1. Introduction

A composite can be defined as a macroscopic combination of two or more structural materials which are insoluble with each other and having different physical and chemical properties. The composite material is manufactured and preferred for many reasons, some being for their strength, light weight, inexpensiveness, etc when compared to traditional materials. Hybrid composites are the fiber reinforced composites made by combining more than two different types of fiber.

Numerous studies have been made experimentally and analytically on hybrid composites. Gergely Czél, Meisam Jalalvand and Michael R. Wisnom [1] proposed elimination of stress concentrations in tensile and compressive testing of unidirectional carbon and epoxy composites. R. Murugan, R. Ramesh and K. Padmanabhan [2] investigated static and dynamic mechanical properties of carbon/epoxy-glass/ epoxy hybrid laminates. K Anand Babu and Dr MD Abid Ali [3] focused his study on the finite element analysis of Glass/Epoxy composite laminate. Aditya Kumar Akshay Agrawal, Ranjan Ghadai and Kanak Kalita [4] conducted his research work in Ansys APDL for the analysis of stress concentration in isotropic and orthotropic laminates. K.Krishnamoorthy and T.Sasikumar [5] carried out his research in predicting the deformation of glass epoxy composite laminates in Ansys and compared it with the experimental values obtained from UTM.

From the literature review, it can be noted that study has been focused on pure laminates and interlayer hybrid laminates. But study on reinforcement at the cut-out locations has not considered. So, the present research deals with the local reinforcements of carbon fibre at the cut out locations and on the orientation of fibre directions on the strength of the material.

2. FEA Analysis

The modelling of the composite tensile test specimens was done in Abaqus CAE software. The models considered for analysis were pure Glass-Epoxy and hybrid Glass-Carbon laminates with orientations of zero degree, ninety degree and forty five degree to the loading directions.

The following are the steps to be followed to model the specimen in Abaqus.

Ÿ Create the part with required dimensions

Ÿ Create the material and feed in the mechanical properties of the material

Ÿ Create composite lay-up

Ÿ Mesh the part

Ÿ Apply boundary conditions and analyse the part

2.1. Tensile Specimen Dimensions

The tensile specimens were modelled according to the ASTM D 3039/ D 3039M standards. The dimensions are given in the table 1 below.

Table 1. Specimen Dimensions

2.2. Material Properties

The material properties of pure glass laminate and glass carbon hybrid laminate are given in the below table 2.

Table 2. Material properties

2.3. Modelling in Abaqus CAE

Figure 1(a) shows the part of zero degree tensile specimen. Figure 1(b) shows adding of the material properties of the zero degree tensile specimens. Figure 1(c) shows the tensile specimen after adding the boundary conditions. Figure 1(d) shows the tensile specimen after meshing.

Figure 1. (a) Creating the part (b) Creating the material (c) Applying boundary conditions (d) Meshing the part

Figure 2 shows the composite layup. It refers to the orientation of the fibres to the loading direction. In figure 2, the composite layup is shown for zero degree tensile specimens. Similarly, ninety degree and forty five degree specimens can be simulated.

Figure 2. Composite layup

Boundary condition that is applied to the specimens is fixed at one end and at the other end the part was loaded with the ultimate load the specimen can withstand. The peak loads for various specimens are given in the table 3.

Table 3. Peak Load of various specimens

3. Results

The maximum in-plane principal stresses were obtained from Abaqus for different specimens. Figure 3 shows the maximum in-plane principal stress for zero degree only glass specimen.

Figure 3. Maximum in-plane principal stress for 00 only glass specimen

Similarly maximum in-plane principal stresses for ninety degree and forty five degree specimens were obtained. The summary of the tensile testing in Abaqus is shown in table 4.

Table 4. Summary of test results

4. Conclusions

The UTS obtained from the Abaqus is compared in the below table 5 for various tensile specimens.

Table 5. UTS for zero degree specimens

Ÿ Only glass laminate has UTS of 436.1 N/mm² while carbon insert glass laminate has UTS of 520 N/mm² which is 19% higher.

Ÿ Only glass laminate with round hole of 6mm dia has UTS of 308 N/mm² while carbon inserted glass laminate has UTS of 360 N/mm² which is 17% higher.

Ÿ Only glass laminate with square hole of 6mm at the centre has UTS of 278.9 N/mm² while hybrid laminate has UTS of 329.6 N/mm² which is 18% higher.

Ÿ Only glass laminate with rhombus shaped hole has UTS of 284.5 N/m² while hybrid glass carbon laminate has UTS of 325.9 N/mm² which is again 18% higher.

Similar comparison can be made for ninety degree and forty five degree specimens which shows an average of 18% increase in UTS with the carbon fibre insert at the cut-out locations.

So, it can be concluded that local reinforcement of carbon fibre at the cut-out locations can be made which increases the strength of the laminate significantly while the weight of the laminate remains same.

ACKNOWLEDGEMENTS

Foremost, I would like to express my deepest gratitude to my guide Mr Mahendra M A, Assistant Prof. Department of Aeronautical Engineering, NMIT, Bangalore, for the continuous support to my research, for his patience, motivation, enthusiasm, and immense knowledge. His guidance helped me in all the time of research.

Apart from my guide, I would like to thank our PG coordinator Dr. Desai Gowda H S, Prof. Department of Mechanical Engineering, NMIT for his kind support.

I am immensely grateful to Dr. P G Mukunda, Prof. Department of Mechanical Engineering, NMIT for sharing his pearls of wisdom with me during the course of this research.

I express my sincere gratitude to Dr. Kiran Aithal S, Professor, Department of Mechanical Engineering, NMIT Bangalore, for his support during the course of this research.

I am privileged to thank Dr. H.C.Nagaraj, Principal, NMIT, Bangalore, for his support during the course of this project work.

Lastly I would like to thank my parents, friends and staff of Mechanical Engineering and Aeronautical Engineering Department of NMIT, Bangalore for their constant support in completing this research.