Strength
Composites are one of the strongest materials around. When you consider the density of the material, composites are much stronger than most other building materials. It’s no surprise they are the material of choice for everything from airplanes to automobiles.
By combining specific resins and reinforcements – and there are a lot of them – you can customize the formulation to meet specific strength requirements of any application. For example, you can alter the ratio of the resin and reinforcement or orient the fibers in one direction or various directions.
Composites are anisotropic, meaning the material properties change depending on the placement and number of layers of reinforcement materials – the fibers. This provides engineering flexibility so designers can tailor properties of the final product. When it comes to strength, there are four primary kinds that affect structural design: specific, tensile, shear and compressive strength.
A material’s strength-to-weight ratio – also called its specific strength – is a comparison of its strength in relation to how much it weighs. The strength of a material divided by its density will give you the specific strength.
Engineers, designers and specifiers are increasingly seeking materials with a high specific strength. Some materials are very strong and heavy, such as steel. Other materials can be strong and light, such as bamboo poles. Composites can be designed to be both strong and light. Because they have very high strength-to-weight ratios, composites are a sought after material for applications where weight is paramount, such as airplanes and cars. Lighter vehicles use less fuel.
Tensile strength refers to the amount of stress a material can handle before it breaks, cracks, becomes deformed or otherwise fails. One measure of tensile strength is flexural strength – a material or structure’s ability to withstand bending. Tensile and flexural strength are important measurements for engineers and designers. Imagine building a bridge deck or a ceiling without knowing how much stress it could take before collapsing?
Tensile strength varies by material and is measured in megapascals (MPa). For example, the ultimate tensile strength of steel ranges from 400 to 690 MPa, while the ultimate strength of carbon fiber reinforced polymer composites ranges from 1,200 to 2,410 MPa, depending on fiber orientation and other design factors.
Shear strength describes how well a material can resist strain when layers shift or slide. It’s important to know the maximum amount of shear stress (or force per unit area) a material can handle prior to failure. This lets engineers and designers know the amount of weight – or load – a structure can support and what may happen to the structure when forces are applied in different directions.
Shear strength in composites varies based on the formulation and design. Composites can be designed so shear stresses are oriented within a plane, transverse to the plane or throughout the layers (interlaminar). There are several ways to control shear properties, including fiber orientation, the sequencing of layers, the type and volume of fibers used, the type and density of core materials and more.
Compressive strength indicates how a material performs when it’s compressed or flattened by pressure. Some materials fracture or break when they hit their compressive strength limit, while others deform permanently.
Lightweight
Composites materials are both strong and light. That’s a winning combination. Who wouldn’t want to work with a material that’s simple to ship and carry? Lightweight composites can save you money and manpower.
Fiber-reinforced composites offer excellent strength-to-weight ratios, exceeding those of other materials. For example, carbon fiber-reinforced composites are 70 percent lighter than steel and 40 percent lighter than aluminum. Producing parts that are light weight is critical to industries such as transportation, infrastructure and aerospace for a variety of reasons. Lightweight composites are easy to handle and install, can reduce costs on projects and help ensure adherence to regulations and standards.
One of the top advantages of using lightweight composites is that they are simple to handle, transport and install. This saves time on projects. Wolf Trap National Park in Virginia installed a pedestrian bridge with FRP decks in 2012. The bridge was 80 percent lighter than a concrete one, making it faster to lift, move and place by crane. The deck was installed in three days, while a concrete one would’ve taken at least four weeks. Lightweight composites also simplify installations in remote locations, such as utility poles in marshlands or pipelines on mountains.
Lighter parts and products often save money. And saving on weight and cost is music to the ears of many end users. NASA and Boeing recently tested an all-composite cryogenic tank used to carry fuel on deep space missions. The tank, one of the largest and lightest ever manufactured, is the latest step toward the planned 8.4-meter tank that could reduce the weight of rocket tanks by 30 percent and cut launch costs by at least 25 percent.
