A composite material is made up of two components that have distinct physical and chemical characteristics. When they are mixed, they form a material that is specialized to do a certain task, and therefore become stronger, lighter, or posses better electrical properties which allows the engineer to pick and choose from materials that are conductive or resistant. They are preferred over traditional materials because they increase the properties of their basic materials and may be used in a variety of applications. Composites can be found in nature too. Long cellulose fibers are bound together by a compound called lignin in a piece of wood, making it a composite.
Brief History of Composites
For thousands of years, humans have used composite materials in a variety of applications. Early Egyptians and Mesopotamian settlers utilized a combination of mud and straw to build robust and enduring structures around 1500 BC. The mix of mud and straw in a brick gives it excellent resistance to squeezing, ripping, and bending. Plywood was made by gluing wood strips at varying angles on top of each other in ancient civilization. Following this, the Egyptians began to manufacture death masks out of linen or papyrus soaked in plaster approximately during 2181 B.C.
In addition to that, the Mongols began developing composite bows about 1200 A.D., which were highly effective at the time. These were fashioned of pine resin-bonded wood, bamboo, bone, cow tendons, horn, and silk. The bows were compressed, and wrapped with birch bark. These bows were incredibly strong and precise. Genghis Khan’s military superiority was aided by the composite Mongolian bows. Many of the most significant breakthroughs in composites were the result of wartime requirements due to their benefits such as light weight and strength. Many composite materials were invented and advanced from the laboratory to practical manufacturing during World War II.
Synthetic resins began to solidify after the industrial revolution, thanks to the process known as polymerization. This newfound understanding of chemistry led to the development of numerous polymers such as polyester, phenolic, and vinyl ester in the early 1900s. Synthetics were then developed, with scientist Leo Baekeland developing Bakelite. Since it didn’t conduct electricity and was heat resistant, it could be employed in a wide range of sectors.
The 1930s were a watershed moment in the development of composites. Owens Corning was the first to introduce glass fiber, as well as the first to establish the fiber reinforced polymer (FRP) sector. The resins developed at this time are still in use today, and unsaturated polyester resins were patented in 1936. Higher-performance resin solutions became available two years later. Carbon fiber was initially invented in 1961 and was made commercially accessible soon after. Then, in the mid-1990s, composites began to gain popularity as a manufacturing and building material due to their lower cost than previously utilized materials.
The Matrix
Yeah, I know what you’re thinking of. It’s not the movie trilogy. In general, a composite consists of three components: (i) the matrix as the continuous phase; (ii) the reinforcements as the discontinuous or dispersed phase, including fiber and particles; and (iii) the fine interphase region, also known as the interface. Engineers may modify the qualities to fit specific requirements by carefully selecting the matrix, reinforcement, and manufacturing technique that binds them all together.
Any material can serve as a matrix material for composite. However, matrix materials are generally ceramics, metals, and polymers. Polymer-matrix materials make up the vast bulk of matrix materials on the market for composites. In composite materials, there are a variety of polymer matrices that may be used. Predominately, we here at Midwest Composites are experts at producing polymer-based products such as Glass Fiber Reinforced Polymer (GFRP), Carbon Fiber Reinforced Polymer (CFRP) & Natural Fiber Reinforced Polymer (NFRP).
Moving on, composites products can also be broken down into two distinct categories: thermoset & thermoplastics. Thermoset-matrix composites are more common than thermoplastic-matrix composites among polymer-matrix composites. Though thermoset and thermoplastic sound similar, their characteristics and uses are vastly different.
Thermoset Vs Thermoplastics
Thermosets
Thermosets are polymers that change from a liquid to a solid after undergoing a chemical reaction or curing. The material has tiny, unlinked molecules known as monomers in its uncured state. The curing process is initiated by the inclusion of a second substance as a cross-linker, curing agent, catalyst, and/or the presence of heat or other activating forces. The molecules cross-link and create substantially longer molecular chains and cross-link networks as a result of this process, causing the substance to solidify. Compared to thermoplastics, thermoset state shift is permanent and irreversible. After that, exposing the material to extreme heat after it has solidified will cause it to deteriorate rather than melt.
Advantages of thermosetting polymers include:
- Allows for flexible product design
- Can be molded with different tolerances
- Capable of varying wall thickness to improve structural integrity
- Components usually cost less than those fabricated from metals – especially for large equipment body panels
- Excellent electrical insulation properties
- Greater resistance to high temperatures
- High dimensional stability
- Highly resistant to corrosion
- Low thermal conductivity
- Lower costs for setup and tooling compared to thermoplastics
- Offers high strength-to-weight ratio to improve product performance
- Water-resistant
- Wide choice for coloring and surface finishes
Thermosetting polymers disadvantages include:
- Can neither be reshaped nor remolded
- Not recyclable
Thermoplastics
Thermoplastics are polymers that can be melted. Heat is used to treat thermoplastic polymers. The plastic melts, liquefies, or softens sufficiently to be treated when enough heat is applied to raise the temperature over its melting point. The plastic forms again into a glasslike solid when the heat source is withdrawn and the temperature of the plastic falls below its melting point. This cycle can be repeated, with the plastic melting and solidifying as the temperature rises above and falls below the melting point. However, because the material’s qualities can deteriorate rapidly in its molten form, there is a practical limit on how many times this reprocessing can be done before the material’s properties deteriorate.
