Fiber-plastic composite

A fiber-plastic composite ( FRP ; also fiber-reinforced plastic or fiber- reinforced plastic , FRP ) is a material consisting of reinforcing fibers and a plastic matrix. The matrix surrounds the fibers that are bonded to the matrix by adhesive interactions. By using fiber materials, fiber-plastic composites have a direction-dependent elasticity behavior (see elasticity law ).

Without a matrix material, the high specific strengths and stiffnesses of the reinforcement fibers cannot be used. A new construction material is only created through a suitable combination of fiber and matrix material. Early attempts to develop resin-bonded fiber composite materials led to the development of linoleum in the mid-19th century . The best-known fiber- reinforced plastic today is glass fiber reinforced plastic (GRP).

Fiber-plastic composites usually have high specific stiffnesses and strengths. This makes them suitable materials in lightweight construction applications . Mainly flat structures are produced from fiber-plastic composites.

The mechanical and thermal properties of fiber-plastic composites can be adjusted using a variety of parameters. In addition to the fiber-matrix combination, the fiber angle, the fiber volume fraction , the layer sequence and much more can be varied.

Fiber-plastic composites belong to the class of fiber-reinforced materials ( fiber composite materials ), which in turn belong to the class of composite materials .

Composite of glass fibers and epoxy resin ( GRP ). The light fibers have a diameter of 1/50 mm and smaller and make up 60% of the volume. Section, microscoped.

Working principle

Symbolic representation of reinforcing fibers in a plastic matrix.

A fiber plastic composite can be seen as a construction. Its elements must be combined in such a way that the desired properties are achieved. The interaction of the specific properties of the fiber material and the matrix material creates a new material.

Task sharing

Due to the high rigidity of the fibers compared to the matrix , they absorb tensile forces in particular. The forces acting on the fibers are directed into the fibers via adhesive forces at the fiber-matrix interface. At right angles to the fiber, the matrix and composite material often have similar moduli of elasticity , which is why no forces are absorbed by the fibers in this direction. See also: elongation enlargement .

The matrix embeds the fibers, ie the fibers are spatially fixed and a simultaneous load introduction and load transfer into a large number of fibers is possible without overloading the individual fiber. In addition, the matrix supports the fibers against buckling when pressure is applied parallel to the fibers . The load is transferred via the adhesion between the fiber and the matrix. It can take place via normal or shear forces . The matrix also has the task of protecting the fibers against environmental influences.

Effectiveness criteria

Size effect in the fiber shape. Comparison of the maximum defect size and the defect-free length.
a: compact material
b: fiber material

Not every fiber-matrix combination makes a meaningful construction material. Three criteria must be met in order to increase the stiffness and strength in the fiber direction in the composite.

1. The elastic modulus of the fibers in the longitudinal direction must be higher than that of the matrix.
   ${\displaystyle E_{\mathrm {Faser,\ l{\ddot {a}}ngs} }>E_{\text{Matrix}}\;}$
2. The elongation at break of the matrix must be higher than that of the fibers.
   ${\displaystyle \varepsilon _{\text{Matrix, Bruch}}>\varepsilon _{\text{Faser, Bruch}}}$
3. The tensile strength of the fibers in the longitudinal direction must be greater than that of the matrix.
   ${\displaystyle R_{\mathrm {Faser,\ l{\ddot {a}}ngs} }>R_{\text{Matrix}}\;}$

Effectiveness of the fiber form

Symbolic representation of the orientation of the molecular chains through stretching in fiber materials.

The fiber is superior to the compact material. This affects both the strength and the modulus of elasticity. The following effects make the fiber superior to the compact form:

Size effect : The maximum size of a defect is limited in a fiber. A spherical air pocket, for example, cannot have a diameter larger than the fiber diameter. So there are no major errors. In addition, there is an effect based on the statistical distribution of the errors. This greatly increases the fault-free length of a fiber. In the case of very thin fibers, long stretches are created before a defect occurs. These effects only increase the strength of the fiber, not its stiffness .

Orientation : During the manufacture of fibers, the crystal or molecular planes are oriented. Suitable processes are spinning and drawing. Figuratively speaking, a flexible ball of wool becomes a strand of stiff wool. Materials with long-chain molecules ( polyethylene fibers, aramid fibers , carbon fibers ) are particularly suitable for creating a high degree of orientation. As a rule, the increasing orientation is accompanied by anisotropy of the fiber. With natural fibers such as hair, wool, hemp, sisal, etc., orientation occurs during growth. Orientation mainly increases stiffness.

