ENERGY ABSORPTION ASSEMBLY

Abstract

Assembly for energy absorption, comprising m number of substantially straight steel wires and n number of curved steel cords, at least one of the m number of substantially straight steel wires having a tensile strength of at least 1000 MPa and an elongation at fracture of at least 5%, at least one of the n number of curved steel cords having a tensile strength of at least 2000 MPa and an elongation at fracture of at least 2%, wherein m and n are integers m>1, n>1, and at least one of the m number of substantially straight steel wires and at least one of the n number of curved steel cords are fixed together along their longitudinal direction, and the elongation at fracture of at least one of the m number of substantially straight steel wires is at least 2% larger than the elongation at fracture of at least one of the n number of curved steel cords such that the elongation curve of the assembly comprises three zones (11, 11, 12, 12, 13, 13), wherein a first zone (11,11) is characterized by an elastic deformation of the substantially straight steel wires, a second zone (12,12) is characterized by the plastic deformation of the substantially straight steel wires and a third zone (13,13) is composed of the continued plastic deformation of the substantially straight steel wires and the elastic deformation of the curved steel cords.

Claims

1. An assembly for energy absorption, comprising m number of substantially straight steel wires and n number of curved steel cords, at least one of the m number of substantially straight steel wires having a tensile strength of at least 1000 MPa and an elongation at fracture of at least 5%, at least one of the n number of curved steel cords having a tensile strength of at least 2000 MPa and an elongation at fracture of at least 2%, wherein m and n are integers, m1, n1, and at least one of the m number of substantially straight steel wires and at least one of the n number of curved steel cords are fixed together along their longitudinal direction, and the elongation at fracture of at least one of the m number of substantially straight steel wires is at least 2% larger than the elongation at fracture of at least one of the n number of curved steel cords such that the elongation curve of the assembly comprises three zones, wherein a first zone is characterized by an elastic deformation of the substantially straight steel wires, a second zone is characterized by the plastic deformation of the substantially straight steel wires and a third zone is composed of the continued plastic deformation of the substantially straight steel wires and the elastic deformation of the curved steel cords.

2. An assembly for energy absorption according to claim 1, wherein at least one of the m number of substantially straight steel wires have a tensile strength of at least 1000 MPa, preferably at least 1500 MPa, and an elongation at fracture of at least 10%, preferably at least 15%.

3. An assembly for energy absorption according to claim 2, wherein at least one of the m number of substantially straight steel wires is high-carbon steel wire having as steel composition: a carbon content ranging from 0.40 weight percent to 0.85 weight percent, a silicon content ranging from 1.0 weight percent to 2.0 weight percent, a manganese content ranging from 0.40 weight percent to 1.0 weight percent, a chromium content ranging from 0.0 weight percent to 1.0 weight percent, a sulphur and phosphor content being limited to 0.025 weight percent, the remainder being iron, said steel wire having as metallurgical structure: a volume percentage of retained austenite ranging from 4 percent to 20 percent, the remainder being tempered primary martensite and untempered secondary martensite.

4. An assembly for energy absorption according to claim 1, wherein at least one of the m number of substantially straight steel wires has a diameter D.sub.w in the range of 0.5 to 8 mm.

5. An assembly for energy absorption according to claim 1, wherein said at least one of the m number of substantially straight steel wires have a tensile strength R.sub.m of at least 1500 MPa for wire diameters below 5.0 mm and at least 1600 MPa for wire diameters below 3.0 mm and at least 1700 MPa for wire diameters below 0.50 mm.

6. An assembly for energy absorption according to claim 1, wherein said at least one of the m number of substantially straight steel wires is wrapped with said at least one of the n number of curved steel cords along their longitudinal direction.

7. An assembly for energy absorption according to claim 1, wherein said at least one of the m number of substantially straight steel wires has a length of L.sub.w and said at least one of the n number of curved steel cords has a length of L.sub.c, and 1.02*L.sub.wL.sub.c1.20* L.sub.w, and preferably 1.07*L.sub.wL.sub.c1.08* L.sub.w.

8. An assembly for energy absorption according to claim 1, wherein said at least one of the m number of substantially straight steel wires has a diameter of D.sub.w and said at least one of the n number of curved steel cords has a diameter of D.sub.c, and 0.8*D.sub.wD.sub.c1.2*D.sub.w.

