A HELMET COMPRISING AN IMPACT MITIGATING STRUCTURE

Abstract

The present invention relates to a helmet comprising an impact mitigating structure, the impact mitigating structure comprising: a first layer; and a second layer; wherein one or more of a material property, a mechanical property and a geometrical property of the impact mitigating structure is arranged to, when the impact mitigating structure is subject to an impact, facilitate at least partial fracturing of the second layer such that at least a portion of the second layer is able to move relative to the first layer.

Claims

1. A helmet comprising an impact mitigating structure, the impact mitigating structure comprising: a first layer; and a second layer; wherein one or more of a material property, a mechanical property and a geometrical property of the impact mitigating structure is arranged to, when the impact mitigating structure is subject to an impact, facilitate at least partial fracturing of the second layer such that at least a portion of the second layer is able to move relative to the first layer.

2. The helmet as claimed in claim 1, wherein the impact mitigating structure is arranged to set a particular threshold force of the impact at or above which the second layer is arranged to fracture.

3. The helmet as claimed in claim 1 or 2, wherein the particular force at which the second layer is arranged to fracture is between 10 N and 100 N, e.g. between 30 N and 70 N, e.g. approximately 50 N.

4. The helmet as claimed in claim 1, 2 or 3, wherein the second layer has a fracture toughness of between 0.1 MPa m.sup.1/2 and 10 MPa m.sup.1/2, e.g. between 0.5 MPa m.sup.1/2 and 5 MPa m.sup.1/2, e.g. between 1 MPa m.sup.1/2 and 3 MPa m.sup.1/2.

5. The helmet as claimed in any one of the preceding claims, wherein the first layer and/or the second layer comprises one or more protrusions arranged to facilitate at least partial fracturing of the second layer when the impact mitigating structure is subject to an impact.

6. The helmet as claimed in any one of the preceding claims, wherein the impact mitigating structure comprises one or more fracture initiating members adjacent the second layer, wherein the one or more fracture initiating members are arranged to facilitate at least partial fracturing of the second layer when the impact mitigating structure is subject to an impact.

7. The helmet as claimed in any one of the preceding claims, wherein the second layer is shaped to form one or more points and/or lines of weakness in the second layer, wherein the one or more points and/or lines of weakness are arranged to facilitate at least partial fracturing of the second layer.

8. The helmet as claimed in claim 7, wherein the second layer comprises a plurality of points and/or lines of weakness and the second layer is arranged to at least partially fracture at least one of the plurality of points and/or lines of weakness or between at least two of the plurality of points and/or lines of weakness.

9. The helmet as claimed in claim 7 or 8, wherein the one or more points and/or lines of weakness are defined by material properties of the second layer.

10. The helmet as claimed in claim 7, 8 or 9, wherein the second layer comprises a material having one or more impurities therein, wherein the one or more impurities defines the one or more points and/or lines of weakness.

11. The helmet as claimed in any one of claims 7 to 10, wherein the second layer comprises one or more fibres and/or one or more seeding particles, wherein the one or more fibres and/or the one or more seeding particles are arranged to form the one or more points and/or lines of weakness.

12. The helmet as claimed in any one of claims 7 to 11, wherein the one or more points and/or lines of weakness are defined by geometrical properties of the second layer.

13. The helmet as claimed in any one of claims 7 to 12, wherein the thickness of the second layer at the one or more points and/or lines of weakness is less than the thickness of the surrounding regions of the second layer.

14. The helmet as claimed in any one of claims 7 to 13, wherein the one or more points and/or lines of weakness comprise one or more indentations, voids, grooves, slots and/or apertures in the second layer.

15. The helmet as claimed in any one of the preceding claims, wherein the first layer and/or the second layer comprises one or more protrusions and/or the impact mitigating structure comprises one or more fracture initiating members adjacent the second layer and/or the second layer comprises one or more points and/or lines of weakness, wherein the one or more protrusions, the one or more fracture initiating members and/or the one or more points and/or lines of weakness are arranged to define one or more segments of the second layer.

16. The helmet as claimed in claim 15, wherein the second layer comprises between 3 and 1000 segments, e.g. between 50 and 500 segments, e.g. between and 300 segments, e.g. between 100 and 150 segments.

17. The helmet as claimed in claim 15 or 16, wherein the segments extend over the entirety of the second layer.

18. The helmet as claimed in claim 15, 16 or 17, wherein the segments are arranged relative to the geometrical features of the helmet.

