WO2019186157A1

WO2019186157A1 - Drop towers

Info

Publication number: WO2019186157A1
Application number: PCT/GB2019/050876
Authority: WO
Inventors: Ian Coles; Graham Barnes; Richard Roberts; Miles PRICE
Original assignee: Engenuity Limited
Priority date: 2018-03-27
Filing date: 2019-03-27
Publication date: 2019-10-03
Also published as: GB201804930D0

Abstract

A drop tower (2) for impact testing a sample (8) comprising at least one vertical guide (4), a sample holder (6) for receiving a sample (8) to be tested and an impact assembly (9) arranged to move vertically on the vertical guide (4). The drop tower (2) further comprises a lifting arrangement (14) for lifting the impact assembly (9) upwards and away from the sample holder (6) and a release arrangement (22) for releasing the impact assembly (9), thereby allowing it to move downwards into contact with the sample holder (6) or a sample (8) therein. An energy dissipation arrangement (24) comprising a mass block (26) is arranged beneath the impact assembly (9), resting on at least one resilient member (28) and thereby arranged in use to absorb energy from the impact assembly (9).

Description

Drop Towers

The present invention relates to drop towers and improvements thereof.

Drop towers are often used for impact testing a wide variety of different components and materials. They can be used to assess how a specific component or material responds to an impact, i.e. how a component or material absorbs energy from the impact.

Drop towers typically comprise an impact part arranged to be raised and then dropped in order to come into contact with a sample to simulate an impact. The impact part is often relatively heavy in order simulate typical impact conditions which the tester wishes to investigate. Often, to increase the impact energy of the impact part, the impact part may be further laden with a large mass. During operation, the impact part and mass are typically raised to a predetermined height and subsequently released thereby falling and impacting the sample. The impact part typically falls under gravity until it impacts the sample. By raising the impact part to a fixed, known, height, along with knowledge of the mass of the impact part, and any additional mass added to increase its energy, it is possible to determine the increase in potential energy of the impact part and thus the energy the impact part will impart onto the sample. With knowledge of this energy, it is possible to carry out analysis on various samples to determine how they respond to impacts with specific energies.

Impact testing can be used to assess how a particular component or material will respond to certain impacts. In particular, it may be possible to simulate typical impacts which a component would be expected to experience in its typical use, for example vehicle components which may at some point in their lifetime experience a collision, for example with another vehicle. Impact testing can also, for example, be used to carry out sophisticated analysis of particular components and depending on the particular test being used, it may be possible to identify weak spots or component design which affects the components ability to absorb impacts. Often when undergoing impact testing, samples may exhibit complete failure. This failure may, for example, be complete shattering, deformation or crack initiation depending on the component, its material and the height/weight of the impact part. When a drop tower is used for impact testing, as the impact part impacts the sample within the drop tower, the sample typically fractures thereby absorbing the energy from the impact part. However, if the sample within the drop tower is defective and exhibits complete failure upon impact, the component may not be able to absorb much, if any, energy from the impact part. In this situation, the impact part will typically come into direct contact with the base of the drop tower with little to none of its energy having been absorbed. Due to the fact that the impact part often has a very high mass, or is laden with a high mass, this sudden direct impact can result in the impact part or other parts of the drop tower being damaged.

The present invention aims to provide an improved drop tower and when viewed from a first aspect provides a drop tower for impact testing a sample, the drop tower comprising:

at least one vertical guide;

a sample holder for receiving a sample to be tested;

an impact assembly arranged to move vertically on the vertical guide;

a lifting arrangement for lifting the impact assembly upwards and away from the sample holder;

a release arrangement for releasing the impact assembly, thereby allowing it to move downwards into contact with the sample holder or a sample therein; and an energy dissipation arrangement comprising a mass block arranged beneath the impact assembly, resting on at least one resilient member and thereby arranged in use to absorb energy from the impact assembly.

As will be understood by those skilled in the art, as the impact assembly is lifted upwards by the lifting arrangement, its gravitational potential energy is increased. The increase in gravitational potential energy is directly proportional to the mass of the impact assembly and the height through which it is lifted. As the impact assembly is released, and allowed to fall downwards, the gravitational potential energy of the impact assembly is, largely, converted into kinetic energy. Of course there will be a small amount of energy loss, e.g. due to friction and air resistance, but generally the gravitational potential energy is largely converted into kinetic energy. As the impact assembly impacts the sample holder or sample therein, the kinetic energy will then theoretically, at least partially, be absorbed by the sample therein as it deforms or fractures.

However, in certain situations the sample within the sample holder may be defective or otherwise incapable of absorbing sufficient kinetic energy from the impact to bring the impact assembly to a controlled stop. With prior art drop towers, in such a set of circumstances, the impact assembly would typically impact the sample holder, or other part of the drop tower, which is incapable of absorbing the energy in an appropriate manner. This often results in the impact assembly, or the part which it comes into contact with, being damaged, often beyond repair. Given that drop towers and their components are often very expensive items this is clearly undesirable.