Some fiber types, such as glass fiber or basalt fiber, have no orientation within the fibers. These fibers are amorphous . The advantage of the fiber form lies solely in the use of the size effect with the reduction of imperfections.

Amorphous fibers that are drawn off from the melt have another advantage: On their surface, internal compressive stresses arise on cooling. The residual compressive stresses increase the strength of the fiber by preventing the fiber from cracking. See also: ESG glass

Mechanical observation levels

Fiber-reinforced plastics are considered on different mechanical levels. The level of consideration depends on whether global dimensions of the composite or those of the individual reinforcement fibers are of interest.

Micromechanics

Micromechanics consider the individual fibers embedded in the matrix. There is a two-phase mixture. With the help of micromechanics, the stresses and strains in the fiber and matrix can be calculated. Micromechanics enables the elastic properties of the fiber-reinforced plastic composite to be calculated from the properties of the fiber and matrix ( see: classical laminate theory ).

Macromechanics

In the macromechanics of fiber reinforced plastics, the composite is viewed as homogeneous. That is, its properties are independent of the location. However, its properties are still directional. With the help of macromechanics, global stress and strain values ​​are obtained. They can be understood as the mean sizes above the fiber and matrix.

Macromechanics is used to describe the behavior of components.

Reinforcement fibers

Inorganic reinforcing fibers

Inorganic fibers have an amorphous structure. Their advantages are the high temperature resistance and the mostly low price. The raw materials for glass and basalt fibers in particular are almost entirely available.

• Basalt fibers
• Boron fibers
• Fiberglass
• Ceramic fibers
• Silica fibers
• Carbon fiber
• Quartz fibers

Metallic reinforcement fibers

• Steel fibers

Organic reinforcement fibers

Organic fibers have a high degree of orientation. Their module lengthways and across the fiber differs significantly. Organic fibers decompose or melt at high temperatures. However, this temperature limit can be very different.

• Aramid fibers
• Carbon fiber
• PBO fibers
• Polyester fibers
• Nylon fibers
• Polyethylene fibers
• Polymethyl methacrylate fibers

Natural fibers

→ Main article : Natural fiber reinforced plastic

Renewable reinforcing fibers have a predominantly low density compared to other reinforcing fibers. Since their mechanical properties are poor, they are not used in structural components. Their main area of ​​application, in combination with thermoplastic matrix materials, is in cladding components and in general where a certain material thickness is to be achieved (with light weight) without the maximum tensile strength of the fibers being important. As a short cut, they are used as a cheap extender (filler material).

• Flax fibers
• Hemp fiber
• Wood fiber
• Sisal fibers

Naming of reinforcement fiber bundles

Based on the designation of yarns , bundles of reinforcing fibers, so-called rovings , are named with the yarn count tex . The larger the Tex number, the higher the length weight of the fiber bundle. A roving of 4800 tex, for example, weighs 4.8 g per meter.

In the case of carbon fibers in particular , the designation based on the number of individual filaments has established itself. A 12k roving accordingly consists of 12,000 individual filaments. The Tex number can be converted into the number of filaments via the density of the fiber.

Classification according to the fiber length

Short fibers L = 0.1 to 1 mm

Short fibers are used in injection molding technology and can be processed directly with an extruder . There are thermoplastic granulates which have already been provided with short fibers with a certain fiber volume fraction or fiber mass fraction .

Long fibers L = 1 to 50 mm

Long fibers can also be processed in extruders . You can find them to a large extent in fiber spraying . Long fibers are often mixed with thermosetting plastics as fillers.

Continuous fibers L> 50 mm

Continuous fibers are used as rovings or fabrics in fiber-reinforced plastics. Components with continuous fibers achieve the highest levels of rigidity and strength.

Semi-finished fiber products

Since the individual fiber filaments are difficult to handle, the dry fibers are combined into semi-finished products. The manufacturing processes originate to a large extent from textile technology such as weaving , braiding or embroidery .

• Fabrics
  Fabrics are created by interweaving continuous fibers such as rovings . The weaving of fibers inevitably goes hand in hand with an undulation of the fibers. The undulation causes in particular a reduction in the compressive strength parallel to the fibers. Therefore, fabrics are used for mechanically high-quality fiber-plastic composites.