19. The helmet as claimed in any one of claims 15 to 18, wherein the segments are arranged to surround one or more vents in the helmet.

20. The helmet as claimed in any one of claims 15 to 19, wherein the second layer is arranged to fracture, when the impact mitigating structure is subject to an impact, to facilitate at least partial detachment of at one or more segments from the second layer.

21. The helmet as claimed in claim 20, wherein the one or more at least partially detached segments are arranged to, when the impact mitigating structure is subject to an impact from an object, facilitate movement of the second layer with respect to the impacting object.

22. The helmet as claimed in claim 20 or 21, wherein the one or more at least partially detached segments are arranged to, when the impact mitigating structure is subject to an impact, be freed from the impact mitigating structure.

23. The helmet as claimed in claim 20, 21 or 22, wherein the second layer is arranged to, when the impact mitigating structure is subject to an impact, bend between the partially detached segment and the second layer.

24. The helmet as claimed in any one of claims 15 to 23, wherein the second layer comprises a plurality of smaller segments arranged in a region of higher surface curvature of the second layer and/or in a region of a perturbation on the first layer and/or the second layer.

25. The helmet as claimed in any one of the preceding claims, wherein the first layer comprises a hard membrane between the first layer and the second layer.

26. The helmet as claimed according to one of the preceding claims, wherein the second layer forms an outer shell that is non-congruent with respect to the first layer, wherein when the impact mitigating structure is subject to an impact, the outer shell is configured to fracture such that at least a portion of the outer shell is able to move relative to the first layer.

27. The helmet as claimed in claim 26, wherein the outer shell, when the impact mitigating structure is subject to an impact, is configured to flatten to facilitate relative movement of the outer shell with respect to the first layer.

28. The helmet as claimed in claim 1 or as claimed in one of the claims 2 to 27, wherein the second layer is integrally formed with the first layer, the first layer forming an energy absorbing layer or a part of an energy absorbing layer.

29. The helmet as claimed in one of the preceding claims, wherein the impact mitigating structure comprises an intermediate layer configured to facilitate relative movement between the first and second layers.

30. The helmet as claimed in claim 29, wherein in the intermediate layer comprises a plurality of rolling elements.

31. The helmet as claimed in claim 30, wherein each rolling element of said plurality of rolling elements has a rolling resistance less than 0.3.

32. The helmet as claimed in claim 30 or 31, wherein the rolling elements are hard and stiff.

33. The helmet as claimed in one of the claims 30 to 32, wherein each rolling element of said plurality of rolling elements is spherical.

34. The helmet as claimed in one of the claims 30 to 33, wherein each rolling element of said plurality of rolling elements comprises a diameter in the range from 1 mm to 4 mm.

35. The helmet as claimed in one of the preceding claims, wherein the impact mitigating structure comprises a fracturing mechanism that is configured to resist a relative movement between the second layer and the first layer.

36. The helmet as claimed in claim 35, wherein the fracturing mechanism is configured to create a geometric locking or a mechanical locking between layers.

37. The helmet as in claim 35 or 36, wherein the fracturing mechanism is configured to increase a resistance of rolling of the rolling elements.

Description

[0125] Certain embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0126] FIG. 1 shows schematically a view of a conventional impact mitigating structure;

[0127] FIG. 2A shows schematically a cross-sectional view of a conventional helmet;

[0128] FIG. 2B shows schematically a cross-sectional view of the helmet of FIG. 2A as a result of an impact;

[0129] FIG. 3 shows schematically a view of a helmet in accordance with an embodiment of the present invention;

[0130] FIG. 4 shows schematically a view of a helmet in accordance with an embodiment of the present invention;

[0131] FIG. 5A shows schematically a view of an impact mitigating structure in accordance with an embodiment of the present invention;

[0132] FIG. 5B shows schematically a view of the impact mitigating structure of FIG. 5A after an impact;

[0133] FIG. 5C shows schematically a view of another impact mitigating structure of FIG. 5B after an impact;

[0134] FIG. 6 shows schematically a cross-sectional view of a helmet in accordance with an embodiment of the present invention;

[0135] FIG. 7 shows schematically a cross-sectional view of a helmet of FIG. 6 during an impact;

[0136] FIG. 8 shows schematically another cross-sectional view of a helmet of FIG. 6 during an impact;

[0137] FIG. 9 shows schematically a cross-sectional view of a helmet during an impact in accordance with an embodiment of the present invention;

[0138] FIG. 10 shows schematically a cross-sectional view of a helmet in accordance with an embodiment of the present invention;

[0139] FIG. 11 shows schematically a cross-sectional view of a helmet in accordance with an embodiment of the present invention;

[0140] FIG. 12 shows a schematically a cross-sectional view of a helmet in accordance with an embodiment of the present invention, wherein the helmet comprises a second layer in form of a non-congruent outer shell configured to fracture on impact; and

[0141] FIG. 13 shows the outer shell of FIG. 12 upon fracturing.

