GRP components material

a GRP components material is a multi-phase or a mixer material consisting of generally two main components ( a bedding matrix and strengthening fibers). By mutual reciprocal effects of the two components receives this characteristics with high order as everyone of the two components individually taken part.

Table of contents

general

in contrast to past composite materials, like e.g. Reinforced concrete,with the introduction of extremely thin fibers (some µm diameters) the effect of the specific firmness is used. This connection was discovered in the twenties by Griffith and reads: A material in fiber form has a often larger firmness than the same material in other form in grain.The thinner the fiber is, the more largely is their firmness.The cause for this lies in an increasing rectification of the molecule chains with more removing surface the available. There with same firmness the heavy, firm component to be thus saved and by an easier replaced can, developsMaterial with a high specific firmness (relationship from firmness and weight).

There the fibers depending upon demand to be aligned and in its density (number per surface) be adapted know, develop with the help of appropriate manufacturing processes custom-made construction units. In order to affect the firmness in different directions, becomeinstead of individual fibers fabric or clutch of eggs uses, which is manufactured before the contact with the matrix.

function mode

the characteristics with high order of a GRP components material are only reached by the interaction of both components. From two components thus three working phases in the material result: Very muchcourse-firm fraying, a relatively soft, it bedding matrix and both components a connecting boundary layer.

conditions for the reinforcement effect of fibers

not all combinations of fiber and matrix materials lead to an increase of the firmness and the rigidity of the new group. Three must Conditions fulfilled its, so that in fiber-parallel direction a reinforcement effect occurs:

  1. <math> E_ {\ rm {fiber, lengthwise}}> E_ {\ rm {matrix}}< /math>
  2. <math> \ epsilon_ {\ rm {break, matrix}}> \ epsilon_ {\ rm {break, fiber}}< /math>
  3. <math> R_ {\ rm {fiber, lengthwise}}> R_ {\ rm {matrix}}< /math>

Perpendicularly to the fiber no increase of the strengtheningnesses usually arises. Reason is the stretch enlargement.

his appearance gives

  • tasks of the components the matrix to the GRP components material. Both thatColor and the surface texture are few borders set. In mechanical regard she must hold the strengthening fibers in her position and transfer and distribute tensions between them. Regarding the durability it has the task, the fibers before external mechanical and chemical influencesto protect.
  • The fibers give the necessary firmness to the GRP components material. Apart from the tensile strength, if the material on pressure is stressed, also the bending strength can play a role.
  • The boundary layer serves the stress transmission between the two components. It transfers very abstract forms excluding thrust and knowsassume if the thrust for example by pure friction been made. In other cases however, for example with thrust over sticking adhesion, it is manufacture-technically intended and physically available. In the latter case the fibers before the first contact are coated with the matrix with a coupling means, which chemically alsoboth components to react knows and as continuous a transition as possible guaranteed.

An important factor with the calculation of GRP components materials is the Volumenverhältnis (fiber percentage by volume) between fibers and matrix. The higher the portion of fibers is, the more firmly, however also rigid and more inflexibly becomes the material.This can lead to problems, if certain deformations are exceeded.

principle of the power transmission

Abb.:1 Veranschaulichung der Spannungsübertragung in Faserverbundwerkstoffen mit Darstellung der mitwirkenden Länge und der Spannungsverteilung in der Faser.
fig.: 1 illustration of the stress transmission in GRP components materials with representation of the participating length and the power distribution board in the fiber.

As represented in illustration 1, it is in case of one concentrates appliedTraction power not possibly to let these attack directly at the fibers since these are covered by a matrix layer always. The traction power affects thus only the matrix in the form of concentrated tensions and by this on the most next-lying fibers is distributed. The size of this “spreading field” (thoseparticipating length of a fiber) depends on the stress ratio between fiber and matrix: Large participating lengths, a rigid matrix with soft fibers result in a soft matrix combined with rigid fibers result in small participating lengths. Tensions do not have to be applied however necessarily in concentrated form, a variantfor the production from tensions e.g. is. an applied moment. The action principle does not change.

Abb.:2 Veranschaulichung des Funktionsprinzips druckbeanspruchter, in eine Matrix eingebetteter Fasern.
Fig.: 2 illustration of the operational principle more pressure-stressed, into a matrix of embedded fibers.

