in high strength structural parts  the weight of the structural parts manufactured from the heavyweight materials is more  which subsequently affects the vehicle""s functional attributes. Therefore  there is a need for alternate materials that could be used for the production of lightweight structural parts having high strength.
[003] Nowadays composite materials have become a popular replacement for many metals that are used to produce structural parts  as the composite materials are lighter when compared to the metals. Composite laminates are commonly used in the process of manufacturing structures having complicated shapes. Composite laminates are assemblies of layers or plies of fibrous composite materials which can be joined by any manufacturing process to provide required engineering properties  including in-plane stiffness  bending stiffness  strength  coefficient of thermal expansion and so on. However  there are number of complex engineering issues that must be considered when replacing a metal part with a composite laminates as the structure requires high strength and strength to weight ratio. Conventionally  engineers use composite laminates having symmetric quasi isotropic layup sequence for building structures to avoid in-plane and out of plane coupling effect of the structure under load. Symmetric composite laminates are the assemblies of layers or plies of fibrous composite materials in a specified orientation and sequence such that the stacking sequence of plies below the laminate mid plane is a mirror image of stacking sequence of plies above the laminate mid plane (?i=?(n+1)-i must be true for all values of “i”). The term “mid plane” as discussed throughout this specification refers to plane containing all the midpoints in the thickness direction of the laminate before applying the external loads.
[004] Further  the structures manufactured from symmetric composite laminates possess high strength and strength to weight ratio. For example  Table 1 shows a tabular column depicting a quasi-isotropic symmetric layup sequence for sixteen ply composite laminate.

Table 1
Ply. No. Stacking Sequence (in degree)
1 0
2 90
3 45
4 -45
5 -45
6 45
7 90
8 0
9 0
10 90
11 45
12 -45
13 -45
14 45
15 90
16 0
The stacking sequence of top eight layers (above the mid plane) forms a mirror image of the bottom eight layers (below the mid plane). Further  the two dimensional mechanical properties of each ply are depicted in table 2
Table 2
Two Dimensional mechanical properties of ply
E1 (GPa) 136
E2 (GPa) 10
G12 (GPa) 4.55
?12 0.3
t (mm) 0.125

wherein  E1 and E2 represents young’s modulus of elasticity along the x axis and y axis respectively  G12 represents shear modulus in the xy plane  ?12 Poisson’s ration in xy plane along the x axis and t represents thickness of the ply.
[005] Furthermore  the global stiffness matrix for the symmetric composite laminates having the mechanical properties as described in table 2 and the layup sequence as provided in table 1 is identified and provided in table 3. As it can be deduced from table 3  structures produced by symmetric composite laminates (as described in table 1) having mechanical properties as described in table 2 provides constraint conditions of the three stiffness matrices namely extensional-shear (in-plane) stiffness matrix (A matrix) bending-twisting (out-of-plane) stiffness matrix (D matrix) and null coupling stiffness matrix (B matrix). However  in actual practice symmetric quasi isotropic layup sequence of the composite laminates results in the structure having additional weight  which subsequently reduces the performance of the structures.
Table 3
Global Stiffness Matrix
A (N/mm) 116289.4523 36723.1310 0.0000 0.0000 0.0000 0.0000 B (N)
36723.1310 116289.4523 0.0000 0.0000 0.0000 0.0000
0.0000 0.0000 39783.1606 0.0000 0.0000 0.0000
B (N) 0.0000 0.0000 0.0000 43653.6462 10323.3461 495.4663 D (N-mm)
0.0000 0.0000 0.0000 10323.3461 37708.0504 495.4663
0.0000 0.0000 0.0000 495.4663 495.4663 11343.3560

[006] On the other hand  structure manufactured from composite laminates having non-symmetric layup sequence offers most of the times in-plane and out of plane coupling matrix (an unwanted structural behaviour) thereby makes the non-symmetric layup sequence partially inefficient. Non- symmetric layup sequence is the assembly of layers or plies of fibrous composite materials in a specified orientation and sequence such that the stacking sequence of plies below the laminate mid plane are not a mirror image of stacking sequence of plies above the laminate mid plane (?i??(n+1)-i must be true for at least one value of “i”). Fig. 1a and Fig. 1b depict symmetric layup sequence (100) and non-symmetric layup sequence (200) of an eight ply composite laminate that exists in prior arts.
[007] Therefore  there is a need of non-symmetric layup sequence for composite materials that could avoid in-plane and out of plane coupling effect. Further  there is a need of non-symmetric layup sequence of composite materials that could overcome the aforementioned drawbacks of existing technologies.