Composites are often the answer when applications need to meet specific standards and regulations. The most notable example relates to fuel efficiency. Within the automotive industry, meeting Corporate Average Fuel Efficiency (CAFE) standards of 36.6 mpg by 2017 and 54.5 mpg by 2025 provides impetus for using lightweight materials. Major OEMs have optimistic plans – often involving composites – to drastically reduce the gross weight of vehicles. In 2013, GM introduced the Chevrolet Silverado Cheyenne concept vehicle featuring some carbon fiber-reinforced parts. It’s approximately 200 pounds lighter than the base curb weight of the 5.3L Silverado. Volkswagen created the Transporter, a utility concept truck weighing just 3.5 tons. It saves on diesel consumption and carbon dioxide emissions by providing 40 percent more payload and up to 30 percent savings in shipments.
Corrosion Resistance
Products made from composites provide long-term resistance to severe chemical and temperature environments. Composites are often the material choice for outdoor exposure, chemical handling applications and other severe environments.
Composites do not rust or corrode. There are many examples of glass fiber reinforced polymer ductwork being in service in chemical manufacturing plants for more than 25 years, operating in harsh chemical environments 24 hours a day, seven days a week. Composites offer corrosion-resistant solutions for many industries, including air pollution control, chemical processing, desalination, food and beverage, mineral processing and mining, oil and gas, pulp and paper, solid waste landfill and water and wastewater treatment.
Corrosion resistance is determined by the choice of resin and reinforcement used within the composite application. There are various resin systems available which provide long-term resistance to nearly every chemical and temperature environment. The choice of reinforcements is much more limited but crucial for certain chemical environments. Properly designed composites have a long service life and minimum maintenance.
- History of Corrosion Composites
In 1953, the first high-performance industrial corrosion resins were developed by Atlas Chemical and Hooker Chemical Companies. The pulp and paper and chemical processing industries were quick to recognize the benefits and use composites in their processing equipment.
In 1961, the Amoco Division of Standard Oil introduced the first underground gasoline storage tank. Between 1961 and 1965, Shell Oil and Owens Corning researched corrosion-resistant solutions, ultimately producing the first commercial line of large composite underground storage tanks.
During the 1970s, the use of composites in industrial applications became widespread. Then in 1989, the American Society of Mechanical Engineers published the seminal design standard for FRP tanks, Reinforced Thermoset Plastic Corrosion-Resistant Equipment. By the 1990s, the corrosion industry had accumulated 40 years of experience and case histories to build a positive performance record.
- Resin’s Role in Corrosion Resistance
One of the primary functions of resins in composites is to protect the fibers they surround. There are dozens of resins designed to provide corrosion resistance. Each unique formulation offers protection against specific conditions, such as caustic solutions, acidic environments, alkaline environments, oxidizing chemicals and high temperatures.
The first corrosion resins employed bisphenol fumurate and chlorendic anhydride resin chemistries. Subsequently, isophthalic resins were developed and became the mainstay of corrosion-resistant resins. Isophthalic resins – along with epoxy vinyl ester resins – are commonly used today.
- Reinforcement’s Role in Corrosion Resistance
While the same resin matrix will typically be used throughout the composite structure, reinforcements may be used in three specific areas of the laminate. A fiberglass or synthetic veil is used at the inner surface of the laminate. The inner surface is the interface of the composite and corrosive material. The veil serves to provide a resin-rich (90% resin) surface for the composite while preventing micro-cracks in the resin which would otherwise occur if a resin-only surface (or gel coat) was attempted. The next layer is the chopped fiberglass layer which provides a more robust backup for the veil and is also resin-rich (70% resin). This layer is usually considerably thicker than the veil layer and when combined with the veil layer forms a 100 to 200 mil thick corrosion barrier. The last layer, and by far the thickest layer is the structural portion of the laminate. Different forms of fiberglass reinforcements can be used in this layer to provide a high glass content (35% resin, 65% reinforcement) structural layer: direct draw single-end rovings, fabrics, or choppable reinforcements.
There is a vast choice of materials used for the veil layer since this is the first line of defense against a corrosive assault. C-glass, E-CR glass, several types of synthetics thermoplastic non-wovens and carbon veil are the main material choices for veils. Each has a specific environment where they excel. E-glass is almost never used due to its poor corrosion performance. The material choices for the chopped fiberglass layer and the structural layer narrow considerably to E-glass and E-CR glass.