In case of from lengthwise pressure, as it arises also when bend, working to the fiber direction, the matrix functions like a beddingand the fiber (the fiber bundle) like a flexibly bedded bar, see also illustration 2. Here important material properties are the matrix rigidity k and the flexural rigidity of the fiber E·I (rigidity multiplies by the surface moment of inertia). The computation becomes now very many more complex, there now except the almostTensile strength of the fiber also their diameter because of the surface moment of inertia a role plays. The case pressure becomes since center of the sixties 20. Century investigates and represents this very day a scientific challenge. By computer application and modern FEM of programs is at present tried, the theoretical beginningsto prove and reconstruct numerically. The problems lie on the one hand in the fact that it concerns a stability problem and thus substantial effects can have already smallest changes in the material composition on the yieldable forces. On the other hand a highly developed multi-phase material fails in various way anddifferent mechanisms alternate during the failure and cause themselves partly mutually. Pressure failure takes place very suddenly, fast and partly without preliminary warning. Thus he is to be observed very badly, what makes the analysis more difficult.

materials

apart from the purely mechanical characteristics, thus that, above all durability and matters of price a large role play necessary computed firmness with the choice of the materials. In order to ensure a good functioning, the rigidities of the two components should be co-ordinated, so that arising force points can distribute themselves well in the material. In detail becomethe following materials assigned

fibers

  • glass fibers
    glass fibers are mainly because of their relatively small price the most frequently used fiber types. There are glass fiber types for different operational areas.
  • Carbon fibers
    see there.
  • Keramikfasern
    endless Keramikfasern from alumina, Mullit (mixing oxide from alumina and silicon oxide), SiBCN, SiCN, SiCetc. are expensive special fibers for high temperature-loadable composite materials with a ceramic matrix. The non-oxidic fibers are won, similarly as carbon fibers, from organic resins, in which beside carbon also silicon is contained.
  • Aramide fibers
    see there.
  • Boron fibers
  • steel fibers
  • natural fibers
  • nylon fibers
    fibers with a high elongation at rupture are of advantage, ifthe construction unit of impacts to take up must and this characteristic for the calculation is determining.

matrix

the choice of the matrix divides the GRP components materials into two groups: Fiber-reinforced plastics and different.

during the synthetic resins and elastomers up to their hardening by precipitation liquid are present are thermoplastics firmly. The duroplastischen synthetic resins are usually glass brittle and do not deform not plastic. Fiber-reinforced plastics from thermoplastic can later be transformed.

The micro and macro soaking of the fibersis simpler with synthetic resins than with firm thermoplastics. Thermoplastics are heated up for soaking or solved in a solvent.

types and manufacturing process

fiber-reinforced concrete

concrete or cement can throughWould add from fibers its tensile strength increase. The fiber chips have only few centimeters of length (the high elastic module of the concrete makes long fibers unreasonable) and orientationless in the matrix are distributed. The result is an isotropic material. The fibers are touched like normal addition with the concreteand together in a formwork hardened.

isotropic ones fiber-reinforced plastics

isotropic one fiber-reinforced plastics are manufactured economically in the injection moulding procedure. The short fiber chips are squirted thereby together with the matrix material into the form.

They can be manufactured however also by a special layering by fabrics.Construction units with such a layering call one an quasi-isotropic laminate.

SMC Sheet mol thing Compound

with this kind of fiber-reinforced plastics becomes in a prefabrication from resins, hardeners, fillers, additives, etc. and pieces of glass fiber to approx. 2.5 cm length a so-called resin mat manufactured.After a ripe time (storage time), some days with approx. °C, the viscosity of the resin mat of honey-like increases 30-40 to wachsfest. With this, dependent on the resin mat prescription can the mat defines viscosity which can be specified be processed.

The subsequent treatment effected then in heated tools in the pressing. The resin matbecomes, depending upon construction unit size and - geometry, into exactly defined sizes cut and after a defined inserting plan in the tool platziert. When closing the press the resin mat in all tools is distributed.