• Scrim
  In a scrim, the fibers are ideally parallel and stretched. Only continuous fibers are used. Scrims are held together by paper or thread stitching.

• Multiaxial layers
  If the fibers are not exclusively oriented in the plane, one speaks of multiaxial layers. Usually the additional fibers are oriented perpendicular to the plane of the laminate in order to improve the delamination and impact behavior.

• Embroidery
  If you want to apply individual rovings not only in a stretched manner, but also on any desired paths, embroidery is used. The rovings are embroidered onto a carrier material (e.g. a fleece) and thus fixed. Embroideries are often used in the area of ​​load introduction, since a complex fiber orientation is often required here. Embroideries are used as preforms for the RTM ( Resin Transfer Molding ) process.

• Braids
  The braiding can be made of rovings braided mainly hoses that serve the production of pipes, containers, or generally hollow components.

• Mats
  If components with quasi-isotropic properties are to be manufactured, fiber mats are ideal. The mats usually consist of short and long fibers, which are loosely connected to each other with a binding agent. By using short and long fibers, the mechanical properties of components made of mats are inferior to those of woven fabrics.

• Nonwovens
  Nonwovens are z. B. made by needling long fibers. Applied as a thin layer, they serve to protect the surface or to reduce surface waviness. The mechanical properties are quasi-isotropic and inferior to those of tissues.

• Fine
  cuts Fine cuts are mainly used as fillers. You can increase the mechanical properties of pure resin areas and, if necessary, reduce the density.

• Spacer
  fabrics Spacer fabrics are used to produce sandwich structures.

Fiber sizes

When processing fibers, for example weaving, a protective coating - the size  - is applied to the fibers (sizing). This is particularly necessary with notch-sensitive fibers such as glass fiber. Such a size is called a weave size. It is usually removed again after weaving.

The size can also serve as an adhesion promoter between the fiber and the matrix. For this, however, the size must be matched to the corresponding matrix system. Fibers with an epoxy size ( silane size ) can only be used to a limited extent in thermoplastics . An adhesion-promoting application can considerably increase the fiber-matrix adhesion.

Environmental influences

The assessment of environmental influences on fiber-plastic composites is differentiated. Since the material is not homogeneous on a micromechanical level, the environmental influences have different effects on the fiber and matrix material. In addition to the effect on the individual components, the resulting consequences for the network must always be taken into account.

Influence of moisture

The influence of moisture primarily affects the matrix material, since most fiber materials do not absorb moisture. Aramid and natural fibers are an exception . The polymer matrix materials absorb moisture, this applies to both thermoplastics and thermosets. The absorption of moisture occurs through diffusion and is therefore largely dependent on the time and the concentration gradient. This makes computational detection difficult.
The following phenomena occur when moisture is absorbed:

• Weight gain
• Decrease in the glass transition temperature
• Decrease in the modulus of elasticity of the matrix material
• Creation of residual stresses from the source
• Decrease in fiber-matrix adhesion
• Decrease in the strength of the matrix material
• Increase in material damping
• Increase in the elongation at break of the matrix material
• Osmosis damage (with corresponding concentration differences in the laminate)

Weight gain . In the case of aircraft in particular, the increase in weight of the structure due to moisture should not be neglected. The more fiber-plastic composites are built into an aircraft, the more water it absorbs. Most fiber-plastic composites are ideally dry after their production. Only after conditioning or storage in a humid atmosphere do they reach their final weight due to moisture absorption.

Glass transition temperature . The glass transition temperature drops significantly as the moisture content of the composite increases. This can lead to the glass transition temperature of a fiber-plastic composite falling below the operating temperature. This softens the matrix and the component fails. This effect is especially in a hot and humid ( hot-wet relevant) climate. When choosing the temperature limits for the fiber-plastic composite, the expected humidity must always be taken into account. A conservative hedging can by the boiling test ( boiltest done). In this test, the component is stored in boiling water for several hours and then tested in a hot and humid state.

Influence of temperature

The influence of temperature primarily affects the matrix material. The fiber material is also influenced by temperatures, but the effects are often small compared to the matrix. The matrix material therefore dominates the temperature behavior. Therefore, the effects described below do not occur with every fiber-matrix combination.

Mechanical effects

Temperature differences result in micromechanical stresses when the fiber and matrix material have different coefficients of thermal expansion. These tensions occur between the fiber and the matrix and are to be assessed as negative, since they stress the fiber-matrix interface. This can lead to premature failure of the network.