9. An assembly for energy absorption according to claim 1, wherein said at least one of the m number of substantially straight steel wires wrapped with said at least one of the n number of curved steel cords is immersed in a polymer matrix.

10. An assembly for energy absorption according to claim 9, wherein said polymer matrix is made from polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyamide (PA), high-density polyethylene (HDPE) or polyethylene terephthalate (PET).

11. An assembly for energy absorption according to claim 1, wherein at least one of the m number of substantially straight steel wires and at least one of the n number of curved steel cords are fixed together along their longitudinal direction by stitched yarns at a plurality of locations.

12. An assembly for energy absorption according to claim 1, wherein at least one of the m number of substantially straight steel wires and at least one of the n number of curved steel cords fixed together along their longitudinal direction by stitched yarns is on a textile carrier.

13. An assembly for energy absorption according to claim 1, wherein said at least one of the m number of substantially straight steel wires has a tensile strength of TSw, said at least one of the n number of curved steel cords has a tensile strength of TSc, and said assembly has a tensile strength of TSa, and wherein TSa0.7 *(TSw+TSc).

14. A method of using an assembly for energy absorption according to claim 1 for reinforcing guard rails, impact beam or a part of the bodywork subject to impact.

15. A guardrail, comprising at least one elongate beam having fixing means for its connection to support means and extending horizontally between the support means, said beam being reinforced with at least one assembly for energy absorption as claim 1.

Description

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

[0027] FIG. 1 illustrates load-elongation curves of substantially straight steel wire (a), straight steel cord (b) and assemblies (c) and (d) according to the invention.

[0028] FIG. 2 is a schematic view of a guard rail made by the energy absorption assemblies of the invention subject to a collision of a high speed car.

[0029] FIG. 3 illustrate an assembly for energy absorption according to the present invention.

[0030] FIG. 4 shows a measured and a synthetical load-elongation curve of an assembly.

[0031] FIG. 5 shows energy absorption as a function of the elongation of the assembly.

[0032] FIG. 6 shows the measured load-elongation curves vs. the synthetical curves of assemblies with different surplus cords.

[0033] FIG. 7 presents the simulation with respect to the load taken by the curved cord with a 7.0% surplus length and the straight wire as a function of elongation or strain.

[0034] FIG. 8 shows the load-elongation curves of assemblies with different curved cords and similar surplus length.

[0035] FIG. 9 shows another assembly for energy absorption according to the present invention.

[0036] FIG. 10 shows an energy absorption assembly in a textile carrier.

MODE(S) FOR CARRYING OUT THE INVENTION

[0037] The present invention describes a steel wire having high strength and very high ductility. This type of steel wire can be produced by a method in a continuous process using an absolutely available chemical composition without expensive micro alloying elements such as Mo, W, V or Nb.

[0038] As an example, the substantially straight steel wire according to the present invention can be produced as follows.

[0039] The steel wire has following steel composition: [0040] a carbon content ranging from 0.40 weight percent to 0.85 weight percent, e.g. between 0.45 and 0.80 weight percent, e.g. between 0.50 and 0.65 weight percent; [0041] a silicon content ranging from 1.0 weight per cent to 2.0 weight percent, e.g. between 1.20 and 1.80 weight percent; [0042] a manganese content ranging from 0.40 weight per cent to 1.0 weight percent, e.g. between 0.45 and 0.90 weight percent; [0043] a chromium content ranging from 0.0 weight per cent to 1.0 weight percent, e.g. below 0.2 weight percent or between 0.40 and 0.90 weight percent; [0044] a sulphur and phosphor content being limited to 0.025 weight percent, [0045] the remainder being iron and unavoidable impurities. In addition, the steel wire may comprise low amounts of alloying elements, such as nickel, vanadium, aluminium or other micro-alloying elements all being individually limited to 0.2 weight percent.

[0046] The process comprises the following steps: [0047] a) austenitizing said steel wire above Ac.sub.3 temperature during a period less than 120 seconds; this austenitizing can occur in a suitable furnace or oven, or can be reached by means of induction or a combination of a furnace and induction; [0048] b) quenching said austenitized steel wire between 180 C. and 220 C. during a period less than 60 seconds; quenching can be done in an oil bath, a salt bath or in a polymer bath; [0049] c) partitioning said quenched steel wire between 320 C. and 460 C. during a period ranging from 10 seconds to 600 seconds; partitioning can be done in a salt bath, in a bath of a suitable metal alloy with low melting point, in a suitable furnace or oven, or can be reached by means of induction or a combination of a furnace and induction.

