Fiberglass is a technical material. Properties, application and price of fiberglass

GLASS FIBER(fiberglass), molded from the melt. inorg. glass. There are continuous glass fiber-complex glass filaments with a length of 20 km (or more), a diameter of 3-50 microns, and a staple glass fiber with a length of 1-50 cm, a fiber diameter of 0.1-20 microns.

Receipt. Continuous glass fiber is obtained by spinning a beam of thin melts. glass melt with subsequent, drawing, oiling and winding of the complex thread on a bobbin at high (10-100 m/s) linear speeds. Staple glass fiber is formed by breaking a jet of melt. glass after leaving the die, hot or other methods. It is also obtained by cutting complex threads.

Twisted complex threads, unidirectional tapes, tows are made from continuous glass fiber. Complex glass filaments are distinguished by the composition of the glass, the average fiber diameter (3-15 microns or more), the number of filaments (50-800), twist. From twisted thread, nets, ribbons are made on looms. Glass ones are distinguished by the type of weave (plain, twill, satin, etc.) and density (the number of threads per 1 cm in warp and weft). Their width varies within 500-1200 mm, thickness - 0.017-25 mm, weight 1 m 2 -25-5000 g. Bundles and tapes are obtained by connecting 10-60 complex threads. Staple glass fibers and strands of threads cut from reels (length 0.3-0.6 m) are used for the manufacture of glass wool, canvases, mats, plates. Canvases made from chopped fiberglass or continuous filaments, usually resin or fur. firmware.

The composition and properties of glass fiber are determined by the composition and properties of the fiber-forming glass from which it is made. Depending on the composition, several are distinguished. brands of such glass (Table 1).

A-glass is also called soda-lime, C-glass is sodium borosilicate, E-glass is aluminoborosilicate, S-glass is magnesiaaluminosilicate. Naib. important characteristics glass fibers are given in table. 2.

Raise glass fiber (compared to the original glass) is explained in different ways: by "freezing" the isotropic structure of high-temperature glass or by the presence of a strong surface layer (thickness approx. internal layers.

Under short-term loading, the glass fiber behaves almost like an elastic brittle body, obeying up to rupture. When lasting under the action of the load, there is an increase in , elastic aftereffect, depending on the composition of the glass and . As the fiber diameter increases, the resistance to bending and torsion increases and decreases when stretched. In the wet, in and out water solutions The surfactant of glass fiber is reduced by 50-60%, but is partially restored after.

From high-alkaline A-glass, fibers are obtained that are less resistant to than E-glass fibers, but resistant to action.

Higher chem. resistance compared to A-glass provides C-glass. The weight loss of fibers from such glasses during processing is 0.02-0.05 g/m, and when processed with alkaline solutions - 0.3-2.5 g/m.

S-glass fibers have max. high and elevated .

Depending on the thickness; weave density and type of surface treatment glass may have high values coefficient light transmission (up to 64%), sound absorption (up to 90% at frequencies of 500-2000 Hz), reflections (up to 80%).

Application. Glass fibers serve as structural, electrical, sound and heat insulators. materials. They are used in the production of filter materials, glass, etc. As a rule, A-glass is processed into and used in the form of mats and plates for sound and heat insulation. Glass fiber materials due to the high have a small coefficient "

All glass fibers can be conditionally divided into two large classes: cheap fibers general use and expensive fibers special application. Almost 90% of all glass fibers that are produced today in the world are grade E glass fibers. The requirements for such fibers are detailed, for example, in the ASTM D578-98 standard. The remaining 10% percent are special purpose fibers. Most fiberglass grades got their name due to their specific properties:

- - low electrical conductivity;
- - high strength;
- - high alkali resistance;
- - low dielectric constant;
- - significant thermal stability;
‐ C (chemical)– high chemical resistance;
‐ M (modulus)– high elasticity;
‐ A (alkali)-high content alkali metals, soda-lime glass.

For electrical insulation, only alkali-free (or low-alkali) aluminosilicate or aluminoborosilicate glass fibers are used. For structural fiberglass, as a rule, alkali-free magnesium aluminosilicate or aluminoborosilicate glass fibers are used. For non-responsible fiberglass, alkali-containing fiberglass can also be used.

The mechanical characteristics of glass fibers directly depend on the production method, the chemical composition of the glass, temperature and environment. Continuous glass fibers made of alkali-free and quartz magnesium aluminosilicate glass have the greatest strength. The increased content of alkalis in the original glass significantly reduces the strength of glass fibers.

