Introduction to composites
When two or more materials are combined on a macroscopic scale to make a third material, the resulting material is called as “composite material”. If the materials are combined on a macroscopic scale, the naked eye can identify the components of composite materials. If we design it properly the properties of composite material are far better compared with the properties of its components or constituents. Composite materials uncovers material that is unique in relation to all as relatable to point of heterogeneous materials.
The strong fibres continuous or discontinuous fibres which are covered by a material known as matrixes (acts as a binding material) is being embedded in composites. The matrix solidly holds those fibres and further more will transmit load to the fibres. If we design it properly the properties of composite materials that can be improved are strength, stiffness, corrosion resistance, weight, fatigue life, thermal insulation, etc.
Practically at the same time, all properties cannot be improved and there will be no such requirement. The purpose of creating composite material is that, it should satisfy its design requirements. If we design a composite material in a well defined manner, than the property of composite material is far better than the property of its components or constituents.
Fibers and Matrix
While manufacturing any composite material the bond is developed between fiber and matrix.The mechanical properties depends on manufacturing.
Fibers
The fibers consist of millions of strands, each of these strands having diameter ranging from 4 to 18 micrometers.
The fibers may be:
- Long fibers, available in form of sheets of certain feet, they are cut to required size during casting time.
- Short/small fibers are available in length of several centimeters or several millimeters, for injection molding they are more suitable.
Types of Fibers:
- Glass fiber
- Polyester
- Carbon fiber
- Aramid
- Boron fiber
The glass fibers are usually generated by stretching heaten glass (silicon + sodium carbonate: T > 1000oC ) through a small orifices which consists of plate made up of copper alloy.
The various fiber forms are as follows:
- Uni-dimensional: Fibers are oriented only in one direction.
- Bi-dimensional: Fibers are oriented in both the direction.
- Tri-dimensional: Fibers which will be oriented in many directions, more than two directions.
Matrix
Matrix is just a binding material to hold the fibers stiff enough and to transfer the load coming over matrix to fibers.
Types of matrix forms:
- Mineral matrix: these matrix consists of various types of minerals like magnesium, phosphorus and suitable for relatively high temperature.
- Polymeric matrix: these matrix pocess thermoplastic resins.
- Metal matrix: they pocess two constituents – a metal and another material.
- Ceramic matrix: these involve ceramic particles embedded in them.
For our study the polymeric matrix i.e., the epoxy which is used is LY556 (Aradalite) and HY951 (Aradur).
Application of Composite Materials
The composite materials have wide range of applications in various field of engineering and technologies a few are listed below:
Civil Engineering
- Composite is used to cast the concrete moulds.
- Composite materials are used in manufacture of septic tanks and public toilets.
- They are used to strengthen or retrofit the damaged structural components (beams, columns) damaged during seismic and fire hazard.
- They are used to make partition doors, windows, furniture and bathroom materials.
- They are used to build domes, chimneys and shells.
- They are used to manufacture hydraulic turbines.
Electrical and Electronics
- Top casing of television, AC and antennas.
- They are used to produce stem and blades of wind turbine
- Support for circuit breakers, printed circuits and insulation for electric construction.
Mechanical and Automobile
- They are used to make crank, shafts, bearings and helmets.
- All components of passenger aircrafts, helicopter body and blades.
- Most widely used for railway bodies, suspension arm, chassis and railing
- The body of bus, trucks and cars are made using composite material which requires high stiffness.
Military and defense:
- They are used to produce bullet proof jackets, helmets.
- They are used to manufacture of tanks, aircrafts, submarines and naval ships
- Composite materials are used to make low weight cruise and nuclear missiles
Objectives
- To study buckling behaviour for Uni- Directional angle ply, glass-epoxy laminated composite plate specimens and its influence by fibre orientation and aspect ratio which are examined and determined experimentally.
- To carry out FEM analysis of the buckling of laminated composite plate in ANSYS workbench and comparing the FEM results with experimental results and to obtains the percentage error.
- To study the buckling behaviour of glass epoxy, cross ply uni-directional, laminated composite plate specimen and its influence by fibre orientation and aspect ratio which are examined and determined experimentally.