This problem is addressed by drop towers in accordance with the present invention as the energy dissipation arrangement may absorb energy from the impact assembly. Therefore, instead of the impact assembly being stopped suddenly, its impact may be absorbed by the energy dissipation arrangement comprising the mass block and the at least one resilient member. This may bring the impact assembly to a more controlled stop. Accordingly, drop towers in accordance with the present invention do not rely on the impact being absorbed by the sample and so may be operated with a defective sample or even with no sample at all, without, at least in preferred embodiments, the risk of the drop tower, or its components, being damaged.

Whilst the drop tower according to the present invention is particularly well suited to absorbing energy from the impact when the sample exhibits complete failure, it is also, advantageously, well suited to absorbing excess energy in impacts when a sample doesn’t fail. For example, an operator may carry out a test in which the impact assembly carries an excessive amount of energy at its impact point, the sample may not necessarily fail and may instead only absorb some of the impact energy. Advantageously, the energy dissipation arrangement can absorb any excess energy not dissipated by the sample, and thereby avoid unnecessary damage to the drop tower. The impact assembly may come into direct contact with the sample received in the sample holder, i.e. the sample may protrude from the sample holder such that the impact assembly may come into direct contact with the sample. However, as will be appreciated, there are various ways in which the force of the impact may be transferred and this need not necessarily be via direct contact with the sample. For example, the sample holder, and sample held therein, may be configured such that the impact assembly impacts a portion of the sample holder which transfers the force from the impact to the sample. This force may be transferred in any desired manner, for example to apply a compressive force to the sample or alternatively to apply a tensional force to the sample.

The specific arrangement of the impact assembly may be used to determine exactly how the impact assembly impacts the sample holder or sample therein and the specific point at which any force is transferred to the energy dissipation

arrangement, for example in situations where the impact assembly possesses excess energy. In a set of embodiments, the impact assembly is adjustable such that the point at which the energy dissipation arrangement absorbs energy from the impact assembly can be adjusted. For example, the impact assembly may comprise a downwardly extending portion which extends from a base of the impact assembly and the extent of the downwardly extending portion may be adjusted to adjust the vertical position at which the impact assembly transfers energy to the energy dissipation arrangement. The mass block would typically be expected to have sufficient mass that it can appropriately absorb the kinetic energy from the impact assembly. As will be appreciated, if the mass of the mass block were to be too low, a sudden impact would likely result in the mass block being quickly displaced which could potentially result in damage to other parts of the drop tower and reduce the opportunity of the sample to be exposed to the maximum portion of the potential impact energy. In a set of embodiments the mass block has at least half the mass of the impact assembly. The mass could be the same as or greater than the impact assembly but this is not essential. The mass of the impact assembly may be adjustable and so in a set of embodiments the mass of the mass block is at least, preferably greater than, half the heaviest possible mass of the impact assembly, i.e. when the impact assembly is fully laden with any additional mass. In another set of embodiments the mass of the mass block can be adjusted. Of course movement of the mass block as it absorbs energy from the impact assembly will also be dependent on the stiffness, and number, of resilient members on which it rests.

Due to the at least one resilient member on which the mass block rests, when the energy dissipation arrangement absorbs energy from the impact assembly, it may be caused to oscillate. As will be appreciated, depending on the weight of the components involved, this oscillatory motion may take some time come to a rest which may be undesirable, particularly when an operator wants to carry out repeat testing. Therefore, in a set of embodiments the energy dissipation arrangement further comprises at least one dampener. The damper will dampen any oscillatory motion and therefore more quickly bring the mass block to a controlled rest.

In a set of embodiments the drop tower comprises a plurality of resilient members. The plurality of resilient members may be evenly spatially distributed underneath the mass block.

The at least one resilient member may take any suitable form that is capable of absorbing or storing energy. For example, the at least one resilient member may comprise an elastomeric element, e.g. a rubber block or tube, that can be compressed to absorb energy. As the impact assembly will often have a relatively large mass in order for it to carry out appropriate testing, the mass block will also at least have an equivalent mass and so it may be necessary for the at least one resilient member to be capable of supporting a large mass even before accounting for the need to absorb energy from the impact assembly. The Applicant has recognised that a spring, particularly a metallic spring, may be particularly suitable as a resilient member for supporting the mass block. Therefore, in a set of embodiments the at least one resilient member comprises a spring, for example a coiled spring.

As discussed above, the mass of the impact assembly, and the height to which it is lifted, contribute to the kinetic energy the impact assembly imparts onto the sample holder or sample therein. The height to which the impact assembly is lifted will also determine the speed at which the impact assembly impacts the sample holder or sample therein. Depending on the sample being tested, and the type of test an operator wishes to carry out on the sample, it may be necessary to increase the energy, i.e. impact energy, the impact assembly is capable of imparting to the sample holder or sample therein and/or increase the speed of impact, for example if an operator wants to imitate the conditions a sample will experience in a particular situation, e.g. a motor vehicle component in a crash scenario. Accordingly, in a set of embodiments the drop tower comprises a further resilient member arranged to accelerate the impact assembly towards the sample holder after the impact assembly has been released by the release arrangement. It will be appreciated that by accelerating the impact assembly this will, typically, increase the speed of the impact and also increase the energy of the impact assembly. The provision of a further resilient member may allow for more control over the type of test which is being carried out. For example, an operator may be able to selectively use the further resilient member to increase the energy and/or speed of the impact.

