WO2019175065A1

WO2019175065A1 - Method for creating a prestress on a component made of steel, metal or an alloy by means of an sma plate, and component prestressed in such a manner

Info

Publication number: WO2019175065A1
Application number: PCT/EP2019/055924
Authority: WO
Inventors: Elyas GHAFOORI; Masoud MOTAVALLI
Original assignee: Re-Fer Ag; Eidgenössische Materialprüfungs- und Forschungsanstalt Empa
Priority date: 2018-03-15
Filing date: 2019-03-08
Publication date: 2019-09-19

Abstract

According to this method, an external prestress is produced on at least one side of a component surface of a component (1) made of steel, metal or an alloy. For this purpose, at least one SMA plate (2) is placed as tension element on the surface of the component (1) and adhesively bonded on both sides at its end regions to the component (1) by an adhesive bond (3) by means of epoxy resin (4). The SMA plate (2) is then heated, with the result that it permanently contracts and thus exerts a permanent tensile stress on the component (1). In the case of a corrosion-susceptible component, the existing coating is removed and then the corrosion-susceptible metal load-bearing substrate of the component (1) is provided with a coating as corrosion protection. Electrochemical corrosion is thus prevented after applying the SMA plate (2), that is to say an ion flow between the old metal or the alloy and the applied SMA plate (2) is prevented.

Description

Method for creating a prestress on a component made of steel, metal or an alloy, by means of an SMA plate and such a prestressed component

In Switzerland alone exist over 5Ό00 old railway bridges made of steel, some still riveted structures. Many of these old bridges show signs of fatigue. This manifests itself in micro-cracks on the metal top. Also in aircraft, in which usually aluminum is used, or in other metals resp. their alloys, the same problem exists. The following is a method to close such fatigue cracks by means of an external biasing force and to keep closed, to strengthen the component and thus to extend its service life.

In the prior art, cracks due to fatigue metal surfaces with tissues or layers of reinforcing fibers made of carbon, glass or other materials are pasted over. Usually, a carbon fiber with a high tensile modulus (E> 500 GPa) is used. The higher the tensile modulus is selected, the sooner the tensile force of the fiber can be activated. However, another crack opening is always necessary to activate slack applied reinforcement layers. Such reinforcing fabrics or scrims are glued to the component with an adhesive which is applied over the entire surface of the reinforcement. As an example, epoxy resins or other adhesives are used.

The object of the invention, it is against this background, a method for creating an external bias on a component surface of a metal or an alloy. Thus, the so-equipped component and finished end product should be strengthened and the cracking should be effectively suppressed, yes even existing cracks should be closed and kept closed, whereby the life or the service life of a metal component can be extended.

With the present invention, this object is achieved in such a way that SMA plates are used to produce a load-bearing reinforcement layer. This new reinforcement method does not need an additional crack opening to activate the reinforcement. With this reinforcement method, the fatigue cracks are closed again thanks to pre-stressing and the service life of the metal component is thereby considerably extended.

On the basis of Figure 1, which shows a H-steel constructor 1, which was reinforced by means of a SMA plate 2, the method will be explained hereinafter.

SMA is an abbreviation for Shape Memory Alloy, so a shape memory alloy and refers to a steel of iron (Fe) as a base. Nickel-titanium Fe-SMAs and other composites are low-cost materials used to pre-stress concrete parts and structures. These SMAs are described, for example, in EP 2 141 251 B1 with Swiss priority of 25 June 2018. While most metals always have the same crystal structure up to their melting point, shape memory alloys have two different structures or phases, depending on the temperature. The shape transformation is thus based on the temperature-dependent lattice transformation to one of these two crystal structures. It is a so-called allotropic transformation. As a rule, there is the austenite-called high-temperature phase and the martensite-called low-temperature phase. Both can merge into each other by temperature change - so it is a two-way effect possible. The structural transformation is independent of the rate of temperature change. To initiate the phase transformation, the parameters temperature and mechanical stress are equivalent, that is, the conversion can be brought about not only thermally, but also by a mechanical stress. Applications of SMA reinforcements on concrete or other materials by means of similar SMA strips are described in WO 2014/166003 A2. In principle, the design for the reinforcement of components made of steel, metal or alloys is analogous to the statics for prestressed reinforced concrete structures. Existing standards and guidelines for tempering steel are also used for Fe-SMA systems. The producible preloads s _r, o range from 300 MPa up to 400 MPa, with a tensile strength of> 900 MPa and an elongation at break> 40%. SMA tension elements show a similar relaxation behavior as conventional tempering steel. Such SMA strips are connected to a concrete structure either by traction with each other or separately connected to one or more end or intermediate anchors that penetrate into the structure or the component with the same. These end or intermediate anchors in the form of, for example, dowels or steel nails always penetrate the SMA strips. An additional bonding of the SMA strip between these mechanical end and intermediate anchors with the component can optionally be provided. The bond serves as additional safety reserve for the component.

