DE1923622A1 - Composite - Google Patents

Description

ROLLS-ROYCE LIMITED * Derby / England (Great Britain)

Composite

The invention relates to a method for producing a composite material and the composite material produced therefrom.

The erfindungsgemäiäe process for producing a composite material characterized by the following successive Verfahren3Sohrittes (1) heating a polyacrylonitrile · polymers or copolymers in fiber form in an oxygen-containing atmosphere to a temperature in the range of 15O ⁰ C bie JOO ° Cj (2) heating the fiber material in an inert atmosphere to a temperature in the range from 900 ⁰ C to 1200 ⁰ C; and (»Embedding a plurality of the fibers obtained from the two above process steps in a

the fibers are made according to the second method »- aahritt placed in foil form »and this · foils eodann sur formation of the composite material applied

Htm * # rÄ can erbara Tiira applied to 41 '? "" FDEN, brror * dit ·· su Foli' s are auegelegt "where odann to IbUm" part

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cured wisely to make them easier to handle j the partially cured foils are then placed on top, compacted and finally to form the composite material completely hardened »

The impregnation of the films with the carrier resin can be carried out by Spray on or immerse.

An epoxy-NovoIac resin in conjunction with a latent catalytically active hardener containing boron trifluoride can be used. Alternatively, depending on the Other resin systems can also be used for the different properties desired for the finished composite material.

The importance of the present invention is based on the knowledge that the properties of a composite material intended for practical purposes do not necessarily require the highest possible achievable value of the Young's modulus; rather, some reduction in the value of this parameter of the fiber material can be allowed if this reduction is accompanied by an improvement in other properties. This is especially true when one considers the bond strength between the fiber and the resin support into consideration _s that to a large extent other properties such example, the shear and torsional strength determines the composite material.

So far prepared the achievement of satisfactory values this bond strength with the available carbon materials Difficulties, and various methods have been tried to solve this problem.

The known processes for the production of high-strength carbon as «rä encompass an abeehll« stiii «n so called% r & phi-

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The process step in which the fiber is heated to a temperature in the range of 1500 ⁰ G upwards.

(Such a process isfc, for example, in patent .......

(Patent application P 16 46 946.8 of April 6, 1906 of the same Anroelderin with priority claim from the British Application No. 14,476 / 65 dated April 6, 1965).)

The invention is based on the knowledge that a very good bond strength can be achieved if the temperature of the final heat treatment step is reduced or this final heat treatment can be omitted entirely. In this way, those properties which depend on the strength of the bond between the fiber material and the carrier resin are improved quite considerably, while the other properties retain values which are more than sufficient for the intended use. Even though this brings about a certain reduction in the value of the Young ¹ modulus, it still maintains a value that is above the value of comparable materials, and the improvement in torsional and flexural strength makes the material obtained in this way much better special is tailored to the needs and requirements of, for example, plug-in unit drive superstructures. This is particularly true of fan blades and the like, for which the low weight and high Young's modulus value make such composites attractive, but with good flexural and composite strength required in view of bird impact and aerodynamic requirements.

In the following examples, materials that are produced according to the Processes according to the invention are compared with similar materials which are subjected to "graphitization" and therefore do not conform to the present invention.

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For the material produced according to the invention, the fiber material was produced by winding a fiber made of "Courtelle" polyacrylonitrile (PAN) copolymer of 1 1/2 denier onto a frame, the PAN in air for seven hours on one voroxydiert temperature of 220 ⁰ C and then the fiber in an inert atmosphere v / hile a period of about four hours to a temperature of ⁰ C 10GO heated.

The fiber obtained is cut from the frame for the production of material foils; the films are then sprayed with a solution of epoxy novolac resin (in the specific example described, CIBA LY 55 & was used) with a latent catalytically active boron trifluoride hardener (in the specific example, Shell Chemicals BF ^ .400 was used). The films obtained in this way were dried and ^{partially cured by heating to a temperature of 80 °} C. in air in order to facilitate handling.

For the production of objects from the foils, and especially for the production of the test specimens required for testing the material properties of this material, several foils impregnated with resin are placed on top of one another until the required thickness is reached so that all the fibers run parallel; The stacked films are then compacted in a press with a pressure of a few 400 psi (= * pounds per square inch) and simultaneously heated to 165 ° C for ten minutes; then the foils are removed from the press and post-cured in an oven for four hours at δΟ ^C C to completely cure the resin. The cured object is then processed, if necessary, to produce the required test specimen or to shape it in some other way.

