Preparation of polymer composite materials. Composite materials

During this method, pre-prepared fillers are used. Thanks to this method, high homogeneity of the product is guaranteed for strength, and indicators are controlled. However, the quality of the resulting product depends to a high degree on the skill and experience of the workers.

The production of hand-molded fiberglass products is divided into several stages. The first stage is called preparatory, during which the surface of the matrix of the expected product is cleaned, then degreased and finally a layer of release wax is applied. At the end of the first stage, the matrix is ​​covered with a protective and decorative layer - gelcoat. Thanks to this layer, the outer surface of the future product is formed, the color is set and protection is provided from harmful factors such as water, ultraviolet light and chemical reagents. Negative matrices are mainly used to produce the finished product. After the special gelcoat layer has dried, you can move on to the next stage, which is called molding. During this stage, initially cut glass material is placed into the matrix; another type of filler can also be used. Further the process is underway formation of the “skeleton” of the expected product. Then the resin with the catalyst, pre-mixed, is applied to the prepared glass material. The resin must be evenly distributed using brushes and soft rollers throughout the matrix. The last stage can be called rolling. It is used to remove air bubbles from a laminate that has not yet hardened. If they are not removed, this will affect the quality of the finished product, so the laminate must be rolled with a hard roller. Once the finished product has hardened, it is removed from the mold and subjected to machining, which includes drilling holes, trimming excess fiberglass around the edges, etc.

Advantages of this method:

• exists real opportunity obtain a product of complex shape and considerable size with minimal investment;
• the design of the product can be easily changed, since embedded parts and fittings are introduced into the product, and the price of the equipment and the required equipment is quite low;
• To make the matrix, any material is used that is able to maintain its proportions and shape.

Disadvantages of this method:

• significant costs manual labor;
• productivity is quite low;
• the quality of the product will depend on the qualifications of the molder;
• This method is suitable for producing small-scale products.

2. Spraying.

This method is suitable for small and medium-scale production. The spraying method has many advantages over contact molding, even though there are some costs involved in purchasing equipment for this method.

A special installation allows you to apply a protective coating and plastic. Due to this, there is no need for preliminary cutting of the material and preparation of the binder, as a result of which the part of manual labor is sharply reduced. Special installations automatically accurately count the doses of resin and hardener, and they also cut the roving into pieces required sizes(0.8 - 5 cm). After the cutting process, parts of the thread must fall into the binder stream and become saturated during transfer to the matrix. Through manual labor, the compaction process for fiberglass in the matrix is ​​carried out using a rolling roller.

A number of advantages in the production of fiberglass by spraying:

• time and useful space are saved due to the fact that there is no need to cut the material and prepare the binder;
• it is possible to reduce the number of production areas by reducing the number of specially prepared places for molding;
• the product molding speed increases;
• control over product quality is simplified;
• the wage fund is significantly saved;
• Due to the fact that roving is a relatively inexpensive material, the cost of the resulting product is significantly reduced.

When the binder is prepared in small quantities, then during manual molding up to 5% of the binder remains on the tools and walls of the container, which is quite uneconomical. It is known that the quality of the resulting product will depend on the skill and experience of the installation operator. This method uses the same tooling as during hand molding.

3. Pultrusion.

Pultrusion technology is based on the continuous production of uniaxially oriented profile products from fibrous plastics. A profile product with a constant cross-section from a suitable material can be obtained by pultrusion.

Thanks to a special pultrusion machine, a fiberglass profile is produced. Such a machine consists of a section for supplying reinforcing materials, a die, a section for impregnation, a pulling unit, and a control unit heating elements and from the trimming section. It is better to strengthen the oriented fiber package in a dry state and impregnate it with a polymer composition pumped through the dry package. Thanks to this technology, air will not get into the material. Excess resin will flow back into the pan and be recycled. Roving, which is used as a reinforcing material, is unwound from reels in a dry state and collected into a bundle in a special way. Then the material enters the impregnation device - this is a special bath with resin, where it is completely wetted with polyester, epoxy or other binder. Then the already impregnated material is sent to a heated die, the task of which is to form the profile configuration. Then the composition hardens at the specified temperature. The result was a fiberglass profile, the configuration of which follows the shape of the die.

It has been proven that products produced by pultrusion have superior properties to parts made by classical molding methods. The increase in cost of this method is due to a number of advantages that are characteristic of this process. Benefits include strict control of fiber tension and directionality, reduced pores, and maintaining a constant fiber content in the composite. It is obvious that even the interlayer shear property is clearly improved. On this moment Several variants of the basic pultrusion process have been developed, which are of interest to many and mean a lot to the industry. Their advantages are good electrical, physical, chemical and thermal properties, high performance and excellent dimensional tolerance. One of these pultrusion methods is precisely intended for the production of permanent plate and sheet semi-finished products.

However, each method has its drawbacks. This method is characterized by such a disadvantage as the speed of the process, which will depend on the temperature and rate of hardening of the binder. It is usually small for low heat resistant polyester resins. Another disadvantage is that it is difficult to provide a constant cross-section of the product along its length, with the exception of products with not particularly complex shape sections - square, round, I-beam and others. To obtain the product, you must use only threads or strands. However, for Lately These shortcomings of the method for producing profile products were gradually eliminated and the use of this process expanded noticeably. A composition that is based on polyvinyl ethers and epoxy resins are used as polymer matrices. The use of such polymer matrices based on polysulfone, polyethersulfone and plasticized polyimide makes it possible to achieve a molding speed of rods with a diameter of about five mm at a speed of about one hundred and two m/min.

To obtain complex reinforced profile products, it is necessary to use the method of drawing layered materials that consist of fibrous mats or fabrics. Currently, methods have been developed for producing tubular products that combine winding of a spiral layer and broaching. Wind turbine blades, which have complex profile cross-section, can be cited as an example of the use of materials with a complex reinforcement pattern. Tooling has already been developed for molding semi-finished products for automotive leaf springs, which have a curved surface and a variable cross-section.

4. Winding.

One of the most promising methods for molding fiberglass products is the fiber winding method, due to the fact that it creates the required filler structure in the products depending on their shape and operating characteristics. Thanks to the use of strands, tapes, threads as fillers, it ensures maximum strength of products. Moreover, such fillers are the cheapest.