Advantages of thermoplastics include:
- Adheres well to metal
- Allows for quality aesthetic finishes
- Capable of reshaping after curing without much effect to material properties (recyclable)
- Chemical and detergent resistant
- Good electrical insulation properties
- Enhanced anti-slip properties
- Resistant to impact
- Offers options for both hardened crystalline and rubbery surfaces
- Resistant to chipping
- Resists corrosion well
Disadvantages of thermoplastics include:
- Ability to soften when heated makes it less suitable for some applications
- Often more expensive option than thermosetting polymers
Thermoplastic and thermoset materials both have a position in the market. Thermosets, in general, have a long history and a well-established market position, usually have cheaper raw material prices, and frequently allow simple wetting of reinforcing fibre and easy shaping to final component geometries. To put it another way, thermosets are frequently easier to work with than thermoplastics. Thermoplastics are often more durable and less brittle than thermosets. They may be more chemically resistant, do not require cooling as frequently as uncured thermosets (prepreg materials), and are more readily recycled and repaired.
Thermoplastics are the most widely used plastics, particularly in non-reinforced applications. Thermosets are employed in non-reinforced applications for a specific purpose where their unique properties provide a benefit. Thermoset dominates in the reinforced or composites sector, while thermoplastic is employed exclusively in areas where its specific benefits are critical. Thermoset accounts for approximately 80% of the total material utilized in composites.
Reinforcements
Fibers, flakes, and particles can all be used as composite reinforcements. Each has its own set of qualities that may be added to composites, and hence each has its own set of uses. Fibers are the most often utilized form in composite applications, and they have the greatest impact on the composite materials’ qualities. The high aspect ratio between length and diameter of the fibers allows for excellent shear stress transmission between the matrix and the fibers, as well as the capacity to process and fabricate composite parts in a variety of forms utilizing various procedures.
Polymer-matrix composites have been reinforced using a variety of fibers. Carbon fibers, glass fibers, aramid fibers & natural fibers. For ages, glass fibers have been utilized as reinforcement, particularly by Renaissance Venetian glass craftsmen. There are various types of glass fiber, these include:
- Grade A is high alkali grade glass, originally made from window glass.
- Grade C is chemical-resistant grade glass for acid environments or corrosion.
- Grade D is low dielectric grade glass, good transparency to radar (quartz glass).
- Grade E is electrical insulation grade; this is the most common reinforcement grade.
- Grade M is high modulus grade glass.
- Grade R is reinforcement grade glass; this is the European equivalent of S-glass.
- Grade S is high strength grade glass, a common variant is S2-glass. This fiber has higher temperature resistance than E-glass. It is also significantly more expensive.
Grade E-glass fiber that is compatible with epoxy & polyester based resin
Moving on, carbon fibers are fibers about 5–10 micrometers in diameter and composed mostly of carbon atoms. Carbon fibers have several advantages including high stiffness, high tensile strength, low weight, high chemical resistance, high temperature tolerance, low thermal expansion and good electrical conductivity. These properties have made carbon fiber very popular in aerospace, civil engineering, military, and motorsports, along with other competition sports. However, they are relatively expensive when compared with similar fibers, such as glass fibers..
Based on modulus, strength, and final heat treatment temperature, carbon fibers can be classified into the following categories:
Based on the mechanical properties, carbon fibers can be grouped into:
- Ultra-high-modulus, type UHM (modulus >450Gpa)
- High-modulus, type HM (modulus between 350-450Gpa)
- Intermediate-modulus, type IM (modulus between 200-350Gpa)
- Low modulus and high-tensile, type HT (modulus < 100Gpa, tensile strength > 3.0Gpa)
- Super high-tensile, type SHT (tensile strength > 4.5Gpa)
Based on precursor fiber materials, carbon fibers are classified into:
- PAN-based carbon fibers
- Pitch-based carbon fibers
- Mesophase pitch-based carbon fibers
- Isotropic pitch-based carbon fibers
- Rayon-based carbon fibers
- Gas-phase-grown carbon fibers
Based on final heat treatment temperature, carbon fibers are classified into:
- Type-I, high-heat-treatment carbon fibers (HTT), where final heat treatment temperature should be above 2000°C and can be associated with high-modulus type fiber.