[0142] Impact mitigating structures act to protect a user or an object by absorbing and/or deflecting energy from an impact. In oblique impacts, which are a common form of impact, the impact mitigating structure may be subject to significant linear and tangential forces. These forces can cause a rapid deceleration of the user and/or object, which may cause serious damage. Embodiments of the present invention aim to provide an improved impact mitigating structure which reduces the risk of serious damage to the user being protected by the impact mitigating structure during an impact on the impact mitigating structure.

[0143] FIG. 1 shows schematically a plan view of a conventional impact mitigating structure 2. The impact mitigating structure 2 comprises a first layer 4 and a second layer 6 positioned on top of the first layer 4. The second layer 6 does not contain any points and/or lines of weakness, e.g. it is a uniform layer. The first layer 4 may formed from expanded polystyrene and the second layer 6 may be a polycarbonate shell. The impact mitigating structure 2 may be implemented in a helmet, e.g. in the helmet shown in FIG. 2A.

[0144] FIG. 2A shows schematically a cross-sectional view through a conventional helmet 20. The helmet comprises a first layer 24 and a second layer 26. For example, the first layer 24 may be an expanded polystyrene (EPS) foam impact absorbing layer and the second layer 26 may be an outer polycarbonate shell. The helmet 20 includes two vents 34, 35 which allows air to propagate through the helmet 20, providing an airflow for ventilation of the head (not shown) protected by the helmet 20. The vents 34, 35 are formed from openings in both the first layer 24 and the second layer 26.

[0145] FIG. 2B demonstrates the reaction of the helmet 20 shown in FIG. 2A to an impact. The force of the impact is represented in FIG. 2B by the arrow 38. As shown in FIG. 2B, the impact causes the second layer 26 to break at undefined locations in the second layer 26. During and/or after an impact, the sections created by the breaks in the second layer 26 may be obstructed and/or prevented from moving with respect to the first layer 24. This is due to the edges of the section of the second layer being caught in the vents 34, 35 (in the first layer). This is an example of geometric locking.

[0146] FIGS. 3 to 11 show impact mitigating structures according to various embodiments of the present invention.

[0147] FIG. 3 shows schematically a side view of a helmet 100 according an embodiment of the present invention. The helmet 100 is formed from an impact mitigating structure 102. The impact mitigating structure 102 has the following components: a first inner layer 104, a second outer layer 106 and a honeycomb layer 103. The second layer 106 is positioned outside of (e.g. stacked on top of) the first layer 104, and the first layer 104 is positioned on (e.g. stacked on top of) the honeycomb layer 103.

[0148] In the helmet 100, the first layer 104 is an impact absorbing structure comprising an EPS foam impact absorbing layer. The second layer 106 is a polycarbonate shell. The thickness of the second layer 106 is (substantially) less than the first layer 104. The first layer 104 and the second layer 106 comprises a plurality of vents 110, which allow air flow to the head protected by the helmet 100 (not shown).

[0149] The honeycomb layer 103 may provide additional impact absorption. The honeycomb layer 103 may also improve the fit of the helmet 100 to a user's head. The honeycomb layer 103 comprises a plurality of hollow cells. The hollow cells may allow an improved fit of the helmet 100 and/or improve the circulation of air throughout the helmet 100.

[0150] The second layer 106 includes multiple lines of weakness 108. The lines of weakness 108 may be formed by a series of indentations (e.g. notches), grooves, slots, perforations and/or impurities in the outer surface of the second layer 106.

[0151] The multiple lines of weakness 108 define the outline of a number of segments 112 of the second layer 106.

[0152] FIG. 4 shows schematically a side view of a helmet 200 according to another embodiment of the present invention. Similarly to the helmet 100 shown in FIG. 3, the helmet 200 shown in FIG. 4 includes a first inner layer 204 (e.g. a EPS foam impact absorbing layer) and a second outer layer 206 (e.g. a polycarbonate shell).

