CH663758A5 - METHOD FOR PRODUCING A COMPOSITE WITH HIGH TENSILE STRENGTH CONSISTING OF A PLASTIC MATRIX WITH EMBEDDED REINFORCEMENT. - Google Patents

Description

DESCRIPTION

The invention is based on a production method for a composite material according to the preamble of claim 1.

Plastics are provided both in pure form and with fillers and / or reinforcing elements, which are widely used in technology. Their physical and especially their mechanical properties can be significantly influenced by reinforcements with glass and mineral fibers, carbon fibers etc. As with ordinary steel-reinforced concrete, the resilience of such composite materials is decisively limited by the first appearance of cracks in the plastic matrix. This is generally related to the local exceeding of the tensile strength or a similar material characteristic such as yield strength, fatigue strength, etc. of the material.

The reinforcement methods used up to now and the resulting plastic-based products are no longer sufficient for numerous purposes. Often the otherwise excellent properties of the plastics cannot be fully exploited due to the poor strength of the composite.

There is therefore a need for new, mechanically more resilient materials with good physical and chemical properties such as high electrical resistance and corrosion resistance.

The invention is based on the object of specifying a production method for a composite material based on plastics, wherein the risk of crack formation during operation can be avoided and the load can be increased compared to conventionally reinforced plastics thanks to higher mechanical strength, in particular tensile strength. The manufacturing process should be simple and not require any special fixtures depending on local conditions.

This object is achieved by the features specified in the characterizing part of claim 1.

The invention is described on the basis of the following exemplary embodiments which are explained in more detail by means of figures. It shows:

Figure 1 is a perspective view of the composite material in rod or plate form with uniaxial reinforcement.

Figure 2 is a perspective view of the composite material in plate form with two-axis reinforcement.

Figure 3 is a sectional view of the composite material in plate form with two-axis reinforcement by wire mesh.

4 shows a perspective illustration of the composite material in block form with three-axis reinforcement;

Figure 5 is a perspective view of the composite material in plate form with biaxial reinforcement by sheets.

6 shows a cross section through a casting mold with composite material in tubular form;

Fig. 7 shows a longitudinal section through the composite material in tubular form with helical reinforcement.

In Fig. 1, the composite material in bar or plate shape is shown in perspective. 2 is the uniaxial prestressed reinforcement in the form of axially parallel, longitudinally aligned wires made of a shape memory alloy. 1 is the plastic matrix enclosing the reinforcement 2 on all sides.

Fig. 2 shows a perspective view of the composite material in plate form. The reference numerals correspond to those in FIG. 1. The reinforcement 2 here consists of a plurality of alternating, at right angles, groups of prestressed wires arranged in parallel planes.

Fig. 3 shows a representation of the composite material in sheet form in section. The prestressed reinforcement 3 is designed here as a wire mesh, which is embedded in two parallel layers in the plastic matrix 1, the two layers being offset from one another in each case by half a mesh size in both directions.

4, the composite material is shown in perspective in block form. This is a version with triaxial reinforcement, formed by shares of parallel, orthogonally crossing wires. The reference numerals correspond to FIG. 1.

Fig. 5 shows a perspective view of the composite material in plate form with two-axis reinforcement. The prestressed reinforcement4,5 is made in sheet metal. The sheet metal planes are parallel to the plane of the plate made of the plastic matrix 1. The reinforcement 4, with its prestressing, has an x orientation as the first layer, while the reinforcement 5 has a y orientation as the second layer. Both orientations are perpendicular to each other. The dashed arrows 6 each indicate the direction of the tension in the reinforcement 4, 5, which corresponds to the direction of stretching of the respective sheet. The short, full arrows 7 indicate the direction of the prestress in the plastic matrix 1. The latter is therefore prestressed in the reinforced zone in both directions of the slab level.

Fig. 6 shows a cross section through a casting mold with composite material in tubular form. 9 represents the casing, 10 the core of the casting mold for the plastic matrix 1. The prestressed reinforcement 8 has a tubular shape and is arranged coaxially to the casting mold.

