A composite of carbon fibers bound with epoxy or another resin. With low density and high modulus and strength, it excels in specific stiffness and is used in aircraft, automobiles and sporting goods.
Japanese name: CFRP(炭素繊維強化プラスチック)
CFRP (carbon-fiber-reinforced plastic) appears in 6 practice questions across 3 topics, including Materials selection and design, Composite materials, Polymers and composites.
Field: Composite materials
CFRP is a composite of carbon fibers about 5–7 µm in diameter bound with a thermosetting resin such as epoxy or with a thermoplastic. Carbon fiber has a low density of about 1.8 g/cm³ and a Young's modulus of about 230 GPa for standard grades and several hundred GPa for high-modulus grades. In the fiber direction of unidirectional material, its specific stiffness (Young's modulus/density) is more than three times that of steel or aluminum alloys, and it also resists fatigue well, so it is used for the wings and fuselages of aircraft where weight must be saved, automobiles, wind turbine blades, fishing rods, golf clubs and more.
Unidirectional material is strong and stiff along the fibers, but perpendicular to the fibers and in in-plane shear it shows only low values close to those of the resin. Real parts are therefore made as laminates stacking plies of different orientations, such as 0°, ±45° and 90°, placing fibers to match the directions of load. When similar in-plane properties are wanted in every direction, a quasi-isotropic layup is used. The through-thickness direction is supported by the resin alone, so interlaminar strength is low and impact readily causes internal delamination, which requires attention.
Carbon fiber conducts electricity and has a noble electrode potential, so direct contact with aluminum alloys readily causes galvanic corrosion of the aluminum. At joints, a layer of glass fiber is interposed or titanium alloy fasteners are used. CFRP made with thermosetting resin cannot be melted after curing, so recycling is difficult, and technologies to recover the fibers by pyrolysis and other methods are being developed. Voids and fiber waviness from molding reduce strength, so parts are inspected by ultrasonic testing and similar methods.
Answer: C. CFRP excels in specific stiffness but conducts electricity, so it readily causes galvanic corrosion in contact with aluminum alloys
Carbon fiber has a density of about 1.8 g/cm³, lower than glass fiber (about 2.5 g/cm³), and a Young's modulus of about 230 GPa or more, over three times that of glass fiber (about 70 GPa), so CFRP excels in specific stiffness and specific strength and is used in aircraft and sporting goods. However, it is expensive, and because carbon fiber conducts electricity and has a noble electrode potential, contact with aluminum alloys readily causes galvanic corrosion of the aluminum; countermeasures include placing a layer of glass fiber between them. It is CFRP that conducts electricity, not GFRP. Transparency to radio waves and high insulation are characteristics of GFRP, which is used for radomes, electrical insulating parts, and inexpensive boat hulls and bathtubs.
Answer: B. About 3.3
The specific modulus is 140/1.6 = 87.5 for CFRP and 210/7.9 ≈ 26.6 for steel (both in GPa/(g/cm³)), so the ratio is 87.5/26.6 ≈ 3.3. CFRP has the lower Young's modulus itself, but its density is about one fifth, so at equal weight it is about 3.3 times as stiff. About 0.67 compares only the moduli (140/210), and about 4.9 looks only at the density ratio (7.9/1.6). Note that this value applies only in the fiber direction; perpendicular to the fibers, the specific modulus is far lower than that of steel. Real structures compensate for direction by laminating, so the specific-stiffness advantage is smaller than this value.
In specific strength and specific stiffness, the tensile strength and Young's modulus in the fiber direction divided by density, it far exceeds steel. But its strength perpendicular to the fibers and through the thickness is low, so it is not stronger than steel in every direction.
CFRP is generally used for parts where lightness and stiffness are critical and a high price is acceptable, and GFRP for parts where cost must be kept down or where electrical insulation or transparency to radio waves is required.
CFRP itself does not rust as metals do, but the resin can degrade from moisture absorption and ultraviolet light. It can also promote galvanic corrosion of metals it contacts, so joints with dissimilar materials need countermeasures.
Carbon fiber has a density of about 1.8 g/cm³, lower than glass fiber (about 2.5 g/cm³), and a Young's modulus of about 230 GPa or more, over three times that of glass fiber (about 70 GPa), so CFRP excels in specific stiffness and specific strength and is used in aircraft and sporting goods.
Which correctly compares carbon-fiber-reinforced plastic (C…The specific modulus is 140/1.6 = 87.5 for CFRP and 210/7.9 ≈ 26.6 for steel (both in GPa/(g/cm³)), so the ratio is 87.5/26.6 ≈ 3.3.
Which value is closest to the ratio CFRP/steel of the speci…The mass of a stiffness-limited tie is proportional to ρ/E, so the mass ratio CFRP/steel is (1.6/70)/(7.8/210) = 0.0229/0.0371 ≈ 0.62.
A tie of fixed length and tensile stiffness is made of stee…They have excellent dimensional stability, heat resistance and solvent resistance, and are used as semiconductor encapsulants, printed circuit boards and the matrix of CFRP.
Which is a characteristic of thermosetting resins?In bending, stiffness increases rapidly as the section grows, so low-density materials are favored, which is why wood and CFRP are strong performers as beams.
A beam of square cross section with fixed length and bendin…Young's modulus Material index (performance index) GFRP (glass-fiber-reinforced plastic) Specific stiffness Galvanic corrosion Thermosetting resin Life cycle assessment Ceramic matrix composite Critical fiber length Delamination