Introduction
CFRP (Carbon Fiber Reinforced Plastic) is a composite that employs reinforcing carbon fibers to deliver to exceptional strength and stiffness while remaining lightweight. Widely used in aerospace, automotive, and sporting equipment, one of CFRP’s key characteristics is its flexural strength—a key indicator of structural capacity.
In this column, we explore the flexural strength properties of CFRP, its evaluations methods, and ways it is being leveraged today.
Understanding the Flexural Strength of CFRP
Flexural strength indicates the material’s ability to withstand bending-induced forces loads. When a material is bent, both compressive and tensile stresses act simultaneously across its cross-section. The maximum stress the material can sustain before failure under these combined stresses defines its flexural strength. The high tensile strength of the carbon fibers, together with the solidifying effect of the resin, creates superior flexural strength—resistance to bending loads—while maintaining the low overall weight of the CFRP.
Characteristics of CFRP’s Flexural Strength
The flexural strength of CFRP varies greatly depending on the carbon fiber type and orientation, resin type, and manufacturing methods employed. Understanding how these factors affect the final outcome is essential for optimization and correct utilization of CFRP.
Types of Carbon Fiber
Different types of carbon fiber have different strengths and moduli. A high-strength carbon fiber will also enhance the flexural strength of CFRP.
Fiber Orientation
The strength of CFRP is strongly influenced by fiber configuration and orientation. Alignment of fibers with the primary tensile (loading) direction will maximize the tensile strength and stiffness in that direction. In contrast, multidirectional fiber layups distribute the stresses more evenly, improving its flexural strength and performance under bending loads.
Resin Type
Common CFRP resins include epoxy resins, polyurethane resins, and vinyl ester resins. The properties of the resin strongly influence the flexural strength of the composite—the tougher the resin, the higher the flexural strength.
Manufacturing Method
CFRP can be manufactured using a variety of processes, including compression molding, injection molding, press molding, and laminate fabrication. Differences in processing methods and conditions influence fiber–resin bonding quality, leading to variations in flexural strength.
Evaluating the Flexural Strength of CFRP
The following tests are commonly used to measure and evaluate the flexural strength of CFRP:
Three-point Bending Test
In the three-point bending test, a CFRP specimen is supported at the center and loaded at both ends to measure the bending strength. The maximum bending moment occurs at the center of the specimen, and the flexural strength is determined from the applied load and displacement at failure.
Four-point Bending Test
In the four-point bending test, the CFRP specimen is supported at both ends while two load points are applied near the center. This test applies a more uniform load to the center of the specimen, allowing for more precise evaluation of the flexural strength.
Accelerated Life Test
The accelerated life test measures how the flexural strength of CFRP changes over time. Changes in durability and flexural strength of CFRP are observed while applying humidity, temperature change, and repetitive loading.
Leveraging CFRP’s Flexural Strength
CFRP’s superior flexural strength is an important factor in a wide variety of applications. It is typically and effectively used in the following applications.
Aerospace Industry
CFRP is widely used in aircraft structural components. Aircraft require lightweight and high-strength materials, and CFRP’s superior bending strength is a major advantage. CFRP is used in aircraft wings, fuselages, and engine parts, contributing to improved fuel efficiency and durability.
Automotive Industry
CFRP is used in body and chassis components to reduce the weight of automobiles. Its flexural strength plays a major role in enhancing safety, through impact absorption during collisions.
Sporting Equipment
CFRP is used extensively in sporting goods, such as bicycle frames, golf clubs and ski boards, where flexural strength and low mass is critical to overall product handling and performance.
Buildings and Structures
CFRP is also used to reinforce structures with high durability demands such bridges and high-rise buildings. Its lightweight allows for use as a reinforcing material with minimal impact to the overall mass of structure.
