EP0098825A1 - Fibres for the reinforcement of mouldable materials with a hydraulic or other bonding agent, and their manufacture - Google Patents

Abstract

Reinforcement of a moldable material by means of fibers comprised of a filiform body provided at each of each ends with an anchoring device consisting of one or a plurality of volumes of any shapes and of which all cross-section dimensions are larger than the diameter of the filiform body.

Description

The present invention relates to filiform elements, called fibers, which can be used for reinforcing moldable materials with a binder of the hydraulic type or not.

With regard to the reinforcement of moldable materials with a hydraulic binder, the technique of reinforcing concrete with metal fibers, filiform elements of short length in steel for example, is currently in common use; the properties of concrete reinforced with these fibers are now well known and several types of fibers from different sources intended for very specific applications are currently available.

These different types of fibers can be characterized by their reinforcing effect on the composite material, an effect caused by their geometric and mechanical characteristics.

In order to be able to objectively compare several different types of fibers, it is useful to recall the behavior and the reinforcement process of a composite material with a brittle matrix, reinforced by fibers of ductile material.

This behavior depends on the effect of the fibrous reinforcement in the matrix in the vicinity of a crack appeared following the brittleness of the matrix, the crack having been caused by an exceeding of the tensile stress of rupture due to dimensional variations (thermal , hygrometric) or to bending or tensile stresses.

Ideally, fiber reinforcement provides an increase in the breaking energy of the composite material compared to the brittle matrix material.

The increase in energy required for breaking corresponds to the energy required for lengthening and breaking the fibrous reinforcement.

This explanation of the intervention of the fibrous reinforcement makes it clear the need to achieve a perfect connection between the ductile fibers and the fragile matrix.

• - Les fibres longues et droites représentées en figure 1.

By applying these principles, it is easy to characterize the different types of fibers currently available:

• - The long and straight fibers shown in Figure 1.

Only the adhesion tensions prevailing along the fiber-matrix interface can cause the fiber to anchor in the matrix.

It is shown that in order to be able to urge the fiber in tension until reaching a tensile tension close to the breaking of the latter, its diameter would have to be at least 200 times smaller than its length; for practical reasons of implementation, it is excluded to use fibers which would have such a geometric characteristic.

Long fibers with hooks at their ends.

Three different types are shown in Figure 2. The presence of hooks at the ends makes it possible to attach the fiber to the matrix.

The behavior of the fiber depends on the behavior of the hooks in the matrix.

It has been found experimentally that whatever the geometry of the hooks (number of opposite curvatures, radius of curvature), the energy necessary to unfold them is always lower than the energy of rupture by traction of the fiber; it follows that often the fibers provided with hooks are not brought into a state close to rupture in a crack in the matrix but are released by unfolding the hooks.

As a conclusion, it is accepted that the hooks at the ends, if they considerably improve the behavior of the composite material, are not sufficient to obtain the ideal behavior.

Fibers with sinusoidal undulations distributed over their entire length.

In this case, the unfolding energy is again much lower than the breaking energy by traction of the fiber; the number of undulations along a fiber does not compensate for the too large radius of curvature of each undulation.

These fibers are shown in Figure 3.

Straight smooth fibers comprising in their length flattened parts which can also be located at their ends.

These fibers are shown in Figure 4.

In this case, the attachment carried out without the folds inducing stiffness losses, is limited in its performance because it is too aggressive for the matrix.

Indeed, as it is experimentally observed when the fiber is subjected to a tensile force, the matrix can be sheared by the flattened parts, resulting in harmful loosening.

Rough fibers, straight or not.

These fibers are shown in Figure 5.

In this case, the roughness and / or the curvatures are insufficient to achieve a hooking.

• - Concevoir une fibre s'accrochant parfaitement à la matrice c'est-à-dire ne se déchaussant jamais ni du fait de la fibre elle-même, ni du fait d'une rupture de la matrice au voisinage du moyen d'ancrage.

The reasoned comparison of the various fibers currently available helps to understand the problem posed:

• - Conceive a fiber that clings perfectly to the matrix, that is to say, never takes off either due to the fiber itself, or due to a rupture of the matrix in the vicinity of the anchoring means.

With such a type of fiber, the breaking energy of the composite material would be that of the fragile matrix, increased by that of the fibrous reinforcement.

The present invention relates to a steel fiber for example, intended to reinforce a matrix material, concrete for example by never removing shoes from it, neither because of the fiber itself, nor because of the matrix by breaking thereof in the vicinity of 1 ^_'the anchor.

To this end, the reinforcing fiber comprises at each end according to the invention an anchoring device consisting of one or more volumes of any shape whose all transverse dimensions are greater than the diameter of the filiform body.

The anchoring device can be constituted at each end of a single volume called the head, which can have a shape which is increasingly swollen towards the ends of the fiber and even have a part with symmetry of revolution.

The generating curve of this solid of revolution can be such that the intersection of the tangent at any point of this curve with the external lateral surface of the filiform body of the fiber is always in the very volume of the head; the heads can however also be partly or entirely of cylindrical shape.

It has been found that the desired fiber must have a filiform body provided at each of its ends with a head whose internal part, that is to say the part in contact with the filiform body, is of solid form of revolution such that the angle between the tangent at any point of the generating curve and the axis of the filiform body has a maximum value between - 20 and 60 °. The value of this angle will depend, to obtain the ideal behavior, on the nature of the material constituting the fiber.

As an example, steel, for increasingly weak mechanical qualities requires increasingly higher head angles and for increasingly high mechanical qualities requires increasingly weak head angles.