The further resilient member may be compressed by the impact assembly itself as it is lifted upwards by the lifting arrangement. Alternatively, the further resilient member may be compressed by any other suitable means, for example means separate from the impact assembly itself. It will be appreciated that by providing a further resilient member which accelerates the impact assembly, the kinetic energy of the impact assembly at the point of impact will comprise the gravitational potential energy the impact assembly gains through lifting the impact assembly upwards and also the energy imparted to the impact assembly from the potential energy of the compressed further resilient member.

In embodiments wherein the impact assembly compresses the further resilient member, the lifting arrangement may need to be capable of lifting the impact assembly and also compressing the further resilient member. Of course the further resilient member may comprise any suitable member, e.g. an elastomeric block or a spring, e.g. a metallic coiled spring.

The Applicant has recognised that the provision of a further resilient member is not the only way that the speed and/or energy of the impact assembly may be increased. Therefore, in a set of embodiments the drop tower further comprises a hydraulic or pneumatic ram arranged to accelerate the impact assembly towards the sample holder after the impact assembly has been released by the release arrangement. Of course the drop tower may comprise a further resilient member or a hydraulic or pneumatic ram, or it may comprise both.

As will be appreciated, the energy of the impact assembly upon impact with the sample holder or sample therein will be dependent on the mass of the impact assembly, the height from which it is dropped and any additional energy which is imparted to the impact assembly, e.g. via the further resilient member discussed above. Any one of these factors may be varied in order to vary the impact energy of the impact assembly.

The Applicant has recognised that often, drop towers are used in laboratories and test facilities where the height of the room in which they are used is restricted. Accordingly, the maximum height the impact assembly may be lifted will correspondingly be restricted which ultimately limits the total energy an impact assembly may carry at the point of impact. The Applicant has also recognised that typically in order to be able to achieve the desired impact speeds the impact assembly has to be raised to its maximum height to obtain such speeds.

Accordingly, as the impact assembly is typically raised to its highest point, changing the drop height is no longer a means for use in varying the impact energy of the impact assembly. Therefore, in order to change the impact energy, the Applicant has recognised that changing the mass of the impact assembly is a relatively easy to implement solution. To obtain impact assemblies which have sufficient energy upon impact, it is often necessary to add a considerably large mass to the impact assembly.

The mass may be increased by arranging individual weights on, and above, an impact portion of the impact assembly. However, the Applicant has recognised that arranging the weights above the impact assembly can be problematic. For example if the masses are above the impact portion they need to be removed from the drop tower when reducing the mass of the dropped portion. This is time consuming and also requires lifting equipment. Moreover, arranging the weights in this manner typically results in the impact assembly, in failure situations, coming into contact with a sample holder or base of the drop tower. Therefore, in a preferred set of embodiments the impact assembly comprises: a horizontal portion arranged such that it can move into contact with the sample holder or a sample therein; and a weight portion which extends below the horizontal portion such that the centre of mass of the impact assembly is below the horizontal portion. The Applicant has recognised that by arranging a weight portion underneath the horizontal portion, in tests where the sample is faulty, or indeed there is no sample present in the sample holder, the weight portion may come into contact with the energy dissipation arrangement, rather than the impact assembly coming into contact with the sample holder or any other part of the drop tower, thereby reducing the stress/strain imparted onto the horizontal portion of the impact assembly and thus reducing the chance of the drop tower being damaged. This arrangement may be considered to be an“underslung” arrangement whereby the weight portion is arranged under the horizontal portion.

A further advantage of arranging the weight portion below the horizontal portion, instead of above it, is that it allows the impact assembly to be raised to a greater height than if the weight portion were to extend mainly upwardly above the horizontal portion. This means that drop towers can be made more compact, therefore allowing them to be used in more compact environments, and/or it allows the impact assembly to be raised to a greater height for a given ceiling height, thereby increasing the energy which may imparted upon impact, thus potentially allowing the drop tower to be used for a greater variety of tests and/or samples.

The Applicant has recognised that a weight portion extending below the horizontal portion is novel and inventive in its own right and therefore when viewed from a second aspect the present invention provides a drop tower for impact testing a sample, the drop tower comprising:

at least one vertical guide;

a sample holder for receiving a sample to be tested;

an impact assembly comprising:

a horizontal portion arranged such that it can move into contact with the sample holder or a sample therein; and

a weight portion which extends below the horizontal portion such that the centre of mass of the impact assembly is below the horizontal portion. Of course the drop tower of this second aspect of the invention may also include any of the features of the embodiments of the first aspect of the invention. In particular, in a set of embodiments the drop tower further comprises:

As previously, in a set of such embodiments the mass block has at least half the mass of the impact assembly. The mass could be the same as or greater than the impact assembly but this is not essential.