It comes to two phenomena:

  1. Flowing the resin mat in the tool has as a consequence,that it can come at the corners of the tool (in addition, at ridges and cathedrals) to meeting one another different flow fronts. With not sufficient penetration of the flow fronts it comes then to so-called binding seams. At these binding seams the mechanical characteristics of the construction unit are partly clearly reducedopposite the remaining construction unit.
  2. The lighter and finer components of the resin mat (resins, additives etc.) flow faster than the larger components (glass fibers, fillers). Thus it can come with long flow ways at the construction unit borders to an enrichment of the smaller components, it is formed a “resin layer”. ThisResin layer is brittle and can lead to smaller flakings when mechanical load.

After a curing time of several minutes at increased temperature their height of the used resin system depends - the finished construction unit can be taken out of the form, must however due to the still high construction unit temperaturesto be cooled carefully evenly, so that it does not come to microcracks in the construction unit. SMC construction units are usually more highly loadable - due to the larger Faserlänge than with BMC - than BMC construction units. SMC construction units can be used during appropriate interpretation also in painted ranges of vision.

laminates

This group uses all advantages of the individual fiber adjustment. They consist usually of several laid on top of each other fiber mats with different main grains. For its production there are several procedures:

  • Hand putting procedures (laminate)
    the fiber semi-finished material (fabrics/clutches of eggs/fiber mats) are draped by hand on a form and soaked with synthetic resin. This connection between fiber andOne calls matrix matrix complex. Subsequently, they are aired out with the help of a role by pressing. Thus not only air vorhandendene in the structure of laminate, but also surplus resin are to be removed. This procedure is so often repeated, until the desired layer strength is present. One speaks also ofa “wet in wet” - procedures. After applying all layers the construction unit hardens by the chemical reaction of the resin with the hardener out. The procedure places no large requirements against the tools and is suitable also for very large construction units. It is often used in the series production,where light construction units are desired, in addition, to be economically produced is.
    Advantages are small tools and equipment expenditure, opposite which the lower construction unit quality (smaller fiber content) and the high manual expenditure, which presuppose trained Laminierer, stand. The open processing of the resin places high requirements against thatIndustrial safety.
  • Handpresent with Vakuumpressen
    after bringing in all reinforcement and Sandwichmaterialen the form with a Trennfolie, a suction fleece and a vacuum foil are covered. Between the vacuum foil and the form a negative pressure is produced. This causes that the group is pressed together. Possibly still contained air becomessucked off. Surplus resin is taken up by the suction fleece. So a still higher construction unit quality can be obtained in relation to the hand rest method.
  • Prepreg - technology
    with matrix material pre-impregnated (thus) fiber mats already soaked on the form is presented. The resin is no longer liquid thereby, but has an easily sticky firm Consistency. The group is aired out afterwards by means of vacuum bag and hardened afterwards, frequently in the autoclave, under pressure and heat. The prepreg procedure is due to necessary (cooling systems, autoclave) and the fastidious processing (temperature management) one of the most expensive manufacturing processes. It makes that possible apart from the fiber winding andInjection and infusion procedure however the highest construction unit qualities. The procedure finds particularly in air and space travel, in the engine haven, as well as for achievement sport devices application.
  • Transfer moldings
    with that transfer moldings or also Resin transfer Moulding (RTM)
    can be inserted dry fibers into a form and afterwards with liquidResin under pressure to be flowed around. The resin is hardened by warmth. Fiber orientation can be adapted thereby by sewing and stick procedure in the preform by purposeful placing to the load cases.
  • Vacuum infusion
    Vakuumaufbau
    structure of vacuum
    Fertiges Bauteil
    finished construction unit
    with this procedure becomes the dry synthetic material (Rovings, mats, clutch of eggs, fabric…) on onewith parting agent coated form drapes. Over it a separation fabric as well as a distributor medium are put, which are to facilitate the even flowing of the resin. By means of vacuum sealing volume the foil is sealed against the form and the construction unit afterwards with the help of a vaccum pump (usually rotary vane pumps) is evacuated. The air pressure pressestogether and it fixes the inserted parts. The liquid resin kept at a moderate temperature is pressed by means of the atmospheric pressure into the synthetic material. In order to prevent that surplus resin comes after passing the fibers into the vaccum pump it is installed, before the pump a resin brake and/or case of resin. Afterthe fibers completely soaked are prevented, will the resin supply and the soaked FVK can after hardening be released from form. The curing time depends on the selected matrix material (resin) and the temperature. Advantage of this procedure is even and nearly nonporous soaking of the fibers and thus thosehigh quality of the produced construction units as well as the reproductibility. Today already construction units become like e.g.Rotor blades for wind energy plants with a length manufactured of more than 50 meters with this procedure. Advancements to the vacuum infusion procedure are the differential Pressure Resin transfer Moulding (DP-RTM) and singleLINE Injection - procedure (SLI).

