1-Introduction to Polymer Composites

Polymer Composites P.E. 406

Polymer Composites

Contents Conventional Engineering Materials Introduction to Polymer Composites Classification of Polymer Composites Characteristics of Polymer Composites Applications of Polymer Composites 2

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Conventional Engineering Materials 3

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Conventional Engineering Materials  There are more than 60,000 materials available to engineers for the design and manufacturing of products for various applications.  Due to the wide choice of materials, today’s engineers are posed with a big challenge for the right selection of a material and the right selection of a manufacturing process for a particular application. 

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Broad Classification of Materials 

These materials, depending on their major characteristics (e.g., stiffness, strength, density, and melting temperature), can be broadly divided into four main categories:

1.Metals 2.Plastics 3.Ceramics 4.Composites 5

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Typical Properties of Some Engineering Materials

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Typical Properties of Some Engineering Materials

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Metals Dominating materials for structural uses  Provide the largest design and processing history  The common metals are iron, aluminum, copper, magnesium, zinc, lead, nickel, and titanium.  Through the principle of alloying, thousands of new metals are created. 

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Metals Metals are, in general, heavy as compared to plastics and composites.  Metals have high stiffness, strength, thermal stability, and thermal & electrical conductivity.  Due to their higher temperature resistance than plastics, they can be used for applications with higher service temperature requirements. 

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Plastics Most common engineering materials over the past two decades.  In the past 5 years, the production of plastics on a volume basis has exceeded steel production.  Due to their light weight, easy processability, and corrosion resistance, plastics are widely used for automobile parts, aerospace components, and consumer goods. 

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Plastics With the help of a manufacturing process, plastics can be formed into near-net-shape or net-shape parts.  They can provide high surface finish and therefore eliminate several machining operations.  This feature provides the production of lowcost parts. 

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Plastics Not used for high-temperature applications because of their poor thermal stability.  The operating temperature for plastics is less than 100°C. (Some plastics can take service temperature in the range of 100 to 200°C without a significant decrease in the performance)  Plastics have lower melting temperatures than metals and therefore they are easy to process. 

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Plastic Items

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Ceramics Have strong covalent bonds and therefore provide great thermal stability and high hardness.  Technically they are inorganic non-metallic materials which are formed by the action of heat  Ceramics have the highest melting points of engineering materials  Most rigid of all materials  Possess almost no ductility, so fail in brittle fashion 

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Ceramics Generally used for high-temperature and highwear applications and are resistant to most forms of chemical attack.  Require high-temperature for fabrication.  Difficult to machine  Require expensive cutting tools, such as carbide and diamond tools. 

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Ceramic Items 16

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Composites Historically they are old but in 1960 composites start capturing the attention of industries with the introduction of polymeric-based composites.  Common applications include: 

 automotive

components  sporting goods  aerospace parts  consumer goods  marine industries  oil industries 17

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Composites Increased awareness regarding product performance and increased competition in the global market for lightweight components fueled their growth.  Among all materials, composite materials have the potential to replace widely used steel and aluminum, and many times with better performance. 

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Composites 

Polymer composite components can save:  60

to 80% in component weight by replacing steel components  20 to 50% weight by replacing aluminum parts

Ø Ø Today, it appears that composites are the materials of choice for many engineering applications and Polymer-based Composites are important than all other types.  19

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COMPOSITES’  ITEMS

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COMPOSITES’  ITEMS

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Polymer Composites 22

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Composites - General Definition 

A composite material is made by combining two or more materials to give a unique combination of improved properties, such that each component retains its physical identity.  Composite

obey the “principle of combined action”, i.e; the mixture gives “averaged” properties.



The above definition is more general and can include metals alloys, plastic co-polymers, minerals, and wood.

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Polymer Composites Fiber-reinforced polymer composite materials differ from the above materials in that the constituent materials are different at the molecular level and are mechanically separable.  In bulk form, the constituent materials work together but remain in their original forms.  The final properties of composite materials are better than constituent material properties. 

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Composite Examples in Nature Wood is a composite of cellulose fibers in a matrix of natural glue called lignin.  Husks or straws mixed with clay for house building  The shell of snails and oysters  Human nails 

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Formation of Composite Materials The main concept of a composite is that it contains reinforcing material in a matrix material.  Typically, polymer composite material is formed by reinforcing fibers in a matrix resin. 