Summary
CFRP offers excellent flexural strength, making it a key material in applications requiring high structural strength, lightweight performance. CFRP’s flexural strength is significantly influenced by the carbon fiber type, fiber orientation, resin, and manufacturing method. Optimizing these factors will maximize CFRP’s inherent properties and structural performance.
We expect that CFRP will continue to evolve as technologies advance, leading to expanded applications in more diverse areas.
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ABOUT UCHIDA - 55 years since our founding
We leverage a wealth of technical expertise as a CFRP molding and processing manufacturer using FRP, GFRP, and CFRP materials. We offer a one-stop solution, encompassing design, analysis, manufacturing, secondary processing, assembly, painting, quality assurance, and testing.
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DMG森精機 - VS1000/40/2050
X軸：2,050mm（ストローク） ／ Y軸：1,000mm ／ Z軸：600mm ／ テーブル作業面：2,250×1,000mm
ASHIDA MFG Co., Ltd.
Autoclave Oven 2
Size : Ø1,150x1,000mm / Operating temperature : at normal temperature - 400℃ / Design pressure : 2.0Mpa (maximum working pressure) / Vacuum system : back suction system / Vacuum units : 5
ASHIDA MFG Co., Ltd.
Autoclave Oven 3
Size : Ø3,000x6,000mm / Operating temperature : at normal temperature - 200℃ / Distribution accuracy : ±2.5℃less / Heating rate : 4.0℃/min. (empty furnace) / Cooling rate : 4.0℃/min. (empty furnace) / Design pressure : 0.99Mpa (maximum working pressure) / Working pressure : 0.7Mpa less (if no specification from the manufacuturer 0.3Mpa around) / Pressure accuracy : ±0.02Mpa（for pressure setting of ０ - 0.99Mpa/cm²） / Boost pressure accuracy : 0 - 0.03Mpa/min / Pressure source : compressed air (regular use) / Vacuum system : back suction system / Vacuum units : 10
Oven
Size : W1,000xH1,000xD1,000mm / Temperature range : Environmental Temperature +20 - 300℃ / Temperature elevation capability : Environmental Temperature (20 - 40℃) - 300℃ / 45min less / Vacuum system : back suction system / Vacuum units : 10
ESPEC CORP.
Temperature & Humidity Chamber
INSTRON
Static Universal Testing Machine 5985
Oven
Size : W7,000xH3,000xD2,000mm / Temperature range : Environmental Temperature +20 - 300℃ (Max) / Temperature elevation capability : Environmental Temperature (20 - 40℃) - 300℃ / 60min less / Vacuum system : back suction system / Vacuum units : 10
NEO
X axis : 4,000mm (stroke) / Y axis : 2,000mm / Z axis : 1,200mm / C axis : 0° - ±270° / B axis : 0° - ±110° / Table working place : 4,000x2,000mm
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Painting booth
Various painting, and clear finish is done in dedicated painting booth
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Finishing process, such as trimming, drilling, and bonding, surface treatment of the molded product type and is done in a private booth
Toshiba Matrixeye EX (Ultrasonic flaw detector)
Matrix-Arrey : 32
AMETEK CREAFORM Metra
SCAN750 Elite (3D scan)
Olympus Corp.
Inverted Microscopes
Oven
Size : W450xH450xD450mm / Temperature range : Environmental Temperature +20 - 650℃ / Temperature elevation capability : Environmental Temperature+50 - 650℃/120min less
Cutting Plotter Table working place : W1,500xL3,500mm
SHIMA SEIKI MFG., LTD
Cutting Plotter
KUKA
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Krauss Maffei
Epoxy resin injection machine Resin 60L ／ Hardener 25L
Krauss Maffei
630t Press machine Height total 5,200mm ／ Length max 1,500mm ／ Width max 1,200mm ／ Whole cycle time per component part 240sec
DMG森精機 - NV5000B/40
X軸：1,020mm（ストローク） ／ Y軸：510mm ／ Z軸：510mm ／ テーブル作業面：1,320×600mm
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