[0153] The second layer 206 includes multiple lines of weakness 208, which define a number of segments 212. In FIG. 4, the lines of weakness 208 track from the front to rear of the second layer 206, such that the segments 212 are formed as a series of elongated strips of the second layer 206. The width of the segments 212 may vary across the helmet. For example, the width of the segments 212 may be smaller towards the edges 216 of the second layer 206 (e.g. where the curvature of the second layer 206 is greater) and the width of the segments 212 may be larger towards the centre 214 of the second layer 206 (e.g. where the curvature of the second layer 206 is smaller).

[0154] FIG. 5A shows schematically a plan view of an impact mitigating structure 402 which may be incorporated into a helmet in accordance with an embodiment of the present invention. For example, the impact mitigating structure 402 may be implemented in the helmets 100, 200 shown in FIGS. 3 and 4. Similarly to the impact mitigating structure 302 shown in FIG. 1, the impact mitigating structure 402 shown in FIG. 5A includes a first layer 404 and a second layer 406 positioned on top of the first layer 404. However, unlike in FIG. 1, the second layer 406 of the impact mitigating structure 402 comprises a series of lines of weakness 408. The lines of weakness 408 define the borders between different segments 412 of the second layer 406.

[0155] In the particular arrangement shown in FIG. 5A, the arrangement of the lines of weakness 408 forms (substantially) triangular interleaving segments 412.

[0156] The lines of weakness 408 are positioned more sparsely (i.e. having a greater separation between adjacent lines of weakness) towards the centre (of the surface) of the second layer 406. Therefore, larger segments 412a are located at the centre of the second layer 406 and smaller segments 412b are located towards the edges of the second layer 406.

[0157] The lines of weakness 408 shown in FIG. 5A are formed from perforations in the second layer 406. However, the lines of weakness may be may be perforations, apertures, grooves, slots, indentations (e.g. notches), voids and/or formed by impurities in the second layer 406.

[0158] FIG. 5B shows schematically a plan view of the impact mitigating structure 402 of FIG. 5A, which shows an example of the effect of an impact (exceeding a certain threshold) on the impact mitigating structure 402 shown in FIG. 5A. During and/or after the impact, the second layer 406 fractures along one or more (e.g. all) of the lines of weakness 408. In the particular example shown in FIG. 5B, all of the lines of weakness 408 have fractured. However, it will be appreciated that not all the lines of weakness 408 may fracture. The fracturing of the lines of weakness 408 may, for example, depend on the magnitude and the location of the impact (on the impact mitigating structure 402).

[0159] The fracturing of the lines of weakness 408 shown in FIG. 5B allows the segments 412 to (e.g. completely or partially) separate from each other. The segments 412 can then translate (e.g. move) relative to each other and the first layer 404. The fracturing of the lines of weakness 408 and movement of the segments 412 with respect to the first layer 404 dissipates a portion of the energy imparted by an impact so as to reduce the energy transferred to an object (e.g. a head) protected by the impact mitigating structure (e.g. the helmet). The effects of the fracturing of the lines of weakness 408 and the movement of the segments 412 will described in more detail in relation to FIGS. 6 to 9.

[0160] FIG. 5C shows schematically a plan view of an impact mitigating structure 452, that shows another example of the effect of an impact (exceeding a certain threshold) on an impact mitigating structure 452 including a first layer 454 and a second layer 456. In FIG. 5C, the points or lines of weakness in the second layer 456 cause the second layer 456 to fragment (e.g. stochastically) into a number of irregular segments 462 when subject to an impact. The stochastic fragmenting of the second layer 456 may occur when fracturing occurs between (e.g. randomly) isolated points of weakness (e.g. that are not connected in a line).

[0161] FIG. 6 shows a cross-sectional view through a helmet 600 in accordance with an embodiment of the present invention. The helmet 600 comprises a first layer 604 and a second layer 606. The helmet 600 includes two vents 614, 615 which allow air to propagate through the helmet 500, providing ventilation to the head (not shown) protected by the helmet. Although not visible in FIG. 6, the second layer 606 includes a number of points or lines of weakness defining a number of segments, e.g. as shown in FIGS. 3, 4, 5A or 5C.

