WO2024095045A1 - Pièce à haute résistance et à haut élancement présentant d'excellentes propriétés d'absorption d'énergie et d'anti-intrusion - Google Patents

Pièce à haute résistance et à haut élancement présentant d'excellentes propriétés d'absorption d'énergie et d'anti-intrusion Download PDF

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Publication number
WO2024095045A1
WO2024095045A1 PCT/IB2022/060637 IB2022060637W WO2024095045A1 WO 2024095045 A1 WO2024095045 A1 WO 2024095045A1 IB 2022060637 W IB2022060637 W IB 2022060637W WO 2024095045 A1 WO2024095045 A1 WO 2024095045A1
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Prior art keywords
slenderness
tensile strength
materials
ratio
part according
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PCT/IB2022/060637
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English (en)
Inventor
Clément PHILIPPOT
Arnaud Cocu
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Arcelormittal
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Priority to PCT/IB2022/060637 priority Critical patent/WO2024095045A1/fr
Priority to PCT/IB2023/060759 priority patent/WO2024095103A1/fr
Publication of WO2024095045A1 publication Critical patent/WO2024095045A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D21/00—Understructures, i.e. chassis frame on which a vehicle body may be mounted
    • B62D21/15—Understructures, i.e. chassis frame on which a vehicle body may be mounted having impact absorbing means, e.g. a frame designed to permanently or temporarily change shape or dimension upon impact with another body
    • B62D21/152—Front or rear frames
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D21/00—Understructures, i.e. chassis frame on which a vehicle body may be mounted
    • B62D21/15—Understructures, i.e. chassis frame on which a vehicle body may be mounted having impact absorbing means, e.g. a frame designed to permanently or temporarily change shape or dimension upon impact with another body
    • B62D21/157—Understructures, i.e. chassis frame on which a vehicle body may be mounted having impact absorbing means, e.g. a frame designed to permanently or temporarily change shape or dimension upon impact with another body for side impacts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D25/00—Superstructure or monocoque structure sub-units; Parts or details thereof not otherwise provided for
    • B62D25/02—Side panels
    • B62D25/025—Side sills thereof
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D25/00—Superstructure or monocoque structure sub-units; Parts or details thereof not otherwise provided for
    • B62D25/08—Front or rear portions
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/62—Quenching devices
    • C21D1/673—Quenching devices for die quenching
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys

Definitions

  • High strength high slenderness part having excellent energy absorption and anti-intrusion properties The present invention relates to a high strength structural part having excellent energy absorption properties in the case of a side impact and a longitudinal impact.
  • the present invention relates to a structural part for use in an automotive vehicle.
  • High strength high slenderness structural parts play an important role in the crash resistance of a vehicle. They are long and narrow assemblies comprising a hollow cavity. In the case of a crash, such parts can be impacted on their side, i.e. in a direction generally transversal to the length direction, or can be impacted in a generally longitudinal direction. When impacted on its side, this type of structural part generally bends under the load of the impact.
  • the bending behavior of the part plays a crucial role in the absorption of the energy of the impact and in resisting intrusion of the impactor into the vehicle.
  • Good energy absorption and anti-intrusion is very important to minimize the consequences of the impact on the occupants of the vehicle and on the rest of the vehicle structure.
  • anti-intrusion is also very important in guaranteeing the integrity of the battery pack and / or the hydrogen tank, which in turns plays an important role in guaranteeing the safety of the vehicle occupants.
  • high strength high slenderness structural parts play a fundamental role in promoting the safety of the vehicle’s occupants in the case of a side impact.
  • the resistance to side impacts of a vehicle is considered a major safety issue and is measured by several normalized tests such as for example: -the US New Car Assessment Program’s (USNCAP) pole tests, in which a vehicle having an initial lateral speed of 32.2km/h impacts on its side a fixed pole.
  • USNCAP US New Car Assessment Program
  • IIHS side moveable deformable barrier
  • MDB side moveable deformable barrier
  • - Figure 1 is a schematic of a high slenderness part according to an embodiment of the invention, with Figure 1a being an insert detailing the definition of the different angles defined in the description
  • - Figure 2 is a schematic of the three-point bending test performed in examples 1 and 2 of the description below.
  • - Figure 3 is the graphic rendition at the end of the 3-point bending simulation of example 1 in the case of part I1w, which is according to an embodiment of the present invention.
  • - Figure 4 is the graphic rendition at the end of the 3-point bending simulation of example 2 in the case of part I1w, which is according to an embodiment of the present invention.
  • - Figure 5 is the graphic rendition at the end of the compression test simulation of example 3 in the case of part I1 (left of the figure), which is according to an embodiment of the present invention and of part R4 (right of the figure), which is not according to the invention.
  • the slenderness ratio commonly used in Leonhard Euler’s buckling theory, is defined by the following formula, where L is the length of the part, expressed in mm, S is the area of its straight section, expressed in mm2, and Imin is the minimum quadratic moment of area in the section being considered.
  • the minimum quadratic moment of area lmin expressed in mm 4 over a cross section A in a set of cartesian coordinates (x,y) is defined by the following formula:
  • the minimum quadratic moment of area Imin for a hollow rectangular section having outer dimension b and h and inner dimensions b1 and h1 is calculated using the following formula:
  • the minimum quadratic moment of area lmin for a hollow annular section having outer radius R and inner radius R1 is calculated using the following formula:
  • a part can be considered to have a high slenderness when its slenderness ratio is above 10, preferably when the slenderness ratio is above 15, even more preferably when the slenderness ratio is above 20.
  • the bending angle of a part is representative of the ability of the part to resist deformation without the formation of cracks.
  • the bending angle was measured in the rolling direction, i.e. the direction along which the steel sheet travelled during the hot-rolling step.
  • the bending angle was measured using a laser measurement device.
  • the samples are cut-out from flat areas of the part. If necessary, small size samples are taken to accommodate for the total available flat area on the part.
  • the rolling direction on the hot stamped part is not known, it can be determined using Electron Back-Scattered Diffraction (EBSD) analysis across the section of the sample in a Scanning Electron Microscope (SEM).
  • EBSD Electron Back-Scattered Diffraction
  • ODF Orientation Density Function
  • fracture strain refers to the fracture strain criterion defined by Pascal Dietsch et al. in “Methodology to assess fracture during crash simulation: fracture strain criteria and their calibration”, in Metallurgical Research Technology Volume 114, Number 6, 2017.
  • the fracture strain is the equivalent strain within the material at the deformation point when the critical bending angle has been reached.
  • the critical bending angle defines the angle at which the first cracks are detected on the extrados of a sample which has been deformed according to the standardized VDA- 238-100 Standard.
  • bottle refers to the mode of deformation of a part subjected to a compressive load, typically a high slenderness part, where the part progressively absorbs the mechanical energy of the compressive load by forming a series of successive waves resulting from successive local buckling deformations.
  • the length of the part as measured in the direction of the compressive load is smaller after the deformation than the initial length of the part in said direction.