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7 shows a longitudinal section through the composite material in tubular form. 1 is the plastic matrix in which the prestressed reinforcement 11 is embedded in a spiral shape. In the present case, the helix consists of a wire layer wound on an inner cylinder made of plastic matrix 1, the turns of which do not touch each other and which is encased by the outer cylinder made of plastic matrix. However, the composite material in the form of a tube can also be designed according to FIG. 6 as a helix cast in plastic matrix 1 with turns lying one on top of the other.

Embodiment I

See Figure 1.

A composite material designed as a flat bar was constructed from a plastic matrix 1 and a reinforcement 2 in wire form from a shape memory alloy. The latter had the following composition:

Ni: 45% by weight

Ti: 45% by weight

Cu: 10% by weight

Start of transformation into austenite: As = 50 ° C.

The wires had a diameter of 0.5 mm and a length of 100 mm. They were solution annealed at 800 ° C for 30 min and then quenched to room temperature. The oxide skin was removed in a stain consisting of 1 part HCl, HN03 and H20. The wires were then stretched at room temperature in a pulling device by 4%, based on the original length, and fastened as a parallel sheet in a casting mold, so that their center distance from one another and from the bottom of the casting mold was 1.5 mm. This reinforcement 2 was now encased by a plastic matrix 1 in the form of an epoxy resin at a height of 3 mm and cured at 40 ° C. The glass transition temperature of the plastic matrix 1 used was 80 ° C. After curing, the whole was removed from the casting mold and the protruding ends of the wires of the reinforcement 2 were cut off flush to the size of the plastic matrix 1. Now the flat bar was subjected to a heat treatment at a temperature of 70 ° C. The shape memory effect (one-way effect) was induced in the reinforcement2: the wires contracted and were subjected to tension. They exerted a corresponding compressive prestress on the surrounding plastic matrix 1. The composite material was then cooled to room temperature, whereby the one-way effect was retained and thus the corresponding prestress.

Embodiment II

See Figure 3.

0.5 mm wires were made from the same shape memory alloy as given in Example I and cold drawn in the manner indicated. A reinforcement 3 in the form of a wire mesh with a center distance of 2 mm (1 mm mesh size) was produced from the wires. Two such wire meshes (cross mesh) with the dimensions 100 x 100 mm were mounted in a center rod of 2 mm from each other and from the bottom in parallel in a casting mold and poured into a plastic matrix 1 according to Example I. The further treatment was carried out exactly according to Example I. By means of the crosswise reinforcement 3, the composite material was prestressed biaxially, so that it could withstand increased tensile stress practically in every direction of its plane.

The amplification can also be carried out in accordance with FIG. 2.

Embodiment III

See Figure 4.

According to Example I, 0.5 mm thick wires were prepared as reinforcement 2 and in a prismatic mold

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attached that they formed a three-axis arrangement of orthogonal, equidistant coulters in all three dimensions. The center distance between two adjacent parallel wires of the same coulter and that of parallel coulters with each other was 3 mm, the center distance between two orthogonally crossing wires was 1.5 mm. The three-dimensional structure was cast in epoxy resin as a plastic matrix 1 and the whole was further treated according to Example I. Thanks to the reinforcement 2, the plastic matrix 1 was prestressed in all directions so that the composite material had increased tensile strength practically independent of the external direction of loading.

Embodiment IV

See Figure 5.

To produce a composite material in the form of a 50 mm thick plate that can be subjected to bending, two sheets of a shape memory alloy according to Example I were first prepared. The sheets had the dimensions 200x200x0.5 mm. After the usual pretreatment, the sheets were stretched parallel to a longitudinal edge by 4% each. The first sheet (prestressed reinforcement 4) was fastened in a casting mold at a distance of 5 mm from the floor in such a way that the direction of stretching was in the direction of a selected x-axis (1st layer: x-orientation). The second sheet (prestressed reinforcement 5) was then installed at a distance of 5 mm and offset by 90 ° in the direction of the y-axis (2nd layer: y-orientation). The mold was now filled with the plastic matrix 1 up to a height of 50 mm. Everything else resulted from the treatment according to Example I. The directions of the stresses are indicated by arrows 6 and 7. When the plate was subjected to bending, the stresses acting on the tension side in the plastic matrix 1 were reduced by prestressing, so that the plate could be subjected to higher loads.