To produce the not designed according to the invention The reference material was based on the same starting fiber, which was wound on a frame in the same way

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was. The Paser was then else, as described above, heat-treated in a similar V /, However, it was brought in this case, after at 1000 ⁰ G going on, "carbonation" in a high temperature oven and in an inert atmosphere for about five hours at 1750 ⁰ Then the fiber was removed from the oven and made into articles in exactly the same manner as described above for the material according to the invention.

Furthermore, the results of the tests carried out on material specimens are not stated. In the tables below, material A means the material produced according to the invention, while material B is the material not produced according to the invention. It should be noted that in all cases the fiber content is given in vol. this volume fraction depends mainly on the spacing of the fibers in the films that are placed on top of one another to produce the objects; the material properties show a dependency on this volume fraction.

Table 1 shows a comparison of the "short beam shear strength" of the materials. To obtain these results, a standard test with the dimensions (O.650 + 0.01 ") x (0.250 + O.OO5") x (0.060 ± 0.001 ") was carried out on two rollers of O.25O arranged at a distance of O.6OO""and deformed under the action of a similar roller equidistant between these rollers. The arrangement was such that the fibers lay in the direction of the longitudinal axis of the specimen. It is generally agreed that the breaking strength from such a test is related can be added to the interlaminar shear strength and with materials of the type in question here this gives a good indication of the bond strength between the fiber and the carrier or matrix material.

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TABLE I.

SMALL ROD SHEAR STRENGTH (PS! = British pounds / square inch) (Short Beam Shear Strength (FSI))

material A • ■ Material A Material B - Material B 55 % fiber 67 lb fiber 50 % fiber 60 % fiber. 872O 4600 319O * 2000 5975 47IO 286O 218O 6024 4720 3290 2190 6913 4770 2820 235O 8381 476O 3C60 2420 8341 4800 3320 2440 8303 4810 3150 2450 7829 5020 3310 2480 8189 5210 3320 2640 7120 5310 3340 8830 5350 32OO 8337 5650 319O - 5690 5830 6090 62C0 6410 67OO 698c

As can be seen, the fourths for the material A according to the invention are about three times as good as those for the material B, which is an indication that the bond strength could be significantly improved. It can also be seen that the fourth changes considerably as a function of the fiber volume fraction, and that this change is different between the two materials. In fact, it can be assumed that the material according to the invention has an optimal fiber volume, which depends on the optimal fiber volume fraction of the,

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Material*; B noteworthy ver-schirJeii .5 st; -.

Table 11 relates to the final flexural strength of the materials, measured on a rod measuring 4.5 ".χ 0.5" χ 0.2 "(span / depth ratio = 2C)., And a three-point bending test with a 4" distance between the centers. The chamfering device runs in the same direction along the longitudinal axis of the rod.

TABLE II
Ultimate Flexural Strength (tonnes / square inch)

Material Λ Material B 6 ^ Yj fiber 60 pounds of fiber 58.5 39 59.4 39.7 6I.5 40.7 63.3 41.5 65.7 43.O 65.9 43.2 64.0 46.0

Here, too, in the case of the material A according to the invention, an increase of about £ 50 can be found; the fiber volume fractions are Ewar different, but practically insignificant, since the scatter would probably cover ^{the under 1} "hied of 5 % with any material production.

Table III shows the values of Young's modulus (= modulus of elasticity) compared with each other along the fiber direction, as they result when measured with standard tensile tests. In in this case, no one-fourths are given, but minimum values ci for certain special fiber proportions.

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TABLE III '

Minimum normal values of the modulus of elasticity (in British pounds per square *

Material A Material B 64 % fiber 17.2 χ ΙΟ ⁶ 60 % fiber 22.5 ac ΙΟ ⁶ 67 % fiber 17 6 χ ΙΟ ⁶
72 % fiber Ιδ.7 Χ ΙΟ ⁶

With regard to this special property, material A is not quite as good as material Bj, however, as explained at the beginning, it has emerged that this is not a particularly nasty waste for many practical applications and is considerably outweighed by the improvement of other properties * (Let it be stresses that it is necessary because of the anisotropy of the material to provide each one direction for that property.)

Table IV again shows minimum normal values for the final Tensile strength measured by conventional methods.

