Composite systems play a critical role in the maintenance and repair of essential infrastructure. These systems must be capable of performing across diverse operating environments, pressures, and temperature ranges. Over the past several decades, advancements in this technology have significantly enhanced overall performance.
Components of a Carbon Fiber Composite Repair System
The two key components of a carbon fiber composite repair system are the reinforcing fabric and the saturating resin. The reinforcing fabric is composed of carbon fibers and a sizing agent that helps the resin interact with the fibers. The carbon fiber acts as the composite’s foundational strength component. Its superior strength and stiffness, when compared with fiberglass composites, makes it a better alternative for many reinforcement applications, especially reinforcing steel. New carbon fiber composites, like ultra-high modulus fibers, are expanding the range of structural repairs that are now possible.
The second component of the composite repair system is the saturating resin. Most repair companies use epoxy-based resins, but other resins are also used. The epoxy systems are typically either heat-cured or feature two-component, ambient cure, zero-VOC resins:
Part A, the resin, is the base component that often contains other additives that control the viscosity, reaction rate, hang, and interlaminar shear strength of the epoxy.
Part B, the curing agent, initiates a chemical reaction when mixed with Part A. The resulting epoxy matrix is saturated throughout the carbon fiber before it is applied to the repaired surface.
Epoxy resins offer a wide range of properties and will typically influence the maximum temperature limit of a repair, the chemical resistance of the repair, the toughness of the composite, and the overall bond strength of the repair.
What Makes a High-Performing Composite Repair?
A high-performing composite repair system relies on the joint properties of both the carbon fiber and epoxy resin, working in tandem to reinforce the repaired surface. The exceptional strength and stiffness of the carbon fiber fabric allows it to effectively reinforce metal structures, distributing and sharing the load to prevent further damage or failure. Various options offer different levels of strength and stiffness, allowing for optimal performance for a range of applications and operating conditions.
While the carbon fiber holds the biggest influence on the overall strength of the composite, the epoxy plays a critical role in effectively securing bonds to the surface and between the layers of the fiber. The addition of the polymer acts as a protective barrier against solvents, acids, and other harsh chemicals. The polymer will also influence the tensile strength and tensile modulus of the final composite.
How Composite Properties Influence Performance
Material properties can influence the performance of a composite repair system. Several of the most important properties are listed below.
Tensile Strength
Tensile strength is the material’s ability to withstand pulling forces without breaking. An epoxy carbon composite can generate tensile strength between 90,000 to 130,000 psi, due to the reinforcing properties of the carbon fiber. In contrast, a neat epoxy will only reach 10,000 to 20,000 psi – a significant reduction in strength when only the epoxy is present. This difference demonstrates the critical role of carbon fiber in the system.
Tensile Modulus
Tensile modulus measures stiffness and resistance to deformation under stress. A higher tensile modulus is an indicator that the system will resist failure under extreme loads and conditions. The higher the tensile modulus, the more the composite will take on the load in a condition where a pipe or tank is repaired with a composite.” The higher modulus of carbon fiber, when compared to fiberglass reinforcements, makes it a much better reinforcing technology for steel.
Coefficient of Linear Thermal Expansion
Each composite system should be tested to determine what its coefficient of linear thermal expansion is, in both the X and Y direction. This property is critical for reinforcements where the temperature will fluctuate or where the application temperature is significantly different from the operating temperature. The closer the coefficient is to the substrate, the less strain is caused by thermal cycling.
Other properties, such as the viscosity of the epoxy resin, can also influence the performance and application of the carbon fiber composite. A lower viscosity resin can enhance the absorption and saturation of carbon fiber, ensuring each layer has complete fiber wet-out. Conversely, too low of a viscosity can result in run-out and incomplete saturation, adversely affecting the properties of the repair, especially liquid tightness.
