WO2003047848A1

WO2003047848A1 - Composite structural panels

Info

Publication number: WO2003047848A1
Application number: PCT/GB2002/005401
Authority: WO
Inventors: Sean Mccarten
Original assignee: Swansea Institute Of Higher Education
Priority date: 2001-11-30
Filing date: 2002-12-02
Publication date: 2003-06-12
Also published as: GB0128675D0; AU2002349135A1

Abstract

The composite structural panel comprises a bonded layer structure, including, a first layer of sheet material plastically deformed to form an array of peak and through formations complementarily on opposed faces of the layer; and a second layer of sheet material bonded in face adjacent face relationship with the first layer. The layers are preferably bonded using adhesive and a foam filler is introduced in aerosol between the layers which cures. The panel provides improved shock/impact absorbency characteristics and is particularly suitable for use as an automotive body panel.

Description

Composite Structural Panels

The present invention relates to composite structural panels and in particular to such panels suitable for use in shock or impact absorption situations, particularly in automotive applications.

Energy absorbent structural panels are known and used in the automotive industry and may be suitable for other structural applications. Aluminium honeycomb is a strong and lightweight material consisting of a core structure layer bonded between two outer facing membranes or surfaces frequently used for applications involving impact/energy absorption. An inhibiting factor in the use of such aluminium honeycomb structures is the relatively high cost.

The present invention seeks to provide a composite structural panel providing good energy absorption characteristics using manufacturing techniques and materials enabling cost reduction benefits.

According to a first aspect, the present invention provides composite structural panel comprising a bonded layer structure, including:

i) a first layer of sheet material plastically deformed to form an array of peak and trough formations complementarily on opposed faces of the layer; and ii) a second layer of sheet material bonded in face adjacent face relationship with the first layer.

Preferably, the panel includes a third layer of sheet material bonded in face adjacent face relationship with the first layer, one of the second and third layers being situated on the obverse face side of the first layer, the other being situated on the reverse face side of the first layer.

The arrangement preferably provides a panel to be built up from layers including a plurality of deformed first layers layed up intermediate substantially flat layers (corresponding to the second and third layers) .

Beneficially, the panel includes an energy absorbent filler material in the voids between the peak and trough formations of the first layer and the second and/or third facing layers. The energy absorbent filler material preferably comprises expanded polyurethane foam or the like.

According to a second aspect, the invention provides a method of manufacturing a composite structural panel, the method comprising:

i) deforming a sheet material between press elements in a forming press, the press elements including respective complementarily arrays of deforming elements, so as to produce an array of peak and trough formations complementarily on opposed faces of the sheet material;

ii) laying up the press-formed sheet with at least one further sheet of material in face adjacent face relationship; and

iii) securing the layered up sheets such that peaks of the press formed sheet are fixed with corresponding portions of the adjacent layed-up further sheet.

It is greatly preferred that the sheets are secured to one another by bonding using an adhesive material at the zones of contact of the peak and trough formations with the contiguous second and/or third layers of sheet material the filler material is beneficially introduced between the already bonded sheets in fluid or aerosol form and expands to cure to a solid foam condition in situ between the adjacent sheets. Beneficially, the filler material fills (preferably substantially entirely) both the peak and the trough formations. This provides good structural integrity and shock/impact absorbent characteristics for the panel.

The peak and trough formations are preferably substantially pyramidal or conical in shape. Beneficially, the peak and trough formations are substantially identical in shape (for example, cross-section) and dimensions. Beneficially, the outer surface of the peak and trough formations at their terminal (contact) points are curve- form (preferably dome or hemispherical shaped) . This reduces stress concentrations compared with flat-topped formations and provides enhanced energy distribution and absorption upon deformation at impact conditions experienced by the panel.

The peak formations are preferably aligned along transverse

(preferably substantially perpendicular) axes. The trough formations are preferably correspondingly aligned. In this direction of alignment, the peak formations aligned are preferably separated by a saddle portion of less depth than the trough formations.