The features described below may be applied to embodiments of either aspect of the invention.

Drop towers are typically relatively expensive devices and so it may be beneficial for a single drop tower to be capable of testing a wide variety of different samples, e.g. those produced from different materials and/or those which have different shapes and/or sizes. Depending on the particular sample being tested, the desired impact energy will vary and so it is preferable that the impact energy of the impact assembly may be adjusted. Therefore, in a set of embodiments the mass of the impact assembly is adjustable. In a further set of embodiments, the mass of the weight portion is adjustable. As discussed above, the mass of the impact assembly is directly proportional to the impact energy of the impact assembly, therefore by adjusting the mass of the impact assembly, e.g. the weight portion, it is possible to adjust the impact energy of the impact assembly.

In embodiments comprising an adjustable weight portion, the weight portion preferably comprises a plurality of discrete sections which can be removably connected to the weight portion. The discrete sections may be arranged in a stack below the horizontal portion and therefore the discrete sections may be arranged such that they can be selectively attached to the impact assembly, thus leaving any non-attached sections behind when the impact assembly is raised. This is advantageous in avoiding the time and lifting equipment needed to remove the non- attached sections from the drop tower. It also allows the discrete sections not being used to supplement the mass block and thus enhance the ability of the energy dissipation arrangement to absorb impacts.

This may be achieved by any suitable means, for example the discrete sections may comprise threaded apertures which engage with a threaded rod extending from the horizontal portion thereby allowing connection of the two components. The impact assembly may be moveable from a first, lower position, in which the impact assembly contacts the sample holder or the sample therein, and a second, raised position, from which the impact assembly is released. In such a set of

embodiments, the discrete sections may be attached when the impact assembly is in the first position. By selectively attaching the discrete weight portions, in any of the ways described above, it is possible to avoid an operator having to physically lift and arrange masses on top the impact assembly, of course this is typically very difficult given the large masses which are often involved. Accordingly, such an embodiment provides a more user friendly drop tower in which the impact energy of the impact assembly can easily be adjusted.

In a further set of embodiments the weight portion further comprises discrete sections arranged to rest on top of the mass block. The Applicant has recognised that by arranging the discrete sections in this manner, any non-connected discrete sections will remain on the mass block and thereby advantageously increase the mass of the mass block improving its ability to dissipate energy during testing.

As discussed previously, one of the problems of prior art drop towers is that due to the fact that a large amount of the mass of the impact assembly is above the contact point of the impact assembly, as the impact assembly impacts the sample holder or a sample therein, the contact point, i.e. the horizontal section, experiences a large force. This has been known to cause the impact assembly to become damaged and eventually break if the horizontal section is stopped by the sample. This effect can be minimised by allowing the weight portion to come into contact with the mass block when the sample has completely failed or unable to absorb any more energy, instead of the horizontal portion coming into contact with the sample holder. Therefore in a set of embodiments the impact assembly is arranged such that the weight portion comes into contact with a/the mass block of a/the energy dissipation arrangement. Of course the weight portion may not necessarily come into direct contact with the mass block as it envisaged that in certain embodiments there may be an intermediate component or arrangement therebetween. The skilled person will understand such contact may be determined to be when kinetic energy from the weight portion is transferred to the mass block. This contact can be arranged to prevent damage to the fixture holding the sample or to control the energy imparted to the sample

The impact assembly may be arranged such that under normal testing conditions, i.e. when the sample is able to absorb at least a significant portion of the energy from the impact assembly, then the weight portion does not contact the mass block. However, when the sample is unable to absorb the energy, or when there is no sample in the sample holder, the weight portion does contact the mass block. In this arrangement a large amount of the impact force will therefore be transferred through the weight portion instead of the horizontal portion and thus reduce the risk of damage to the impact assembly.

In a set of embodiments the impact assembly has a mass of between 10-500 kg.

In order for the dissipation arrangement to suitably absorb energy from the impact assembly, it is should be sufficiently heavy. Therefore, in a set of embodiments, the mass block has a mass greater than 50 kg, preferably greater than 150 kg, more preferably greater than 500 kg.

Typically, when the impact assembly impacts the sample holder or sample therein, the sample may fracture, often shattering into multiple pieces. In order to analyse how the sample responds to the impact it is known to video or photograph the impact using a camera. It is necessary to precisely align the camera with the sample in the sample holder in order obtain a video which may be used to analyse how the sample responds. Typically drop towers comprise a shielding arrangement which is a safety requirement to protect operators from any material which is ejected from the sample holder as a sample undergoes an impact test. Of course it is necessary to gain access to the sample holder in order to replace a sample held therein and so the shield may comprise an access point in the form of a door. The Applicant has recognised that opening the door may necessitate moving the camera which may result in an operator having to spend a significant amount of time realigning the camera with the sample or sample holder.