[0050] After the quenching step b), which occurs between M.sub.s, the temperature at which martensite formation starts and M.sub.f, the temperature at which martensite formation is finished, retained austenite and martensite has been formed. During the partitioning step c), carbon diffuses from the martensite phase to the retaining austenite in order to stabilize it more. The result is a carbon-enriched retained austenite and a tempered martensite.

[0051] After the partitioning step c), the partitioned steel wire is cooled down to room temperature. The cooling can be done in a water bath. This cooling down causes a secondary untempered martensite, next to the retained austenite and the primary tempered martensite.

[0052] Preferably, the austenitizing step a) occurs at temperatures ranging from 920 C. to 980 C., most preferably between 930 C. and 970 C. Preferably, the partitioning step c) occurs at relatively high temperatures ranging from 400 C. to 420 C., more preferably from 420 C. to 460 C. The inventor has experienced that these temperature ranges are favourable for the stability of the retaining austenite in the final high-carbon steel wire.

[0053] The produced steel wire for further processing for example has a diameter of 0.92 mm. Several samples are made by wrapping different steel cords respectively around the steel wire. Table 1 shows the weight, load at fracture, tensile strength and elongation at fracture obtained for each individual element.

TABLE-US-00001 TABLE 1 Properties of steel wire and cords used in the invention. Maximum Tensile Elongation at Weight load F strength TS fracture At (g/m) (N) (N/mm.sup.2) (%) Steel wire 5.22 1203 1697 13.5 3 0.265 + 9 0.245 4.68 1876 3151 2.45 2 0.54 3.59 1143 2503 2.81 3 0.54 5.39 1762 2569 2.75 2 0.54 + 2 0.54 7.25 2246 2436 2.78

[0054] The cords used with well-defined constructions are shown in Table 1. For example, 30.265+90.245 indicates three filaments having a diameter of 0.265 mm in the first or inner layer, around by a second or outer layer having 9 filaments each having a diameter of 0.245 mm.

[0055] In this embodiment, one wire 31 is wrapped with one cord 33 constructing as an assembly 30 as shown in FIG. 3. Table 2 and table 3 are listed the tested samples with individual cord construction, different surplus length, the number (#) of spirals for the wrapping of cords on the wire, the maximum load of the assembly (Fm) and its proportion to the sum of maximum load of the wire and cord (% of Fm sum), the elongation at fracture (At), and observations on which element is broken first when fracture occurs (Fracture first @). The test assemblies in table 2 are made from bright wire, i.e. the wire without coatings. The straight steel wire in the test assemblies in table 3 are over extruded with PE and have a final diameter 1.45 mm. These extruded steel wires have better corrosion protection and allow more surplus length in the steel cord.

[0056] Herein the surplus or the over length of steel cod is selected by the following criteria: surplus<At of steel wireAt of steel cord. As shown in table 2 and table 3, the elongation at which ultimate tensile strength of the assembly is reached can be tuned from the elongation value where steel cord fractures (2%) up to almost the elongation value of the steel wire fractures (13%). The tensile strength of the assemblies reaches at least 70% of the sum of the strength of the individual components.

[0057] FIG. 4 shows the load-elongation curve of an assembly with 30.265+90.245 cord having a 6.5% surplus length. In FIG. 4, curve A is the measured curve in the test while curve A is a synthetical curve by adding the load-elongation graph of the steel cord to the graph of steel wire after a certain elongation (6.5% in this case). The energy absorption as a function of elongation of the assembly is shown in FIG. 5. Curve A is the energy absorption as measured while curve B is the energy absorption calculated in line with the curve A of FIG. 4. The assembly can continuously absorb energy up to 123 Joule on 1 meter with an elongation at about 7.3 cm.

