Polymer and Metal Matrix Composites - Essay Example

POLYMER AND METAL MATRIX COMPOSITES Polymer and Metal Matrix Composites Introduction A material is described as a composite material if it is comprised of two or more constituents either in combination of phases or distinct phases. The materials are bonded along the interface of the composite. The constituents of the composite originate from separate ingredient materials which make up the composite. The two main basic components of a composite material are the reinforcement and the matrix. Classification of most composite material is done with respect to the matrix material. Based on the matrix material, composites can be classified into polymer matrix composites, metal matrix composites and ceramic matrix composites. Another nomenclature involves the use of reinforcement in classification where polymers may be classified into fibers (multifilament, monofilaments, short filaments and long filaments), skeletons or particles. Polymer matrix composites Polymer matrix composite comprises of carbon, glass or other high strength fibers bonded by a thermoset or thermoplastic resin. The materials resulting from this bond is stiff, very strong and is able to withstand corrosion. Among the inherent advantages especially to manufacturing and machining is that the PMC assume flat, sharply sculptured contours or curved surfaces with ease. The materials are also very cheap. PMC materials are used as an option to steel. Fiber As mentioned earlier, polymer materials are comprised of the fiber and the matrix, the main fuction of the matrix material is to surport and surrounds the reinforcement fiber. It also aids in maintaining the fiber in position. The reinforcement materials impacts special mechanical and physical properties to the matrix material. Due to the availability of different fiber and matrix materials, the material engineer can select different materials for fiber and the matrix thus enhance the resulting polymer composite material. Matrix Commercially available polymer matrix materials are also refereed to as resin solutions. They include vinyl ester, epoxy resin, polyester, phenolic, polypropylene, polyamide, among others. The most common fiber is the fiber glass; other mineral fibers are also used. Properties The strength of the composite polymer material depends upon the ratio of fiber and the matrix material. Generally as the fiber content increases the strength also increases. Some of physical properties of these materials are that there are orthotropic and not isotropic. This means that their strength depends on the direction of the application of the force. It has been found out that PMC stiffness depends upon the applied force and load. This is in contrast with metallic materials that are generally isotropic meaning that they have the same stiffness irrespective of the orientation of the applied force. Repeated shock, impacts and other cyclic stresses can cause the material to separate between two layers. This condition is called delamination. Composites have also be found to fail both at a macroscopic and microscopic scale, the material are subjected to composite buckling, which causes crushing of the material. The material can also fail in tension due to a pulling force. Other polymer composites have been found to be brittle and have limited strengths. The strength of the composite material depends upon individual material properties, the size and distribution of the fiber and the composite, the volume fraction of individual composite materials. The shape of the constituents' materials and the nature of the interface between the fiber and the matrix Among the inherent properties of polymer composites includes high strength and stiffness, high temperature stability as compared to their individual components, low density, high corrosion resistance and low surface wear. Polymer materials can be divided into two main categories, these include the short fiber reinforced polymer materials and continuous fiber reinforced polymer materials. Polymer matrix composite long fiber The long fiber polymer composite material belongs to the class of the polymer composite materials but differs from the short fiber in that its structure has long fibers oriented in a given direction depending on the forces they are exposed to. They consist of fiber filaments running along the length of the pellets. The resulting material exhibits high strength, stiffness and wear resistance. The material is more resistance to high temperatures. The most inherent advantages of this type of composite material is the ability of the material to be recycled and ability to resist tensile loads. This type of fiber is also refereed to as the continuous fiber reinforced material. It has a laminated or a layered structure and is available in different styles. Manufacturing methods Pultrusion process is one of the most common methods used to manufacture the long fibers. The process involves pulling of continuous fiber through a melted polymer. The process is carried out in a processing die. After the pulling the composite strands are cooled and then chopped to form pellets. The pultrusion method is typically different from the short fibers manufacturing process in that, for short fiber, chopped reinforcement fibers are melted with a plastic resign and convectional extrusion techniques used. A process referred to 'wet out' is used to ensure that the fibers are coated with the thermoplastic resin. This ensures that the resulting material is free from loose fibers. Length of fiber The standard length for the long fibers is 11 millimeters though the size varies from 6mm to 12 mm. This length allows the material to be processed in the standard injection molding equipment. Studies have shown that, stress transmission to the reinforcing fibers is more efficient when using long fibers. However, very long fibers are difficult to manufacture. Fiber material The convectional material for to manufacture long fiber composites is fiber glass, other materials that are commonly used include aramid fiber which resists wear, stainless steel which dissipates a lot of heat and carbon fiber which provide flexural modulus and reduce the weight of the composite. Properties Some of the inherent properties of long fiber composites are They offer good resistance to surface wears They Provide better impact resistance and have high rigidity at high temperature, typical test have reveled that long fiber composites have strength that are five times the short fiber at elevated temperatures. They have high resistance to creep (slow degradation of a material due to thermal and mechanical vibrations) The materials are able to retain the modulus even at elevated temperature Superior strength as compared to the short fibers High resistance to thermal degradation. There are able to resist high temperatures Metal Matrix Composite The metal matrix composite has at least two constituents, one of them being a metal and the other material may be a metal or another