The fiber winding process can be described as a relatively simple method in which reinforcing material in the form of a permanent roving (tow) or thread (yarn) is wound onto a rotating mandrel. Special mechanisms monitor the winding angle and the location of the reinforcing material. These devices move at a speed that matches the rotation of the mandrel. The material is wrapped around the mandrel in the form of strips touching each other, or in some special pattern until the mandrel surface is completely covered. Successive layers can be applied at one angle or at different angles winding until the required thickness is reached. The winding angle varies from very small, which is called longitudinal, to large - circumferential. This arrangement implies 90 0 relative to the axis of the mandrel, covering all spiral angles of this interval.

Thermosetting resin serves as a binder for the reinforcing material. In the wet winding process, the resin is applied directly during the winding itself. The dry winding process is based on the use of roving, which is pre-impregnated with resin in the B-stage. Hardening is carried out at increased temperature without excess pressure. The final stage of the process is based on taking the product from the mandrel. If necessary, finishing operations can be carried out: mechanical processing or grinding. The basic winding process is characterized by many options, which differ only in the nature of the winding, as well as design features, combination of materials and type of equipment. The structure must be wound as on a surface of rotation. However, it is possible to mold products of another type, for example, by compressing a still unhardened wound part inside a closed mold.

The design looks like a smooth cylinder, pipe or tubing, the diameter of which ranges from several centimeters to several tens of centimeters. Winding allows you to form products of conical, spherical and geodesic shapes. To get vessels high pressure and storage tanks, an end cap must be inserted into the winding. It is possible to form products that will work under non-standard loading conditions, for example, external or internal pressure, compression loads or torque. Thermoplastic pipes and high-pressure metal vessels are strengthened when wound with external bands. The resulting products are characterized high degree accuracy. However, there is another side to the winding process; this process is characterized by lower production speeds. The advantage is that absolutely any permanently reinforcing material is suitable for winding.

Various types of machines can be used for the winding process, from various lathes and chain-driven machines to more complex computerized units characterized by three or four axes of motion. Machines that continuously produce pipes are also used. To facilitate winding of large tanks, portable equipment should be designed at the installation site.

The main advantages of the winding method:

• a method of laying material that is profitable from an economic point of view due to the speed of the process;
• possibility of adjusting the resin/glass ratio;
• low dead weight, but high strength;
• this method is not prone to corrosion and rotting;
• relatively inexpensive materials;
• good structure of laminates, due to the fact that the profiles have directional fibers, and good content of glass materials.

5. Pressing.

The pressing process consists of directly imparting the desired shape product under the influence of high pressure, which is formed in the mold at a temperature of rapid hardening of the material. Due to external pressure in the material that is pressed, its compaction and partial destructuring of the previous structure occurs. The friction between contacting particles of material, which is formed during compaction, causes the generation of thermal energy, which will definitely lead to the melting of the binder. After the material enters a viscoplastic state, it spreads in the mold under pressure, forming a coherent and compacted structure. The hardening process is based on the cross-linking reaction of macromolecules due to polycondensation between the free groups of the binder. The reaction requires heat, during which low molecular weight, volatile substances are released, such as methanol, water, formaldehyde, ammonia, etc.

Parameters for direct pressing technology:

• preheating temperature;
• pressing pressure;
• pressing temperature;
• temporary exposure under pressure;
• prepress parameters;

Pressure acts directly on the material in the mold cavity during direct pressing, so mold parts may wear out prematurely. Depending on the size of the product, the pressing cycle can range from 4 to 7 minutes. Direct pressing of plastics for reinforcement has two types, which depend on how the fiber filler is impregnated:

• Dry, pre-impregnated canvases and fabrics are pressed;
• They are pressed with impregnation exactly in the mold.

The first method is more popular. To produce products of relatively simple shapes, direct pressing is used. Due to the high demands placed on the quality of the outer surface of the part, automatic installations were created for dosing components when preparing prepreg blanks. Special automatic manipulators have been designed that load packages of blanks into multi-cavity press molds. The new generation of high precision presses are equipped with modern systems control, thanks to which it is possible to obtain parts with a high-quality surface, and their cost is approximately the same as steel parts.

6. SMC technology.

A serious obstacle to the spread of composite materials is the poor adaptation of traditional technologies for their production to the needs of modern large-scale production, which is also fully automated. Today, composite parts still remain “piece goods”. Expensive labor of experienced personnel makes a high contribution to the cost share of these materials. Despite this, for last years We have made significant progress in preparing automated methods for producing composites. SMC technology has become one of the most popular developments.

The final products using this technology are subject to a two-stage process. The first stage of the technology is characterized by the fact that prepreg is produced on an automatic conveyor unit, and already at the second stage the prepreg is processed in steel molds into finished parts. Let us describe these stages in more detail. Unsaturated polyester resin is used as the base for the binder material. Its advantages include low price And a short time curing. The reinforcing component is chopped fiberglass, which is randomly distributed throughout the volume of the sheet. Long-term storage for several months at room temperature is ensured by the resin curing system. Chemical thickeners increase the viscosity of the binder after the glass fiber has been impregnated by several orders of magnitude, thereby improving the manufacturability of the prepreg and also increasing its shelf life. Mineral fillers, which are introduced into the binder in large quantities, increase the fire resistance of finished products and, and the quality of their surface noticeably improves.

The resulting prepreg can be processed in an automatic process thanks to pressing in heated steel molds. These molds are similar in design to injection molds for thermoplastics. Thanks to the binder formulation, the prepreg hardens at a temperature of 150 C and a pressure of 50-80 bar at a speed of ~30 sec/mm of thickness. Very low curing shrinkage is important feature SMC technologies. Due to the high content of mineral filler and special thermoplastic additives, shrinkage is up to 0.05%. The resulting products have an impact strength of 50-100 kJ/m2, and a destructive bending strength of 120-180 MPa. It is economically feasible to use SMC technology when obtaining high-quality composite products in large quantities from several thousand to hundreds of thousands per month. Hundreds of thousands of similar materials are produced on the European market per year. The electric power, automobile and railway industries are the largest consumers of these materials.