OBJECT OF INVENTION
[008] The principal object of this invention is to provide a non-symmetric composite laminates without in-plane and out of plane coupling effect.
[009] Another object of the invention is to provide a non-symmetric composite laminates without coupling effect that could be used for structural applications.
[0010] A further object of the invention is to provide a non-symmetric composite laminates that could provide quasi isotropic behavior for the structures.
[0011] A further object of the invention is to provide a non-symmetric composite laminates that is not restricted to any particular angle.

BRIEF DESCRIPTION OF FIGURES
[0012] This invention is illustrated in the accompanying drawings  throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings  in which:;
[0013] Fig. 1a and Fig. 1b depict symmetric layup sequence and non-symmetric layup sequence of an eight ply composite laminate that exists in prior arts.
[0014] Fig. 2a  2b and 2c depict a polar chart illustrating quasi-isotropic laminate properties such as Young’s Modulus of elasticity  Shear Modulus and Poisson’s Ratio respectively according to an embodiment of the present invention.
[0015] Fig. 3a depicts the graph illustrating the critical reserve factor of for the simply supported plate manufactured by quasi-isotropic & symmetric layup sequence and quasi-isotropic & non-symmetric layup sequence according to an embodiment of the present invention.
[0016] Fig. 3b depicts a graph illustrating the increase in Eigen value for the simply supported plate manufactured by quasi-isotropic & non-symmetric layup sequence over simply supported plate manufactured by quasi-isotropic & symmetric composite laminate according to an embodiment of the present invention.
[0017] Fig. 3c depicts a graph illustrating the enhancement in performance for the simply supported plate manufactured by the quasi-isotropic & non-symmetric composite layup sequence over the simply supported plate manufactured by quasi-isotropic and symmetric layup sequence according to an embodiment of the present invention.