Macromechanically, temperature differences in layered fiber-plastic composites lead to tensions between the layers of the composite. The tensions are higher, the greater the angle difference between the fiber angles in the composite. The reason for this is the different thermal expansion parallel and perpendicular to the grain direction. This is independent of whether the fiber material used expands isotropically or transversalisotropically.

High temperatures cause the module of the matrix material to drop. The softening results in a decrease in the matrix-dominated modules of the composite. Since the fiber material often only softens much later than the matrix material, the fiber-parallel module changes only very slightly under the influence of temperature. As a rule, the strengths of the composite also decrease, in particular the compressive strength parallel to the fibers. Depending on the matrix type, the glass transition temperature , the melting temperature or the decomposition temperature of the matrix material form the temperature limit .

Particularly unpleasant properties of fiber-plastic composites are the strongly accelerated creep and relaxation under high temperatures. This particularly applies to loads transverse to the fiber direction, since the loads are transmitted here via the matrix material. Creep and relaxation can be minimized if the fiber-plastic composite is designed according to the network theory . If the fiber material itself is affected by creep and relaxation, the design according to the network theory is largely ineffective with regard to the temperature behavior.

With regard to the unreinforced matrix material, the creep and relaxation behavior of the composite is significantly more favorable.

High temperatures

In addition to the influences mentioned above, other effects occur at high temperatures. The extent to which they occur depends primarily on the matrix material.

• Moisture absorption increases
• Diffusion rate increases
• Media attack is accelerated
• Aging is accelerated
• Attenuation increases
• Impact increases
• Elongation at break increases
• Decrease in fiber-matrix adhesion

Low temperatures

The thermal expansion coefficients are no longer constant at low temperatures, but are reduced. In addition, the stiffness of both the fiber and the matrix increases.

Influence of radiation

High-energy radiation (ultraviolet, infrared, X-ray, cosmic and radioactive radiation) initially causes an improvement in the mechanical properties of epoxy resins in a low dose with shorter exposure via post-curing. However, higher doses and / or longer exposure times lead to a reduction in the original strength. Polyester resins are even decomposed when exposed to strong radiation.

Influence of corrosive media

Fiber-plastic composites are also used in areas with severe corrosion, such as in sewage. In the case of strong alkalis, saponification occurs with polyesters, accompanied by embrittlement and degradation reactions. The fibers, especially E-glass fibers, are attacked in strong alkalis and strong acids. This can be remedied by higher-quality resins such as vinyl ester and epoxy resin, higher-quality fibers and resin-rich chemical protective layers that reduce the penetration of media. In addition to the stability of the materials used and the diffusion behavior of the matrix, the void-free processing and the fiber-matrix connection also play a decisive role in durability.

Matrix systems

A basic distinction is made between fiber-reinforced plastics with a thermoplastic ( thermoplastic ) and thermoset ( thermoset ) matrix.

Thermoplastic matrix

In principle, all common thermoplastics can be used as the matrix . Fiber-reinforced plastics with a thermoplastic matrix can be subsequently reshaped or welded. After the matrix has cooled down, fiber-reinforced plastics with a thermoplastic matrix are ready for use. However, they soften at an elevated temperature. Their tendency to creep decreases with increasing fiber content. Examples of suitable thermoplastic materials at high temperatures are:

• Polyetheretherketone (PEEK)
• Polyphenylene sulfide (PPS)
• Polysulfone (PSU)
• Polyetherimide (PEI)
• Polytetrafluoroethylene (PTFE)

Thermosetting matrix

Fiber-reinforced plastics with a thermosetting matrix can no longer be reshaped after the matrix has hardened or cross-linked. However, they have a high temperature range . This is especially true for hot-curing systems that are cured at high temperatures. The temperature limit is determined by the position of the glass transition temperature . Fiber-reinforced plastics with a thermoset matrix usually have the highest strengths.

The following resins are used as the matrix. Percentage is the mass share in production in 2005 in Europe:

• Epoxy resin (EP) 2%
• unsaturated polyester resin (UP) 8%
• Vinyl ester resin (VE)
• Phenol-formaldehyde resin (PF) 38%
• Diallyl phthalate resin (DAP)
• Methacrylate resin (MMA)
• Polyurethane (PUR)
• Amino resins
  • Melamine resin (MF / MP) 7%
  • Urea resin (UF) 45%

Resin systems that are used to manufacture fiber-matrix semi-finished products in mass production are therefore most widespread . Not all of the resins listed above are completely processed using fiber composite technology. Some of them are also used as adhesives or casting compounds.