In a set of embodiments the drop tower further comprises: a shield arrangement, at least partially surrounding the impact testing arrangement, comprising a door for gaining access to at least the sample holder, and wherein the door comprises an optically transparent portion for observing the sample holder; and a camera mounted on the door relative to the optically transparent portion so as to be capable of observing the sample holder, such that the camera is disposed in a

predetermined position relative to the sample holder when the door is closed.

Mounting the camera according to this embodiment means that each time the door is closed the camera will be in the desired position relative to the sample holder and it will not be necessary for an operator to adjust the alignment of the camera. This may make changing samples within the drop tower easier and less time consuming which may allow for more samples to be tested.

The Applicant has recognised that the arrangement of a camera on the door of the shield arrangement is novel and inventive in its own right and therefore when viewed from a third aspect, the present invention provides a drop tower for impact testing a sample, the drop tower comprising:

an impact testing arrangement comprising at least a sample holder and a vertically moveable impact assembly;

a shield arrangement, at least partially surrounding the impact testing arrangement, comprising a door for gaining access to at least the sample holder, and wherein the door comprises at an optically transparent portion for observing the sample holder; and

a camera mounted on the door relative to the optically transparent portion so as to be capable of observing the sample holder, such that the camera is disposed in a predetermined position relative to the sample holder when the door is closed.

The shield arrangement may comprise a variety of different materials. For example it may be made from: steel mesh, glass and/or Perspex. Some preferred embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which: Fig. 1 shows an illustrative embodiment of a drop tower in accordance with the first and second aspects of the present invention;

Fig. 2 shows the drop tower of Figure 1 with a discrete section of mass attached to the impact assembly;

Fig. 3 shows the drop tower of Figure 1 with the impact assembly in a raised position;

Fig. 4 shows the drop tower of Figure 1 at the stage where the impact assembly has been released and has come into contact with the sample;

Fig. 5 shows the drop tower of Figure 1 after which the sample has failed to absorb an impact;

Fig. 6 shows the drop tower of Figure 1 with multiple discrete sections attached to the impact assembly; and

Fig. 7 shows a drop tower housed within a shield arrangement in accordance with the third aspect of the present invention.

Figure 1 shows an illustrative embodiment of a drop tower 2 in accordance with the first and second aspects of the present invention. The drop tower 2 comprises two vertical guides in the form of vertical guide rails 4 which guide some of its components in a vertical direction, as discussed in more detail below. A sample holder 6 is provided for retaining a sample 8 which is often referred to as a ‘coupon’. The drop tower 2 comprises an impact assembly 9 which comprises a horizontal portion 10 arranged to impact the sample 8, and a plurality of discrete weight sections 12a, 12b, 12c which may be attached to the horizontal portion 10 to increase the mass of the impact assembly. In the configuration shown in Figure 1 , the discrete weight portions 12a, 12b, 12c are not attached to the horizontal portion 10 such that the impact assembly effectively only consists of the horizontal portion 10. In the embodiment shown, the horizontal portion 10 is guided by the vertical guide rails 4 such that it is only able to move vertically.

Also provided is a lifting arrangement 14 for lifting the impact assembly 9. The lifting arrangement 14 comprises a cable 16, e.g. a steel braided cable, which passes over a series of pulleys 18 and a drum 20. The drum 20 may be driven by any suitable means (not shown) e.g. manually by hand using a crank or using an electric motor. One end of the cable 16 is attached to the horizontal portion 10, of the impact assembly 9, via a release arrangement 22. The release arrangement 22 allows the horizontal portion 10 to be released from the cable 16 when a drop test is being carried out. As will be appreciated by those skilled in the art, as the cable 16 is wound around the drum 20, this will cause the impact assembly 9, comprising the horizontal portion 10 and any attached discrete weight sections 12a, 12b, 12c to be lifted away from the sample 8, thereby increasing the potential energy of the impact assembly 9.

Arranged at the base of the drop tower 2 is an energy dissipation arrangement 24 comprising a mass block 26 mounted on a resilient member 28. In the embodiment shown the resilient member 28 is in the form of a coiled spring. The resilient member 28 is mounted to the base 32 of the drop tower 2. Also arranged between the base 32 and the mass block 26 is a dampener 30. In the configuration shown in Figure 1 , wherein the discrete weight sections 12a, 12b, 12c are not attached to the horizontal portion 10 of the impact assembly 9, the plurality of discrete weight sections 12a, 12b, 12c are arranged on top of the mass block 26 and thereby acts to increase the mass of the energy dissipation arrangement.

Arranged at the top of the drop tower 2 is a further resilient member 34 which is mounted to the ceiling 36 of the drop tower 2. This further resilient member 34 may be used to increase the potential energy of the impact assembly 9 when it is lifted to a raised position thereby increasing the impact energy of the impact assembly 9.