[0162] Operation of embodiments of the present invention will now be described with reference to FIGS. 7 and 8. FIGS. 7 and 8 show cross-sectional views of the helmet shown in FIG. 6 and demonstrate the possible behaviours of the helmet 600, in particular the behaviour of the second layer 606, as a result of an impact. It will be appreciated that the helmets of FIG. 3, 4 or 6, or the impact mitigating structures shown in FIGS. 5A, 5B and 5C.

[0163] FIG. 7 shows a similar cross-sectional view of the helmet 600 as seen in FIG. 6. The direction of the force of the impact is represented by the arrow 618. In an impact exceeding a certain threshold (e.g. a greater force than a user could reasonably exert on a helmet during normal use), sufficient energy required to at least partially fracture the lines of weakness (not shown) is imparted to the second layer 606. The fracturing of the lines of weakness fragments the second layer 606 into a plurality of disconnected, separated segments 612.

[0164] In the embodiment shown in FIG. 7, the segments are (substantially) smaller than the dimensions of the vents 614, 615. This allows the segments 612 to move with respect to the first layer 604, for example by falling through the vents 614, 615, being ejected from the helmet or moving across of the outer surface of the first layer 604, without their continued movement being prevented by the vents 614, 615. The size of the segments 612 substantially reduces the risk of geometric locking (as described above with reference to FIG. 2B).

[0165] FIG. 8 shows an enlarged (zoomed in) cross-sectional view of the helmet 600 of FIG. 6, demonstrating the behaviour of the segments 612 during and/or after an impact. The (surface of the) impacting object 620 is also shown in FIG. 8. For example, the impacting object could be the surface of a road. The segments 612 formed in the impact (as described in relation to FIG. 7) may respond to the impact in various ways.

[0166] One or more of the segments 612a may be ejected through the vents 614 in the first layer 604. Another set of segments 612b may be ejected from the helmet, e.g. away from the outer surface of the first layer 604. The ejected segments 612b may carry away a portion of the energy transferred to the helmet 600 from an impact, therefore dissipating energy from the impact. This reduces the energy transferred to the first layer 604 and then to the head (not shown) protected by the helmet 600.

[0167] Another set of segments 612c may help to facilitate the movement of the impacting object 620 with respect to the first layer 604 (and thus the head protected by the helmet). The segments 612c are configured to move (e.g. rotate, roll, translate) in order to facilitate the translation of the impacting object 620 with respect to the first layer 604. In such embodiments, it may be beneficial for the segments (i.e. the second layer) to be formed from a low friction material or be coated with a low friction coating. The movement of the segments 612c may help to reduce the oblique forces transferred through the helmet 600, which helps to reduce the rotational movement of the head protected by the helmet during an impact.

[0168] FIG. 9 shows schematically a cross-sectional view through part of a helmet 700 during an impact with an impacting object 720. The helmet 700 seen in FIG. 9 is similar to the helmet shown in FIG. 6, in that helmet 700 includes a first layer 704 and a second layer 706 which includes a plurality of lines of weakness (not visible) defining a plurality of segments.

[0169] However, in the embodiment shown in FIG. 9, whilst the second layer partially fractures along the plurality of lines of weakness as a result of an impact, the second layer does not completely fracture such that a plurality of segments forming the second layer 706 complete separate from one another. Instead, as seen in FIG. 9, the partial fracturing of the second layer along the lines of weakness allows the second layer 706 to deform (e.g. bend) along the lines of weakness. This increases the flexibility of the second layer 706, allowing to second layer 706 to bend and continue moving relative to the first layer 704, such that the second layer 706 moves into (e.g. the vents in) the first layer 704. This reduces the risk of the movement of the first layer 704 and the second layer 706 being prevented and/or obstructed (i.e. reducing the risk of geometric locking). The arrangement shown in FIG. 9 also reduces the risk of small segments of a fragmented second layer from causing damage, e.g. to the eyes of the user of the helmet.

[0170] FIG. 10 shows schematically a cross-sectional view of a helmet 800 in accordance with an embodiment of the invention. The helmet 800 includes a first, inner, impact absorbing layer 804 and a second, outer, shell layer 806. One or more protrusions 808 are formed on the first layer 804, facing the second layer 806. One or more protrusions 810 are formed on the second layer 806, facing the first layer 804. The protrusions 808, 810 may be point-like and act on the second layer 806 at a discrete point, or the protrusions 808, 810 may be longitudinally extended (in the form of a raised strip) to act on the second layer 806 along a line.