Table 1. Chemical composition of some glasses for obtaining a continuous fiber.

Table 2. Physical and mechanical properties of some grades of glass fiber.

Glass E

Chemical composition
To date, 2 types of E-grade glass fiber are produced in the world. In most cases, E-glass contains 5-6 wt. % boron oxide. Current environmental regulations in the US and Europe prohibit the release of boron into the atmosphere. At the same time, it is known that in the process of glass formation, as well as in subsequent glass melting processes, the glass mass is depleted of some components due to their volatilization. Of the charge components, the highest volatility is boric acid and its salts, lead oxide, antimony oxide, selenium and some of its compounds, as well as chlorides. The volatility, calculated for 1% oxide content in ordinary glasses, is for individual oxides in wt. %: Na2O (from Na2CO3) 0.03, K2O (from K2CO3) 0.12, B2O3 0.15, ZnO 0.04, РbО 0.14, CaF2 up to 0.5. Thus, modern enterprises are forced to install expensive filtration systems.

As an alternative, it is possible to obtain boron-free E-glasses based on the SiO 2 –Al 2 O 3 –CaO–MgO system.

Commercial grade E glass fiber is produced on the basis of the SiO 2 –Al 2 O 3 –CaO–MgO–B 2 O 3 system or the SiO 2 –Al 2 O 3 –CaO–B 2 O 3 system. Products derived from the latter system generally still contain a small amount of magnesium oxide (up to 0.6 wt.%), which is associated with the characteristics of the raw materials that I use to obtain glasses.

It is important to note that the exact composition of glass fiber E can differ from each other not only for different manufacturers, but even for different plants of the same company. This is primarily due to the geographical location of the enterprise and, as a result, the availability of raw materials. In addition, different enterprises exercise different control over technological process and methods for its optimization.

The composition of boron-containing glass fiber and glass fiber without boron oxide is significantly different from each other. The content of silicon oxide in grade E boron-containing glasses is 52-56%. For glass fiber without boron oxide, the content of silicon oxide is somewhat higher and lies in the range of 59-61%. The content of aluminum oxide for both types of glass E is close and amounts to 12-15%. The content of calcium oxide also differs slightly - 21-23%. The content of magnesium oxide in glass varies widely. For glasses obtained on the basis of ternary systems, it is less than 1%, and is a consequence of the inhomogeneity of the raw material. If the mixture contains dolomite, the content of magnesium oxide can reach 3.5%. Distinctive feature Boron-free E-glasses are increased content in them, titanium oxide is from 0.5 to 1.5%, while in classic E glass its content is in the range of 0.4-0.6%.

Features of obtaining
The temperature for obtaining fibers from boron-containing E-glass is 1140-1185 °C. The melting point is 1050-1064 melting points. Unlike their environmentally friendly counterpart, boron-containing E-glass fibers have a 110 °C lower production temperature, which is 1250-1264 °C, and a melting point of 1146-1180 °C. Softening temperatures for fibers based on boron-containing E-glasses and E-glasses without boron oxide are 830–860°C and about 916°C, respectively. A higher temperature for producing environmentally friendly glass fibers based on E-glass leads to an increase in energy consumption for their production, and, as a result, an increase in cost.

Properties
The mechanical properties of both types of E-glass fibers are almost the same. Tensile strength is 3100-3800 MPa. However, the elastic modulus of fibers without boron oxide is somewhat higher (80–81 GPa) than that of conventional fibers (76–78 GPa). The main difference of grade E glass fiber without boron is more than 7 times greater acid resistance (exposure at room temperature within 24 hours in a 10% sulfuric acid solution). In terms of acid resistance, these fibers approach chemically resistant fibers based on ECR glass.

The density of boron-containing glass fibers is somewhat lower (2.55 g/cm 3 ) compared to its environmentally friendly counterpart (2.62 g/cm 3 ). The density of E-glass is higher than other types of glass (excluding ECR glass).

With an increase in the boron content in such glasses, the refractive index and the linear expansion coefficient decrease. Boron-free E-glasses have a higher dielectric constant, which is 7 at room temperature and 1 MHz. Therefore, boron-containing fibers are more often used in the production of electronic boards and in aerospace industry. In the wide production of composites, this difference is not so critical.