According to the present invention, plates or flat steels made of SMA are bonded to a reinforcing layer to be reinforced on a steel, metal or alloy component to be reinforced. Non-ferrous metals such as aluminum, copper, nickel, lead, tin, zinc, brass and bronze come into question here as metals. However, the bonding does not take place over the entire surface of the SMA plate 2 as in the reinforcement with fiber layers or fiber fabrics necessary. Rather, a bonding takes place only in the region of the end anchors, that is at the two end regions of the SMA plate 2. Only there is the SMA plate 2 coated on its support surface with an epoxy resin 4 or other suitable adhesive and then onto the support 1 launched. In the past decades, two-component adhesives based on epoxy resins have asserted themselves or with each other for bonding these materials together. These two-component adhesives are also referred to as structural adhesives or structural adhesives. Depending on the epoxy resins used in the formulation, additional materials such as fillers and additives used, these adhesives provide different adhesion and use properties, in which case additionally the various viscosity settings and other processing properties interact. The adhesives industry, however, offers a variety of adhesive systems for the bonding of steels, metals, non-ferrous metals and alloys. These do not necessarily have to be 2-component products or based on epoxy. Depending on the application, it is also possible to use hot-curing 1K epoxy resins, special formulations based on 2-component polyurethane (PUR), and also the acrylate adhesives (MMA), which have been increasingly used in recent years. In addition to the reactive systems, other types of adhesives are also suitable for this areal use. Dominant are contact adhesives based on raw materials polychloroprenes. The raw materials based on polychloroprenes (CR) show good adhesion properties for bare and also surface-treated metals. These are usually dissolved in solvents, occasionally dispersed in water and are application-oriented rolled, sprayed, painted, doctored or applied in other processes. Contact adhesives must be applied on both sides of the materials, then ventilated and immediately joined within the open time. Such adhesives provide an immediate initial strength, the bonded parts can be processed immediately thereafter. The middle part of the SMA plate 2 remains adhesive-free and is heated after hardening of the bond by means of heat supply specifically. As a result of this heating creates a phase change from austenite to martensite and thus a permanent contraction of the SMA plate 2 and thus on the bonding a local bias on the surface of H-Stahlbauträgers 1 or if applied to another steel component of any profile or design accordingly same.

Compared to the disclosure of WO 2014/166003 A2, a preload is possible according to the present method, without mechanical intermediate or end anchors made of steel must be used. In the case of reinforcements of a metal base, which shows signs of fatigue, anchors of whatever type should not penetrate into the component. Penetrating anchors weaken the already fatigued component namely inevitable and in addition, which is of course undesirable. According to the present method, the introduction of force takes place only in the area of the adhesive surfaces, without causing any damage in the metal substrate. The process is described in detail below: The surface of the metal component 1 to be reinforced is prepared locally in the region of the adhesive surface or, if necessary, over the entire surface of the SMA reinforcement. For this, a possibly existing coating, for example an old color protective coating, is removed. If necessary, a coating is applied to the corrosion-prone metal substrate. This coating serves as corrosion protection of the underlying metal part, to prevent electrochemical corrosion, that is, to prevent an ion current between the old metal or the old alloy and the applied SMA plate 2. This coating is important because SMA plates 2 made of high quality Stainless steel are made. If the high-quality SMA stainless steel is placed directly on a non-stainless steel or on aluminum, electrochemical corrosion would inevitably begin. However, when an SMA is combined with a stainless steel, an intermediate coating is not necessary. On this thus prepared surface of the steel or metal component 1, the SMA plate 2 is provisionally fixed as shown in the figure and glued to the steel or metal component 1 only in the region of the two-sided end anchors 3. The adhesive used is preferably an epoxy resin 4, namely a product with a high glass transition temperature, higher than 100 ° C. to 200 ° C. An improvement in the glass transition temperature of the adhesive can be achieved, for example, thanks to a temperature control of the adhesive surface. The heating of the SMA between the adhesive surfaces to 150 ° C to 400 ° C should be done at a distance from the adhesive surface, so that the glass transition point TG of the adhesive is not exceeded. However, the heating of the SMA plate 2 should under no circumstances reach the critical temperature of the adjacent steel or metal at which plastic deformation thereof occurs. Additional thermal isolation between the SMA heating area 5 and the SMA bonding area is not normally necessary, but may be optional.

