M. Nithiyakumar
Lecturer, Department of Textile Technology,
SSM Academy of Textiles & Management, Erode.
mnithiyakumar@gmail.com

D. Gopalakrishnan
Lecturer, South India Institute of Fashion Technology,
229 A, Sathya Moorthi Road,
Ramnagar, Coimbatore – 641 009,
textilesamurai@rediffmail.com

Because of excellent characteristics, such as low weight or high strength and stiffness, fibre-reinforced composites have found a large dispersal in several areas of technical applications. However, because of increasing environmental consciousness and demands of legislative authorities, the manufacture, use, and removal of traditional composite structures, commonly using synthetic fibre materials such as glass, carbon, or aramid, are considered more critically. For that reason the substitution of the traditionally used synthetic fibre materials by natural fibres has become an emerging area of interest and development in polymer science and industrial applications. Despite ecological gains, like less environmental impact of the later product within the formation, usage, and disposal period, further technical and economical benefits result from this strategy. To improve the performance and durability of timber structures, fibre-reinforced polymer (FRP) composites are increasingly being used as reinforcements for wood. Current applications of wood reinforcement have focused on the use of FRP strips or fabrics bonded to wood members.

In this competitive world, engineers must find the high performance natural composite structures. To assist that there are so many Computer Aided Engineering tools are utilized. ANSYS 9.0 is the one of the successful Finite Element Modeling software. It is very flexible to design the composite models and to analyze them. In this work, three numbers of coir reinforced wooden ply boards are obtained from a manufacturer. They are with three different thicknesses and three types of layer configurations. The tensile stress, deflection and the density values are studied. With the ANSYS 9.0 software five different models are developed and the tensile stress and deforming behavior are analyzed. The input data like density, young’s modulus, shear modulus and poison’s ratio are given to construct the models. Among the five models, two models are Phenolic jute and coir reinforced wooden composites. In these models one wooden layer is eliminated.

There is very large tensile stress value difference between the original boards and the developed models. But the deformation characteristics are same for the both. It is found that there are so many manufacturing faults in the obtained models and the results from the ANSYS 9.0 are theoretical values. By considering these aspects, it could be correlated with the result values. According to the ANSYS 9.0, it is suggested that jute reinforced composites show the good improvement in tensile stress in lower thickness. The inclusion of jute reinforcement could eliminate one layer of wood and it is advantageous for reduced weight and higher aesthetic values.

From the Figures, it is seen that the load is distributed to all the layers and all over the area. The edges are well gripped and there is no deformation. So the layers were not bent and only the elongation has happened. The Figures show clearly that the deformations are controlled by the composite energy of the material. Even though the layers are separated into individual, their movement or tendency for the separation is controlled by the next layers.

The Figures could be classified into two sets. The Model 1 and 2 are considered as one set and the remaining are the other set. That is, the separation of the layers of Model 1 is same as Model 2. But in other three models, the layers are not separated in to individual. As they are thicker than the previous two models, they could not be deformed much.

Model 4 is coming in between Model 3 and 5 in tensile stress. The deformations are same for these three models. The 4 is slim than model 5 but gives the equal performance. This sleekness gives good aesthetic value and smooth surface because of jute non woven material, and the weight is so reduced. So the handling is easier. Jute fibre is cheaper than wood. So the cost will be reduced for considerable amount. From all the above points, one satisfactory thing is that the elimination of wooden material saves the green for some more time.

CONCLUSION

In this study, three different thicknesses of Coir reinforced wooden ply boards were obtained from the ply board manufacturer and they were tested for tensile stress in bending. The actual and theoretical density values of the boards were calculated. Then, five computational models were developed by using ANSYS 9.0 Finite Element Software package and the tensile stress was studied. From the above mentioned studies the following inferences are made.

1. The tensile stress values of the boards are increasing with the increment of the thickness. The deflection is decreasing with the increasing thickness.
2. The density values are much lower than the average values.
3. The void percentage is above 35% for all the boards. This shows that poor impregnation of nonwoven material into the resin. Because of this fault the mechanical behavior of the boards has been affected and this lead to poor tensile stress values.
4. In the five computational models the tensile stress is increasing with the increasing thickness and the deflection also increases.
5. The Jute containing boards are so stiff and the deflection is reducing with increasing thickness.
6. Even though the tensile stress values of computational models are incomparable with the real boards, the deformation tendency is same for both the models. Hence, the mechanical behavior could be correlated.
7. It is suggested that the inclusion of the Phenolic Jute layers gives higher stiffness for the boards and eliminates one layer of wood. It could be got the higher level of mechanical properties with the lower thickness. With this suggestion, the elimination of wood leads to reduction in cost. The sleekness gives higher aesthetic value and easy handling.