Glass S

For the first time the chemical composition of glass under the brand name S-glass was patented by Owens Corning in 1968 (patent 3402055). The composition of this glass included 55-79.9% SiO 2 , 12.6-32% Al 2 O 3 , 4-20% MgO. The creation of S grade fiberglass was driven by the rapid development composite materials in the USA at that time and, as a result, the need to create fiberglass with high strength and modulus of elasticity. Currently, glass under this brand is produced on the basis of SiO 2 -Al 2 O 3 -MgO or SiO 2 -A 2 O 3 -MgO-CaO systems. In exceptional cases, BeO 2 , TiO 2 , ZrO 2 are added to S-glass.

Features of obtaining
Due to the high content of refractory oxides, S-glass has a very high temperature softening 1015-1050 °C. Accordingly, the fiber production temperature is also high - about 1200 °C, which is comparable to AR glass fiber.

Properties
Grade S fiberglass has record strength and modulus values ​​for this class of materials. The best products made from S-glass are in no way inferior in quality to carbon fiber and, like the latter, are mainly used in the aerospace field. The strength of the fibers at room temperature is 4500-4800 MPa, the modulus of elasticity is 86-87 GPa, the strength of the best fiber samples of the VMP brand is up to 7000 MPa.

AR glass

Chemical composition
In the early 70s, the English company Pilkington Brothers developed and began to produce in industrial scale high-zirconium Cemfil glass fiber for cement reinforcement. Subsequently, this brand was transferred to Saint-gobain, at present, OwensConing and the Japanese company Nippon electric glass are the main manufacturer of AR glass-based fiberglass. Alkali-resistant glasses are produced on the basis of the ZrO 2 -SiO 2 -Na 2 O system. The content of expensive zirconium oxide in them varies between 15-23%. Since the melting point of pure zirconium oxide is quite high (2715 C), a significant amount of alkali metals is added to the glass, most often Na2O 18-21%.

Features of obtaining
Refractory compositions significantly complicate the technology of fiber production, in addition, zirconium-containing raw materials are scarce and expensive for the manufacture of mass products. Therefore, the issue of improving the composition of glasses for reinforcing cement continues to be relevant. The temperature for obtaining fibers from AR glass is 1280-1320 °C, the melting point is 1180-1200 °C.

Properties
The tensile strength of AR glass based fibers is rather low, around 1500-1700 MPa. Modulus of elasticity 72-74 GPa. Such fibers are the heaviest among all types of glass fibers, their density is about 2.7 g/cm3.

Since the main field of application of AR-glass-based fibers is the reinforcement of cements and concretes, the main characteristic of such fibers is their stability in an alkaline environment. The weight loss after boiling in a saturated NaOH solution for AR glass fibers is 2-3%. For comparison, the same characteristic for basalt fibers is 6-7%.

ECR glass

Chemical composition
For the first time, fiberglass under the brand name ECR-glass (in some sources it is indicated as chemically resistant E-glass) began to be produced in 1974. This glass contains up to 3% TiO2 and up to 3% ZnO. It is completely incorrect to call this glass a variety of E-glass, since, according to the requirements of international standards, E-glass should not contain zirconium oxide at all, and besides, the content of TiO2 in ECR glasses exceeds the required 1.5%. Fiberglass based on ECR glass does not contain boron oxide, which has a positive effect on the environmental friendliness of production. Often, up to 3% Li2O is added to the composition of ECR ​​glass fiber.

Features of obtaining
Titanium oxide is a flux, its significant content leads to a noticeable decrease in the viscosity of the glass and, as a consequence, the temperature of fiber production. Zirconium oxide has a positive effect on the chemical resistance of glass. The fiber spinning temperature of ECR ​​glass is about 1218°C, which is lower than that of E-glass fiber. At the same time, for glasses with a high content of lithium oxide, the fiber production temperature is higher than that of glass fiber E and is about 1235 °C. In fact, this means that zinc oxide is a more efficient melter than boron oxide, moreover, it is more environmentally friendly and gives additional beneficial features fiberglass.

Properties
ECR fiberglass has been developed specifically for use in aggressive environments, for example, resistance in acidic environments is 4-5 times higher. At the same time, the strength of these fibers remains at the level of glass fiber E and is about 2800-3000 MPa, the elastic modulus is about 80-83 GPa. Although the melting and fiberization of the ECR is carried out at more than low temperatures its cost exceeds the cost of glass fiber E due to the presence of expensive components.