Beneficially, the peak and trough formations are press formed in a deep drawing process . This provides a significant advantage in that peak and trough formations of significantly greater depth may be formed then with roll- forming techniques. The energy absorption characteristics are thus improved. For good technical characteristics, it is preferred that the formations are deep drawn to have a sheet thickness (t) to trough/peak formation depth (d) ratio substantially in the range 35< ^d/_t <85.

Beneficially, the panel is cut out at an inclined angle to the direction of rolling of the sheet material, preferably such that one of the axis of alignment of the peaks or troughs is aligned with the rolling direction. This gives preferred mechanical properties due to anisotropy present within the rolled sheet.

The invention is particularly suited to shock/impact absorbent vehicle body panels. The panels are beneficially of a steel material and may, for example, comprise tin- plate material . ' A panel so constructed combines good shock/impact characteristics with low cost.

According to a further aspect of the invention, there is provided a press for manufacturing a deformed sheet having an array of peak and trough formations complementarily on opposed faces of the sheet, the press comprising:

i) a first press table including an array of regularly spaced projecting deformation elements; and

ii) a second press table arranged adjacent the first press table, the second press table including an array of regularly spaced projecting deformation elements,

wherein;

the first and second tables are movable relative to one another between a retracted position in which the sheet may be introduced into and removed from the press, and in an advanced position in which the projecting deformation elements of respective tables overlap, the projecting deformation elements in the first array being non-aligned with the projecting deformation elements in the second array, the projecting elements in the arrays being regularly spaced with respect to one another. The invention will now be further described in specific embodiments by way of example only and with reference to the accompanying drawings in which:

Figure 1 is a schematic sectional view of a composite structural panel in accordance with the invention;

Figure 2 is a perspective view of a layer of core sheet material 2 comprising the structural panel of Figure 1 ;

Figure 3 is a schematic representation showing the cut of the first panel layer compared to the rolling direction of the sheet ;

Figures 4a to 4c are end plan and side views respectfully of an upper press portion for forming the sheet layer of Figure 2 ;

Figures 5a to 5c are views corresponding to those of Figure 4a to 4c of a lower portion of the press arrangement; and

Figure 6 is a perspective view of a deformation pin mounted in an array in the platens of the press portions of Figures 4 and 5.

Referring to the drawings, there is shown a structural composite panel 1 comprising a core (first) layer of sheet material 2 plastically deformed (deep drawn) to form an array of peak 3 and trough 4 formations complementarily on opposed faces of the sheet layer 2. Cover sheet facing layers 5 , 6 of sheet material are bonded to the peaks 3 and troughs 4 (as will be described in detail hereafter) to ensure the structural integrity of the composite panel 1.

Expanded polyurethane foam is introduced into the void portions between the peaks 3 and troughs 4 and the cover sheet layers 5, 6.

Typically the sheet layers 2, 5 and 6 are of a metallic material, and these may be of the same metallic sheet material for each of the respective layers 2, 5, 6. Alternatively, sheet layers of differing metallic material composition may be used. The preferred materials are discussed later in this document.

Core layer 2 is deep drawn to the plastically deformed condition to form the peaks 3 and troughs 4. The metallic material of the sheet layer 2 therefore needs to have appropriate mechanical properties to permit deep drawing. Aluminium honeycomb structures have previously been proposed. For the preferred specific applications of the present invention in which relatively low cost materials are required, steel materials are preferred. Difficulties have been encountered in producing all steel alternatives to aluminium honeycomb, primarily due to the mechanical properties of aluminium being different to those of steel, steel being more prone to corrosion, of greater density, and less ductile than aluminium materials. A significant benefit of the present invention is the development of producing a deep drawn core sheet of steel material. A significant benefit of ensuring that all three layers 2, 5 and 6 are of the same material (preferably steel) relates to recyclability which now is a major consideration in the automotive industry in particular.