- Industry Design Standards
If you’re planning a project using corrosion-resistant composites, the design will likely need to adhere to industry standards. The most widely used standards for corrosion applications are issued and maintained by ASTM International and the American Society of Mechanical Engineers (ASME). All standards address the basic issues of scope of applicability, design, materials, construction, quality control, testing and record keeping.
Design Flexibility
Composites pack a powerful one-two punch with their ability to be molded into complex shapes at a relatively low cost. This offers designers, engineers and architects a freedom not typically found with other competing materials.
Because composites are a blend of reinforcing fibers, resins and additives, they can be manufactured to meet an array of requirements. Designers are free to create exciting new products and, in many cases, are only limited by their imagination. Applications ranging from sports cars to wind blades take advantage of the inherent design flexibility of composites to produce complex shapes, add specific properties and enhance aesthetics.
One of the biggest benefits of composites is the ability to mold them into complicated shapes more easily that most other materials. Intricate shapes and contours are possible without the need for high-pressure tools because composites are formed when the resin cures – or solidifies – during production. So composite parts can easily take on many shapes, whether they’re created in low volumes manually or manufactured using high-volume, automated processes.
Having options when it comes to the shape of parts and products is advantageous for nearly every industry that uses composites. Recreational boats have long been built with FRP composites because these materials can be easily molded into complex shapes, which improve boat design while lowering costs.
Designers like working with composites because parts can be tailor-made to have strength and stiffness in specific directions and areas. For instance, a composite part can be made to resist bending in one direction. The strategic placement of materials and orientation of fibers allows companies to design parts and products to meet unique property requirements.
Being able to address high stress and strain areas is critical in several markets, such as sports and recreation, where both high-end and everyday applications count on composites. By aligning fibers in various patterns laterally across layers, you can improve the torsional rigidity – the layers ability to resist twisting forces.
People are often drawn to composites because of aesthetics, with companies marketing the “carbon fiber look” on everything from phone covers to countertops. The popularity of the exposed weave appearance derives from the automotive industry, where high-end cars rely on carbon fiber-reinforced composites to not only enhance performance, but also reflect style. For example, include exposed carbon fiber roofs, door handles, wing mirrors and interiors.
But aesthetics aren’t reserved solely for luxury markets. Composite surfaces can be molded to simulate any finish or texture, from smooth to coarse. Consumers opt for composite countertops because they can be formed into any shape and customized into any color. Handles and knobs on household appliances look stylish and feel good to the touch. With composites, designers have endless options to create beautiful products.
Durability
Composite structures have an exceedingly long life span. Combine this with their low-maintenance requirements and composites become the material of choice for a host of applications.
How long do composites last? There is no easy answer. That’s because many of the original composite structures put in place more than 50 years ago have not yet come to the end of their lives. Composites hold up well against fatigue and are resistant to environmental factors such as U.V. damage, temperature fluctuations, moisture and chemical exposure. They also require less scheduled and unexpected maintenance.
Composites are strong, allowing them to withstand repeatedly applied loads. This is particularly important for infrastructure applications such as bridge decks, which support traffic 24 hours a day. Many of the nation’s deteriorating bridges are being renovated with FRP decks.
Composites are hardy, holding up well in all kinds of weather. And can withstand up to 146 mph winds and resist saltwater corrosion.
The aerospace industry provides a great example of how composites require less maintenance than competing materials. Consider Boeing’s twin-engine jet airliners: The composite tail of the Boeing 777 is 25 percent larger than the 767’s aluminum tail. But it requires 35 percent fewer scheduled maintenance hours, according to the company. This is because composites are less susceptible to corrosion and fatigue than metal.
These three composite applications showcase the material’s durability:
· The Chevrolet Corvette has been built with FRP composites since 1953. That year, 300 Corvettes were manufactured, and more than two-thirds are still around today.
· The first all-composite bridge in the United States – the No Name Creek span in Kansas – was installed nearly 20 years ago. It’s still in service and shows no signs of damage.
· In 1963, a composite gasoline tank was buried at a service station in Chicago. When it was dug up 25 years later, the tank was in good condition, showing no signs of leakage, structural distress or corrosion. Experts predicted the tank could’ve lasted another 25 years.
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