Glass D

At present, D-glass fibers are more of an exotic than a real product in the glass fiber market, as many board manufacturers are opting to use alternative glass fibers instead. For example, ultra-pure silica fibers, E-glass hollow fibers also have lower dielectric characteristics than the widely used E glass fiber. However, quartz fibers have a lower modulus of elasticity, which is important in the manufacture of printed circuit boards, and hollow fibers lose their dielectric properties in high humidity conditions.

Chemical composition
The electronics industry often requires materials with very low dielectric constants. The electrical properties of fibers are determined by properties such as volume resistivity, surface conductivity, dielectric constant, and dielectric loss tangent. In most cases, E-glass is used as a reinforcing filler in the production of circuit boards, however, the reduction in the size of printed circuit boards places increased demands on glass fibers. To solve this problem, glass compositions of brand D have been developed. Such glasses and fibers are obtained on the basis of the SiO2-B2O3-R2O system. The content in glasses with low dielectric characteristics of silicon oxide reaches 74-75%, boron oxide - up to 20-26%. To reduce the production temperature, alkali metal oxides (up to 3%) are added to this system. Sometimes silicon oxide is partially replaced by aluminum oxide (up to 15%).

Properties
The high content of boron oxide leads to a significant decrease in the dielectric constant and dielectric loss tangent in D-glasses compared to E-glass.

Features of obtaining
Because of high cost D-glass fibers are currently produced only in small batches. In addition, the high content of boron oxide in them makes their manufacturing process very difficult, which is associated with the high volatility of this component during the melting of the charge. The softening temperature of D-glasses is 770 °C.

quartz glass

Quartz fibers are used in cases where significant thermal stability is required. Quartz fibers with a SiO2 content of less than 95% (generally referred to as silica fibers) are obtained by acid treatment of fibers of aluminoborosilicate composition, widely used for the manufacture of alkali-free fibers, and from sodium silicate with various additives. Silica fibers obtained by leaching fibers from rocks, are not inferior to silica fibers produced by the industry. The application temperature of silica fibers is 1200 °C.

Ultra-pure quartz fibers (SiO2 content of more than 99%) are obtained by dry spinning from aqueous solution liquid glass. Such fibers are produced under the brand name Silfa and are used for thermal protection. In the USSR, quartz fibers were obtained by the rod method: by pulling a thread from a drop of the heated end of the rod or by blowing the resulting drop with an acetylene-oxygen or oxy-hydrogen flame. The production of quartz fiber can also be carried out in two stages: obtaining fibers with a diameter of 100-200 microns, and then blowing them up with a stream of hot gases. The fibers are collected on a conveyor and formed into either mats or rovings. The melting temperature of such fibers is 1750 °C. At T = 1450-1500 °C, sintering (deformation in the solid phase) occurs, but without softening. In conditions long-term operation and heat exchanger, products made of quartz fiber are resistant up to T = 1200°C, above which their strength decreases due to crystallization. Currently, such fibers are produced under the brand name quartztel and astroquartz.

Properties
Ultrapure silica fibers are mainly used in the aerospace industry where high temperature resistance is required. Combining high thermal stability, strength and radio transparency for ultraviolet radiation and longer wavelength radiation, such fibers are used to make aircraft fairings.

Used materials from study guide"Glass fibers". S.I. Gutnikov, B.I. Lazoryak, Seleznev A.N.

Most in demand on Russian market are
mat and fabric fiberglass…

Fiberglass (or fiberglass) is a modern high-tech material, which, due to its unique performance properties, has found wide application in everyday life, in the industrial and construction industries. To obtain its original properties, this material is mixed with special polymer resins. Working with fiberglass requires some initial skills, but it will not be difficult for anyone to learn the basic methods.

Performance characteristics of fiberglass

Fiberglass is made in the form of a canvas, consisting of intertwined glass fibers (glass filaments). The threads themselves are made from E - glass, which is distinguished by its heat-resistant and fire-resistant qualities. In addition, fiberglass is an environmentally friendly material. In the construction field, fiberglass is usually used as a heat and waterproofing layer in various critical structures. Also, with the help of fiberglass, you can build a reinforcing base under roofing. In the construction of the roof, frame fiberglass is often used, in the manufacture of which a non-twisted strand and roving are used.