Embodiment V

See Fig. 6.

To produce a composite material in the form of a tube, a reinforcement 8 was first produced as a thin-walled tube (0.5 mm wall thickness) from a memory alloy. The inside diameter of the tube was 15 mm. After the customary pretreatment according to Example I, the tube was expanded by 4% in diameter over a mandrel, inserted concentrically into a round casting mold consisting of the jacket 9 and the core 10, and cast on both sides with the plastic matrix 1. After the hardening of the plastic matrix, the heat treatment was carried out according to example I. When the pipe was subjected to internal pressure, the ring tensile stresses occurring in the plastic matrix 1 were partially reduced by compressive prestressing and absorbed by the reinforcement 8. This allowed the pipe to withstand higher internal pressures without radial cracks.

Embodiment VI

See Fig. 7.

The composite material in the form of a tube was designed with a prestressed reinforcement 11 in a spiral shape. First, a wire made of a shape memory alloy according to Example I was treated, including cold stretching by 4%. Now the wire was wound onto an already hardened plastic tube with the desired inside diameter and the resulting spiral was fixed. Then the whole thing was encased in a mold with the plastic mass lying outside,

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cured and heat treated. The reinforcement 11 can also have a helical shape in the form of a dense wire layer, the individual turns touching one another.

In deviation from this method, the reinforcement 11 can also be produced as a free-standing helix and, according to example V, can be encapsulated on the outside and inside with a plastic matrix 1. All other procedural steps remain the same.

The invention is not limited to the exemplary embodiments. The basic idea is to induce a compressive prestress in the parts of the plastic matrix 1 which are subjected to tension by a prestress generated in situ by means of a heat treatment of the material in the reinforcement 2, which prestress reduces the tensile stresses occurring during operation to an admissible level. This is done with the aid of a reinforcement 2, which is made of a thermoelastic material, preferably a shape memory alloy of the type Cu / Al, Cu / Al / Ni, Cu / Zn, Cu / Zn / Al, (As = 80 to 150 ° C), Ni / Ti or

Ni / Ti / Cu (As = up to 80 ° C). The condition is that the characteristic temperatures behave as follows:

Th <As <TG,

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in which

Th = hardening temperature (processing temperature) of the plastic matrix 1

Tg = glass transition temperature (softening temperature) of the plastic material matrix 1

As = transition temperature of the thermoelastic material (example: reinforcement 2) from the low to the high temperature phase.

Epoxy or polyester resins 15 can be used as the plastic matrix 1. All of the examples given can also contain, as reinforcement 2, a thermoelastic plastic in fiber, fabric, rope, plate or tube shape.

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3 sheets of drawings

Claims (8)

663 758 PATENT CLAIMS 1. A method for producing a composite material with high tensile strength, consisting of a plastic matrix with embedded reinforcement, characterized in that a thermo-elastic material showing a shape memory effect is used as the reinforcement and that the reinforcement embedded in the plastic matrix is triggered by a shape memory effect , the reinforcement under tensile heat treatment is forced to exert a prestress on the plastic matrix. 2. The method according to claim 1, characterized in that a thermo-elastic plastic of high tensile strength is used as reinforcement. 3. The method according to claim 1, characterized in that a one-way effect shape memory alloy is used as reinforcement, the low-temperature phase is in the range of the processing or hardening temperature of the plastic. 4. The method according to claim 3, characterized in that the reinforcement (2) is embedded in the form of at least one family of parallel wires or bands in the plastic matrix. 5. The method according to claim 4, characterized in that the reinforcement (2) in the form of 2 or 3 orthogonally intersecting sets of parallel wires is embedded. 6. The method according to claim 3, characterized in that the reinforcement (3) is embedded in the form of at least one wire mesh. 7. The method according to claim 3, characterized in that the reinforcement (4,5) in the form of at least one sheet on one side of the plastic matrix (1) is embedded in this matrix, which side is intended as a tensile side for a bending load. 8. The method according to claim 3, characterized in that the reinforcement (8, 11) in the form of a tube or a spiral is embedded on all sides in the plastic matrix (1).