The filiform elements called "fibers" described above can be manufactured by the use of several methods.

In fact, according to a method, a filiform element of indefinite length with a diameter equal to the largest transverse dimension of the head is subjected, by passage between a pair of grooved rolling cylinders, the grooves of which are provided with notches spaced from one another. , a reduction of dia meter over its entire length except that heads are formed at the locations of the notches cut along the grooves of the rolling rolls.

The next step in this process is to regularly cut the continuous laminated filamentary member to produce fibers of precise length with a head at each end.

Another method is carried out by striking a hammer on each end of a filiform element, without a head, having a diameter equal to that of the body of the fiber, each end being maintained during striking by a matrix so as to obtain a head of desired shape.

A third process is carried out by forming a drop at the ends of the filiform body at a temperature close to the melting point of the constituent material. After this forming, it can be quenched to improve the mechanical qualities of the fiber.

• - les figures 6A et 6B représentent schématiquement un appareil suivant l'invention ;
• - la figure 7 représente le détail X de la figure 6A ;
• - la figure 8 représente en vue frontale le couple de cylindres de la figure 6A ;
• - la figure 9 représente en coupe le détail Y de la figure 6B ;
• - la figure 10 représente en perspective quelques exemples d'éléments obtenus à l'issue des procédés utilisés.

The invented methods are now described in more detail with reference to the attached drawings in which:

• - Figures 6A and 6B schematically show an apparatus according to the invention;
• - Figure 7 shows the detail X of Figure 6A;
• - Figure 8 shows in front view the pair of cylinders of Figure 6A;
• - Figure 9 shows in section the detail Y of Figure 6B;
• - Figure 10 shows in perspective some examples of elements obtained at the end of the processes used.

In these different figures, the same reference notations designate the same elements.

As illustrated in FIG. 6A, the wound wire generally designated by the reference notation 1 is drawn towards a rolling apparatus 2 consisting of a pair of fluted rolling cylinders regularly provided over their length with matrix slots of the fiber heads, of which FIGS. 7 and 8 give an example so as to reduce the diameter of the wire as a base material up to the diameter of the filiform body of the fiber except at the location of the heads of these fibers.

This rolling apparatus 2 provides a wire of diameter smaller than the initial diameter and provided with regular spacing of swellings. The shearing device 4 cuts the wire thus obtained at mid-volume of each swelling to create the fibers provided with their heads.

As illustrated in FIG. 6B, the wound wire generally designated by the reference numeral 1 is drawn towards a shearing apparatus producing straight filiform elements 6 of short constant length which must be gripped individually, pinched at their ends between two dies, as in figure 9, generating with the help of hammers striking the desired heads in their exact form.

It is understood that the invention is not limited to the details described above. It can undergo many modifications which do not change its scope.

Claims (19)

1. Reinforcement of a moldable material called "matrix" by elements of slender shape comprising a filiform body provided at each of its ends with an anchoring device for reinforcing the matrix, characterized in that the anchoring device consists of one or more volumes of any shape, all of whose transverse dimensions are greater than the diameter of the filiform body. 2. Reinforcement according to 1 with the characteristic that the anchoring device at each end consists of a single volume, called "head" of any shape, at least part of which is of transverse dimensions greater than the diameter of the filiform body. 3. 'Reinforcement elements according to 1 or 2 with the characteristic that the heads have a part of shape which is more and more swollen towards the ends. 4. Elements according to any one of claims 1 to 3 with the characteristic that by traversing the fiber along its longitudinal axis, from its center towards the end, the swollen part succeeds a completely extreme part of any shape. 5. Reinforcement elements according to one or more of claims 1 to 4 with the characteristic that the heads include a part with symmetry of revolution. 6. Reinforcement elements according to claim 5 with the characteristic that the tangent at any point to the generating curve of the part of revolution cuts the extension of the external surface of the filiform body at a point belonging to the head itself. 7. Reinforcement elements according to claim 6 with the characteristic that the tangent at any point of the generating curve forms with the main axis of the filiform body an angle of maximum value between 20 and 60 °. 8. Reinforcement elements according to one or more of claims 1 to 7 with the characteristic that the material constituting it is steel. 9. A method of obtaining the filamentary reinforcing elements described according to one or more of claims 1 to 8 with the characteristic that the basic material is a wound wire of diameter equal to the largest transverse dimension of the head of the reinforcement. 10. The following method, claim 9 with the characteristic that the reduction in diameter of the wire is obtained by rolling by means of a couple of superimposed rolling cylinders provided with grooves whose depth is equal to the radius of the filiform element obtained. 11. The method of claim 10 with the characteristic that swelling is obtained by the presence of matrix notches thereof, regularly distributed along the grooves. 12. The method of claim 11 with the characteristic that the filiform element obtained is cut regularly at mid-volume of the swellings. 13. A method of obtaining the filamentary reinforcing elements described according to one or more of any of claims 1 to 8 with the characteristic that the basic material is a wound wire of diameter equal to that of the filiform body of the reinforcement. 14. The following method 13 with the characteristic that the wound wire is cut regularly to the desired length. 15. Method according to 13 and 14 with the characteristic that the elements thus obtained are pinched at their ends between two dies generating with the help of hammers striking the desired heads. 16. The method of claim 14 with the characteristic that the desired heads are hot formed. 17. The method of claim 16 with the characteristic that the fibers thus obtained undergo a quenching treatment. 18. The method of claim 16 with the characteristic that the desired heads are formed from a frozen drop by cooling. 19. Installation for carrying out the methods according to one or more of claims 9 to 15.

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