7. RTM (Resin Transfer Molding) method.

The RTM method is based on the impregnation and injection molding of composites, during which the binder is transferred into a closed matrix that already contains fillers or preforms. Various fabrics of various weaves can act as reinforcing material, for example, multi-axial or emulsion material, and powdered glass mats. The binder is a resin that gels in 50-120 minutes and has a low dynamic viscosity. GOST 28593-90 determines the viscosity and gelation time of the resin.

This method is perfect for standard volumes of 500 -10,000 products per year. The design of the matrix consists of composite or steel forms that repeat the external contours of the part on both sides. The structures have high temperature characteristics that are held in place by the precise alignment of enclosed steel frames that are supported at the clamping points.

This method is ideal for the production of matrices from 0.2m2 to 100m2. The matrix design consists of composite or steel forms. The circuit matrix consists of a lighter and more flexible design. The halves of the matrix are connected to each other under the influence of vacuum.

Advantages of RTM technology:

• automated production, which reduces the random nature of human intervention;
• there is a reduction and control of the amount of raw materials used;
• the impact of the material on the environment is reduced;
• working conditions have been improved;
• relatively durable products are created due to better impregnation;
• relatively cheap equipment.

Composite materials , or, as they are commonly called, composites, have revolutionized many industries and have become popular in high-tech products that must be lightweight but at the same time highly resistant to mechanical stress. The expected economic benefits in high-tech projects such as developments in the field of military and space technology are associated primarily with lightweight, high-temperature resistant composite materials, which reduce the weight of the final products, operating costs and fuel consumption.

Modern aviation, both military and civilian, would be significantly less effective without composite materials.

In fact, the requirements of this particular industry for materials (which, on the one hand, must be light, and on the other hand, sufficiently strong) were the main guiding force in their development and development. It is now generally accepted that aircraft wings, tails, propellers, and engine turbine blades are made of modern composite materials. The same applies to most of their internal structure and fuselage parts. Some small aircraft already have bodies made entirely of composite materials. In large commercial aircraft, such materials are typically used in the wings, tail surfaces, and body panels. Composite connectors for internal connections , supplied to the market in accordance with its needs and consumer requirements, successfully replace previous connectors, which were made of brass, nickel, aluminum, bronze or stainless steel. Composite connectors are ideal for use in environments environment , where resistance to high temperatures and compliance with electromagnetic compatibility requirements are required. When used, there is virtually no release of toxic gaseous products and, in particular, and most importantly, halogens. Composite materials are stronger than steel, they provide high corrosion resistance, and have more high reliability

and durability, and at the same time they also have significantly less weight than their steel counterparts.

Production of composite materials Composites are made up of several individual materials. The purpose of creating a composite material is to create some new substance that combines the properties of its constituent parts in the most. Composite materials have two components: a matrix (binder) and reinforcing elements (fillers).

To create a composite material, at least one component of each type is required. For the matrix, most modern composite materials use thermoplastic or thermoset plastics (also called resins). Plastics are polymers that hold together reinforcing elements, and they help define the desired physical properties final product.

Thermoplastic plastics are characterized by the fact that they are hard low temperatures, but soften when heated. Although they are used less frequently than thermoset plastics, they do have some advantages, such as higher fracture toughness, longer shelf life as raw materials, and recyclability. Using thermoplastic plastics is safer and less polluting workplace, because when preparing them for direct use there is no need for organic solvents to harden them.

Series Deutsch ACT represents high performance composite connectors, made in accordance with the standard MIL-DTL-38999.

The performance of any connector depends on the performance of its component parts. The use of composite materials in the ACT series increased the strength of the connector body and thread locking mechanism, resulting in the number of possible mating cycles reaching 1500. The use of composite materials also increased the corrosion resistance of the connectors (2000 hours in salt spray conditions). In addition, this series of connectors are designed with locking latches, which have a beneficial effect on performance and durability. life cycle connector.

Thermosetting plastics, or thermoset plastics, in their original form are in a liquid state, but harden and become solid (vulcanize) after they are heated. The hardening process is irreversible, so these materials no longer become soft when exposed to high temperatures. When the plastic matrix is ​​reinforced with glass fibers, for example, thermosets successfully resist wear and tear and are highly durable even in harsh environments. Such materials provide both design flexibility and high electrical strength.

If we classify composites according to the matrix material, we distinguish: thermoset composites, composites using short (chopped) fibers and thermosets with long fibers or reinforced with fibers. Most known materials for such matrices: polyesters (polyester), epoxy resins, phenol-formaldehyde, polyimides, polyamides and polypropylene. Ceramics, carbon and metals are also used as matrices for some very specific applications. For example, ceramics are used when the material is exposed to very high temperatures, and carbon is used for products that are subject to friction and wear.

Polymers Not only are they used as a matrix material, they are also used as well-proven reinforcing materials to strengthen composites. For example, Kevlar is a polymer fiber that is very strong and adds stiffness combined with toughness to the composite material. Although glass fibers are the most commonly used reinforcement option, composites can also use metal reinforcement in the form of rebar to reinforce other metals, such as in metal matrix composites (MMC). Compared to polymer matrix composites, MMCs are more resistant to ignition and can operate over a wider temperature range, are non-hygroscopic, have higher electrical conductivity and thermal conductivity, are resistant to radiation exposure and do not emit toxic gases. However, they tend to be more expensive than the counterparts they replace and are used where their higher specifications and properties may justify the increased cost.

Today these materials Most often they are used in aircraft components and space systems.

Strength and resistance to elevated temperatures are the most important characteristics in polymers used for high-tech applications. Products intended for commercial and military space applications must be manufactured using so-called engineering plastics or other specialized high-temperature polymers. Engineering plastics such as polyetherimide (PEI), polyphthalamide (PPA), polyphenylene sulfide (PPS) and polyesterimide (PAI) are designed and intended specifically for use at elevated operating temperatures. Resins such as polyetheretherketone (PEEK) and various liquid crystal polymers (LCPs) can also withstand extremely high temperatures. These modern high-tech plastics also meet toxic emissions requirements and are flame resistant.

Advantages of using composite materials

We depend on composite materials in a number of aspects of our daily lives. Fiberglass-based composite materials were developed back in the late 40s of the last century; they are the first modern composite materials and are still widely used today. In the total volume of composite materials currently produced, fiberglass-based materials occupy approximately 65%. You may be using products made from fiberglass composite material without even realizing it.