large one spatial construction units

concerns it large, thin-walled construction units, then Endlosfasern are used and processed in the following procedures:

  • Fiber winding
    the fiber wire wrapping method is a technology to the placing of continuous fraying ranks (Rovings) on the form. It becomes with a resin soaking procedurecoupled. With this procedure fibers are positioned very tautly and closely closed-up with a high dimensional accuracy. For the winding of the fibers a body is necessary, which gives its later shape to the construction unit. One calls this body as usual with prototypes the core. Also with the fiber winding differentiatesone between lost and re-usable cores. With the lost cores the possibility consists of manufacturing it for example of sand yielding nuclear material that in the construction unit remains (for example Fahrradrahmen). If a hollow body is to be manufactured, then foam material cores can be for example chemically dissolved. Re-usable cores are usually manufactured from aluminum. ThoseRemovability limits the organization liberty of many construction units. Examples are fiber-wound lighthouses, coverings of streetcar railroad cars and penalties or silos, with which the fibers are rolled up as on a Nähgarnrolle on the core. The number of fiber layers is adapted to the arising bending moment.

    As impregnation methods are usually:
    • The Endlosfaser and/or the strand is led first by a Tränkbad, in which it is moistened with the matrix material and then around a form is wound.
    • Prepreg fiber courses are rolled up, which are hardened afterwards according to the Preprepreg technology (see above).
    • Ungetränkte fibers are wound,thereafter with a resin grouting method (see above) to be soaked.

profiles with unidirectionally aligned fibers

of profiles with smaller dimensions and continuous cross sections are manufactured very efficiently in the strand pulling procedure.

safety precautions with the processing

eye protector and Schutzhandschuhe place a minimum protection from thatContact with the resin system ago. Resin and particularly hardeners and Bescheleuniger contained frequently material, which also works apart from their Giftigkeit allergy-promoting. In the hardened condition however partly even food authenticity is reached.

Accelerators and hardeners are never together-given directly. Both components can react violently with one another, existsDanger of injury. Therefore the accelerator in all rule before mixing with the hardener is added to the resin.

When mechanical working on (Zerspanen) of fiber-reinforced plastics very fine particles develop depending upon type of fiber to be lung usual can. Therefore a mouth protection is mandatory.

Carbon fiber dust can throughits electrical conductivity electrical devices damage. Therefore the treatment under explosion protection is accomplished.

areas of application

of GRP components materials surround us in all areas of life, usually without we are aware of its. The spectrum reaches from dresses, furniture, household appliances up to mehrstöckigen buildings, bridges andspace travel. One considers that wood is also a GRP components material. Everywhere where it is worthwhile itself economically and permits the environment (chemical conditions, temperature, humidity) it, the seduction is largely, elegant, precise, to use economic and artificially manufactured multi-phase systems. This, although the necessity in many cases notis present and conventional alternatives for prestige reasons to be not sufficiently examined.

Instead of enumerating here the infinite application type, would possibly be. a reflection over the sense and nonsense of the replacement of composite materials manufactured by conventional materials through often with high energy expenditure more attached. Straight ones with fiber-reinforced plastics circle boththe raw materials, which want to be pumped, refined from the earth and prepared chemical, and the final products, for whose production often large manufacturing plants are needed, of those it however only one handful gives in the world, our globe before she their application to find.

