A composite of glass fibers bound with resin. It is less stiff than CFRP but inexpensive, electrically insulating and transparent to radio waves, and is used for boat hulls, bathtubs, printed circuit boards and more.
Japanese name: GFRP(ガラス繊維強化プラスチック)
GFRP (glass-fiber-reinforced plastic) appears in 1 practice question across 1 topic, including Composite materials.
Field: Composite materials
GFRP mainly uses fibers of E-glass (an aluminoborosilicate glass developed for electrical insulation), with a Young's modulus of about 72 GPa, a density of about 2.55 g/cm³ and diameters of roughly 10–20 µm. Stronger and stiffer S-glass fibers also exist and are used for parts such as aircraft components. The resins include thermosets, such as inexpensive unsaturated polyester, highly corrosion-resistant vinyl ester and epoxy with excellent strength and adhesion, as well as thermoplastics such as polyamide. The fiber surfaces are treated with silane coupling agents to improve adhesion to the resin.
GFRP is strong, but not especially stiff. For a unidirectional laminate with 60% fiber volume fraction, the rule of mixtures gives a Young's modulus in the fiber direction of about 45 GPa and a density of about 2.0 g/cm³, so its specific stiffness is somewhat lower than steel's. In mats with randomly oriented fibers, the modulus falls further, to a fraction of that. GFRP parts are therefore often sized by deflection before strength, and sections are enlarged or reinforced with ribs. The key to design is how to make up for the lack of stiffness while exploiting the strength.
Glass fibers are used as bundled rovings, chopped strand mats made of short scattered strands, woven fabrics and other forms. Molding methods include hand lay-up, in which fibers are laid in a mold and resin is applied layer by layer; SMC, in which sheets of fiber and resin are press-molded; and filament winding, in which fibers are wound onto pipes and tanks. Uses are wide-ranging: boat hulls, bathtubs, septic tanks, piping, wind turbine blades, automotive body panels and printed circuit boards (FR-4, made of glass cloth and epoxy). Because it transmits radio waves, GFRP is also used for radar domes (radomes).
Under sustained load in a moist environment, small surface cracks in glass fibers can grow slowly, and the fibers may break at stresses below their short-term strength (static fatigue). E-glass is vulnerable to acids and can suffer stress corrosion cracking of the fibers in acidic environments, so acid-resistant glasses such as ECR glass are used. Degradation of the resin by water absorption and ultraviolet light also needs attention. GFRP made with thermosetting resins is hard to recycle, and discarded wind turbine blades and similar items are crushed and used as raw material or fuel for cement production.
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.
FRP refers to fiber-reinforced plastics in general; with glass fibers it is GFRP and with carbon fibers CFRP. In Japan, plain “FRP” often means the GFRP used for boats and bathtubs.
It varies greatly with the molding method; as a rough guide, hand lay-up mats are around 20% by volume, while pultrusion and filament winding reach about 50–60%. The higher the content, the stronger and stiffer the material.
No. Both glass fibers and resin are insulators, so it can be used for parts that need electrical insulation and for radomes that must transmit radio waves. This is a major difference from CFRP, which uses conductive carbon fibers.
It is CFRP that conducts electricity, not GFRP.
Which correctly compares carbon-fiber-reinforced plastic (C…CFRP (carbon-fiber-reinforced plastic) Young's modulus Specific stiffness Galvanic corrosion Ceramic matrix composite Critical fiber length Delamination Metal matrix composite Quasi-isotropic laminate Silane coupling agent