[0171] When the helmet 800 is subject to an impact, the protrusions 808, 810 act to concentrate the stress experienced by the second layer 806, as a result of the force of the impact, thus facilitating the fracturing of the second layer 806, e.g. at the locations at which the protrusions 808, 810 act on the second layer 806. As with previous embodiments, once the second layer 806 has been fractured, the fractured portion is then able to move relative to the first layer 804.

[0172] FIG. 11 shows schematically a cross-sectional view of a helmet 900 in accordance with an embodiment of the invention. The helmet 900 is similar to the helmet 800 shown in FIG. 10, in that it includes a first, inner, impact absorbing layer 904 and a second, outer, shell layer 906. However, instead of protrusions 808, 810 formed on the first and second layers 804, 806, the helmet 900 comprises a plurality of fracture initiating members 908 (in the form of hard balls or strips) positioned between the first layer 904 and the second layer 906. The fracture initiating members 908 may be point-like balls and act on the second layer 906 at a discrete point, or the fracture initiating members 908 may be longitudinally extended (in the form of a strip) to act on the second layer 906 along a line.

[0173] The helmet 900 also comprises a hard membrane coating 910 on the first layer 904, between the first layer 904 and the fracture initiating members 908.

[0174] When the helmet 900 is subject to an impact, the fracture initiating members 908 act to concentrate the stress experienced by the second layer 806, as a result of the force of the impact. The hard membrane coating 910 prevents the fracture initiating members 908 from becoming embedded in the first layer 904, thus facilitating the fracturing of the second layer 906, e.g. at the locations at which the fracture initiating members 908act on the second layer 806. As with previous embodiments, once the second layer 906 has been fractured, the fractured portion is then able to move relative to the first layer 904.

[0175] FIGS. 12 to 13 show schematic cross-sectional views of a helmet 1000 according to an embodiment of the present invention. The helmet 1000 comprises an impact mitigating structure 1002. In particular, the impact mitigating structure 1002 has the following components: a first inner layer 1004, a second outer layer 1006 and an intermediate layer 1005. Particularly, the second layer 1006 is positioned outside of (e.g. stacked on top of) the first layer 1004, and the intermediate layer 1005 is arranged between the second and the first layer 1006, 1004. The first layer 1004 can comprise an energy absorbing layer. Further, according to an embodiment, the intermediate layer 1006 can comprise or be formed out of a plurality of rolling elements 1007 that can be designed as described herein (e.g. rigid spheres having e.g. a diameter in the range from 1 mm to 4 mm). The rolling elements 1007 facilitate relative movement of the second layer 1006 with respect to the first layer 1004 by allowing movement of the second layer 1006 (or parts thereof) with the rolling elements 1007 rolling underneath the second layer 1006 (or parts thereof) upon an impact. However, also intermediate layers 1005 are conceivable that do not comprise such rolling elements 1007, but facilitate relative movement due to alternative material properties or structures.

[0176] Particularly, as shown in FIGS. 12 and 13, the second layer 1006 forms a non-congruent outer shell 1006 with respect to the underlying first layer 1004. FIG. 12 shows the outer shell 1006 before an impact exerting a force F onto the helmet 1000.

[0177] As indicated in FIG. 13, the non-congruent outer shell 1006 is configured to fracture on impact into a plurality of fractured portions 1060 that then move relative to the inner first layer 1004 on the intermediate layer 1005, wherein (if present) the rolling elements 1007 facilitate the movement of the individual fractures portion 1060 with respect to the first layer 1004 by rolling underneath them. In other words, the non-congruent outer shell 1006 breaks upon impact to facilitate sliding or moving of the fractured portions 1060 on the rolling rolling elements 1007 (in case the intermediate layer 1005 comprises rolling elements 1007) or on an alternative intermediate layer without rolling elements 1007.

[0178] Thus it will be appreciated by those skilled in the art that an impact mitigating structure according to embodiments of the present invention, in which the one or more points of weakness are arranged to fracture as a result of an impact to facilitate the movement of a first layer and a second layer with respect to the each other, helps to reduce the forces transferred through the impact mitigating structure, e.g. to a user or object being protected by the structure. This may provide benefits over known impact mitigating structures and, particularly when the impact mitigating structure is a helmet, provide significant benefits over known helmets, e.g. in helping to reduce brain injuries. It will further be appreciated however that many variations of the specific arrangements described herein are possible within the scope of the invention, such as combinations of features taken from the embodiments shown.