REFERENCES

1.Bledzki. A.K., Gassan. J., 1999, “Composites Reinforced with Cellulose Based Fibres”, Progress in Polymer Science, pp 221 – 274

2.Carlos Gonz�alez, Javier LLorca,” Multiscale Modeling of Fracture in Fiber-Reinforced Composites”,

3.Dieter H. Mueller, Andreas Krobjilowski, “New Discovery in the Properties of Composites Reinforced with Natural Fibers”, Journal of Industrial Textiles, Vol. 33, No. 2—October 2003, pp 111- 130

4.Gregg A. Ambur, Gerald G. Trantina, “Predicting Failure in Thermoplastic Composites”, Machine Design; Apr 20, 1989; 61, 8; ProQuest Science Journals, pg. 91

5.Jang-Kyo Kim, Yiu-Wing Mai, 1998, “Engineered Interfaces in Fiber Reinforced Composites”, Elsevier, New York

6.James E. Mark, 1999,”Polymer Data Handbook”, Oxford University Press, London

7.Julio F. Davalos, “Characterization of Bonded Interfaces for Wood-Fiber Reinforced Polymer Composites”, 3rd International Conference on Advanced Engineered Wood Composites, July 10 – 14, 2005 Bar Harbor, ME, USA

8.Kimberly Kurtis, “Polymers & Fiber Reinforced Polymeric Composites”, CEE 3020 Materials of Construction, Georgia Tech

9.Minjie Chen; Chaoying Wan; Yong Zhang; Yinxi Zhang, 2005, “Fibre Orientation and Mechanical Properties of Short Glass Fibre Reinforced PP Composites”, Polymers & Polymer Composites, 13, 3, ProQuest Science Journals

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12.Rizov.V; Harmia T; Reinhardt. A; Friedrich. K, 2005, “Fracture Toughness of Discontinuous Long Glass Fiber Reinforced Polypropylene: An Approach Based on a Numerical Prediction of Fibre Orientation in Injection Molding”, Polymers & Polymer Composites; 13, 2; ProQuest Science Journals, pg 121

13.Sanjay K. Mazumdar, 2002, “Composites Manufacturing – Materials, Product and Process Engineering”, CRC Press, London

14.Sudhakaran Pillai. M., Vasudev. R., 2001, “Applications of Coir in Agricultural Textiles”, International Seminar of Technical Textiles

15.Torres. F G; D�az. R M., 2004, “Morphological Characterisation of Natural Fibre Reinforced Thermoplastics (NFRTP) Processed by Extrusion, Compression and Rotational Moulding”, Polymers & Polymer Composites, 12, 8; ProQuest Science Journals, Pg. 705

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17.www.naturaindia.com

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19.Hull. D., Clyne. T.W., 1996, An Introduction to Composite Materials”, Cambridge University Press, Cambridge

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1. Introduction

Composites, the wonder material with light-weight, high strength-to-weight ratio and stiffness properties have come a long way in replacing the conventional materials like metals, woods etc. These materials are derived by combining two or more individual materials with intent of achieving superior properties/performance compared to each individual material. These materials offer some significant advantages to metals in many structural applications due to the flexibility of selecting various combinations of fibre reinforcement and resin matrix. The reinforcing fibres are the primary load carriers of the composite material, with the matrix component transferring the load from fibre to fibre. Selection of the optimal reinforcement form and material is dependent on the property requirements of the finished part [13].

Biocomposites are natural fibre composites are defined as composite materials composed of biodegradable natural fibres as reinforcement and biodegradable or non-biodegradable polymers as the matrix [7]. The advantages of natural fibres over traditional reinforcing fibres such as glass and carbon fibres are their low cost, low density, high toughness, acceptable specific strength, enhanced energy recovery, recyclability and biodegradability. Biocomposites derived from natural fibres and traditional synthetic thermoplastics or thermosets are mot sufficiently environmentally benign because the matrix resins are non-biodegradable. However these Biocomposites may maintain the balance between economic and environmental issues for a variety of industrial applications like automobile, construction, consumer products and others.