Also thatKnowledge thinks and wants before the choice of these materials to be studied about such circumstances is.

computation of the flexible characteristics

the flexible characteristics of GRP components materials are computed on the basis of the characteristics of elementary monolayers (unidirectional layers). This computation method is as classical laminate theory admits. Fabrics are illustrated thereby as two, unidirectional layers turned to an angle of 90°. Influences by the Ondulation of the fibers in the fabric are considered by reducing coefficients. A design method for weight-optimal laminates is the network theory.

Result of the classical laminate theory are the so-calledEngineer constants of the composite material <math> \ E_x has, \ has E_y, \ has G_ {XY}, \ has \ nu_ {XY}, \ has \ nu_ {yx}< /math> and the disk disk rigidity matrix. This matrix consists of the following elements:

  • Disk rigidity matrix <math> A< /math>
  • Disk rigidity matrix <math> D< /math>
  • Ouple matrix <math> B< /math>

On the basis these stencils the reactions of the composite material to disk loads

  • can: Standard voltages <math> \ sigma_1, \ sigma_2< /math> and thrust <math> \ tau_ {12}< /math> inthe level
  • disk loads: Bending moments <math> m_1, m_2< /math> and Drillmoment <math> m_ {12}< /math>

are computed.

The ouple matrix couples thereby the disk loads in reverse with the disk deformations and. For practice from interest it is that an occupied ouple matrix leads to thermal delay. Since also thermal stretches are coupled, GRP components construction units forgave themselves,their ouple matrix is occupied. A goal many research project is it to use the couplings in the disk disk rigidity matrix purposefully constructionally.

For the exact expiration of computation is referred to the literature and text books.

computation and proof

the strength check, in particular of fiber reinforced plastics groups, are made by break criteria. Due to thatFirmness anisotropy of most GRP components materials special break criteria are necessary for fiber reinforced plastics groups.

It exists a multiplicity of different break criteria and concomitantly checking methods. Often individual companies have (e.g. in the military or civilian large aircraft construction) develops own proof procedures.


computation programs

Compositor

of this Excel - program was baseda development of the institute for plastics processing (IKV) is the RWTH Aachen. It contains - apart from the computation of the layer tensions and the engineer constants according to the classical laminate theory - a module, in which the Puck' effect level criteria (see: Break criteria for fiber reinforced plastics groups) for a firmness analysis are implemented. Besidethe layer-wise tensions are thus also failure loads calculable.

ESAComp

ESAComp was developed on behalf space driving Europe ESA. In addition, it offers an interface to FE-programs, it can without FE-program be used. Apart from the schichtenweise stress analysis failure loads can with the help of different break criteriaare determined.

ESAComp at Institut for lightweight construction DO Helsinki developed.

Lami Cens

a free of charge available, Excel application for the determination of important characteristics of fiber-reinforced plastic laminates, which can be served simply, became from Professor. Dr. - engineer H. Spark develops. Thus semi-finished material can be selected and stacked menu-led,as is the case for laminating. Lami Cens determines production-specific characteristic values such as laminate strength and - weight, Fasergewicht, resin consumption and characteristic cost values. The engineer constants for the homogeneous disk load (moduli of elasticity <math> E_x< /math> and <math> E_y< /math>, Schubmoduln <math> G_ {XY}< /math>, Querdehnzahlen <math> \ nu_ {XY}< /math> and <math> \ nu_ {yx}< /math>) are computed with the help of the classical laminate theory. A firmness analysis is not possible.

Downloadand use after registration free of charge with http://www.r-g.de under laminate computation.

literature

  • A.A. Griffith. The phenomenon OF rupture and flow in solids. Philosophical Transactions OF the Royal Society OF London, 221A: 163-198, 1920.
  • M. Flemming and S. Roth. GRP components building methods, Springer 2003, ISBN 3-540-00636-2
  • Michaeli, Huybrechts and Wegener.Dimension with GRP components plastics, Hanser 1994, ISBN 3-446-17659-4
  • honour stone (Hrsg.): GRP components plastics - materials, processing, characteristics, Hanser 2006, ISBN 3446227164
  • A. Puck: To firmness analysis of fiber matrix laminates, Hanser 1996, ISBN 3-446-18194-6, to the Runterladen [
work on] see

also fiber reinforced plastics group

Internet references

 

  > German to English > de.wikipedia.org (Machine translated into English)