Use of the drop tower will be described with reference to Figures 2-5. Figure 2 shows the drop tower 2 in a configuration whereby a first discrete weight section 12a is attached to the horizontal portion 10 of the impact assembly 9. By attaching the discrete weight portion 12a to the horizontal portion 10, the mass of the part of the impact assembly 9 which will be raised, and once released come into contact with the sample 8, is increased. As discussed above, the impact energy of the impact assembly 9 is directly proportional to its mass, therefore increasing its mass will increase its impact energy.

In this particular embodiment, the first discrete weight section 12a is attached to the horizontal portion 10 using bolts 38. The bolts 38 may engage with the horizontal portion 10 and discrete weight portion 12a via any suitable means, e.g. through corresponding threads on the bolts 38, the horizontal portion 10 and the discrete weight portion 12a. As will be appreciated, the use of the bolts 38 to engage and attach the weight portion 12a means that it is not necessary for a user to manually lift and place the discrete weight portion 12a on top of the horizontal portion 10. Instead, a user may simply screw in the bolts 38 until they engage and hold the discrete weight portion 12a to the horizontal portion 10. This requires significantly less effort than physically lifting the discrete weight portion 12a, particularly given that in most cases each discrete weight portion will be very heavy, and therefore this system makes adjusting the weight of the impact assembly 9 easier.

Furthermore, due to the arrangement of the discrete weight portions 12a, 12b, 12c on top of the mass block 26, when one of the discrete weight portions 12a is attached to the horizontal portion 10 in the manner seen in Figure 2, the remaining discrete weight portions 12b, 12c, remain‘inactive’ and rest on top of the mass block 26. Advantageously, the‘inactive’ discrete weight portions 12b, 12c which remain on the mass block 26 increase the total mass of the energy dissipation arrangement and therefore may assist in dissipating energy.

As seen in Figure 2, when the discrete weight portion 12a is attached to the horizontal portion 10 and the horizontal portion 10 just contacts the top of the sample 8, there is a gap 39 formed between the discrete weight portion 12a and the discrete weight portion 12b which remains on top of the mass block 26. The exact size of this gap 39 will determine the distance through which the horizontal portion 10 impacts the sample 8. Accordingly, as discussed previously, the size of this gap 39 may be tuned to change the point at which the two discrete weight portions 12a, 12b come into contact with one another thus tuning the amount of energy which may be absorbed by the sample before the energy is dissipated by the energy dissipation arrangement 24. For example, the gap 39 may be chosen to be small, such that the two discrete weight portions 12a, 12b quickly come into contact, perhaps even before the sample has failed. As will be appreciated, the size of the gap 39 relative to the other components will depend on the vertical position of the impact assembly 9. Figure 3 shows the drop tower 2 as seen in Figure 2, when the impact assembly 9 has been lifted to a raised position from which the impact assembly 9 may be released. It can be seen that in this raised position, the impact assembly 9 acts to compress the further resilient member 34. The result of compressing the further resilient member 34 is that the potential energy of the further resilient member 34 will be increased and therefore when the impact assembly 9 is released, this potential energy, or at least a significant proportion of it, will be imparted to the impact assembly 9 thereby increasing its impact energy. In the embodiment shown, the lifting arrangement 14 must be able to lift the impact assembly 9, along with any attached discrete weight portions, and drive the impact assembly 9 to compress the further resilient member 34. Typically, the further resilient member 34 may have a high spring constant such that it is capable of imparting a significant amount of energy to the impact assembly 9. Therefore, the lifting arrangement 14 must be driven by a suitable means that is capable of compressing the further resilient member 34, for example the drum 20 may be driven by a suitably geared electric motor (not shown). It will be appreciated that the drum is not essential and that other arrangements could be used.

The release arrangement 22 may comprise an electronic or mechanical control designed to accommodate the large force acting on the impact assembly 9.

Figure 4 shows the drop tower 2 after the impact assembly 9 has been released and the horizontal portion 10 has impacted the sample 8. It can be seen that as the horizontal portion 10 impacts the sample 8, the sample 8 physically deforms as it absorbs the energy of the impact.

Figure 5 shows the drop tower 2 at the point at which the sample 8 has completely failed and therefore unable to absorb any further energy from the impact assembly 9. In the embodiment shown, at this point, instead of the horizontal portion 10 suddenly impacting the sample holder 6, the discrete weight portions 12a which are attached to the impact horizontal portion 10 come into contact with the‘inactive’ discrete weight portions 12b, 12c, which are arranged on top of the mass block 26 of the energy dissipation arrangement 24. In other words the horizontal portion 10 and the discrete weight portions12a, 12b, 12c are arranged such that there is a gap 40 between the base of the horizontal portion 10 and the sample holder 6 such that the horizontal portion 10 cannot come into contact with the sample holder 6. By taking the impact at the two sides of the horizontal portion 10, rather than in the middle via the sample holder 6, damage to the horizontal portion 10 and to the sample holder 6 is minimised and thus longevity of the apparatus is ensured.