The ever-increasing number of manufacturers of composite materials and the growth of their offerings on the market allows consumers to choose required material taking into account a number of their advantages, such as:

• Composites are incredibly lightweight and are therefore increasingly used in internal connection systems (connectors) where low weight is a factor. For most of these applications, the typical weight savings when using composites compared to aluminum is approximately 40%, and 80% compared to brass and stainless steel parts.
• Composite materials are extremely durable. As an example, high-strength fiber-structured composites are widely used in body armor. Thanks to the high strength of such composite materials, soldiers are well protected from shrapnel and bullets.
• Composites are very resistant to aggressive chemicals and will never rust or corrode. This is precisely why the maritime industry was one of the first to adopt them for use.
• Polymer plastics are less susceptible to mechanical resonance, so parts with threaded connections made from such materials are less likely to loosen and come loose when exposed to shock and strong vibration.
• Some composites are not electrically conductive. This is important because composite materials are often needed where strength and high electrical insulating properties are needed.
• Composites can weaken magnetic fields, reduce the effect of magnetic fields on corrosion and dampen the so-called “acoustic signature”, that is, the acoustic radiation characteristic of each device, which is very important property when developing products for which a low probability of detection is important.

Parts made of composites will fracture under stress with a much lower degree of probability than parts made of metal. Small crack in metal part

can develop into a catastrophic one, very quickly and with very serious consequences. Fibrous materials in their complex composite structure can distribute internal stress and block the expansion of small cracks. The load in any composite is distributed throughout its fibers, it is the fibers that carry all the load, so their type, number, orientation and linearity determine their effectiveness. Fiberglass composites are used for applications that simultaneously require stiffness, high electrical insulation properties, and abrasion resistance. Carbon fibers in composite materials are used for applications requiring high strength and stiffness. The resin matrix in the composite, distributed between the fibers, protects them and keeps the fibers in their correct location and orientation. The type of matrix resin determines its absorption properties, both to water (hygroscopicity) and to chemical compounds, mechanical properties when high temperatures

, compressive strength and mechanical rigidity. In addition, the type of resin determines the manufacturing method of the final product and its relative cost. alternative types

resins and manufacturing methods.

The most important of all the advantages of composite materials is their strength and rigidity, combined with low specific gravity. It is most difficult to design complex parts from composites that take advantage of the listed properties, but at the same time must perform necessary requirements by geometric dimensions, installation and functional use. But by selecting the appropriate combination of reinforcing material and matrix material, manufacturers can ensure that the product has all the necessary characteristics that will meet the requirements for both its specific design and the specific purpose of its use.

Electrical connectors that provide power and data transmission in military and aerospace products are constantly becoming smaller and lighter. Many military customers are looking for smaller, lighter and more flexible solutions that meet stringent industrial requirements for strength and durability. Recent Developments in the Field constructive solutions and materials have made it possible to make a leap in the technology of production and execution of connectors, which ensure both their high technical characteristics and the necessary requirements for environmental protection.

Composites are the basis of many modern projects in the field of development of devices with minimally noticeable effects. One of them is unmanned aerial vehicles (UAVs). Composite materials were very actively used in their design, resulting in the possibility of their detection only at close range.

Composites provide high durability and stiffness, making them suitable materials for systems used in avionics.

These materials offer reduced weight, high strength and durability that far exceed those of many metals and non-composite thermosets.

Special condition environment in space requires special components that can be used in outer space conditions; in addition, they must meet the requirements for the absence of toxic gas emissions and be made of non-magnetic materials. Carbon-based composites are the main material in modern launch vehicles and heat shields of reusable spacecraft. They are also widely used in antenna reflectors, spacecraft traverses, payload bay adapters, interconnect structures, and reusable spacecraft heat shields.

It is an undeniable fact that composite materials are increasingly being developed to meet the specific requirements of internal connection systems; despite the increasing complexity of both their design and the manufacturing process, these materials, due to their properties, are worth using. The stumbling block when using composites is usually their cost. Although they themselves production processes Manufacturing when composite materials are used is often more efficient, but the raw materials themselves are expensive. Of course, composites will never be able to completely replace traditional materials, such as steel, but the significant advantages of composites provide real cost savings, reducing fuel consumption and saving on system maintenance as a whole, increasing the service life for a large number of defense and space products. Without a doubt, we should be aware of all the possibilities that composites can give us.

Based on materials from the website www.connectorsupplier.com
Jenny Bieksha, Bishop & Associates Inc.
Translation: Vladimir Rentyuk
The article was published in the journal “Bulletin of Electronics” No. 1 2014

Composite materials – artificially created materials that consist of two or more components that differ in composition and are separated by a pronounced boundary, and which have new properties designed in advance.

The components of the composite material are different geometrically. A component that is continuous throughout the entire volume of a composite material is called matrix. A discontinuous component separated within the volume of a composite material is called fittings. The matrix gives the required shape to the product, influences the creation of the properties of the composite material, and protects the reinforcement from mechanical damage and other environmental influences.

Organic and inorganic polymers, ceramic, carbon and other materials can be used as matrices in composite materials. The properties of the matrix determine the technological parameters of the process of obtaining the composition and its: density, specific strength, operating temperature, resistance to fatigue failure and exposure to aggressive environments. Reinforcing or strengthening components are evenly distributed in the matrix. They, as a rule, have high , and in these indicators they are significantly superior to the matrix. Instead of the term reinforcing component, the term filler can be used.

Classification of composite materials

According to filler geometry composite materials are divided into three groups:

• with zero-dimensional fillers, the sizes of which in three dimensions are of the same order;
• with one-dimensional fillers, one of the sizes of which is significantly larger than the other two;
• with two-dimensional fillers, two sizes of which are significantly larger than the third.

According to the arrangement of fillers, three groups of composite materials are distinguished:

• with a uniaxial (linear) arrangement of filler in the form of fibers, threads, whiskers in the matrix parallel to each other;
• with a biaxial (planar) arrangement of reinforcing filler, mats of whiskers, foil in a matrix in parallel planes;
• with a triaxial (volumetric) arrangement of the reinforcing filler and the absence of a preferential direction in its location.