The main types of fiberglass

Modern technologies for the production of fiberglass allow you to create several types of this material. Each type of material is designed for a specific area of ​​\u200b\u200buse and differs significantly from other types in its characteristics.

Textured Fiberglass Tape
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Electrical insulating fiberglass. This type material is used as a heat and electrical insulating layer. Can be used in making different types lightweight fiberglass.

Structural fiberglass. In combination with fiberglass, it forms building materials with increased strength and high impact strength.

Fabric based on basalt fiber. Has excellent thermal insulation properties. Used as an insulating layer.

Silica fiberglass. This material is an excellent substitute for asbestos, capable of withstanding temperatures up to 1800 degrees. Such fiberglass is considered a completely environmentally friendly raw material, which cannot be said about asbestos.

A roll of fiberglass (weighing approximately 40 kg)…

Fiberglass Applications

Roving fiberglass. Due to its wide temperature range, this material is most often used in various industries.

It should be added that all these types of fiberglass have several main qualities that are observed in each type of this material. Such operational characteristics are environmental friendliness, chemical resistance, durability and great strength. In addition, almost all types of glass fabrics have high thermal insulation qualities.

What was known about fiberglass in the last century? Video.

Photo: moldmakingninja.com, cnbm2007.en.made-in-china.com, taishanjinyu.com

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Reading time: 3 minutes

There are wonderful technologies, thanks to which the substance changes its properties literally to the opposite. As a result of one such transformation, fragile and sonorous glass turns into soft matter with new, amazing qualities. This is the so-called fiberglass.

Production

Fiberglass is technical material, which is obtained from fiberglass threads impregnated with the so-called oiling agent - an emulsion containing paraffin. Production in demand national economy technical fabrics are always regulated by state standards. Fiberglass is no exception, it is produced in strict accordance with GOST 19907-83.

Let's take a closer look at what it is, fiberglass? The raw material for the material is silicate glass containing aluminum and boron. It is melted in special furnaces and pressed through the thinnest holes-dies. The resulting fibers are soft, elastic and particularly thin. Their diameter is often much smaller than a human hair and ranges from 3 to 100 micrometers. They are incredibly light, for example, the weight of 1 m 2 of E3 / 2-100 fiberglass is only 120 g. At the same time, they have incredible strength. The length of the fibers, which is 20 kilometers, is also striking.

Tightly twisted threads are wound on bobbins and sent for further processing to shuttle or shuttleless looms, where different ways weaving and fiberglass is created.

The fibers of the woven material are connected into several threads. Non-woven glass fiber does not have such bundles: the threads lay down one at a time.

Fiberglass properties

The material has paradoxical qualities for tissues.

• Flammability and incombustibility. Fiberglass withstands short-term exposure to open flame.
• Ecological purity and absolute non-toxicity.
• Chemical and biological inertness. Products endure treatment with alkalis and acids, they do not rot and are not a nutrient substrate for microorganisms.
• Immunity to ultraviolet rays.
• Unparalleled strength, exceeding that of steel wire.
• Durability that knows no competition.
• Absence of phenomena such as mechanical wear and corrosion.

Types of matter and their use

Fiberglass grades differ in resistance to impacts chemical substances and high loads. The properties of the material are largely influenced by the method of weaving the threads. For example, electrically insulating fabrics are created by linen weaving, structural - linen and satin, and filtering fabrics - also by the twill method. So the material is the following types:

• Structural - the most popular, they are used for fiberglass reinforcement and for the production of reliable structures in the automotive, aviation and shipbuilding industries.
• Roving - the best materials for glass roofing material. (Roving is a flat strand of fiberglass, which is obtained by splicing several threads.) They are also used to make the hulls of yachts, boats, cars, and parts of aircraft.
• Insulating - in demand in the manufacture of heat or waterproofing.

• Electrical insulating - less popular fiberglass. It goes to the production of printed circuit boards, false dielectrics, as well as to the electrical insulation of heat pipes.
• Basalt - withstand temperatures up to +700 ° C.
• Silica fabrics are the most heat-resistant fabrics that can withstand up to +1200 ° C. They are used as blankets during welding, they are used to sew first-aid protection in case of fire.

Other applications

In addition to these areas, fiberglass is used to manufacture roofing materials: cheaper smooth and non-deforming, but more expensive frame ones.

Used for insulation and waterproofing of houses, pipelines and cars.