[001 1] The heating of the SMA plate 1 or the SMA flat profile between the adhesive anchors done by infrared emitters, hot air, gas or other heating methods. The heating can be carried out simultaneously or in stages over the entire route to be heated. When heating step by step, a heating beam of 1 m to 2 m heating length is produced in stages over the whole to be heated SMA section until the desired temperature is reached on all sections as a result of heat transfer from the heating beam to the SMA plate 2.

As a variant, there is a backfill 6 between the SMA plate 2 and the support base. By a backfilling 6 with, for example, putty or other material prevents water from entering between the SMA plate and the old component to be reinforced.

As a variant, the SMA reinforcing plate 2 or the component 1 in the region of the applied SMA reinforcing plate 2 or the entire component after applying the SMA reinforcing plate 2 are completely provided a special coating, which as additional corrosion protection and / or as fire protection. For example, there are swelling on the market epoxy coatings, which significantly improve the fire resistance of such components.

digits directory

1 component

2 SMA plate

3 final anchorage

4 epoxy resin

5 SMA heating area

6 adhesive area

Claims

claims

1. A method for creating an external bias on at least one side of a component surface of a component (1) made of steel, metal or an alloy, characterized in that at least one SMA plate (2) as a tension element on this surface of the component (1) placed and bonded on both sides at its end regions as an end anchorage (3) to the component (1) by means of an adhesive and subsequently heated, to produce a permanent tensile stress on the component (1).

2. The method according to claim 1, characterized in that before placing the SMA plate (2), the surface of a corrosion-susceptible component (1) is freed from an existing coating and then the corrosion-prone metal substrate of the component (1) with a coating as corrosion protection is provided to prevent electrochemical corrosion, that is to prevent an ion current between the old metal or alloy and the applied SMA plate (2) as an SMA tension element.

3. The method according to claim 1, characterized in that prior to placing the SMA plate (2), the surface of a corrosion-prone component (1) in the form of a non-stainless steel or metal component or before placing on a component made of aluminum to be covered Surface is provided with a coating as corrosion protection, to prevent electrochemical corrosion, that is, to prevent an ion current between the old steel, metal, alloy or aluminum, and the applied SMA plate (2) as a tension element.

4. The method according to claim 1, characterized in that an SMA plate (2) made of a stainless steel alloy is adhered to the component (1), in which case an intermediate coating is essential.

5. The method according to any one of the preceding claims, characterized in that is used as the adhesive one of the following types of adhesive: • 1-component epoxy resin, with a glass transition temperature higher than 100 ° C to 200 ° C,

• 2-component Epodix resin, with a glass transition temperature higher than 100 ° C to 200 ° C,

• acrylate adhesive (MMA),

• Contact adhesive based on polychloroprenes.

6. The method according to any one of the preceding claims, characterized in that the adhesive surface is tempered to support the bonding by means of adhesive, for faster reaching the glass transition temperature of the adhesive.

7. The method according to any one of the preceding claims, characterized in that after curing of the bond to produce the contraction of the SMA plate (2) and thus to produce a permanent bias the SMA plate (2) to a temperature of 150 ° C to 400 ° C is heated and while maintaining such a distance to the adhesive surfaces that the Tg of the adhesive is not reached, and also the critical temperature of the component to be reinforced (1), in which uses the plastic deformation, is not achieved.

8. The method according to any one of the preceding claims, characterized in that between the heating region of the SMA plate (2) and its glued end anchors (3) a thermal insulation material between the SMA plate (2) and the component to be reinforced (1) is to reduce the heat transfer from the SMA flap (2) on the component (1).

9. The method according to any one of the preceding claims, characterized in that the heating of the SMA plate (2) takes place in the region between their adhesive anchors by means of infrared radiator, hot air blower, gas burner or by means of electrical resistance heating.

10. The method according to any one of the preceding claims, characterized in that the heating of the SMA plate (2) over the entire distance to be heated of the SMA plate (2) takes place uniformly and simultaneously.

11. The method according to any one of claims 1 to 9, characterized in that the heating of the SMA plate (2) by stepwise heating takes place.

12. The method according to any one of the preceding claims, characterized in that between the SMA plate (2) and the support (1) outside the bonding sites, a backfill (6) is used to prevent ingress of water or moisture.

13. The method according to any one of the preceding claims, characterized in that the reinforced component is completely provided with a fire protection coating.

14, member (1) made of steel, metal or an alloy, characterized in that it is reinforced with at least one adhered to one of its surfaces SMA plate (2) on train by this SMA plate (2) by heating of Austenite state was transferred to the martensite state.