GB2324847A - Energy absorbing device - Google Patents

Abstract

An energy absorbing device based on a peeling process comprises a steel strip 44 which is fixed to a side plate 42 by a structural adhesive 47. In use, when a force is applied to the plate 48, this force is transmitted to the strip 44 and when it reaches a yield limit the adhesive will fail and the strip will peel off the side plate 42, undergoing plastic deformation and dissipating energy. The thickness of the strip can be chosen to preselect the force at which the strip will start to peel. A further embodiment using a peeling tube is also disclosed.

Description

Energy Absorbing Device This invention relates to the energy absorbing devices.

Energy absorbing devices are the devices that absorb the energy of impact and attenuate its effects. They are demanded in automobiles, air crafts, trains, ships, elevators and so on. Energy absorbing devices have been developed so far, using different sorts of energy dissipating phenomena. These include crushing tubes (laterally or axially), inverting tubes, buckling and folding of plates, stretching and bending metal rods and strips and etc. But all of them suffer from some disadvantages. These problems could be a low yield point or poorly defined load deflection curve, low capacity of energy dissipation, large volume, absence of post impact strength and so on. Existence of these problems has meant that the use of energy absorbing devices specially in the structures would be with some restrictions so there is a necessity for a new device.

According to the present invention, energy absorbing device is produced by using peeling process.

Specific embodiments of the invention will now be described by the way of two examples of the device. In the first example of the device which is based on peeling of plates, is explained and in the second example the device which is based on peeling of tubes is described.

With reference to the accompanying drawing related to example one, in which: Figure 1 shows the device in perspective.

Figure 2 shows the perspective of the device while the box is open.

Figure 3 Shows the frame of the device.

Figure 4 Shows the bar of device.

Figure 5 shows the bent mild steel strip.

Figure 6 shows the longitudinal section of the device.

Figure 7 shows the cross section A-A of device in big scale.

Figure 8 shows the detail of the connection of peeling plate in big scale.

Figure 9 shows plastic deformation the shell part of strip.

Figure 10 shows peeling of strip.

Figure 11 shows the end stage of peeling.

Fig 1 shows the first and base form of the device that I have invented for energy absorbing purposes. Its main parts are a frame (Fig 3), a bar (Fig 4), and a suitably formed mild steel strip (Fig 5). The frame itself has been formed from Two plates 40 and 41 , two channel form profiles 42 (fig 3) which have been made by welding plates together. The plates 40 and 42 are screwed to the channel plates 42. Two plates 43 (fig 1) are used to cover the device and also to strengthen the rigidity of the side plates 42. The bar goes through the frame and is connected to it by a strip 44 made from mild steel plate (Fig 2 and Fig 6). This strip is screwed firmly to the bar by suitably shaped connection parts 45 , 46 and is stuck to the frame by a structural adhesive 47 or any other kind of materials or other type of attachment which fails under peeling forces. This connection is shown in more detail in Fig 8. The bar is guided inside the frame by plate 40 and connection part 45 This part is in smooth contact from two sides with peeling plate 44 and from the other sides with cover plates 43.

As it is shown in Fig 8, the strip has formed a shell between bar and frame and connect them by this shell. If we apply a force on the top of bar, this shell will be affected and will sustain the load as an elastic shell as far as the stresses is lower than the yield point of the material of strip. The strength of this shell depends on its form, supports, thickness and material. With suitably choosing these items, the collapse load of the shell can be adjusted to whatever desired. If the force exceeds this limit, for example in the case of high impact, the shell will collapse and go under plastic deformation (Fig 9) and finally the strip will start to peel away the frame (Fig 10). During this peeling, the strip is bent between frame and bar and a high amount of energy is dissipated. Generally, during the collapse of the shell, translated force falls down and then rise to a level which remain constant during peeling process, it means that the load deflection curve would almost get a rectangular elastic-plastic form.

When the bar gets the end (Fig 11), as well as tolerating large amount of energy, It will work like an ordinary compressive component. At this stage the frame and bar start to beer the applied force together (due to existence of plate 48) and the device will find a high compressive strength. The relatively soft material plate 49 (fig. 6) has been used to have smooth transfer from the behaviour of device during peeling process (which is plastic) to the behaviour of the device after the end of peeling process (which is elastic) . Until this stage, the damaged part will be only the steel strip and the device could be reused by cleaning failed glue and replacing the strip.