To improve the performance and durability of timber structures, fibre-reinforced polymer (FRP) composites are increasingly being used as reinforcements for wood [7]. Current applications of wood reinforcement have focused on the use of FRP strips or fabrics bonded to wood members. Nowadays coir-ply boards with oriented jute as face veneer and coir plus waste rubber wood inside are widely used. Phenol formaldehyde is used as matrix material. Two major categories of composite boards namely, coir-ply boards (jute rubber wood coir) as plywood substitute and natural fibre reinforced boards (jute coir) as MDF substitutes have been developed. These natural materials have all the properties required for a general purpose board and can be used in place of wood or MDF boards for partitioning, false ceiling, surface paneling, roofing, furniture, cupboards, wardrobes etc [17].

Today engineers must design closer to material limits in order to meet cost and weight requirements. Safely design close to a material’s failure point, an engineer must be able to define when and where failure will occur. However, determining the point and mode of failure requires an accurate characterization of mechanical properties. Unfortunately, while this type of data is readily available for most isotropic materials, it is only now being gathered for anisotropic composite materials [14]. In the recent years, computer simulation is emerging as an attractive approach to predict load distribution and failure of composite materials. Finite element commercial software packages have been introduced by which the design can be optimized to reduce material costs and production time. In these packages, ANSYS 9.0 is a successful computer aided engineering tool to analyze the behavior of composite materials.

2. METHODOLOGY

2.1 Obtaining the Coir and Jute Fibre Reinforced Wooden Boards

Coir, Jute and rubber wood composite boards in 3 different thicknesses using Phenol Formaldehyde as a matrix were obtained from a coir ply board manufacturer. Natural hard fibres such as coir and jute impregnated with phenolic resins were used for manufacturing these boards. While the MDF substitute boards were made only by jute and coir bonded by phenolic resin, the coir ply boards were manufactured with jute, coir & rubber wood waste veneers inside. A very thin layer of jute fibres impregnated with phenolic resin was overlayed as face veneer for improved aesthetics and to give a wood like smoother finish. The basic process involved in making coir ply comprises forming non-woven mats of the coir fibre (with the fibres standing end-on to provide stiffness), spraying the mats with phenol formaldehyde resin, hot-pressing the sheets in a multi-daylight hydraulic press with a heating system and later trimming to required sizes. The density of the ply can be changed with the pressure used. Depending on densities, the coir composite can be used like particle board, ply board, medium density fibre board or hard board [17].

2.2 Testing of the Composite Boards
2.2.1 Tensile Stress in Bending

The Maximum Tensile Stress and deflection for Bending for the composite materials were tested in Amsler’s Universal Wood Testing Machine. The machine was set to 400 kg range. The valve was closed. Zero adjustment was made on the dial. The dimensions of the cross section of the specimens were measured. The distance between the centre and supports was measured. The specimen was placed symmetrically on the supports. The load was applied slowly and continuously until the failure of specimen took place. The maximum load and the maximum deflection at failure were noted down.

2.3 DEVELOPMENT OF COMPUTATIONAL COMPOSITE MODELS

The computational composite models were developed with ANSYS 9.0 Finite Element software package. The developed models were deformed by applying load and the tensile stress and deflection were analysed.

2.3.1 ANSYS 9.0

The analysis with this CAE tool was carried out to determine the stress distribution in the layers of the composite material and the deformation of the material. The Finite Element Method is a series of numerical techniques used in solving Boundary value problems, Initial value problems and Eigen value problems. The basic process on finite elements is to divide the domain into pieces (or) elements, appropriates the equations governing the problem for each element as a function of selected values and solve for such values. Once this has been done, the element equations are referred in order to obtain appropriate solution variables of the problem. The factor such as density, young’s modulus, shear modulus, poison’s ratio and thickness and other dimensions were taken into considerations.

ANSYS is a complete FEA software package used by engineers worldwide in virtually all fields of engineering:

•Structural
•Thermal
•Fluid, including CFD (Computational Fluid Dynamics)
•Electrical/Electrostatics
•Electromagnetic

The reasons for choosing ANSYS for the analysis are as follows:

  • The various modules of ANSYS such as : ANSYS Multiphysics, ANSYS Mechanical, ANSYS Professional and ANSYS FLOTRAN

  • Solving a fracture mechanics problem involves performing a linear elastic or elastic-plastic static analysis and then using specialized post processing commands or macros to calculate desired fracture parameters

ANSYS allows us to model composite materials with specialized elements called layered elements. Once if it would be built a model using these elements, it could be done any structural analysis (including nonlinearities such as large deflection and stress stiffening).