Figures 1 and 2 show a deep drawn steel sheet layer 2 having peaks 3 and troughs 4. The overall nature of the peak and trough arrangement is generally "egg-box" like in configuration. The peaks 3 and troughs 4 are generally pyramidal shaped and of substantially the same shape and configuration, the walls 31 of troughs 4 being common with walls 31 of adjacent peaks 3. This arrangement has been found to give good energy/impact absorbance characteristics and convenient to be deep draw-formed to the required depth. The invention permits the depth dimension (d) of the peaks 3 and troughs 4 to be significantly greater than can be achieved by roll-forming techniques. The ratio of sheet thickness (t) to (d) preferred and obtainable for the panel of the present invention is substantially in the range 35< ^d/ <85. The terminal portions of the peaks 3 and troughs 4 are curve-form hemispherical domes 34 providing curved contact zones bonded by the adhesive to the adjacent sheet layers 5, 6. This configurations has been found to give good bonded adhesion, and improved technical performance. The hemispherical- dome terminal portions improve impact/energy absorption and reduces stress concentrations that would occur with flat-topped terminal portions to the peaks 3 and troughs 4. The peak formations are aligned along transverse (substantially perpendicular) axes. The trough formations are correspondingly aligned. In this direction of alignment, the peak formations aligned are preferably separated by a saddle portion 35 of less depth than the trough formations.

The "egg-box" configuration matrix has been shown to have improved failure performance in tensile and other performance testing.

The die set arrangement for producing the deep drawn pressed core sheet 2 of Figure 2 is shown in Figures 4 and 5. The arrangement comprises an upper portion shown in Figures 4a to 4c and a lower portion shown in Figures 5a to 5c. The arrangement generally includes a linear bearing, a blank holder and permits the required lubrication for deep drawing.

Both upper and lower portions include a respective blank holder perimeter 10, 11 arranged to sandwich the peripheral edges of the blank between respective faces 10a, 11a. Each blank holder 10, 11 is provided with corner bolts 12 which also pass through respective pin platens 13, 14. There is sufficient clearance between the holes in pin platens 13, 14 and the bolts 12 to permit the pin platens 13, 14 to slide toward and away from the respective blank holder 11, 12. Springs 15 act to normally bias the respective pin platens 13, 14 away from the respective blank holders 10, 11. Pin platens 13, 14 include receiving shouldered apertures 16 for receiving an array of deformation pins 17.

An exemplary pin 17 is shown most clearly in Figure 6 and comprises a bolt portion 18 including a head 19, received and retained in the shoulder of respective apertures 16. The threaded forward portion 20 is arranged to threadably mate with a threaded recess 21 provided in projecting portion 22 of the pin 17. A linear bearing 23 is provided intermediate bolt 18 and projecting pin portion 22. In use the pins 17 are mounted in the respective relevant platen 13, 14 projecting toward the opposed respective platen. The arrangement of the pins is such that they are non- aligned but regularly spaced transversely with respect to pins in the pin array of the opposed platen. This ensures that the required "egg-box like" configuration can be produced in the sheet when deformed. The pins 17 have a hemispherical dome-shaped head portion 25 including fringe 26.

In use a sheet to be deep drawn is arranged between upper and lower press portions sandwiched between respective blank holders 10 and 11. The press is then operated to move platens 13, 14 toward one another to ensure that the respective pins 17 in each array engage and deform (deep draw) the appropriate portion of the sheet material. Subsequent to deformation the platen tables 13, 14 separate and the now deformed core sheet material 2 may be removed.

The deformed core sheet 2 may be laid up with other sheets to form various designs of panel, for example the arrangement shown in Figure 1 having face sheet layers 5, 6 secured to peaks and troughs 3 and 4. Various alternatives for securing the peaks 3 and troughs 4 to the facing layers 5, 6 have been investigated. For example mechanical joining (by rivetting or the like, or fusion welding) . The most preferred method for securing at the interface between the peaks 3 and troughs 4 and respective facing layers 5, 6 has been found to be by using adhesive material (chemically bonding) . The adhesive forms a permanent, rigid connection between the materials being bonded. Single-component and two-component adhesives have been investigated. For the all steel material bonded structure preferred in accordance with the present invention, epoxy resin bonding materials have been preferred. An example of a suitable bonding resin material is material commercially available under the trade mark 3M (registered trade mark) designation 2216.