[0058] The measured load-elongation curves vs. the synthetical curves of assemblies with different surplus cords (30.265+90.245) are compared in FIG. 6. As shown in FIG. 6, curves A, B, C, and D are the measured curve in the test while curves A, B, C and D are synthetical curve by adding the load-elongation graph of the steel cord to the graph of steel wire after an elongation of 2.6%, 4%, 5.5% and 6.50% respectively. In the tested range, the assembly with 6.5% surplus cord shows much better elongation and energy absorption capabilities than the others. The inventors further ran a simulation with respect to the load taken by the curved steel cord with a 7.0% surplus and the straight wire as a function of elongation or strain. The result of simulation is illustrated in FIG. 7. Curve D shows the force taken by the curved steel cord while curve S shows the force taken by the straight steel wire. It indicates when the elongation of the assembly below the surplus of the curved steel cord, the steel wire takes more load force than the curved steel wire. Shortly after the elongation of the assembly is bigger than the surplus length of the curved steel cord, the steel cord would take more load force than the straight steel wire.

TABLE-US-00002 TABLE 2 Tested samples of a bright steel wire having a diameter of 0.92 mm wrapped with different cords. Sample Surplus % of Fm no. Cord construction length % # spirals/m Fm sum. At (%) Fracture first @ 1 3 0.265 + 9 0.245 2.8 41 2868 93 4.45 Cord 2 3 0.265 + 9 0.245 4 46 2841 92 4.94 Cord 3 3 0.265 + 9 0.245 5.5 53 2488 81 5.32 Cord 4 3 0.265 + 9 0.245 6 56 2813 91 6.76 Cord 5 3 0.265 + 9 0.245 6.4 57 2599 84 6.73 Cord 6 3 0.265 + 9 0.245 6.5 58 2740 89 7.25 Cord 7 2 0.54 7.2 64 2006 89 7.22 Wire 8 2 0.54 12 82 1482 63 6.08 Wire 9 3 0.54 1.7 29 2771 94 3.01 Cord 10 3 0.54 2.7 37 2815 95 4.13 Cord 11 3 0.54 4 49 2241 76 4.14 Cord 12 3 0.54 6.4 59 2617 88 7.43 Cord&Wire 13 2 0.54 + 2 0.54 2.9 46 3262 95 4.80 Cord 14 2 0.54 + 2 0.54 7.5 63 2841 82 7.43 Cord&Wire

TABLE-US-00003 TABLE 3 Tested samples of a steel wire over extruded with PE and wrapped with different cords. Sample Surplus % of Fm no. Cord construction length % # spirals/m Fm sum. At (%) Fracture first @ 15 2 0.54 12 80 1613 69 6.97 Cord 16 3 0.54 7.7 60 2393 81 7.55 Cord 17 3 0.54 10 70 2454 83 8.88 Wire 18 2 0.54 + 2 0.54 6.9 57 2792 81 7.23 Wire

[0059] The load-elongation curves of assemblies with different curved cords and similar surplus length are compared in FIG. 8. As shown in FIG. 8, curves A, B, C, D, E respectively present load-elongation graphs of a bright steel wire having a diameter of 0.92 mm (curve A), and sample no. 7 (curve B), 12 (curve C), 14 (curve D) and 6 (curve E) in table 2. It shows the cord construction together with the surplus length can influence the tensile strength and the energy absorption of the assemblies.

[0060] As another embodiment, instead of wrapping one cord on one wire, several cords and several wires are fixed together by stitches. As shown in FIG. 9, an assembly for energy absorption 90 comprises two curved steel cords 93 in a waved shape and three substantially straight steel wires 91 being stitched together by steel filaments or yarns, e.g. nylon, high tensile PET or HDPE. The maximum and minimum of the waved steel cords contacts periodically with the two adjacent straight steel wires along their longitudinal direction and are secured with the steel wire by stitches. The stitches can be applied with a woven net as shown in FIG. 9. The straight steel wires are substantially parallel to each other and the waved steel cords are also preferably parallel to each other. Such assembled cords and wires are in the form of strip or ribbon. In a preferred example, the assembly 100 made from the curved steel cords 103 and substantially straight steel wires 101 is carried by a textile, e.g. via stitching as shown in FIG. 10.

[0061] According to the present invention, a guardrail may be made from the energy assembly as described above. Preferably, the assemblies are immersed in a HDPE or PA matrix. Alternatively, such assemblies may be used to repair or reinforce the existing road safety barriers, e.g. the W-shaped or waved shaped beam as mentioned in the background. For instance, a guardrail comprises at least one elongate beam, e.g. made of steel, plastic, HDPE or PA, having fixing means for its connection to support means, e.g. poles, and extending horizontally between the support means, and wherein the beam may be reinforced with at least one assembly for energy absorption as described above.