Ø The reinforcements can be fibers, particulates, or whiskers Ø The matrix materials can be metals, plastics, or ceramics.

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Formation of Composite Materials

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Formation of Composite Materials The reinforcements can be made from polymers, ceramics, and metals.  The fibers can be continuous, long, or short.  Composites made with a polymer matrix have become more common and are widely used in various industries.  They can be thermoset or thermoplastic resins. 

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Polymer Composites The reinforcing fiber or fabric provides strength and stiffness to the composite, whereas the matrix gives rigidity by transferring stress and environmental resistance.  Reinforcing fibers are found in different forms, from long continuous fibers to woven fabric to short chopped fibers and mat. 

 Each

configuration results in different properties.

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Continuous & Short Fiber Composites The properties strongly depend on the way the fibers are laid in the composite.  The important thing to remember about composites is that the fiber carries the load and its strength is greatest along the axis of the fiber.  Long continuous fibers in the direction of the load result in a composite with properties far exceeding the matrix resin itself. The same material chopped into short lengths yields lower properties than continuous fibers. 

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Continuous & Short Fiber Composites

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Continuous & Short Fiber Composites Depending on the type of application (structural or nonstructural) and manufacturing method, the fiber form is selected.  For structural applications, continuous fibers or long fibers are recommended; whereas for nonstructural applications, short fibers are recommended. 

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Functions of Fibers and Matrix Both reinforcements (fibers mostly) and matrix are complimentary to each other.  They use each other’s properties in such a manner that overall properties of the composites are improved. 

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Functions of Fibers To carry the load. In a structural composite, 70 to 90% of the load is carried by fibers.  To provide stiffness, strength, thermal stability, and other structural properties in the composites.  To provide electrical conductivity or insulation, depending on the type of fiber used. 

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Functions of Matrix The matrix material binds the fibers together and transfers the load to the fibers. It provides rigidity and shape to the structure.  The matrix isolates the fibers so that individual fibers can act separately. This stops or slows the propagation of a crack.  The matrix provides a good surface finish quality to the polymer composite. 

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Functions of Matrix The matrix provides protection to reinforcing fibers against chemical attack and mechanical damage (wear).  Depending on the matrix material selected, performance characteristics such as ductility, impact strength, etc. are also influenced. A ductile matrix will increase the toughness of the structure.  The failure mode is strongly affected by the type of matrix material used in the composite as well as its compatibility with the fiber. 

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Interface 

An interface is the surface formed by: a

common boundary of reinforcing fiber and supporting matrix that is in contact with each constituent  maintains the bond in between for the transfer of loads 

“An interface is the region of significantly changed chemical composition that constitutes the bond between the matrix and the reinforcement”.

Ø Ø It has physical and mechanical properties that are unique from those of the fiber or the P.E. 406 matrix. Polymer Composites

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Interphase “Geometrical surface of the classic fiber-matrix contact as well as the (transition) region of finite volume extending therefrom, wherein the chemical, physical and mechanical properties vary either continuously or in a stepwise manner between those of the bulk fiber and the matrix material.”  In other words, the interphase exists in some terminal point in the fiber, passes through the actual interface and enters the matrix, embracing all the volume altered during the consolidation or fabrication process from the original fiber and matrix materials. 

Ø Ø Interface is specific to each fiber-matrix P.E. 406 system. Polymer Composites

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Interface - Schematic Diagram

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Classification of Polymer Composites 40

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Matrix       

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Reinforcement       

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Reinforcement  

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Reinforcement  

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Reinforcement   

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Reinforcement           

"Whiskers" are very strong because they don't contain

defects, P.E. 406

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i.e., notch sensitivity is eliminated because there Polymer Composites

Reinforcement

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Reinforcement  

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Reinforcement

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Reinforcement   

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Reinforcement

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Reinforcement

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Reinforcement  

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Reinforcement

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Reinforcement

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Reinforcement

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Composite Benefits

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Summary Ø Composites are classified according to:  

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Composites enhance matrix properties:   

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--the matrix material (CMC, MMC, PMC) --the reinforcement geometry (particles, fibers, layers). --MMC: enhance σy, TS, creep performance --CMC: enhance Kc --PMC: enhance E, σy, TS, creep performance

Structural: 

--Based on build-up of sandwiches in layered form. 58

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Summary 

Particulate-reinforced:  

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--Elastic modulus can be estimated. --Properties are isotropic.