DETAILED DESCRIPTION OF INVENTION
[0018] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly  the examples should not be construed as limiting the scope of the embodiments herein.
[0019] The embodiments herein provide a non-symmetric layup sequence for composite laminates and the use of such non-symmetric layup sequence of composite laminates for building structural parts without in-plane and out of plane coupling effect. Referring now to the drawings  and more particularly to FIGS. 1 through 3  where similar reference characters denote corresponding features consistently throughout the figures  there are shown embodiments.
[0020] Throughout the description the term “isotropy” refers to the laminate characteristic having mechanical properties that are uniform in all directions. The term “anisotropy” refers to the laminate characteristic having mechanical properties that are non uniform in all directions. “Quasi Isotropic” refers to the laminate characteristic having in-plane isotropic mechanical properties (XY plane but not in YZ and XZ planes). “In-plane and out of plane coupling” refers to the laminate characteristic having bending responses while axial loads are applied and axial responses while bending loads are applied. “Performance” refers to at least one of buckling load carrying capacity  reserve factor and natural frequency of a structure (which varies according to the application of structure)  and “polar chart” refers to a chart that represents behavior of various mechanical properties in 360 degree of a plane  and the properties are represented along the radius. Further  although “asymmetric layup sequence” appears to correspond to the “non- symmetric layup sequence”  it is to be noted that asymmetric layup sequence is the assembly of layers or plies of fibrous composite materials in a specified orientation and sequence such that the stacking sequence of plies below the laminate mid plane forms a negative or opposite mirror image of stacking sequence of plies above the laminate mid plane. Hence  asymmetric layup sequence is substantially different from non-symmetric layup sequence. Further  the present invention is directed to non-symmetric composite laminates without in-plane and out of plane coupling effect.
[0021] The non-symmetric composite laminate includes plurality of composite plies. In an embodiment  the non symmetric composite laminate includes at least ten composite plies in the increasing order of even numbers. For example  the number of composite plies could be in the order of 10 + N  wherein N is selected from even numbers other than zero. Further  the composite plies are selected from at least one of unidirectional composite plies or multidirectional composite plies. However  it is also within the scope of invention that the non-symmetric layup sequence according to the present invention can include any other type of composite plies without otherwise deterring the intended function of the non-symmetric layup sequence as can be deduced from this description. In the multidirectional composite plies  fibers can be placed in any desired direction in a two-dimensional space  along which better stiffness (or strength) is desired. Further  unidirectional composite plies are a thin layer (ply) of composite. It contains parallel  continuous fibers and provides extremely high stiffness properties in the fiber direction.
[0022] In an embodiment  the non-symmetric composite laminates without in plane and out of plane coupling effect can be obtained by laminating the composite plies in the order of 2p /N Repeats  wherein N is obtained by dividing the number of layers into several even numbers greater than 5. Further  laminating composite plies in the order of 2p /N Repeats results in plurality of blocks in the order of 2p /N1 + 2p /N2 + 2p /N3 +….+ 2p /Nn  wherein N1  N2  N3… Nn is obtained by dividing the number of layers into several even numbers greater than 5. Further  each block holds symmetric layup sequence. The non-symmetric layup sequence according to an embodiment of the present invention is obtained by the following equation.
2p /N (non-symmetric) = 2p /N1 (symmetric) + 2p /N2 (symmetric) + 2p /N3 (symmetric) +…. + 2p /Nn (symmetric)  wherein N1  N2  N3… Nn is obtained by dividing the number of layers into several even numbers greater than 5.
Further  the in-plane and out of plane coupling effect of the blocks are avoided as each block holds a quasi-isotropic and symmetric layup sequence  thereby joining these quasi-isotropic symmetric layup sequences results in the non-symmetric layup sequence without in-plane and out of plane coupling effect. In an embodiment  the number of layers (N) is divided into several blocks of even numbers greater than 5 (N1  N2 and so on)  such that addition of the blocks should result in a non-symmetric layup sequence. For example  16 layer composite plies should not be stacked in the sequence of 2p /8 + 2p /8  as this will result in a symmetric layup sequence.
[0023] For example  table 4 depicts a non-symmetric layup sequence of 16layer composite plies according to an embodiment of the present invention. The 16 layer composite plies are divided in to two blocks having 10 layers (N1=10 an even number greater than 5) and 6 layers (N2=6 an even number greater than 5) respectively. Further  each block holds symmetric layup sequence  thereby results in the order of 2p /10(symmetric layup sequence) and 2p /6 (symmetric layup sequence).
2p /16(non-symmetric) = 2p /10 (symmetric) + 2p /6 (symmetric)
Table 4
Ply. No. Stacking Sequence
1 0
2 36
3 -36
4 72
5 -72
6 -72
7 72
8 -36
9 36
10 0
11 0
12 60
13 -60
14 -60
15 60
16 0

[0024] It should be noted that the aforementioned configuration of non symmetric layup sequence is provided for the ease of understanding of the embodiments of the invention. Further  it is also within the scope of invention that the non-symmetric layup sequence of 16layer composite plies can be obtained by certain other configuration. For example  16 layer composite plies can be arranged in the order of 2p /6 (symmetric) + 2p /10 (symmetric). Similarly  22 layers can be arranged in the order selected from the group of (10 + 6 + 6) or (12 + 10) or (14 + 8) or (8 + 14) and so on.
[0025] The composite laminates obtained from the non-symmetric layup sequence as discussed in the present invention provides quasi isotropic behavior for the structures. Fig. 2a  2b and 2c depict a polar chart illustrating quasi-isotropy of laminate properties such as Young’s Modulus of elasticity  Shear Modulus and Poisson’s Ratio respectively according to an embodiment of the present invention. The polar chart represents behavior of the properties in 360 degree. Further  the length r depicts the behavior of properties. The constant length of r as obtained in the polar chart 2a  2b and 2c illustrates that there is identical mechanical properties around 360 degree.
[0026] It should be noted that the aforementioned configuration of non-symmetric layup sequence and the examples are provided for the ease of understanding of the embodiments of the invention. However  certain embodiments may have a different configuration of the components and certain other embodiments may exclude certain components. For example  the structure as discussed throughout the description is not restricted to structures used in aircraft industries. However  the structure can include any type of laminated thin plates  laminated beams  laminated shells or laminated stiffened panels. Therefore  such embodiments and any small modification without otherwise deterring the intended function of the non-symmetric layup sequence as is apparent from this description and drawings are also within the scope of this invention.
[0027] As is evident from the above description  with the non-symmetric layup sequence discussed herein  the objectives as was set forth initially will be achieved. Further  the structures obtained from the non-symmetric layup sequence are observed to have enhanced performance than the structures obtained from symmetric layup sequence.
[0028] Table 6 depicts a non-symmetric layup sequence of 16layer composite plies according to an embodiment of the present invention. Further  each layer is a unidirectional composite ply. Furthermore  the mechanical properties of the ply are depicted in table 5.
Table 6
2D mechanical properties of ply
E1(GPa) 136
E2(GPa) 10
G12(GPa) 4.55
?12 0.3
t(mm) 0.125
Xt (MPa) 1314
Xc (MPa) 1220
Yt (MPa) 43
Yc (MPa) 168
S (MPa) 48