Elastomeric matrix

Typical representatives of elastomers as a matrix in fiber-reinforced plastics are rubber and polyurethane (PUR). Due to their low stiffness, elastomers are not used in structural components. Loop-shaped components such as V- belts or toothed belts are an exception .

Choice of a matrix system

The choice of matrix system determines the application limits of the fiber-reinforced plastic. In addition to the mechanical properties of the matrix such as the modulus of elasticity, there are a number of other criteria:

• Operating temperature range ( melting point , glass transition temperature )
• Media resistance (acidic, basic)
• Radiation resistance (UV radiation)
• Long-term behavior ( creep , relaxation )
• Moisture absorption
• Impact strength

Pre-impregnated semi-finished products

In addition to the pure fiber semi-finished products ( fabric , fleece , etc.) there are a number of pre-impregnated fiber-matrix semi-finished products . These semi-finished products are mostly in sheet, tape or strand form.

Thermoplastic semi-finished products

GMT is the abbreviation for glass mat reinforced thermoplastics . During production, glass fiber fabrics or glass nonwovens are processed into semi-finished products in conjunction with thermoplastics (mostly PP). These semi-finished products can be further processed after being heated by pressing. GMT mats are available with different fiber lengths. However, the assumption that a GMT component with continuous fibers has a higher strength is usually not true. Parts that have a small cross-section and are mixed with short fibers have greater strength. One reason for this is that the continuous fibers are compressed and kinked during pressing. This has a negative effect on the stability under load.

The combination with other reinforcing fibers besides glass fiber is possible.

LFT is the abbreviation for long fiber reinforced thermoplastics . In the G-LFT process, long fibers in granulate form (PP matrix) are brought from an open extruder directly into a compression mold and shaped. In the D-LFT process, the matrix (mostly PP) is plasticized in an extruder and mixed with continuous fibers shortened to length in a mixer. The fiber-containing plasticate is then pressed into shape.

Duroplastic semi-finished products

SMC (Sheet Molding Compound) consists of short and long fibers. It is available in sheet form and is processed using the hot pressing process. Aggregates prevent the matrix from sticking to tools and thus make the semi-finished product manageable. An unsaturated polyester resin (UP) is often used as the matrix. If the component requires high impact strength , vinyl ester resins (VE)are alsoused. Other matrix systems also exist. The hardening of the fiber-reinforced plastic takes place through increased temperature and possibly additional pressure.

BMC (Bulk Molding Compound) consists of short and long fibers. It is in the form of a doughy, shapeless mass. The composition is similar to that of SMC. The curing takes place as with SMC.

Prepregs (Preimpregnated Fibers) consist of continuous fibers (filament yarns). Prepregs are usually delivered rolled up as tape-shaped goods. The continuous fibers can be in the form of unidirectional tapes ( UD tapes ), woven tapes or multiaxial fabrics in the prepreg. The curing takes place as with SMC and BMC in normal industrial applications. In the high-performance area with carbon fibers as reinforcement, prepregs are processed into components in an autoclave.

recycling

The way in which a fiber-plastic composite can be reused depends on its matrix system. For all composites, however, it is not possible to completely recycle materials, as is the case with metals.

Special matrix systems with natural fibers occupy a special position. Some of these are completely biodegradable. Such composites, however, have low strengths and stiffnesses and are therefore only used for components that are subject to low mechanical loads.

Thermosetting and elastomeric composites

Fiber-plastic composites with such matrix systems can only be recycled to a very limited extent. In most cases, chemical extraction of the fibers is prohibited for environmental and cost reasons. One possibility is to grind the components. The powder obtained in this way can be used as an extender, for example in SMC and BMC .

Thermoplastic composites

Material recycling of thermoplastic fiber-plastic composites is partly possible. To do this, the component is shredded and reused as short fiber reinforced plastic. However, the properties of the plastic degrade as a result of the period of use and the renewed melting. Such recycled granulates are therefore only used in subordinate applications. Furthermore, long or continuous fibers are not retained. This significantly reduces the mechanical quality of the recyclate.

Processing method

The methods for manufacturing components from fiber-plastic composites depend primarily on the type of semi-finished products used. Some processes can be used with both impregnated and dry semi-finished products.