The modified form of device is being described as second example. In this example, peeling of tube has been used for creating an energy absorbing device. With reference to the accompanying drawing, related to example two, in which: Figure 12 shows the front view of the device.

Figure 13 shows the device in perspective.

Figure 14 shows the longitudinal section ofthe device.

Figure 15 shows the inner tube 50.

Figure 16 shows the longitudinal section ofthe device in a big scale.

Figure 17 shows the connection of the inner tube in large scale.

Figure 18 shows the cross section B-B of the device in a big scale.

Figure 19 shows the device under load.

Figure 20 shows plastic deformation of the shell part of the inner tube.

Figure 21 shows peeling process of the inner tube.

Figure 22 shows the end stage of peeling.

Figure 23 shows longitudinal section of the device in tensile form.

Figure 24 shows the connection of the inner tube in large scale in the tensile form of device.

Figure 25 shows the device under load in the tensile form of device.

Figure 26 shows plastic deformation of the shell part of the inner tube in the tensile form.

Figure 27 shows peeling process of tube in the tensile form.

Figure 28 shows the end stage of peeling in the tensile form of device.

Figure 29 shows the connection of the inner tube in compressive form of the device for its protection from tensile forces.

Figure 30 shows longitudinal section of the device in the tensile form with an additional tube.

Figure 3 1 shows peeling process of tube in the tensile form with additional tube.

Figure 32 shows the connection of the inner tube in large scale in the tensile form of device with an additional tube.

Figure 33 shows the connection of the inner tube with high yield limit.

Figure 34 shows the load deflection curve of the device.

Figure 35 shows the framework equipped with energy absorbing device.

Figure 36 shows the framework in large deflected form.

The device is shown in Figl2. Its longitudinal section is shown in Fig 14. This longitudinal section is illustrated in bigger scale in fig 16.This is the modified form ofthe device which can be also used as a structural member in the structures, like a tensile or compressive bar. It is formed from three major parts: The lower tube 51, the upper tube 52, and the inner tube 50 that absorbs the energy of impact. The inner tube is stuck to the lower tube by an industrial adhesive 47 or any other kind of materials or other type of attachments which fails under peeling forces and attached firmly to the upper tube by suitably shaped connection parts 53 and 54. These connection parts are screwed together by an hexagonal socket head screw 56 (fig. 16 ) or other type of attachments may be used. This connection has been shown in fig. 17 with more detail and bigger scale. The faces of connection parts 53 and 54 that are in contact with inner tube 50 are made course enough to produce sufficient friction. The top edge of the inner tube has formed to an axisymmetric shell. The strength of this shell is important for the device and defines its yield limit. Its strength depends on the parameters of the shell (its shape ,thickness, supports and material). By suitably choosing these items, the collapse load ofthe shell can be adjusted to whatever desired. This load is the yield load of the device under impact loads As is shown in Fig 19 , when we apply a force on the top of the upper tube, the shell part of inner tube will be affected and will sustain the load as long as the load is lower than the yield limit of the shell. If the force exceeds this limit, the shell will collapse and will go under plastic deformations (Fig 20) and finally the inner tube will start to peel away the lower tube (Fig21). During this peeling and failure of the glue (or the other sort of used attachments), the inner tube will be also inverted and great amount of energy is dissipated.

When peeled to its full extent the device will behave like an ordinary compressive bar (fig22). The upper and lower tubes start to beer the applied force together and the device will posses again an elastic behaviour. A soft material plate 58 (fig 14) is used to make a smooth transfer at the end of peeling process from plastic (during peeling process) to elastic (at the end of peeling) behaviour. Until this stage, the damaged part will be only the inner tube and the device could be reused by replacing the set of inner and lower tube. The device has been designed properly which this set could be changed easily.

Generally, during the collapse of the shell, at first the translated force will fall down and then will rise and by starting of peeling process, it will reach to a constant level. The load deflection curve of the device will have a general variation as shown in fig.34. Point (a) shows end of elastic deflections and point (b) is the start point of peeling process. The point (c) shows the end of peeling process. Between points c and d is the behaviour of soft material plate which makes a smooth transfer to a new elastic curve which shows behaviour of the whole parts of the device that work together.

