Patent Grant
10655288
The present invention relates to an assembly for energy absorption, to a process for manufacturing such an assembly, and the applications of such an assembly.
A wide variety of energy absorbing means are available for use in situations where it is desirable to absorb or dissipate the energy of an impact.
For ease of reference only, the present invention will now be described with regard to road applications, where impact of an erratic vehicle particularly at high speeds e.g. on the motor way with a stationary object for example a pole or a guardrail can cause severe injury and/or death to occupants travelling in the vehicle. To reduce the damage to vehicle and occupants during a collision, a number of assemblies have been devised to absorb and/or transfer the energy from the impact. Similarly, vehicles that have been driven off the road should be significantly slowed down or even should be completely stopped by contact with an energy absorbing means, reducing the danger when entering areas of risk.
New constructions or designs of safety barriers have been proposed to improve the capabilities of energy absorption. The safety barriers currently in use are normally made of various materials such as steel and concrete. These materials have disadvantages connected with their cost and their heavy weight. The early publications of steel reinforced thermoplastics (SRTP) can be found in patent applications of FR1306419 and CH449689. A further improved construction is disclosed in U.S. Pat. No. 3,776,520, where a steel rod insert is embedded in thermoplastic resin material and the steel rod has a predetermined geometry to produce a controlled failure pattern when the guardrail is subjected to sufficient impact. Chinese utility model CN201087331 and International patent application W02013107203 respectively disclose a W-shaped or wave-shaped guardrail panel both provided with reinforcing rods. Current road barrier systems are continuously and incrementally improved to increase their performance.
It is an object of the present invention to provide an assembly having good energy absorption when being subjected to an impact.
It is another object of the present invention to provide a guard rail with better energy absorption than conventional guard rails in prior arts.
According to a first aspect of the present invention, there is provided an assembly for energy absorption, comprising m number of substantially straight steel wires and n number of curved steel cords, at least one of and preferably each 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 and preferably each 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 and preferably each of the m number of substantially straight steel wires is at least 2% larger than the elongation at fracture of at least one of and preferably each 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.
As a preferred example, at least one of and preferably each 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%.
Herein, the term “wire” refers to a single filament or single elongated element like rod. In the content of the present invention, ‘cords’ can also be interpreted as ‘strands’. It is typically made up of several single filaments and in particular it refers to a plurality of single filaments twisted together. The filaments are twisted with an intended lay length to form a strand or a cord. The cord according the present invention may have any construction. For instance, the cord is formed by twisting two or three steel filaments. Alternatively cords can be made in layers wherein a layer of filaments is twisted with a layer lay length around a center filament or precursor strand resulting in a layered cord (for example a 3+9+15 cords wherein a core strand of 3 filaments twisted together is surrounded by a layer of 9 filaments and finally with a layer of 15 filaments). The “curved steel cords” in this content means steel cords being in non-straight form and having certain curvature. For example, the curved steel cords are in a spiral shape by wrapping around the substantially straight steel wire. As another example, the curved steel cords have waved shape. As a preferred example, the breaking load of the assembly for energy absorption according to the invention is taken by the substantially straight steel wires in a range from 20 to 70%, and the rest is taken by the curved steel cords. More preferably, the breaking load of assembly is taken by the substantially straight steel wires in a range from 40 to 60%.
According to the invention, at least one of the m number of substantially straight steel wires may be high-carbon steel wire having as steel composition:
In the present invention, the at least one of the m number of substantially straight steel wires may have a diameter Dw in the range of 0.5 to 8 mm e.g. in the range of 0.5 to 3 mm, and may have a tensile strength Rm 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.
According the invention, 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 at “fixation points” along their longitudinal direction at substantially regular intervals. Herein, “fixed together” means that at these fixation points, the substantially straight steel wires and the curved steel cords cannot move freely relative to each other. This fixation of the substantially straight steel wires and the curved steel cords can have different variants. For instance, the substantially straight steel wires and the curved steel cords can be fixed together by welding, immersed in a polymer matrix or by clamping. As an example, the substantially straight steel wires and the curved steel cords can be fixed together by wrapping the curved steel cords around the substantially straight steel wires. As another example, the substantially straight steel wires and the curved steel cords are fixed together by stitched yarns at a plurality of locations.