- To carry out numerical analysis of laminated composite plate in ANSYS workbench 19 and comparing the numerical results with experimental results and to obtaining a percentage error.
- Comparative study of angle ply and cross ply.
Methodology
- Calculation of material required for preparation of specimen.
- Testing of specimen of various ply orientation and aspect ratio.
- Numerical study is carried out in FEM software ANSYS for various parameters.
- The behaviour of cross ply orientation and aspect ratio will be studied.
- To investigate the accuracy of experimental and numerical study.
- Comparing both results and finding out the percentage error.
Organization of Thesis
The thesis involves following chapters:
Chapter 1 states introductory part of composite material, type of composite materials and its application in various engineering sectors.
Chapter 2 states the literature study carried out pertaining to the present thesis from various journal papers and books.
Chapter 3 states the methodology involved in fabrication of laminated composite plate, computation of mechanical property of laminate and also to calculate material quantity to prepare a laminated specimen.
Chapter 4 states buckling test of laminated plate using a compression testing machine 10 ton capacity.
Chapter 5 states numerical analysis of laminated composite plate using finite element software ANSYS workbench.
Chapter 6 states the discussion of results which are obtained after carrying out experimental and finite element study for varying aspect ratio, ply orientation and discussion based on result obtained.
Chapter 7 states the conclusion of results obtained and future work to be carried out for the present thesis work.
Literature Review
Dr. Prathap Kumar M., Dr. Prema Kumar W P [1] had carried out buckling analysis on rectangular plates with and without cutouts. It was observed that critical buckling stress for finite element analysis was more compared to experimental study. The properties of materials were given by the supplier and those mechanical properties were adopted for analysis. The value was maximum for 0o orientation and minimum for 45o fabric orientation. The plates with holes had greater impact on buckling of laminated specimens. Based on the study carried out buckling stress value was comparatively more for 0o orientation. The plate having circular holes yielded more compared to plate with square and rectangular holes.
Jayaram Mohanty, Shishir Kr. Sahu [2] studied both the finite element study and experimental behavior for single and many splited layers of glass/epoxy woven clamped free edges. It was seen that both experimental and finite element exhibited a good relativity between them. The aspect ratio, number of composite layers and fiber degree placing had a lot of influence on buckling behavior of laminated plates. The buckling load decreased as fiber orientation was increased from 0ୈ to 30ୈ . It was also found that as the a/b ratio went on increasing the critical buckling phenomenon of single delaminated composite decreased.
H Ersen Balcioglu, Mehmet Aktas [3] carried out investigation on effect of delaminated shape and size of lateral buckling of E-glass epoxy composite. Six delaminated shapes were obtained changing aspect ratio of 0.50, 0.67, 0.75, 1.33, 1.67 and 2.00.The study exhibited a minimal error. It was found that the 4th and 5th layer was sliced apart. It was also seen that with reduction in cross-section of composite the buckling load was also found decreasing.
Yeliz Pekbey, Onur Sayman [4] they studied the compression test on epoxy glass laminate and comparison of result with finite element software ANSYS (version6.1). It was found that strength increased considerably as a/b ratio went on increasing. The buckling strength resistivity was found to be more for 0ୈ ply orientation rather than other ply orientations.
Puneeth B M, M Mohan Kumar, M Nagabhushana [5] studied how the buckling affected the property of woven glass epoxy laminate, by both conducting compression test and by using finite element software – MSC Nastran. At first the test study was carried out on aluminum metallic plate and was compared with fem results for the sake of validation, later the glass epoxy lamina was studied for various lengths to thickness ratio, its orientation and aspect ratios.
The fiber orientation had greater influence on buckling of composite. The buckling value was found to be uniform when the aspect value was changed from1.0 to 1.7. The fabric orientation having 0ୈ stacking processed greater buckling strength compared to that of a 45ୈ fabric orientation.
Husain Mehdi, Anil Kumar, Arshad Mahmood, Manoj Saini [6] carried out the evaluation of mechanical properties of GFRP, Nylon, GFRP- aluminum and also Nylon- aluminum. Based on the study result carried out it was seen that the GFRP being placed between two layer of aluminum processed greater strength and high ductility value.
Stephen W. Tsai,Daniel Gay [7] the text book on “Composite materials design and application” have explained the importance of composite material in mere future, its application and manufacturing process. They have explained the effect of ply orientation and aspect ratios, the computation of mechanical properties of laminated composite plate including the Tsai-Hill failure criterion.
In this paper the glass epoxy laminated composite plates are prepared by hand lay- up technique. By using a simple formulation we find a poison‟s ratio, young‟s modulus and shear modulus further the investigation is carried out for dynamic analysis, transverse and longitudinal vibration by testing . for a various ply orientation and volume fraction and this can be inspected by theoretical analysis.
In this case the numerical analysis of laminated composite plate for a buckling response of glass epoxy.and boundary condition are clamped and unclamped sides of the plate with a ply orientation and aspect ratio. The modelling, meshing and analysis is carried out in ANSYS 14.5 APDL software . the different holes are modelled such as square, rectangular and circular and analysed by applying uniaxial compression load the maximum load that the plate can bear before can be examined.
In this study the experimental on laminated composite plate for a different cut-out shapes and to examine the effect of deflection and stress of angle ply and cross ply with a various boundary conditions, aspect ratio of 1 and 2 then investigating the deflection and stresses results with a numerical analysis ANSYS software. Thus a effect of amplitude results for square hole and circular hole with aspect ratio will be determined.
In this paper, the composite laminate of 150mmx50mmx3mm are prepared and buckling testing of specimen is done for clamped free condition for various cut-outs such as rectangle, circular and elliptical shape and investigated by FEM software ANSYS and obtaining percentage error.
Outcomes of literature survey:
- From the literature reviews studied we came to know that many of them carried out study using ANSYS, NASTRAN software.
- The material properties for fibers and resin were resolved either from supplier’s data or from reference case study.
- The effect of fabric orientation and aspect ratio had greater influence on buckling behavior of composite lamina.
Fabrication of Laminated Composite Plates
Casting & Molding of Laminated Composite Plate
The laminated composite plates may be casted either by using hand layup technique or Spraying/vacuum technique. The hand layup technique is most widely used and is used for our current study also.
Hand layup Technique
The contact mould is an open mould (A3 sheet may be used), the fiber layers are placed one over the other and each layer is impregnated with resin. The layers are compacted by using a roller so as to remove any entrapped air bubbles between fiber layers. Once all layers are placed a heavy load is placed over the casted sample and allowed to cure for duration of 24 hours.
Spraying Technique
It is an extension of hand layup technique. This process consists of a spraying machine which is allowed to spray epoxy resin under high pressure. The fibers are also sprayed in form of chopped minute fibers. Matrix and fibers may be sprayed simultaneously or separately.
A gel is applied within the mould surface so that we can easily separate the laminated composite plate from mould after casting. Curing is done either at room temperature or elevated temperature.
For our present study the hand layup technique was adopted. This method was adopted because it was simple and involved less labor work. The percentage of fiber and matrix 60:40 by weight. The materials used in fabrication of laminated composite plate:
- E-glass fibers (200GSM)
- Epoxy (LY556 aradalite)
- Hardener (HY 951)
The surface was cleaned properly with thinner and made sure was flat surface. A plastic sheet (A3) was placed on the cleaned flat floor and the edges were fixed by using paper tape. The glass fibers were cut to a size of 230 mm x 230 mm, in case ply orientations with 30o, 45o& 60o the glass fibers were cut to the required orientation using a protector and setsquares. The aradalite and the hardener were mixed thoroughly in a mug, by using a brush the mixed solvent was applied on the open mould.
The first layer of glass fiber was laid on the open mould applied with solvent and was rolled by using a roller so as to remove any entrapped air bubbles. The solvent was applied again over the first layer and the next layer of glass fiber was placed over the other and again rolled using a roller, it was seen that the fiber orientation was taken care while placing the glass fibers one over another.
The process was continued till the last glass fiber layer was laid and the top of the last layer was applied with the solvent and an transparent paper was placed over the top of upper most layer and was rolled using a roller and some dead weight was placed over it and allowed to curing for a period of minimum 48 hours, before cut to the exact required dimension.