TABLE IV

Ultimate Tensile Strength (in tonnes per square inch)

Material A Material B 60 % fiber 60 % fiber 70 80

Accordingly, the material according to the invention shows a slight reduction in the ultimate tensile strength.

In Table V typical values are given as they can be seen with conventional standard test methods for the Young ¹ module (Elaettal-

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modulus of capacity) were determined in a direction perpendicular to the fibers.

TABLE V

Transverse modulus of elasticity (in British pounds per square inch)

Material A Material B 65 % fiber 60 & fiber

1Λ χ ΙΟ ⁶ Ο.? χ 10 ⁶

This shows the improved bond strength through the Improvement of this property in the direction across the fibers by a factor of 2.

Table VI relates to the torsional modulus of the materials, again measured by standard conventional methods. The table shows typical values of this parameter.

TABLE VI

Torsional modulus (in British pounds / square inches)

material χ 10 ^& A. Material B % fiber 0. 66 X 10 ⁶ 67 p 0.86 χ 10 ⁶ 57 4th fiber 0. 66 X ΙΟ ⁶ 72 % 0.90 58 fiber 0. 75 X ! O ⁶ 63 t fiber & Fiber

It is recognized that a substantial improvement is achieved (up to 50%) with regard to this material characteristic ₅ which is very important in objects such as blades for gas turbine engines have to endure what TorsionskrSfte, not only as a result of centrifugal and aerodynamic Dz "uckk? Äffcen occur, but also ηηά Xm increased dimensions

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as a result of bird impact loads that are many times over greater than the causes mentioned earlier can be.

From the results reported above it is clear that da3 the use of the material according to the invention is significant Improvement in the. Provides overall properties. Of course, in the test tests given above, the carrier resin was, and could be, the same in all cases other resins can readily be used. It would then also be wtederura when using the invention Process to expect better properties, than they would otherwise wax with the same resin system. As obvious applicable resins include other epoxy resins, polyimide resins as well as other resins in embossing, depending on the required Properties such as shelf life, ease of manufacture, etc.

Since the fiber material of the materials A and B has a spec. Has a weight of 1 · 75 g / o! Ir or 1.bO g / cm- ³ , composite materials produced using the relevant materials would differ in their specific weight in the same ratio as the specific weights of the fibers with the same fiber volume fraction,

It follows that the specific properties of a composite material with fibers of type A according to the invention be improved.

Indeed, the improvements achieved by the invention are not exhausted in the results reported above. Preliminary tests show that both pressure and impact resistance are improved by about 50% when the invention is used.

The above reported results kipper custody on fibers * DL®

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-Xl-

kelnerlel surface treatment to improve adhesion experienced between the carrier resin and the fibers. Of course, in connection with the present invention to further improve the properties of the composite material Processes such as surface etching, for example Find application.

- patent claims -

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Claims (10)

- 12 -. Claims A process for producing a composite material, gels e ti nzelohnet by the following successive process steps: (I) heating a Polyacrylnltril polymers or copolymers in fiber form in an oxygen-containing atmosphere to a temperature in the range from 150 ⁰ C to 300 ⁰ C; (2) heating the fiber material in an inert atmosphere to a temperature in the range from 900 ^° C. to 1200 ^° C.; and (3) embedding a plurality of the fibers obtained from the two above process steps in a carrier resin. " 2. The method according to claim 1, characterized in that the Pasern after the second process step be laid out in film form for embedding in the plastic carrier body. 3. The method according to claim 2, characterized in that the films according to the third process step be placed on a composite material. 4. The method according to claim 2, characterized in that the synthetic resin is applied to the fibers prior to their interpretation is applied in film form. 5. The method according to claim 4, characterized in that the synthetic resin is then partially cured in the films. 6. The method according to claim 5 * thereby g e k e η η ζ e i 0 h - « net that the partially cured foils to form a composite material are applied, which then is hardened to the end « ^l 909887/1538 BAD ORlGlHAL 7. The method naoh claim 1, characterized in that the embedding of the fibers in the synthetic resin carrier by spraying the synthetic resin onto the fibers. 6. The method according to claim 1 »characterized in that the embedding of the fibers in the synthetic resin is carried out by dipping the fibers into the synthetic resin. 9. The method naoh claim 3, characterized «that an epoxy novolac resin with boron trifluoride is used as the synthetic resin as a latent katalyisoh hardener. 10. Composite material produced by the method according to a or more of the preceding claims. BATH ORIGINAL