2.3.2 Modeling Composites

Composites are somewhat more difficult to model than an isotropic material such as iron or steel. It is needed to take special care in defining the properties and orientations of the various layers since each layer may have different orthotropic material properties. In this section, it would be concentrated on the following aspects of building a composite model:

•Choosing the proper element type
•Defining the layered configuration
•Specifying failure criteria
•Following modeling and post processing guidelines

2.3.3 Development of Theoretical Model

In this work, five models were developed for analyses of the composite boards. They were constructed with the following configuration, and they were arranged one by one.

Model 1 (M1): 3 Layers (2 Phenolic Coir 1 Wood)
Model 2 (M2): 5 Layers (2 Phenolic Coir 1 Wood 2 Phenolic Jute)
Model 3 (M3): 5 Layers (3 Phenolic Coir 2 Wood)
Model 4 (M4): 7 Layers (4 Phenolic Coir 3Wood)
Model 5 (M5): 7 Layers (3 Phenolic Coir 2 Wood 2 Phenolic Jute)

The following Table 2.1 shows the thickness of the individual layers and also the total thickness of the models.

The Models M1, M3 and M5 were constructed with respect to the obtained composite boards’ layer configuration. The other two models M2 and M4 were developed with the new layer configuration which was included with the thin Phenolic Jute layers.

The following Table 2.2 shows the required input data which were fed to construct the layer. These specifications would be used by the software package to calculate the mechanical behavior of the models while they were deformed by applied loads.

The coir and Jute nonwovens which were impregnated with Phenolic resin were considered as isotropic materials. Because of the different mechanical properties with the grain direction, wood is considered as orthotropic material.

3. RESULTS AND DISCUSSIONS

The obtained three types of composite boards were tested in Amsler’s Universal Wood Testing Machine for tensile stress in bending. The load range was set in 0 – 4000 N. The boards were deformed and the tensile stress was calculated. The density and the void percentage of the boards were also calculated by using the formulae which are noted in section 2. In ANSYS software package, five models were developed as shown in the Table 2.1. Among them, three models were developed with the configuration of the obtained boards and two models were developed with new layer combinations which were included with thin layers of Phenolic Jute. Those five models were deformed by applied load and they were analyzed with the ANSYS software. The obtained results were compared with real values.

3.1 PROPERTIES OF COIR REINFORCED WOODEN COMPOSITE BOARDS

3.1.1 Thickness of the Boards

The composite were obtained in three different thicknesses. The following Table 3.1 shows the layer particulars of the boards.



3.1.2 Bending Properties of the Developed Composite Materials

The tensile stress and deflection values of the composite boards which were tested in Amsler’s Universal Wood Testing Machine are shown in Table 3.2.

In the Table 3.2 it is clearly noted that the tensile stress is increasing with the thickness and the deflection is reducing. But the tensile stress for the Board 3 is tremendously increasing. The deflection is lower than the other boards and the tensile stress in bending is directly related with the deflection. The Boards 1 and 2 are thin materials compared with the Board 3. They have one and two layers of wood. So the samples are flexible and free to bend. B3 consists three thick layers of wood and the young’s modulus value of the wood is around 16 GPa. Hence the B3 is so stiff and will not bend easily. So it can withstand for heavy loads for small deflection.

3.1.3 Density of the Developed Composite Boards

The actual and theoretical densities and the void percentage of the composite boards were calculated by using the formula which is given in section 2. The values are shown in Table 3.3.

In the obtained Boards, the density is not uniform and there is very large difference with the theoretical values. The void percentage is more than 35% in all boards. This infers that the materials were not properly impregnated into the resin. The densities of all the materials used in the boards are above 1.2 g/cc including the resin and the density of the board should be come at least 1.2 g/cc. With this improved density the void percentage would be 15. This void difference leads to the poor bondage with wood and the fibres which inturn affects the strength values [19]. If this fault will be eliminated the strength will be increased tremendously.
From the above discussion, it is known that the composite boards are not properly reinforced by the fibres.

3.2 Evaluation of Computational models with Ansys9.0

Five models were developed with the different thicknesses in ANSYS 9.0 software package. The layer configurations are discussed in section 2. The models were deformed by applied load. The tensile stress and deflection are shown in Table 3.4.

The same trend is followed in the developed models also that is the tensile stress is gradually increasing with the increasing thickness. But in the deflection values, the first thing is that the deflection is increasing with the thickness. Also the above values are retabulated into two different sets as shown in Table 3.5, with respect to their layer configuration such as wood and jute.