  • Hot stamping is a forming technology for steel which involves heating a blank up to a temperature at which the microstructure of the steel has at least partially transformed to austenite, forming the blank at high temperature by stamping it and quenching the formed part to obtain a microstructure having a very high strength, possibly with an additional partitioning or tempering step in the heat treatment. Hot stamping allows to obtain very high strength parts with complex shapes and presents many technical advantages. It should be understood that the thermal treatment to which a part is submitted includes not only the above-described thermal cycle of the hot stamping process itself, but also possibly other subsequent heat treatment cycles such as for example the paint baking step, performed after the part has been painted in order to bake the paint.
  • a blank refers to a flat sheet, which has been cut to any shape suitable for its use.
  • a blank has a top and bottom face, which are also referred to as a top and bottom side or as a top and bottom surface. The distance between said faces is designated as the thickness of the blank.
  • the thickness can be measured for example using a micrometer, the spindle and anvil of which are placed on the top and bottom faces. In a similar way, the thickness can also be measured on a formed part. Hardness is a measure of the resistance to localized plastic deformation induced by mechanical indentation.
  • the hardness measurements are made using a Vickers indenter according to standard ISO 6507- 1.
  • the Vickers hardness is expressed using the unit Hv.
  • the heat affected zone is the area of material surrounding a weld which has been heated up during the welding operation.
  • the heat affected zone can have weaker mechanical properties. Indeed, the heat affected zone undergoes a thermal treatment akin to tempering, which can lead to softening.
  • the cross tensile strength also known as the alpha-CTS value for spot weld resistance reflects the strength of a spot weld in the case of a cross tensile type of loading and is expressed as the ratio of maximum cross tensile strength to the product of the weld nugget diameter by the average thickness of the steel sheets to be joined.
  • the alpha-CTS value is obtained by the following protocol: -providing, according to ISO 14272 standard as published on March 1 st 2016, a cross welded assembly of two metal samples having thicknesses t1 and t2 and each measuring 100mm*50mm, the weld nugget having a diameter d, -measuring the cross tensile strength (CTS), expressed in kN, of said assembly according to ISO 14272 standard as published on March 1 st 2016, -computing alpha-CTS expressed in kN/mm2 as the ratio of said CTS expressed in kN to the product of the average thickness by the weld nugget diameter, each expressed in mm:
  • CTS cross tensile strength
  • T is the transverse direction along which the part extends perpendicular to said longitudinal direction
  • Z is the elevation direction, perpendicular to the plane formed by the L and T directions.
  • the referential is represented in each figure.
  • the figure is a 2D flat representation, the axis which is outside of the figure is represented by a dot in a circle when it is pointing towards the reader and by a cross in a circle when it is pointing away from the reader, following established conventions.
  • the directional terms “top”, “up”, “upper”, “above”, “bottom”, “low”, “lower”, “below” etc. are defined according to the Z elevation direction.
  • the directional terms “front” and “back” are defined according to the L direction.
  • a high slenderness part 1 extends in a main longitudinal direction L between two ends E1 and E2 and in a transverse direction T. It comprises a hollow volume 4 encased between a top part 3 and a bottom part 2.
  • the high slenderness part 1 is made by forming separately and then joining together the top part 3, and the bottom part 2.
  • the top part 3 and the bottom part 2 are joined together by welding, for example by spot welding on flanges 6, which produces spot welds 5.
  • the top part 3 has a generally omega shape
  • the bottom part 2 is a flat closing plate.
  • the top part 3, is generally omega shaped
  • the bottom part 2 also has a generally omega shape (this is for example the case in the parts of example 2, which will be detailed further below).
  • the high slenderness part is made in a single piece integrating both the top and bottom parts.
  • the high slenderness part is made by extrusion.
  • the high slenderness part is formed by roll forming.
  • the high slenderness part is made from a formed metallic tube.
  • High slenderness parts abound in vehicle architectures, some examples are the front parts joining the front crash boxes to the rocker assembly, the rear parts joining the rear crash boxes to the rocker assembly, cross members extending transversally in the vehicle, the rocker panels themselves etc.
  • the battery pack is usually framed by a set of high slenderness parts designed to protect the battery cells in case of an impact.
  • a high slenderness part is generally attached to the rest of the vehicle structure at each of its ends E1 and E2. When the vehicle is involved in a crash, part of the energy of the crash can be transmitted to the high slenderness part by the parts to which it is attached.
  • the high slenderness part will be submitted to a generally compressive load exerted between its ends E1 and E2 and resulting from a force F1, depicted on figure 1, transmitted by the surrounding elements to which the part is attached to, and a resulting resistive force R1 coming from the resistance of the other elements to which the part is attached to at its other end.
  • Said compressive force F1 will not necessarily be strictly parallel to the longitudinal direction and can form an angle ⁇ with the L axis, as depicted on figure 1a. As will be detailed later in the example, this situation corresponds to the compressive load testing and associated numerical simulation. In the rest of the description, it will be referred to as the compressive mode.
  • the impact force can also have at least a component directed following a direction perpendicular to the longitudinal direction, for example in the elevation direction.
  • the part will be submitted to a form of 3 points bending load, the force F2 being applied on one side and resistive forces in the opposite direction coming from the resistance of the other elements to which the part is attached to at both ends E1, E2 (said forces are not depicted on figure 1 for clarity’s sake).