According to the nature of the components, composite materials are divided into four groups:

• composite materials containing a metal or alloy component;
• composite materials containing a component of inorganic compounds of oxides, carbides, nitrides, etc.;
• composite materials containing a component of non-metallic elements, carbon, boron, etc.;
• composite materials containing a component of organic compounds, epoxy, polyester, phenolic, etc.

The properties of composite materials depend not only on the physicochemical properties of the components, but also on the strength of the bond between them. Maximum strength is achieved if the formation of or occurs between the matrix and the reinforcement.

In composite materials with zero-dimensional filler The metal matrix is ​​most widely used. Metal-based compositions are strengthened by uniformly distributed dispersed particles of varying dispersion. These materials are different.

In such materials, the matrix absorbs the entire load, and dispersed filler particles prevent the development of plastic deformation. Effective hardening is achieved with a content of 5...10% filler particles. Particles of refractory oxides, nitrides, borides, and carbides serve as reinforcing fillers. Dispersion-strengthened composite materials are produced by powder metallurgy methods or by introducing reinforcing powder particles into a liquid molten metal or alloy.

Composite materials based on aluminum oxide (Al 2 O 3) reinforced with aluminum oxide particles have found industrial application. They are produced by pressing aluminum powder followed by sintering (SAP). The advantages of SAP appear at temperatures above 300 o C, when aluminum alloys soften. Dispersion-strengthened alloys retain the hardening effect up to a temperature of 0.8 T pl.

SAP alloys are satisfactorily deformed, easily machined, welded, etc. SAP produces semi-finished products in the form of sheets, profiles, pipes, and foil. Blades of compressors, fans and turbines, and piston rods are made from them.

In composite materials with one-dimensional fillers Strengtheners are one-dimensional elements in the form of whiskers, fibers, wires, which are held together by a matrix into a single monolith. It is important that the strong fibers are evenly distributed in the plastic matrix. To reinforce composite materials, continuous discrete fibers with cross-sectional sizes from fractions to hundreds of micrometers are used.

Materials reinforced with whisker-like monocrystals were created in the early seventies for aircraft and space structures. The main way to grow whiskers is to grow them from supersaturated steam (PC process). To produce especially high-strength whisker crystals of oxides and other compounds, growth is carried out according to the P-J-C mechanism: the directed growth of crystals occurs from a vapor state through an intermediate liquid phase.

Whiskers are created by drawing liquid through dies. The strength of crystals depends on the cross-section and smoothness of the surface.

Composite materials of this type are promising as... To increase the efficiency of heat engines, gas turbine blades are made of nickel alloys reinforced with sapphire threads (Al 2 O 3), this makes it possible to significantly increase the temperature at the turbine inlet (the tensile strength of sapphire crystals at a temperature of 1680 o C is above 700 MPa).

Reinforcement of rocket nozzles from tungsten and molybdenum powders is carried out with sapphire crystals both in the form of felt and individual fibers, as a result of which it was possible to double the material at a temperature of 1650 o C. Reinforcing the impregnating polymer of fiberglass laminates with thread-like fibers increases their strength. Cast metal reinforcement reduces it in structures. Strengthening glass with non-oriented whiskers is promising.

To reinforce composite materials, metal wire made of different metals is used: steel of different compositions, tungsten, niobium, depending on the operating conditions. Steel wire is processed into woven meshes, which are used to produce composite materials with reinforcement oriented in two directions.

For the reinforcement of light metals, boron and silicon carbide fibers are used. Especially valuable properties possess carbon fibers, they are used for reinforcing metal, ceramic and polymer composite materials.

Eutectic composite materials– alloys of eutectic or close to eutectic composition, in which the strengthening phase is oriented crystals formed during the process of directional crystallization. Unlike conventional composite materials, eutectic ones are obtained in one operation. A directional oriented structure can be obtained on ready-made products. The shape of the resulting crystals can be in the form of fibers or plates. Directed crystallization methods are used to produce composite materials based on cobalt, niobium and other elements, therefore they are used in a wide temperature range.

Introduction

Introduction

A composite material is a heterogeneous solid material consisting of two or more components, among which we can distinguish reinforcing elements that provide the necessary mechanical characteristics of the material, and a matrix that ensures the joint operation of the reinforcing elements. The mechanical behavior of a composite is determined by the relationship between the properties of the reinforcing elements and the matrix, as well as the strength of the bond between them. The efficiency and performance of the material depend on the correct choice of initial components and the technology of their combination, designed to ensure strong connection between components while maintaining their original characteristics. As a result of the combination of reinforcing elements and the matrix, a complex of properties of the composite is formed, which not only reflects the initial characteristics of its components, but also includes properties that the isolated components do not possess. In particular, the presence of interfaces between the reinforcing elements and the matrix significantly increases the crack resistance of the material, and in composites, unlike metals, an increase in static strength does not lead to a decrease, but, as a rule, to an increase in fracture toughness characteristics.

Advantages of composite materials:

High specific strength;

High rigidity (elastic modulus 130...140 GPa);

High wear resistance;

High fatigue strength;

It is possible to produce dimensionally stable structures from CM, and different classes of composites may have one or more advantages.

The most common disadvantages of composite materials:

High price;

Anisotropy of properties;

Increased knowledge intensity of production, the need for special expensive equipment and raw materials, and therefore developed industrial production and the country's scientific base.

1. Classification of composite materials

Composites are multicomponent materials consisting of a polymer, metal, carbon, ceramic or other base (matrix), reinforced with fillers made of fibers, whiskers, fine particles, etc. By selecting the composition and properties of the filler and matrix (binder), their ratio , orientation of the filler, it is possible to obtain materials with the required combination of operational and technological properties. The use of several matrices (polymatrix composite materials) or fillers of different natures (hybrid composite materials) in one material significantly expands the possibilities of regulating the properties of composite materials. Reinforcing fillers absorb the main share of the load of composite materials.

Based on the structure of the filler, composite materials are divided into fibrous (reinforced with fibers and whiskers), layered (reinforced with films, plates, layered fillers), dispersed reinforced, or dispersion-strengthened (with filler in the form of fine particles). The matrix in composite materials ensures the solidity of the material, the transmission and distribution of stress in the filler, and determines heat, moisture, fire and chemical reactions. durability.

Based on the nature of the matrix material, polymer, metal, carbon, ceramic and other composites are distinguished.