The selection of the process depends on the number of pieces to be produced and the geometric dimensions of the component. Since many structures can also be produced alternatively with other semi-finished products and processes, economic criteria play an important role in the selection.

Process for pre-impregnated semi-finished products

• Autoclave process
• Fiber syringes
• Press
• Pultrusion process
• Injection molding
• Winding process

Process for dry semi-finished products

• Hand lamination
• Resin injection process
• Winding process

Design and calculation

The design and calculation of the fiber-plastic composite is described in the VDI 2014. Older guidelines, such as the VDI 2013, have been withdrawn and are no longer valid.

Stiffness

The elastic properties of fiber composite materials are calculated on the basis of the properties of elementary individual layers ( unidirectional layers ). This calculation method is known as the classical laminate theory . Tissues are displayed as two unidirectional layers rotated at an angle of 90 °. Influences caused by the undulation of the fibers in the tissue are taken into account by reducing factors. A design method for weight-optimal laminates is the network theory .

The result of the classic laminate theory are the so-called engineering constants of the composite material and the pane-plate stiffness matrix. This matrix consists of the following elements: ${\displaystyle {\hat {E}}_{x},{\hat {E}}_{y},{\hat {G}}_{xy},{\hat {\nu }}_{xy},{\hat {\nu }}_{yx}}$

• Disc stiffness matrix ${\displaystyle A}$
• Plate stiffness matrix ${\displaystyle D}$
• Coupling matrix ${\displaystyle B}$

Based on these matrices, the reactions of the composite material can be

• Disc loads: normal stresses and shear in the plane ${\displaystyle \sigma _{1},\sigma _{2}}$ ${\displaystyle \tau _{12}}$
• Plate loads : bending moments and torsional moment ${\displaystyle m_{1},m_{2}}$ ${\displaystyle m_{12}}$

be calculated.

The coupling matrix couples the disk loads with the disk deformations and vice versa. It is of interest in practice that an occupied coupling matrix leads to thermal distortion. Since thermal expansions are also coupled, fiber composite components whose coupling matrix is ​​occupied distort. The aim of many research projects is to use the couplings in the disk-plate stiffness matrix in a targeted manner.

A rough interpretation is possible with the network theory . It neglects the work of the matrix and thus assumes the worst case. The network theory is used, among other things, for components in which the matrix must be expected to soften or melt.

Strength verification

Breakage failure of CFRP under the influence of compressive force

The strength verification is carried out with the help of break criteria for fiber-reinforced plastics . These can be differentiating, i.e. differentiating the types of fracture, or general. A blanket proof says nothing about the type of failure. A differentiating criterion is used in VDI 2014 ( inter-fiber breakage criterion according to Puck ).

Tests play an important role in the strength verification of components made of fiber-reinforced plastic. Since the adhesion conditions between fiber and matrix are not known, an experimental check can rarely be dispensed with. Furthermore, combined environmental influences such as media attack and high temperatures can only be assessed through an experiment.

Application examples

• Carbon fiber reinforced plastic (CFRP, coll .: "Carbon") is used in aircraft construction , in industrial components and also often in sports. It can be found, for example, in Formula 1 cars, racing bikes and inline speed skating shoes.
• Use of prepregs to manufacture printed circuit boards (PCBs)
• Micarta with vegetable fibers and epoxy resin
• Hard tissue with vegetable fibers and phenolic resin
• FFU synthetic wood for railway sleepers

literature

• H. Schürmann: Constructing with fiber-plastic composites . Springer, 2005, ISBN 3-540-40283-7 .
• PG Rose: High Strength Carbon Fibers: Manufacture and Properties . VDI-Verlag, 1977, ISBN 3-18-404027-5 .
• M. Neitzel, P. Mitschang: Handbook composite materials: materials, processing, application . Hanser Fachbuchverlag, 2004, ISBN 3-446-22041-0 .
• GW Ehrenstein: Fiber composite plastics . Hanser, 2006, ISBN 3-446-22716-4 .
• Chokri Cherif (Ed.): Textile materials for lightweight construction - techniques, processes, materials, properties . Springer-Verlag, Berlin Heidelberg 2011, ISBN 978-3-642-17991-4 .

Individual evidence

1. ↑ AVK - Industrial Association for Reinforced Plastics eV (Ed.): Handbook fiber composite plastics: Basics processing applications. 3rd edition, Vieweg Teubner, 2010, p. 16. Google Books
2. ↑ Source: AVK ( Memento of the original from October 18, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. .