  • this situation corresponds to the 3-point bending test and associated numerical simulation. In the rest of the description, it will be referred to as the bending mode.
  • a high slenderness part needs to absorb a high amount of crash energy without significant occurrence of cracks. Indeed, by absorbing a high amount of crash energy the part will minimize the amount of energy which is transmitted to the rest of the vehicle structure and to its occupants. Moreover, it is important to prevent crack occurrence to preserve the vehicle structural integrity and to prevent intrusion into the vehicle passenger cell or into the battery cell compartment. Because the direction in which an impact will occur in real life conditions cannot be predicted, it is important to absorb energy without significant crack occurrence both in the compressive mode and the bending mode. This will ensure a very robust behavior of the vehicle, whatever the crash conditions may be.
  • the inventors have found that by providing a part having a high slenderness ratio, for example above 10, preferably above 15, even more preferably above 20, made from materials having a tensile strength above 1300 MPa, preferably 1500MPa, a bending angle in the longitudinal direction above 70° and a yield strength to tensile strength ratio strictly lower than 0.85, preferably below 0.82, even more preferably below 0.80, it was possible to absorb a high amount of energy while minimizing the occurrence of cracks both in compressive and bending mode.
  • a high tensile strength material as detailed above, it is possible to absorb a high amount of energy because the deformation of the part resulting from the crash force necessitates a high amount of energy.
  • the risk is that under the effect of the crash force the high slenderness part starts to crack and that cracks propagate in the part leading to failure of the part.
  • the part is no longer structurally sound and stops being efficient in absorbing further energy and preventing intrusion.
  • the inventors have found that this could be remedied by using materials which have a high bending angle. Indeed, the folds which are formed in the deformed areas will not lead to the occurrence of cracks as long as the deformation angles measured within these folds does not exceed the maximum bending angle of the materials made to form the part. Furthermore, the inventors have found surprisingly that it was interesting to keep the yield strength to ultimate tensile strength ratio below a given maximum level.
  • the material used to manufacture at least a portion of the high slenderness part or the entire high slenderness part is a steel sheet comprising the following elements expressed in weight% : C : 0.15 - 0.25 % Mn : 0.5 – 1.8 % Si : 0.1 – 1.25 % Al : 0.01 – 0.1 % Cr : 0.1 – 1.0 % Ti: 0.01 - 0.1 % B: 0.001 - 0.004 % P ⁇ 0.020 % S ⁇ 0.010 % N ⁇ 0.010 % and comprising optionally one or more of the following elements, by weight percent: Mo ⁇ 0.40 % Nb ⁇ 0.08 % Ca ⁇ 0.1 % the remainder of the composition being iron and unavoidable impurities resulting from the smelting.
  • the remainder of the composition of the steel is iron and impurities resulting from the elaboration process.
  • the level of impurities resulting from the elaboration process will depend on the production route used. For example, when using a Blast Furnace route with a low level of steel scrap (recycled steel), the level of impurities will remain very low. On the other hand, when elaborating the steel using an electric furnace, with a very high ratio of recycled scrap steel, the level of impurities will be significantly increased. In this latter case, for example, the level of Cu can go up to 0.25%, Ni can go up to 0.25%, Sn can go up to 0.05%, As can go up to 0.03%, Sb can go up to 0.03% and Pb can go up to 0.03%.
  • the invention will now be illustrated by the following examples, which are by no way limitative.
  • the examples will compare the performance of a high slenderness part according to the invention with reference parts having the same geometry but different material properties. It will be shown that the parts according to the invention exhibit a better energy absorption and less crack occurrence than the reference parts.
  • the behavior of the parts in compressive mode and in bending mode will be assessed.
  • the behavior of the parts was simulated using LS-DYNA R11.1.0.
  • the mesh size used is 3mm.
  • the number of deleted elements is an evaluation of the amount of fracture that occurs during the crash. Because the failure modelling does not take into account the propagation of cracks, it can be said that the effect of fracture on the overall results is probably underestimated in the simulations and that in actual physical crash tests the energy absorption levels would probably be lower when the number of deleted elements is high because of failure propagation and eventual total failure of the part (such as for example the part being cut in two). It should be noted that such catastrophic failure is an issue for energy absorption but also for the overall behavior of the part in the predicted crash scenario of the vehicle. Indeed, it disrupts the anticipated load path and means that the different parts of the vehicle will travel in uncontrolled directions because they are not anymore joined together.
  • Example 1 In a first example, referring to figure 1, the simulated high slenderness part 1 is made by forming separately and then joining together the top part 3, which is a generally omega shaped part, and the bottom part 2, which is a flat closing plate by spot welding on flanges 6, which produces spot welds 5. The joining is performed by 20 spot welds on each side every 30mm along each flange. Each spot weld 5 has a 5.1mm diameter nugget and the heat affected zone is simulated by a 3mm ring around each nugget.
  • the high slenderness part 1 has the following dimensions: - omega shaped top part 3 having a sheet metal thickness of 1,5mm before forming, - bottom part 2, a flat closing plate, having a sheet metal thickness of 1,0mm before forming, -length L of 600mm -closing plate 2 having a total width in the transverse direction of 130mm, comprising two flanges 6 of 25mm each.