Fiber-reinforced: 

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--Elastic modulus and TS can be estimated along fiber direction. --Properties can be isotropic or anisotropic depending upon alignment.

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Characteristics of Polymer Composites 60

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Advantages of Composites Provide capabilities for part integration  Provide in-service monitoring or online process monitoring  They have a high specific stiffness (stiffnessto-density ratio). Composites offer the stiffness of steel at one fifth the weight and equal the stiffness of aluminum at one half the weight. 

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Advantages of Composites The specific strength (strength-to-density ratio) of a composite material is very high. Due to this, airplanes and automobiles move faster and with better fuel efficiency.  The fatigue strength (endurance limit) is much higher for composite materials. Steel and aluminum alloys exhibit good fatigue strength up to about 50% of their static strength. Unidirectional carbon/epoxy composites have good fatigue strength up to almost 90% of their static strength. 

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Advantages of Composites They offer high corrosion resistance.  Composite materials offer increased amounts of design flexibility. For example, the coefficient of thermal expansion (CTE) of composite structures can be made zero by selecting suitable materials and lay-up sequence. Because the CTE for composites is much lower than for metals, composite structures provide good dimensional stability.  Net-shape or near-net-shape parts & complex shapes can be produced 

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Advantages of Composites Composites offer good impact properties  Noise, vibration, and harshness (NVH) characteristics are better than metals.  Tailoring material properties to meet performance specifications can be achieved thus avoiding the over-design of products.  The cost of tooling required for composites processing is much lower 

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Drawbacks of Composites The materials cost for composite materials is very high compared to that of steel and aluminum. It is almost 5 to 20 times more than aluminum and steel on a weight basis.  The lack of high-volume production methods limits the widespread use of composite materials.  Lack of a database & design literature 

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Drawbacks of Composites The temperature resistance of composite parts depends on the temperature resistance of the matrix materials. Because a large proportion of composites uses polymer-based matrices, temperature resistance is limited by the plastics’ properties.  Composites absorb moisture, which affects the properties and dimensional stability of the composites. 

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Summary - Advantages/Disadvantages

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Applications of Polymer Composites 68

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Composites Markets The products fabricated by composites are stronger and lighter.  Broadly speaking, the composites market can be divided into the following industry categories: aerospace, automotive, construction, marine, corrosion resistant equipment, consumer products, appliance/business equipment, and others. 

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COMPOSITES MARKETS

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The Aerospace Industry Among the first industry to realize the benefits of composites  Airplanes, rockets, and missiles all fly higher, faster, and farther with the help of composites  The aerospace industry primarily uses carbon fiber composites because of their highperformance characteristics. 

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The Aerospace Industry 

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The hand lay-up technique is a common manufacturing method for the fabrication of aerospace parts; RTM and filament winding are also being used. Military aircrafts, such as the F-11, F-14, F-15, and F16, use composite materials to lower the weight of the structure. Typical mass reductions achieved for the above components are in the range of 20 to 35%. The mass saving in fighter planes increases the payload capacity as well as the missile range.

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Composite Components in Aircraft Applications

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COMPOSITE COMPONENTS IN  AIRCRAFT APPLICATIONS

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COMPOSITE COMPONENTS IN  AIRCRAFT APPLICATIONS

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COMPOSITE COMPONENTS IN AIRCRAFT APPLICATIONS

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COMPOSITE COMPONENTS IN  AIRCRAFT APPLICATIONS

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The Aerospace Industry The major reasons for the use of composite materials in spacecraft applications include weight savings as well as dimensional stability.  In low Earth orbit (LEO), where temperature variation is from –100 to +100°C, it is important to maintain dimensional stability in support structures.  Carbon epoxy composite laminates can be designed to give a zero coefficient of thermal expansion.  Passenger aircrafts such as the Boeing 747 and 767 use composite parts to lower the weight, 78 increase the payload, and increase the fuel P.E. 406 efficiency. Polymer Composites 

The Automotive Industry Composites are the “material of choice” in some applications of the automotive industry by delivering high-quality surface finish, styling details, and processing options.  Manufacturers are able to meet automotive requirements of cost, appearance, and performance utilizing composites. 

