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.

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 1/2  and 10 MPa m 1/2 , e.g. between 0.5 MPa m 1/2  and 5 MPa m 1/2 , e.g. between 1 MPa m 1/2  and 3 MPa m 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.