  • -height of the hollow volume 4 of 60mm Given the mesh size of 3mm, the above-described part is composed of a total number of 24331 elements.
  • the slenderness factor below was calculated for a perfectly rectangular part having the same hollow volume 4 and the same sheet metal thickness. That is to say, the slenderness factor is calculated without taking into account the contribution of the flanges, which will be very minimal.
  • the factors h1 and h correspond respectively to the inner height (i.e.60mm) and outer height (i.e.
  • example 1 is a simulation of a 3-point bending test, which reflects the bending behavior of a part.
  • the test conditions are as follows: -the part 1 is placed on two cylindrical support structures 9 each having a diameter of 50mm -an impactor 7 weighing 370kg and having a rounded punch head 8 with a diameter of 50mm applies a force F2 and travels at an initial speed of 8m/s.
  • table 1 the results of the crash tests of a part I1 using a material according to the invention, is compared with that of 4 different parts R1 – R4, which use materials with are not according to the invention.
  • the material characteristics of R1 – R4 which are outside of the invention are underlined.
  • the results are expressed in terms of total energy absorption and energy absorption before the onset of failure, both measured in kJ, as provided directly by the simulation software.
  • the moment in the test at which the first crack occurs is indicated as a ratio of the penetration level of the impactor when the first crack occurs to the maximum penetration of the impactor at the end of the test (referred to as “%crush” in the table).
  • the number of deleted elements is also indicated, as it gives a good indication of the level of fracture in the part resulting from the crash.
  • the levels of absorbed energy before and after the onset of failure are detailed separately because it is generally considered that in a real-life collision, once cracks start to appear they are likely to spread throughout the part and greatly affect the performance of the part.
  • the part made with the material according to the invention shows no failure both with and without taking into account the welds.
  • the total amount of absorbed energy is just under that of R2 and R3.
  • the parts made with R2 and R3 start to crack at respectively 59% and 56% of punch penetration, that is, just over half way through the test. If crack propagation was taken into account, it is likely that the total amount of absorbed energy of R2 and R3 would drop. In any case, it would be much safer to choose the part I1 as a safety part submitted to a transversal bending load as it will absorb a very high amount of energy and will be significantly less liable to fail due to crack propagation under load.
  • Example 2 The high slenderness part of example 2 is a double omega shaped part, meaning that both the top part 3 and the bottom part 2 have an omega shape. They are joined by spot welding them to each other using spot welds 5 applied on flanges 6. As for the two previous examples, the joining is performed by 20 spot welds on each side every 30mm along each flange. Each spot weld 5 has a 6.1mm diameter nugget and the heat affected zone is simulated by a 3mm ring around each nugget.
  • the geometry of the part is as follows: - omega shaped top part 3 and bottom part 2 having a sheet metal thickness of 1,5mm before forming, -length L of 600mm -bottom part 2 having a total width in the transverse direction of 130mm, comprising two flanges 6 of 25mm each.
  • -height of the hollow volume 4 of 120mm Given the mesh size of 3mm, the above-described part is composed of a total number of 25650 elements.
  • the slenderness factor is calculated without taking into account the contribution of the flanges, which will be very minimal.
  • FIG. 1 example 2 results
  • Figure 4 is a graphic rendition at the end of the test in the case of part I1w, showing the total deformation of the part once the punch has run its course.
  • I1 does not crack under the bending load and while it has a slightly lower energy absorption level than R2 and R3 in the no-weld scenario, the fact that it does not crack at any point makes I1 the material of choice for a robust safe and reliable safety part.
  • I1w has superior performances in energy absorption than all comparative examples.
  • the simulated high slenderness part 1 has the same geometrical characteristics as in the first example (a simple omega shape with a closing plate).
  • the diameter of the weld nuggets is 8.1mm, instead of 5.1mm in example 1.
  • the heat affected zone is simulated by a 3mm ring around each nugget.
  • the part is impacted longitudinally, simulating a compression test.
  • the part 1 is fixed at one end and impacted at its other end by a flat impactor 10 travelling at an angle ⁇ of 10° with the longitudinal direction and having an initial impact velocity of 16m/s and a mass of 417kg.
  • Figure 4 is a graphic representation of the end of the simulation of the compression test of examples 3 on the part I1 made with the inventive material and R4 made with a reference material.
  • Table 3 example 3 results Looking at the comparative energy absorption and failure rate of parts impacted transversally with a 10° angle made with a material according to an embodiment of the invention, it appears to yield superior results to all the reference materials. In particular, the amount of absorbed energy is significantly higher with and without taking into account the behavior of the welds. Referring to figure 5, it can be seen that part I1 absorbs a high amount of energy by bottling (as seen by the folds that form on the impacted end of the part). On the other hand, part R4 absorbs less impact energy despite its significantly higher tensile strength because of the high amount of crack formation. As a conclusion of these three examples, the parts made according to an embodiment of the present invention behave better in bending and compressive mode than comparative parts. They are therefore most suitable for high slenderness structural parts in vehicle architectures.