Fiberglass fabrics are used to make parts for apparatus and machine tools that are unique in strength and configuration.

In the 1970s, colored fiberglass was even used to decorate interiors. Then they were very fashionable curtains, lampshades and floor lamps from this fabric.

The incombustibility of the material is the basis for the use of fiberglass in some flammable industries today.

Recycling Feature

Fiberglass is a non-toxic material that can be disposed of like any other construction garbage. However, when it is crushed, many microparticles enter the air, which can cause itching on the skin, enter the respiratory tract and harm health. When disposing of glass materials, certain rules must be observed.

• Work with gloves and masks.
• Turn on exhaust ventilation.
• Minimize the number of cuts.
• Wet the cloth while grinding.
• Discarded material must be kept in sealed bags and workplace requires timely and thorough cleaning.

This unusual material today has become an integral part of our lives. Whether we travel by train, fly by plane, travel by car, or surf the ocean on a cruise ship, we are surrounded by objects made of fiberglass or fiberglass. Lightweight, reliable, environmentally friendly products make life more aesthetic and comfortable, and our planet cleaner.

The strength of L-glass and S-glass monofilaments is 3.4 and 4.5 GPa, respectively. The standard deviation is approximately ±10%. The values ​​given are the average of a large number of individual measurements. The distribution of strength values ​​in these measurements usually follows a histogram (Figure 16.1) compiled by Owens-Corning Fiberglass. The obtained values ​​cover the range from close to zero (in the lower section of the histogram) to approaching the theoretical limit of 10.3 ... 13.8 GPa (in the upper section). The reason for such a wide scatter is the presence of defects in the fibers and the impact on them various factors environment . Humidity is the main factor. Atmospheric moisture acts on defective areas in the fiber, especially when it is in a stressed state, which leads to growth

Cracks and the final destruction of the fiber. This mechanism of stress corrosion occurs in both static fatigue assessment and tensile testing. Cracks in the fiber develop from large surface defects that occur during the drawing process or during the subsequent production of rovings from the fibers, as well as from relatively small surface pitting, which may have been formed during drawing or developed under the action of corrosion under load or without it. In fiberglass, in addition, there may be internal sinks.

Tensile test results for strands or bundles of fiber are about 20% lower than average values ​​for monofilament. After rupture of individual fibers in the bundle, the remaining fibers bear a large load. As a result, the final strength is reduced. In fact, the strength of the strand can be calculated with high accuracy from the strength distribution curve of the monofilament. The unequal tension of the fibers within the deformable strand produces a similar progressive fracture effect.

According to fiberglass companies, rovings with a large number of individual ends (single strands), but usually no more than 60, have about the same specific strength as rovings with a single end (in the form of a bundle). Such a conclusion is based on the assumption that when individual strands are connected in a roving, the dispersion of mechanical properties does not increase significantly.

The diameter of monofilaments is another parameter that affects their tensile strength. In experiments carried out under strictly controlled conditions, it was shown that the strength of a monofilament does not decrease with an increase in diameter to the maximum dimensions for an industrial fiber. However, for practical purposes, it is quite clear that the strength of large diameter fibers is lower than that of smaller diameter fibers. Permissible strength values ​​are regulated by military specifications і?-60346 for the roving used for winding. Minimum value for a roving made of L-glass fibers with a diameter G (0.09 ... 0.010 mm) is 1.93 GPa. For fibers of a larger diameter, i.e., up to caliber T (0.023 ... 0.024 mm), the maximum allowable value of tensile strength is 1.38 GPa.

The strength of the fiber also depends on the test method of the cured composites. While maintaining the fibers in a straightened state and their uniform loading, the strength of unidirectional composites is not lower or even higher than the strength of the threads. When testing fibers using the “NOL ring” method, their strength can reach 2.76 ... 3.1 GPa. On the other hand, with a thicker winding of products bigger size the maximum strength does not exceed 2.07 GPa. Strength values ​​for such structures are lower for a number of reasons: fiber damage during winding; misalignment or poor collimation; unequal - 202
measured tension of the layers during winding; voltage change during the transition from inner layers to the outside; the appearance of random local stresses.

The general conclusion is that when determining the strength of a material for structural analysis, the composite should be tested, not the fiber itself. Comparison with the data obtained during the testing of strands indicates the effectiveness of the method of their production. Detailed stress analysis is required to determine the true stress of a fiber at the time of failure.