Set 1 is tabulated as the models which are developed according with the obtained boards. They consist only with Phenolic Coir and the Wood. They are M1, M3 and M5.

The second set of two new models consist the Phenolic Jute with coir and wood. They are M2 and M4. It is shown that the deflection values of the first set are higher than the second set.

In the above Table, the deflection of the models M3 and M5 are higher than the models M2 and M4.

Before coming to analyze the Table 3.5, it has to be clear that the incomparable difference of the tensile stress values of the real materials and the developed models. The values which are given in the Table 3.4 could not be compared with the values given in Table 3.2. The following points might be considered for coming to the conclusion.

First thing is that the natural materials are not homogeneous. It could not be got the materials with the same quality all over the regions which are produced and the properties will be changed region to region and season to season. But ANSYS 9.0 will consider that the materials are homogeneous.

The second thing is that the input data values for the individual layers which were given to construct the model were taken only from the literatures. The individual layer properties like Phenolic Coir and wood were not tested.

The role of the resin with the wood is only for surface bonding and the resin will not enter into the wood. In the Coir nonwoven material the resin plays a vital role. But it is found in Table 3.3 that the void percentage is more than 35%. It is an important criterion for the lower mechanical behavior of the boards. As already discussed, the composite boards are not properly reinforced by the fibres. The stiffness and strength of those boards are only because of the wooden material. The variation in the thickness of the layers of the obtained boards and discontinuation in wooden layers is also another important criterion for the lower tensile stress in bending.

But in ANSYS 9.0 software package, the above said drawbacks were not considered. It is considered that all the layers are homogeneous and they are tightly packed. The layers are properly meshed. The meshing transfers the load applied in accordance with the layer particulars. So the values obtained from the ANSYS 9.0 are purely theoretical values.

The most important thing which should be considered is the testing method of the models. In the Amsler’s Wood Testing Machine, the samples were simply placed on the supports and they were subjected to bend. So the freedom to bend is more for the samples. They deflect up to the maximum limit. That’s why the deflection values are so high than the developed models. But in ANSYS 9.0, the edges of the models were gripped firmly and they were subjected to deform. So, only the elongation of the models was happened and they were not bent.

Hence, the values of the obtained boards and developed model could not be compared. But there a good agreement is shown that the tensile stress values are increasing with thickness and the material configurations. With this agreement, it could be correlated the values with the real boards. Even though there is a vast difference in the stress values, the results obtained from the ANSYS 9.0 are only in accordance with the individual layer configurations which were fed by us. Hence, it could be considered that the values might be used to modify the real boards.

In the analysis of the Table 3.4, the deflection is increasing with the thickness. As discussed before, the models were gripped firmly and they were subjected to bent. So the layers are elongated up to their limit. Because of this reason the models were not deflected much as the real models. The maximum deflection is only 8 mm. But in real boards, the flexibility is more for thin boards and they were bent up to 36 mm.

The deflecting behavior is divided into two sets. One is with the configuration of the real boards and the other set is newly designed models. It is seen that in the first set, the deflection is increasing with the thickness and in second set, they are decreasing. In the first set, the materials used are Phenolic Coir and Wood. The young’s modulus of the Phenolic Coir is only 4.3 GPa. The modulus value of the wood is so high up to 16 GPa in grain direction. But there is a drawback with the wood is that the modulus value is only 1 GPa at perpendicular to the grain direction. This difference was considered in the developed models of the first set.

But in Set 2, one wooden layer was eliminated and the Phenolic Jute layers were included. The modulus value of the jute is up to 40 GPa, and the modulus value of Phenolic Jute was given as 7.5 GPa. The modulus value is higher than Phenolic Coir. The elongation of the Coir is up to 40%. But the elongation for Jute is only 1.5%. The introduction of the Phenolic Jute layers shows very good improvement in tensile stress values. With this usage of jute layers, one wooden layer could be eliminated.

Compared with Model 2, the thickness of the Phenolic Jute used in Model 4 is higher. The stiffness of the Model is automatically raised. This is the reason for the reduced deflection with the increasing thickness in Set 2.

Figure 3.1 to 3.10 show the deformation details of the models as obtained with the ANSYS 9.0. The Figures show the bending behavior of the models. The distribution of the stress is shown by different colours. The value of the stress is matched with colour on the layers of the model. Below the model the stress scale is given.