- Type-II, intermediate-heat-treatment carbon fibers (IHT), where final heat treatment temperature should be around or above 1500°C and can be associated with high-strength type fiber.
- Type-III, low-heat-treatment carbon fibers, where final heat treatment temperatures should not be greater than 1000°C. These are low modulus and low strength materials.
Lastly, there are natural fibers. Natural fibers are fibers that are neither synthetic or man-made and are classified according to whether they come from animals, minerals, or plants. Natural fibers are an example of a capable reinforcement that might be used to replace synthetic reinforcement. Natural plant fibers are completely biodegradable and generated purely from vegetative resources. Due to its outstanding qualities, Natural Fiber-Reinforced Polymer (NFRP) has gotten a lot of interest in a lot of applications. According to current indications, the industry’s interest in natural fiber composites will continue to rise rapidly over the world. Natural fiber-reinforced polymer composites and natural-based resins are being widely used to replace conventional synthetic polymer or glass fiber-reinforced materials.
Processes / Composites Manufacturing Techniques
Composite materials can be manufactured in a variety of ways. The materials, part design, performance, and end-use or application will all influence the process chosen to fabricate a part. We here at Midwest Composites are extremely adept at a number of these composite manufacturing techniques. These include:
1) Open Molding
Hand lay-up is a manual composite material fabrication process that uses open contact molding. Resin is applied to fibers in the form of woven, knitted, stitched, or bonded textiles. The mold is first treated with mold release agent, then dried fibers or textiles are deposited on the mold, then liquid resin is poured and dispersed over the fiber beds. Rollers or brushes are commonly used, although nip-roller-type impregnators, which employ revolving rollers and a resin solution to force resin into textiles, are becoming more popular. Wet the fibers and eliminate air trapped in the lay-ups with a roller or brush. A few layers of fibers are wetted, and the laminates are allowed to cure under normal circumstances. More layers are applied after these ones have cured.
Spray-up is another open-mold composite application technique. The spray lay-up approach is seen as an extension of the hand lay-up technique. The mold is initially treated with mold release agent in this procedure. After the mold release has been applied, a gelcoat is sprayed as either one thick layer or two thin layers in a way that the mold’s functional surface is completely covered in gelcoat. The next step which consists of spraying the first layer of the laminate can be done once the gelcoat layer is almost fully cured. A chopper spray cannon is used to spray the fiber and catalyzed resin into the mold at a viscosity of 500–1000 cps. The cannon slices continuous fiber tow into small bundle lengths, then blows the short fibers straight into the sprayed resin stream, allowing the fiber to be coated with the resin as it is sprayed onto the mold.
2) Resin Transfer Molding (RTM)
Resin transfer molding (RTM), often known as liquid molding, is a straightforward procedure. The mold is initially treated with mold release agent in this method. The dry reinforcement, usually a preform, is then inserted into the mold, which is finally sealed. Low viscosity resin and catalyst are metered and mixed before being injected into the mold under low to moderate pressure through injection ports, following predesigned routes through the preform. In the RTM process, low-viscosity resin is utilized to guarantee that the resin penetrates the preform fast and fully before gelling and curing, which is especially important with thick composite components.
3) Vacuum Assisted Resin Transfer Molding (VARTM)
Vacuum-assisted resin transfer molding is the fastest-growing molding technology (VARTM). The distinction between VARTM and RTM is that in VARTM, the pressure difference between the atmosphere and the void created by the vacuum helps to push the resin through the laminate, but in RTM, resin is injected into the laminate. The VARTM method does not need a lot of heat or pressure. VARTM often uses low-cost tooling, allowing it to create huge, complicated components in a single shot at a cheap cost.
As a result, there is no practical difference in the materials used in a “Open Mold or Contact Molding” product vs one molded using RTM, LRTM, or VARTM / Vacuum Infusion. The truth remains that the resin and fiber are essentially the same for each process, therefore if the fiber to resin ratio was consistent and the fiber distribution cross sectionally in the laminate was the same, any process method would ultimately provide the same molded component performance. The open mold technique, as well as the RTM and LRTM processes, all share the same fiber loading ratio of 30 percent weight fiber to 70 percent resin. The VARTM or Vacuum Infusion process is a variation of the process techniques; in this approach, the fiber loading increases to 60 to 70 percent by weight of the laminate, with the remaining 40 to 30 percent being resin.
4) Light Resin Transfer Molding (LRTM)
Light Resin Transfer Molding, or Light RTM, is a process by which composite products are manufactured using a closed mold system. The closed mold consists of an “A” side mold (base mold) and a semi-rigid “B” side mold (counter mold) that is sealed to the “A” side mold using vacuum pressure. Resin is drawn into the resulting cavity under vacuum.
The resin infusion may be assisted by a resin injection pump, which will accelerate the infusion process. Once an “A” side mold is cured, the “B” side mold is removed and the part is demolded from the “A” side mold.