The epoxy resin material is applied to the respective peaks and troughs of the core layer 2. The layed-up arrangement including core layer 2 and one or both of facing layers 5, 6 is then pressed together to allow the resin to harden. Subsequently, an energy absorbent medium (typically polyurethane foam) is injected in aerosol form into the void spaces between the peaks 3 , troughs 4 and facing sheet layers 5, 6 and permitted to expand and cure. In certain embodiments it is envisaged that the polyurethane foam would not be required. However, the presence of the filler material foam improves the impact energy absorbance of the arrangement. Additionally, foam expanded in situ is preferred to solid preformed foam inserted into the spaces between the peaks 3 and troughs 4. Test specimens of composite panels formed in accordance with the invention have been prepared and subjected to material testing.

An arrangement comprising a tin plate (mild steel) core "egg-box like" configuration deep drawn deformed core sheet 2 and facing sheets 5, 6 were bonded as described above. A second test specimen included successive layers of deep drawn deformed sheets 2 and facing sheets 5 laid up and bonded. A further specimen included a structure of Figure 1 including foam filling. A further test specimen included a structure of successively built up deformed deep drawn core layers 2 and interposed facing layers 5, the voids being filled with expanded polyurethane foam material.

The range of density for all four test specimens was between 300 kg/m³ and 450kg/m³ with the foam filled specimens being the densest. The density of all four designs compares with a value of density for typical aluminium honeycomb of, for example, 82kg/m³.

The four sample specimens were impact tested. It was found that the polyurethane foam filled specimens absorbed more energy than the unfilled specimens. However, all relevant designs absorbed over 95% of the energy translated in the impact .

For the deformed core sheet material layer 2 and facing layers 5, 6, corrosion resistant alloy steels (such as stainless steel) or polymer coated mild steels (for example tin plate) may be used in order to minimise the risk of corrosion.

The present invention provides a composite structural panel particularly suitable for automotive use in situations of impact amelioration or crumple zones. The arrangement utilising steel provides significant cost benefits in terms of comparison with known aluminium honeycomb solutions whilst ensuring good technical performance. Deep drawn "egg-box type" configuration for the core sheet layer 2 manufactured by a two-way pressed design adhesively bonded between suitable facing layers and polyurethane filled provides the best overall technical performance. Laminated steel sheet layers are preferred to minimise the risk of corrosion leading to failure.

Claims

CLAIMS ;

1. Composite structural panel comprising a bonded layer structure, including:

i) a first layer of sheet material plastically deformed to form an array of peak and trough formations complementarily on opposed faces of the layer; and

ii) a second layer of sheet material bonded in face adjacent face relationship with the first layer.

2. A composite structural panel according to claim 1, including a third layer of sheet material bonded in face adjacent face relationship with the first layer, one of the second and third layers being situated on the obverse face side of the first layer, the other being situated on the reverse face side of the first layer.

3. A composite structural panel according to claim 1 or claim 2, the first, second and/or third layers being substantially of metallic material.

4. A composite structural panel according to claim 3, the second and third layers being fusion bonded (welded, brazed or the like) to the first layer.

5. A composite structural panel according to any preceding claim, the first, second and/or third layers being mechanically joined (for example by rivetting or the like) .

6. A composite structural panel according to any preceding claim, the first, second and/or third layers being chemically bonded by means of adhesive bonding material or the like.

7. A composite structural panel according to claim 6, the adhesive bonding material comprising an epoxy resin.

8. A composite structural panel according to any preceding claim being a vehicle body panel .

9. A composite structural panel according to any preceding claim, wherein for the first layer, the ratio of the sheet thickness (t) to the peak to trough dimension (d) is substantially in the range

35< ^d/_t <85.

10. A composite structural panel according to any preceding claim, wherein the structural panel includes an expanded polymer filler material sandwiched between the first and second (and/or third) layers.