The Impact of Working Times & Cure Environment
Factors such as the working time of the epoxy during application and the curing environment also play a critical role in repair performance. Saturation efficiency, working time, and viscosity affect how the repair is installed. If a saturated resin cures too quickly, applicators must overcome the challenge of having a short application window.
The curing environment has also been shown to have some impact on the performance of the repair. Advanced FRP’s recently published study, Can It Take the Heat: Analyzing the Behavior and Performance of Composite Repair Systems in Elevated Temperature Environments, demonstrated that fiber-reinforced composites perform differently at different cure temperatures, especially for those operating in elevated-temperature environments. Testing protocols should be in place to understand the critical relationship between cure temperature and its impact on the composite system.
The Role of Expert Application
The effectiveness and longevity of a composite repair depend not only on high-quality materials but also on the techniques used during application. Improper installation can result in poor adhesion, uneven points in the repair, and inadequate performance. Proper handling, preparation, and installation ensure the correct repair is made and performs as intended.
During application, proper alignment of the carbon fiber layers onto the surface of the repair is crucial to maximizing repair strength and load distribution. Additionally, epoxy resins have a limited working time before they begin to cure. This requires precise and efficient application within the allowable timeframe so that resins don’t increase in viscosity. This can inhibit effective saturation and hinder the application process. Other factors, such as poor handling and uncontrolled curing environments, can lead to improper polymerization and bond failure over time. Finally, poor material handling or improper curing environments can lead to reduced glass transition temperatures and reduced bond strength both to the substrate and between the layers of the composite.
Proper application substantially increases the likelihood of long-term performance, lowers maintenance costs, and avoids potentially hazardous failures in the future. This is why major codes, like ASME PCC-2, require that all applicators be thoroughly trained and certified by the manufacturer of the composite repair system.
Using an Experienced Partner
Working with an experienced and highly qualified partner leads to successful, long-lasting results. Advanced FRP has a team of experts to guarantee quality composite repair solutions. We offer hands-on training opportunities for technicians and engineers to ensure you are well-equipped with the skills needed to properly install carbon fiber composite repairs.
If you are not sure where to start, Advanced FRP offers a free consultation to help you assess your project and determine repair needs tailored to your specific application.
Innovations in Carbon Fiber Composite Repairs: Properties, Performance, and Applications
Composite systems play a critical role in the maintenance and repair of essential infrastructure. These systems must be capable of performing across diverse operating environments, pressures, and temperature ranges. Over the past several decades, advancements in this technology have significantly enhanced overall performance.
Components of a Carbon Fiber Composite Repair System
The two key components of a carbon fiber composite repair system are the reinforcing fabric and the saturating resin. The reinforcing fabric is composed of carbon fibers and a sizing agent that helps the resin interact with the fibers. The carbon fiber acts as the composite’s foundational strength component. Its superior strength and stiffness, when compared with fiberglass composites, makes it a better alternative for many reinforcement applications, especially reinforcing steel. New carbon fiber composites, like ultra-high modulus fibers, are expanding the range of structural repairs that are now possible.
The second component of the composite repair system is the saturating resin. Most repair companies use epoxy-based resins, but other resins are also used. The epoxy systems are typically either heat-cured or feature two-component, ambient cure, zero-VOC resins:
Epoxy resins offer a wide range of properties and will typically influence the maximum temperature limit of a repair, the chemical resistance of the repair, the toughness of the composite, and the overall bond strength of the repair.
What Makes a High-Performing Composite Repair?
A high-performing composite repair system relies on the joint properties of both the carbon fiber and epoxy resin, working in tandem to reinforce the repaired surface. The exceptional strength and stiffness of the carbon fiber fabric allows it to effectively reinforce metal structures, distributing and sharing the load to prevent further damage or failure. Various options offer different levels of strength and stiffness, allowing for optimal performance for a range of applications and operating conditions.
While the carbon fiber holds the biggest influence on the overall strength of the composite, the epoxy plays a critical role in effectively securing bonds to the surface and between the layers of the fiber. The addition of the polymer acts as a protective barrier against solvents, acids, and other harsh chemicals. The polymer will also influence the tensile strength and tensile modulus of the final composite.