As an example, at least one of the m number of substantially straight steel wires is wrapped with at least one of the n number of curved steel cords along their longitudinal direction. In a particular example, one steel wire is wrapped with one curved steel cord taken as one assembly. It is noted that the length of the wrapped curved steel cord is longer that the length of the substantially straight steel wire. For instance, at least one of the m number of substantially straight steel wires has a length of Lw and the at least one of the n number of curved steel cords has a length of Lc, and 1.02*Lw≤Lc≤1.20* Lw. In the other word, the surplus length or the over length of the curved steel cord with respect to the substantially straight steel wire is preferably in the range of 2% to 20%. More preferably, 1.07*Lw≤Lc≤1.08* Lw. Most preferably, the surplus length is around 7.5%. In addition, such an assembly may be immersed in a polymer matrix selected from polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyamide (PA), high-density polyethylene (HDPE) or polyethylene terephthalate (PET). The substantially straight steel wires and the curved steel cords are preferably coated with metallic corrosion resistant coating e.g. zinc, zinc aluminium or zinc aluminium magnesium alloy. The metallic corrosion resistant coating may be in a range of 10 to 600 g/m2. By placing the assembly in a polymer matrix, the required metallic coating can be reduced to 20 to 200 g/m2, e.g. 50 g/m2 or 100 g/m2.
As another example, at least one of them 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. It is possible to secure one substantially straight steel wire together with one curved steel cord by stitched yarns along their longitudinal direction. It is also possible to secure a plurality of substantially straight steel wire together with a plurality of curved steel cord, wherein one substantially straight steel wire is next to one curved steel cord, and stitched together with the curved steel cord by yarns along their longitudinal direction. The curved steel cords are preferably periodically crimped or in a periodic wave shape. More preferably, the assembly of the fixed substantially straight steel wires and the curved steel cords is carried on a textile carrier. Thus, the assembly is in the form of a reinforced strip or ribbon and easy to handle in application.
According to a preferred example, said at least one of the m number of substantially straight steel wires has a diameter of Dw and said at least one of the n number of curved steel cords has a diameter of Dc, and 0.8*Dw≤Dc≤1.2*Dw. In the other word, the derivation of the diameter of the substantially straight steel wire from the diameter of the curved steel cord is preferably within 20%. As an example, the two diameters are comparable and the derivation between two diameters is within 5%.
The advantage of the assembly for energy absorption according to the present invention is to utilize two type of energy absorbing elements and the combination of both provide unique and excellent energy absorbing characteristic. The first element, i.e. the substantially straight steel wire has high elongation at fracture and reasonable tensile strength. The second element, i.e. the curved cord, has very high tensile strength and reasonable elongation at fracture. These two elements work together as an assembly can provide both high tensile strength and high elongation at fracture. In other words, the elements within the assembly are interconnected in such a way, to increase the amount of energy that is absorbed and/or transferred to the assembly from an external impact. An engineering stress-strain curve is typically constructed from the load deformation measurements. In the test a specimen is subjected to a continually increasing uniaxial tensile force while simultaneous observations are made of the deformation of the specimen. Deformation or elongation is the change in axial length divided by the original length of the specimen. The relationship of the stress-strain or load-elongation that a particular material displays is known as that particular material's stress-strain or load-elongation curve. A load-elongation curve of a straight steel wire and a straight steel cord is respectively illustrated in
More importantly, such an assembly used as guard rail or part of guard rail can be designed to provide additional safety measures together with other elements, e.g. the poles. As shown in
Additionally, it would also be an advantage to have an assembly that could be quickly and easily manufactured using readily available materials. It would be a further advantage to have an assembly that could be constructed in a range of shapes, such as square, a line, a strip, to suit a range of applications without being expensive to construct. The assembly for energy absorption according to the invention can be used as guard rails or for reinforcing guard rails, impact beam or a part of the bodywork subject to impact. In particular, a guardrail according to the present invention comprises at least one elongated beam having fixing means for its connection to support means and extending horizontally between the support means, wherein said beam is reinforced with at least one assembly for energy absorption as in the invention.
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.
As an example, the substantially straight steel wire according to the present invention can be produced as follows.
The steel wire has following steel composition:
The process comprises the following steps:
After the quenching step b), which occurs between Ms, the temperature at which martensite formation starts and Mf, 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.
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.
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.
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.
The cords used with well-defined constructions are shown in Table 1. For example, “3×0.265+9×0.245” 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.
In this embodiment, one wire 31 is wrapped with one cord 33 constructing as an assembly 30 as shown in
Herein the surplus or the over length of steel cod is selected by the following criteria: surplus<At of steel wire−At 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.
The measured load-elongation curves vs. the synthetical curves of assemblies with different surplus cords (3×0.265+9×0.245) are compared in
The load-elongation curves of assemblies with different curved cords and similar surplus length are compared in
As another embodiment, instead of wrapping one cord on one wire, several cords and several wires are fixed together by stitches. As shown in
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 16156819 | Feb 2016 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/052729 | 2/8/2017 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2017/144275 | 8/31/2017 | WO | A |
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| Number | Date | Country |
|---|---|---|
| 449689 | Apr 1968 | CH |
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| Entry |
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| Number | Date | Country | |
|---|---|---|---|
| 20190017236 A1 | Jan 2019 | US |