From the other technical points of the device, as it is shown in fig 16, the lateral rigidity of the lower tube is strengthened at the fist point of peeling process by a single ring 55.

The connection part 53 is formed suitably to act as guiding part for moving of the upper tube 51 inside inner tube 50. This part has smooth contact with inner tube 50 Usual hinge connections is used in putting the device in the structures. In two dimensional structures, simple hinge connection 57 and in three dimensional, sphere hinges are used.

If there is a possibility of acting tensile forces on the device, the guiding neck and connection parts should be arranged to protect the device from these tensile forces, as it is shown in fig 29.

The ring 63 which is fit to the shell part of the inner tube, is used to transfer the tensile load between lower and upper tubes.

The device has been designed to be changed easily to a tensile form by only connecting the upper tube to the bottom threads of connection part 53, as it is shown in figure 23. In figure 24, the connection of tubes has been shown in bigger scale. Figure 26 shows the plastic deformation of the shell part of the peeling tube and picture 27 shows its peeling process. In fig. 28, the end of peeling is shown which the device behave like an ordinary tensile member. The soft material ring 59 (fig 23) is here to have a smooth transfer at the end of peeling process. The connection part 53 has a suitable form to ensure the post impact resistance of the device at the end of peeling process.

In the tensile form of the device, the natural inversion diameter of the peeling tube is the amount that makes a minimum translated force (except for the first stages of peeling process).

Figure 30 shows another tensile form of the device which has a compulsory inverting diameter.

An additional tube 65 has been used to make desired inverting diameter for peeling tube. The length of this tube should be about half of the inner tube. Figure 31 shows the end of peeling process in this case. In figure 32, its connections have been shown in bigger scale.

In the all of the cases that has mentioned above for this modified form of the device, we can increase the yield strength of the device by using the ring 63 and sticking it by glue to the shell and with the screw to the lower tube, the same as shown in fig33.

From the above figures we can distinguish the following properties ofthe device: In a compact forum, it has the capacity of dissipating high amounts of energy.

Its post impact resistance is perfectly reliable.

It has a well defined yield point that can be adjusted to any desired load.

These are the properties which previously have not all been found together in a single device.

In view of these properties we can see that the device could be used as a tensile or compressive bar in the structures to raise their impact resistance. Under service load they will behave like ordinary members but in the case of high impact loads they will limit the translation of force and will protect the structure.

For example, if we use few tensile form of the device in the lower part of a framework (the members which have been distinguished by dash in fig 35) we can get a high resistance against excessive impact loads. Under service loads they will work like the others ordinary components but at the high loads they will open and as well as absorbing the energy they will result in large deformations to the framework (Fig 36). In spite of these large deflections the structure will keep its strength. The only damaged parts tnat should be changed are energy absorbing devices.

In general, all kind of steel structures can be strengthened with the use of this device. Specially the supports of structures can be equipped by these members to isolate the structure from other parts of construction.

We can distinguish Following privileges for the use of this member in the structures: 1- It improve impact strength of structures, by absorbing the energy.

2- It isolate the structure from its supports, so we will have controlled shock wave transfer to the other parts of construction.

3- It improves ultimate strength of structures by allowing them to have large deflections in a safe manner. Usually structures find a better position under load if they have large displacements.

Claims (1)

1. l-According to the present invention, energy absorbing device is produced by using peeling process.

   2-An energy absorbing device as claimed in claim 1 wherein plate is stuck to the other plate with an adhesive- or any other sort of attachments which fails under peeling process- and is peeled for absorbing the energy.

   3-An energy absorbing device as claimed in claim 1 wherein tube is stuck to the other tube with an adhesive- or any other sort of attachments which fails under peeling process- and is peeled for absorbing the energy.

   4-An energy absorbing device as claimed in claim three wherein the tube- which is peeled- has been formed as an axisymmetric shell in the adjacency of the connection parts for producing a desired yield limit for the device.

   5-An energy absorbing device as claimed in claim three or four wherein the connection parts are designed symmetrical enough for using the device either as a compressive or a tensile bar.