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The Automotive Industry Today, composite body panels have a successful track record in all categories — from exotic sports cars to passenger cars to small, medium, and heavy truck applications.  In 2000, the automotive industry used 318 million pounds of composites.  Because the automotive market is very costsensitive, carbon fiber composites are not yet accepted due to their higher material costs. Automotive composites utilize glass fibers as main reinforcements. 

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Average Use of Composites in Automobiles

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The Sporting Goods Industry Sports and recreation equipment suppliers are becoming major users of composite materials.  The growth in usage has been greatest in highperformance sporting goods (golf shafts, tennis rackets, snow skis, fishing rods, etc.)and racing boats.  These products are light in weight and provide higher performance, which helps the user in easy handling and increased comfort. 

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Marine Applications The market for recreational transport include bicycles, motorcycles, pleasure boats, snowmobiles, and water scooters.  Composite materials are used in a variety of marine applications such as passenger ferries, power boats, buoys, etc. because of their corrosion resistance and light weight, which gets translated into fuel efficiency, higher cruising speed, and portability. 

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Marine Applications The majority of components are made of glassreinforced plastics (GRP) with foam and honeycomb as core materials.  About 70% of all recreational boats are made of composite materials  Composites are also used in offshore pipelines for oil and gas extractions. 

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Composite Components in Marine Applications

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Marine Applications The motivation for the use of GRP materials for Oil and Gas applications includes reduced handling and installation costs as well as better corrosion resistance and mechanical performance.  Another benefit comes from the use of adhesive bonding, which minimizes the need for a hot work permit if welding is employed. 

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Consumer Goods Composite materials are used for a wide variety of consumer good applications, such as sewing machines, doors, bathtubs, tables, chairs, computers, printers, etc.  The majority of these components are short fiber composites made by molding technology such as compression molding, injection molding, and RTM. 

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Construction and Civil Structures The construction and civil structure industries are the second major users of composite materials.  The driving force for the use of glass- and carbon-reinforced plastics for bridge applications is reduced installation, handling, repair, and life-cycle costs as well as improved corrosion and durability. 

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Construction and Civil Structures It also saves a significant amount of time for repair and installation and thus minimizes the blockage of traffic.  Composite usage in earthquake and seismic retrofit activities is also booming. The columns wrapped by glass/epoxy, carbon/epoxy, and aramid/epoxy show good potential for these applications. 

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CONSTRUCTION AND CIVIL  STRUCTURES

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Industrial Applications The use of composite materials in various industrial applications is growing.  Composites are being used in making industrial rollers and shafts for the printing industry and industrial drive shafts for cooling-tower applications. 

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Industrial Applications Filament winding shows good potential for the above applications. Injection molded, short fiber composites are used in bushings, pump and roller bearings, and pistons.  Composites are also used for making robot arms and provide improved stiffness, damping, and response time. 

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Barriers in Composite Markets The primary barrier to the use of composite materials is their high initial costs in some cases, as compared to traditional materials.  Regardless of how effective the material will be over its life cycle, industry considers high upfront costs, particularly when the life-cycle cost is relatively uncertain. This cost barrier inhibits research into new materials.  In general, the cost of processing composites is high, especially in the hand lay-up process. Here, raw material costs represent a small fraction of the total cost of a P.E. 406 finished product. Polymer Composites 

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Barriers in Composite Markets There is already evidence of work moving to Asia, Mexico, and Korea for the cases where labor costs are a significant portion of the total product costs.  The recycling of composite materials presents a problem when penetrating a high-volume market such as the automotive industry, where volume production is in the millions of parts per year.  With the new government regulations and environmental awareness, the use of composites has become a concern and poses a big 94 challenge for recycling. 

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Reference 

Chapter # 1

Handbook of polymer composites for engineers 







by Leonard Hollaway  Chapter # 2

Composites Manufacturing 

by Sanjay K. Mazumdar



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