wherein  E1 and E2 represents young’s modulus of elasticity along the x axis and y axis respectively  G12 represents shear modulus along the xy axis  u12 Poisson’s ration in xy plane along the x axis  t represents thickness of the ply  Xt and Xc represents axial tensile and compressive strengths of the ply respectively along the X axis  Yt and Yc represents axial tensile and compressive strengths of the ply respectively along Y axis and S represents in the shear strength of the ply in XY Plane.
[0029] Further  16 layers of composite ply are divided in to two blocks having 10 layers (N1>5 and an even number) and 6 layers (N2>5 and an even number) respectively. Further  each block holds symmetric layup sequence  thereby results in the 16 layer non-symmetric composite laminate having the order of 2p /10(symmetric layup sequence) and 2p /6 (symmetric layup sequence).
Table 5
Ply. No. Stacking Sequence
1 0
2 36
3 -36
4 72
5 -72
6 -72
7 72
8 -36
9 36
10 0
11 0
12 60
13 -60
14 -60
15 60
16 0

[0030] A simply supported plate of dimensions 200 mm along X direction and 700 mm along Y direction is manufactured by the quasi-isotropic non-symmetric layup sequence as depicted in Table 6 and the ply mechanical properties as depicted in Table 5 is subjected under a bi axial compression loads of 20N/mm along the x-axis and 20N/mm along the y axis. Further  the simply supported plate manufactured by the quasi-isotropic non-symmetric layup sequence is observed to have improved performance compared to the simply supported plate manufactured by the quasi-isotropic symmetric layup sequence. For example  the Eigen value under stability analysis of the simply supported plate manufactured by the quasi-isotropic non-symmetric layup sequence is observed to be in the order of 0.602406194 which is higher than the simply supported plate manufactured by the quasi-isotropic symmetric layup sequence. Further  the Eigen value of the simply supported plate manufactured by the symmetric composite laminate is found to be in the order of 0.56224668.
[0031] Further  Fig. 3a depicts the graph illustrating the critical reserve factor of for the simply supported plate manufactured by the quasi-isotropic symmetric layup sequence and quasi-isotropic non-symmetric layup sequence according to an embodiment of the present invention. In Fig. 3a X axis represents simply supported plate manufactured by the quasi-isotropic symmetric layup sequence and quasi-isotropic non-symmetric layup sequence respectively and Y axis represents the critical reserve factor values. Further  it could be observed from Fig. 3a that the critical reserve factor for the simply supported plate manufactured by the quasi-isotropic symmetric layup sequences equal to the critical reserve factor for the simply supported plate manufactured by the quasi-isotropic non-symmetric layup sequence.
[0032] Similarly  Fig. 3b depicts a graph illustrating the increase in Eigen values for the simply supported plates manufactured by the quasi-isotropic non-symmetric layup sequence and quasi-isotropic symmetric layup sequence. In Fig. 3b X axis represents simply supported plate manufactured by the quasi-isotropic symmetric layup sequence and quasi-isotropic non- symmetric layup sequence respectively and Y axis represents the Eigen values.
[0033] Further  Fig. 3c depicts a graph illustrating the enhancement in performance (in terms of percentage) for the simply supported plate manufactured by the quasi-isotropic non-symmetric layup sequence over the simply supported plate manufactured by the quasi-isotropic symmetric layup sequence. In Fig. 3c X axis represents simply supported plates manufactured by the quasi-isotropic symmetric layup sequence and quasi-isotropic non- symmetric layup sequence respectively and Y axis represents the percentage of increase in performance. Further  Table 7 represents the comparison between various performance factors for the simply supported plate manufactured by the symmetric composite laminate and non- symmetric composite laminate respectively.
Table 7
Performance factors simply supported plate manufactured by the quasi-isotropic symmetric layup sequence simply supported plate manufactured by the quasi-isotropic non-symmetric layup sequence
Critical Reserve factor 57.03686 57.03686
Eigen Value 0.5622 0.6024
% of Enhancement 6.999460241