How Composite Properties Influence Performance
Material properties can influence the performance of a composite repair system. Several of the most important properties are listed below.
Tensile Strength
Tensile strength is the material’s ability to withstand pulling forces without breaking. An epoxy carbon composite can generate tensile strength between 90,000 to 130,000 psi, due to the reinforcing properties of the carbon fiber. In contrast, a neat epoxy will only reach 10,000 to 20,000 psi – a significant reduction in strength when only the epoxy is present. This difference demonstrates the critical role of carbon fiber in the system.
Tensile Modulus
Tensile modulus measures stiffness and resistance to deformation under stress. A higher tensile modulus is an indicator that the system will resist failure under extreme loads and conditions. The higher the tensile modulus, the more the composite will take on the load in a condition where a pipe or tank is repaired with a composite.” The higher modulus of carbon fiber, when compared to fiberglass reinforcements, makes it a much better reinforcing technology for steel.
Coefficient of Linear Thermal Expansion
Each composite system should be tested to determine what its coefficient of linear thermal expansion is, in both the X and Y direction. This property is critical for reinforcements where the temperature will fluctuate or where the application temperature is significantly different from the operating temperature. The closer the coefficient is to the substrate, the less strain is caused by thermal cycling.
Other properties, such as the viscosity of the epoxy resin, can also influence the performance and application of the carbon fiber composite. A lower viscosity resin can enhance the absorption and saturation of carbon fiber, ensuring each layer has complete fiber wet-out. Conversely, too low of a viscosity can result in run-out and incomplete saturation, adversely affecting the properties of the repair, especially liquid tightness.
The Impact of Working Times & Cure Environment
Factors such as the working time of the epoxy during application and the curing environment also play a critical role in repair performance. Saturation efficiency, working time, and viscosity affect how the repair is installed. If a saturated resin cures too quickly, applicators must overcome the challenge of having a short application window.
The curing environment has also been shown to have some impact on the performance of the repair. Advanced FRP’s recently published study, Can It Take the Heat: Analyzing the Behavior and Performance of Composite Repair Systems in Elevated Temperature Environments, demonstrated that fiber-reinforced composites perform differently at different cure temperatures, especially for those operating in elevated-temperature environments. Testing protocols should be in place to understand the critical relationship between cure temperature and its impact on the composite system.
The Role of Expert Application
The effectiveness and longevity of a composite repair depend not only on high-quality materials but also on the techniques used during application. Improper installation can result in poor adhesion, uneven points in the repair, and inadequate performance. Proper handling, preparation, and installation ensure the correct repair is made and performs as intended.
During application, proper alignment of the carbon fiber layers onto the surface of the repair is crucial to maximizing repair strength and load distribution. Additionally, epoxy resins have a limited working time before they begin to cure. This requires precise and efficient application within the allowable timeframe so that resins don’t increase in viscosity. This can inhibit effective saturation and hinder the application process. Other factors, such as poor handling and uncontrolled curing environments, can lead to improper polymerization and bond failure over time. Finally, poor material handling or improper curing environments can lead to reduced glass transition temperatures and reduced bond strength both to the substrate and between the layers of the composite.
Proper application substantially increases the likelihood of long-term performance, lowers maintenance costs, and avoids potentially hazardous failures in the future. This is why major codes, like ASME PCC-2, require that all applicators be thoroughly trained and certified by the manufacturer of the composite repair system.
Using an Experienced Partner
Working with an experienced and highly qualified partner leads to successful, long-lasting results. Advanced FRP has a team of experts to guarantee quality composite repair solutions. We offer hands-on training opportunities for technicians and engineers to ensure you are well-equipped with the skills needed to properly install carbon fiber composite repairs.
If you are not sure where to start, Advanced FRP offers a free consultation to help you assess your project and determine repair needs tailored to your specific application.