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Abstract

L'invention couvre une pièce structurale à haut élancement présentant une excellente résistance à l'écrasement et une excellente absorption d'énergie à la fois en mode de flexion et de compression et étant constituée de matériaux présentant une résistance à la traction supérieure à 1 300 MPa, un rapport entre la limite d'élasticité YS et la résistance à la traction UTS des matériaux strictement inférieurs à 0,85, un angle de flexion supérieur à 70° et présentant un rapport d'élancement supérieur ou égal à 10.
PCT/IB2022/060637 2022-11-04 2022-11-04 Pièce à haute résistance et à haut élancement présentant d'excellentes propriétés d'absorption d'énergie et d'anti-intrusion WO2024095045A1 (fr)

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PCT/IB2022/060637 WO2024095045A1 (fr) 2022-11-04 2022-11-04 Pièce à haute résistance et à haut élancement présentant d'excellentes propriétés d'absorption d'énergie et d'anti-intrusion
PCT/IB2023/060759 WO2024095103A1 (fr) 2022-11-04 2023-10-25 Pièce à haute résistance et à haut élancement présentant d'excellentes propriétés d'absorption d'énergie et d'anti-intrusion

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PCT/IB2022/060637 WO2024095045A1 (fr) 2022-11-04 2022-11-04 Pièce à haute résistance et à haut élancement présentant d'excellentes propriétés d'absorption d'énergie et d'anti-intrusion

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PCT/IB2023/060759 WO2024095103A1 (fr) 2022-11-04 2023-10-25 Pièce à haute résistance et à haut élancement présentant d'excellentes propriétés d'absorption d'énergie et d'anti-intrusion

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20170008119A1 (en) * 2014-03-14 2017-01-12 Nippon Steel & Sumitomo Metal Corporation Welded structure and method for manufacturing the same
WO2020002285A1 (fr) * 2018-06-26 2020-01-02 Tata Steel Nederland Technology B.V. Acier martensitique laminé à froid à haute résistance et haute aptitude au cintrage et son procédé de production
WO2020239891A1 (fr) * 2019-05-28 2020-12-03 Tata Steel Ijmuiden B.V. Bande, tôle ou ébauche en acier pour la fabrication d'une pièce estampée à chaud, et procédé d'estampage à chaud d'une ébauche pour former une pièce
US20220332371A1 (en) * 2019-09-05 2022-10-20 Arcelormittal Rear structure for an electric vehicle

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20170008119A1 (en) * 2014-03-14 2017-01-12 Nippon Steel & Sumitomo Metal Corporation Welded structure and method for manufacturing the same
WO2020002285A1 (fr) * 2018-06-26 2020-01-02 Tata Steel Nederland Technology B.V. Acier martensitique laminé à froid à haute résistance et haute aptitude au cintrage et son procédé de production
WO2020239891A1 (fr) * 2019-05-28 2020-12-03 Tata Steel Ijmuiden B.V. Bande, tôle ou ébauche en acier pour la fabrication d'une pièce estampée à chaud, et procédé d'estampage à chaud d'une ébauche pour former une pièce
US20220332371A1 (en) * 2019-09-05 2022-10-20 Arcelormittal Rear structure for an electric vehicle

Non-Patent Citations (6)

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H.-J. BUNGE: "Texture Analysis in Materials Science - Mathematical Methods", 1982, BUTTERWORTH CO
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PASCAL DIETSCH ET AL.: "Methodology to assess fracture during crash simulation: fracture strain criteria and their calibration", METALLURGICAL RESEARCH TECHNOLOGY, vol. 114, no. 6, 2017, XP002798776, DOI: 10.1051/METAL/2016065
STANISLAW KLIMEK: "Simulation of Spot Welds and Weld Seams of Press-Hardened Steel (PHS) Assemblies", INTERNATIONAL AUTOMOTIVE BODY CONGRESS, 2008
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