[0034] As is evident from the above description  with the non-symmetric layup sequence discussed herein  the performance of the structures could be enhanced up to 7% depending upon at least one of geometry  application of the structure and so on.
[0035] Furthermore  the global stiffness matrix for the non-symmetric composite laminates having the mechanical properties as described in table 6 and the layup sequence as provided in table 5 is identified and provided in table 8. As it can be deduced from table 8  quasi-isotropic non-symmetric composite layup sequences provide null coupling stiffness matrix(B) matrix  Extension Shear stiffness Matrix (A Matrix) and Bending twisting stiffness matrix. However  in actual practice these non symmetric quasi isotropic layup sequences offers increasing functional performance than the symmetric quasi isotropic layup sequences without any inplane out of plane coupling effect..

Table 8
Global Stiffness Matrix
A (N/mm) 116289.4523 36723.1310 0.0000 0.0000 0.0000 0.0000 B (N)
36723.1310 116289.4523 0.0000 0.0000 0.0000 0.0000
0.0000 0.0000 39783.1606 0.0000 0.0000 0.0000
B (N) 0.0000 0.0000 0.0000 46596.155 11578.495 1060.542 D (N-mm)
0.0000 0.0000 0.0000 11578.495 32255.243 1073.421
0.0000 0.0000 0.0000 1060.542 1073.421 12598.505

[0036] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can  by applying current knowledge  readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept  and  therefore  such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore  while the embodiments herein have been described in terms of preferred embodiments  those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

Claims
We Claim:
1. A non symmetric laminate without in-plane and out of plane coupling  said non-symmetric laminate comprising:
plurality of plies  wherein
said plurality of plies are divided into at least two blocks; and
each of said block possess quasi-isotropic and symmetric layup sequence.

2. The non symmetric laminate as claimed in claim 1  wherein said plies are selected from at least one of unidirectional composite plies or multidirectional composite plies.

3. The non symmetric laminate as claimed in claim 1 is configured to produce structures having better performance.

4. The non symmetric laminate as claimed in claim 3  wherein said performance is at least one of strength  stiffness  buckling load capacity  resistance to vibrations based on the application of the structure.

5. The non symmetric laminate as claimed in claim 3  wherein said structures can be selected from at least one of laminated thin plates  laminated beams  laminated shells or laminated stiffened panels.

6. The non symmetric laminate as claimed in claim 1  wherein said plurality of plies include even number of plies greater than ten.

7. The non symmetric laminate as claimed in claim 1  wherein each of said block include even number of plies greater than five.

8. A method for providing non symmetric laminates without in-plane and out of plane coupling  said method comprising:
providing plurality of plies; and
dividing said plurality of plies into at least two blocks  wherein
each of said block possess quasi-isotropic and symmetric layup sequence.

Dated: 06th Day of June 2012 Signature:
Dr Kalyan Chakravarthy
(Patent Agent)

ABSTRACT
A non symmetric laminate without in-plane and out of plane coupling effect. The non-symmetric laminate includes plurality of plies that are selected from at least one of unidirectional composite plies or multidirectional composite plies. Further  the plurality of plies are divided into at least two blocks such that each block possesses quasi-isotropic and symmetric layup sequence.