Composite materials with a metal matrix are a metal material (usually Al, Mg, Ni and their alloys) strengthened with high-strength fibers (fibrous materials) or finely dispersed refractory particles that do not dissolve in the base metal (dispersion-strengthened materials). The metal matrix binds the fibers (dispersed particles) into a single whole.

Composite materials with a non-metallic matrix have found wide application. Polymer, carbon and ceramic materials are used as non-metallic matrices. The most widely used polymer matrices are epoxy, phenol-formaldehyde and polyamide. Carbon matrices, coked or pyrocarbon, are obtained from synthetic polymers subjected to pyrolysis. The matrix binds the composition, giving it shape. Strengtheners are fibers: glass, carbon, boron, organic, based on whisker crystals (oxides, carbides, borides, nitrides and others), as well as metal (wires), which have high strength and rigidity.

According to the mechanism of reinforcing action, composite materials with a fibrous filler (reinforcer) are divided into discrete ones, in which the ratio of fiber length to diameter is relatively small, and those with continuous fiber. Discrete fibers are arranged randomly in the matrix. The fiber diameter ranges from fractions to hundreds of micrometers. The greater the ratio of fiber length to diameter, the higher the degree of strengthening.

Often the composite material is layered structure, in which each layer is reinforced with a large number of parallel continuous fibers. Each layer can also be reinforced with continuous fibers woven into a fabric that represents the original shape, matching the width and length of the final material. Often the fibers are woven into three-dimensional structures.

Composite materials differ from conventional alloys in higher values ​​of tensile strength and endurance limit (by 50–10%), elastic modulus, stiffness coefficient and a reduced susceptibility to cracking. The use of composite materials increases the rigidity of the structure while simultaneously reducing its metal consumption. The strength of composite (fibrous) materials is determined by the properties of the fibers; the matrix should mainly redistribute stresses between the reinforcing elements. Therefore, the strength and elastic modulus of the fibers must be significantly greater than the strength and elastic modulus of the matrix. Rigid reinforcing fibers perceive stresses arising in the composition during loading, giving it strength and rigidity in the direction of fiber orientation.

To strengthen aluminum, magnesium and their alloys, boron fibers are used, as well as fibers from refractory compounds (carbides, nitrides, borides and oxides) having high strength and elastic modulus. For the reinforcement of titanium and its alloys, molybdenum wire, sapphire fibers, silicon carbide and titanium boride are used. Increasing the heat resistance of nickel alloys is achieved by reinforcing them with tungsten or molybdenum wire. Metal fibers are also used in cases where high thermal and electrical conductivity are required. Promising strengtheners for high-strength and high-modulus fibrous composite materials are whiskers made of aluminum oxide and nitride, silicon carbide and nitride, boron carbide, etc. Metal-based composite materials have high strength and heat resistance, while at the same time they are low-plasticity. However, fibers in composite materials reduce the rate of propagation of cracks initiated in the matrix, and sudden brittle failure almost completely disappears. Distinctive feature fibrous uniaxial composite materials are anisotropic mechanical properties along and across the fibers and low sensitivity to stress concentrators. The anisotropy of the properties of fiber composite materials is taken into account when designing parts to optimize properties by matching the resistance field with the stress fields. It must be taken into account that the matrix can transmit stress to the fibers only if there is a strong bond at the reinforcing fiber-matrix interface. To prevent contact between fibers, the matrix must completely surround all fibers, which is achieved when its content is at least 15-20%. The matrix and fiber should not interact with each other (there should be no mutual diffusion) during manufacturing and operation, as this can lead to a decrease in the strength of the composite material. Reinforcement of aluminum, magnesium and titanium alloys with continuous refractory fibers of boron, silicon carbide, titanium boride and aluminum oxide significantly increases heat resistance. A feature of composite materials is the low rate of softening over time with increasing temperature.

The main disadvantage of composite materials with one- and two-dimensional reinforcement is the low resistance to interlayer shear and transverse breakage. Materials with volumetric reinforcement do not have this.

Unlike fibrous composite materials, in dispersion-strengthened composite materials the matrix is ​​the main load-bearing element, and dispersed particles inhibit the movement of dislocations in it.

High strength is achieved with a particle size of 10-500 nm with an average distance between them of 100-500 nm and uniform distribution them in the matrix. Strength and heat resistance, depending on the volumetric content of strengthening phases, do not obey the law of additivity. Optimal content of the second phase for various metals varies, but usually does not exceed 5-10 vol. %. The use of stable refractory compounds (oxides of thorium, hafnium, yttrium, complex compounds of oxides and rare earth metals) that do not dissolve in the matrix metal as strengthening phases allows maintaining the high strength of the material up to 0.9-0.95 Tm. In this regard, such materials are often used as heat-resistant. Dispersion-strengthened composite materials can be obtained on the basis of most metals and alloys used in technology. The most widely used aluminum-based alloys are SAP (sintered aluminum powder).

2. Composition, structure and properties of composite materials

The properties of composite materials depend on the composition of the components, their combination, quantitative ratio and strength of the bond between them. Reinforcing materials can be in the form of fibers, strands, threads, tapes, multilayer fabrics. The hardener content in oriented materials is 60-80 vol.%, in non-oriented materials (with discrete fibers and whiskers) 20-30 vol.%. The higher the strength and elastic modulus of the fibers, the higher the strength and stiffness of the composite material. The properties of the matrix determine the shear and compressive strength of the composition and the resistance to fatigue failure. In layered materials, fibers, threads, tapes impregnated with a binder are laid parallel to each other in the laying plane. Flat layers are assembled into plates. The properties are anisotropic. For the material to work in a product, it is important to take into account the direction of the acting loads. It is possible to create materials with both isotropic and anisotropic properties. You can lay the fibers at different angles, varying the properties of the composite materials. The flexural and torsional rigidities of the material depend on the order in which the layers are laid across the thickness of the package. Reinforcers of three, four or more threads are used. Most Applications has a structure of three mutually perpendicular threads. Reinforcers can be located in the axial, radial and circumferential directions. Three-dimensional materials can be of any thickness in the form of blocks or cylinders. Bulky fabrics increase peel strength and shear strength compared to laminated fabrics. A system of four threads is constructed by decomposing the reinforcement along the diagonals of the cube. The structure of four threads is equilibrium and has increased shear rigidity in the main planes. However, creating four-directional materials is more difficult than creating three-directional materials.