In the situation described above, the remaining kinetic energy of the impact assembly is transferred to the energy dissipation arrangement 24. This energy is transferred via the first discrete weight portion 12a which comes into contact with the second discrete weight portions 12b and third discrete weight portion 12c which rest on top of the mass block 26 of the energy dissipation arrangement 24. The impact energy of the impact assembly 9 is dissipated via inertial acceleration of the mass block 26, along with the mass of the discrete weight portions 12b, 12c that rest upon it. As the mass block 26 is accelerated, and therefore moved, its movement is resisted by the resilient member 28. The resilient member 28 alone may result in oscillatory motion of the mass block 26 which may take some time to come to rest. Accordingly, the dampener 30 acts to damp any oscillatory motion and quickly bring the mass block 26 to rest.

The sample holder 6 is arranged on top of the mass block 26 which forms part of the energy dissipating arrangement. It will be appreciated that a significant force through the sample holder 6 would cause the mass block 26 to move and thus dissipate energy being put through the sample holder 6. This is not desirable when a sample is undergoing typical testing, and has not yet failed, or absorbed all of the energy, as if some of the energy is dissipated away, the test may not be an accurate representation of the energy the sample is able to absorb. Accordingly, the resilient member 28, arranged beneath the mass block 26, may be preloaded in order to reduce any initial movement of the mass block 26 when the sample is undergoing standard testing. It will be appreciated that preloading the resilient member 28 in this way will mean that the resilient member 28 may only allow any, or significant, movement of the mass block 26 when the impact assembly 9 actually comes into contact with the mass block 26, directly or indirectly via the discrete weight sections 12a, 12b, 12c. Furthermore it will be appreciated that the greater the mass of the mass block, the less undesirable movement there will be of the sample during testing. Additionally, whilst not illustrated, a load cell may be arranged between the impact assembly 9 and the sample 8. With a load cell arranged in this manner it may be possible to measure the force imparted onto the sample 8 upon impact. In addition or alternatively, a load cell may also be arranged between the sample 8 and the sample holder 6.

Whilst not illustrated in these drawings, the position of the impact assembly, and the position of the energy dissipating arrangement, particularly the mass block, may be measured via any suitable means, e.g. using a camera, to determine displacement of the sample during testing.

Figure 6 shows the drop tower 2 as seen in previous Figures wherein all three discrete weight sections 12a, 12b, 12c are attached to horizontal portion 10 of the impact assembly 9. When all of the discrete weight sections 12a, 12b, 12c, are attached as shown, when the impact assembly 9 comes into contact with the sample 8, in situations where the sample 8 fails, or is incapable of absorbing all of the energy of the impact assembly 9, the lowermost discrete weight section 12c will come into direct contact with the mass block 26. In order to appropriately dissipate energy, as discussed previously, the mass of the mass block 26 is sufficiently high - e.g. greater than or equal to half the mass of the impact assembly 9. As the mass of the impact assembly 9 may be increased by adding the discrete weight portions 12a, 12b, 12c, the mass of the mass block assembly is greater than or equal to the combined mass of the horizontal portion 10 and the mass of the three discrete weight portions 12a, 12b, 12c.

Figure 7 illustrates an embodiment of the invention, in which a drop tower 2’ is encased in a shielding arrangement 42. In the embodiment shown, the shielding arrangement 42 is in the form of a Perspex box which surrounds the drop tower 2’. The shield arrangement 42 comprises an access door 44 which allows an operator to gain access to the drop tower 2’ within the shielding arrangement 42. Attached to the access door, on the outside of the shielding arrangement, is a camera 46, which is mounted on a mounting bracket 46. The access door 44 is preferably made from an optically transparent material so that an image of the sample holder 6’ and sample 8’ can be obtained by the camera 46. The mounting bracket 48 is arranged such that the camera is directed towards the sample holder 6’ and sample 8’ within shielding arrangement 42.

An operator may open the access door 44 to gain access to the sample 8’ within the shielding arrangement 42. By virtue of the camera 46 being mounted to the access door 44, when the access door 42 is opened, the camera 46 will be moved out of the way to permit access. When the access door 44 is subsequently closed, the camera 46 will be moved back to the exact position where it was previously. Therefore, as described above, this arrangement ensures that the camera 46 is always mounted in the exact same position with respect to the sample 8’ and sample holder 6. Additionally, by arranging the camera 46 on the outside of the shielding arrangement 42, the camera 46 does not need to be capable of being resistant to the impact of any pieces of the sample 8’ which may shatter and break away during testing.

Claims

1. A drop tower for impact testing a sample, the drop tower comprising:

at least one vertical guide;

a sample holder for receiving a sample to be tested;

an impact assembly arranged to move vertically on the vertical guide;

2. The drop tower as claimed in claim 1 wherein the impact assembly is adjustable such that the point at which the energy dissipation arrangement absorbs energy from the impact assembly can be adjusted.

3. The drop tower as claimed in claim 2 wherein the impact assembly comprises a downwardly extending portion which extends from a base of the impact assembly and wherein the extent of the downwardly extending portion may be adjusted to adjust the vertical position at which the impact assembly transfers energy to the energy dissipation arrangement.