11. A composite structural panel according to claim 10, wherein the expanded polymer filler material comprises expanded polyurethane foam.

12. A composite structural panel according to claim 10 or claim 11, wherein the expanded polymer filler substantially fills the peak and trough formations.

13. A composite structure panel according to any preceding claim, wherein the respective peak and trough formations are aligned along intersecting transverse axes .

14. A composite structural panel according to claim 13, wherein the respective peak and trough formations are aligned along intersecting perpendicular axis.

15. A composite structural panel according to any preceding claim, wherein the peak and trough formations are substantially of the same shape and dimensions .

16. A composite structural panel according to any preceding claim, wherein the peak and trough formations have a curve-form terminal portion defining a contact node contiguous with the second and/or third layers of the structure.

17. A composite structural panel according to claim 16, wherein the peak and trough formations have a domed terminal portion defining the contact node contiguous with the second and/or third layers of the structure.

18. A composite structural panel according to any preceding claim, wherein the peak and trough formations are generally pyramidal or conical in shape .

19. A composite structural panel according to claim 18, wherein the peak and trough formations have a curve- form terminal portion defining a contact node contiguous with the second and/or third layers of the structure, an angular section step lying between the general pyramidal or conical surface of the formation and the curve-form terminal portion.

20. A composite structural panel according to any preceding claim, the first layer of sheet material comprising material deep drawn to form the complementary peak and trough formations.

21. A composite structural panel according to any preceding claim, wherein the first and second layers are secured to one another at contact nodes comprising the peaks of the first layer.

22. A composite structural panel according to any of claims 2 to 21, wherein the first and third layers are secured at contact nodes comprising the troughs of the first layer.

23. A composite structural panel according to any preceding claim, wherein the first and second layers of sheet material comprise the same material .

24. A composite structural panel according to any preceding claim, including a third layer of sheet material bonded in face adjacent face relationship with the first layer, one of the second and third layers being situated on the obverse face side of the first layer, the other being situated on the reverse face side of the first layer, the first second and their layers comprising the same material.

25. A composite structural panel according to any preceding claim, the first layer of sheet material comprising a steel material.

26. A composite structural panel according to claim 25, the first layer of sheet material comprising mild steel .

27. A composite structural panel according to claim 26, the first layer of sheet material comprising polymer coated mild steel .

28. A composite structural panel according to claim 26 or claim 27, the first layer of sheet material comprising tin plate material .

29. A method of manufacturing a composite structural panel, the method comprising:

30. A method according to claim 29, wherein the filler material is introduced into the space between the press formed sheet and the further sheet .

31. A method according to claim 30, wherein the filler material comprises a hardenable foam material.

32. A method according to claim 31, wherein the filler material comprises a polyurethane foam material.

33. A method according to any of claims 30 to 32, wherein the filler material is introduced between the already bonded layers in aerosol form and expands to fill the voids of the peak formations and the trough formations.

34. A method according to any of claims 29 to 33, wherein the first layer of sheet material comprises a steel material.

35. A method according to claim 34, wherein the first layer of sheet material comprises mild steel.

36. A method according to claim 35, wherein the first layer of sheet material comprises polymer coated mild steel and/or tin plate material.

37. A method according to any of claims 29 to 36, wherein the layered up sheets are bonded at contact zones using an adhesive material .

38. A press for manufacturing a deformed sheet having an array of peak and trough formations complementarily on opposed faces of the sheet, the press comprising:

i) a first press table including an array of regularly spaced projecting deformation elements; and ii) a second press table arranged adjacent the first press table, the second press table including an array of regularly spaced projecting deformation elements, 5 wherein;

the first and second tables are movable relative to one another between a retracted

10 position in which the sheet may be introduced into and removed from the press, and in an advanced position in which the projecting deformation elements of respective tables overlap, the projecting deformation elements in

15 the first array being non-aligned with the projecting deformation elements in the second array, the projecting elements in the arrays being regularly spaced with respect to one another.

20