Composite materials reinforced with high-strength and high-modulus continuous fibers are most widely used in construction and technology. These include: polymer composite materials based on thermosetting (epoxy, polyester, phenol-formaldehyde, polyamide, etc.) and thermoplastic binders, reinforced with glass (fiberglass), carbon (carbon fiber), organic (organoplastic), boron (boroplastics), etc. .fibers; metal composite materials based on Al, Mg, Cu, Ti, Ni, Cr alloys, reinforced with boron, carbon or silicon carbide fibers, as well as steel, molybdenum or tungsten wire; composite materials based on carbon reinforced with carbon fibers (carbon-carbon materials); composite materials based on ceramics reinforced with carbon, silicon carbide and other heat-resistant fibers and SiC. When using carbon, glass, amide and boron fibers contained in the material in an amount of 50-70%, compositions with a specific strength and elastic modulus 2-5 times greater than those of conventional structural materials and alloys were created. In addition, fibrous composite materials are superior to metals and alloys in fatigue strength, heat resistance, vibration resistance, noise absorption, impact strength and other properties. Thus, reinforcing Al alloys with boron fibers significantly improves their mechanical characteristics and makes it possible to increase the operating temperature of the alloy from 250-300 to 450-500 °C. Reinforcement with wire (from W and Mo) and fibers of refractory compounds is used to create heat-resistant composite materials based on Ni, Cr, Co, Ti and their alloys. Thus, heat-resistant Ni alloys reinforced with fibers can operate at 1300-1350°C. In the manufacture of metal fiber composite materials, the application of a metal matrix to the filler is carried out mainly from a melt of the matrix material, by electrochemical deposition or sputtering. The molding of products is carried out by Ch. arr. by impregnating a frame of reinforcing fibers with a metal melt under pressure up to 10 MPa or by combining foil (matrix material) with reinforcing fibers using rolling, pressing, extrusion when heated to the melting point of the matrix material.

One of the common technological methods for the production of polymer and metal fiber and layered composite materials is the growth of filler crystals in a matrix directly during the manufacturing process of parts. This method is used, for example, in the creation of eutectic heat-resistant alloys based on Ni and Co. Alloying melts with carbide and intermetallic compounds, which form fibrous or plate-like crystals when cooled under controlled conditions, leads to strengthening of the alloys and makes it possible to increase their operating temperature by 60-80oC. Carbon-based composite materials combine low density with high thermal conductivity, chemical. durability, constancy of dimensions under sudden temperature changes, as well as an increase in strength and elasticity modulus when heated to 2000 °C in an inert environment. High-strength composite materials based on ceramics are obtained by reinforcement with fibrous fillers, as well as metal and ceramic dispersed particles. Reinforcement with continuous SiC fibers makes it possible to obtain composite materials characterized by increased viscosity, flexural strength and high resistance to oxidation at high temperatures. However, reinforcement of ceramics with fibers does not always lead to a significant increase in its strength properties due to the lack of elastic state of the material at a high value of its elastic modulus. Reinforcement with dispersed metal particles makes it possible to create ceramic-metallic materials (cermets) with increased strength, thermal conductivity, and resistance to thermal shocks. In the manufacture of ceramic composite materials, hot pressing, pressing followed by sintering, and slip casting are usually used. Reinforcement of materials with dispersed metal particles leads to a sharp increase in strength due to the creation of barriers to the movement of dislocations. Such reinforcement ch. arr. used in the creation of heat-resistant chromium-nickel alloys. The materials are produced by introducing fine particles into molten metal, followed by conventional processing of the ingots into products. The introduction of, for example, ThO2 or ZrO2 into the alloy makes it possible to obtain dispersion-strengthened heat-resistant alloys that operate for a long time under load at 1100-1200°C (the service limit of conventional heat-resistant alloys under the same conditions is 1000-1050°C). A promising direction for creating high-strength composite materials is the reinforcement of materials with whiskers (whiskers), which, due to their small diameter, are practically free of defects found in larger crystals and have high strength. Of most practical interest are crystals of Al2O3, BeO, SiC, B4C, Si3N4, AlN and graphite with a diameter of 1-30 microns and a length of 0.3-15 mm. Such fillers are used in the form of oriented yarn or isotropic layered materials such as paper, cardboard, and felt. The introduction of whisker crystals into a composition can give it unusual combinations of electrical and magnetic properties. The choice and purpose of composite materials are largely determined by the loading conditions and operating temperature of parts or structures, technol. possibilities. Polymer composite materials are the most accessible and mastered. A large range of matrices in the form of thermosetting and thermoplastic polymers provides a wide selection of composite materials for operation in the range from negative temperatures to 100-200 ° C for organoplastics, up to 300-400 ° C for glass, carbon and boron plastics. Polymer composite materials with a polyester and epoxy matrix operate up to 120-200°C, with phenol-formaldehyde - up to 200-300°C, polyimide and organosilicon - up to 250-400°C. Metal composite materials based on Al, Mg and their alloys, reinforced with fibers from B, C, SiC, are used up to 400-500 ° C; composite materials based on Ni and Co alloys operate at temperatures up to 1100-1200 °C, those based on refractory metals and compounds - up to 1500-1700 °C, those based on carbon and ceramics - up to 1700-2000 °C. The use of composites as structural, heat-shielding, anti-friction, radio and electrical and other materials makes it possible to reduce the weight of a structure, increase the resources and power of machines and units, and create fundamentally new components, parts and structures. All types of composite materials are used in the chemical, textile, mining, metallurgical industries, mechanical engineering, transport, for the manufacture of sports equipment, etc.

3. Economic efficiency of using composite materials

The areas of application of composite materials are not limited. They are used in aviation for highly loaded parts (skin, spars, ribs, panels, compressor and turbine blades, etc.), in space technology for units of power structures of devices, for stiffening elements, panels, in the automotive industry to lighten bodies, springs, frames, body panels, bumpers, etc., in the mining industry (drilling tools, combine parts, etc.), in civil engineering(bridge spans, elements of prefabricated structures of high-rise buildings, etc.) and in other areas of the national economy.

