SANDWICH PANEL, INSERT THEREFOR, STRUCTURE COMPRISING SANDWICH PANELS AND METHOD OF JOINING SUCH PANELS

Abstract: A sandwich panel (1, 2) comprising a core material (3) sandwiched between plate members (4), and an insert member (9) locally replacing the core (3) and having a profile so as to intermesh with an appropriately profiled member on the unit to which it is to be connected. Further described is a method of connecting sandwich panels comprising a core material sandwiched between plate members, to a unit, comprising inserting an insert member having a profiled side so as to interlock with an appropriately profiled member on the unit to which it is to be connected.

Description: SANDWICH PANEL, INSERT THEREFOR, STRUCTURE COMPRISING SANDWICH PANELS AND METHOD OF JOINING SUCH PANELS The invention relates to methods of joining sandwich panels and to sandwich panels themselves having means to connect to other sandwich panels or other structural or non structural units. Sandwich panels comprise a core material (such as honeycomb) sandwiched between plates of stiff material. These composite panels, have application in a wide variety of areas due to significant mass savings and their high strength/stiffness to weight ratio and thus their use in lightweight structures. Thus they have application in the construction, aerospace and other fields. It is a requirement that these panels be joined so to form a structure in such a way that they are able to withstand and transmit loads. Alternative methods of joining sandwich panels have been developed. Figure la shows as simple way of joining two panels at 90°. This is done by extending one of the plates of one of the panels and using adhesive to connect to the cut end of the other. This joint is however extremely weak in many modes. Alternatively cleats are known which produce fairly strong jointing between panels. These cleats consists of shaped plates which are used in a variety of modes. Figure 1 b, c and d shows panels joined at 90° and a "T" joint respectively. The panels of figure lb are joined in each case by two L-shaped cleats 7. The interface between the panels and the joining surface of the cleats are provided with adhesive. Alternatively the cleats may be mechanically fastened or a combination of both. In an alternative mode the cleats are shaped 8 to provided a slot for insertion of the panels as shown in figure lc. This has the advantage in providing a stronger connection. However the use of cleats is not without problems. Firstly there is the problem that cleats are additional components which add to the cost as well as the increase in time in joining and assembling sandwich panels. Cleats having slots for insertion of the panels have to be accurately sized which is problematic. Heat or cold will often complicate accurate fitting as there is frequently thermal mismatch. In addition the use of cleats does not provide smooth joining. This not only detracts from the aesthetic appearance of the structure but introduces small steps internally and externally. These may reduce aerodynamic performance in particular applications as well making it more difficult to install units internally. It is an object of the invention to provide a method of joining sandwich panels which is simple, effective and provides a good joint such that forces are transmitted across members efficiently. The invention comprises a sandwich panel comprising a core material sandwiched between plate members, and an insert member locally replacing the core and having a profile so as to intermesh with an appropriately profiled member on the unit to which it is to be connected. The insert is preferably corrugated. It is preferably fabricated from a high strength lightweight material such as carbon fibre reinforced plastic. The advantages are that the corrugated sections interlock on assembly providing additional surface areas for adhesive in shear. No matching of honeycomb or other filler material is required. The joining gives a lightweight structure with good compression strength and excellent distribution of forces (especially shear). The appropriate use of a potting compound is preferred. The invention will hereinafter be described by way of example only and with reference to the following figures of which: Figure 2 shows an embodiment of the corrugated joint. Figure 3 shows various profiles of insert members. Figure 4 shows 45° and 135° angle joints using the corrugated design Figure 5 shows a corrugated section bonded into a honey comb sandwich panel. Figure 6 shows a further embodiment of the invention whereby the insert is used in a "T" joint Figure 2 shows two honeycomb panels 1 and 2 each having a honeycomb centre 3 sandwiched between two face skin plates 4. One of the skin plates of each panel is extended such that it is greater in length that its opposite plate. The honeycomb core does not extend to the edge of the short plate but terminates a short distance from it. A corrugated member 9 is inserted between the two plates of each panel such they extend from the honeycomb material to be flush with the longer plate. In assembly the two panels are effectively joined by pushing the panels together such that the corrugated inserts mate to produce a snug fit. Adhesive in preferably applied. Figure 3 shows a corrugated section bonded into a honey comb sandwich panel. The skilled person would understand that the inserts can be of any suitable shape. The corrugations may be of a wide variety of shapes, such as square or rectangular. Moreover the inserts do not need to be corrugated. Figure 4 show various end profiles of inserts. Figure 4 a, b, shows a corrugated insert, a solid rectangular cut-out insert. As far these profiles are concerned they are preferably uneven such that the distance β and α are substantially the same thus allowing a good fit of identical inserts with each other. This leads perforce to the distance δ being less than β and α and thus to "uneven" inserts. The main consideration is that they have a profile which can mate with a profile on another insert so as to produce a snug fit. Preferably the inserts extend between the faceskins down to the core material (honeycomb). Preferably the inserts are corrugated as this allows for a lightweight insert with large stiffness. To improve further the integrity of the join, adhesive is preferably used. Figures 5 shows two honey comb panel comprising plates and honey-comb filler, joined at 45° and 135°. Each panel angle joints comprising inserts suitable angled and profiled. The cross-hatched "area" shows the bond area which is in shear. Figure 6 shows a further embodiment of the invention whereby the insert is used in a "T" joint. Two sandwich panels are shown 1, 2. A corrugated insert 9 is bonded between two faceskins 3 a, b of the panel with the inner face skin 3a removed at the location of the joint. The adjoining panel has an insert 10 which has lugs 11 that correspond to the pitch of the corrugated section. These may be manufactured from a composite block, which is inserted between the skin plates of the panel. In this embodiment although the inner skin has been cut the forces within the skin can be transferred by the adhesive in shear through the corrugated section.

Claims: Claims 1. A sandwich panel comprising a core material sandwiched between plate members, and an insert member locally replacing the core and having a profile so as to intermesh with an appropriately profiled member on the unit to which it is to be connected. 2. A sandwich panel as claimed in claim wherein one of the plate members is longer than the other and said insert extend so as to be substantially flush with the edge of said longer plate. 3. A sandwich panel as claimed in claim 1 or 2 wherein said insert member is corrugated. 4. An insert suitable for as sandwich panel as claimed in any of the preceding claims. 5. An insert as claimed in claim 4 which is uneven. 6. A structure comprising one or more sandwich panels as claimed in claim 1, 2 or 3. 7. A method of connecting a sandwich panel comprising a core material sandwiched between plate members, to a unit, comprising inserting an insert member having a profiled side so as to interlock with an appropriately profiled member on the unit to which it is to be connected. 8. A method as claimed in claim 7 wherein said unit is a sandwich panel, also comprising a substantially identical insert member.

Inventors: DANDO GLYN CHARLES, DANDO, GLYN, CHARLES
Applicants: DANDO GLYN CHARLES, SECR DEFENCE, DANDO, GLYN, CHARLES, THE SECRETARY OF STATE FOR DEFENCE
Application year: 2000
Main classification: F16B5
IPC codes: F16B5