While LRTM can be a better alternative to open molding for most items, it does need that the product be developed for the process and that the molds used be built for the process. A typical blunder is to use this procedure to make a part that was originally designed for open molding. Consider the benefits and drawbacks of the LRTM process before designing or redesigning your goods to take advantage of them.
5) Compression Molding
Compression molding is a precise and potentially quick method of making high-quality composite parts in large quantities. In the mold, the material is manually or robotically deposited. The mold halves are sealed togetherwith hydraulic presses. The cycle time varies based on the size and thickness of the component. This method creates high-strength, complicated pieces in a range of sizes. Thermosetting prepregs, fiber-reinforced thermoplastic, molding compounds such as sheet molding compound (SMC), bulk molding compound (BMC), and chopped thermoplastic tapes are among the composites usually treated by compression molding.
6) Additive manufacturing
Industries Applicable
A laminar structure is the most common type of fiber-reinforced polymer, which is created by stacking and connecting thin layers of fiber and polymer until the required thickness is achieved. A varying level of anisotropy in composite qualities can be produced by manipulating the fiber orientation among layers in laminate constructions. Corrosion resistance, light weight, strength, cheaper material prices, greater productivity, design flexibility, and durability are just a few of the advantages of composites.
1) Aerospace
The potential of composite materials for large-scale applications in aerospace has been demonstrated by major original equipment manufacturers (OEMs) like as Airbus and Boeing. NASA is always on the lookout for new ideas and space solutions for rockets and other spacecraft from composite producers. In commercial, civilian, and military aircraft applications, thermoset composites are being specified for bulkheads, fuselages, wings, and other uses. Composites are also used in air-foil surfaces, antenna structures, compressor blades, engine bay doors, fan blades, flywheels, helicopter transmission structures, jet engines, radar, rocket engines, solar reflectors, satellite structures, turbine blades, turbine shafts, rotor shafts in helicopters, wing box structures, and other areas.
2) Automotive & Mass Transit
3) Military & Defence
The increasing use of composites and innovations in material blends and fabrication has enabled composite component manufacturers to satisfy the need for military vehicle components. Armored vehicles have traditionally used steel armor for protection – however, this gives rise to heavy structures that provide logistical problems in transporting the vehicles to a battle site. A typical military vehicle can weigh around 60t and even smaller vehicles weigh around 23t. This major hindrance has led to a major increase in the development of composite armored vehicles. The materials used in composites include Kevlar, glass fiber and carbon fiber. Glass fiber is around 20-30% lighter when compared to steel but for 50 -60% lighter weight, carbon fiber composites need to be adopted.
4) Construction and Infrastructure
Construction is one of the largest markets for composites globally. The composites can be made to have a very high strength and ideal construction materials. Thermoset composites are replacing many traditional materials for home and offices’ architectural components including doors, fixtures, molding, roofing, shower stalls, swimming pools, vanity sinks, wall panels, and window frames. Composites are used all over the world to help construct and repair a wide variety of infrastructure applications, from buildings and bridges to roads, railways, and pilings
Composite Properties
Polymer composite materials are lightweight, which improves the fuel efficiency of composite cars while still providing structural stability. They also have a high strength-to-weight ratio and are more heat resistant. Depending on the kind of matrix, reinforcement, ratio between them, formulations, and manufacturing process, composites have extremely variable characteristics and uses. One of the most important variables in obtaining better fiber reinforcement polymer composite qualities is the bonding strength between the fiber and the polymer-matrix in the composite. Furthermore, composites has various advantageous features such as :
- It is light in weight and have low density.
- It has high creep resistance.
- Strength-to-weight and stiffness-to-weight are greater than in steel or aluminum.
- Fatigue properties are higher than normal engineering metals.
- Composites cannot corrode like steel.
- Ease of fabrication of large advanced structural shapes.
- The ability to include sensors into the fabric to monitor its performance.
- It has excessive resistance to impression damage.
Conclusion & Summary
Composites have several advantages, including the ability to utilize a large range of material combinations, allowing for design flexibility. In addition, the composites may be readily molded into complex forms. Materials can be specially designed to meet specific requirements. Composites are lighter in weight than most woods and metals, and they have a lower density than many metals. They are more durable than other materials. Weather and strong chemicals have no effect on the materials. Composites have a high life expectancy and require little upkeep. The design options for composite goods are diverse because to the large diversity of available reinforcement, matrix, and their shapes, manufacturing techniques, and each resulting in their own distinct composite products. As a result, a composite and its production method may be selected to best suit the growing rural societies in which the items would be manufactured and used.
Leave a comment below if you have any interesting ideas or concepts that is relevant to the topic above. Furthermore, let us know what is your preferred manufacturing techniques out of the ones we’ve listed today.