material. Ceramic or an organic compound are used in conjunction with the metals. When the polymer has three materials it is refereed to as a hybrid composite. Matrix The matrix for the MMC is a monolithic material to which the reinforcement is embedded. The matrix is usually lighter than the reinforcement. Some of the most common matrix materials used include, aluminum, titanium, magnesium, cobalt and cobalt-nickel Reinforcement The reinforcement material is embedded in the matrix. It helps in improving of the wear resistance and the structural property of the material. As the case of polymer composites, the MMC can be either discontinuous or continuous. Discontinuous reinforcement form the short fiber composite and are manufactured using processes such as forging, extrusion, rolling and other standard metal working techniques. Polycrystalline diamond tooling is commonly used and the fibers are highly isotropic. Continuous reinforcement leads to the formation of monofilament long fibers. The most commonly used materials are carbon fiber and silicone carbide. The resulting MMC is highly anisotropic. Methods of manufacture There are three main methods used to manufacture composite metals, these includes Solid state method Vapor deposition method Liquid state methods. (i)Solid state methods Powder blending and consolidation: this methods uses a discontinuous reinforcement material Mixed and bonded through compaction, degassing and thermo mechanical treatment with a powdered metal Foil diffusion: long fibers are sand witched with layers of a metal foil Liquid state methods Electroplating: the composite material is formed by electrolysis, Spray deposition: continuous fibers are spayed with molten metal Squeeze casting: molten metal is injected with fibers placed in it to form a given shape Reactive processing: a chemical reaction occurs with the reactants forming the matrix and the reinforcement fiber. Vapor deposition Physical vapor deposition: a thick cloud of metallic vapor coats the reinforcement fiber as it is passed through. Controlled unidirectional solidification: utilizes the principle that solidification of an alloy can results to a macrostructure with two phases, one in lamella and the other in fiber form Properties The main properties of MMC include: The resulting material has high strength and stiffness as compared to the individual materials The materials has low density The resulting material has high thermal and electrical conductivity High resistance to corrosion High resistance to wear The material has an adjustable thermal expansion coefficient. Question 1, Part 2 Manufacture of wind vane blades. Introduction Wind energy is one of the fastest upcoming technologies; wind energy can be used to provide energy by harnessing the energy of the moving air masses. The main parts of a wind turbine system is The blade: the part that is rotated by the force of moving wind The roller bearing: the provide the axle for rotary motion The generator, rotated to produce electricity The turbine; turned by the wind energy The main engineering requirement for the formation of a wind vane blade include The wind vane turbine must be light and be made of a material with low density Must be made of materials which can withstand high force Must resist wear by Enviromental corrosion Must withstand high UV rays Must withstand high temperature Must have high strength and stiffness, to resist the axially imposed torque. The wind vane can be manufactured using the polymer composite long fiber material; the material used to manufacture it is a combination of the fiber glass of lengths 12 mm and a matrix made of polyethylene. The reasons for selecting the long fiber are They offer good resistance to surface wears Provide better impact resistance and have high rigidity at high temperature. They have high resistance to creep (slow degradation of a material due to thermal and mechanical vibrations) which are common in wind turbine systems. Superior strength as compared to the short fibers Question 2 Manufacturing process for wind turbine blade The method that can be used for the manufacture of the wind vane blade is the Pultrusion method. This method is used to form long fiber matrix composite material. Tooling The main tools used for the extrusion are tooling dies. These dies are cheaply availed and are produced by machining steel or are made from ceramic dies. When the material passes through the die, it initiates the cure reaction. The machine is configured that its speed corresponds to the curing time. The resign exits from the die after it is fully cured. The die must have high rigidity and high toughness. It must also be designed to international standards Diagram of the protrusion die; Source: (made in china. Com, 2009, Pultrusion Die. < http://www.made-in-china.com/showroom/yaocao/product-detailXMxmQEvzFaYu/China-Pultrusion-Die.html> ) Method of manufacture Pultrusion process: source :( Kalpakjian S.2001. Manufacturing Engineering and Technology. Forming and Shaping Plastics and Composite Materials. ) Pultrusion manufacturing process helps in the production of continuous length of many structural shapes. The main raw materials used in this process include a reinforcing fiber and a liquid resin mixture used with fillers, activities and resin Pultrusion involves the pulling of the materials instead of pushing. The pulling is done through a heated dies made of steel. The process involves the pulling of material s continuously to form fiber glass mat and fiberglass roving. During the process, the reinforcement are saturated with a resin mixture and this process is normally referred to as wet out The diagram below shows the schematic diagram for the pultrusion process Diagram 3: showing the pultrusion process (Pultrusion Industry Council. 2009. products & process: process description. [Online] Available at http://www.acmanet.org/pic/products/description.htm . Accessed 9 august 2009. ) Creels are used for positioning of reinforcements and feeding them to the guides. Proper positioning is necessary to ensure that the reinforcement is placed at it right position in the composite. The reinforcement is impregnated with a resign solution using a resin impregnator On leaving the impregnator the reinforcement which is coated with the resign passes through preformer which removes the excess resin and helps in shaping the material. The material then enters the die where thermosetting takes place. The heating energy is supplied by electrical power. The cured dies are then cut to the required size and shape References Made in china. Com, 2009, Pultrusion Die. [Online]. Available at < http://www.made-in-china.com/showroom/yaocao/product-detailXMxmQEvzFaYu/China-Pultrusion-Die.html> ) Pultrusion industry council. 2009. Products & Process: Process Description. [Online]. available at. http://www.acmanet.org/pic/products/description.htm . Accessed 16 august 2009. William, D. 2008. Materials science and Engineering, an introduction. New York Wiley and sons publishing Read More