Application composite materials provide a new qualitative leap in increasing the power of engines, energy and transport installations, reducing the weight of machines and devices. Composite materials with a non-metallic matrix, namely polymer carbon fibers, are used in the shipbuilding and automotive industries (racing car bodies, chassis, propellers); Bearings, heating panels, sports equipment, and computer parts are made from them. High-modulus carbon fibers are used for the manufacture of aircraft parts, equipment for the chemical industry, X-ray equipment and others. Carbon fibers with a carbon matrix replace various types of graphite. They are used for thermal protection, aircraft brake discs, and chemically resistant equipment. Products made from boron fiber are used in aviation and space technology (profiles, panels, compressor rotors and blades, propeller blades, helicopter transmission shafts, etc.). Organofibers are used as insulating and structural materials in the electrical and radio industry, aviation technology, etc.

List of used literature

Gorchakov G.I., Bazhenov Yu.M. Construction materials/ G.I. Gorchakov, Yu.M. Bazhenov. – M.: Stroyizdat, 1986.

Construction materials / Edited by V.G. Mikulsky. – M.: ASV, 2000.

General course of building materials / Ed. I.A. Rybyeva. – M.: Higher School, 1987.

Construction materials / Edited by G.I. Gorchakova. – M: Higher School, 1982.

Evald V.V. Construction materials, their production, properties and testing / V.V. Ewald. – St. Petersburg: L-M, 14th edition, 1933.

Composite material

Composite material (composite, KM) - an artificially created heterogeneous continuous material consisting of two or more components with a clear interface between them. In most composites (with the exception of laminates), the components can be divided into a matrix and the reinforcing elements included in it. In composites for structural purposes, reinforcing elements usually provide the necessary mechanical characteristics of the material (strength, stiffness, etc.), and the matrix (or binder) ensures the joint operation of the reinforcing elements and their protection from mechanical damage and aggressive chemical environments.

The mechanical behavior of the composition is determined by the relationship between the properties of the reinforcing elements and the matrix, as well as the strength of the bond between them. The efficiency and performance of the material depend on the correct selection of the original components and the technology of their combination, designed to ensure a strong connection between the components while maintaining their original characteristics.

As a result of the combination of reinforcing elements and the matrix, a complex of properties of the composition is formed, which not only reflects the initial characteristics of its components, but also includes properties that the isolated components do not possess. In particular, the presence of interfaces between the reinforcing elements and the matrix significantly increases the crack resistance of the material, and in compositions, unlike homogeneous metals, an increase in static strength does not lead to a decrease, but, as a rule, to an increase in fracture toughness characteristics.

To create the composition, a variety of reinforcing fillers and matrices are used. These are getinaks and textolite (laminated plastics made of paper or fabric glued with thermosetting glue), glass and graphite plastic (fabric or wound fiber made of glass or graphite, impregnated with epoxy adhesives), plywood... There are materials in which thin fiber from high-strength alloys is embedded aluminum mass. Bulat is one of the oldest composite materials. In it, thin layers (sometimes threads) of high-carbon steel are “glued” together with soft low-carbon iron.

Recently, materials scientists have been experimenting with the goal of creating materials that are more convenient to manufacture, and therefore more efficient. cheap materials. Self-growing crystalline structures glued into a single mass are being studied polymer glue(cements with additives of water-soluble adhesives), thermoplastic compositions with short reinforcing fibers, etc.

Classification of composites

Composites are usually classified according to the type of reinforcing filler:

• fibrous (reinforcing component - fibrous structures);
• layered;
• filled plastics (reinforcing component - particles)
  • bulk (homogeneous),
  • skeletal (initial structures filled with a binder).

Advantages of composite materials

The main advantage of CM is that the material and structure are created simultaneously. An exception is prepregs, which are semi-finished products for the manufacture of structures. It is worth immediately stipulating that CMs are created to perform these tasks, and accordingly cannot contain all possible advantages, but when designing a new composite, the engineer is free to give it characteristics that are significantly superior to the characteristics of traditional materials when fulfilling a given purpose in a given mechanism, but inferior to them in any other aspects. This means that CM cannot be better than traditional material in everything, that is, for each product the engineer carries out all the necessary calculations and only then chooses the optimum between materials for production.

• high specific strength (strength 3500 MPa)
• high rigidity (elastic modulus 130…140 - 240 GPa)
• high wear resistance
• high fatigue strength
• It is possible to manufacture dimensionally stable structures from CM
• ease

Moreover, different classes of composites may have one or more advantages. Some benefits cannot be achieved simultaneously.

Disadvantages of composite materials

Composite materials have a fairly large number of disadvantages that hinder their spread.

High price

The high cost of CM is due to the high knowledge intensity of production, the need to use special expensive equipment and raw materials, and therefore the developed industrial production and scientific base of the country.

Anisotropy of properties

Low impact strength

High specific volume

Hygroscopicity

CM can also absorb other liquids with high penetrating ability, for example, aviation kerosene.

Toxicity

During operation, CMs can emit fumes that are often toxic. If CM is used to make products that will be located in close proximity to humans (the composite fuselage of the Boeing 787 Dreamliner may serve as such an example), then additional research into the effects of CM components on humans is required to approve the materials used in the manufacture of CM.

Low operational efficiency

Composite materials have low manufacturability, low maintainability and high operating costs. This is due to the need to use special labor-intensive methods, special tools for modification and repair of objects from CM. Often, objects made from CM are not subject to any modification or repair at all.

Areas of use

Consumer goods

Characteristic

The technology is used to form additional protective coatings on surfaces in steel-rubber friction pairs. The use of technology allows you to increase the duty cycle of seals and shafts industrial equipment working in an aquatic environment.

Composite materials are composed of several functionally distinct materials. The basis of inorganic materials is magnesium, iron, and aluminum silicates modified with various additives. Phase transitions in these materials occur at fairly high local loads, close to the ultimate strength of the metal. In this case, a high-strength metal-ceramic layer is formed on the surface in an area of ​​high local loads, due to which it is possible to change the structure of the metal surface.

• armor for military equipment

Literature

• Vasiliev V.V. Mechanics of structures made of composite materials. - M.: Mechanical Engineering, 1988. - 272 p.
• Karpinos D. M. Composite materials. Directory. - Kyiv, Naukova Duma

see also

Notes

Links

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