4. The drop tower as claimed in any preceding claim wherein the mass of the mass block is at least half the heaviest possible mass of the impact assembly.

5. The drop tower as claimed in any preceding claim wherein the mass of the mass block can be adjusted.

6. The drop tower as claimed in any preceding claim wherein the energy dissipation arrangement further comprises at least one dampener.

7. The drop tower as claimed in any preceding claim comprising a plurality of resilient members.

8. The drop tower as claimed in claim any preceding claim wherein the at least one resilient member comprises a spring.

9. The drop tower as claimed in any preceding claim comprising a further resilient member arranged to accelerate the impact assembly towards the sample holder after the impact assembly has been released by the release arrangement.

10. The drop tower as claimed in any preceding claim

further comprising a hydraulic or pneumatic ram arranged to accelerate the impact assembly towards the sample holder after the impact assembly has been released by the release arrangement.

11. The drop tower as claimed in any preceding claim wherein the impact assembly comprises: a horizontal portion arranged such that it can move into contact with the sample holder or a sample therein; and a weight portion which extends below the horizontal portion such that the centre of mass of the impact assembly is below the horizontal portion.

12. A drop tower for impact testing a sample, the drop tower comprising:

at least one vertical guide;

a sample holder for receiving a sample to be tested;

an impact assembly comprising:

a weight portion which extends below the horizontal portion such that the centre of mass of the impact assembly is below the horizontal portion.

13. The drop tower as claimed in claim 12 further comprising:

14. The drop tower as claimed in claim 13 wherein the impact assembly is adjustable such that the point at which the energy dissipation arrangement absorbs energy from the impact assembly can be adjusted.

15. The drop tower as claimed in claim 14 wherein the impact assembly comprises a downwardly extending portion which extends from a base of the impact assembly and wherein the extent of the downwardly extending portion may be adjusted to adjust the vertical position at which the impact assembly transfers energy to the energy dissipation arrangement.

16. The drop tower as claimed in any of claims 13 to 15 wherein the mass of the mass block is at least half the heaviest possible mass of the impact assembly.

17. The drop tower as claimed in any of claims 13 to 16 wherein the mass of the mass block can be adjusted.

18. The drop tower as claimed in any of claims 13 to 17 wherein the energy dissipation arrangement further comprises at least one dampener.

19. The drop tower as claimed in any of claims 13 to 18 comprising a plurality of resilient members.

20. The drop tower as claimed in any of claims 13 to 19 wherein the at least one resilient member comprises a spring.

21. The drop tower as claimed in any of claims 13 to 20 comprising a further resilient member arranged to accelerate the impact assembly towards the sample holder after the impact assembly has been released by the release arrangement.

22. The drop tower as claimed in any of claims 13 to 21 further comprising a hydraulic or pneumatic ram arranged to accelerate the impact assembly towards the sample holder after the impact assembly has been released by the release arrangement.

23. The drop tower as claimed in any of claims 1 to 11 or 13 to 22 wherein the mass of the impact assembly is adjustable.

24. The drop tower as claimed in any of claims 1 to 11 or 13 to 23 wherein the mass of the weight portion is adjustable.

25. The drop tower as claimed in claim 24 wherein the weight portion comprises a plurality of discrete sections which can be removably connected to the weight portion.

26. The drop tower as claimed in claim 25 wherein the discrete sections are arranged in a stack below the horizontal portion such that they can be selectively attached to the impact assembly, thus leaving any non-attached sections behind when the impact assembly is raised.

27. The drop tower as claimed in claim 25 or 26 wherein the impact assembly is moveable from a first, lower position, in which the impact assembly contacts the sample holder or the sample therein, and a second, raised position, from which the impact assembly is released and arranged such that the discrete sections can be attached when the impact assembly is in the first position.

28. The drop tower as claimed in any of claims 25 to 27 wherein the weight portion further comprises the discrete sections arranged to rest on top of the mass block.

29. The drop tower as claimed in any of claims 1 to 11 or 13 to 28 wherein the impact assembly is arranged such that when the sample is unable to absorb the energy, or when there is no sample in the sample holder, the weight portion contacts the mass block.

30. The drop tower as claimed in any of claims 1 to 11 or 13 to 29 wherein the mass block has a mass greater than 50 kg, preferably greater than 150 kg, more preferably greater than 500 kg.

31. The drop tower as claimed in any preceding claim wherein the impact assembly is arranged such that the weight portion comes into contact with a/the mass block of a/the energy dissipation arrangement.

32. The drop tower as claimed in any preceding claim wherein the impact assembly has a mass of between 10-500 kg.

33. The drop tower as claimed in any preceding claim further comprising: a shield arrangement, at least partially surrounding the impact testing arrangement, comprising a door for gaining access to at least the sample holder, and wherein the door comprises an optically transparent portion for observing the sample holder; and a camera mounted on the door relative to the optically transparent portion so as to be capable of observing the sample holder, such that the camera is disposed in a predetermined position relative to the sample holder when the door is closed.

34. A drop tower for impact testing a sample, the drop tower comprising: