Seminar On Laminated Composites

University Visvesvaraya College of Engineering

A seminar on: Laminated Composites

Presented by: Praveengouda Patil

Contents 1) Introduction to composites and classification 2) Introduction to Laminated composites 3) Characteristics of Laminated composites 4) Design and failure analysis of laminated composites 5) Fabrication methods 6) Applications of Laminated Composites

Laminated Composites: Let us begin with understanding what a composite is and its classification. Composite: It’s a homogenous material obtained by the synthetic assembly of two or more materials. This will have a selected filler or re inforcing element and a matrix binder bounded together to obtain the desired characteristics.

The classification of composites based on the Reinforcement used:

Laminates: A composite material made up of a single ply or layers or a series of layers with each layer consisting of a Reinforcing fiber imbedded in a matrix. Each layer is oriented in a predetermined manner in order to maximize the properties of the laminate. Some common examples of the laminated composites: Plywood – made up of wood veneer laminas. Safety glass – Made of glass and resin binders Kevlar -49 --- used in Tires manufacturing, Phenolic paper grades --used in for rigid electrical insulation for items such as panels, boards, insulating sleeves etc. Polyester glass etc.

Characteristics of Laminates 1) 2) 3) 4)

They are rigid with high strength to wait ratio. Good Electrical resistance Resistance to chemicals and weather. Good directional properties

Classification of Laminates Based on the orientation of the fibers in the lamina the Laminated composites are classified into 5 types as follows: 1) Unidirectional Laminates The fibers are parallel to the direction of the load application and are oriented in a single direction. Unidirectional layers are as shown in Figure .

The advantages of unidirectional layers are: 1) They have high rigidity (maximum number of fibers in one direction). 2) The ply can be used to wrap over long distance. Then the load transmission Of the fibers is continuous over large distance. 3) They have less waste.

The disadvantages of unidirectional layers are 1) The time for wrapping is long. 2) One cannot cover complex shapes using wrapping. Example: Carbon/epoxy unidirectional: Width 300 or 1000 mm, preimpregnated with resin; usable over a few years when stored at cold temperature (–18C). 2) Bidirectional laminates The fibers are arranged in two directions in the matrix of each lamina. And also The fibers can be oriented in different directions in different laminas.

3) Multidirectional laminates The fibers can be oriented in any direction in the lamina. The fibers can be arranged in different directions in different laminas.

4) Woven Fabric Laminates The fibers in these laminates are in the form of textile fabric produced by interlacing strands at more or less equal to right angles

Advantages of Woven Fabric laminate 1) These provide properties that are more balanced in the 0 to 90 degrees directions than unidirectional laminates 2) The fabrication time is less compared to that of multidirectional laminates The disadvantage with woven fabric laminate is that they have low tensile strength and modulus.

5) Interplay hybrid laminates : These are made of separate layers of low elongation fibers and high elongation fibers Example for high elongation fibers – E-Glass or Kevlar-49 Example for low elongation fibers –high modulus carbon fiber.

Design of a Laminated Composite Design of a laminated composite involves constraints on optimizing. The constraining factors are listed as follows 1) Cost, The cost of raw materials and the fabrication costs need to be kept in mind. 2) Mass, it’s an important factor as related to aerospace and automobile industry to reduce energy cost. 3) Stiffness (To limit deformations) related to aircraft skins to limit buckling. 4) Thermal and Moisture expansion coefficients as related to space antennas to maintain dimensional stability. Some of the mechanical Design issues are discussed below: 1) Environmental effects: The temperature & humidity: plays a vital role in the life of the composite. These may lesser the adhesion of the fiber-matrix interface, such as between glass & epoxy. Epoxy matrices softer at high temperature effecting properties. Effect of moisture absorption to flexural modulators is as shown below. 2) Interlaminar stresses: Developed due to the mismatch of elastic module & angle between the layers of laminated composites. These are developed between the layers. These stresses can cause edge delamination of the b/w the layers thus reducing the life of the laminated structure. 3) Impact resistance: Impact reduces the strength of the laminates & also initiates de-lamination in composites. And also it’s difficult to identify the damages visually. The impact resistance depends on: interlaminar strength, stacking sequence & nature of the impact, such as velocity, mass & size of the impacting object. 4) Fracture resistance: Mechanics of fracture is not simple due to first: in composites cracks developed in a composite can grow in the form of fiber breaks, matrix & debonding between layers. Second: no single critical stress intensity factors & strain energy release rates determine the fracture mechanics process – still as open field.

5) Fatigue resistance: The structures subjected to repeated cycles of landing reduce the life of the composite. The factors influencing fatigue properties are: the laminate stacking, fiber & matrix properties, fiber volume fraction, interfacial bonding, etc.

Importance of Ply Orientation One of the fundamental advantages of laminates is their ability to adapt and control the orientation of fibers so that the material can best resist loadings. It is therefore important to know how the plies contribute to the laminate resistance, taking into account their relative orientation with respect to the loading direction.

Loaded than previously.

Considering the working mode of the plies as discussed in the previous section, the most frequently used orientations are represented as in Figure 5.10.The direction called “0” corresponds to either the main loading direction, a preferred direction of the piece under consideration, or the axis of the chosen coordinates. Note: One also finds in real applications plies with orientations 30and 60

Figure 5.6 Effect of Ply Orientation

Fabrication of Laminated Composites 1) Open Molding or wet lay process : a) Creation of a master model (pattern). From which molds are created. b) Master model is waxed with a release wax for easy removal of the composite. c) Applying tooling gel coat on the surface of the master model. The gel coat is allowed to gel before applying any laminated material. d) After the gel coat is ready a spray gun is used to laminate short fiber composites. Used in: bath tubs, boat ship hulls, aerospace applications.

Some other processes used in the fabrication of laminates are included below : 1) Filament winding process: pressure vessels, pipes, rocket motor, castings, chem. Storage tanks, etc.., 2) RTM (resin transfer molding): used in helmets, doors, hockey sticks, bicycle frames, windmill blades, automotive parts, and aircrafts parts. 3) Pultrusion process : application : Beams, channels, tubes, grating systems flooring, walkways, handrails, ladders, light poles, bridges, etc.., Finishing Operations Cutting of Fabric and Trimming of Laminates Some components need a large number of fabric layers (many dozens, can be hundreds). For the small and medium series, it can be quite expensive to operate manually for following The form of a cut. Respect the orientation specified by the design. Minimizing waste. There is a tendency to produce a cut or a drape automatically with the following Characteristics: _ a programmed movement of the cutting machine _ a rapid cutting machine, such as an orient able vibrating cutting knife or a laser beam with the diameter of about 0.2 mm and a cutting speed varying from 15 to 40 meters/minute, depending on the power of the laser and the thickness of the part. Example: With a draping machine MAD Forest-Line (FRA), the draping is done in two steps by means of two distinct installations: _ a cutting machine that produces a roller to which the cut pieces are attached (cassettes) _ a depositing machine which uses the cassette of cut pieces to perform the draping. The two operations are shown schematically in Figure

Applications of laminated Composites 1) Laminated composites find their application in Aircraft , a schematic below shows the applications in detail:

Figure: shows the different parts of the Helicopter blade.

2) The most common applications are in making beams, channels, tubes, grating systems, flooring and equipment support, walkways and bridges, handrails, ladders, light poles, electrical enclosures

3) The structures typically made from Laminated composites include : helmets, doors, hockey sticks, bicycle frames, windmill blades, sports car bodies, automotive panels, and

aircraft parts. Some aircraft structures made by the RTM process include spars, bulkheads, control surface ribs and stiffeners, fairings, and spacer blocks.